TWI697371B - System and method for sensing cable fault detection in a saw - Google Patents

Abstract

A method for detection of a fault in a sensing cable within a saw detects potential failures in a sensing cable that is part of an object detection system in the saw. The method includes generating a predetermined excitation signal transmitted through a first conductor and a second conductor in the sensing cable, detecting a return signal from the first conductor and the second conductor in the sensing cable in response to the predetermined excitation signal, identifying a signal-to-noise ratio (SNR) of the return signal, and generating an output indicating a fault in the sensing cable in response to the SNR of the return signal being below a predetermined value.

Description

System and method for sensing cable fault detection in saw

The present disclosure is generally related to power tools, and more specifically, the present disclosure is related to systems and methods for detecting contact between blades and objects in a saw.

Claim of priority

This application claims the priority of U.S. Provisional Application No. 62/131,977 filed on March 12, 2015. The title of the case is "System and Method for Drop Arm Control in Table Saws (SYSTEM AND METHOD FOR CONTROL OF A DROP ARM IN A TABLE SAW)", this article incorporates its complete content by reference. This application also claims the priority of U.S. Provisional Application No. 62/132,004 filed on March 12, 2015, the title of which is "TABLE SAW WITH DROPPING BLADE", This article incorporates its complete content by reference.

Cross reference

This application is cross-referenced to U.S. Application No. 15/060,649 filed on March 4, 2016, the entire content of which is incorporated herein by reference.

Detection systems or sensing systems have been developed for use in various types of manufacturing equipment and power tools. These detection systems can be operated to trigger a reaction device by detecting or sensing the proximity or contact of the operator's limbs with specific parts of the equipment. For example, the existing capacitive touch sensing system in the table saw will detect the contact between the operator and the blade.

FIG. 1 shows a detection system 90 based on the prior art capacitive sensing, which is incorporated in the table saw 1. The detection system 90 drives an excitation voltage that is electrically coupled to the movable blade 22 of the saw 1 and detects the current drawn from the blade 22. When the blade 22 contacts a conductive object (for example, the operator's hand, finger, or other body part, and work piece), the amplitude or phase of the detected current and/or excitation voltage will change. These changed characteristics will be used to trigger the operation of a reaction system 92. For example, the reaction system 92 will stop the movement of the blade 22 by braking and/or stop the operation of the blade 22 by moving the blade 22 below the cutting area. An example of the reaction system 92 uses an explosive charge to drive a brake (not shown in the figure) into the blade 22 to stop the movement of the blade 22. In addition, or instead, an embodiment of the reaction system 92 disintegrates a blade support member (not shown in the figure) in order to push the blade 22 below the surface of the table 14.

The embodiment of the detection system 90 shown in FIG. 1 includes an oscillator 10 that generates a time-varying signal on the line 12. The time-varying signal is any suitable signal type, for example, it includes a sine wave, the sum of multiple sine waves, a chirped waveform, a noise signal, etc. The frequency of the signal is selected so that a detection system can distinguish the contact between a first object (for example, a finger or hand) and a second object (for example, wood or other materials) to be cut by the power tool. In the embodiment of Figure 1, the frequency is 1.22MHz; however, other Frequency and non-sine wave shape. The oscillator 10 will be locally grounded by the saw table 14 or other metal structures. As shown in FIG. 1, the blade 22 is placed vertically in an opening defined by the saw table 14 (or a working surface or a cutting surface or a platform).

The oscillator 10 is connected to two voltage amplifiers or buffers 16, 18 via a line 12. The first voltage amplifier 16 has an output connected to the line 20, which in operation connects the output of the oscillator to the saw blade 22. A current sensor 24 operatively connects a signal from the line 20 to the line 26, which is then fed to the amplifier 28, which is connected to a processor 30 via the line 32. For example, the current sensor 24 is a current sensing transformer, a current sensing resistor, a Hall Effect current sensing device, or other suitable current sensors. An output line 34 from the processor 30 is operatively connected to the reaction system 92, so that if a preset condition (for example, to indicate contact between the blade 22 and the first object) is detected, The processor 30 will trigger the reaction system 92.

The signal on line 26 represents the instantaneous current drawn by blade 22. Because the saw blade 22 is in motion during the operation of the table saw, the connection is achieved via an excitation plate 36 which is arranged substantially parallel to the blade 22. The plate 36 is driven by the first voltage amplifier 16 and is configured to have a capacitance of about 100 picofarads (pF) based on the blade 22 in the embodiment of FIG. 1. The flat plate 36 is held in a stable position based on the side edge of the blade 22. The excitation plate 36 is configured to follow the blade 22 when the height and the bevel angle of the blade 22 are adjusted for the operation of the saw 1.

In the embodiment of FIG. 1, the capacitance between the first object and the saw table 14 (or the power line to ground, if present) falls in the range of about 30 pF to 50 pF. When the capacitance between the excitation plate 36 and the saw blade 22 exceeds that between the first object and the saw table 14 If the capacitance is larger, the detection thresholds will not be unduly affected by the change of the plate-to-blade capacitance. In the configuration of FIG. 1, the plate 36 is arranged parallel to the blade 22 on the side where the blade 22 is seated on the shaft 37, so that the change in the thickness of the blade does not affect the blade 22 and the plate 36 The space between. Other excitation methods can also be used to achieve the same effect, including contact via a crankshaft bearing or brush contact with the shaft or the blade.

In the detection system 90, the second amplifier 18 is connected to a shield 38, and the amplifier 18 drives the shield 38 to the same potential as the excitation plate 36. In addition, the sensor in the detection system 90 also monitors the level of the current drawn by the shield 38 as appropriate. The shield 38 extends around the blade 22 under the table 14 and is separated from the blade 22 at the top of the table 14 by a certain distance in the configuration of FIG. 1. The configuration of the shield 38 will reduce the static capacitance between the blade 22 and the workbench 14. If the workbench is not electrically connected to the ground, it can serve as a ground plane. In various embodiments, the shield 38 is a continuous mesh bag, or a specific type of shield that is electrically equivalent to a faraday cage at the excitation frequency generated by the oscillator 10, the shield 38 Depending on the situation, it may include a device that moves with the blade adjustment, or the device is large enough to accommodate the blade adjustment and various blades that are adapted to the table saw. In the configuration of FIG. 1, the shield 38 moves with the blade adjustment and includes a throat area at the top 14 of the table.

The processor 30 will perform various pre-processing steps and perform a trigger action to detect the condition indicating the contact between the first object and the blade 22. The processor 30 optionally includes one or more associated analog-to-digital (A/D) converters. The blade current signal from the current sensor 24 is directed to one or more of the A/D converters, which generates a corresponding digital signal. In some embodiments, a represents the blade 22 and the The blade voltage signal that excites the voltage difference between the plates 36 is directed to an A/D converter to generate a digital blade voltage signal. The processor 30 receives the digitized signal and performs various digital signal processing operations and/or calculates derivative parameters based on the received signal. The processor 30 analyzes the adjusted blade signal or performs other calculations to detect the contact condition between the first object and the blade 22.

This prior art saw requires the use of conductive material to form the blade 22, which is also electrically connected to the crankshaft 37. Non-conductive blades and blades containing non-conductive coatings will prevent the contact detection systems in these prior art saws from operating correctly. In addition, the blade 22 and the shaft 37 must also be electrically connected to a ground plane for the contact detection system for effective operation. The ground connection requirement must also allow the saw 1 to be electrically connected to a correct ground, such as ground spikes, metal pipes, or other suitable grounds, which must keep the table saw 1 in a fixed position . Other types of table saws include portable table saws that can be transported between workstations that provide ground connections that may be inconvenient or impractical. In addition, the need for grounding connection will increase the complexity of the setup and operation of the non-portable table saw. Therefore, it would be beneficial to improve the contact detection system so that the blades in portable and non-portable table saws do not need to be electrically grounded.

In one of the embodiments, the present invention provides a method for detecting a fault in a sensing cable inside a saw. The method includes: using a signal generator to generate a predetermined excitation signal, the predetermined excitation signal is transmitted through a first conductor and a second conductor in the sensing cable, and the first conductor is electrically connected To a flat plate in the saw and the second conductor is electrically connected to an implement in the saw, the implement is positioned at a predetermined distance from the plate Departure; use a controller to detect a return signal corresponding to the excitation signal passing through the first conductor and the second conductor in the sensing cable; use the controller to identify the return signal Signal-to-noise ratio (SNR); and in response to the return signal's SNR below a preset value, using the controller and a user interface device in the saw to generate an output to represent the sensing cable There is a fault.

In a further embodiment, the method includes using the controller to turn off the motor in the saw before generating the preset activation signal, so that the fault in the cable can be identified when the motor is kept off.

In a further embodiment, the method includes using a clock source in the saw to generate a sinusoidal signal at a predetermined frequency.

In a further embodiment, the method includes: using an amplifier to generate an amplified sinusoidal signal based on the sinusoidal signal from the clock source; and transmitting the amplified sinusoidal signal via the sensing cable.

In a further embodiment, the method includes using a clock source in the saw to generate a series of delta pulses at a predetermined frequency.

In a further embodiment, the method includes using the controller to deactivate the operation of the motor in the saw in response to the SNR being below a predetermined threshold.

In a further embodiment, the method includes using a first coil in a transformer in the saw to transmit the predetermined excitation signal from the signal generator to the first conductor in the sensing cable With the second conductor.

In a further embodiment, the method includes using the controller to receive a return signal flowing through a third conductor in the sensing cable, the third conductor being electrically connected to the plate and And is electrically connected to an analog-to-digital converter associated with the controller.

In another embodiment, the present invention provides a system for detecting a fault in a sensing cable in a saw. The system includes: a sensing cable including a first conductor and a second conductor; a flat plate which is electrically connected to the first conductor in the sensing cable; and an appliance where the appliance is positioned At a predetermined distance from the plate and the appliance is electrically connected to the second conductor in the sensing cable; a signal generator configured to generate a predetermined excitation signal, the predetermined It is assumed that the excitation signal will be transmitted through the first conductor and the second conductor of the sensing cable; a user interface device; and a controller connected to the signal generator, the user interface device and the The first conductor and the second conductor of the sensing cable. The controller is configured to: operate the signal generator to generate the predetermined excitation signal; detect a return signal corresponding to the first conductor and the first conductor passing through the sensing cable The excitation signal of the two conductors; identifying the signal-to-noise ratio (SNR) of the return signal; and in response to the SNR of the return signal being below a preset value, the user interface device is used to generate an output for representing the sensing cable There is a fault in the line.

In a further embodiment, the system includes a motor configured to move the appliance during operation, and the controller is operatively connected to the motor. The controller is configured to turn off the motor before operating the signal generator to generate the predetermined activation signal, so as to be able to identify the fault in the cable when the motor remains turned off.

In a further embodiment, the signal generator includes a clock source configured to generate a sinusoidal signal at a predetermined frequency as the excitation signal.

In a further embodiment, the signal generator includes an amplifier configured to generate an amplified sinusoidal signal based on the sinusoidal signal from the clock source.

In a further embodiment, the signal generator includes a clock source, which is configured to generate a series of incremental pulses at a predetermined frequency.

In a further embodiment, the system includes a motor configured to move the appliance during operation, and the controller is operatively connected to the motor. The controller is further configured to disable operation of the motor in response to the SNR being below the predetermined threshold.

In a further embodiment, the system includes a transformer, the first coil of which is connected to the first conductor in the sensing cable and the second conductor in the sensing cable, and the signal is generated The device is configured to transmit the preset excitation signal to the first conductor and the second conductor via the first coil.

In a further embodiment, the system includes a third conductor in the sensing cable, the third conductor electrically connected to the plate and electrically connected to an analog to digital associated with the controller converter. The controller is configured to receive the return signal flowing through the third conductor in the sensing cable.

1: table saw

10: Oscillator

12: Line

14: saw table

16: voltage amplifier or buffer

18: Voltage amplifier or buffer

20: Line

22: removable blade

24: Current sensor

26: Line

28: Amplifier

30: processor

32: Line

34: output line

36: Exciting Tablet

37: crankshaft

38: shield

90: Detection System

92: reaction system

100: saw

102: Object Detection System

104: Workbench

106: power supply

108: saw blade

109: Crankshaft

110: user interface device

112: Electric motor

118: Appliance Enclosure

119: Throat

120: tablet

124: Capacitor

132: Appliance Response Mechanism

140: Digital Controller

142: Memory

143A: Demodulator

143B: Demodulator

144: Clock Source

146: Amplifier

150: Transformer

152: first coil

154: second coil

164: Part of the human body

172: Printed Circuit Board (PCB)

174: Control TRIAC

180: resistor

182: Ground

304: board

306: Thermoplastic rail base

310: Orbit

312: Track

320: bezel

330: Cleaver

332: Blade bezel

352: bevel adjustment grip

354: Height adjustment grip

404: Non-conductive casing

408: Non-conductive casing

412: Plastic support member

502: Shell

504A: Hat

504B: Hat

504C: Hat

504D: Hat

506: Hook

512: cover

516: Antenna

524A: Main component

524B: main component

524C: Main component

524D: main component

526: Hook

528A: Indicator

528B: Indicator

528C: Indicator

528D: Indicator

540: Lamp cap assembly parts

544: Main component assembly

550: Printed Circuit Board (PCB)

552A: Light Emitting Diode (LED)

552B: Light Emitting Diode (LED)

552C: Light Emitting Diode (LED)

552D: Light Emitting Diode (LED)

560: base member

612: lip

708: Ferrite choke

720: Sensing cable

724: Data Cable

732: pull-down resistor

736: Power Cable

738: Ferrite choke

740: Ferrite choke

742: Cable

743A: thyristor

743B: thyristor

802: body

832: connection location

836: connection location

838: connection position

852: first inner conductor

856: Electrical Insulator

862: second metal conductor

864: external insulator

866: Metal fixing clip

872: Connect the base

876: Connect the base

904: Capacitive sensor

908: Capacitive sensor

912: Capacitive sensor

920: Cutting direction

1350: Shaft

1354: commutator

1358A: Brush

1358B: Brush

1362A: Spring

1362B: Spring

1366A: Base

1366B: Base

Figure 1 shows a schematic diagram of a prior art table saw, which includes a prior art detection system for detecting contact between a human body and a saw blade.

The schematic diagram of a table saw shown in FIG. 2 includes an object detection system configured to confirm whether a saw blade in the saw is in contact with an object during the rotation of the saw blade.

Fig. 3 is an external view of one embodiment of the table saw of Fig. 2.

Fig. 4 is a cross-sectional view of selected components in the saw of Fig. 2, which includes a blade, a shaft, and a sensor plate.

FIG. 5A is an external view of the user interface device in the saw of FIG. 2.

FIG. 5B shows a view of the user interface device of FIG. 5A with the casing removed.

FIG. 5C is a cross-sectional view of the user interface device of FIG. 5B.

FIG. 5D shows an exploded view of the devices in the user interface of FIGS. 5A to 5C.

FIG. 6A shows an exploded view of an assembly of a charge-coupled plate and a crankshaft in one of the embodiments of the saw of FIG. 2.

Figure 6B shows a cross-sectional view of the device depicted in Figure 6A.

FIG. 7 shows a schematic diagram of additional details of the object detection system and other devices in one of the embodiments of the saw of FIG. 2.

FIG. 8A shows a schematic diagram of a sensing cable installed in one of the embodiments of the saw of FIG. 2.

Figure 8B shows a cross-sectional view of the devices in a coaxial sensing cable.

FIG. 8C shows a schematic diagram of connecting a first conductor in the sensing cable to a flat plate in the saw of FIG. 8A.

FIG. 8D shows a schematic diagram of the base located at one of the positions for connecting a second conductor in the sensing cable to an appliance enclosure in the saw of FIG. 8A.

FIG. 8E shows a schematic diagram of the base at another position for connecting a second conductor in the sensing cable to an appliance enclosure in the saw of FIG. 8A.

FIG. 9A shows a schematic diagram of a plurality of capacitive sensors which are arranged in a throat plate to surround a blade in one of the embodiments of the saw of FIG. 2.

FIG. 9B shows a block diagram of the operation process of a table saw using the capacitive sensor of FIG. 9A.

FIG. 10 shows a block diagram of the process of monitoring the action of the appliance response mechanism in one of the embodiments of the saw of FIG. 2 and disables the saw after the number of activations of the appliance response mechanism exceeds a preset number of times. Perform maintenance.

FIG. 11 shows a block diagram of a process for measuring the profiling profile of different material types in the work piece of the object detection system used in the saw of FIG. 2.

FIG. 12 shows a block diagram of the process of measuring the capacitance in the body of the operator of the saw of FIG. 2 in order to adjust the operation of the object detection system in the saw.

FIG. 13A is a schematic diagram of components in a motor of one embodiment of the saw of FIG. 2.

FIG. 13B shows a block diagram of the process of measuring the wear of a brush in the motor depicted in FIG. 13A based on the electrical resistance value of the brush.

The system shown in FIG. 13C is based on the pressure measurement performed by the spring of the commutator in the motor that pressurizes a brush in the motor depicted in FIG. 13A to move the motor. Block diagram of the process of brush wear.

FIG. 14 shows a block diagram of a process for diagnosing a fault in a sensing cable of one embodiment of the saw of FIG. 2.

For the purpose of understanding the principles of the embodiments described herein, reference will now be made to the drawings and descriptions in the following written specification. These references are not intended to limit the scope of the main content. This patent also covers any alternatives and amendments to the illustrated embodiments, and those familiar with the related technology of this document will understand the further application of the principles of the described embodiments.

As used in this article, the term "power tool" means having one or more Any tool that has moving parts that are moved by actuators (for example, electric motors, internal combustion engines, hydraulic or pneumatic cylinders, and the like). For example, power tools include, but are not limited to: bevel saws, miter saws, table saws, circular saws, reciprocating saws saw), jig saw, band saw, cold saw, cutter, impact drive, angler grinder, drill ), joining machine (jointer), nail driver (nail driver), sander (sander), trimmer (trimmer) and router (router). As used herein, the term "implement" refers to a moving part of the electric tool, which is at least partially exposed during the operation of the electric tool. Examples of appliances in power tools include, but are not limited to: rotating and reciprocating saw blades, drill bits, routing bits, grinding disks, grinding wheels, and the like. As explained below, a sensing circuit integrated with an electric tool is used to stop the movement of the appliance, so as to prevent the operator from contacting the appliance when the appliance is moving.

As used herein, the term "apparatus response mechanism" refers to a saw that retracts an implement (e.g., a blade or any other suitable position) from a position that may touch a work piece or a part of the operator's body. The device for moving the appliance), which will quickly stop the movement of the appliance, or retract and stop the appliance at the same time. As described below in the embodiment of a table saw, one form of the appliance response mechanism includes a movable drop arm that is mechanically connected to an appliance (for example, a blade) and a shaft. The instrument response mechanism includes a pyrotechnic charge, which is detected by an object detection system in response to the detection result of the contact between a part of an operator's body and the blade during the operation of the saw operating. The explosive charge forces the drop arm and the blade to move below the surface of the workbench, so that the blade can be quickly retracted from the contact with the operator. In other embodiments of the device response mechanism, a mechanical Or a motorized blade brake will quickly stop the movement of the blade.

FIG. 2 shows a schematic diagram of the components in a saw 100, and FIG. 3 shows an appearance diagram of one embodiment of the saw 100. The table saw 100 includes a work table 104 through which the saw blade 108 extends to cut work pieces, such as wood blocks. The table saw 100 further includes: an electric motor 112 that rotates a shaft 109 to drive the saw blade 108; an appliance enclosure 118; and an appliance response mechanism 132. For the purpose of explanation, FIG. 2 depicts a cutting blade 108; however, those familiar with the technology will understand that the blade 108 can be any appliance that can be used in the saw 100, and it will be understood that the blade 108 is only cited It is for the purpose of explanation. In the saw 100, the appliance enclosure 118 includes a height adjustment sliding frame and a bevel sliding frame, which surround the blade 108, and the appliance enclosure 118 can be called a blade enclosure or "shield" instead, It surrounds the blade 108 or other suitable implements in the saw 100. As shown in FIG. 3, a portion of the blade 108 extends upward through an opening in the throat plate 119 to above the surface of the table 104. A living knife 330 and a blade guard 332 are positioned above the blade 108.

Inside the saw 100, the appliance enclosure 118 is electrically isolated from the blade 108, the shaft 109, the top surface of the table 104, and a flat plate 120. In one of the embodiments, the appliance enclosure 118 includes a throat plate 119, which is formed of an electrical insulator (for example, a thermoplastic). The throat plate 119 includes an opening for allowing the blade 108 to extend above the surface of the table 104. The throat plate 119 is flush with the surface of the workbench 104, and provides further electrical isolation for the height adjustment sliding frame and the bevel sliding frame in the blade 108 and the appliance enclosure 118, so as to be separated from the surface of the workbench 104 Electrical isolation. The general configuration of the table 104, the blade 108, and the motor 112 is well known in the art for cutting work pieces and will not be described in more detail herein. For the sake of clarity, some devices commonly used in table saws have been omitted in FIG. 2, such as guide rails for work pieces, blade height adjustment mechanisms, and blade baffles.

The saw 100 further includes an object detection system 102, which includes a digital controller 140, a memory 142, a clock source 144, an amplifier 146, a transformer 150, and demodulators 143A and 143B. The object detection system 102 is electrically connected to the plate 120 and is electrically connected to the blade 108 through the appliance enclosure 118 and the shaft. The controller 140 in the object detection system 102 is operatively connected to the user interface device 110, the motor 112, and the appliance response mechanism 132. During the operation of the saw 100, the object detection system 102 detects an electrical signal caused by the change of the capacitance level between the blade 108 and the plate 120 when an object contacts the rotating blade 108. An object may include a work piece, for example, a block of wood or other materials cut by the saw 100 during normal operation. The object detection system 102 also detects the contact between the blade 108 and other objects (which may include the hand of the saw operator or a part of the body), and responds to the detection of the blade 108 and other objects other than the work piece. The contact between objects activates the device response mechanism 132. The additional structure and operation details of the object detection system 102 will be described in more detail below.

In the saw 100, the worktable 104 is electrically isolated from the saw blade 108, the crankshaft 109, and other components in the appliance enclosure 118 as shown in FIGS. 2 and 3. In one of the embodiments, the surface of the workbench 104 is formed of a conductive material, such as steel or aluminum. At the surface of the table 104, a non-conductive throat plate 119 separates the blade 108 from the surface of the table 104. Below the workbench 104, one or more electrically insulated bases (which fix the workbench 104 to the frame of the saw 100) electrically isolate the workbench 104 from other devices inside the saw. As shown in Figure 2, in some embodiments, the workbench 104 utilizes an electrical cable It is electrically connected to ground 182. This ground connection reduces or eliminates static electricity buildup on the workbench 104, which can prevent improper electrostatic discharge that would reduce the accuracy of object detection during the operation of the saw 100.

In addition to the ground connection of the workbench 104, the blade 108 and the appliance enclosure 118 are also connected to the ground 182 via a high-resistance cable (which includes a large-value resistor 180, for example, a 1 MΩ resistor). The appliance enclosure 118 is connected to the ground 182 via a first cable and a resistor 180 (which provides a high-resistance connection wire connected to the ground). The blade 108 is also connected to the ground 182 through the shaft 109 via a second cable and resistor 180. The high-resistance connecting wires used for the blade 108 and the enclosure 118 of the appliance to ground will also reduce the accumulation of electrostatic charges on these devices. When the prior art detection device requires a low-resistance ground connection line (for example, a direct connection using an electrical cable with a resistance value of less than 1Ω) in order to use a low-impedance connection line directly connected to the ground to detect a blade and The contact between an object eliminates the need for the high resistance grounding cable in the saw 100 during the operation of the object detection system 102. Instead, these high-resistance cables will only reduce the electrostatic effect in the saw 100 to reduce potential false alarm detection events; however, even without any ground connection, the object detection system 102 will still have a detection blade The complete function of the contact between 108 and an object. An alternative embodiment would use different materials in either or both of the plate 120 and the blade 108 in order to reduce static build-up in the saw 100 and there is no need to use between the blade 108 or the appliance enclosure 118 and ground. To any connecting line.

The table saw 100 includes a supporting board 304 which is placed on the rails 310 and 312. The support plate 304 is configured to move to a predetermined position in a direction parallel to the blade 108 above the worktable 104 during operation, so as to guide the work piece through the saw 100. In the saw 100, the supporting board 304 is electrically isolated from the worktable 104. For example, in Figure 3, an electrical insulation The thermoplastic rail base 306 of the edge couples the support plate 304 to the rail 310. A plastic baffle (not shown in the figure) at the bottom of the supporting board 304 and another baffle 320 at the top of the supporting board 304 electrically isolate the supporting board 304 from the workbench 104 in the saw 100 . In some embodiments, the backing board 304 includes another electrical insulator, which is positioned on the side of the backing board 304 facing the blade 108 to ensure that the backing board 304 and the blade 108 are simultaneously engaged by a work piece. The electrical isolation between the board 304 and the blade 108.

Referring again to FIG. 2, the saw 100 also includes a detection system 102 that detects the contact between an object and the blade 108 during the operation of the saw 100. In one of the configurations, some or all of the components in the detection system 102 are placed on one or more printed circuit boards (PCB). In the embodiment of FIG. 2, a separate PCB 172 supports a power supply 106 and a control TRIAC 174. The power supply 106 receives an alternating current (AC) power signal from an external power source (for example, a generator or a power facility supplier), and supplies power to the motor 112 via the TRIAC 174 so as to supply power to the sensor Devices in the system 102. Different PCBs used for the sensing system 102 and the power supply 172 will isolate the digital controller 140 and the power supply 106 and the TRIAC 174 in order to improve the cooling effect of the digital electronics in the controller 140 and isolate the controller 140 from Electrical noise. In the embodiment of FIG. 2, the power supply 106 is a switching power supply, which converts an AC power signal from an external power source into a direct current (Direct Current, at one or more voltage levels). DC) power signal to supply power to the controller 140, the clock source 144, and the amplifier 146. The detection system 102 and the devices placed in the detection system 102 are electrically isolated from a ground. The power supply 106 serves as a local ground for the devices placed in the detection system 102.

In the saw 100, the plate 120 and the blade 108 form a capacitor 124, wherein a small air gap between the plate 120 and the blade 108 acts as a dielectric. The plate 120 is a conductive plate, for example, a steel or aluminum plate, which is positioned at a predetermined distance from the blade 108, and there is a parallel alignment between the plate 120 and the blade 108 to form There are two sides of the capacitor 124 with an air gap dielectric. The transformer 150 includes a first coil 152 and a second coil 154. In the saw 100, the flat plate 120 is a metal planar member, which is electrically connected to the coil 152 in the transformer 150. The plate 120 is electrically isolated from the appliance enclosure 118 and the blade 108 by a predetermined air gap, so as to form the capacitor 124. The plate 120 is also called a Charge Coupled Plate (CCP) because the plate 120 cooperates with the blade 108 to form one side of the capacitor 124. In one of the embodiments, a plastic support member will hold the plate 120 at a predetermined distance with the blade 108 as a reference. The blade 108 and the blade shaft 109 are electrically isolated from the surrounding body 118, the plate 120, the drop arm in the appliance reaction mechanism 132, and other devices in the saw 100. For example, in the saw 100, one or more electrically insulated plastic sleeves will cause the shaft 109, the blade 108 and the appliance enclosure 118, the drop arm in the appliance reaction mechanism 132, and the saw 100 Other devices are electrically isolated. In addition, the saw blade 108 and the crankshaft 109 are also electrically isolated from the ground. Therefore, the blade object detection system in the saw 100 is operated in an "open loop" configuration, in which the capacitor 124 is formed by the plate 120 and the blade 108, and the saw blade 108 and the shaft 109 are connected to the saw 100 The other devices in it are kept electrically isolated. Compared with the prior art sensing system where the saw blade is electrically grounded, the open loop configuration increases the capacitance between the plate 120 and the saw blade 108. The larger capacitance in the saw 100 improves the signal-to-noise ratio of the signal used to detect the contact between the saw blade 108 by the operator.

As shown in FIG. 2, the plate 120 is electrically connected to the first in the transformer 150 One side of a coil 152, and the appliance enclosure 118 is electrically connected to the other side of the first coil 152. In one of the embodiments, the saw 100 includes a single coaxial cable that includes two electrical conductors for establishing the two electrical connections. In one of the configurations, the center conductor element of the coaxial cable is connected to the plate 120 and the first terminal of the first coil 152 in the transformer 150. The outer sheath of the coaxial cable is electrically connected to the blade 108 via the enclosure 118 and the shaft 109, and is electrically connected to the second terminal of the first coil in the transformer 150. The structure of the coaxial cable provides a shielding function for transmitting electrical signals from the flat panel 120 and the enclosure 118 of the appliance, while attenuating electrical noise appearing in the saw 100.

Figure 4 depicts a cross-sectional view of the blade 108, shaft 109, and plate 120 in more detail. In FIG. 4, the non-conductive sleeves 404 and 408 will engage the crankshaft 109. For example, the non-conductive sleeves 404 and 408 include electrically insulating plastic layers, ceramic layers, or other insulating layers, which electrically isolate the crankshaft 109 from other components in the saw 100. In the illustrative example of FIG. 4, the sleeves 404 and 408 include bearing shafts for rotating the crankshaft 109 during operation. The blade 108 only physically engages the shaft 109, and is electrically isolated from other components in the saw 100. In FIG. 4, a plastic support member 412 will hold the plate 120 in a position separated from the blade 108 by a predetermined distance, and at the same time electrically isolate the plate 120 from other components in the saw 100.

6A and 6B respectively show an exploded view and a front view of the device shown in FIG. 4. 6A depicts the flat plate 120 and the supporting member 412, which are fixed to the supporting frame for holding the shaft 109 by a set of screws. Electrical isolation is maintained between the plate 120 and the shaft 109 and other components in the enclosure 118. The screws may be non-conductive or the screw holes in the support frame contain non-conductive threads to maintain the electrical isolation . The supporting member 412 includes a The lip 612 surrounds the outer periphery of the flat plate 120 and extends outward beyond the surface of the flat plate 120. The lip 612 provides additional protection and electrical isolation for the plate 120 during operation of the saw 100. Specifically, the lip portion 612 prevents contact between the blade 108 and the plate 120 due to temporary shaking that may occur during the rotation of the blade 108 when the blade 108 cuts the work piece during the operation of the saw 100. FIG. 6B further depicts the lip 612 of the support member 412 extending around the plate 120.

FIG. 7 depicts additional details of one embodiment of the object detection system 102 and the power supply and control PCB 172 of FIG. 2 in more detail. In the configuration of FIG. 7, some cables used to connect different devices in the saw 100 include ferrite chokes, for example, ferrite chokes 708, 738 coupled to cables 724, 736, and 742, respectively And 740. The cable 742 connects the TRIAC 174 to the motor 112, and the ferrite choke 740 reduces noise in the current conducted through the cable 742 when the TRIAC 174 is activated, so as to supply power to the motor 112. As discussed in more detail below, the ferrite chokes 708 and 738 will reduce the noise in the data cable 724 and the power cable 736, respectively, and these cables will connect the object detection system 102 to the power supply And control PCB 172. In the configuration of FIG. 7, the sensing cable 720 (which includes the first conductor connected to the plate 120 and the second conductor electrically connected to the saw blade 108) does not pass through a ferrite choke. Similarly, a motor tachometer cable (not shown in the figure) used to connect the motor 112 to the controller 140 also does not pass through a ferrite choke. As known in the art, the ferrite chokes filter high frequency noise in the cables connected to the controller 140 and other devices in the object detection system.

Figure 7 also depicts thyristors 743A and 743B. The thyristor 743A connects the third terminal of the transformer 150 to the demodulator 143A for demodulating the in-phase component of the sensing signal. The thyristor 743B connects the fourth terminal of the transformer 150 to the second demodulator 143B for Demodulate the quadrature phase component of the sensing signal. The thyristors 743A and 743B are "dual wire" thyristors, which are also called Shockley diodes. They will switch to conduction in response to an input signal exceeding a predetermined breakdown voltage, but they do not need to be placed A separate gate control signal is in the switched on state. The thyristors 743A and 743B are configured to have a breakdown voltage which is slightly higher than the normal voltage amplitude of the sensing signal, so as to reduce the effect of random noise in the input of the demodulators 143A and 143B. However, if an object (for example, a human hand) touches the blade 108, then the input voltage will exceed the breakdown threshold level of the thyristors 743A and 743B, and both the thyristors 743A and 743B will switch to Turn on, so that the spike signal and the sensed signal are respectively led to the demodulators 143A and 143B. The thyristors 743A and 743B are unnecessary components in the embodiment of FIG. 7, and the alternative configuration of the object detection system 102 may omit these thyristors.

In FIG. 7, the data cable 724 passes through the ferrite choke 708, and the data cable 724 connects the controller 140 to the power supply 106 and the TRIAC 174 on the power supply PCB 172. In addition, the pull-down resistor 732 connects the data cable 724 between the controller 140 and the power supply PCB 172 to a local ground (for example, the one located on the PCB of the object detection system 102 A copper ground plane) in order to provide additional noise reduction in the signal transmitted above the cable 724. The pull-down resistor and ferrite choke enable the data cable 724 to use a preset command protocol (for example, I ² C) on the first PCB of the object detection system 102 and the power supply 106 and TRIAC 174 The second PCB 172 carries control signals over a long distance. For example, in one of the configurations of the saw 100, the data cable 724 has a length of about 0.75 meters and transmits an I ² C signal from the controller 140 to the power supply 106 and the command logic associated with the TRIAC 174. The power cable 736 passes through the ferrite choke 738, and the power cable 736 provides power from the power supply 106 to the controller 140 and other devices in the object detection system 102. Although Figure 7 depicts a separate data cable 724 and power cable 736; however, in another embodiment, a single cable will be simultaneously between the power supply PCB 172 and the components in the object detection system 102 Provide data connection and power connection. The single-cable embodiment also uses a ferrite choke to reduce the effect of noise in the same manner as the configuration of FIG. 7.

8A to 8E depict in more detail the coaxial cable connecting the plate 120 and the blade 108 to the detection system 102. FIG. 8A depicts an enclosure 802 containing the PCB and other components in the SCU implementing the object detection system 102 and other control components in the saw 100. The sensing cable 720 is electrically connected to both the sensing plate 120 and the blade 108. 8A and 8B, the sensing cable 720 is a coaxial cable, which has: a first inner conductor 852; an electrical insulator 856, which surrounds the inner conductor 852 and the inner conductor and a The second metal conductor 862 is separated; and an outer insulator 864 surrounding the second conductor 862. In the configuration of FIG. 8A, the first conductor 852 is connected to the plate 120 and is connected to the first terminal of the transformer 150 in the object detection system 102 as shown in FIG. The second conductor 862 is electrically connected to the blade 108 and is connected to the second terminal of the transformer 150 in the object detection system 102 as shown in FIG. 2.

Although FIG. 8B depicts a coaxial cable; however, an alternative embodiment uses a twisted pair cable, which includes two different conductors twisted to each other in a spiral pattern. One or two conductors in the twisted-pair cable are surrounded by an electrical insulator to isolate the conductors from each other. In addition, a shielded twisted pair cable includes an external shield, for example, a metal sheet, which wraps around the twisted pair cable and reduces external electrical noise on the conductors in the twisted pair cable The effect.

8A depicts the single sensing cable 720 connected to the flat plate 120 at position 832 and connected to the angle sliding frame and the height adjustment sliding frame of the appliance enclosure 118 at positions 836 and 838. FIG. 8C depicts in more detail that the first conductor in the sensing cable 720 is connected to the plate 120 at position 832. A metal fixing clip 866 is attached to the plate 120 and attached to the first conductor 852 in the sensing cable 720 to establish an electrical connection. In the configuration of FIG. 8C, the fixing clip 866 is inserted between the flat plate 120 and the supporting member 412 to ensure a stable connection between the sensing cable 720 and the flat plate 120. In some embodiments, the fixing clip 866 is welded to the plate 120.

Although the second conductor 862 is electrically connected to the blade 108; however, because the blade 108 will rotate during the operation of the saw and because the blade 108 is usually a removable device, the second conductor 862 is not directly connected. Is physically connected to the blade 108. Instead, the second guide system is connected to the appliance enclosure 118. In some embodiments of the saw, the surrounding body 118 actually includes a plurality of components, for example, the height adjustment sliding frame and the bevel sliding frame in the saw 100. In order to ensure a consistent electrical connection, the second conductor in the single sensing cable 720 is connected to each of the height adjustment carriage and the angled carriage, so as to maintain reliable electrical connection with the blade 108 connection. For example, in FIG. 8, the second guide system in the sensing cable 720 is connected to the height adjustment carriage at position 836 and is connected to the angled carriage at position 838.

Figure 8D and Figure 8E depict two different base positions, which connect the second conductor of the sensing cable 720 to the appliance enclosure 118 at two different positions, including a height adjustment sliding frame and an inclined sliding frame Both. As shown in FIG. 8D, the second conductor is electrically connected to and physically connected to the appliance enclosure 118 at a position 836 using a connection base 872. Outermost The insulator 864 is removed from the sensing cable 720 in the connection base 872 to establish an electrical connection with the appliance enclosure 118. In some embodiments, the connection base 872 is formed by a metal sleeve to surround and engage a part of the second conductor 862 in the sensing cable 720. As described above, the appliance enclosure 118 is electrically connected to the shaft 109 and the blade 108, and the cable base 872 will be mounted on the second conductor 862 and the blade in the sensing cable 720 via the height adjustment sliding frame. Provide reliable electrical connection between 108. FIG. 8E depicts another configuration of the connection base 876, which fixes the sensing cable 720 to the bevel slide frame at position 838 and the second conductor 862 in the sensing cable 720 and the appliance enclosure Provide reliable electrical connection between 118. In one of the embodiments, the connection base 876 is also formed by a metal sleeve to enclose a part of the second conductor 862 in the sensing cable 720 so as to communicate with the blade through the instrument enclosure 118 108 Establish an electrical connection.

As shown in FIGS. 2 and 7, the controller 140 is operatively connected to the power supply 106 and the TRIAC 174 on the separate PCB 172 via a data line. In the embodiment of the saw 100, the data line is a multi-conductor cable, such as an HDMI cable, and the controller 140 transmits command information to the PCB 172 using the I ² C protocol. The controller 140 may use the I ² C protocol to receive status data or data from a sensor (for example, an on-board temperature sensor) on the PCB 172 as appropriate. The ferrite choke 708 will reduce the electrical noise in the data cable 724 and the ferrite choke 738 will reduce the electrical noise in the power cable 736. Filling the resistor 732 also reduces the noise flowing through the data cable 724. In one of the embodiments, the data cable 724 includes a physical configuration that conforms to the High-Definition Multimedia Interface (HDMI) standard, and includes multiple shielded twisted-pair conductors; however, the data The cable 724 does not transmit video data and audio data during the operation of the saw 100. In the embodiment of FIG. 2, the data cable has a length of about 0.75 meters to connect the separated PCBs 102 and 172.

During operation, the controller 140 will send a signal to inform the TRIAC 174 to supply current to the motor 112 via a gate in the TRIAC. Once triggered, as long as at least one preset level of the current from the power supply 106 passes through the TRIAC 174 to supply power to the motor 112, the TRIAC 174 will remain activated. The power supply 106 changes the amplitude of the current delivered to the motor 112 to adjust the rotation speed of the motor 112 and the saw blade 108. In order to turn off the motor 112, the power supply will reduce the power level supplied to the TRIAC 174 below the preset holding current threshold and the TRIAC 174 will be switched to non-conduction. In the embodiment of FIG. 2, the TRIAC 174 will enable the operation of the motor 112 at different speed levels and can start/stop without using a repeater normally required in the prior art electric saw. In the illustrative example of FIG. 2, the TRIAC 174 transmits an AC electrical signal to the motor 112; however, alternative embodiments can be replaced by a DC motor that receives DC power.

The associated components in the controller 140 and the detection system 102 are sometimes referred to as Saw Control Unit (SCU). The SCU is electrically isolated from other devices in the saw 100 except for power connection wires, control wires, and sensor data connection wires between the detection system 102 and other devices in the saw 100. In the saw 100, the controller 140 is also responsible for controlling other operations in the saw 100 that are not directly related to the detection object contacting the blade 108, such as starting and stopping the motor 112. In the embodiment of FIG. 2, the SCU is located outside the enclosure 118, the detection system 102 is placed on a non-conductive plastic support member, and the detection system 102 is configured to avoid the detection system The ground plane of 102 is placed parallel to any metal components inside the saw 100 in order to reduce the electrical noise transmitted to the conductive circuit in the detection system 102.

In the saw 100, the clock source 144 and the drive amplifier 146 in the sensing circuit generate a time-varying electrical signal, which is guided through the first coil 152 in the transformer 150, the capacitive coupling plate 120, and the blade 108 And the appliance enclosure 118. The time-varying electrical signal is called "sensing current" because the controller 140 senses the contact between the blade 108 and a part of the human body with reference to the amplitude change of the sensing current. The time-varying electrical signal is a complex value signal, which includes both an in-phase component and a quadrature-phase component. The sensing current passes through the first coil 152 in the transformer 150 and reaches the plate 120. The change in the first coil caused by the discharge between the plate 120 and the blade 108 will generate an excitation signal in the second coil 154 of the transformer 150. The excitation signal is another complex value signal, which corresponds to the sensing current through the first coil 152.

The controller 140 in the sensing circuit is operatively connected to the motor 112, the second coil 154 in the transformer 150, and the mechanical appliance reaction mechanism 132. The controller 140 includes one or more digital logic devices, including: a general-purpose central processing unit (CPU), a microcontroller, a digital signal processor (Digital Signal Processor), and an analog-to-digital converter ( Analog to Digital Converter (ADC), Field Programmable Gate Array (FPGA), Application Specific Integrated Circuit (ASIC), and any other digital devices suitable for the operation of the saw 100 or Analog device. The controller 140 includes a memory 142 that stores programmed instructions for the operation of the controller 140 and data corresponding to the maximum-minimum variation threshold, data corresponding to the variation threshold, or corresponding to The frequency response threshold data is used to identify whether the sampling of the sensing current flowing through the blade 108 indicates that the saw blade 108 is rotating or has stopped.

During the operation of the sensing circuit, the clock source 144 will generate at a predetermined frequency. Generate a time-varying signal, for example, a sine wave. In the embodiment of FIG. 2, the clock source 144 is configured to generate a signal at a frequency of 1.22 MHz, which is known to be conducted through the human body. The amplifier 146 generates the sensed current as an amplified version of the signal from the clock source 144, which has sufficient amplitude to drive the transformer 150 and the capacitor 124 for detection by the controller 140. In the embodiment of FIG. 2, although the saw 100 uses amplitude modulation (Amplitude Modulation, AM) to generate the sensing signal; however, in an alternative embodiment, the sensing signal may also use frequency modulation and phase modulation. Change, or other suitable modulation techniques.

該控制器140會在預設頻率量測該經解調變的信號，例如，100KHz取樣率並 且每一個取樣之間有10微秒的週期，以便辨識該複數值信號的振幅A之中的變化。 During the operation of the sensing circuit, the controller 140 receives the in-phase component I of the excitation signal in the second coil 154 via the first demodulator 143A and receives the excitation via the second demodulator 143B. The quadrature component Q of the signal. The transformer 150 isolates the sensing current flowing through the first coil 152, the plate 120, the saw blade 108, and the appliance enclosure 118 and supplies the in-phase and quadrature-phase components of the signal to the demodulator 143A of the controller 140. With 143B. Because the demodulators 143A and 143B generate electrical noise, the transformer 150 reduces or eliminates the effect of the noise on the first coil 152 and the sensing current. In one configuration, the transformer 150 is a 1:1 transformer, wherein the first coil 152 and the second coil 154 have the same number of turns. In an alternative configuration, the ratio of the coils among the first coil 152 and the second coil 154 is selected so as to increase or decrease the signal to be demodulated and monitored by the controller 140. The controller 140 includes one or more ADCs, filters, and other signal processing devices needed to generate digital representations of the amplitudes of the in-phase signal I and the quadrature signal Q. The controller 140 regards the amplitude of the sensing current A at a given time as the Pythagorean sum of the in-phase and quadrature components in each sample as shown in the following formula:

The controller 140 measures the demodulated signal at a preset frequency, for example, a sampling rate of 100KHz and a period of 10 microseconds between each sample, so as to identify the change in the amplitude A of the complex value signal .

When the motor 112 rotates the blade 108, the rotating blade 108 will contact various objects, including wooden blocks and other work pieces. Although a small part of the charge accumulated on the blade 108 will flow into the work piece; however, the conductivity of the wooden work piece is quite low, and the controller 140 in the sensing circuit will continue to enable the motor 112 To rotate the saw blade 108. For example, when the blade 108 engages a wooden block, the controller 140 usually measures a small change in the sensing current A; however, the change in the sensing current is regarded as corresponding to the wood. Or other materials with low conductivity.

When the work piece (for example, wood) has a low conductivity, another object (for example, a part of the human body) will have a higher conductivity and absorb a larger part of the charge on the blade 108 when the part approaches the blade 108. In FIG. 2, a portion 164 of the human body (for example, a hand, finger, or arm) is represented by a charged cloud, which represents the flow of electric charge from the blade 108 to the human body. The contact between the human body and the blade 108 will effectively change the capacitance level, because both the human body and the saw blade 108 will receive charges from the sensing current. When the human body 164 contacts the blade 108, the controller 140 recognizes the contact between the human body 164 and the blade 108 as a rapid increase in the amplitude A of the sensing current. In response to the rapid increase in the amplitude of the sensing signal, the controller 140 turns off the motor 112, turns on the appliance response mechanism 132 to stop the movement of the blade 108, and retracts the blade 108 before it contacts the human body 164 as appropriate.

In the configuration of Figure 2, even when the detection system 102 is isolated from the ground and the human body 164 is isolated from the ground (for example, when the operator wears rubber-soled shoes), the human body still has sufficient conductivity and capacitance The coefficient draws charge from the blade 108. Therefore, the detection system Although 102 and the human body 164 do not share a common electrical ground; however, the controller 140 can still confirm the contact between the human body 164 and the blade 108 by confirming the rapid increase of the identified sense current amplitude A. Although the absolute value of the amplitude A may change during the operation of the saw 100; however, the controller 140 can still confirm the contact with the human body 164 in response to the increased amplitude and time of the relative value of the amplitude A. During the operation of the saw 100, the controller 140 is configured to confirm contact with the human body 164 and to turn off the motor 112 and turn on the appliance reaction mechanism 132 so as to stop the saw blade 108 in a time period of about 1 millisecond.

In the saw 100, the controller 140 turns off the electric motor 112 in response to confirming the contact between the blade 108 and a part of the human body. In the saw 100, due to the momentum accumulated by the saw blade 108 during operation, the saw blade 108 usually continues to rotate for a period of several seconds. The instrument response mechanism 132 is configured to stop the saw blade 108 in a very short period of time; lower the saw blade 108 below the worktable 104, which will retract the saw blade 108 from contact with the human body; Or, stop and retract the blade 108 at the same time. In the saw 100, the instrument response mechanism 132 includes a drop arm, which is mechanically connected to the saw blade 108. The appliance response mechanism 132 also includes a explosive pack configured to pull the drop arm into the housing of the saw and away from the surface of the workbench 104. The controller 140 operates the explosive pack to move the drop arm and the blade 108 downward in response to detecting the contact between a part of the operator's body and the blade 108. The appliance reaction mechanism retracts the blade 108 below the surface of the workbench 104.

In some configurations of the saw 100, the controller 140 is configured to lock the operation of the saw 100 after the explosive device is fired a predetermined number of times. For example, in the configuration of the saw 100, the appliance response mechanism 132 includes a dual explosive drug with a total of two "shots" package. Each operation of the reaction mechanism of the device will consume a burst of explosives in a "monoshot" operation. The operator removes and reinserts the explosive device so as to place the second explosive pack in the correct position for moving the drop arm during the continuous operation of the appliance reaction mechanism 132. The controller 140 stores a record of the number of activations of the appliance response mechanism 132 and prevents the saw 100 from being activated during the locking process after the number of activations exceeds a preset number (for example, one, two, or more activations). In an embodiment of the saw 100 connected to a data network (for example, the Internet), the controller 140 will send a network notification to the service provider or warranty provider during the lock operation as appropriate. The locking process will allow the service provider to diagnose potential problems with the operation of the saw 100 or the use procedure of the saw 100 in response to the frequent operation of the appliance response mechanism 132.

In addition to sensing the contact between an object and the saw blade 108 when the saw blade 108 is moving, the sensing circuit in the saw 100 is also configured to confirm whether the saw blade 108 is running when the motor 112 is turned off. mobile. For example, the controller 140 will confirm that the saw blade 108 is to be activated after an operator operates the user interface 110 to start the saw 100 to cut one or more work pieces and then operates the user interface 110 to turn off the motor 112 The time period to continue rotating. For example, the user interface 110 includes: an on/off switch for operating the saw 100; a speed control input device; and a status indicator, which provides information related to the operating state of the saw 100, for example, whether the saw is Ready to operate or a failure has occurred. The user interface device 110 is also known as a human machine interface (HMI).

The saw 100 is configured to operate with a blade 108 and a blade shaft 109 that are isolated from electrical ground. Although the control electronics on the circuit boards 102 and 172, the plate 120, and the appliance enclosure 118 may not be connected to the real ground ground in some configurations; however, this These devices share a common ground plane, for example, the common ground plane formed by the metal chassis of the saw or the common ground plane formed by the ground planes formed on the circuit boards of 102 and 172. As described above, during the contact detection process, the controller 140 will recognize the spikes in the current level of the sensing signal. However, the electrical noise generated in the saw 100 will generate false alarm detection events or miss detection events because the noise will interfere with the detection of the sensing signal. In the saw 100, the PCBs 102 and 172 include ferrite core chokes, which act as low-pass filters to reduce the effect of noise. In addition, circuit cables and data cables also pass through the ferrite core to reduce noise. The power supply 106 includes a ferrite choke coil and a brake fluid to reject low-speed transient noise in the power signal received from the power grid, generator, or other power source.

5A to 5D depict a part of one embodiment of the user interface device 110 in more detail. FIG. 5A shows an appearance view of a device status display, which includes a housing 502, a plurality of indicator lights 528A to 528D, and a cover plate 512 for a short-range antenna. During operation, the controller 140 activates one or more of the indicator lights 528A to 528D to indicate different status information related to the saw 100. For example, the indicator light 528A indicates that the saw 100 is ready for operation. The indicator light 528B indicates that the appliance response mechanism 132 has been operated and the explosive pack in the appliance response mechanism 132 should be reset. The indicator light 528C indicates that the user should check the fault code. The indicator light 528D indicates that the saw 100 needs maintenance after the appliance reaction mechanism has been operated for more than a preset number of times. As shown in FIG. 5A, the indicators 528A to 528D provide a simplified interface. Alternative embodiments include a different indicator light arrangement or include additional input devices and output devices, such as video display screens, touch input devices, and the like.

Although the display indicators 528A to 528D provide simplified direct output feedback to the operator to use the saw 100 normally; however, in some cases, the saw 100 will send more complex diagnostic and configuration data to an external device. The controller 140 and the user interface device 110 may transmit more complex diagnostic data and other information related to the saw 100 to an external computing device via the short-range wireless antenna under the cover 512 as appropriate. Examples of the diagnostic data collected by the controller 140 and optionally transmitted by the wireless transmitter and antenna 516 include: the voltage present in the sensing circuit; the level of the sensor signal; it is used to indicate the response mechanism of the appliance 132 Whether the explosive device (pyro) in the pyro is armed or disarmed; it generates a test signal for the firing line of the pyro, but does not send a signal with sufficient amplitude to trigger the single firing operation of the pyro ; Detect the presence or absence of the pyro; check the resistance range of the sensor cable connected to the plate 120 and the appliance enclosure 118 or other cables in the saw 100 for corrosion or wire damage; A "tackle pulse" is generated to identify the disconnection in the circuit supplying power to the motor 112; and to identify the fault in the motor 112 during the power-on self-test.

As shown in FIG. 5B, the short-range wireless antenna 516 is formed by a preset arrangement of multiple conductor lines on the PCB supporting the indicator lights 528A to 528D. Figures 5B and 5C depict semi-transparent caps 504A to 504D, which form the externally visible surface of each of the indicator lights 528A to 528D, respectively. The housing 502 protects the antenna 516 from damage by external elements, and at the same time allows the antenna to be placed outside the saw 100 to communicate with external electronic devices. The antenna 516 is operatively connected to a wireless transceiver, such as NFC, Bluetooth, IEEE 802.11 protocol series compatible wireless transceiver ("Wi-Fi"), or other suitable short-range wireless transceiver. An internal electronic device (for example, a smart phone, a tablet computer, a portable notebook computer, or other mobile electronic device) will receive data from the saw 100 through a wireless communication channel and use it as appropriate Use the wireless communication channel to transmit information to the saw. For example, a smart phone will receive diagnostic data from the saw 100, and a software application running on the smart phone will display detailed diagnostic information to an operator or maintenance technician to help maintain the Saw 100. The software application can allow the operator to input configuration information of operating parameters of the saw 100 that cannot be directly accessed through the simplified input device 110 as appropriate. For example, in one of the configurations, the software application allows the operator to input the maximum RMP rate of the motor 112 and the blade 108. In another configuration, the software application allows the operator to transmit the identification code of the material type that the saw 100 will cut during operation, for example, different types of wood, ceramics, plastics, and the like.

In another configuration, the saw 100 includes a locking mechanism to prevent the saw 100 from operating unless the mobile electronic device with the correct encryption key is located within a preset distance of the saw 100. The mobile electronic device will send an encrypted authorization code to the saw 100 in response to the query from the saw 100 to unlock the saw 100 for operation. When the mobile electronic device is removed from the vicinity of the saw 100, a subsequent query will fail and the saw 100 will remain inactive.

Figure 5C depicts a cross-sectional view of the indicator lights 528A to 528D. Each indicator light includes a semi-transmissive cap (for example, the cap 504A on the indicator 528A), and an opaque body member 524A guides light from a light source (for example, LED) to The translucent cap. In the indicator light 528A, an LED 552 placed on the PCB projects light through an opening in the opaque body member 524A and the translucent cap 504A. The opaque body member 524A has a tapered shape with a narrow end surrounding the first opening of the LED 552A and a wider end having a second opening for engaging the translucent cap 504A. Should you The light-transmitting member 524A prevents the light from the LED 552A from passing through and produces erroneous illumination in any of the other indicator lights 528B to 528D. The configuration of FIG. 5C allows the indicator lights in the user interface device 110 to operate in direct daylight conditions and prevents incorrect lighting of incorrect indicator lights during operation.

Figure 5D depicts an exploded view of the selected device of Figures 5A to 5C. FIG. 5D depicts the indicator cap assembly 540, which is formed of a molded plastic member, and includes translucent indicator caps 504A to 504D for indicator lights 528A to 528D. The indicator cap assembly 540 also includes an attachment member, for example, a hook 506, which is formed by the molded plastic member of the indicator cap assembly 540 to fix the caps to use Other devices in the interface device 110. The body member assembly 544 is another molded plastic member, which includes opaque body members 524A to 524D corresponding to the cap portions 504A to 504D. Each of the opaque body members 524A to 524D includes a first opening and a second opening. The first opening is aligned with one of the LEDs 552A to 552D, and the second The opening engages one of the caps 504A to 504D. The body member assembly 544 also includes attachment members, for example, hooks 526, which connect the opaque body members to other devices in the user interface device 110. The PCB 550 includes a plurality of physical placement positions and a plurality of electrical connection lines for operating the user interface device 110. Specifically, FIG. 5D depicts Light Emitting Diodes (Light Emitting Diode, LED) 552A to 552D, which are aligned with the first openings in the corresponding opaque members 524A to 524D and provide light to the caps of the indicator lights 528A to 528D. Parts 504A to 504D. The PCB 550 also includes an antenna 516, which is formed by a preset pattern composed of a plurality of conductor lines on the PCB for wireless communication with the user interface device 110. In some embodiments, PCB 550 also directly supports a wireless transceiver; in other embodiments, the wireless transceiver Integrated with the controller 140. The indicator cap assembly 540, the main body assembly 544, and the PCB 550 are disposed on a base member 560, which is a molded plastic member in the embodiment of FIG. 5D. The base member 560 fixes the components of the user interface device 110 to the housing of the saw 100.

The user interface device 110 shown in FIG. 3 is installed on the outside of the housing of the saw 100. The base member 560 attaches the components in the user interface device 110 to the outside of the housing in the saw 100, where the user can easily see the indicator lights 528A to 528D. Furthermore, the antenna 516 on the PCB 550 is positioned outside the electrical shield of the saw 100, and it provides a full perspective view of the power supply 106 to communicate with short-range external wireless devices and to transmit and receive any wireless transmissions on the antenna 516 and the PCB 550. The device is isolated from the electrical noise source in the saw 100. A data cable (not shown in the figure) connects the controller 140 placed on the PCB inside the casing of the saw 100 to the user interface device 110 outside the saw.

Although the user interface device 110 described above includes a plurality of indicator lights and a wireless data interface; however, in some configurations, the saw 100 also includes an additional data interface device. For example, in one of the embodiments, a universal serial bus (USB) or other suitable wired data connector is operatively connected to the controller 140. The saw 100 includes a USB port near the back of the inclined sliding frame. The USB port is hidden so that ordinary operators cannot see it; however, maintenance personnel can move the inclined sliding frame to the leftmost inclined position or the rightmost inclined position and pass through the back of the housing of the saw 100 To locate the USB port and access the USB port. The USB port is connected to an external computing device for performing diagnostic operations and maintenance operations. The USB connection can also allow maintenance personnel to update the controller 140 that has been stored in the controller 140 during the operation of the saw 100. Software programs in the memory 142.

Referring again to the saw configuration of FIG. 2, in one of the operating modes, the controller 140 in the saw 100 uses an adaptive threshold processing process to identify the current corresponding to the contact between an operator and the blade 108 Spikes in order to control the operation of the appliance response mechanism 132. During the adaptive threshold process, the controller 140 recognizes the average signal position of the sensing signal in a predetermined period of time (for example, 32 sampling periods lasting 320 microseconds at a sampling rate of 100KHz) quasi. The controller 140 applies a preset bias value to the detected average level and uses the sum of the average value and the bias level as an adaptability threshold. The controller 140 will update the average threshold value based on a relatively small change in the average level of the sensed signal due to electrical noise, which prevents when the level of the sensed signal is only due to the A false alarm contact event is detected when the electrical noise in the sensing signal changes. If a contact occurs between the operator and the blade 108, the rapid spike in the sensing current will exceed the preset deflection level, and the controller 140 will detect the contact and activate the appliance response mechanism 132.

In an optional embodiment of the adaptive threshold detection process, the controller 140 also recognizes the signal-to-noise ratio in the sensing signal in response to detecting a spike in the sensing signal current. to Noise Ratio, SNR) in order to further reduce the possibility of false alarm detection. The controller 140 refers to the average value of the signal in a predetermined time window divided by the variance of the signal level in the same time window to identify the SNR. In one of the configurations, the controller 140 implements a block calculation process to reduce the computational complexity of identifying the SNR, which allows the controller 140 to identify the SNR within the operating timing constraints of the operation of the appliance reaction mechanism 132. During the block calculation process, the controller 140 will recognize that the signal is in multiple relatively short blocks (for example, in The average value of 32 sampling periods lasting 320 microseconds in the sampling rate of 100KHz) is averaged and the calculated block average values are stored in a memory. The controller 140 then identifies the SNR in a series of blocks, for example, in one embodiment, eight consecutive time blocks in 2560 microseconds.

The controller 140 will identify based on the difference between the eight "local" average values appearing in each of the eight blocks and the single "global" average value of all eight blocks The single variance value of all blocks. The controller 140 only recognizes the SNR based on the eight average values and the identified variance value, and does not recognize the average value and variance of all 256 different samples. The block calculation process will greatly reduce the computing power required to identify the SNR. The controller 140 will continue to identify additional samples over time during operation and update the SNR samples after removing the oldest block in the set of eight blocks to accommodate newer samples. After identifying the SNR, the controller 140 will determine whether the SNR level is within the preset minimum threshold when a sensing current spike that exceeds the detection threshold of the contact between the operator and the blade 108 is detected the following. If the SNR level is too low, it means a weak signal level lower than the detected noise level, then the controller 140 will not operate the appliance response mechanism 132, so as to prevent the operator from actually failing A false alarm operation occurs when the blade 108 is not touched.

Another optional configuration of the adaptive threshold processing process includes an operation to detect electrostatic discharge from the blade 108 and prevent the electrostatic discharge event from being incorrectly recognized as a contact between the operator and the blade 108. During the operation of the saw 100, the rotating blade may accumulate static electricity and discharge the static electricity to a device inside the saw 100 or to an external object, such as a work piece. The electrostatic discharge often produces a momentary positive in the sensing signal. A voltage spike or a negative voltage spike, which is similar to a spike that appears in response to the contact between the operator and the blade 108. However, the amplitude of spikes caused by electrostatic discharge is often several times larger than any spikes caused by contact with the operator. Therefore, in some embodiments, the controller 140 not only recognizes human contact in response to the amplitude of the sensing signal exceeding the adaptive threshold, but the controller 140 also responds to the peak amplitude at an upper threshold ( It is higher than the initial detection threshold) to identify human contact, so as to avoid the false alarm operation of the appliance reaction mechanism 132 in response to an electrostatic discharge event.

The adaptive threshold processing process can be used in a variety of operating modes of the saw 100, including the operating mode of the saw 100 performing "DADO" cutting. As known in the art, during the DADO cutting operation, the blade 108 will cut a groove through all or a part of a work piece; however, it will not completely cut the work piece into two separate parts. Many DADO cuts produce grooves thicker than a single saw blade, and the saw 100 is operated with multiple saw blades placed on the shaft 109 to form the thicker grooves. The multiple saw blades act as an antenna and receive electrical noise from various sources inside and outside the saw 100, which will reduce the signal-to-noise ratio during DADO cutting.

In some embodiments, the controller 140 also detects the contact between the operator and the blade 108 during a long period of time during the DADO cutting operation, so as to resolve the high noise level that appears in the detection signal. quasi. For example, in one of the configurations, the controller 140 will identify spikes in the current level that exceed the adaptive threshold for contact detection in the first sampling period. In a high-noise environment, the noise spike may also produce a large spike that exceeds the adaptability threshold level; however, a real contact event will produce a relatively uniform spike in the current. It is in several sampling periods (for example, at a sampling rate of 100KHz Up to 10 cycles) are maintained above the critical value. The controller 140 recognizes the spike level changes in multiple sampling periods. If the spike maintains a high amplitude and does not change the level by a large amount in several sampling periods, then the controller 140 will confirm that the blade 108 is in contact with the operator and will activate the appliance response mechanism 132. However, if the controller 140 determines that there is a large variation in the level of the sensing current spike, then the controller 140 will confirm that the changes in the sensing current are caused by noise and not The device response mechanism 132 will be operated. Even in a long detection period, the total detection and operation time of the object detection system 102 still occurs within a period of only a few milliseconds, so as to maintain the effectiveness of the appliance response mechanism 132.

Although the adaptive threshold process will improve the accuracy of contact detection during DADO cutting; however, it is not necessary to use the adaptive threshold process during the DADO cutting process, and the adaptive threshold process can also be used Used in other operating modes of the saw 100.

During the operation of the saw 100, the controller 140 may implement a fault detection process as appropriate to identify faults in the cable connecting the sensor plate 120 or the appliance enclosure 118 to the detection system 102. The controller 140 recognizes hard faults through a continuity test, for example, a complete disconnection in the cable. When the cable is at least intermittently connected but the quality of the connection cannot allow the sensing signal to reach the sensor plate 120 and allow the controller 140 to detect the sensing current flowing through the capacitor 124, so-called "soft" will occur. "Soft fault". In one of the configurations, the controller 140 will first identify the soft fault before starting the motor 112. The controller 140 generates a sensing current flowing through the sensing cable when the motor 112 is kept off and the electrical noise level in the saw 100 is relatively low. If the amplitude or noise level of the sensing signal deviates from the expected value by greater than the preset operating tolerance threshold, then the controller 140 will confirm that the sensing cable is There is a soft fault. The controller 140 generates an error signal via the user interface device 110 and prevents the motor 112 from starting in response to detecting a hard fault or a soft fault in the sensing cable before the sensing cable is repaired or replaced .

In some embodiments, the saw 100 is characterized by the capacitance levels of different operators contacting a capacitive sensor located at a predetermined contact position of the saw. For example, in one of the embodiments, the saw 100 includes a metal handle. When an operator grasps the handle, it registers the capacitance, conductance, and other electrical characteristics of the operator's hand. In other embodiments, a capacitive sensor may be placed in a track or other surface in the saw 100, and the operator may touch the capacitive sensor during the typical operation of the saw 100. The controller 140 receives sensor data corresponding to the electrical characteristics of each operator and adjusts the blade contact detection threshold and other operating parameters to improve the accuracy of each operator's blade contact detection result.

In some embodiments, the saw 100 uses the sensing signal to perform pattern detection to identify the state of the blade 108 during operation. For example, in one of the embodiments, the controller 140 recognizes the element in the sensing signal corresponding to the tooth collision between the blade 108 and a work piece. The controller 140 will use a tachometer or other RPM sensor to identify the rotation rate of the blade 108 as appropriate, and the controller 140 will receive data corresponding to the size and number of teeth on the blade 108 in order to use 108 Confirm the expected tooth impact frequency when engaging the work piece. The controller 140 uses the expected tooth impact frequency to help identify the sensing signal that may correspond to the contact between the operator and the blade 108, or only corresponds to the electrical noise generated by a tooth hitting the work piece.的sensing signal.

In some embodiments of the saw 100, when the saw 100 cuts different types of materials, the controller 140 stores the identified profiling profile of the sensing signal. for example, The saw 100 cuts through all kinds of wood or wood blocks with different moisture levels in order to recognize the amplitude and noise level of the sensing signal detected when cutting a plurality of different types of wood or other materials . The profiling profile generation process may be carried out at the factory before the saw 100 is shipped as appropriate. During the subsequent operation, the operator will provide input to characterize the type of material to be cut by the saw 100, and the controller 140 will retrieve the stored profile of the expected sensing signal parameters from a memory. In order to help identify the expected sensing signal when cutting the work piece.

FIG. 9A shows another embodiment of an object detection sensor suitable for use with the saw 100 or the object detection system 102 among other saw embodiments. In FIG. 9A, the throat plate 119 includes capacitive sensors 904, 908, and 912. Each of the sensors 904, 908, and 912 is a capacitive sensor, and they can detect contact with or very close to the surface of the corresponding capacitive sensor due to changes in capacitance near the sensor. The presence of human hands or other body parts. On the contrary, a work piece (for example, wood) will produce very different capacitance changes, so that a controller (for example, the controller 140 shown in FIG. 2) can distinguish the work piece from the body part of the human body. The capacitive sensors 904 to 912 are arranged along the cutting direction 920, which corresponds to the advancing direction of the work piece when the blade 108 cuts the work piece. The capacitive sensor 904 is arranged in an area spanning the front of the saw blade 108. Viewed from the front of the saw blade 108, the capacitive sensors 908 and 912 are arranged on the left-hand side and the right-hand side in a conformal manner to the saw blade 108, respectively.

As shown in FIG. 9A, each of the capacitive sensors 904 to 912 occupies a predetermined area of the throat plate 119, for example, the rectangular area shown in FIG. 9A or another geometric shape. In some embodiments, the capacitive sensors 904 to 912 not only detect proximity to the Corresponding to the presence of the human body part of the sensor, the position of the human body part above the sensor and the speed and direction of the human body part moving over time are also detected. The thermoplastic throat plate 119 isolates the capacitive sensors 904 to 912, the blade 108, the surface of the table 104, and other devices in the saw.

The operation process 950 of the capacitive sensors 904 to 912 in the saw 100 is shown in FIG. 9B. In the following description, the process 950 for implementing a certain function or action will describe the operation of a controller so as to cooperate with other devices in the saw used to implement the function or action to execute stored program instructions. For the purpose of explanation, the process 950 will be described in conjunction with the embodiment of FIG. 9A and the saw 100.

The process 950 begins with the saw 100 being activated and the motor 112 moving the blade 108 to cut the work piece (block 954). During operation, the capacitive sensors 904 to 912 will generate the capacitive sensing signals, so that the detection side is located in the throat plate 119 and surrounds the blade 108 of the capacitive sensors 904 to 912 The presence of objects on the surface (block 958).

If the controller 140 recognizes the change in the capacitance level of one or more of the capacitive sensors 904 to 912 based on the change in the RC time constant of the capacitive sensing signal, then the controller 140 Then, before an object (for example, a work piece or a human body part) contacts the saw blade 108, it is first detected that the object appears in the area near the saw blade (block 962). For example, in some embodiments, the capacitive sensors 904 to 912 include: a plurality of capacitive sensing elements, which form one of the plates in a capacitor; and a non-conductive dielectric It will cover the capacitive sensing elements and the surfaces of the capacitive sensors 904 to 912. An oscillator in the capacitive sensors uses an RC circuit to generate a time-varying capacitive sensing signal. The RC circuit is determined by the capacitive sensor in each sensor. Components and a preset resistor. As known in the art, the RC time constant will change in response to the change of the capacitance C in the RC circuit, and the capacitive sensor or an external control device will use the time-varying signal Change is the basis to recognize contact with objects. An object positioned above the surface of one of the sensors 904 to 912 acts as a second plate of a capacitor and produces a change in the capacitance level of the sensor.

If the controller 140 confirms that there is no object at the proximal end of the capacitive sensors (block 962) or the controller 140 confirms that a detected object produces a minimum capacitance change corresponding to a work piece other than a human body part (Block 966), then the saw 100 will continue to operate to cut a work piece (Block 970). Conductive objects (for example, the operator's fingers or other body parts) will produce relatively large capacitance changes, while non-conductive objects (for example, wooden work pieces) will produce small capacitance level changes. As mentioned above, the characteristics of a work piece (for example, wood) will produce a capacitance change in the sensors 904 to 912 that is significantly different from that of the human body, so that the controller 140 can distinguish the work piece and very close to the Some capacitive sensors 904 to 912 are human body parts.

During the process 950, if the capacitive sensors generate a signal corresponding to a very large capacitance change (which corresponds to a hand or other body part very close to the capacitive sensors 904 to 912), then , The controller 140 will generate a warning output before the object contacts the blade 108, turn off the motor 112, or activate the appliance response mechanism 132 (block 974). In the configuration where the detected object does not actually touch the blade but has moved to the preset distance of the blade, the controller 140 will turn off the motor 112 to stop the saw blade 108, but it will not The instrument response mechanism 132 is turned on unless the object detection system 102 described above detects that the object actually touches the blade. In other embodiments, if the capacitive sensing If the devices 904 to 912 detect an object corresponding to a human body part, the controller 140 will generate a warning signal on the workbench 104 before turning off the motor 112 or operating the appliance response mechanism 132, for example, allowing the operation The light seen by the reader. In some embodiments, if the object contacts the blade 108, the object detection system 102 first operates the appliance response mechanism 132 before the blade 108 is completely stopped or before the object contacts the blade 108.

In some embodiments of the process 950, each of the capacitive touch sensors 904 to 912 includes a two-dimensional grid of sensing elements, and the sensing elements can allow the contact sensing The sensor generates a plurality of capacitive detection signals corresponding to the positions in the two-dimensional area covered by each of the capacitive sensors. In some configurations, if a human body part is detected at the first position on one of the sensors 904 to 912 but beyond the first predetermined distance from the blade 108, the controller 140 A warning signal is generated, and then if the object moves the preset distance of the blade 108, the controller 140 turns off the motor 112. Furthermore, the controller 140 or other control devices will also identify the moving path and speed of the object based on a series of object positions generated by the unique sensing elements in the capacitive sensors 904 to 912 over time. . If the movement path indicates that an object (for example, a human hand) is likely to touch the blade 108 at a certain point of the path, then the controller 140 will turn off the motor 112 or generate the warning as described above Output. In addition, in some configurations, the controller 140 activates the instrument response mechanism 132 to retract the blade 108 or other instruments before actual contact between the blade 108 and the operator's hand or other body part. For example, if the detected position of the operator's hand is within the preset distance of the blade 108 or the movement path trajectory of the hand on the capacitive sensors will intersect the blade 108, then, The controller 140 will start the appliance response as appropriate before the actual contact with the blade 108 occurs. Mechanism 132. Of course, the capacitive sensors 904 to 912 and the process 950 can cooperate with the object detection system 102 described above to detect that the body part of the operator appears near the blade 108 and detect the body part and the The actual contact operation between the blades 108 is performed back and forth.

In addition to the operation of the object detection system 102 described above, the saw 100 will be further configured to implement different configurations and diagnostic procedures, so as to maintain the reliability of the saw in a wide range of different materials and cause damage. Can the operation of the saw. For example, the saw 100 may be configured to keep a record of the number of times the appliance reaction mechanism has been activated, so as to ensure that the saw 100 is properly maintained.

Figure 10 shows a block diagram of a process 1000 for monitoring the reaction mechanism of the appliance in the saw. In the following discussion, the process of implementing a certain function or action will be described. 1000 will describe the operation of a controller to execute stored program instructions in order to cooperate with one or more devices in the saw to implement the function Or action. For the purpose of explanation, the process 1000 will be explained with the saw 100.

The process 1000 starts by activating the appliance response mechanism (block 1004). In the saw 100, the controller 140 activates the appliance response mechanism 132 in response to detecting contact with an object other than the work piece (for example, the operator's hand). In one embodiment of the saw 100, an explosive pack in the instrument response mechanism 132 is fired to retract the blade 108 below the level of the table 104. The controller 140 increments the count retained in the non-volatile portion of the memory 142 to keep a record of the number of times the appliance reaction mechanism has been activated during the operation of the saw 100 (block 1008). As known in the art, even if the saw 100 has been turned off and connected to power failure, the non-volatile memory (for example, a solid-state data storage device or a magnetic data storage device) will retain stored data for a long time cycle.

When the total number of activations of the appliance response mechanism 132 remains below a preset threshold (for example, the appliance response mechanism 132 is activated five times), the process 1000 and the operation of the saw 100 will continue (block 1012). If the number of activations of the appliance response mechanism exceeds the preset threshold (block 1012), the controller 140 will disable the operation of the saw 100 until the saw 100 performs the maintenance procedure (block 1016). For example, in one of the configurations, the controller 140 will ignore any input signal from the user interface 110 to activate the saw 100, and the motor 112 will remain off when the saw 100 is disabled. The controller 140 generates an output indicator signal through the user interface 110 as appropriate to notify the operator that the saw 100 has been disabled and needs maintenance.

Process 1000 will continue during maintenance operations. In addition to any necessary maintenance to repair or replace the mechanical or electrical components in the saw 100, the maintenance operation further includes resetting the counter value in the memory of the saw 100 so that the saw 100 can be restored to Operation status (block 1020). In one embodiment, the maintenance process includes connecting an external programming device (for example, a PC or other computerized programming device) to a maintenance port (for example, a universal serial bus (USB) port) in the saw 100 ), used to retrieve diagnostic data from the memory 142 and reprogram the memory 142 to reset the counter storing the number of times the appliance reaction mechanism has been activated. The use of an external programming device allows the saw 100 to be reused after maintenance, and at the same time, the saw can be kept inactive until proper maintenance is performed.

In the event that the appliance response mechanism 132 performs an unusually large number of activations, the process 1000 will ensure that the saw 100 remains deactivated before maintenance. This maintenance operation will ensure that all components in the saw 100 will operate correctly and that the object detection system 102 will accurately detect the contact between objects other than the work piece and the saw blade 108.

As mentioned above, the object detection system 102 will respond to the blade 108 and any objects (which include the work pieces cut by the saw during normal operation, and may include other objects including the body part of the saw operator, causing the The appliance responds to the contact between the mechanism) and receives the input signal. During the operation of the saw 100, the object detection system 102 receives an input signal corresponding to the capacitance level change in the capacitor 124 formed by the plate 120 and the blade 108, and the capacitance level change corresponds to the working part And potential contact with objects other than the work piece. For example, in some cases, wood with high moisture content may be confused with part of the operator's body during saw operation. The process 1100 shown in FIG. 11 is used to generate the signal profiling profile generated by different material types in various work pieces, so as to improve the accuracy of object detection. In the following discussion, the process of implementing a certain function or action 1100 will describe the operation of a controller to execute stored program instructions to cooperate with one or more devices in the saw to implement the function Or action. For the purpose of explanation, the process 1100 will be explained with the saw 100.

The process 1100 starts when the saw cooperates with the enabled object detection system 102 to operate but the appliance response mechanism 132 is disabled (block 1104). Operating the saw 100 without enabling the appliance response mechanism occurs under controlled conditions such as the manufacturer's equipment or approved maintenance equipment. During the process 1100, the saw 100 will cut various materials that are suitable for the work piece of the saw, but it may be mistakenly believed to correspond to a human body part or that the trigger should have a reaction mechanism 132 when it touches the rotating blade 108. Sensing signals of other objects.

The process 1100 will continue, so that the saw 100 will record the sensing signal generated by the object detection system 102 at the preset time when the work piece first starts to contact the blade 108, The sensing signal generated during cutting when the work piece moves through the blade 108 and the sensing signal generated when the work piece is disengaged from the blade 108 to complete the cutting (block 1108). The recorded sensing signal information usually includes spikes in the sensing signal related to changes in the capacitance level in the capacitor 124. For example, the initial peak that appears when the work piece first contacts the rotating blade 108 may be similar to the initial peak that occurs when an object other than the work piece first contacts the rotating blade 108.

In another embodiment of the process 1100, the saw 100 includes an additional sensor other than the capacitive sensor formed by the capacitor 124, which can detect features of the work piece material different from the operator's body. For example, one of the embodiments further includes one or more infrared sensors, which are arranged on the riving knife 330 shown in FIG. 3. The infrared sensors generate the frequency response profile of the infrared light reflected from the work piece. The controller 140 is operatively connected to the infrared sensors to record the frequency response of the material in the work piece.

The process 1100 will continue, so that the controller 140 or a processor located in an external computing device will recognize the recorded sensing signal and the prediction of the object that can trigger the appliance response mechanism in the saw 100 It is assumed that the sensing signal analyzes the difference between the contours (block 1112). For example, as described above, the controller 140 uses an adaptive threshold processing process to identify the spikes in the sensed current corresponding to the hand when the blade 108 is contacted or other parts of the human body. The spike corresponding to the contact with the human hand includes an amplitude profile and a time profile. The controller 140 recognizes the preset contour of a human body part and the initial peak that appears when the work piece first touches the rotating blade 108 and when the blade 108 cuts the work piece and disengages the work piece. The difference in amplitude and duration between any subsequent spikes that appear.

The controller 140 or the external processor then generates a detection profile specific to the test material based on the difference between the recorded sensing signals and the preset object detection profile of the human body (block 1116) . In one of the embodiments, the controller 140 generates a profiling profile with an amplitude value range near the amplitude of the recorded spike in the sensing signal when the blade 108 engages the predetermined material in the work piece. The amplitude value range of the spike does not include the critical amplitude of the spike amplitude of the operator's preset profiling profile, so as to ensure that the controller 140 does not incorrectly identify the sensing signal corresponding to the operator as a work piece. Therefore, the range of amplitude values corresponding to different work pieces will be changed based on the difference between the recorded spikes produced by the contact between the blade 108 and the work piece material and the preset profile corresponding to the human body. . The controller 140 will also generate a sensor corresponding to the work piece based on the difference between the time range of the spike from the work piece and the expected time duration of the spike in the profiling profile contacting the human body. The time range of the duration of the spikes in the signal. The updated profiling profile allows the controller 140 to compare the possible contact with a part of the human body to distinguish the sensing signal from the capacitor 124 corresponding to the contact between the blade 108 and the work piece made of a predetermined type of material .

As mentioned above, in an alternative embodiment, the controller 140 generates a profile based on the data from the infrared sensors to identify the frequency response range of the material in the work piece. And distinguish the frequency response range from the preset frequency response range associated with the operator. The controller 140 uses the preset frequency response range for the operator stored in the memory 142 to ensure that the frequency response range in the profile of the material does not overlap the preset profile of the operator. For example, in one of the configurations, the memory 142 stores the frequency response profile of the near-infrared response, and these frequency response profile For a wide range of human skin tones, there will be a peak response at a wavelength of about 1080nm and a minimum response at a wavelength of about 1580nm. Other types of materials of various work pieces have peak infrared frequency response and minimum infrared frequency response at different wavelengths, and the controller 140 will be at the wavelength corresponding to the work piece (but it will not overlap the response corresponding to the human skin A profile with a frequency response range of both the peak response value and the minimum response value is generated at the wavelength).

During the process 1100, the updated profile of the test material is stored in the memory 142 (block 1120). During the connection operation when the object detection system 102 and the instrument response mechanism 132 are enabled, the controller 140 will use the stored profile information of the test material to reduce the sense of contact between the work piece and the saw blade 108. The change in the measured signal is mistaken for the potential occurrence probability of a false detection event corresponding to the contact between the operator and the saw blade. For example, if the saw 100 is cutting a special type of material in the profile stored in the memory 142, as long as any spike in the sensing signal in the object detection system 102 remains corresponding to the material Within the amplitude range and time duration range of the type of stored profile, then the controller 140 will continue to operate the saw 100. In some configurations, the memory 142 stores the profiling profiles of various types of materials cut by the saw 100 during operation. The operator will provide an input to the saw 100 as appropriate to specify the type of material to be cut, so that the controller 140 can use a stored profile for the appropriate type of material in the work piece.

As described above, the object detection system will measure the change in the sensing signal via the capacitor 124 in response to the contact between the object and the rotating saw blade 108. The memory 142 stores the preset threshold information so that the controller 140 can cooperate with the above-mentioned adaptive threshold value. The process is used to detect the contact between the operator's body and the blade 108. However, the body of a unique operator may present different capacitance levels between different individuals, and the capacitance level of a body may also change over time due to various reasons. Examples of factors that affect the operator's capacitance level include, but are not limited to: the temperature and humidity in the environment near the saw, the physiological makeup of each operator, the degree of sweating of the operator, and Similar factors. FIG. 12 depicts a process 1200 for measuring the capacitance level of an individual operator during the operation of the saw 100 so that the saw 100 can adjust the object detection threshold for different individuals. In the following discussion, the process of implementing a certain function or action 1200 will describe the operation of a controller to execute stored program instructions to cooperate with one or more devices in the saw to implement the function Or action. For the purpose of explanation, the process 1200 will be explained with the saw 100.

The process 1200 is measured from the saw 100 during the operation of the saw through a capacitive sensor formed in the handle touched by the operator or in other preset contact positions on a surface of the saw 100 The operator's capacitance level starts (block 1204). Taking the example of FIG. 3 as an example, it is located at the base plate 304, the front rail 310, the bevel adjustment handle 352, the height adjustment handle 354, or one or more of the other surfaces of the saw that the operator will touch during operation. The capacitive sensor among many will generate the capacitance level measurement value in the operator's hand. The operator does not need to continuously touch the capacitive sensor during the operation of the saw 100; however, the controller 140 will update the capacitive sensor as appropriate when the operator touches one or more of the capacitive sensors. The measured capacitance level.

The process 1200 will continue, so that the controller 140 will correct the threshold level (block) for detecting contact with objects other than the work piece (for example, the operator's body). 1208). The controller 140 will lower the default peak amplitude detection threshold of the sensing signal in response to the measured capacitance level being lower than the preset internal level. This may occur when the operator’s skin is abnormally dry or other environmental factors degrade the operator Effective capacitance in the body. The controller 140 corrects the threshold value based on the difference between the default capacitance level suitable for a wide range of operators and the measured capacitance level (which may be higher or lower than the inner capacitance level). Lowering the threshold level actually increases the detection sensitivity between the operator and the saw blade 108 in the saw 100. The controller 140 may increase the critical value in response to identifying a large capacitance value among the operators as appropriate. In some embodiments, the controller 140 limits the maximum threshold level during object detection to ensure that the object detection system 102 retains the ability to detect the contact between the operator and the blade 108, because it improves detection The threshold level will actually reduce the sensitivity of the object detection system 102.

The process 1200 will continue so that the saw 100 will operate to cut the work piece, and the object detection system 102 will use the modified detection threshold to detect that a potential operator touches the blade 108 (block 1212). As mentioned above, if the operator’s hand or other body part touches the rotating blade 108, the controller 140 will use the adaptive threshold processing process described above to compare the sensing signals obtained through the capacitor 124. The amplitude of the spike and the modified critical value are measured. Because the controller 140 corrects the detection threshold based on the operator's measured capacitance, the process 1200 allows the saw 100 to detect the contact between the operator and the saw blade 108 with improved accuracy.

In the saw 100, the motor 112 includes one or more brushes, which engage a commutator. The use of brushes in electric motors is well known in the art. Over time, the brushes will wear out, which reduces the efficiency of the motor, and the worn out brushes often produce sparks. These sparks are not conducive to the operation of the motor 112, and in some cases, these sparks may also produce The electrical noise detected by the object detection system 102 is generated. FIG. 13A depicts an example of the shaft 1350, commutator 1354, and brushes 1358A and 1358B in the motor 112. The springs 1362A and 1362B press the brushes 1358A and 1358B, respectively, to make them contact the commutator 1354. In many embodiments, the brushes 1358A and 1358B are formed of graphite. In the motor 112, the bases 1366A and 1366B are formed in a housing of the motor 112 and engage the springs 1362A and 1362B, respectively. In one of the embodiments, the bases 1366A and 1366B include pressure sensors, which measure the squeezing force applied by the springs 1362A and 1362B. In another embodiment, the bases 1366A and 1366B generate induced currents flowing through the springs 1362A and 1362B and the corresponding brushes 1358A and 1358B, so as to identify the electrical resistance level through the brushes.

Because the worn-out brush will not only reduce the operating efficiency of the motor 112; it may also introduce additional electrical noise in the sensing signal of the object detection system 102. Therefore, the saw 100 will detect the motor 112 as appropriate. The brush is worn and an output is generated through the user interface 110 to indicate that the worn brush should be replaced. FIG. 13B depicts a first embodiment of a process 1300 for measuring brush wear in the motor 112. In the following description, the process 1300 of implementing a certain function or action will describe the operation of a controller (for example, the controller 140 in the saw 100) to execute stored program instructions to cooperate with the saw 100. Other devices in the implementation of the function or action.

During the process 1300, a power source located in each of the bases 1366A and 1366B will generate a current flowing through the corresponding brushes 1358A and 1358B (block 1304). In one of the embodiments, the current passes through the cables connected to the brushes 1358A and 1358B to allow the brushes 1358A and 1358B in the saw 100 to operate normally. In another configuration, the current will pass the squeezing force exerted by the springs 1362A and 1362B. In another implementation In the example, the bases 1366A and 1366B and the corresponding brushes 1358A and 1358B. The current is generated during the diagnostic mode when the saw motor 112 is turned off, and the current level used in the process 1300 is lower than the driving current used to generate rotation in the motor shaft 1350 during the operation of the motor 112. During the process 1300, the controller 140 or the controller integrated with the motor 112 will measure the electrical resistance level through the brushes, and compare the measured electrical resistance level with a preset resistance. Value threshold (block 1308). For example, the measurement of the electrical resistance level includes measuring the voltage level or the current level of the current flowing through each of the brushes 1358A and 1358B in the diagnostic mode, and applying Ohm's law to obtain The resistance value (for example, R=E/I, which can be used for the measured voltage E and the preset current I, or for the preset voltage E and the measured current I). Once the resistance drops below a preset threshold, the controller 140 generates an output signal through the user interface 110 to indicate that the brushes should be replaced (block 1312). When the brushes wear and become thinner, the resistance will decrease, which will reduce the total resistance of the springs 1362A and 1362B and the corresponding brushes 1358A and 1358B. In some configurations, the controller 140 will also disable the operation of the saw 100 until any worn-out brushes are replaced, and the controller 140 will perform the process 1300 again to confirm that the new brushes are not worn.

Figure 13C depicts a second embodiment of a process 1320 for measuring brush wear in a motor. In the following description, the process of implementing a certain function or action 1320 will describe the operation of a controller (for example, the controller 140 in the saw 100) to execute stored program instructions to cooperate with the saw 100 Other devices in the implementation of the function or action.

In the process 1320, the spring bases 1366A and 1366B each include a pressure sensor that measures the pressing force of the corresponding springs 1362A and 1362B during the diagnostic mode when the motor 112 is turned off (block 1324). When the brushes 1358A and 1358B are worn out, The corresponding springs 1362A and 1362B expand to press the brushes onto the commutator 1354. The squeezing force of the springs 1362A and 1362B will decrease as the springs expand. The controller 140 or one of the motors 112 is operatively connected to the pressure sensors and compares the measured pressure levels from the pressure sensors with a preset pressure threshold (Block 1328). Once the pressure sensors in the bases 1366A and 1366B measure that the squeezing force of the springs 1362A and 1362B has fallen below a predetermined threshold, the controller 140 will generate an output through the user interface 110 A signal to indicate that the brushes should be replaced (block 1332). In some configurations, the controller 140 will also disable the operation of the saw 100 until any worn brushes are replaced, and the controller 140 will perform the process 1320 again to confirm that the new brushes are not worn.

As described above, during operation, the object detection system 102 receives multiple sensing signals via a single sensing cable including two different conductors (for example, the coaxial cable 720 shown in FIG. 8B). In a high-vibration environment, such as the saw 100, the sensing cable 720 may suffer wear and failure over time, and eventually the cable needs to be replaced during maintenance of the saw. If the sensing cable 720 is broken and disconnected from any of the PCB of the object detection system 102, the flat panel 120, or the enclosure 118 of the appliance, then the PCB will not detect any sensing signals and will The saw 100 is deactivated until the single sensing cable 720 is repaired. However, in some cases, the sensing cable 720 suffers from a "soft fault" in which the cable does not completely interrupt the connection, but continues to operate with very poor performance in the saw. The PCB 102 will continue to receive the sensing signal, but a fault in the sensing cable 720 will introduce noise or attenuate the sensing signal, which will reduce the accuracy of the object detection system 102. FIG. 14 shows a block diagram of a process 1400 for diagnosing a soft fault in the sensing cable 720. In the description below The process 1400 of implementing a certain function or action will describe the operation of a controller (for example, the controller 140 in the saw 100) for executing stored program instructions to cooperate with other devices in the saw 100 Implement the function or action.

The process 1400 starts when the object detection system 102 generates a predetermined excitation signal during the diagnostic mode (block 1404). In one of the embodiments, the controller 140 activates the clock source 144 to generate the same sinusoidal sensing signal used during the operation of the saw 100 by amplitude modulation. In another embodiment, the clock source 144 generates a pulse train, which includes a series of delta pulses with a preset frequency, for the controller 140 to use the sensing cable 720 and the capacitor 124 Receive an output corresponding to the unit pulse wave response. In a further embodiment, the clock source 144 may generate any suitable preset signal capable of diagnosing potential faults in the sensing cable 720. During this diagnostic mode, the motor 112 in the saw 100 is turned off and there is minimal electrical noise present in the saw.

The process 1400 will continue, so that the controller 140 will recognize the signal-to-noise ratio (SNR) of the detected excitation signal (block 1408). In the saw 100, the controller 140 detects a return signal in response to the excitation signal from the clock source 144 and the amplifier 146, which passes through the sensing cable 720 and the flat plate 120 and the saw blade 108 of the capacitor 124. Because the clock source 144 and the driving amplifier 146 generate the excitation signal with a predetermined amplitude and modulation, the controller 140 will use a predetermined measurement technique known in the art to identify the SNR. Of course, even in the closed saw, the excitation signal will still suffer a certain degree of attenuation via the sensing cable 720 and the capacitor 124, and a certain degree of noise (for example, Janson-Nyquist noise ( Johnson-Nyquist noise)) will definitely appear in the sensing circuit. As used in the context of the process 1400, the SNR measurement also includes measuring the signal strength attenuation value, which does not include directly measuring the noise. for example, The predetermined excitation signal is generated to have a predetermined amplitude, and the controller 140 measures the amplitude of the return signal. A certain degree of attenuation is expected in the return signal, and in a properly functioning sensing cable, the preset amplitude level of the signal strength of the return signal is confirmed empirically and stored in the memory 142 . However, if the amplitude of the return signal drops below a predetermined level, the controller 140 will identify a potential fault in the sensing cable 720.

In an alternative configuration, the sensing cable 720 includes a third conductor that is electrically isolated from the first conductor and the second conductor in the sensing cable. In one embodiment, the third conductor is formed as a part of a second twisted pair cable in the sensing cable 720; in another embodiment, the sensing cable includes two Coaxial components to form three separate conductors. One end of the third conductor is connected to the plate 120 in the same manner as the first conductor shown in FIG. 8C. The other end of the third conductor is connected to an analog-to-digital converter (ADC), which is placed on the PCB of the object detection system to provide a digital version of the sensing signal Give to the controller 140. During the process 1400, the controller 140 measures a return signal based on the excitation signal flowing through the third conductor, rather than based on the excitation signal flowing through the first conductor and the second conductor.

The controller 140 recognizes whether the measured SNR of the excitation signal drops below the preset minimum SNR ratio suitable for operating the object detection system 102 (block 1412). The fault in the sensing cable 720 will attenuate the level of the received signal, introduce additional noise into the sensing cable 720, or at the same time attenuate the signal strength and increase the noise that will degrade the SNR. If the SNR remains above the preset threshold, then the sensing cable 720 is deemed to have a normal function and the saw 100 will continue to operate (block 1416). However, if the measured SNR is If the threshold is below the preset threshold, then the controller 140 will generate an output to indicate that there is a potential fault in the sensing cable (block 1420). In the saw 100, the controller 140 generates the output through the user interface 110 to alert the operator of a potential cable failure. In some configurations, the controller 140 disables the operation of the saw 100 until the sensing cable 720 is repaired or replaced.

It should be understood that the above-mentioned and other features and function variations or alternatives can be combined into many other different systems, applications, or methods in a desired manner. Those who are familiar with the technology can achieve various unpredictable or unpredictable alternatives, modifications, changes, or improvements, and the present invention also hopes to cover them in the scope of subsequent patent applications.

Also exposed here is:

Regulation 1: A method for detecting a fault in a sensing cable in a saw, which includes: using a signal generator to generate a predetermined excitation signal, and the predetermined excitation signal passes through the sensing cable A first conductor and a second conductor in the wire are transmitted, the first conductor is electrically connected to a flat plate in the saw and the second conductor is electrically connected to an appliance in the saw, the appliance Is positioned at a predetermined distance from the plate; a controller is used to detect a return signal corresponding to the excitation passing through the first conductor and the second conductor in the sensing cable Signal; use the controller to identify a signal-to-noise ratio (SNR) of the return signal; and use the controller and a user interface in the saw in response to the SNR of the return signal below a preset value Device to generate an output to represent one of the sensing cables malfunction.

Regulation 2: The method according to Regulation 1, which further includes: first turning off a motor in the saw by the controller before generating the preset activation signal, so that the motor in the cable can be identified when the motor is kept off The failure.

Regulation 3: According to the method of Regulation 1, the generating the predetermined excitation signal further includes: using a clock source in the saw to generate a sine signal at a predetermined frequency.

Regulation 4: The method according to Regulation 3, which further includes: using an amplifier to generate an amplified sinusoidal signal based on the sinusoidal signal from the clock source; and transmitting the amplified sinusoidal signal via the sensing cable .

Regulation 5: According to the method of Regulation 1, the generating the predetermined excitation signal further includes: using a clock source in the saw to generate a series of incremental pulse waves at a predetermined frequency.

Regulation 6: The method according to 1, further comprising: in response to the SNR being below the predetermined threshold, using the controller to disable the operation of a motor in the saw.

Regulation 7: The method according to Regulation 1, which further comprises: using a first coil in a transformer in the saw to transmit the preset excitation signal from the signal generator to the sensing cable The first conductor and the second conductor.

Regulation 8: The method according to Regulation 1, which further includes: using the controller to receive a return signal flowing through a third conductor in the sensing cable, the first The three conductors are electrically connected to the plate and are electrically connected to an analog to digital converter associated with the controller.

Regulation 9: A system for detecting a fault in a sensing cable in a saw, comprising: a sensing cable including a first conductor and a second conductor; a flat plate, the flat plate being Is electrically connected to the first conductor in the sensing cable; an appliance, the appliance is positioned at a predetermined distance from the plate and the appliance is electrically connected to the first conductor in the sensing cable Two conductors; a signal generator configured to generate a preset excitation signal, the preset excitation signal will be transmitted through the first conductor and the second conductor of the sensing cable; a user interface Device; and a controller connected to the signal generator, the user interface device, and the first conductor and the second conductor of the sensing cable, the controller being configured to: operate the signal Generator to generate the preset excitation signal; detect a return signal corresponding to the excitation signal passing through the first conductor and the second conductor in the sensing cable; identify the return signal A signal-to-noise ratio (SNR); and in response to the SNR of the return signal being below a predetermined value, the user interface device is used to generate an output to indicate a fault in the sensing cable.

Regulation 10: The system according to Regulation 9, which further comprises: a motor configured to move the appliance during operation; and the controller is operatively connected to the motor and configured to: The motor is turned off before the signal generator is operated to generate the preset activation signal, so that the fault in the cable can be identified when the motor remains turned off.

Regulation 11: According to the system of Regulation 9, the signal generator further includes: a clock source configured to generate a sinusoidal signal at a predetermined frequency as the excitation signal.

Regulation 12: According to the system of Regulation 9, the signal generator further includes: an amplifier configured to generate an amplified sinusoidal signal based on the sinusoidal signal from the clock source.

Regulation 13: According to the system of Regulation 9, the signal generator further includes: a clock source configured to generate a series of incremental pulses at a predetermined frequency.

Regulation 14: The system according to Regulation 9, which further comprises: a motor configured to move the appliance during operation; and the controller is operatively connected to the motor and is further configured to: respond Disable the operation of the motor when the SNR is below the predetermined threshold.

Regulation 15: The system according to Regulation 9, further comprising: a transformer, a first coil of which is connected to the first conductor in the sensing cable and the second conductor in the sensing cable; And the signal generator is configured to transmit the preset excitation signal to the first conductor and the second conductor via the first coil.

Regulation 16: The system according to Regulation 1, which further includes: a third conductor in the sensing cable, the third conductor being electrically connected to the plate and electrically connected to a controller associated with the controller An analog to digital converter; and The controller is further configured to: receive the return signal flowing through the third conductor in the sensing cable.

Claims (10)

A method for detecting a fault in a sensing cable in a saw, comprising: using a signal generator to generate a predetermined excitation signal, the predetermined excitation signal passing through the sensing cable The first conductor is electrically connected to a flat plate in the saw and the second conductor is electrically connected to an appliance in the saw, the appliance being positioned at A predetermined distance away from the plate; using a controller to detect a return signal corresponding to the excitation signal passing through the first conductor and the second conductor in the sensing cable; using The controller recognizes a signal-to-noise ratio (SNR) of the return signal; and in response to the SNR of the return signal being below a preset value, the controller and a user interface device in the saw are used to generate An output is used to indicate a fault in the sensing cable. The method according to item 1 of the scope of patent application further includes: before generating the preset activation signal, first turning off a motor in the saw by the controller, so that the cable can be identified when the motor is kept off Of the failure. According to the method of item 1 of the scope of patent application, generating the predetermined excitation signal further includes: using a clock source in the saw to generate a sinusoidal signal at a predetermined frequency. The method according to item 3 of the scope of patent application, further comprising: generating an amplified sine signal with an amplifier based on the sine signal from the clock source; and transmitting the amplified sine signal via the sensing cable signal. According to the method of item 1 of the scope of patent application, generating the predetermined excitation signal further includes: generating a series of incremental pulse waves at a predetermined frequency by using a clock source in the saw. According to the method of claim 1, further comprising: in response to the SNR being below the predetermined threshold, using the controller to disable the operation of a motor in the saw. The method according to item 1 of the scope of patent application, further comprising: using a first coil in a transformer in the saw to transmit the preset excitation signal from the signal generator to the sensing cable The first conductor and the second conductor. The method according to item 1 of the scope of the patent application, further comprising: using the controller to receive a return signal flowing through a third conductor in the sensing cable, the third conductor being electrically connected to the plate and being electrically connected To an analog-to-digital converter associated with the controller. A system for detecting a fault in a sensing cable in a saw, comprising: a sensing cable, which includes a first conductor and a second conductor; a flat plate, the flat plate is electrically connected to The first conductor in the sensing cable; an appliance, the appliance is positioned at a predetermined distance from the plate and the appliance is electrically connected to the second conductor in the sensing cable; A signal generator configured to generate a preset excitation signal, the preset excitation signal will be transmitted through the first conductor and the second conductor of the sensing cable; a user interface device; and A controller connected to the signal generator, the user interface device and the sensor For the first conductor and the second conductor of the cable, the controller is configured to: operate the signal generator to generate the predetermined excitation signal; and detect a return signal corresponding to passing through the sensor Test the excitation signal of the first conductor and the second conductor in the cable; identify a signal-to-noise ratio (SNR) of the return signal; and use in response to the SNR of the return signal below a preset value The user interface device generates an output to indicate a fault in the sensing cable. The system according to claim 9 further includes: a motor configured to move the appliance during operation; and the controller is operatively connected to the motor and configured to: Turn off the motor before operating the signal generator to generate the preset activation signal, so that the fault in the cable can be identified when the motor remains turned off.

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