TW201643021A - Object proximity detection in a saw - Google Patents

Abstract

A method for detection of proximity between an object and an implement in a table saw includes operating a motor in the table saw to move the implement, generating, with a capacitive sensor formed in a throat plate around the implement in the table saw, a capacitance signal during operation of the operation of the motor, identifying, with a controller operatively connected to the capacitive sensor, an object in proximity to the capacitive sensor in response to a change in a level of capacitance in the capacitance signal, and deactivating, with the controller, the motor in the table saw in response to the change in the capacitance signal indicating a capacitance level that exceeds a predetermined threshold corresponding to a body part of an operator.

Description

Object proximity detection in the saw

The present disclosure is generally related to a power tool and, more specifically, to the system and method for detecting an object approaching a blade in a saw.

Priority claim

The present application claims priority to U.S. Provisional Application Serial No. 62/131,977, filed on March 12, 2015, which is entitled "System and Method for Falling Arm Control in Table Saws (SYSTEM AND) METHOD FOR CONTROL OF A DROP ARM IN A TABLE SAW)", the entire contents of which are incorporated herein by reference. The present application also claims priority to U.S. Provisional Application Serial No. 62/132,004, filed on March 12, 2015, entitled "TABLE SAW WITH DROPPING BLADE", This document is incorporated by reference in its entirety.

Cross reference

The present application cross-references copending U.S. Application Serial No. 15/XXX, XXX, filed on March 4, 2016, the entire disclosure of which is incorporated herein by reference.

Detection systems or sensing systems have been developed for use in various types of manufacturing facilities Beyond the power tools. Such detection systems are operable to trigger a reaction device by detecting or sensing an operator's limb approaching or contacting a particular component of the device. For example, a capacitive touch sensing system in a table saw detects contact between the operator and the blade.

Shown in FIG. 1 is a detection system 90 based on prior art capacitive sensing that is incorporated into 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 current drawn from the blade 22. When the blade 22 contacts a conductive object (e.g., an operator's hand, fingers, or other body parts, and a workpiece), the amplitude or phase of the detected current and/or excitation voltage changes. These altered features can be used to trigger the operation of a reaction system 92. For example, the reaction system 92 disables operation of the blade 22 by braking to stop the movement of the blade 22 and/or by moving the blade 22 below the cutting zone. One example of reaction system 92 would use an explosive charge to drive a brake (not shown) into blade 22 to stop the movement of blade 22. Additionally or alternatively, an embodiment of reaction system 92 disintegrates a blade support member (not shown) to urge the blade 22 below the surface of table 14.

The embodiment of detection system 90 shown in FIG. 1 includes an oscillator 10 that produces a time varying signal on line 12. The time varying signal is any suitable signal type, for example, it includes a sine wave, a sum of a plurality of sine waves, a chirp waveform, a noise signal, and the like. The frequency of the signal is selected such that a detection system can discern contact between a first object (e.g., a finger or hand) to be cut by the power tool and a second object (e.g., wood or other material). In the embodiment of Figure 1, the frequency is 1.22 MHz; however, other frequencies as well as non-sinusoidal shapes can be used. The oscillator 10 will be grounded locally with a saw table 14 or other metal structure. As shown in Figure 1, the blade 22 is placed vertically by the saw table 14 (or the working surface or cut Cut into the surface defined by the surface or the platform).

Oscillator 10 is connected via line 12 to two voltage amplifiers or buffers 16, 18. The first voltage amplifier 16 has an output connected to the line 20 which operatively connects the output of the oscillator to the saw blade 22. A current sensor 24 operatively connects a signal from line 20 to line 26, which is then fed to amplifier 28, which is coupled to a processor 30 via 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 type of current sensor. An output line 34 from processor 30 is operatively coupled to reaction system 92 such that if a predetermined condition is detected (for example, to indicate contact between blade 22 and the first object), The processor 30 triggers 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 operation of the table saw, the connection is achieved via an excitation plate 36 that is disposed substantially parallel to the blade 22. The plate 36 is driven by a first voltage amplifier 16, and in the embodiment of FIG. 1 is configured with a capacitance of about 100 picofarads (pF) with reference to the blade 22. The plate 36 is held in a stable position with respect to the side of the blade 22. The excitation plate 36 is configured to follow the blade 22 when the height and bevel angle of the blade 22 are adjusted as the operation of the saw 1 is adjusted.

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

In the detection system 90, the second amplifier 18 is coupled 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 current drawn by the shield 38 as appropriate. The shield 38 extends around the blade 22 under the table 14 and is spaced a specific distance from the blade 22 positioned at the top end of the table 14 in the configuration of FIG. The configuration of the shield 38 reduces the static capacitance between the blade 22 and the table 14, which can act as a ground plane if the table is not electrically connected to ground. In various embodiments, the shield 38 is a continuous mesh pocket or a particular type of shield electrically equivalent to a faraday cage at the excitation frequency generated by the oscillator 10, the shield 38 Depending on the situation, a device that moves with the blade adjustment is included, or the device is large enough to accommodate adjustment of the blade and various blades that are adapted to the table saw. In the configuration of FIG. 1, the shield 38 will move with the blade adjustment and include a throat region of the table top end 14.

Processor 30 performs various pre-processing steps and performs a triggering action to detect conditions indicative of 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 current sensor 24 is directed to one or more of the A/D converters, which produces a corresponding digital signal. In some embodiments, a blade voltage signal representative of the voltage difference between the blade 22 and the excitation plate 36 is directed to an A/D converter for generating a digital blade voltage signal. The processor 30 receives the digitized signal and Various digital signal processing operations and/or computational derived parameters are implemented based on the received signals. The processor 30 analyzes the adjusted blade signal or performs other operations to detect conditions indicative of contact between the first object and the blade 22.

This prior art saw requires the use of a conductive material to form the blade 22, which is also electrically connected to the crankshaft 37. Non-conducting blades and blades containing non-conductor coatings can prevent the contact detection system of these prior art saws from operating properly. In addition to this, the blade 22 and the crankshaft 37 must also be electrically connected to a ground plane for the contact detection system for efficient operation. The need for a ground connection must also allow the saw 1 to be electrically connected to a proper ground, such as a ground spike, a metal tube, or other suitable ground, which must hold 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 potentially inconvenient or impractical ground connections. In addition, the need for a ground connection also increases the complexity of the setup and operation of the non-portable table saw. Therefore, the improved contact detection system makes it advantageous to have blades in portable and non-portable table saws that do not require an electrical ground connection.

In one embodiment, the present invention provides a method for detecting the proximity between an object and an appliance in a table saw. The method includes operating a motor in the table saw for moving the appliance, and utilizing a capacitive sensor formed in the throat plate to surround the table saw during operation of the motor Generating a capacitive signal; responsive to a change in capacitance level in the capacitive signal, utilizing a controller operatively coupled to the capacitive sensor to identify an object proximate to the capacitive sensor; and responsive The change in the capacitance signal indicates that a capacitance level exceeding a preset threshold value corresponding to a body part of the operator is utilized The controller is to close the motor in the table saw.

In a further embodiment, the method includes: utilizing the controller to identify that the object corresponds to a workpiece in response to the change in the capacitance level being less than a predetermined threshold; and continuing to operate the motor to allow the The appliance engages the workpiece.

In a further embodiment, the method includes utilizing the controller to generate a one for the operator in response to the change in the capacitance signal indicating that the capacitance level exceeds a predetermined threshold corresponding to the body portion of the operator Warning signal.

In a further embodiment, the method includes: generating, by the capacitive sensor, a plurality of capacitive sensing elements arranged on a surface of the capacitive sensor in a predetermined two-dimensional arrangement Capacitance signal; using the controller to reference the plurality of capacitive sensing signals to identify a position of the object above the surface of the capacitive sensor; and responsive to a position of the object at a predetermined distance of the device And the change in the capacitance signal indicates that the capacitance level exceeds a predetermined threshold corresponding to the body portion of the operator, and the controller is utilized to generate an alert signal for the operator.

In a further embodiment, the method includes responding to the position of the object within the predetermined distance of the appliance and the change in the capacitance signal indicates that the predetermined threshold value corresponding to the body portion of the operator is exceeded The controller is used to close the motor in the table saw.

In a further embodiment, the method includes responding to the position of the object within the predetermined distance of the appliance and the change in the capacitance signal indicates that the predetermined threshold value corresponding to the body portion of the operator is exceeded The controller is used to activate an instrument reaction mechanism in the table saw.

In a further embodiment, the method includes utilizing the controller to identify a movement path of the body portion of the operator based on the plurality of capacitive signals from the capacitive sensor; and at the operator The controller is utilized to initiate an appliance reaction mechanism among the saws in response to the trajectory of the moving path intersecting the appliance prior to the contact between the body portion and the appliance.

In another embodiment, the present invention provides a table saw. The table saw includes: an implement extending through an opening in a throat panel; a motor operatively coupled to the appliance; and a capacitive sensor positioned in the throat panel The capacitive sensor is configured to generate a capacitive signal during operation of the motor; and a controller operatively coupled to the motor and the capacitive sensor. The controller is configured to: operate the motor to move the appliance; identify an object proximate the capacitive sensor in response to a change in capacitance level in the capacitive signal; and responsive to the capacitive signal The change therein indicates that the motor in the table saw is closed by exceeding a capacitance level corresponding to a predetermined threshold value of a body portion of the operator.

In a further embodiment, the controller in the table saw is configured to: identify that the object corresponds to a workpiece in response to the change in the capacitance level being less than a predetermined threshold; and continue to operate the a motor to allow the appliance to engage the workpiece.

In a further embodiment, the controller in the table saw is configured to responsive to a change in the capacitance signal indicative of the capacitance level exceeding a predetermined threshold corresponding to the body portion of the operator A warning signal is generated for the operator.

In a further embodiment, the controller in the table saw is configured to: a plurality of capacitors arranged on a surface of the capacitive sensor in a predetermined two-dimensional arrangement Generating a plurality of capacitive signals at the sensing element; identifying the position of the object above the surface of the capacitive sensor with reference to the plurality of capacitive sensing signals; and responsive to the position of the object at the device A warning signal is generated for the operator that is outside the preset distance and the change in the capacitance signal indicates that the capacitance level exceeds a predetermined threshold corresponding to the body portion of the operator.

In a further embodiment, the controller in the table saw is configured to be responsive to the position of the object within the predetermined distance of the appliance and the change in the capacitance signal indicates that the excess corresponds to the operator The capacitive level of the preset threshold of the body portion closes the motor in the table saw.

In a further embodiment, the table saw includes an appliance reaction mechanism and the controller is operatively coupled to the appliance reaction mechanism. The controller is configured to be responsive to the position of the object within the predetermined distance of the appliance and the change in the capacitive signal indicative of the capacitance level exceeding a predetermined threshold corresponding to the body portion of the operator The instrument reaction mechanism in the saw is activated in a timely manner.

In a further embodiment, the table saw includes an appliance reaction mechanism and the controller is operatively coupled to the appliance reaction mechanism. The controller is configured to identify a path of movement of the body portion of the operator based on the plurality of capacitive signals from the capacitive sensor; and between the body portion of the operator and the appliance The appliance reaction mechanism in the saw is activated in response to the trajectory of the moving path intersecting the appliance prior to generating the contact.

In a further embodiment of the table saw, the throat plate is formed by an electrical insulator for isolating the capacitive sensor and the device.

1‧‧‧Table saw

10‧‧‧Oscillator

12‧‧‧ lines

14‧‧‧ saw table

16‧‧‧Voltage amplifier or buffer

18‧‧‧Voltage amplifier or buffer

20‧‧‧ lines

22‧‧‧Removable blade

24‧‧‧ Current Sensor

26‧‧‧ lines

28‧‧‧Amplifier

30‧‧‧ Processor

32‧‧‧ lines

34‧‧‧Output line

36‧‧‧Inspired tablet

37‧‧‧Axis

38‧‧‧Shield

90‧‧‧Detection system

92‧‧‧Reaction system

100‧‧‧ saw

102‧‧‧Object Detection System

104‧‧‧Workbench

106‧‧‧Power supply

108‧‧‧Saw blade

109‧‧‧Axis

110‧‧‧User interface device

112‧‧‧Electric motor

118‧‧‧Device enclosure

119‧‧‧throat

120‧‧‧ tablet

124‧‧‧ capacitor

132‧‧‧ Apparatus response mechanism

140‧‧‧Digital Controller

142‧‧‧ memory

143A‧‧‧Demodulation Transducer

143B‧‧‧Demodulation Transducer

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‧‧‧Resistors

182‧‧‧ Grounding

304‧‧‧ boards

306‧‧‧Thermal track base

310‧‧‧ Track

312‧‧‧ Track

320‧‧ ‧ baffle

330‧‧‧劈

332‧‧‧blade baffle

352‧‧‧Bevel adjustment handle

354‧‧‧ Height adjustment grip

404‧‧‧ Non-conductive casing

408‧‧‧ Non-conductive casing

412‧‧‧Plastic support members

502‧‧‧ Shell

504A‧‧‧Cap

504B‧‧‧Cap

504C‧‧‧Cap

504D‧‧‧Cap

506‧‧‧Hook

512‧‧‧ cover

516‧‧‧Antenna

524A‧‧‧ body components

524B‧‧‧ body components

524C‧‧‧ body components

524D‧‧‧ body components

526‧‧‧Hook

528A‧‧‧ indicator

528B‧‧‧ indicator light

528C‧‧‧ indicator light

528D‧‧‧ indicator light

540‧‧‧ indicator cap assembly

544‧‧‧ Body 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‧‧‧Information cable

732‧‧‧ Pull-down resistor

736‧‧‧Power cable

738‧‧‧ ferrite choke

740‧‧‧ ferrite choke

742‧‧‧ cable

743A‧‧‧ thyristor

743B‧‧‧ thyristor

802‧‧‧ enclosure

832‧‧‧ Connection location

836‧‧‧ Connection location

838‧‧‧Connected location

852‧‧‧First internal conductor

856‧‧‧Electrical insulator

862‧‧‧Second metal conductor

864‧‧‧External insulator

866‧‧‧Metal clip

872‧‧‧Connecting base

876‧‧‧Connecting base

904‧‧‧Capacitive sensor

908‧‧‧Capacitive sensor

912‧‧‧Capacitive sensor

920‧‧‧ cutting direction

1350‧‧‧ shaft handle

1354‧‧ ‧ commutator

1358A‧‧‧ brushes

1358B‧‧‧ brushes

1362A‧‧ Spring

1362B‧‧ Spring

1366A‧‧‧Base

1366B‧‧‧Base

Figure 1 is a schematic illustration of a prior art table saw including a prior art detection system for detecting contact between a human body and a saw blade.

2 is an outline of a table saw including an object detection system configured to confirm whether the blade contacts an object during rotation of a saw blade in the saw.

Figure 3 is an external view of one of the embodiments of the table saw of Figure 2.

4 is a cross-sectional view of selected one of the saws of FIG. 2, including a blade, a crankshaft, and a sensor plate.

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

Figure 5B is a view of the user interface device of Figure 5A with the outer casing removed.

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

An exploded view of the device among the user interfaces of Figures 5A through 5C is shown in Figure 5D.

Figure 6A is an exploded view of a charge coupled plate and crankshaft assembly of one of the embodiments of the saw of Figure 2.

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

Figure 7 is a schematic illustration of additional details of the object detection system and other devices in one of the embodiments of the saw of Figure 2.

Figure 8A is a schematic illustration of a sensing cable mounted in one of the embodiments of the saw of Figure 2.

Figure 8B is a cross-sectional view of the device among the coaxial sensing cables.

Figure 8C is a schematic illustration of the connection of a first conductor of the sensing cable to a flat panel in the saw of Figure 8A.

Figure 8D is a schematic illustration of the base at one of the locations for attaching a second conductor of the sensing cable to an enclosure of the saw of Figure 8A.

Figure 8E is a schematic illustration of the base at another location for attaching a second conductor of the sensing cable to an enclosure of the saw of Figure 8A.

Figure 9A is a schematic illustration of a plurality of capacitive sensors arranged in a throat plate around a blade in one of the embodiments of the saw of Figure 2.

Figure 9B is a block diagram showing the operation of a table saw using the capacitive sensor of Figure 9A.

Figure 10 is a block diagram showing a process for monitoring the action of the appliance reaction mechanism in one of the embodiments of the saw of Figure 2 and disabling the saw after the number of starts of the appliance reaction mechanism exceeds a preset number of times Carry out maintenance.

Figure 11 is a block diagram showing the process of measuring the profile of different material types among the workpieces of the object detection system used in the saw of Figure 2.

Figure 12 is a block diagram showing the process of measuring the capacitance in the body of the operator of the saw of Figure 2 to adjust the operation of the object detection system in the saw.

Figure 13A is a schematic illustration of the device among the motors of one of the embodiments of the saw of Figure 2.

Figure 13B is a block diagram showing the process of measuring the wear of the brush based on the electrical resistance value of a brush among the motors depicted in Figure 13A.

Figure 13C is a measurement of the electrical pressure based on the pressure measurement of the spring of a commutator that is moved into the motor by a brush in the motor depicted in Figure 13A. A block diagram of the process of brush wear.

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

For the purposes of understanding the principles of the embodiments described herein, reference will now be made to the drawings and description in the written description below. These references do not limit the intent of the scope of the main content. The present patents also cover any alternatives and modifications of the illustrated embodiments, and further application of the principles of the described embodiments will be apparent to those skilled in the art.

As used herein, the term "power tool" refers to any tool having one or more moving parts that are actuated by an actuator (eg, an electric motor, an internal combustion engine, a hydraulic cylinder, or a steam cylinder). Analog) to move. For example, power tools include, but are not limited to, bevel saws, miter saws, table saws, circular saws, reciprocating saws (reciprocating) Saw), jig saw, band saw, cold saw, cutter, impact drive, angler grinder, drill (drill) ), a jointer, a nail driver, a sander, a trimmer, and a router. As used herein, the term "implement" refers to a moving component of the power tool that is at least partially exposed during operation of the power tool. Examples of appliances among 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 a power tool can be used to stop the movement of the appliance to avoid contact between the operator and the appliance while the appliance is moving.

As used herein, the term "apparatus reaction mechanism" means that the saw is retracted from a position where it may contact a work piece or contact a part of the operator's body (eg For example, a blade or any other suitable moving device, which quickly stops the movement of the appliance, or simultaneously retracts and suspends the appliance. As described below in a table saw embodiment, one form of appliance reaction mechanism includes a movable drop arm that is mechanically coupled to an implement (e.g., a blade) and a crankshaft. The appliance reaction mechanism includes a pyrotechnic charge that is detected by an object detection system during operation of the saw in response to detection of contact between a portion of an operator's body and the blade. operating. The burst charge forces the drop arm and blade to move below the surface of the table to quickly retract the blade from contact with the operator. In other embodiments of the appliance reaction mechanism, a mechanical or motorized blade brake will quickly stop the movement of the blade.

2 is a schematic view of a device in a saw 100, and FIG. 3 is an external view of one embodiment of the saw 100. The table saw 100 includes a table 104 through which the saw blade 108 extends to cut a workpiece, such as a block of wood. The table saw 100 further includes an electric motor 112 that rotates a shaft 109 for driving the saw blade 108; an appliance enclosure 118; and an appliance reaction mechanism 132. For purposes of explanation, FIG. 2 depicts a cutting blade 108; however, those skilled in the art will appreciate that the blade 108 can be any device that can be used in the saw 100 and will recognize that the blade 108 is only For the purpose of interpretation. Among the saws 100, the appliance enclosure 118 includes a height adjustment carriage and a beveled carriage that encloses the blade 108, and the appliance enclosure 118 can be substituted for what is referred to as a blade enclosure or "shield". It encloses the blade 108 or other suitable appliance in the saw 100. As shown in FIG. 3, a portion of the blade 108 extends upwardly through an opening in the throat plate 119 above the surface of the table 104. A riving knife 330 and blade baffle 332 are positioned above the blade 108.

Inside the saw 100, the appliance enclosure 118 is electrically isolated from the blade 108, the crankshaft 109, the top surface of the table 104, and a flat plate 120. In one embodiment, the appliance enclosure 118 includes a throat plate 119 that is formed from an electrical insulator (eg, a thermoplastic). The throat plate 119 includes an opening for extending the blade 108 above the surface of the table 104. The throat plate 119 is flush with the surface of the table 104 and provides further electrical isolation between the height adjustment carriage and the bevel carriage in the blade 108, the appliance enclosure 118, and the surface of the table 104. Electrically isolated. The general configuration of table 104, blade 108, and motor 112 is well known in the art for cutting workpieces and will not be described in greater detail herein. For the sake of clarity, some of the devices commonly used in table saws have been omitted in Figure 2, such as rails for workpieces, blade height adjustment mechanisms, and blade baffles.

The saw 100 further includes an object detection system 102 that 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 coupled to the tablet 120 and is electrically coupled to the blade 108 through the appliance enclosure 118 and the crankshaft. Controller 140 within the object detection system 102 is operatively coupled to user interface device 110, motor 112, and appliance response mechanism 132. During operation of the saw 100, the object detection system 102 detects electrical signals caused by changes in the level of capacitance between the blade 108 and the plate 120 when an object contacts the rotary blade 108. An object may contain a work piece, such as a piece of wood or other material that the saw 100 cut during normal operation. The object detection system 102 also detects contact between the blade 108 and other objects (which may include the operator's hand or a portion of the body) and is responsive to detecting the blade 108 and the workpiece. The appliance reaction mechanism 132 is activated by contact between the objects. The additional structure and operation of the object detection system 102 will be described in more detail below. Section.

Among the saws 100, the table 104 is electrically isolated from the saw blade 108, the crankshaft 109, and other components within the appliance enclosure 118 as shown in FIGS. 2 and 3. In one embodiment, the surface of the table 104 is formed from a conductive material, such as steel or aluminum. At the surface of the table 104, a non-conductive throat plate 119 isolates the blade 108 from the surface of the table 104. Below the table 104, one or more electrically insulated bases that will secure the table 104 to the frame of the saw 100 will electrically isolate the table 104 and other components within the saw. As shown in FIG. 2, in some embodiments, table 104 is electrically coupled to ground 182 using an electrical cable. This ground connection reduces or eliminates static buildup on the table 104, which can prevent improper electrostatic discharge that can reduce object detection accuracy during 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 ground 182 via a high resistance cable (which includes a large amount of resistor 180, for example, a 1 MΩ resistor). The appliance enclosure 118 is coupled to ground 182 via a first cable and a resistor 180 (which provides a high resistance connection to ground). Blade 108 is also coupled to ground 182 via a second cable and resistor 180 through crankshaft 109. The high resistance connection line for the blade 108 and the enclosure 18 connected to ground also reduces the accumulation of electrostatic charge on such devices. When the prior art detection device requires a low resistance ground connection (for example, a direct connection using an electrical cable having a resistance of less than 1 Ω) to detect a blade with a low impedance connection directly connected to the ground. The contact between objects does not require a high resistance grounding cable in the saw 100 during operation of the object detection system 102. Instead, the high resistance cables only reduce the electrostatic effects in the saw 100 to reduce potential false alarm detection events; However, even without any ground connection, the object detection system 102 will have the full function of detecting contact between the blade 108 and an object. Alternate embodiments may use different materials in either or both of the plate 120 and the blade 108 in order to reduce static buildup in the saw 100 and eliminate the need for the blade 108 or the appliance enclosure 118 and ground. Go to any cable.

Table saw 100 includes a plate 304 that is placed over tracks 310 and 312. The plate 304 is configured to move to a predetermined position in a direction parallel to the blade 108 above the table 104 during operation to guide the workpiece through the saw 100. Among the saws 100, the plate 304 is electrically isolated from the table 104. For example, in FIG. 3, an electrically insulated thermoplastic track base 306 will couple the plate 304 to the track 310. A plastic baffle (not shown) at the bottom of the plate 304 and another baffle 320 positioned at the top of the plate 304 electrically isolate the plate 304 from the table 104 in the saw 100. . In some embodiments, the plate 304 includes another electrical insulator positioned on the side of the plate 304 that faces the blade 108 to ensure compliance when the workpiece simultaneously engages the plate 304 and the blade 108. 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 contact between the object and the blade 108 during operation of the saw 100. In one configuration, some or all of the devices in the detection system 102 are disposed on one or more Printed Circuit Boards (PCBs). 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 (eg, a generator or power facility supplier) and supplies power to the motor 112 via the TRIAC 174 to supply power to the sensing. A device in system 102. Different PCBs for sensing system 102 and power supply 172 The digital controller 140 and the power supply 106 and TRIAC 174 are isolated to improve the cooling effect of the digital electronics within the controller 140 and to isolate the controller 140 from electrical noise. In the embodiment of FIG. 2, power supply 106 is a switched power supply that converts AC power signals from an external power source to direct current at one or more voltage levels (Direct Current, The DC) power signal is supplied to the controller 140, the clock source 144, and the amplifier 146. The detection system 102 and the devices disposed in the detection system 102 are electrically isolated from a ground ground. The power supply 106 acts as a local ground for the devices disposed in the detection system 102.

Among the saws 100, the plate 120 and the blade 108 form a capacitor 124 in which a small amount of air gap between the plate 120 and the blade 108 acts as a dielectric. The plate 120 is a conductive plate, such as a steel or aluminum plate, positioned at a predetermined distance from the blade 108, with a parallel alignment between the plate 120 and the blade 108 to form Two sides of capacitor 124 having an air gap dielectric. Transformer 150 includes a first coil 152 and a second coil 154. Among the saws 100, the plate 120 is a metal planar member that is electrically connected to the coil 152 in the transformer 150. The plate 120 is electrically isolated from the appliance enclosure 118 by a predetermined air gap and electrically isolated from the blade 108 to form the capacitor 124. The plate 120 is also referred to as a Charge Coupled Plate (CCP) because the plate 120 cooperates with the blade 108 to form one side of the capacitor 124. In one embodiment, a plastic support member holds the plate 120 at a predetermined distance based on the blade 108. The blade 108 and the blade shaft 109 are electrically isolated from the enclosure 118, the plate 120, the drop arm in the appliance reaction mechanism 132, and other components in the saw 100. For example, among the saws 100, one or more electrically insulated plastic sleeves will place the shaft 109 and the blade 108 with the appliance enclosure 118, the drop arm of the appliance reaction mechanism 132, and the saw 100. The other devices are electrically isolated. In addition to this, 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 flat plate 120 and the blade 108, and the saw blade 108 and the crankshaft 109 are coupled to the saw 100. Other devices in it remain electrically isolated. The open loop configuration increases the capacitance between the plate 120 and the saw blade 108 as compared to prior art sensing systems in which the saw blade is electrically grounded. The larger capacitance in the saw 100 improves the signal to noise ratio of the signal used to detect the contact between the saw blades 108 by the operator.

As shown in FIG. 2, the plate 120 is electrically connected to one side of the first coil 152 among the transformers 150, and the appliance enclosure 118 is electrically connected to the other side of the first coil 152. In one embodiment, the saw 100 includes a single coaxial cable that includes two electrical conductors to establish the two electrical connections. In one configuration, the center conductor element of the coaxial cable is coupled to the first terminal of the first coil 152 of the flat panel 120 and the transformer 150. The outer jacket of the coaxial cable is electrically coupled to the blade 108 via the enclosure 118 and the crankshaft 109 and is electrically coupled to the second terminal of the first coil of the transformer 150. The structure of the coaxial cable provides shielding for transmitting electrical signals from the plate 120 and the enclosure 18 while attenuating electrical noise present in the saw 100.

Figure 4 depicts a cross-sectional view of the blade 108, the crankshaft 109, and the plate 120 in greater detail. In FIG. 4, non-conductive sleeves 404 and 408 will engage the shaft 109. For example, the non-conductive sleeves 404 and 408 comprise an electrically insulating plastic layer, a ceramic layer, or other insulating layer that electrically isolates the shaft 109 from other components in the saw 100. In the illustrative example of FIG. 4, the sleeves 404 and 408 include a bearing shaft for rotating the shaft 109 during operation. The blade 108 only physically engages the crankshaft 109 and is protected from other components in the saw 100. Electrically isolated. In FIG. 4, a plastic support member 412 holds the plate 120 in a position spaced a predetermined distance from the blade 108 while electrically isolating the plate 120 from other components in the saw 100.

6A and 6B show an exploded view and a front view, respectively, of the device shown in Fig. 4. FIG. 6A depicts a flat plate 120 and a support member 412 that are secured to a support frame for holding the crankshaft 109 using a set of screws. Maintaining electrical isolation between the plate 120 and the shaft 109 and other components in the enclosure 118, the screws may be non-conductive or the helical apertures in the support frame contain non-conductive threads to maintain electrical isolation . The support member 412 includes a lip 612 that surrounds the outer periphery of the plate 120 and extends outward beyond the surface of the plate 120. The lip 612 provides additional protection and electrical isolation for the panel 120 during operation of the saw 100. In particular, the lip 612 will prevent contact between the blade 108 and the plate 120 due to transient sloshing that may occur during rotation of the blade 108 during operation of the saw 100 during blade 100 cutting of the workpiece. FIG. 6B further depicts a lip 612 that extends around the support member 412 of the plate 120.

FIG. 7 depicts in greater detail additional details of one of the object detection system 102 and power supply and control PCB 172 of FIG. In the configuration of FIG. 7, certain cables used to connect different devices in the saw 100 include ferrite chokes, such as ferrite chokes 708, 738 that are coupled to cables 724, 736, and 742, respectively. And 740. Cable 742 connects TRIAC 174 to motor 112, and ferrite choke 740 reduces noise in the current conducted through cable 742 when TRIAC 174 is activated to supply power to motor 112. As discussed in more detail below, the ferrite chokes 708 and 738 reduce noise in the data cable 724 and the power cable 736, respectively, which connect the object detection system 102 to the power supply. With the control PCB 172. In the configuration of Figure 7, the sensing cable 720, which includes the first conductor that is connected to the plate 120 and the second conductor that is electrically connected to the saw blade 108, does not pass through a ferrite choke. Similarly, a motor tachometer cable (not shown) for connecting the motor 112 to the controller 140 also does not pass through a ferrite choke. As is known in the art, the ferrite chokes filter high frequency noise that is coupled to the controller 140 and the cables of 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 demodulation transformer 143A for demodulating the in-phase component of the sensed signal. The thyristor 743B connects the fourth terminal of the transformer 150 to the second demodulation transformer 143B for demodulating the quadrature phase component of the sensed signal. The thyristors 743A and 743B are "dual-wire" thyristors, also known as Shockley diodes, which switch to turn on in response to an input signal exceeding a preset breakdown voltage, but 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 that is slightly above the normal voltage amplitude of the sensed signal in order to reduce the effects of random noise among the inputs of the demodulators 143A and 143B. However, if an object (eg, a human hand) is in contact with the blade 108, then the input voltage will exceed the collapse threshold level of the thyristors 743A and 743B, and both the thyristors 743A and 743B will switch to It is turned on so that the spike signal and the sense signal are led to the demodulators 143A and 143B, respectively. The thyristors 743A and 743B are optional devices in the embodiment of FIG. 7, and alternative configurations of the object detection system 102 may omit such thyristors.

In FIG. 7, data cable 724 passes through ferrite choke 708, which connects controller 140 to power supply 106 and TRIAC 174 on power supply PCB 172. In addition, pull-down resistor 732 connects data cable 724 between controller 140 and power supply PCB 172 to a local ground (eg, on the PCB of object detection system 102). A copper ground plane) to provide additional noise reduction among the signals transmitted over the cable 724. The pull-down resistor and the ferrite choke can cause the data cable 724 to utilize a predetermined command protocol (eg, I ² C) in the first PCB of the object detection system 102 and the power supply 106 and the TRIAC 174 The second PCB 172 carries a control signal over a long distance. For example, in one configuration 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. Power cable 736 will pass through ferrite choke 738, which will provide power from power supply 106 to controller 140 and other components in object detection system 102. Although FIG. 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 devices in the object detection system 102. Provide data connection and power connection. The single cable embodiment also uses a ferrite choke to reduce the effects of noise in a manner similar to the configuration of FIG.

8A-8E depict the coaxial cable connecting the tablet 120 and the blade 108 to the detection system 102 in more detail. FIG. 8A depicts a perimeter 802 that contains the PCB and other devices in the SCU that implements the object detection system 102 and other control elements in the saw 100. The sensing cable 720 is electrically connected to both the sensing plate 120 and the blade 108. As shown in FIG. 8A and FIG. 8B, the sensing cable 720 is a coaxial cable having a first inner conductor 852, an electrical insulator 856 surrounding the inner conductor 852 and the inner conductor and the inner conductor. The second metal conductor 862 is separated; and an outer insulator 864 surrounds the second conductor 862. In the configuration of FIG. 8A, the first conductor 852 is connected to the tablet 120 and is connected to the object as shown in FIG. A first terminal of transformer 150 in system 102 is detected. The second conductor 862 is electrically coupled to the blade 108 and is coupled to a second terminal of the transformer 150 in the object detection system 102 as shown in FIG.

Figure 8B depicts a coaxial cable; however, an alternate embodiment utilizes a twisted pair cable comprising two different conductors that are twisted together in a spiral pattern. One or both of the conductors of the twisted pair cable are surrounded by an electrical insulator to isolate the conductors from one another. In addition, a shielded twisted pair cable includes an outer shield, such as a foil that wraps around the twisted pair cable and reduces external electrical noise on the conductors in the twisted pair cable. Effect.

The single sensing cable 720 is depicted in FIG. 8A connected to the panel 120 at location 832 and to the angled carriage and height adjustment carriage at the locations 836 and 838 to the appliance enclosure 118. FIG. 8C depicts in more detail that the first conductor of the sensing cable 720 is coupled to the flat panel 120 at location 832. A metal clip 866 is attached to the plate 120 and attached to the first conductor 852 in the sense cable 720 for establishing an electrical connection. In the configuration of FIG. 8C, the retaining clip 866 is interposed between the flat plate 120 and the support member 412 to ensure a secure connection between the sensing cable 720 and the flat plate 120. In some embodiments, the clip 866 is welded to the plate 120.

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 typically in the form of a removable device, the second conductor 862 is not directly It is physically connected to the blade 108. Instead, the second guide system is coupled to the appliance enclosure 118. In some saw embodiments, the enclosure 118 actually includes a plurality of components, such as a height adjustment carriage and a bevel carriage in the saw 100. A second guide among the single sensing cables 720 to ensure a consistent electrical connection The experience is coupled to each of the height adjustment carriage and the angled carriage to maintain a reliable electrical connection with the blade 108. For example, in FIG. 8, a second guide system among the sensing cables 720 is coupled to the height adjustment carriage at position 836 and to the angled carriage at position 838.

8D and 8E depict two different base positions that connect the second conductor of the sensing cable 720 to the appliance enclosure 118 at two different locations, including a height adjustment carriage and a bevel carriage. Both. As shown in FIG. 8D, the second conductor is electrically connected to and physically connected to the appliance enclosure 118 at a location 836 using a connection mount 872. The outermost insulator 864 is removed from the sensing cable 720 inside the connection base 872 for establishing an electrical connection with the appliance enclosure 118. In some embodiments, the connection base 872 is formed by a metal sleeve for enclosing and engaging a portion of the second conductor 862 of the sensing cable 720. As described above, the appliance enclosure 118 is electrically coupled to the crankshaft 109 and the blade 108, and the cable base 872 adjusts the second conductor 862 of the carriage within the sensing cable 720 and the blade via the height. Provide a reliable electrical connection between 108. 8E depicts another configuration of a connection base 876 that secures a sensing cable 720 to the beveled carriage at position 838 and a second conductor 862 among the sensing cables 720 and the instrument enclosure Provide a reliable electrical connection between 118. In one embodiment, the connection base 876 is also formed by a metal sleeve for enclosing a portion of the second conductor 862 of the sensing cable 720 for accessing the blade via the instrument enclosure 118. 108 establish an electrical connection.

As shown in FIGS. 2 and 7, controller 140 is operatively coupled to power supply 106 and TRIAC 174 on 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 will receive status data or data from sensors (e.g., on-board temperature sensors) at the PCB 172 using the I ² C protocol as appropriate. The ferrite choke 708 will reduce electrical noise in the data cable 724 and the ferrite choke 738 will reduce electrical noise in the power cable 736. The fill-in resistor 732 will also reduce noise flowing through the data cable 724. In one embodiment, the data cable 724 includes a physical configuration conforming to the High-Definition Multimedia Interface (HDMI) standard, which includes a plurality of sets of shielded twisted conductors; however, the data Cable 724 does not transmit video material and audio material during operation of saw 100. In the embodiment of FIG. 2, the data cable has a length of about 0.75 meters to connect the separate PCBs 102 and 172.

During operation, controller 140 will signal TRIAC 174 to supply current to motor 112 via a gate in the TRIAC. Once triggered, the TRIAC 174 will remain activated as long as at least one predetermined level of current from the power supply 106 is passed through the TRIAC 174 for powering the motor 112. The power supply 106 changes the amplitude of the current delivered to the motor 112 to adjust the rotational speed of the motor 112 and the saw blade 108. To shut down the motor 112, the power supply will reduce the power level supplied to the TRIAC 174 below a preset hold current threshold and the TRIAC 174 will switch to non-conductance. In the embodiment of FIG. 2, the TRIAC 174 can enable operation of the motor 112 at different speed levels and can be activated/deactivated without the need for a repeater typically required in prior art power saws. In the illustrative example of FIG. 2, the TRIAC 174 will conduct an AC electrical signal to the motor 112; however, an alternate embodiment may be substituted with a DC motor that receives DC power.

The controller 140 and associated devices in the detection system 102 are sometimes referred to as Saw Control Units (SCUs). In addition to the detection system 102 and the saw The SCU is electrically isolated from the other devices in the saw 100, except for the power connections, control connections, and sensor data connections between the other devices in the sub-100. Among the saws 100, the controller 140 is also responsible for controlling other operations in the saw 100 that are not directly related to detecting object contact with the blade 108, such as starting and shutting down the motor 112. In the embodiment of FIG. 2, the SCU is located outside the appliance enclosure 118, the detection system 102 is disposed on a non-conductor plastic support member, and the detection system 102 is oriented to avoid the detection system. The ground plane of 102 is placed parallel to any metal component inside the saw 100 to reduce electrical noise transmitted to the conductive traces in the detection system 102.

Among the saws 100, the clock source 144 and the drive amplifier 146 in the sensing circuit generate a time varying electrical signal that is directed through the first coil 152, the capacitive coupling plate 120, and the blade 108 among the transformers 150. And the enclosure 118 of the appliance. The time varying electrical signal is referred to as "sensing current" because the controller 140 senses the contact between the blade 108 and a portion of the human body with reference to changes in the amplitude of the sensed current. The time varying electrical signal is a complex value signal that includes both a phase component and a quadrature phase component. The sense current will pass through the first coil 152 in the transformer 150 to the plate 120. A change in the first coil due to the discharge between the plate 120 and the blade 108 produces an excitation signal in the second coil 154 of the transformer 150. The excitation signal is another complex value signal that corresponds to the sense current through the first coil 152.

Controller 140 among the sensing circuits is operatively coupled to motor 112, second coil 154 among transformers 150, and 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), Analog to Digital Converter (ADC), Field Programmable Gate Array (FPGA), Application Specific Integrated Circuit (ASIC), and operation for saw 100 Any other digital device or analog device. The controller 140 includes a memory 142 that stores programmed instructions for operation of the controller 140 and data corresponding to a maximum-minimum variation threshold, data corresponding to a threshold value of the variance, or corresponding to A data of the frequency response threshold value that is used to identify whether the sample taken from the sense current flowing through the blade 108 indicates that the saw blade 108 is rotating or has been aborted.

During operation of the sensing circuit, the clock source 144 produces a time varying signal, such as a sine wave, at a predetermined frequency. 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 conduct through the body. Amplifier 146 produces the sensed current as an amplified version of the signal from the clock source 144 having sufficient amplitude to drive transformer 150 and capacitor 124 for detection by controller 140. In the embodiment of FIG. 2, the saw 100 uses amplitude modulation (AM) to generate the sensing signal; however, in an alternative embodiment, the sensing signal can also utilize frequency modulation and phase modulation. Change, or other suitable modulation techniques to produce.

During 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 demodulation transformer 143A and receives the excitation via the second demodulation transformer 143B. The orthogonal component Q of the signal. The transformer 150 isolates the sense current flowing through the first coil 152, the plate 120, the saw blade 108, and the instrument enclosure 118 and the demodulation transformer 143A that supplies the in-phase component and quadrature phase component of the signal to the controller 140, respectively. With 143B. Because the demodulators 143A and 143B generate electrical noise, the transformer 150 reduces or eliminates the effects of the noise on the first coil 152 and the sense current. In one configuration, the transformer 150 is a 1:1 transformer, wherein the first coil 152 and the second coil 154 have an equal number of turns. In an alternative configuration, the ratio of the coils in the first coil 152 and the second coil 154 are selected 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 means needed to generate digital representations of the amplitudes of the in-phase signals I and quadrature signals Q. The controller 140 considers the amplitude of the sense current A at a given time as the Pythagorean sum of the in-phase component and the quadrature component in each sample as shown by the following formula: A = The controller 140 measures the demodulated signal at a preset frequency, for example, a 100 KHz sampling rate and a period of 10 microseconds between each sample to identify changes in the amplitude A of the complex value signal. .

As the motor 112 rotates the blade 108, the rotating blade 108 will contact different objects, including wood blocks and other work pieces. A small portion of the charge accumulated on the blade 108 will flow into the workpiece; however, the conductivity of the wood workpiece is relatively 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 block of wood, the controller 140 typically measures a small change in the sense current A; however, changes in the sense current are considered to correspond to the wood. Or other materials with low conductivity.

When a workpiece (eg, wood) has a low conductivity, another object (eg, a portion of the body) will have a higher conductivity and absorb a larger portion of the charge on the blade 108 as the portion approaches the blade 108. In Figure 2, a portion 164 of the human body (e.g., hand, finger, or arm) is represented by a charged cloud cloud that represents charge flow from the blade 108 to the human body. The contact between the human body and the blade 108 effectively changes the capacitance level because both the human body and the saw blade 108 will A charge is received from the sense current. When the body 164 contacts the blade 108, the controller 140 recognizes the contact between the body 164 and the blade 108 as a rapid increase in the amplitude A of the sense current. In response to a rapid increase in the amplitude of the sensed signal, the controller 140 turns off the motor 112, opens the appliance reaction mechanism 132 to abort the motion of the blade 108, and optionally retracts the blade 108 before it contacts the body 164.

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

In the saw 100, the controller 140 will turn off the electric motor 112 in response to confirming contact between the blade 108 and a portion of the human body. In the saw 100, the saw blade 108 typically continues to rotate for a period of a few seconds due to the momentum of the saw blade 108 accumulated during operation. The appliance reaction mechanism 132 is configured to suspend the saw blade 108 in a very short period of time; the saw blade 108 is lowered below the table 104, which retracts the saw blade 108 from contact with the human body; Alternatively, the blade 108 is simultaneously suspended and retracted. In the saw 100, the appliance reaction mechanism 132 includes a drop arm that is mechanically coupled to the saw blade 108. The appliance reaction mechanism 132 Also included is an explosive charge package configured to pull the drop arm into the outer casing of the saw and away from the surface of the table 104. The controller 140 operates the explosive cartridge to move the drop arm and the blade 108 downward in response to detecting contact between a portion of the operator's body and the blade 108. The appliance reaction mechanism retracts the blade 108 below the surface of the table 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 has been fired a predetermined number of times. For example, in the configuration of the saw 100, the appliance response mechanism 132 includes a total of two "shot" double burst kits. Each operation of the appliance's reaction mechanism consumes an explosive packet in a "monoshot" operation. The operator removes and reinserts the explosive device to place the second explosive packet in the correct position for moving the drop arm during the subsequent operation of the appliance reaction mechanism 132. The controller 140 will store a record of the number of activations of the appliance reaction mechanism 132 and prevent the saw 100 from being activated during the lockout process after the number of starts exceeds a preset number of times (eg, one, two, or more times of activation). In an embodiment of the saw 100 that is coupled to a data network (e.g., the Internet), the controller 140 optionally sends a network notification to the service provider or warranty vendor in the locking operation. The locking process may cause the service provider to diagnose potential problems with the operation of the saw 100 or the use of the saw 100 in response to frequent operation of the appliance reaction mechanism 132.

In addition to sensing the contact between an object and the saw blade 108 while the saw blade 108 is moving, the sensing circuitry in the saw 100 is also configured to confirm whether the saw blade 108 is being mobile. For example, the controller 140 will confirm that the saw blade 108 is to be actuated by the operator to operate the user interface 110 to cut the saw 100 to cut one or more workpieces and The user interface 110 is then operated to close the motor 112 and continue to rotate for a period of time. For example, the user interface 110 includes: a start/stop switch for operating the saw 100; a speed control input device; and a status indicator that provides information regarding the operational status of the saw 100, eg, whether the saw has Ready to operate or have failed. The user interface device 110 is also referred to as a Human Machine Interface (HMI).

The saw 100 is configured to operate in conjunction with the blade 108 and the blade shaft 109 that are isolated from electrical ground. The control electronics on boards 102 and 172, plate 120, and appliance enclosure 118 may not be connected to the actual ground ground in some configurations; however, such devices share a common ground plane, for example, A common ground plane formed by the metal chassis of the saw or a common ground plane formed by the ground planes formed on the circuit boards 102 and 172. As described above, during the contact detection process, the controller 140 recognizes a spike in the current level of the sense signal. However, the electrical noise generated in the saw 100 may cause a false positive detection event or a false negative detection event because the noise may interfere with the detection of the sensing signal. In saw 100, the PCBs 102 and 172 contain ferrite core chokes that act as low pass filters to reduce the effects of noise. In addition, the circuit cable and data cable will also pass through the ferrite core to reduce noise. The power supply 106 includes a ferrite choke and a thyristor for rejecting low speed transient noise from power signals received from the power grid, the generator, or other power sources.

5A-5D depict a portion of one embodiment of the user interface device 110 in more detail. FIG. 5A is an external view of a device status display including a housing 502, a plurality of indicator lights 528A to 528D, and a cover 512 for a short range antenna. During operation, the controller 140 activates one or more of the indicator lights 528A through 528D for use in the table. Different status information related to the saw 100 is shown. For example, indicator light 528A indicates that saw 100 is ready for operation. Indicator light 528B indicates that appliance response mechanism 132 has been operated and that the explosive charge package within appliance response mechanism 132 should be reset. Indicator light 528C indicates that the user should query the fault code. Indicator light 528D indicates that saw 100 requires maintenance after the appliance reaction mechanism has been operated more than a preset number of times. As shown in Figure 5A, the indicator lights 528A through 528D provide a simplified interface. Alternative embodiments include a different indicator arrangement or additional input and output devices, for example, including a video display screen, a touch input device, and the like.

The display indicators 528A-528D provide simplified direct output feedback to the operator for normal use of the saw 100; however, in some cases, the saw 100 transmits more complex diagnostic and configuration information to external devices. The controller 140 and the user interface device 110 can 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 diagnostic data collected by controller 140 and transmitted using wireless transceiver and antenna 516 as appropriate include: voltages present in the sensing circuitry; levels of sensor signals; used to indicate appliance response mechanisms 132 Whether the pyro device (pyro) is stated or disarmed state information; generates a test signal for the pyro firing line without transmitting a signal having an amplitude sufficient to trigger the single shooting operation of the pyro Detecting the presence or absence of the pyro; checking the range of resistance to rust or wire breakage in the sensor cable connected to the plate 120 and the enclosure 18 of the appliance or other cables in the saw 100; A "tackle pulse" is generated to identify a disconnection in the line providing power to the motor 112; and to identify a fault in the motor 112 during the power-on self test.

As shown in FIG. 5B, the short-range wireless antenna 516 is supported by an indicator light 528A. A predetermined arrangement of a plurality of conductor lines on the PCB to 528D. 5B and 5C depict semi-transmissive cap portions 504A-504D that form an externally visible surface of each of the indicator lights 528A-528D, respectively. The housing 502 protects the antenna 516 from external elements while allowing the antenna to be placed outside of the saw 100 for communication with external electronics. Antenna 516 is operatively coupled to a wireless transceiver, such as an NFC, Bluetooth, IEEE 802.11 protocol family of compatible wireless transceivers ("Wi-Fi"), or other suitable short range wireless transceivers. An internal electronic device (eg, a smart phone, tablet, portable notebook, or other mobile electronic device) receives information from the saw 100 via a wireless communication channel and uses the wireless communication channel to transmit information as appropriate Give the saw. For example, a smart phone receives diagnostic data from the saw 100, and a software application executing on the smart phone displays detailed diagnostic information to an operator or maintenance technician to help maintain the Saw 100. The software application can optionally cause the operator to enter configuration information for the operational parameters of the saw 100 that are not directly accessible via the simplified input device 110. For example, in one configuration, the software application can allow an operator to enter the maximum RMP rate of the motor 112 and the blade 108. In another configuration, the software application allows the operator to transmit an identification code of the type of material that the saw 100 will cut during operation, such as different types of wood, ceramic, plastic, 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 within a predetermined distance of the saw 100. The mobile electronic device transmits an encrypted authorization code to the saw 100 in response to a 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 will Sub 100 will remain inactive.

Figure 5C depicts a cross-sectional view of indicator lights 528A through 528D. Each indicator light includes a half-transmissive cap portion (eg, cap portion 504A on indicator light 528A), and an opaque body member 524A directs light from a source (eg, LED) to The translucent cap. Among the indicator lights 528A, an LED 552 disposed on the PCB projects light through an opening in the opaque body member 524A and the translucent cap portion 504A. The opaque body member 524A has a tapered shape with a narrow end that surrounds the first opening of the LED 552A and a wider end that has a second opening for engaging the translucent cap portion 504A. The opaque member 524A prevents light from the LED 552A from passing through and producing erroneous illumination among any of the other indicator lights 528B through 528D. The configuration of Figure 5C can cause the indicator lights in the user interface device 110 to operate in direct daylight conditions and prevent erroneous illumination of incorrect indicator lights during operation.

Figure 5D depicts an exploded view of the selected device of Figures 5A-5C. Figure 5D depicts an indicator cap assembly 540 formed from a molded plastic member that includes translucent indicator cap portions 504A through 504D for indicator lights 528A through 528D. The indicator cap assembly 540 further includes an attachment member, such as a hook portion 506 formed by the molded plastic member of the indicator cap assembly 540 for securing the caps to use Other devices among the interface devices 110. The body member assembly 544 is another molded plastic member that includes opaque body members 524A-524D corresponding to the cap portions 504A-504D. Each of the opaque body members 524A-524D includes a first opening and a second opening, the first opening aligning one of the LEDs 552A-552D, and the second The opening will engage one of the cap portions 504A-504D. The body member assembly 544 also includes an attachment member, such as a hook Portion 526, which connects the opaque body members to other devices in the user interface device 110. The PCB 550 includes a plurality of physical placement locations for operating the user interface device 110 and a plurality of electrical connections. Specifically, FIG. 5D depicts Light Emitting Diodes (LEDs) 552A through 552D that align with the first openings of the corresponding opaque members 524A through 524D and provide light to the caps of the indicator lights 528A through 528D. Parts 504A to 504D. The PCB 550 also includes an antenna 516 formed by a predetermined pattern 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 is integrated with controller 140. The indicator cap assembly 540, the body member assembly 544, and the PCB 550 are disposed in a base member 560, which in the embodiment of Figure 5D is a molded plastic member. The base member 560 secures the components of the user interface device 110 to the outer casing of the saw 100.

The user interface device 110, which is shown on the exterior of the housing of the saw 100, is shown in FIG. The base member 560 attaches the components of the user interface device 110 to the exterior of the housing in the saw 100 where the user can easily see the indicator lights 528A-528D. Moreover, the antenna 516 on the PCB 550 is positioned outside of the electrical shield of the saw 100, which provides a full perspective view of the power supply 106 for communication with the short range external wireless device and any wireless transmission on the antenna 516 and PCB 550. The device is isolated from the electrical noise source within the saw 100. A data cable (not shown) connects the controller 140, which is placed on the PCB within the housing of the saw 100, to the user interface device 110 on the exterior of the saw.

The user interface device 110 depicted above includes a plurality of indicator lights and a wireless data interface; however, in some configurations, the saw 100 also includes additional data. Interface device. For example, in one embodiment, a Universal Serial Bus (USB) or other suitable wired data connector will be operatively coupled to the controller 140. The saw 100 includes a USB port near the rear of the bevel carriage. The USB port is hidden so that the general operator cannot see it; however, the maintenance personnel can move the bevel carriage to the leftmost tilt position or the rightmost tilt position and via the back of the housing of the saw 100. An opening is located to locate the USB port and access the USB port. The USB port is connected to an external computing device for performing diagnostic operations as well as maintenance operations. The USB connection also allows the maintenance personnel to update the software program that the controller 140 would have stored in the memory 142 during the operation of the saw 100.

Referring again to the saw configuration of FIG. 2, in one of the modes of operation, the controller 140 within the saw 100 utilizes an adaptive threshold process to identify the current corresponding to contact between an operator and the blade 108. A spike is provided to control the operation of the appliance reaction mechanism 132. During the adaptive threshold process, the controller 140 will recognize the average signal level of the sensed signal over a predetermined period of time (eg, 32 sample periods of 320 microseconds in a sampling rate of 100 KHz). quasi. The controller 140 applies a predetermined bias value to the detected average level and uses the sum of the average and the skew level as an adaptive threshold. The controller 140 updates the average threshold based on a relatively small change in the average level of the sensed signal due to electrical noise, which prevents the level of the sensed signal from being A false positive contact event is detected when the electrical noise in the sensing signal changes. If a contact occurs between the operator and the blade 108, a rapid spike in the sense current will exceed the predetermined skew level, and the controller 140 will detect the contact and activate the appliance response mechanism 132.

In a non-essential embodiment of the adaptive threshold detection process, the controller 140 also identifies a signal to noise ratio among the sensed signals in response to detecting a spike in the sensed signal current (Signal To Noise Ratio, SNR) to further reduce the possibility of false positive detection. The controller 140 identifies the SNR by dividing the average value of the signal in a predetermined time window by the variance of the signal level in the same time window. In one configuration, the controller 140 implements a block calculation process to reduce the computational complexity of identifying the SNR, which can cause the controller 140 to recognize the SNR within operational timing constraints of the operation of the appliance response mechanism 132. During the block calculation process, the controller 140 will recognize the average of the signal in a plurality of relatively short blocks (for example, 32 sampling periods of 320 microseconds in a sampling rate of 100 KHz) and The calculated average value of the block is stored in a memory. Controller 140 then identifies the SNR in a series of blocks, for example, in one of the embodiments, eight consecutive time blocks in 2560 microseconds.

The controller 140 identifies 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. A single variation of all blocks. The controller 140 will only recognize the SNR based on the eight average values and the identified variance values, rather than identifying the average and variance in all 256 different samples. This block calculation process greatly reduces the computational power required to identify the SNR. The controller 140 will continue to recognize additional samples over time during operation and update the SNR samples to accommodate newer samples after removing the oldest block in the set of eight blocks. After identifying the SNR, the controller 140 determines whether the SNR level is at a preset minimum threshold when detecting a sensing current spike that exceeds a detection threshold of contact between the operator and the blade 108. the following. If the SNR level is too low In other words, it indicates a weak signal level below the detected noise level, then the controller 140 does not operate the appliance reaction mechanism 132 to prevent false alarms when the operator does not actually touch the blade 108. operating.

Another non-essential configuration of the adaptive threshold process includes an operation to detect electrostatic discharge from the blade 108 and to prevent electrostatic discharge events from being incorrectly identified as contact between the operator and the blade 108. During operation of the saw 100, the rotating blade can accumulate static electricity and release static electricity to the device inside the saw 100 or to an external object, such as a work piece. The electrostatic discharge often produces a momentary positive or negative voltage spike in the sensed signal that is similar to a spike that occurs in response to contact between the operator and the blade 108. However, the amplitude of the peak due to electrostatic discharge is often several times larger than any peak produced by contact with the operator. Thus, in some embodiments, the controller 140 not only recognizes human body contact in response to the amplitude of the sensing signal that exceeds the adaptive threshold, but the controller 140 also responds to the peak amplitude at an upper threshold ( It is below the initial detection threshold to identify human contact in order to avoid false alarming of the appliance response mechanism 132 in response to an electrostatic discharge event.

The adaptive threshold process can be used in a variety of modes of operation of the saw 100, including the mode of operation in which the saw 100 performs a "DADO" cut. As is known in the art, during a DADO cutting operation, the blade 108 cuts a groove through all or a portion of a workpiece; however, the workpiece is not completely cut into two separate portions. Many DADO cuts create grooves that are thicker than a single saw blade, and the saw 100 is mated with a plurality of saw blades that are placed together on the crankshaft 109 to operate to form the thicker grooves. The plurality of saw blades act as an antenna and receive electrical noise from various sources inside and outside of the saw 100, which reduces Signal to noise ratio during DADO cutting.

In some embodiments, the controller 140 also detects contact between the operator and the blade 108 during a longer period of time during the DADO cutting operation to resolve high noise levels present in the detection signal. quasi. For example, in one of the configurations, the controller 140 identifies a spike in the current sampling level that exceeds the adaptive threshold for contact detection in the first sampling period. In a high-noise environment, the noise spikes may also produce large spikes that exceed the adaptive threshold level; however, a true contact event produces a relatively consistent spike in the current. It remains above this threshold for several sampling periods (for example, up to 10 cycles at a sampling rate of 100 KHz). Controller 140 will recognize peak level changes in multiple sampling periods. If the spike remains at a high amplitude and does not change a large amount of levels during a number of sampling periods, then 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 confirms that there is a large variation in the level of the sense current spike, then the controller 140 will confirm that the changes in the sense current are due to noise and not The appliance reaction mechanism 132 will be operated. Even during longer detection periods, the total detection and operation time of the object detection system 102 still occurs in a period of only a few milliseconds in order to maintain the effectiveness of the appliance response mechanism 132.

The adaptive threshold process will improve the accuracy of contact detection during DADO cutting; however, the adaptive threshold process is not necessarily required during the DADO cutting process, and the adaptive threshold process is equally applicable. Used in other modes of operation of the saw 100.

During operation of the saw 100, the controller 140 implements a fault detection process as appropriate to identify the cable connecting the sensor plate 120 or the appliance enclosure 118 to the detection system 102. A fault in the line. The controller 140 identifies a hard fault through a continuity test, such as a complete disconnection in the cable. The so-called "soft" occurs when the cable is at least intermittently connected but the quality of the connection does not allow the sense signal to reach the sensor panel 120 and the controller 140 detects the sense current flowing through the capacitor 124. Fault (soft fault). In one configuration, the controller 140 will identify the soft fault prior to starting the motor 112. The controller 140 generates a sense current flowing through the sense cable when the motor 112 remains off and the electrical noise level in the saw 100 is relatively low. If the amplitude or noise level of the sensed signal deviates from the expected value by more than a predetermined operational margin threshold, the controller 140 will confirm that there is a soft fault in the sense cable. The controller 140 generates an error signal via the user interface device 110 and prevents the motor 112 from being activated in response to detecting a hard or soft fault in the sensing cable before the sensing cable is repaired or replaced. .

In some embodiments, the saw 100 is characterized by a capacitance level of a different operator that is in contact with a capacitive sensor positioned at a predetermined contact location of the saw. For example, in one embodiment, the saw 100 includes a metal handle that, when an operator grips the handle, registers the capacitance, conductance, and other electrical characteristics of the operator's hand. In other embodiments, a capacitive sensor will be placed in a track or other surface in the saw 100 that the operator can contact during 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 operational parameters to improve the accuracy of each operator's blade contact detection results.

In some embodiments, the saw 100 utilizes the sensed signal to perform pattern detection to identify the state of the blade 108 during operation. For example, in one embodiment, the controller 140 recognizes that the sensing signal corresponds to a tooth impact between the blade 108 and a workpiece. Elements. The controller 140 will use a tachometer or other RPM sensor to identify the rate of rotation 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 for use in the blade. 108 engages the workpiece to confirm the expected tooth impact frequency. The controller 140 will use the expected tooth impact frequency to help identify a sensing signal that may correspond to the contact between the operator and the blade 108, or only correspond to the electrical noise generated by the impact of the workpiece at a tooth. Sensing signal.

In certain embodiments of the saw 100, when the saw 100 cuts a different type of material, the controller 140 stores the identified profile of the sensed signal. For example, the saw 100 cuts through a variety of wood or blocks of different moisture levels to identify the amplitude of the sensed signal detected when cutting a plurality of different types of wood or other materials and The noise level. The profile extraction process is performed at the factory prior to transporting the saw 100 as appropriate. During subsequent operations, the operator provides input to characterize the type of material that the saw 100 is about to cut, and the controller 140 retrieves the stored profiled profiles of the expected sensed signal parameters from a memory. In order to help identify the expected sensing signal when cutting the workpiece.

Another embodiment of the object detection sensor for use with the object detection system 102 of the saw 100 or other saw embodiment is shown in FIG. 9A. 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 that is capable of detecting a contact that is in contact with or very close to the surface of the corresponding capacitive sensor due to a change in capacitance near the sensor. The presence of a human hand or other body part. Conversely, a work piece (eg, wood) produces a very different change in capacitance so that a controller (eg, controller 140 shown in FIG. 2) distinguishes the work piece from the body of the human body. Body part. The capacitive sensors 904-912 are arranged along a cutting direction 920 that corresponds to the direction of advancement of the workpiece as the blade 108 cuts a workpiece. Capacitive sensors 904 are arranged in a region that is in 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, respectively, in a manner that conforms to the saw blade 108.

As shown in FIG. 9A, each of the capacitive sensors 904 through 912 occupies a predetermined area of the throat plate 119, such as the rectangular area shown in FIG. 9A or another geometric shape. In some embodiments, the capacitive sensors 904 to 912 not only detect the presence of a body part of the human body close to the corresponding sensor, but also detect that the body part of the body is above the sensor. The position and the speed and direction of movement of the body part of the body over time. The thermoplastic throat 119 isolates the capacitive sensors 904-912 and the blade 108, the surface of the table 104, and other components within the saw.

The operation 950 of the capacitive sensors 904 to 912 in the saw 100 is shown in FIG. 9B. The process 950, which is described in the following description for implementing a function or action, describes the operation of a controller to execute stored program instructions in conjunction with other devices in the saw for performing the function or action. For purposes of explanation, process 950 will be described in conjunction with the embodiment of FIG. 9A and saw 100.

Process 950 is initiated from saw 100 and motor 112 moves blade 108 to begin cutting the workpiece (block 954). During operation, the capacitive sensors 904-912 generate the capacitive sensing signals to detect the proximity of the capacitive sensors 904-912 surrounding the blade 108 in the throat plate 119. The presence of an object on the surface (block 958).

If the controller 140 changes the RC time constant of the capacitive sensing signal Based on the identification of the capacitance level changes of one or more of the capacitive sensors 904 to 912, the controller 140 will be associated with an object (eg, a workpiece or a body part). The object is detected to be present in the area adjacent the saw blade prior to contact between the saw blades 108 (block 962). For example, in some embodiments, the capacitive sensors 904 to 912 include: a plurality of capacitive sensing elements that form one of a plurality of capacitors; and a non-conductive dielectric And covering the capacitive sensing elements and covering the surfaces of the capacitive sensors 904 to 912. An oscillator in the capacitive sensors generates an hour-varying capacitive sensing signal using an RC circuit, the RC circuit consisting of a capacitive component in each of the sensors and a predetermined one. A resistor is formed. As is known in the art, the RC time constant changes in response to a change in the magnitude of the capacitance C in the RC circuit, and the capacitive sensor or an external control device is among the time varying signals. Change based to identify contact with objects. An object positioned above the surface of one of the sensors 904-912 acts as a second plate of a capacitor and produces a capacitive level change of the sensor.

If the controller 140 confirms that there are no objects 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 workpiece rather than a body part of the body. (Block 966), then the saw 100 continues to operate to cut a work piece (block 970). Conductive objects (eg, the operator's fingers or other body parts) can produce relatively large changes in capacitance, while non-conducting objects (eg, wood work pieces) can produce small changes in capacitance levels. As described above, a feature of a work piece (e.g., wood) can produce a change in capacitance that is significantly different from the body part of the body among the sensors 904 to 912 so that the controller 140 can distinguish the work piece and very close to the The body parts of the human body of the capacitive sensors 904 to 912.

During the process 950, if the capacitive sensors produce a signal corresponding to a very large amount of capacitance change (which corresponds to the hand or other body part being very close to the capacitive sensors 904 to 912), then The controller 140 will generate an alert output, turn off the motor 112, or activate the appliance reaction mechanism 132 (block 974) before the object contacts the blade 108. In the configuration in which the detected object does not actually touch the blade but has moved to a predetermined distance within the blade, the controller 140 turns off the motor 112 and stops the saw blade 108, but does not The appliance reaction mechanism 132 is turned on unless the object detection system 102 described above is utilized to detect that the object actually contacts the blade. In other embodiments, if the capacitive sensors 904-912 detect an object corresponding to a body part of the human body, the controller 140 will work before turning off the motor 112 or operating the appliance reaction mechanism 132. A warning signal is generated on the station 104, for example, a light that is visible to the operator. In some embodiments, if the object contacts the blade 108, the object detection system 102 will first operate the appliance reaction mechanism 132 before the blade 108 is fully aborted or before the object contacts the blade 108.

In some embodiments of process 950, each of the capacitive touch sensors 904-912 includes a two-dimensional sensing element grid that allows the contact sensing to be sensed. The device generates a plurality of capacitive detection signals corresponding to locations within the two-dimensional region covered by each of the capacitive sensors. In some configurations, the controller 140 detects a body part of the body at a first location on one of the sensors 904-912 but beyond a first predetermined distance from the blade 108. A warning signal is generated and then the controller 140 turns off the motor 112 if the object moves the predetermined distance of the blade 108. Moreover, the controller 140 or other control device may also identify the series of object positions generated by the unique sensing elements of the capacitive sensors 904 to 912 over time. The path and speed of the object. If the moving path indicates that an object (eg, a human hand) is likely to contact the blade 108 at a certain point in the path, then the controller 140 turns off the motor 112 or generates the alert as described above. Output. In addition, in some configurations, the controller 140 activates the appliance reaction mechanism 132 to retract the blade 108 or other appliance prior to actual contact between the blade 108 and the operator's hand or other body part. For example, if the position of the detected 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 activates the appliance reaction mechanism 132 as appropriate prior to the actual contact with the blade 108. 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 an operator's body part is present near the blade 108 and detect the body part and the The actual contact operation between the blades 108 is performed before and after.

In addition to the operation of the object detection system 102 described above, the saw 100 is further configured to implement different configurations and diagnostic procedures to maintain the reliability of the saw over a wide range of different materials and to Can operate the saw. For example, the saw 100 will be configured to maintain a record of the number of times the appliance reaction mechanism has been activated to ensure proper maintenance of the saw 100.

Figure 10 is a block diagram of a process 1000 for monitoring the appliance reaction mechanism among the saws. The process 1000 for implementing a function or action in the following discussion describes the operation of a controller for executing stored program instructions to perform the function in conjunction with one or more of the devices. Or action. For purposes of explanation, process 1000 will be described in conjunction with saw 100.

Process 1000 begins by activating the appliance reaction mechanism (block 1004). In the saw In 100, controller 140 activates appliance response mechanism 132 in response to detecting contact with an object other than the workpiece (eg, the operator's hand). In one embodiment of the saw 100, an explosive packet within the appliance reaction mechanism 132 will fire 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 maintain a record of the number of times the appliance reaction mechanism has been initiated during operation of the saw 100 (block 1008). As is known in the art, even if the saw 100 has been turned off and disconnected from power, the non-volatile memory (eg, a solid state data storage device or a magnetic data storage device) will retain the stored data for a long period of time. cycle.

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

Process 1000 continues during the maintenance operation. 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 to allow the saw to return to Operational state (block 1020). In one embodiment, the maintenance process includes connecting an external stylized device (eg, a PC or other computerized stylized device) to the saw 100. a maintenance port (e.g., a universal serial bus (USB) port) for extracting diagnostic data from the memory 142 and reprogramming the memory 142 to reset the number of times the device reaction mechanism has been activated. Counter. The use of an external stylized device allows the saw 100 to be re-used after maintenance while allowing the saw to remain disabled until proper maintenance is performed.

If the appliance reaction mechanism 132 performs an unusually large number of starts, the process 1000 will ensure that the saw 100 remains disabled until maintenance is performed. This maintenance operation will ensure that all of the components within the saw 100 will operate correctly and that the object detection system 102 will accurately detect contact between objects other than the workpiece and the saw blade 108.

As described above, the object detection system 102 will respond to the blade 108 and any objects that contain the workpiece that the saw cut during normal operation, and may include other objects, such as the body portion of the saw operator, thereby causing the object to be activated. The input signal is received by contact between the appliance reaction mechanisms. During operation of the saw 100, the object detection system 102 receives an input signal corresponding to a change in capacitance level in the capacitor 124 formed by the plate 120 and the blade 108, the capacitance level change corresponding to the and workpiece Contact between and contact with objects outside the work piece. For example, in some cases, wood with a high moisture content may be confused with a portion of the operator's body during saw operation. The process illustrated in Figure 11 is a process 1100 for generating a profile profile of signals produced by different material types among various workpieces to improve the accuracy of object detection. The process 1100 for implementing a function or action in the following discussion describes the operation of a controller for executing stored program instructions to perform the function in conjunction with one or more of the saws. Or action. For purposes of explanation, the process 1100 will be described in conjunction with the saw 100.

Process 1100 operates from the saw with the enabled object detection system 102 The operation begins when the appliance response mechanism 132 is disabled (block 1104). Operating the saw 100 in the absence of enabling the appliance's reaction 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 suitable for use in the work piece of the saw, but may produce a trigger reaction mechanism 132 that is mistaken for a body part of the human body or should be in contact with the rotating blade 108. Sensing signals of other objects.

Process 1100 will continue such that the saw 100 records a sensing signal generated at a predetermined time in the object detection system 102 at the beginning of the workpiece's initial contact with the blade 108 during the cutting of the workpiece as it moves through the blade 108. The resulting sensed signal and the sensed signal generated when the workpiece is disengaged from the blade 108 to complete the cut (block 1108). The recorded sensed signal information typically includes spikes in the sensed signal that are related to changes in capacitance levels in capacitor 124. For example, the initial spike that occurs when the workpiece first comes into contact with the rotating blade 108 may be identical to the initial spike produced by an object other than the workpiece just beginning to contact the rotating blade 108.

In another embodiment of process 1100, saw 100 includes an additional sensor other than a capacitive sensor formed by capacitor 124 that is capable of detecting features of the workpiece material that are different from the operator's body. For example, one of the embodiments further includes one or more infrared sensors that are disposed on the file 330 shown in FIG. The infrared sensors produce a profile of the frequency response of the infrared light reflected from the workpiece. Controller 140 is operatively coupled to the infrared sensors to record the frequency response of the material within the workpiece.

Process 1100 will continue such that the controller 140 or a processor located in an external computing device recognizes the recorded sensing signal and triggers the saw The preset sensing signal of the object of the appliance reaction mechanism among 100 parses the difference between the contours (block 1112). For example, as described above, the controller 140 uses an adaptive threshold process to identify spikes in the sensed current that correspond to the hand contacting the blade 108 or other portions of the body. The peak corresponding to the contact with the human hand includes an amplitude profile and a time profile. The controller 140 recognizes a predetermined contour of a body part of the human body and an initial spike that occurs when the workpiece first contacts the rotary blade 108 and when the blade 108 cuts the work piece and disengages the work piece The amplitude between any successive spikes and the difference in duration of time.

The controller 140 or the external processor then generates a detection profile profile unique to the test material based on the difference between the recorded sensing signals and the preset object detection profile of the body of the human body (block 1116). . In one embodiment, the controller 140 produces a profile profile having a range of amplitude values near the amplitude of the recorded spike that falls within the sensed signal as the blade 108 engages the predetermined material in the workpiece. The range of amplitude values for the spike does not include the critical amplitude of the spike amplitude of the operator's preset profile profile to ensure that the controller 140 does not incorrectly identify the sensory signal corresponding to the operator as a workpiece. Therefore, the range of amplitude values corresponding to different workpieces will vary based on the difference between the recorded peaks resulting from the contact between the blade 108 and the workpiece material and the preset profile contour corresponding to the body of the human body. . The controller 140 will also generate a response corresponding to the difference from the time range from the peak of the workpiece and the expected duration of the spike in the profile profile in contact with the body of the human body. The time range of the peaks in the signal lasts for a length of time. The updated profile profile allows the controller 140 to distinguish between the blade 108 and the workpiece made of the predetermined type of material against possible contact with a portion of the body of the human body. The sense of contact comes from the sensed signal of capacitor 124.

As mentioned above, in an alternative embodiment, the controller 140 generates a profile profile based on the data from the infrared sensors to identify the frequency response range of the material in the workpiece. And distinguishing the frequency response range from a predetermined frequency response range associated with the operator. The controller 140 uses the preset frequency response range stored in the memory 142 for the operator to ensure that the frequency response range within the profile profile of the material does not overlap the operator's preset profile profile. For example, in one configuration, the memory 142 stores a frequency response profile profile of the near infrared response that is a peak response at a wavelength of about 1080 nm for a wide range of human skin tones and is at about 1580 nm. There is a minimum response at the wavelength. Other types of materials for various workpieces have a sharp infrared frequency response and a minimum infrared frequency response at different wavelengths, and the controller 140 will correspond to the wavelength of the workpiece (but it does not overlap the response corresponding to human skin) A profile of the frequency response having a peak response value and a minimum response value is generated at the wavelength).

During process 1100, the updated profile profile of the test material is stored in memory 142 (block 1120). During the subsequent operation of the object detection system 102 and the appliance reaction mechanism 132, the controller 140 uses the stored profile information of the test material to reduce the contact between the workpiece and the saw blade 108. The change occurring in the measured signal is mistaken for the potential occurrence of a false positive detection event corresponding to the contact between the operator and the saw blade. For example, if the saw 100 is cutting a particular type of material stored in the profiled profile in the memory 142, as long as any spike in the sensed signal in the object detection system 102 remains in the corresponding material. The amplitude range of the stored profile profile and the time holding Within the continued length range, then controller 140 will continue to operate saw 100. In some configurations, the memory 142 stores a profiled profile of the various types of materials that the saw 100 cut during operation. The operator will optionally provide an input to the saw 100 to detail the type of material to be cut in order for the controller 140 to use a stored profile profile for the appropriate type of material among the workpieces.

As described above, the object detection system measures changes in the sensed signal via capacitor 124 in response to contact between the object and the rotating saw blade 108. The memory 142 stores preset threshold information for the controller 140 to detect contact between the operator's body and the blade 108 in conjunction with the adaptive threshold process described above. However, the unique operator's body may present different capacitance levels between different individuals, and the capacitance level of a body may change over time for a variety of reasons. Examples of factors that affect the operator's capacitance level include, but are not limited to, the temperature in the environment near the saw and the ambient humidity, the physiological makeup of each operator, the degree of sweating of the operator, and Similar factors. 12 depicts a process 1200 for measuring the capacitance level of individual operators during operation of the saw 100 to allow the saw 100 to adjust object detection thresholds for different individuals. The process 1200, which is described in the following discussion for implementing a function or action, describes the operation of a controller for executing stored program instructions to perform the function in conjunction with one or more of the devices. Or action. For purposes of explanation, process 1200 will be described in conjunction with saw 100.

Process 1200 measures from the saw 100 during operation of the saw via a capacitive sensor formed in a handle that is contacted by an operator or other predetermined contact location on a surface of the saw 100. The operator's capacitance level begins (block 1204). Take the picture of Figure 3 By way of example, one or more of the other surfaces of the saw 304, the front rail 310, the bevel adjustment grip 352, the height adjustment grip 354, or other surface of the saw that the operator would contact during operation. The capacitive sensor produces a capacitance level measurement in the operator's hand. The operator does not need to continuously contact the capacitive sensor during operation of the saw 100; however, the controller 140 updates the condition as the operator contacts one or more of the capacitive sensors. The measured capacitance level.

Process 1200 will continue with the controller 140 correcting the threshold level for detecting contact with an object other than the work piece (e.g., the operator's body) (block 1208). The controller 140 may decrease the default peak amplitude detection threshold of the sensing signal in response to the measured capacitance level being less than the preset internal positioning level, which may occur when the operator's skin is abnormally dry or other environmental factors are lowered. When the effective capacitance in the body is at the time. The controller 140 will correct the threshold based on the difference between the internal capacitance level applicable to a wide range of operators and the measured capacitance level (which may be higher or lower than the internal positioning 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 threshold in response to recognizing a large amount of capacitance among the operators as appropriate. In some embodiments, the controller 140 limits the maximum threshold level in object detection to ensure that the object detection system 102 retains the ability to detect contact between the operator and the blade 108 because of increased detection. The threshold level actually reduces the sensitivity of the object detection system 102.

Process 1200 will continue such that saw 100 will operate to cut the workpiece and object detection system 102 will use the corrected detection threshold to detect potential operator contact with blade 108 (block 1212). As described above, if the operator's hand or other body part contacts the rotating blade 108, the controller 140 utilizes the adaptive nature described above. The threshold value process compares the amplitude of the measured spikes among the sensed signals taken via capacitor 124 and the corrected threshold. Because the controller 140 corrects the detection threshold based on the operator's measured capacitance, the process 1200 can cause the saw 100 to detect contact between the operator and the saw blade 108 with improved accuracy.

Among the saws 100, the motor 112 includes one or more brushes that engage a commutator. The use of brushes in electric motors is well known in the art. As time passes, the brushes wear out, which reduces the efficiency of the motor, and the worn brushes often generate sparks. These sparks can be detrimental to the operation of the motor 112, and in some cases, the sparks can also generate electrical noise detected by the object detection system 102. FIG. 13A depicts an example of a shank 1350, a commutator 1354, and brushes 1358A and 1358B among the motors 112. Springs 1362A and 1362B are respectively pressurized to brushes 1358A and 1358B to contact commutator 1354. In many embodiments, brushes 1358A and 1358B are formed from graphite. Among the motors 112, bases 1366A and 1366B are formed in a housing of the motor 112 and engage springs 1362A and 1362B, respectively. In one embodiment, the bases 1366A and 1366B include pressure sensors that measure the squeezing force applied via the springs 1362A and 1362B. In another embodiment, the bases 1366A and 1366B generate an induced current flowing through the springs 1362A and 1362B and the corresponding brushes 1358A and 1358B for identifying electrical resistance levels via the brushes.

Because the worn brush not only reduces the operating efficiency of the motor 112; it may also introduce additional electrical noise into the sensing signal of the object detecting system 102, so the saw 100 will detect the motor 112 as appropriate. The brush wears and produces an output 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. Describe an implementation in the instructions below The function or action process 1300 will describe the operation of a controller (e.g., controller 140 in the saw 100) for executing stored program instructions to perform the function in conjunction with other devices in the saw 100. Or action.

During process 1300, a power source positioned in each of the bases 1366A and 1366B produces a current that passes through the corresponding brushes 1358A and 1358B (block 1304). In one embodiment, the current is passed through a cable that is coupled to the brushes 1358A and 1358B for normal operation of the brushes 1358A and 1358B in the saw 100. In another configuration, this current will pass the squeezing force applied by springs 1362A and 1362B. In another embodiment, the bases 1366A and 1366B and the corresponding brushes 1358A and 1358B. This current is generated during the diagnostic mode in which the saw motor 112 is turned off, and the current level used in the process 1300 will be lower than the drive current used to generate rotation in the motor shank 1350 during operation of the motor 112. During the process 1300, the controller 140 or the controller integrated with the motor 112 measures the electrical resistance level via the brushes, and compares the measured electrical resistance level with a predetermined resistance. Value threshold (block 1308). For example, the measurement of the electrical resistance level includes measuring the voltage level or 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 This resistance is derived (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 predetermined 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 decreases, which reduces the total resistance through the springs 1362A and 1362B and the corresponding brushes 1358A and 1358B. In some configurations, the controller 140 also disables the operation of the saw 100 until any worn brushes are replaced, and the controller 140 will again Process 1300 is implemented to confirm that the new brush is not worn.

FIG. 13C depicts a second embodiment of a process 1320 for measuring brush wear in a motor. The process 1320 of implementing a function or action in the following description will describe the operation of a controller (e.g., controller 140 in the saw 100) for executing stored program instructions to cooperate with the saw 100. Other devices in the implementation of this function or action.

In process 1320, spring bases 1366A and 1366B each include a pressure sensor that measures the squeezing force of corresponding springs 1362A and 1362B during the diagnostic mode when motor 112 is turned off (block 1324). When brushes 1358A and 1358B are subject to wear, corresponding springs 1362A and 1362B expand to pressurize the brushes onto commutator 1354. The squeezing force in the springs 1362A and 1362B decreases as the springs expand. A controller 140 or a controller of the motor 112 is operatively coupled to the pressure sensors and compares the measured pressure levels from the pressure sensors with a predetermined pressure threshold. (block 1328). Once the pressure sensors in the bases 1366A and 1366B measure that the pressing forces of the springs 1362A and 1362B have dropped below a predetermined threshold, the controller 140 generates an output through the user interface 110. A signal indicating that the brushes should be replaced (block 1332). In some configurations, controller 140 may also disable operation of saw 100 until any worn brushes are replaced, and controller 140 may again perform process 1320 to confirm that the new brushes are not wearing any wear.

As described above, during operation, the object detection system 102 receives a plurality of sensing signals via a single sensing cable (eg, the coaxial cable 720 shown in FIG. 8B) that includes two different conductors. In a high vibration environment, such as saw 100, sensing cable 720 may experience wear and failure over time, and finally require cable replacement during saw maintenance. If the sensing cable 720 breaks and is disconnected from any of the PCB, the tablet 120, or the appliance enclosure 118 of the object detection system 102, then the PCB will not detect any sensing signals and will The saw 100 is disabled until the single sense cable 720 is repaired. However, in some cases, the sensing cable 720 suffers from a "soft failure" in which the cable does not completely break the connection, but continues to operate with very poor performance among the saws. The PCB 102 will continue to receive the sense signal, but the fault in the sense cable 720 will introduce noise or attenuate the sense signal, which will reduce the accuracy of the object detection system 102. A block diagram of a process 1400 for diagnosing soft faults in sensing cable 720 is shown in FIG. The process 1400, which is described in the following description for implementing a function or action, describes the operation of a controller (e.g., controller 140 in the saw 100) for executing stored program instructions to cooperate with the saw 100. Other devices in the implementation of this function or action.

Process 1400 begins with object detection system 102 generating a predetermined firing signal during the diagnostic mode (block 1404). In one embodiment, controller 140 activates clock source 144 to utilize amplitude modulation to produce the same sinusoidal sensing signal as used during saw 100 operation. In another embodiment, the clock source 144 generates a pulse train comprising a series of preset frequency delta pulses for the controller 140 to pass through the sensing cable 720 and the capacitor 124. An output corresponding to a unit pulse wave response is received. In a further embodiment, the clock source 144 can generate any suitable preset signal capable of diagnosing a potential fault in the sensing cable 720. During this diagnostic mode, the motor 112 in the saw 100 is turned off and minimal electrical noise is present within the saw.

Process 1400 will continue such that 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 In response to a return signal from the excitation signal of the clock source 144 and the amplifier 146, it passes through the sensing cable 720 and the plate 120 of the capacitor 124 and the saw blade 108. Because the clock source 144 and the driver amplifier 146 generate the excitation signal having a predetermined amplitude and modulation, the controller 140 recognizes the SNR using a preset measurement technique known in the art. Of course, even in a saw that has been turned off, the firing signal will suffer a certain degree of attenuation via sensing cable 720 and capacitor 124, and a certain degree of noise (eg, Jensen-Nyquist noise ( Johnson-Nyquist noise)) must appear in the sensing circuit. As used in the context of process 1400, the SNR measurement also includes a measured signal strength attenuation value that does not include direct measurement noise. For example, the preset 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 predetermined amplitude level of the signal strength of the return signal is empirically confirmed and stored in 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 of the sensing cable. In one embodiment, the third conductor is formed as part of a second twisted pair cable of the sensing cable 720; in another embodiment, the sensing cable includes two A coaxial component for forming three separate conductors. One end of the third conductor is connected to the flat plate 120 in a similar manner to the first conductor as shown in FIG. 8C. The other end of the third conductor is coupled to an analog to digital converter (ADC), the analog to digital converter (ADC) being disposed on the PCB of the object detection system for providing a digital version of the sensed signal To the controller 140. During process 1400, controller 140 is A return signal is measured based on the excitation signal flowing through the third conductor, rather than based on an excitation signal flowing through the first conductor and the second conductor.

The controller 140 will recognize whether the measured SNR of the excitation signal has dropped below a predetermined minimum SNR ratio suitable for operating the object detection system 102 (block 1412). A fault in the sense cable 720 attenuates the level of the received signal, introduces additional noise into the sense cable 720, or both attenuates the signal strength and increases noise that would compromise the SNR. If the SNR remains above the predetermined threshold, then the sense 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 below the predetermined threshold, controller 140 will generate an output to indicate 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 to potential cable faults. In some configurations, controller 140 disables operation of saw 100 until the sensing cable 720 is repaired or replaced.

It should be understood that variations of the above-described and other features and functions, or alternatives thereof, may be combined into many other different systems, applications, or methods in a desired manner. Those skilled in the art will be able to devise various alternatives, modifications, variations, and improvements which are presently unforeseen or unpredictable, and the present invention is also intended to be covered by the scope of the appended claims.

Claims (15)

A method for detecting the proximity between an object and an appliance in a table saw, comprising: operating a motor in the table saw to move the appliance; utilizing the during operation of the motor A capacitive sensor formed in the throat plate surrounding the instrument in the table saw generates a capacitive signal; operatively coupled to the capacitor in response to a change in a capacitance level of the capacitive signal a controller of the capacitive sensor to identify an object proximate to the capacitive sensor; and responsive to a change in the capacitive signal indicative of a capacitance level exceeding a pre-correspondence to a body portion of an operator The controller is used to close the motor in the table saw with a threshold. The method of claim 1, further comprising: utilizing the controller to identify that the object corresponds to a workpiece in response to the change in the capacitance level being less than the predetermined threshold; and continuing to operate the motor In order to allow the appliance to engage the work piece. The method of claim 1, further comprising: utilizing the controller in response to the change in the capacitance signal indicating that the capacitance level exceeds the predetermined threshold corresponding to the body portion of the operator The operator generates a warning signal. The method of claim 1, further comprising: utilizing the capacitive sensor to perform a plurality of capacitive sensing on a surface of the capacitive sensor in a predetermined two-dimensional arrangement Generating a plurality of capacitive signals at the component; using the controller to reference the plurality of capacitive sensing signals to identify a location of the object above the surface of the capacitive sensor; The controller is utilized in response to the position of the object being outside a predetermined distance of the appliance and a change in the capacitance signal indicating that the capacitance level exceeds the predetermined threshold corresponding to the body portion of the operator A warning signal is generated for the operator. The method of claim 4, further comprising: responsive to the position of the object within the predetermined distance of the appliance and a change in the capacitance signal indicating that the capacitance level exceeds the corresponding to the operator The predetermined threshold of the body portion is utilized by the controller to close the motor in the table saw. The method of claim 4, further comprising: responsive to the position of the object within the predetermined distance of the appliance and a change in the capacitance signal indicating that the capacitance level exceeds a corresponding to the operator The predetermined threshold of the body portion utilizes the controller to initiate an appliance reaction mechanism among the saws. The method of claim 4, further comprising: utilizing the controller to identify a movement path of the body portion of the operator based on the plurality of capacitive signals from the capacitive sensor; The controller is utilized to initiate an appliance reaction mechanism among the saws in response to a trajectory of the movement path intersecting the appliance prior to the operator's body portion making contact with the appliance. A table saw comprising: an implement extending through an opening in a throat panel; a motor operatively coupled to the appliance; and a capacitive sensor positioned on the throat panel The capacitive sensor is configured to generate a capacitive signal during operation of the motor; a controller operatively coupled to the motor and the capacitive sensor, the controller configured to: operate the motor to move the appliance; responsive to a capacitance of the capacitive signal Identifying an object proximate to the capacitive sensor by a change in level; and turning off the change in response to a change in the capacitance signal indicating that a capacitance level exceeds a predetermined threshold corresponding to a body portion of an operator The motor in the table saw. According to the table saw of claim 8, the controller is further configured to: recognize that the object corresponds to a work piece in response to the change in the capacitance level being less than the preset threshold; and continue operation The motor is adapted to engage the tool with the workpiece. According to the table saw of claim 8, the controller is further configured to: responsive to a change in the capacitance signal, indicating that the capacitance level exceeds the preset threshold corresponding to the body portion of the operator The value produces a warning signal for the operator. According to the table saw of claim 8, the controller is further configured to: perform a plurality of capacitive sensing from a surface arranged in a preset two-dimensional arrangement on the surface of the capacitive sensor Generating a plurality of capacitive signals at the component; identifying the position of the object above the surface of the capacitive sensor with reference to the plurality of capacitive sensing signals; and pre-processing the device in response to the position of the object A change in the capacitance signal and a change in the capacitance signal indicates that the capacitance level exceeds the predetermined threshold corresponding to the body portion of the operator to generate an alert signal for the operator. According to the table saw of claim 11, the controller is further configured to: in response to the position of the object being within the preset distance of the appliance and the change in the capacitance signal indicating the capacitance level The motor in the table saw is closed beyond the predetermined threshold corresponding to the body portion of the operator. A table saw according to claim 11 further comprising: an appliance reaction mechanism; and the controller is operatively coupled to the appliance reaction mechanism and further configured to: responsive to the position of the object The change in the predetermined distance of the appliance and the change in the capacitance signal indicates that the capacitance level exceeds the predetermined threshold corresponding to the body portion of the operator to initiate the appliance reaction mechanism in the saw. A table saw according to claim 11 further comprising: an appliance reaction mechanism; and the controller is operatively coupled to the appliance reaction mechanism and further configured to: the sensor from the capacitive sensor Identifying a movement path of the body portion of the operator based on the plurality of capacitance signals; and intersecting the instrument with a trajectory in response to the movement path before the body portion of the operator makes contact with the instrument The instrument reaction mechanism in the saw is activated. A table saw according to claim 8 wherein the throat plate is formed by an electrical insulator for isolating the capacitive sensor and the device.