CN220699518U - Power tool - Google Patents

Abstract

The power tool described herein includes: outputting a tool; a motor driving the tool output; a battery pack interface; a power switching network coupled between the battery pack interface and the motor; and a controller coupled to the power switching network to control operation of the motor. The controller is configured to operate the motor at a no-load speed and detect a load condition of the power tool at start-up. The load state indicates whether the power tool is in a loaded state or an unloaded state. The controller is further configured to incrementally ramp the speed of the motor from the unloaded speed to the selected speed when the power tool is in the loaded state, and to incrementally ramp the speed of the motor from the selected speed to the unloaded speed when the power tool is in the unloaded state.

Description

Power tool

Cross Reference to Related Applications

The present application claims the benefit of U.S. provisional patent application No. 63/048,441 filed on 7/6/2020 and U.S. provisional patent application No. 63/118,183 filed on 11/25 2020, the entire contents of which are incorporated herein by reference.

Technical Field

Embodiments described herein relate to automatically controlling the speed of a power tool to provide additional control over the operation of the tool and to prevent excessive battery drain and overheating of power tool components.

Disclosure of Invention

One embodiment provides a power tool comprising: outputting a tool; a motor driving the tool output; a battery pack; a power switching network coupled between the battery pack and the motor; and a controller coupled to the power switching network to control operation of the motor. The controller is configured to operate the motor at a no-load speed and detect a load condition of the power tool at start-up. The load state indicates whether the power tool is in a loaded state or an unloaded state. The controller is further configured to incrementally ramp the speed of the motor from the unloaded speed to the selected speed when the power tool is in the loaded state, and to incrementally ramp the speed of the motor from the selected speed to the unloaded speed when the power tool is in the unloaded state.

In some aspects, the power tool further includes a speed switch configured to move between a plurality of positions corresponding to a plurality of settings, each setting corresponding to a different operating speed, the selected speed being selected using the speed switch, and a switch trigger configured to turn the power tool on and off.

In some aspects, one of the plurality of settings corresponds to an automatic mode, wherein the controller is further configured to operate the motor at a selected speed at start-up when the speed dial does not select the automatic mode.

In some aspects, the power tool further comprises a current sensor disposed in a current path between the battery pack interface and the motor, wherein a load condition of the power tool is detected using the current sensor.

In some aspects, the controller is further configured to: measuring the first current and the second current using a current sensor; determining a difference between the first current and the second current; determining whether a difference between the first current and the second current exceeds a predetermined deviation threshold; determining that the power tool is in a loaded state when a difference between the first current and the second current exceeds a predetermined deviation threshold, wherein determining whether the second current exceeds a predetermined load current threshold is performed when the difference between the first current and the second current does not exceed the predetermined deviation threshold; determining that the power tool is in a loaded state when the second current exceeds a predetermined load current threshold; and determining that the power tool is in an unloaded state when the second current does not exceed the predetermined load current threshold.

In some aspects, the power tool further includes a fast response filter and a slow response filter configured to average the current through the current sensor over a longer period of time than the fast response filter.

In some aspects, the fast response filter and the slow response filter are implemented using hardware components.

In some aspects, the fast response filter and the slow response filter are implemented as software within the controller.

In some aspects, the power tool further includes a controller further configured to perform a soft start at start-up.

Another embodiment provides a power tool including: outputting a tool; a motor driving the tool output; a battery pack; a power switching network coupled between the battery pack and the motor; a current sensor; and a controller coupled to the current sensor and the power switching network to control operation of the motor. The controller is configured to measure the first current and the second current using the current sensor. The controller is further configured to determine a difference between the first current and the second current, and determine whether the difference between the first current and the second current exceeds a predetermined deviation threshold. The controller is further configured to determine that the power tool is in a loaded state when a difference between the first current and the second current exceeds a predetermined deviation threshold, and to determine whether the second current exceeds a predetermined load current threshold when the difference between the first current and the second current does not exceed the predetermined deviation threshold. The controller is further configured to determine that the power tool is in the loaded state when the second current exceeds the predetermined load current threshold, and to determine that the power tool is in the unloaded state when the second current does not exceed the predetermined load current threshold.

In some aspects, the power tool further includes a fast response filter and a slow response filter configured to average the current through the current sensor over a longer period of time than the fast response filter.

In some aspects, the fast response filter and the slow response filter are implemented using hardware components.

In some aspects, the fast response filter and the slow response filter are implemented as software within the controller.

In some aspects, the controller is further configured to: operating the motor at a no-load speed at start-up; detecting a load condition of the power tool, the load condition indicating whether the power tool is in a loaded or unloaded state; incrementally ramping up the speed of the motor from the no-load speed to a selected speed when the power tool is in a loaded state; and incrementally ramping down the speed of the motor from the selected speed to a no-load speed when the power tool is in an unloaded state.

In some aspects, the controller is further configured to perform a soft start at start-up.

In some aspects, the power tool further includes a speed switch configured to move between a plurality of positions corresponding to a plurality of settings, each setting corresponding to a different operating speed, the selected speed being selected using the speed switch, and a switch trigger configured to turn the power tool on and off.

In some aspects, one of the plurality of settings corresponds to an automatic mode, wherein the controller is further configured to operate the motor at a selected speed at start-up when the speed dial does not select the automatic mode.

Another embodiment provides a method of operating a power tool based on a load condition of the power tool. The method includes operating a motor at a no-load speed at start-up using a controller and a power switch network of the power tool, and detecting a load condition of the power tool using the controller. The load state indicates whether the power tool is in a loaded state or an unloaded state. The method further includes incrementally ramping the speed of the motor from the unloaded speed to a selected speed using the controller when the power tool is in the loaded state, and incrementally ramping the speed of the motor from the selected speed to the unloaded speed using the controller when the power tool is in the unloaded state.

In some aspects, the method further includes determining whether an automatic mode is selected, and when the automatic mode is not selected, operating the motor at a selected speed at start-up.

In some aspects, the method further comprises: measuring a first current and a second current using a current sensor of the power tool; determining, using a controller, a difference between the first current and the second current; determining, using the controller, whether a difference between the first current and the second current exceeds a predetermined deviation threshold; determining, using the controller, that the power tool is in a loaded state when a difference between the first current and the second current exceeds a predetermined deviation threshold, wherein determining, using the controller, whether the second current exceeds a predetermined load current threshold when the difference between the first current and the second current does not exceed the predetermined deviation threshold; determining, using the controller, that the power tool is in a loaded state when the second current exceeds a predetermined load current threshold; and determining, using the controller, that the power tool is in an unloaded state when the second current does not exceed the predetermined load current threshold.

In some aspects, the method further includes averaging the measured current over a first time period using a fast response filter to determine a first current, and averaging the measured current over a second time period using a slow response filter to determine a second current, the second time period being longer than the first time period.

In some aspects, the method further comprises performing a soft start at start-up.

Another embodiment provides a method for detecting a load condition of a power tool. The method includes measuring a first current and a second current using a current sensor of the power tool. The method also includes determining, using a controller of the power tool, a difference between the first current and the second current, and determining, using the controller, whether the difference between the first current and the second current exceeds a predetermined deviation threshold. The method further includes determining, using the controller, that the power tool is in a loaded state when a difference between the first current and the second current exceeds a predetermined deviation threshold, and determining, using the controller, whether the second current exceeds a predetermined load current threshold when the difference between the first current and the second current does not exceed the predetermined deviation threshold. The method further includes determining, using the controller, that the power tool is in a loaded state when the second current exceeds the predetermined load current threshold, and determining, using the controller, that the power tool is in an unloaded state when the second current does not exceed the predetermined load current threshold.

In some aspects, the method further includes averaging the measured current over a first time period using a fast response filter to determine a first current, and averaging the measured current over a second time period using a slow response filter to determine a second current, the second time period being longer than the first time period.

In some aspects, the method further includes operating a motor of the power tool at a no-load speed at start-up using a controller and a power switch network of the power tool; detecting, using a controller, a load condition of the power tool, the load condition indicating whether the power tool is in a loaded state or an unloaded state; when the power tool is in a loaded state, incrementally ramping the speed of the motor from the unloaded speed to the selected speed using the controller; and incrementally ramping down the speed of the motor from the selected speed to a no-load speed using the controller when the power tool is in an unloaded state.

In some aspects, the method further comprises performing a soft start at start-up.

In some aspects, the method further includes determining whether an automatic mode is selected, and when the automatic mode is not selected, operating the motor at a selected speed at start-up.

Before any embodiments are explained in detail, it is to be understood that the embodiments are not limited in their application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The embodiments may be practiced or carried out in a variety of different ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings.

In addition, it should be understood that embodiments may include hardware, software, and electronic components or modules that, for purposes of discussion, may be shown and described as if most of the components were implemented solely in hardware. However, one of ordinary skill in the art will recognize, based on a reading of this detailed description, that in at least one embodiment, the electronic-based aspects may be implemented in software (e.g., stored on a non-transitory computer-readable medium) executable by one or more processing units (e.g., a microprocessor and/or an application specific integrated circuit ("ASIC")). Thus, it should be noted that embodiments may be implemented using a number of hardware and software based devices as well as a number of different structural components. For example, the terms "server," "computing device," "controller," "processor," and the like as described in the specification may include one or more processing units, one or more computer readable medium modules, one or more input/output interfaces, and a plurality of different connections (e.g., a system bus) connecting the components.

Relative terms such as "about," "substantially," and the like, as used in connection with a quantity or condition, will be understood by those of ordinary skill in the art to encompass the stated value and have the meaning dictated by the context (e.g., the term includes at least the degree of error associated with measurement accuracy, tolerances associated with particular values [ e.g., manufacturing, assembly, use, etc. ], and the like). Such terms should also be considered to disclose ranges defined by the absolute values of the two endpoints. For example, the expression "about 2 to about 4" also discloses the range "2 to 4". Relative terms may refer to percentages (e.g., 1%, 5%, 10%, or more) of the indicated value being added or subtracted.

It should be understood that while some of the figures show hardware and software located within a particular device, these depictions are for illustrative purposes only. The functions described herein as being performed by one component may be performed by multiple components in a distributed fashion. Also, functions performed by multiple components may be combined and performed by a single component. In some embodiments, the illustrated components may be combined or divided into separate software, firmware, and/or hardware. For example, the logic and processes may be distributed among multiple electronic processors rather than being located in and executed by a single electronic processor. Regardless of how the hardware and software components are combined or partitioned, the hardware and software components may reside on the same computing device or may be distributed among different computing devices connected by one or more networks or other suitable communication links. Similarly, components described as performing a particular function may also perform additional functions not described herein. For example, a device or structure that is "configured" in some way is configured at least in that way, but may also be configured in ways that are not explicitly listed.

Other aspects of the embodiments will become apparent by consideration of the detailed description and accompanying drawings.

Drawings

Fig. 1 is a perspective view of a power tool according to some embodiments.

FIG. 2 is a block diagram of the power tool of FIG. 1 according to some embodiments.

FIG. 3 is a flowchart of a method for automatically ramping the speed of the power tool of FIG. 1, according to some embodiments.

FIG. 4 is a flowchart of a method for detecting a load on the power tool of FIG. 1, according to some embodiments.

Detailed Description

Fig. 1 illustrates a perspective view of an example power tool 100. In the illustrated example, the power tool 100 is a multi-function tool. However, the present disclosure is equally applicable to other electrically powered power tools, such as saws (jigsaw, reciprocating saw, miter saw, etc.), grinders (angle grinders, disc grinders, etc.), drivers/drills (hammer drills, impact drivers, etc.), and the like. The power tool 100 includes a housing 110 that supports a tool output, such as a tool bit 120 operated by a motor 220 (shown in fig. 2). The power tool 100 includes a battery pack interface 130 to removably receive a battery pack 270 (shown in fig. 2). The battery pack 270 provides operating power for the power tool 100. The battery pack 270 is, for example, an 18 volt (V) lithium ion battery pack. In other embodiments, the battery pack 270 may have different nominal voltages (e.g., 12V, 36V, etc.) and different battery chemistries (e.g., nickel-cadmium, etc.).

The power tool 100 also includes a switch trigger 140 and a speed switch or speed dial 150. In the illustrated example, the switch trigger 140 is a two-position switch provided on the housing 110 and is internally connected to an on/off switch. In the first position, the switch trigger 140 turns off the power tool 100 such that power from the battery pack 270 is disconnected. In the second position, the switch trigger 140 turns on the power tool 100 such that power from the battery pack 270 is provided to the motor 220 of the power tool 100. The speed dial 150 is a rotatable dial provided on the housing 110. The speed dial 150 may be rotated to select a speed setting for the power tool 100. The speed dial 150 may include a plurality of settings, each setting corresponding to a different operating speed. One of the settings may correspond to an "automatic mode," which results in a control technique as described below. In some embodiments, the speed ramping (mapping) technique described herein is implemented for any speed setting selected using the speed dial 150. In other embodiments, the speed ramping techniques described herein are implemented for a subset of speed settings (e.g., for automatic mode settings), which may be selected using the speed dial 150. In some embodiments, the switch trigger 140 is a variable speed trigger such that the switch trigger 140 is used to both turn on the power tool 100 and select the operating speed of the power tool 100.

Fig. 2 is a simplified block diagram of the power tool 100. In the illustrated example, the power tool 100 includes a controller 210, a motor 220, a power switching network 230, a user input 240, a current sensor 250, and a battery pack 270.

The controller 210 includes a plurality of electrical and electronic components that provide power, operational control, and protection to the components and modules within the controller 210 and/or the power tool 100. For example, the controller 210 includes, among other things, a processing unit 305 (e.g., a microprocessor, microcontroller, electronic processor, electronic controller, or another suitable programmable device), a memory 310, an input unit 315, and an output unit 320. The processing unit 305 includes, among other things, a control unit 325, an ALU 330, and a plurality of registers 335 (shown as a set of registers in fig. 2), and is implemented using a known computer architecture (e.g., modified harvard architecture, von neumann architecture, etc.). The processing unit 305, memory 310, input unit 315 and output unit 320, as well as the various modules or circuits connected to the controller 210, are connected by one or more control buses and/or data buses (e.g., common bus 340). For illustrative purposes, a control bus and/or a data bus is generally shown in FIG. 2. The use of one or more control buses and/or data buses for interconnection and communication between various modules, circuits, and components will be known to those skilled in the art in view of the embodiments described herein. In some embodiments, controller 210 is implemented partially or entirely on a Field Programmable Gate Array (FPGA), application Specific Integrated Circuit (ASIC), or the like.

Memory 310 is a non-transitory computer readable medium and includes, for example, a program storage area and a data storage area. The program storage area and the data storage area may comprise a combination of different types of memory, such as ROM, RAM (e.g., DRAM, SDRAM, etc.), EEPROM, flash memory, hard disk, SD card, or other suitable magnetic, optical, physical, or electronic memory device. The processing unit 305 is connected to the memory 310 and executes software instructions that can be stored in RAM of the memory 310 (e.g., during execution), ROM of the memory 310 (e.g., on a generally permanent basis), or another non-transitory computer readable medium such as another memory or disk. Software included in the implementation of the power tool 100 may be stored in the memory 310 of the controller 210. The software includes, for example, firmware, one or more application programs, program data, filters, rules, one or more program modules, and other executable instructions. The controller 210 is configured to retrieve from the memory 310 and execute, among other things, instructions related to the control processes and methods described herein. In other constructions, the controller 210 includes additional components, fewer components, or different components.

In the illustrated example, motor 220 is a brushless direct current (BLDC) motor. In some embodiments, motor 220 may be an AC motor, a DC motor, a switched reluctance motor, or the like. In some embodiments, a position sensor (e.g., hall sensor, back emf detector) is provided with motor 220. The position sensor outputs motor feedback information, such as an indication (e.g., a pulse), as the magnet of the rotor rotates across the surface of the position sensor. Based on motor feedback information from the position sensor, the controller 210 may determine the position, speed, and acceleration of the motor 220. The controller 210 also receives user control from user input 240 (e.g., from the speed dial 150). In response to the motor feedback information and the user control, the controller 210 transmits a control signal to the power switching network 230 to drive the motor 220.

The power switching network 230 is implemented as an inverter bridge. The power switching network 230 includes a plurality of high-side power switching elements (e.g., field effect transistors [ FETs ]) and a plurality of low-side power switching elements. The controller 210 provides control signals to control the high-side FET and the low-side FET to drive the motor 220 based on motor feedback information and user control as described above. To drive motor 220, controller 210 enables a first high-side FET and a first low-side FET pair (e.g., by providing a voltage at the gate terminal of the FETs) for a first period of time, the first high-side FET and the first low-side FET being connected to different non-inverting terminals of motor 220. In response to determining that the rotor of motor 220 has rotated based on the pulses from the position sensor, controller 210 disables the first FET pair and enables the second FET pair. In response to determining that the rotor of motor 220 has rotated based on the pulse(s) from the position sensor, controller 210 disables the second FET pair and enables the third FET pair. In response to determining that the rotor of motor 220 has rotated based on the further pulse(s) from the position sensor, controller 210 disables the third FET pair and returns to enabling the first FET pair. This sequence of cycle-enabled FET pairs is repeated to drive motor 220. Further, in some embodiments, the control signal comprises a Pulse Width Modulated (PWM) signal having a duty cycle that is proportional to the speed setting selected by the speed dial 150, thereby controlling the speed or torque of the motor 220. In some embodiments, power switching network 230 includes a triac (triac) (e.g., when motor 220 is an AC motor), a single FET (e.g., when motor 220 is a DC motor), and the like. In some embodiments, controller 210 controls power switch network 230 based on user control to control the speed or torque of motor 220.

The user inputs 240 include, for example, a switch trigger 140 and a speed dial 150. In some embodiments, the user input 240 may also include a forward/reverse switch, a transceiver to receive input from a connected smart phone application, and the like.

The current sensor 250 is disposed on a current path between the battery pack 270 and the motor 220. In the illustrated example, the current sensor 250 is disposed between a negative terminal of the battery pack 270 and a negative terminal of the power switch network 230. In some embodiments, the current sensor 250 is disposed between the positive terminal of the battery pack 270 and the positive terminal of the power switch network 230. In other embodiments, the current sensor 250 is coupled to the motor phase coil.

The controller 210 includes a fast response filter 345, a slow response filter 350, and an overload detector 355. Although the fast response filter 345, the slow response filter 350, and the overload detector 355 are shown as separate modules, these modules may be within a program storage area of the memory 310. In some embodiments, the fast response filter 345, the slow response filter 350, and the overload detector 355 may be implemented in hardware using filter and comparator components. A current sensor 250 disposed in the current path provides a current signal to a fast response filter 345, a slow response filter 350, and an overload detector 355 in the controller 210. The current sensor 250 and the fast response filter 345 are together referred to as a first current sensor, the current sensor 250 and the slow response filter 350 are together referred to as a second current sensor, and the current sensor 250 and the overload detector 355 are together referred to as a third current sensor.

The fast response filter averages the current through the current sensor 250 over a shorter period of time than the slow response filter 350. For example, the current sensor 250 averages the current over 50 ms. In some embodiments, the first current sensor averages the current over a period of time between 1 ms and 100 ms. The fast response filter 345 provides an indication of the fast response current to the controller 210. The slow response filter 350 averages the current through the current sensor 250 over a longer period of time than the fast response filter 345. For example, the second current sensor averages the current over 250 ms. In some embodiments, the second current sensor averages the current over a period of time between 200 ms and 300 ms. The slow response filter 350 provides an indication of the slow response current to the controller 210.

During operation, the speed of the power tool 100 is controlled to provide a suitable amount of power for working on a workpiece. The power tool 100 includes two load states: (i) a loaded state; and (ii) an unloaded state. In the loaded state, the tool tip 120 contacts the work piece and performs work on the work piece (e.g., sawing through material, driving fasteners, scraping the work piece, etc.). In the unloaded state, the tool tip 120 is not in contact with the work piece. In the loaded state, a higher speed is generally required for optimal power delivery to the cutter head 120. Conversely, in the unloaded state, higher speeds will result in excessive battery drain and excessive noise. The controller 210 performs load-based speed control to prevent excessive battery consumption and excessive noise. Specifically, the controller 210 increases the speed of the power tool 100 to correspond to the selected speed and decreases the speed of the power tool 100 to a predetermined no-load speed.

In some examples, the difference between the no-load speed and the selected speed may be significant based on the selected output speed. A sudden increase or decrease between the no-load speed and the selected speed may negatively impact the user's experience. To improve the user experience, the controller 210 may ramp up gradually (e.g., incrementally) from the no-load speed to the selected speed and ramp down gradually (e.g., incrementally) from the selected speed to the no-load speed. In one example, for incremental ramping, the controller 210 may increase the PWM duty cycle by 2% every 1 millisecond. Similarly, for incremental ramping down, the controller 210 may decrease the PWM duty cycle by 2% every 1 millisecond. The ramp up and ramp down curves may be preprogrammed into the controller 210. The ramp up and ramp down of the speed may be linear, however, the ramp up and ramp down curves need not be linear between the start point and the end point.

FIG. 3 is a flow chart of an example method 400 for automatically ramping the speed of the power tool 100. The method 400 includes performing a soft start of the power tool 100 using the controller 210 (at block 405). During start-up, a significant amount of in-rush current may flow from the battery pack 270 to the power tool 100, which may damage electrical components of the power tool 100. To prevent inrush current, the power tool 100 operates at a low speed during start-up. The controller 210 controls the PWM duty cycle to perform soft start.

The method 400 includes operating (at block 410) the motor 220 of the power tool 100 at a no-load speed at start-up using the controller 210. After the soft start is complete, the controller 210 may ramp the speed up to the no-load speed. The no-load speed is, for example, a default speed (e.g., 15000 rpm) preprogrammed into the controller 210. The method 400 includes determining (at block 415) using the controller 210 whether a load detect flag is set. The controller 210 determines the load state of the motor 220 based on the current detected by the controller 210, as further described below with respect to the method 500 (shown in fig. 4). When the controller 210 determines that the power tool 100 is in the loaded state, the controller 210 sets a load detection flag. In some embodiments, the controller 210 may wait until the no-load speed stabilizes, after which it determines whether the load detection flag is set.

When the load detect flag is not set, method 400 includes determining, using controller 210, whether the speed of motor 220 is greater than a no-load speed (at block 420). For example, the controller 210 may detect the speed of the motor 220 using a position sensor. When the speed of motor 220 is not greater than the no-load speed, method 400 returns to block 415. When the speed of motor 220 is greater than the no-load speed, method 400 includes ramping down (at block 425) the speed of motor 220 using controller 210. The controller 210 decreases the PWM duty cycle to decrease the speed of the motor 220. For example, the controller 210 reduces the PWM duty cycle by 2%. The method 400 then returns to block 415.

When the load status detection flag is set, the method 400 includes increasing a load trigger count (at block 430) using the controller 210. In some embodiments, the controller 210 may wait until the load condition is steadily detected, after which the speed of the motor 220 is increased. The controller 210 implements a counter, i.e., a load trigger count, to accumulate the time the power tool 100 is loaded. The method 400 includes determining, using the controller 210, whether the load trigger count exceeds a predetermined load trigger count threshold (at block 435). The predetermined load trigger count threshold may be set during manufacture based on analog data. In one example, the predetermined load trigger count threshold is set to 4. When the load trigger count does not exceed the predetermined load trigger count threshold, the method 400 returns to block 420.

When the load trigger count exceeds the predetermined load trigger count threshold, the method 400 includes ramping up (at block 440) the speed of the motor 220 using the controller 210. The controller 210 increases the PWM duty cycle to increase the speed of the motor 220 (e.g., to 20000 rpm). For example, the controller 210 increases the PWM duty cycle by 2%. The method 400 includes determining (at block 445) using the controller 210 whether a load status detection flag is set. When the load status detection flag is set, the method 400 uses the controller 210 to determine if the speed of the motor 220 is below the selected speed (at block 450). When the speed of motor 220 is not less than the selected speed, method 400 returns to block 445. When the speed of motor 220 is below the selected speed, method 400 returns to block 440.

When the load status detection flag is not set, the method 400 includes increasing (at block 455) a no-load trigger count using the controller 210. In some embodiments, the controller 210 may wait until a no-load condition is steadily detected, after which the speed of the motor 220 is reduced. The controller 210 implements a counter, i.e., a no-load trigger count, to accumulate the time the power tool 100 is loaded. The method 400 includes determining (at block 460) using the controller 210 whether the no-load trigger count exceeds a predetermined no-load trigger count threshold. The predetermined no-load trigger count threshold may be set during manufacture based on analog data. The predetermined no-load trigger count threshold may generally be set to be greater than the predetermined load trigger count threshold. In one example, the predetermined load trigger count threshold is set to 9. When the no-load trigger count does not exceed the predetermined no-load trigger count threshold, the method 400 returns to block 450. When the no-load trigger count exceeds the predetermined no-load trigger count, the method 400 returns to block 425. The method 400 is repeated until the power tool 100 is turned off.

The power tool 100 is, for example, a multi-function tool that may be used to perform work on several workpieces. Typically, the user does not shut down the power tool 100 before switching from the first work piece to the second work piece. This results in the power tool 100 operating at a high speed (e.g., corresponding to a particular maximum speed setting) while idling. The method 400 detects this idle mode (i.e., unloaded state) and reduces the motor speed to a no-load speed, thereby conserving battery power and also preventing the power tool 100 from overheating. In some embodiments, the method 400 may be implemented only in the "automatic mode" selected. For example, the power tool 100 includes an "automatic" or "A" speed setting (e.g., separate from a particular maximum speed setting (e.g., 1-10)). When the power tool is set to the automatic mode, the method 400 detects idle (i.e., unloaded) and reduces the motor speed to a no-load speed.

FIG. 4 is a flowchart of an example method 500 for detecting a load condition of the power tool 100. In the illustrated example, the method 500 includes measuring a first current using a first current sensor (at block 505). As discussed above, the first current sensor provides a first indication of the current flowing through motor 220. Specifically, the first current sensor provides a first indication of the current value averaged over a relatively short period of time. The method 500 further includes measuring (at block 510) a second current using a second current sensor. As discussed above, the second current sensor 260 provides a second indication of the current flowing through the motor 220. Specifically, the second current sensor 260 provides a second indication of the current value averaged over a longer period of time.

The method 500 includes determining (at block 515) a difference between the first current and the second current using the controller 210. In some embodiments, the controller 210 subtracts the second current from the first current. The method 500 includes determining, using the controller 210, whether a difference between the first current and the second current exceeds a predetermined deviation threshold (at block 520). The controller 210 compares the difference between the first current and the second current to a predetermined deviation threshold.

When the difference between the first current and the second current exceeds a predetermined deviation threshold, the method 500 includes setting a Load Detection Flag (e.g., load_detection_flag= 1) using the controller 210 (at block 525). In some embodiments, the method 400 and the method 500 are implemented by the controller 210 as parallel processes. When the controller 210 sets the load detection flag in method 500, the load state detection value is updated in method 400 using, for example, interrupts or inputs.

When the difference between the first current and the second current does not exceed the predetermined deviation threshold, the method 500 includes determining, using the controller 210, whether the second current exceeds the predetermined load current threshold (at block 530). The controller 210 compares the second current to a predetermined load current threshold. When the second current exceeds the predetermined load current threshold, the method 500 proceeds to block 525. When the second current does not exceed the predetermined Load current threshold, the method 500 includes resetting a Load Detection Flag (e.g., load_detection_flag= 0) using the controller 210 (at block 535). Resetting the load detection flag corresponds to not setting the load detection flag. At start-up, the load detection flag may be reset to 0. The method 500 is repeated continuously during operation of the power tool 100 to determine the load condition of the power tool 100. The method 500 allows the controller 210 to accurately detect the load condition of the power tool 100.

Accordingly, embodiments described herein provide, among other things, automatic ramp load sensing for a power tool.

Claims (15)

1. A power tool, comprising:

outputting a tool;

a motor configured to drive the tool output;

a power switching network coupled between the battery pack interface and the motor; and

a controller connected to the power switching network to control operation of the motor, the controller configured to:

the motor is operated at no-load speed at start-up,

detecting a load condition of the power tool, the load condition indicating whether the power tool is in a loaded or unloaded state,

incrementally ramping up the speed of the motor from the no-load speed to a selected speed when the power tool is in the loaded state, and

when the power tool is in the unloaded state, the speed of the motor is incrementally ramped down from the selected speed to the unloaded speed.

2. The power tool of claim 1, wherein the power tool further comprises:

a speed switch configured to move between a plurality of positions corresponding to a plurality of settings, each setting corresponding to a different operating speed, the speed switch being used to select the selected speed; and

a switch trigger configured to turn the power tool on and off.

3. The power tool of claim 2, wherein one of the plurality of settings corresponds to an automatic mode, wherein the controller is further configured to:

when the speed switch does not select the automatic mode, the motor is operated at the selected speed at start-up.

4. The power tool of claim 1, wherein the power tool further comprises:

and a current sensor disposed on a current path between the battery pack interface and the motor, wherein a load state of the power tool is detected using the current sensor.

5. The power tool of claim 4, wherein the controller is further configured to:

the first current and the second current are measured using the current sensor,

determining a difference between the first current and the second current,

determining whether a difference between the first current and the second current exceeds a predetermined deviation threshold,

when the difference between the first current and the second current exceeds the predetermined deviation threshold, determining that the power tool is in the loaded state,

wherein when the difference between the first current and the second current does not exceed the predetermined deviation threshold,

determining whether the second current exceeds a predetermined load current threshold,

determining that the power tool is in the loaded state when the second current exceeds the predetermined load current threshold, an

When the second current does not exceed the predetermined load current threshold, it is determined that the power tool is in the unloaded state.

6. The power tool of claim 5, wherein the power tool further comprises:

a fast response filter; and

a slow response filter configured to average the current through the current sensor over a longer period of time than the fast response filter.

7. The power tool of claim 6, wherein the fast response filter and the slow response filter are implemented using hardware components.

8. The power tool of claim 1, wherein the controller is further configured to perform a soft start at start-up.

9. A power tool, comprising:

a power switching network coupled between the battery pack interface and the motor;

a current sensor disposed on a current path between the battery pack interface and the motor; and

a controller coupled to the current sensor and the power switching network to control operation of the motor, characterized in that the controller is configured to:

the first current and the second current are measured using the current sensor,

determining a difference between the first current and the second current,

determining whether a difference between the first current and the second current exceeds a predetermined deviation threshold,

when the difference between the first current and the second current exceeds the predetermined deviation threshold, determining that the power tool is in a loaded state,

wherein when the difference between the first current and the second current does not exceed the predetermined deviation threshold,

determining whether the second current exceeds a predetermined load current threshold,

determining that the power tool is in the loaded state when the second current exceeds the predetermined load current threshold, an

When the second current does not exceed the predetermined load current threshold, it is determined that the power tool is in an unloaded state.

10. The power tool of claim 9, wherein the power tool further comprises:

a fast response filter; and

a slow response filter configured to average the current through the current sensor over a longer period of time than the fast response filter.

11. The power tool of claim 10, wherein the fast response filter and the slow response filter are implemented using hardware components.

12. The power tool of claim 10, wherein the controller is further configured to:

the motor is operated at no-load speed at start-up,

detecting a load condition of the power tool, the load condition indicating whether the power tool is in the loaded state or the unloaded state,

incrementally ramping up the speed of the motor from the no-load speed to a selected speed when the power tool is in the loaded state, and

when the power tool is in the unloaded state, the speed of the motor is incrementally ramped down from the selected speed to the unloaded speed.

13. The power tool of claim 12, wherein the controller is further configured to perform a soft start at start-up.

14. The power tool of claim 12, wherein the power tool further comprises:

a speed switch configured to move between a plurality of positions corresponding to a plurality of settings, each setting corresponding to a different operating speed, the speed switch being used to select the selected speed; and

a switch trigger configured to turn the power tool on and off.

15. The power tool of claim 14, wherein one of the plurality of settings corresponds to an automatic mode, wherein the controller is further configured to:

when the speed switch does not select the automatic mode, the motor is operated at the selected speed at start-up.