阅读说明：本技术 使用电动工具的速度控制进行热管理的系统和方法 (System and method for thermal management using speed control of a power tool ) 是由 C·H·伊普玛 于 2019-09-05 设计创作，主要内容包括：本发明公开了一种电动工具和一种用于电动工具的热管理的方法。电动工具包括壳体,位于壳体内的电动机,以及连接到电动机的电子处理器。电子处理器被配置为以第一速度操作电动机并且确定电动工具是否已经没有负载达预定时间量,其中电动机在预定时间量期间已经以第一速度操作。响应于确定电动机已经没有负载达预定时间量,电子处理器以低于第一速度的第二速度操作电动机。电子处理器还在以第二速度操作电动机时确定电动工具是否负载,并且响应于确定电动机有负载,以第一速度操作电动机。(The invention discloses a power tool and a method for thermal management of a power tool. The power tool includes a housing, a motor located within the housing, and an electronic processor connected to the motor. The electronic processor is configured to operate the motor at a first speed and determine whether the power tool has been unloaded for a predetermined amount of time, wherein the motor has been operating at the first speed during the predetermined amount of time. In response to determining that the motor has been unloaded for the predetermined amount of time, the electronic processor operates the motor at a second speed that is lower than the first speed. The electronic processor also determines whether the power tool is loaded while operating the motor at the second speed and operates the motor at the first speed in response to determining that the motor is loaded.)

1. A power tool, comprising:

a housing;

a motor located within the housing;

a shift dial movable between a plurality of positions to select an operating speed of the motor; and

an electronic controller connected to the motor and the shift dial, the electronic controller configured to:

operating the motor at a first speed corresponding to the speed selected by the variable speed dial,

determining whether the power tool has been unloaded for a predetermined amount of time, wherein the motor has operated at the first speed during the predetermined amount of time,

in response to determining that the motor has been unloaded for the predetermined amount of time, operating the motor at a second speed that is lower than the first speed,

determining whether the power tool is loaded while operating the motor at the second speed, an

Operating the motor at the first speed in response to determining that the motor is loaded.

2. The power tool of claim 1, wherein the predetermined amount of time is at least 1 minute.

3. The power tool of claim 1, wherein the electronic processor is further configured to:

determining whether the power tool has been continuously unloaded during the predetermined amount of time, an

In response to determining that the power tool has been continuously unloaded during the predetermined amount of time, determining that the motor has been unloaded for the predetermined amount of time.

4. The power tool of claim 3, wherein the electronic processor is further configured to:

determining that the power tool is unloaded;

initiating a timer in response to determining that the power tool is not loaded, wherein the timer expires when the timer counts to the predetermined amount of time;

determining whether the power tool is unloaded during a period from a start of the timer to an expiration of the timer; and

determining that the power tool has been continuously unloaded during the predetermined amount of time when the power tool is unloaded during the time from the start of the timer to the expiration of the timer.

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

determining whether the power tool is loaded after starting the timer but before the timer expires; and

resetting the timer in response to determining that the power tool is loaded after the timer is started but before the timer expires.

6. The power tool of claim 5, further comprising a current sensor for measuring current flowing to the motor, wherein the electronic processor is further configured to:

measuring an instantaneous current flowing to the motor using the current sensor;

comparing the instantaneous current to a predetermined current threshold;

determining that the power tool is not loaded when the instantaneous current is below the predetermined current threshold; and

determining that the power tool is loaded when the instantaneous current is at or above the predetermined current threshold.

7. The power tool of claim 6, wherein to determine whether the power tool is unloaded during a period from the start of the timer to the expiration of the timer, the electronic processor is configured to determine whether the power tool is unloaded during a period from the start of the timer to the expiration of the timer at discrete time intervals.

8. The power tool of any one of claims 1-7, wherein operating the motor at the first speed and the second speed further comprises operating the motor using open loop speed control or closed loop speed control.

9. A method for thermal management of a power tool, the method comprising:

operating, using an electronic processor of the power tool, the motor at a first speed, the first speed corresponding to a speed selected by a variable speed dial of the power tool;

determining, using the electronic processor, that the power tool has not been loaded for a predetermined amount of time, wherein the motor has operated at the first speed during the predetermined amount of time;

in response to determining that the motor has not been loaded for the predetermined amount of time, operating, using the electronic processor, the motor at a second speed that is lower than the first speed,

determining, using the electronic processor, that the power tool is loaded while operating the motor at the second speed, an

Operating, using the electronic processor, the motor at the first speed in response to determining that the motor is loaded.

10. The method of claim 9, wherein the predetermined amount of time is at least 1 minute.

11. The method of claim 9, further comprising:

determining whether the power tool has been continuously unloaded during the predetermined amount of time, an

In response to determining that the power tool has been continuously unloaded during the predetermined amount of time, determining that the motor has been unloaded for the predetermined amount of time.

12. The method of claim 11, further comprising:

determining that the power tool is unloaded;

initiating a timer in response to determining that the power tool is not loaded, wherein the timer expires when the timer counts to the predetermined amount of time;

determining whether the power tool is unloaded during a period from a start of the timer to an expiration of the timer; and

determining that the power tool has been continuously unloaded during the predetermined amount of time when the power tool is unloaded during the time from the start of the timer to the expiration of the timer.

13. The method of claim 12, further comprising:

determining whether the power tool is loaded after starting the timer but before the timer expires; and

resetting the timer in response to determining that the power tool is loaded after the timer is started but before the timer expires.

14. The method of claim 13, further comprising:

measuring an instantaneous current flowing to the motor using a current sensor;

comparing the instantaneous current to a predetermined current threshold;

determining that the power tool is not loaded when the instantaneous current is below the predetermined current threshold; and

determining that the power tool is loaded when the instantaneous current is at or above the predetermined current threshold.

15. The method of claim 14, wherein determining whether the power tool is unloaded during a period from the start of the timer to the expiration of the timer comprises: determining whether the power tool is unloaded at discrete time intervals from the start of the timer to the expiration of the timer.

16. A power tool, comprising:

a housing;

a motor located within the housing; and

an electronic controller connected to the electric motor, the electronic controller configured to:

operating the motor at a first speed,

determining whether the power tool has been unloaded for a predetermined amount of time, wherein the motor has operated at the first speed during the predetermined amount of time,

in response to determining that the motor has been unloaded for the predetermined amount of time, operating the motor at a second speed that is lower than the first speed,

determining whether the power tool is loaded while operating the motor at the second speed, an

Operating the motor at the first speed in response to determining that the motor is loaded.

17. The power tool of claim 16, wherein the predetermined amount of time is at least 1 minute.

18. The power tool of claim 16, wherein the electronic processor is further configured to:

determining whether the power tool has been continuously unloaded during the predetermined amount of time, an

In response to determining that the power tool has been continuously unloaded during the predetermined amount of time, determining that the motor has been unloaded for the predetermined amount of time.

19. The power tool of claim 18, wherein the electronic processor is further configured to:

determining that the power tool is unloaded;

initiating a timer in response to determining that the power tool is not loaded, wherein the timer expires when the timer counts to the predetermined amount of time;

determining whether the power tool is unloaded during a period from a start of the timer to an expiration of the timer; and

determining that the power tool has been continuously unloaded during the predetermined amount of time when the power tool is unloaded during the time from the start of the timer to the expiration of the timer.

20. The power tool of claim 19, wherein the electronic processor is further configured to:

determining whether the power tool is loaded after starting the timer but before the timer expires; and

resetting the timer in response to determining that the power tool is loaded after the timer is started but before the timer expires.

Technical Field

The present invention relates to controlling the speed of a power tool to prevent overheating of power tool components.

Background

Power tools are commonly used for a variety of work operations. During operation, heat may build up in some components of the power tool. If these heats are not properly managed or controlled, they may cause problems or dangers.

Disclosure of Invention

In a first aspect, the present invention provides a power tool including a housing, a motor located within the housing, a variable speed dial movable between a plurality of positions to select an operating speed of the motor, and an electronic controller connected to the motor and the variable speed dial. The electronic processor is configured to operate the motor at a first speed corresponding to a speed selected by the variable speed dial. The electronic processor is further configured to determine whether the power tool has been unloaded for a predetermined amount of time, wherein the motor has operated at the first speed during the predetermined amount of time. In response to determining that the motor has been unloaded for the predetermined amount of time, the electronic processor operates the motor at a second speed that is lower than the first speed. The electronic processor also determines whether the power tool is loaded while operating the motor at the second speed. In response to determining that the motor is loaded, the electronic processor operates the motor at a first speed. In some embodiments, the predetermined amount of time is at least 1 minute. For example, the predetermined amount of time is between 1 minute and 5 minutes, 1 minute and 6 minutes, 1 minute and 10 minutes, 1 minute and 15 minutes, 2 minutes and 10 minutes, 3 minutes and 10 minutes, 5 minutes and 10 minutes, or 5 minutes and 15 minutes.

In one embodiment of the first aspect, the electronic processor is further configured to: the method further includes determining whether the power tool has been continuously unloaded for a predetermined amount of time, and determining that the motor has been unloaded for the predetermined amount of time in response to determining that the power tool has been continuously unloaded for the predetermined amount of time.

In one embodiment of the first aspect, the electronic processor is further configured to: determining that the power tool is unloaded; starting a timer in response to determining that the power tool is not loaded, wherein the timer expires when the timer counts to a predetermined amount of time; determining whether the power tool is unloaded during a time period from a start of the timer to an expiration of the timer; and determining that the power tool has been continuously unloaded during the predetermined amount of time when the power tool is unloaded during the time from the start of the timer to the expiration of the timer.

In one embodiment of the first aspect, the electronic processor is further configured to: after starting the timer but before the timer expires, determining whether the power tool is loaded; and resetting the timer in response to determining that the power tool is loaded after the timer is started but before the timer expires.

In one embodiment of the first aspect, the power tool further comprises a current sensor for measuring current flowing to the motor, wherein the electronic processor is further configured to: measuring an instantaneous current flowing to the motor using a current sensor; comparing the instantaneous current to a predetermined current threshold; determining that the power tool is not loaded when the instantaneous current is below a predetermined current threshold; and determining that the power tool is loaded when the instantaneous current is at or above the predetermined current threshold.

In one embodiment of the first aspect, to determine whether the power tool is unloaded during a time interval from the start of the timer to the expiration of the timer, the electronic processor is configured to determine whether the power tool is unloaded during a time interval from the start of the timer to the expiration of the timer.

In one embodiment of the first aspect, operating the motor at the first speed and the second speed further comprises operating the motor using open loop speed control or closed loop speed control.

In a second aspect, the invention provides a method for thermal management of a power tool, the method comprising operating, using an electronic processor of the power tool, a motor at a first speed, the first speed corresponding to a speed selected by a variable speed dial of the power tool. The method also includes determining, using the electronic processor, that the power tool has not been loaded for a predetermined amount of time, wherein the motor has operated at the first speed during the predetermined amount of time. In response to determining that the motor has been unloaded for the predetermined amount of time, the electronic processor operates the motor at a second speed that is lower than the first speed. The method also includes determining, using the electronic processor, a load of the power tool when operating the motor at the second speed. In response to determining that the motor is loaded, the electronic processor operates the motor at a first speed. In some embodiments, the predetermined amount of time is at least 1 minute. For example, the predetermined amount of time is between 1 minute and 5 minutes, 1 minute and 6 minutes, 1 minute and 10 minutes, 1 minute and 15 minutes, 2 minutes and 10 minutes, 3 minutes and 10 minutes, 5 minutes and 10 minutes, or 5 minutes and 15 minutes.

In one embodiment of the second aspect, the method further comprises: the method further includes determining whether the power tool has been continuously unloaded for a predetermined amount of time, and determining that the motor has been unloaded for the predetermined amount of time in response to determining that the power tool has been continuously unloaded for the predetermined amount of time.

In one embodiment of the second aspect, the method further comprises: determining that the power tool is unloaded; starting a timer in response to determining that the power tool is not loaded, wherein the timer expires when the timer counts to a predetermined amount of time; determining whether the power tool is unloaded during a time period from a start of the timer to an expiration of the timer; and determining that the power tool has been continuously unloaded during the predetermined amount of time when the power tool is unloaded during the time from the start of the timer to the expiration of the timer.

In one embodiment of the second aspect, the method further comprises: after starting the timer but before the timer expires, determining whether the power tool is loaded; and resetting the timer in response to determining that the power tool is loaded after the timer is started but before the timer expires.

In one embodiment of the second aspect, the method further comprises: measuring an instantaneous current flowing to the motor using a current sensor; comparing the instantaneous current to a predetermined current threshold; determining that the power tool is not loaded when the instantaneous current is below a predetermined current threshold; and determining that the power tool is loaded when the instantaneous current is at or above the predetermined current threshold.

In one embodiment of the second aspect, determining whether the power tool is not loaded during a period from the start of the timer to the expiration of the timer comprises: it is determined whether the power tool is unloaded at discrete time intervals from the start of the timer to the expiration of the timer.

In a third aspect, the present invention provides a power tool comprising a housing, a motor located within the housing, and an electronic processor connected to the motor. The electronic processor is configured to operate the motor at a first speed. The electronic processor is further configured to determine whether the power tool has been unloaded for a predetermined amount of time, wherein the motor has operated at the first speed during the predetermined amount of time. In response to determining that the motor has been unloaded for the predetermined amount of time, the electronic processor operates the motor at a second speed that is lower than the first speed. The electronic processor further determines whether the power tool is loaded while operating the motor at the second speed. In response to determining that the motor is loaded, the electronic processor operates the motor at a first speed. In some embodiments, the predetermined amount of time is at least 1 minute. For example, the predetermined amount of time is between 1 minute and 5 minutes, 1 minute and 6 minutes, 1 minute and 10 minutes, 1 minute and 15 minutes, 2 minutes and 10 minutes, 3 minutes and 10 minutes, 5 minutes and 10 minutes, or 5 minutes and 15 minutes.

In one embodiment of the third aspect, the electronic processor is further configured to: the method further includes determining whether the power tool has been continuously unloaded for a predetermined amount of time, and determining that the motor has been unloaded for the predetermined amount of time in response to determining that the power tool has been continuously unloaded for the predetermined amount of time.

In one embodiment of the third aspect, the electronic processor is further configured to: determining that the power tool is unloaded; starting a timer in response to determining that the power tool is not loaded, wherein the timer expires when the timer counts to a predetermined amount of time; determining whether the power tool is unloaded during a time period from a start of the timer to an expiration of the timer; and determining that the power tool has been continuously unloaded during the predetermined amount of time when the power tool is unloaded during the time from the start of the timer to the expiration of the timer.

In one embodiment of the third aspect, the electronic processor is further configured to: after starting the timer but before the timer expires, determining whether the power tool is loaded; and resetting the timer in response to determining that the power tool is loaded after the timer is started but before the timer expires.

Drawings

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

FIG. 1B is a perspective view of the power tool of FIG. 1A with a portion of the housing removed.

Fig. 2 is a block diagram of the power tool of fig. 1A according to some embodiments of the invention.

Fig. 3 is a flow chart of a method of thermal management of the power tool of fig. 1A according to some embodiments of the present invention.

Detailed Description

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

Fig. 1A to 1B show a power tool 100 including a housing 105, a handle 110, a blade 120, a power switch 130, and a shift dial 140. In the example shown, the power tool 100 is a jigsaw. However, the embodiments described below are applicable to any power tool. Referring to fig. 2, the power tool 100 includes an electronic processor 150, a memory 160, a motor 170, an inverter bridge 180, a discharge switch 190, and a current sensor 195. In the illustrated example, the power tool 100 is a cordless battery powered jigsaw that receives operating power from a battery pack 197 connected thereto. In other embodiments, the power tool 100 may be a wired Alternating Current (AC) jigsaw that receives operating power from, for example, a wall outlet.

The electronic processor 150 may be implemented, for example, as a microprocessor, microcontroller, field programmable gate array, application specific integrated circuit, or the like. The memory 160 may be part of the electronic processor 150 or may be a separate component. Memory 160 may include, for example, a program storage area and a data storage area. The memory 160 stores executable instructions that, when executed by the electronic processor 150, cause the power tool 100 to perform the functions described herein. For example, the electronic processor 150 controls the motor 170 and the supply of current between the power source and the motor 170. Together, the electronic processor 150 and the memory 160 may form an electronic controller.

The motor 170 may be a brushless dc motor. Inverter bridge 180 includes a plurality of Field Effect Transistors (FETs) coupled between battery pack 197 and motor 170. The electronic processor 150 controls the pulse width modulation duty cycle of the plurality of FETs to operate and control the speed of the motor 170, for example, through a gate driver (not shown) that may be separate or incorporated into the electronic processor 150. The electronic processor 150 can operate the motor using closed loop speed control, open loop speed control, or a combination of both. In particular, in the present embodiment, operating the motor 170 at the selected speed may include: operate the motor 170 at a particular speed using closed loop speed control, operate the motor 170 at a particular duty cycle using open loop speed control, or a combination of both. In closed-loop speed control, for example, the electronic processor 150 receives a desired speed (e.g., through the variable speed dial 140), drives the inverter bridge 180 at an initial Pulse Width Modulation (PWM) duty cycle, detects the speed of the motor 170 (e.g., using a hall sensor), and adjusts the PWM duty cycle up or down to achieve the desired speed. In open loop speed control, for example, the electronic processor 150 receives a desired speed (e.g., via the variable speed dial 140), accesses a lookup table stored in the memory 160 to obtain a PWM duty cycle that maps to the desired speed, and drives the inverter bridge 180 at the PWM duty cycle obtained from the memory 160.

The power tool 100 includes a transmission 175 (fig. 1B) to convert the rotational motion of the motor 170 into reciprocating motion to reciprocate the blade 120. That is, the rotation of the motor 170 is converted into a stroke of the blade 120. The Stroke Per Minute (SPM) of the blade 120 (i.e., the tool output speed) is set by controlling the Revolutions Per Minute (RPM) of the blade 120 (i.e., the motor speed). Thus, by controlling the motor speed (e.g., via open-loop or closed-loop speed control), the tool output speed is also controlled. The power tool 100 is activated by actuating the power switch 130. In the illustrated example, the power switch 130 is a slidable switch that is movable between an ON (ON) position, in which the power tool 100 is turned ON to operate the motor 150, and an OFF (OFF) position; in the off position, the supply of power to the motor 170 is terminated. In some embodiments, sliding the power switch 130 to the activated position may close the discharge switch 190, allowing current to flow from the power source to the motor 170. Similarly, sliding the power switch 130 to the closed position may open the discharge switch 190, thereby terminating the flow of current between the power source and the motor 170. In some embodiments, the power switch 130 may be a different kind of switch, such as a button, a trigger, and the like. In other embodiments, rather than directly controlling the discharge switch 190, the power switch 130 provides a signal to the electronic processor 150, which in turn, the electronic processor 150 controls the discharge switch 190 based on the signal received from the power switch 130.

The variable speed dial 140 is used to select the operation speed of the electric power tool 100. The shift dial 140 may include a plurality of settings, each setting corresponding to a different operating speed. In one example, the variable speed dial 140 may include 6 settings corresponding to a speed between 800 Strokes Per Minute (SPM) and 3500 SPM. The shift dial 140 may also be used to set the power tool 100 in the automatic control start mode. In the automatic control start mode, the motor 170 operates at a low speed (e.g., a speed corresponding to 1500 SPM) before a load is detected, and when a load is detected, the speed rises to a maximum speed (e.g., a speed corresponding to 3500 SPM). Herein, the load refers to the workpiece engaged by the blade 120. The current sensor 195 measures the current flowing to the motor and provides an indication of the amount of current flowing to the electronic processor 150.

Operating the power tool 100 at high speed for a long period of time may generate heat in the power tool 100. The heat generated during these periods may damage the electrical components of the power tool 100. When the jigsaw 100 (i.e., the power tool 100 is operating on a workpiece) is loaded, the power tool 100 may automatically shut down due to battery discharge before excessive heat is generated. However, when the power tool 100 is operating at high speed for an extended period of time (e.g., 10 minutes, 15 minutes, or more) without a load, the power tool 100 may generate excessive heat, which may damage components of the power tool 100. This may occur, for example, when the user has installed the jigsaw 100 for hands-free operation, has started the power tool 100, and has forgotten to return to the power tool 100 to turn off the power tool 100.

Returning to FIG. 1B, a perspective view of the power tool 100 of FIG. 1A is shown with a portion of the housing 105 removed. In the example shown, the housing 105 is a clamshell housing, and half of the clamshell housing is removed in fig. 1B. With the housing portions removed, the internal components of the power tool 100 are visible, including the electric motor 170, the transmission 175, and a battery pack terminal block 198 for coupling to a battery pack 197.

Fig. 3 shows a flow chart of a method 200 for thermal management of the power tool 100. The method 200 includes activating a timer (at block 210) using the electronic processor 150 and operating the motor 170 at a first speed corresponding to the speed selected by the variable speed dial 140 (at block 220) using the electronic processor 150. The user may select the speed setting using the shift dial 140. The variable speed dial 140 sends a signal corresponding to the selected speed to the electronic processor 150. When the user actuates the power switch 130, the electronic processor 150 activates the timer and operates the motor at the selected speed (i.e., the first speed). As described above, controlling the motor speed may include setting the PWM duty cycle of the FET (open loop speed control) and/or controlling the revolutions per minute of the motor 170 to a particular value (closed loop speed control) that corresponds to the selected strokes per minute. The revolutions per minute may be obtained by dividing the strokes per minute by the gear reduction ratio of the transmission. In some embodiments, the speed is not selected using the variable speed dial 140, but rather the selected speed is a predetermined value stored in the memory 160 (e.g., at the time of manufacture). In some embodiments, instead of using the variable speed dial 140 and the power switch 130, the power tool 100 includes a variable speed trigger that can be pressed by a user and provide a signal to the electronic processor 150 for activating and deactivating the power tool 100, and also for inputting a selected speed for the motor 170.

The method 200 also includes determining, using the electronic processor 150, whether the power tool 100 is unloaded (at block 230). In one embodiment, the electronic processor 150 detects a load condition based on the amount of current flowing through the motor 170. For example, the electronic processor 150 determines that the power tool is not loaded when the instantaneous current is below a current threshold (e.g., 20 amps) and determines that the power tool is loaded when the instantaneous current is above the threshold. In other embodiments, the electronic processor 150 determines that the tool 100 is loaded or unloaded based on a change in motor speed above a threshold, a change in acceleration above a threshold, a change in average current above a threshold, combinations thereof, or by monitoring other tool parameters.

When the electronic processor 150 determines that the power tool 100 is loaded, the electronic processor 150 resets the timer (at block 240) and returns to block 220. The timer continues to be reset by cycling through blocks 220, 230, and 240 while the power tool 100 continues to be loaded.

When the electronic processor 150 determines that the power tool 100 is not loaded (at block 230), the method 200 includes determining, using the electronic processor 150, whether a predetermined amount of time has elapsed (at block 250). The electronic processor 150 determines whether a predetermined amount of time has elapsed based on a timer. For example, in response to determining that the current value of the timer exceeds the predetermined amount of time by the comparison operation, the electronic processor 150 determines that the predetermined amount of time has elapsed. The predetermined amount of time may be selected to allow the power tool to continue operating at a selected speed without generating excessive heat. In some embodiments, the predetermined amount of time is, for example, 1 minute, 2 minutes, 3 minutes, 5 minutes, 6 minutes, 10 minutes, 15 minutes, or the like. In some embodiments, the predetermined amount of time is between 1 minute and 5 minutes, 1 minute and 6 minutes, 1 minute and 10 minutes, 1 minute and 15 minutes, 2 minutes and 10 minutes, 3 minutes and 10 minutes, 5 minutes and 15 minutes, or any intermediate range within these ranges, or the like. The predetermined amount of time is selected to prevent excessive heat generation, rather than placing the tool at a lower speed when the tool is unloaded. That is, instead of performing the load-based speed control and selecting the time to prevent the hysteresis, the predetermined amount of time is selected to prevent excessive heat generation, and the predetermined amount of time is configured to be longer than the time to switch between the load speed and the no-load speed. When the predetermined amount of time has not elapsed, the electronic processor 150 continues to operate the motor 170 at the first speed (returning to block 220).

When the predetermined amount of time has elapsed, the method 200 includes operating (at block 260) the motor 170 at a second speed using the electronic processor 150, the second speed being lower than the first speed. The electronic processor 150 operates the motor 170 at a reduced speed (e.g., a speed corresponding to 1500 SPM) (e.g., via open or closed loop speed control) to prevent the power tool 100 from generating excessive heat. The method 200 also includes determining, using the electronic processor 150, whether the power tool 100 is loaded (at block 270). As described above with respect to block 230, the electronic processor 150 can use a current-based technique to determine whether the power tool 100 is loaded, or can use motor speed, acceleration, average current, or other techniques to determine whether the power tool 100 is loaded. When the electronic processor 150 determines that the power tool 100 is not loaded, then the electronic processor 150 continues to operate the power tool 100 at the second speed.

When the electronic processor 150 determines that the power tool 100 is loaded, the method 200 includes operating the motor 170 at a first speed (at block 280) using the electronic processor 150, the first speed corresponding to the speed selected by the variable speed dial 140. In some embodiments, the method 200 repeats, returning to block 210 to restart the timer.

Thus, in at least some embodiments, by cycling through blocks 210, 220, 230, 240, and 250, and continuously resetting the timer while the power tool 100 is loaded, the electronic processor 150 can effectively operate the motor at the first speed unless the power tool 100 is unloaded for at least a predetermined amount of time. In particular, the method 200 includes determining whether the power tool 100 is continuously unloaded for the duration of the predetermined time period. The electronic processor 150 measures the instantaneous current flowing to the motor 170 or other motor parameter used to measure the load. The electronic processor 150 compares the instantaneous current to a predetermined current threshold and determines that the power tool 100 is not loaded when the instantaneous current is below the threshold. When the instantaneous current is at or above the threshold, the electronic processor 150 determines that the power tool 100 is loaded. The electronic processor 150 repeats the above steps (i.e., measures the instantaneous current), compares the measured current to a predetermined current threshold, and determines the load condition of the power tool 100 at discrete time intervals. For example, the electronic processor 150 repeats the above steps every few milliseconds (e.g., every 50 milliseconds or 100 milliseconds). Thus, in at least some embodiments, the electronic processor 150 determines that the power tool 100 is continuously unloaded for the duration of the predetermined period of time when the measured instantaneous current is below the threshold at each discrete interval during the predetermined period of time.

Then, in at least some embodiments, the electronic processor 150 effectively operates the motor at the second speed by cycling between blocks 260 and 270 until the power tool 100 is loaded, at which time the speed is ramped back up to the first speed (at block 280).

One advantage of the above method is: preventing excessive heat generation and damage to the electronic components of the power tool 100.

Accordingly, the embodiments described herein provide, among other things, systems and methods for thermal management using speed control of a power tool.