WO2022178774A1

WO2022178774A1 - Power tool having variable output

Info

Publication number: WO2022178774A1
Application number: PCT/CN2021/077945
Authority: WO
Inventors: Huanfa XIE; Zhongkang FANG; Hai Bo Ma; Chao Wen; Yongmin Li
Original assignee: Techtronic Cordless Gp
Priority date: 2021-02-25
Filing date: 2021-02-25
Publication date: 2022-09-01
Also published as: EP4076859A1; CN115551679A; EP4076859A4

Abstract

A power tool (100) includes an output member (108) adapted to generate an output, a motor (104) adapted to drive the output member, and a control system (112) adapted to control an operation of the motor. The control system includes a power source (124) and a power switching device (126) interconnecting the power source to the motor adapted to apply a PWM drive signal from the power source to the motor, and a controller (118) adapted to control the power switching device and monitoring at least one operating characteristic of the power tool and adjusting the frequency of the PWM drive signal in response to a predetermined change in the operating characteristic to thereby cause the output member to regulate the output.

Description

POWER TOOL HAVING VARIABLE OUTPUT

FIELD OF INVENTION

The present disclosure relates generally to power tools, more particularly, to a control scheme that controls output of a power tool based on user’s inputs and power tool’s operation parameters.

BACKGROUND OF INVENTION

Electrical power tools, such as variable speed drills and power screwdrivers, typically include a motor control circuit that is adapted to control the speed, torque or power as an output of the tool by receiving a direct input from a user. The desired output is usually selected by the user by varying the position of the trigger switch only.

With power tool developing, application scenarios required by customers are more and more complex. However, traditional power tools usually work at a fixed driving frequency, which causes power tool customer requirement can be hardly fulfilled. Meanwhile, conventional power tool controls suffer from certain disadvantages. For example, conventional controls can be awkward to manipulate while holding the power tool. The user is often required to hold the tool with a first hand and set or change operating controls with a second hand, and controls may take up substantial space or be awkwardly located, thereby making setting or changing control operations difficult.

SUMMARY OF INVENTION

In the light of the foregoing background, it is an object of the present invention to provide an alternate power tool and its operation method based on users input and power tool’s feedback, which eliminates or at least alleviates the above technical problems.

The above object is met by the combination of features of the main claim; the sub-claims disclose further advantageous embodiments of the invention.

One skilled in the art will derive from the following description other objects of the invention. Therefore, the foregoing statements of object are not exhaustive and serve merely to illustrate some of the many objects of the present invention.

Accordingly, the present invention, in one aspect, is a power tool includes an output member adapted to generate an output, a motor adapted to drive the output member, and a control system adapted to control an operation of the motor. The control system includes a power source and a power switching device interconnecting the power source to the motor adapted to apply a PWM drive signal from the power source to the motor, and a controller adapted to control the power switching device and monitoring at least one operating characteristic of the power tool and adjusting the frequency of the PWM drive signal in response to a predetermined change in the operating characteristic to thereby cause the output member to regulate the output.

Preferably, the operating characteristic includes at least one of following characteristics, an input from a user, and an operation parameter of the power tool.

More preferably, the input from a user includes at least one of pressing an operator actuable trigger switch which controls the value of power or different PWM duty/frequency supplied to the motor, and selecting a preset operation mode of the power tool which includes at least one of following modes, a high speed mode, a medium speed mode and a low speed mode.

According to one variation of the preferred embodiments, the predetermined change includes varying actuated position of the trigger switch.

Alternatively, the predetermined change includes changing a selected preset operation mode.

Preferably, the operation parameter includes at least one of following parameters, a temperature of the motor, a temperature of power switching device particularly, the temperature of the MOEFET circuit, current flowing through the motor, a voltage across the motor, a rotation speed of the motor, and a threshold of PWM duty.

More preferably, the predetermined change includes an increase in the operation parameter above a corresponding predetermined threshold.

Alternatively, the predetermined change includes a decrease in the operation parameter below a corresponding predetermined threshold.

Alternatively, the predetermined change corresponds to an acceleration rate the operation parameter above a corresponding predetermined threshold.

Alternatively, the predetermined change corresponds to a deceleration rate the operation parameter below a corresponding predetermined threshold.

Preferably, the controller is adapted to control the output member to enter and being kept in an OFF state in response to a predetermined change of a primary operation parameter of the power tool.

More preferably, wherein the primary operation parameter of the power tool is selected from following parameters, a temperature of the motor, current flowing through the motor, a voltage across the motor, a rotation speed of the motor, a switched path of a trigger, a range of PWM duty, and a selected operation mode.

Preferably, the regulating of the output includes changing the output PWM duty, and/or PWM output frequency.

In another aspect, the present invention is a method of a method of controlling a power tool having a motor driven by a PWM drive signal, and adapted to drive an output member to generate an output. The method includes the steps of a) monitoring at least one operating characteristic of the power tool by a controller, and b) adjusting a frequency of the PWM drive signal in response to a predetermined change in the operating characteristic to regulate the output of the output member by the controller. Preferably, the motor is driven by a power source and a power switching device interconnecting the power source to apply a PWM drive signal from the power source to the motor.

More preferably, the input from a user includes at least one of pressing an operator actuable trigger switch which controls the value of power supplied to the motor, and selecting a preset operation mode of the power tool which includes at least one of following modes, a high speed mode, a medium speed mode and a low speed mode.

Preferably, the operation parameter includes at least one of following parameters, a temperature of the motor, current flowing through the motor, a voltage across the motor, and a rotation speed of the motor.

Alternatively, the predetermined change includes a comparison result of the operation parameter above, equals to, or below a corresponding threshold.

More preferably, the primary operation parameter of the power tool is selected from following parameters, a temperature of the motor, a temperature of power switching device particularly, the temperature of the MOEFET circuit, current flowing through the motor, a voltage across the motor, a rotation speed of the motor a switched path of a trigger, a range of PWM duty, and a selected operation mode.

Preferably, the regulating of the output includes changing the output PWM duty, and PWM output frequency.

The advantage of the present invention is that it can be concluded as the operation mode of the power tool can be determined or adjusted according to a user's input and one or more monitored operation parameter of the power tool by switch the output PWM duty or frequency, so that the power tool can be used in different working scenarios, or switch operation modes automatically. In addition, the power tool provided by the present application can be preset with multiple operation modes to facilitate the user to apply the corresponding operation mode in different scenarios, which helps the user and improves the efficiency in operation. Furthermore, for some abnormal working conditions in the power tool, such as the high temperature of the motor, the operation of the power tool can be timely interrupted. Such interruption can be made in the absence of user intervention to achieve a technical effect of protecting the power tool when there is an abnormal working condition occurs.

BRIEF DESCRIPTION OF FIGURES

The foregoing and further features of the present invention will be apparent from the following description of preferred embodiments which are provided by way of example only in connection with the accompanying figures, of which:

Fig. 1 is an illustration of a power tool internal structure according to a first embodiment of the present invention.

Fig. 2 shows a schematic circuit diagram of the power tool in Fig. 1.

Fig. 3 shows a flowchart of an exemplary control method according to a second embodiment of the present invention.

Fig. 4 shows a flowchart of an exemplary control method according to a third embodiment of the present invention.

Fig. 5 shows a flowchart of an exemplary control method according to a fourth embodiment of the present invention.

Fig. 6 shows a flowchart of an exemplary control method according to a fifth embodiment of the present invention.

Fig. 7 shows a flowchart of an exemplary control method according to a sixth embodiment of the present invention.

Fig. 8 shows a flowchart of an exemplary control method according to a seventh embodiment of the present invention.

Fig. 9 shows a flowchart of an exemplary control method according to an eighth embodiment of the present invention.

Fig. 10 shows a schematic diagram of the PWM signal related to a actuated position of the trigger to modulate the power tool in Fig. 1

Fig. 11 shows a schematic diagram of operation status of the power tool in Fig. 1.

Figs. 12A to 12C show examples of different PWM signals to modulate the driving signal of the motor according to various embodiments of the invention.

In the drawings, like numerals indicate like parts throughout the several embodiments described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention now will be described more fully with reference to the accompanying drawings, in which embodiments of the invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout this application.

Referring to Fig. 1, according a first embodiment of the invention there is a provided a portable power tool 100 which may be a corded or cordless (battery-powered) portable device, such as a screwdriver, drill, etc. The power tool 100 includes a housing 102, a motor 104, a transmission gear assembly 106, an output member 108 (such as, a rotary output component) , a power supply module 110, and a control system112. The housing 102 accommodates most of the essential components for normal operation. The transmission gear assembly 106 is coupled between the motor 104 and the output member 108 to provide an altered output driving force for example with different speeds, torques, and frequencies. The motor 104 can be a brushed or brushless motor. A trigger 114 is configured on the housing 102 as a first user input device for the user to manually operate the power tool 100. Moreover, at least one press button or control knob 116 is configured on the housing 102 as a second user input device to toggle the control system 112 between different preset operation modes. In addition, the control system 112 carries electronic components such as a controller 118 and a memory 120 (as hereinafter described) . The power supply module 110 carries sub-components such as a power source 124 and a power switching device 126. The power source 124 can be a battery pack in the case of a cordless power tool, or it can be an AC-DC convertor in the case of a corded power tool where the power tool is connected to the mains supply via a power cord (not shown) .

Turning now to Fig. 2, the controller 118 of the power tool 100 is connected to the motor 104 for controlling the operation of the motor 104. The power supply module 110 is connected to the motor 104 for powering the motor 104 in order to perform normal operation of the power tool 100. The power source 124 and the power switching device 126 interconnecting to the motor 104 is adapted to apply a PWM drive signal from the power source 124 to the motor 104. The controller 118 is adapted to control the power switching device 126 by adjusting the frequency of the PWM drive signal applied on to the output member 108 (shown in Fig. 1) in order to regulate the output. Generally, the controller 118 is responsive to a predetermined change in the operating characteristic to provide a control signal to the power switching device 126. The predetermined change in the operating characteristic includes not only an input from a user, but also a sensed operation parameter change or feedback of the power tool 100. The trigger 114 is electrically connected to the controller 118 so that it can be used to accept inputs from the user and then provide corresponding signals to the controller 118.

Regarding a first input from the user, the controller 118 is adapted to monitor the user actuating behavior to the trigger 114. The user actuating behavior includes the duration that the user presses down the trigger 114, and the degree of the user’s pressing action. As those skilled in the art would understand, the trigger of power tools are often designed to generate different control signals, for example on a linear basis or PWM control signal, depending on to extent to which the user presses down the trigger. If the user only presses the trigger slightly, this would lead to the trigger generating a signal of a relatively small value, or a low duty cycle PWM signal. If the user presses the trigger heavily using a relatively large force, then the trigger will generate a signal of a relatively large value, or a high duty cycle PWM signal.

In addition, the controller 118 is adapted to monitor the user selecting behavior to the press button 116 as a second input from the user. The memory 120 is connected to the controller 118 and stores a varying pattern of the operation of the power tool and certain preset operation modes. The preset operation modes correspond to different application scenarios to improve the torque, temperature and other performance characteristics of the power tool 100. The preset operation modes include, but not limited to, a high rotation speed mode, a medium rotation speed mode and a low rotation speed mode. In response to the selection of a operation mode by the user, the controller 118 is adapted to output a corresponding preset PWM frequency to the power switching device 126, and modulate the operation of motor 104, in order to regulate the output of the power tool 100. Thus, an appropriate operation mode can be selected by or via the controller 118 to precisely meet the anticipated conditions of a specific application.

Regarding the operation parameter change or feedback of the power tool 100, the controller 118 is further connected with a sensor 122 to monitor various motor status and other operation parameters and in particular variations in the performance of the motor 104. The sensor 122 connects to the motor 104, and is adapted to detect, measure, or otherwise obtain operation parameters of the motor 104. In other words, a varying pattern of these status and parameters may be recorded, which contains not only a single value but also a dynamic variation of these status and parameters versus time. Such operation parameters include but not limited to the temperature of the motor 104, the temperature of power switching device, particularly, the temperature of the MOEFET circuit, the current flowing through the motor 104, the voltage across the motor 104, the output torque of the motor 104, and the rotation speed of the motor 104, etc. The rotation speed of the motor 104 can be for example represented by revolutions per minute (RPM) . The output torque of the motor 104 may be directly measured by using either optical devices or mechanical torque measuring devices, or it may be measured indirectly based on the current of the motor 104. In case the motor 104 is a stepping motor, then the steps or angular positions that the motor that has traveled may also be detected by the sensor 122 and transferred to the controller 118.

A predetermined change in the operation parameters can be determined when a) an increase in the sensed operation parameter above a corresponding predetermined threshold; b) a decrease in the sensed operation parameter below a corresponding predetermined threshold; c) an acceleration rate in which the operation parameter rises above a corresponding predetermined threshold; d) a deceleration rate in which the operation parameter drops below a corresponding predetermined threshold. For example, if the sensed motor current exceeds 200%of the normal motor current, or it exceeds 150%of the normal motor current over an extended period of day ten seconds, or it decreased abruptly within a short period of say pone second, then a predetermined change will be identified and reported to the controller 118. When such changes occur, the controller 118 will adjust the frequency of the PWM drive signal to the motor 104, which in turn regulates the output of the power tool 100, or will switch the operation mode of the power tool 100 by changing the output PWM frequency. It is readily understood that other techniques for assessing the signal received from the sensor are within the scope of the present invention. In some embodiments, the predetermined change includes a comparison result of the operation parameter above, equals to, or below a corresponding threshold. In a different embodiment, the power tool may only include a press button for selecting preset operation modes, or a trigger for controlling the output according to an actuated position, and these are still within the scope of the present invention.

Referring to Fig. 3 to Fig. 8, several

exemplary method

200, 300, 400, 500, 600 and 700 for regulating the output of a power tool is illustrated. Such methods can be applied on the power tool 100 illustrated in Figs 1-2, but it is not limited to as such, the other power tools may also adopt the same or similar method.

In the method 200 of Fig. 3, a first operation parameter, for example the motor current is selected as an operation parameter to be monitored to identify a predetermined change in the operation parameter. First, the method starts at Step 201, and then at Step 202 the controller 110 determines whether power is supplied to the power tool. As the power tool can be a corded or cordless (battery-powered) tool, the power supply may be provided with a power plug, a battery or any other power supply method known in this field. If there is no power detected, then power is not being supplied to the motor 104 as indicated at Step 204, where the method 200 ends. The END Step 204 comprises at least one of the following operations, a) interrupting the current operation of the power tool, b) shutting down the motor but keeping operation of other components, c) maintaining the current operation of the power tool, and any other termination events as known to a skilled person in art. In this case, there is no need to monitor any changes in the operation parameters. Conversely, if power is detected, then power is being supplied to the motor. In some embodiments, when power is supplied to the power tool, the power tool may await a user’s input, for example pressing a trigger or selecting an operation mode to control the motor to operate in a certain frequency. Alternatively, the power tool may automatically start to operate in a certain frequency. The output frequency will be regulated due to an additional input from the user, or a feedback of a predetermined change in the operation parameter as described below.

If power is on, then in Step 208 the sensor monitors the first operation parameter that indicates the value of the first operation parameter, such as the motor current. At Step 210, the value of the first operation parameter is compared to a given threshold to determine whether there is a predetermined change of the first operation parameter. At stated above, the predetermined change in the first operation parameters can be determined when a) an increase in the first operation parameter above a predetermined threshold; b) a decrease in the first operation parameter below a predetermined threshold; c) an acceleration rate in which the first operation parameter rises above a predetermined threshold; d) a deceleration rate in which the first operation parameter drops below a predetermined threshold, and e) a comparison result of the operation parameter above, equal to, or below a predetermined threshold. For example, if the value of the first operation parameter is at or below a certain threshold, as in the case of current limit, then the controller determines that the motor operates normally. Thus, the circuit will return to Step 201. On the other hand, if the value of the first operation parameter exceeds the threshold, then the controller identifies a predetermined change and hence regulates the output of the power tool in Step 230.

In some embodiments, to determine an acceleration rate or deceleration rate of the first operation parameter, at Step 210 the controller may compare a mathematical function of the first operation parameter (e.g., a first or second derivative of the first operation parameter such as a rate of change of first operation parameter) to a threshold value. In yet another variation, the first operation parameter threshold values may vary depending on other tool conditions (e.g., a motor speed or the mode of the transmission) . Then, at Step 230, the controller produces regulate output of the power tool. At Step 230, the step of regulating the output of the power tool includes the actions of: a) changing the output PWM frequency, b) interrupting the power to the motor, c) increasing or decreasing the power to the motor to a non-zero value, d) pulsing the motor, e) braking the motor, and f) switching the operation mode from one to another one. It is readily understood that other techniques for regulating the output of a power tool are within the scope of the present invention.

Referring to Fig. 4, a second exemplary method 300 for regulating the output of a power tool is illustrated. For the sake of brevity only differences in method 300 as compared to that in Fig. 3 is described.

Steps

301, 302, 304, 308, 310 and 330 are largely similar to their counterparts in Fig. 3, with certain differences described below. In method 300, the various operation parameters involve priority. For example, a first operation parameter such as the motor current is more of an essential operation parameter to identify any determined change than a second operation parameter like the motor temperature. Hence, the first operation parameter will be sensed and monitored first, as illustrated in steps 300 to 310. If the monitored first operation parameter is identified as a predetermined change, at step 330, the controller will regulate the output of the power tool irrespective of the value of the second operation parameter.

On the other hand, if the first operation parameter is determined to be normal, then at Step 312, the sensor monitors a second operation parameter. At Step 314, the value of second operation parameter is compared to a given threshold value to determine whether there is a predetermined change. For example, if the value of the second operation parameter is at or below the threshold, then the controller determines that the motor operates normally. Therefore, the controller will return to Start 301. On the other hand, if the second operation parameter exceeds the threshold, then the controller determines that a predetermined change of the second operation parameter has occurred. Similarly to that in method 200 of Fig. 3, at Step 314 the microcontroller compares a mathematical function of the second operation parameter. Then, at step 330, the controller generates a signal to regulate the output of the power tool. In method 300, the monitored operation parameters could be more than two, such as the motor current, temperature, voltage and rotation speed could be all taken into consideration, with relative priorities.

Referring to Fig. 5, a third exemplary method 400 for regulating an output of a power tool is illustrated. For the sake of brevity only differences in the method 400 as compared to that in Fig. 3 is described.

Steps

401, 402, 404, 408, 410 and 430 are largely similar to their counterparts in Fig. 3, but any difference will be described below. In method 400, the different operation parameters involve no priorities. In other words, if any monitored operation parameter exceeds its given threshold, the controller regulate the output of power tool. In method 400, the monitored operation parameters could be more than two, like the motor current, the temperature, the voltage and the rotation speed, which could be all taken into consideration without priorities, as shown by the arrow 440. Meanwhile, the output of detected predetermined change of two different operation parameters is the same in method 400. Such design could save the storage space in memory, and making programing of preset operation mode of power tool more compact.

Referring to Fig. 6, a fourth exemplary method 500 for regulating an output of a power tool is illustrated. For the sake of brevity only differences in the method 500 as compared to that in Fig. 5 is described.

Steps

501, 502, 504, 508, 510, 512, 514 and 540 are largely similar to their counterparts in Fig. 5, but any difference will be described below. In method 500, the different operation parameters involve no priorities. Meanwhile, the different detected predetermined changes will result a different output of power tool, as shown in

Steps

510 and 520. For example, set the motor current as the first operation parameter, and the motor temperature as the second operation parameter. If the motor current exceeds the given current threshold, then the controller change the output PWM frequency. If the temperature exceed the given temperature threshold, then the circuit switch the output PWM frequency again to interrupt the current operation of motor, in order to produce a protection of the motor and power tool.

Particularly, in an embodiment, the motor is modulated by PWM signal of different frequencies, and the modulation of motor by PWM comprises at least one of the followings actions: a) changing the output PWM frequency b) applying a plurality of different driving modes (high speed, medium speed, low speed and etc. ) to the motor; c) applying a plurality of different duty time of PWM; d) applying a plurality of different cycle time of PWM. By such actions, output of power tool is regulated. Similar to the method 400, in method 500, the monitored operation parameter could be more than two, like the motor current, the temperature, the voltage and the rotation speed, which could be all taken into consideration without priorities, shown by the arrow 540.

Referring to Fig. 7, a fifth exemplary method 600 for regulating an output of a power tool is illustrated. For the sake of brevity only differences in the method 600 as compared to that in Fig. 4 is described.

Steps

601, 602, 604, 608, 610 and 630 are largely similar to their counterparts in Fig. 4, but any difference will be described below. In method 600, two or more operation parameter are taken into consideration for regulate output of power tool, for example an instantaneous current as a first operation parameter which exceeds threshold might not be harmful to the power tool, but a current which exceeds threshold for a given period of time as a second operation parameter should be monitored and taken necessary controls by the controller. As shown in Steps 610 to 630, if the current is monitored exceeding the threshold, the sensor continues to monitor the period of time of the current exceed the threshold. If the period of time is longer than a given value, at Step 630, the controller regulates output of power tool, for example changing the output PWM duty. If not, the method 600 will return to the start of the algorithm the. Similar to other embodiments described above, in method 600, the monitored operation parameter could be selected from the motor current, the temperature, the voltage, the rotation speed, the selection of an operation mode, the user’s behavior to a trigger (including releasing the trigger, pressing the trigger softly, heavily, or fully) , and different ranges of PWM duty (from 0%to 100%) , and might be more than two. Meanwhile, when two different operation parameters are selected, for example the current and temperature, a technical effect of preventing false notification or alarm could be achieved. In a variation, a skilled person in art could understand that, the combination of determination of the change of two or more parameters as stated in

Step

608, 610, 620 and 622 can be packaged as one determination step, and comprised as a sub-step in

Step

210, 310, 410 and 510 in

exemplary method

200, 300, 400, and 500. In another words, the

Step

210, 310, 410 and 510 could be regarded as a determination of more than one operation parameters as illustrated in method 600, and will not beyond the scope of present application.

In a variation, in the above exemplary methods, after the Step of regulating output of power tool, like 230 or 630, the controller is further configured to continue monitoring the operation parameters, if a further predetermined change is detected, for example the current is lower than a given threshold over a certain period of time, the controller is configured to regulate the output of power tool again.

Referring to Fig. 8, a sixth exemplary method 700 for regulating an output of a power tool is illustrated. For the sake of brevity only differences in the method 700 as compared to that in Fig. 7 is described.

Steps

701, 702, 704, 708, 710 and 730 are largely similar to their counterparts in Fig. 7, but any difference will be described below. In method 700, two or more output frequency of power tool determined by different scenarios are shown herewith. As shown in

Steps

702 and 706, after the power is supplied to the power tool, with or without an input from a user, the power tool’s output is modulated with a PWM frequency A. Then, as shown in

Steps

708, 710 and 730, a first operation parameter is monitored and compared to a threshold to determine whether there is a predetermined change, for example the motor current exceeds a current limit, then at Step 730, the controller regulates the output of power tool, by regulating and keeping output of power tool as PWM frequency B. Then, the controller and sensor continues to monitor a second operation parameter of the power tool, if a corresponding predetermined change is detected in Step 722, the controller further regulates the output of power tool, by regulating and keeping output of power tool back to PWM frequency A. Similar to other embodiments described above, in method 700, the monitored operation parameter could be selected from the motor current, the temperature, the voltage and the rotation speed and other parameters related to power tool’s operation, and might be more than two.

In a variation, a skilled person in art could understand that, the method 700 can be configured to monitor more than two operation parameter, and correspondingly switch to different output frequency. In some embodiments, if a predetermined change of the second operation parameter detected, the output frequency will be changed to a different frequency other than A and B, and will not beyond the scope of present application.

Other than the operation parameters described in the above exemplary methods, the operation parameters may also include the inputs or control provided by the user, for example, pressing an operator actuable trigger switch which controls the value of power supplied to the motor, and selecting a preset operation mode of the power tool which includes at least one of following modes, a high speed mode, a medium speed mode and a low speed mode. Thus, the output of the power tool could be control and regulate by both user’s inputs and feedback of the power tool. For example, if the power tool is an electric screwdriver, the working modes can be switched from a high PWM frequency to a lower PWM frequency output for driving other working members. The screwdriver is operated at the high PWM frequency initially for a period of time. When the sensor detects the motor current exceeds a current threshold, the controller controls the output to switch to a lower PWM frequency for reducing the losses of MOSFET switch.

In another embodiment, the power tool may comprise a battery pack, the sensor is adapted to detect a temperature, current and voltage of the battery pack or the temperature of the output member as the monitored operation parameter. The controller can switch the output frequency of the motor as a predetermined change detected, for example when the temperature of the battery pack is higher than a preset value, the output is switched to a lower PWM frequency to reduce the current, thereby achieving over temperature protection and over current protection for the power tool and battery pack.

According to one example, as shown in Fig. 9, seventh exemplary method 800 for regulating an output of a power tool by a PWM signal is illustrated. In such example, the operation parameter is selected as the PWM duty, and the predetermined change is identified as the change of the duty thereof. At Step 802, the controller determines whether the PWM duty is more than 50%or not, if yes, the power tool will set the PWM output frequency to 10K Hz as a first operation mode at Step 804; if not, the power tool will set the PWM output frequency to 1K Hz at Step 806, which is a second operation mode. Then, at step 808, the power tool will determine whether the power tool enters over current state or current limit state or motor stall state by an input of operation mode selecting by the user. If not, the method goes back to Step 802 to set the sensor and controller continues to monitor the PWM duty. If yes, then the controller will generate a signal to set the PWM output frequency to 2K Hz, which increases the output power of an output member. After that, the controller is adapted to determine whether power tool exits current state or current limit state or motor stall state by an input of operation mode selecting by the user or a feedback signal generated by the power tool itself. If not, the operation mode of the power tool maintains. If yes, the method goes back to Step 802 to set the sensor and controller continues to monitor the PWM duty. Those skilled in the art can understand that the detailed values of above mentioned operation parameters, for example PWM duty at 50%, and PWM output frequency at 10K Hz are just for illustration propose only. The adopted different values, for example PWM duty at 60%or different operation parameters, like a motor current or temperature of MOSFET circuit will not beyond the scope of present application.

According to one example, as shown in Fig. 10, one of the user’s input is pressing an operator actuable trigger switch to control the controller 118 sets the duty rate of the pulse width of the PWM signal corresponding to varying actuated position of the trigger switch. If the trigger switch is released, then no PWM duty will be generated. According to the actuated position of the trigger switch, the PWM duty increases from 0%level to 100%level, which further regulates the output power or frequency of the motor. Meanwhile, the constant speed trigger could also be applied in the present invention. Those skilled in the art can understand that Fig. 10 only shown an example of the PWM signal corresponding to varying actuated position of the trigger. In other embodiment, the power tool may output a fixed PWM duty signal or variable PWM duty signal controlled by the actuated position. The linear relationship and piecewise linear relationship between the PWM signal corresponding to varying actuated position of the trigger are still within the scope of present invention.

Referring to Fig. 11, according to another example the output power of the power tool is represented by the PWM which modulates the motor. As shown, different PWM cycle A, B, C according to different PWM frequency are applied to regulate the output of a power tool. Each cycle is corresponding to a preset or special operation mode of the power tool. The changes between the different cycles is in response to a predetermined change in the selected operating characteristic to thereby cause the output member to regulate the output.

Referring to Fig. 12A to 12C, the PWM waveforms includes one or more of a) constant duty cycle PWM as shown in Fig. 12A; b) a combination of increasing duty cycle PWM and decreasing duty cycle PWM as shown in Fig. 12B and 12C.

In the case of a constant duty cycle PWM as shown in Fig. 12A, the output of motor operates under a constant PWM, which represents that the power tool operates normally and there is not any user’s input or feedback control of the power generated to interrupt the current operation. Meanwhile, as shown in Fig. 12A, the PWM frequency can be defined as 1/cycle time.

In the case of mixed PWM signals with different duty cycles are shown in Fig. 12B and 12C, where the output of motor varies from a low PWM frequency (which may correspond to a high rotation speed) for a period of time in Fig. 12B, then a higher PWM frequency (which may correspond to a low rotation speed for a period of time) or a high PWM frequency for a period of time, then a lower PWM frequency for a period of time in Fig. 12C. Thus a varying frequency output is produced to by the power tool to satisfy different operation scenarios are shown in Fig. 12B and 12C. The change between the low duty and high duty is caused by the determined changes in above mentioned operation parameters or user’s input.

While the invention has been illustrated and described in detail in the drawings and foregoing descr iption, the same is to be considered as illustrative and not restrictive in character, it being understood that only exemplary embodiments have been shown and described and do not limit the scope of the invention i n any manner. It can be appreciated that any of the features described herein may be used with any embodi ment. The illustrative embodiments are not exclusive of each other or of other embodiments not recited he rein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set f orth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims.

Claims

A power tool comprising:

an output member adapted to generate an output,

a motor adapted to drive the output member, and

a control system adapted to control an operation of the motor, the control system comprising:

a power source and a power switching device interconnecting the power source to the motor adapted to apply a PWM drive signal from the power source to the motor, and

a controller adapted to control the power switching device and to monitor at least one operating characteristic of the power tool and to adjust the frequency of the PWM drive signal in response to a predetermined change in the operating characteristic to thereby cause the output member to regulate the output.
The power tool of claim 1, wherein the operating characteristic includes at least one of following characteristics, an input from a user, and an operation parameter of the power tool.
The power tool of claim 2, wherein the input from a user includes at least one of pressing an operator actuable trigger switch which controls the value of power supplied to the motor, and selecting a preset operation mode of the power tool which includes at least one of following modes, a high speed mode, a medium speed mode and a low speed mode.
The power tool of claim 3, wherein the predetermined change includes varying actuated position of the trigger switch.
The power tool of claim 3, wherein the predetermined change includes changing a selected preset operation mode.
The power tool of claim 2, wherein the operation parameter includes at least one of following parameters, a temperature of the motor, a temperature of power switching device, current flowing through the motor, a voltage across the motor, an value of PWM duty, and a rotation speed of the motor.
The power tool of claim 6, wherein the predetermined change includes an increase in the operation parameter above a corresponding predetermined threshold.
The power tool of claim 6, wherein the predetermined change includes a decrease in the operation parameter below a corresponding predetermined threshold.
The power tool of claim 6, wherein the predetermined change corresponds to an acceleration rate the operation parameter above a corresponding predetermined threshold.
The power tool of claim 6, wherein the predetermined change corresponds to a deceleration rate the operation parameter below a corresponding predetermined threshold.
The power tool of claim 6, wherein the predetermined change includes a comparison result of the operation parameter above, equals to, or below a corresponding threshold.
The power tool of claim 1, wherein the output is regulated by changing the output PWM duty, and/or output PWM frequency.
The power tool of claim 2, wherein the controller is adapted to control the output member to enter and being kept in an OFF state in response to a predetermined change of a primary operation parameter of the power tool.
The power tool of claim 11, wherein the primary operation parameter of the power tool is selected from following parameters, a temperature of the motor, a temperature of power switching device, current flowing through the motor, a voltage across the motor, an value of PWM duty, and a rotation speed of the motor.
A method of controlling a power tool having a motor driven by a PWM drive signal, and adapted to drive an output member to generate an output, wherein the motor is driven by a power source and a power switching device interconnecting the power source to apply a PWM drive signal from the power source to the motor, the method comprising:

monitoring at least one operating characteristic of the power tool by a controller, and

adjusting a frequency of the PWM drive signal in response to a predetermined change in the operating characteristic to regulate the output of the output member by the controller.
The method of claim 15, wherein the operating characteristic includes at least one of following characteristics, an input from a user, and an operation parameter of the power tool.
The method of claim 16, wherein the input from a user includes at least one of pressing an operator actuable trigger switch which controls the value of power supplied to the motor, and selecting a preset operation mode of the power tool which includes at least one of following modes, a high speed mode, a medium speed mode and a low speed mode.
The method of claim 17, wherein the predetermined change includes varying actuated position of the trigger switch.
The method of claim 17, wherein the predetermined change includes changing a selected preset operation mode.
The method of claim 16, wherein the operation parameter includes at least one of following parameters, a temperature of the motor, a temperature of power switching device, current flowing through the motor, a voltage across the motor, an value of PWM duty, and a rotation speed of the motor.
The method of claim 20, wherein the predetermined change includes an increase in the operation parameter above a corresponding predetermined threshold.
The method of claim 20, wherein the predetermined change includes a decrease in the operation parameter below a corresponding predetermined threshold.
The method of claim 20 wherein the predetermined change corresponds to an acceleration rate the operation parameter above a corresponding predetermined threshold.
The method of claim 20, wherein the predetermined change corresponds to a deceleration rate the operation parameter below a corresponding predetermined threshold.
The method of claim 20, wherein the predetermined change includes a comparison result of the operation parameter above, equals to, or below a corresponding threshold.
The method of claim 15, wherein, the output is regulated by changing the output PWM duty, and/or output PWM frequency.