CN115551679A

CN115551679A - Power tool with variable output

Info

Publication number: CN115551679A
Application number: CN202180005248.5A
Authority: CN
Inventors: 谢焕发; 方仲康; 马海波; 文超; 李永民
Original assignee: Techtronic Cordless GP
Current assignee: Techtronic Cordless GP
Priority date: 2021-02-25
Filing date: 2021-02-25
Publication date: 2022-12-30
Also published as: EP4076859A1; WO2022178774A1; EP4076859A4

Abstract

The power tool (100) includes an output member (108) configured to generate an output, a motor (104) configured to drive the output member, and a control system (112) configured to control operation of the motor. The control system includes a power supply (124) and a power switching device (126) interconnecting the power supply and the motor, the power switching device being capable of applying a pulse width modulated drive signal from the power supply to the motor; and a controller (118) configured to control the power switching device and monitor at least one operating characteristic of the power tool, and to adjust the frequency of the pulse width modulated drive signal in response to a predetermined change in the operating characteristic, thereby causing the output member to adjust the output.

Description

Power tool with variable output

Technical Field

The present disclosure relates generally to power tools and, more particularly, to control schemes for controlling the output of power tools based on user input and operating parameters of the power tools.

Background

Power tools that are powered electrically, such as variable speed drills and power screwdrivers, typically include a motor control circuit that is capable of controlling the speed, torque or power output as a tool by receiving direct input from a user. The user typically selects the desired output simply by changing the position of the trigger switch.

With the development of power tools, the application scenes required by customers are more and more complicated. However, conventional power tools typically operate at a fixed drive frequency, which makes it difficult to meet the customer needs of the power tool. Also, conventional power tool controllers suffer from certain drawbacks. For example, conventional controls may be difficult to operate while holding the power tool. Often, the user needs to hold the tool with a first hand and set or change the operating controls with a second hand, and the controls may occupy a significant amount of space or be inconveniently located, making setting or changing the control operations difficult.

Disclosure of Invention

In view of the above background, it is an object of the present invention to provide an alternative power tool and method of operation thereof based on user input and power tool feedback, which obviates or at least mitigates the above technical problems.

The above object is achieved by the combination of features in the main claim; the dependent claims disclose further advantageous embodiments of the invention.

Other objects of the present invention will be apparent to those skilled in the art from the following description. Accordingly, the foregoing statements of purpose are not exhaustive and serve only to illustrate some of the many purposes of the present invention.

Accordingly, in one aspect, the present invention is a power tool that includes an output member capable of producing an output, a motor capable of driving the output member, and a control system capable of controlling the operation of the motor. The control system includes a power source and a power switching device interconnecting the power source and the motor, the power switching device being capable of applying a pulse width modulated drive signal from the power source to the motor, and a controller capable of controlling the power switching device, monitoring at least one operating characteristic of the power tool, and adjusting a frequency of the pulse width modulated drive signal in response to a predetermined change in the operating characteristic, thereby causing the output member to adjust the output.

Preferably, the operating characteristics include at least one of the following characteristics: input from a user, and operating parameters of the power tool.

More preferably, the input from the user comprises at least one of pressing an operator-actuatable trigger switch that controls the value of power provided to the motor or different pulse width modulation duty cycles/frequencies and selecting a preset operating mode of the power tool, the preset operating mode comprising at least one of: a high speed mode, a medium speed mode, and a low speed mode.

According to a variant of the preferred embodiment, said predetermined variation comprises a change of the actuation position of the trigger switch.

Optionally, the predetermined change comprises changing the selected preset operating mode.

Preferably, the operating parameters include at least one of the following: the temperature of the motor, in particular the temperature of the mains switching device, the temperature of the MOEFET circuit, the current through the motor, the voltage across the motor, the value of the pulse width modulation duty cycle, the rotational speed of the motor, and the threshold value of the pulse width modulation duty cycle.

More preferably, the predetermined change comprises an increase in the operating parameter above a respective predetermined threshold.

Optionally, the predetermined change comprises a decrease in the operating parameter below a respective predetermined threshold.

Optionally, the predetermined variation corresponds to a rate of increase of the operating parameter being above a respective predetermined threshold.

Optionally, the predetermined variation corresponds to a rate of decrease of the operating parameter being below a respective predetermined threshold.

Preferably, the controller is configured to control the output member to enter the closed state and remain in the closed state in response to a predetermined change in a primary operating parameter of the power tool.

More preferably, the main operating parameters of the power tool are selected from the following parameters: temperature of the motor, current flowing through the motor, voltage across the motor, rotational speed of the motor, switching path of the trigger, range of pulse width modulation duty cycle, and selected operating mode.

Preferably, the adjusting of the output comprises varying the output pulse width modulation duty cycle and/or the pulse width modulation output frequency.

In another aspect, the invention is a method of controlling a power tool having a motor driven by a pulse width modulated drive signal, the motor being capable of driving an output member to produce an output. The method comprises the following steps: a) Monitoring, by the controller, at least one operating characteristic of the power tool, and b) adjusting a frequency of the pulse width modulated drive signal in response to a predetermined change in the operating characteristic, thereby adjusting, by the controller, an output of the output member. Preferably, the motor is driven by a power source and a power switching device interconnected with the power source to apply a pulse width modulated drive signal from the power source to the motor.

More preferably, the input from the user comprises at least one of depressing an operator-actuatable trigger switch that controls the value of power provided to the motor and selecting a preset mode of operation of the power tool, the preset mode of operation comprising at least one of: a high speed mode, a medium speed mode, and a low speed mode.

Preferably, the operating parameters comprise at least one of the following parameters: temperature of the motor, current flowing through the motor, voltage across the motor, and rotational speed of the motor.

Optionally, the predetermined change corresponds to a rate of increase of the operating parameter being above a respective predetermined threshold.

Optionally, the predetermined variation comprises a comparison of the operating parameter above, equal to or below a respective threshold.

Preferably, the controller is configured to control the output member to enter the closed state and remain in the closed state in response to predetermined changes in the main operating parameters of the power tool.

More preferably, the main operating parameters of the power tool are selected from the following parameters: the temperature of the motor, in particular the temperature of the power switching device, the temperature of the MOEFET circuit, the current flowing through the motor, the voltage across the motor, the rotational speed of the motor, the switching path of the trigger, the range of the pulse width modulation duty cycle, and the selected operating mode.

Preferably, adjusting the output comprises varying the output pulse width modulation duty cycle and/or the pulse width modulation output frequency.

The invention has the advantages that the following conclusion can be drawn: the operating mode of the power tool may be determined or adjusted by switching the output pulse width modulation duty cycle or frequency based on user input and one or more monitored operating parameters of the power tool, such that the power tool may be used in different operating scenarios, or may be automatically switched between operating modes. In addition, multiple operating mode can be predetermine to the power tool that this application provided to make things convenient for the user to use corresponding operating mode in the scene of difference, this can help to the user and improve the operating efficiency. In addition, the operation of the power tool may be interrupted in time for some abnormal operating conditions in the power tool, such as a high temperature of the motor. Such interruption may be performed without user intervention to achieve the technical effect of protecting the power tool in the event of abnormal operating conditions.

Drawings

The foregoing and further features of the invention will become apparent from the following description of preferred embodiments, which are provided by way of example only, with reference to the accompanying drawings, in which:

fig. 1 is a diagram of the internal structure of a power tool according to a first embodiment of the present invention.

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

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

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

Fig. 5 shows a flow chart 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 a pulse width modulated signal associated with an actuated position of a trigger for modulating the power tool of fig. 1.

Fig. 11 shows a schematic view of an operating state of the power tool in fig. 1.

Fig. 12A to 12C show examples of different pulse width modulation signals for modulating a motor drive signal according to various embodiments of the present invention.

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

Detailed Description

Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This 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. In the present application, like reference numerals refer to like elements.

Referring to fig. 1, according to a first embodiment of the present invention, a portable power tool 100 is provided, and the power tool 100 may be a wired or wireless (battery-powered) portable device, such as a screwdriver, a drill, or the like. The power tool 100 includes a housing 102, a motor 104, a drive gear assembly 106, an output member 108 (e.g., a rotary output component), a power module 110, and a control system 112. The housing 102 contains most of the basic components for normal operation. A transmission gear assembly 106 is coupled between the motor 104 and the output member 108 to provide a varying output drive force, for example, having different speeds, torques, and frequencies. The motor 104 may be a brushed or brushless motor. The housing 102 is configured with a trigger 114 as a first user input device for a user to manually operate the power tool 100. In addition, at least one button or control knob 116 is provided on the housing 102 as a second user input device for switching the control system 112 between different preset operating modes. In addition, the control system 112 carries electronic components, such as a controller 118 and memory 120 (described below). The power module 110 carries subcomponents such as a power supply 124 and a power switching device 126. The power source 124 may be a battery pack in the case of a cordless power tool, or the power source 124 may be an ac-dc converter in the case of a wired power tool, wherein the power tool is connected to a mains power source 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 module 110 is connected to the motor 104 for supplying power to the motor 104 in order to perform normal operation of the power tool 100. The power supply 124 and a power switching device 126 interconnected with the motor 104 are capable of applying a pulse width modulated drive signal from the power supply 124 to the motor 104. The controller 118 is capable of controlling the power switching device 126 by adjusting the frequency of the pulse width modulated drive signal applied to the output member 108 (shown in fig. 1) to regulate the output. Generally, the controller 118 is responsive to predetermined changes in the operating characteristics to provide control signals to the power switching device 126. The predetermined change in the operating characteristic includes not only input from the user, but also sensed changes in operating parameters 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 input from a user and then provide a corresponding signal to the controller 118.

With respect to the first input from the user, the controller 118 can monitor the user actuation behavior of the trigger 114. The user actuation behavior includes the duration of time the user presses the trigger 114, and the degree of the user's pressing action. As will be appreciated by those skilled in the art, the trigger of a power tool is typically designed to generate different control signals, such as a linear-based control signal or a pulse width modulated control signal, depending on the extent to which the user presses the trigger. If the user only slightly presses the trigger, this will cause the trigger to generate a signal having a relatively small value, or a low duty cycle pulse width modulated signal. If the user presses the trigger hard with a relatively large force, the trigger will generate a signal having a relatively large value, or a high duty cycle pulse width modulated signal.

In addition, the controller 118 can monitor user selection behavior of the buttons 116 as a second input from the user. The memory 120 is connected to the controller 118 and stores the changing modes of operation of the power tool as well as certain preset operating modes. The preset operating modes correspond to different application scenarios to improve torque, temperature, and other performance characteristics of the power tool 100. The predetermined operating modes include, but are not limited to, a high speed mode, a medium speed mode, and a low speed mode. In response to a user selection of an operating mode, the controller 118 is capable of outputting a corresponding preset pulse width modulation frequency to the power switching device 126 and modulating the operation of the motor 104 to adjust the output of the power tool 100. Thus, an appropriate mode of operation may be selected by or via the controller 118 to precisely meet the anticipated conditions of a particular application.

With respect to changes in or feedback of the operating parameters of the power tool 100, further, the controller 118 is coupled to sensors 122 to monitor various motor conditions and other operating parameters, particularly changes in the performance of the motor 104. The sensor 122 is connected to the motor 104 and is capable of detecting, measuring, or otherwise obtaining an operating parameter of the motor 104. In other words, a pattern of change of these states and parameters may be recorded, which pattern of change not only contains individual values, but also dynamic changes of these states and parameters with respect to time. Such operating parameters include, but are not limited to, the temperature of the motor 104, the temperature of the power switching device, particularly 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 rotational speed of the motor 104, among others. The rotational speed of the motor 104 may be represented, for example, by Revolutions Per Minute (RPM). The output torque of the motor 104 may be measured directly by using optical or mechanical torque measurement devices, or may be measured indirectly based on the current of the motor 104. Where the motor 104 is a stepper motor, the step or angular position that the motor has traveled may also be detected by the sensor 122 and communicated to the controller 118.

The predetermined change in the operating parameter may be determined when a) the sensed operating parameter increases above a corresponding predetermined threshold; b) When the sensed operating parameter falls below a corresponding predetermined threshold; c) The rate of increase of the operating parameter is higher than a respective predetermined threshold; d) The rate of decrease of the operating parameter drop is below a corresponding predetermined threshold. For example, if the sensed motor current exceeds 200% of the normal motor current, or exceeds 150% of the normal motor current for a long period of ten seconds, or decreases abruptly for a short period of one second, a predetermined change will be determined and reported to the controller 118. When such a change occurs, the controller 118 will adjust the frequency of the pulse width modulated drive signal delivered to the motor 104, and thus the output of the power tool 100, or the controller 118 will switch the operating mode of the power tool 100 by changing the output pulse width modulation frequency. It will be readily appreciated that other techniques for evaluating the signals received from the sensors are also within the scope of the present invention. In some embodiments, the predetermined change comprises a comparison of the operating parameter above, equal to, or below a respective threshold. In various embodiments, the power tool may include only a button for selecting a preset operating mode, or a trigger for controlling the output depending on the actuation position, and these remain within the scope of the present invention.

Referring to fig. 3-8, several

exemplary methods

200, 300, 400, 500, 600, and 700 for adjusting the output of a power tool are illustrated. These methods may be applied to the power tool 100 shown in fig. 1-2, but are not limited thereto, and other power tools may also employ the same or similar methods.

In the method 200 of fig. 3, a first operating parameter, such as motor current, is selected as the operating parameter to be monitored to determine a predetermined change in the operating parameter. First, the method starts in step 201, and then in step 202, the controller 110 determines whether to supply power to the power tool. Since the power tool may be a wired or wireless (battery powered) tool, the power source may be provided with a power plug, a battery, or any other power supply method known in the art. If no power is detected, the motor 104 is not powered, as shown at step 204, and the method 200 ends at step 204. The ending step 204 includes at least one of a) interrupting the current operation of the power tool, b) turning off the motor but maintaining the operation of other components, c) maintaining the current operation of the power tool, and any other termination event known to those skilled in the art. In this case, there is no need to monitor any changes in the operating parameters. Conversely, if power is detected, the motor is being powered. In some embodiments, when power is supplied to the power tool, the power tool may wait for a user input, such as pressing a trigger or selecting an operating mode to control the motor to operate at a particular frequency. Alternatively, the power tool may automatically begin operating at a particular frequency. As described below, the output frequency will be adjusted due to additional input from the user, or feedback of a predetermined change in an operating parameter.

If the power is on, the sensor monitors a first operating parameter, such as motor current, indicative of a first operating parameter value in step 208. In step 210, the value of the first operating parameter is compared to a given threshold to determine if there is a predetermined change in the first operating parameter. As described above, the predetermined change in the first operating parameter may be determined when a) the first operating parameter increases above a predetermined threshold; b) When the first operating parameter falls below a predetermined threshold; c) The rate of increase of the first operating parameter is above a predetermined threshold; d) A rate of decrease of the first operating parameter drop below a predetermined threshold, and e) a comparison of the operating parameter being above, equal to, or below the predetermined threshold. For example, if the value of the first operating parameter is equal to or below a certain threshold (as in the case of current limiting), the controller determines that the motor is operating properly. Thus, the loop of the method will return to step 201. On the other hand, if the value of the first operating parameter exceeds the threshold, the controller determines the predetermined change and adjusts the output of the power tool accordingly in step 230.

In some embodiments, to determine the rate of acceleration or deceleration of the first operating parameter, the controller may compare a mathematical function of the first operating parameter (e.g., a first or second derivative of the first operating parameter, such as the rate of change of the first operating parameter) to a threshold value in step 210. In another variation, the first operating parameter threshold may vary depending on other tool states (e.g., motor speed or mode of transmission). Then, in step 230, control generates a regulated output of the power tool. In step 230, the step of adjusting the output of the power tool comprises the operations of: a) changing the output pulse width modulation frequency, b) interrupting the power supply to the motor, c) increasing or decreasing the power supply 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. It will be readily appreciated that other techniques for adjusting the output of the power tool are also within the scope of the present invention.

Referring to FIG. 4, a second exemplary method 300 for adjusting the output of a power tool is shown. For the sake of brevity, only the differences of the method 300 compared to fig. 3 are described.

Steps

301, 302, 304, 308, 310 and 330 are largely analogous to their counterparts in fig. 3, with some differences as described below. In the method 300, the various operational parameters relate to priorities. For example, a first operating parameter, such as motor current, is a more basic operating parameter than a second operating parameter, such as motor temperature, for identifying any determined change. Thus, as shown in steps 300 through 310, a first operating parameter will first be sensed and monitored. If the monitored first operating parameter is determined to be a predetermined change, then in step 330, the controller will adjust the output of the power tool regardless of the value of the second operating parameter.

On the other hand, if the first operating parameter is determined to be normal, then the sensor monitors the second operating parameter in step 312. In step 314, the value of the second operating parameter is compared to a given threshold to determine if there is a predetermined change. For example, if the value of the second operating parameter is equal to or below the threshold, the controller determines that the motor is operating properly. Thus, the controller will return to start 301. On the other hand, if the second operating parameter exceeds the threshold, the controller determines that a predetermined change in the second operating parameter has occurred. Similar to method 200 in fig. 3, in step 314, the microcontroller compares the mathematical function of the second operating parameter. Then, in step 330, the controller generates a signal to adjust the output of the power tool. In method 300, more than two operating parameters may be monitored, such as motor current, temperature, voltage, and speed, which may all be considered in terms of relative priority.

Referring to FIG. 5, a third exemplary method 400 for adjusting the output of a power tool is shown. For the sake of brevity, only the differences of the method 400 compared to fig. 3 are described.

Steps

401, 402, 404, 408, 410 and 430 are largely similar to their counterparts in fig. 3, but any differences will be described below. In the method 400, the different operating parameters do not relate to priority. In other words, the controller adjusts the output of the power tool if any of the monitored operating parameters exceeds its given threshold. In method 400, more than two operating parameters may be monitored, such as motor current, temperature, voltage, and speed, which may all be considered without priority, as indicated by arrow 440. Meanwhile, in method 400, the outputs of the detected predetermined changes in the two different operating parameters are the same. Such a design saves memory space in the memory and makes the programming of the preset operating mode of the power tool more compact.

Referring to FIG. 6, a fourth exemplary method 500 for adjusting the output of a power tool is shown. For the sake of brevity, only the differences of method 500 compared to fig. 5 are described.

Steps

501, 502, 504, 508, 510, 512, 514 and 540 are largely similar to their counterparts in fig. 5, but any differences will be described below. In method 500, the different operating parameters do not relate to priorities. At the same time, different predetermined changes detected will result in different outputs of the power tool, as shown in

steps

510 and 520. For example, motor current is set to a first operating parameter and motor temperature is set to a second operating parameter. The controller varies the output pulse width modulation frequency if the motor current exceeds a given current threshold. If the temperature exceeds a given temperature threshold, the circuit again switches the output pulse width modulation frequency to interrupt the current operation of the motor to produce protection for the motor and power tool.

Specifically, in one embodiment, the motor is modulated by pulse width modulation signals having different frequencies, the modulation of the motor by pulse width modulation comprising at least one of: a) Changing the output pulse width modulation frequency; b) Applying a plurality of different drive modes (high speed, medium speed, low speed, etc.) to the motor; c) Applying a plurality of different pulse width modulation duty cycle times; d) A plurality of different pulse width modulation cycle times are applied. By such action, the output of the power tool is adjusted. Similar to method 400, in method 500, more than two operating parameters may be monitored, such as motor current, temperature, voltage, and speed, all of which may be considered without priority, as indicated by arrow 540.

Referring to FIG. 7, a fifth exemplary method 600 for adjusting the output of a power tool is shown. For the sake of brevity, only the differences of method 600 compared to fig. 4 are described.

Steps

601, 602, 604, 608, 610 and 630 are largely similar to their counterparts in fig. 4, but any differences will be described below. In method 600, two or more operating parameters are considered to adjust the output of the power tool, e.g., an instantaneous current exceeding a threshold as a first operating parameter may not be detrimental to the power tool, but a current exceeding the threshold over a given period of time as a second operating parameter should be monitored and the controller take the necessary control. If the current is monitored to exceed the threshold, the sensor continues to monitor the current for a period of time that exceeds the threshold, as shown in steps 610 through 630. If the time period is longer than the given value, control regulates the output of the power tool, such as changing the pulse width modulation duty cycle of the output, in step 630. If the time period is not longer than the given value, the method 600 will return to the beginning of the algorithm. Similar to the other embodiments described above, in method 600, the monitored operating parameter may be selected from motor current, temperature, voltage, speed, selection of operating mode, user action on the trigger (including releasing the trigger, lightly pressing, heavily pressing, or fully pressing the trigger), and a different range of pulse width modulation duty cycles (from 0% to 100%), and may be more than two. Meanwhile, when two different operating parameters (e.g., current and temperature) are selected, a technical effect of preventing a false notification or a false alarm can be achieved. In one variation, a combination of determinations of two or more parameter changes as described in

steps

608, 610, 620, and 622 may be packaged into one determination step and included as sub-steps in

steps

210, 310, 410, and 510 of

exemplary methods

200, 300, 400, and 500, as will be appreciated by those skilled in the art. In other words,

steps

210, 310, 410, and 510 may be considered a determination of more than one operating parameter as shown in method 600 and are not beyond the scope of the present application.

In one variation, in the above exemplary method, after the step of adjusting the output of the power tool (e.g., 230 or 630), the controller is further configured to continue monitoring the operating parameter, and if a further predetermined change is detected, such as the current falling below a given threshold for a given period of time, the controller is configured to again adjust the output of the power tool.

Referring to FIG. 8, a sixth exemplary method 700 for adjusting the output of a power tool is shown. For the sake of brevity, only the differences of method 700 compared to fig. 7 are described.

Steps

701, 702, 704, 708, 710 and 730 are largely similar to their counterparts in fig. 7, but any differences will be described below. The method 700 herein illustrates two or more output frequencies of the power tool determined by different conditions. After power is supplied to the power tool, the output of the power tool is modulated at the pulse width modulation frequency a, whether or not there is an input from the user, as shown in

steps

702 and 706. The first operating parameter is then monitored and compared to a threshold to determine if there is a predetermined change, such as the motor current exceeding the current limit, as shown in

steps

708, 710 and 730, and the controller then adjusts the output of the power tool by adjusting and maintaining the output of the power tool at the pulse width modulation frequency B in step 730. The controller and sensor then continue to monitor the second operating parameter of the power tool, and if a corresponding predetermined change is detected in step 722, the controller further adjusts the output of the power tool by adjusting the output of the power tool back to and maintaining it at the pulse width modulation frequency a. Similar to the other embodiments described above, in method 700, the monitored operating parameters may be selected from motor current, temperature, voltage, and speed, as well as other parameters related to the operation of the power tool, and may be more than two.

In one variation, the method 700 may be configured to monitor more than two operating parameters and switch to different output frequencies accordingly, as will be appreciated by those skilled in the art. In some embodiments, if a predetermined change in the second operating parameter is detected, the output frequency will change to a different frequency than A and B and will not be outside the scope of the present application.

In addition to the operating parameters described in the above exemplary methods, the operating parameters may also include user-provided inputs or controls, such as pressing an operator-actuatable trigger switch for controlling a motor power supply value, and selecting a preset operating mode of the power tool, including at least one of: a high speed mode, a medium speed mode, and a low speed mode. Thus, the output of the power tool can be controlled and regulated by user input as well as feedback from the power tool. For example, if the power tool is an electric screwdriver, the operating mode may be switched from a high pulse width modulated frequency to a lower pulse width modulated frequency output to drive other working members. Initially, the screwdriver was operated at a high pulse width modulation frequency for a period of time. When the sensor detects that the motor current exceeds the current threshold, the controller controls the output to switch to a lower pulse width modulation frequency to reduce the losses of the MOSFET switches.

In another embodiment, the power tool may include a battery pack, and the sensors may be capable of sensing the temperature, current, and voltage of the battery pack or the temperature of the output member as the monitored operating parameters. The controller may switch the output frequency of the motor when a predetermined change is detected, for example when the temperature of the battery pack is above a preset value, the output is switched to a lower pulse width modulation frequency to reduce the current, thereby achieving over-temperature protection and over-current protection of the power tool and the battery pack.

According to one example, as shown in FIG. 9, a seventh exemplary method 800 of regulating an output of a power tool via a pulse width modulated signal is shown. In this example, the pulse width modulation duty cycle is selected as the operating parameter, and the predetermined variation is determined as a variation in the pulse width modulation duty cycle. In step 802, the controller determines whether the pulse width modulation duty cycle is greater than 50%, and if so, in step 804 the power tool sets the pulse width modulation output frequency to 10K Hz as the first operating mode; if not, the power tool will set the pulse width modulated output frequency to 1K Hz in step 806, which is the second mode of operation. Then, in step 808, the power tool will determine whether the power tool has entered an over-current condition or a current limit condition or a motor stall condition via input from the user selected operating mode. If not, the method returns to step 802 to set the sensor and the controller continues to monitor the pulse width modulation duty cycle. If so, the controller will generate a signal to set the pulse width modulated output frequency to 2K Hz, which increases the output power of the output member. The controller can then determine whether the power tool has exited the over-current condition or the current limit condition or the motor stall condition by input from the user selected operating mode or by a feedback signal generated by the power tool itself. If not, the operating mode of the power tool remains unchanged. If so, the method returns to step 802 to set the sensor and the controller continues to monitor the pulse width modulation duty cycle. Those skilled in the art will appreciate that the detailed values of the above-described operating parameters, such as a 50% pulse width modulation duty cycle and a 10K Hz pulse width modulation output frequency, are presented for illustrative purposes only. Different values used, such as a 60% pulse width modulation duty cycle or different operating parameters, such as motor current or temperature of the MOSFET circuit, would not be outside the scope of the present application.

According to one example, as shown in fig. 10, one of the user inputs is to press an operator-actuatable trigger switch to control the controller 118 to set a duty cycle of a pulse width of the pulse width modulated signal corresponding to a change in an actuated position of the trigger switch. If the trigger switch is released, no pulse width modulation duty cycle is generated. Depending on the actuation position of the trigger switch, the pulse width modulation duty cycle is increased from a 0% level to a 100% level, thereby further regulating the output power or frequency of the motor. Meanwhile, a constant speed trigger may also be applied to the present invention. Those skilled in the art will appreciate that fig. 10 shows only an example of a pulse width modulated signal corresponding to varying trigger actuation positions. In other embodiments, the power tool may output a fixed pulse width modulated duty cycle signal or a varying pulse width modulated duty cycle signal controlled by the actuation position. Corresponding linear and piecewise linear relationships between the pulse width modulated signal and the varying trigger actuation positions are also within the scope of the invention.

Referring to FIG. 11, according to another example, the output power of the power tool is represented by pulse width modulation of a modulation motor. As shown, different pwm periods a, B, C are applied to regulate the output of the power tool according to different pwm frequencies. Each cycle corresponds to a preset operating mode or a specific operating mode of the power tool. The variation between different cycles is responsive to a predetermined variation in the selected operating characteristic to cause the output member to adjust the output.

Referring to fig. 12A through 12C, the pulse width modulated waveform includes one or more of: a) Pulse width modulation of constant duty cycle as shown in fig. 12A; b) A combination of increasing duty cycle pulse width modulation and decreasing duty cycle pulse width modulation as shown in fig. 12B and 12C.

As shown in fig. 12A, with constant duty cycle pulse width modulation, the output of the motor is operated at constant pulse width modulation, which indicates that the power tool is operating properly and no user input or power feedback control is generated to interrupt the current operation. Meanwhile, as shown in fig. 12A, the pulse width modulation frequency may be defined as 1/cycle time.

As shown in fig. 12B and 12C, in the case of a hybrid pulse width modulation signal having different duty ratios, where the output of the motor is varied from a low pulse width modulation frequency (which may correspond to a high rotational speed) for a period of time in fig. 12B, then a higher pulse width modulation frequency (which may correspond to a low rotational speed for a period of time) or a high pulse width modulation frequency for a period of time, and then a low pulse width modulation frequency for a period of time in fig. 12C. Thus, the power tool produces a varying frequency output to meet the different operating conditions shown in fig. 12B and 12C. The change between the low duty cycle and the high duty cycle is caused by a determined change in the operating parameter or user input as described above.

While the invention has been illustrated and described in detail in the drawings and foregoing description, 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 in any way. It is to be understood that any feature described herein may be used with any embodiment. The illustrative embodiments are not mutually exclusive or exclude other embodiments not enumerated herein. Accordingly, the present invention also provides embodiments that include combinations of one or more of the above illustrative embodiments. Modifications and variations may be made to the invention described herein without departing from the spirit and scope of the invention, which should therefore be limited only by the appended claims.

Claims

1. A power tool, comprising:

an output member capable of producing an output of,

a motor capable of driving the output member, an

A control system capable of controlling operation of the motor, the control system comprising:

a power supply and a power switching device interconnecting the power supply and the motor, the power switching device being capable of applying a pulse width modulated drive signal from the power supply to the motor, an

A controller configured to control the power switching device, monitor at least one operating characteristic of the power tool, and adjust the frequency of the pulse width modulated drive signal in response to a predetermined change in the operating characteristic, thereby causing the output member to adjust the output.

2. The power tool of claim 1, wherein the operating characteristic comprises at least one of: input from a user, and operating parameters of the power tool.

3. The power tool of claim 2, wherein the input from the user includes at least one of pressing an operator-actuatable trigger switch that controls a value of power provided to the motor and selecting a preset operating mode of the power tool, the preset operating mode including at least one of: high speed mode, medium speed mode, and low speed mode.

4. The power tool of claim 3, wherein the predetermined change includes changing an actuation position of the trigger switch.

5. A power tool according to claim 3, wherein the predetermined change comprises changing the selected preset operating mode.

6. The power tool of claim 2, wherein the operating parameter comprises at least one of: a temperature of the motor, a temperature of the power switching device, a current flowing through the motor, a voltage across the motor, a value of a pulse width modulation duty cycle, and a rotational speed of the motor.

7. The power tool of claim 6, wherein the predetermined change comprises an increase in the operating parameter above a respective predetermined threshold.

8. The power tool of claim 6, wherein the predetermined change comprises the operating parameter falling below a respective predetermined threshold.

9. The power tool of claim 6, wherein the predetermined change corresponds to a rate of increase of the operating parameter above a respective predetermined threshold.

10. The power tool of claim 6, wherein the predetermined change corresponds to a rate of decrease of the operating parameter being below a respective predetermined threshold.

11. The power tool of claim 6, wherein the predetermined change comprises a comparison of the operating parameter being above, equal to, or below a respective threshold.

12. The power tool of claim 1, wherein the output is regulated by varying an output pulse width modulation duty cycle and/or an output pulse width modulation frequency.

13. The power tool of claim 2, wherein the controller is configured to control the output member to enter and remain in a closed state in response to a predetermined change in a primary operating parameter of the power tool.

14. The power tool of claim 11, wherein the main operating parameters of the power tool are selected from the following parameters: a temperature of the motor, a temperature of the power switching device, a current flowing through the motor, a voltage across the motor, a value of a pulse width modulation duty cycle, and a rotational speed of the motor.

15. A method of controlling a power tool having a motor driven by a pulse width modulated drive signal and capable of driving an output member to produce an output, wherein the motor is driven by a power supply and a power switching device interconnected with the power supply to apply the pulse width modulated drive signal from the power supply to the motor, the method comprising:

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

Adjusting a frequency of the pulse width modulated drive signal in response to a predetermined change in the operating characteristic to adjust the output of the output member by the controller.

16. The method of claim 15, wherein the operating characteristics include at least one of: input from a user, and operating parameters of the power tool.

17. The method of claim 16, wherein the input from the user comprises at least one of pressing an operator-actuatable trigger switch that controls a value of power provided to the motor and selecting a preset operating mode of the power tool, the preset operating mode comprising at least one of: a high speed mode, a medium speed mode, and a low speed mode.

18. The method of claim 17, wherein the predetermined change comprises changing an actuation position of the trigger switch.

19. The method of claim 17, wherein the predetermined change comprises changing the selected preset operating mode.

20. The method of claim 16, wherein the operating parameters include at least one of: a temperature of the motor, a temperature of a power switching device, a current flowing through the motor, a voltage across the motor, a value of a pulse width modulation duty cycle, and a rotational speed of the motor.

21. The method of claim 20, wherein the predetermined change comprises an increase in the operating parameter above a respective predetermined threshold.

22. The method of claim 20, wherein the predetermined change comprises a decrease in the operating parameter below a corresponding predetermined threshold.

23. The method of claim 20, wherein the predetermined change corresponds to a rate of increase of the operational parameter being above a respective predetermined threshold.

24. The method of claim 20, wherein the predetermined change corresponds to a rate of decrease of the operational parameter being below a respective predetermined threshold.

25. The method of claim 20, wherein the predetermined change comprises a comparison of the operating parameter being above, equal to, or below a respective threshold.

26. The method of claim 15, wherein the output is regulated by varying an output pulse width modulation duty cycle and/or an output pulse width modulation frequency.