CN110417324B

CN110417324B - Electric drill

Info

Publication number: CN110417324B
Application number: CN201810665544.8A
Authority: CN
Inventors: 陈伟鹏; 杨德中; 李文成
Original assignee: Nanjing Chervon Industry Co Ltd
Current assignee: Nanjing Chervon Industry Co Ltd
Priority date: 2018-04-28
Filing date: 2018-06-26
Publication date: 2022-01-04
Anticipated expiration: 2038-06-26
Also published as: CN110405702A; CN110405250A; CN110405250B; CN110417325A; CN110417324A; CN110417330B; CN110417331A; CN110417331B; CN110417330A; CN110417325B

Abstract

The invention discloses an electric drill. According to the invention, duty ratios under different working conditions are determined according to the analysis of the characteristic parameters of the motor of the electric drill, particularly the rotating speed n of the motor, and the duty ratios are used for controlling the driving circuit to drive the motor to operate. The invention can realize the optimized control of the motor by adjusting the duty ratio only through calculating the duty ratio without changing circuit hardware or mechanical structure of the electric tool, thereby realizing the optimization of working performances such as output torque of the electric tool.

Description

Electric drill

Technical Field

The invention relates to the field of electric tools, in particular to an electric drill.

Background

The existing electric tool can be powered by a battery pack and drives a motor to operate through a driving circuit. However, in the current electric tool, especially the handheld electric tool based on the 1P battery pack, the impact current of the battery pack and the output torque of the motor are difficult to control under a heavy load condition.

The maximum impact current of the existing electric tool, particularly a circular saw or an electric drill, under the locked-rotor state can reach 100A or even more. The high rush current will seriously damage the power supply means of the power tool, such as a battery pack, thereby affecting the safety of the power tool.

Therefore, due to safety consideration, an overload protection device is arranged in the conventional electric tool, but the device can directly turn off the motor when the heavy load state of the electric tool reaches a preset threshold value so as to avoid impact on the power supply device caused by the current on the motor side. In this overload protection mode, the motor is generally required to be turned off when the maximum output torque of the handheld electric tool reaches 3.5n.m, that is, the electric tool can actually bear a load of only 3.5 n.m. Under the heavy load condition, the anti-stalling ability and the user experience of the existing electric tool are difficult to meet the requirements.

Therefore, there is an urgent need to improve the maximum output torque of the electric power tool.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide an electric drill.

In order to achieve the above object, the present invention adopts the following technical solutions:

the present invention provides firstly an electric drill comprising: a motor including a stator and a rotor; a transmission for connecting the rotor with a drill bit; the driving circuit is used for outputting a switching signal to drive a rotor of the motor to operate; the control unit is used for outputting a driving signal to control the driving circuit; and the power supply device supplies power to the motor, the drive circuit and the control unit. Wherein the control unit is arranged to determine a change Δ PWM of the duty cycle from a change Δ n of the motor speed, wherein the change Δ PWM of the duty cycle is obtained by a function f (Δ n), wherein the change Δ PWM of the duty cycle is in a range of 0.02 to 0.05; and outputting a corresponding driving signal to the driving circuit based on the change quantity delta PWM of the duty ratio to control the rotor of the motor to operate and output the driving force. Thereby, the maximum impact current of the drill may be no more than 30A, and/or the stalling current of the drill may be no more than 50A.

Optionally, the electric drill further comprises a motor detection module; the motor detection module is used for detecting and obtaining the motor rotating speed n; the motor detection module is integrated in the control unit or is separately listed outside the control unit.

Optionally, in the electric drill, the motor speed is obtained by the motor detection module through calculation by detecting a voltage and/or a current and/or a rotor position of the motor, where the voltage of the motor includes a terminal voltage and/or a phase voltage of the motor, and the current of the motor includes a bus current and/or a phase current of the motor.

Optionally, in the electric drill, the power supply device includes a battery pack with a number of stages of 1P.

Optionally, in the electric drill, the duty ratio of the driving signal is determined by the following steps: firstly, according to the characteristic parameters of the power supply device in the electric drill and/or the electricityCharacteristic parameters of the electric drill are calculated, the duty ratio of a driving signal in the electric drill and the side current I of the power supply device under different working conditions of the power supply device and/or the motor under different working conditions are calculated_bThe relationship between and/or the duty cycle of the drive signal and the motor side current I_mThe relationship between; then, according to the duty ratio of the driving signal and the current I of the power supply device side_bThe relationship between and/or the motor-side current I_mThe duty ratio of the driving signals is determined to be the same motor side current I_mSide current I of lower and power supply device_bThe duty cycle corresponding to the smaller.

Optionally, in the electric drill, if the motor rotation speed n is in a low rotation speed and heavy load state, the current I on the power supply device side and the duty ratio of the driving signal are used to drive the motor to rotate_bThe duty ratio of the drive signal and the motor side current I_mDetermining the duty ratio of the driving signal as the motor side current I under the working condition_mThe maximum corresponding duty cycle.

The invention also provides another electric drill, which comprises: a motor including a stator and a rotor; a transmission for connecting the rotor with a drill bit; the driving circuit is used for outputting a switching signal to drive a rotor of the motor to operate; the control unit is used for outputting a driving signal to control the driving circuit; and the battery pack is used as a power supply device for supplying power to the motor, the driving circuit and the control unit. Wherein the control unit is configured to determine a variation Δ PWM of a duty ratio according to a variation Δ n of the motor rotation speed, wherein the variation Δ PWM of the duty ratio is obtained by a function f (Δ n), and the variation Δ PWM of the duty ratio is in a range of 0.05 to 0.08, and output a corresponding driving signal to the driving circuit based on the variation Δ PWM of the duty ratio to control the rotor of the motor to operate and output the driving force.

The invention also provides another electric drill, which comprises: a brushless motor including a stator and a rotor; a transmission for connecting the rotor with a drill bit; the driving circuit is used for outputting a switching signal to drive the rotor of the brushless motor to operate; the control unit is used for outputting a driving signal to control the driving circuit; and the power supply device is used for supplying power to the brushless motor, the drive circuit and the control unit. Wherein the control unit is arranged to determine a change in duty cycle Δ PWM from the change in the motor characteristic parameter Δ x, wherein the change in duty cycle Δ PWM is obtained by a function f (Δ x); and outputting a corresponding driving signal to the driving circuit based on the change quantity delta PWM of the duty ratio to control the rotor of the brushless motor to operate and output the driving force. Wherein the variation Δ PWM of the duty ratio is in the range of 0.02-0.08

Optionally, the power drill as described above, has an output torque capacity of not less than 5 n.m.

Optionally, in the electric drill, the motor characteristic parameter x includes: motor speed, current, output torque.

An electric drill comprising: a motor including a stator and a rotor; a transmission for connecting the rotor with a drill bit; the driving circuit is used for outputting a switching signal to drive a rotor of the motor to operate; the control unit is used for outputting a driving signal to control the driving circuit; and the power supply device supplies power to the motor, the drive circuit and the control unit. Wherein the control unit is arranged to determine a change in duty cycle Δ PWM from a change in motor speed Δ n, wherein the change in duty cycle Δ PWM is obtained by a function f (Δ n), wherein the change in duty cycle Δ PWM is in a range of 0.02 to 0.08; and outputting a corresponding driving signal to the driving circuit based on the change quantity delta PWM of the duty ratio to control the rotor of the motor to operate and output the driving force.

Advantageous effects

According to the method, the duty ratios under different working conditions are determined according to the analysis of the characteristic parameters of the motor. When the electric tool, such as a circular saw or an electric drill, is used, the corresponding duty ratio can be directly obtained in a table look-up or calculation mode according to the motor characteristic parameter x obtained in real time, and the corresponding driving signal is output according to the duty ratio to control the motor to operate, so that the performance of the electric tool is optimized.

The invention obtains the corresponding power supply device characteristic parameter V and the motor characteristic parameter x by utilizing the existing circuit hardware or mechanical structure of the electric tool, and can obtain the corresponding duty ratio data to realize the optimal control of the motor only by adding simple table look-up or operation control. In particular, the maximum output torque of the electric power tool can be controlled to be not less than 5 n.m.

Drawings

Fig. 1 is an external structural view of a first embodiment of a power drill according to the present invention;

FIG. 2 is a schematic diagram of circuitry within a first embodiment of the present invention;

FIG. 3 is a schematic view of the external structure of a circular saw according to a second embodiment of the present invention;

FIG. 4 is a schematic diagram of circuitry in a second embodiment of the present invention;

FIG. 5 is a schematic view of an external structure of an angle grinder according to a third embodiment of the present invention;

FIG. 6 is a schematic diagram of circuitry in a third embodiment of the present invention;

FIG. 7 is a schematic diagram of a simulation system of the present invention;

FIG. 8 is a schematic basis for selecting a PWM duty cycle in a first state of the simulation system;

fig. 9 is a flowchart illustrating a motor control method according to a first embodiment of the present invention;

FIG. 10 is a graph comparing the maximum rush current of the first embodiment of the present invention compared to the prior art;

FIG. 11 is a comparison of the reloading torque of the first embodiment of the invention compared to the prior art;

fig. 12 is a comparison of a locked rotor test of the first embodiment of the present invention compared to the prior art.

Detailed Description

The invention is described in detail below with reference to the figures and the embodiments.

The motor control method and the motor control system provided by the invention can be suitable for most of hand-held electric tools. The duty ratios corresponding to different working conditions are obtained only by analyzing the characteristic parameters V and/or the motor characteristic parameters x of the power supply device, and in the process of the electric tool, the driving circuit is controlled to drive the motor to operate according to the duty ratios corresponding to the characteristic parameters V and/or the motor characteristic parameters x of the power supply device, which are obtained in real time, so that the maximum impact current of the electric tool and the maximum output torque of the electric tool can be optimized.

The following describes specific embodiments of the present invention by taking three typical electric tools as examples.

In a first embodiment of the present invention, in combination with fig. 1, there is provided an electric drill, which has a mechanical structure specifically including: housing 11, output member 12, motor 13, transmission assembly 14, PCB (Printed Circuit Board) Circuit Board 15, and power supply device 16. Wherein, the housing 11 is used for accommodating the motor 13, the transmission assembly 14, the PCB circuit structure and the like, and one end of the housing 11 is also used for installing the output member 12. In the view shown in fig. 1, the motor 13, the PCB circuit structure 15 and the power supply device 16 are shielded by the housing 11 and are not directly exposed to the view shown in fig. 1. In the front-rear direction, the housing 11 may further include a main housing portion 111 and a head housing portion 112, wherein the main housing portion 111 may be used for accommodating the motor 13, the transmission assembly 14, and the PCB circuit structure 15, and the head housing portion 112 may be connected to the output member 12. In the left-right direction, the main housing part 111 may be symmetrically disposed with respect to a cross-section of the structure shown in fig. 2, and at both sides of the cross-section, the main housing part 111 may include a left housing part and a right housing part, respectively, which are symmetrical to each other. The output member 12 is for outputting power, for example, for a power drill, the output member 12 may be specifically selected to be a chuck capable of holding a drill bit. The motor 13, the transmission assembly 14 and the PCB circuit structure 15 are all arranged in the shell 11, the power supply device 16 is used for supplying power to all electronic devices in the electric drill, the PCB circuit structure 15 is used for controlling the motor 13 to operate, the motor 13 is used for driving the transmission assembly 14, and the transmission assembly 14 is used for transmitting power output by the motor 13 to the output piece 12 so as to drive the output piece 12 to output the power.

For controlling the operation of the motor 13, referring to fig. 2, the PCB circuit structure 15 may specifically include the following circuit hardware: the device comprises a power supply control module, a power supply device detection module, a control unit, a drive circuit and an optimal duty ratio storage device. The power control module, the power supply device detection module, the control unit, the drive circuit, the optimum duty cycle storage device and the motor 13 are all enclosed by the housing 11.

The power supply 16 of the hand-held power drill shown in fig. 2 may be selected from a battery pack, which may be formed by combining a plurality of battery cells, or an ac power source. For example, in the present embodiment, the battery units may be connected in series to form a single power branch to form a 1P battery pack. The output voltage of the battery pack is subjected to voltage change through a specific power supply control module, and the power supply voltage suitable for a power supply device detection module, a control unit, a driving circuit, an optimal duty ratio storage device, a motor and the like is output to supply power for the power supply device detection module, the control unit, the driving circuit, the optimal duty ratio storage device, the motor and the like. Those skilled in the art will appreciate that the power supply 16 may alternatively be an ac power source, which converts the input ac power via a corresponding power control module, and may also supply power to the power supply detection module, the control unit, the driving circuit, the optimal duty cycle storage device, the motor, and the like.

The power control module can select a special power chip, or directly realize the purpose by processing alternating current signals output by the power supply through a hardware circuit, such as rectification, filtering, voltage division, voltage reduction and the like by taking an alternating current power supply as an example.

Referring to fig. 2, the driving circuit is electrically connected to the three-phase electrode U, V, W of the motor 13 to drive the motor. The driving circuit specifically comprises a switching circuit, and the switching circuit is used for outputting a driving signal to a three-phase electrode of the motor according to the control of the controller so as to control the rotor of the motor to operate. The driving circuit has an input terminal, an output terminal, and a sampling terminal. As shown in fig. 2, the switching circuit includes switching elements VT1, VT 2, VT 3, VT 4, VT 5, VT 6. The switching elements VT1 to VT 6 may be field effect transistors, IGBT transistors, or the like. In this embodiment, taking a field effect transistor as an example, the gate terminal of each switching element is used as the input terminal of the driving circuit, and is electrically connected to the driving signal port of the controller, and each drain or source of the switching element is electrically connected to the stator of the motor. The switching elements VT 1-VT 6 change the conducting state according to the driving signal output by the controller, thereby changing the voltage state loaded on the brushless motor winding by the battery pack and driving the motor 13 to operate.

In order to rotate the motor, the driving circuit has a plurality of driving states, in a driving state, the stator of the motor generates a magnetic field, and the control unit is configured to output a corresponding driving signal to the driving circuit according to a rotor rotation position of the motor (a rotor rotation position of the motor, which can be obtained by sampling a bus current of the motor and/or a terminal voltage of the motor and performing corresponding calculation by a motor detection module in the controller in the embodiment) so as to switch the driving states of the driving circuit, so that the magnetic field generated by the stator rotates to drive the rotor to rotate, thereby driving the motor.

Wherein the control unit is arranged to determine the change in duty cycle Δ PWM primarily from the change in the motor characteristic parameter Δ x, wherein the change in duty cycle Δ PWM is obtained by a function f (Δ x).

Alternatively, the control unit may be further configured to determine a change amount Δ PWM of the duty ratio based mainly on the change amount Δ x of the motor characteristic parameter and the power supply device characteristic parameter V, wherein the change amount Δ PWM of the duty ratio is obtained by a function f (Δ x, V).

Optionally, the control unit may be further configured to determine a change amount Δ PWM of the duty ratio according to the change amount Δ x of the motor characteristic parameter, the number P of battery pack stages, and the power supply device characteristic parameter V, wherein the change amount Δ PWM of the duty ratio is obtained by a function f (Δ x, V, P).

The function operation result of the characteristic parameters of the motor and the like can be stored in the optimal duty ratio storage device in advance and obtained by the control unit by inquiring the optimal duty ratio storage device. The duty cycle adjustment process can refer to fig. 9:

firstly, a motor detection module samples a motor and calculates to obtain a motor characteristic parameter x. The motor characteristic parameter x may include, but is not limited to: motor speed n, stator or rotor position, torque, motor current, etc. And calculating to obtain the optimal duty ratio corresponding to the working condition of the gear according to the actual working condition of the battery pack and the motor characteristic parameter x through a function f (delta x), determining a corresponding PWM (Pulse Width Modulation) driving signal according to the duty ratio, and outputting the corresponding driving signal to a driving circuit according to the rotating position of the motor rotor and the duty ratio. The drive circuit thus drives the motor in accordance with the drive signal.

Here, the optimum duty ratio may be fixedly stored in the storage device. For example, according to the analysis of the motor characteristic parameter x, the optimal duty ratio obtained by calculating the function f (Δ x) under different working conditions is stored in advance to form a PWM table. Therefore, the controller can obtain the duty ratio by directly inquiring corresponding data in the storage device, and the performance of the current electric drill can be optimized by outputting corresponding driving signals according to the duty ratio. Specifically, the selection of the optimal duty ratio under different working conditions can realize the current I on the power supply side_bAnd motor side current I_mAnd (4) optimizing. For example, by adjusting the duty cycle by the function f (Δ x), the same motor side current I can be obtained_mWhen the motor performance is the same, the current I on the power supply side is enabled_bSmaller, i.e. a more power-supply friendly duty cycle. By selecting the duty ratio of the corresponding PWM-type driving signal in the mode, the invention can effectively control the maximum impact current of the battery pack through the selection of the duty ratio, and ensure the maximum torque output by the motor when needed, thereby achieving the optimization of the overall working performance of the electrical tool. The optimal duty cycle under different conditions will be described in detail below with reference to the principles shown in fig. 7 and 8.

In the circuit hardware of the embodiment, the power supply device detection module, the motor detection module and the optimal duty ratio storage device can be realized by using a special chip, and can also be directly realized in the control unit through a functional module integrated in the control unit. The control Unit can select a corresponding DSP (Digital Signal Processor, Digital Signal processing) chip, an ARM (Advanced Instruction Set Computer, Reduced Instruction Set Computer) Machine (RISC microprocessor) chip, a single chip microcomputer (MCU, micro control Unit, Microcontroller Unit), and the like to implement according to the requirement of the electric tool for processing the internal data Signal.

In the electric drill to which the above-described technique is applied, in the maximum impact current test, referring to the experimental data comparison chart shown in fig. 10, in a state where the torque reaches 3n.m or more, the maximum impact current can be restricted to be kept at 30A or less (solid line in fig. 10). With prior art power drills (shown in phantom in figure 10), the maximum impact current increases with torque, quickly exceeding the 30A limit. Excessive impact current can damage the power supply of the drill. Particularly, the temperature of the battery pack can be significantly increased under the condition of direct current power supply, and the service life of the battery pack is influenced. By adopting the technology of the invention, the electric drill is still friendly to the battery pack under the heavy load state of large torque, and the irreversible damage of overcurrent and temperature rise to the battery pack can be effectively avoided.

Fig. 11 is a graph showing the comparison of the maximum torque output of the electric drill to which the present invention is applied in a heavy load state, compared with the prior art. The drill shown in figure 11 using the prior art overload protection mechanism (solid line in figure 11) is implemented such that after the output torque reaches 3.7n.m, the protection is activated by the overload, causing the motor to stall. The electric drill using the technology of the invention (the curve marked with a triangle in fig. 11) always controls the current below the overload threshold value under the heavy load state, so the output torque of the electric drill can reach nearly 6N.m, which is nearly 2 times of the prior art.

Fig. 12 is comparative data of a locked rotor test performed by an electric drill using the technique of the present invention, compared to the prior art. When the motor is completely locked, the rotating speed is close to 0 or the back electromotive force is close to 0, the electric drill (shown in dark color in figure 12) in the prior art is applied, the output torque is only 33N.m, and the maximum impact current is as high as 100A; compared with the prior art, the output torque of the electric drill (shown in light color in fig. 12) adopting the technology of the invention is improved by 10 percent and reaches 36N.m, and the maximum impact current is reduced by 30 percent and is only 70A, so that the electric drill is more friendly to a battery pack.

In a second embodiment of the present invention, in combination with the handheld circular saw shown in fig. 3, the mechanical structure of the handheld circular saw specifically includes:

a base plate 20 for contacting a workpiece; a chassis 21 mounted on the base plate; a blade cover 213 connected to the housing; a saw blade shaft 22 for supporting the saw blade in the blade housing to rotate so as to cut the workpiece; the motor 23 is arranged in the shell and comprises a stator and a rotor; a motor shaft 231 driven by a rotor of the motor; and the transmission device 24 is used for connecting the motor shaft and the saw blade shaft and transmitting the rotary motion of the motor shaft to the saw blade shaft so as to drive the saw blade to run. The transmission may specifically comprise a reduction mechanism, such as a worm gear and worm meshing with each other, or a reduction gearbox. The worm gear or the reduction box can comprise gear structures with different gear ratios or synchronous belt transmission structures with different synchronous wheel radiuses. In a preferred embodiment of the present invention, the motor is a brushless motor.

The operation of the hand held circular saw also relies on the electronic components being mounted on the PCB 25 which is contained within the housing 21 and not exposed to the view shown in fig. 3. Referring to fig. 4, the PCB 25 specifically includes the following circuit hardware: the device comprises a power supply control module, a battery detection module, a controller and a driving circuit. The power control module, the battery detection module, the controller and the driving circuit motor 23 are all sealed by the casing 21. The controller also stores, temporarily stores or buffers PWM table data, and the PWM table data comprises duty ratio data of PWM modulation signals, namely duty ratio data of driving signals, generated according to a function f (-) under different power supply device characteristic parameters V and/or different motor characteristic parameters x.

Referring to fig. 4, the electronic components of the hand-held circular saw work together in a manner similar to the electronic devices in the power drill of the first embodiment. The difference is that the control unit is specifically selected as a controller with a storage function in this embodiment, and in this embodiment, the circular saw is directly powered by the battery pack, and the rotational position of the rotor in the motor is directly obtained by the position sensor, so that the rotational speed information of the motor can be obtained by simply calculating through the controller. The motor speed n can therefore be selected as a specific motor characteristic. Therefore, the motor characteristic parameter x can be detected and calculated through the position sensor signal, and in the embodiment, the detection of the motor rotating speed n is specifically referred to. Therefore, in the embodiment, a step of sampling the bus current, the phase current or the terminal voltage of the motor in the embodiment can be omitted, and a complex operation process of the controller on the sampling signals is omitted. The detection of the motor speed n by the motor detection module can be realized by a simple calculation in the position sensor and the controller, such as accumulation, timing or integral operation.

The duty ratio of the drive signal output by the controller is obtained by looking up the PWM table as a simplification of the calculation of the function f (Δ x, V), similarly to the first embodiment. The query process can refer to fig. 9 as well:

firstly, a battery detection module samples and obtains an actual working condition of a battery pack, such as a battery pack voltage V, as a specific characteristic parameter of a power supply device, of course, the characteristic parameter V of the power supply device is not limited to the battery pack voltage, and may also be selected from a voltage of the power supply device, a battery pack current, a temperature, a remaining power amount, a battery pack SOC parameter (SOC, State of Charge, which is generally a ratio of a battery pack charging capacity to a rated capacity), an internal resistance of the power supply device, and the like; the rotation position of the motor rotor is obtained by the position sensor, and the rotation speed n of the motor is obtained as a specific motor characteristic parameter x by calculating the change rate of the rotor position by matching with the controller. And then searching a gear corresponding to a PWM table according to the voltage V of the battery pack and the rotating speed n of the motor, so that the optimal duty ratio corresponding to the function f (delta n, V) calculation under the working condition can be obtained, a corresponding driving signal in a PWM form is determined according to the duty ratio, and the corresponding driving signal is output to a driving circuit according to the duty ratio according to the rotating position of a rotor of the motor. The drive circuit thus drives the motor in accordance with the drive signal. In the function f (Δ n, V), Δ n represents the amount of change in the motor rotation speed.

Specifically, in this embodiment, the duty ratio data corresponding to the function f (Δ n, V) value stored in the PWM table may be stored according to the following table structure. Each unit of the table may store the optimal duty ratio corresponding to different working conditions, that is, for the present embodiment, store the duty ratio data corresponding to different battery pack voltages V and different motor rotation speeds n. For example, when the battery detection module obtains that the actual working condition of the battery pack falls into the V1 gear of the voltage condition of the battery pack, and the control module determines that the motor characteristic parameter x falls into the N3-N4 gears according to the motor detection module or the position sensor, the controller checks a table, correspondingly selects the duty ratio duty2 to output a driving signal to the driving circuit, and the driving circuit drives the motor to operate according to the driving signal. Here, the specific selection of duty ratios (duty1, duty2, … …) by the function f (Δ n, V) will be specifically analyzed in the following embodiment in conjunction with the principles shown in fig. 7 and 8.

The PWM table storage device can be realized by a cache, a storage unit, an internal memory and the like in the electric tool, and can also be updated and cached in real time by a cloud in a wireless mode.

TABLE 1

Comparing the duty ratio data in the table above, it can be seen that the variation Δ PWM of the duty ratio of each gear is in the range of 0.02 to 0.08. More specifically, when the motor speed n is selected as a specific motor characteristic parameter, the change Δ PWM of the duty ratio and the change Δ n of the motor speed may have the following relationship: when the delta n change interval is 500-1000rpm, the corresponding duty ratio change interval is in the range of 0.02-0.05; when the delta n change interval is 1000-1500rpm, the corresponding duty ratio change interval is in the range of 0.05-0.08. The control unit outputs a corresponding driving signal to the driving circuit based on the variation delta PWM of the duty ratio to control the rotor of the motor to operate and output driving force. Since the duty ratio is adjusted from 0.02 to 0.08 according to the function f (Δ n, V), the same motor side current I can be obtained_mWhen the motor performance is the same, the current I on the power supply side is enabled_bSmaller, i.e. a more power-supply friendly duty cycle. By selecting the duty ratio of the corresponding PWM-type driving signal in the mode, the invention can effectively control the maximum impact current of the battery pack through the selection of the duty ratio, and ensure the maximum torque output by the motor when needed, thereby achieving the optimization of the overall working performance of the electrical tool.

Those skilled in the art will appreciate that different power tools may have different parameters and different battery packs may have different characteristics, and thus different duty cycle variations may be matched, for example, a duty cycle variation range of 0.02-0.05 may be selected to match one power tool parameter in one embodiment, and a duty cycle variation range of 0.05-0.08 may be selected to match another power tool parameter in another embodiment.

In a third embodiment of the present invention, an application of the motor control technique of the present invention to an electric tool will be described with reference to fig. 5, which shows an electric tool represented by an angle grinder.

The mechanical structure of the electric power tool shown in fig. 5 specifically includes:

a housing 31, a motor 33, an output member 32, and a circuit member 35. Of course, in the present embodiment, for the angle grinder, the transmission device 34 and the clamping device 36 may be further included.

Wherein, the housing 31 is formed with a containing cavity 313 for containing the motor 33, the transmission 34 and the circuit component 35, and the housing 31 can be formed with a handle for being held by a user. For an angle grinder, the housing 31 may be generally in the shape of a straight line. The motor 33 is used for driving the output member 32 to output power, and the motor 32 may further include a motor shaft for outputting power. The output member 32 is used to output power to the gripping device 36, thereby driving the gripping device 36 to rotate. The transmission 34 is used to transmit power between the motor shaft of the motor 33 and the output member 32. A clamping device 36 can mount the abrasive sheet to output member 32 to cause the abrasive sheet to abrade the workpiece as carried by output member 32. The housing 31 may further include a fan for dissipating heat generated by the heat generating device inside the electric tool, so as to ensure that the angle grinder can operate in a normal thermal environment.

The operation of the angle grinder also relies on the coordinated control of the various electronic components mounted on the circuit member 35. The circuit component 35 is accommodated in the housing 31, and as shown in fig. 6, the circuit component 35 specifically includes the following circuits: the device comprises a power control chip, a battery detection module, a motor detection module, a controller and a drive circuit. The power control chip, the battery detection module, the motor detection module, the controller, the driving circuit and the motor 33 are all enclosed by the shell 31.

Referring to fig. 6, the circuit modules in the angle grinder all work in a coordinated manner similar to the electronic devices in the power drill of the first embodiment. The difference is that in this embodiment, the motor detection module is separately disposed outside the controller, and the function of the power supply device detection module, that is, the function of detecting the battery, is implemented through a sampling port inside the controller. In this embodiment, the motor detection module may obtain the rotor rotation position or the motor rotation speed according to the motor by sampling the phase current and/or the terminal voltage of the motor and matching with corresponding calculation, and reflect the motor characteristic parameter x with the motor rotation speed n. In this embodiment, the magnitude of the current signal output by the battery pack can be collected by the sampling resistor R3 serially connected to one side of the battery pack, and the current signal is input to the battery detection module, and the battery detection module uses the battery pack current, the number of stages P, and the like obtained by calculation as the characteristic parameters V of the power supply device. The controller performs a function operation according to the electrode rotation speed n, the power supply device characteristic parameter V, and the number P of battery pack stages to obtain a variation Δ PWM ═ f (Δ n, V, P) of the corresponding duty ratio, and determines the duty ratio accordingly. To simplify the calculation, the characteristic parameters of the power supply device in the present embodiment may also be calculated by selecting the battery pack voltage. And calculating to obtain a duty ratio according to the function delta PWM (pulse width modulation) ═ f (delta n, V, P), and outputting a corresponding driving signal to the driving circuit according to the duty ratio and the rotor rotation position of the motor so as to enable the driving circuit to switch the driving state, so that the magnetic field generated by the stator rotates to drive the rotor to rotate, and further the motor is driven.

Specifically, the duty ratio of the driving signal output by the controller is obtained by performing a function operation on a variation Δ PWM ═ f (Δ n, V, P) of the duty ratio:

firstly, a battery detection module samples and acquires the actual working condition of a battery pack, such as the voltage V of the battery pack; and calculating and obtaining a motor characteristic parameter x, such as the motor speed n, by the motor detection module. And then calculating and obtaining the variation delta PWM (pulse width modulation) of the duty ratio corresponding to the working condition according to the battery pack voltage V, the motor rotating speed n and the battery pack grade number P, and calculating and obtaining a corresponding optimal duty ratio according to the variation delta PWM, and adjusting a PWM signal according to the duty ratio to obtain a driving signal suitable for the current working condition of the angle grinder. The controller outputs the driving signal to the driving circuit according to the duty ratio according to the rotor rotation position of the motor. The drive circuit thus drives the motor in accordance with the drive signal.

In this embodiment, the controller may directly perform the calculation on the function f (·) to obtain the corresponding duty ratio data, so that the PWM table storage device in the above embodiment may be omitted, and the optimal duty ratio corresponding to different working conditions may also be optimally selected. The duty ratio is specifically the duty ratio of a driving signal for driving the motor to operate under different motor characteristic parameters x and/or battery pack working conditions. Similar to the above embodiment, when the battery detection module obtains the battery pack voltage V equal to 25.2V and the battery pack number P equal to 1, the control module may specifically select one relationship between the change Δ PWM of the duty ratio and the change Δ n of the motor speed according to the function f (·): when the variation quantity delta n of the rotating speed of the motor is between 500 and 1000rpm, the variation quantity delta PWM of the duty ratio is correspondingly in the range of 0.02 to 0.05; when the variation Δ n of the motor speed is between 1000 and 1500rpm, the variation Δ PWM of the duty ratio is in the range of 0.05 to 0.08.

Here, for the function f (-) can be obtained by:

a power tool simulation system model as shown in fig. 7 is first established based on the circuit characteristic parameters of a particular power tool. The circuit characteristic parameters of the power tool to be considered in the model include: power supply unit characteristic parameters and motor characteristic parameters. The characteristic parameters of the power supply device may include, but are not limited to: the voltage, the residual electric quantity, the SOC parameter of the battery pack, the internal resistance of the power supply device and the like of the power supply device; the motor characteristic parameters may include, but are not limited to: motor speed, position, torque, etc.

For example, a battery pack is used as a power supply device, and an AC power supply is used as a power supply device. In the electric tool control model shown in fig. 7, the battery pack outputs the power supply side current I according to the different stages P and/or the characteristic parameters under the working conditions_bThe controller outputs driving signals according to different duty ratios to drive the motor to operate, and at the moment, the motor outputs corresponding motor side current I according to characteristic parameters corresponding to the working conditions of the motor_m。

Respectively simulating different battery pack working conditions and different motor characteristic parameters x to respectively obtain the duty ratio of the driving signal and the current I at the power supply side under the working conditions (different battery pack working conditions and different motor characteristic parameters x)_bMotor side current I_mThe relationship (2) of (c). For example, taking the working condition of the battery pack as the voltage condition of the battery pack, that is, the V2 gear, and the motor characteristic parameter x falls into the N10-N11 gear as examples, the duty ratio of the driving signal and the current I on the power supply side are obtained through simulation_bMotor side current I_mThe relationship (2) of (c). This relationship can be represented by the curve shown in fig. 8.

Due to the motor side current I_mProportional to the output torque of the motor, therefore, the current I on the motor side under the working condition can be obtained by inquiring figure 8_mThe highest point B of the curve is the point with the maximum output torque, namely the optimal output performance of the motor, and the duty ratio of the corresponding driving signal under the working condition is 65%. At the motor side current I corresponding to the output torque of the motor_mAt 49A, the curve shown in fig. 8 is consulted to find two duty cycles to achieve this torque. But the power supply side current I corresponding to the duty ratio of the point A_bAnd is small, it can be confirmed that the point a is a battery-friendly point, which corresponds to a driving signal duty ratio of 39% in this condition.

According to the analysis of the working condition of the battery pack and the motor characteristic parameter x, whether the battery is prone to be protected or the large torque is output under the working condition or the working condition is compromised. Taking the working condition of the battery pack as the voltage condition of the battery pack, namely the V2 gear, and the motor characteristic parameter x falling into the N10-N11 gear as examples, when the condition that the battery is prone to be protected, namely the maximum impact current to the battery pack needs to be limited, the duty ratio corresponding to the point A can be correspondingly selected to be 39% of the optimal duty ratio under the working condition; when large torque is output under one working condition, 65% of the duty ratio corresponding to the point B can be correspondingly selected as the optimal duty ratio under the working condition. Alternatively, the duty cycle may be compromised and the optimum duty cycle may be determined A, B for a point between conditions. Generally, the duty ratio required to be adjusted in this way varies from 0.02 to 0.08. And storing the selected optimal duty ratio under the working condition in a position corresponding to duty5 in table 1 according to the working condition V2 gear of the battery pack and the characteristic parameters xN 10-N11 gear of the motor. And by analogy, duty ratio data corresponding to different working conditions in the PWM table are determined one by one and stored into the table. Alternatively, the process of adjusting the duty ratio according to the characteristics of the electric power tool, that is, the process of adjusting the duty ratio according to the characteristic parameters of the power supply device and the motor, may be fitted through the function f (·), or the PWM table may be directly fitted. The function f (-) is calculated to replace the storage of specific duty ratio data, so that the duty ratio can be directly adjusted according to real-time working conditions.

Therefore, when the electric tool is used, once the actual working condition is judged to fall into the V2 gear of the battery pack and the xN 10-N11 gear of the motor characteristic parameter, the duty5 is correspondingly determined to be used as the corresponding duty ratio directly in a table look-up mode or through fitting of a function f (·), and the corresponding strategy is used for controlling and outputting the driving signal of the corresponding duty ratio to the driving circuit so as to drive the motor to run. Through the selection of the optimal duty ratio in the simulation process, the effect close to the simulation can be obtained in the implementation and application, so that the limitation on the maximum impact current of the electric tool and the improvement on the maximum output torque are realized, and the improvement on the ratio of the maximum output torque of the electric tool to the power supply capacity can also be realized. Specifically, by the above-described technique, it is possible to make the electric power tool output the maximum torque of not less than 5n.m, and/or make the electric power tool output the maximum torque to the power source capacity ratio of not less than 3Nm/Ah, and/or make the maximum rush current of the electric power tool not more than 30A.

Under other conditions, the selection, storage and query modes of the duty ratio are similar to those described above, and are not described herein again.

The skilled person can understand that when the electric tool is in the working conditions of low speed, large torque and the like close to the locked rotor, the performance optimum point B is generally required to be correspondingly selected as the basis of the duty ratio under the working conditions, so as to improve the heavy load performance of the tool and break through the locked rotor.

Under the working conditions of complete stalling of the electric tool and the like, compromise between the characteristics of battery protection and large output torque can be realized by selecting the point A with smaller current.

The selection of the optimal duty ratio corresponding to different working conditions can be suitable for most electric tools. When the method is applied to a specific electric tool product, the specific numerical value of the duty ratio can be determined only by correspondingly adjusting parameters in the electric tool simulation system model shown in fig. 7 according to the use requirement and the circuit characteristics of the tool and carrying out corresponding simulation.

For the existing electric tool, the invention does not need to change circuit hardware or mechanical structure, only stores the PWM table (table 1) corresponding to the tool in advance, or directly executes the f (-) function through the operation of the control unit, thus realizing the optimal control of the motor with the optimal duty ratio and further realizing the optimization of the working performance of the electric tool.

Referring to the test data of fig. 10 to 12, the present invention can easily control the maximum inrush current of the battery pack in the electric power tool to be less than 30A and the maximum output torque of the electric power tool to be not less than 5 n.m. In particular, in the locked state shown in fig. 12, for example, when the motor speed reaches 20% or less of the original speed, the locked current of the electric power tool may be limited to 70A or less.

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It should be understood by those skilled in the art that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by using equivalent alternatives or equivalent variations fall within the scope of the present invention.

Claims

1. An electric drill comprising:

a motor including a stator and a rotor;

a transmission for connecting the rotor with a drill bit;

the driving circuit is used for outputting a switching signal to drive a rotor of the motor to operate;

the control unit is used for outputting a driving signal to control the driving circuit;

the power supply device is used for supplying power to the motor, the drive circuit and the control unit;

an optimal duty cycle storage configured for the control unit to query an optimal duty cycle;

characterized in that the control unit is arranged to determine a variation Δ PWM of the duty cycle, obtained by a function f (Δ n, V), as a function of the variation Δ n of the motor speed and of a power supply device characteristic parameter V, wherein the variation Δ PWM of the duty cycle is comprised between the range 0.02 and 0.05; outputting a corresponding driving signal to the driving circuit based on the variation delta PWM of the duty ratio to control the rotor of the motor to operate and output driving force; the electric drill can output the maximum torque not less than 5N.m or the maximum impact current not more than 30A based on the optimal duty ratio under different working conditions.

2. The electric drill of claim 1, further comprising a motor detection module; the motor detection module is used for detecting and obtaining the motor rotating speed n; the motor detection module is integrated in the control unit or is separately listed outside the control unit.

3. The drill according to claim 1, wherein the power supply means comprises a battery pack of order 1P.

4. An electric drill comprising:

a motor including a stator and a rotor;

a transmission for connecting the rotor with a drill bit;

the battery pack supplies power to the motor, the driving circuit and the control unit;

the control unit is configured to determine a variation Δ PWM of a duty ratio according to a variation Δ n of a rotation speed of the motor and a characteristic parameter V of a power supply device, wherein the variation Δ PWM of the duty ratio is obtained by a function f (Δ n, V), and the variation Δ PWM of the duty ratio is in a range of 0.05 to 0.08, and output a corresponding driving signal to the driving circuit based on the variation Δ PWM of the duty ratio to control a rotor of the motor to operate and output a driving force; the electric drill can output the maximum torque not less than 5N.m or the maximum impact current not more than 30A based on the optimal duty ratio under different working conditions.

5. An electric drill comprising:

a brushless motor including a stator and a rotor;

a transmission for connecting the rotor with a drill bit;

the driving circuit is used for outputting a switching signal to drive the rotor of the brushless motor to operate;

the power supply device is used for supplying power to the brushless motor, the drive circuit and the control unit;

characterized in that the control unit is arranged to determine a variation Δ PWM of the duty cycle from the variation Δ x of the motor characteristic parameter and the power supply device characteristic parameter V, the variation Δ PWM of the duty cycle being obtained by a function f (Δ x, V); outputting a corresponding driving signal to the driving circuit based on the variation delta PWM of the duty ratio to control the rotor of the brushless motor to operate and output driving force; the electric drill can output the maximum torque not less than 5N.m or the maximum impact current not more than 30A based on the optimal duty ratio under different working conditions.

6. An electric drill according to claim 5, wherein the duty cycle variation Δ PWM is in the range 0.02 to 0.08.

7. An electric drill comprising:

a motor including a stator and a rotor;

a transmission for connecting the rotor with a drill bit;

characterized in that the control unit is arranged to determine a variation Δ PWM of the duty cycle, obtained by a function f (Δ n, V), as a function of the variation Δ n of the motor speed and of a characteristic parameter V of the power supply device, wherein the variation Δ PWM of the duty cycle is comprised between the range of 0.02 and 0.08; outputting a corresponding driving signal to the driving circuit based on the variation delta PWM of the duty ratio to control the rotor of the motor to operate and output driving force; the electric drill can output the maximum torque not less than 5N.m or the maximum impact current not more than 30A based on the optimal duty ratio under different working conditions.