CN116404918A - Electric tool and control method thereof - Google Patents

Abstract

The invention discloses an electric tool and a control method thereof, the electric tool comprises: a motor comprising a rotor and a multi-phase stator winding; a driving circuit including a plurality of high-side switching elements and a plurality of low-side switching elements; a position detecting unit for detecting a rotor position during operation of the motor; the controller is at least electrically connected with the driving circuit and the position detection unit and is used for controlling a switching element in the driving circuit to change the conduction state so as to control the working state of the motor; the controller is configured to: when a brake signal is detected, acquiring a rotor position of the motor; switching from the driving state to a target freewheel state by the driving circuit according to the rotor position control; during the process that the driving circuit is in the target follow current state, the motor rotates to generate braking current, and the motor can be braked.

Description

Electric tool and control method thereof

Technical Field

The invention relates to the field of electric tools, in particular to an electric tool and a control method thereof.

Background

In the braking process of the electric tool, a mode of short-circuiting a motor three-phase winding is generally adopted for braking, the braking force generated by the braking mode is overlarge, huge reverse energy flows backward, devices can be possibly damaged, and potential safety hazards can be brought. For example, when the braking force of the polishing tool is too large, accessories on the tool may fly out, and safety accidents are caused.

Disclosure of Invention

In order to solve the defects in the prior art, the invention aims to provide an electric tool capable of slowly braking.

The invention adopts the following technical scheme:

a power tool, comprising: a motor comprising a rotor and a multi-phase stator winding; a driving circuit including a plurality of high-side switching elements and a plurality of low-side switching elements; a position detecting unit for detecting a rotor position during operation of the motor; the controller is electrically connected with at least the driving circuit and the position detection unit and is used for controlling a switching element in the driving circuit to change the conduction state so as to control the working state of the motor; the controller is configured to: when a brake signal is detected, acquiring a rotor position of the motor; switching from a driving state to a target freewheel state by the driving circuit according to the rotor position control; during the process that the driving circuit is in the target follow current state, the motor rotates to generate braking current, and the motor can be braked.

Optionally, the controller is configured to: determining a two-phase target conduction winding with lag commutation according to the rotor position; and switching the driving circuit from a driving state to a target follow current state for shorting the target conducting winding.

Optionally, the controller is configured to: and adjusting a target conduction winding according to the change of the rotor position in the process that the driving circuit is in the target freewheel state.

Optionally, the controller is configured to: and modulating the duty ratio of the PWM signal, and controlling any one or two switching elements in the follow current circuit of the driving circuit in the target follow current state to be on-off at a preset frequency.

Optionally, the controller is configured to: controlling the driving circuit to switch from the target freewheel state to a first freewheel state; the switching element which is conducted by the driving circuit in the first follow current state is the switching element which is connected with the adjusted target conduction winding.

Optionally, each low-side switching element of the driving circuit is connected in parallel with a first voltage dividing circuit, or each high-side switching element of the driving circuit is connected in parallel with a first voltage dividing circuit; the first voltage dividing circuit includes a first switching element and a first resistor connected in series.

Optionally, each low-side switching element of the driving circuit is connected in series with a second voltage dividing circuit, or each high-side switching element of the driving circuit is connected in series with a second voltage dividing circuit.

Optionally, the second voltage dividing circuit includes a second resistor.

Optionally, the second voltage dividing circuit includes a second switching element and a third resistor connected in parallel.

A power tool control method, the power tool comprising: a motor comprising a rotor and a multi-phase stator winding; a driving circuit including a plurality of high-side switching elements and a plurality of low-side switching elements; a position detecting unit for detecting a rotor position during operation of the motor; the controller is electrically connected with at least the driving circuit and the position detection unit and is used for controlling a switching element in the driving circuit to change the conduction state so as to control the working state of the motor; the method comprises the following steps: when a brake signal is detected, acquiring a rotor position of the motor; switching from a driving state to a target freewheel state by the driving circuit according to the rotor position control; during the process that the driving circuit is in the target follow current state, the motor rotates to generate braking current, and the motor can be braked.

The invention has the advantages that: an electric tool capable of soft braking is realized.

Drawings

FIG. 1 is a block diagram of an electric tool according to an embodiment of the present invention;

FIG. 2 is a block diagram of a power tool according to an embodiment of the present invention;

FIGS. 3a and 3b are schematic diagrams of a motor winding three-phase short circuit brake;

FIG. 4 is a schematic diagram showing the change of rotor position during operation of a motor according to an embodiment of the present invention;

FIGS. 5a, 5b and 5c are schematic diagrams showing the relationship between rotor position and winding back-emf during operation of a motor according to an embodiment of the invention;

FIG. 6a is a schematic diagram of a motor control circuit according to an embodiment of the present invention in normal operation;

FIG. 6b is a schematic diagram of a freewheel state of the motor control circuit;

FIG. 6c is a schematic diagram of a freewheel state of a motor control circuit provided in accordance with an embodiment of the present invention;

FIG. 6d is a schematic diagram of a motor control circuit according to an embodiment of the present invention during braking;

FIG. 6e is a schematic diagram of a freewheel state of a motor control circuit provided in accordance with an embodiment of the present invention;

FIG. 7 is a schematic diagram of a driving circuit according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of a driving circuit according to an embodiment of the present invention;

FIG. 9 is a schematic diagram of a driving circuit according to an embodiment of the present invention;

fig. 10 is a flowchart of a motor braking process provided by an embodiment of the present invention.

Detailed Description

The invention is described in detail below with reference to the drawings and the specific embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

The electric tools applicable to the technical scheme of the invention comprise electric tools such as polishing tools, electric drills, electric circular saws, reciprocating saws, miter saws, impact wrenches, impact screwdrivers, hammer drills and the like, and other types of electric tools can fall within the protection scope of the invention as long as the following disclosed technical scheme can be adopted.

In the embodiment of the present application, referring to the electric power tool shown in fig. 1, the electric power tool 100 includes at least a housing 10, a motor 11 in the housing, a power source 12, an operation switch 13, a working head 14, and the like. The casing 10 houses a motor, a control circuit board and a transmission structure (not shown). The housing 10 is also formed with a grip 101 for a user to grip. Wherein the operation switch 13 can be turned on or off by a user operation.

Referring to the circuit block diagram of the electric tool shown in fig. 2, the driving system of the motor 11 includes at least a power source 12, a driving circuit 13, a controller 14, and a position detecting unit 15.

In one embodiment, the motor 11 is a brushless direct current motor (BLDC). In one embodiment, the motor 11 is a non-inductive BLDC. In one embodiment, motor 11 is a sensored BLDC. In the present application, the brushless dc motor may be an inner rotor motor or an outer rotor motor, and the motor includes at least three-phase stator windings A, B, C, where the three-phase windings may be star-shaped or delta-shaped.

In one embodiment, the power source 12 may be selected to be an ac power source, i.e., 120V or 220V ac mains may be connected through the power interface. In one embodiment, the power source 12 may alternatively be a battery pack, which may be comprised of a set of battery cells, for example, the battery cells may be connected in series in a single power branch to form a 1P battery pack. The battery pack output voltage is subjected to voltage variation by a specific power control module, such as a DC-DC module, and a power supply voltage suitable for the driving circuit 13, the motor 11, and the like is output to supply power thereto. Those skilled in the art will appreciate that the DC-DC module is a well-established circuit structure and may be selected accordingly according to the specific parameter requirements of the power tool.

The driving circuit 13 is electrically connected to the stator windings A, B, C of the motor 11 for transferring current from the power source 12 to the stator windings A, B, C to drive the motor 11 to rotate. In one embodiment, the driving circuit 13 includes a plurality of switching elements Q1, Q2, Q3, Q4, Q5, Q6. The gate terminal of each switching element is electrically connected to the controller 14 for receiving a control signal from the controller 14, which may be a PWM signal. The drain or source of each switching element is connected to the stator winding A, B, C of the motor 11. The switching elements Q1-Q6 receive control signals from the controller 14 to change the respective conductive states, thereby changing the current applied by the power supply 12 to the stator windings A, B, C of the motor 11. In one embodiment, the drive circuit 13 may be a three-phase bridge driver circuit including six controllable semiconductor power devices (e.g., FETs, BJTs, IGBTs, etc.). It will be appreciated that the switching element may be any other type of solid state switch, such as an Insulated Gate Bipolar Transistor (IGBT), a Bipolar Junction Transistor (BJT), etc.

In order to drive the motor 11 shown in fig. 2 to rotate, the driving circuit 13 has a plurality of driving states, and the rotation speed or the steering of the motor 11 may be different in different driving states. The process of the controller 14 controlling the driving circuit 13 to change different driving states to obtain different rotation speeds or steering directions of the motor 11 will not be described in detail.

In one embodiment, the operation switch 13 may output a start signal or a shut down signal or a brake signal or a deceleration signal or a acceleration signal, etc. to the controller 14 after being triggered by a user in a set manner. So that the controller 14 can control the switching elements in the driving circuit 13 to change the conducting state according to the received signals so as to achieve the corresponding control purpose.

For the controller 14 to control the driving circuit 13 to switch to the braking state, it is common to control the shorting of the three-phase windings of the motor 11 in such a way as to brake the motor 11. Taking fig. 3a and 3b as an example, the broken line part in the drawing indicates disconnection, and the implemented part indicates connection. In fig. 3a and 3b, the high-side switching elements Q1, Q3, Q5 of the driving circuit 13 are all on and the low-side switching elements Q2, Q4, Q6 are all off, or the low-side switching elements Q2, Q4, Q6 are all on and the high-side switching elements Q1, Q3, Q5 are all off. When braking in the above manner, the motor 11 has a larger braking current, and a larger braking force can be obtained, however, in some tools, the larger braking force can have some potential safety hazards, such as grinding disc flying possibility of grinding tools.

In order to solve the problems, the following scheme is adopted:

during operation of the three-phase brushless motor, the rotor position is as shown in fig. 4: in FIG. 4, the magnetic potential during the phase change of the two-phase windingWill change and mainly comprise the magnetic potential F of the rotor _Rotation And the stator magnetic potential F of the stator winding _{Fixing device} . Each time the rotor rotates by 60 degrees of electrical angle, the motor performs phase change, that is, each phase winding occupies a phase band of 60 degrees, the rotor corresponds to different position information in six different phase bands, and the PWM driving signal output by the controller 14 can have a plurality of different signal combinations. In one embodiment, signal 0 is used to represent the off state of the winding and signal 1 is used to represent the on state of the winding. In fig. 4, the broken line indicates a hall scale formed when the hall positions of the three-phase windings are parallel to the rotor direction, and the hall position of the stator winding can be determined according to the change in the rotor position. Specifically, the hall positions of the three-phase windings, the PWM signal combination form output by the controller, and the conduction states of the corresponding stator windings are shown in table 1:

TABLE 1

Hall position	PWM signal combination	Stator winding on-state
			(0，1，0)	(1，0，X)	A+B-
(0，1，1)	(1，X，0)	A+C-
			(0，0，1)	(X，1，0)	B+C-
(1，0，1)	(0，1，X)	B+A-
			(1，0，0)	(0，X，1)	C+A-
(1，1，0)	(X，0，1)	C+B-

The following 0 of the hall position in table 1 indicates that the hall position of the corresponding winding falls at the S pole of the rotor, and the following 1 of the hall position indicates that the hall position of the corresponding winding falls at the N stage of the rotor. In table 1, the following 0 represents conduction of the lower tube of the corresponding winding, the following 1 represents conduction of the upper tube of the corresponding winding, and the following X represents non-conduction of the upper tube and the lower tube of the corresponding winding.

When the stator windings are in different conduction states, the counter potential between the windings of each phase is shown in fig. 5 a. At a counter potential e of A, B winding _AB Illustratively, e is during stator winding A+C-conduction and B+C-conduction _AB Gradually decreasing. If the motor braking process occurs at e _AB In the reduced section, the braking force generated by the motor is also small. E when A+B-is on and B+A-is on _AB Maximum; if the motor braking process occurs at e _AB In the maximum section, the braking force generated by the motor is also maximum.

The present application can detect the position of the rotor by the position detection unit 15. In one embodiment, the rotor position detection unit 15 may include a hall sensor capable of detecting the rotor position. In one embodiment, the rotor position detection unit 15 is capable of detecting the counter potential of the stator winding and determining the rotor position from the counter potential.

In one embodiment, the controller 14 may acquire the rotor position of the motor through the position detection unit 15 when detecting the brake signal, and further control the driving circuit 13 to switch from the driving state to the target freewheel state according to the rotor position of the motor. During the target freewheel state of the drive circuit 13, the motor rotates to generate a braking current that brakes the motor.

For example, as shown in fig. 6a, the motor is normally driven in a +c-on state, if the controller 14 detects a braking signal during this process, the driving circuit 13 is controlled to switch to the freewheel state shown in fig. 6b, and in this freewheel state, the rotor can continue to rotate to generate braking current after the freewheel is completed. As can be seen from FIG. 5a, e is within the A+C-conduction interval _CA At maximum, if the controller 14 controls the driving circuit 13 to switch from the driving state shown in fig. 6a to the state of freewheeling through the windings a and C shown in fig. 6b, the generated braking force is large. As can be seen from FIG. 5a, e is within the A+C-conduction interval _AB Smaller, so that the controller 14 can control the drive circuit 13 to switch from the drive state shown in fig. 6a to the target freewheel state shown in fig. 6c, i.e. a freewheel state through the winding A, B; in the B+C-conduction interval, e _AB Smaller, the controller 14 can control the drive circuit 13 to switch from the drive state shown in fig. 6a to the target freewheel state shown in fig. 6c, i.e. the freewheel state through windings a and B. Optionally, in the B+C-conduction interval, e _CA Also smaller, the controller 14 can control the drive circuit to switch from the drive state shown in fig. 6a to a state (not shown) freewheeling through the winding A, C. In summary, it can be seen that the stator winding that is conducting in the target freewheel state lags the winding that is actually conducting. Thus, the controller 14 may determine the two-phase target conductive winding of the hysteretic commutation based on the detected rotor position, thereby switching the drive circuit 13 from the drive state to the target freewheel state shorting the two-phase target conductive winding.

In both the a + C-and B + C-conduction intervals shown in fig. 5a, the controller 14 may control the drive circuit to switch to a target freewheel state for the freewheeling through windings a and B. That is, when the rotor position is at the target interval within the box of fig. 5a, the motor may be braked by switching to the target freewheel state, in which the windings A, B freewheel. The range of the target section is 120 °. In an alternative implementation, the target interval shown in fig. 5a may also be extended back and forth by 30 ° as shown in fig. 5b, i.e. the target interval may range from 90 ° to 150 °. The requirement of large braking force under special working conditions can be met by expanding the target interval. In an alternative implementation, the target interval shown in fig. 5a may also be narrowed to a certain extent as shown in fig. 5c, i.e. the target interval may be in the range of 60 ° to 120 °. The magnitude of the braking force can be further modulated by narrowing the target interval, and the accuracy of braking force control is met.

After the drive circuit 13 finishes freewheeling in the target freewheeling state, the motor continues to rotate, and a braking current in the opposite direction to the drive current or the freewheeling current can be generated as shown in fig. 6d, so that the motor can be braked.

During the time that the drive circuit 13 is in the target freewheel state, the position of the motor rotor may change. The controller 14 may monitor the position of the motor rotor in real time and adjust the two-phase target conduction winding based on the rotor position to adjust the target freewheel state. That is, the freewheel circuit that generates the braking current may also vary as the rotor position varies during braking of the motor.

In one embodiment, during the time when the driving circuit 13 is in the target freewheel state, the controller 14 may modulate the duty cycle of the PWM signal to control either or both switching elements in the freewheel circuit of the driving circuit 13 in the target freewheel state to be turned on and off at a preset frequency. That is, in the target freewheel state, the switching element in the freewheel circuit may be turned on and off at a preset frequency, so that the braking force can be further reduced, and the purpose of slow braking is achieved. Specifically, the magnitude of the preset frequency may be adjusted according to different braking force requirements of different tools, which is not limited herein. In one embodiment, the controller 14 may also modulate the PWM frequency of the PWM signal during the target freewheel state of the driving circuit 13, and may further reduce the braking force to achieve a slow braking. It will be appreciated that the controller 14 will be constant in modulating the PWM signal duty cycle and will be constant in modulating the PWM frequency. Alternatively, the controller 14 may also modulate the duty cycle and PWM frequency simultaneously.

In one embodiment, the controller 14 may control the drive circuit 13 to switch from the target freewheel state to the first freewheel state illustrated in fig. 6 e. The on-state of the switching elements in the drive circuit 13 in the first freewheel state may coincide with the on-state of the switching elements in the drive circuit 13 shown in fig. 6a, except for the flow direction of the current. It will be appreciated that in the target freewheel state, the rotor position of the motor may change, and after the change of the motor position, the target conducting winding in the target freewheel state may change, so that the conducting state of the switching element in the drive circuit 13 in the first freewheel state shown in fig. 6e may also be inconsistent with the conducting state of the switching element in the drive circuit 13 shown in fig. 6 a. For example, as shown in fig. 6e, when the drive circuit 13 is in the first freewheel state, the current in the circuit is still the induced current of the motor output, flowing from the motor winding to the power supply side. The motor control system as shown in fig. 6e further comprises an energy storage element 16 connected in parallel with the drive circuit 13. Thus, in the first freewheel state, the first freewheel circuit is actually configured of the energy storage elements 114, Q1, Q4 and the motor winding A, B, with the energy storage element 16 being able to absorb the brake current output from the motor. In one embodiment, the energy storage element 114 is a capacitor.

After the induced current shown in fig. 6e is freewheeled, if the motor is not fully braked, the current on the power supply 12 side can continue to drive the motor through the circuit shown in fig. 6e, and the synchronous freewheel braking process shown in fig. 6a, 6c and 6d can be performed again in sequence. After each time the braking process is performed to the freewheel state shown in fig. 6e, if the motor has not completely stopped rotating, the process may still be continuously and cyclically performed.

In one embodiment, the motor may complete braking in the target freewheel state illustrated in FIG. 6d without continuing to cyclically execute the synchronous freewheel braking procedures illustrated in FIGS. 6a, 6c and 6 d.

In one implementation, each low-side switching element of the driving circuit 13 may be connected in parallel with a first voltage dividing circuit, respectively, as shown in fig. 7. When the driving circuit 13 shown in fig. 7 is used to perform braking, the control process of switching the controller 14 from the driving state to the target freewheel state is identical to the synchronous freewheel braking process shown in fig. 6c and 6d, except that the controller 14 is turned on the first voltage dividing circuit in parallel with Q6 instead of Q6 to form the target freewheel state shown in fig. 7. Optionally, the first voltage dividing circuit may include a first switching element and a first resistor connected in series, where the first switching element may be the same as Q1 to Q6, and the first resistor may perform dynamic braking in a target freewheel state, and may reduce braking time on the basis of ensuring soft-braking. In an alternative implementation, a first voltage dividing circuit may be connected in parallel to each high-side switching element of the driving circuit 13, which can achieve the above effect.

In one embodiment, each low-side switching element of the driving circuit 13 may be connected in series with a second voltage dividing circuit, respectively, as shown in fig. 8. Alternatively, the second voltage dividing circuit may be connected in series to the drain or source of the low-side switching element. Alternatively, the second voltage dividing circuit may be a second resistor. In the braking process, the freewheel circuit in the target freewheel state has more second resistors than the target freewheel states shown in fig. 6c and 6d, so that the braking power can be reduced to a certain extent. In one implementation, the second voltage dividing circuit may also be connected in series with the high-side driving element of the driving circuit 13, which can achieve the above-mentioned effects.

In an alternative implementation, the second voltage dividing circuit includes a second switching element and a third resistor connected in parallel as shown in fig. 9. In the normal driving state of the motor, the controller 14 can control the second switching element in fig. 9 to be turned on, so as to short the third resistor, and avoid affecting the driving power. When the braking signal is detected, the controller 14 may control the second switching element to be turned off to switch in the third resistor, so as to achieve the purpose of reducing the braking power.

Referring to fig. 10, the brake control method of the electric tool includes the steps of:

s101, judging whether a brake signal exists.

If yes, go to step S102, otherwise continue to detect. Wherein the brake signal may be generated by a user by activating an operating switch or otherwise controlling the tool.

S102, acquiring the rotor position of the motor.

S103, the driving state of the driving circuit is controlled to be switched to a target follow current state according to the rotor position.

In this embodiment, the control flow for the electric tool may be referred to the description in the above embodiment, and will not be repeated here.

Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.

Claims (10)

1. A power tool, comprising:

a motor comprising a rotor and a multi-phase stator winding;

a driving circuit including a plurality of high-side switching elements and a plurality of low-side switching elements;

a position detecting unit for detecting a rotor position during operation of the motor;

the controller is electrically connected with at least the driving circuit and the position detection unit and is used for controlling a switching element in the driving circuit to change the conduction state so as to control the working state of the motor;

the controller is configured to:

when a brake signal is detected, acquiring a rotor position of the motor;

switching from a driving state to a target freewheel state by the driving circuit according to the rotor position control;

during the process that the driving circuit is in the target follow current state, the motor rotates to generate braking current, and the motor can be braked.

2. The power tool of claim 1, wherein:

the controller is configured to:

determining a two-phase target conduction winding with lag commutation according to the rotor position;

and switching the driving circuit from a driving state to a target follow current state for shorting the target conducting winding.

3. The power tool of claim 2, wherein:

the controller is configured to:

and adjusting a target conduction winding according to the change of the rotor position in the process that the driving circuit is in the target freewheel state.

4. The power tool of claim 2, wherein:

the controller is configured to:

and modulating the duty ratio of the PWM signal, and controlling any one or two switching elements in the follow current circuit of the driving circuit in the target follow current state to be on-off at a preset frequency.

5. A power tool according to claim 3, wherein:

the controller is configured to:

controlling the driving circuit to switch from the target freewheel state to a first freewheel state;

the switching element which is conducted by the driving circuit in the first follow current state is the switching element which is connected with the adjusted target conduction winding.

6. The power tool of claim 1, wherein:

each low-side switching element of the driving circuit is respectively connected with a first voltage dividing circuit in parallel, or each high-side switching element of the driving circuit is respectively connected with a first voltage dividing circuit in parallel;

the first voltage dividing circuit includes a first switching element and a first resistor connected in series.

7. The power tool of claim 1, wherein:

each low-side switching element of the driving circuit is respectively connected with a second voltage dividing circuit in series, or each high-side switching element of the driving circuit is respectively connected with a second voltage dividing circuit in series.

8. The power tool of claim 7, wherein:

the second voltage dividing circuit includes a second resistor.

9. The power tool of claim 7, wherein:

the second voltage dividing circuit includes a second switching element and a third resistor connected in parallel.

10. A power tool control method, the power tool comprising: a motor comprising a rotor and a multi-phase stator winding; a driving circuit including a plurality of high-side switching elements and a plurality of low-side switching elements; a position detecting unit for detecting a rotor position during operation of the motor; the controller is electrically connected with at least the driving circuit and the position detection unit and is used for controlling a switching element in the driving circuit to change the conduction state so as to control the working state of the motor; the method comprises the following steps:

when a brake signal is detected, acquiring a rotor position of the motor;

switching from a driving state to a target freewheel state by the driving circuit according to the rotor position control;

during the process that the driving circuit is in the target follow current state, the motor rotates to generate braking current, and the motor can be braked.

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