阅读说明：本技术 电动工具 (Electric tool ) 是由 米田文生 于 2018-04-17 设计创作，主要内容包括：一种电动工具,具备：永磁同步电动机；以及控制部,其控制所述永磁同步电动机的动作,其中,所述控制部具备限制单元,所述限制单元基于规定的紧固扭矩,以规定的最大设定值限制有助于所述永磁同步电动机的扭矩产生的电流。所述控制部利用所述永磁同步电动机的转速或者角速度来校正并运算有助于所述扭矩产生的电流的最大设定值。另外,所述控制部使用下式来运算有助于所述扭矩产生的电流的最大设定值i<Sub>δ</Sub>*<Sub>max</Sub>。i<Sub>δ</Sub>*<Sub>max</Sub>＝K(T-J·dω/dt+T0)。在此,K、J为常数,dω/dt为所述永磁同步电动机的角速度的微分值,T为规定的目标紧固扭矩,T0为规定的损失扭矩。(An electric power tool is provided with: a permanent magnet synchronous motor; and a control unit that controls an operation of the permanent magnet synchronous motor, wherein the control unit includes a limiting means that limits a current contributing to torque generation of the permanent magnet synchronous motor at a predetermined maximum set value based on a predetermined tightening torque. The control unit corrects and calculates a maximum set value of a current contributing to the torque generation using the rotational speed or the angular velocity of the permanent magnet synchronous motor. The control unit calculates a maximum set value i of a current contributing to the torque generation using the following equation δ * max 。i δ * max K (T-J · d ω/dt + T0). Here, K, J is a constant, dω/dt is a differential value of the angular velocity of the permanent magnet synchronous motor, T is a predetermined target tightening torque, and T0 is a predetermined loss torque.)

1. An electric power tool is provided with:

a permanent magnet synchronous motor; and

a control unit for controlling the operation of the permanent magnet synchronous motor,

the electric power tool is characterized in that,

the control unit includes a limiting means for limiting a current contributing to torque generation of the permanent magnet synchronous motor at a predetermined maximum set value based on a predetermined tightening torque.

2. The power tool of claim 1,

the control unit corrects and calculates a maximum set value of a current contributing to the torque generation, using the rotational speed or angular velocity of the permanent magnet synchronous motor.

3. The power tool of claim 2,

the control unit calculates a maximum set value i of a current contributing to the torque generation using the following equation_δ*_max，

i_δ*_max＝K(T-J·dω/dt+T0)

Here, K and J are constants, d ω/dt is a differential value of the angular velocity of the permanent magnet synchronous motor, T is a predetermined target tightening torque, and T0 is a predetermined loss torque.

Technical Field

The present disclosure relates to an electric power tool including a motor control unit that controls a motor, for example.

Background

Electric tools such as drills are generally set to a torque by a mechanical chuck mechanism. However, in recent years, attempts have been made to convert the electron into an electron. As an example of such an attempt, for example, patent document 1 proposes an electric power tool in which a fastening torque is calculated from a motor drive current and a motor rotation speed, and the motor is stopped if the fastening torque is equal to or more than a preset fastening torque.

Further, for example, patent document 2 discloses a control device for an electric screwdriver, the control device including: the screw tightening torque is detected, and the drive torque is intermittently supplied to the chuck until completion of tightening is detected based on the detected torque.

Disclosure of Invention

Problems to be solved by the invention

However, the method of patent document 1 has a problem that the tightening torque cannot be accurately set, such as the following:

(1) the motor drive current contains a field current of the motor that does not contribute to the rotation torque,

(2) inertial energy of the rotating body, etc. are not considered.

An object of the present disclosure is to solve the above problems and to provide an electric power tool capable of setting a tightening torque more accurately only by motor control, thereby enabling omission or simplification of a mechanical chuck structure.

Means for solving the problems

An electric power tool according to an aspect of the present disclosure includes:

a permanent magnet synchronous motor; and

a control unit for controlling the operation of the permanent magnet synchronous motor,

wherein the control unit includes a limiting means for limiting a current contributing to torque generation of the permanent magnet synchronous motor at a predetermined maximum set value based on a predetermined tightening torque.

ADVANTAGEOUS EFFECTS OF INVENTION

By the above-described means, the generated torque of the motor can be controlled only by the current contributing to the generation of torque. In addition, the current value contributing to the generated torque can be dynamically limited to a maximum value that takes into account the influence of inertial energy of the rotating body and the like.

Therefore, according to the electric power tool of the present disclosure, the tightening torque can be set more accurately only by the motor control, and the mechanical chuck mechanism can be omitted or simplified.

Drawings

Fig. 1 is a block diagram showing a configuration example of an electric power tool according to embodiment 1 of the present disclosure.

Fig. 2 is an analysis model diagram of the motor 1 of the electric power tool of fig. 1.

Fig. 3 is a block diagram showing a detailed configuration example of the electric power tool of fig. 1.

Fig. 4 is a block diagram showing a detailed configuration example of the speed control unit 17 in fig. 3.

Fig. 5 is a timing chart showing an operation example when the screw of the electric power tool of fig. 1 is tightened.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the respective drawings referred to, the same portions are denoted by the same reference numerals, and the overlapping description of the same portions is omitted in principle. In the drawings referred to, elements denoted by the same reference symbols (θ, ω, and the like) are the same. For simplicity of description, the state quantities and the like may be denoted by symbols only. That is to say that the position of the first electrode,for example, sometimes "estimate motor speed ω_e"simply by" ω_e", but both have the same meaning.

Fig. 1 is a block diagram showing a configuration example of an electric power tool according to embodiment 1 of the present disclosure. In fig. 1, the electric power tool according to embodiment 1 is, for example, an electric screwdriver or the like, and includes a motor 1, an inverter circuit unit 2, a motor control unit 3, a gear 4, a chuck 5, and a user interface unit (UI unit) 6.

In fig. 1, the motor 1 is, for example, a three-phase permanent magnet synchronous motor in which a rotor (not shown) is provided with a permanent magnet and a stator (not shown) is provided with an armature winding. In the following description, when simply referred to as an armature winding and a rotor, they refer to an armature winding provided in a stator of the motor 1 and a rotor of the motor 1, respectively. The motor 1 is, for example, a salient pole machine (motor having salient polarity) typified by an embedded magnet type synchronous motor (IPMSM), but may be a non-salient pole machine. Here, the motor 1 is rotatably coupled to a chuck 5 for attaching a screw rotating bit (bit) via a gear 4, for example.

The inverter circuit unit 2 supplies a three-phase ac voltage including a U-phase, a V-phase, and a W-phase to an armature winding of the motor 1 in accordance with a rotor position of the motor 1. The voltage supplied to the armature winding of the motor 1 is set as a motor voltage (armature voltage) V_aThe current supplied from the inverter circuit unit 2 to the armature winding of the motor 1 is set as a motor current (armature current) I_a。

The motor control unit 3 has a position sensorless control function, for example, and uses the motor current I_aThe rotor position, the rotational speed, and the like of the motor 1 are estimated, and a signal for operating the motor 1 at a desired rotational speed and a target tightening torque is supplied to the inverter circuit unit 2.

The desired rotation speed and the target tightening torque are preset in the user interface 6, and are output to the motor control unit 3 as the motor speed command value ω, in conjunction with a trigger switch (not shown) operated by the user^*Target tightening torque T^*。

Fig. 2 is an analysis model diagram of the motor 1 of the electric power tool of fig. 1. Fig. 2 shows U-phase, V-phase, and W-phase armature winding fixing shafts. In a rotating coordinate system that rotates at the same speed as the magnetic flux generated by the permanent magnet 1a constituting the rotor of the motor 1, the direction of the magnetic flux generated by the permanent magnet 1a is defined as the d-axis, and the estimated axis for control corresponding to the d-axis is defined as the γ -axis. Although not shown, a phase advanced by an electrical angle of 90 degrees from the d axis is referred to as a q axis, and a phase advanced by an electrical angle of 90 degrees from the γ axis is referred to as an estimated axis, that is, a δ axis. Coordinate axes of a rotating coordinate system in which d-axis and q-axis are selected as coordinate axes are referred to as d-q-axis (real axis). The rotational coordinate system (estimated rotational coordinate system) in the control is a coordinate system in which the γ axis and the δ axis are selected as coordinate axes, and the coordinate axes are referred to as γ - δ axes.

The d-q axis rotates, and the rotational speed thereof (i.e., the rotational speed of the rotor of the motor 1) is referred to as an actual motor speed ω. The gamma-delta axis also rotates, and its rotational speed is referred to as the estimated motor speed omega_e. In the d-q axis that is rotating at a certain moment, the phase of the d axis is represented by θ (actual rotor position θ) with reference to the U-phase armature winding fixed axis. Similarly, in the γ - δ axis that is rotating at a certain instant, θ is used with respect to the U-phase armature winding fixed axis_e(estimation of rotor position θ)_e) Indicating the phase of the gamma axis. Then, the axis error Δ θ between the d axis and the γ axis (axis error Δ θ between the d-q axis and the γ - δ axis) is represented by Δ θ — θ_eAnd (4) showing. In addition, parameter ω^*ω and ω_eExpressed in electrical angular velocity.

In the following description, the gamma voltages v are used_γDelta axis voltage v_δD-axis voltage v_dAnd q-axis voltage v_qRepresenting motor voltage V_aThe gamma-axis component, the delta-axis component, the d-axis component and the q-axis component of (1) are measured by a gamma-axis current i_γDelta axis current i_δD axis current i_dAnd q-axis current i_qRepresenting motor current I_aA gamma-axis component, a delta-axis component, a d-axis component, and a q-axis component.

In addition, the，R_aIs the motor resistance (resistance value of armature winding of motor 1), L_d、L_qThe inductance values are d-axis inductance (d-axis component of inductance of the armature winding of the motor 1), q-axis inductance (q-axis component of inductance of the armature winding of the motor 1), and Φ_aIs the armature interlinkage magnetic flux generated by the permanent magnet 1 a. Furthermore, L_d、L_q、R_aAnd phi_aThese values are values determined when manufacturing a motor drive system for an electric power tool, and these values are used for calculation by the motor control unit 3.

Fig. 3 is a block diagram showing a detailed configuration example of the electric power tool of fig. 1. In fig. 3, the motor control unit 3 is configured to include a current detector 11, a coordinate converter 12, a subtractor 13, a subtractor 14, a current control unit 15, a magnetic flux control unit 16, a speed control unit 17, a coordinate converter 18, a position/speed estimation unit 20, and a step-out detection unit 21.

The current detector 11 is composed of, for example, a hall element, and detects a motor current I supplied from the inverter circuit unit 2 to the motor 1_aCurrent (current flowing through armature winding of U phase) i of (c)_UAnd a V-phase current (current flowing through the armature winding of the V-phase) i_V. These currents may be detected by various conventional current detection methods in which a shunt resistor or the like is incorporated in the inverter circuit unit 2. The coordinate transformer 12 receives the U-phase current i from the current detector 11_UAnd V phase current i_VBased on the estimated rotor position θ from the position/velocity estimating unit 20_eAnd converting them into gamma-axis currents i by the following formula (1)_γ(current for controlling magnetic flux of motor) and delta-axis current i_δ(electric current directly contributing to the generation of the rotational torque of the motor in proportion to the supplied torque of the motor)

[ number 1 ]

The position/velocity estimating unit 20 estimates and outputs an estimated rotor position θ_eAnd estimating motor speed ω_e. With respect to estimating rotor positionSet theta_eAnd an estimation method of estimating the motor speed ω e, for example, the method disclosed in patent document 3 can be used.

The speed control unit 17 controls the motor speed command value ω supplied from the user interface unit 6^*The estimated motor speed ω supplied from the position speed estimating section 20 is subtracted_eThe result of the subtraction (ω)^*-ω_e) Input to, for example, PI (proportionlntergral: proportional integral) controller 51 (fig. 4), thereby generating δ -axis current command value i_δ ^*. Delta axis current command value i_δ ^*Is expressed as motor current I_aDelta axis current i of delta axis component of_δThe value of the current that should be followed. The magnetic flux control unit 16 outputs a γ -axis current command value i_γ ^*. At this time, the δ -axis current command value i is referred to as necessary_δ ^*And estimating motor speed ω_e. Gamma axis current command value i_γ ^*Is expressed as motor current I_aGamma axis current i of the gamma axis component of_γThe value of the current that should be followed.

The subtractor 13 outputs a γ -axis current command value i from the magnetic flux control unit 16_γ ^*Subtracting the gamma-axis current i output by the coordinate transformer 12_γTo calculate the current error (i) as a result of the subtraction_γ ^*-i_γ). The subtractor 14 outputs a delta axis current command value i from the speed control unit 17_δ ^*Subtracting the delta axis current i output by the coordinate transformer 12_δTo calculate the current error (i) as a result of the subtraction_δ ^*-i_δ)。

The current control unit 15 receives the respective current errors calculated by the subtractors 13 and 14 so as to control the gamma axis current i_γFollow the gamma axis current command value i_γ ^*And make the delta axis current i_δCommand value i of current following delta axis_δ ^*Calculating the gamma axis voltage command value v_γ ^*And delta axis voltage command value v_δ ^*And output.

The coordinate converter 18 estimates the rotor position θ based on the position and speed estimation unit 20_eCome inLine gamma axis voltage command value v_γ ^*And delta axis voltage command value v_δ ^*Is inverse transformed, thereby generating a voltage represented by the motor voltage V_aU-phase voltage command value V of U-phase component, V-phase component, and W-phase component of (a)_u ^*Voltage command value V of voltage V_v ^*And W phase voltage command value v_w ^*The voltage command values of the three phases thus constituted are output to the inverter circuit unit 2. The following equation (2) is used for the inverse transform.

Number 2

The inverter circuit unit 2 is based on three-phase voltage command values (v) indicating voltages to be applied to the motor 1_u ^*、v_v ^*And v_w ^*) Generates a pulse width modulated signal to be associated with the three-phase voltage command value (v)_u ^*、v_v ^*And v_w ^*) Corresponding motor current I_aIs supplied to the armature winding of the motor 1 to drive the motor 1.

The step-out detection unit 21 estimates the rotational speed of the rotor by using an estimation method different from the estimation method of the rotational speed of the rotor adopted by the position and speed estimation unit 20 (see, for example, patent document 4), and if the difference between the estimated rotational speed and the estimated rotational speed is large, the motor 1 is regarded as being out of step and is forcibly stopped.

Fig. 4 is a block diagram showing a detailed configuration example of the speed control unit 17 in fig. 3. In fig. 4, the output of the PI controller 51 is based on the subtraction result (ω) of the subtractor 50^*-ω_e) Generating a delta axis current command value i before current limitation_δ ^*And output to the limiter 52. The output of the PI controller 51 is the maximum set value i of the limiter 52_δ ^* _maxIn the following case, the limiter 52 directly outputs the output of the PI controller 51. On the other hand, when the output of the PI controller 51 exceeds the maximum set value i of the limiter 52_δ ^* _maxWhen it is, output will i_δ ^*Is limited to i_δ ^* _maxThe resulting value. The limit value calculation unit 53 calculates the maximum setting value i of the limiter 52 using the following expression (3)_δ ^* _maxAnd successively updates the maximum set value i of the limiter 52_δ ^* _max。

i_δ ^* _max＝K(T-J·dω/dt+T0)···(3)

Here, K, J is a constant, d ω/dt is a differential value of the angular velocity of the motor, and T is a predetermined target fastening torque. T0 is a predetermined loss torque, and for example, T0 may be set in advance in the internal memory of the limit value calculation unit 53 in the form of a table or the like as a dependent variable of the angular velocity ω of the motor. In addition, the motor speed ω can also be estimated_eInstead of the angular velocity ω of the motor.

As described above, the δ -axis current is a current proportional to the supply torque of the motor, and does not include an excitation current or the like that does not directly contribute to the generation of the rotation torque of the motor. Further, the command value i for the δ -axis current is dynamically set using the above equation (3)_δ ^*A restriction is made. Therefore, the tightening torque can be controlled more accurately in consideration of the inertial energy of the rotating body and the like.

In other words, when the load torque suddenly increases due to the screw position to be operated by the electric power tool, the delta axis current increases due to the increase in the load torque, and the delta axis current is limited to the maximum setting value of expression (3) in the end. At this time, although the rotation speed of the motor is also reduced, the inertial energy and the loss torque of the rotating body are reduced with the reduction in the rotation speed of the motor. Therefore, the maximum set value (current proportional to the supply torque of the motor) of expression (3) becomes large, and finally passes through i_δ ^* _maxK (t) makes the δ -axis current constant. Then, immediately before the motor stops, the motor is out of step or the motor rotation speed becomes a predetermined value or less (for example, zero), and the motor 1 is stopped when this is detected (fig. 5).

Therefore, according to the present embodiment, when the load torque suddenly increases due to the screw being the work target of the electric power tool being set, the motor is decelerated and finally stopped, but the motor current gradually increases as the motor rotation speed decreases from the setting of the rotor to the completion of fastening, and fastening can be performed with a fixed torque during this period. Therefore, the tightening torque can be set more accurately, and the mechanical chuck mechanism can be omitted or simplified.

Description of the reference numerals

1: an electric motor; 2: an inverter circuit unit; 3: a motor control unit; 4: a gear; 5: a chuck; 6: a user interface section (UI section); 11: a current detector; 12: a coordinate transformer; 13, 14: a subtractor; 15: a current control unit; 16: a magnetic flux control unit; 17: a speed control unit; 18: a coordinate transformer; 19: a subtractor; 20: a position and velocity estimation unit; 21: an out-of-step detection unit; 50: a subtractor; 51: a PI controller; 52: a limiter; 53: a limit value calculation unit.