JP2005102371A - Driving unit for power tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller for an electric tool which can enlarge lock torque even in an induction motor and can be used for the same application as a series motor. <P>SOLUTION: Three-phase drive currents Iu, Iv, and Iw of a three-phase induction motor 12 for rotating a grinder 10 are converted into a d-axis current Iq and a d-axis current Id, and on the basis of these results of the q-axis current Iq and d-axis current Id, the rotational speed of the induction motor 12 is PWM-controlled by a PWM control circuit 22 and an inverter circuit 16. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power tool drive device.

  An induction motor (induction motor) is used as a drive source for an electric tool (Patent Document 1).

For example, examples of the electric tool include a blade sharpener and a high-frequency grinder.
Japanese Patent Application Laid-Open No. 7-142928

  As an advantage of the induction motor as described above, there is a small drop in the rotational speed even if the torque is increased to a certain extent, and there is no brush and the life is long. However, the induction motor has a problem that the lock torque is small.

  Therefore, an induction motor is rarely used as a drive source for a general electric tool, and a series motor having a large lock torque is mainstream. However, this series motor has a problem that the brush life is shorter than that of the induction motor.

  Therefore, in view of the above problems, the present invention provides a control device for an electric tool that can increase the lock torque even in an induction motor and can be used for the same application as a series motor.

  The invention according to claim 1 is a drive device for an electric tool driven by a three-phase induction motor, wherein the inverter circuit supplies a three-phase drive current to a stator winding of the induction motor, and the inverter circuit A PWM control circuit for supplying a PWM signal; drive current detection means for detecting the three-phase drive current; a d-axis current that is a current component corresponding to a magnetic flux based on the detected three-phase drive current; A three-phase / two-phase conversion means for converting to a q-axis current that is a current component corresponding to the torque of the induction motor, a speed detection means for detecting the rotational speed of the induction motor, and a speed command signal for outputting a speed command signal Based on the output means, the converted q-axis current, the detected rotation speed, and the speed command signal, a control signal is sent to the PWM control circuit so that the rotation speed corresponds to the speed command signal. A force control means is a drive device for an electric tool, characterized in that it comprises a.

  The invention according to claim 2 is the power tool drive device according to claim 1, wherein the control means controls the torque to increase as the q-axis current increases.

  The invention according to claim 3 is the drive device for the electric tool according to claim 1, wherein the control means controls the torque to decrease when the q-axis current decreases.

  In the power tool drive device according to the first aspect of the present invention, the control means is based on the q-axis current corresponding to the torque of the induction motor, the detected current rotation speed of the induction motor, and a speed command signal input from the outside. Then, a control signal is output to the PWM circuit so that the rotation speed corresponds to the speed command signal, and the PWM circuit outputs a PWM signal to the inverter circuit to rotate the induction motor.

  As described above, the rotational speed can be maintained without reducing the torque by performing vector control of the rotational speed using the q-axis current which is a current component corresponding to the torque.

  In the power tool drive device according to the second aspect of the present invention, the q-axis current increases when the drive is stopped due to some cause of the power tool to enter the lock torque state. Control to go up. As a result, the conventional problem that the lock torque is small can be solved.

  In the power tool drive device according to the third aspect of the invention, the control means can control the torque to decrease when the torque becomes light and the q-axis current decreases, thereby realizing energy saving.

  Hereinafter, the grinder 10 which is one of the electric tools of one Embodiment of this invention is demonstrated based on FIG. 1 and FIG.

(1) Structure of the grinder 10 FIG. 2 is a perspective view of the grinder 10 according to the present embodiment. An induction motor 12 as a drive source is built in the frame 50 of the grinder 10 and is provided at the side of the frame 50. The rotation speed can be changed by a certain speed adjustment switch 52.

(2) Configuration of Drive Device 14 The configuration of the drive device 14 of the induction motor (induction motor) 12 that drives the grinder 10 will be described based on the block diagram of FIG.

  The drive device 14 includes an inverter circuit 16, a rectifier circuit 18, an AC power supply 20, a PWM control circuit 22, a three-phase / two-phase conversion circuit 24, a speed detection circuit 26, a two-phase / three-phase conversion circuit 32, a trigger. Circuit 34.

  The inverter circuit 16 causes a three-phase drive current to flow through the three-phase (u-phase, v-phase, w-phase) stator windings 36u, 36v, 36W of the induction motor 12. The inverter circuit 16 includes six transistors Tr1 to Tr6 that are power switching semiconductors, and a diode is connected in parallel to the switching transistors Tr1 to Tr6 in the reverse direction. Further, detection resistors R1, R2, and R3 for detecting a three-phase drive current are connected. Further, a DC power source is supplied from the AC power source 20 to the inverter circuit 16 through the rectifier circuit 18.

  The PWM control circuit 22 supplies a PWM signal to the gate terminals of the six switching transistors Tr1 to Tr6. The PWM control circuit 22 performs pulse width modulation based on three-phase voltages Vu, Vv, and Vw, which will be described later, and turns on / off the switching transistors Tr1 to Tr6 at a predetermined timing.

  The three-phase / two-phase conversion circuit 24 converts the AD converted drive currents Iu, Iv, and Iw into a d-axis current Id that is a current component corresponding to the magnetic flux and a current component that is a current component corresponding to the torque of the induction motor 12. It converts into shaft current Iq.

次に、このように変換した二相の電流Ｉα，Ｉβをｑ軸電流Ｉｑとｄ軸電流Ｉｄに（２）式を用いて変換する。

速度検出回路２６では、３個のホールＩＣ２８，２８，２８からの位置検出信号に基づいて誘導モータ１２の回転子の回転角θと回転速度ωを検出する。 In this conversion method, the three-phase drive currents Iu, Iv, and Iw are converted into two-phase Iα and Iβ as shown in the equation (1).

Next, the two-phase currents Iα and Iβ converted in this way are converted into a q-axis current Iq and a d-axis current Id using the formula (2).

The speed detection circuit 26 detects the rotation angle θ and the rotation speed ω of the rotor of the induction motor 12 based on the position detection signals from the three Hall ICs 28, 28, 28.

  The control unit 30 receives the rotation angle θ and the rotation speed ω from the speed detection circuit 26, the q-axis current Iq and the d-axis current Id from the three-phase / two-phase conversion circuit 24, and the speed command from the trigger circuit 34. Signal S is input. Based on these signals, a d-axis voltage Vd and a q-axis voltage Vq are output. This control method will be described later.

  The trigger circuit 34 outputs a speed command signal S in accordance with the operating state of the speed adjustment switch 52 of the grinder 10 shown in FIG.

この変換された二相の電圧Ｖα，Ｖβを、三相の電圧Ｖｕ，Ｖｖ，Ｖｗに（４）式に基づいて変換する。

この変換された三相の電圧Ｖｕ，Ｖｖ，Ｖｗを前記したＰＷＭ制御回路２２に出力する。 In the two-phase / 3-phase conversion circuit 32, the d-axis voltage Vd and the q-axis voltage Vq are first converted into a two-phase voltage based on the equation (3).

The converted two-phase voltages Vα, Vβ are converted into three-phase voltages Vu, Vv, Vw based on the equation (4).

The converted three-phase voltages Vu, Vv, Vw are output to the PWM control circuit 22 described above.

(3) Control Method of Grinder 10 Next, a control method of the drive device 14 of the grinder 10 having the above configuration will be described.

  The user of the grinder 10 tries to rotate the grinder 10 at a predetermined rotation speed by turning on the power supply and adjusting the speed adjustment switch 52. The trigger circuit 34 outputs a speed command signal S to the control unit 30 in accordance with the speed adjustment switch 52. The control unit 30 outputs the q-axis voltage Iq and the d-axis voltage Id to the two-phase / three-phase conversion circuit 32 in accordance with the speed command signal S.

  In the 2-phase / 3-phase conversion circuit 32, the q-axis voltage Iq and the d-axis voltage Id are converted into the three-phase voltages Vu, Vv, Vw as described above and output to the PWM control circuit 22.

  The PWM control circuit 22 outputs PWM signals to the gate terminals of the six switching transistors of the inverter circuit 16 in accordance with the three-phase voltages Vu, Vv, and Vw.

  The inverter circuit 16 outputs the three-phase drive currents Iu, Iv, Iw to the three-phase stator windings 36u, 36v, 36w by turning on / off the switching transistor in accordance with the PWM signal, and the induction motor. 12 is rotated.

  Further, the three Hall ICs 28, 28, 28 represent the rotation state of the rotor of the induction motor 12 by a position detection signal and output it to the speed detection circuit 26. The speed detection circuit 26 outputs the current rotation angle θ and rotation speed ω of the rotor to the control unit 30 based on the position detection signals from the three Hall ICs 28, 28, 28 sent thereto.

  The control unit 30 compares the speed command signal S with the input current rotational angle θ and the rotational speed ω, and sets the d-axis voltage Id so that the current rotational speed ω becomes the rotational speed ω corresponding to the speed command signal S. The q-axis voltage Iq is feedback controlled.

  During the PWM control as described above, the grinder 10 may be locked, and the grinder 10 may stop rotating. In this case, the q-axis current Iq converted by the three-phase / two-phase conversion circuit 24 increases. This is because the q-axis current Iq increases as the torque increases. The controller 30 detects that the grinder 10 is in the locked state by increasing the input q-axis current Iq, and controls the q-axis voltage Vq and the d-axis voltage Vd so that the lock torque of the induction motor 12 is increased. .

  As a result, the lock torque at the time of locking, which has been considered to be small in the past, can be increased, and the operation can be facilitated.

  Conversely, when the torque of the induction motor 12 decreases, the q-axis current Iq also decreases, so the control unit 30 controls the 2-phase / 3-phase conversion circuit 32 accordingly.

  Thereby, the grinder 10 can be rotated with energy saving without giving more torque than necessary.

  The present invention is not limited to a grinder, and can be used as a driving device for a power tool such as a blade sharpener or a drill.

It is a block diagram of the drive device of the grinder which shows one Embodiment of this invention. It is a perspective view of a grinder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Grinder 12 Induction motor 14 Drive device 16 Inverter circuit 18 Rectifier circuit 20 AC power supply 22 PWM control circuit 24 3 phase / 2 phase conversion circuit 26 Speed detection circuit 28 Hall IC
30 Control Unit 32 2-Phase / 3-Phase Conversion Circuit 34 Trigger Circuit

Claims (3)

A power tool drive device driven by a three-phase induction motor,
An inverter circuit for supplying a three-phase drive current to the stator winding of the induction motor;
A PWM control circuit for supplying a PWM signal to the inverter circuit;
Drive current detection means for detecting the three-phase drive current;
Three-phase / two-phase conversion means for converting a d-axis current that is a current component corresponding to a magnetic flux and a q-axis current that is a current component corresponding to the torque of the induction motor based on the detected three-phase drive current. When,
Speed detecting means for detecting the rotational speed of the induction motor;
Speed command signal output means for outputting a speed command signal;
Control means for outputting a control signal to the PWM control circuit based on the converted q-axis current, the detected rotation speed, and the speed command signal so as to obtain a rotation speed corresponding to the speed command signal;
A power tool drive device characterized by comprising: The control means includes
The power tool drive device according to claim 1, wherein the torque is controlled to increase when the q-axis current increases. The control means includes
The power tool drive device according to claim 1, wherein the torque is controlled to decrease when the q-axis current decreases.

Images