JPH0755074B2 - Motor holding torque control method - Google Patents

Description

The present invention relates to a method for controlling a holding torque of a synchronous servo motor.

[Conventional technology]

FIG. 9 shows the structure of a servo motor incorporating an electromagnetic brake in a conventional robot drive servo motor.

The conventional servomotor shown in FIG. 9 generates a holding (braking) torque by exciting an electromagnetic brake built in the brake unit 11, so a strong magnetic circuit is required, and usually a copper wire coil wound several hundred turns. Since the component parts made of steel and iron are required, its weight is much larger than the holding (braking) torque, and the volume of the brake part that can be installed in the motor is also very large as shown in Fig. 9. There is. There is also a drawback that a separate DC power source is required for the brake.

[Problems to be Solved by the Invention]

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a non-contact holding torque generating structure that can be downsized and a driving method thereof.

[Means for Solving the Problems]

The present invention has been made to solve the above problems,
In a synchronous AC motor that has a multi-phase AC winding in the stator and a field is formed by using permanent magnets in the rotor, the stator and rotor in the motor are made of the same magnetic material as the number of motor pole pairs. The configured convex teeth and the same number of permanent magnets facing each other are provided. When the motor shaft is held, the motor shaft is held by the attracting force (holding torque) in the rotating direction that acts between the facing convex teeth and the permanent magnets. The pulsation of the same polarity as the motor of the brake part generated by the holding torque by the convex teeth and the permanent magnets is added to the motor command current by adding the direct current component to the The cogging torque is generated to cancel each other to obtain a normal output having no cogging torque.

〔Example〕

FIG. 1 is a cross-sectional view of an embodiment in which a holding torque generating device according to the present invention (an example in which the number of motor poles is 8) is incorporated into a motor, and FIG. 2 is an X of the holding torque generating device portion. −
X-ray sectional view, FIG. 3 is a motor control circuit diagram, and the holding torque generating device according to the present invention is, as shown in FIG. 2, a ring 2 having magnetic convex teeth 1 having the same number of pole pairs as the motor. And the convex teeth 1 attached to the rotor 4 and the same number of permanent magnets 3 arranged to face each other.

In FIG. 1, 6 is a frame, 7 is a stator, 8 is a bearing, and 9 is a sensor part. Now, in FIG. 1, torque T _B (holding torque) generated when the toothed ring 2 is fixed and the rotor 4 is rotated clockwise.
Is However, w: magnetic energy stored in the gap θ: given by the rotation angle (mechanical angle). w is Where H (θ) is the magnetomotive force of the magnet P (θ) is the permeance l is the thickness of the magnet, and the number of teeth is N and the electrical angle is the torque required for rotation (holding torque). T _B is (However, θ = N ·) can be written. If the gap between the tooth and the permanent magnet is made so that the inside of the braces in the above equation becomes a sine wave, the inside of the braces will be Asin (N), so T _B is Becomes

Also, consider adding a DC current _If to the synchronous machine to rotate the output shaft of the motor. Considering this in the two-phase motor model shown in FIG. 4, in the case of a synchronous machine, the rotor current is i _A
＝ O, i _B ＝ I. At that time, if the rotor is attracted and stopped at an arbitrary angle with the stator, the stator current i
i _α = I _f cos and i _β = I _f sin may be applied to _α and i _β , respectively. Also when'll rotate the output shaft in this state, the motor generates the cogging torque T _e, the torque T _e is _{T e = P · M · (} i α · i A -i β · i B) where p : Number of pole pairs M: Mutual inductance is expressed as T _e = -P ・ M ・ I ・ I _f sin, and if M ・ I = Φ, then T _e = −P ・ Φ ・ I _f sin …… (2 ).

Torque fluctuation of the holding torque expressed by the equation (1),
The torque fluctuation of the cogging torque expressed by the equation (2) is shown in FIGS. 5 (a) and 5 (b).

Since both equations (1) and (2) are sinusoidal, If the number N of brake teeth and the direct current I _f are selected so that, the cogging torque generated by the direct current of the motor is generated by the disk with the convex teeth and the permanent magnet as shown in FIG. 5 (c). The holding torques can cancel each other out.

(T _B + T _e = 0) Therefore, if I _f and N are set as described above, in the motor having the structure shown in FIG. 1, when the motor rotates, the direct current I _f is added to the motor command current I to operate the motor. The cogging due to the holding torque generated in the holding torque generating portion can be canceled in the motor, and the normal output without the cogging torque can be taken out. (FIG. 3 shows the portion of the control unit to which the direct current I _f is added.) On the other hand, assuming a stop time, the motor current I and the direct current I _f
Since both I _f are 0, only the holding torque of the holding torque generating portion described above works and the motor output shaft is fixed by the holding torque.

Therefore, if the command power is cut off during motor operation, the rotation of the motor rotor is braked by the normal dynamic brake (connecting a resistor to the motor) and finally the holding torque causes the rotor to face the permanent magnet and convex teeth. Hold anywhere you want to stop.

FIG. 6 shows a motor drive circuit diagram including a control unit of a holding torque generating mechanism when applied to an actual three-phase synchronous machine.

[Action]

By using the above driving method and the holding torque generating structure of a thin disk with teeth attached to the rotor with permanent magnets attached, it is possible to manufacture a holding torque generating mechanism that is extremely thin compared to conventional brakes. Become.

[Different Examples]

FIG. 7 shows a different embodiment, in which the brake disc 23 with convex teeth is provided on the rotary shaft 5, and the permanent magnet 3 for brake having the yokes 20 on both sides is provided on the frame 21 so that the gap is in the axial direction. It was made to become.

Further, FIG. 8 shows an example in which the permanent magnet 3 is projected to the holding torque generating mechanism side of the rotor of the motor portion for a long time and is used as a permanent magnet for braking.

〔The invention's effect〕

As described above, according to the present invention (1). It is possible to manufacture a small and flat holding torque generating mechanism, and the motor volume is significantly reduced.

(2). Brake power supply is unnecessary.

There is a great effect.

[Brief description of drawings]

1 is a sectional view of an embodiment of the present invention, FIG. 2 is a sectional view taken along line XX, FIG. 3 is a control circuit diagram of the embodiment, FIG. 4 is a model diagram of a two-phase electric motor, and FIG. FIG. 6 is a diagram showing changes in cogging torque and holding torque, FIG. 6 is a drive circuit diagram when applied to a three-phase synchronous machine, FIG. 7 is a sectional view of a different embodiment (axial gap type), and FIG. FIG. 9 is a sectional view of a different embodiment, and FIG. 9 is a sectional view of a motor in which a conventional electromagnetic brake is incorporated. 1 ... Convex teeth 2 ... Ring 3 ... Permanent magnet 4 ... Rotor 5 ... Rotary shaft 6 ... Frame 7 ... Stator 8 ... Bearing 9 ... Sensor section 10 ... Sensor section 11 ... Brake Part 12 …… Motor part 20 …… Yoke 21 …… Frame 22 …… Gap 23 …… Convex toothed disc

Claims (1)

[Claims] 1. In a synchronous AC motor having a stator having a multi-phase AC winding and a rotor having a permanent magnet for forming a field, a stator and a rotor in the motor have a number of motor pole pairs. Providing convex teeth made of the same number of magnetic materials and the same number of permanent magnets arranged facing them, when the motor shaft is held, attractive force in the rotating direction (holding torque) that acts between the opposing convex teeth and permanent magnets. ) Holds the motor shaft, and when driving, the pulsation of the same polarity of the motor of the brake part generated by the holding torque by the convex teeth and the permanent magnet is added to the motor command current by adding the direct current component to the pulsation of the motor part. A method of controlling a motor holding torque, characterized in that a cogging torque having an opposite phase is generated to cancel the cogging torque so as to obtain an output without a normal cogging torque.