JPH05220641A - Driving device - Google Patents

Abstract

PURPOSE:To secure a high responsiveness even when a small motor with small inertia is employed by adding a weight on the rotor side of the servo motor, reducing the ratio of the inertia on the servo motor side to the inertia on the driven part side, and providing a control means to execute the driving control of the servo motor. CONSTITUTION:An inertia load 6 is added to a rotor 2 of a servo motor 1, and the ratio of the inertia (JM+JA) on the servo motor 1 side to the inertia JL of the driven part 4 side is reduced for the part rear of the power shaft coupling 3. Thus, if the gain affordability in the high frequency region where the phase becomes -180 deg. is kept constant, the gain in the low frequency region can be increased, the reduction of the responsiveness can be suppressed and the high responsiveness can be secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device for driving a feed shaft of a machine tool, each axis of a robot, etc. by a servo motor, and more particularly to a drive device having improved responsiveness of the servo motor.

[0002]

2. Description of the Related Art Conventionally, a drive system of a servo motor having a load such as table movement of a machine tool has a frequency of 100 to 1
The characteristic of the mechanical system may disappear in the range of 50 Hz, and the characteristics may change from the state of motor inertia + load inertia to the state of only motor inertia. When the amount of gain decrease due to the ratio of the motor inertia J _M and the load inertia J _L is G, G = 20log (J _M / (J _M + J _L )) = 20log (1 /
(1 + N)) N = J _L / J _M. That is, when J _l = J _M , the inertia ratio N = 1
G = 20log (1 / (1 + 1)) =-6 dB Similarly, if J _L = J _M × 9, then the inertia ratio N = 9, and G = 20log (1 / (1 + 9)) =-20 dB. .. This can be seen in the Bode diagram as shown in FIG.
If the load connected to the motor shaft is a rigid body, the gain will decrease uniformly as described above, but in an actual machine there will be non-linear elements such as rattling, twisting, and bending in the power transmission member, so it will not be uniform. However, as shown in FIG. 5, the gain characteristic is due to the full-load inertia at low frequencies, and the gain characteristic is close to no load at high frequencies.

Therefore, on the Bode diagram of FIG. 5, this switching frequency seems to have a natural frequency. In particular, when the ratio of the inertia of the servo motor and the inertia of the load (inertia ratio N) is large, the gain gap between them is large, and therefore the gain jump also becomes large. On the other hand, since the stability of the servo system is determined by the gain margin in the high frequency region where the phase is -180 degrees, it is necessary to secure the stability in the gain characteristic under no load. Therefore, when the gain of the speed loop is high, the stability of the speed loop cannot be ensured, so that it is unavoidable that only the low speed loop gain can be used, and the accuracy of the machine cannot be improved. Therefore, in the past, in order to obtain a high speed loop gain and ensure a high response, a large motor with a large motor inertia had to be adopted in order to reduce the inertia ratio.

[0004]

However, the adoption of a large-sized motor for ensuring high response is unnecessarily large in terms of output and is unreasonable in terms of space and cost. On the other hand, as the servo motor technology has improved, the motor itself has become smaller and higher in output, and it has become possible to use a sufficiently small motor for output. However, since the problem of inertia ratio does not change, when a small motor is adopted, there is a problem that the inertia ratio becomes large and the responsiveness must be lowered. The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a drive device that can employ a small motor to ensure high responsiveness.

[0005]

In order to achieve the above object, a drive device of the present invention has a servomotor, a rotor of the servomotor, and an inertia larger than the rotor, and is driven by the servomotor. And a power transmission member connecting the driven part to each other, adding a heavy load to the rotor side of the servomotor to reduce the ratio between the inertia on the servomotor side and the inertia on the driven part side, and A control means for driving and controlling the servo motor is provided.

[0006]

In the drive device configured as described above, the inertia on the servo motor side is increased and the inertia ratio N can be reduced by adding a heavy object. By reducing the inertia ratio N, apparently the change in gain when the characteristics change from the motor inertia + load inertia state to the motor inertia only state G = 20
log (J _M / (J _M + J _L )) = 20 log (1 / (1+
N)) N = J _L / J _M can be reduced. Therefore, if the gain margin in the high frequency region where the phase is −180 degrees is kept constant, the gain in the low frequency region can be made higher, and the decrease in response can be reduced to ensure high response.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the drive device. The servo motor 1 is driven by the servo amplifier 11. The servo amplifier 11 receives a speed command from the position control unit 13 and the tacho generator (TG) 1
The velocity feedback signal from 2 is returned to form a velocity loop. The position pulse feedback signal from the encoder 14 is returned to the position controller 13 to form a position loop. Servo amplifier 11 and position control unit 1
Reference numeral 3 constitutes a control means in the present invention for driving and controlling the servo motor 1. FIG. 2 is a sectional view showing the first embodiment. The rotor shaft 2 of the servomotor 1 is driven by the shaft coupling 3 to the driven portion 4
Is connected to the shaft 5. The shaft coupling 3 constitutes the power transmission member of the present invention. An inertial load 6 as a heavy object is integrally attached to the rotor shaft 2. The inertia of the inertial load 6 is J _A , the inertia of the shaft coupling 3 on the servo motor side is J _CM , the inertia of the driven part of the shaft coupling 3 is J _CL , the inertia of the driven part 4 is J _L , and the inertia of the servo motor 1 is When the inertia of the rotor and J _M, inertia ratio N _{is, N = (J L + J} CL) / (J M + J CM + J a) , and the can be reduced inertia ratio N by mounting the inertial load 6, reduction of the response Can be reduced.

Now, J _M = 1, J _L = 10, J _CM = J _CL
= 0, consider the case of J _A = 1 and J _A = 0. When the inertial load J _A = 0, the transfer function in the low frequency region is A (ω) / (J _M + J _L ) = A (ω) / (1 + 10) =
A (ω) / 11 In the high frequency region, A (ω) / J _M = A (ω) / 1 = A (ω). On the other hand, when the inertial load J _A = 1, the transfer function in the low frequency region is A (ω) × (12/11) / (1 + 1 + 10) = A
(Ω) / 11 In the above equation, 12/11 is a coefficient for equalizing the transfer function in the low frequency region when the inertial load J _A = 0, and is realized by adjusting the gain of the speed loop. Also,
The transfer function in the high frequency region when the inertial load J _A = 1 is: A (ω) × (12/11) / (1 + 1) = A (ω) ×
(6/11), and the transfer function at high frequencies in the inertial load J _A = 1 is reduced to about 1/2 as compared with the transfer function A in the high frequency range (omega) in the inertial load J _A = 0 .. Therefore,
By attaching the inertial load 6, the gain margin increases and the gain becomes stable accordingly. Therefore, when J _A = 1 the transfer function A (ω) is larger than when J _A = 0, that is, the gain of the system can be increased.

FIG. 3 is a sectional view showing a second embodiment.
The driven part side hub 32 of the shaft coupling 3 shown in FIG. 3 is formed of an aluminum material, but the servo motor side hub 31 is formed of an iron material in order to have a function as an inertia load, and the shape of the driven part side is also the driven part. It is made larger than the side hub 32. The inertia ratio N at this time is N = (J _L + J _CL ) / (J _M + J _CM ), but the inertia J _CM on the servomotor side of the shaft coupling 3 is
Is large, the inertia ratio N can be made small, and the decrease in responsiveness can be suppressed.

Although the shaft coupling 3 is used as the power transmission member in the embodiments described above, the same can be said when a gear, a belt wheel or the like is used as the power transmission member other than the shaft coupling.

[0011]

As described above in detail, the present invention has the above-mentioned structure and adds a heavy load to the rotor side of the servomotor,
Since the ratio between the inertia on the servo motor side and the inertia on the driven portion side is made small, there is an excellent effect that high responsiveness can be secured even if a small motor having a small inertia is adopted.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of a drive device.

FIG. 2 is a sectional view showing a first embodiment.

FIG. 3 is a sectional view showing a second embodiment.

[Figure 4] Bode diagram

[Figure 5] Bode diagram

[Explanation of symbols]

 1 Servo motor 2 Rotor shaft 3 Shaft coupling (power transmission member) 4 Driven part 6 Inertial load (heavy load)

Claims (1)

[Claims] 1. A drive device comprising: a servo motor; and a rotor for the servo motor and a power transmission member having a larger inertia than the rotor and connecting a driven portion driven by the servo motor. A heavy load is added to the rotor side of the servo motor to reduce the ratio of the inertia on the servo motor side to the inertia on the driven part side, and a control means for driving and controlling the servo motor is provided. Drive.