JP2002186270A - Servo control device - Google Patents

Abstract

(57) [Problem] In the prior art, the compensation amount of the torque ripple is stored in the amplifier side, so that the effect of the compensation is sufficient for the torque ripple having a large variation for each motor such as cogging torque. There was a problem that can not be obtained. SOLUTION: A storage device 21 mounted on a motor side for storing information on the cogging torque of the motor, and receives information on the cogging torque stored in the storage device 21 when the power is turned on. A compensator 6 that calculates a compensation amount from a mechanical angle that is an output of the connected encoder 2 and an adder 7 that adds the compensation amount that is an output of the compensator 6 to a torque command are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo control device for driving a motor, and more particularly to a device for compensating a cogging torque existing in the motor.

[0002]

2. Description of the Related Art A conventional torque ripple compensator is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-284286.
As shown in FIG. In the figure, 1 is a motor, 2 is an encoder, 3 is a speed controller, 4 is a current amplifier, 5 is a differentiator, and 6 is a torque ripple compensator. FIG. 4 is a block diagram of speed control of a general servo motor except for the torque ripple compensator 6. The encoder 2 detects the rotation angle θ of the rotor of the motor 1. The differentiator 5 differentiates the rotation angle θ and outputs the rotation speed ω of the rotor. Speed controller 3 outputs the sum of a constant multiple of the integral of the deviation of the speed command omega rotational speed of _r and rotor omega. The output of the speed controller 3 is a torque command _Tr , and is directly input to the current amplifier 4 when there is no torque ripple compensator 6. Current amplifier 4
Supplies the motor 1 with a current i proportional to the torque command _Tr . The torque ripple compensator 6 operates as follows. That is, when the motor is driven by the servo amplifier,
Motors produce torque ripple that varies periodically with the angle of rotation of the motor for various reasons. Therefore, the adder 7 compensates for the compensation amount T so as to cancel the torque ripple.
adding _c to the torque command T _r, enter the added amount T _r ^c to the current amplifier 4, to compensate for torque ripple. According to the technique disclosed in Japanese Patent Application Laid-Open No. 7-284286, the torque ripple compensation amount _Tc is determined by changing the rotation angle θ and the torque command _Tr (or current I).
A method of creating and storing a table as a function of and a method of calculating with an arithmetic expression α (T _r ) cos (A · θ + φ) are described. In this case, α (T _r ), A, and φ must be stored.

[0003]

However, in the prior art, since the compensation amount of the torque ripple is stored in the amplifier side, the effect of the compensation for the torque ripple having a large variation for each motor such as cogging torque is reduced. However, there was a problem that was not obtained sufficiently. Therefore, an object of the present invention is to provide a servo control device having a cogging torque reduction effect capable of sufficiently obtaining a compensating effect even for a cogging torque having a large variation for each motor.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a servo control device for detecting a rotation angle and a rotation speed of a motor and performing speed control. A storage device for storing cogging torque information, and receiving the cogging torque information stored in the storage device when the power is turned on, and compensating for the cogging torque information and a mechanical angle which is an output of an encoder connected to the motor. A compensator for calculating the amount, and an adder for adding a compensation amount, which is the output of the compensator, to the torque command. ΣA _n
This servo control device is characterized by storing an order n, an amplitude A _n , and a phase B _n by approximating sin (nθ + B _n ) (where θ indicates a mechanical angle).

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, the parts different from the conventional example are 21 storage devices, which are preferably mounted in an encoder directly connected to the motors, but may be any other locations unique to each motor. The storage device 21 stores information on the cogging torque of the motor 1. The information on the cogging torque is transmitted to the servo amplifier (servo control device) immediately after the power is turned on. The compensator 6 calculates the compensation amount _Tc based on this information and the rotation angle of the motor 1 which is the output of the encoder 2, and adds the compensation amount _Tc to the torque command _Tr . First, the cogging torque information stored in the storage device 21 will be described. Generally, the cogging torque τ _c is a periodic function of the mechanical angle of the motor, and can be expressed by Equation 1.

[0006]

(Equation 1)

Here, θ is a mechanical angle, n is an order, and A _n is n
The amplitude of the second harmonic, _Bn, is the phase of the nth harmonic. A _n and B _n are different for each motor. In the storage device 21,
n, _An and _Bn are stored. These pieces of information can be obtained by measuring the cogging torque for each motor. Generally, to approximate the cogging torque, several orders may be used, and the storage capacity may be small. Next, the compensation amount will be described. Since the generated torque τ ₀ of the motor is proportional to the motor current and the motor current is proportional to the torque command, the generated torque τ _{0 of the} motor can be expressed by Expression 2.

[0008]

(Equation 2)

[0009] Here, T _r is the torque command, is k _T is the torque constant, k _i is a proportional constant of the current amplifier. When the motor has a cogging torque, the output torque τ of the motor is the sum of the generated torque τ _{0 of the} motor and the cogging torque τ _c , and is expressed by Expression 3.

[0010]

[Equation 3]

[0011] Therefore, as shown in the examples, by adding the compensation amount T _c of the torque command T _r to compensate for cogging torque, and inputs the addition amount T _r ^c to the current amplifier 4. Compensation amount T _c
The information of the cogging torque n, with A _n, and B _n rotation angle theta, given by Equation 4.

[0012]

(Equation 4)

As a result, the output torque τ of the motor is given by
As shown by, the cogging torque is compensated and becomes equal to the generated torque τ _{0 of the} motor.

[0014]

(Equation 5)

[0015]

As described above, according to the present invention, the effect of sufficiently compensating for the cogging torque having a large variation among the motors and reducing the torque ripple can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional technique.

[Description of Signs] 1 Motor 2 Encoder 21 Storage 3 Speed Controller 4 Current Amplifier 5 Differentiator 6 Compensator 7 Adder

Claims (3)

[Claims] 1. A servo control device for detecting a rotation angle and a rotation speed of a motor and performing speed control, the storage device being mounted on the motor side and storing information on a cogging torque of the motor; A compensator that receives the cogging torque information stored in the storage device and calculates a compensation amount from the cogging torque information and a mechanical angle that is an output of an encoder directly connected to the motor; and a compensator output. A servo control device comprising: an adder that adds a compensation amount to a torque command. As wherein information of the cogging torque, by approximating the cogging torque and _{ΣA n sin (nθ + B n} ) ( in θ here showing the mechanical angle), and stores order n, the amplitude A _n, the phase B _n The servo control device according to claim 1, wherein: 3. The servo control device according to claim 1, wherein the motor side is inside the encoder.