JP3005369B2 - Servo system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo system, and more particularly to a software servo system used in, for example, a capstan servo or a drum servo of a VTR.

[0002]

2. Description of the Related Art In a conventional servo system, the order of a lag filter is always primary, or primary when the rotation of a motor is in a transient state, and secondary when the rotation of the motor is in a steady state. was there.

[0003]

[0004]

In such a conventional servo system, when the order of the lag filter is kept constant, the rotation of the motor becomes unstable in a transient state or a steady state, and the motor becomes unstable between the transient state and the steady state. Even when the order of the lag filter is switched, there is a problem that the rotation of the motor becomes unstable because the output signal of the lag filter suddenly changes by the switching. Therefore, a main object of the present invention is to provide a stable servo system.

[0005]

[0006]

According to the present invention, there is provided a servo system including a lag filter for synthesizing an output of a low-order filter and an output of a high-order filter, comprising: acceleration detecting means for detecting acceleration of rotation of the motor; A servo system, wherein the synthesis ratio of the outputs of the low-order filter and the high-order filter is controlled such that the ratio of the output of the high-order filter increases when the acceleration is small.

[0007]

The servo system is constituted by, for example, a microcomputer (hereinafter, "microcomputer"), and the microcomputer receives an FG signal and a PG signal from a capstan motor or a drum motor. The rotation speed is detected based on the FG signal, and the phase is detected based on the PG signal. The microcomputer further detects the acceleration based on the difference between the periods of the FG signal.

In the present invention, the order of the lag filter, for example, the combined ratio of the first order and the second order is changed according to the acceleration. Therefore, the higher the acceleration, the higher the ratio of the first order (lower order filter), the more stable the transient response in the transient state where the acceleration is higher, and the larger the ratio of the second order (higher order filter) in the steady state with the lower acceleration The low-frequency gain increases.

[0009]

According to the present invention, the motor can be stably controlled regardless of the transient state or the steady state.

[0010]

Referring to FIG. 1, a servo system 10 of this embodiment includes a motor 12, such as a drum motor or a capstan motor. The motor 12 outputs an FG signal indicating the rotation frequency and a PG signal indicating the rotation phase, and these are input to the microcomputer 16 via the amplifiers 14a and 14b. Then, the microcomputer 16 executes a so-called software servo based on the FG signal and the PG signal, and outputs a control signal. In response, the driver 18 drives the motor 12.

The software servo is executed as an FG interrupt routine according to a flowchart shown in FIG. That is, in the first step S1, the rotation speed S of the motor 12 is detected based on the FG signal. Next, in step S3, the FG signal input to the microcomputer 16 and the FG signal input to the
The period of the signal is detected, and the acceleration K of the rotation of the motor 12 is detected based on the difference. Further, in step S5, the rotation phase P of the motor 12 is detected based on the PG signal. The detected rotational speed S, acceleration K and phase P are then substituted into Equation 1 in step S7, and the rotational speed S and phase P are combined according to the acceleration K.
However, in the case of Equation 1, the maximum value of the acceleration K is “7” and the minimum value is “1” (1 ≦ K ≦ 7).

[0012]

G = (8−K) S / 8 + KP / 8 The combined data G is subsequently subjected to lag filter processing in step S9. That is, the primary lag filter output F ₁ and the secondary lag filter data F ₂ are obtained based on the synthesized data G, and these are substituted into Expression ₂ to obtain a normalized value K ′ (0 ≦ K ′ ≦ 1) of the acceleration K. ) Depending on F ₁ and F
₂ is synthesized.

[0013]

A = F ₁ × K ′ + (1−K ′) × F _{2 The} combined data A is converted into an analog signal in step S 11 and output from the microcomputer 16. Then, the driver 18 drives the motor 12 according to the output signal.

From the composite data G of Equation 1, the composite data G when the acceleration K is maximum (transient state) is as shown in Equation 3, and the composite data G when the acceleration K is minimum (steady state).
Is as shown in Equation 4.

[0015]

G = S / 8 + 7P / 8

[0016]

G = 7S / 8 + P / 8 That is, the greater the acceleration, the greater the phase ratio. That is, in the transient state where the acceleration is large, the ratio of the phase becomes large, so that the pull-in time becomes short. In addition, as the acceleration is smaller, the rate of the speed is larger, whereby the rotation unevenness in the steady state where the acceleration is smaller is eliminated, and the motor rotates stably.

Further, the acceleration K 'is obtained from the composite data A of the equation (2).
Is large (transient state), the ratio of the primary lag filter becomes large, and when the acceleration K 'is small (steady state), 2
The ratio of the secondary lag filter increases. The motor 12 operates stably by changing the ratio of the order of the filter as described above.
This will be described with reference to FIG. FIG. 3 shows the transient response characteristics of the motor speed. When the ratio of the primary lag filter is large, the transient response is stable, and when the ratio of the secondary lag filter is large, the transient response is unstable. FIG. 4 shows the frequency characteristics of the servo gain. When the ratio of the primary lag filter is large, the low-frequency gain is low, but when the ratio of the secondary lag filter is large, the low-frequency gain is high. In this embodiment, since the ratio between the primary lag filter and the secondary lag filter continuously changes in accordance with the change in acceleration, a discontinuous point is generated, and the rotation of the motor 12 becomes unstable. Never.

[0018]

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing the operation of the embodiment in FIG. 1;

FIG. 3 is a graph showing a transient response characteristic of a rotation speed of a motor.

FIG. 4 is a graph showing frequency characteristics of a servo gain of the embodiment of FIG. 1;

[Explanation of symbols]

 10: Servo system 12: Motor 16: Microcomputer 18: Driver

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H02P 5/00

Claims (1)

(57) [Claims] 1. A servo system including a lag filter for synthesizing an output of a low-order filter and an output of a high-order filter, comprising: acceleration detection means for detecting an acceleration of rotation of the motor; Wherein the output ratio of the low-order filter and the high-order filter is controlled so as to increase the output ratio.