JPS63110988A - Controller for rotational speed - Google Patents

Abstract

PURPOSE:To keep loop gains constant regardless of the angular velocity of a body of revolution by forming the term (omega; angular velocity of body of revolution) of omega<2> obtained by arithmetic operation into a control loop. CONSTITUTION:A period detector 11 detects a period T as the number of clocks included in the high level period of a frequency signal FG from a pickup 3. A reference value T0 is subtracted from the detected period T in a subtraction circuit 12, and an error T is obtained from the reference value T0. The error T is transmitted over a gain correction circuit 13. The gain correction circuit 13 acquires (2pi/T)<2>=omega<2> from the detected period T from the period detector 11, and multiplies the error T by omega<2> and obtains a linearized output data T'= Tx(2pi/T)<2>. The output data T' from the gain correction circuit 13 is transmitted over a capstan motor 1 through an amplifier 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rotation control device suitable for application to, for example, a capstan speed servo of a VTR.

[Summary of the invention]

This invention applies when the speed of a rotating body is controlled so that the period of a frequency signal corresponding to the rotational speed of the rotating body becomes a value at a target rotational speed, and when the target rotational speed varies variously. In addition, the loop gain can be automatically corrected according to the change, so that rotation control can be performed well even when the angular velocity changes continuously.

[Conventional technology]

For example, in a VTR, the speed control of a tape feeding capstan has conventionally been configured as shown in FIG.

That is, (1) is a capsun drive motor, (2) is a capsun drive motor that rotates coaxially with this drive motor (1), and
1) is a frequency signal generator that obtains a frequency signal according to the rotational speed, and (3) is a pickup that obtains the frequency signal as an output. This frequency signal generator (2) may be magnetic, electrostatic or optical.

For example, duty ratio from pickup (3) is 50%
The frequency signal FG (m4 diagram A), which is a rectangular signal, is supplied to the angular velocity ω detection circuit (4). This angular velocity detection circuit (4) functions as a frequency-voltage conversion circuit that outputs a voltage corresponding to the period of the frequency signal FC. For example, as shown in FIG. By measuring the number of pulses with a counter and converting the measured value to voltage by D/A conversion,
The voltage output shown in the figure is obtained.

This voltage output is supplied to a comparison circuit (7) via a switch circuit (5) and a gain control resistor circuit (6), and is compared with a reference voltage from a reference voltage source (8).
The comparison output is supplied to the cab scan drive motor (1) via the amplifier (9). Therefore, motor Tl)
is controlled to rotate at such a speed that the period T of the signal FG becomes a constant period To according to the reference voltage.

In this case, since the gain characteristics of the angular velocity detection circuit (4) are taken into account, the relationship between the two becomes a hyperbolic relationship as shown in FIG. 5A. Therefore, the gain characteristic is the slope of the tangent to this hyperbola at a specific angular velocity ω. In other words,
The above speed control system exhibits a nonlinear gain characteristic of l/ω2 with respect to the angular velocity ω, as shown in FIG. 5B.

Therefore, in the speed control system as described above, gain correction is required each time the target speed is changed in order to keep the characteristics of the control loop constant.

In the conventional circuit shown in FIG. 3, a switch circuit (5) and a resistor circuit (6) are means for this gain correction.

That is, (10) is a mode control circuit, which controls the reference voltage source (8) according to each mode such as normal playback, S P/L P mode such as in the case of 8 mm video, double speed playback mode, etc. While the voltage value is changed, the switch circuit (5) is switched according to the mode, and the resistors R1 to R4 of the resistance circuit (6) are switched, thereby performing gain correction.

[Problem that the invention seeks to solve]

However, in this method of performing gain correction each time the resistance value is switched, as the number of modes increases, the number of gain correction resistors increases accordingly.

Furthermore, if it is applicable to a system where the angular velocity changes continuously, such as speed control with a constant linear velocity in an optical disk player, theoretically an infinite number of gain corrections are required, and the resistance described above is This cannot be handled by value switching.

This invention improves this point.

[Means for solving problems]

In the present invention, a signal processing means is provided as the gain correction means so as to keep the control loop gain constant regardless of changes in the angular velocity ω of the rotating body.

Specifically, since the speed control system exhibits a nonlinear gain characteristic of 1/ω2 with respect to an angular velocity of 0, a term of 02 calculated by calculation is provided in the control loop in order to linearize this nonlinear term.

[Effect]

The correction term for linearization is calculated by calculation,
If a calculation means with a fast signal processing speed is used, the calculation means is installed in the control loop. If not, the mode can be changed by preparing a table of terms calculated in advance for linearization. Even if there are a large number of them, they can be easily dealt with.

〔Example〕

FIG. 1 shows an embodiment in which the present invention is applied to the speed control of a tape feeding capstan motor as described above, and the same parts as in the conventional example shown in FIG. 3 are given the same numbers. .

In this example, the frequency signal FC from the pickup (3) is supplied to the period detection circuit (11), and the period detection circuit (11) generates a high-speed rectangular wave signal FG with a duty ratio of 50% as in the previous example. The period T is detected as the number of clocks included in the level period. This detection period T
is supplied to a gain correction circuit (13), which will be described later, and also to a subtraction circuit (12). Then, in this subtraction circuit, the target motor (
1) A reference value T corresponding to the period of the signal FC at the rotation speed.

(also expressed as a count value) is subtracted to obtain the error ΔT from the reference value To. Since this error ΔT has a nonlinear gain characteristic as described above,
This error ΔT is supplied to a gain correction circuit (13).

This gain correction circuit (13) performs nonlinear-linear conversion. If this gain correction circuit (13) has a fast signal processing speed, (2π/T)2=ω2 is obtained from the detection period T from the period detection circuit (11), and this is multiplied by the error ΔT. The linearized output data ΔT
'- and obtained as an analog output voltage from this gain correction circuit (13).

This analog output voltage is then supplied to the capstan motor (1) via the amplifier (14), and the capstan motor (1) has a frequency of the signal FG of 1/T.

It is controlled so that

The gain correction circuit (13) has a signal processing speed so fast (
If not, as shown in FIG.
ω for Te3... 12. ω. 22゜ω032
. . is determined by calculation, and this is written in RAM as an address, for example, the reference period Tot + Te21 Te3 . . . Then, the reference period is To □,
Every time Te2... changes, the corresponding ω
o12. ω022... is read from the RAM, and this ωo12. The control voltage to the motor (1) is obtained by multiplying the error ΔT by the value of ω02' and converting this into an analog voltage.

Note that this gain correction operation can be executed using a microcomputer.

As described above, the loop gain becomes constant regardless of the rotational speed of the motor (1), and it is also possible to make the speed variable continuously.

Therefore, the present invention can be applied to a speed servo with a constant linear velocity in a disc playback device.

〔Effect of the invention〕

According to this invention, a gain correction term calculated by calculation is set and inserted in the speed control loop in order to make the nonlinear gain characteristic of the control voltage linear, so that the loop can be looped regardless of the angular velocity of the rotating body. Gain can be kept constant. Since the gain correction term is determined by calculation, it can easily be used even when the speed changes continuously.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the inventive device, Fig. 2 is a diagram for explaining an example of the main parts of the invention, Fig. 3 is a block diagram of an example of the conventional device, and Fig. 4 is the same. FIG. 5, which is a diagram for explanation, is a diagram showing the gain characteristics of the period detection circuit. (11 is a capstan motor, (2) is a frequency signal generator, (11) is a period detection circuit, and (13) is a gain correction circuit.

Claims (1)

[Claims] The period T of the frequency signal from means for generating a frequency signal corresponding to the rotational speed of the rotating body is detected, and the rotational speed of the rotating body is controlled by a control voltage formed based on the detected period value. has a control loop that controls the frequency signal so that the frequency is 1/T_0 (T_0 is the period of the frequency signal at the target rotational speed), and within this control loop there is a nonlinear gain characteristic. A rotational speed control device comprising means for setting a term obtained by calculation in order to linearize the term.