JPH09107694A - Servo system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a feedback amount small when a voltage between both ends of a motor is large, to make the feedback amount large when the voltage is small and to obtain a natural control operation both in a high-speed operation and a slow operation in a servo system which drives the motor by a position control loop and by a speed control loop. SOLUTION: A voltage between both ends of a motor 18 is input, as a control signal, to a pulse-width modulator 28. An output voltage, from a tachogenerator, which is input to a comparator 14 changes the ON/OFF period of an analog switch 26 in such a way that the value becomes small when the voltage between both ends is large and that the value becomes large when the voltage between both ends is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo system used for controlling a moving object whose speed changes rapidly, and more particularly to a servo system for driving a motor used for zooming and panning operations of a surveillance camera. It is about.

[0002]

2. Description of the Related Art Position control technology using a DC servo system is widely used in various fields. However, if it is attempted to control the movement of the object only by the position control loop, it tends to become unstable by increasing the gain. Therefore, the speed control loop is usually used together. That is, for example, a motor with a DC tacho-generator is used, and its output is negatively fed back and controlled so as not to pass a target value.

[0003]

However, in the case of performing such control, when the feedback amount from the tachogenerator becomes large, the operation is stable during constant speed driving, especially at low speed, but the operation changes rapidly. The delay of the position control at the time of starting or stopping the operation becomes large, and it becomes difficult to achieve the target control operation. Of course, on the contrary, if the feedback amount from the tacho generator is too small, it makes no sense to use the speed control loop together. For example, the influence of the load fluctuation becomes large at low speed operation, and the operation target moves awkwardly. .

In particular, panning of a camera platform such as a surveillance camera,
In tilting or zooming servo operations, switching between ultra-slow operation, normal moving operation, and high-speed moving operation is often performed, and each of these operations requires smooth moving operation without rattling. Become. For example, if the feedback amount of the speed control loop is set to be small in the super slow operation of zooming, the zooming of the image on the screen may be temporarily stopped, resulting in unnatural zooming. On the contrary, if the feedback amount of the speed control loop is large in the normal or high-speed moving operation, it takes time to move to the predetermined position. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a servo system that enables a natural control operation during both high speed operation and slow operation.

[0005]

A servo system according to the present invention is a servo system for driving and controlling a motor by a position control loop and a speed control loop, and detects a motor rotation speed for generating an output according to the rotation speed of the motor. Means for reducing the output value from the motor rotation speed detection means when the voltage across the motor is high, and a feedback value that increases the output value from the motor rotation speed detection means when the voltage across the motor is low. A quantity adjusting means is provided in the speed control loop. A voltage control amplifier can be used as the feedback amount adjusting means.

The feedback amount adjusting means turns on / off the passage of the output from the motor rotation speed detecting means, and the on / off period of the analog switch according to the voltage across the motor. And a pulse width modulating means for changing The servo system of the present invention can be suitably used especially when the motor drives a predetermined operation part of the platform.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing a circuit in a servo system according to a first embodiment of the present invention. This servo system uses a drive signal from a control device 10 (for example, a controller for remotely operating a platform) as a first drive signal.
Is output to a motor 18 (for example, a zoom unit drive motor of a camera provided on a platform) via the comparator 12, the second comparator 14, and the amplifier 16 to drive the motor 18. .

The motor 18 is interlocked with the tachogenerator 20 and the potentiometer 22, and the rotational speed of the motor 18 and the position of the operated object are detected by these, and speed control and position control are performed. That is, the position control loop in this servo system is composed of the potentiometer 22, the first comparator 12, the amplifier 16 and the motor 18, and is output from the potentiometer 22 to the first comparator 12 according to the position of the operated object. The voltage value of the control device 10
The motor 18 is driven in such a direction as to coincide with the voltage value according to the target value.

The speed control loop in this servo system includes a tacho generator 20, a voltage control amplifier (VCA) 24, which will be described later, a second comparator 14, an amplifier 16 and a motor 18, and the tacho generator 20 to the voltage control amplifier.
Negative feedback control is performed so that the voltage value corresponding to the speed of the motor 18 output to the second comparator 14 via 24 matches the voltage value from the comparator 12.

Here, the operation of the voltage control amplifier 24 used as the feedback amount adjusting means in this embodiment will be described. The voltage between both ends of the motor 18 is input to the voltage control amplifier 24 as a control signal. The voltage control amplifier 24 reduces the output value (feedback amount) of the rotation speed signal of the motor 18 input to the second comparator 14 when the voltage between both ends is large, and the voltage between both ends is small. At times, voltage control is performed so that the output value (feedback amount) of the rotation speed signal of the motor 18 input to the second comparator 14 is increased. The increasing / decreasing relationship between the voltage value across the motor and the feedback amount may be a linearly changing relationship or a stepwise changing relationship.

As a result, the speed control tends to be suppressed when the motor 18 rotates at a high speed, while sufficient speed control can be obtained when the motor 18 rotates at a low speed, resulting in a natural control operation during both high speed operation and slow operation. Will be possible. FIG. 2 is a block diagram showing a circuit in the servo system according to the second embodiment of the present invention. In this embodiment, the same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, the feedback amount adjusting means is the first
The present invention is characterized in that a combination of an analog switch 26 and a pulse width modulation means (PWM) 28 is used in place of the voltage control amplifier 24 used in the embodiment. In general, the pulse width modulator is less expensive than the voltage controlled amplifier described above, so that the cost can be reduced according to this embodiment. The analog switch 26 is from the tacho generator 20 to the second comparator.
It turns on / off the passage of the output to 14. That is, the voltage signal from the tachogenerator 20 corresponding to the rotation of the motor 18 is generated only when the analog switch 26 is on.
It is output from the tacho generator 20 to the second comparator 14.

The voltage across the motor 18 is input to the pulse width modulator 28 as a control signal. Then, the pulse width modulation means 28 reduces the output value of the rotation speed signal of the motor 18 input to the second comparator 14 when the voltage between both ends is large, and the second value when the voltage between both ends is small. The ON / OFF period of the analog switch 26 is changed so that the output value of the rotation speed signal of the motor 18 input to the comparator 14 of FIG. More specifically, the pulse width modulating means 28 reduces the duty ratio of the pulse signal for turning on / off the analog switch 26 when the voltage across the motor 18 is high, and when the voltage across the motor 18 is low, The control is performed so that the duty ratio of the pulse signal is increased. The relationship between the voltage across the motor and the duty ratio may be a linearly changing relationship or a stepwise changing relationship.

FIG. 3 is a graph for explaining an example of the control operation in the second embodiment described above. This figure shows a slow operation (for example, voltage across the motor in this embodiment).
This shows the control at the time of switching from 2.5 V, rotation speed 3 rpm) to high speed operation (for example, voltage across the motor 7 V, rotation speed 50 rpm). That is, in this control, during the slow operation, the duty ratio of the pulse signal is set to 80% and the feedback amount is increased to drive the motor 18 gently and smoothly to the output value 2V of the potentiometer, for example. In the high speed operation, the duty ratio of the pulse signal is set to 5% and the feedback amount is set to be small so that the operated object can be quickly moved to the target position.

Here, during high speed operation, since the torque of the motor is large, the load fluctuation is unlikely to occur, and therefore the necessity of speed control is small. Further, since the speed is high, the observer cannot perceive the jagged movement. Therefore, it can be said that the adverse effect of reducing the feedback amount during high-speed operation is small. As a result, the operation of the motor does not become awkward when the slow operation is switched to the high speed operation, and a natural control operation can be performed during the high speed operation and the slow operation. Although the control operation when switching from the slow operation to the high speed operation is shown in this figure, the same effect can be obtained when the control operation is performed in the reverse procedure when switching from the high speed operation to the slow operation. .

The servo system of the present invention is not limited to that of the above-described embodiment, and various modifications can be made. For example, although the tacho generator is used as the motor rotation speed detection means in the above-described embodiment, any detector that detects the motor rotation speed (rotation angle) and outputs a current or voltage corresponding thereto can be used. It is not limited. Further, in the above-mentioned embodiment, the zoom unit drive motor of the camera provided on the platform is exemplified, but the servo system of the present invention is not limited to this, and operation of panning and tilting of the platform is possible. Of course, it can also be used for a motor-operated operation unit other than a tripod head.

[0017]

As described above, according to the present invention,
Motor rotation speed detecting means for generating an output according to the rotation speed of the motor, and when the voltage across the motor is large, the output value from the motor rotation speed detecting means is small, and when the voltage across the motor is small, By providing the feedback amount adjusting means for increasing the output value from the motor rotation speed detecting means in the speed control loop, the operation of the motor does not become awkward at the time of switching between the slow operation and the high speed operation,
Natural control operation is possible during both high speed operation and slow operation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit of a servo system according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit in a servo system according to a second embodiment of the present invention.

FIG. 3 is a graph showing an example of control operation in the servo system shown in FIG.

[Explanation of symbols] 10 Control device 12 First comparator 14 Second comparator 16 Amplifier 18 Motor 20 Tachometer 22 Potentiometer 24 Voltage control amplifier 26 Analog switch 28 Pulse width modulator

Claims (4)

[Claims] 1. In a servo system for driving and controlling a motor by a position control loop and a speed control loop, a motor rotation speed detecting means for generating an output according to the rotation speed of the motor, and a voltage between both ends of the motor are large. A feedback amount adjusting means is provided in the speed control loop so that the output value from the motor rotation speed detecting means is sometimes small, and the output value from the motor rotation speed detecting means is large when the voltage across the motor is small. Servo system characterized by 2. The servo system according to claim 1, wherein the feedback amount adjusting means is a voltage controlled amplifier. 3. The feedback amount adjusting means turns on / off the passage of the output from the motor rotation speed detecting means, and the on / off period of the analog switch according to the voltage across the motor. 2. The servo system according to claim 1, further comprising pulse width modulation means for changing 4. The servo system according to claim 1, wherein the motor drives a predetermined operation unit of the platform.