JPH0822153B2 - Electric motor speed controller - Google Patents

Description

The present invention relates to a speed control device for an electric motor used for driving an optical system of a copying machine having a reduction ratio function, for example.

[Conventional technology]

In copiers, individual drive of optical system by DC servo motor is widely used to facilitate reduction function. The rotation speed control is generally a highly accurate PLL control. Hereinafter, a conventional example will be described with reference to the drawings.

4 and 5 show an example of a conventional speed control device for an electric motor used for driving an optical system of a copying machine.

In FIG. 4, the waveform shaping circuit 1 waveform-shapes the output of the frequency generator (hereinafter referred to as FG) 9 connected to the electric motor 8. The output of the waveform shaping circuit 1 is input to the first frequency-voltage converter (hereinafter referred to as the first F / V) 2. The output of the waveform shaping circuit 1 and the output of the reference oscillator 4 are input to the phase comparator (hereinafter referred to as PD) 3 and the output of PD 3 outputs the phase difference between them.

The output of the reference oscillator 4 is input to the second frequency-voltage converter (hereinafter referred to as the second F / V) 5. First F / V
2, the PD3 and the second F / V5 are additively smoothed by the additive smoothing path 6. The output of the addition smoothing circuit 6 is input to the drive circuit 7,
The voltage applied to the electric motor 8 is controlled to control the speed. Then, the electric motor 8 is started / stopped by the start signal 10.

The output of the second F / V 5 is a speed command voltage for giving the motor 8 a controlled rotation speed. This speed command voltage is
It is given when the reduction ratio is selected, and is usually a constant value when the electric motor 8 is started.

In the case of PLL control, one of the issues is the synchronization pull-in time. This will be described with reference to FIG. 1 in FIG. 5 is a target value of the rotation speed given by the speed command voltage,
Reference numeral 2 indicates the rotation speed of the electric motor 8. Also, 1 ', 2'
Is the target value and the rotation speed at low speed as well.

For example, in the case of high speed 2, when the activation signal 10 is applied, the drive circuit 7 applies the entire voltage to the electric motor 8 to accelerate it. The servo motor has a small mechanical constant and can rise quickly, but it overshoots due to a delay in the transmission system of the circuit. After the overshoot, the drive circuit 7 reduces the voltage until the electric motor 8 is braked, so that the motor 8 is decelerated free. When the rotation speed falls below the target value, the speed is accelerated again, and after some overshoot, synchronous pull-in is performed.

From the viewpoint of the copying machine, the synchronization pull-in timing is related to the distance at which the image starts to be output. That is, at the rotation speed 2, the run-up distance is required until the speed reaches a constant value, which affects the external dimensions of the copying machine.

Since the run-up distance is the time integral of the rotation speed, for example, when the rotation speed is high such as 2, the run-up distance is longer than when it is low like 2 ', and the highest speed is the most severe condition for synchronous pull-in. .

Copiers aim to achieve higher speeds by increasing the number of copies per minute. Therefore, the synchronization pull-in condition becomes more severe.

[Problems to be solved by the invention]

In order to solve these problems, since the synchronization pull-in is determined by the first overshoot as described above, it is necessary to minimize the transmission delay of the circuit. The most effective means for this is to increase the number of FG9 pulses. However, in this method, i) the outer shape of FG must be increased, so that the inertia becomes large. In addition, the outer dimensions of the motor become large. ii) It has drawbacks such as expensive FG.

On the other hand, it is also effective to apply a short-circuit brake to the electric motor 8 after the first overshoot and release the brake when the speed is reduced below the target. However, in this case, i) mechanical vibration occurs due to the brake. ii) There is a drawback that the detection circuit for the target value is necessary and expensive.

SUMMARY OF THE INVENTION The present invention provides a speed control device for an electric motor which compensates for the above drawbacks in terms of cost, and which is a cheapest and easiest method for short-circuiting the synchronous pull-in.

[Means for solving problems]

In order to solve the above problems, the present invention provides a second F / V
It is equipped with a delay circuit in order to slowly raise the output voltage of.

Action The present invention has the above-mentioned configuration, by gradually raising the output of the second F / V5, that is, the speed command voltage,
Overshoot can be reduced and the sync pull-in time can be short-circuited.

First Embodiment A first embodiment of a motor speed control device according to the present invention will be described below.
This will be described with reference to FIG. 2, FIG. 2 and FIG. The same components as those of the conventional configuration are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, since the output of F / V5 in FIG. 2 is transmitted to the delay circuit 11 by the start signal 10, the speed command voltage which is the output of the delay circuit 11 rises slowly after the start signal 10 is input. Go up,
After a certain period of time, the voltage becomes constant. FIG. 2 shows a concrete example of the delay circuit. Before activation, the transistor Tr is on and discharges the electric charge of the capacitor C, but at activation, the transistor Tr is turned off and the speed command voltage is accumulated in the capacitor C, and after a certain period of time, becomes a constant value. Reference numeral 1 in FIG. 3 denotes a target value of the rotation speed based on the speed command voltage, and 2 denotes the rotation speed of the electric motor. When the activation signal is applied at t = 0,
Since the speed command voltage gradually rises, the target value rises as shown by 1 in FIG.

On the other hand, since the feedback system follows the target value, the output of the drive circuit 7 is controlled even at the time of starting. Therefore, as shown by 2 in FIG. 3, the overshoot of the rotation speed of the electric motor 8 can be controlled to be extremely small, and the falling time to the target value can be short-circuited. As a result, the synchronous pull-in time can be short-circuited as compared with the conventional example, and the overshoot is extremely small, so that it is very effective for short-circuiting the run-up distance until image output.

The delay circuit 11 is inexpensive and can be easily realized by using a capacitor and a resistor.

As described above, according to the present invention, the conventional basic PLL is used.
By providing the control circuit with an inexpensive and easy delay circuit that can be configured with a minimum of resistance and a capacitor, the synchronization pull-in time can be short-circuited.

[Brief description of drawings]

FIG. 1 is a block diagram of a speed control device for an electric motor showing an embodiment of the present invention, FIG. 2 is a configuration diagram of the delay circuit, and FIG. 3 is a rotational speed of the electric motor shown in FIG. Value), FIG. 4 is a block diagram showing an example of a conventional speed control device for an electric motor, and FIG. 5 is a characteristic diagram showing the rotational speed of the electric motor shown in FIG. 4 and its target value (command value). Is. 1 ... Waveform shaping circuit, 2 ... First F / V converter, 3 ...
Phase comparator, 4 ... Reference oscillator, 5 ... Second F / V converter, 6 ... Addition smoothing circuit, 7 ... Driving circuit, 8 ... Motor, 9 ... Frequency generator, 10 ... Start signal, 11 ... Delay circuit.

Claims (2)

[Claims] 1. A frequency generator connected to an electric motor, a waveform shaping circuit for shaping an output waveform of the frequency generator, and a first frequency-voltage converter for converting an output frequency of the waveform shaping circuit into a voltage. And a phase comparator that compares the output of the waveform shaping circuit with the output of the reference oscillator and outputs a phase difference, and an addition that amplifies and smoothes the output of the first frequency-voltage converter output and the phase comparison output. A smoothing circuit, a drive circuit that converts the output of the addition smoothing circuit into a voltage applied to the electric motor and that starts and stops the electric motor according to a start signal, and the addition smoothing circuit that converts the output frequency of the reference oscillator into a voltage. In a speed control device for an electric motor, which is provided with a second frequency-voltage converter for outputting to the output of the second frequency-voltage converter, the delay of slowly increasing the output voltage of the second frequency-voltage converter by applying the start signal. It said circuit second frequency - provided after the voltage converter, speed control unit for an electric motor, characterized in that the application of the output of the delay circuit to the adder smoothing circuit. 2. The speed control device for an electric motor according to claim 1, wherein the delay circuit comprises a capacitor and a resistor.