JPH0436237Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a motor control circuit suitable for application to a capstan motor of a tape recorder, and relates to an improvement of a motor control circuit that can continuously vary the rotational speed of the motor.

First, a motor control circuit for a conventional VTR capstan motor will be described with reference to FIG. 1 is a capstan motor (DC motor), 2
is a frequency generator that generates a detection frequency signal having a frequency corresponding to the rotational speed of the motor 1. Reference numeral 6 denotes an input terminal to which a command frequency signal having a frequency corresponding to the command rotational speed of the motor 1 is supplied. 9
is an error amplification circuit that compares the detected rotational speed of the motor 1 and the commanded rotational speed for the motor 1 and supplies the motor 1 with a drive voltage Vo based on the error. This error amplification circuit 9 is composed of frequency-voltage conversion circuits 4 and 5 and an error amplifier 3. Reference numeral 7 denotes a level comparator that generates a control signal SW for switching and controlling the current direction of the motor 1.

A detected frequency signal from the frequency generator 2 corresponding to the detected rotational speed of the motor 1 and a command frequency signal from the input terminal 6 corresponding to the commanded rotational speed are supplied to frequency-voltage converters 4 and 5, respectively.
Detection voltage Vm and command voltage output from each
Vc is supplied to the error amplifier 3. Here, the output resistance of the frequency-voltage converter 4 is r, and the error amplifier 3
Assuming that the feedback resistance is R, the error amplifier 3 outputs the following output voltage Vo.

Vo=Vc-(R/r)(Vm-Vc)...(1) By the way, the gain of the motor control system is determined by the feedback resistance R.
determined by. In this example, R=r is set, and the output voltage Vo is Vo=Vc-(Vm-Vc) (2). That is, the output voltage is the command voltage minus the difference between the detected voltage and the command voltage.
The obtained output voltage is applied to the motor 1 as the drive voltage Vo.
is supplied to

Furthermore, the detected voltage from the frequency-voltage converter 4
Vm is attenuated through a variable attenuator (volume) 8 for adjusting the brake release point and then supplied to the level comparator 7, and the command voltage Vc from the frequency-voltage converter 5 is directly applied to the level comparator 7. The comparison output is the control signal.
It is supplied to the motor 1 as a SW, and its current direction is switched and controlled.

An equivalent circuit for this switching control is shown in FIG. The switching devices 21 and 22 each have a movable contact C that receives the control signal SW.
The control signal SW is switched to L.
Fixed contact a is selected when the signal is at the (low) level, and fixed contact b is selected when the signal is at the H (high) level. When the fixed contacts a of the switches 21 and 22 are selected, the current direction is positive (this is referred to as the drive voltage being in positive phase) and the rotating shaft of the motor 1 rotates in a predetermined direction.
Furthermore, when the fixed contacts b of the switches 21 and 22 are selected, the direction of current conduction is reversed (this is referred to as the drive voltage being in reverse phase), and a rotational force is applied to the rotating shaft of the motor 1 in a direction opposite to the above-mentioned predetermined direction. is given, and the rotation of the rotating shaft in the predetermined direction is controlled.

In this motor control circuit, for example, during playback, the tape running speed is set to several times (several tens of times) to the normal speed.
The rotation speed of the motor 1 can be continuously varied from 1 times to several fractions (several 10 times) of the steady rotation speed. 1) and continuously variable.

The operation of this motor control circuit will be explained below. The rotation speed of motor 1 is Nm, and the command rotation speed is
Let it be Nc. When Nm=Nc, command rotation speed Nc
A command voltage Vc corresponding to the voltage is supplied to the motor 1 as a drive voltage Vo. When Nm<Nc, the difference voltage (Vc - Vm) according to the above command voltage Vc and Nc - Nm
The added voltage is supplied to the motor 1 as the drive voltage Vo. When Nm＞Nc, the above command voltage
Differential voltage (Vm-Vc) according to Nm-Nc from Vc
The voltage from which is subtracted is supplied to the motor 1 as the drive voltage Vo. Then, when the damping ratio set by the level adjuster 8 is α (≦1), αNm≦
When Nc, the control signal SW becomes L level, the positive phase drive voltage Vo is supplied to the motor 1, and αNm>
At the time of Nc, the control signal SW becomes H level, and the drive voltage Vo of the opposite phase is supplied to the motor 1, so that the motor 1 is brought into a braking state.

Therefore, when the command rotational speed Nc is increased from Nco to Nch, the direction of energization to the motor 1 does not change, and the drive voltage Vo supplied to the motor 1 increases by the voltage corresponding to the rotational speed difference Nch - Nco. The motor 1 is then accelerated.

Also, when the command rotational speed Nc is slightly decreased from Nco to Ncl, the direction of energization to the motor 1 does not change, and the drive voltage Vo supplied to the motor 1 is only a voltage corresponding to the rotational speed difference Nco - Ncl. The motor 1 is lowered and decelerated.

Furthermore, if the command rotational speed Nc is significantly decreased from Nco to Ncl, the direction of energization to motor 1 is reversed and the drive voltage supplied to motor 1 is
When Vo decreases by a voltage corresponding to the rotational speed Nco-Ncl, and then the rotational speed difference Nco-Ncl becomes less than a certain value, the current direction to the motor returns to the original and deceleration continues, thus causing the motor 1 to decelerate quickly. It will be done.

By the way, in such a motor control circuit, when the command rotational speed for the motor is switched from high speed to low to ultra-low speed, the control signal from the level comparator 7
It is difficult to apply braking by switching the current direction of the motor 1 based on the SW, and the resistance to noise (noise due to disturbances, ripples in the power supply voltage, etc.) is low. That is, when the commanded rotational speed of the motor 1 is low to very low,
If the setting of the brake release point is critical, it will take a long time to reach the command rotation speed. If the brake is released too quickly, the rotational speed of the motor 1 will be slowed down, and if it is released too slowly, hunting will occur.

In view of this, the present invention proposes a motor control circuit that can quickly, reliably, and stably decelerate when the commanded rotational speed for the motor is switched from high speed to low to ultra-low speed.

One embodiment of the present invention will be described in detail below with reference to FIG. 2. In FIG. 2, parts corresponding to those in FIG. Reference numeral 9 denotes an error amplification circuit that compares the detected rotational speed of the DC motor 1 and the commanded rotational speed for the motor 1 and supplies the motor 1 with a drive voltage Vo based on the error, and has the same configuration as in FIG. It is.

10 is the detection frequency Fm according to the detected rotation speed
and the command frequency Fc according to the command rotation speed, and when Fm<Fc, the positive phase drive voltage Vo becomes Fm
> When Fc, the reverse phase drive voltage Vo is the motor 1
This is a motor braking circuit that controls braking of the motor 1 by switching and controlling the direction of energization of the motor 1 so that the current is supplied to the motor 1. In this case, the detection frequency Fm and the command frequency Fc are selected so that when the detected rotation speed and the command rotation speed match, Fc<Fm.

The configuration of the motor control circuit 10 will be explained.
Frequency generator 2 according to the detected rotational speed of the motor 1
A detected frequency signal whose frequency is Fm' is supplied to the frequency divider (counter) 11 to obtain a desired frequency division ratio k (0<
Detection frequency Fm lowered by k<1)
The detected frequency signal of Fc is supplied to the frequency comparator 12, and the command frequency signal of the command frequency Fc from the input terminal 6 corresponding to the command rotation speed is supplied to the frequency comparator 12, and both are compared, and the comparison output is The output is supplied to a brake control circuit that controls the braking of the motor 1, which is comprised of a flip-flop circuit 13, and is configured to switch the current direction of the motor 1 in accordance with the output thereof.

Also, the relationship between the detected frequency Fm and the command frequency Fc when the detected rotation speed and the command rotation speed match is
When Fm=βFc (0<β<1), this β is the variable range of the command rotation speed, the inertia of motor 1,
It is arbitrarily selected depending on the motor load, etc.

Next, the operation of the motor control circuit shown in FIG. 2 will be explained. When the command rotational speed Nc is increased from Nco to Nch, the direction of energization to the motor 1 does not change, and the drive voltage Vo supplied to the motor 1 increases by a voltage corresponding to the rotational speed difference Nch - Nco, and the motor 1 is accelerated.

Also, when the command rotational speed Nc is slightly decreased from Nco to Ncl, the direction of energization to the motor 1 does not change, and the drive voltage Vo supplied to the motor 1 is only a voltage corresponding to the rotational speed difference Nco - Ncl. The motor 1 is lowered and decelerated.

Furthermore, a case where the command rotational speed Nc is significantly lowered from Nco to Ncl will be explained with reference to FIG. That is, when the tape running speed is to be decelerated from 1 times the steady speed to t (<1) times, the command frequency Fc is decreased from f ₁ to f ₁ '. At this time, since Fm>Fc, the detection frequency Fm changes from f ₂ to f ₂ ′
The current direction to the motor 1 is in the reversed state until the rotational speed difference Nco-Ncl decreases by a voltage corresponding to the rotational speed Nco-Ncl, and the driving voltage Vo supplied to the motor 1 decreases by a voltage corresponding to the rotational speed Nco-Ncl. , that is, when the detection frequency Fm becomes less than f ₂ ', the current direction to the motor returns to the detection frequency.
The deceleration continues until Fm reaches f ₂ ″, and thus the motor 1 is quickly decelerated.

According to the present invention described above, the current direction to the motor is switched based on frequency comparison only when the speed deviation exceeds a certain value, so the braking point can be set accurately and disturbances in the control system caused by frequent switching can be avoided. Vibration is reduced, and therefore, when the commanded rotational speed for the motor is switched from high speed to low to very low speed, the speed can be decelerated quickly, reliably, and stably.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional motor control circuit, Fig. 2 is a block diagram showing an embodiment of the motor control circuit according to the present invention, Fig. 3 is an operating curve diagram, and Fig. 4 is a motor energization diagram. This is an equivalent circuit for direction switching control. 1 is a DC motor, 2 is a frequency generator, 3 is an error amplifier, 4 and 5 are frequency-voltage converters, 6 is a command frequency signal input terminal, 9 is an error amplifier circuit, and 10 is a motor braking circuit.

Claims (1)

[Claims for Utility Model Registration] The detected rotational speed of a DC motor 1 configured to switch the direction of driving voltage and the commanded rotational speed for the DC motor 1 are compared, and the above-described size is determined according to the error. An error amplifying circuit 9 supplies a drive voltage to the DC motor 1 and controls the detected rotational speed so that the commanded rotational speed coincides with the detected rotational speed. Divide by 0<k<1) to obtain frequency Fm (=
kFm′); a frequency comparison circuit 12 that compares the frequency Fm with the command frequency Fc corresponding to the command rotation speed;
When Fc, the control signal determines the energization direction on the side where the DC motor 1 normally rotates, and when Fm<Fc, generates a control signal that determines the energization direction on the side where the DC motor 1 rotates in the opposite direction to the normal rotation. A motor control circuit comprising a control circuit 13.