JPH06217573A - Motor control circuit - Google Patents

Abstract

PURPOSE:To minimize the variation of the stopping position of a tape so as to improve the quality of reproduced pictures at the time of slow reproduction by minimizing the backward oscillation of the tape at the time of stopping a capstan motor. CONSTITUTION:The capstan control section 11 of a microcomputer 1 brakes a capstan motor 4 by inverting the driving current of the motor 4 outputted from a drive control circuit 3 by outputting a brake signal to the circuit 3. When the motor 4 is braked, a limiter voltage switching section 15 outputs a limiter voltage in the braking current reducing direction to the circuit 3 and, when the rotating speed of the motor 4 becomes lower than a prescribed value, namely, when reels are stopped thereafter, quickly stops the motor 4 by giving a limiter voltage in the braking current increasing direction to the circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control circuit for controlling the rotation of a capstan motor of a video tape recorder (VTR), and more particularly to a motor stop control.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an example of a conventional motor control circuit of this type. When the capstan motor 4 is intermittently driven, the capstan control unit 11 in the microcomputer 1 firstly applies a maximum voltage to the capstan motor 4 at the time point a as shown in FIG. 4 (A). The error signal is output to the drive control circuit 3 via the filter circuit 2. As a result, the drive control circuit 3 supplies the full current to the capstan motor 4 as shown in FIG.
And the capstan motor 4 in the stopped state is rotated. The rotation speed of the capstan motor 4 is the speed detection unit F.
The speed detection unit FG-A detected by G-A and FG-B.
4B, the speed detection pulse signal as shown in FIG. 4B is output to the amplifier 5, and the speed detection unit FG-B outputs the speed detection pulse signal as shown in FIG. 4C to the amplifier 6. The speed detection pulse signal amplified by the amplifier 5 is waveform-shaped by the Schmitt circuit 7 and then input to the rotation direction detection unit 12 in the microcomputer 1. on the other hand,
The speed detection pulse signal from the speed detection unit FG-B is amplified by the amplifier 6 and then waveform-shaped by the Schmitt circuit 8, and then the speed detection unit 13 in the microcomputer 1.
Entered in. The speed detection unit 13 compares the input speed detection pulse signal with a reference signal, outputs an error signal corresponding to the difference to the capstan control unit 11, and rotates the input speed detection pulse signal as it is. It outputs to the direction detection unit 12.

Next, the capstan control unit 11 is shown in FIG.
The servo control operation for rotating the capstan motor 4 at a constant speed is started from the point of time B, and the capstan error for rotating the capstan motor 4 constantly based on the error signal obtained from the speed detection unit 13. A signal is created and output to the drive control circuit 3 via the filter circuit 2. As a result, the drive control circuit 3 outputs the data shown in FIG.
The capstan motor current as shown in (F) is supplied to the capstan motor 4. In this way, when the capstan motor 4 enters the constant speed rotation state, the capstan control unit 1
1 outputs a brake signal as shown in FIG. 4D to the drive control circuit 3 at the time of c. At this time, the capstan control unit 11 outputs a capstan error signal for braking the capstan motor 4 to the drive control circuit 3 via the filter circuit 2 as shown in FIG. As a result, the drive control circuit 3 supplies the reverse rotation current as shown in FIG. 4 (F) to the capstan motor 4 from the time point C, and brakes the capstan motor 4.

Here, the speed detection pulse signals detected by the speed detection unit FG-A and the speed detection unit FG-B are set so as to have a phase difference of 90 degrees, and the capstan motor 4 moves in the forward direction. When rotating, Fig. 4 (B),
As shown in (C), the phase of the speed detection pulse signal output from the speed detection unit FG-A leads the phase of the speed detection pulse signal output from the speed detection unit FG-B by 90 degrees,
When the capstan motor 4 is rotating in the reverse direction, its phase is delayed by 90 degrees. Rotation direction detector 1
2 observes the phase relationship between the two speed detection pulse signals input from the speed detection units FG-A and FG-B, and when the phase relationship between the two signals reaches a predetermined condition, the capstan motor 4 reverses ( It is determined that the capstan motor has stopped), and this is notified to the capstan control unit 11. In the example of FIG. 4, the rotation direction detection unit 12 detects the reverse rotation of the capstan motor 4 at the time point d. Upon receiving this news,
The capstan control unit 11 releases the brake signal at the time point of D in FIG. As a result, the drive control circuit 3 generates the capstan motor current for rotating the capstan motor 4 in the forward direction based on the capstan error signal (see FIG. 4A) output from the capstan control unit 11. Since the capstan motor 4 is supplied as shown in (F), the capstan motor 4 is re-accelerated from the time point d. Since the capstan control unit 11 sets the capstan error signal to 0 at the time of (e) in FIG. 4A, the drive control circuit 3 calculates the capstan motor current supplied to the capstan motor 4 at this time. 0 as shown in 4 (F)
And The capstan control unit 11 gives a current limiting signal as shown in FIG. 4 (E) to the drive control circuit 3 at the time of the intermittent slow control of the capstan motor 4 as described above, and outputs from the drive control circuit 3. The maximum value of the capstan motor current is controlled as shown in FIG.

By the way, in the conventional VTR using the capstan motor 4 as a drive source, a reel belt drive system is mainly used as a system for transmitting the power of the capstan motor 4 to the capstan. Has become. When this reel belt drive system is adopted, in order to smoothly shift the tape from the intermittent slow state to high speed running such as fast forward or rewind mode, the load torque on the reel side is compared with the load torque of the capstan motor 4. It is usually set large. Therefore, in the intermittent slow running mode of the tape, there is a difference between the stop characteristic of the capstan motor 4 and the stop characteristic of the reel, and energy generated by this difference is accumulated in the belt of the reel, and when the tape running is stopped, The energy causes the capstan motor 4 to swing back, and the stop position of the tape may fluctuate. Moreover, in recent VTRs, the gap of the video head tends to be narrowed in order to improve the image quality, so that the tracking margin during the intermittent slow reproduction is reduced. Therefore, if the stop position of the tape is changed due to the rocking back of the capstan motor at the stop as described above, there is a disadvantage that the tracking is deviated and the reproduction image quality is deteriorated.

[0006]

When the capstan motor is braked by the conventional motor control circuit as described above, in the reel belt drive system, it occurs due to the difference in load torque between the capstan motor and the reel. It cannot absorb the swing-back energy, and this energy causes the motor to swing back when the reel stops, which causes the tape stop position to fluctuate. There was a drawback that it worsened.

In view of the above, the present invention eliminates the above-mentioned drawbacks, and even in a model adopting a reel belt drive system, the fluctuation of the stop position of the tape is minimized by minimizing the swinging back when the capstan motor is stopped. It is an object of the present invention to provide a motor control circuit capable of improving the reproduction image quality during slow reproduction.

[0008]

According to the present invention, in a motor control circuit for reversing the direction of current supplied to a rotating motor to brake the motor, the motor is braked and then the motor is rotated. Detecting means for detecting that the number of rotations is below a predetermined value, and increasing the brake current supplied to the motor from the time when the detection of the rotation of the motor is below a predetermined value by the detecting means And a current increasing means for controlling the current.

[0009]

In the motor control circuit of the present invention, the detecting means detects that the rotational speed of the motor has become equal to or less than the predetermined value after the motor is braked. The current increasing means increases the brake current supplied to the motor from the time when the detecting means detects that the rotation of the motor has become equal to or less than a predetermined value. As a result, the rotation of the motor is equal to or less than a predetermined value, that is, the braking force applied to the motor increases from the time when the rotation of the reel stops, so that the motor is suddenly stopped and the stop characteristic of the motor and the stop characteristic of the reel are matched. It is possible to minimize the swinging back when the motor is stopped.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a motor control circuit of the present invention. Reference numeral 1 denotes a microcomputer that performs various processes for controlling the rotation speed of the capstan motor 4, and includes a capstan control unit 11 and a rotation direction detection unit 1.
2. It has a speed detection unit 13 and a pulse observation unit 14. 2 is a filter circuit for compensating for the gain of the capstan error signal output from the capstan control unit 11. 3
Is a drive control circuit that supplies a capstan motor current to the capstan motor 4 to drive it, and 4 is a capstan motor that rotates a reel (not shown) via a belt,
Reference numerals 5 and 6 denote amplifiers for amplifying the speed detection pulse signal, and 7 and 8
Is a Schmitt circuit that shapes the waveform of the speed detection pulse signals output from the amplifiers 5 and 6, 9 is a Schmitt circuit 7,
A speed detection circuit for detecting the speed detection pulse signal input from 8 is a frequency voltage converter for converting the speed detection signal input from the speed detection circuit 9 into a voltage proportional to its frequency, and two types of different polarity are provided. Output voltage of output port 1,
Output from the output port 2 to the limiter voltage switching unit 15.
Reference numeral 15 is a limiter voltage switching unit for controlling the limiter voltage applied to the drive control circuit 3 in response to a switching signal from the pulse observing unit 14, and FG-A and FG-B are speed detection pulses proportional to the rotation speed of the capstan motor 4. It is a speed detection part that generates a signal, and 9
It is designed so that a phase difference of 0 degree is generated.

Next, the operation of this embodiment will be described. The capstan control unit 11 of the microcomputer 1 drives the capstan error signal for fully rotating the capstan motor 4 through the filter circuit 2 at the time point a in FIG. 2A during the intermittent slow drive of the capstan motor 4. It is output to the control circuit 3 to start rotating the capstan motor 4, and then, at the time of B, a capstan error signal for rotating the capstan motor 4 at a constant speed is output, and at the time of C, the capstan motor 4 is output. Outputs a capstan error signal for braking 4. Further, the capstan control unit 11 gives a capstan error signal to the drive control circuit 3, and at the same time, the period from the time points a to c and the time points d to e in FIG. 2 and the current as shown in FIG. A limit signal is given to the drive control circuit 3. During this period, the speed detection unit FG-
Speed detection pulse signals as shown in FIGS. 2B and 2C are generated from A and FG-B, and these speed detection pulse signals are sent to the microcomputer 1 via the amplifiers 5 and 6 and the Schmitt circuits 7 and 8. And to the speed detection circuit 9. The control from the time points a to c in FIG. 2 is the same as that of the conventional circuit shown in FIG.

By the way, the speed detection circuit 9 detects the two speed detection pulse signals input from the Schmitt circuits 7 and 8 to obtain a speed detection signal as shown in FIG. And the pulse observation unit 14. The frequency-voltage converter 10 converts the speed detection signal input from the speed detection circuit 9 as shown in FIG. 2 (E) into a limiter voltage corresponding to the frequency as shown in FIGS. 2 (F) and (G). Then, the limiter voltage shown in FIG. 2 (F) is output from the output port 1 to the limiter voltage switching unit 15, and the limiter voltage shown in FIG. 2 (G) is output from the output port 2 to the limiter voltage switching unit 15. .

When the capstan motor 4 is controlled to rotate at a constant speed and reaches the time point C in FIG. 2, the capstan control unit 11 gives a brake signal as shown in FIG. 2D to the drive control circuit 3. At the same time as braking the capstan motor 4, the output of the current limiting signal to the drive control circuit 3 as shown in FIG. 2H is stopped. At this time, the pulse observing unit 14 switches the limiter voltage switching unit 15 at the time point when the capstan control unit 11 outputs the brake signal,
A limiter voltage as shown in FIG. 2F output from the output port 1 of the frequency voltage converter 10 is applied to the drive control circuit 3. Therefore, from the time point c in FIG. 2 to the time point a in FIG. 2, the capstan motor 4 is driven by the drive control circuit 3 from FIG.
The capstan motor current in the decreasing direction as shown in (I) is supplied and the brake is applied. Pulse observation unit 14
During this period, the period of the speed detection signal input from the speed detection circuit 9 as shown in FIG. 2 (E) is observed, and when the time point a when the cycle t _n becomes the cycle T or more is detected, the limiter voltage switching unit 15 is detected. 2G to supply the drive control circuit 3 with the limiter voltage output from the output port 2 of the frequency-voltage converter 10 as shown in FIG. The limiter voltage output from the output port 2 is opposite in polarity to the limiter voltage output from the output port 1 as shown in FIG. The current supplied to the stun motor 4 is increased.

Therefore, from the time point (a), the capstan motor current in the increasing direction is supplied to the capstan motor 4 as shown in FIG. 2 (I), and the braking force on the capstan motor 4 is increased. It will be. After that, the rotation direction detection unit 12 detects the reverse rotation of the capstan motor 4 (stop of the capstan motor 4) at the time point D in FIG. 2, and notifies the capstan control unit 11 and the pulse observation unit 14 of this. As a result, the capstan control unit 11
Stops the brake signal output to the drive control circuit 3 as shown in FIG. 2 (D) and gives a current limit signal to the drive control circuit 3 as shown in FIG. 2 (H). At this time,
The pulse observing unit 14 changes the limiter voltage switching unit 15 at the time point d.
Is switched to stop the supply of the limiter voltage output from the output port 2 of the frequency voltage converter 2 to the drive control circuit 3. As a result, the drive control circuit 3 supplies the capstan motor current as shown by (I) in FIG. 2 to the capstan motor 4, so that the capstan motor 4 is re-accelerated in the forward direction from the time point d. After that, the capstan control unit 11 stops the output of the capstan error signal as shown in FIG.
Since the output of the current limit signal is stopped as shown in (H),
The capstan motor current supplied from the drive control circuit 3 to the capstan motor 4 becomes 0 at time e as shown in FIG. 2 (I), and the stop control of the capstan motor 4 ends.

According to this embodiment, the capstan motor 4
2B, the limiter voltage in the direction of decreasing the brake current supplied to the capstan motor 4 as shown in FIG. 2F is initially supplied to the drive control circuit 3, but the rotation speed of the capstan motor 4 is When the number of revolutions becomes equal to or lower than a predetermined number of times (time point a), a control for giving a limiter voltage to the drive control circuit 3 as shown in FIG. After (time point a), control for rapidly stopping the capstan motor 4 can be performed. Therefore, the stop characteristic of the capstan motor 4 can be brought close to the stop characteristic of the reel, and after the capstan motor 1 is stopped, it is possible to minimize the generation of energy that rocks back the capstan motor 1 and the tape stop position. Can be almost eliminated. As a result, the tracking deviation at the time of the intermittent slow reproduction is eliminated, and the quality of the reproduced image can be improved.

[0016]

As described above, according to the motor control circuit of the present invention, even when the reel belt drive system is used, the tape can be stopped by minimizing the swinging back when the capstan motor is stopped. The position fluctuation can be minimized to improve the playback image quality during slow playback.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a motor control circuit of the present invention.

FIG. 2 is a time chart for explaining the operation of the capstan motor during intermittent slow drive by the motor control circuit shown in FIG.

FIG. 3 is a block diagram showing an example of a conventional motor control circuit.

FIG. 4 is a time chart for explaining the operation of the capstan motor during intermittent slow drive by the motor control circuit shown in FIG.

[Explanation of symbols]

1 ... Microcomputer 2 ... Filter circuit 3 ... Drive control circuit 4 ... Capstan motor 5,6 ... Amplifier 7,8 ... Schmidt circuit 9 ... Speed detection circuit 10 ... Frequency voltage converter 11 ... Capstan control unit 12 ... Rotation direction Detection unit 13 ... Velocity detection unit 14 ... Pulse observation unit FG-A, FG-B ... Velocity detection unit

Claims (1)

[Claims] 1. A motor control circuit for reversing the direction of current supplied to a rotating motor to brake the motor, wherein the number of rotations of the motor is below a predetermined value after the motor is braked. And a current increasing means for increasing the brake current supplied to the motor from the time when the rotation of the motor is detected to be below a predetermined value by the detecting means. A motor control circuit characterized by the above.