JPS6027105B2 - DC reel motor control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method used to control the rotational speed of a reel motor in a magnetic tape recording/reproducing device.

Such magnetic tape recording and reproducing devices are used as video tape recorders (hereinafter referred to as VTRs), and in particular VTRs.
In this case, low-speed reproduction and high-speed reproduction are required, and in this case, the magnetic tape (hereinafter referred to as tape) is run by rotation of a tape reel rather than rotation of a capstan.

FIG. 1 is a schematic diagram showing a tape running system in a conventional VTR. A tape 2 is sent out from a tape reel 1 on the supply side via guide posts 3 to 5, and is passed through a magnetic head for recording and reproducing video signals. to the head drum 6 where the
After passing through the drum 6 and guide post 7, the running of the tape is controlled by a capstan 8 and a pinch roller 9, and a timer roller 10 for detecting the running distance of the tape is rotated. 11.

Note that the tape reels 1 and 11 are operated by reel motors 12 and 1.
3, and rotates at a predetermined speed.

However, during recording and constant speed playback, the running of the tape 2 is controlled by the rotation of the cabstan 8;
During fast forwarding, rewinding, low speed playback, high speed playback, etc., there is a limit to the rotational speed control of the capstan 8, so the tape reel 1, driven by the reel motor 12 or 13 is
The tape 2 is caused to run by the rotation of the tape 11.

Therefore, when the tape 2 is run at a constant speed during low-speed playback, high-speed playback, etc., the rotational speed of the timer roller 10, which represents the running speed of the tape 2, is detected by a speed detector 14 such as an optical fin sensor or a magnetic sensor. After the detection, the frequency discriminator 15 detects a frequency change from the speed signal obtained by this, and the reel motor 3
The rotational speed of the tape 2 is controlled to keep the running speed of the tape 2 constant.

Note that the drive amplifier 16 is provided with a corresponding control signal 17 during recording, reproduction, etc.

However, especially when the tape 2 is run at a low speed, load fluctuations based on changes in the running state of the tape 2 applied to the tape reel 11 cannot be ignored with respect to the drive torque of the reel motor 13, and the reel motor 13 is a DC motor. In portable VTRs and the like using the tape reel 11, it is extremely difficult to run the tape 2 at a constant low speed while covering load fluctuations on the tape reel 11.

The present invention aims to fundamentally eliminate such drawbacks of the conventional art, and by adding a few circuits, the present invention provides a DC reel motor that can run the tape at a stable speed over a wide range from low speed to high speed. This provides a control method. The details of the present invention will be explained below with reference to FIG. 2 and subsequent figures showing embodiments.

FIG. 2 is a block diagram showing the control system of the reel motor 13, and the waveforms of each part are as shown in the time chart of FIG. 3.

That is, the pulsed speed signal a from the speed detector 14 is given to the frequency discriminator 21, and in this step, the speed signal a
The frequency change is detected and becomes the detection output b, which is converted into a voltage change in the positive and negative directions with respect to the reference speed.

On the other hand, the leading edge of the speed signal a is detected by a pulse generator 22 such as a monostable multipipelator, and the gate pulse e is generated.
Therefore, in order to control the sampling circuit 23 such as a gate circuit, the leading edge of the detection output b is extracted and differentiated, and this is the output of the capacitor 24 and resistor 2.
When applied to the charging/discharging circuit connected in parallel with 5, the capacitor 24 holds the peak value according to the speed change, and produces an output e having an area determined according to the time constant of the charging/discharging circuit.

Further, the detection output b is averaged by the low frequency wave generator 26,
This becomes an average speed signal d, and if this and the output e of the charging/discharging circuit are added by the adder 27, the average speed signal d is obtained.
The output e has a curved waveform and represents an average speed change and a differential speed change.

Therefore, the output of the adder 27 is applied to the drive amplifier 29 via the switch 28 as a control signal with a polarity that suppresses speed changes, and the output of the amplifier 29 drives the reel motor 1.
3, differential speed control is performed in addition to average speed control, and because the differential speed control causes rapid torque changes, it is possible to quickly stabilize the speed changes of tape 2. .

Furthermore, since the area of the output e is determined according to the time constant of the charging/discharging circuit, an ideal control state can be achieved by setting the time constant of the charging/discharging circuit according to the characteristics of the reel motor 13 and tape running system. .

Note that the predetermined speed may be set by changing the operating point by applying a bias voltage to the frequency discriminator 21, and any speed can be selected.

In addition, depending on the conditions, the sampling circuit 23 may be a differentiating circuit, or an integrating circuit may be used instead of the low frequency wave generator 24, and various modifications are possible.

As is clear from the above explanation, according to the present invention, differential speed control is performed, so the response speed is quick, and changes in the tape running speed due to load fluctuations on the tape reel are completely stabilized. A remarkable effect can be obtained in the magnetic tape recording and reproducing rhombosphere.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional tape running system, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a time chart showing waveforms of various parts in FIG. 13... Reel motor, 14... Speed detector, 21... Frequency discriminator, 22...
...Pulse generator, 23...Sampling circuit, 24...
...Capacitor, 25...Resistor, 26...
...Low range wave generator, 27... Adder, 29...
・Drive amplifier. Figure l Figure 2 Figure 3

Claims (1)

[Claims] 1. In a magnetic tape recording and reproducing device that runs a magnetic tape by rotating a tape reel, detecting a frequency change in a speed signal representing the running speed of the magnetic tape, and averaging the detected force to obtain an average speed signal, Differentiating the signal detected by the frequency change and applying it to a charging/discharging circuit that maintains a peak value corresponding to the speed change of the magnetic tape and has a time constant according to the characteristics of the magnetic tape running system;
A method for controlling a DC reel motor, characterized in that the output of the charging/discharging circuit and the average speed signal are added together and used as a control signal for a reel motor that rotates the tape reel.