JPH0334632B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a VTR (video tape recorder), and particularly to a VTR that performs a braking operation when transitioning from high-speed operation to constant-speed operation.

(b) Prior art To ensure a smooth transition from high-speed operation such as high-speed search or n-times speed mode to constant-speed operation without the tape becoming loose, the capacitor that had previously rotated at high speed was used. It is necessary to apply a brake to the stun motor to make it rotate during standard driving. This kind of thing has also been done, for example, in Japanese Patent Application Laid-Open No. 58-35757.

In the conventional example shown in FIG. 4, the rotation frequency detection signal (FG) that depends on the rotation of the capstan motor 1
The output a of the frequency divider 4, which divides the output of the limiter 3 which limits the amplitude of the output of the generator 2 which generates , is converted into a frequency-divided output a by the sawtooth waveforming circuit 5 as shown in FIG. 5b.
When a triangular wave that rises after a fixed time T delay from the rising edge of is sampled and held at the falling timing of the output a of the frequency divider 4, the output of the sample and hold circuit 6 becomes as shown in FIG. 5c. The relationships when the rotational frequency of the capstan motor 1 increases are shown in a', b', and c' in FIG. In the synthesis circuit 7, the speed error voltage c from the sample and hold circuit 6 is applied to the capstan motor 1 through a DC amplifier 8 and a drive circuit 9. In this control loop, for n-times speed operation in search etc., a voltage nE1 times n times the voltage E1 applied at constant speed is applied to the control loop through the DC voltage amplifier 8, for example, and the frequency divider 4
This can be achieved by setting the frequency division ratio to 1/n.

At the time of transition from n times speed operation to constant speed operation, brake voltage P1 is applied via synthesis circuit 7 to prevent tape slack from occurring. At that time, a signal for rotating the motor in the reverse direction is applied from the terminal 12 to the drive circuit 9. In addition, terminal 12
If the signal applied from is high level, the motor will rotate in the forward direction, and if it is low level, the motor will rotate in the reverse direction. FIG. 6 shows waveforms of various parts when transitioning from n-times high-speed operation to constant-speed operation. In FIG. 6, P1 is the brake voltage applied from the terminal 10 to the combining circuit 7, P2 is the motor forward/reverse signal applied from the terminal 12 to the drive circuit 9, and c is the speed error voltage generated from the sample and hold circuit 6.
The speed error voltage c is from high-speed operation mode A to time t1.
When switching to regular operation mode B, the voltage oscillates as shown in the figure, and settles down after a while.

In this way, there are variations in the starting force depending on the rotation angle of the motor and the starting force of individual motors, so the conventional method of applying a constant brake voltage for a certain period of time reduces the rise time from high-speed operation such as search to constant operation speed. (The time it takes for the oscillating voltage to settle to a predetermined voltage) is long and unstable.

(c) Object of the Invention Therefore, an object of the present invention is to provide a video tape recorder that can quickly shift from high-speed operation to constant-speed operation.

(D) Structure of the Invention The present invention reduces the speed error voltage that occurs when switching from high-speed operation to constant-speed operation by providing a suppressing means that prevents the speed voltage in the speed control system from exceeding a predetermined reference voltage. This is designed to end the vibration quickly.

(e) Embodiment In FIG. 1 in which the present invention is implemented, the same parts as in FIG. 4 are given the same symbols and redundant explanation will be omitted. In FIG. 1, 13 is a comparator that compares the reference voltage Eo and the speed error voltage C from the sample-and-hold circuit 6, and generates an output when the speed error voltage c exceeds the reference voltage. This switch means is turned on by the output of the comparator 13 and disables the brake voltage P1 applied from the terminal 10 to the combining circuit 7.

The operation of such a circuit will be explained with reference to FIG.

First, when a signal for constant-speed playback operation is given to the system controller (not shown) of the VTR during high-speed search operation, the signal is sent to the combining circuit 7 at terminal 1.
A brake voltage P1 is applied to the drive circuit 9 from the terminal 12, and a negative pulse-like reverse signal P2 is applied to the drive circuit 9 from the terminal 12.
is applied. At this time, the voltage at the terminal 11 has been switched from the n-fold voltage nE1 to the voltage E1 in the normal constant speed operation mode, and the division ratio of the frequency divider 4 has also been switched to the division ratio in the constant speed operation mode. shall be
The voltage c of the sample and hold circuit 6 tends to oscillate greatly from the switching time t1, but when it exceeds the reference voltage Eo, an output is generated from the comparator 13 and the switch means 14 is turned on, so that the brake voltage P1 is inactive for its ON period D. Therefore, the speed error voltage c from the sample and hold circuit 6 is limited by the reference voltage Eo, and its vibration energy is suppressed. Where the speed error voltage is lower than the reference voltage, the brake voltage is input to the combining circuit 7. In this way, as shown by the solid line in FIG. 2c, the voltage quickly converges to a predetermined voltage without repeating subsequent oscillations. Incidentally, the dotted line waveform indicates vibration in a case other than the present invention. In this way, the time from the search operation to the constant speed operation is shortened, and the transient operation is also stabilized. In particular, in the past, it took a long time for the speed error voltage to converge due to variations in the starting force of the motor, but the disadvantages caused by such variations can be improved. Figure 3 shows a specific example of the main part, 15 is an IC with the product number BA6321 made by ROHM, the output of frequency divider circuit 4 is input to pin 8, and this output is sent to the sawtooth waveforming circuit. 5 and sample hold circuit 6
is supplied to 15 and 16 are charge/discharge capacitors externally connected to pins 9 and 10,
They form part of the sawtooth wave forming circuit 5 and the sample hold circuit 6, respectively. Sampling hold circuit 6
The speed error voltage that is the output of the IC 15 once goes out from the IC 15 through the 11th pin, and then enters the IC 15 again from the 13th pin through the resistors R1 and R2. that time,
It is combined with the phase error voltage of the phase servo system applied from terminal 19 through resistor R8. The speed error voltage etc. input from pin 13 is input to the operational amplifier 21.
It is added as a positive input and output from pin 15. Reference numeral 20 indicates a terminal connected to the DC amplifier 8 of FIG. R4 and R5 are bleeder heights connected between pin 11 and ground, Q is a switching transistor whose base is connected to the connection midpoint M, and its collector is connected to terminal 18 for brake voltage input via resistor R7. The emitter is connected to ground. In this embodiment, the reference voltage Eo mentioned above is the voltage that appears at pin 11 when the switching transistor Q is turned on. Reference numeral 17 denotes a terminal to which a cue signal is applied during a search, and the cue signal is applied to the speed control system through a resistor R6 and a switching diode D1. Brake voltage P1 applied to terminal 18 is also applied to the speed control system through resistor R7 and switching diode D2. However, according to the present invention, when the switching transistor Q is turned on, the brake voltage is invalidated during the ON period. In the case of FIG. 3, the composite circuit 7 in FIG. 1 corresponds to an external line extending from pin 11 to pin 13.

In addition, in the configuration shown in Fig. 3, a comparator is provided with a predetermined reference voltage as one input and the output of pin 11 as the other input, and the output of this comparator drives the switching transistor Q. Needless to say, it may be configured to do so.

(F) Effects of the Invention According to the present invention, the transient operation when moving from high-speed operation to constant-speed operation ends quickly, and the transient operation is also stabilized, which is useful.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing the configuration of the main parts of a video tape recorder embodying the present invention, and FIG. 2 is an operational waveform diagram thereof. FIG. 3 is a circuit diagram showing essential parts of another embodiment of the present invention. FIG. 4 is a block circuit diagram showing the configuration of the main parts of a conventional video tape recorder, and FIGS. 5 and 6 are operational waveform diagrams thereof. c...Speed error voltage, Eo...Reference voltage, Q...
...Switching transistor, 13...Comparator,
14... Switch means.

Claims (1)

[Claims] 1. In a video tape recorder that applies a brake voltage to a speed control system of a capstan motor when transitioning from high-speed operation to constant-speed operation, a comparator that compares a speed error voltage in the speed control system with a reference voltage; . . A video tape recorder, further comprising a suppressing means comprising a switch means for inactivating the brake voltage during the output period of the comparator.