JPH05342705A - Servo system of videotape recorder - Google Patents

Abstract

PURPOSE:To restrain the generation of a disordered image during a vibration and to restrain a jitter at a standstill by a method wherein the loop gain of a servo system for a VTR is made high during the vibration and it is made low at a standstill. CONSTITUTION:A loop-gain control system 1 differentiates the output of an angular velocity sensor used to correct a hand shake and obtains an angular acceleration. The angular acceleration is compared with a threshold value by means of comparators 13 to 15. A result is detected by means of a decoder 16. Switches 17 to 20 are selected, and gains G1 to G4 are set. Thereby, even when a VTR is at a standstill or it is being vibrated, it is possible to set an optimum loop gain.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for controlling a loop gain of a servo system in a video tape recorder (hereinafter referred to as a VTR), particularly a portable VTR such as a camera-integrated VTR.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing an example of the configuration of a servo system in a conventional VTR. In the figure, in order to match the rotation phase of the motor 61 to the reference phase, the RAMP creation circuit 51 creates a ramp voltage based on the reference phase signal (PHASE • REF). Then, the signal from the pulse generator (PG) 62 for detecting the rotation phase of the motor 61 is delayed by the delay circuit 66 for a predetermined time, and the sample hold circuit 52 samples and holds the ramp voltage. Here, the reference phase signal is a frequency-divided signal of the vertical synchronizing signal in the video signal during recording, and is an output signal of the reference oscillator during reproduction. Further, the delay circuit 66 is composed of mono-multi, etc., and by adjusting the variable resistor 66R, it delays so as to sample and hold the central level of the lamp voltage etc. when the reference phase signal and the rotation phase of the motor 61 match. Time is set. Therefore, the output of the sample hold circuit 52 becomes a phase error signal between the reference phase signal and the rotation phase of the motor 61.

Further, in order to keep the rotation speed of the motor 61 at a predetermined value, the output of a frequency generator (FG) 63 for detecting the rotation speed of the motor 61 is shaped into a rectangular wave by a waveform shaping circuit 54 and a delay circuit 55. Delays for a certain time by RAM
Output to the P creation circuit 56. Then, the waveform shaping circuit 54
A sampling pulse is created by the gate pulse creating circuit 59 based on the output of the above, and the ramp voltage is sampled and held by the sample and hold circuit 57. Here, like the delay circuit 66, the delay circuit 55 is composed of a mono-multi, etc., and by adjusting the variable resistor 55R, the motor 6
When 1 is rotating at a predetermined rotation speed, the delay time is set so as to sample and hold the central level of the lamp voltage and the like. Therefore, the output of the sample hold circuit 57 becomes a speed error signal between the predetermined rotation speed and the rotation speed of the motor 61.

The outputs of the sample and hold circuit 52 and the sample and hold circuit 57 are added by the adder 53, amplified by the driver 60, and supplied to the motor 61. With the above configuration, the rotation speed and the rotation phase of the motor 61 can be matched. Here, if the loop gain of the servo system of the VTR is increased, the responsivity to the disturbance is improved. Therefore, when considering the vibration from the outside, it is better to set the loop gain high. However, if the loop gain is high, jitter will increase at rest, so in consideration of image stability, the loop gain should be set low. In a portable VTR, it is necessary to consider external vibrations when carrying the device and to consider image stability when the device is stationary. Therefore, the loop gain is set at a compromise between them.

[0005]

However, in the conventional VTR servo system, the loop gain is set to a compromise between external vibration and jitter at rest, so that the loop gain at rest is more than necessary. It was high, which was a cause of deterioration of jitter. In addition, since the loop gain is kept low during vibration, image distortion was likely to occur. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a VTR servo system capable of increasing the loop gain during vibration and decreasing the loop gain during standstill.

[0006]

In order to solve the above problems, the present invention provides a means for differentiating the output of an angular velocity sensor to a servo system of a VTR, and a gain control in which the gain changes according to the output of this means. And means are provided. Also,
According to the present invention, the servo system of the VTR is provided with means for differentiating the output of the camera shake correction angular velocity sensor and gain control means for changing the gain according to the output of this means.

[0007]

According to the present invention, since the servo system of the VTR is constructed as described above, the angular acceleration is obtained by differentiating the output of the angular velocity sensor. Then, the loop gain of the servo system is controlled according to this angular acceleration. This realizes a reduction in jitter when stationary and an improvement in image quality when the VTR body is vibrating. Further, according to the present invention, the output of the angular velocity sensor used for camera shake correction is used, and this is differentiated to obtain the angular acceleration. Then, the loop gain of the servo system is controlled according to this angular acceleration. As a result, jitter is reduced and V
Realizes image quality improvement when the TR body is vibrating.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. (First Embodiment) FIG. 1 shows a VTR according to the first embodiment of the present invention.
2 is a block diagram showing the configuration of the servo system of FIG. 1, which shows a loop gain control system 1 for changing the loop gain during vibration and at rest, a phase control system 2 for adjusting the rotation phase of the motor 7 to a reference phase, and a rotation speed of the motor 7. It is composed of a speed control system 3, a PWM circuit 4, a low-pass filter 5, a driver 6, a motor 7, and a frequency generator (FG) 8 for adjusting to a predetermined value. The loop gain control system 1, the phase control system 2 and the speed control system 3 are realized by software of a microcomputer (not shown).

FIG. 2 is a flow chart showing the operation of the loop gain control system in the first embodiment of the present invention.
FIG. 3 is a characteristic diagram of a loop gain control system in the first embodiment of the present invention. The operation of the loop gain control system will be described below with reference to FIGS. The output of the camera shake correction angular velocity sensor (not shown) of the VTR is converted into a digital signal by the A / D converter 11 (S1 in FIG. 2) and differentiated by the differentiating circuit 12 (S2 in FIG. 2). Differentiator circuit 12
The output X of is a value indicating the angular acceleration. Since there are two systems for camera shake correction angular velocity sensor, one for vertical direction and the other for horizontal direction,
The output for the horizontal direction or the output for the vertical direction may be used alone, or they may be used in an appropriate combination.

The output of the differentiating circuit 12 is the comparator 13-
15 and are supplied to respective threshold values Vth1 and Vth.
2, Vth3 is compared, and the magnitude relation is compared with the decoder 16
Is detected (S3 to S5 in FIG. 2). Then, the outputs of the decoder 16 select the switches 17 to 20 for setting the desired gains G1 to G4 (S in FIG. 2).
6-S9). That is, if the angular acceleration is larger than Vth1, the switch 17 is selected to set the gain G = G1, and V
If it is larger than th2 and up to Vth1, the switch 18
Is selected to set the gain G = G2, and if the value is larger than Vth3 and up to Vth2, the switch 19 is selected to set the gain G to G2.
= G3, and if it is up to Vth3, the switch 19 is selected to set the gain G = G4. As shown in FIG. 3, G1, G2, G3, and G4 are set to have a difference of about 6 dB.

FIG. 4 is a flow chart showing the operation of the phase control system in the first embodiment of the present invention. The operation of the phase control system will be described below with reference to FIGS. 1 and 4.
In the subtractor 31 of FIG. 1, the ATF (Automatic)
The reference phase signal (PHASE / REF) is subtracted from the Track Finding error signal P, and the error P1 from the reference phase is detected (S11 and S1 in FIG. 4).
2). This deviation is multiplied by K3 by the amplifier 32 to become P2 (S13 in FIG. 4) and input to the integrator 33 and the adder 34. The output P3 of the integrator 33 (S14 in FIG. 4) and the output P2 of the amplifier 32 are added by the adder 34 to become P4 (S15 in FIG. 4), which is supplied to the speed control system 3.

FIG. 5 is a flow chart showing the operation of the speed control system in the first embodiment of the present invention. The operation of the speed control system will be described below with reference to FIGS. 1 and 5.
In the subtractor 42 of FIG. 1, the output of the frequency generator (FG) 8 delayed by the one-sample delay circuit 41 is subtracted, and the rotation speed Y of the motor 7 is detected (S21 of FIG. 5). Then, the subtractor 43 subtracts the reference speed signal (SPEED.REF), and the error Y from the reference speed is detected (S22 in FIG. 5). This error Y is multiplied by K1 by the amplifier 45 and becomes Y1 (S2 in FIG. 5).
3) is input to the adder 44 and the adder 48. Adder 4
4, Y1 and the output P4 of the phase control system are added, integrated by the integrator 46, multiplied by K2 by the amplifier 47 to become Y2, and input to the adder 48 (S2 in FIG. 5).
3). Next, the output Y3 of the adder 48 is multiplied by the gain G set in the loop gain control system (S24 in FIG. 5), and the value Y4 is set in the PWM circuit 4 (S2 in FIG. 5).
5).

The PWM circuit 4 generates a pulse having a duty corresponding to Y4 and outputs it to the low pass filter 5. P
The output of the WM circuit 4 is smoothed by the low-pass filter 5, amplified by the driver 6, and supplied to the motor 7. As described above, according to this embodiment, the loop gain becomes large when the angular acceleration of the VTR is large, and becomes small when the angular acceleration is small. Therefore,
Since the loop gain can be increased during vibration and the loop gain can be decreased during stationary, it is possible to suppress the occurrence of image disturbance during vibration and the deterioration of jitter during stationary. Also,
It is not necessary to provide a dedicated sensor for detecting the angular velocity.

In this embodiment, the gain G is set to G1 to G4.
However, it may be changed at 5 or more or 3 or less levels. Further, the loop gain control system 1, the phase control system 2, and the speed control system 3 may be configured by hardware. Further, the CTL pulse may be used instead of the ATF error signal as the input signal of the phase control system 3.

(Second Embodiment) FIG. 6 is a block diagram showing the structure of a servo system of a VTR according to a second embodiment of the present invention. Here, parts corresponding to those in FIG. 7 are assigned the same numbers. As is clear from a comparison between FIG. 6 and FIG. 7, the feature of this embodiment is that the output of the camera shake correction angular velocity sensor 64 is differentiated by the differentiating circuit 65 to detect the angular acceleration, and the gain control amplifier 58 is based on this. It is configured to control the gain of. The relationship between the output of the differentiating circuit 65 and the gain of the gain control amplifier 58 may be the same as in FIG. Further, the gain control amplifier 58 may control the gain after adding the outputs of the sample hold circuit 52 and the sample hold circuit 57.

The present invention is not limited to the above-mentioned embodiments, but various modifications can be made within the scope of the present invention, and they are not excluded from the scope of the present invention. For example, in each of the above embodiments, the output of the angular velocity sensor for camera shake correction is used, but a dedicated angular velocity sensor may be provided. Further, although each of the above-described embodiments is a servo system that performs speed control and phase control, the present invention can also be applied to a servo system that only performs speed control.

[0017]

As described in detail above, according to the present invention, the optimum loop gain can be set when the VTR is stationary or vibrating, so that the image quality is improved. Further, since the vibration of the VTR is detected by using the output of the angular velocity sensor for camera shake correction, a dedicated sensor for detecting the vibration is unnecessary.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a servo system of a VTR according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of the loop gain control system in the first embodiment of the present invention.

FIG. 3 is a characteristic diagram of a loop gain control system in the first embodiment of the present invention.

FIG. 4 is a flowchart showing the operation of the phase control system in the first embodiment of the present invention.

FIG. 5 is a flowchart showing the operation of the speed control system in the first embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a VTR servo system according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing an example of a configuration of a servo system in a conventional VTR.

[Explanation of symbols]

 1 loop gain control system 2 phase control system 3 speed control system 58 gain control amplifier 64 angular velocity sensor 12,65 differentiating circuit

Claims (2)

[Claims] 1. A servo system for a video tape recorder, comprising: (a) means for differentiating the output of an angular velocity sensor; and (b) gain control means for changing the gain according to the output of the means. 2. A servo system for a video tape recorder according to claim 1, wherein an output of an image-sensing angular velocity sensor is used.