JPS5984367A - Capstan servo circuit - Google Patents

Abstract

PURPOSE:To enable specified running speed of a tape in an eight mm. video tape recorder that has only a capstan servo-mechanism by changing injection signal for each field and detecting a tracking error to be inputted at an intermediate point of video track. CONSTITUTION:A pilot signal for tracking is separated by an LPF1 and a reversible counter 2 that has RF switching pulse as counting input performs addition and subtraction according to an output D given corresponding to the multiple. An injection signal change-over circuit 3 having the counting output as input changes bit output and inputs to a multiplication circuit 4. The multiplication output is inputted to a switching circuit 9 passing through filters 16K, 46K and through the first and the second detectors 7, 8, and input to a comparator circuit 10 is changed for each field. The output that has sample held 12 the comparison output is inputted to a capstan control circuit 13 to control rotation of a capstan motor, and the tape can be advanced at a specified speed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides the following advantages:
This invention relates to a capstan servo circuit used in 8mm video that records a tracking pilot signal on a video track.

For 8mm video, four types of tracking pilot signals are recorded on the video track and POM rack instead of the control track, and the DTP servo controls the vertical position of the video head and the tape speed. This enables ATF servo (capstan servo). The DTP servo operates so that the video head correctly scans the center of the track during normal playback and scans a single track during special playback.

Further, the ATF servo controls the rotational phase of the capstan motor in accordance with a tracking error output obtained by reproducing a tracking pilot signal. When performing high-speed playback in a normal VTR, the branch output of the playback control signal is used as the capstan servo comparison signal, but the tracking error output is used for the ATF servo in 8mm video. . This tracking error output uses the difference frequency between four types of tracking/arm pilot signal frequencies, and the difference frequency with the tracking pilot signal of the adjacent track is:
One side is 16KH! 2i and the other frequency is selected to be abKH2. That is, the frequency of the tracking pilot signal is ft=102KH2 for the first signal, f, -1113K HZ Im for the second signal, and f for the fifth signal.
s= 164 KW zllm, 4th signal is f4-14
8KH2i, respectively, and their frequencies are cyclically switched at the field period. When playing,
In order to reproduce these tracking pilot signals and obtain a tracking error/output, an injection signal with the same frequency as the tracking pilot signal of the track to be scanned is input to a multiplier circuit together with the regenerated tracking pilot signal, and the multiplication is performed. The output may be separated by 16 filters and 46 filters, and the comparison output obtained by comparing the levels may be used as the tracking error output. The tracking control principle described above is well known, and further explanation will be omitted.

ATF servo is essential for 8mm video,
DTP servo is not essential as in a normal VTR. Therefore, regarding 8mm video without DTP servo, ATF
To achieve this, it will be as follows. FIG. 1 is a diagram illustrating switching between a scanning trace and an injection signal for a track pattern, and the numbers in the diagram are the identification numbers of the tracking pilot signals of the corresponding tracks, and are
Respond to signals. As is clear from the figure, in the normal reproduction scan trace (FA) on the track pattern, the tracking pilot signal is sequentially switched in field units.
In the triple-speed reproduction scan trace (FB), the tracking pilot signal is switched three times in one field. Furthermore, in the triple reverse reproduction scan trace (PC), the tracking pilot signal is switched five times in one field, and the switching order is also discontinuous for each field. Therefore, switching the injection signal during normal playback is easy as shown in A, but switching during triple speed playback requires complicated setting of the switching timing during the field as shown in B+. Furthermore, when switching during triple reverse playback, not only the setting of the switching timing but also the selection of the injection signal becomes complicated, as shown in C.

Therefore, the present invention has been developed in view of the fact that the injection signal switching operation for an 8mm video that has only an ATF servo mechanism is complicated and costly compared to the injection signal switching operation for an 8mm video that also has a DTP servo mechanism. The purpose of this project is to propose a new and effective capstan servo circuit that aims to standardize the injection signal switching circuit by reusing the injection signal switching circuit of the 8mm video that has only a servo mechanism and the 8mm video that has a DTP servo mechanism. It is.

In consideration of the fact that the desired tracking state at the midpoint of the video track is the same for both 8mm videos with a DTP servo mechanism and 8mm videos without a DTP servo mechanism, the present invention switches the injection signal for each field and It is characterized by being configured to detect a tracking error to be input to the capstan servo at an intermediate point.

A simple injection signal switching order for an 8 mm video with a DTP servo mechanism will be explained below. Generally, the multiple for double-speed playback is selected to be an odd number because the recording track performs azimuth recording. It has been confirmed that there are only two types of switching order in odd-numbered double speed playback.

That is, -7 times, -3 times, 1 times, 5 times, 9 times, ・
In the case of..., the switching order is...→f1→f! →
The positive order is f3 → f4 → ..., and in the case of ..., -9 times, -5 times, -1 times, 3 times, 7 times, ..., the switching order is ... → f4 The reverse order is →f3→ra→f1→... Therefore, depending on the multiple of double-speed reproduction, it is sufficient to switch the injection signal in field units in the forward or reverse direction. Generally, the multiple is 4n+1 (however, n
is an integer and the sign indicates the direction), the switching order may be in the positive direction, and when the multiple is 4n+5, the switching order may be in the reverse direction.

Hereinafter, the present invention will be explained according to an illustrative embodiment. In this embodiment, the above-described injection signal switching circuit is applied to an 8 mm video camera having only an ATF servo mechanism. FIG. 2 shows a circuit according to an embodiment of the present invention, and FIG. 3 shows a waveform diagram of its essential parts. In the following explanation, for convenience of explanation, only the tracking pilot signal weighted on the video track is extracted to perform ATF servo.

First, in this embodiment, a tracking pilot signal of 200K is obtained from the reproduced video signal obtained after switching.
H! They are separated by a low-pass filter (1) whose passband is below Z. On the other hand, a 2-bit reversible counter (2) which receives the RF switching pulse (RF) for head output switching as a counting input performs addition or subtraction counting according to the index output (Dl) issued according to the multiple thereof. 3 In the case of double reverse playback, the reversible counter (2) performs subtraction counting, and the bit output is...4→3→2→1→4...
and changes. The injection signal switching circuit (3) which receives this count output as input is...→f4→f3→f2→f1→...
Switch the signal in this order.

This injection signal and filter output are input to a multiplication circuit (4). This multiplication output is input to the filter (5) at 16 and the filter (6) at 46, and is then input to the first and second detection circuits +
71 (input to 81. Both shear wave outputs are input to a switching circuit (9) which uses the lower bit output of the reversible counter (2) as a switching input, and a comparison circuit (input to 1ω is switched for each field. Comparison) The tracking error output obtained by
3, and when 3 times reverse reproduction is performed, the state becomes as shown in CP-3 in FIG. For each output waveform in the figure, the dotted line indicates when the phase is leading, the dashed line indicates when the phase is slow, and
The solid lines indicate each output waveform during normal operation. As is clear from these waveform diagrams, the output level at the center of the video track corresponds to tracking error.

Therefore, in this embodiment, the RF switching pulse (:RF
) into the sampling pulse generation circuit (11),
The RF switching pulse (RF) is delayed by 172 fields and the sampling pulse (SP) (see Fig. 6) is input to the sample hold circuit (I2).The sampling pulse generation circuit (11) includes a variable mono-multiple The sampling timing can be changed.The output obtained by sampling and holding the comparison output is input to a well-known capstan control circuit αj, which controls the rotation of the capstan motor and causes the tape to run at a predetermined running speed. .

As described above, according to the present invention, the 8 mm video capstan servo circuit can be shared with a simple circuit regardless of the presence or absence of a DTP servo mechanism, and the effect is great.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a conventional capstan servo, FIG. 2 is a circuit block diagram of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of an error output waveform. Explanation of main figure numbers (2)... Reversible counter, (3)... Injection signal switching circuit, (4)... Multiplication circuit, +17J... Sample hold circuit.

Claims (1)

[Claims] (1) In 8mm video, where four types of tracking pilot signals are sequentially switched and recorded superimposed on the video signal.
A 2-bit reversible counter that counts or subtracts RF switching pulses according to the double speed, and an injection signal that emits four types of injection signals that subtract the frequency from the tracking pilot signal according to the count value of the reversible counter. A generator circuit, a multiplier circuit that multiplies the reproduction tracking pilot signal and injection signal, a comparator circuit that compares the levels of the 16 Hz acid component and 46 KHz component in the multiplication output and generates an error output, and a A capstan servo circuit that enables double-speed playback by disposing a sample hold circuit that samples a tracking error output, and a capstan control circuit that controls the rotation of a capstan motor based on the sample hold output.