JPS5827886B2 - automatic tracking device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a helical scanning video recorder (VTR), and more particularly to an automatic tracking system for optimally tracking a read head during playback of discontinuous recording tracks in such a VTR. Regarding equipment.

A reading head is attached to a piezoelectric element like a bimorph,
It is well known that a bimorph can be caused to perform automatic tracking of a readout point by applying a required drive voltage.

Tracking position information is multiplied by the upper envelope waveform of the playback video signal and the excitation wave given to the palmorph (balanced modulation)
is given as a relative positional deviation error between the recording track and the read head.

In this case, if there is a phase delay due to frequency dependence in driving the bimorph, a phase shift will occur between the excitation wave and the actual vibration of the bimorph, which will affect the output of the balanced modulator.
For this reason, the amount of feedback is not the optimum amount, which poses a problem of system stability and prevents accurate tracking.

An object of the present invention is to solve the above-mentioned problems with an extremely simple configuration.

The figure shows one embodiment of the present invention, in which 10 is a piezoelectric element such as a bimorph supported in a cantilever in a rotary head, and a video head 12 is attached to the free end of the piezoelectric element.

One surface of the bimorph is maintained at a constant potential (eg, ground level as shown), and the other surface is given a bimorph deflection signal from the bimorph drive section 14.

16 is a few minutes away from the bimorph constant potential surface in the direction of bimorph displacement, 11n711. They are electrode plates of about 3 to 4 mmM that are positioned apart and have a difference between their constant potential and high voltage.

This plate is placed close to the free end of bimorph 10.

In this manner, bimorph 10 and plate 16 form a capacitor.

Deflection of the bimorph with respect to plates 16 results in a capacitance change that is inversely proportional to the distance between the capacitor plates.

Plate 16 is connected to a high input impedance buffer amplifier 17 containing two FETs 18 and 20.

This amplifier 17 receives two power supply voltages V1 and 2.

This intensifier operates to conserve the charge on the capacitor formed by plate 16 and bimorph 10 and to effect voltage balancing across this capacitor.

When the charge on the plate 16 is conserved, a voltage is obtained that is proportional to the distance between the capacitor plates, that is, the amount of deflection of the bimorph.

This voltage is applied via a bandpass filter 22 to one input of a multiplier (balanced modulator) 24.

Note that the dotted line in the figure indicates a shield plate that electrostatically shields the buffer amplifier 17.1. Grounded.

On the other hand, the RF output from the video head 12 is transmitted to the RF amplifier 2.
6, and this is used as the playback output, and
AM detection is performed by the 1-envelope detector 28 and applied to the other input of the balanced modulator 24 via the bandpass filter 30.

When in automatic tracking mode, bimorph 10 is caused to vibrate by an excitation frequency fc from excitation wave generator 32.

Tracking errors occur in the video head output as a result of amplitude fluctuations in the excitation frequency.

This amplitude fluctuation is detected by the RF amplifier 26 and the upper envelope detector 2.
8, input to the balanced modulator 24 via the bandpass filter 30.

The two bandpass filters 22 and 30 are the two bandpass filters 22 and 30 of the balanced modulator 24.
Moves to make the phase delays of the two input signals the same.

The output of balanced modulator 24 is provided to twin T filter 34.

This filter 34 removes twice the excitation wavenumber 2fc from the balanced modulator output.

Therefore, the twin T filter 34 provides a voltage proportional to the displacement of the bimorph.

This voltage signal is input to an amplifier 36, where the mechanical constants of the bimorph are electrically compensated.

The compensated signal from amplifier 36 is then sent to summing point 38
is added to the output from the excitation wave fc generator 32, and is supplied to the drive unit 14 for driving the bimorph.

With such a configuration, feedback without phase difference is possible.

Since the structure is simple, it can be easily placed in a limited space within the rotating drum.

Since the displacement of the bimorph itself can be directly detected, the bimorph can be controlled even when switching heads.

[Brief explanation of drawings]

The figure is a circuit diagram of an embodiment of the present invention, in which 10 is a piezoelectric element such as a bimorph, 16 is a detection plate, 22 and 30 are bandpass filters, 24 is a balanced modulator (multiplier), and 28 is an upper envelope detection. 32 is an excitation wave generator, and 34 is a twin T filter.

Claims (1)

[Claims] 1 Equipped with a piezoelectric element capable of deflecting a rotating head in a direction perpendicular to its scanning direction, the piezoelectric element is excited with a signal of a predetermined frequency, and an amplitude-modulated envelope signal of the reproduced output obtained from the rotating head is In a recording/reproducing apparatus that controls the position of the piezoelectric element based on the included tracking error signal, a deflection detection circuit for detecting the deflection of the piezoelectric element is provided, and the output of the deflection detection circuit is connected to the one-velop signal. An automatic tracking device configured to perform multiplication and supply the multiplication output as the tracking error signal to the piezoelectric element.