JPS58208950A - Pickup device - Google Patents

Abstract

PURPOSE:To prevent damage of a recording medium, by a jitter control signal to a time base coil, and also superposing it onto a needle pressure compressing coil. CONSTITUTION:A jitter control signal is impressed to a time base coil 11, adsorption and repulsion of a magnet 4 fixed to a cantilever 3 are controlled, and a pickup needle 1 tracks the center of a recording groove of a recording medium 2. This jitter control signal is impressed to a needle pressure impressing coil 12, too, to which a current corresponding to set pressure is impressed and the coil 12 controls turning of a lever 3 through a magnet 4 in accordance with the superposed control signal, by which generation of floating of the needle 1, etc. by the jitter control is prevented, and damage of the recording medium 2 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves relatively scanning a pickup needle over concentric tracks or spiral tracks of a disc-shaped recording medium made of a conductive material on which information signals are recorded as changes in geometric shapes. The present invention relates to a pickup device suitable for use in a capacitive video disc player that detects and reproduces this information signal as a change in capacitance.

In general, in this type of video disc player, when playing back from a disc-shaped recording medium on which video signals have been recorded in advance, speed fluctuations (time pace fluctuations) in the relative speed between the recording medium and the pickup needle due to various reasons occur, so-called jitter. occurs. Possible causes of this include uneven rotation of the turntable during playback, shaking, eccentricity, and vibration of the recording medium. Needless to say, it is desirable that this jitter be as small as possible.

Therefore, in conventional video disc players, various countermeasures against jitter have been taken. As an example, FIG. 1 shows a pickup device capable of jitter compensation. In FIG. 1, reference numeral 1 denotes a pickup needle, which detects a prerecorded video signal by coming into contact with the recording groove of the recording medium 2.

Reference numeral 3 denotes a cantilever made of a thin pipe made of metal such as aluminum.The pick-up needle 1 is attached to the tip of the cantilever, and the magnet 4 is attached to the other end. A lead (fine metal wire) 5 is connected, and this fly lead 5
The other end is electrically connected to a thin metal cartridge plate 7 attached to the end of the cartridge 6.

On the other hand, a cartridge terminal 9 is implanted at the end of the circuit board 8, and the cartridge plate 7 is inserted into and contacted with this cartridge terminal 9. As a result, the video signal detected from the pink-up needle l is guided to the cartridge plate 7 via the fly lead 5, and further to the circuit board 8 via the cartridge terminal 9.

On the other hand, the magnet 4 attached to the other end of the cantilever 3 is attached to the IJ edge 6. It is elastically supported by damper rubber IO bridged between both side plates of. Further, a time base (jitter compensation) coil 11 is arranged on a concentric axis extending from the cantilever 3.

Further, a stylus pressure applying coil 12 is arranged above the magnet 4, and a constant DC current is supplied to this coil 12, thereby applying an appropriate stylus pressure to the pick-up needle l at the tip of the cantilever 3. .

Here, we will explain the jitter compensation operation of the pickup device configured as above.
A control current is supplied to the time base coil 11 in accordance with the phase difference obtained by comparing the synchronization signal in the video signal detected in the video signal with the reference signal.

At this time, a magnetic field corresponding to the control current is generated in the time base coil 11, which generates an attractive force or a repulsive force in the magnet 4, and the cantilever 3
is displaced in the x-x'l direction against the elastic force of. As a result, the pick-up needle l is moved forward or backward along the recording groove of the recording medium 2 depending on the magnitude of the control current, and thus the relative speed between the pick-up needle l and the recording medium 2 is always kept constant and jitter is compensated. be done.

By the way, in the above pickup device, the magnet 4 and the time base coil 11 are on the extension line of the pickup needle l and the cantilever 3. Therefore, when the magnet 4 is attracted by the coil 11, the needle tip floats and the needle pressure is reduced. Not only is it easy to cause needle skipping because of the weight, but there is also a risk of fluctuations in the detection output from the pick-up needle l. On the other hand, when the magnet 4 is repelled, the tip of the needle digs into the recording medium 2, and there is a risk that the pickup needle l may damage the recording medium 2.

The present invention has been made in view of these points, and an object of the present invention is to provide a pickup device that eliminates the drawbacks of the conventional devices described above.

That is, the present invention provides a pickup device that does not easily cause needle skipping or damage to the recording medium when correcting jitter of the pickup needle using a time base coil and a magnet.

The following will explain the embodiments shown in the drawings.

FIG. 2 shows an example of a stylus pressure drive circuit used in the pickup device of the present invention, and this stylus pressure drive circuit 13 includes a stylus pressure applying coil 12, transistors Q1sQ2,
It is composed of resistors R1 and R2, and a variable resistor VR for adjusting stylus pressure. In this circuit 13, the stylus pressure application coil 12 is usually
A direct current according to the set value by the variable resistor VR flows through the coil 12, and at this time a magnetic field corresponding to this direct current is generated in the coil 12, which causes the magnet 4 shown in Fig. 1 to rotate counterclockwise. A rotational torque is generated, and as a result, an appropriate needle pressure is applied to the pick-up needle l at the tip of the cantilever 3.

Note that 14 is a jitter compensation circuit composed of the time base coil 11 and other transistors Q3eQ4, etc. In this circuit 14, as described above, the synchronization signal in the video signal detected by the pickup needle l is used as the reference signal. A control signal corresponding to the phase difference obtained by comparison is supplied to the time base coil 11. At this time, the magnet 4 shown in FIG. 1 is attracted or repelled depending on the magnetic field generated by the coil 11, and as a result, the pickup needle 1 is moved forward or backward along the recording groove of the recording medium 2, and thus the relative speed between the pickup needle 1 and the recording medium 2 is always kept constant and jitter is compensated for.

In this embodiment, the jitter control signal obtained for jitter compensation as described above is also particularly supplied to the stylus force drive circuit 13, that is, this jitter control signal is applied to the base of the transistor Q, thus controlling the stylus force. The component of the jitter control signal is superimposed on the direct current flowing through the applying coil 12. Therefore, in this case, by the jitter compensation operation described above, the magnet 4 is
Even if the needle pressure of the pick-up needle l is about to decrease as a result of being attracted, at this time the needle pressure applying coil 12
As a result, the counterclockwise rotational torque acting on the magnet (4) increases, and the needle pressure of the pick-up needle (1) is kept constant. Conversely, when the time base coil 11 repulses the magnet 4 and the stylus pressure of the pick-up needle l attempts to increase, the current flowing through the stylus pressure application coil 12 decreases, and as a result, the magnet 4 The rotational torque acting on the pick-up needle l is thus reduced, and the needle pressure of the pick-up needle l is thus kept constant.

According to the pickup device of the present invention, even if a change in stylus pressure occurs on the pickup needle by performing jitter compensation on the pickup needle using the time base coil and a magnet as described above, at this time, even if a change in stylus pressure occurs in the pickup needle, the time base coil and the magnet are used to compensate for the jitter of the pickup needle. The alternating current component is superimposed on the stylus pressure applying coil, thereby canceling out and eliminating changes in both stylus pressures, so that the pick-up needle is always kept at a constant stylus pressure.

Therefore, if the pickup device of the present invention is used, the pickup needle will always move over the recording medium with a constant stylus pressure, which will reduce the occurrence of needle skipping and damage to the recording medium by the stylus tip. .

[Brief explanation of drawings]

FIG. 1 is a partially cutaway side view of a capacitive pickup device, and FIG. 2 is a circuit diagram of a stylus force drive circuit used in the pickup device of the present invention. l...Pickup needle, 2...Recording medium, 3...
Force/tilever, 4... Magnet, 11... Time base coil, 12... Needle pressure application coil, 13...
-Stylus pressure drive circuit, 14... jitter compensation circuit.

Claims (1)

[Claims] 1. A cantilever with a pick-up needle attached to one end and a magnet attached to the other end, a Yuko coil placed on the concentric axis of this magnet, and a stylus pressure applying coil placed near this magnet. , while supplying a jitter control signal to the time base coil, a current superimposed with this jitter control signal is also supplied to the stylus pressure application coil, so that the stylus pressure applied by the pickup needle to the recording medium is constant. A pickup device characterized by: