JPH0421267B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a signal pickup device for reproducing information signals of disc-shaped information recording carrier reproducing devices such as video discs and audio discs, which are information signal reproducing devices.

Conventional configurations and their problems Video disks, audio disks, etc. include mechanical, optical, and capacitance methods depending on the recording and reproducing method of video signals, audio signals, etc. Especially in the case of capacitance methods. There are two types: a grooved type in which the disk has a groove for guiding the transfer of the information signal reading element, and a non-grooved type in which there is no groove. When reproducing information signals from a non-grooved disk, a pick-up arm is required to follow the radial distortion (eccentricity) of the information signal caused by the mechanical characteristics of the disk and to perform accurate signal reproduction. A control means such as tracking control is required to drive and displace the motor in a predetermined direction.

In addition, fluctuations appear in the relative speed between the signal recorded on the disk and the information signal reading element due to eccentricity or vertical waviness (face runout) caused by mechanical deformation of the disk, etc. This causes a time axis error (jitter) in the reproduced signal. In order to correct this, a control means is required to drive and displace the pickup arm by a predetermined amount in the tangential direction of the disk.

FIG. 1 shows a principle diagram regarding signal reading using the grooveless capacitive method. The disk 1 rotates at high speed (for example, 900 rpm) in the A direction, and receives a main information signal 2, tracking guide signals 3 and 4, and a tracking control signal once per rotation (not shown) during tracking control signal processing. A third tracking control signal that alternately switches between 3 and 4 is recorded. These signals are extracted as changes in capacitance occurring between the disk 1 and the electrode 6 provided on the stylus 5. Tracking control is then performed by correctively displacing the position of the stylus 5 in the direction B in accordance with the tracking control signal so that the electrode 6 accurately traces the main information signal 2 and extracts the signal accurately. Furthermore, in order to correct the time axis error (jitter), the position of the stylus 5 is corrected and displaced in the C direction using the jitter correction signal.

FIG. 2 is a perspective view showing the conventional structure of a signal pickup device, partially in section. The stylus 5 is attached to the pick-up arm 7 via a stylus holder 43, and a magnet 8 is fixed to the pick-up arm 7.
The vicinity of the magnet 8 position is supported by a suspension 9 made of a viscoelastic material such as rubber. A stylus pressure coil [not shown], tracking coils 10 and 11, and a jitter coil 12 are arranged to be magnetically coupled to the magnet 8, and by attracting or repelling the magnet 8, the stylus When a pressing force is applied to the disk 5, the disk 1 is simultaneously moved and displaced in the B direction or the C direction, thereby performing tracking or jitter correction control.

In the conventional signal pickup device having such a configuration, the drive characteristics of the pickup arm 7,
In other words, the characteristics when the pickup arm 7 is driven in the B direction by the tracking coils 10 and 11 [hereinafter sometimes referred to as tracking drive characteristics]
Also, the pick-up arm 7 is connected to the jitter coil 12.
The characteristics when the disc is driven in the C direction (hereinafter sometimes referred to as jitter drive characteristics) greatly influence control characteristics such as tracking control and jitter control for accurately reproducing signals recorded on the disk.

The tracking drive characteristics will be explained as an example.
FIG. 3 is an example of a transfer function between the tracking drive current and the displacement of the pickup arm 7, which represents the tracking drive characteristics, where 13a, 13b, and 13c represent the amplitude characteristics [hereinafter sometimes referred to as tracking characteristics], and 13d represents the phase. The characteristics [hereinafter sometimes referred to as tracking phase characteristics] are shown.
13b is between the amplitude region characterized by the stiffness of the suspension 9 in the B direction shown in 13a, and the acceleration region shown in 13c characterized by the mass of the pick-up arm 7, the attached magnet 8, and others. 14 is the amplitude, 15 is the acceleration, and 16 is the velocity.

The characteristic near 13a in the figure is suspension 9.
is affected by the temperature characteristics of the material forming the suspension. Generally, butyl rubber or silicone rubber is used as the material for the suspension, but if control characteristics are important, butyl rubber is used, and if temperature characteristics are important, silicone rubber is used.

Figure 4 shows the tracking drive characteristics when butyl rubber is used for the suspension.
Amplitude characteristics at 20℃, 17b are transfer characteristics at 20℃, 18
a is the amplitude characteristic at 50℃, 19a is the amplitude characteristic 1 at 0℃
9b shows the transfer characteristics at 0°C. As can be seen from this figure, when butyl rubber is used for the suspension, the amplitude changes with temperature changes, which adversely affects control characteristics.

Next, Figure 5 shows the tracking drive characteristics at 20°C when silicone rubber is used as the suspension material. 20a is an amplitude characteristic, and 20b is a transport characteristic. In this case, since the temperature characteristics of the material are good, although not shown in the drawings, the characteristics change less with respect to temperature changes. However, due to the poor damping properties of the material, the amplitude at the resonant frequency becomes large (generally said to have a large resonance magnification, hereinafter referred to as the resonance magnification), which poses a problem in tracking control, jitter control, etc. I have something to come.

In this way, temperature characteristics and control characteristics are generally contradictory to each other.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a signal pickup device that is stable and has excellent temperature characteristics, overcoming the drawbacks of the control characteristics of the signal pickup device when a silicone rubber material is used for the suspension.

Structure of the Invention The signal pick-up device of the present invention has a pick-up arm that has a reading element at one end for reading an information signal recorded on a disc-shaped information recording carrier, is supported by an elastic body at the other end, and has a permanent magnet in a part. is provided with an electromagnetic coil magnetically coupled to the permanent magnet, the reading element is configured to be driven and displaced in at least one of the radial direction and the tangential direction, and the reading element is configured to be displaced in the radial direction or the tangential direction. A magnetic detector is provided near the permanent magnet to detect an electrical signal corresponding to a change in direction, and an electrical signal corresponding to the moving speed of the reading element is sent to a reading element drive circuit based on the detection signal of the magnetic detector. It is characterized in that the control characteristics are stabilized by applying velocity feedback to prevent deterioration of temperature characteristics due to the material of the elastic body.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 6 to 10.

The disadvantage of using silicone rubber for the suspension as described above is that the resonance magnification at the resonance frequency is large. In order to compensate for this drawback, a method for suppressing the resonance magnification of the resonance frequency will be explained.

For example, taking tracking characteristics as an example, the speed of the pick-up arm reaches its maximum due to the amplitude characteristics at the resonance frequency, and an electrical signal corresponding to the speed of the pick-up arm in the B direction is detected and fed back to its own drive amplifier. [hereinafter sometimes referred to as velocity feedback], the resonance magnification of the resonance frequency can be freely controlled according to the amount of feedback. Then, the feedback amount may be set so that the control characteristics are improved. Similar results can be obtained with respect to jitter drive characteristics.

Next, it will be explained how the drive characteristics of the pickup arm are improved by means of detecting speed and speed feedback.

FIG. 6 shows an embodiment of the signal pickup arm device of the present invention, which differs greatly from the conventional example in that magnetic detectors 21 and 22 are provided near the magnet 8. These magnetic detectors 21, 22
For this purpose, a Hall element or the like is used which has excellent sensitivity to the displacement of the magnet.

Next, a method for detecting the speed of the pickup arm in the B direction or the C direction will be explained using FIGS. 7 to 9.

As shown in FIG. 7, the magnetic detectors 21 and 22 are arranged near the magnet 8, and when the pickup arm 7 is not driven in the B direction or the C direction, the output of each magnetic detector is biased. When the magnet 8 approaches in the B direction or the C direction, the output increases, and as it moves away from the magnet 8, the output decreases. Speed detection in the B direction is performed by the magnetic detectors 21 and 2 when the magnet 8 moves in the B direction.
Since the outputs of 2 are output in opposite phases to each other as shown in FIG. 8, 23 and 24, the crosstalk component in the C direction can be canceled by differentially amplifying the outputs of the magnetic detectors 21 and 22. do,
A good output corresponding to the displacement in the B direction can be obtained, and in order to generate a signal corresponding to the speed, it is necessary to pass the signal through a differentiating circuit. Next, speed detection in the C direction will be explained. When the magnet 8 moves in the C direction, the outputs of the magnetic detectors 21 and 22 are output in the same phase as shown in FIG. 9, 25. Therefore, by adding and amplifying the outputs of the magnetic detectors 21 and 22, it is possible to cancel the crosstalk component in the B direction and obtain a good output according to the displacement in the C direction, and further to make the signal according to the speed. To do this, just pass it through a differential circuit.

In this way, signals corresponding to the speeds of the pickup arm in the B direction and the C direction can be detected.

Next, the control of the signal pickup device of the present invention will be explained using the block diagram of FIG. The main information signal and tracking signal recorded on the disk 1 are detected as electrical signals by a pickup circuit 26, and the main information signal is processed by an image/audio processing circuit 27 and displayed on a television receiver 29. Also, a jitter correction signal is created in this image processing circuit. The tracking signal is also detected as an electrical signal by the pickup circuit 26 and converted into a tracking control signal by the tracking signal processing circuit 28. In addition, magnetic detectors 21 and 2 are used to detect the speed of the pick-up arm 7.
2 are amplified by preamplifiers 35 and 37, respectively, and then input to an adder circuit 36 and an operation circuit 38,
The output signal of the adder circuit 36 is converted into a speed signal by a differentiating circuit 44, and then input to a speed feedback processing circuit 33 for tracking control. The jitter correction signal undergoes frequency characteristic correction in the phase compensation circuit 32,
After being input to the speed feedback processing circuit 33 and setting an appropriate feedback amount, the TBC drive circuit [time axis drive circuit]
34, the jitter coil 12 is driven, the pickup arm is driven and displaced in the tangential direction of the disk, and jitter correction is performed. In addition, the tracking signal is transmitted to the phase compensation circuit 2.
9 performs frequency characteristic correction, and speed feedback processing circuit 3
0 and set an appropriate feedback amount, the tracking drive circuit 31 amplifies the power, drives the tracking coils 10 and 11, drives the pickup arm 7 in the radial direction of the disk 1, and performs tracking correction. This is what we do.

With this configuration, the tracking characteristics of the signal pickup are improved as shown in FIG.
In FIG. 11, 40a shows the tracking characteristics when a silicon suspension with excellent temperature characteristics is used, and 40b shows the phase characteristics at that time. Then, when the velocity is returned as described above,
Depending on the amount, amplitude characteristics as shown at 41a and 42a and phase characteristics as shown at 41b and 42b are obtained. Also, although not shown in the figure,
A similar effect can be obtained regarding jitter characteristics.

Effects of the Invention As explained above, according to the signal pickup device of the present invention, the displacement of the reading element in the radial direction or the tangential direction is detected and an electric signal corresponding to the moving speed of the reading element is fed back to the reading element drive circuit. Since it is configured to apply speed feedback, even if a silicone rubber material is used for the suspension of the reading element, it can have excellent temperature characteristics and stable control characteristics.

[Brief explanation of drawings]

Figure 1 is a principle diagram of signal reading using a grooveless capacitive method, Figure 2 is a perspective view of a conventional signal pickup device, Figure 3 is a tracking drive characteristic diagram, and Figure 4 is a suspension using butyl rubber. FIG. 5 is a tracking drive characteristic diagram at 20°C when silicone rubber is used as the suspension material. FIG. 6 is a perspective view of an embodiment of the signal pickup device of the present invention. 7 to 9 are explanatory diagrams of speed detection of the pickup arm, FIG. 10 is a block diagram of the control circuit of the signal pickup device, and FIG. 11 is an explanatory diagram of improved tracking characteristics. 1... Disc, 5... Stylus, 7... Pick up arm, 8... Magnet, 9... Suspension, 10, 11... Tracking coil, 12... Jitter coil, 21, 22... Magnetic detector, 31...Tracking drive circuit, 3
0, 33... Speed feedback processing circuit, 34... TBC
Drive circuit, 36... Addition circuit, 37, 38... Differential circuit, 44, 45... Differential circuit.

Claims (1)

[Scope of Claims] 1. A pick-up arm having a reading element for reading an information signal recorded on a disk-shaped information recording carrier at one end, supported by an elastic body at the other end, and having a permanent magnet in a part; An electromagnetic coil magnetically coupled to a permanent magnet is disposed so that the reading element can be driven and displaced in at least one of the radial direction and the tangential direction, and the reading element is configured to be driven and displaced in the radial direction or the tangential direction. A magnetic detector is provided near the permanent magnet to detect an electric signal corresponding to the moving speed of the reading element, and based on the detection signal of the magnetic detector, an electric signal corresponding to the moving speed of the reading element is returned to the reading element drive circuit to determine the speed. A signal pickup device configured to apply feedback. 2. The signal pickup device according to claim 1, wherein the detection signal of the magnetic detector is differentiated and fed back to the reading element drive circuit.