JPS6240769B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pick-up device that reproduces a recorded signal from a recording disk, on which the signal is recorded as mechanical deformation along a spiral track, through a reproduction needle. The structure is such that stable contact with the disk can be obtained.

Compared to conventional audio records, video discs such as VHD format that record video signals have higher band signals than conventional audio records, so the signal segments that are formed unevenly depending on the signal during tracking are more pronounced than those on audio records. It is much smaller and the disk rotates ten times faster.

In the above-mentioned video disk reproducing apparatus, the signal recorded in the track is detected as a change in electrical capacitance by a signal detection needle attached to the tip of a cantilever. The cantilever is designed so that the needle always follows the track without moving away from the relative displacement between the needle and the track due to unevenness caused by warpage of the disk or eccentricity of the track.
It is designed with tracking performance as the main focus.

Furthermore, unlike conventional audio record playback devices, pick-up devices for video discs do not extract signals by detecting the movement of a cantilever moved by a needle in response to signals using electromagnetic conversion means. The signal is directly detected as a change in capacitance using a signal detection needle attached to the tip of the cantilever. However, the signal detection needle moves up and down according to the unevenness of the recorded signal segment, and the cantilever also moves accordingly.

Since the signal segments recorded on video discs are small, the stylus pressure must be extremely low (for example, about 1/100th of that of conventional audio record pickup devices) to prevent the stylus from damaging them, and the rotational speed must be high. High tracking characteristics are required to be able to follow the minute tracks of the disc.

For this reason, in this type of video disc playback device, in order to reduce the stylus pressure, the entire pickup device is placed on a rail and guided by the rail to be translated in parallel in the radial direction of the video disc. A cantilever with a signal detection needle is attached to the bottom surface of the pickup device. Therefore, in this case, the needle pressure applied to the signal detection needle is independent of the weight of the entire device.
Statically, it is determined by the weight of the cantilever and the signal detection needle (the latter is extremely small compared to the former), and can be made extremely small. If the cantilever is biased by a spring, the spring force is added.

On the other hand, when the video disk rotates, dynamic stylus pressure occurs if there is surface deflection due to warping of the disk or eccentricity of the track. If the distance is V, then F=kZV. Here, k is a constant. Therefore, in order to reduce the dynamic stylus pressure, it is necessary to reduce the mechanical impedance, and for this purpose, the cantilever structure must have as little mass as possible, but the amount of unevenness and eccentricity of the disk must be reduced. Taking this into account will determine the required length of the cantilever to a certain extent, which will also determine the mass of the cantilever as a whole. To this end, the cantilever is divided halfway along its length and connected by a spring section to divide the mass, thereby lowering the mechanical impedance seen from the tip of the needle and improving tracking characteristics.

FIG. 2 shows an example of such a conventional cantilever. A spring portion 4 is provided between the two divided cantilever bodies 5 and 6 to connect them.
In FIG. 2, reference numeral 9 indicates a spring portion that supports the entire device and supports it on a pickup device, 7 indicates a signal detection needle, and 8 indicates a recording disk. The cantilever bodies 5 and 6 usually have a circular or square cross-sectional shape.

Note that it is also substantially concentric that something like the spring portion 4 is not provided and the cantilever main body is actively given elasticity.

FIG. 1 shows the mechanical impedance of such a cantilever. Solid line 1 is the mechanical impedance of a cantilever without a spring section in the middle.
Solid line 2 is the mechanical impedance of a cantilever with a spring section 4 in the middle as shown in Figure 2, and in the case of solid line 2, the mechanical impedance can be lowered than in the case of curve 1 at frequencies above _O. It shows. Note that mechanical impedance in both vertical and horizontal directions exhibits characteristics as shown in FIG. These frequencies are in a much lower band than the recorded signal. In addition, in the mechanical impedance characteristics shown in FIG. 1, the troughs of the curves indicate resonance points. If the lower resonance frequency is ₁ , then It is expressed as Here, K is the composite stiffness of the two spring parts 4 and 9 in FIG. 2, and M is the mass of the entire cantilever, and ₁ is determined by these.

As mentioned above, in the conventional cantilever device, the needle can be easily tracked with respect to vertical and horizontal displacements by dividing the mass and lowering the mechanical impedance of the cantilever in the vertical and horizontal directions.

In the mechanical impedance curve shown in Figure 1,
The point where needle skipping is most likely to occur, that is, where tracking is poor, is at point 3, which is called the anti-resonance point.

The frequency _O of this anti-resonance point 3 is determined by the mass M of the entire cantilever and the stiffness K ₁ of the spring portion 4 seen from the tip of the needle as follows.

Furthermore, when the frequency _O of the anti-resonance point 3 changes, the mechanical impedance also changes.

In FIG. 1, the dashed line 11 is an impedance curve determined by the mass of the entire cantilever, and 12
is an impedance curve determined by the stiffness of the spring portion 4.

The spring part 4 in FIG.
If the elastic body has the same stiffness in the vertical and horizontal directions, the anti-resonance point 3 as seen in Fig. 1 will be The frequency is the same in the longitudinal impedance characteristic curve and the lateral impedance characteristic curve of the cantilever.

At this anti-resonance point 3, the mechanical impedance becomes maximum and tracking becomes the worst.
When the needle tip receives vibrations at this frequency, 1 appears in Figure 2.
This is because, as shown by 0, a resonance mode is created in which both ends of the cantilever serve as fulcrums and the amplitude is maximum at the center. In other words, since the entire cantilever fits into a certain shape and resonates, it becomes extremely difficult to drive the needle tip from the outside with a tracking coil, etc., and the excessive vibration causes resistance to the needle pressure. This is because needle skipping occurs in which the needle tip separates from the disc. Of course, the recording signal is in a much higher band than these frequencies.

Therefore, in conventional cantilever devices where the cross-sectional shape of the cantilever is circular or square, and the anti-resonance points in the vertical and horizontal directions coincide with the same frequency, 10 in FIG. Various resonance modes occur simultaneously in both the vertical and horizontal directions, and as they interact with each other, control of the needle tip is increasingly inhibited, and the tracking characteristics are further deteriorated.

Another problem with this anti-resonance is that when a longitudinal resonance mode occurs, as shown in 10 in Figure 2, the angle of the cantilever changes greatly at the tip of the signal detection needle 7. This means that the needle tip moves relative to the disk. This state is schematically shown in FIG. 13
indicates the direction of rotation of the disc 8. At this time, speed unevenness occurs between the hand 7 and the signal segment, which appears as jitter on the playback screen. Therefore, when designing a cantilever, it is necessary to suppress the resonance mode of the cantilever so that the jitter is as small as possible, and to eliminate relative movement at the tip of the needle. As mentioned above, if the longitudinal and lateral anti-resonance points coincide, when the longitudinal vibration due to the warp of the disk and the lateral vibration due to the eccentricity of the track occur simultaneously at a frequency of _O , they will not interact with each other. This is not preferable because they influence each other and increase the resonance mode. Furthermore, even when only longitudinal or lateral displacement is acting on the cantilever, if a longitudinal or lateral resonance mode occurs at this anti-resonance frequency, the spring parts 4 and 9 supporting the cantilever will move toward one side. Since the vibration in one direction is transmitted a little to the other direction, this also induces a resonance mode in the other direction, causing jitter,
Tracking will become worse.

In this way, it is desirable that the stylus force applied to the signal detection needle 7 be small in order to improve the tracking characteristics, and attempts have been made to reduce the stylus force by dividing the weight by the spring part. Even if the stylus pressure is reduced in this way, in conventional cantilever devices, the anti-resonance points in the vertical and horizontal directions are equal, which tends to cause cantilever resonance, and when the vibrations due to resonance become large, the signal detection stylus will decrease the stylus pressure. The disadvantage is that the needle moves away from the surface of the disk, causing needle skipping and poor tracking.

The purpose of the present invention is to eliminate the above-mentioned drawbacks by reducing the mechanical impedance of the cantilever to reduce the stylus force, and even if the stylus force is reduced in this way, large vibrations due to resonance may not occur. The object of the present invention is to provide a device that can improve tracking characteristics without any problems.
To this end, the present invention is characterized in that the mass of the cantilever is divided, and the anti-resonance points in the vertical and horizontal directions of the cantilever are set at different frequencies so that they do not influence each other due to resonance. It is.

In the first embodiment of the present invention, as shown in FIG.
By connecting the cantilever bodies 5 and 6 with the spring part 4, the mechanical impedance is reduced, thereby reducing the stylus pressure and improving the tracking characteristics.The stiffness seen from the needle tip of the spring part 4 is also improved in the vertical direction. By setting different values in the horizontal direction, the anti-resonance points in both directions have different frequencies,
Resonant vibrations in both directions are prevented from influencing each other to prevent needle skipping or tracking errors due to excessive vibrations.

In addition, in the second embodiment of the present invention, the stylus force is reduced by mass division, and both or one of the cantilever bodies 5 and 6 in FIG. 2 is easily bent vertically or horizontally. structure (for example, a plate shape as shown in Fig. 4), so that the stiffness of the cantilever body as seen from the needle tip is different in the vertical and horizontal directions, and the anti-resonance points in both directions have different frequencies. Resonant vibrations in both directions are prevented from influencing each other to prevent needle skipping or tracking errors due to excessive vibrations.

Thus, according to the cantilever of the present invention,
By providing an elastic member such as a spring section in the middle of the cantilever to divide the mass, the mechanical impedance of the cantilever can be reduced compared to the case where no elastic member is provided, and the stylus force can also be reduced. In addition to making it easier to drive for tracking, since the antiresonance frequencies in the vertical and lateral directions of the cantilever are different, the resonance modes in the vertical and lateral directions at the antiresonance point do not affect each other. , it is possible to prevent excessive vibration due to their mutual influence, and it is possible to prevent the signal detection needle from separating from the recording disk, thereby stabilizing the contact relationship of the recording disk and eliminating tracking errors caused by needle skipping. can be prevented. In this way, tracking characteristics and jitter characteristics can be improved.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram showing the mechanical impedance characteristics of the cantilever, Fig. 2 is a side view schematically showing the cantilever, and Fig. 3 is a side view schematically showing the state of the regenerating needle in the resonance mode of the cantilever. , FIG. 4 is a sectional view of a cantilever according to an embodiment of the present invention. 4...Spring part, 5, 6...Cantilever body, 7
...Signal detection needle, 8...Recording disk.

Claims (1)

[Claims] 1. The cantilever main body, which holds a signal detection needle that contacts the recording disk and an element that converts the movement of the signal detection needle into an electrical signal at one end, is divided in the middle, and the entire cantilever as seen from the signal detection needle is An elastic member is provided to connect the divided cantilever bodies so as to reduce mechanical impedance and generate an anti-resonance point, and the anti-resonance points in the vertical direction and the lateral direction of the cantilever viewed from the signal detection needle are different from each other. A pick-up device characterized by being set to a frequency.