JPS634271B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking servo pull-in method in a recorded information reading device.

Recorded information reading devices such as video disc players and PCM disc players generally have a pick-up for reading information because of the presence of eccentricity, which is a deviation between the center of rotation of the disc during recording and the center of rotation during playback. The relative position of the disk in the radial direction with respect to the recording track is always shifted. Further, due to so-called precession in which the center of rotation of the recording disk in the information reading device moves, a relative positional shift in the radial direction of the disk occurs between the pickup and the recording track. Therefore, a tracking servo device is used in order to keep the pickup accurately tracking the recording track at all times while apparently eliminating the relative positional deviation in the disk radial direction.

This tracking servo device has means for generating a tracking error signal having a level and polarity depending on the distance and direction between the pickup and the recording track, and this tracking error signal causes the pickup to move in the radial direction of the disk. It is configured to control movement.

For example, in the case of an optical recorded information reading device, when the center of the information reading spot light ₁ coincides with the center of one recording track T1 as shown in FIG. 1A, two tracking spots The positions of the spot lights 2 and ₃ are set such that a portion of each spot light 2 and 3 is on the track _T1 , and the portions of the spot lights 2 and 3 on the track T1 are equal in size. Therefore, pick up spot light 1
3 crosses the track in the right direction while maintaining this positional relationship, the signal corresponding to the difference in light amount between the tracking spot lights 2 and 3 has a sine-like waveform as shown in FIG. Therefore, it can be seen that this signal becomes a tracking error signal having a level and polarity depending on the separation distance in the disk radial direction between the recording track and the reading spot light and the direction thereof. In addition, each time t ₁ to _{t 5} in FIG. 1A
The tracking error signals in each case are shown at each time _t1 to _t5 in B.

Now, when the information reading device starts operating or when a mechanical disturbance is applied to the device, the tracking servo loop is in an open state in order to prevent the pickup from moving excessively due to the generation of a large tracking error signal. In order to operate the tracking servo loop normally, it is necessary to control the tracking servo loop to the closed state. At this time, a tracking error signal as shown in FIG. 1B is generated due to the blurring of the recording track due to eccentricity or precession as described above. Now, suppose that the tracking servo loop is closed at time _t1 , and the relative velocity between the recording track and the reading spot light 1 at this time is _v0.
(m/sec), and the moving acceleration by the pick-up actuator that moves the spot light is g.
(m/sec ² ), and for simplicity, if there is even a slight tracking error, the circuit will respond instantaneously and the actuator will be able to move the pick-up spot light with an acceleration of g (m/sec ² ). do.

Therefore, the position x where the pick-up spot light exists t seconds after the tracking servo loop is closed is x=-1/2gt ² +v ₀ t (1). The relative speed v between the pickup and the truck at this time is v=v ₀ −gt (2). Here, if the relative velocity v becomes zero by the time the pick-up reaches the position shown at time _t3 , in other words, while the pick-up moves by 1/2 track pitch, for example, about 0.8 μm, then the pick-up will reach the initial position shown at time _t1 . Normally, normal tracking servo operation is performed and the tracking servo is pulled in. however,
If the relative initial velocity v ₀ between the pickup and the recording track is large or the acceleration g of the actuator is small, the relative velocity v will not become zero even when the position corresponding to time t ₃ is reached. The situation at this time will be discussed using the waveform shown in FIG. FIG. 2A shows the tracking error signal waveform, and each time t ₁ to _{t 5} corresponds to each time t ₁ to _{t 5} in FIG. 1, and if there is even a slight tracking error, the actuator A force acts in the direction corresponding to its polarity, and the pickup is accelerated with an acceleration of g. Therefore, when the tracking servo loop is closed, the potential energy of the pickup changes as shown in FIG.

When the servo loop is closed at time _t1 in FIG. 2, the pickup reaches a position corresponding to time _t3 while being decelerated while converting kinetic energy into potential energy. Assuming that the relative velocity between the pickup and the recording track is not zero at this position and is still only v ₁ , then it is accelerated in the direction of increasing the relative velocity v while losing potential energy, and at time t ₃ → t ₄ → Move to the position corresponding to t ₅ . Furthermore, at a position corresponding to time t ₅ →t ₆ →t ₇ , the relative velocity v decreases while losing kinetic energy. Therefore, if resistance forces such as friction with respect to speed are ignored, the same speed v ₁ will be maintained at time t ₇ in the same direction as at time t ₃ . In other words, the pickup has to cross many recording tracks, making it impossible to pull the pickup onto a predetermined recording track.

In this way, when the pick-up crosses a number of recording tracks, an AC error signal having a cycle equal to the track interval is generated, and the tracking servo system that controls the tracking actuator with this error signal is able to detect the error. It is stable during a half cycle of the signal (for example, t ₁ to t ₃ ) and unstable during the other half cycle (for example, t ₃ to _{t 5} ). Stability and instability here refer to the decrease and increase, respectively, of the kinetic energy in the tracking servo system when the pickup passes through the relevant section. In such a system, the pulling of the tracking servo system must necessarily be completed within a stable half cycle, and together with the impossibility of pulling the servo system mentioned above, in reality the tracking servo system Good and easy retraction of the material becomes extremely difficult.

In the conventional tracking servo pull-in method, the tracking servo loop is turned on by detecting only when the pick-up is at the approximate center of the recording track, so the servo system may or may not be stable. The loop is turned on regardless of whether the servo is turned on or not, making it difficult to pull in the servo.

Furthermore, a configuration as described in, for example, Japanese Patent Laid-Open No. 54-33724 has also been proposed. To explain this technique with reference to FIG. 2 of the drawings attached to this specification, the tracking servo is opened during a period (t ₂ to _{t 4} ) and closed during a period (t ₄ to _{t 6} ). or closed during the period ( _t1 to _t3 ) and opened during the period ( _t3 to _t5 ). However, in the former case, the servo is closed during the period when the kinetic energy increases (t ₄ to t ₅ ) and opened during the period when it decreases (t ₂ to _{t 3} ), so the time required for the servo to lock in and stabilize is The drawback is that it takes too much time. On the other hand, in the latter case, in principle, the servo is opened during the period when the kinetic energy increases (t ₃ to t ₅ ) and closed during the period when the kinetic energy decreases (t ₁ to t ₃ ); There isn't. However, during the period in which kinetic energy increases or decreases, a signal whose phase is ahead or behind the tracking error signal by 1/4 period is differentiated by a differentiating circuit to obtain a signal that is in phase with or in phase with the tracking error signal. However, since the signal is detected by comparing it with a predetermined limit value, the limit value cannot be set to zero. In other words, when the predetermined limit value is set to zero, when the information reading spot passes over a predetermined track, goes a little too far, and returns to the track again (when the servo is about to lock in), the signal before differentiation decreased slightly from its peak and then increased again.
This is because the differentiated signal shifts from positive to negative and then shifts from negative to positive again, so a signal to open the servo is output, and the servo cannot be locked in after all. Therefore, in order to prevent this, the limit value is set to a predetermined value other than zero, and the predetermined value is set by focusing on the fact that even if there is a transition from negative to positive, the positive peak that occurs in such a case does not become very large because the relative speed is slow. It becomes necessary to set the value to a value slightly larger than the positive peak at that time. the result,
If the limit value is too small, the lock-in operation becomes uncertain, and if the limit value is too large, the period in which the servo is closed becomes longer even during the period when the kinetic energy is increasing, which is similar to the former embodiment, and the servo locks in. The disadvantage is that it takes a long time. The present invention has been made in view of the above points, and its object is to provide an inexpensive tracking servo pull-in method for a recorded information reading device that can ensure lock-in operation and shorten the lock-in time. Our goal is to provide the following.

In the present invention, at the time of zero crossing of the tracking error signal, the level of the signal whose phase is 1/4 cycle ahead or behind the tracking error signal is higher than the reference level or is at a lower level. The tracking servo loop is characterized in that it detects whether the system is in the state of

An embodiment of the present invention will be described below with reference to FIG. In the figure, _T1 is a recording track, 1 is a reading spot light, and 2 and 3 are tracking spot lights, as in FIG. The reflected light from the reading spot light 1 is converted into an electrical signal A by a photoelectric conversion element 4, and then AGC (automatic gain control) is performed.
The signal is amplified by an amplifier 5. This output is input to an LPF (low pass filter) 6, and is used to record, for example, audio data whose carrier frequency is relatively low and whose frequency characteristics are not affected much by the linear velocity of the recording track.
Only the FM signal band is extracted. The output of this LPF 6 is detected by an envelope detector 7 and becomes an envelope signal B, which is compared with a reference level V ₁ in a level comparator 8. If the input level is higher than this level V ₁ , it becomes a high level, and if it is lower, it becomes a high level. The configuration is such that a comparison output C that is at a low level is generated when

On the other hand, the reflected light from the tracking spot lights 2 and 3 is transmitted to the corresponding photoelectric conversion elements 9 and 10, respectively.
Each output is applied to the differential amplifier 11 and becomes a tracking error signal D. This error signal D is applied to a drive amplifier 14 via an equalizer amplifier 12 and a servo loop switch 13 for frequency phase compensation. The actuator 15 is driven by the output of the amplifier 14, and the movement of the pickup spot light is controlled.

Also, tracking error signal D is LPF16
The noise components and the like are removed by the above and applied to the zero cross detector 17. The detector 17 detects a zero cross of the tracking error signal D, and a detection signal E is generated at each zero cross timing. These zero-crossing detection signals E are generated synchronously when the reading spot light 1 crosses approximately the center of a recording track and when it crosses approximately the center between recording tracks, as shown in FIG. The timing signals become the first and second timing signals.

These first and second timing signals E and the comparison output C from the comparator 8 are inputted to a timing control circuit 18 which may be constituted by a D-type flip-flop, for example, and are used as control signals for on/off control of the servo loop switch 13. F is generated.

FIG. 4 is a waveform diagram showing the operation of each part in the circuit block of FIG. 3, and waveforms A to F in both figures indicate signals corresponding to husband and wife. Now, if the detection signal E is generated from the zero cross detector 17 at time t ₁ (see FIG. 4D), then the comparator 8 (in this case, the reference level V ₁ is set to zero)
Since the output C of is at a high level, this means that the pickup has crossed approximately the center of the recording track _T1 .
This timing signal E causes the timing control circuit 18 to generate a high-level control signal F that turns on the servo loop switch 13, and as a result, the tracking servo system operates. Therefore,
While the pick-up moves from time t ₁ to t ₂ to t ₃ , the actuator 15 is accelerated by the servo system in a direction that reduces the relative speed. When passing the position corresponding to time _t3 , the comparison output C is at a low level, which means that the pickup is passing approximately at the center between the tracks. Therefore, a low level control signal F is generated from the control circuit 18 in accordance with the timing signal E, and the servo loop switch 13 is activated.
is turned off, the tracking servo loop is opened, and the actuator 15 moves from time t ₃ → t ₄ → t ₅
It moves at approximately constant velocity.

Furthermore, since the loop switch 13 is turned on during the transition from time _t5 to time _t6 to time _t7 , the pickup is accelerated again in the direction of decreasing the relative speed. Therefore, in an unstable region of the tracking servo system, that is, in a region where the servo works in the direction of increasing the relative speed between the track and the pick-up, the servo loop is kept open and the servo system works in the direction of decreasing the relative speed. Since the servo loop is closed only in a stable region, the relative speed decreases each time the pickup crosses the track, ensuring that it is drawn into the recording track.

If the servo is about to lock in,
For example, in FIG. 1, spot light 1 passes from the left side of track T ₁ to the center of track T ₁ (time t 1 ), and then moves slightly to the right (time t ₁ ).
(before reaching the position shown at t ₂ ), the RF envelope drops slightly from its peak (but does not reach zero) and increases again, but the tracking error signal shows at time t ₁ . Since it does not become zero until it returns to that position, the detection signal E is not output and the control signal F is not inverted.

In the above, the case where the pick-up crosses the track to the right as shown in Fig. 1 has been explained, but if the pick-up crosses the track to the left,
Of the waveform diagrams shown in FIGS. A to F, the tracking error signal shown in D is the same as the case where the tracking error signal crosses to the right, except that it has an opposite phase to the case shown. In other words, when the pick-up crosses to the right, signal D is approximately 1/4 cycle ahead of signal B, and the servo loop is closed when signal D is positive and open when it is negative. On the other hand, when the pickup crosses to the left, signal D is delayed by approximately 1/4 period in phase with respect to signal B, and the servo loop is open when signal D is positive and closed when signal D is negative. Therefore, it is not necessary to provide two means corresponding to the direction in which the pickup traverses the track.

As described above, according to the present invention, a signal whose phase is approximately 1/4 cycle ahead or behind the tracking error signal is detected, and the detected signal is detected at the zero-cross point of the tracking error signal. Since the servo loop detects whether the level is higher or lower than the reference level and opens and closes the tracking servo loop at the zero-crossing point in response to this state, the servo loop increases the kinetic energy. The opening and closing of the servo loop can correspond exactly to periods of increase and decrease in kinetic energy without being closed during periods and open during periods of decrease, so that relative speeds are The servo loop can be closed without any shortage. Therefore, even if the relative speed is large or the acceleration produced by the actuator is small, tracking retraction is possible reliably.
Moreover, the time required for retraction can be shortened. Furthermore, not only can an inexpensive actuator be used, but the servo circuit also has the advantage of not being complicated.

Note that although the case of an optical recording/reading device has been described above, it is also applicable to a capacitance type device. Furthermore, the example shown in FIG. 3 is not limited to this, and various modifications can be made.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the positional relationship between the recording track and the pickup spot light and the tracking error waveform, FIG. 2 is a diagram showing the relationship between the tracking error waveform and the pickup potential energy, and FIG. 3 is a diagram showing the relationship between the tracking error waveform and the pickup potential energy. Circuit block diagram of the embodiment,
FIG. 4 is an operational waveform diagram of each part in the circuit block of FIG. 3. Explanation of symbols of main parts, 1... spot light for reading, 2, 3... spot light for tracking, 7...
...Envelope detector, 8...Level comparator, 1
1... Differential amplifier, 13... Servo loop switch, 15... Actuator, 17... Zero cross detector, 18... Timing control circuit.

Claims (1)

[Claims] 1. A tracking servo pull-in method for a recorded information reading device having a tracking servo loop for causing the pickup to follow the track based on a tracking error signal in order to reproduce information recorded on a track by pickup. Detects the zero-crossing point of the tracking error signal, and detects a signal that is generated when the pickup crosses the track and that is approximately 1/4 period in advance or in phase with respect to the tracking error signal. and comparing the level of the detection signal with a predetermined reference level,
Detecting whether the level of the detection signal is higher or lower than the reference level at the zero-crossing point, and when one of the two states is present, at the zero-crossing point. A tracking servo retraction method characterized in that the tracking servo loop is opened and, in the other state, the tracking servo loop is closed at the zero cross point.