JPS6333207B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for a tracking actuator in an optical information reading device.

Optical video discs have recesses called pits arranged on the circular disc surface to form concentric or spiral tracks, and the length and spacing of these pits determines the video information. recorded.

Information is read from the video disk by making light incident on a video track consisting of pits on the disk and demodulating the reflected light, which is modulated depending on the presence or absence of pits. Such an information recording disk reading device is provided with a so-called tracking servo device so that the irradiated light always accurately tracks the video track of the disk.

FIG. 1 is a diagram schematically showing an example of a tracking servo device, in which a light beam irradiated from a light source 1 such as a helium neon laser is transmitted through a collimator lens 2,
The light passes through the beam splitter 3 and the λ/4 plate 4, and further through the tangential mirror 5, the tracking mirror 6, and the focus lens 7, and is focused onto the recording surface of the video disk 8. The reflected light passes through the focus lens 7, tracking mirror 6, and tangential mirror 5, and enters the λ/4 plate 4 and beam splitter 3, where the incident light and the reflected light that read the information are effectively combined. separated into

The reflected light separated by the beam splitter 3 is separated into servo light and signal reproduction light by another beam splitter 11. The reproduction light is detected by a light receiving element (not shown), undergoes signal processing, and is reproduced into a video signal. One servo light passes through the cylindrical lens 12 and enters the light-receiving surface of the light-receiving element 9 placed after it.

The light receiving element 9 generates a tracking servo signal that controls the rotation of the tracking mirror 6, and also controls the vertical movement of the focus lens 7 with respect to the disk 8 so that the irradiated light is always focused on the recording surface. It is also configured to generate a focus servo signal for use. For this purpose, the light receiving element 9 is divided into four parts 9a, 9b, 9c and 9d as shown in FIG.
By taking advantage of the property that the position on the optical axis where the light beam passing through this lens 12 converges is different in the plane including the generatrix of , and in the plane perpendicular to it, the four mutually independent light-receiving surfaces of the light-receiving element 9 are The positional relationship between the recording surface and the focus lens 7 is determined by detecting and measuring the shape of the beam of light projected onto the lens 7.
Focus servo is performed by controlling the vertical movement of.

On the other hand, for tracking servo, adjacent elements 9a, 9d, 9b, 9c of this light receiving element 9 are set as a set, and the sum of each output, ie, Va+
Va, Vb+Vc are input to the comparison amplifier 10 at the next stage, and the differential voltage Ve is used as a control signal for the tracking servo. For this purpose, the cylindrical lens 12,
By appropriately setting the relative relationship between the light receiving element 9 and the video track, tracking servo control signals as described below can be obtained.

That is, so-called coarse adjustment is performed by varying the relative position in the radial direction between the video disk and the irradiation light so that the irradiation light tracks on the video track using a radial feed motor. Fine adjustment of tracking is required because eccentricity necessarily exists between the center of rotation and the center of rotation. For fine adjustment, a tracking mirror is installed and a tracking servo is used.
The rotation center of the tracking mirror is set when the center of the focus lens is on the center line of a predetermined track that should be located directly below it, and when the two are separated, the rotation of the mirror is controlled in accordance with the separation distance. Therefore, when the two coincide, a pit projection 20 as shown in FIG. 3a occurs,
When the two are separated, a pit projection 20 as shown in FIG. 2B can be produced. Therefore, an error signal (tracking servo control signal) corresponding to the rotation angle of the tracking mirror 6 from the reference rotation position is outputted as the output Ve of the comparison amplifier 10. This control signal Ve
The tracking mirror 6 can be rotated by a necessary angle using the above-mentioned method, so that the light beam can be controlled to always accurately track on the video track despite the above-mentioned eccentricity.

Note that the tangential mirror 5 controls the position of the light beam in the tangential direction of the video track and has the role of a time base collector, and its details will be omitted.

In such a configuration, if the video track is greatly distorted for some reason during recording, or due to disturbance during playback, the level of the error signal Ve may increase significantly compared to the normal state. Since the rotation of the tracking mirror 6 is controlled in accordance with this large signal Ve, the rotation angle at this time becomes extremely large, and as a result, an excessive force is applied to the pivot mechanism of the tracking mirror, causing damage. There is a risk of

Therefore, the present invention makes it possible to prevent damage to the tracking mirror assembly including the tracking mirror pivot mechanism by limiting the excessive rotational movement of the tracking mirror in the optical information reading device as described above. An object of the present invention is to provide a tracking actuator in an optical information reading device.

The tracking actuator in the optical information reading device of the present invention monitors an error signal for the tracking servo or a signal corresponding thereto, and when the signal changes beyond a predetermined level range, the tracking actuator activates the tracking servo loop. The present invention is characterized in that the loop is broken at an arbitrary point to prevent excessive rotation of the tracking mirror.

The present invention will be explained below with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention. The output Ve (see FIGS. 1 and 2) of the comparison amplifier 10 which receives the output of the light receiving element 9 is connected to a drive amplifier for driving the tracking mirror. The width is increased by 13.
Based on this amplified output A, a current flows through the drive coil L, and the tracking mirror 6 is rotated by a desired angle, thereby performing a tracking servo operation.

Furthermore, this amplified output A is input to the next stage DC voltage detector 14, and the DC component B in the error signal Ve is detected. As this DC voltage generator 14, for example, a smoothing circuit consisting of a capacitor or a resistor can be used. The DC voltage B is the comparator 15a, 15
The signal is inputted to the window comparator 15 consisting of .b. That is, DC voltage B is applied to the non-inverting terminals (+) and inverting terminals (-) of the comparators 15a and 15b,
The inverting terminals (-) and non-inverting terminals (+) of the comparators 15a and 15b are connected to reference voltages that determine the upper and lower limit levels of the window comparators, respectively.
V _RH and V _RL are applied. The outputs of both comparators are connected in common and become a circuit output C, which disconnects the tracking servo loop.

FIG. 5 is a diagram showing operation waveforms of each part in FIG. 4, and equivalent signals are indicated by the same symbols in both figures. Under normal servo operating conditions, the error signal Ve for servo control, that is, the drive amplifier output A, has a sinusoidal waveform of nHz (30Hz as an example), assuming the disk rotation speed is nr.ps, as shown in Figure 5A. It becomes a signal. The reason for this is that since it is difficult in manufacturing to match the track center of a video disk with the rotation center, there is always an eccentricity between the two, and each rotation of the disk has a sine pattern. The error signal is obtained. Its amplitude is proportional to the size of eccentricity.

Therefore, the DC level in that case is at zero level as shown in Figure B, and the tracking mirror swings in a sine shape around the rotation angle corresponding to this zero level in accordance with the eccentricity of the disk to perform tracking. This means that the action is being taken.

Assuming that the video track is greatly distorted at time _t1 , the level of the error signal Ve changes either upward or downward with respect to the zero level. Therefore, the reference voltage level of the window comparator 15
If V _RH and V _RL are set vertically by a predetermined value with respect to the zero level, an abnormality in the tracking mirror rotation angle can be detected. At this time, the reference voltage levels V _RH and V _RL are the DC component B of the error signal Ve.
By setting it lower than the maximum value of , it is possible to detect excessive swing of the rotation angle. Therefore, the output signal C of the comparator 15 is applied to the DC voltage generator 14.
When output B exceeds the reference level V _RH , or
It becomes high level only when it falls below V _RL . This high-level detection signal C turns off an analog switch (not shown) provided at a predetermined location in the servo loop, thereby cutting off the tracking servo loop and preventing abnormal rotation of the tracking mirror 6. Become.

As described above, according to the present invention, the tracking servo control signal for driving the tracking mirror is monitored, and the servo loop is cut off when this signal changes beyond a predetermined level range. Therefore, abnormal rotation of the tracking mirror is prevented, thereby preventing mechanical damage to the tracking mirror assembly.

It should be noted that the above-described embodiments and examples of the tracking servo device can be modified in various ways, such as by moving the objective lens, which is just one example, and it goes without saying that the present invention is not limited to these.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing an example of a tracking servo device, FIG. 2 is a diagram showing a tracking servo signal generation circuit, FIG. 3 is a diagram explaining the operation of FIG. 2, and FIG. The figure is a block diagram showing one embodiment of the present invention, and FIG. 5 is an operation waveform diagram of each part of FIG. 4. Explanation of symbols of main parts, 6...Tracking mirror, 8...Video disk, 14...DC voltage generator, 15...Window comparator.

Claims (1)

[Claims] 1 A tracking actuator that is freely displaceable to control the radial position of a scanning spot that scans a recording track on a recording surface of a recording medium, and an error signal that represents the amount of deviation of the scanning spot in the radial direction with respect to the recording track. A tracking servo means is provided, comprising a means for generating an error signal, and a drive means for displacing the tracking actuator in response to the error signal to reduce the amount of deviation. The optical information reading device reads information on a recording track by scanning the error signal, the optical information reading device comprising: a detection means for detecting a DC component included in the error signal; and a predetermined level lower than the maximum level of the DC component of the error signal. a comparison means that compares a level reference voltage with the DC component and generates a control signal when the absolute value of the DC component becomes larger than the absolute value of the reference voltage, and is responsive to the control signal. A protection device for a tracking actuator in an optical information reading device, characterized in that the tracking actuator is disabled from displacing the tracking actuator in response to the error signal.