JPH0341287Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a control circuit for an information reading device that controls focus, tracking, tangential, etc. in a video disc playback device or the like.

For example, the control circuit of this type of information reading device, taking the focus control circuit of an optical information reading device as an example, guides the reflected light of the light irradiated onto the disk surface to a photodiode divided into four parts. The amount of focus shift was detected from the amount of light irradiated to each.

The output signal from this detector has S-shaped characteristics as shown in Figure 1, so generally
called character characteristics.

In the conventional example, the range indicated by area A in Figure 1 is originally the range to which the servo is applied, but if for some reason the output signal of the detector deviates from area A and enters area B or area C, the servo will not be activated. I had a problem with it coming off.

Therefore, in order to prevent the servo from coming off, in-focus detection is performed so that the pick-up is located in the servo area by detecting the level of the playback signal, etc., and the playback signal becomes out-of-focus, where the pick-up moves out of the servo area. When the level falls below a predetermined level, a method is used in which the focus servo loop is temporarily opened and then the servo system is restarted.

However, this method of restarting the servo system after becoming out-of-focus has a problem in that the servo system must be restarted each time out-of-focus occurs.

This idea was made in order to solve the above-mentioned problems, and provides a control circuit for an information reading device that can quickly converge to the in-focus point without causing the servo to come off once the servo is started. The purpose is to

An embodiment of this invention will be described below based on the drawings.

FIG. 2 is a block diagram in which this invention is applied to a focus servo circuit of an optical information reading device, in which 1 is a detector to which an output signal from a pickup (not shown) is supplied, and 2 and 3 are detectors 1 and 3. first and second comparators for detecting whether the pick-up is located in the in-focus area based on the output signal of the
Reference numerals 4 and 5 indicate third and fourth comparators for detecting whether the pickup is located in the servo area based on the output signal of the detector 1, and the first to fourth comparators 2 to 5 are used for comparison. The voltages correspond to the potentials E ₁ to E ₄ shown in FIG. 1, and the first to fourth comparators ₂ to ₅ are high ( H) level output signal.

Note that the potentials E ₁ and E ₄ are negative potentials.

Reference numeral 7 designates a first flip-flop, whose set terminal S is supplied with the output signal of the third comparator 4, and whose reset terminal R is supplied with the output signal of the first comparator 2.

Reference numeral 8 indicates a second flip-flop, the set terminal S of which is supplied with the output signal of the fourth comparator 5, and the reset terminal R of which is supplied with the output signal of the second comparator 3.

Reference numeral 9 indicates a NOR gate that receives output signals from the first and second flip-flops 7 and 8 and an initial drive bias circuit 15, which will be described later, and 10 indicates a hold circuit, in which the output signal from the NOR gate 9 changes from H level to low (L). The output signal of the detector 1 when the level changes is sampled and held.

11 is a voltage follower circuit with high input impedance as a buffer that receives the output signal of the hold circuit 10; 12 is an amplifier that receives the output signals of the voltage follower circuit 11 and the initial drive bias circuit 15, which will be described later; and 13 is a drive. The circuit shown in FIG. 1 drives a focus motor 14 that moves an objective lens (not shown) based on the output signal of an amplifier 12.

Reference numeral 15 denotes a bias circuit for initial startup, which is triggered by pressing an external button (not shown) at startup, and outputs a bias voltage for initial startup to the NOR gate 9 and the amplifier 12.
When an H level output signal is supplied from the first comparator 2, the initial startup bias voltage is no longer output.

Next, the operation will be explained.

Note that before operation, the objective lens is far away from the disk surface, so the detector 1
The output signal of is zero, and the output signals of the first to fourth comparators 2 to 5 are at L level.

When the external button is pressed in the above-mentioned state to operate the initial startup bias circuit 15, a bias voltage is output from the initial startup bias circuit 15, which drives the focus motor 14 via the amplifier 12 and drive circuit 13. , the objective lens approaches the disk surface.

Note that the bias voltage from the initial start-up bias circuit 15 is also supplied to the NOR gate 9 as an H level output signal, so as long as this bias voltage is supplied, the output signal of the NOR gate 9 will be at the L level, and the hold circuit 10 gate is closed.

When the objective lens approaches the disk surface and the output signal from the detector 1 begins to appear, first, the output signal from the detector 1 exceeds the level of the potential _E2 , so that the output signal from the second comparator 3 goes high, the second flip-flop 8 is reset, and the output signal at the output terminal Q goes low.

Next, as the output signal from the detector 1 exceeds the level of the potential E3, the output signal of the third comparator ₄ becomes H level, the first flip-flop 7 is set, and the output signal of the output terminal Q becomes It becomes H level.

Furthermore, as the output signal from the detector 1 exceeds the level of the potential _E1 , the output signal from the first comparator 2 becomes H level, and the first flip-flop 7
is reset and the output signal of the output terminal Q becomes L level, and the initial startup bias circuit 15
Bias voltage is no longer output.

As mentioned above, when the output signal of the first comparator 2 becomes H level, all the inputs of the NOR gate 9 become L level.
level, so the output signal of NOR gate 9 is H.
level, the gate of the hold circuit 10 is opened and the output signal of the detector 1 is supplied to the focus motor 14 via the hold circuit 10, voltage follower circuit 11, amplifier 12 and drive circuit 13.

Therefore, in order to change the output signal of the detector 1 in the area A as shown in FIG. 3a, the input to the drive circuit 13 becomes as shown in FIG. 3b, and focus servo is performed.

By the way, when the output signal of the detector 1 approaches the area B or C from area A and exceeds the level of potential E ₃ or E ₄ as shown in FIG. Since the output signal of the flip-flop becomes H level and the first flip-flop 7 or the second flip-flop 8 is set, its output terminal Q
The output signal of becomes H level.

In this way, the first flip-flop 7 or the second flip-flop
When any of the flip-flops 8 is set, the output signal of the NOR gate 9 becomes L level,
Since the gate of the hold circuit 10 is closed, the level of the output signal of the detector 1 at that time, that is, the potential
E ₃ or E ₄ is held.

In this case, the levels of potentials E ₃ and E ₄ are large, so
The input to the drive circuit 13 is as shown in FIG. 4b, and the focus motor 14 moves the objective lens in the direction in which the output signal of the detector 1 becomes smaller.

When the output signal of the detector 1 changes from the potential E ₃ to the level of the potential E ₁ or from the potential E ₄ to the level of the potential E ₂ , the output of the first comparator 2 or the second comparator 3 at that point Since the signal becomes H level, the first flip-flop 7 or the second flip-flop 8 is reset and the output signal at the output terminal Q becomes L level.

Therefore, the output signal of NOR gate 9 becomes H level, the gate of hold circuit 10 is opened, and servo is performed as described above.

Note that FIGS. 4a and 4b show operating characteristics in extreme cases.

Although the above embodiment has been described as an example in which the present invention is applied to a focus servo circuit of an optical information reading device, it is clear that the present invention can also be applied to a pickup control circuit such as a tracking servo circuit or a tangential servo circuit.

As described above, according to this invention, since the servo does not come off, there is no need to restart the servo system as in the past, improving operability and returning to the in-focus area quickly. There is an effect.

Since there is no need for in-focus detection, the focus servo system can be made independent from other circuits, eliminating the need for interconnections between the circuits, resulting in lower costs.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the output characteristics of the detector, Figure 2 is a characteristic diagram showing the output characteristics of the detector.
The figure shows a block diagram of this invention applied to the focus servo circuit of an optical information reader, Figure 3a shows the output characteristics of the detector during normal servo, and Figure 3b
is the input characteristic diagram of the drive circuit during normal servo,
FIG. 4a is a diagram of the output characteristic of the detector when the servo is abnormal, and FIG. 4b is a diagram of the input characteristic of the drive circuit when the servo is abnormal. 1...Detector, 2...First comparator, 3...Second
Comparator, 4...Third comparator, 5...Fourth comparator,
7...First flip-flop, 8...Second flip-flop, 9...Nor gate, 10...Hold circuit, 11...Voltage follower circuit, 12...Amplifier, 13...Drive circuit, 14...Focus motor, 15... Bias circuit for initial startup.

Claims (1)

[Claims for Utility Model Registration] A detector that outputs an output signal with an S-shaped characteristic according to the amount of deviation of a pick-up from a focused position; A control circuit for an information reading device comprising: a servo system for correcting the amount of light; , a servo area comparator that detects from the output signal of the detector whether or not the pickup is located in a servo area wider than the focused area; the pickup is located in the servo area;
When the servo area signal is supplied from the servo area comparator, a servo signal is output, and when the pickup is out of the servo area and a non-servo area signal is supplied from the servo area comparator, the servo signal is output. a servo signal output circuit that outputs a non-servo signal until it detects passage of the pickup through the focused area based on the output of the focused area comparator; and an output of the detector when the servo signal is supplied. A hold circuit that outputs a signal to the servo system and, when the non-servo signal is supplied, holds the output signal of the detector immediately before being supplied and outputs it to the servo system. A control circuit for an information reading device.