JPH0521697Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a focus search device suitable for use in, for example, an optical disc player.

[Summary of the idea]

This device connects the connection point between the positive and negative current sources and the capacitor arranged in parallel to the input side of the first amplifier, and connects the connection point between the positive current source and the capacitor to the first amplifier.
a second switch between the output resistor of the first amplifier and the reference voltage source;
In a focus search device, the connection point between the output resistor and the second switch is connected to the input side of the second amplifier, and the first and second switches are controlled by a system control circuit. 2
When the focus search starts from the initial state where the first switch is on, only the first switch is turned off by the output from the system control circuit, and the charge stored in the capacitor is discharged. By preventing the objective lens from dropping suddenly, mechanical noise is prevented from occurring due to collision between the objective bobbin holding the objective lens and an optical pickup main body having, for example, a semiconductor laser arranged around the objective bobbin. This is how it was done.

[Conventional technology]

As a conventional focus search device, for example, the third
Something like the one shown in the figure has been proposed. In Fig. 3, 1 is a disk, 2 is a spindle motor, and 3
is an optical pickup that includes an objective lens and the like.
The focus error signal from the optical pickup 3 passes through a buffer 4 and is supplied to an inverting input terminal of an operational amplifier 7 via a resistor 6 of a focus servo circuit 5. A non-inverting input terminal of operational amplifier 7 is grounded via resistor 8 . The output signal of the operational amplifier 7 is supplied to a focus coil 10 via a drive circuit 9.

11 is a positive current source, one end of which is connected to the positive power supply terminal +B, and the other end connected to the switch FS.
1 to the non-inverting input terminal of the operational amplifier 12. Further, 13 is a negative current source, one end of which is connected to the negative power supply terminal -B, and the other end connected to the non-inverting input terminal of the operational amplifier 12. Non-inverting input terminal of operational amplifier 12 and current source 1
A capacitor 14 and a resistor 15 are connected in parallel between the connection point of switch FS1 and switch FS1 and ground. Note that the current flowing through the current source 11 is twice the current flowing through the current source 13. For example, if the current of the current source 11 is 11 μA, the current of the current source 13 is 22 μA.

The inverting input terminal of the operational amplifier 12 is connected to its own output terminal, and this output terminal is grounded via a resistor 17 and a switch FS2.
The junction point of the resistor 17 is connected to the inverting input terminal of the operational amplifier 7 via a resistor 18 and is also connected to the output side of the operational amplifier 7 via a resistor 19 .

20 is a system control circuit, and this system control circuit 20 receives a signal FOK indicating that the level of the RF signal from the optical pickup 3 has exceeded a certain value, and a signal FZC indicating that the focus error signal is 0. are being supplied. Further, when a play button (not shown) is pressed, the system control circuit 20 switches the switch FS1 according to a program to be described later.
and controls FS2 on/off.

Next, the method of controlling the switches FS1 and FS2 by the system control circuit 20 and its related operations will be explained with reference to FIGS. 4 and 5.

When a play button (not shown) is pressed, the system control circuit 20 operates according to the program shown in FIG. 4 in response. At step (A), that is, at time _t1 in FIG. 5, the system control circuit 20 has already turned on the switches FS1 and FS2, and the capacitor 14
More current flows in and charges the connection point _P1 , so that the connection point P1 is at a predetermined potential, for example, +V volts as shown in FIG. 5A. Also, at this time, since the switch FS2 is in the on state, the output potential of the operational amplifier 7 is the reference potential, that is, 0 volts, as shown in FIG. 5B.

Next, in step (B), that is, at time _t2 in FIG.
Turn switch FS2 off while keeping FS1 on. Then, since the potential at the connection point _P1 remains at +V volts as shown in FIG. The output potential becomes -V volts as shown in FIG. 5B.

Next, the system control circuit 20
At (c), wait for a predetermined period of time, for example, 1 second. During this period (t ₂ ~
t ₃ ), the potential at the connection point P ₁ is + as shown in Figure 5A.
Since V volts are connected, the output potential of the operational amplifier 7 is also connected to -V volts as shown in FIG. 5B. In step (2), the built-in timer is reset and a new predetermined time, for example 1 second, is set. Then, at step (e), that is, time t ₃ in FIG.
System control circuit 20 is switch FS2
Turn off switch FS1 while keeping it off.
Then, the charge stored in the capacitor 14 is discharged through the current source 13, and the potential at the connection point _P1 gradually decreases as shown in FIG. 5A. On the other hand, the output potential of the operational amplifier 7 gradually increases as shown in FIG. 5B.

In step (F), the system control circuit 20
It is determined whether the level of the RF signal is above a certain value, and if it is above a certain value, that is, if the signal FOK indicating that the level of the RF signal has become above a certain value is supplied from the optical pickup 3. , step
Proceed to (g). In step (T), the system control circuit 20 determines whether the focus error signal is 0 or not, and if it is 0, the optical pickup 3 supplies a signal FZC indicating that the focus error signal is 0. If so, at step ie, time _t3 ' in FIG. 5, both switches FS1 and FS2 are turned on to complete the focus search operation. In other words, the focus is on.
At this time, the capacitor 14 is charged again by the current source 11, so that the potential at the connection point _P1 gradually increases toward +V volts and becomes constant, as shown by the solid line in FIG. 5A. Also, at this time, a focus error signal appears on the output side of the operational amplifier 7 via the buffer 4, as shown by the solid line in FIG. 5B. Then, since the focus search is completed in step (re), the series of program operations ends.

On the other hand, if the level of the RF signal does not exceed a certain value in step (F), or if the focus error signal is not 0 in step (G), the system control circuit checks in step (N) whether a predetermined period of time, for example, 1 second, has elapsed. It is determined in step 20, and if it has not expired, the process returns to step (F); if it has, the system control circuit 20 determines whether or not the search has been performed a predetermined number of times, for example, four times.

If the search has not been performed four times in step (L), then in step (B), that is, at time _t4 in FIG. 5, the system control circuit 20 turns on switch FS1 while keeping switch FS2 in the off state. Then, as shown by the broken line in FIG. 5A, the potential at the connection point _P1 , which had been gradually decreasing until then, starts to rise at time _t4 because the capacitor 14 is now charged. Furthermore, when the switch FS2 is in the off state, the potential of the connection point _P1 is inverted and output, so the output potential of the operational amplifier 7 is the fifth
It changes as shown by the broken line in Figure B.

Below, repeat the operations from step (B) to step (L) in the same manner as above, and at step (L)
If the focus search is repeated four times, that is, the focus search is not turned on even after four searches, the focus search is deemed to have failed, and the series of program operations is terminated at step (T).

[Problem that the invention attempts to solve]

By the way, as mentioned above, the switches FS1 and FS2
In the case of the conventional device in which the switch FS1 is turned on and the switch FS2 is turned off (step (B)) at time _t2 , the output potential of the operational amplifier 7 suddenly changes from +V volts to -V volts. As the change occurs, the objective bobbin holding the objective lens of the optical pick-up 3 is momentarily pulled downward, and as a result, the objective bobbin and the optical pick-up body disposed around it, for example, having a semiconductor laser, Collisions and generates mechanical noise.

Conventionally, electrical measures were taken to prevent this mechanical noise, such as applying a mute to the output stage.

This invention has been made in view of the above, and aims to provide a focus search device that can eliminate the collision itself between the object bobbin and the optical pickup body, and can prevent the generation of mechanical noise.

[Means for solving problems]

The focus search device according to this invention consists of a first amplifier 12 connected to a connection point _P1 between positive and negative current sources 11, 13 and a capacitor 14 arranged in parallel; a first switch FS1 disposed between the output resistor 17 of the first amplifier 12 and the reference voltage source; The connection point _P1 of the second switch FS2 is connected, and a focus error signal is supplied to the second amplifier 7, which has a focus coil 10 connected to its output side, and the second amplifier 7 is moved up and down by the focus coil 10. an objective lens, and first and second switches FS1,
System control circuit 20 that controls FS2
The objective lens is in the initial state when the second switch FS2 is on, and when the second switch FS2 is on, the objective lens is in the initial state when the second switch FS2 is on.
When the first switch FS1 is switched from on to off while FS2 is off, it is controlled in the upward direction, and when the second switch FS2 is off, the first switch FS1 is
In the focus search circuit that is controlled in the downward direction when the switch is switched from off to on, the system control circuit 20 controls the first and second switches.
At the start of focus search from the initial state where both FS1 and FS2 are on, capacitor 1 is
4, and after the predetermined time has elapsed, the first switch FS1 is turned on and the second switch FS2 is turned off, thereby preventing the objective lens from falling suddenly. There is.

[Effect]

The first and second switches in the initial state at time t ₁
FS1 and FS2 are turned on, the connection point _P1 is set to a predetermined potential, for example +V volts, and the output potential of the second amplifier 7 is set to 0 volts. Next, at time t ₁ ', while the second switch FS2 remains on, the first switch FS2 is turned on.
Only switch FS1 is turned off. Then,
The capacitor 14 is discharged via the negative current source 13, and the potential at the connection point _P1 becomes 0 volts. In this state, even if the first switch FS1 is turned on and the second switch FS2 is turned off at time _t2 , the output potential of the second amplifier 7 remains at 0 volts at this moment, so the objective The lens will not drop suddenly. Therefore, collision between the held objective lens and the optical pickup body is prevented, and no mechanical noise is generated.

〔Example〕

Hereinafter, one embodiment of this invention will be described in detail based on FIGS. 1 and 2.

Note that the circuit configuration of this embodiment is substantially the same as that in FIG. 3, so it is omitted to attach it again.
Refer to FIG. 3 if necessary.

FIG. 1 shows a flowchart when the switches FS1 and FS2 are controlled by the system control circuit 20 in this embodiment. In the figure, parts corresponding to those in FIG. Explanation will be omitted.

In this embodiment, steps (wa) and (f) are inserted between step (a) and step (b). At step (W), that is, time t ₁ ' in FIG. 2 (assuming that the time in FIG. 2 corresponds to the time in FIG. 5), the system control circuit 20 keeps the switch FS2 in the on state. , first switch
Only FS1 is turned off. Then, the charge stored in the capacitor 14 is discharged through the current source 13, and the potential at the connection point _P1 gradually decreases from +V volts to 0 volts as shown in FIG. 2A. On the other hand, since the second switch FS2 remains on, the output potential of the operational amplifier 7 is as shown in FIG.
As shown in , it is 0 volts.

Next, in step (f), wait for a predetermined period of time, for example, 250 milliseconds. In other words, it takes 250 milliseconds to discharge from time t ₁ ' to t ₂ .

Then, step (B), that is, time t ₂ in FIG.
In the same way as above, the system control circuit 2
0 turns switch FS1 on, switch FS2
turn off. Then, since the potential at the connection point _P1 is 0 volts as shown in FIG. 2A at this time, the output potential of the operational amplifier 7 is 0 volts as shown in FIG. 2B.

Next, the system control circuit 20
At (c), wait for a predetermined period of time, for example, 1 second. During this period (t ₂ ~
_t3 ) The potential at the connection point _P1 gradually increases from 0 volts to +V volts as shown in FIG. As shown in FIG. 2B, the voltage gradually decreases from 0 volts to -V volts.

What should be noted here is the change in the output potential of the operational amplifier 7 at time _t2 . That is, in the conventional case, when the switch FS1 was turned on and the switch FS2 was turned off at time _t2 , the output potential of the operational amplifier 7 changed from 0 volts to -V volts, but in this embodiment, it changes from 0 volts, that is, to -V volts. This means that it remains at the reference potential and does not change. As mentioned above, in this embodiment, switch FS1 is turned off at time t ₁ ', and switch FS1 is turned off.
This is because the capacitor 14 was previously discharged by turning on the FS2, and the potential at the connection point _P1 was set to 0 volts, that is, the reference potential at time _t2 .

Therefore, in the past, when the focus was down at time _t2 , the objective bobbin was momentarily pulled downward and collided with the optical pickup main body, generating mechanical noise, but in this embodiment, the objective bobbin Since it is not pulled downward, it does not collide with the optical pickup body, and no mechanical noise is generated.

[Effect of idea]

As described above, according to this invention, when the first and second switches switch from the initial state of being on to the first
When the first and second switches are turned on and off, respectively, when the focus is down, the second Since the output potential of the operational amplifier is prevented from changing, the objective bobbin that holds the objective lens is prevented from falling suddenly, and there is no collision between the objective lens and the optical pickup body, and no mechanical noise is generated. .

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an embodiment of this invention, FIG. 2 is a diagram for explaining the operation of this invention, FIG. 3 is a circuit diagram showing an example of a conventional device, and FIGS. This figure is a diagram for explaining the operation of FIG. 3. 7 and 12 are operational amplifiers, 11 and 13 are current sources,
14 is a capacitor, 17 is an output resistor, 20 is a system control circuit, and FS1 and FS2 are switches.

Claims (1)

[Claims for Utility Model Registration] A first amplifier to which connection points of positive and negative current sources and a capacitor arranged in parallel are connected; and a first amplifier arranged between the positive current source and the capacitor. a second switch disposed between the output resistor of the first amplifier and the reference voltage source; and a connection point between the output resistor and the second switch on the input side. A focus error signal is also supplied to control a second amplifier having a focus coil connected to its output side, an objective lens that is raised and lowered by the focus coil, and the first and second switches. and a system control circuit, wherein the objective lens is in an initial state when the second switch is on, and is raised when the second switch is off and the first switch is switched from on to off. In the focus search circuit, the focus search circuit is controlled in a downward direction when the second switch is in an off state and the first switch is switched from off to on. From an initial state in which both switches are on, the first switch is controlled to be off for a predetermined period of time at the start of focus search, thereby discharging the charge stored in the capacitor, and after the predetermined period of time has elapsed, the first switch is turned off. A focus search device characterized in that a sudden drop of the objective lens is prevented by turning on the second switch and turning off the second switch.