JPS624906Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus servo activation control device for a recorded information reading device, and more particularly to a focus servo activation control device for driving and controlling a focus lens when activating a focus servo system.

In an optical information reading device, reading is performed by irradiating a pick-up spot light onto the recording surface of a recording disk as a recording medium and using the reflected or transmitted light. It is necessary to accurately converge the spot light, and therefore a focus servo device is provided to control the position of the focus lens.

In this servo device, if the distance between the focus lens and the recording surface when the spot light is accurately focused on the disk recording surface is D ₀ , then if the lens is at that position, a focus servo error will occur. The magnitude of the signal is zero, and on the other hand, when the distance between the lens and the recording surface becomes larger or smaller with respect to D ₀ , the magnitude of the error signal becomes larger and smaller depending on the degree of separation. These signals are output as signals with different polarities. Afterwards,
The characteristics of the focus error signal with respect to the distance between the lens and the recording surface exhibit a so-called S-curve characteristic centered at the distance D ₀ , and the motor that drives the focus lens is controlled by this error signal. As a result, the lens is moved up and down with respect to the recording surface, so that the spot light is always accurately focused on the recording surface even if the recording surface is warped.

Before starting the information reading operation, the focus lens is usually placed farthest from the disk recording surface, and in this initial state, the focus servo loop is turned on (closed) and the servo is turned on. In this case, since the spot light is not converged on the recording surface and is in a so-called out-of-focus state, it is impossible to obtain a focus error signal from the light that has passed through the recording surface, and therefore servo operation is impossible. For that purpose, the focus servo loop is turned off (open).
The focus servo is activated by applying a start signal from outside to drive the lens moving motor, moving the focus lens to the vicinity of the distance D ₀ , and then turning on the loop. It is configured.

In this case, conventionally, a pulsed signal of a constant level is used as a motor drive signal at the time of startup, and therefore the torque of the motor is approximately constant. At this time, the focus lens needs to start moving at a certain speed from a resting state, and needs to move against frictional force. Therefore, with the conventional method of driving a motor with a constant torque using a drive signal of a constant level, it is not only difficult to drive the focus lens in a constant and stable manner, but also
There is a drawback that the time required to move the lens to a position sufficient to turn on the focus servo loop, that is, the time required to move the lens to the working distance is considerable.

Therefore, an object of the present invention is to provide a focus servo activation control device for a recorded information reading device that can perform stable movement driving when activating a focus lens and shorten the travel time to the working distance. That's true.

The focus servo activation control device according to the present invention is characterized in that an activation signal having an amplitude that gradually attenuates from an initial level to a final level is generated and used as a driving signal for a lens driving means.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of an embodiment of the present invention, and shows the convergence state of the pick-up spot light, that is, the normal distance D ₀ between the focus lens and the recording surface.
A focus error signal D indicating the amount of deviation and its direction is amplified by an equalizer amplifier 1 that performs frequency and phase compensation, and is sent to a drive circuit 4 for a focus lens moving motor M via a servo loop switch 2 and an adder 3. It is applied as a drive signal. Therefore, when the server loop switch 2 is on, the motor M moves the focus lens by the servo operation of the focus servo system so that the error signal is always zero, and the spot light is always accurately placed on the recording surface. It is something that will be converged.

A starting signal generating circuit 5 is provided which operates in response to a focus-on signal A to generate a starting signal B at a constant level.This signal B is input and a differential signal generating circuit 6 having a relatively large time constant performs positive differentiation. A signal C is generated. This signal C is applied to the drive circuit 4 via the adder 3.

On the other hand, the focus error signal D is input to the level comparator 7 and compared with the reference level _E1 , and when the input level falls below this reference level _E1 , a comparison detection signal is generated to trigger the switch control circuit 8. It becomes input. In response to this trigger input, a switch control signal E is generated to turn on the loop switch 2, and in response to the generation timing of the comparison detection signal, the output B of the activation signal generation circuit 5 is generated.
is designed to disappear.

FIGS. 2A to 2E are waveform diagrams of signals A to E in the blocks in _FIG . A high level pulse is generated. Since the time constant of the differential signal generating circuit 6 is selected to be relatively large, the signal has an initial level V ₁ at time t ₁ and gradually attenuates toward a final level V ₂ as shown in FIG. 2C. The amplitude differential signal C passes through the adder circuit 3 and becomes an input to the drive circuit 4 .
At this time, the output of the comparator 7 has not changed and remains at a low level, so the control output E of the switch control circuit 8 is at a low level, the switch 2 is off, and the servo loop is off. It is in. Therefore, the only drive input to the drive circuit 4 is the differential starting signal shown in _FIG . As a result, the starting torque becomes large, which sufficiently overcomes the static friction force of the focus lens and enables smooth starting of the lens.

After the lens is started, the drive signal level gradually attenuates according to the time constant of the differentiating circuit 6 and changes toward the final level _V2 determined by the circuit constant in the differentiating circuit 6, so the motor torque changes accordingly. gradually decreases, and as a result, it becomes possible to move the lens at a substantially constant and stable speed.

When the lens approaches the recording surface and reaches near the normal distance _D0 , the level of the error signal D becomes near zero, and a comparison detection signal is generated starting from the comparator 7. In response to this generation timing, the loop switch is activated. 2 turns on, the generation of the activation signal B of the activation signal generating circuit 5 also stops. Therefore, normal focus servo operation will be performed after this time _t2 .

FIG. 3 shows a concrete example of the motor drive circuit 4 and the differential signal generation circuit 6 in the circuit block of FIG. 1, and the same parts as in FIG. 1 are given the same reference numerals. First, the drive circuit 4 includes a drive amplifier 41
and a resistor for detecting the induced voltage of motor M.
Consisting of R ₁ to R ₃ and a differential amplifier 42, resistor R ₄
and _R5 constitute a feedback circuit of the amplifier 42, and the output of the amplifier 42 is connected to the drive amplifier 4 by a switch 43.
It controls the return to 1.

By doing this, motor M and resistance R ₁ to _{R 3}
constitutes a bridge, and the internal resistance of motor M is
If R ₀ is set in the relationship R ₀ · R ₃ = R ₁ · R ₂ , a voltage corresponding to the induced voltage of the motor M, that is, the drive current, will be applied to the differential input to the differential amplifier 42. Become. Therefore, while the switch 43 is on, the motor M, the bridge circuit, the amplifiers 42 and 41
A servo loop is formed and a constant speed servo circuit that keeps the moving speed of the motor M constant is obtained. Therefore, if the switch 43 is controlled to be on while the output B of the starting signal generating circuit 5 exists, that is, while the focus servo loop is off, it is possible to obtain a substantially constant motor movement speed. Become. However, if the servo moves in a direction that reduces the moving speed of the motor M due to an imbalance in the bridge circuit, as mentioned above, the motor torque will be insufficient and the moving force of the focus lens will decrease, causing it to come to a standstill. Affected by friction, stable lens movement becomes difficult. Therefore, by applying the differential pulse C as a drive signal to such a constant speed servo system, the above-mentioned drawbacks can be eliminated, good startup is possible, and the lens can be moved at a constant speed.

Incidentally, the differential signal generation circuit 6 includes a differential capacitor.
It consists of C ₁ and differential resistor R ₁ , and only positive direction signals are derived through diodes D ₁ and D ₂ . In order to determine the final level _V2 of the differential signal C, a resistor _R2 is connected in parallel to the capacitor _C1 .
is inserted, and V ₂ is selected to have a level proportional to R ₁ /(R ₁ +R ₂ ). The other configurations and operations are completely the same as those shown in FIGS. 1 and 2, and their explanations will be omitted.

As described above, according to the present invention, the initial startup of the focus lens can be performed smoothly and stably with an extremely simple configuration, so that the time required to reach the working distance can be further shortened, and the subsequent servo This ensures stable lock-in operation.

In particular, in devices with a structure in which a focus lens, a spot irradiation source, etc. are provided below the recording surface of a recording disk, it is necessary to drive the focus lens upward to the vicinity of the recording surface against gravity at startup. , the present invention is suitable for use in such devices. It is also applicable to a pickup structure in which a small irradiation source such as a semiconductor laser is used and integrated with a focus lens, and in this case, the entire pickup is driven to move.

Note that each circuit example shown above is not limited to this, and various modifications can be made.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of the circuit of FIG. 1, and FIG. 3 is a block diagram including a specific example of a part of the circuit of FIG. 1. Explanation of symbols of main parts, 2...Servo loop switch, 4...Drive circuit, 6...Differential signal generation circuit, 8...Switch control circuit.

Claims (1)

[Claims for Utility Model Registration] (1) A focus lens that turns off the focus servo loop and starts moving the focus lens to converge the pick-up spot from the farthest position from the recording surface to the recording surface or its vicinity. The focus servo activation control device includes lens driving means for moving the focus lens, and generating a activation signal that gradually attenuates from a predetermined initial level to a predetermined final level at the start of the movement to drive the lens. An apparatus characterized in that it includes means for generating a start signal as a drive signal for the means. (2) The apparatus according to claim 1, wherein the activation signal generating means includes a differentiating circuit that receives a pulse-like signal of a constant level and generates a differential-like signal.