JPS6412015B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus control device, and more particularly to an optical focus control device having a configuration for irradiating a light beam through an objective lens onto a signal recording surface of an optical disk in order to detect a signal recorded on an optical disk. The present invention relates to a focus control device in a type disc player.

In a player (reproducing machine) that reproduces signals recorded at high density on an optical disc (hereinafter referred to as "disc") such as a compact disc player, the light beam for reading the signal is narrowed down to an extremely small spot. It is necessary to precisely align this spot position with the signal recording surface of the disk (this alignment is hereinafter referred to as a "focus point"). Therefore, a servo-type focus control device is indispensable in order to maintain the above-mentioned matching relationship without being affected by external vibrations to the player or surface runout of the disk.

First, a conventional focus control device will be explained with reference to FIGS. 1 to 4.

In FIG. 1, reference numeral 1 denotes a light source for signal reading, which generates, for example, a laser beam. 2 is a collimating lens for adjusting the spread of the light beam generated from the light source; 3 is a beam splitter for separating the light beam from the light source 1 toward the disk 4 and the reflected light from the disk 4; 5 is a beam splitter for separating the light beam for signal reading. This is an objective lens that focuses on a minute spot, and is attached to the bobbin 7 as shown in the figure. Reference numeral 6 denotes a drive coil wound around the outer cylindrical portion 7b of the bobbin 7, which together with the objective lens 5 and the bobbin 7 constitutes a movable portion 37 of the focus adjustment mechanism 36. Reference numeral 8 denotes a magnetic circuit forming a non-movable portion 38 of the focus adjustment mechanism, and the drive coil 6 portion is inserted into a gap 39 of this magnetic circuit 8. When current flows through the drive coil 6, the movable part 37 is given a driving force and moves in the vertical direction. Note that a hollow 8a is formed in the magnetic circuit 8, and the inner cylinder portion 7a of the bobbin 7 is located within the hollow 8a. The light beam can therefore pass through the focus adjustment mechanism. 9 is a cylindrical lens that gives astigmatism to the reflected light; 10 is a 4-split photodetector that detects the amount of reflected light in four areas; 11 is a 4-split photodetector that combines all the detector outputs of the 4-split detector 10 to calculate the total amount of reflected light. 12 is a subtraction amplifier that generates a focus error signal from the difference between the two sets of 4-split detectors, and 13 is a phase compensation circuit that improves the performance of the focus servo system. 14
is a loop switch that opens and closes the focus servo loop. It operates according to the C terminal input (control input). When the C terminal input is low level, the contact _P1 side is connected to the output terminal, and the C terminal When the input is high level, connect to the output terminal on the contact _P2 side. A drive circuit 15 is connected to the output end of the loop switch 14 and supplies current to the drive coil 6 to provide driving force to the movable part 37. 1
A comparator 6 outputs a high level "H" when the DC component of the amount of reflected light is above a certain value, and a window comparator 17 outputs an "H" level when the absolute value of the focus error signal is above a certain value.
18 is a flip-flop whose Q output becomes a low level "L" when the reset terminal R is R = "H", and the Q output becomes "H" when the trigger terminal T changes from "L" to "H"; 19 is a positive logic NAND gate. Reference numeral 20 denotes a terminal to which a focus servo on/off command is applied, and the focus servo on/off command is set to "H" for on and "L" for off. Reference numeral 21 denotes a pull-in signal generator which receives a focus servo on/off command from the terminal 20 and generates an output to be described later.

Next, the operation shown in FIG. 1 will be explained, but first, a method for detecting a focus error signal will be described using FIG. 2. The same reference numerals in FIG. 2A and FIG. 1 represent the same contents. 4-split photodetector 10 in Figure 2 A
The hatched portion X shown in FIG. It is set to increase in horizontal length. The combined output of A and A' of the 4-split photodetector 10 (A+A') and B
Comparing the combined output (B+B') of B', if the incident light is vertical in the figure, (A+A') >(B+B'), but if it is horizontal, (A+A') <(B+B'), that is, a focus error signal. is obtained as the difference between (A+A') and (B+B'), and the subtraction amplifier 12 performs this function.

On the other hand, the total output of the 4-split photodetector 10, that is, A+A'+B+B' is the entire reflected light and is obtained as the output of the summing amplifier 11, and the signal recorded on the disk 4 is detected from the alternating current change of this reflected light. taken out. Note that if the deviation from the focused state is large, vignetting in the 4-split photodetector 10 or vignetting on other optical paths may cause the 4-split photodetector 1 to
Since the proportion of reflected light incident on 0 decreases,
The focus error signal and the absolute value of the reflected light level as the output of the summing amplifier 11 decrease.

The principle described above is shown in graphs in FIGS. 2B and 2C.

In the normal operation of the focus servo system shown in FIG. 1, region A of the focus error detection characteristic shown in FIG. 2 C is used, and current is supplied to the drive coil 6 so that the focus error becomes 0. . In order to improve the accuracy of the focus servo system, this A
When the detection sensitivity in the area, that is, the focus error detection change is △V, and the distance change between the light beam spot position and the disk is △X, the larger the ratio △V/△X is, the more advantageous it is, but if it is too large, The area A becomes narrower and the stability of the initial pull-in operation of the focus servo decreases. The initial state of the focus servo system is generally region C in FIG. 2C, and since the focus error detection sensitivity is 0 in this region, the focus servo pull-in operation is not performed. In addition, the B area also does not have the original detection characteristics, and the focus servo cannot be reliably pulled in.

Next, the operation shown in FIG. 1 will be described. FIG. 3 shows the waveforms of various parts related to the pull-in operation in FIG. shows the output voltage of
d indicates the position of the objective lens 5, line l ₁ indicates that it is close to disk 4, line l ₂ indicates that it is close to disk 4.
It shows that it is far from. e is the summing amplifier 11
f indicates the output voltage of the subtracting amplifier 12, that is, the reflected light level, and f indicates the output of the subtracting amplifier 12, and thus the focus error voltage. g indicates the output of flip-flop 18.

In FIG. 1, the focus servo on/off command a applied to the terminal 20 is “L” in the initial state.
Since the output of the NAND gate 19 is set to "H", the flip-flop 18 is in a reset state, and the C terminal input of the loop switch 14 is set to "L". In this way, when the C terminal input is "L", the loop switch 14 is set to the contact _P1 side and supplies the output of the pull-in signal generator 21 to the drive circuit 15. The pull-in signal generator 21 is, for example, a PNP transistor as shown in FIG.
It consists of TR ₁ and resistors R ₁ , R ₂ , R ₃ , and the fourth
As shown in Figure 2, when a low level input is applied to the input terminal IN, the output from the output terminal OUT becomes high level, and conversely, when the input is high level, the output becomes low level. Therefore, in the initial state, a positive voltage is applied to the drive circuit 15. Since the drive circuit 15 has a polarity that provides a driving force in the direction in which the movable part 37 moves away from the disk 4 when the input voltage is positive, in the initial state where the output of the pull-in signal generator is a large positive voltage, as shown in FIG. in the lowest position.

Now, when the focus servo on/off command changes to "H" at t= _t0 in FIG. Gives driving force in the direction. At this point, the amount of reflected light is extremely small, so the output of the comparator 16 is "L", so the flip-flop 18 continues to be held in the reset state through the NAND gate 19. The speed at which the movable part 37 approaches the disk is determined by friction, viscosity, etc. between the movable part 37 and the non-movable part 38, and by the moving coil 6 in the method shown in FIG. It is determined by the balance between the resulting driving force and the gravity acting on the movable part 37, and the negative voltage output value of the retraction signal generator 21 is selected so that this speed is sufficiently small [see FIG. 4B].

As the movable part 37 approaches the focused state by moving the movable part 37, the reflected light level (Fig. 3e) increases, and when this exceeds the threshold level _V1 of the comparator 16, the comparator 16 as shown in Fig. 3b increases. The output is inverted and outputs “H”, flip-flop 1
8 is released (t=t ₁ ), and the flip-flop 18 becomes ready to accept a trigger. Movable part 3
7 further approaches the disk 4 and the focus error (FIG. 3 f) exceeds the threshold level ±V ₂ of the window comparator 17 when moving from area B to area A in FIG. The output of Q is inverted from "L" to "H", triggers the flip-flop 18, and changes its Q output from "L" to "H". This causes the loop switch 14 to switch to the contact _P2 side and close the focus servo loop (t= _t2 ).
Here, the focus loop is closed near the boundary between the B area and the A area, not in the A area in FIG. This method is adopted for reasons such as providing a margin for the response speed of the focus servo loop.

In the device shown in FIG. 1 described above, the movable part is not supported by an elastic body such as a spring or rubber.
When the focus servo is not operating, there is no holding force to fix the movable part at a specific position, which causes the following inconvenience. In other words, the component of gravity acting on the movable part in the moving direction, which is one of the determining factors for the moving speed when searching for a focused point, changes depending on the player's tilt, so the moving speed may become excessive or vice versa. In some cases, the movable part does not move despite the driving force from the drive coil 6.
Further, when searching for a focused point, the movable part may move suddenly due to vibrations or shocks being applied to the player.

Such inconveniences not only make it virtually impossible to apply the system to portable players or vehicle-mounted players, but also pose a practical problem for stationary players.

On the other hand, in order to avoid such inconveniences, methods have been proposed in which the movable parts are supported by elastic bodies such as springs or rubber, but even in that case, the stiffness of the supporting material is not necessarily high. As a result, a problem arises in that the stability of focus servo retraction decreases due to the influence of the gravitational force of the movable part and disturbances such as vibration and impact. Moreover, other problems arise, such as unnecessary resonance in high frequencies and linearity deterioration in the relationship between the driving force and the amount of displacement of the movable part.

Therefore, the main object of the present invention is to provide a focus control device that provides a suitable holding force to the movable part even in areas where the focus servo does not operate, without using support means such as rubber or elastic bodies. .

To summarize the present invention, the focus adjustment mechanism includes:
A capacitor whose capacitance value changes depending on the position of the movable part is provided, the position of the movable part represented by the capacitance value of the capacitor means is detected by a position detection means, and a position for setting the position of the movable part is provided. A circuit is provided for generating a setting signal by a position setting signal generating means and generating a difference between the output of the detecting means and the position setting signal,
The output of this circuit is applied to the drive coil to provide a holding force to the movable part even in a region where the original focus servo loop does not operate.

The above objects and other objects and features of the present invention will become more apparent from the detailed description given below with reference to the drawings.

FIG. 5 is a block diagram of a focus control device having a second servo loop (hereinafter referred to as "position servo loop") according to the present invention and configured to perform a focus servo pull-in operation. ,
Components that are the same as those in FIG. 1 are given the same reference numerals. Fifth
In the figure, 23 is a capacitive plate attached to the bobbin 7 of the drive section coil 6. 24 is a high frequency oscillator, and a resonant circuit is formed by the capacitance existing between the capacitive plate 23 and the magnetic circuit 8. The high frequency signal generated by the high frequency oscillator 24 is transmitted to the band amplifier 2.
The signal is selectively amplified at step 5, converted to direct current by an FM detector 26, and becomes one input of a differential amplifier 27 having phase compensation characteristics. 28 is a position setting signal generator having a similar role to the pull-in signal generator 21 in FIG.

Figure 5 and Figure 1 are exactly the same loop when the focus servo is operating normally, and the focused point search for focus servo retraction is
The movable part 37 starts from the farthest position from the disk 4 and gradually approaches the disk 4, and the conditions for closing the focus servo loop are the same based on the level determination of the amount of reflected light and the focus error. Therefore, a description of these points will be omitted, and the position servo loop, which is the gist of the present invention, will be described.

First, the movable part 3 used in FIG.
The position detection principle of No. 7 will be described below. For position detection, the oscillation frequency of the high-frequency oscillator 24 is determined by the capacitance value of the capacitive means consisting of the grounded portion of the magnetic circuit 8 and the capacitive plate 23, so this oscillation frequency is detected by FM detection as the position detecting means. When detected by the detector 26,
A DC voltage is generated depending on the frequency (and thus the capacitance value). When the movable part 37 having the objective lens 5 approaches the disk 4, the opposing area of the magnetic circuit 8 and the capacitive plate 23 decreases, and as a result, the capacitance value decreases and the oscillation frequency of the high frequency oscillator 24 increases, and the FM detector 26 output voltage increases. As a result, a change in the position of the movable portion 37 can be interpreted as a change in voltage. For the purpose of explanation, it is assumed that the position detection voltage obtained from the FM detector 26 is OV when the movable part 37 is farthest from the disk 4, and becomes a positive voltage when it approaches the disk 4. Bandwidth amplifier 25 serves to remove noise contained in the oscillation signal. One input of the differential amplifier 27 is the position detection voltage, and the other input is supplied with the position setting voltage. If the loop gain of the position servo system is sufficiently high, the position of the movable part is controlled so that the position detection voltage and the position setting voltage are equal. Therefore, during focus servo pull-in operation,
By making the position setting voltage slope-like, it is possible to cause the movable part to perform a desired operation, and the position-setting signal generator 28 generates this slope-like position setting voltage. FIG. 6A shows the position setting signal generator 28 connected to the collector ground.
A PNP transistor _Q1 , a resistor R connected between its emitter and the positive power supply +Vcc, a capacitor C connected between the emitter and ground, and a base connected to the emitter and a collector connected to the positive power supply +Vcc.
The emitter is connected to diode D and resistor R _E
An example is shown in which an NPN transistor Q ₂ is connected to the load power supply through Vcc. The voltage waveforms of the input terminal 40 and output terminal 41 are the sixth
As shown in Figure B, when the focus servo on/off command from terminal 20 in Figure 5 is input to input terminal 40, a slope-shaped position setting voltage is output due to the integral action of resistor R and capacitor C. .

FIG. 7 shows voltage waveforms at various parts in FIG.
8, is the objective lens position, is the output of the summing amplifier 11, is the output of the comparator 16, is the output of the subtraction amplifier 12, and is the output of the flip-flop 18.

Next, the operation shown in FIG. 5 will be explained. First, when the focus servo off command "L" is applied to the terminal 20, the movable part 37 is held at the farthest position from the disk 4 by the position servo loop, but the focus servo on command "L" is applied to the terminal 20. When "H" is applied at t= _t0 in FIG. 7, the output of the position setting signal generator 28 rises as shown in FIG. The differential amplifier 27 uses the position setting signal as a reference signal to compare the position detection signal from the FM detector 26, and its output is applied from the loop switch 14 to the drive coil through the drive circuit 15. This position servo loop is controlled by the differential amplifier 27 so that the position detection signal becomes the same as the position setting signal, but since the position setting signal rises in a slope shape, the position of the movable part 37 is also controlled by the disk. It will move towards 4. When the distance between the disk 4 and the objective lens 5 reaches an appropriate value due to this movement, the focus servo system starts operating as described in the operation of FIG. When the focus servo system operates in this manner, the loop switch 14 is set to the contact _P2 side, which means that the position servo loop does not operate on the movable portion 37. Note that since the pull-in operation of the focus servo system has already been described, the explanation will be omitted here.

As described above, when the focus servo system does not work, a stable holding force by the position servo loop acts on the movable part 37.

Note that the capacitor plate 23 may be installed in a part of the bobbin 7, but considering that there is play in the fitting between the movable part and the magnetic circuit 8, it is preferable to install it all around the bobbin 7. it is obvious. Further, this capacitive plate 23 can also be installed on the coil side, for example, on the outside of the coil.

Furthermore, it is also possible to use a conductive metal as the bobbin 7, thereby making it unnecessary to install a capacitor plate.

Now, in the above embodiment, the capacitive plate for position detection is installed in the bobbin, but if there is no space, as shown in FIG. 31 may be provided. It is clear that even if the capacitor plate 30 and the electrode plate 31 are replaced with each other, the same effect can be obtained.

This embodiment of FIG. 8 is effective when the space for the magnetic gap is small.

Alternatively, as shown in FIG. 9, a capacitor plate 32 may be provided above the bobbin 7, and an electrode plate 34 may be attached to the objective lens hole 33a of the cover 33, one end of which is fixed to the magnetic circuit 8. At that time, cover 3
If the electrode plate 34 is attached using the objective lens hole 33a of No. 3, and the capacitor plate 32 is configured so that the tip of the capacitor plate 32 is the same as the tip of the cover 33 when the objective lens 5 protrudes the most, the movable part 37 Without restricting the movable range, the non-movable part 38 and the disk 4
This has the advantage that it can be formed without reducing the spacing between the two.

In FIGS. 8 and 9, the same parts as those shown in FIG. 1 are designated by the same reference numerals. Also in the cases of FIGS. 8 and 9, it is obvious that it is advantageous to provide the capacitor plate and the electrode plate over one circumference.

In the above, an example was shown in which both or one of the electrode plate and the capacitor plate was newly provided, but the coil 6 may also be used as the capacitor plate, paying attention to the fact that the coil 6 is conductive. The example in this case is shown in the 10th example.
This is shown in the block diagram in Figure. In Figure 10, the fifth
Components that are the same as those in the figures are given the same reference numerals. The operation is basically the same as that described in the explanation of FIG. 5, so a description thereof will be omitted, but a new trap circuit 35 is added. This is to prevent the high frequency signal from entering the input of the high frequency oscillator 24 through the focus servo system.
The advantage of the embodiment shown in FIG. 10 is that there is no need to provide a capacitive plate.

Note that the capacitance detection mechanism described above captures changes in the area of opposing surfaces as changes in capacitance, and has better linearity than the method that captures changes in distance between opposing surfaces as changes in capacitance. Depending on the configuration, the required linearity may not be satisfied in some cases. In this method, even such a case can be dealt with by changing the shape of the capacitive plate in terms of area, thickness, or direction of the opposing surfaces.Furthermore, when using a coil as a capacitive plate, It is clear that this problem can be solved by changing the number of windings depending on the location.

As described above, according to the present invention, apart from the original focus servo system, a position servo loop is provided to control the movable part using a signal representing the position of the movable part, and until the focus servo system operates, Since the movable part is held stably by this position servo loop, the movable part to move the position of the signal reading optical spot is not required during the search for a focused point for focus servo pull-in. It has the effect of preventing movement and is extremely effective. In addition, as a means to express the position of the movable part, a capacitance means whose capacitance value changes depending on the position of the movable part is provided, so the structure is simple and it is easy to achieve excellent linearity in the movement of the movable part. There is an effect that it can be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional focus control device. FIG. 2 is a diagram showing the principle of focus error detection in FIG. 1. FIG. 3 is an operation waveform diagram of each part in FIG. 1. FIG. 4 is a diagram showing a specific configuration of a part of FIG. 1. FIG. 5 is a block diagram of a focus control device embodying the present invention, and FIG. 6 is a diagram showing a specific configuration of a part thereof. FIG. 7 is an operation waveform diagram for explaining the operation of FIG. 5. FIGS. 8 and 9 are sectional views showing essential parts of other different embodiments of the present invention. FIG. 10 is a block diagram of still another embodiment of the present invention. In the figure, 4 is a disk, 5 is an objective lens,
6 is a drive coil, 7 is a bobbin, 8 is a magnetic circuit, 1
5 is a drive circuit, 23, 30, 32 are capacitor plates,
26 is an FM detector (position detection means), 27 is a differential amplifier, 28 is a position detection signal generator, 31, 34
33 is an electrode plate, 33 is a cover, 36 is a focus adjustment mechanism, 37 is a movable part, 38 is a non-movable part, and 39 is a magnetic circuit gap.

Claims (1)

[Claims] 1. The objective lens and the drive coil are integrated to form a movable part, and the drive coil is inserted into a magnetic circuit gap of the non-movable part,
A focus adjustment mechanism that moves the movable part when a current flows through the drive coil, and detects a deviation between a focal position of the light beam transmitted through the objective lens and a signal recording surface of an optical disk disposed opposite to the objective lens. A focus control device comprising a focus error detection means and a means for supplying a drive current to the drive coil according to an output of the focus error detection means, the focus control device being provided in the focus adjustment mechanism to Capacitive means whose capacitance value changes depending on the position of the movable part; Position detection means which detects the position of the movable part represented by the capacitance value; and Generates a position setting signal for setting the position of the movable part. A servo loop is provided, comprising: position setting signal generating means; a circuit for generating a difference between the output of the position setting signal generating means and the output of the position detecting means; and means for applying the output of the circuit to the coil. A focus control device characterized by: 2. The focus control device according to claim 1, wherein the capacitive plate is formed by a capacitive plate provided on the movable portion and a magnetic circuit portion of the non-movable portion. 3. Claim 2, wherein the capacitor plate is provided all around the inside or outside of the drive coil bobbin in the movable part.
Focus control device as described in . 4. The focus control device according to claim 3, wherein the shape of the capacitive plate is changed so that the detection characteristic by the position detection means maintains linearity. 5. The focus control device according to claim 4, wherein the thickness of the capacitive plate is varied along the longitudinal direction of the bobbin. 6. The capacitor means is formed of a capacitor plate provided on the incident side of the light flux with respect to the objective lens of the drive coil bobbin in the movable part, and an electrode plate attached to the non-movable part to face the capacitor plate. A focus control device according to claim 1, characterized in that: 7 Claims characterized in that the shape of both or one of the capacitive plate and the electrode plate is changed along the longitudinal direction so that the position detection characteristic as an output of the position detection means maintains linearity. The focus control device according to item 6. 8. The capacitor means includes a capacitor plate provided on the exit side of the light flux with respect to the objective lens of the drive coil bobbin in the movable part, and an electrode plate provided along the objective lens hole of the cover provided in the non-movable part. A focus control device according to claim 1, characterized in that it is formed by: 9. The focus control device according to claim 1, wherein the capacitive means is formed by the drive coil of the movable part and a magnetic circuit of the non-movable part.