JPH02263329A - Auto-focus circuit - Google Patents

Abstract

PURPOSE:To reset a focus servo state in a short time by performing a focus searching operation in a range smaller than a searching range set at the time of starting if the applied focus servo is released. CONSTITUTION:An auto-focus circuit 1 switches a focus search state to a focus servo state while an objective lens 34 is approaching to or parting from the surface of a rotary encoder disk 22. If the applied focus servo is released, the focus search range is changed so that the lens 34 can perform a focus searching operation in a range smaller than the preceding movable range. Thus the released focus servo state can be reset in an extremely short time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an autofocus circuit used in a reflective optical rotary encoder device or the like.

(Prior Art) In recent years, optical rotary encoder devices have been widely used. This optical rotary encoder device optically detects the rotational speed and position of the drive shaft of the object to be measured by directly connecting the input shaft of the device to the drive shaft of the object to be measured.

This optical rotary encoder device includes a transmission type that detects slits and pits by changes in transmitted light due to rotation of a rotary encoder disk with slits and pits, and a transmission type that detects slits and pits by changes in transmitted light due to the rotation of a rotary encoder disk with slits and pits. There is a reflective type that detects these slits and pits based on changes in reflected light due to rotation.

This reflective optical rotary encoder device has slits or pits (four parts or convex parts) formed on the surface of a low-reflection encoder disc by a manufacturing method for optical discs, compact discs, etc. in a predetermined direction in the circumferential direction of the disc. Encoder tracks arranged in a ring pattern are read by a laser reader by converting changes in the intensity of reflected laser beams into electrical signals.

FIG. 4 is a configuration diagram showing an example of a rotary encoder disk used in the device shown in FIG. The figure (C) is an enlarged sectional view taken along the line X--X of the figure (B).

In the figure, a rotary encoder disk 22 is made of, for example, polycarbonate resin, and has a predetermined number of pits 24, which are concave or convex portions, formed in a ring shape at equal intervals on one surface, manufactured by a method for manufacturing compact disks or the like. A disc-shaped substrate 22a made of a transparent plastic such as, a reflective film 22b formed by vapor deposition or sputtering of a metal such as aluminum on the surface of the substrate 22a on which the pits 24 are formed, and a reflective film 22b that is closely adhered to the reflective film 22b. A protective film 22c made of ultraviolet curing resin or the like is laminated as a protective film 22c.

In the following description, an example will be described in which the pit 24 is a convex portion with respect to the land portion 25 which is a flat portion other than the pit 24 when viewed from the base tM22a side.

The length of the pit 24 in the circumferential direction is determined by a laser beam from a laser reader (not shown) provided in a reflective optical rotary encoder device (described later) for reading the pit 24 from the substrate 22a side. The width in the radial direction is narrower than the diameter of the light spot 35, for example, approximately 1/4, and the height is, for example, optically approximately 1/4 of the wavelength λ of the laser beam. It is formed equivalent to 4. Further, the length of the land portion 25 in the circumferential direction between the pits 24 is formed to be equal to the length of the pit 24 in the circumferential direction.

The uneven pattern of the encoder track 23, in which the pits 24 and the land portions 25 between the bits are arranged alternately in a ring shape and concentrically with the center hole 26, is read by a laser reading device to be described later.

The rotary encoder disk 22 configured as described above is used by being incorporated into a reflective optical rotary encoder disk in which an autofocus circuit according to an embodiment of the present invention and a conventional example are used.

FIG. 3 is a schematic configuration diagram showing an example of a reflective rotary encoder device in which an embodiment of the present invention and a conventional autofocus circuit are used.

A reflective optical rotary encoder device 51 incorporating a conventional autofocus circuit 41 includes, in addition to the autofocus circuit 41, the rotary encoder disk 22, a laser reader 28, and the like.

This rotary encoder disk 22 is fixed to an input shaft 27 whose center hole 26 is supported by a bearing (not shown), and rotates integrally with the input shaft 27 . This input shaft 27 is directly connected to a drive shaft (not shown) of the object to be measured, and is rotationally driven thereby.

Then, the laser reading device 28 detects the pits 24 of the encoder track 23 and the land portions 25 between the pits.
The rotational speed and position of this drive shaft are detected by reading the uneven pattern caused by the drive shaft.

That is, this laser reading device 28 includes a semiconductor laser oscillator 29, a grating polarizing plate 30, and a collimating lens 3.
1. Polarizing beam splitter 32. 1/4 wavelength plate 33, objective lens 34, cylindrical lens 37, photodiode 38
It is composed of etc.

The laser beam from this semiconductor laser oscillator 29 is divided into three beams by this grating polarizing plate 30. These three beams are connected to the collimating lens 31,
Polarizing beam splitter 32. Light spots (A) 35A and light spots ( F
) 35F1 is irradiated as a light spot (B) 35B.

These three light spots (A), (F), and l) are collectively referred to as a light spot 35. This central light spot (F) 35F
The light spots (A
) 35A and (B) 35B are for tracking servo or this encoder track 2 with a phase shift of 90'' in electrical angle.
It is used for the A-phase and B-phase outputs, which are the read outputs of 3.

The reflected light of the three beams reflected on the surface of the reflective film 22b of the rotary encoder disk 22 passes through the objective lens 34 and the 1/4 wavelength plate 33, and passes through the 1/4 wavelength plate 33.
3 twice, it has a 90'' phase difference from the incident light, so it passes without being reflected by the polarizing beam splitter 32, passes through the cylindrical lens 37, is converted into an electrical signal by the photodiode 38, and is output. .

Here, when the light spot 35 illuminates the land portion 25 between the bits, most of this reflected light enters the photodiode 38 . Also, this light spot 35
illuminates this bit 24, this bit 24
Since there is a difference in optical path length of (1/4 wavelength) x 2 between the reflected light from the top of the land portion 25 and the reflected light from this land portion 25,
This reflected light interferes with each other and is diffracted, thereby reducing its intensity. The intensity change of this reflected light is 1. This photodiode 38 converts the signal into an electrical signal.

Next, in the reflective optical rotary encoder devices 21 and 51 using the autofocus circuits 1 and 41 of the embodiment of the present invention and the conventional example, the mounting accuracy of the rotary encoder disk 22 to the input shaft 27 will be explained. The so-called autofocus, which causes the focal point of the light spot 35 of the laser beam to follow the plate surface of the disk 22, will be explained.

This autofocus is performed by driving a focus servo actuator 39 by the autofocus circuits 1 and 41 based on the output signal from the photodiode 38, and thereby moving the objective lens 34 up and down with the driving force of the focus servo actuator 39. This is to correct the objective lens 34 to the correct focal position, and when the focus servo is out of order due to startup or impact, the objective lens 34 is moved up and down significantly and moved slowly to the focal position. It is comprised of a focus servo that is controlled so that the focus automatically follows the plate surface after the objective lens 34 moves slowly with focus position.

FIG. 5 is an explanatory diagram of the focus servo in the apparatus of FIG. 3, and FIG.
B) shows the case where the plate surface is at the correct focal position, and (C) shows the case where the plate surface is too far away.

Reflected light spora corresponding to the central light spot (F) 35F of the photodiode 38 in FIG. 3) (F) 3
The portion receiving 6F is a four-division photodiode 38F, as shown in FIG. The two diagonal outputs of the four-division photodiode 38F are combined and supplied to the autofocus circuits 1 and 41. As shown in FIG. 3B, when the plate surface of the rotary encoder disk 22 is at the correct focal position, the reflected light spot (F) 36F evenly hits the four-division photodiode 38F; The outputs of the autofocus circuits 1 and 41 become 0, and the focus servo actuator 39 does not operate. Same figure (A)
, as shown in (C), this rotary encoder disk 2
If the plate surfaces of No. 2 are too close or too far away, the reflected light spot (F) 36 is
The shape of F is an ellipse, and as a result, a focus servo signal is output from the autofocus circuits 1 and 41. By driving this focus servo actuator 39 in accordance with this focus servo signal, the objective lens 34 is corrected to the correct focal position. By the above operation, the light spot 35 of the laser beam is controlled so that it is always focused on the surface of the reflective film 22b of the rotary encoder disk 22.

Next, regarding the operation of the autofocus circuit 41,
It will be explained in further detail.

FIG. 6 is a block diagram showing an example of a conventional autofocus circuit, and FIG. 7 is a waveform diagram illustrating the operation of the circuit shown in FIG. The conventional autofocus circuit 41 is as follows:
This is a well-known device that is also used in compact disc playback devices and the like, and the aforementioned switching control between focus search and focus servo is performed by the microcomputer 49.

At startup, due to variations in processing and assembly accuracy of the rotary encoder disk 22, laser reader 28, etc.,
Since the focus of the objective lens 34 is significantly shifted from the surface of the rotary encoder disk 22, this focus search is performed first.

That is, as shown in FIG. 6, when a 7-source switch (not shown) provided in the device 51 is turned on, a timing pulse a, which is a rectangular wave, is sent from the microcomputer 49 to the triangular wave generating circuit 18. The triangular wave generating circuit 18 generates an up-down signal which is a triangular wave in which the voltage increases during the high period of the timing pulse a and decreases during the low period. At startup, the focus loop on signal i, which will be described later and which is the output of this microcomputer 49, is low, so the electronic switch (1)
11 is off, electronic switch (2) 12 is inverter 13
A is turned on, and this up/down signal is supplied to the focus servo actuator current drive amplifier 20. The focus servo actuator current drive amplifier 20 causes a current to flow through the focus servo actuator 39 based on the up/down signal, and is driven by the focus servo actuator 39 to move the objective lens 34 up and down. A focus search is performed.

In FIG. 3, this objective lens 34 is shown in FIG. ), and the decreasing period moves from the upper limit point toward the lower limit point (in the direction away from the plate surface), and the period is, for example, about 1 to 3 seconds.

While the objective lens 34 is moving from the lower limit point to the upper limit point, when the focal point of the objective lens 34 approaches the plate surface of the rotary encoder disk 22, the 4-split photo as shown in FIG. Output signal (A
+C) and (B+D) are output. This output signal (A
+C) and (B+[)) are (A+C) voltage outputs C and (B
+D) voltage output d, and the (A+C) voltage output C and (B+D) voltage output d are supplied to an addition circuit 3 and a subtraction circuit 4, respectively.

In this adder circuit 3, the (A+C) voltage output C and (B+D) voltage output d are added, and (A+C)+(
B+D) becomes the addition output e and is supplied to the comparison circuit 45. In this comparison circuit 45, this (A10) + (B
D) The addition output e is compared with the reference voltage E8, and as a result of this comparison, the focus ready signal g, which is a rectangular wave that remains high only during the period when the addition output e is equal to or higher than the reference voltage 88, is output to the microcomputer 49. supplied to When this focus ready signal g becomes high,
This indicates that there is a possibility of switching from the focus search to focus servo, and after detecting the rise of the focus ready signal g from low to high, the microcomputer 49 waits for the next command.

On the other hand, in the subtraction circuit 4, the (A+C) voltage output C and the (B+D) voltage output d are subtracted, resulting in a (A+C)-(B+D) subtracted output f.

This (A + C) - (B + D) subtraction output f is usually called an S curve, and as shown in Figure 7, the one that appears in the middle of the increasing period of the up-down signal S is an inverted S-shape, and decreases. The one that appears in the middle of the period is S-shaped, and this inverted S
The point passing through the 0 potential point in the center of the letter and the S-shape is the focused point. This (A0C)-(B0D) subtraction output f is,
The Ov passing detection circuit 46 detects the timing of passing through this 0 potential point, and changes from high to low at the timing of passing through the 0 potential point of this inverted S shape, and low at the timing of passing through the 0 potential point of this S shape. A focus zero cross signal, which is a rectangular wave that switches from low to high, is supplied to the microcomputer 49.

In this microcomputer 49, the focus loop-on signal i is generated by the focus ready signal g and the focus zero cross signal.

In the conventional autofocus circuit 41, the focus search is switched to focus servo only when the objective lens 34 approaches the plate surface of the rotary encoder disk 22, so this focus loop The on signal i is a rectangular wave that changes from low to high at the fall timing of this focus zero cross signal from high to low, and changes from high to low at the fall timing of this focus ready signal g.

This focus loop on signal i turns on the electronic switch (1) 11 and turns off the electronic switch (2) 12 during this high period, so the (A+C)-(B
+D) The subtraction output f is supplied to the focus servo actuator current drive amplifier 20 via the phase compensation and amplification circuit 19, and as described above in FIG.
- (B+D>The objective lens 3 is controlled by the focus servo actuator 39 so that the subtraction output f becomes 0.
The focal position of No. 4 is controlled and the focus servo is applied. That is, the focus loop-on signal i causes switching from the focus search to the focus servo.

Normally, this switching from focus search to focus servo is performed in the middle of the first increasing period of the up-down signal, but for some reason this switching fails in the middle of this first increasing period. In this case, this switching is performed during the next increasing period of the up/down signal. FIG. 7 illustrates the case where this switching fails in the middle of this initial increase period.

Once the focus servo is applied, as mentioned above,
The focus of the objective lens 34 automatically follows the surface of the rotary encoder disk 22, and normally this focus servo continues to work until the power switch is turned off, but if a large impact is applied, etc. , this focus servo may come off.

The latter half of the waveform diagram in FIG. 7 shows a case where the focus servo is off. As shown in the figure, when this focus servo is off, the (A+C) voltage output C and (B+D) voltage output d both become O, so the focus ready signal g becomes low, and the focus loop on signal i also becomes low. Therefore, the electronic switch (1) 11 is turned off and the electronic switch (2) 12 is turned on, and by repeating exactly the same operation as at the time of startup, the focus search described above is performed, and as in the case described above. Can be switched to focus servo.

(Problem to be Solved by the Invention) Conventional autofocus circuit 41 having the above configuration
As mentioned above, if a large impact is applied and the focus servo is disengaged, the focus search switch is turned off again.
There was a problem in that it took a long time. Until the focus servo is applied again, the detection signal output of the encoder track 23 of the reflective optical rotary encoder device 51 using the autofocus circuit 41 is 0, so the reliability of this detection signal is This is a big problem for low-resolution encoder devices.

Furthermore, as described above, this conventional autofocus circuit 41 uses the four microcomputers, so there is a problem in that digital noise is large. The reflective optical low-reflection encoder device 51 using this autofocus circuit 41 is equipped with a high-precision wideband amplifier in order to output the detection signal in the form of a sine wave over a wide band from DC to several ml (z). , this digital noise is a big problem because it has an adverse effect on this broadband amplifier.

The present invention has been made with attention to the above points, and therefore, when the focus servo is disconnected, the focus servo is reactivated in a very short time. The purpose is to provide a focus circuit.

(Means for Solving the Problems) The autofocus circuit of the present invention is used in a reflective optical device including a reflective optical information recording plate and a laser reading device for reading information on the recording plate, By controlling the focus servo actuator that drives the objective lens of the reading device, a focus search is performed to move the focal point of the objective lens to the focal point on the plate surface of the recording plate, and this focal point is reached by this focus search. and a focus servo that automatically follows this plate surface to perform an autofocus operation, and when the reflective optical device is started, the autofocus circuit automatically switches between a triangular wave generating means that outputs a triangular wave with a relatively small period and small amplitude when the focus servo is off after switching the large amplitude triangular wave to the focus servo; and a 4-division photodetector of the laser reading device. an addition circuit that adds and outputs two outputs obtained by combining two outputs on diagonal lines from each other, and a subtraction circuit that subtracts and outputs the two outputs; A focus loop switching means for switching and outputting the subtraction output for performing the focus servo when the focus is in focus, and switching and outputting the triangular wave for performing the focus search when the focus is not present, and the output of the focus loop switching means, Focus servo actuator driving means for driving the focus servo actuator to perform the focus search according to the amplitude and period of the voltage increase and decrease of the triangular wave, and to perform the focus servo using the subtraction output so that the subtraction output becomes zero. The present invention is configured to include an autofocus circuit and a driving means.

Further, in the autofocus circuit of the present invention, in the autofocus circuit, a focus loop switching means switches from the focus search to the focus servo at a timing earlier than the timing at which the focus of the objective lens reaches the in-focus point. It is configured to have the following.

(Example) The autofocus circuit of the present invention includes the objective lens 34
During the approach and separation from the plate surface described above, the focus search is switched to the focus servo, and if the focus servo is switched off after being applied as described above, the objective lens 34 is By switching the focus search range so that the focus search is performed in a narrower range than the movable range of the focus servo, the return to the focus servo when the focus servo is lost can be performed in an extremely short time.

As shown in FIG. 3, a reflective optical rotary encoder device 21 incorporating an autofocus circuit 1 according to an embodiment of the present invention differs from the above-described device 51 only in this autofocus circuit 1. Therefore, descriptions of parts similar to those described in the conventional technical description will be omitted.

FIG. 1 is a block diagram showing an embodiment of an autofocus circuit of the present invention, and FIG. 2 is a waveform diagram illustrating the operation of the circuit shown in FIG. The autofocus circuit 1 according to the embodiment of the present invention is similar to the autofocus circuit 41 of the conventional example described above.
However, since the functions have been improved as described above, the same parts as in the conventional example are given the same reference numerals, and the explanation thereof will be omitted.

At startup, the focus search is first performed as in the case of the conventional example described above.

In FIG. 1, the focus detection circuit 10 and the inverter 13BS? IS child switch (S) 14, electronic switch (
4) 15, timing pulse generation circuit (1) 16, timing pulse generation circuit (2) 17, and triangular wave generation circuit 1
8 constitutes a triangular wave generation means for performing this focus search, and also includes a comparison circuit (1) 5, a comparison circuit (2) 6, a comparison circuit (3) 7, a timing processing circuit 8,
The flip-flop circuit 9, electronic switch (1) 11, electronic switch (2) 12, and inverter 13A constitute a focus loop switching means for switching between this focus search and the aforementioned focus servo.

As shown in the figure, when a power switch (not shown) provided in the device 21 is turned on, the focus detection flag signal from the focus detection circuit 10, which will be described later, is low at startup. , this electronic switch (3)
14 is turned on by this inverter 13B, this electronic switch (4) 15 is turned off, and a timing pulse (1) a, which is a rectangular wave, is supplied from this timing pulse generation circuit (1) 16 to this triangular wave generation circuit 18. In this triangular wave generation circuit 18, this timing pulse (
1) An up-down signal (1) b is generated which is a triangular wave in which the voltage increases during the period when a is high and decreases during the period when it is low. This up-down signal (1)b is substantially the same as the up-down signal in the conventional example described above in FIG. At startup, the focus loop on signal j from the flip-flop circuit 9, which will be described later, is low, so the electronic switch (1) 11 is off and the electronic switch (2) is off.
) 12 is turned on by the inverter 13A, and this up/down signal (1)b is supplied to the focus servo actuator current drive amplifier 20. The focus servo actuator current drive amplifier 20 causes a current to flow through the focus servo actuator 39 based on the up/down signal H)b, and a focus search is performed in the same manner as in the conventional example described above.

When the focus of the objective lens 34 approaches the plate surface of the rotary encoder disk 22 during movement of the objective lens 34 due to this focus search, an output signal is output from the four-split photodiode 38F as in the conventional example. (
A+C) and (B+D) are output, and this output signal (A+C) and (B+D) are output.
+C) and (B+D) are (A+C) voltage outputs C and (B+) by current/voltage conversion circuits 2A and 2B, respectively.
D) Converted to voltage output d, added by addition circuit 3 and subtraction circuit 4
are supplied respectively. In the adder circuit 3, the (A+C) voltage output C and the (B+D) voltage output d are added to form an (A+C)+(B+D) addition output e, which is supplied to the comparison circuit (1) 5. This comparison circuit (1) 5
, this (A+C)+(B+D) addition output e is compared with the reference voltage E8□, and as a result of this comparison, the focus ready signal is a square wave that is high only during the period when this addition output e is equal to or higher than the reference voltage E8□. A signal g is supplied to the flip-flop circuit 9 and the focus detection circuit 10.

On the other hand, in the subtraction circuit 4, the (A+C) voltage output C and (B+D)? [The pressure force d is subtracted, and (A
+C) - (B+D) The subtraction output is f, and this (A+C)
-(B+D) subtraction output f is supplied to the comparison circuit (2) 6 and the comparison circuit (3) 7.

This (A+C)-(B+D) subtraction output f is determined by the reference voltage ES which is slightly larger than OV in this comparison circuit (2) 6.
2, and as a result of this comparison, the comparison output (2)h becomes a comparison output (2)h which is a rectangular wave that is high only during the period when this subtraction output f is equal to or higher than this reference voltage ES2, and this comparison circuit (
3) 7 is compared with a reference voltage E83 that is slightly smaller than 0■, and as a result of this comparison, the comparison output (3) i is a rectangular wave that remains high only during the period when this subtracted output f is below this reference voltage E83. becomes. The comparison output (2) h and the comparison output (3) i correspond to the focus zero cross signal in the conventional example described above in FIG. 7, and include information on the switching timing from the focus search to the focus servo. and are respectively supplied to the timing processing circuit 8.

In this timing processing circuit 8 and the flip-flop circuit 9, the timing pulse (1) a is
, when the focus servo is off, refer to timing pulse (2) g, which will be described later, and use this comparison output (2) h and (3).
i, the focus loop-on signal j is generated based on the focus ready signal g. This focus loop on signal j changes from low to high at the timing of the falling of the comparison outputs (2) h and (3) i from high to low, and changes from high to low at the timing of the falling of this focus ready signal g. This is a square wave.

The falling timing of the second comparison output (2) h is such that the center part of the inverted S-shape of the (A+C)-CB+D) subtraction output f is slightly earlier than the in-focus point of the reference voltage E82. This is the timing of passing through a potential point,
Further, the falling timing of the comparison output (3) i is determined by the timing pulse (1) a or (2) g.
, the center part of the S-shape of this subtracted output f is set to the reference voltage E at a timing slightly earlier than the in-focus point.
This is the timing of passing through the 83rd potential point.

This focus loop on signal j turns on the electronic switch (1) 11 and turns off the electronic switch (2) 12 during this high period, so this (A+C)-(B
+D) The subtraction output f is supplied to the focus servo actuator current drive amplifier 20 via the phase compensation and amplification circuit 19, and the focus servo is applied as in the case of the conventional example described above. That is, the focus loop-on signal j causes switching from the focus search to the focus servo.

In the autofocus circuit 1 according to the embodiment of the present invention, this focus search causes the focus of the objective lens 34 to arrive at a timing slightly earlier than the timing at which the focal point of the plate surface of the rotary encoder disk 22 is reached. ,
Since this switching from focus search to focus servo is performed, this switching is performed reliably,
Further, this switching is possible in the middle of the above-mentioned increase period and decrease period of the up-down signal.

Normally, this switch from focus search to focus servo is performed during the first increasing period of this up/down signal, but if for some reason this switching fails during this increasing period. This switching occurs in the middle of a decreasing period following this increasing period. FIG. 2 illustrates the case where this switch fails during this initial increase period.

Also, the latter half of the waveform diagram in Figure 2 is similar to the conventional example,
- The diagram shows a case where the focus servo is turned off after it has been turned on.

As shown in the figure, when the focus servo is off, the focus loop on signal j becomes low as in the conventional example, so the electronic switch (1) 11 is turned off and the electronic switch (2) 12 is turned off. is turned on.

On the other hand, when the power switch is turned on, the device 21
The focus detection circuit 10 is reset by a reset signal from a power-on reset circuit 40 provided for this purpose. In this focus detection circuit 10, when the focus ready signal g supplied from the comparison circuit (1) 5 is high for a predetermined period or more, it changes from low to high;
The focus detection flag signal k, which changes from high to low, is output by this reset signal. This focus detection flag signal indicates that the focus servo is once applied after the power switch is turned on, and when this focus detection flag signal k goes from low to high, the electronic switch (3) 14 OFF, the electronic switch (4) 15 is turned ON, and the timing pulse (2)g from the timing pulse generation circuit (2) 17 is supplied to the triangular wave generation circuit 18. Since this timing pulse (2) g is a rectangular wave with a shorter period than the timing pulse (1) a, the up-down wave is a triangular wave based on this timing pulse (2) g that is output from this triangular wave generation circuit 18. The signal (2) m has a shorter period, the same as the timing pulse (2) g, and a smaller amplitude than the up/down signal (i) b. FIG. 2 shows an example in which both the period and the amplitude are 1/2.

When the focus servo is off, the focus of the objective lens 34 is close to the plate surface of the rotary encoder disk 22, so based on the short-period, small-amplitude up-down signal (2)m, By the same operation as in the case of startup described above, a focus search is performed in a range narrower than the movable range of the objective lens 34, and the focus servo is switched as in the case described above.

The autofocus circuit 1 according to the embodiment of the present invention described above switches from the focus search to the focus servo during the approach or separation of the objective lens 34 from the surface of the rotary encoder disk 22. At the same time, if the focus servo is applied and then disengaged as described above, the focus search range is switched so that the objective lens 34 performs focus search in a narrower range than the aforementioned movable range. When the focus servo is lost, the return to the focus servo is performed in a very short time.

Also, due to this focus search, the focal point of the objective lens 34 reaches the focal point of the plate surface of the rotary encoder disk 22 at a timing that is a little earlier than the timing when
Since this switching from focus search to focus servo is performed, this switching is reliably performed.

In addition, unlike the circuit 41 of the prior art example, the circuit is constructed with a simple circuit without using a microcomputer, so there is no digital noise as described above, and there is no increase in cost.

Note that the autofocus circuit of the present invention has a reflection type optical rotary encoder device 2 as described above as an embodiment.
Although an example of the autofocus circuit 1 used in the autofocus circuit 1 has been described, the present invention is not limited thereto, and can be used in a reflective optical linear encoder device and a reflective optical device having a ground-like configuration.

(Effects of the Invention) The autofocus circuit of the present invention having the above configuration has the following features:
The focus search is switched to the focus servo during the approach and separation of the objective lens from the plate surface, and if the focus servo is turned off after being applied, the search range is narrower than the search range at startup. Since this focus search is performed in the circuit, when the focus servo is turned on and then turned off, the return to the focus servo is done in a very short time, and the accuracy of information reading of the device using this circuit is improved. improves.

Furthermore, since the focus search is switched to the focus servo at a timing earlier than the timing when the focus of the objective lens reaches the in-focus point, this switch is reliably performed and the focus is Return to servo in an extremely short time becomes more reliable.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the autofocus circuit of the present invention, FIG. 2 is a waveform diagram explaining the operation of the circuit of FIG. 1, and FIG. FIG. 4 is a schematic configuration diagram showing an example of a reflective optical rotary encoder device using an autofocus circuit; FIG. 4 is a configuration diagram showing an example of a rotary encoder disk used in the device shown in FIG. 3; 6 is a block diagram showing an example of a conventional autofocus circuit, and FIG. 7 is a waveform diagram explaining the operation of the circuit shown in FIG. 6. 1.41... Autofocus circuit, 3... Addition circuit, 4... Subtraction circuit, 5... Comparison circuit (■) 6...
- Comparison circuit (2) 7... Comparison circuit (3) 8... Timing processing circuit, 9... Flip-flop circuit, 10... Focus detection circuit, 11... Electronic switch (1), 12 ...Electronic switch (2), 14...Electronic switch (3), 15...Electronic switch (4), 13A, 13B...Inverter, 16...Timing pulse generation circuit (1), 17・・・
- Timing pulse generation circuit (2), 18... Triangular wave generation circuit, 20... Focus servo actuator current drive amplifier (focus servo actuator drive means), 21.25... Reflective optical rotary encoder device (reflective type optical device), 22... rotary encoder disk (reflection type optical information recording plate), 28... laser reading device, 34... objective lens, 38F... 4-division photodiode (4 39...Focus servo actuator.

Claims (2)

[Claims] (1) Used in a reflective optical device that includes a reflective optical information recording plate and a laser reader that reads information on the recording plate, and controls a focus servo actuator that drives the objective lens of the laser reader. By this,
A focus search for moving the focal point of the objective lens to a focal point on the plate surface of the recording plate, and a focus servo for automatically following the focal point reached by this focus search to this plate surface are automatically performed. The autofocus circuit is configured to switch to perform an autofocus operation, and when the reflective optical device is activated, a triangular wave with a relatively large period and large amplitude is applied to the focus servo, and after the focus servo is switched to the triangular wave, the focus servo is activated. A triangular wave generating means that outputs a triangular wave with a relatively small period and small amplitude when the signal is off, and two diagonally diagonal outputs from the four-split photodetector of the laser reading device are combined and outputted by adding together two outputs. an addition circuit and a subtraction circuit that performs subtraction and outputs the subtraction output for performing the focus servo when the focal point of the objective lens is approximately at the in-focus point based on the addition output and the subtraction output; includes a focus loop switching means for switching and outputting the triangular wave for performing the focus search; and an output of the focus loop switching means to perform the focus search according to the amplitude and period of voltage increase and decrease of the triangular wave, and to perform the subtraction output. and a focus servo actuator driving means for driving the focus servo actuator to perform the focus servo using the subtracted output so that the subtracted output becomes zero. (2) The invention further comprises a focus loop switching means for switching from the focus search to the focus servo at a timing earlier than the timing at which the focus of the objective lens reaches the in-focus point. The autofocus circuit described in item 1.