JPH10104021A - Optical encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a condensing optical encoder having a structure wherein a scale plate is readily manufactured with high accuracy and the resolution is readily changed. SOLUTION: A scale plate 40 of an optical type rotary encoder 10 comprises a glass substrate 41 wherein a first reflection section 42 and a second reflection section 43 with equal widths each having different reflection ratio are alternatively formed on the surface thereof 411. For example, the first reflection section has a total reflection film and the second reflection section has a half mirror film. A quantity of a receiving light by a photodetector is changed in the sine wave corresponding to a position of a light spot formed by the emission light. An encode pulse signal can be formed based on the quantity of the receiving light. The scale plate can be readily and accurately manufactured compared to the case that a signal which is changed in the sine wave using two-layer reflection section having a step in the light axis direction is formed. Even when a relationship between the width of the reflection section and the diameter of the optical spot is changed, it is possible to obtain the encode pulse signal having the duty ratio of 50%,, thereby readily changing the resolution of the encoder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder for optically detecting a moving direction and a moving position of a moving member.

[0002]

2. Description of the Related Art FIG. 10 shows the principle of a commonly used optical encoder. This optical encoder 1
0B is a light emitting element 7 such as a laser diode (LED).
And a photodetector 8 such as a photodiode (PD),
A movable slit plate 6 having slits formed at a constant pitch is arranged, and a fixed slit plate 9 is arranged between the movable slit plate 6 and the photodetector 8. When the moving slit plate 6 attached to a moving member (not shown) moves, an optical path between the light emitting element 7 and the photodetector 8 is intermittently blocked. As a result, the photodetector 8 outputs an output waveform signal according to the moving state of the moving member on which the moving slit plate 6 is attached. The output pulse signal is shaped by the signal processing circuit 8A to obtain an encode pulse signal.

In an optical encoder, it is necessary to obtain first and second encode pulse signals (A-phase signal and B-phase signal) whose phases are shifted by 1/4 cycle in order to detect the moving direction. For this purpose, the light emitting element 7 and the photodetector 8 are set to (n
+1/4) period (n is an integer), and
The kind of encoding pulse signal is obtained.

[0004]

Here, an optical encoder having a high resolution can be realized by using an optical system employed in an optical pickup or the like.

FIG. 7 shows the entire configuration of a condensing type optical encoder proposed by the present applicant. As shown in this figure, the optical encoder 10A
A, two optical units 20A and 30A for focusing light on the scale plate 40A and detecting return light from the scale plate 40A, and these optical units 20A and 30A.
And a pulse signal forming circuit 50A for forming two encode pulse signals whose phases are shifted by 1/4 cycle based on the amount of return light received by A and 30A.

[0006] The scale plate 40A has a glass substrate 41A, and on the back surface thereof, a first reflector 42A and a second reflector 43A are formed in this order from the front side of the substrate 41A. The first reflecting plate 42A includes a reflecting portion 421 having a constant width for reflecting light and a transmitting portion 42 having a constant width for transmitting light.
2 are alternately formed at regular intervals (period λ). The second reflecting plate 4 is provided with respect to the reflecting portion 421 of the first reflecting plate 42A.
The reflecting surface of 3A is formed at the position where it is retracted. The step in the direction of the optical path between them is set to 波長 of the wavelength of the light emitted from the optical unit 20A. Therefore, the light reflected by the reflector 421 and the light reflected by the second reflector 43A are out of phase by 180 °, and cancel each other.

The arrangement of the first and second optical units 20A and 30A is set as follows. That is, the position A where the light emitted from the first optical unit 20A converges as a light spot on the scale plate 40A.
The distance d between the light emitted from the second optical unit 30A and the position B at which the light emitted from the second optical unit 30A converges as a light spot on the scale plate 40A is d = (n ± (1/4) λ (n is an integer)... (1) The first and second optical units 20A and 30A are attached to the guide shaft 2 while maintaining this positional relationship.

Since the first and second optical units 20A and 30A have the same configuration, the first optical unit 20A
Only the configuration of A will be described below.

The first optical unit 20A has a housing 29A attached to the guide shaft 2.
Inside the housing 29A, a forward path for condensing light emitted from the light emitting element 21A on the scale plate 40A, and a photodetector 27A arranged in a different direction from the light emitting element 21A for returning light from the scale plate 40A. And an optical system having a return path for guiding to

On the outward path, a half mirror 23A and an objective lens 25A are arranged in this order from the light emitting element 21A toward the scale plate 40A. On the return path, the objective lens 2 is moved from the scale plate 40A to the photodetector 27A.
5A and the half mirror 23A are arranged in this order. Here, the reflection surface 231 of the half mirror 23A is set at a predetermined angle so as to separate outgoing light from the light emitting element 21A and return light from the scale plate 40A.

In the first optical unit 20A, the diameter of the light spot converged on the scale plate 40A by the objective lens 25 is adjusted by the reflection portion 421 (transmission portion 42) of the first reflection plate 42A.
The width is adjusted to be substantially equal to the width of 2). As shown in FIG. 8, the diameter 2r of the light spot may be smaller than the width W of the reflection portion 421 of the first reflection plate 42A. In this case, for example, when the light intensity per unit area of the light spot 100 is uniform, the beam diameter r of the light spot 100 may be adjusted to about 0.8 times the width W of the reflection part 421. When the light intensity per unit area of the light spot 100 is non-uniform,
What is necessary is just to adjust the relationship such that the light amount of the return light from 1 and the light amount of the return light from the second reflection plate 43A become substantially equal.

In the first optical unit 20A having this configuration, the light emitted from the light emitting element 21A is transmitted to the objective lens 25A.
A focuses on the scale plate 40A as a light spot. The return light of the output light reflected by the scale plate 40A is guided to the return path.

The return light guided to the return path is directed to the objective lens 25A.
And returns to the half mirror 23A. Half mirror 23
A part of the return light returning to A is reflected by the reflection surface 231 of the half mirror 23A, changes its traveling direction by approximately 90 degrees, and is separated from the light emitted from the light emitting element 21A. The return light whose traveling direction has been changed by the half mirror 23A is guided to the photodetector 27A. The photodetector 27A includes a light receiving element such as a photodiode (PD), and returns light is detected by the light receiving element.

Here, the step between the first reflector 42A and the second reflector 43A is, as described above, one wavelength of the emitted light.
/ 4. Therefore, when the irradiation area of the light spot on the reflection unit 421 and the irradiation area of the second reflection plate 43A are equal, the cancellation between the return light from the reflection unit 421 and the return light from the second reflection plate 43A is cancelled. Since the matching is maximum, the amount of light received by the photodetector is minimum. As the irradiation area becomes larger on one side and becomes smaller on the other side, the degree of cancellation of return light from both sides decreases with this, and the amount of light received by the photodetector increases. . When the irradiation area on one side becomes maximum, the amount of light received by the photodetector becomes maximum.

Accordingly, when the optical unit 20A and the scale plate 40A move relatively, the output waveform P (a) of the photodetector 27A becomes a sine waveform as shown in FIG. This output waveform P (a) is converted to a pulse signal forming circuit 50A.
, A first encode pulse signal Va having a rectangular wave shape is formed. That is, in the pulse signal forming circuit 50A, a constant reference potential Vo passing through the midpoint level of the output waveform P (a) is set in advance, and this reference potential Vo is set.
And the output waveform P (a).
By comparing the output waveform P (a) with the reference potential Vo, a first encode pulse signal (A-phase signal) Va having a high-level to low-level ratio (duty ratio) of 50% is obtained.
Is obtained.

Note that the second optical unit 30A having the same configuration as the first optical unit 20A also has a photodetector 37A.
, A sinusoidal output waveform P (b) is obtained. The position B where the light emitted from the second optical unit 30A converges as a light spot on the scale plate 40A and the first optical unit 2
The first and second optical units 20A and 30A so that the distance d from the position A where the light emitted from 0A converges as a light spot on the scale plate 40A satisfies Expression (1).
Is arranged. Therefore, the second optical unit 30A
Is shifted from the output waveform P (a) by 1/4 cycle. That is, the phase of the second encode pulse signal Vb formed by the pulse signal forming circuit 50A based on the output waveform P (b) from the second optical unit 30A is 1/4 that of the first encode pulse signal Va. Period shift.

As a result, the first and second encode pulse signals Va and Vb whose phases are shifted by 1/4 cycle can be obtained. Based on these pulse signals Va and Vb, the moving direction and the moving direction of the scale plate 40A can be obtained. Position and the like can be detected.

Here, the optical encoder 10 having this configuration
In A, if a focusing error occurs in the light spot formed on the scale plate 40A, a highly accurate encoded pulse signal cannot be obtained. Therefore, it is desirable to mount an autofocus mechanism. For example,
A cylindrical lens is arranged on the optical path before the photodetector 37A to give astigmatism to the return light,
A focusing error may be avoided by finely adjusting the position of the condenser lens in the optical axis direction based on the light spot shape of the return light formed on the light receiving surface of A.

The optical encoder 10 constructed as described above
A has the following problems to be solved.

First, the first and second reflectors 42A,
A and B phase encode pulse signals Va and Vb utilizing the fact that the step of 42B becomes 1/4 of the wavelength of light
Have gained. In this configuration, the first reflector 42A and the second
Unless a step between the reflection plate 43A and the reflection plate 43A is accurately formed, a target characteristic cannot be obtained. In a large scale plate, it is difficult to form the step with high accuracy, and in a device such as a length measuring machine that requires a large scale plate, a highly accurate encoded pulse signal may not be obtained. .

Second, as described with reference to FIG.
The amount of light received by the photodetector is minimized when the amounts of light reflected from the first and second reflectors 42A and 42B are equal. Therefore, it is necessary to maintain a predetermined relationship between the width or the period λ of the reflection portion of the reflection plate and the diameter of the light spot formed thereon. If this relationship is not satisfied, adverse effects such as a failure to obtain an output with desired accuracy will occur. Further, when one dimension is changed, the other dimension must be changed accordingly.

For example, in FIG. 8, when the width of the reflecting portion 421 of the first reflecting plate 42A is made larger than the diameter of the light spot, the entire light spot 100 becomes the first reflecting plate 4A.
When formed on the 2A reflector 421 and when formed on the second reflector 43A, the amount of light received by the photodetector becomes maximum. In addition, the period during which the amount of received light is maximum becomes longer, and during that period, the waveform of the detector output becomes flat. As a result, as can be seen from FIG. 9B, the output waveform P (a) obtained from the photodetectors 27A and 37A.
And P (b) are compared with a reference voltage Vo passing through the middle point between the output waveforms P (a) and P (b).
The duty ratio of b does not become 50%. In order to solve such a problem, it is necessary to redesign the optical system and increase the diameter of the light spot.

Further, for example, when the width of the reflecting portions of the first and second reflecting plates is reduced to increase the resolution, it is necessary to reduce the diameter of the light spot accordingly.
That is, it is necessary to redesign the optical system of the optical unit, which is inconvenient and leads to an increase in cost.

It is conceivable to form only a single reflector on the scale plate 40A. In this case, the amount of light received by the photodetector is zero while the light spot is located on the transmission part between the reflection parts of the reflection plate. This makes it impossible to activate the autofocus function. Therefore, in an optical encoder having an autofocus function, it is necessary that the photodetector can always receive return light.

An object of the present invention is to propose an optical encoder of a light condensing system capable of solving the above-mentioned problems.

[0026]

In the optical encoder according to the present invention, the above-mentioned problem is solved by forming two kinds of reflecting portions having different reflectances on the scale plate.

That is, the optical encoder of the present invention comprises:
A scale plate having a plurality of first and second reflecting portions arranged alternately; an optical unit for focusing light on the scale plate and detecting return light from the scale plate; Pulse signal forming means for forming an encode pulse signal based on the position information of the scale plate from the amount of light received by the return light, the optical unit comprising: a laser light source; and a light spot for emitting light from the laser light source. And a photodetector that detects the return light from the scale plate. Here, the first and second reflecting portions of the scale plate have different reflectances for the emitted light.

In the optical encoder according to the present invention, since the amount of light is different between the return light from the first reflector and the return light from the second reflector, the return light depends on the position where the light spot is formed on the scale plate. Changes the amount of light. Therefore, an encode pulse signal is formed based on the change in the light amount.
Making the reflectances of the first and second reflecting portions different can be easily realized by, for example, selecting a material for forming these reflecting portions, and the setting of the reflectance can be easily controlled. Therefore, according to the present invention, a large scale plate having a target characteristic can be easily and accurately manufactured. Therefore, even in a device requiring a large scale plate such as a length measuring machine, high accuracy can be obtained. An optical encoder capable of forming an encoded pulse signal can be realized.

In the present invention, the first reflecting portion formed on the scale plate is a high reflection mirror, and the second reflecting portion is
Can be adopted as a half mirror.

Further, as the scale plate, a transparent substrate transparent to the emitted light, a highly reflective film as the first reflective portion formed on the surface of the transparent substrate at a predetermined period, A configuration including a half mirror film as the second reflection portion formed so as to cover the surface of the transparent substrate on which the reflection film is formed can be adopted.

Here, in the present invention, it is desirable to adopt a configuration in which the first and second reflecting portions having the same width are alternately arranged.

With this configuration, the duty ratio can be reduced to 50% even if the diameter of the light spot is not set to have a predetermined relationship with the width dimension of the first and second reflecting portions.
Can be obtained. For example,
The amount of return light is maximum when the most part of the light spot is located only on the first reflection part having a high reflectance, and the most part of the light spot is located on the second reflection part having a low reflectance. Minimum when located only in the part. And
The light spot forming position is from the first reflecting portion to the second reflecting portion,
Alternatively, the amount of light increases or decreases with the movement. Therefore, regardless of the diameter of the light spot, the change characteristic of the amount of received light is such that the positive side portion and the negative side portion have the same width with respect to the midpoint level. Therefore, even if the widths of the first and second reflectors are changed, the duty ratio can be reduced to 50 without changing the beam diameter of the light spot.
% Encoding pulse signal can be obtained. In other words, even when the resolution of the scale plate is changed, it is not necessary to change the design of the optical system.

Next, in addition to the above configuration, the optical encoder of the present invention detects a focusing error signal based on the detection result of the photodetector and adjusts the position of the condenser lens in the optical axis direction. It employs a configuration having an automatic focusing mechanism. Since the first and second reflection portions formed on the scale plate each have a predetermined reflectance, the photodetector can always receive the return light, and therefore always perform appropriate focusing. Can be.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical encoder to which the present invention is applied will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of an optical encoder. The optical encoder 10 includes a scale plate 40
An optical unit 20 that focuses light on the scale plate 40 and detects return light from the scale plate 40;
And a pulse signal forming circuit 50 for forming two encode pulse signals whose phases are shifted by 周期 cycle based on the amount of light received by the optical unit 20.

FIGS. 1 and 2A show a cross-sectional structure of the scale plate 40, and FIG. 4 shows a pattern of a reflection portion formed on the scale plate 40. FIG. This scale plate 4
0 has a glass substrate (transparent substrate) 41 transparent to the wavelength of the light emitted from the optical unit 20. Surface 411 of glass substrate 41 on the side opposite to the light incident side
Is a total reflection film made of, for example, chromium (first reflection portion)
42 are formed at a constant interval (period) λ. On the glass substrate surface 411 on which the total reflection film 42 is formed, a half mirror film 43 is formed so as to cover the total reflection film 42. In this example, the total reflection film 42 and the half mirror film 43
Are formed such that their widths are the same (λ / 2).

Here, some of the generally used total reflection films have a reflectance that is not completely 100%. The term “total reflection film” used in the present specification includes a high reflection film having a reflectance of about 80% or more.

As shown in FIG. 2 (B), as the scale plate 40, a half mirror film 43 is formed on the entire surface 411 of the glass substrate 41, and thereafter, a uniform width is formed on the surface at regular intervals. The total reflection film 42 may be formed.

Next, the configuration of the optical unit 20 will be described with reference to FIG. The optical unit 20 includes a housing 29 attached to the guide shaft 2.
A light emitting element (laser light source) is provided inside the housing 29.
It has a forward path for converging outgoing light emitted from 21 to scale plate 40, and a return path for guiding reflected light from scale plate 40A to photodetector 27 arranged in a direction different from that of light emitting element 21. Optical system.

On the outward path, the spectral element 22, the half mirror 23, and the objective lens 25 are arranged in this order from the laser light source 21 toward the scale plate 40. The spectroscopic element 22 is a lens having a predetermined diffraction condition, such as a grating lens. When the light emitted from the laser light source 21 passes through the spectroscopic element 22, at least the zero-order diffracted light (main beam) L0 and the diffracted light ± Primary light (sub-beam)
The light is set to be split into L1 and L2. The directions of diffraction of the diffracted lights L0, L1, and L2 by the spectroscopic element 22 are based on the position where the main beam L0 is formed as a light spot on the scale plate 40 and the sub beam L
If the interval d between the position 2 and the position where the light spot is formed on the scale plate 40 is λ, the formation period of the total reflection film 42 and the half mirror film 43 of the scale plate is λ, then d = (n ± １ ／) λ ( (n is an integer) (1). The spectral element 22 of this example is adjusted so that d = (1 ± 1/4) λ. This interval d can be finely adjusted by rotating the spectroscopic element 22 around the optical axis. Of course, the optical unit 2
The whole 0 may be rotated around the optical axis.

In FIG. 1, one of the sub-beams (diffraction + first-order light) L1 is omitted, but this sub-beam L1 is formed to be point-symmetric with the sub-beam L2 with respect to the main beam L0. Therefore, if the sub-beam L2 satisfies the expression (1), the interval between the position where the sub-beam L1 condenses as a light spot on the scale plate 40 and the position where the main beam L0 condenses satisfies the expression (1).

Next, on the return path, the objective lens 25 and the half mirror 2 move from the scale plate 40 toward the photodetector 27.
3. The cylindrical lens 26 and the photodetector 27 are arranged in this order. The half mirror 23 is an optical element for separating outgoing light from the laser light source 21 and return light from the scale plate 40 from the outgoing light and guiding the light to the photodetector 27. The cylindrical lens 26 is for giving astigmatism to the return light to the photodetector 27, and an autofocus mechanism described later is used to shape the light spot of the return light formed on the light receiving surface of the photodetector 27. Based on this, a focusing error is detected, and the position of the objective lens 25 in the optical axis direction is finely adjusted to perform an autofocus operation.

FIG. 3 shows the structure of the light receiving surface of the photodetector 27. The photodetector 27 of this example includes a four-division light receiving element (first light receiving means) 271 having four light receiving surfaces 271a to 272d for receiving return light of the main beam L0 from the scale plate 40, and the light receiving element 271. Light receiving elements (second light receiving means) arranged on both sides of the element 271 for receiving return light of the sub beams L1 and L2 from the scale plate 40
272 and 273 are provided. These light receiving elements 2
71, 272, and 273 are manufactured on the same chip by a semiconductor process.

The operation of generating an encode pulse in the optical encoder 10 having this configuration will be described. Laser light source 2
The light emitted from 1 is diffracted by the spectroscopic element 22, and is emitted from the spectroscopic element 22 as the zero-order diffracted light (main beam) L0 and the diffracted ± first-order lights (sub beams) L1 and L2. Main beam L0 emitted from spectral element 22
And the sub beams L1 and L2 are guided to the objective lens 25. The main beam L0 and the sub-beams L1 and L2 guided to the objective lens 25 are condensed as light spots on the scale plate 40 by the objective lens 25, respectively.

As shown in FIG. 4, if the main beam L0 is condensed as a light spot 100 on the reflection film 42 at the position A (0) of the scale plate 40, the sub beams L1 and L2 are shifted to the position A (0). Along the relative movement direction of the optical unit 20 and the scale plate 40 with respect to (1 + ／) λ
Light beams 101 and 102 are condensed at distant positions A (+) and A (-), respectively. In FIG. 4, the light spots 100, 101, 10
2 shows a case in which the diameter of 2 is set to be the same as the width of the total reflection film 42 of the scale plate 40.

Here, in equation (1), if the spectral element 22 is set so that the interval between the light spots is (1-1 / 4) λ, the sub-beams L1 and L2 are positioned at the position A '(+ ) And the light spots 101 and 102 at the position A ′ (−).

The converged main beam L0 and sub-beams L1 and L2 are applied to the total reflection film 42 and the half mirror film 43.
And is guided to the return path as return light. Each return light guided to the return path reaches the cylindrical lens 26 via the objective lens 25 and the half mirror 23. After astigmatism is given through the cylindrical lens 26, the light receiving elements 271 and 27 of the photodetector 27
2, and 273, respectively. That is, the return light of the main beam L0 from the scale plate 40 is condensed as a main spot on the quadrant light receiving element 271 located at the center, and the return lights of the sub beams L1 and L2 from the scale plate 40 are received by the light receiving elements 272 and 273. Each is collected as a side spot.

When the most spots of the light spot 100 of the main beam L0 and the light spots 101 and 102 of the sub-beams L1 and L2 are located on the total reflection film 42, the amount of each return light from the scale plate 40 becomes maximum. Becomes
Conversely, when most of the light spots 100, 101, and 102 are located on the half mirror film 43,
The amount of each return light from the scale plate 40 is minimized. For this reason, when the optical unit 20 and the scale plate 40 relatively move, the total reflection film 42 is formed at an interval of λ, so that the light receiving element 271 that receives the return light of the main beam L0 from the scale plate 40 is formed. Output waveform P (0)
Is a sine waveform with a period λ as shown in FIG. This output waveform P (0) corresponds to the light receiving surface 271 of the four-divided light receiving element 271.
a to 271d are obtained as the sum of the outputs.

The output waveforms P (1) and P (2) of the light receiving elements 272 and 273 for receiving the return lights of the sub beams L1 and L2 from the scale plate 40 also have sine waveforms as shown in FIG. Positions A (+) and A of light spots 101 and 102 of sub-beams L1 and L2
Since (−) is apart from the position A (0) of the light spot 100 of the main beam L0 by (1 + ０) λ, the phase is shifted by １ ／ period with respect to the output waveform P (0). It has a sine waveform with a period λ. Further, the output waveform P (1) of the sub-beam L1 and the output waveform P (2) of the sub-beam L2 have an inverted relationship. The levels of these output waveforms P (1) and P (2) are the same as the main beam L, which is the zero-order diffracted light because the sub-beams L1 and L2 are diffracted ± first-order lights.
It becomes lower than the output waveform P (0) based on the return light of 0.

In this way, each light receiving element 271, 27
2, and the output waveforms P (0), P obtained from 273
(1) and P (2) are processed in the pulse signal forming circuit 50 as described below, and an encoded pulse signal is obtained.

FIG. 6 is a block diagram of the pulse signal forming circuit. As shown in this figure, in the pulse signal forming circuit 50, each of the light receiving surfaces 271a to 271 of the four-division light receiving element 271 that has received the return light of the main beam L0 from the scale 40.
Output signals from 1d are amplified by the amplifiers 501 to 504, respectively, and the amplified output signals are fully added by the adder 511. As a result, an output waveform P ′ (0) obtained by amplifying the output waveform P (0) at a predetermined amplification factor is obtained.

The light receiving elements 272 and 2 receiving the return light of the sub-beams L1 and L2 from the scale plate 40, respectively.
73, the output waveforms P (1) and P (2)
05 and 506, the output waveforms P ′ (1) and P ′ (2) after amplification are output from the comparator 521.
Are compared. As a result, a second encode pulse signal (B-phase signal) Vb in which the ratio (duty ratio) between the high level and the low level is 50% is obtained.

Further, output waveforms P ′ (1) and P ′ (2) amplified by amplifiers 505 and 506 are added by adder 512, whereby a signal of a constant potential level is obtained. Further, the signal having the constant potential level is amplified by the amplifier 507 at an appropriate amplification factor so as to pass through the middle point of the output waveform P ′ (0). As a result, a reference potential Vo for forming an encode pulse signal is obtained from the output waveform P ′ (0).

The output waveform P ′ (0) is output to the comparator 52
2 is compared with the reference potential Vo, the ratio between the high level and the low level (duty ratio) is 50%, and the phase of the first encode pulse signal (（) is shifted from the second encode pulse signal Vb by １ ／ cycle. (A-phase signal) Va is obtained. In this manner, the first and second encode pulse signals Va and Vb are output from the pulse signal forming circuit 50.

Here, the optical encoder 10 is provided with an autofocus mechanism for automatically correcting the defocus of the light spot. This autofocus mechanism detects a focusing error signal by an astigmatism method. That is, since the returning light of the main beam L0 from the scale plate 40 is converted to an astigmatic wavefront by the cylindrical lens 26, the shape of the main spot 200 condensed on the four-divided light receiving element 271 when focused is achieved. Is circular, but if the focus is out of focus, it becomes elliptical as shown by the broken line in FIG. Therefore, a focusing error signal can be obtained based on the amount of light received at each light receiving portion of the four-divided light receiving element 271.

Referring to FIG. 6, in the optical encoder 10, first, the scale plate 4 of the main beam L0
Of the four light receiving surfaces 271a to 271d of the four-segment light receiving element 271 that receives the return light from 0, two pairs of light receiving surfaces 271a, 271c, 271b, and 2 at the point target position
The outputs of 71d are added by adders 601 and 602.
These two added outputs are compared by the comparator 621. When the focus is out of focus, there is a difference between these signals, and a corresponding out-of-focus signal appears at the output of the comparator 621. Based on this focus shift signal, the objective lens 25 is moved by the objective lens moving mechanism 63 via the objective lens drive circuit 61 in a direction in which the focus shift is eliminated.

Here, in this example, the total reflection film 42 and the half mirror film 43 are alternately formed on the scale plate 40, so that the light spot of the emitted light is formed at any position. The return light can be detected on the side of the photodetector. Therefore, for example, as in the case where the total reflection film and the transmission portion are alternately formed, the return light cannot be detected while the transmission portion is irradiated with light, and the adverse effect that the autofocus function does not work occurs. do not do.

(Other Embodiments) In the above description, a total reflection film is formed as a first reflection portion and a half mirror film is formed as a second reflection portion on a scale plate. Instead of the total reflection film, a reflection film having a reflectance of 50% or more may be employed, and instead of the half mirror film, a reflection film having a reflectance of less than 50% may be employed. In any case, the reflectances of the first and second reflecting portions may be relatively different.

[0059]

As described above, the optical encoder according to the present invention employs a configuration in which two types of reflection portions having different reflectivities are alternately formed as a scale plate, so that the return light from the scale plate can be reduced. By changing the amount of light, an encode pulse signal relating to the position information of the scale plate is obtained. Therefore, the scale plate can be manufactured more easily and more accurately than in a case where a two-layer reflecting portion is formed with a step in the optical axis direction.

Further, by adopting a configuration in which the first and second reflecting portions formed on the scale plate are alternately formed with the same width, the width of these reflecting portions and the diameter of the light spot formed on the reflecting portion are adopted. Can be obtained even if the magnitude relationship changes. Therefore, even when the resolution of the optical encoder is changed by changing the width of the first and second reflecting portions, there is an advantage that it is not necessary to change the design of the optical system.

Further, since the first and second reflecting portions formed on the scale plate each have a predetermined reflectance, even if the light spot irradiates any reflecting portion,
Return light can always be detected on the photodetector side. Therefore, there is an advantage that the autofocus function can always be operated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a light collecting type optical encoder to which the present invention is applied.

2A is a sectional view showing a scale plate of the optical encoder of FIG. 1, and FIG. 2B is a sectional view showing another example of the scale plate.

FIG. 3 is an explanatory diagram showing a light spot shape of return light formed on a light receiving surface of each light receiving element of the photodetector of the optical encoder of FIG. 1;

FIG. 4 is an explanatory diagram showing a positional relationship between a main beam and a sub beam collected as a light spot on a scale plate of the optical encoder of FIG. 1;

5 is a waveform diagram showing an output waveform obtained from a light receiving element of a photodetector of the optical encoder of FIG.

FIG. 6 is a block diagram showing a schematic configuration of a pulse signal forming circuit of the optical encoder of FIG. 1;

FIG. 7 is a schematic configuration diagram of an optical encoder proposed by the present applicant.

FIG. 8 is an explanatory diagram showing a relationship between a width of a reflecting portion of a scale plate and a beam diameter of a light spot.

9A is a waveform diagram showing first and second encode pulse signals obtained from the optical encoder of FIG. 7, and FIG. 9B is a diagram showing a reflection portion and a transmission of a scale plate rather than a diameter of a light spot; FIG. 9 is a waveform diagram showing first and second encode pulse signals when the width of the section is wide.

FIG. 10 is a principle diagram of a general optical encoder.

[Explanation of symbols]

 Reference Signs List 10 optical encoder 20 optical unit 21 laser light source 23 half mirror 25 objective lens 26 cylindrical lens 27 photodetector 40 scale plate 41 glass substrate (transparent substrate) 42 total reflection film (first reflection part) 43 half mirror film (first) 2 reflection part) 50 pulse signal forming circuit

Claims (5)

[Claims] 1. A method according to claim 1, wherein a plurality of first and second alternately arranged first and second arrays are arranged.
A scale plate having a reflecting portion, an optical unit that focuses light on the scale plate and detects return light from the scale plate, and a position of the scale plate based on an amount of the return light received from the optical unit. Pulse signal forming means for forming an encoded pulse signal based on the information, the optical unit, a laser light source, a condensing lens that focuses the light emitted from the laser light source as a light spot on the scale plate, A light detector for detecting the return light from the scale plate, wherein the first and second reflection portions of the scale plate have different reflectances for the outgoing light. Optical encoder. 2. The optical encoder according to claim 1, wherein the first reflection section is a high reflection mirror, and the second reflection section is a half mirror. 3. The method according to claim 1, wherein:
A transparent substrate that is transparent to the outgoing light, a high-reflection film as the first reflection portion having a constant width formed at a predetermined interval on the surface of the transparent substrate, and the high-reflection film formed with the high-reflection film An optical encoder, comprising: a half-mirror film as the second reflection portion formed so as to cover a surface of a transparent substrate. 4. The optical encoder according to claim 1, wherein the first and second reflecting portions having the same width are formed alternately. 5. The method according to claim 1, further comprising detecting a focusing error signal based on a detection result of the photodetector, and adjusting a position of the condenser lens in an optical axis direction. An optical encoder having an auto-focus mechanism for performing the operation.