JP2005091023A - Optical encoder and imaging device equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical encoder with high resolution by enhancing the S/N ratio (maximum intensity/minimum intensity) of a signal acquired with the movement of a scale. <P>SOLUTION: An optical pattern of the movable scale 102 and that of a fixed scale 103 are disposed at a prescribed interval, the optical patterns each having transmitting parts and screening parts alternately disposed at prescribed pitches, thereby removing the effect of diffracted light owing to the optical patterns and of filtering light. Preferably, the movable scale 102 is in contact with the fixed scale 103. Further, the percentage of the transmitting part is made larger than that of the screening part on at least one of the scales 102 and 103. This makes it possible to further remove the effect of filtering light. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical encoder, and more particularly to an optical encoder that performs digital output. In particular, the present invention relates to an optical encoder suitable for a scale pitch of 0.1 mm or less, and further 0.05 mm or less. Further, the present invention relates to an imaging apparatus provided with the same.

  There is a need for a position detection device having a resolution of the order of several μm in various industrial equipment, precision machines, and the like. For example, in the case of a camera, it is necessary to detect the position of a focusing lens for autofocus and to detect the amount of movement of a lens or image sensor for camera shake correction. In addition, these detection devices are required to have high performance, downsizing, and low cost because of the demand for downsizing and cost reduction of cameras.

  An optical encoder is one of low-cost position detectors. For example, as shown in FIG. 10, the optical encoder includes a type having a light emitting element 101, a main scale 112, and a light receiving element 110 (hereinafter referred to as a configuration A), and moving between the light emitting element 101 and the light receiving element 110. There is a type having a scale 102 and a fixed scale 103 (hereinafter referred to as configuration B). In the configuration A and the configuration B, the main scale 112, the moving scale 102, and the fixed scale 103 are arranged such that the light shielding portions and the transmission portions are alternately arranged at the predetermined pitch P with the same area. In the optical encoder of configuration A, the light receiving area (opening) of the light receiving element 110 is substantially the same as the area of the light shielding portion, and the main scale 112 moves relative to the pair of the light emitting element 101 and the light receiving element 110. In the optical encoder of configuration B, the light emitting element 101, the light receiving element 110, and the fixed scale 103 are fixed in position, and the moving scale 102 moves relatively. In any configuration, the amount of light reaching the light receiving element 110 from the light emitting element 101 changes due to the movement of the main scale 112 or the moving scale 102. This change is detected by the light receiving element 110, and a digital signal is obtained by comparing an output signal from the light receiving element 110 with an arbitrarily provided threshold value. FIG. 11 shows signal processing for obtaining a digital signal. A threshold value A and a threshold value B are provided for a signal representing the light intensity obtained by the light receiving element 110 (A). The threshold A and the threshold B are substantially intermediate values between the maximum intensity and the minimum intensity. The signal is binarized to 1 and 0 when the threshold B is exceeded and then exceeds the threshold A, and when the signal is below the threshold A and below the threshold B (B). The reason why the threshold value is provided with hysteresis is to prevent errors caused in binarization due to signal fluctuation caused by noise. In order to reduce the error of the detected movement amount, it is preferable that the hysteresis is small with respect to the intensity change (the difference between the threshold value A and the threshold value B is small). Next, the rising and falling edges of the binarized signal are pulsed (C). The movement amount of the movement scale is detected by counting the pulse signals. When the moving scale 102 moves by the scale pitch, the intensity of the signal changes for one period. Therefore, when one pulse is counted, it can be seen that the moving scale 102, that is, the moving body is displaced by half the length of the scale pitch. Hereinafter, the method shown in FIG. 11 is referred to as a two-division method. The resolution of the optical encoder based on the two-division method is half the scale pitch.

  Examples of methods for improving the detection resolution using these encoders include a method of reducing the scale pitch and a method of interpolating the detected light intensity change by signal processing. An example of the latter method is described in Patent Document 1 below. Patent Document 1 discloses a four-division method for generating a digital counter having a minimum unit of 1/4 of the scale pitch from two signals having different phases by π / 2, a resistance division method for performing divisions of four or more, and time modulation. The law is described. Further, Patent Document 1 discloses a displacement amount detection method for calculating a displacement amount of a scale by obtaining a phase angle of a signal from a displacement amount based on a four-division method.

JP-A-5-248850

  If the scale pitch is reduced in order to improve the detection resolution of the optical encoder, diffraction due to the scale pitch occurs in both configurations A and B. As a result, the light that should originally be blocked by the scale enters the light receiving element, and the S / N ratio of the signal decreases. The signal S / N ratio here is the maximum signal intensity (output value of the light receiving element when the transmittance is maximum) / minimum signal intensity (output value of the light receiving element when the transmittance is minimum). is there.

  Further, in the optical encoder of configuration B, as shown in FIG. 12, (a) light is supposed to be blocked, but leakage light is generated, or (b) light that should be transmitted is blocked. . As a result, the S / N ratio of the signal decreases. A decrease in the S / N ratio of the signal results in a decrease in position detection accuracy. In general, the scale pitch of an optical encoder is 0.1 mm or more, and those smaller than that are difficult to put into practical use for the above reasons. Therefore, there is a limit to the detection resolution.

  On the other hand, the method described in Patent Document 1 in which the detection resolution of the optical encoder is improved by signal processing also has problems such as leakage light shown in FIG. When the S / N ratio of the signal is lowered, the phase angle of the signal cannot be detected with high accuracy, and the position detection accuracy is lowered. That is, it is necessary to improve the S / N ratio even in a method for improving the position detection accuracy by interpolating a signal.

  In order to avoid the above-mentioned problems such as leakage light, there is a method in which parallel light is incident on the scale. However, for this purpose, a point light source such as a laser diode and a collimator lens are required, which increases costs.

  The present invention has been made in view of the above points, and an object thereof is to improve the position detection accuracy of an optical encoder by improving the S / N ratio of a signal.

To achieve the above object, according to a first aspect of the present invention, there is provided a fixed scale having an optical pattern arranged at a predetermined pitch and a movable scale opposed to the fixed scale so as to be movable relative to the fixed scale. Fixed and equipped with a moving scale having an optical pattern arranged, a fixed scale and a light source unit that irradiates light to the moving scale, and a light receiving unit that detects a change in light intensity from the light source unit as the moving scale moves. An optical encoder that detects the relative movement position of a scale and a moving scale, and satisfies the following conditional expression.
d ₁ ≦ 2.5 × P ₁
Here, d ₁ is the distance between the optical pattern of the moving scale and the optical pattern of the fixed scale, and P ₁ is the scale pitch of the moving scale and the fixed scale.

  Since the distance between the fixed scale and the moving scale is set to a predetermined value or less, the influence of diffraction by the scale and the influence of leakage light are eliminated, and a signal with a high S / N ratio can be obtained. As a result, highly accurate position detection is possible.

  The scale pitch of the fixed scale and the moving scale is preferably 50 μm or less. High-precision position detection is possible.

  It is preferable that the optical pattern of the fixed scale and the optical pattern of the moving scale are arranged to face each other. The distance between the optical pattern of the moving scale and the optical pattern of the fixed scale can be reduced, and a signal having a high S / N ratio can be obtained.

  The fixed scale and the moving scale are preferably in contact with each other. S / N ratio does not fluctuate and stable detection accuracy is obtained.

According to a second aspect of the present invention, there is provided a main scale having an optical pattern in which transmission regions and light shielding regions are alternately arranged at a predetermined pitch, a light source unit that irradiates light to the main scale, and an opening smaller than the light shielding region of the main scale. And at least one light-receiving unit that receives light from the light source unit that has passed through the main scale, and the pair of the light source unit and the light-receiving unit and the main scale are relatively movable, and the movement position is detected. An optical encoder that satisfies the following conditional expressions.
d ₂ ≦ 2.5 × P ₂
However, d ₂ is the distance between the opening of the light receiving portion optical pattern of the main scale, P ₂ is a scale pitch of the main scale.

  The scale pitch of the main scale is preferably 50 μm or less. High-precision position detection is possible.

  It is preferable that the optical pattern of the main scale and the light receiving unit are arranged to face each other. The distance between the optical pattern of the main scale and the light receiving portion can be reduced, and a signal with a high S / N ratio can be obtained.

  In the first and second aspects of the invention, a liquid that is lubricious and transmits light is filled between the moving scale and the fixed scale, or between the main scale and the opening of the light receiving unit. It is desirable that The frictional resistance of the scale can be reduced. Further, since it is not necessary to provide a protective film for the scale, the distance between the moving scale and the fixed scale or the distance between the main scale and the opening of the light receiving unit can be shortened, and a signal with a high S / N ratio can be obtained. It is done.

  According to a third aspect of the present invention, a fixed scale having an optical pattern in which transmissive areas and non-transmissive areas are alternately arranged at a predetermined pitch is disposed opposite to the fixed scale so as to be movable relative to the fixed scale. A moving scale having an optical pattern in which transmission regions are alternately arranged at the same pitch as the fixed scale, a light source unit that irradiates light to the fixed scale and the moving scale, and a light source unit that transmits the fixed scale and the moving scale An optical encoder that detects the relative movement position of the fixed scale and the moving scale, and a light receiving section that receives light from the light source section reflected by either the fixed scale or the moving scale. In addition, the non-transmission area of at least one of the fixed scale and the moving scale is larger than the transmission area. Since the influence of the leakage light of the scale can be reduced, a signal with a high S / N ratio can be obtained.

  In the first, second and third inventions, it is desirable that the moving scale or the main scale is given a tension in the moving direction. The distance between the scales and the distance between the scale and the light receiving unit can be stabilized, and the S / N ratio of the signal can be stabilized.

  According to a fourth aspect of the present invention, there is provided an imaging optical system that forms an optical image of a subject, an imaging element that converts an optical image formed by the imaging optical system into an electrical signal, and a drive that moves a lens of the imaging optical system in the optical axis direction. And an optical encoder according to any one of claims 1 to 10, which detects the amount of movement of the lens and the lens moved by the driving unit.

  Since the optical encoder from which the influence of diffraction and leakage light is removed is provided, the lens position can be detected with high accuracy, and as a result, highly accurate lens control can be performed.

  It is possible to prevent a decrease in the S / N ratio due to scale diffraction or leakage light, and to perform highly accurate position detection. In an optical encoder with a scale pitch of 0.1 mm or less, especially 0.05 mm or less, it was difficult to detect the position with high accuracy due to the decrease in the S / N ratio. It becomes. When the optical encoder according to the present invention is used in an imaging apparatus, the position of a lens or the like can be detected with high accuracy, so that more accurate lens driving is possible and high-quality images are obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that, in the above-described conventional example and the embodiments described below, the same portions and corresponding portions are denoted by the same reference numerals, and redundant description is appropriately omitted.

  FIG. 7 is a block diagram illustrating a schematic configuration of an imaging apparatus according to an embodiment of the present invention. The imaging device 50 includes an imaging optical system 20 that creates an optical image of a subject, an imaging device 7 that changes the optical image into an electrical signal, an image processing unit 21 that processes an electrical signal from the imaging device 7, and zooming and autofocusing. A lens driving unit 23 having an actuator and a driving mechanism, an optical encoder 100 for detecting a lens position, a lens driving unit 23, an image processing unit 21 and the like, and a control unit 25 for controlling the entire imaging device 50, It has.

  The imaging optical system 20 forms an optical image of the subject on the imaging surface of the image sensor 7. The image sensor 7 is an image sensor in which a plurality of pixels are two-dimensionally arranged, and is, for example, a CCD (Charge Coupled Device). An optical image of a subject formed by the imaging optical system is converted into an image signal of R (red), G (green), and B (blue) color components (a signal composed of a signal sequence of pixel signals received by each pixel). Photoelectrically converted to output.

  The image signal is subjected to analog image processing, digital image processing, image compression processing, or the like in the image processing unit 21 as necessary. The image signal processed by the image processing unit 21 is recorded in a memory (not shown), or in some cases via a cable or converted into an infrared signal, and then recorded in an external personal computer (PC) or an external storage medium. Or

  An output signal from the optical encoder 100 is output to the control unit 25 as a digital signal. The optical encoder will be described later.

  The control unit 25 includes a microcomputer and detects the position of a lens included in the imaging optical system 20 based on an output from the optical encoder 100. Further, it controls output of the image processing unit 21, the lens driving unit 23, or image data.

  Next, the lens driving unit 23 of the imaging device 50 will be described. FIG. 6 shows a lens driving unit of the imaging device 20 including an optical encoder. The lens driving unit 23 is a friction drive type actuator 10a, 10b that transmits a driving force via a frictional force, and independently drives the ball frames 5, 6 that hold the lens.

  The actuators 10a and 10b are obtained by fixing bases 1a and 1b and drive shafts 3a and 3b to both ends of the piezoelectric elements 2a and 2b in the expansion and contraction direction, respectively. The drive shafts 3a and 3b are biased by the leaf springs 4b (only one is shown) in the grooves of the ball frames 5 and 6, and are frictionally coupled to the ball frames 5 and 6. Then, a drive voltage having a sawtooth pulse waveform, for example, is applied to the piezoelectric elements 2a and 2b, and the drive shafts 3a and 3b are vibrated at different speeds depending on the directions in the axial directions as indicated by arrows 90 and 92. 6 is moved along the drive shafts 3a and 3b. The ball frames 5 and 6 are guided in the optical axis direction by the guide shaft 8.

  A moving scale 102 is provided on the ball frames 5 and 6. The imaging device 50 is provided with an optical encoder 100 including a moving scale 102 in order to detect the amount of movement of the lens frames 5 and 6 (the optical encoder for the lens frame 5 is shown except for the moving scale 102). do not do).

  Next, the configuration of the optical encoder 100 will be described with reference to FIGS. FIG. 1 is a cross-sectional view of the optical encoder 100, and FIG. 2 is an enlarged cross-sectional view of the moving scale 102 and the fixed scale 103. Although not shown, a circuit is provided that converts an electrical signal from the light receiving element 110 into a digital signal and outputs the digital signal. The light emitting element 101, the fixed scale 103, and the light receiving element 110 are fixed to a fixed object 105. As shown in FIGS. 6 and 1, the fixed object 105 has a substantially U-shape. The light receiving element 110 is disposed on one of two opposing surfaces, and the light emitting element is disposed on the other side. 101 and a fixed scale 103 are fixed. One side of the opposite surface of the fixed object has a convex shape that is inclined in the moving direction of the lens, and the fixed scale 103 is fixed in an arcuate shape along this shape.

  One end of the moving scale 102 is directly fixed to the ball frame 6, and the other end is fixed to the ball frame 6 via a tension spring 104. The moving scale 102 is in a state of being pressed and in contact with the fixed scale 103, and moves integrally with the lens frame 6 while being in contact with the fixed scale 103 as the lens frame 6 moves in the optical axis direction. Since the moving scale 102 is in close contact with the fixed scale 103, the leakage light and transmitted light amount are not reduced as shown in FIGS. 12A and 12B, and the S / N ratio of the detection signal is reduced. do not do. Further, the S / N ratio of the detection signal does not change. In addition, since the moving scale 102 is pressed by the fixed scale 103 having an arcuate shape, wear abrasion due to the corner of the fixed object 105, which is a member to which the fixed scale is attached, and prevention of the central portion from being lifted due to poor contact are prevented. it can. An error may occur in the measurement value due to the fixed scale 103 being fixed in an arcuate shape, but this can be corrected by signal processing.

  The light emitting element 101 of the present embodiment is a light emitting diode, and is preferably disposed on the curvature center side of the fixed scale 103. This is because light is incident on the scale as perpendicularly as possible, thereby further reducing the influence of leakage light. The light emitting element 101 is not limited to a light emitting diode, and may be another element such as a laser diode. In addition, a phototransistor is used for the light receiving element 110. This is not limited to this element, but may be another element such as a photodiode.

  As shown in FIG. 2, the moving scale 102 and the fixed scale 103 have light shielding patterns 102b and 103b formed on substrates 102a and 103a made of transparent transparent polyethylene terephthalate (PET), respectively. Protective films 102c and 103c are formed thereon. The light shielding patterns 102b and 103b are made of aluminum and are manufactured by a general photolithography technique. The light shielding patterns 102b and 103b formed on the substrate are arranged so as to face each other. The protective films 102c and 103c are provided to prevent the light shielding pattern from being worn by sliding, and are made of a transparent ultraviolet curable resin. The thinner the protective film, the smaller the distance between the light shielding patterns 102b and 103b and the less the influence of leakage light or the like, but conversely the sliding wear resistance decreases. Therefore, in this embodiment, the thickness of the protective film on the pattern is set to 5 μm to balance the reciprocal relationship between the decrease in the S / N ratio and the sliding wear resistance.

The moving scale 102 of the present embodiment has a scale pitch of 8 μm and a duty ratio of 0.5. The scale pitch of the fixed scale 103 is 8 μm, and the duty ratio is 0.6. The distance between the light shielding pattern 102b of the moving scale 102 and the light shielding pattern 103b of the fixed scale 103 (hereinafter referred to as the distance between scales) is 10 μm because the thickness of the protective film on the pattern is 5 μm. The duty ratio is the length of the light shielding part with respect to one cycle of the scale pattern.
Duty ratio = light shielding area length / (light shielding area length + transmission area length)
It is. The distance from the light emitting element 101 to the fixed scale 103 is 1 mm, and the length of the light receiving element 110 in the scale moving direction is 0.15 mm. FIG. 3 shows a change in light intensity detected by the light receiving element 110. The horizontal axis is the amount of movement of the moving scale, the vertical axis is the light intensity, and the light intensity when there is no scale is 100. As shown in FIG. 3, a sufficient S / N ratio is obtained, and it is possible to provide a threshold value with two values and provide hysteresis. FIG. 4 is a graph showing the relationship between the distance between scales and the scale transmittance and the relationship between the distance between scales and the S / N ratio in this embodiment. The horizontal axis is the distance between the scales (mm), and the vertical axis is the S / N ratio calculated by the maximum transmittance (MAX), the minimum transmittance (MIN), and the maximum and minimum transmittances of the scale. is there. As the distance between the scales decreases, the maximum transmittance increases and the minimum transmittance decreases. This is because light leakage due to the scale and leakage light are reduced. In the case of this embodiment, the distance between scales is 0.01 mm, so the S / N ratio is 38. When the duty ratios of the moving scale 102 and the fixed scale 103 are both 0.5, the S / N ratio and the distance between the scales are approximately inversely proportional, and the S / N ratio and the scale pitch are approximately directly proportional. There is a relationship.

  Next, the relationship between the duty ratio and the S / N ratio will be described. The present embodiment is characterized in that the duty ratio of the fixed scale is larger than 0.5. When the duty ratio of the fixed scale is greater than 0.5, leakage light as shown in FIG. 12A can be suppressed. When the duty ratio is greater than 0.5, the maximum transmittance decreases, but the light intensity can be increased by increasing the power of the light source. However, it is difficult to reduce the minimum transmittance unless leakage light is suppressed. Therefore, in order to improve the S / N ratio, it is necessary to suppress leakage light.

  FIG. 5 shows the relationship between the distance between the scales and the S / N ratio when the duty ratio of the fixed scale is changed. As the duty ratio increases, the S / N ratio improves even at the same distance between scales. In other words, if the duty ratio is set large, the S / N ratio does not decrease even if the distance between the scales is increased. In the present embodiment, if the duty ratio is 0.6 or more, the thickness of the protective film 103c can be increased to improve the sliding wear resistance. Further, even when the moving scale 102 and the fixed scale 103 are not brought into contact with each other, the influence of diffraction and leakage light can be reduced. In this case, since the sliding load due to the contact of both scales is eliminated, the driving load is reduced. However, when the duty ratio is increased, the transmittance of the scale is lowered, and thus the noise is likely to be generated due to the influence of the thermal noise etc. of the light receiving element 110. Therefore, sufficient power is given to the light emitting element 101. Is desirable.

Here, the moving scale 102 and the fixed scale 103 desirably satisfy the following conditional expression (1), and more desirably satisfy the conditional expression (1 ′).
d ₁ ≦ 2.5 × P ₁ (1)
d ₁ ≦ 1.5 × P ₁ (1 ′)
However,
d ₁ : distance between the optical pattern of the moving scale and the optical pattern of the fixed scale,
P ₁ : Scale pitch of moving scale and fixed scale,
It is.

When the inter-scale distance d ₁ is larger than 2.5 times the scale pitch P ₁ , the influence of leakage light becomes large and a sufficient S / N ratio cannot be obtained. For example, when the amount of movement is detected by the two-division method, there is a difference depending on the intensity of the light source, but based on the light source intensity that is generally used, the S / N ratio is required to accurately detect with hysteresis. Is preferably 4 or more. From FIG. 5, in the case of a scale pitch of 8 μm, when the duty ratio is 0.5 and the distance between scales is about 20 μm, the S / N ratio is about 4, and the distance between scales is about 2.5 times the scale pitch. Yes.

  The S / N ratio and the distance between scales are approximately inversely proportional, and the S / N ratio and scale pitch are approximately directly proportional. Therefore, when the scale pitch is 20 μm and both scales have a duty ratio of 0.5, In order to achieve the S / N ratio of 4, the distance between the scales is 50 μm from FIG. When a scale of 20 μm or less is used, detection accuracy of 10 μm or less can be obtained by the two-segment method.

  When higher resolution is required, it is necessary to interpolate the signal, so a higher S / N ratio is required, but it is optimal in consideration of the amount of light emitted from the light emitting element, the distance between scales, etc. What is necessary is just to determine a duty ratio and the distance between scales.

Next, a second embodiment according to the present invention will be described. The imaging device of the second embodiment has the same configuration as the imaging device of the first embodiment, but only the optical encoder is different. A cross-sectional view of an optical encoder 200 according to the second embodiment is shown in FIG. The difference from the optical encoder of the first embodiment is that the type of configuration A does not have the fixed scale 103. The light receiving area of the light receiving element 110 (the opening of the light receiving element) is smaller than the light shielding area of the main scale 112. The scale pitch of the main scale 112 of this embodiment is 0.1 mm, and the distance between the opening of the light receiving element and the optical pattern of the main scale 112 is 0.2 mm. As a result, the S / N ratio can be improved without detecting diffracted light that has entered the main scale pattern unrelated to the light receiving element. The structure of the main scale 112 is the same as that of the moving scale 102 of the first embodiment. The surface on the side where the light shielding pattern of the main scale is formed is preferably on the light receiving element 110 side. Thereby, the space | interval of the light receiving element 110 and a light shielding pattern can be made small, and the influence of a diffracted light can be suppressed. In the second embodiment, it is desirable to satisfy the following conditional expression (2), and it is more desirable to satisfy the conditional expression (2 ′).
d ₂ ≦ 2.5 × P ₂ (2)
d ₂ ≦ 1.5 × P ₂ (2 ′)
However,
d ₂ : distance between the optical pattern of the main scale and the aperture of the light receiving element,
P ₂ : Scale pitch of the main scale,
It is.

When the distance d ₂ is greater than 2.5 times the scale pitch P _2, sufficient S / N ratio under the influence of diffraction can not be obtained.

  As a modification of the optical encoder of the second embodiment, a plurality of light receiving elements 110 may be provided. In this case, the light receiving elements 110 are arranged at a pitch that is an integral multiple of the scale pitch of the main scale 112. Thereby, the light from the light source 101 can be used effectively, and the influence of the noise component of the detection signal can be reduced. Further, when the light receiving element 101 is larger than the light shielding pattern, an opening smaller than the light shielding pattern 112b may be provided on the incident surface side of the light receiving element 110 so that light in a region other than the opening is not guided to the light receiving element 101. . If this opening and the main scale 112 are arranged so as to satisfy the conditional expression (2), the same effect can be obtained. By providing this opening, the detection area of the light receiving element 110 is not limited. That is, the opening (light receiving area) of the light receiving element 110 may be larger than the light shielding pattern. Further, a plurality of apertures smaller than the light shielding pattern at an integer multiple pitch of the light shielding pattern of the main scale 112 are arranged on the incident surface side of the light receiving element 101, and the openings are arranged so as to satisfy the main scale 112 and the conditional expression (2). Then, light can be used effectively and the influence of diffracted light can be suppressed. The provision of such an opening and the fact that the opening (light receiving area) of the light receiving element 110 is smaller than the light shielding pattern are equivalent to each other, and hence are referred to as the opening of the light receiving element without particular distinction.

  Next, a third embodiment according to the present invention will be described. The imaging device of the third embodiment has the same configuration as the imaging device of the first embodiment, but only the optical encoder is different. FIG. 9 schematically shows a cross section of the scale portion of the optical encoder 300 according to the third embodiment. The optical encoder 300 differs from the optical encoder 100 of the first embodiment in the position of the light receiving element 110, the moving scale 102, and the fixed scale 103. What is the scale pitch of the moving scale 102 and fixed scale 103? 0.05 mm, and the duty ratio is both 0.5. The distance between the opening of the light receiving element 110 and the optical pattern of the moving scale 102 is 0.2 mm.

  The opening of the light receiving element 110 is disposed in substantially contact with the moving scale 102. Thereby, the diffracted light by the scale does not wrap around and the S / N ratio is not lowered. Further, the moving scale 102 and the fixed scale 103 are in contact with each other.

  The moving scale 102 and the fixed scale 103 of the optical encoder 300 have a light shielding pattern formed on the substrate itself. That is, the substrate surface or the entire substrate is colored (dyed) to form a pattern. The colored portion is, for example, black and forms a light shielding region. With this configuration, the protective film as shown in FIG. 2 is not necessary, and the distance between the scales can be made substantially zero.

  In the embodiment described above, an optical encoder having a scale pitch of 0.1 mm or less is used. However, conditional expressions (1) and (1 ′), and conditional expressions (2) and (2 ′) are scale pitches. Even if it is applied to an optical encoder having a diameter of more than 0.1 mm, it is effective.

  Although the conditional expressions (1), (1 ′), (2), (2 ′) and the condition that the duty ratio is larger than 0.5 can be improved, the S / N ratio can be improved. By combining, the S / N ratio can be further improved.

  In addition to the embodiments described above, various modifications are possible. For example, each embodiment is an example of a transmission type, but a reflection type is also effective as a modification of the first embodiment. The light receiving element 110 is arranged on the same side as the light emitting element 101, and a non-reflective region (absorption or transmission region) and a reflective region are arranged on a scale arranged at least on the side opposite to the light source (light receiving) side among the moving scale and the fixed scale. A reflection type can be configured by forming a pattern composed of (non-transmission region). A signal having a large S / N ratio can be obtained by arranging the moving scale and the fixed scale so as to satisfy the conditional expression (1), or by making the duty ratio of the non-reflective region larger than 0.5.

  Moreover, in the said embodiment, although the fixed scale is arrange | positioned at the light source side, a fixed scale may be arrange | positioned at the light receiving element side. In the above embodiment, the duty ratio of the fixed scale is set to be larger than 0.5. However, the duty ratio of the moving scale may be made larger than 0.5 instead of the fixed scale, and there is a difference in effect. Absent. Alternatively, the duty ratio may be larger than 0.5 for both scales.

  In the first embodiment, the protective film is provided to protect the light shielding pattern formed on the substrate from sliding, but the protective film is not necessarily provided. Further, instead of the protective film, the space between both scales may be filled with a transparent transparent liquid. This can reduce frictional resistance and further reduce the distance between scales.

FIG. 3 is a diagram schematically showing a cross section of the optical encoder of the first embodiment. It is a figure which expands and shows the cross section of a scale typically. It is a figure which shows the change of the light intensity detected with the light receiving element. It is a graph which shows the relationship between the distance between scales and scale transmittance | permeability, and the relationship between the distance between scales and S / N ratio. It is a graph which shows the relationship between the distance between scales and S / N ratio at the time of changing Duty ratio. It is a figure which shows the lens drive part of the imaging device of 1st Embodiment. It is a block diagram which shows schematic structure of the imaging device of 1st Embodiment. It is a figure which shows typically the cross section of the optical encoder of 2nd Embodiment. It is a figure which shows typically the cross section of the scale part of the optical encoder of 3rd Embodiment. It is a figure which shows the conventional optical encoder. It is a figure which shows the signal processing for obtaining the digital signal of an optical encoder. It is a figure showing the cause which reduces S / N ratio.

Explanation of symbols

5, 6 Ball frame 7 Imaging element 20 Imaging optical system 50 Imaging apparatus 100 Optical encoder 101 Light emitting element 102 Moving scale 103 Fixed scale 104 Tension spring 105 Fixed object 110 Light receiving element 112 Main scale

Claims (11)

A fixed scale having optical patterns arranged at a predetermined pitch;
A moving scale having an optical pattern arranged to be movable relative to the fixed scale and arranged at the same pitch as the fixed scale;
A light source unit for irradiating light to a fixed scale and a moving scale;
A light receiving unit that detects a change in intensity of light from the light source unit as the moving scale moves, and an optical encoder that detects a relative moving position of the fixed scale and the moving scale,
An optical encoder that satisfies the following conditional expression,
d ₁ ≦ 2.5 × P ₁
However,
d ₁ : distance between the optical pattern of the moving scale and the optical pattern of the fixed scale,
P ₁ : Scale pitch of moving scale and fixed scale,
It is. The optical encoder according to claim 1, wherein a scale pitch of the fixed scale and the moving scale is 50 μm or less. The optical encoder according to claim 1, wherein the optical pattern of the fixed scale and the optical pattern of the moving scale are arranged to face each other. The optical encoder according to claim 1, wherein the fixed scale and the moving scale are in contact with each other. A main scale having an optical pattern in which transmission areas and light-shielding areas are alternately arranged at a predetermined pitch;
A light source unit that emits light to the main scale;
Having an opening smaller than the light-shielding region of the main scale, and comprising at least one light receiving unit that receives light from the light source unit that has passed through the main scale,
An optical encoder that detects a moving position of a pair of a light source unit and a light receiving unit and a main scale that is relatively movable,
An optical encoder that satisfies the following conditional expression,
d ₂ ≦ 2.5 × P ₂
However,
d ₂ : distance between the optical pattern of the main scale and the aperture of the light receiving unit,
P ₂ : Scale pitch of the main scale,
It is. 6. The optical encoder according to claim 5, wherein a scale pitch of the main scale is 50 μm or less. The optical encoder according to claim 5, wherein the optical pattern of the main scale and the light receiving unit are arranged to face each other. 2. A liquid having lubricity and transmitting light is filled between the moving scale and the fixed scale, or between the main scale and the opening of the light receiving unit. 5. The optical encoder according to 5. A fixed scale having an optical pattern in which transmission regions and non-transmission regions are alternately arranged at a predetermined pitch;
A moving scale having an optical pattern that is arranged so as to be movable relative to the fixed scale, and in which transmissive areas and non-transmissive areas are alternately arranged at the same pitch as the fixed scale;
A light source unit for irradiating light to a fixed scale and a moving scale;
A light receiving unit that receives light from the light source unit that has passed through the fixed scale and the moving scale, or light from the light source unit that is reflected by a non-transmissive region of either the fixed scale or the moving scale, and the fixed scale, An optical encoder for detecting a relative movement position of a movement scale,
An optical encoder, wherein a non-transmission area of at least one of a fixed scale and a moving scale is larger than a transmission area. 10. The optical encoder according to claim 1, wherein tension is applied to the moving scale or the main scale in a moving direction. An imaging optical system for forming an optical image of a subject;
An image sensor that converts an optical image formed by the imaging optical system into an electrical signal;
A drive unit that moves the lens of the imaging optical system in the optical axis direction;
An image pickup apparatus comprising: the optical encoder according to claim 1 that detects a moving amount of a lens that is moved by a driving unit.

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