KR101227125B1 - Optical encoder and displacement measurement method using the same - Google Patents

Abstract

The present invention relates to an optical encoder capable of miniaturization and an economical optical encoder and a displacement measuring method using the same, which can measure an absolute angle of high resolution with one track, and includes a light emitting part for irradiating light and a reflective member for reflecting light of the light emitting part. And a moving member having a diffraction grating disposed between the light emitting portion and the reflecting member in a direction crossing the traveling direction of light and arranged at a constant pitch along the moving direction, and with respect to the moving member in the same direction as the light emitting portion. Provided are an optical encoder having a first light receiving portion disposed and reflected by at least a portion of light reflected by a reflective member and diffracted by a diffraction grating, and a displacement measuring method using the same.

Description

Optical encoder and displacement measurement method using the same

 The present invention relates to an optical encoder and a displacement measuring method using the same, and more particularly, to an optical encoder and a displacement measuring method using the same, which can measure a high resolution absolute displacement with one track.

Motors used in precision instruments such as industrial robots and automation equipment are equipped with encoders to detect and control the rotation angle of the motor. An encoder is an electro-mechanical device that converts displacement of a moving object into an analog signal or a digital signal, and is mainly installed on a rotating shaft and used to measure the rotation angle or rotation speed of the rotating shaft.

There are two types of encoders, an incremental encoder and an absolute encoder.

The incremental encoder can measure the rotation angle by accumulating the pulse signal obtained from the light receiving unit as the disk on which the regular pattern is recorded rotates. Incremental encoders have the advantage of high resolution and high speed control, but they can only measure relative changes in angles, so if the power is turned off, the rotation angle is not immediately known even when the power is turned on. there is a problem.

Absolute encoders make the disc pattern different for each angle, and can read the unique pattern to measure the corresponding absolute angle. Absolute encoder has the advantage of knowing the rotation angle immediately when the power is applied, but it is difficult to miniaturize, low resolution, and slow control speed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical encoder suitable for miniaturization and cost reduction, and a displacement measuring method using the same, capable of measuring high resolution absolute displacement with one track.

According to one aspect of the invention, the light emitting portion for irradiating the light, the reflective member for reflecting the light of the light emitting portion, and disposed between the light emitting portion and the reflective member to move in a direction crossing the direction of light travel along the moving direction A moving member having a diffraction grating arranged at a constant pitch, and a first light receiving light interfering with the moving member in the same direction as the light emitting portion and reflected by at least a portion of the light diffracted by the diffraction grating, which is reflected by the reflective member An optical encoder having a light receiving unit is provided.

In the present invention, the moving member may be a rotating disk that rotates about a rotating shaft provided in the center.

In the present invention, a lens interposed between the light emitting portion and the moving member, the lens irradiated from the light emitting portion may be further provided with a lens.

In the present invention, the first signal processing unit for calculating the relative displacement from the interference light obtained by the first light receiving unit may be further provided.

In the present invention, the first light receiving unit may be disposed to correspond to a point where at least a portion of the diffracted light meets and causes interference while passing through the diffraction grating.

In the present invention, a plurality of first light receiving units may be provided.

In the present invention, the reflective member may be disposed to be attached to one surface of the movable member.

In the present invention, the reflective member and the moving member may be horizontal.

In the present invention, the reflective member and the movable member can be inclined.

In the present invention, the diffraction grating may include a light transmitting part having a width corresponding to any one of two different values so as to form an identifiable code for each section.

In the present invention, the width of the light transmitting portion may be 1/3 or 2/3 of the pitch of the diffraction grating.

In the present invention, the light irradiated from the light emitting portion may further include a second light receiving portion for receiving light reflected from the surface of the diffraction grating.

In the present invention, the second signal processing unit for calculating the absolute displacement from the reflected light obtained by the second light receiving unit may be further provided.

According to another aspect of the invention, the step of irradiating light to the moving member having a diffraction grating disposed at a constant pitch along the moving direction, the light incident on the diffraction grating is diffracted and reflected by the reflective member, the diffraction grating And receiving the interference light that passes through and receives at least a portion of the diffracted light, and calculates a relative displacement of the moving member from the interference light.

In the present invention, the moving member may be a rotating disk that rotates about a rotating shaft provided in the center.

In the present invention, the diffraction grating may include a light transmitting part having a width corresponding to any one of two different values so as to form an identifiable code for each section.

In the present invention, the width of the light transmitting portion may be 1/3 or 2/3 of the pitch of the diffraction grating.

In the present invention, the method may further include receiving light reflected from the surface of the diffraction grating and calculating an absolute displacement from a signal of the received light.

In the present invention, the method may further include combining a relative displacement and an absolute displacement.

In the present invention, by adjusting the distance or angle with respect to the moving member of the reflective member, the position where the diffracted light meets to form the interference light can be adjusted.

By the optical encoder and the displacement measuring method using the same structure as described above, it is possible to measure absolute displacement of high resolution while being suitable for miniaturization and cost reduction with one track.

1 is a perspective view schematically showing an optical encoder according to an embodiment of the present invention.
FIG. 2 is a schematic perspective view of a portion of the optical encoder of FIG. 1. FIG.
3 is a plan view schematically illustrating a portion of an optical path of the optical encoder of FIG. 1.
4 is a plan view illustrating an embodiment of a slit pattern of an optical encoder.
5 is a perspective view schematically showing a modification of the optical encoder according to the embodiment of FIG. 1.
FIG. 6 is a flowchart illustrating steps of a displacement measuring method using an optical encoder according to the embodiment of FIG. 1.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following drawings, like reference numerals refer to like elements, and the size of each element in the drawings may be exaggerated for clarity and convenience of explanation.

1 is a perspective view schematically showing an optical encoder according to an embodiment of the present invention, Figure 2 is a perspective view schematically showing a part of the optical encoder of FIG.

1 and 2, the optical encoder according to the present embodiment includes a light emitting unit 30 for irradiating light, a reflective member 20 for reflecting light from the light emitting unit 30, and a light emitting unit 30. And a moving member 10 disposed between the reflective member 20 and the reflective member 20 in a direction crossing the traveling direction of light, and having a diffraction grating 11 disposed at a constant pitch p along the moving direction, A first light disposed in the same direction as the light emitter 30 with respect to the moving member 10 and receiving light that is reflected by the reflective member 20 and at least a part of the light diffracted by the diffraction grating 11 interferes with the moving member 10 The light receiving part 41 is provided. In addition, a part of the light irradiated from the light emitting part 30 may be further reflected by the surface of the diffraction grating 11 of the moving member 10, and may further include a second light receiving part 42 which receives the reflected light. have.

The moving member 10 may be a rotating disk having a central portion fixed to the rotating shaft 50. Therefore, the movable member 10 is disposed to be rotatable about the rotation center axis line together with the rotation shaft 50. However, the moving member 10 is not limited to the rotating disk, and may be in various forms, and the moving member 10 may be a rotating member, and includes all members moving in various ways such as a linear moving member.

On the moving member 10, a diffraction grating 11 having a constant pitch p is disposed along the circumference of the rotation axis 50 at a predetermined distance from the rotation axis 50. The diffraction grating 11 has a form in which a plurality of light transmitting portions 11a and light blocking portions 11b are alternately arranged in succession. The pitch p of the diffraction grating 11 is a straight line distance of one side of the light transmitting portion 11a perpendicular to the rotational direction and one side of the light transmitting portion 11a perpendicular to the rotational direction of the diffraction grating 11. Corresponds to

The width of the light transmitting part 11a may be smaller than the wavelength λ of light, so that diffraction may occur easily. The light transmitting portion 11a of the diffraction grating 11 may be an slit-shaped opening penetrating the moving member 10, but is not limited thereto, and includes a depression and a protrusion, and a region corresponding to the depression or the protrusion is The diffraction grating comprised from the member, such as glass which has transparency, etc. are also included.

In order to increase the angular resolution, the diffraction grating 11 is preferably formed in a region adjacent to the circumference of the moving member 10.

The light emitting unit 30 is disposed in one direction of a surface on which the diffraction grating 11 of the moving member 10 is formed, and irradiates light to one region of the diffraction grating 11. Since the moving member 10 moves relative to the light emitting part 30, the position of the diffraction grating 11 to which light is irradiated changes as the moving member 10 moves.

The light emitting unit 30 may be a light emitting diode (LED) or a laser. Between the light emitting unit 30 and the moving member 10 may further include a collimator (collimator) such as a lens 60 so that the light irradiated from the light emitting unit 30 proceeds in parallel, the light emitting unit 30 And lens 60 may be integrally formed.

When light is irradiated to the diffraction grating 11 by the light emitting part 30, part of the light is reflected directly on the surface of the diffraction grating 11, and the other part is transmitted through the light transmitting part 11a of the diffraction grating 11. While diffracted.

Light transmitted through the light transmitting portion 11a of the diffraction grating 11 is diffracted, and the diffracted light is reflected by the reflecting member 20 and is incident on the diffraction grating 11 again. The light reincident to the diffraction grating 11 is diffracted again by the light transmitting part 11a of the diffraction grating 11.

The reflective member 20 may be a reflective mirror coated with silver (Ag), aluminum (Al), or the like.

At least a portion of the light transmitted twice through the diffraction grating 11 by the reflective member 20 meets each other and causes interference. Since the light passes through different paths, interference occurs due to a phase difference according to the difference in the light paths, and as the moving member 10 moves, the difference between the light paths of the two light changes, so that the intensity of the interference light in one region is increased. Change. In this case, the intensity of the interference light may vary in the form of a triangular wave or a sinusoidal wave.

The first light receiving portion 41 is disposed in an area where the interference light is formed, and receives an optical signal causing interference and converts it into an electrical signal. The relative moving distance of the moving member 10, that is, the relative displacement can be calculated from the interference signal. In this embodiment, since the displacement corresponds to the rotation angle, the relative rotation angle can be calculated from the displacement.

The reflective member 20 may be disposed in parallel with the surface of the moving member 10 having the diffraction grating 11 or may be inclined. In addition, the distance between the reflective member 20 and the movable member 10 can be adjusted, and the reflective member 20 is coated on one surface of the movable member 10 on which the diffraction grating 11 is formed by coating or the like. It may be arranged to be attached.

Since the light path varies depending on the distance between the reflective member 20 and the movable member 10 or the angle formed by the two surfaces, the position where the light meets again by adjusting it, that is, the position where the first light receiving portion 41 is disposed Can be adjusted.

Therefore, when a plurality of first light receiving portions 41 are arranged, the distance between the first light receiving portions 41 can be adjusted.

The first signal processing unit 71 may correct the error from the signal obtained by the first light receiving unit 41 and multiply to calculate information about relative displacement having high resolution and precision.

Light reflected directly from the surface of the diffraction grating 11 is received by the second light receiving portion 42. The second light receiving portion 42 is disposed to be symmetrical with the light emitting portion 30 with respect to the surface perpendicular to the surface on which the diffraction grating 11 is disposed. Since the light emitter 30 is disposed at a predetermined distance from the vertical plane, the incident light and the reflected light are spatially separated.

In addition, since the light reflected from the surface of the diffraction grating 11 and the light reflected from the reflective member 20 are also spatially separated, the first light receiving portion 41 and the second light receiving portion 42 are spaced apart from each other. The distance between the first light receiving portion 41 and the second light receiving portion 42 can be adjusted by changing the distance or angle of the reflective member 20 and the moving member 10 as described above.

The diffraction grating 11 has a light shielding portion 11b disposed between the light transmitting portion 11a and the light transmitting portion 11a, and the light blocking portion 11b has better surface reflection than the light transmitting portion 11a. . If the light transmitting portion 11a is an opening, the reflectance at the light transmitting portion 11a will be approximately zero.

The width of the light transmitting part 11a may have any one of two different values so as to form an identifiable code for each section.

The second light receiver 42 is an image pickup device that receives the received light and converts the received light into an electrical signal. The second light receiver 42 may be a one-dimensional or two-dimensional photodiode array or a charge coupled device (CCD).

 The second light receiving unit 42 detects light having information on the arrangement of the light transmitting unit 11a and the light blocking unit 11b of the diffraction grating 11 and converts the light into an electrical signal, and the second light receiving unit 42 ) By the second signal processor 72 connected to the absolute displacement, that is, the absolute rotation angle corresponding thereto. This will be described later.

The first signal processor 71 and the second signal processor 72 may be integrally formed.

The high resolution absolute displacement can be measured by combining the relative displacement of the high resolution obtained by the first light receiving part 41 with the information about the absolute displacement obtained by the second light receiving part 42.

3 is a plan view schematically illustrating a portion of an optical path of the optical encoder of FIG. 1.

Referring to FIG. 3, a path of light diffracted through the light transmitting part 11a of the diffraction grating 11 among the light emitted from the light emitting part 30 to the moving member 10 is schematically illustrated. Light reflected directly from the surface of the moving member 10 is omitted in this figure.

Light emitted from the light emitting portion 30 is incident on the diffraction grating 11 of the moving member 10 and diffracted while passing through the light transmitting portion 11a. At this time, the light is diffracted in a specific direction according to Equation 1 according to the wavelength λ and the incident angle θi.

(1)

p (sinθm + sinθi) = mλ

Here, p is the pitch of the diffraction grating 11, m is the diffraction order, θ m is the exit angle.

FIG. 3 shows only the case where θ i is 90 degrees, the diffraction order m is 0, and -1 and +1. The diffracted light is reflected by the reflecting member 20 and is incident again to the moving member 10. The light reincident to the moving member 10 is diffracted in a specific direction again according to Equation 1 above.

At this time, light having a diffraction order of zero among the light diffracted in the first order by the moving member 10 is reincident to the moving member 10 so that light having a diffraction order of +1 in the second diffracted light (0, + 1) And light having a diffraction order of -1 is re-entered to the moving member 10 among the first diffracted light so that a region where light (-1, -1) having a diffraction order of -1 meets in the second diffracted light exist. Since the path of the two light travels is different, there is a phase difference, causing interference in the region. The phase difference changes according to the moving distance of the moving member 10.

Similarly, light having a first order diffraction order of zero and a second order diffraction order of -1 (0, -1), and light having a first order diffraction order of +1 and a second order diffraction order of +1 (+1, +1) This meeting area exists.

The first light receiver 41 is disposed in the region to receive an interference signal and convert it into an electrical signal. The first light receiver 41 may be a photodiode array or a plurality of first light receivers 41.

In this embodiment, the first light receiving portion 41 is disposed in an area where (0, + 1) and (-1, -1) meet and an area where (0, -1) and (+ 1, + 1) meet, respectively. The case is illustrated.

4 is a plan view illustrating an embodiment of a slit pattern of an optical encoder.

Referring to FIG. 4, the diffraction grating 111 is disposed on the moving member 110. The diffraction grating 111 is arranged at a constant pitch p and includes a light transmitting part 111a and a light blocking part 111b. The width of the light transmitting part 111a may have any one of d1 and d2 and is continuously disposed on the moving member 110 along the rotational direction to form a code that can be identified for each section. The width of the light blocking unit 111b has any one of p-d1 and p-d2. Here, p means pitch and d1, d2 means the width of the light transmitting portion (111a).

At this time, d1 may be 1/3 times the pitch p, and d2 may be 2/3 times the pitch p.

When the width of the light transmitting part 111a is d1, it may correspond to the binary number “0”, and in the case of d2, it may correspond to the binary number “1”. In other words, the diffraction grating 111 forms a binary code consisting of a continuous array of zeros and ones.

The diffraction grating 111 may be applied to the optical encoder according to the exemplary embodiment of FIG. 1. A part of the light irradiated to the diffraction grating 111 from the light emitting part 30 is reflected on the surface of the diffraction grating 111 to reach the second light receiving part 42.

In this case, the second light receiver 42 may acquire light corresponding to the plurality of light transmitting parts 111a and the light blocking parts 111b and converts the light into an electrical signal. The obtained light may not be reflected in the light transmitting part 111a or only a part of light is reflected, and the light is relatively well reflected in the light blocking part 111b, and thus may have a substantially pulse shape. Since the width of such a pulse varies depending on the widths d1 and d2 of the light transmitting part 111a, a binary code signal composed of 0 and 1 can be obtained from the pulse signal.

This embodiment illustrates an optical encoder having a resolution of an absolute rotation angle of 3 bits from light reflected at the surface of the diffraction grating 111. This is an example for explaining the principle of the present invention can be implemented in various resolutions, the resolution may be more than 10 bits.

This embodiment has a binary code signal of "001011100". In this case, the second light receiver 42 reads the binary code signal in units of 3 bits. That is, as the moving member 110 rotates, six signals of “001”, “010”, “101”, “011”, “111”, “110”, and “100” can be read, and each signal is read. Has a unique value and corresponds to rotation angles of 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees, and 315 degrees, respectively. This represents a case where the resolution is 3 bits, that is 45 degrees.

By the above method, the absolute displacement of the moving member 110 can be calculated by the second light receiving portion 42, and the resolution corresponding to the pitch p of the diffraction grating 111 can be obtained. However, as described above, since the interference signal of the light diffracted by the diffraction grating 111 is received by the first light receiver 41, a relatively high resolution relative displacement signal can be obtained. Thus, the first light receiver 41 and the second light receiver can be obtained. By combining the signals obtained at the light receiving portion 42, it is possible to calculate a high resolution absolute displacement, that is, an absolute rotation angle corresponding thereto.

5 is a perspective view schematically showing a modification of the optical encoder according to the embodiment of FIG. 1.

Referring to FIG. 5, the other configuration is the same as that of FIG. 1, and there is a difference only in the position where the moving member 210 and the diffraction grating 211 are disposed on the moving member 210.

The central portion of the moving member 210 is fixed to the rotation shaft 250, is arranged to be rotatable about the rotation center axis line, the disk portion 215 and the disk portion 215 horizontal to the rotation axis 250. Along the circumference of, the extension portion 217 extends perpendicularly to the disk portion 215.

The diffraction grating 211 is disposed at a constant pitch p 'along the perimeter of the extension 217.

The light emitter 230, the reflective member 220, the first light receiver 241, and the second light receiver 242 are disposed to correspond to the arrangement of the diffraction grating 211. In the present exemplary embodiment, the light emitting unit 230 and the light receiving unit 241 and 242 are disposed outside the disk unit 215, and the reflective member 220 is disposed inside the disk unit 215. It may also be configured in reverse.

FIG. 6 is a flowchart illustrating steps of a displacement measuring method using an optical encoder according to the embodiment of FIG. 1. Since the displacement measuring method is mentioned together with the optical encoder in FIGS. 1 to 4, the following description will be briefly provided.

Referring to FIG. 6, the method includes irradiating light to the moving member 10 (S100), receiving interference light (S130), and calculating a relative displacement (S140). In addition, the method may further include receiving the light reflected from the surface of the diffraction grating 11 (S110), calculating the absolute displacement (S120), and combining the relative and absolute displacements (S150). have.

In the step S100 of irradiating light to the moving member 10, the light emitting unit 30 and the reflective member 20 are disposed between the moving member 10 having the diffraction grating 11 and the moving member 10. And aligning and irradiating light to the moving member 10 from the light emitting unit 30. At this time, the light is irradiated to correspond to the diffraction grating 11 disposed on the moving member 10.

The reflective member 20 may be attached to the opposite surface where the light emitting portion 30 of the moving member 10 is disposed by coating or the like, and may be separately spaced apart from the moving member 10 by a predetermined interval. .

Receiving the interference light (S130) includes the step of receiving by the first light receiver 41 the interference light reflected by the reflective member 20 and formed by the light diffracted by the diffraction grating 11. do. In this case, the first light receiver 41 is disposed to correspond to the region where the diffracted light meets as described with reference to FIG. 3. At this time, the position of the first light receiving portion 41 is determined by adjusting the distance and angle between the reflective member 20 and the moving member 10, and the interference light is received by the first light receiving portion 41.

The calculating of the relative displacement (S140) includes calculating the relative displacement of the moving member 10 from the interference light received by the first light receiving portion 41. Since the interference light may be in the form of a substantially triangular wave or sinusoidal wave, it may be multiplied and corrected to yield a high resolution relative displacement.

The diffraction grating 11 may include a light transmitting part 11a having a width corresponding to any one of two different values so as to form an identifiable code for each section, and the width of the light transmitting part 11a is It may be 1/3 or 2/3 of the pitch p of the diffraction grating 11.

Receiving the light reflected from the surface of the diffraction grating 11 (S110) and calculating the absolute displacement (S120) receives the light reflected from the surface of the diffraction grating 11 by the second light receiving portion 42 And calculating an absolute displacement therefrom.

Combining the relative displacement and the absolute displacement (S150) is a combination of the information on the high resolution relative displacement obtained in the first light receiving portion 41, and the information on the absolute displacement obtained in the second light receiving portion 42 by combining a high resolution Measuring an absolute displacement.

Although the above-described embodiment of the present invention has been described with respect to the rotating member, the moving member is not limited to this, and includes all members moving in various ways such as a linear moving member, and the displacement is a linear moving distance and a rotation angle. It includes all of them.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

10: moving member 11: diffraction grating
11a: light transmitting portion 11b: light blocking portion
20: reflection member 30: light emitting portion
41: first light receiver 42: second light receiver
50: axis of rotation 60: lens
71: first signal processor 72: second signal processor

Claims (20)

Light emitting unit for irradiating light;
A reflective member for reflecting light of the light emitting portion;
A moving member disposed between the light emitting unit and the reflective member to move in a direction crossing a traveling direction of light and having a diffraction grating disposed at a constant pitch along the moving direction; And
And a first light receiving portion disposed in the same direction as the light emitting portion with respect to the moving member and receiving light that is reflected by the reflective member and at least a portion of the light diffracted by the diffraction grating interferes with the moving member. The method according to claim 1,
The moving member is an optical encoder which is a rotating disk rotating about a rotation axis provided in the center. The method according to claim 1,
An optical encoder interposed between the light emitting portion and the moving member, the lens further comprises a lens for making the light emitted from the light emitting portion into parallel light. The method according to claim 1,
An optical encoder further comprising a first signal processing unit for calculating a relative displacement from the interference light obtained by the first light receiving unit. The method according to claim 1,
And the first light receiving portion is disposed to correspond to a point where at least a portion of the diffracted light meets and causes interference while passing through the diffraction grating. The method according to claim 1,
And an optical encoder having a plurality of first light receiving units. The method according to claim 1,
And the reflective member is disposed to be attached to one surface of the movable member. The method according to claim 1,
And the reflecting member and the moving member are horizontal. The method according to claim 1,
And the reflective member and the movable member are inclined. The method according to claim 1,
The diffraction grating includes an optical encoder having a light transmission part having a width corresponding to any one of two different values so as to form an identifiable code for each section. The method of claim 10,
And the width of the light transmitting portion is 1/3 or 2/3 of the pitch of the diffraction grating. The method according to claim 10 or 11,
And a second light receiver configured to receive light reflected from the surface of the diffraction grating by light emitted from the light emitter. The method of claim 12,
And a second signal processing unit for calculating an absolute displacement from the reflected light obtained by the second light receiving unit. Irradiating light on a moving member having a diffraction grating disposed at a constant pitch along the moving direction;
Light incident on the diffraction grating is diffracted and reflected by a reflecting member to receive interference light passing through the diffraction grating and formed by at least a portion of the diffracted light meet and form; And
Calculating a relative displacement of the moving member from the interference light. 15. The method of claim 14,
The moving member is a displacement measuring method is a rotating disk that rotates about a rotation axis provided in the center. 15. The method of claim 14,
The diffraction grating includes a light transmitting part having a width corresponding to any one of two different values to form an identifiable code for each section. 15. The method of claim 14,
And the width of the light transmitting portion is 1/3 or 2/3 of the pitch of the diffraction grating. The method according to claim 16 or 17,
Receiving light reflected from a surface of the diffraction grating; And
Calculating an absolute displacement from the signal of the received light. 19. The method of claim 18,
Combining the relative displacement with the absolute displacement. The method of claim 14,
And adjusting a distance or angle of the reflective member to the moving member to adjust a position at which the diffracted light meets to form interference light.

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