JP2001141523A - Rotary encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance angle resolution for a rotary encoder utilizing a moire inference fringe. SOLUTION: This encoder is provided with a rotary FZP array 11 wherein plural rotary FZPs 111a having the same focal distance are arranged inside the first circumferential part 11a of a rotary disk 10 at pesrcibed spacing, and wherein rotary FZPs 111b, 111c having the same focal distance within the same circumferential part are arranged in at least one circumferential part in an inner side of the first circumferential part 11a to interpolate a space between the rotary FZPs 111a, LEDs 14, 15 for emitting parallel beams from a direction orthogonal to the rotary FZP array, plural fixed FZPs 122a-122c arranged in a row to correspond to the circumferntial parts in a radial direction of the rotary disk 10 by the same number as the number of the circumfernetial parts in an incident position of transmitted beams in the rotary FZPs, and different slightly in their focal distances from the focal distances of the rotary FZPs in the circumferential parts corresponding thereto, and two-split PDs 16a-16c arranged in a position where a moire FZP generated by moire intefernce between the rotary FZPs and the fixed FZPs coverges the emitted beams.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary encoder for detecting a rotation angle by using moire interference fringes generated when a Fresnel zone plate is superimposed.

[0002]

2. Description of the Related Art When one straight line group or curve group is overlapped with another straight line group or curve group at a predetermined angle or less, a moire interference fringe is newly formed by a group of straight lines or curves connecting the intersections of the two. It is known as a band-shaped pattern formed. That is, as shown in FIG. 4, when the slits 30 and the slits 31 made of light and dark fringes are overlapped, moire interference fringes 32 are generated. Here the slits 30, 31
Assuming that the mutual intersection angle, that is, the inclination is θ, and the fringe interval between the slits 30 and 31, that is, the lattice constant, is w, when θ is sufficiently small, the moire interference fringe interval W is expressed by Expression 1.

[0003]

[Equation 1] W ≒ w / θ

Equation 1 shows that the moire interference fringe interval W is substantially equal to a value obtained by multiplying the lattice constant w by 1 / θ. That is, the moire interference fringe device in which the two slits 30 and 31 intersect at the predetermined angle θ has an action of enlarging the grating structure. Slit 3 for fixed slit 30
When 1 moves in the direction of arrow A in the figure (the direction orthogonal to the slit 31), the moire interference fringes 32 also move. Slit 3
By measuring the displacement of the moiré interference fringe 32 in which the displacement in the direction of arrow A of 1 is magnified 1 / θ times, the detection accuracy can be improved as compared with the case where the displacement of the slit 31 is directly measured. Note that each time the slit interval w moves by one, the moire interference fringes 32 also move by one.

FIG. 5 shows a configuration of a conventional rotary encoder utilizing the above-described moire interference fringe technique. In the figure, a fixed slit plate 21 is arranged below a rotating slit plate 20, and parallel light is emitted from above the rotating slit plate 20 by a LED 22 via a lens 23. The light transmitted through the rotary slit plate 20 is transmitted through the fixed slit plate 21 and then passed through the phototransistors 24 and 25.
Incident on. Here, the slit of the rotary slit plate 20 corresponds to one slit 31 in FIG. 4, and the slit of the fixed slit plate 21 corresponds to the other slit 30 in FIG.
Is equivalent to With the rotation of the rotary slit plate 20, the moire interference fringes formed by the transmitted light of both slit plates 20, 21 move, and the displacement is changed by the phototransistor 2.
If measured from the output signals of 4, 25, the rotating slit plate 2
A rotation angle of 0 can be detected.

[0006]

In recent years, there has been a demand for further improving the angular resolution of a rotary encoder using moiré interference fringes. Therefore, the present invention improves the angular resolution of a rotary encoder by using moiré interference fringes generated when the Fresnel zone plates described below are superimposed.

[0007]

First, position displacement is detected with high resolution using moire interference fringes generated when two Fresnel zone plates (hereinafter, referred to as FZPs) having slightly different focal lengths are superimposed. The method is known from the following document: Reference: S. Kawai et al., “Highly Precise Alignments Usin”
g Moire DiffractionMethods ”, Japanies Journa1 of
Applied Physics Vol 37 (1998) pp. 3691-3694.

The outline of this method will be described below. FZP is
As shown in FIG. 3, two opaque rings and transparent rings are concentrically and alternately arranged, and have a lens function of condensing light. When two FZPs 50 and 51 formed so as to have slightly different focal lengths overlap each other, Moire interference occurs and a new FZP
P occurs. The above-mentioned literature discloses a method for performing high-resolution position detection using this phenomenon.

The principle of position detection will be described with reference to FIG. In FIG. 2, the reference FZP 51 is a fixed FZP.
P. Another FZP is a moving FZP50,
Move with respect to the reference FZP 51. These two FZPs
As a result of the moiré interference caused by the overlap of 50 and 51, a part of the new FZP (moire FZP53 shown in FIG. 2) is generated. When the moving FZP 50 moves at the speed v in a state where the parallel FZPs 50 and 51 are irradiated with the parallel light beam 52, the moving speed V of the moiré FZP 53 (moire FZ
The focal point moving speed of P53) is expressed by Expression 2.

[0010]

V = f1.v / (f2-f1) = Mv

Here, f1 is the focal length of the reference FZP 51, and f2 is the focal length of the moving FZP 50. Also, M
= F1 / (f2-f1). As is clear from Equation 2, the moving speed V of the moire FZP53 is equal to the moving speed FZP50.
Is multiplied with respect to the moving speed v, and the multiplication factor M increases as the difference (f2-f1) between the focal length f2 of the moving FZP 50 and the focal length f1 of the reference FZP 51 decreases. By detecting the movement of the focal position of the moiré FZP 53 by the two-division photodiode 54, it is possible to detect the movement amount and the movement direction of the movement FZP 50, and furthermore, the position of the movement FZP 50 with high resolution.

The rotary encoder according to the present invention is configured to detect angular displacement by applying the above-described principle of position detection. That is, in the invention described in claim 1, a plurality of rotating FZPs having the same focal length are arranged at predetermined intervals in a first circumferential portion of a rotating disk, and one or more rotating FZPs inside the first circumferential portion are arranged. The rotation FZP having the same focal length within the same circumference is rotated by the rotation FZP of the first circumference.
Rotational FZ sequentially arranged so as to interpolate the mutual interval
A P array, a light source device that irradiates parallel light from a direction perpendicular to the rotating FZP array, and a radial number of the rotating disk in a position where the transmitted light of the rotating FZP is incident, the same number as the number of the circumferential portions. A plurality of fixed FZs arranged in a row corresponding to the circumferential portion and having a focal length slightly different from the focal length of the rotating FZP of the corresponding circumferential portion.
P, and a photodetector arranged at a position where moiré FZP generated by moiré interference between the rotating FZP and the fixed FZP condenses irradiation light from the light source device.

According to a second aspect of the present invention, in the first aspect of the present invention, the light receiver is divided into two parts along the rotation direction of the rotating disk.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1A is a perspective view illustrating a configuration of an embodiment of a rotary encoder according to the present invention. In the figure, reference numeral 10 denotes a rotating disk, and a rotation F
A ZP array 11 is formed. Rotating FZP array 1
1 is provided on a first circumferential portion 11a located at the outermost periphery of the rotating disk 10 with a rotating FZP having a focal length f2.
A plurality of rotations FZP (in the sense of ZP) 111a are arranged at predetermined intervals over the entire circumference. Further, the rotation FZ having the focal length f2 is similarly applied to the second circumferential portion 11b and the third circumferential portion 11c inside the first circumferential portion 11a.
A plurality of P111b and 111c are arranged at predetermined intervals over the entire circumference. Here, for convenience of explanation, the rotation F
Although it has been described that the focal lengths of the ZPs 111a, 111b, and 111c are all the same f2, they may be different from each other. In other words, if the focal lengths of a plurality of rotating FZPs in the same circumferential portion are the same. good. The rotation FZP 111b of the second circumferential portion 11b and the third circumferential portion 11c,
111c is an adjacent rotating FZP in the first circumferential portion 11a.
111a are sequentially shifted in the circumferential direction so as to interpolate the interval along the circumferential direction of 111a.

An LED 14 and a lens 15 are disposed on the left side of the rotary FZP array 11.
The parallel FZPs 111a to 111c are radiated so that the parallel light having passed through the FZP 5 is orthogonal to the rotating FZP array 11. The LED 14 and the lens 15 constitute a light source device according to the present invention. Further, a fixed reference FZP array 12 is disposed on the right side of the rotating FZP array 11 on the opposite side of the light source device, and the reference FZP array 12 has a small focal length f2 of the rotating FZPs 111a to 111c. FZP with different focal length f1 (rotational FZP
122a to 122c are arranged in a row in the radial direction of the rotating disk 10 corresponding to the respective circumferential portions. Here, the fixed FZPs 122a to 122c are described as all having the same focal length f1, but they may be different from each other. In short, the rotation FZP11 of the circumferential portion of the corresponding rotary FZP array 11 is essential.
It suffices if the focal lengths are slightly different for the focal lengths 1a to 111c. Further, the number of fixed FZPs is equal to the number of circumferential portions of the rotating FZP array 11 (3 in the embodiment). In addition,
Fixed FZPs 122a to 122c are rotating FZPs 111a to
It is arranged at the position where the transmitted light of 111c is irradiated.

On the right side of the reference FZP array 12, the rotary FZPs 111a to 111c and the fixed FZPs 122a to
As a result of the moiré interference caused by the moiré 122c, two-part photodiodes (PD) 16a to 16c are vertically arranged at positions where the irradiation light of the light source device is converged by the newly generated moiré FZP so as to correspond to the fixed FZPs 122a to 122c. Photo diode (PD) array 13 arranged at
Are arranged. These two-part photodiodes 1
Each of 6a to 16c is divided into two along the rotation direction of the rotating disk 10 (rotating FZP array 11).

FIG. 1B shows the rotating FZPs 111a to 111a.
It is explanatory drawing of the positional relationship between 1c and fixed FZP122a-122c. Assuming that the rotating FZP array 11 rotates in the direction of arrow B in the figure and the rotating FZP 111a and the fixed FZP 122a overlap on the optical path of the LED 14, moire FZP occurs on the fixed FZP 122a as shown in FIG. As described above, the moving speed V of the moire FZP
Is the moving speed of the rotating FZP array 11 (rotating FZP 111
a), which is M times the moving speed of a).
In the two-segment photodiode 16a where the ZP condenses the irradiation light of the light source device, the rotating FZP 111a
Can be detected as an electric signal by replacing the moving speed (peripheral speed) v with a moving speed (peripheral speed) V that is M times the moving speed.

Here, since it is easy to convert the peripheral speed into a rotation angle, the rotation angle of the rotary FZP array 11 can be detected from the output signal of the two-part photodiode 16a. Also, a multiplication factor M for determining the angular resolution
Is the focal length f2 of the rotating FZP 111a and the fixed FZP1
Since the difference between the focal length f1 and the focal length f1 of the lens 22a is inversely proportional (f2−f1), by making the difference between the focal lengths f1 and f2 small, the multiplication factor M can be increased and the angular resolution can be increased. Since the moving direction of the moiré FZP varies depending on the rotation direction of the rotating FZP array 11, the rotation FZP array 1
1, ie, the rotation direction of the rotating disk 10 can also be detected.

When the rotating FZP array 11 further rotates, LE
Rotating FZP111b and fixed FZP12 on the optical path of D14
Moiré FZP is also generated when 2b overlaps, and the moving speed of this moiré FZP, in other words, the rotation angle of the rotating FZP array 11, is detected by the two-division photodiode 16b. Similarly, when the rotating FZP 111c and the fixed FZP 122c overlap on the optical path of the LED 14, the rotation angle of the rotating FZP array 11 is detected by the two-part photodiode 16c.

By the above series of operations, the adjacent FZPs 111a (111b, 1b) in the same circumferential portion of the rotating disk 10 are
11c), the angle can be detected for the mutual interval (arrangement pitch), and thereafter, the same operation is repeated. The angle exceeding the arrangement pitch of the FZPs in the same circumferential portion may be calculated based on the number of times of detection of the moiré FZP detected by each of the two divided photodiodes 16a to 16c. As described above, according to the present embodiment, the rotation angle can be detected with high resolution over the entire circumference of the rotating disk 10.

The number of concentric circles provided on the rotating FZP array 11 side is not particularly limited. However, the interval between the rotating FZPs of the first circumferential part on the outermost periphery is set to be the largest from the second circumferential part. The rotation FZP on the inner circumference is arranged to interpolate. Further, as described above, in the present embodiment, the rotation FZP
Have the same focal length and the fixed FZP is the rotating FZ
Although an example in which the same focal length is slightly different from P has been described, the rotating FZP is located on the same circumferential portion but the focal lengths need only be equal, and the focal length of the rotating FZP of the first circumferential portion and the other circles are different. The focal length of the peripheral rotating FZP may be different. The focal lengths of the fixed FZPs need only be slightly different from the focal lengths of the rotating FZPs at the corresponding circumferences of the rotating disk 10, and the focal lengths of all the fixed FZPs do not necessarily have to be equal. In the above embodiment, a two-segment photodiode is used for the two-segment light receiver, but a two-segment phototransistor can be used.

[0022]

As described above, according to the present invention, the rotation angle is detected based on the moving speed of the moiré FZP in which the rotation angle is enlarged by a predetermined multiplication factor. It can be improved than before.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention (FIG. 1A).
FIG. 1 is an explanatory diagram of a positional relationship between a rotating FZP and a fixed FZP (FIG. 1B).

FIG. 2 is an explanatory diagram showing the principle of the present invention.

FIG. 3 is an explanatory diagram of FZP.

FIG. 4 is an explanatory diagram showing moiré interference fringes.

FIG. 5 is a perspective view showing a conventional technique.

[Explanation of symbols]

 Reference Signs List 10 rotating disk 11 rotating FZP array 11a first circumferential part 11b second circumferential part 11c third circumferential part 12 reference FZP array 13 two-part photodiode array 14 LED 15 lens 16a-16c two-part photodiode 111a-111c rotation FZP 122a-122c Fixed FZP

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA07 AA09 AA39 DD03 DD04 FF06 GG07 GG13 JJ05 JJ18 LL04 LL43 MM04 PP13 QQ14 UU01 UU02 UU07 2F103 BA37 CA01 CA05 DA13 EA03 EA06 EA12 EA17 EB12 EB03

Claims (2)

[Claims] 1. A plurality of rotating Fresnel zone plates (hereinafter, referred to as rotating FZP) having the same focal length are arranged at predetermined intervals in a first circumferential portion of a rotating disk, and inside the first circumferential portion. The rotation FZP having the same focal length within the same circumference is rotated by the rotation FZ of the first circumference at one or more circumferences.
Rotation F which is sequentially arranged so as to interpolate the interval between P
A ZP array, a light source device for irradiating parallel light from a direction orthogonal to the rotating FZP array, and a radial number of the rotating disk equal to the number of the circumferential portions at a position where the transmitted light of the rotating FZP is incident. A plurality of fixed Fresnel zone plates (hereinafter, referred to as fixed FZPs) which are arranged in a row so as to correspond to the circumferential portion and whose focal length is slightly different from the focal length of the rotating FZP of the corresponding circumferential portion; A rotary encoder, comprising: a light receiver arranged at a position where a moire Fresnel zone plate generated by moire interference between the rotating FZP and the fixed FZP condenses irradiation light from the light source device. 2. The rotary encoder according to claim 1, wherein the light receiver is divided into two parts along a rotation direction of the rotating disk.