JPH08320240A - Displacement measuring device with zero point position detecting means - Google Patents

Abstract

PURPOSE: To suppress the lowering of zero point position detecting accuracy even if the thickness error of an optical scale is generated by detecting luminous flux through a zero point detecting pattern by a zero point position detecting means to obtain the zero point information of a optical scale. CONSTITUTION: Luminous flux emitted from a light source 1 enters a beam splitter 3 via a collimator lens 2 so as to be split into luminous flux 10, 11. The luminous flux 10 is used to detect the zero point position of an optical scale 9, and the luminous flux 11 is used to detect the displacement information of the scale 9. The luminous flux 10 irradiates the partial area of the optical scale 9 moved by a converging lens 4, becomes luminous flux 10' being reflected by a reflecting slit 8 and enters a zero point detecting sensor 5 through the beam splitter 3. When the slit 8 enters an irradiated area, the reflected light starts entering a sensor 5A first and enters a sensor 5B with a slit delay. The instant the levels of two signals coincide with each other under the condition of comparator potential or more, a zero point detecting circuit 15 generates a signal indicating the zero point position of the scale 9 to detect the zero point position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement measuring device having zero point position detecting means, and in particular an encoder used in the field of industrial machine tools and measuring machines for measuring the amount of movement and rotation of an object. It is suitable for.

[0002]

2. Description of the Related Art Conventionally, in precision machines such as NC machine tools and semiconductor printing equipment, the amount of rotation and the amount of straight movement are 1 μm.
An encoder is used as a high-precision measuring machine that measures with an accuracy of m or less (submicron).

In this type of encoder, a scale (optical scale) having a grating portion having a diffraction grating of several microns / pitch is attached to a moving body, and a head portion composed of a light source, a detection circuit, etc. is fixed to the equipment. Attached to the part,
A pair of diffracted lights generated in the grating portion of this scale are extracted and interfered, the intensity of the interference light is photoelectrically converted to obtain a periodic signal corresponding to the displacement of the diffraction grating, and a reference point signal generated from the scale is generated. The displacement amount of the scale, that is, the displacement amount of the moving body is detected by counting with reference.

In this type of encoder, the detection accuracy of the zero point position, which is the origin of the scale mounted on the moving body of the above-mentioned device, directly affects the detection resolution and the detection accuracy of the moving amount measurement value, and therefore high accuracy is required.

FIG. 6 is a schematic view of a main part of a conventional encoder having a zero point position detecting means. 1 in the figure
Is a light source, which is composed of a semiconductor laser, for example, and emits monochromatic light having a wavelength λ. 2 is a collimator lens, which is a light source
The light flux emitted by 1 is converted into a parallel light flux. In addition, light source 1
And the collimator lens 2 constitutes one element of the light irradiation means LR. 3 is a beam splitter (beam splitting means), 4
Is a condenser lens. Reference numeral 5 is a zero point detection sensor, which is composed of a two-divided sensor and has a first sensor 5A and a second sensor 5B.
Output 5b. Reference numeral 15 is a zero detection circuit, and two signals 5
Generates a zero signal from a and 5b. The zero point detecting sensor 5 and the zero point detecting circuit 15 constitute one element of the zero point position detecting means.

Reference numeral 7 denotes an optical scale, which is coupled to a rotating object (displacement object) not shown and rotates. FIG. 7 is a plan view of the optical scale 7 of FIG. A part of the surface of the disk (disk) part of the optical scale 7 on the annulus is a grating part (displacement information pattern) 7a on which a radial diffraction grating is formed, and the displacement information of the displaced object is obtained by the movement of the grating part 7a. give. 6
Is a zero point detection pattern, and is constructed by installing a reflective slit of width t on the surface of the optical scale 7 on the side of the condensing lens 4 of the disk part. The irradiation light is reflected and the light is incident on the zero point detection sensor 5. The zero point detecting operation of this conventional example will be described. The light beam emitted from the light source 1 becomes a parallel light beam by the collimator lens 2 and enters the beam splitter 3, whereby the light beam is divided into two light beams 10 and 11. The light flux 10 detects the zero point position of the optical scale 7, and the light flux 11 is guided to the grating portion 7a by an optical system (not shown). Displacement information such as is detected.

The light beam 10 is focused and irradiated on a partial area (irradiation area) of the optical scale 7 by the condenser lens 4, and if there is a reflection slit 6 in the irradiation area, the light flux is reflected by this and is focused on the condenser lens 4. Facing each other, this condensing lens 4 forms a substantially parallel light beam 10 ', which passes through the beam splitter 3,
It is incident on the zero point detection sensor 5.

FIG. 3 shows a first signal 5a from the first sensor 5A and a second signal 5b from the second sensor 5B which are then obtained.
FIG. This will be described. As a premise, consider a case where the converging position of the irradiation light beam 10 is on the side farther from the surface of the optical scale 7 when viewed from the condensing lens 4. It is assumed that the optical scale 7 is moving in the direction of the arrow (Fig. 7). At this time, when the reflection slit 6 enters the irradiation area, reflected light is generated by the reflection slit 6 for the first time, and the light reaches the zero point detection sensor 5.

When the reflection slit 6 enters the irradiation area, the reflected light first enters the first sensor 5A, and the incident light on the first sensor 5A increases as the optical scale 7 moves. At some point it reaches its peak. When the reflective slit 6 moves out of the irradiation area due to the movement of the scale 7,
The incident light of 1 on the sensor 5A decreases, and finally the incident light becomes zero. As shown in FIG. 3, the first signal 5a also increases / decreases in proportion to this light amount. On the other hand, the first sensor for the second sensor 5B
The reflected light starts to be incident on the sensor 5A at a short time, reaches a peak, and then decreases. The first and second signals 5a and 5b from both sensors 5A and 5B are input to the zero point detection circuit 15 as signals whose phases are shifted from each other. The zero point detection circuit 15 generates a signal indicating the zero point position of the scale 7 at the moment when the levels of these two signals match under the condition of the comparator potential or higher, and the zero point position of the scale 7 is detected by this.

[0010]

[Problems to be Solved by the Invention] FIG.
When the irradiation width d of the reflective slit formation surface is changed by
It shows how the first signal 5a from the first sensor 5A and the second signal 5b from the second sensor 5B change.

According to FIG. 4, since a cross point of both signals occurs when the irradiation width d ≥t, a zero point signal is generated when the irradiation width d ≥t. On the other hand, since the output value decreases as the irradiation width d increases, the optimum value d ₀ of the irradiation width d is
It can be seen that it is not preferable that the irradiation width d fluctuates from the optimum value d ₀ by ± t or more at 2t.

Here, as shown in FIG. 8, the irradiation light beam 10 irradiates the surface of the scale 7 having a predetermined thickness by the condenser lens 4 with the optimum value of the irradiation width d ₀ = 2t, and the surface of the optical scale 7 is irradiated.
It is supposed to be refracted and condensed according to Snell's law. If an error occurs in the thickness of the optical scale 7 in this state, the irradiation width for irradiating the surface of the optical scale 7
d changes.

When an error of δ occurs in the thickness of the optical scale 7, since the optical scale 7 is attached to a part of a moving body (not shown), the back surface of the scale 7 serves as a mounting surface. The surface 21 shifts upward by δ as shown. Therefore, if the convergence angle of the light beam 10 irradiated from the condenser lens 4 is θ, the irradiation width changes from d ₀ to d ₁ and d ₁ = 2t + 2Δtan θ (1). In other words, if the amount of change in the irradiation width at this time is Δd ₁ , then Δd ₁ = 2δtan θ (2) .If this amount of change Δd ₁ becomes ≧ t, the zero point position detection accuracy decreases and the encoder measurement accuracy decreases. To do.

In view of the above problems, the present invention has a displacement measuring device having a zero point position detecting means, in which the accuracy of the zero point position detection is slow to decrease even if a thickness error occurs in the optical scale, and therefore the measurement accuracy is slow to decrease. For the purpose of providing.

[0015]

DISCLOSURE OF THE INVENTION A displacement measuring apparatus having a zero point position detecting means of the present invention is (1-1) of a transparent flat plate-shaped optical scale in which a light beam from a light irradiating means is attached to a displaced object. When detecting the displacement information of the optical scale by making the detection means detect the light beam that has entered the displacement information pattern, the zero point detection pattern on the surface opposite to the light incident side of the optical scale. Is provided, and the zero point information of the optical scale is obtained by detecting the light beam passing through the zero point detection pattern by the zero point position detecting means.

In particular, (1-1-1) the zero point detecting means has two light receiving elements provided in series in the displacement direction of the displaced object, and the zero point is utilized by using the output signals from the two light receiving elements. I have information. (1-1-2) The displaced object is a rotating object, the optical scale is a rotating body having a disk portion, and the zero point detection pattern is provided along a straight line passing through a rotation center of the disk portion. It is a reflective slit. It is characterized by such things.

[0017]

1 is a schematic view of a part of a first embodiment of a displacement measuring apparatus having a zero point position detecting means of the present invention. In this embodiment, the present invention is applied to a rotary encoder. In the figure, 1 is a light source, which is composed of, for example, a semiconductor laser and emits monochromatic light having a wavelength λ. Reference numeral 2 denotes a collimator lens, which converts the light beam emitted by the light source 1 into a parallel light beam. The light source 1 and the collimator lens 2 form one element of the light irradiation means LR. 3 is a beam splitter (light beam separating means), and 4 is a condenser lens.

Numeral 5 is a zero point detecting sensor, which is a two-divided sensor having a first sensor 5A and a second sensor 5B, and outputs a first signal 5a and a second signal 5b, respectively. .
Reference numeral 15 is a zero point detection circuit, which generates a zero point signal from the two signals 5a and 5b. The zero point detecting sensor 5 and the zero point detecting circuit 15 constitute one element of the zero point position detecting means.

Reference numeral 9 denotes an optical scale, which is coupled to a rotating object (displacement object) not shown and rotates. FIG. 2 is a plan view of the optical scale 9 of FIG. A part of the surface of the disk (disk) part of the optical scale 9 on the annulus is a grating part (displacement information pattern) 9a forming a radial diffraction grating, and the displacement information of the displaced object is obtained by the movement of the grating part 9a. give. The disk portion is made of a transparent material, and the refractive index of the material is n.

Reference numeral 8 denotes a zero point detection pattern, which is a reflection slit of width t installed along the straight line (radius line) passing through the center of the disc on the back surface as seen from the condensing lens 4 of the disc portion of the optical scale 9. Is made up of.

The optical scale 9 is connected to a moving body and is rotatable, and the light source 1, collimator lens 2, beam splitter 3, condensing lens 4 and zero point detecting sensor 5 are provided.
The zero detection circuit 15, the main signal light receiving means, etc. are arranged and fixed in one housing.

The operation of this embodiment will be described. The monochromatic light beam emitted from the light source 1 becomes a parallel light beam by the collimator lens 2 and is incident on the beam splitter 3, whereby the light beam is divided into two light beams 10 and 11. Light flux 10 is used to detect the zero point position of optical scale 9, and light flux 11 is used on the optical scale.
It is used to detect displacement information in item 9.

First, the operation of detecting displacement information will be described. The light flux 11 is further divided into two light fluxes by an optical system (not shown), and irradiates a part of the grating portion 9a, respectively, and undergoes light modulation. Finally, the main signal light receiving means (detection means) receives this light-modulated light flux, and detects displacement information such as the displacement amount and displacement direction of the optical scale 9 from the change in the light amount thereof. (For the configuration relating to the displacement information detection, for example, the configuration disclosed in Japanese Patent Laid-Open No. 62-12814 of the present applicant is applied).

Next, the operation of detecting the zero point position will be described. Luminous flux
The condenser lens 4 condenses and irradiates a partial area (irradiation area) of the optical scale 9 with the condensing lens 4, and the reflection slit 8
If there is, the light beam is reflected by this and goes to the condenser lens 4, and it becomes a substantially parallel light beam 10 'by this condenser lens 4, passes through the beam splitter 3, and is a sensor for zero point detection.
Incident on 5.

FIG. 3 shows the first signal 5a from the first sensor 5A and the second signal 5b from the second sensor 5B which are then obtained.
FIG. This will be described. As a premise, let us consider a case where the converging position of the irradiation light beam 10 is on the side farther from the reflecting slit 8 when viewed from the condensing lens 4.

It is assumed that the optical scale 9 is moving in the direction of the arrow (FIG. 2). At this time, when the reflection slit 8 enters the irradiation area, the reflected light by the slit 8 is generated for the first time, and the light reaches the zero point detection sensor 5.

When the reflection slit 8 enters the irradiation area, the reflected light first enters the first sensor 5A, and the incident light on the first sensor 5A increases as the optical scale 9 moves. At some point it reaches its peak. Optical scale 9
When the reflection slit 8 moves out of the irradiation area by the movement of, the incident light on the first sensor 5A decreases and eventually the incident light becomes zero. As shown in FIG. 3, the first signal 5a also increases / decreases in proportion to this light amount.

On the other hand, the first sensor 5A is connected to the second sensor 5B.
The reflected light starts to enter a little later, reaches a peak, and then decreases. First and second from both sensors 5A, 5B
The signals 5a and 5b are input to the zero point detection circuit 15 as signals whose phases are shifted from each other. The zero point detection circuit 15 generates a signal indicating the zero point position of the optical scale 9 at the moment when the levels of these two signals match under the condition of the comparator potential or higher, and the zero point position of the optical scale 9 is detected by this.

FIG. 4 shows the first case when the irradiation width d of the irradiation light beam 10 on the surface where the reflection slit is formed is changed by the condenser lens 4.
It shows how the first signal 5a from the second sensor 5A and the second signal 5b from the second sensor 5B change.

According to the figure, since the cross points of both signals occur when the irradiation width d ≧ t, a zero point signal is generated when the irradiation width d ≧ t. On the other hand, the output value decreases as the irradiation width d increases, so considering this, the optimum value d ₀ of d is 2t.
It can be seen that it is not preferable that the irradiation width d fluctuates from the optimum value d ₀ by ± t or more.

Here, as shown in FIG. 5, the irradiation light beam 10 is incident on the surface of the scale 9 having a predetermined thickness by the condenser lens 4, is refracted on the surface of the scale 9 according to Snell's law, and the irradiation width on the back surface. It is assumed that the light is focused and irradiated with the optimum value of d ₀ = 2t. When an error occurs in the thickness of the scale 9 in this state, the irradiation width d for irradiating the back surface of the scale 9 changes.

When an error of δ occurs in the thickness of the scale 9, since the scale 9 is attached to a part of the moving body (not shown), the back surface of the scale 9 is the attachment surface, and the scale surface 21 is As shown in the figure, it shifts upward by δ. Therefore, when the convergence angle of the irradiation light beam 10 from the condenser lens 4 with respect to the scale is θ, the irradiation width changes from d ₀ to d ₂ , and d ₂ = 2t + 2δ (tan θ-tan γ) (3). Here, γ is the angle of refraction when the irradiation light beam is incident on the medium having the refractive index n at the incident angle θ from the air, that is, the angle satisfying sin θ = n × sin γ (4). At this time, change amount of irradiation width d is Δd ₂
Then, Δd ₂ = 2δ (tan θ-tan γ) (5).

From equations (2) and (5), the change amount Δ of the conventional example
Comparing d ₁ with the amount of change Δd ₂ in this embodiment, it is clear that | Δd ₁ | ≧ | Δd ₂ |. Therefore, even if there is a thickness error in the disk portion of the optical scale, the variation of the irradiation width from the optimum value d ₀ of the irradiation width is smaller in this embodiment than in the conventional example. The accuracy of position detection does not decrease so much, and therefore the accuracy of encoder measurement does not decrease.

Although the embodiment of the rotary encoder has been described above, the present invention can be applied to not only the rotary encoder but also the linear encoder.

[0035]

According to the present invention, the displacement measuring apparatus having the zero point position detecting means, which has a low deterioration of the accuracy of the zero point position detection even if an error in the thickness of the optical scale occurs, and therefore has a small deterioration of the measurement accuracy, is provided. Has been achieved.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of a displacement measuring device having a zero point position detecting means of the present invention.

FIG. 2 is a schematic view (plan view) of an essential part of the optical scale of Example 1.

[Fig. 3] First and second movements of the optical scale
Explanatory diagram of changes in received light amount (signal) of the sensor

FIG. 4 is an explanatory diagram of the first and second signal changes when the irradiation width of the reflection slit is changed.

FIG. 5 is an explanatory diagram of a change in irradiation width when an error occurs in the thickness of the disc portion of the optical scale in the first embodiment.

FIG. 6 is a schematic view of a main part of a part of an encoder having a conventional zero point position detecting means.

FIG. 7 is a schematic view (plan view) of a main part of a conventional optical scale.

FIG. 8 is an explanatory diagram of a change in irradiation width when an error occurs in the thickness of the disc portion of the optical scale in the conventional example.

[Explanation of symbols]

 1 ---------- Light source 2 ---------- Collimator lens 3 ---------- Beam splitter (beam splitting means) 4 ------ ---- Condenser lens 5 ---------- Zero point detection sensor 5A, 5B ------- 1st and 2nd sensor 6, 8 --------- Zero detection pattern 7, 9 ------- Optical scale 7a, 9a ------- Lattice part 10 --------- Zero detection flux 11 ------- --Displacement information detection light beam 15 --------- Zero detection circuit 21 --------- Scale surface LR --------- Light irradiation means

Claims (3)

[Claims] 1. A light flux from a light irradiating means is incident on a displacement information pattern of a transparent flat plate-shaped optical scale attached to a displacement object, and a light flux passing through the displacement information pattern is detected by a detecting means to detect the optical flux. When detecting the displacement information of the scale, a zero point detection pattern is provided on the surface of the optical scale on the side opposite to the light incident side, and the light beam passing through the zero point detection pattern is detected by the zero point position detecting means to detect the optical scale. Displacement measuring device having zero point position detecting means, characterized in that it obtains zero point information. 2. The zero point detecting means has two light receiving elements provided in series in the displacement direction of the displaced object, and zero point information is obtained by using output signals from the two light receiving elements. A displacement measuring device having the zero point position detecting means according to claim 1. 3. The displacement object is a rotating object, the optical scale is a rotating body having a disk portion, and the zero point detection pattern is a reflection provided along a straight line passing through a rotation center of the disk portion. A displacement measuring device having a zero point position detecting means according to claim 1 or 2, which is a slit.