JPH04102016A - Encoder - Google Patents

Abstract

PURPOSE:To eliminate fluctuation of the amplitude of an output signal from a light- sensing means and to enable precise detection of a state of relative movement by making the opening width of a light-transmitting part of a main scale narrower than that of the light-transmitting part of a subordinate scale. CONSTITUTION:A light flux from a light source 1 is made parallel substantially by a projector lens 2 and falls on a main scale 3. Then, only a light flux 6 passing through a light-transmitting part 3a of the main scale 3 falls on a subordinate scale 4. The light-transmitting part 3a of the main scale 3 and the light-transmitting part 4a of the subordinate scale 4 have the same pitch. The respective opening widths of the light-transmitting parts 3a and 4a are set so that the opening width of the light- transmitting part of the subordinate scale 4 is larger than the width on the subordinate scale 4 of the light flux 6 passing through the light-transmitting part 3a of the main scale 3. Accordingly, all the light flux passing through the light-transmitting part 3a can pass through the light-transmitting part 4a. Besides, the width of a light- intercepting part 4b is set so that the light may not leak to the rear of the subordinate scale 4 when the phases of the main scale 3 and the subordinate scale 4 turn reverse to each other. According to this constitution, the amplitude of a signal detected by a light-sensing means 5 does not change.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an encoder, and in particular, the present invention relates to an encoder that measures the movement state of an object to be measured, such as the amount of movement and the direction of movement. This relates to a rechargeable encoder that performs detection using a main scale (first scale) and a sub scale (second scale).

(Prior Art) Conventionally, rechargeable rotary encoders and linear encoders have been widely used as devices for detecting displacement states related to rotation, movement, etc. of an object to be measured.

FIGS. 5(^) and 5(B) are schematic plane and side views of essential parts of the optical system of a conventional linear encoder designed to detect the state of linear movement of an object to be measured.

There was a problem in that the detection accuracy decreased due to fluctuations in the detection accuracy.

Incidentally, such problems also occur in rotary encoders.

The present invention improves the accuracy of relative movement between the main scale and the sub scale by configuring each element so that the amplitude of the output signal from the light receiving means does not change even if the distance between the main scale and the sub scale changes. The purpose is to provide an encoder that can detect

(Means for Solving the Problems) The encoder of the present invention projects a light beam from a light projecting means onto a first scale in which a light transmitting part and a light shielding part are provided periodically in the form of a slit. The light flux passing through the scale is made incident on a second scale provided with a slit-shaped light transmitting part and a light shielding part having the same period as the first scale, and the light flux passing through the second scale is received by a light receiving means, and the light receiving means In an encoder that detects the relative movement amount of the first scale and the second scale using an output signal from the encoder, the encoder passes through a transparent portion of the first scale;
The present invention is characterized in that the width of the light beam when it enters the second scale is narrower than the aperture width of the light-transmitting portion of the second scale.

For example, in the present invention, the opening width of the transparent part of the first scale is configured to be narrower than the opening width of the transparent part of the second scale, and It is characterized by the fact that a cylindrical lens having refractive power is provided in the periodic arrangement direction of the light part and the light shielding part.

(Embodiment) FIGS. 1A and 1B are schematic plane and side views of essential parts of an optical system according to a first embodiment of the present invention.

Reference numeral 1 on the right side of the figure is a light source, which is composed of, for example, an LED. 3 is a main scale (first scale), which is made up of a slit row in which light-transmitting parts and light-shielding parts are arranged periodically. Reference numeral 2 denotes a light projecting lens, which projects light from the light source 1 onto the main scale 3 as a substantially parallel light beam. The light source 1 and the light projection lens 2 constitute one element of the light projection means. 4 is a sub scale (second scale), which has four scales 4-1.4-2.4-3°4- provided with a slit-shaped light-transmitting part and a light-shielding part with the same period as the main scale 3. It has 4. The four scales 4-1°4-2.4-3.4-4 are, for example, 0 degrees (reference phase) and 90 degrees as shown in FIG.
It is configured to have phases of 180 degrees, 180 degrees, and 270 degrees. Reference numeral 5 denotes a light receiving means, which receives the light flux that has passed through the transparent portions of the main scale 3 and the sub scale 4. The light receiving means 5 has 4 scales corresponding to the four scales 4-1.4-2.43.4-4 of the sub scale 4 as shown in FIG.
It has two photodetectors 5-1°5-2.5-3.5-4.

Reference numeral 10 denotes a detection head, which is constructed by housing each of the above-mentioned elements except for the main scale 3 in a housing. Main scale 3
is movable relative to the detection head 10 in six directions of arrows in the figure.

FIGS. 2(^) and 2(B) are enlarged partial sectional views of one scale 4-1 of the main scale 3 and sub scale 4 in the first embodiment of FIG. 1. Same figure (A).

(B) shows a state in which the main scale 3 and the scale 4-1 are in an in-phase and out-of-phase positional relationship, respectively.

In the figure, a light beam made substantially parallel by the projection lens enters the main scale 3 from the left side of the figure. Then, only the light beam 6 that has passed through the transparent portion 3a of the main scale 3 is incident on the sub scale 4. The transparent portion 3a of the main scale 3 and the transparent portion 4a of the scale 4-1 both have the same period P. Moreover, the opening widths W, W3 of each of the transparent parts 3a and 4a
are set to different values according to conditions described later. The transparent parts 3a and 4a have long openings in the direction perpendicular to the paper surface.

The light beam incident on the main scale 3 does not become a perfectly parallel light beam when a light source 1 having a light emitting part of finite dimensions, such as an LED, is used. Generally, the light beam is spread over a range of a certain angle θ determined by the size of the light emitting part and the focal length of the projection lens 2. In this embodiment, under such conditions, each element is set so that the amplitude of the signal detected by the light receiving means 5 does not change when the interval 1 between the main scale 3 and the sub scale 4 changes. This prevents the detection accuracy of the relative movement amount between the scale 3 and the sub scale 4 from decreasing. That is, in this embodiment, (a) the light beam 6 that is located within the range in which the above-mentioned interval 1 changes and first passes through the transparent part 3a of the main scale 3 on the sub scale 4 as shown in FIG. 2(A); The opening width W3 of the transparent part of the sub scale 4 is determined from the width W2 depending on
The opening widths W, , W of the transparent parts 3a, 4a are set so that
3 is set. This allows all the light beams that have passed through the transparent section 3a to pass through the transparent section 4a.

(B) When the main scale 3 and the sub scale 4 are in an opposite phase state as shown in FIG. At this time, the width of the light shielding portion 4b is set so that no light leaks behind the subscale 4, that is, to the photodetector.

Each element is set so as to satisfy the above conditions (a) and (b), so that the amplitude of the signal detected by the light receiving means does not change.

Expressing the above two conditions (a) and (b) using formulas, W3≧W2 (
1) Right and p-w3≧W2 ・・・・・・・・・・・・・・・(
2). The width W2 of the light beam 6 incident on the subscale 4 is expressed by the symbols θ, iL, w shown in FIGS. 2(A) and 2(B).
, W2=W, +2fLjan (θ/2) −(3
) can be expressed as Putting equations (1) and (2) together, W2≦
If we set W3≦p-w2 and substitute equation (3) into this, we get W, +2J2 jan(θ/2)5w3≦P-(1f,
+2u tan(θ/2))・・・・・・・・・(4
) becomes. In other words, the transparent parts 3a of the main scale 3 and the sub scale 4 are
By determining the aperture widths w1 and w3 of the subscale 4a, the amount of light passing through the transparent portion 4a of the sub scale 4, that is, the amplitude of the output signal can be kept constant. Conversely, give openings W and W3 (4)
The range of interval 1 can also be found from the formula.

Next, more preferable conditions within the range that satisfies equation (4) will be explained.

As is clear from equation (4), W, +211 jan(θ/2)≦P-(W, +242
jan(θ/2)), so from now on W1≦ 1/2・P −21tan(θ/2) −
-----(5). Since W is the aperture width of the transparent portion 3a of the main scale 3, it is better to make it as large as possible in order to effectively utilize the luminous flux. Therefore, by adopting the equality sign in equation (5), W1≦1/2−P −2ILtan(θ/2) is (
4) By substituting into the equation, we get W3=1/2·P.

Next, a concrete numerical example is shown.

(Numerical example 1) If you want to keep the amplitude of the output signal from the light receiving means constant up to 1 = 300 μm at P = 100 μm and θ = 5°, (5
), we obtain W1≦23.8 μm. Subordinate W 1=
23, 8 μm, and W 3 =50 μm.

(Numerical example 2) P = 100 μm, W = 30 μm at θ = 50.

When W3 = 50 μm, the range of interval 1 in which the amplitude of the output signal from the light receiving means does not vary is 1≦22 from equation (4).
Obtain 9 μm.

In the conventional encoder, the aperture width W, , W3 of the main scale and sub scale is W,=W3=172·P, so the amplitude monotonically decreases as the interval l increases from 0.

For comparison, when the width w2 of the light beam 6 when fi=300 μm is calculated using the equation (3) under the condition of the above equation (1), the width W2 of the light beam 6 becomes W2=76 μm. If the illuminance distribution of the luminous flux on the subscale is −-like, the aperture width W3 is w3=5
The proportion of light passing through the transparent part 4a of the 0 μm subscale 4 is the interval! - 50/76 x 100 phrases 66 for 〇 case
%.

On the other hand, in this embodiment, all the light beams pass through when the interval l varies from 1=o to 300 ALm. As a result, the amplitude of the output signal from the light receiving means does not change at all.

FIG. 3 is an enlarged sectional view of a portion of the main scale 11 and the sub scale 12 of the second embodiment of the present invention.

Each element other than the main scale 11 and the sub scale 12 is substantially the same as the structure shown in FIG.

The main scale 11 in this embodiment has a light-transmitting part 11a and a light-shielding part flb arranged periodically at dots P in the shape of a slit, as in the first embodiment. A cylindrical lens li made of a transparent plastic material or the like having refractive power in the arrangement direction
e is provided on the transparent portion 11a.

On the other hand, the sub scale 12 is provided with a slit-shaped light transmitting part 12a and a light shielding part 12b having the same period as the main scale 11. The widths of the light shielding portion 11b of the main scale 11 and the light shielding portion 12b of the sub scale 12 are both 1/2 of the width P.

In this embodiment, when a substantially parallel light beam is incident on the main scale 11, the light beam 13 that has passed through the cylindrical lens lie portion is subjected to a convergence effect within the plane of the paper of FIG. cylindrical lens llc
Let fl be the focal length in the cross section that has a light condensing effect, fl be the focal length of the projecting lens, and be d the size of the light emitting part of the light source, then there will be a width d′ near the focal point of the cylindrical lens llc f1/f2.
A line image of d is formed periodically.

In this embodiment, when the light emitting part size d of the light source is fixed, the width d' of the line image can be made smaller than the width 12a of the transmission part of the sub scale by appropriately selecting the ratio of the focal lengths f1 and fl. can.

Therefore, if the subscale 12 is placed near the focal point of the cylindrical lens lie, even if the distance between the subscale 12 and the main scale 11 changes somewhat with that position as a reference, the light beam 13 will not be vignetted, and the output signal from the light receiving means will not be eclipsed. It is possible to specify a range in which the amplitude does not fluctuate.

For example, if the light emitting part size of the LED as a light source is 200 μm, the focal length of the projection lens is 5 mm, and the focal length of the cylindrical lens tic is 0.5 mm, a line image of about 20 μm is formed.

In this embodiment, the main scale 11 and the sub scale 12 can be arranged under stable conditions with the pitch P=100 μm and the width of the light-transmitting part 5 μm.

FIG. 4 is an enlarged sectional view of a portion of the main scale 14 and sub scale 15 of a third embodiment of the present invention.

Each element other than the main scale 14 and the sub scale 15 is substantially the same as the structure shown in FIG.

In this embodiment, the main scale 14 has a plurality of cylindrical lenses 14a molded from transparent plastic or the like having refractive power in the arrangement direction of the light-transmitting part 15a and the light-blocking part 15b of the sub-scale 15.
It consists of an array of cylindrical lenses arranged in series in a periodic manner (DotsuchiP).

This cylindrical lens array is produced in the same manner as, for example, lenticular molding. In this embodiment, the boundary between adjacent cylindrical lenses 14a corresponds to a light shielding section.

The main scale 14 is constructed by arranging a plurality of cylindrical lenses 14a in succession as described above, and by detecting the light beam passing through the transparent part 15a of the sub scale 15 with a light receiving means. The relative movement amount between the scale and the sub scale 15 is detected.

The cylindrical lens array serving as the main scale 14 of this embodiment does not have a light-shielding portion consisting of a fixed area. Compared to the second embodiment, the efficiency of using the luminous flux is approximately twice as high, and it has the advantage that almost all of the incident luminous flux can be utilized.

In this embodiment, it is also possible to use a refractive light condensing function such as a double prism instead of the cylindrical lens. Also second. The present invention can be applied in the same manner even if the configuration of the third embodiment and the first embodiment are combined.

Incidentally, in each of the above embodiments, a linear encoder has been described, but the present invention can be similarly applied to a rotary encoder.

(Effects of the Invention) According to the present invention, when detecting the relative movement state between the main scale and the sub scale using the light flux passing through the main scale and the sub scale, each element can be configured as described above. Accordingly, it is possible to reduce amplitude fluctuations in the output signal from the light receiving means caused by fluctuations in the distance between the main scale and the sub scale, and to achieve an encoder capable of highly stable and highly accurate detection.

[Brief explanation of the drawing]

Figures 1 (^) and (B) are schematic diagrams of the main parts of the optical system of the first embodiment of the present invention, and Figures 2 (^) and (B) are parts of the main scale and subscale in the first embodiment. Enlarged view, 3rd. FIG. 4 shows the second embodiment of the present invention. A schematic diagram of main parts of the main scale and subscale of the third embodiment, FIG. 5 is a schematic diagram of a conventional linear encoder, FIG. 6 is an explanatory diagram of a part of FIG.
The figure is an explanatory diagram of an output signal waveform in a conventional linear encoder. In the figure, 1 is a light source, 2 is a light projection lens, 3, 11° 14 is a main scale, 4, 12.15 is a subscale, 5 is a light receiving means, 3a, 4a, Ila, 12a, 15a are transparent parts, 3a
, 4b, flb, 12b, and 15b are light shielding parts, and 12 is a detection head. Patent applicant: Canon Co., Ltd. Figure ↓A Roskele special power 1

Claims (3)

[Claims] (1) The light flux from the light projecting means is projected onto a first scale in which light-transmitting parts and light-shielding parts are provided periodically in the form of slits, and the light flux passing through the first scale is transmitted with the same period as the first scale. The light beam is incident on a second scale provided with a slit-shaped light-transmitting part and a light-shielding part, the light flux passing through the second scale is received by a light receiving means, and the output signal from the light receiving means is used to 2
In an encoder that detects the relative movement amount of a scale, a beam width when passing through a transparent portion of the first scale and entering the second scale is narrower than an aperture width of the transparent portion of the second scale. An encoder characterized by being configured as follows. (2) The encoder according to claim 1, wherein the aperture width of the light-transmitting portion of the first scale is configured to be narrower than the aperture width of the light-transmitting portion of the second scale. (3) The encoder according to claim 1, wherein the light-transmitting portion of the first scale is provided with a cylindrical lens having refractive power in a direction in which the light-transmitting portion and the light-blocking portion are periodically arranged.