JPS6253053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an optical scale device, etc., in which a fundamental sine wave, which is a fundamental signal for interpolation operations to improve positional resolution, is generated from a scale with bright and dark striped patterns at a constant pitch. This relates to an optical sine wave encoder that can be directly and easily taken out, and in particular, in an optical sine wave encoder that receives reflected light from the scale through a slit window with a certain width, the maximum sensitivity of the light receiving means. By arranging a point outside the area of the slit window and mainly receiving scattered light from the slit window to extract a sine wave-like signal, the light receiving means and the The object of the present invention is to provide an optical sine wave encoder that does not require precise positioning work with a slit window, is easy to manufacture, and has excellent mass productivity.

In encoders that optically extract a sine wave-like signal with little waveform distortion from a scale with a bright and dark striped pattern at a constant pitch through a slit window with a constant width, conventionally, the reflection from the scale is It was necessary to strictly define the relative position of the light receiving means for receiving light and the slit window. 1st
The figure shows a conventional example, which includes a sensor housing 13 incorporating a light receiving element 11 and a light emitting element 12,
The mask plate 14 having a slit window 15 therein was precisely aligned so that the maximum sensitivity point of the light receiving element 11 was located at the center of the slit window 15. In FIG. 1, Q indicates the sensitivity characteristic of the light receiving element without using the slit window. However, in such a conventional configuration, extremely high precision is required for assembling the encoder, a lot of time is required for assembly work, and mass productivity is poor.

The present invention eliminates the drawbacks of the conventional art, eliminates the need to strictly define the relative position between the light receiving means and the slit window, and enables assembly work that allows a sine wave-like signal to be extracted even with somewhat rough alignment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS This encoder is easy to mass produce and the present invention will be described below with reference to embodiments shown in the drawings. FIGS. 2a and 2b are main part configuration diagrams of an embodiment of the present invention, in which a is a top view and b is a side view. However, in Figures a and b, details of the mechanism for moving the entire encoder including the light emitting means and the light receiving means relative to the scale in parallel are omitted. In Figures a and b, 8 is a scale constructed such that a light and dark striped pattern is applied at a constant pitch L, and the ratio of bright and dark parts within the striped pattern is the same everywhere. A light emitting element such as an infrared light emitting diode that illuminates the scale 8; 1 is a photo transistor or the like that mainly receives the scattered light that is the reflected light from the scale 8 of the light emitting element 2 scattered by the slit window 5; It is a light receiving element. In figures a and b, the light receiving element 1 and the light emitting element 2 are constructed using an integrated photo reflector. 4 is a mask plate attached in contact with the light receiving surface of the photo reflector;
Reference numeral 5 denotes a slit window provided in the mask plate 4 and having a width of L/2 in the longitudinal direction of the scale 8. 3 is a sensor housing for positioning the light receiving element 1 with respect to the mask plate 4. 6 is a lead wire of the light receiving element 1; 7 is a lead wire of the light receiving element 1;
is a lead wire of the light emitting element 2. In addition, in the figure b, PP' is the position of the maximum sensitivity point of the light receiving element 1, MM' is the center position of the slit window 5, and Δl is the distance between the position of the maximum sensitivity point of the light receiving element 1 and the center position of the slit window 5. represents. Δl is determined at a position such that the maximum sensitivity point of the light receiving element 1 is outside the area of the slit window 5 and the light receiving element 1 mainly receives scattered light from the slit window 5. Light from the light emitting element 2 is irradiated through the slit window 5 onto a scale 8 having a bright and dark striped pattern at a constant pitch, and is reflected by the surface of the scale 8. The reflected light enters the slit window 5 again, and the light receiving element 1 mainly receives the scattered light from the slit window 5. The light receiving element 1
When the sensor housing 3 moves relative to the scale 8 while maintaining a constant gap, a periodic waveform synchronized with the period of the striped pattern of the scale 8 is output. In particular, if the gap between the sensor housing 3 and the scale 8 is appropriate, the periodic waveform becomes a sine wave-like signal.

Here, a description will be given of how a sine wave-like signal can be obtained by the encoder of the present invention.
Taking the longitudinal direction of the scale 8 in FIG. 2 as the x-axis, the pitch of the striped pattern on the scale 8 is L, the width of the "bright" part of the striped pattern is W, and the width of the "dark" part is L-.
W, S(x) is a scale brightness density function representing the brightness of the scale 8, x=X is the center position of the slit window 5 on the x-axis, and represents the sensitivity characteristic of the light receiving element 1 through the slit window 5. Let the light-receiving element sensitivity density function be P(x,

S(x) is expressed as follows.

Here, B represents the brightness of the "dark" part of the striped pattern, and K represents the difference between the brightness of the "bright" part and the brightness of the "dark" part of the striped pattern. Further, u(x) is a unit step function, m is the number of striped patterns, and it is assumed that m striped patterns are applied on the scale.

In addition, as the amount of light incident on the slit window 5 increases, the amount of scattered light that is scattered by the slit window 5 and reaches the light receiving element 1 increases.
The light receiving element sensitivity density function P through the slit window 5 of
(x, X) is the center position of the slit window 5 =
It has a peak value at X, and is distributed symmetrically around x=X in the direction in which the x coordinate increases and in the direction in which it decreases. That is, it can be expressed as follows.

P(x-Δx,X)=P(x+Δx,X)
………(2) However, Δx represents the increment of x, and Δx
>0.

Now, assuming that the output voltage of the light receiving element 1 is V(X), V(X) is expressed as follows.

V(X)=∫ ₀ ^mL P(x,X)S(x)dx
(3) Here, since the width of the slit window 5 is L/2, the distribution of the sensitivity density function P(x, X) of the light receiving element 1 through the slit window 5 is x=X It is within ±L/4 around the center. Therefore, in calculating equation (3), it is sufficient to consider the range within ±L/4 around x=X. From equations (1) and (3), V(X) is approximated as shown below.

However, in the above equation, ±
The value of n within the L/4 neighborhood was set to n=i.

As mentioned above, P(x, C
far. Also, let I be the integral of the second term of equation (4). Then, V(X) can be further expressed as follows.

V(X)≒C+KI……(5) C=B∫ ₀ ^mL P(x,X)dx……(6) I=∫ ^iL+W _iL P(x,X)dx……(7) Now , as mentioned above, the light receiving element sensitivity density function P(x,
It is distributed symmetrically in the direction in which the x coordinate increases and in the direction in which it decreases with x=X as the center, and its spread is around ±L/4 with x=X as the center. Moreover, if the gap between the sensor housing 3 and the scale 8 is appropriate, P(x, X) becomes a sine wave-like signal with a limited section. Therefore, consider approximating P(x, X) using trigonometric functions as follows.

Here, A is a constant, and the outline of P(x, X) in equation (8) is shown in FIG. From equations (7) and (8), I becomes as follows.

I=∫ ^iL+W _iL A{cos2π/L(x-X)+1
}dx = AL/πsinπW/Lcos2π/L(X-W/2)
+AW……(9) Also, C becomes as follows from equations (6) and (8).

C=B∫ ^X+L/2 _X-L/2 A{cos2π/L(x
-X)+1}dx =BAL......(10) From equations (5), (9), and (10), the output voltage V of the light receiving element 1
(X) is as shown in the following equation.

V(X)≒BAL+AKW+AKL/πsinπW/Lcos2π/
L (X-W/2) ......(11) This V(X) is the DC component BAL + AKW and the AC component AKL/πsinπW whose amplitude is AKL/πsinπW/L.
/Lcos2π/L(X - W/2), and especially the alternating current component is a sine wave-like signal with a period of L with respect to X. In this way, when the sensor housing 3 moves relative to the scale 8 while maintaining an appropriate gap, the light receiving element 1 generates a sine wave-like signal synchronized with the period of the striped pattern of the scale 8. Output. This situation is shown in FIG. In addition, since the light receiving element 1 mainly receives scattered light from the slit window 5, there is a tolerance in the relative position between the light receiving element 1 and the slit window 5, and the relative position differs from the specification value. Even if there is a slight deviation, the photodetector sensitivity density function P
(x, X) only changes its amplitude, but its outline remains almost unchanged. Changes in amplitude can be compensated for by passing the signal through a variable gain amplifier. Therefore, in the sine wave encoder of the present invention, it is not necessary to strictly define the relative positions of the light receiving means and the slit window, and there is no need for precise positioning work between the position of the light receiving means and the position of the slit window. In addition, deviations from the specification values in the relative position of the light receiving means and the slit window caused by machining errors in the hole for fixing the light receiving means provided in the sensor housing or variations in the dimensions of the sensor itself may also cause the light receiving element to deviate from the specified value. It has almost no effect on the outline of the sensitivity density function P(x, It is excellent and the production cost is low.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the main part showing a conventional example, Fig. 2 a,
b is a top view and a side view of a main part of an embodiment of the present invention, FIGS. 3a and 3b are diagrams for explaining a scale luminance density function and a light-receiving element sensitivity density function, and FIG. 4 is a diagram showing the light-receiving element sensitivity. FIG. 5, which is an explanatory diagram when the density function is expressed mathematically, is a waveform diagram of an example of a sine wave-like signal obtained by the sine wave encoder of the present invention. 1... Light receiving element, 2... Light emitting element, 3... Sensor housing, 4... Mask plate, 5... Slit window, 6... Light receiving element lead wire, 7... Light emitting element lead wire, 8... Scale .

Claims (1)

[Claims] 1. A scale that has a bright and dark striped pattern at a constant pitch and is constructed so that the ratio of bright and dark parts of the striped pattern is the same everywhere, and a scale that moves relative to the scale and It has a slit window having a constant width in the direction of relative movement, and includes a light emitting means for illuminating the scale through the slit window, and a light receiving means for receiving reflected light from the scale through the slit window. and the position of the maximum sensitivity point of the light receiving means is arranged outside the area of the slit window, and among the light reflected from the scale, scattered light from the slit window reaches the light receiving means via the slit window. 1. A sine wave encoder characterized in that the sine wave encoder has a light receiving structure that mainly receives scattered light such that the amount of light exceeds the direct light from the slit window, and is configured to obtain a sine wave-like signal.