JPS6089713A - Absolute type position encoder - Google Patents

Abstract

PURPOSE:To obtain precisely the extent of displacement up to less than one scale pitch by providing a scale board which has gradations repeated at specific pitch and varies in repetition-directional length successively by a specific amount at every time. CONSTITUTION:Light from a light source 1 illuminates the scale board 2 by transmission. Gradations which are repeated at the specific pitch (p) and vary in repetition-directional length by the specific amount (a) at every time are formed on the surface of the scale board 2. A linear image sensor 4 is arranged at a position conjugate to the scale board about a projection lens 3. A processor 6 inputs the output signal of the image sensor 4 and outputs a signal corresponding to an absolute position on the scale board 2 to the image sensor on the basis of the length of an optional scale image and the length from a reference position determined on the image sensor 5 to the center of the optional scale image.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a positron encoder that photoelectrically measures position, and more particularly to an absolute position encoder that can perform absolute position detection.

(Background of the Invention) There are two types of positron encoders: absolute type and incremental type. The absolute type measures the absolute position by reading a coded pattern of several bits that corresponds to the absolute position, and has the disadvantage that high resolution cannot be obtained. there were. On the other hand, the incremental type measures the movement from the reference position by counting the scales attached at equal intervals, and can obtain high resolution, but cannot measure absolute position. Ta.

Therefore, it is conceivable to compensate for the drawbacks of both by providing an incremental AI scale and an absolute scale (coded pattern) together, but this has the drawback that the configuration becomes complicated.

(Object of the Invention) An object of the present invention is to provide an absolute type position encoder that has a simple configuration and has a high resolution comparable to that of an incremental type.

(Summary of the Invention) The present invention provides a scale board having a scale that is repeated in a constant pitch contest and whose length in the repeating direction sequentially changes by a predetermined amount (a). This is an absolute position encoder that performs finer reading than the above-mentioned constant pitch (p) based on the reference position of the detector that reads the absolute address and length, and the position of the scale where the length is read.

(Example) The present invention will be described below based on the example shown in the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment in which the present invention is applied to a position encoder for measuring length, FIG. 2 is an explanatory diagram of the scale pattern on the scale plate used in FIG. 1, and FIG. 1 is a waveform diagram in which the output of the image sensor used in FIG. 1 is sampled and held.

The light from the light source 1 transmits and illuminates the scale plate 2. As shown in FIG. A changing scale (transparent part...shaded part) is formed. Note that the white areas in FIG. 2 are opaque areas. A projection lens 3 is disposed on the opposite side of the light source 1 across the scale plate 2.

A one-dimensional image sensor 4 is placed at a position conjugate with the scale plane on the scale plate 2 with respect to the projection lens B. The -dimensional image sensor 4 is a well-known sensor in which light receiving sections are arranged at a predetermined pitch, and the light receiving sections are sequentially driven by a drive signal from a driving device 5. At this time, the direction in which the light receiving portions of the -dimensional image sensor 4 are arranged is substantially parallel to the direction in which the scales on the scale plate 2 are arranged. And the projection lens
The image of the scale is projected onto the image sensor 4 so that the pitch of the scale of the i scale board 2 is sufficiently larger than the pitch of the light receiving section of the image sensor 4. The processing device 6 inputs the output signal of the image sensor 4 and uses the length of the arbitrary scale image and the length from the reference position set on the image sensor 4 to the center of the above-mentioned arbitrary scale image to calculate the output signal for the image sensor 4. A signal corresponding to the absolute position of the scale plate 2 is output.

That is, in the configuration as described above, when the scale plate 2 moves in the repeating direction of the scale (arrow A) and stops, a waveform obtained by sampling and holding the output signal of the image sensor 4 (the image sensor outputs the sampled and held waveform) ) is as shown in Figure 3(a), then after converting this staircase waveform to a gentle waveform as shown in Figure 6@Φ) through a low-pass filter with an appropriate cutoff frequency, , the waveform can be shaped into a rectangular wave as shown in FIG. 3(C) by using a predetermined reference voltage Vref. According to the waveform in FIG. 3(C), it is easy to know the time T1 from when the start pulse of the image sensor 4 occurs at time to to the center position of the first rectangular wave q. Furthermore, it is easy to know the width Δt1 of the rectangular wave q.

On the other hand, the above T1+Δt can be converted into a length from the frequency of the drive pulse of the image sensor 4 and the pitch of the light receiving part, and since the magnification of the projection lens 3 is also known, the rectangular wave q The width W1 of the corresponding scale will be rounded by calculation. Here, as shown in Figure 2, the widths of adjacent scales always differ by a, and there is only one scale with the same width, so by subtracting IIQiiW, the absolute address of the scale can be determined. You can know. moreover,
The start pulse is at time t. It is possible to read the scale with an accuracy of 1 pitch p or less depending on the length d calculated from the time T1 from the time when it occurs to the center of the width w1 of the scale. In other words, since 1 pitch p of the scale is constant, the length d is 1
/p pitch. Therefore, the width W of the first scale appearing on the image sensor 4 at a certain position. and length d. Keeping this in mind, if we measure the width W and length d of the first scale mark appearing on the image sensor 4 after the scale plate 2 has moved (FIG. 3(a)), we get:
(The length of movement of scale plate 2 between a certain position and the position after movement)
I'll be there for a while.

The display circuit 7 displays the amount of movement of the dial 2 from a certain position based on the signal from the processing circuit 6.

Next, an example of the drive device 5 and the processing device 6 will be described in detail using FIG. 4. The drive device 5 includes a clock pulse generator 50 and a drive circuit 51 including a counter, etc., which inputs the pulses of the clock pulse generator 50, and inputs the start pulse and the drive pulse to the dimensional image sensor 4. On the other hand, the processing device 6 includes a preamplifier 60 that amplifies the output signal of the -dimensional image sensor 4, a sample hold circuit 61 that samples and holds the output signal of the preamplifier 60 using the drive pulse of the drive circuit 51, and an output signal from the sample hold circuit 61. A low-pass filter 62 that converts the stepped waveform into a gentle waveform, a comparison circuit 63 that outputs a low level when the output signal of the low-pass filter 62 is smaller than the reference voltage ref, and a high level when the opposite is true. It has a first terminal for inputting the pulses of the pulse generator 50, and a second terminal for inputting the output pulses of the frequency dividing circuit 64, which divides the pulses of the clock pulse generator 50 so that the frequency is halved and outputs the divided pulses. However, a switch circuit 65 connects the first terminal to the output terminal when the output of the comparison circuit 66 is at a low level, and connects the second terminal to the output terminal when the output is at a high level, and the output terminal of the switch circuit 65 is connected to one terminal. AND circuit 6
6 and a flip-flop whose output terminal is set by the start pulse of the drive plane circuit 51 and reset when the output signal of the comparator circuit 63 switches from high level to low level, and whose output terminal is connected to the other terminal of the AND circuit 66. circuit 6
7, a counter circuit 68 to which the output signal of the AND circuit 66 is input, and a first
A storage command pulse generator 69 outputs a second pulse at the falling edge of the pulse, and a first pulse generator 69 stores the count value of the counter circuit 68 using the first pulse of the storage command pulse generator 69.
A memory circuit 70 , a second memory circuit 71 that stores the calculated value of the counter circuit 68 by the second pulse of the memory command pulse generator 69 , and the above-mentioned It is comprised of an arithmetic circuit 72 that calculates the length using equation (1).

Therefore, from the drive circuit 51 at time t. When a start pulse is generated, the light receiving portion of the image sensor 4 is sequentially driven by the drive pulse, and the sample hold circuit 62 outputs a stepped signal as shown in FIG. 6(a). The output signal of the low-pass filter 62 becomes a smooth signal as shown in FIG.
The waveform is shaped into a rectangular wave like this. The switch circuit 65 is activated at time t. The pulse generator 50 outputs pulses until the rectangular wave rises from
The output pulse of is at time t. The counter circuit 68 counts from the time t2 to the time t2. At time t2, the first pulse generated from the storage command pulse generator 69 causes the first storage circuit 70 to store the above-mentioned count value. From time t2 to time t3 when the output signal of the comparator circuit 63 is at a high level, the switch circuit 65 switches to output the output pulse of the frequency dividing circuit 64, and this pulse is counted by the counter circuit 68. Time t3 when the output signal of the comparison circuit 66 falls
At this time, the flip 70 knob 67 is reset, the AND circuit 66 blocks the input of the pulse to the counter circuit 6'8, and the second memory circuit 71 inputs the counter circuit 68 by the second pulse of the memory command pulse generator 69. The count value of is memorized. Therefore, the first memory circuit 70 stores the time t.
. The number N of pulses of the pulse generator 50 counted from time t2 to time t2 is stored in the second storage circuit 71.

The number N2 of pulses of the pulse generator 50 counted from time to time t1 is stored respectively. Therefore, since the number of pulses N2 corresponds to the time t1, that is, the length d, and the number of pulses (N2-N,) The scale plate 2 for the one-dimensional image sensor 4 is calculated from the measured value of
The absolute position of can be calculated. Preferably, a memory circuit is added, the above-mentioned value is stored in the added memory circuit as a reference value, the scale plate 2 is moved relative to the image sensor 4, and the measured value is subtracted from the above-mentioned reference value. If you add a function to do this, you can know the amount of movement.

Note that in the above example, measurement is performed using the first scale image, but if two or more scale images are generated on the -dimensional image sensor 2, no matter which scale image is used for measurement, The amount of movement measured is the same. That is, as shown in FIG. 3(a), since the interval between the first scale image and the second scale image is constant at the pitch p, the 311th (
In a), there is the relationship d2=d1+p...Equation (2), and on the other hand w2=w, -a-...Equation (3), so the above equation (1) is replaced by the equation ( By substituting d and W obtained from Equation 2) and Eq.

Although the above embodiments have mainly been described with respect to a position encoder for measuring length, the present invention can be similarly applied to a position encoder for measuring angle. In that case, the scale is repeated in the circumferential direction at an equal angular pitch (in this specification, this case is also abbreviated as pitch), and the length in the circumferential direction changes sequentially by a predetermined amount. good.

Furthermore, it is clear that the measurement start time of time T1 is not limited to the time to when the start pulse occurs, as long as it is determined in advance.

Furthermore, in the above embodiment, an example was explained in which the repeating direction of the scale image almost coincides with the arrangement direction of the light receiving parts of the image sensor, but especially in the case of length measurement, the coincidence relationship is actively broken and the scale If the image is projected so that the repeating direction intersects the arrangement direction of the light receiving sections of the image sensor, the resolution can be increased.

(Effects of the Invention) As described above, according to the present invention, the absolute address of a scale can be determined just by using one scale pattern and one image sensor, and the accuracy is improved up to the displacement amount of one pitch or less of the G-scale. It can be packed.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of an apparatus according to an embodiment of the present invention, FIG. 2 is an enlarged view of a scale used in the embodiment of FIG. 1, and FIG. 6 is a diagram of a processing device used in the embodiment of FIG. FIG. 4 is a timing chart for explanation, and FIG. 4 is a block diagram for explaining details of the processing device used in the embodiment of FIG. (Explanation of symbols of main parts) 2...Graduation plate, 3. Intercurve projection lens, 4...Dimensional image sensor, 6
...Surface processing device. Applicant Nippon Kogaku Kogyo Co., Ltd. Agent Takao Watanabe 1st Ward 2nd grade

Claims (1)

[Claims] a scale plate having a scale that repeats at a pitch of 14 and whose length in the repeating direction sequentially changes by a predetermined amount; a one-dimensional image sensor in which light receiving sections are arranged at a predetermined pitch; an optical system that projects an image of the scale onto the image sensor so as to be sufficiently larger than a predetermined pitch; an optical system that inputs an output signal of the image sensor; 3. Processing means for outputting a signal corresponding to the absolute position of the scale plate with respect to the image sensor based on the length from a reference position determined on the image sensor to the center of the arbitrary scale image. Chiron encoder.