JPS61182521A - Detecting scale of absolute displacement - Google Patents

Abstract

PURPOSE:To attain the absolute detection of linear displacement by arranging a linear scale having high resolution and an absolute displacement gauge having rough resolution in parallel and adding a fine counting value of the linear scale to a detecting value of the displacement gauge. CONSTITUTION:The 1st track scale 10 consisting of a scale of 10mum pitches e.g. and having real time property, the 2nd track scale 12 consisting of a scale of 100mum pitches e.g. and the 3rd track scale 14 consisting of a phototransistor 16 and an LED18 as an optical measuring unit are arranged on one substrate in parallel and reading heads having photoelectric converters corresponding to respective scales 10, 12, 14 are also arranged. Thus, the absolute position can be always detected by adding reading values obtained from respective tracks. Consequently, the absolute scale having high resolution can be obtained with a simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a displacement detector that reads the relative position between a scale and a reading head using a charging converter or the like using a light emitting/light receiving element. The present invention relates to the structure of a scale used for absolute position detection, which detects a position with respect to the origin.

Analog detectors such as differential transformers have long been used as high-precision, absolute displacement detectors, but these analog detectors were originally designed to detect minute displacements in a narrow range. Although absolute detection is possible within the detection range, the higher the sensitivity, the narrower the detection range, and there are problems such as requiring A-D conversion for digital display, data processing by computer, etc.

On the other hand, as a digital displacement measuring device, there is a well-known device that reads a scale formed with an optical grating or a magnetic grating using a photoelectric method or a magnetoelectric method, and divides the obtained sinusoidal electric signal and displays it by counting. are in practical use.

Digital scale detection methods are generally divided into two methods: incremental detection and absolute detection. The incremental method uses a coordinate origin at an arbitrary position,
This device counts and detects the increments of divided pulses, and has a simple structure and easy electrical processing of the output, making it suitable for relatively low-speed detection. Disadvantages include the inability to reproduce the position even if the sensor is used, the inability to keep up with high-speed detection, and the accumulation of miscounts due to noise. On the other hand, the absolute detection method detects the position based on a predetermined origin using the coordinate values of a certain coordinate system, and the coordinates are fixed regardless of the measurement history, so there is no need for alignment at the start of measurement. Its features include being able to handle high-speed detection, not changing the origin even when the power is turned off and restarted, and being unaffected by vibrations and noise.

Detectors using these scales have the advantage of being able to obtain high resolution through multi-division, but in the case of multi-division scales, detection has been limited to an incremental method.

This is partly because incremental detection is simpler in electrical processing and device configuration, but also because there is no appropriate means for detecting the absolute position of the detection position with respect to the origin. Even if a fixed origin is set, miscounts due to excessive speed from the fish to the detection position, accumulation of errors due to noise, etc. are unavoidable. It has been considered difficult to put an absolute scale into practical use.

In addition, on the end surface or outer peripheral surface of the rotating disk or rotating cylinder,
Absolute detection is possible in the case of a so-called rotary encoder, which forms a code pattern with holes, slits, light shielding coatings, etc., and detects displacement by reading this with a transmissive or reflective photoelectric converter. In order to increase the resolution, it is necessary to provide a large number of code pattern formation lines and photoelectric converters (for example, 3 lines for 8 pulse detection, 4 lines for 16 pulses, 5 lines for 32 pulses, etc.) etc.) Whether it is a rotating type or a linear type, the base that forms the code pattern and the charging converter become larger and heavier, and the structure becomes more complicated. The problem was that the detector could not be put into practical use.

In order to solve the problems of the prior art, the present invention focuses on the fact that absolute detection is possible within each pitch of a scale signal even if the scale is subdivided. A high-resolution linear scale and a coarse-resolution absolute displacement meter are arranged in parallel as subscales, and a read head with a corresponding photoelectric converter is installed for each, and the fine count value of the main scale is added to the detected value of the subscale. By doing so, a scale capable of detecting seven linear displacements is provided.

An embodiment of the present invention will be described below with reference to the drawings.

In the present invention, a high-resolution main scale and a coarse-resolution 7-piece scale are arranged side by side, but in this embodiment, a high-resolution scale and a coarse-resolution scale are provided as the first track and the second track. , an example in which an optical length measuring device is provided as a third track on the same substrate and reading means corresponding to each of the first, second, and third tracks are provided in the same reading head will be described.

The tlI11 track scale 10 shown in Fig. 1 has the number of divisions required for the minimum reading as small as possible in order to improve real-time (immediate) performance, that is, the ability to track position changes. ) A fine pitch scale, for example, a 10 μs pitch scale is used. Then, the output signal of each pitch scale is divided into 100 by the phase modulation division method, and the minimum reading (resolution) is set to 0.1, Jm.

Although this phase modulation division method is a well-known and publicly used means, its outline will be explained here with reference to FIG. Scale signal E+=A+sin 2πx/p, E2=A2cos
2πx/p.

(p is the pitch of the scale, X is the amount of displacement) as the carrier wave signal c
By modulating and adding os wt and sin u+t, a signal of E=A sin(wt+2πx/p) is obtained. Figure 2 (a) shows X=0 in the above equation.
, that is, represents the waveform of the reference signal As1n wt,
FIG. 2(b) shows the shaped wave signal. Figure 2 (c)
is a clock signal, and FIG. 2(d) shows the waveform when the scale and reading head are displaced by ΔX relative to each other. The phase modulation division method counts the amount of displacement in units of P/N (N is the number of divisions) by interpolating a clock pulse to the phase difference ΔX of this waveform (d) with respect to the reference waveform (b). This ΔX is repeatedly interpolated every sin wt cycle while the displacement is stopped (referred to as "refresh"), so in the normal incremental counting method, a means is taken to adjust the phase difference every cycle, and the interpolated pulse is accumulated. However, in the present invention, this refresh pulse is read as it is as an absolute detection value.

In this embodiment, the pitch of the scale 12 of the second track is ten times the pitch of the scale 10 of the first track. That is, since the pitch of the scale 10 on the first track is 10, the pitch is set to 100, and the output signal is divided into 10 by the phase modulation division method, and the pitch is 10 μm.
Read from 0 to 90-*.

The third track 14 includes a phototransistor 16 and an LED 1
It consists of a simple optical length measuring device that applies the coupling characteristics of 8. This utilizes the principle that the irradiance of light is inversely proportional to the distance, and converts the electric signal obtained by the LEDi8 corresponding to the distance into a linear slope signal over the entire length, and then It is converted into a signal that is reduced step by step for each section corresponding to 1 pitch (100 μm in this embodiment) of the 2-track scale 12, so that a 7-unit detection value of 100 units can be obtained.

In the present invention, the scales 10, 12, and 14 of the first, second, and third tracks are formed on the same substrate, and photoelectric conversion elements corresponding to each scale are formed so that the detected values of each scale can be read simultaneously. are provided on the same reading head. The counting means is a conventionally known counter.

With this configuration, a read signal as shown in FIG. 3 can be obtained from each track. D is the signal of the first track scale 10, and one pitch of this signal is 10IjI1
Divide 1 into 100 to read 0.11AI11. When this is simulated, it becomes a scale like E, and the minute position of the point of scale composition is a count value between O and 9.9 μs.
It can be obtained by going to 1. F is the signal of the second track scale 12, G is its pseudo scale, and in this example, the pitch is 100.
Since it is divided into 0, the reading is 10μm, which is 10IJ.
The m digit of 0 to 90 μm is counted. H is tIIJ3
10 obtained by returning the detection signal at track 14
It represents a signal that decreases step by step every 0 kon, and ■ indicates its pseudo scale. This third track 14 allows the displacement from the origin to the detection position to be 100 over the entire length of the scale.
It is obtained as a numerical value in μs reading.

With such a scale configuration, for example, P-P in FIG.
The distance (Lp) of the position of ' from the origin is L p = T
Rs 10 T R2 + T R+ (In the above formula, TR3, TR2, TR, are the third
track, second track, and first track reading) absolute position detection is possible at all times. In the example shown in Figure 3, the reading of the third track is 4001JIn, the reading of the second track is 70μm1, the reading of the first track is 8.6
Since it is μm, L p = 400-+ 70 marks + 8, 6 IJ
m = 478.6 pm.

In the above description, a configuration using the first, second, and third tracks has been shown as a preferred embodiment, but it is also possible to omit the second track and use the first track scale as 1000 divisions. Although real-time performance is unavoidably impaired as described above when the number of divisions increases, the present invention can be configured with at least one track of high-resolution scale and one track of coarse-resolution absolute scale. I can do it.

In addition, in the above embodiment, an example is shown in which a simple optical measuring device is used as the third track 14, but the method is not limited to this, and the displacement from the origin can be measured by voltage, current, etc. using a linear potentiometer, a charge-coupled device, etc. However, other methods may be used as long as they can be converted into resistors.

Furthermore, the scale pitch, number of divisions, resolution, etc. can be set as appropriate, and the scale itself can be implemented regardless of whether it is photoelectric or magnetoelectric, and is not limited to transmission type, reflection type, etc. be.

As detailed above, according to the present invention, the structure is simple,
A wide-range, high-resolution absolute scale can be obtained without increasing the size or cost. Displacement detection using this scale enables high-speed detection over a wide range and high resolution, and there is no accumulation of miscounts due to noise, etc., and the original value is always maintained even if the power is turned off and turned on again. Is displayed. In addition, compared to conventional detectors such as differential transformers, it not only allows for wide-range digital detection, but also eliminates the zero point drift F, eliminating the need for zero point adjustment, and in the case of multi-point switching measurements, the number of measurement heads can be increased. By simply using this method, a number of excellent effects can be obtained, such as eliminating the need for each zero point and de'in 7g4 rectifier.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a scale configuration showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of a phase modulation division method, and FIG. 3 is an explanatory diagram of a read signal in an embodiment of the present invention. 10, 12.14: 1st, 2nd, 3rd track scale 16: Light emitting element 18: Light receiving element Fig. 1 Fig. 3

Claims (1)

[Claims] In a scale that detects relative displacement between a fixed part and a moving body, at least one track scale that detects a displacement signal by phase-modulating and multi-dividing the signal between the pitches, and another track that detects absolute displacement from the origin. An absolute displacement detection scale characterized by having two displacement detection means arranged side by side on the same board so that they can be detected simultaneously.