SU1583735A1 - Indicating raster for four-channel photoelectric instrument transducer - Google Patents

Abstract

The invention relates to a measurement technique and can be used as part of a four-channel photoelectric measuring transducer. The purpose of the invention is to improve the measurement accuracy by ensuring equality of amplitudes and absolute values of the components of the output signal during raster rotation. Radiation from four sources passes through the optical system, which forms four parallel radiation fluxes, and then through conjugation of the measuring and indicator rasters perpendicular to their surfaces. The indicator raster consists of four sections, in each of which the raster grating is made in the form of two groups parallel strokes crossed by tilting each group by angle α and -α, respectively, relative to the longitudinal axis of the indicator raster, pairs of groups of lines are made with relative fa the reference shift is 0, ϕ / 2, 3ϕ / 2, and ϕ radians, respectively. Having passed the collecting lenses, each radiation flux falls on one of the photodetectors installed in the image plane of the moire pattern formed by the strokes of the measuring raster. The signals with phase shift O and ϕ, as well as ϕ / 2 and 3ϕ / 2, are used to obtain two phase-shifted by ϕ / 2 output signals without a constant component. With the relative movement of the matched rasters, due to the non-linearity of the guides, an uncontrolled spread of the rasters also occurs. The form of execution of the indicator raster in this converter provides for the compensation of phase shifts of the output signals. This eliminates the error in measuring the linear movement of rasters during their uncontrolled reversal and leads to an increase in measurement accuracy. 3 il.

Description

The invention relates to a measurement technique and can be used as part of a four-channel photoelectric measuring transducer for measuring the magnitude of the movements of objects.

The purpose of the invention is to improve the measurement accuracy by ensuring equality of amplitudes and absolute values of the components of the output signal during raster rotation.

FIG. Figure 1 shows the optical layout of a four-channel photoelectric measuring transducer; in fig. 2 - indicator raster of the converter; FIG. 3 shows a vector diagram of the transducer signals.

A photoelectric measuring transducer contains four sources of radiation 1 located along the course of radiation, an optical system 2, a measuring raster 3, an indicator raster 4, four collecting lenses 5 and four photo-detectors 6 mounted behind them. The indicator raster 4 consists of four sections 7-10, on each of which is made of a raster lattice consisting of two groups of parallel strokes crossed by tilting each group at an angle of + a and-a, respectively, relative to the longitudinal axis of the indicator scale. The pairs of groups of strokes in sections 7–10 are made with a relative phase shift of l 3 and gome 0, n, - and l: radians, respectively.

Each of the photodetectors 6 is installed in the image plane of the moire pattern formed by the strokes of the measuring raster 3 and a pair of groups of strokes of the indicator raster 4.

Photoelectric measuring transducer works as follows

The radiation from sources 1 through the optical system 2, which forms four parallel radiation fluxes, perpendicular to the surface of rasters 3 and 4, passes through the interface of these rasters, collects lenses 5 and enters the photodetectors 6. Each of the four parallel streams passes through measurements - a solid raster 3, one of four areas of the indicator raster, one of the collecting lenses 5 and fed to one of the photodetectors 6. When the relative movement of the measuring raster 3 and the indicator raster 4 occurs, the radiation is modulated raster mapping. The slope of the crossing parallel lines at an angle ± ss of the proposed indicator raster 4, as well as of the known, is necessary to reduce the dependence of the output signal amplitude on the angle of rotation of the rasters φ. In this case, the angle a is chosen equal to half the maximum angle of rotation of the rasters (p max.

Photodetectors b convert the modulated radiation into an electrical signal, and the spatial phase shift of the bars of the indicator raster 4 converts the phase shift of the electrical signals of the photodetectors 6. Thus, at the output of the photodetectors 6 opposite the sections 7-10 of the indicator raster 4, electrical signals with relative phasotg 1 tg

Vym shift Oh, TT, - and l radians

respectively. Signals with a phase shift of 0 and just like signals with a phase

g zl shift - and-tr are used to obtain 22

l

neither two phase-shifted weekends

signals without a constant component by counter-switching them. The output signals make it possible to organize a reversible counting of the moire bands with the help of known reading devices.

With the relative linear movement of the rasters 3 and 4, because of the linearity of the guides (not shown) or for other reasons (for example, errors in the synchronous operation of linear motors carrying out a plane-parallel movement of the photoelectric measuring transducer), the mating rasters also rotate at a certain angle f .

In the case of an asymmetrical arrangement of the radiation flux relative to the longitudinal axis of the indicator raster 4, an error in the measurement of displacements appears due to the lack of appropriate compensation for phase shifts of the output signals.

With the proposed implementation of the indicator raster 4, the output signal of each photodetector b is obtained as a result of the conversion of the radiation flux formed by the combined action of crossed strokes (Fig. 2). At the same time, each signal is formed by a single component, the amplitude and phase of which do not depend on the uncontrolled rotation of rasters 3 and 4 on the position of the radiation flux within the surface area of the indicator raster 4,

In the diagram (Fig. 3), the vector A denotes the signal received from the conjugation with the upper (in Fig. 2) section of the indicator raster 4, and the vector B represents the signal from the conjugation with the lower portion. The spatial phase shift between pairs of groups of strokes for the selected raster areas is equal to jt radians, Li) in which the phase of signals A and B changes, respectively, when the mapped rasters 3 and

4 at an angle of p. For this implementation of the indicator raster 4 in the converter, the angles are always equal in magnitude and opposite in sign, and the law of change of signals A and B when rotating rasters 3 and 4 is the same.

Consequently, the vector diagram of signals from photodetectors 6 has the same appearance both for the case when the radiation flux is located symmetrically with respect to the longitudinal axis of the indicator raster 4, and for the case of its displacement relative to this axis, therefore the measurement error of the linear movement of rasters 3 and 4 with their uncontrolled reversal is absent0

However, this will increase the accuracy of the measurements.

Claims (1)

The invention of the indicator raster to a four-channel photoelectric measuring transducer, made with areas formed by groups of parallel strokes, oriented in pairs at angles + a to the longitudinal axis of the indicator raster, pairs of groups of strokes in the areas are made with a relative phase shift of 0, 2, 3, 3 2 and, characterized in that, in order to increase the accuracy of measurements, the indicator raster is made with areas formed by crossing strokes. FIG. one 810Fig 2 A-8 X i% at