CN1100803A - Optical grating displacement measuring device with single harmonic output - Google Patents

Abstract

The measuring device is comprised of light source, focusing lens, black, and white main grating, indicating grating and photoelectric receiving device; the indicating grating is a sinusoidal one in which the light intensity transmissivity of the grating varies with a sine function, the present device eliminates the influence of high order of harmonics, the output of signal is only a single harmonic, the purity of signal harmonics is not influenced by space frequency variation of Moire fringe, and has high contrast, it can be widely used for measuring linear displacement and angular displacement.

Description

Optical grating displacement measuring device with single harmonic output

The present invention relates to use the device of the optical system measuring relative displacement of optoelectronic scanning grating.

Grating is used for the measurement of displacement of the lines and angular displacement to be known by people, contains abundant harmonic wave in the normal light gate signal, and content of high order harmonic generally can account for about 10% of first-harmonic, and these higher hamonic waves have influenced the quality of grating signal.In surveying instrument,, generally can not adopt the method for circuit filtering, and can only carry out optically filtering because measuring speed is non-constant.This studies seldom on the one hand at present, and a kind of method (United States Patent (USP) 3,674,372) of improving the sine of grating signal with the space diaphragm is only arranged.The weak point of this method is: diaphragm only is applicable to the filtering of horizontal and vertical Moire fringe, can't be to the filtering of optical gate Moire fringe; Diaphragm filtering requirements Moire fringe has fixing spatial frequency simultaneously, and grating does not usually satisfy requirement in use; Diaphragm filtering has reduced the contrast of signal, and the DC level drift that the grating homogeneity causes is also more outstanding, and these shortcomings of diaphragm wave filter have limited its usable range greatly.

Purpose of the present invention provides a kind of novel grating measuring device, the grating signal that this device can single harmonic output.

Main points of the present invention are by the structure of grating grid line in the appropriate design optical grating measuring system, make the grating signal single harmonic output.Concrete is that its indication grating is the sinusoidal index grating of the light intensity transmitance of grating line by varies with sinusoidal function.Another feature of the present invention is that its black and white key light grid and sinusoidal indication grating all adopt striated pattern, and sinusoidal index grating has at least a scored area to satisfy along the vertical direction of groove delineation:

$l\left(x\right)=\underset{m=-1}{\overset{-1}{\mathrm{\Σ}}}{l}_{m}e\×p\left(\frac{\mathrm{\Ω\π}\×m}{d}\right)$

。The 3rd feature of the present invention be, black-white grating and sinusoidal indication grating all adopt radial grating, and its sinusoidal indication grating has at least a scored area to satisfy:

$l\left(\mathrm{\θ}\right)=\underset{m=-1}{\overset{+1}{\mathrm{\Σ}}}{l}_{m}e\×p\left(\frac{\mathrm{\Ω\θQm}}{\mathrm{\ω}}\right)$

Fig. 1 is an optical system synoptic diagram of the present invention.

Fig. 2 is the printing opacity function curve of black-white grating line.

Fig. 3 is the light transmission features curve of sinusoidal indication grating delineation line.

Fig. 4 a is black-white grating and the consistent synoptic diagram that forms the optical gate Moire fringe of sinusoidal indication grating groove direction.

Fig. 4 b is that black and white key light grid and sinusoidal indication grating intersect the synoptic diagram that forms horizontal Moire fringe with minute angle.

Fig. 5 is the synoptic diagram of measured angular displacement of the present invention.

1-light source among the figure, the 2-condenser, 3-black and white key light grid, 3 '-black and white key light grid groove, the sinusoidal indication grating of 4-, 4 '-sinusoidal indication grating groove, the 5-photoelectric receiving arrangement, the 6-axle,

Gap between z-black and white key light grid and the sinusoidal indication grating,

X-along with the coordinate of grating line vertical direction,

Y-along with the coordinate of grating line parallel direction,

τ ₀-be the average intensity transmitance of sinusoidal indication grating

τ ₁-be the largest light intensity transmitance and the τ of sinusoidal indication grating ₀Poor.

The present invention is further illustrated with reference to the accompanying drawings.As shown in Figure 1, light source 1 is positioned on the focal plane of condenser 2, and the collimated light that is sent by condenser 2 is successively by getting a very little gap z between the black and white key light grid 3 that face mutually each other and sinusoidal indication grating 4, two gratings, to avoid the two phase mutual friction.Black and white key light grid 3 can be linked together rigidly with some positions parts to be determined among Fig. 1, can move in the double-head arrow indicated direction; A sinusoidal indication grating 4 and a reference component link, and what is called has reference component with respect to position parts to be determined, is the object of reference of position finding.Represent coupling arrangement between grating group and the relative motion parts to be determined with two dotted lines respectively among Fig. 1.Black and white key light grid 3 have identical grating constant d with sinusoidal indication grating 4, and when their grid line 3 ' and 4 ' a little be formed slopely horizontal Moire fringe shown in Fig. 4 b, the perhaps 3 ' consistent optical gate Moire fringe that forms with 4 ' direction is shown in Fig. 4 a.Moire fringe is received by photoelectric receiving arrangement 5, usually contain a plurality of photovalves in the photoelectric receiving arrangement 5, because the effect of sinusoidal indication grating, the output of each photovalve does not all contain higher hamonic wave, have certain phase difference between these photosignals, can be used for the segmentation of grating and debate to etc.

In the two grating optical systems of being made up of black and white key light grid and sinusoidal indication grating shown in Figure 1, black and white key light grid are that according to Fourier optics, the light distribution at the nearly diffractional field z place of grating planar can be expressed as under the collimated light irradiation of λ at wavelength

$(x,z)=\underset{i=-\∞}{\overset{\∞}{\mathrm{\Σ}}}|\left(z\right)e\×p\left(\frac{\mathrm{\Ω\π}\×1}{d}\right)\left(1\right)$

Wherein,

X be along with the coordinate of grating line vertical direction;

l ₁(z) be the amplitude of each harmonic;

D is a grating pitch.

And the light intensity transmitance of sinusoidal indication grating can be expressed as

$l\left(x\right)=\underset{m=-1}{\overset{+1}{\mathrm{\Σ}}}{l}_{m}e\×p\left(\frac{\mathrm{\Ω\π}\×m}{d}\right)---\left(2\right)$

In the photoelectricity receiving device, the light intensity 1 that a certain photovalve receives is the light distribution of black and white key light grid diffraction and the convolution of sinusoidal indication grating light intensity transmitance, is got by formula (1) (2)

$|{\∫}_s\∫|(x_0-x,z)l\left(x\right)d\×\mathrm{dy}$ $=\underset{m=-\∞}{\overset{\∞}{\mathrm{\Σ}}}\underset{m=-1}{\overset{-1}{\mathrm{\Σ}}}{1}_n\left(z\right)l_m{\∫}_s\∫e\×p\left(\frac{{2\mathrm{\πx}}_{0}n+2\mathrm{\π}\×(m-n)}{d}\right)d\×\mathrm{dy}$ $=\underset{m=-\∞}{\overset{\∞}{\mathrm{\Σ}}}\underset{m=-1}{\overset{+1}{\mathrm{\Σ}}}{1}_n\left(z\right)l_{m}e\×p\left(j\frac{2\mathrm{\π}{\×}_{0}n}{d}\right){\∫}_s\∫e\×p\left(j\frac{2\mathrm{\π}\×(m-n)}{d}\right)d\×\mathrm{dy}---\left(3\right)$

Wherein, s is the light area of photovalve;

x ₀Displacement for black and white key light grid.

M is an integer

N is an integer

Normal light electric device light area always is covered with tens of grating lines, and the fraction part of the grating line that the edge, light area is covered can be ignored on engineering fully, and like this, when m ≠ n, the integration in the formula (3) is 0; When m=n, the integration in the formula (4) is s, therefore,

$1\≈\underset{m=-1}{\overset{+1}{\mathrm{\Σ}}}{1}_n\left(z\right)l_{n}e\×p\left(j\frac{2{\mathrm{\π}\×}_{0}n}{d}\right)---\left(4\right)$

This shows that in the displacement measuring device of black and white key light grid and sinusoidal indication grating composition, the output signal of photovalve does not contain the above higher hamonic wave of secondary.

In another kind of format surface (Fig. 5), black and white key light grid 3 along the circumferential direction have identical grating constant ω with sinusoidal indication grating 4; Black and white key light grid 3 and some corners parts to be determined are linked together rigidly, can move in the double-head arrow indicated direction, a sinusoidal indication grating 4 and a reference component link, and represent coupling arrangement between grating group and the relative motion parts to be determined with two dotted lines respectively in Fig. 5.Light source 1 is positioned on the focal plane of condenser 2, the collimated light that is sent by condenser 2 is black and white key light grid 3 and the sinusoidal indication grating 4 by facing mutually each other successively, sinusoidal 4 of indication gratings are got a less scene, black and white key light grid 3 and sinusoidal indication grating 4 formed be similar to Fig. 3, Moire fringe shown in Figure 4, Moire fringe is received by photoelectric receiving arrangement 5, because the effect of sinusoidal indication grating, the output of all photovalves in the photoelectric receiving arrangement 5 does not all contain higher hamonic wave.

Device shown in Figure 5 is similar to Fig. 1, only needs rectilinear coordinates axle x is changed to angular coordinate theta, and grating constant d is changed to ω and gets final product, thereby black and white key light grid and sinusoidal indication grating all adopt radial grating, and wherein sinusoidal indication grating has at least a scored area to satisfy:

$l\left(\mathrm{\θ}\right)=\underset{m=-1}{\overset{-1}{\mathrm{\Σ}}}{l}_{m}e\×p\left(\frac{\mathrm{\Ω\π\θm}}{\mathrm{\ω}}\right),$

Wherein: θ is angular displacement.

The grating measuring device that the present invention adopts black and white key light grid and sinusoidal indication grating to form is only exported single harmonic signal, compares (United States Patent (USP) 3,674,372) with other technology, has the following advantages:

1. sinusoidal indication grating can be made into and existing various indication gratings compatible form mutually, changes under the existing grating measuring device not needing, and just can reach filter effect as long as change a slice indication grating. And the diaphragm wave filter can only exist with own unique form, with existing grating reading device poor compatibility, is unfavorable for promoting.

2. adopt in the measurement mechanism of sinusoidal indication grating, the pure impact that is not subjected to frequency change between Moire fringe of grating signal harmonic wave has overcome the shortcoming of diaphragm wave filter.

3. adopt in the measurement mechanism of sinusoidal indication grating, grating signal has higher contrast, and the diaphragm wave filter is bigger to the impact of signal contrast.

The present invention can be widely used in the measurement of displacement of the lines and angular displacement, exportable single harmonic grating signal, and the certainty of measurement height has good promotional value.

Claims (3)

1, a kind of raster pattern displacement measuring device that can single harmonic output, light source is arranged, and be positioned on the focal plane of condenser, the collimated light beam that condenser sends, successively by black and white key light grid and indication grating adjacent one another are, and photoelectric receiving arrangement, wherein the groove of black and white key light grid and indication grating tilt mutually or direction consistent, and have means that connect mutually with moving component, it is characterized in that said indication grating is that the light intensity transmitance of groove of grating is by the sinusoidal indication grating of varies with sinusoidal function.

2, according to the said raster pattern displacement measuring device that can single harmonic output of claim 1, it is characterized in that, black and white key light grid and sinusoidal indication grating all adopt striated pattern, and sinusoidal indication grating has at least a scored area to satisfy along the vertical direction of groove delineation:

Wherein, x be along with the coordinate of grating line vertical direction, the span of x is the continuous scored area of grating;

τ (x) is the light intensity transmitance of grating line;

τ m is a constant;

$j=\sqrt{-1}$

D is the grating line spacing.

3, according to the said raster pattern displacement measuring device that can single harmonic output of claim 1, it is characterized in that said black and white key light grid and sinusoidal indication grating all adopt radial grating, wherein sinusoidal indication grating has at least a scored area to satisfy:

$l\left(\mathrm{\θ}\right)=\underset{m=-1}{\overset{+1}{\mathrm{\Σ}}}{l}_{m}e\×p\left(\frac{\mathrm{\Ω\θm}}{\mathrm{\ω}}\right)$

Wherein, θ is a grating angle coordinate along the circumferential direction, and the span of θ is the continuous scored area of grating;

τ (θ) is the light intensity transmitance of grating line;

τ _O, τ ₁Be constant;

ω is the grating line angular separation.

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