JPH07286861A - Device and method for optical conversion - Google Patents

Abstract

PURPOSE: To provide a compact optical converter with which the maximum resolution can be obtained by using the interpolation of high accuracy, by projection a pattern of light and shade having a correlation with the geometric structure, onto at least one photosensitive array surface of the shape of an integrated circuit. CONSTITUTION: An integrated circuit 1 comprises a photosensitive increment- measuring range 1A and a photosensitive absolute measuring range 1B. An absolute measuring system of low resolution and that of high resolution have a common luminescent means. They receive radiation of light from a common light source 3 and have a common optical image of both of a code track B to the absolute position of a scale 5, and a code track A to the increment shift, on a common photosensitive detector. When the light and shade pattern having the geometric correlation to the geometric structure of the surface is projected onto at least one photosensitive array surface of the shape of the integrated circuit 1, the interpolation can be performed with the accuracy of the integrated circuit 1 or an outline of the photosensitive surface of the same, as the result of the photosensitivity thereof.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The invention relates to the field of transducers, length transducers and angle encoders, and in particular to optical absolute measuring transducers.

[0002]

BACKGROUND OF THE INVENTION Absolute measurement transducers, especially length transducers, have particular problems. One is that high positional resolution must be obtained for a considerable length. Significant length means more than 1 meter. Also, high position resolution means less than 100 nanometers.

Incremental transducers with long overall length and high position resolution are cheaper than absolute transducers with the same requirements. Absolute measurements generally have a high added cost. For example,
It is possible to combine two separate systems, each with its own illumination and detection components, and with very complex repeat adjustments. Such a converter is RSF's "LCI"
It is a device. Other transducers are very expensive as they require two separate systems, some of which can reach a cost of 15,000 Deutschmarks per 50 centimeters. Such a converter is known from the E.I. M. S. "Spacer" device.

[0004]

As a result, absolute transducers must be well planned and used because they are limited in size, primarily for economic reasons. However, for the purpose of being able to equip all types of precision machines, including inexpensive ones, with high-performance absolute converters, even in fields that were previously dominated by large companies,
SMEs also have the opportunity to compete.

This object has been achieved by the invention as defined in the claims, having a large size and high resolution,
Moreover, it is possible to manufacture an inexpensive absolute converter.

In particular, one basic fact is that well-planned integrated circuit precision (precisi) so that on the one hand the adjustment problem is eliminated and on the other hand interpolation can be used to the utmost limit.
on) is used. To this end, the sensor structure of the present invention comprises a photosensitive detection element, preferably a light-A.
An SIC, which is arranged on the substrate, is provided with an incremental sensitive measurement track and an absolute sensitive measurement track (or detection track) so as to be electrically interconnected, on which for example transmitted light Evaluate conventional standard or scale optical (code) patterns in, or special code patterns for incident light or reflection. Then, preferably, an imaging optical system is connected between the pattern and the detection track. Due to the special design of the detection track, maximum resolution can be obtained with high precision interpolation. As a result of the design according to the invention, in particular, a very obvious miniaturization can be achieved, which is itself advantageous.

[0007]

The transducer according to the invention is an absolute measuring system, and in the case of length transducers, measuring resolutions higher than 100 nm are obtained for measuring lengths of up to several meters. The scale is, for example, a conventional transmitted light glass
It can be a scale, on which is mounted a conventional incremental track with a periodic grating set parallel to the absolute code track. The absolute code is constituted by, for example, a serial code, preferably an m-sequence. In the case of position change, one bit of the absolute code is made equal to one cycle of the incremental track. The scale is imaged on a large scale on the photodetector by an imaging system (optical system). Such a length generator has three specific features.

From a system point of view, the measuring system is integrated in an integrated microstructure. Measuring system,
All elements of the low resolution absolute measurement system and the high resolution incremental measurement system have a common lighting system. That is, they share the light of the same light source and have a common optical image of both code tracks and a common sensitive detector, preferably a light-ASIC, so that both individual measurement systems are automatically and repeatedly adjusted. To be done. Adjustments to the correct signal, focusing of the imaging, and rotation and tilting of the detector with respect to the scale take place simultaneously on both measuring tracks. Therefore, there is no angular error between the two measuring systems.

The measuring system uses a simple imaging system with a reasonable allowance for mounting the measuring head and the guidance of the head with respect to a standard scale. This is the object side telecentry
And a small numerical aperture. This numerical aperture is large enough for incremental grids and resolved absolute codes. Therefore, even when the image is out of focus or the depth of focus is maximum, an image can be obtained at a constant image magnification. The imaging system is provided with a telecentric stop from the center to the rear, for example by plastic injection molding of PMMA or polycarbonate, for example by cheap color printing.
Along with special parts for mounting the optical system, the single-lens system (sin
It has the advantage that it can be manufactured as a gle-lens system).
The imaging element can be configured by a planar diffractive lens (for example, Fresnel lens).

The measurement system uses a special photo-ASIC for detection purposes. The ASIC has a line sensor for scanning an absolute code and a special array of four photodiodes with locally sinusoidally changing surfaces set to project onto a grating. In that case, the quadrature signal of the incremental system is provided.
The sine function of the four photodiodes has a repeating phase position of 90 °. When a bar pattern is projected onto the sinusoidal diode and moved over the four diodes, the quadrature signal is obtained from the nearly ideal individual sinusoidal signal due to the difference in the photocurrents of the diodes. bar·
If the period of the pattern is the same as the period of the sine wave of the diode plane, then the fundamental mathematical properties of the Fourier transform can be exploited, so this signal shape is not the intensity profile or optical defocus of the bar pattern. being independent.

Due to the high precision of geometrical form and shape reproducibility, such as in the production of semiconductor circuits and in particular in CMOS processes where the dimensions are reduced to a minimum, the diode plane is virtually completely localized. Can be made identical to the sine function. If these photodiodes are configured to include several sine periods, the extension of the scale is also evaluated simultaneously during position measurement and the measurement system
For example, it is less susceptible to interference due to dirtying of the scale. A quadrature signal with almost perfect sinusoidal modulation allows very high precision interpolation and greatly improves position resolution. Obviously, this special design of the incremental track can also be used for pure incremental converters with maximum resolution.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below in detail with reference to the drawings. The essential elements of the measuring system according to the invention are shown in FIG. From a system point of view, it is preferable to form it as an integrated micro system. The integrated circuit 1 has a photosensitive incremental measurement range 1 on its substrate.
A and a photosensitive absolute measurement range 1B, which are combined by a processing and amplification circuit IC to form a measurement system. In the preferred embodiment, the two components of the measurement system, the low resolution absolute measurement system and the high resolution incremental measurement system, have a common light emitting means. That is, they receive light from the same light source 3 and have a common light image on both the code track B for the absolute position of the scale 5 and the code track A for the incremental shift, on a common photosensitive detector 1. Photosensitive detector is optical-ASIC
Is preferred. In this case, the optical system in the shape of the lens 2 allows the optical image to be appropriately modified, for example enlarged. As mentioned above, the illumination of the common light source, the image of the common optics, and the detection of the common detector automatically and repeatedly adjust the individual measurement systems. Adjustments or settings for the correct signal, i.e. focusing of the image, take place simultaneously on both measuring tracks. Also,
In FIG. 1, the measured signal is fed from the output of the sensor to the interface transformer for conditioning the signal.
It is also shown passed to 7 and transformed there to a standard 5V for controlling the machine tool 8. It should be borne in mind when using imaging optics that left / right and top / bottom are interchanged.

Shadow castin of illuminated system
If only g) is used, no optical image of the scale can be obtained on the detector without a lens or imaging system. Thus, for example, for the same 20 μm grating period, the same spatial detection allowance needs to be taken into account, as in conventional length conversion systems.

Additional surface 1B and measuring unit or measuring means 1
By removing B, the absolute measuring part, an incremental measuring system with very high interpolation accuracy is obtained. Moreover, the switching allows only the incremental information of the dislocation to be evaluated, so that both an incremental converter and an absolute converter are provided.

When using another optical system in addition to the measurement system, it is better to select the simple imaging system 2. The imaging system 2 has a certain tolerance with respect to the standard scale with respect to the mounting of the measuring head with the light source, the lens and the optical-ASIC and the guidance of the head. This is achieved by means of object-side telecentering and a small numerical aperture. The numerical aperture is chosen large enough for the resolution of the incremental grid and absolute code. Therefore, an image with a constant image magnification can be obtained even when the focus is out of focus or the depth of focus is maximum. Imaging system 2
Can be manufactured as a single-lens system with special parts for mounting the optical system by providing a telecentric stop at the rear center side, for example by means of plastic injection molding of PMMA or polycarbonate, for example by inexpensive color printing There is an advantage. The imaging component is a flat diffractive lens (diffr
activelens).

A sensor according to the invention, in this case an ASIC
Is a line sensor type first photosensitive area for scanning an absolute code, and four interlace photodiodes P1 having a locally sinusoidally changing surface as shown in FIG. P2, P3
And a second photosensitive area in the form of a special array of P4. When projected onto a grating, this sinusoidal array provides the quadrature signal of the incremental system. The sine functions of the four photodiodes have repeating phase positions of diode 1-0 °, diode 2-180 °, diode 3-90 °, and diode 4-270 °. Project the bar pattern onto the sine-wave diodes and move them over the four diodes to 0 ° and 1
80 ° diode photocurrent difference I1-I2, and 90
If a photocurrent difference I3-I4 of the diodes of .degree. And 270.degree. Is produced, this gives a quadrature signal with a nearly ideal sinusoidal individual signal, i.e. a sine and cosine signal in each case. If the period of the bar pattern is the same as the period of the sinusoidal diode surface, then
This signal shape is independent of the intensity profile of the bar pattern and can take advantage of the basic mathematical features of the Fourier transform.

Fabrication of integrated circuits is a proven technology
Maximum accuracy is obtained for reproducibility of the outer shape. In particular, using CMOS technology whose dimensions are reduced to a minimum, the diode plane can be formed completely on the substrate such that it is locally identical to the sine function. These photodiodes have several sine periods (Fig. 2
With a structure such as that shown in Figure 1), the extension of the scale is also evaluated simultaneously during the position measurement, and the measuring system is less susceptible to disturbances, for example due to dirtying of the scale. However, the most important advantage is that the nearly perfect sinusoidally modulated quadrature signal from the latter provides a high degree of very accurate interpolation and improved position resolution. Interpolation is often problematic because it always gives a result, but it is not always possible to trust it.

For the absolute track B and scale 5 on the solid measuring section, for example, an 18-bit word m-code can be used. Incremental tracks have an equidistant grid (equid
istant grating) is used. It has the same periodicity as the regular sinusoidal pattern of the four diode faces of the sensor projecting to the back of the scale. Finally, the absolute signal is combined with the incremental signal to give the absolute position signal value.

FIG. 3-3.1, 3.2 shows an example of the correlation or cooperation of the signals of the incremental track and the absolute track.

The 3.1 incremental track comprises sensor tracks 1A which are sinusoidal in track geometry, two of which are 90 ° phase-shifted, namely the cosine track COS and the sine track SIN. As shown. Also, a scale grating is projected on it and has the same period. Although a trigonometric track is shown reaching the first gap, in practice this pattern extends to as many gaps as the length of the sinusoidal grating electrode extends. Here, the phase shift is 90 °.

At absolute track 3.2, a projection of the m-code can be seen on the sensor grating 1B. PD ₁ is a binary value obtained from the photodiode 1, and PD ₂ is a binary value obtained from the photodiode 2. For this purpose, the binary level is set to be half the maximum signal. In this example, PD ₁ thus has a different binary value than PD ₂ .

3.3 to 3.7 show the individual signal trains and their coupling to the desired absolute signal.

The sine or cosine function S shown in 3.3.
And C, or their pulse train z ′ = shown in 3.4.
The symbols C and z = symbol S together with the phase function φ form the information of the incremental measurement. At 3.6, the binary values PD ₁ and PD ₂ obtained as described above form the information of the absolute measurement. Then, for the sine function, the binary multiplication of Z · PD ₁ and for the cosine function Z ′ · PD
The _second binary multiplication to calculate the corresponding bit b of the absolute code by 3.7 to calculate the absolute position. here,
Depending on how the 3.1 and 3.2 positions were obtained, one or the other bit is indicated, not both.

FIG. 4 shows an embodiment operating on incident light. The shape of the sensor that operates with transmitted light is a perspective scale.
The shape of the (transilluminated scale) greatly affects the shape, and vice versa. However, this can be seen as a very interesting aspect regardless of the present example of the incident light. One of them uses a genuine part machine as a standard or measure to increase the measurement accuracy. In other words, the patterns on typically separate scales are directly impressed on the relevant parts of the machine that make the desired movements, and the one or more incident photosensors are fixedly arranged relative thereto. In such a structure,
For example, since the scale and the machine are not affected by the temperature change, it is possible to prevent the accuracy from decreasing.

The signal produced by the sinusoidal photosensitive surface is exactly sinusoidal in period, from which the sine and cosine analog signals shown at 3.3 in FIG. 3 are derived. In the simplest case, the analog signal can be converted into a square wave signal by a comparator if the basic resolution of the measuring device is appropriate. In this way, four counting stages are obtained from one cycle. When interpolating an analog signal, the fundamental cycle is subdivided into smaller units. The accuracy of the interpolation depends on the accuracy of the fundamental period, the latter on the shape of the analog sine wave signal. If the latter is inaccurate or distorted, there will be a correspondingly incorrect "interpolation scale". A geometrically accurate basic function image (bas
As a result of ic function imaging, integrated circuit manufacturing accuracy, and accurate sinusoidal photosensitive surface, this accuracy is correspondingly applied to the "interpolation scale".

The present invention allows for significant miniaturization of the optical components of the transducer. In particular, in the embodiment according to FIG. 4, by incorporating the central part of the transducer into the machine, the solid measuring part is scanned with the incident light and the transducer becomes part of and operates on the machine. When actually used, it becomes an integral part of the machine and reacts to environmental conditions like the machine itself.

[Brief description of drawings]

FIG. 1 is a measurement principle diagram showing, by a schematic arrangement of individual elements, an example of a device that operates with light that passes through a scale.

FIG. 2 shows a detection track with a high possibility of interpolation.

FIG. 3 is a diagram showing an example of a method for evaluating the correlation between an absolute signal and an incremental signal in the case of FIG.

FIG. 4 is a diagram showing the measurement principle of FIG. 1, which operates with incident light and evaluates evaluation of reflected light from the scale.

[Explanation of symbols]

 1 Integrated Circuit 1A, 1B Photosensitive Incremental Measurement Range 2 Lens 3 Light Source 5 Scale 6 Telecentric Stop 7 Interface Transformer

Claims (18)

[Claims] 1. A method for measuring and utilizing the displacement of a scanning head relative to a solid measure or measuring means, preferably in an optical transducer, wherein at least one photosensitive array surface in the form of an integrated circuit. A pattern of light and shadow (a bar pattern of the same period) having a geometrical correlation with the geometrical structure of the surface is projected on (for example, sinusoidal), and the geometrical shape of the surface of the photosensitive array is projected. Geometrical shape, when projecting the correlated light and shadow patterns onto the surface, as a result of their photosensitivity, such that they can be interpolated with the accuracy of the contour of the integrated circuit or its photosensitive surface, and moved. A method in which an electrical signal train is generated so that it can be used as a measurement or position signal representative of a range of. 2. The method of claim 1, further comprising forming a photosensitive surface, the additional photosensitive surface having another pattern of light and shadow geometrically correlated with a geometric structure of the additional photosensitive surface. By projecting onto an additional photosensitive surface, an electrical signal sequence corresponding to the absolute value is obtained as an additional signal, which is geometrically designed such that it can be sent out as a measurement or position signal. 3. A method according to claim 1, wherein the electrical signals of the photosensitive surface are combined to generate a common position signal. 4. The geometrical structure of the photosensitive surface according to claim 1, wherein the geometrical structure of the photosensitive surface is formed according to a circular function.
A pattern correlated for this purpose, which is projected as a grid, is formed and projected with the same period as the circular function, and the electrical signal sequence is linearly interpolated and sent out as a measurement or position signal. Method. 5. The geometrical structure of the photosensitive surface according to claim 4, wherein the geometrical structure of the photosensitive surface is formed according to a sinusoidal shape, and 0, 90, 180 and 2 are mutually arranged with respect to such sinusoidal surface.
A pattern, arranged with a phase angle of 70 ° and correlated for this purpose, is formed with the same period as the sine function and projected as a grid, and the electrical signal sequence obtained on the four photosensitive surfaces is linearly interpolated. , Relayed as a measurement or position signal. 6. The pattern according to claim 1, wherein the pattern projected on the photosensitive surface is modified by a scale-linear manner by an imaging optical system. Method. 7. A method according to claim 1, wherein the projected pattern is generated in incident light. 8. The projected pattern according to claim 1, wherein the diffractive optical structure or the optically diffusing structure is incident light.
A method characterized by being produced by reflection or diffraction on. 9. The method of claim 8, wherein the projected pattern is imprinted on or located on a portion of the machine. 10. The method according to claim 1, wherein the common optical system projects the absolute code and the reflection code (incremental code) onto a common sensor, preferably an integrated circuit having a sensor surface. how to. 11. The method according to claim 1, wherein
A method characterized by the use of a telecentric optical imaging system on the object side, optimizing the telecentric stop (maximum) to ensure a high light emission which is insensitive to defocus. 12. An optical converter having a light source (3) and at least one photosensitive component surface (1A) in the form of an integrated circuit, said optical converter being consistent with and geometrically correlated with the geometrical structure of said surface. By projecting the applied light and the shadow pattern (A) onto the photosensitive surface (1A), an electric signal sequence is obtained, which is interpolated with the manufacturing accuracy of the integrated circuit or the contour of the surface to measure or position. An optical transducer, wherein the surface is geometrically designed to be relayed as a signal. 13. The method according to claim 12, further comprising an additional light sensitive surface (1B), said additional light sensitive surface being light and shadow geometrically correlated with the geometrical structure of said additional light sensitive surface (1B). By projecting another pattern (B) of the above onto the additional photosensitive surface, an electric signal train corresponding to an absolute value is obtained as an additional signal, which is geometrically designed so as to be able to be transmitted as a measurement or position signal. An optical converter characterized in that. 14. Optical converter according to claims 12 and 13, characterized in that it comprises means (1C) for combining the electrical signals of the photosensitive surface to form a common position signal. 15. The geometrical structure of the photosensitive surface (1A) according to claim 12, wherein said sinusoidal surface has a sinusoidal shape and said sinusoidal surface is repeated to obtain angles of 0, 90, 180 and 270 °. The solid-state measuring part or measuring means (5) formed and correlated with it is formed for projection as a grating (A) of the same period as the sine function and is formed on the four photosensitive surfaces. An optical transducer, characterized in that the columns are linearly interpolated and can be sent out as measurement or position signals. 16. An imaging optics, preferably a telecentric stop (6), according to any one of claims 12 to 15, between said photosensitive surface and the pattern of the projected solid measuring part (5). An optical converter having a telecentric optical imaging system having. 17. The method according to claim 12, comprising a common optical system (2) and a common sensor (1) for imaging an absolute code and a relative code (incremental code, said sensor preferably. An optical converter configured as an integrated circuit having a sensor surface. 18. The decentration insensitive according to any of claims 12 to 15, by using a telecentric optical imaging system (2, 6) on the object side and optimizing the telecentric stop (6). However, an optical converter characterized by ensuring high light emission.