DE19614466B4 - Signal processing arrangement for a position measuring device - Google Patents

Abstract

A signal processing arrangement for a position measuring device has signal generating means which supply at least two periodic optical signals and converter means to generate at least one pair of derived periodic output signals from the periodic signals, each having a defined phase offset from one another. The converter means here comprise optoelectronic detector elements connected in parallel and / or anti-parallel, which are preceded by one or more beam splitting elements which cause at least a part of the periodic optical signals to be divided into partial signals.

Description

The present invention relates to a position measuring device.

A signal processing arrangement for a position measuring device is, for example, from EP 0 271 549 known. It is proposed to transform in a position measuring the evaluated three or more periodic functions each in a pair of also periodic, derived functions having a phase difference of 90 ° to each other. The signals resulting at the output can then be evaluated in a known manner for position determination, for example within an incremental position measuring system. The conversion of the three or more periodic signals applied on the input side takes place by means of converter means which generate the desired output signals with a phase offset of 90 ° by multiplying at least three applied input signals with non-zero coefficients and subsequent additive or subtractive combinations thereof. The actual signal conversion takes place in the proposed solution by means of known electronic components such as differential amplifiers and thus electrically connected electrical resistors. In this type of conversion of the applied input signals therefore results in a certain circuit complexity due to the required converter electronics.

A fundamentally similar problem exists when, for example, only two periodic optical signals are supplied within an incremental position measuring system which have a phase offset from one another which deviates from the desired 90 °. This can be due to a variety of influences in the signal generation, z. B. inaccurately manufactured scale divisions, etc., caused. Even in such a case, it is necessary to establish the defined phase relationship between the present signals to ensure reliable signal processing.

From the EP 0 548 848 B1 is an interferential optical position measuring device with three continuous grids known, the output side provides four incremental signals, which already have the desired phase offset to each other. A further transformation of these signals is not required.

The WO 89/05440 as well as the US 4,983,828 In each case further interferential optical position-measuring devices with a plurality of gratings passed through are disclosed. The output side resulting three, 120 ° out of phase signals are in turn each transformed by means of a transducer electronics in a pair of Ausgnagssignalen having the desired phase offset of 90 °.

The object of the present invention is therefore to provide a position measuring device in which the circuitry complexity for converting at least two periodic signals into at least one pair of defined phase-offset signals can be reduced.

This object is achieved by a position measuring device having the features of claim 1

According to the invention, the conventionally required converter electronics for processing the two or more periodic optical signals to be evaluated are replaced by an arrangement of suitably interconnected optoelectronic detector elements. The converter means include this u. a. the corresponding interconnected optoelectronic detector elements. Consequently, the circuit complexity can be reduced to the effect that the previously used for this purpose, additionally required converter electronics is completely superfluous. On the output side, in the signal processing arrangement of the position measuring device according to the invention, the two periodic, phase-shifted signals of interest are already present, the usual phase offset of these signals being 90 °. The thus prepared signals can then be further processed in interpolation and evaluation electronics for position determination in a known manner.

In addition to the reduction of circuit complexity is due to the now attributable converter electronics quote that the inventive solution also allows an extremely compact design of a position measuring device equipped therewith.

In addition, the position measuring device according to the invention allows a number of various design variants, depending on what is important on the part of the user. Thus, depending on the selected interconnection of the optoelectronic detector elements, it is possible to set output signals which are as offset-free as possible, or else a phase offset which is as precise as possible.

In an advantageous embodiment of the present invention, the proposed beam splitting element can further be dimensioned such that the signal intensities incident on the optoelectronic detector elements correspond to defined-predefined values; Any separately required signal multiplication is omitted in this case.

Further advantages and details of the position measuring device according to the invention will become apparent from the following description of embodiments with reference to the accompanying figures.

It shows

1A and 1B in each case a schematic representation of an embodiment of the signal processing arrangement of the position measuring device according to the invention in a different view;

2A a vector diagram of a way of combining three periodic optical signals;

2 B two circuit arrangements with optoelectronic detector elements, the signal processing based on the vector diagram from 2A guarantee;

Based on the schematic representations of 1A and 1B should first be explained the basic structure of the signal processing arrangement within a position measuring device according to the invention. This shows 1A a side view and 1B a plan view of the position measuring device with the signal processing arrangement. A position measuring device embodied in this way can be used, for example, in a machine tool in order to determine the relative position of a tool and a workpiece with high precision.

The position measuring device comprises signal generating means ( 1 ), which in the illustrated embodiment provide at least three periodic optical signals (R, S, T), which are evaluable for determining the relative displacement of two mutually movable parts. Here, the supplied signals (R, S, T) have a mutual phase offset of preferably 120 ° to each other. The signal generating means ( 1 ) are designed as a so-called three-grid or interferential measuring system, as for example from the EP 163 362 is known; Further, such measurement systems, for example, refer to the publication "Measure lengths in ultraprecision technology" by A. Spies in Feinwerktechnik & Meßtechnik 98 (1990) 10, pp. 406-410. In the manner of signal generation within such a signal generating means ( 1 ) should therefore refer to the publications mentioned; At this point, it will be discussed shortly.

It should also be emphasized at this point that the principle underlying the present invention, as already mentioned, can also be implemented in an analogous manner with only two periodic optical input signals. Thus, it may be necessary to prepare two existing input signals such that they have a defined phase offset of 90 ° to each other. The signal generating means in this case therefore do not provide the signals with the necessary phase relationship.

In the 1A and 1B is a three-emitter, based on an interferential measuring principle, shown with the schematically sketched beam path in a straight line. That of a light source ( 1.1 ), z. B. from an LED, emitted light beam passes through a condenser optics, not shown, as a plane wave to a first scanning graduation ( 1.2 ) and is diffracted by mainly three different spatial directions. At a relative to the first scanning ( 1.2 ) displaceable scale division ( 1.3 ), a further diffraction of the impinging wave trains takes place before the partial beams at a further, second scanning graduation ( 1.4 ) are bent once more. After passing the second scanning graduation ( 1.4 ) interfere the wave trains of the same spatial direction, the intensities of the three interfering beams depending on the phase shift, which from the relative displacement of scale ( 1.3 ) and scan division ( 1.2 . 1.4 ) results. In the case of the shift of scale ( 1.3 ) and scan division ( 1.2 . 1.4 ) result in three periodic, intensity modulated signals

Basically, also in the formation of the signal generating means ( 1 ) as a tri-grating device a wide variety of embodiments can be realized, that is, in addition to the illustrated transmission arrangement with two scanning graduations provided ( 1.2 . 1.4 ), of course, a reflection arrangement can be realized. In this case, a reflective graduation scale would then be used, while only a single scanning graduation is required, from which the incident light bundles are diffracted twice

After re-diffraction at the second scanning graduation ( 1.4 ) is transmitted via a downstream lens ( 1.5 ) an image of the interfering three partial beams in the focal plane of the lens ( 1.5 ) generated. In the focal plane usually three photoelectric elements are arranged as optoelectronic detector elements in the previously known Dreigittergebern, which convert the intensity modulated, periodic optical signals (R, S, T), which have a mutual phase shift of 120 ° to each other in further processable signal streams. For signal evaluation by means of conventional interpolation units, subsequent electronics, etc., however, two mutually phase-shifted by 90 ° signals are required.

Instead of a so-called matching or converter electronics, which so far between the signal generating means ( 1 ) and the downstream evaluation unit ( 2 ) is switched, the signal processing arrangement is now used according to the position measuring device according to the invention.

For this purpose, this comprises a schematically illustrated beam splitting element ( 3 ) to which the signal generating means ( 1 ) supplied optical signals (R, S, T) in the form of three partial beams impinge. As possible embodiments of suitable beam splitting elements ( 3 ) come into consideration, for example, phase grating or divider mirror arrangements, which cause a division of at least a portion of the incoming optical signals in at least two partial signals. In the case of phase gratings used, they are optically designed, for example, with a desired division of the incident light bundles into two partial beams so that diffraction takes place mainly in two spatial directions.

Of course, it is also possible, instead of a single beam splitting element ( 3 ) also provide a plurality of beam splitting elements for this purpose within the signal processing arrangement.

In the illustrated embodiment of the 1A and 1B is the division of the delivered three periodic optical signals (R, S, T) in two sub-signals (R ', R'',S', S '', T ', T'') provided, ie there are then six sub-signals (R ', R'',S', S '', T ', T''). In principle, depending on the design of the subsequent circuit arrangement, a division into more than two partial signals (R ', R ", S', S", T ', T ") can also be carried out. Likewise, it may well be sufficient to divide only a portion of the incident optical signals into at least two sub-signals, for example to divide two optical signals and leave the third unchanged, etc. Accordingly, the beam splitting element or elements ( 3 ) visually execute or to dimension.

The partial signals (R ', R' ', S', S '', T ', T' ') generated in this way act on downstream optoelectronic detector elements (DR', DR '', DS ', DS' ', DT', DT '). '), wherein a separate optoelectronic detector element (DR', DR ", DS ', DS", DT ', DT' ') is required. In the illustrated embodiment, six optoelectronic detector elements (DR ', DR' ', DS', DS ') are therefore due to the division into six partial signals (R', R '', S ', S' ', T', T ''). ', DT', DT '') provided within the position measuring device according to the invention.

The arrangement of the optoelectronic detector elements (DR ', DR ", DS', DS", DT ', DT ") preferably takes place in the focal plane of the lens (FIG. 1.5 ). Optoelectronic detector elements (DR ', DR ", DS', DS", DT ', DT ") include, for example, known photodiodes or photoelements.

The conversion of the initially applied three 120 ° phase-shifted periodic optical signals into a pair of output signals phase-shifted by 90 ° takes place according to the invention by the appropriate interconnection of the optoelectronic detector elements (DR ', DR ", DS', DS '). ', DT', DT ''), ie the appropriately selected detector element arrangement now acts as a conversion means for the input signals. The requisite parallel and / or antiparallel interconnection of the optoelectronic detector elements (DR ', DR', DS ', DS'',DT', DT '') is in the 1A and 1B only schematized via a corresponding interconnection arrangement ( 4 ) indicated. A concrete embodiment of a suitable interconnection arrangement ( 4 ) will be explained in more detail in the following course of the description. There are a number of possibilities for the interconnection and combination of the input signals.

On the output side, in the case of the signal processing arrangement of the position measuring device according to the invention, the two partial signals T0 and T90, which are phase-shifted by 90 °, ultimately result in the downstream evaluation unit (FIG. 2 ) are processable in a known manner for position determination.

The division of at least part of the signal generating means ( 1 ) delivered periodic signals (R, S, T) in each case at least two partial signals (R ', R'',S', S '', T ', T'') can be carried out in a variety of ways as already indicated. In addition, the choice and optical dimensioning of the beam splitting elements ( 3 ) also a defined division of the required signal intensities in the individual sub-signals (R ', R'',S', S '', T ', T'') take place. Alternatively, it is possible to adjust the desired signal intensities for the individual sub-signals (R ', R'',S', S '', T ', T'') in front of the optoelectronic detector elements (DR', DR '). ', DS', DS '', DT ', DT'') filters with certain transmission characteristics are arranged. Furthermore, the sensitivities of the detector elements (DR ', DR ", DS', DS", DT ', DT ") can also be suitably selected for the defined adjustment of the sub-signal intensities. The division of the signal intensities in each case depends on the desired interconnection of the optoelectronic detector elements (DR ', DR ", DS', DS", DT ', DT "), as will be explained in more detail below.

One possibility for suitable interconnection of the optoelectronic detector elements within the in 1A and 1B only schematically indicated interconnection arrangement ( 4 ) and for generating the 90 ° out of phase signals T0 and T90 will now be based on the 2A and 2 B explained. Regardless of the signal combination or interconnection of the optoelectronic detector elements described below, there are, of course, further possibilities that can be realized analogously to the described example on the basis of the teaching of the present invention.

2A Fig. 12 shows a vector diagram of an embodiment with the three 120 ° out of phase, periodic optical signals R, S and T to be processed provided by the signal generating means. For the signal evaluation in the downstream, usual evaluation units, however, a pair of possible offset-free signals T0, T90 is required, which have a phase offset of 90 ° to each other. In order to make such a conversion certain forming operations with the three signals R, S and T are required. Here are a number of ways in which such deformation operations can take place within the signal processing arrangement of the position measuring device according to the invention. The deformation operations provided in each case are made by circuitry via the corresponding parallel and / or anti-parallel circuit of the optoelectronic detector elements.

In the embodiment of 2A results in one of the two output signals, hereinafter referred to as signal T90, from the subtractive combination of the two signals T 'and S', that is T90 ≔ T '- S'. Due to the signal subtraction carried out, an offset-free signal is already present with T90 since the two partial signals T 'and S' were subject to the same offset. The amplitude A of the signal T90 is in the case of this combination with identical normalized to 1 amplitudes A _{0 of} the signals R, S and T then 0.866 A ₀ , ie A (T90) = 0.866 A ₀

A signal T0 phase-shifted by 90 ° is obtained by subtracting the two signal combination terms (R '+ R' ') and (T' '+ S' '), ie T0 ≔ (R' + R ''). (T '' + S '') = R - (T '' + S ''). As can be seen from this example, therefore, not every optical signal (R, S, T) must be divided into at least two sub-signals; Rather, the signal R can be used unchanged in the illustrated signal combination variant. It is therefore necessary for this signal, only a single optoelectronic detector element DR.

Also, the second output signal T0 is offset-free due to the subtraction operation performed. The amplitude A of the signal T0 results in the illustrated signal combination and identical, normalized amplitudes A _{0 of} the signals R, S and T as A (T0) = 1.5 A ₀ .

Accordingly, the two output signals T0 and T90 are offset-free in such a processing, but have different amplitudes. If, on the evaluation side, identical amplitudes of the signals T0 and T90 are desired, it is possible to adjust the amplitude in the generation of the larger of the two signals, ie. H. in the present example for T0, make a corresponding attenuation of the amplitudes in the individual sub-signals used for this purpose so that the outputs result in identical amplitudes for T0 and T90. This can already take place during the division into the partial optical signals, for which purpose then the optical beam splitting elements are dimensioned accordingly. Alternatively, however, filter elements can also be arranged in front of the optoelectronic detector elements which selectively effect this attenuation or the sensitivities of the detector elements are selected accordingly. This results in each case a defined-predetermined signal intensity for the various sub-signals such that result in the signal combination selected in each case the same amplitude signals T0 and T90.

In order to enable such a combination of the originally three signals R, S and T, a division of at least a part of these signals (R, S, T) into several partial signals (S ', S'',T', T '') is therefore required. required, as in the previously described embodiment of 1A and 1B via one or more beam splitting elements ( 3 ), which are arranged upstream of the optoelectronic detector elements (DS ', DS'',DT', DT ''). As already indicated above, a splitting of the signal R can be omitted for this signal combination variant, ie only a single optoelectronic detector element DR is required for this purpose.

The circuit arrangements of the optoelectronic detector elements (DR, DS ', DS'',DT', DT ') suitable for generating the two signals T0 and T90 for a variant according to FIG 2A are in 2 B shown.

The signal T90 results here from the anti-parallel connection of the two optoelectronic detector elements DT 'and DS' for the sub-signals T 'and S'. To generate the second output signal T0, the lower circuitry is off 2 B suitable, that is, a parallel connection of the detector elements DT '' and DS '' and a purpose antiparallel connected detector element DR.

In addition to the illustrated embodiment and the circuitry suitable for this purpose, of course, a variety of other variants of the position measuring device according to the invention for combining the applied periodic optical signals to produce the required output signals (T0, T90) with 90 ° phase offset. For example, more than three periodic optical signals can be present, which are divided by a correspondingly sized beam splitting elements to a required number of detector elements. At least two of the adjacent optical signals are present in each case in periodic form.

Furthermore, it is conceivable to make a division over the beam splitter elements not only into two resulting sub-signals, but to produce, for example, three or more sub-signals. It is therefore possible a flexible adaptation of the position measuring device according to the invention to a wide variety of requirements.

Claims (8)

Position measuring device with a graduation scale ( 1.3 ) and at least one relatively shiftable graduation ( 1.2 . 1.4 ), - that of a light source ( 1.1 ) emitted light beam via a condenser optics as a plane wave to a first scanning ( 1.2 ) and diffracts thereof into mainly three different spatial directions and - at the relative to the first scanning graduation ( 1.2 ) displaceable scale division ( 1.3 ) a further diffraction of the impinging wave trains occurs, - before the partial beams at a further, second scanning graduation ( 1.4 ) are diffracted again and after passing the second scanning graduation ( 1.4 ) the wave trains of the same spatial direction interfere, so that the intensities of the three interfering partial beams depend on the phase shift resulting from the relative displacement of scale ( 1.3 ) and scan division ( 1.2 . 1.4 ) and in the case of the shift of scale ( 1.3 ) and scan division ( 1.2 . 1.4 ) yield three periodic, intensity-modulated signals which have a mutual phase offset of 120 ° to one another and - wherein the three interfering partial beams bundle beam splitting elements ( 3 ), each of which causes a division of the individual partial beams into two partial beams with partial signals (R ', R'',S', S '', T ', T'') and the individual, divided partial beams of several subordinate, optoelectronic detector elements (DR ', DR ", DS', DS", DT ', DT "), whereby for each generated partial signal (R', R", S ', S ", T', T" ) a separate optoelectronic detector element (DR ', DR ", DS', DS", DT ', DT ") is required and the detector elements (DR', DR", DS ', DS ", DT', DT '') are connected in parallel and / or in antiparallel in such a way that, on the output side, a pair of output signals (T0, T90) phase-shifted by 90 ° results. Position measuring device according to claim 1, wherein as a beam splitting element ( 3 ) at least one phase grating in front of the optoelectronic detector elements (DR ', DR', DS ', DS'',DT', DT '') is arranged. Position measuring device according to claim 1, wherein as a beam splitting element ( 3 ) at least one divider mirror in front of the optoelectronic detector elements (DR ', DR', DS ', DS'',DT', DT '') is arranged. Position measuring device according to claim 1, wherein the provided beam splitting elements ( 3 ) are optically dimensioned such that the resulting optical sub-signals (R ', R'',S', S '', T ', T'') have a defined-predetermined signal intensity. Position measuring device according to claim 4, wherein in front of the optoelectronic detector elements (DR ', DR ", DS', DS", DT ', DT ") at least one phase grating as beam splitter element (US Pat. 3 ) is arranged, which divides the incident light beams into different, diffracted partial beams (R ', R ", S', S", T ', T ") of different and defined-predetermined intensity. Position measuring device according to claim 4, wherein in front of at least one optoelectronic detector element (DR ', DR ", DS', DS", DT ', DT ") a filter element is arranged, which defines a predetermined predetermined reduction of the signal intensity of the optical component signals ( R ', R' ', S', S '', T ', T' ') causes. Position measuring device according to claim 1, wherein by the parallel and / or anti-parallel circuit of the optoelectronic detector elements (DR, DS ', DS'',DT', DT '') of three supplied periodic optical signals R, S and T, of which two signals S, T have been split into pairs of sub-signals S ', S ", T', T", the output signal pair T0 ≔ R - (T '' + S ''), T90 ≔ T '- S'. results. Position measuring device according to claim 1, wherein the scale graduation is formed as a reflective graduation scale and the first and second scanning graduation is formed as a single scanning graduation, from which the incident light beams are diffracted twice.

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