DE10244235A1 - Absolute position measuring device compares scanned signals for complementary partial regions of each code element for providing binary information - Google Patents

Abstract

The position measuring device has a scanning unit (AE) for scanning a sequential pseudo-random code (C) having a series of code elements (C1,C2,C3) extending in the measuring direction (X), each having 2 complementary partial regions. The binary information (B1,B2,B3) for each code element is obtained by comparing scanned signals for both partial regions. An Independent claim for an absolute position measuring method is also included.

Description

The invention relates to a position measuring device to determine the absolute position according to claim 1 and a Method for absolute position measurement according to claim 9.

In many areas there is an increase absolute position measuring devices are used, in which the absolute Position information from a code track with one behind the other in the measuring direction arranged code elements is derived. The code elements are thereby in pseudo-random Distribution provided so that a certain number of consecutive Code elements each form a bit pattern. When moving opposite the scanner the code track around a single code element is already a new one Bit pattern formed and over there is a consequence of the entire measuring range to be absolutely recorded of different bit patterns available.

Such a sequential code is called a chain code or a pseudo-random code.

In the publication "Absolute position measurement using optical detection of coded patterns ", by J.T.M. Stevenson and J.R. Jordan in Journal of Physics E / Scientific Instruments 21 (1988), No. 12, pages 1140-1145 states that each code element from a predetermined sequence of two sub-areas with each other complementary optical properties.

In the release is on the GB 2 126 444 A. There is now used to generate the binary information with such Manchester coding proposed the analog scanning signals of the code areas with a compare the given trigger threshold and depending on it one binary Generate information 0 or 1.

This comparison with a fixed trigger threshold has the disadvantage that fluctuations in the analog scanning signals can lead to incorrect generation of the binary information.

The invention is therefore the object an absolute position measuring device with high reliability or to create operational security, with which one as possible error-free generation of the absolute position is possible.

This task is due to the characteristics of claim 1 solved.

The invention is also the Task, a method for determining an absolute position specify with which one if possible error-free generation of the binary Information and thus the absolute position is made possible.

This task comes with the characteristics of claim 9 solved.

Advantageous embodiments of the Invention are in the dependent claims specified.

The invention is explained in more detail with reference to the drawings demonstrate:

1 a position measuring device in a schematic representation;

2 the principle of error checking;

3 the signals for error checking according to 2 ;

4 a position measuring device with an incremental track for generating control signals;

5a analog scan signals of the incremental track;

5b Control signals from the analog scanning signals according to 5a ;

6a a first scanning position of the position measuring device;

6b a second scanning position of the position measuring device;

6c a third scanning position of the position measuring device and

6d a fourth scanning position of the position measuring device.

In 1 A position measuring device designed according to the invention is shown schematically. This position measuring device works according to the optical scanning principle, in which a code C is scanned using the transmitted light method. A scanning device AE, which is arranged to be movable in the measuring direction X relative to the code C, is used to scan the code C.

Code C consists of one in the measuring direction X successive sequence of code elements of the same length C1, C2, C3. Each code element C1, C2, C3 in turn consists of two of equal length in the direction of measurement X next to each other in direct succession arranged partial areas A and B, which are complementary to each other. Complementary means that they have inverse properties, i.e. with optical scanning principle transparent and not transparent or with reflected light scanning are reflective or non-reflective.

The sequential code C is from the scanning device AE, which contains a light source L, the Light over a collimator lens K several successive code elements C1, C2, C3 illuminated. The light is modulated by code C depending on the position, so that there is a position-dependent light distribution behind code C, which is detected by a detector unit D of the scanning device AE becomes.

The detector unit D is a line sensor with a sequence of detector elements D1 to D11 arranged in the measuring direction X. At least one detector element D1 to D11 is uniquely assigned to each subarea A, B of the code elements C1, C2, C3, so that in each relative position of the detector unit D compared to the code C, a scanning signal S1A to S3B is obtained from each subarea A, B. , These scanning signals S1A to S3B become one Evaluation device AW supplied, which the two scanning signals S1A, S1B; S2A, S2B; S3A, S3B of the two subareas C1A, C1B; C2A, C2B; C2A, C2B; C3A, C3B of a code element C1, C2, C3 each compares with one another and generates a digital value or a bit B1, B2, B3 for each code element C1, C2, C3. A sequence of several digital values B1, B2, B3 results in a code word CW which defines the absolute position. When the detector unit D is shifted relative to the code C by the width or length of a code element C1, C2, C3, a new code word CW is generated and a large number of different code words CW are formed over the measuring range to be measured absolutely.

1 shows a current position of the code C relative to the scanning device AE. The detector elements D1 to D11 are successively arranged at a distance of half the width of a partial area C1A to C3B of the code C. This ensures that at least one detector element D1 to D11 is uniquely assigned to a partial area C1A to C3B in each position and does not scan a transition between two partial areas C1A to C3B. In the position shown, the partial area C1A is scanned by the detector element D1 and the partial area C1B by the detector element D3. The detector elements D1, D3 detect the light distribution and, depending on the light intensity, generate an analog scanning signal S1A, S1B proportional to the light intensity. Since the two subareas C1A and C1B are complementary to one another, the intensity of the scanning signals S1A and S1B is also inverse to one another, that is to say the signal levels are spaced far apart.

This signal spacing is now used to generate the binary information B1 by checking which of the two scanning signals S1A, S1B of the code element C1 is larger. This check can be done by forming quotients or by forming differences. Using the example, difference formation is used, for which purpose 1 A trigger module T1 serves as a comparison device. The trigger module T1 generates B1 = 0 if S1A is smaller than S1B and B1 = 1 if S1A is larger than S1B. In the same way, binary information B2 and B3 are obtained by scanning the code elements C2, C3 and comparing the analog scanning signals S2A, S2B; S3A, S3B of subareas C2A, C2B; C3A, C3B each of a code element C2, C3 obtained by trigger modules T2, T3.

A first sequence of complementary to each other trained subarea A, B thus becomes a first digital value and a second sequence of complementary ones Subareas A, B are assigned a second digital value. in the Example becomes the sequence opaque → transparent assigned the value 0 and the sequence transparent → opaque the value 1.

Since the two sub-areas A and B each code element C1, C2, C3 are complementary to each other, is the signal-to-noise ratio the scanning signals S very large. A change the light intensity the light source L influences the scanning signals S of both sections A and B alike.

Because of the complementary design two sub-areas A, B of a code element C1, C2, C3 have to with correct operation of the position measuring device by scanning it Subareas A, B are generated analog scanning signals S, whose difference exceeds a predetermined value. Through observation this difference value allows a good error check. The basis of this error checking is that it can be assumed that if the Difference value by a predetermined amount the binary information B1, B2, B3 is uncertain and therefore for this binary information B1, B2, B3 an error signal F1 is generated.

The principle of generating the error signal F1 is in 2 shown. The analog scanning signals S1A and S1B of the code element C1 are fed to an error checking device P. The error checking device P compares S1A and S1B by forming the difference (S1A-S1B) and checks whether the difference amount exceeds or does not exceed a predetermined comparison value V. If the difference amount (S1A - S1B) does not exceed the predetermined comparison value V, an error signal F1 is output. In 3 these signal relationships are shown.

The arrangement of the two sections A and B of each code element C1, C2, C3 successively directly side by side in measuring direction X has the advantage that the detector elements D1 to D11 next to each other at a short distance in the measuring direction X. can be arranged and thus the position measuring device against rotation of the detector unit D opposite the code C, i.e. against moiré fluctuations is insensitive. Furthermore, the sensitivity to contamination is low, since it can be assumed that both sub-areas A and B of a code element C1, C2, C3 influenced equally become.

The example of the detector elements D1 and D2 shows in 1 Easily recognizable that when the code C is shifted to the left by the length of a partial area A, B, the detector element D1 scans the partial area C1 B and the detector element D3 scans the partial area C2A, that is to say partial areas of two code elements C1, C2. The trigger module T1 can therefore not supply any binary information B1, B2, B3 assigned to a code element C1, C2, C3. Measures are now explained below with which it is ensured that the correct detector elements D1 to D11 are used for code word generation, that is to say the detector elements D1 to D11, which each scan the partial areas of a single code element C1, C2, C3.

Based on 4 to 6 becomes a preferred one Measure described for this. Parallel to the code C is according to 4 arranged an incremental track R with a periodic division of the period length corresponding to the length of a code element C1, C2, C3. The incremental track R is scanned in a known manner by at least two detector elements DR1, DR2 which are offset by ¼ division period in the measuring direction X to generate two analog scanning signals SR1, SR2 which are phase-shifted by 90 °. These analog scanning signals SR1, SR2 are interpolated in a known manner and the interpolated position value is combined with the code word CW, as a result of which the coarse absolute position measurement is refined by the high-resolution incremental measurement.

Through the incremental measurement the length each code element C1, C2, C3 interpolated. By the interpolation value is now a simple distinction between the right and left part a code element C1, C2, C3 possible. A 4-fold interpolation is sufficient to differentiate the subareas A and B, thus a simple triggering of the analog scanning signals SR1, SR2. The resulting bit combination of the digital signals E1, E2 clearly defines the order of sub-areas A, B and it serves as a control signal for determining the detector elements D1 to D11, from which a correct code word CW can be generated. The Digital signals E1, E2 thus define which scanning signals S together are compared and from which scanning signals S digital values B1, B2, B3 for the code word CW can be obtained.

To further explain this process are in the 6a to 6d four different positions P1, P2, P3, P4 of the code C relative to the detector unit D are shown. The detector elements D1 to D11 are arranged in the measuring direction X at intervals corresponding to half the length of a partial area A, B, and two detector elements D1 to D11, which are arranged at a mutual distance corresponding to the length of a partial area A, B, are connected in difference.

In 6a the position P1 is shown, in which the information E1 = 0 and E2 = 0 is obtained from the incremental track R. Bit B1 of code element C1 is formed by forming the difference between detector elements D4 and D6, ie (D4-D6). At position P2 according to 6b E1 = 0 and E2 = 1, so that the detector elements D3 and D5 are selected by a control unit M. At position P3 according to 6c E1 = 1 and E2 = 1, so that the control unit M selects the detector elements D2 and D4 for difference formation. At position P4 according to 6d E1 = 1 and E2 = 0, so that the detector elements D1 and D3 are selected.

The correct detector elements for forming the further bits of the code word CW are determined in the same way. For example, if detector elements D1 and D3 have been selected to form bit B1, detector elements D5 and D7 are used to form bit B2 and to form the bit 83 the detector elements D9 and D11 as in 1 is shown. Where in 1 only the trigger modules T1, T2, T3 used in this current position are shown.

• – Detektorelemente D1 bis D11 sind in Messrichtung X in Abständen entsprechend der halben Länge eines Teilbereiches A, B angeordnet;
• – die Detektorelemente D1 bis D11 bilden eine erste Gruppe (in den 6a bis 6d geradzahlig nummerierte Detektorelemente D2, D4, D6, D8, D10) mit einem gegenseitigen Abstand entsprechend der Länge eines Teilbereiches A, B;
• – die Detektorelemente D1 bis D11 bilden eine zweite Gruppe (in den 6a bis 6d ungeradzahlig nummerierte Detektorelemente D1, D3, D5, D7, D9) mit einem gegenseitigen Abstand entsprechend der Länge eines Teilbereiches A, B;
• – die Detektorelemente D2, D4, D6, D8, D10 der ersten Gruppe sind gegenüber den Detektorelementen D1, D3, D5, D7, D9 der zweiten Gruppe um die halbe Länge eines Teilbereiches A, B versetzt angeordnet;
• – unmittelbar aufeinanderfolgende Detektorelemente einer Gruppe sind jeweils in Differenz geschaltet;
• – von den beiden Gruppen werden nun die Vergleichsergebnisse der Detektorelementenpaare in einem Raster entsprechend der Länge eines Codeelementes C1, C2, C3 zur Bildung des Codewortes CW verwendet, dessen Folge am wenigsten Fehler F erzeugt, gemäß 6d also die Folge (D1-D3)=B1, (D5-D7)=B2 usw.

A further possibility for determining the correct detector elements D1 to D11 or the correct analog scanning signals S consists in comparing all detector elements D1 to D11 which are spaced apart from one another by the length of a partial region A, B. At a distance from a code element C1, C2, C3 there are now detector pairs D1, D3 and D5, D7 - using the example in FIG 6d represented instantaneous position P4- which each scan the difference of the partial areas A, B of a code element C1, C2 in the desired manner. The further pairs of detectors D3, D5 scan successive partial areas B, A of two successive code elements C1, C2 and thus generate them with the aid of 2 explained an error signal F1. In order to determine the correct detector elements D1 to D11, the detector group D1, D3; D5, D7 searched for the least amount of error signals F. In detail, the following arrangement or the following method steps are or are required to carry out this second possible measure:

• - Detector elements D1 to D11 are arranged in the measuring direction X at intervals corresponding to half the length of a partial area A, B;
• - The detector elements D1 to D11 form a first group (in the 6a to 6d even numbered detector elements D2, D4, D6, D8, D10) with a mutual distance corresponding to the length of a partial area A, B;
• - The detector elements D1 to D11 form a second group (in the 6a to 6d odd numbered detector elements D1, D3, D5, D7, D9) with a mutual distance corresponding to the length of a partial area A, B;
• - The detector elements D2, D4, D6, D8, D10 of the first group are offset from the detector elements D1, D3, D5, D7, D9 of the second group by half the length of a partial area A, B;
• - Immediately successive detector elements of a group are each switched in difference;
• - The two groups now use the comparison results of the detector element pairs in a raster corresponding to the length of a code element C1, C2, C3 to form the code word CW, the result of which produces the least error F, according to 6d thus the sequence (D1-D3) = B1, (D5-D7) = B2 etc.

The two subareas A, B of each code element C1, C2, C3 can be designed to be optically scannable, a subarea A then the scanning light is transparent or reflective and the other partial area B is opaque or non-reflective. However, the invention is not limited to the optical scanning principle.

The absolute position measuring device can be used to measure linear or rotary movements with the code C on one of the moving objects and the Scanning device AE attached to the other of the objects to be measured is. The code C can be attached directly to the object to be measured be or on a scale which is then coupled to the object to be measured.

The objects to be measured can the table and the slide of a machine tool, a coordinate measuring machine or the rotor and the stator of an electric motor.

Claims (15)

Position measuring device with - one Code (C), consisting of a sequence of one after the other in the measuring direction X. arranged code elements (C1, C2, C3), each code element (C1, C2, C3) each consist of two sub-areas (A, B) that are mutually related complementary and are arranged in succession in the measuring direction X; - one Scanning device (AE) with several detector elements (D1 to D11) for scanning several code elements (C1, C2, C3) and for formation at least one scanning signal (S) within each sub-area (A, B) of the scanned code elements (C1, C2, C3); - one Evaluation unit (AW) with a comparison device (T1, T2, T3), each of the scanning signals (S) of the partial areas (A, B) one Code element (C1, C2, C3) compared with each other and depending on the Comparison result a binary Information (B1, B2, B3) for forms the code element (C1, C2, C3). Position measuring device according to claim 1, wherein the Comparison device (T1, T2, T3) a device for education the difference of the analog scanning signals (S) of the two sections (A, B) of a code element (C1, C2, C3). Position measuring device according to claim 1 or 2, wherein the scanning signals (S) from successive partial areas (A, B) are each fed to a comparison device (T1, T2, T3) and the evaluation unit (AW) has a control unit (M) which is designed to ensure that the binary information (B1, B2, B3) each from the two sub-areas (A, B) of a code element (C1, C2, C3) can be formed. Position measuring device according to claim 3, wherein parallel for the code (C) at least one track (R) is arranged, its information (E1, E2) is supplied to the control unit (M) and is due to this information (E1, E2) the scanning signals (S) successively Subareas (A, B) of a code element (C1, C2, C3) for formation the binary Information (B1, B2, B3) can be selected. Position measuring device according to claim 4, wherein the Information track (R) is a periodic incremental division. Position measuring device according to one of the preceding Expectations, the evaluation unit (AW) having an error checking device (P), which is designed to measure the difference between the scanning signals (S) Subareas (A, B) of a code element (C1, C2, C3) with a target difference to compare and an error signal if the target difference is undershot (F1). Position measuring device according to one of the preceding Expectations, the two subareas (A, B) of a code element (C1, C2, C3) complementary to each other have optical properties. Position measuring device according to one of the preceding Expectations, the detector elements (D1 to D11) correspondingly at intervals in the measuring direction X. half the length of a partial area (A, B) and two detector elements each (D1 to D11) which are spaced apart according to the Length of a Sub-area (A, B) are arranged in differential. Absolute position measurement method with the following steps - feel a code (C), consisting of a sequence of in the measuring direction X successively arranged code elements (C1, C2, C3), the Code elements (C1, C2, C3) each from two sub-areas (A, B) exist that are complementary to each other and in the measuring direction X are arranged in succession; - Generate at least one Sampling signal (S) within each section (A, B) of the scanned code elements (C1, C2, C3); - Compare the scanning signals (S) the subareas (A, B) of a code element (C1, C2, C3) with each other and - Form a binary Information (B1, B2, B3) from the comparison. The method of claim 9, wherein the comparison is a Difference formation of the analog scanning signals (S) of the partial areas (A, B) is. Method according to one of Claims 9 or 10, with the method step - comparing the scanning signals (S) in each case directly successive sub-areas (A, B) and selecting the scanning signals (S), each of which by Ab keying of the sub-areas (A, B) of a code word (C1, C2, C3) are formed. The method of claim 11, wherein the selection is by a control signal (E1, E2) takes place, which at least by sampling an information track (R) is obtained. Method according to one of the preceding claims 9 to 12, the difference between the scanning signals (S) of the partial areas (A, B) a code element (C1, C2, C3) is formed, the difference is compared with a target difference and if it falls below the Should an error signal (F1) be formed. Method according to one of the preceding claims 9 to 11, the detector elements (D1 to D11) in the measuring direction X in intervals corresponding to half the length a partial area (A, B) are arranged and each of two Detector elements (D1 to D11), which are at a mutual distance according to the length the difference is formed in a partial area (A, B) becomes. The method of claim 14, wherein the difference is compared in each case with a target difference and if it falls below the target difference an error signal (F1) is formed and by binary information obtained from difference formation (B1, B2, B3) of the pairs of detector elements in a grid corresponding to the length of one Code element (C1, C2, C3) can be selected to form the code word CW, the Result least error (F) generated.