Position measurement system having receiver coils which are differentially interconnectable via switching means

Abstract

A position measurement system including a material measure and a scanning device movable relative to one another with respect to a measurement direction. The material measure has a plurality of markings which are arranged in a row with respect to the measurement direction, wherein the scanning device includes a transmitter winding arrangement. Multiple receiver coils are provided which are arranged in a row with respect to the measurement direction. The inductive coupling between the transmitter winding arrangement and the receiver coils is a function of the position of the scanning device with respect to the material measure. The transmitter winding arrangement defines multiple separate transmitter areas which are arranged in a row with respect to the measurement direction. A maximum of one single receiver coil is situated in each of the transmitter areas. At least one switching means is provided via which the two adjacent receiver coils are differentially interconnectable.

Claims

1. A position measurement system comprising: a material measure having a plurality of markings arranged in a row with respect to a measurement direction; and a scanning device that is configured to move relative to the material measure in the measurement direction, the scanning device comprising: a transmitter winding arrangement having a plurality of transmitter areas arranged in a row with respect to the measurement direction; a plurality of receiver coils arranged in a row with respect to the measurement direction, a maximum of one single receiver coil of the plurality of receiver coils being situated in each of the transmitter areas, an inductive coupling between the transmitter winding arrangement and the plurality of receiver coils being a function of a position of the scanning device with respect to the material measure; a plurality of switching devices configured to differentially interconnect at least two adjacent receiver coils of the plurality of receiver coils between a first signal line and a second signal line, the plurality of switching devices having a separate switching device associated with each receiver coil of the plurality of receiver coils; and a differential amplifier connected to the first signal line and the second signal line, wherein the plurality of switching devices is configured to alternately connect the receiver coils of the plurality of receiver coils to the first signal line and the second signal line such that any two directly adjacent receiver coils of the plurality of receiver coils are connected to a different one of the first signal line and the second signal line.

2. The position measurement system according to claim 1, the differential amplifier further comprising: a positive input connected to the first signal line; and a negative input connected to the second signal line.

3. The position measurement system according to claim 1, wherein each switching device of the plurality of switching devices is configured to switch between a first state having a first electrical resistance and a second state having a second electrical resistance, the second electrical resistance being at least 1000 times greater than the first electrical resistance.

4. The position measurement system according to claim 1, wherein the plurality of markings of the material measure are formed by openings in a metal tape, the width and the spacing of each of the openings being an integer multiple of a first division interval .

5. The position measurement system according to claim 4, wherein the plurality of receiver coils are each separated by a distance corresponding to a second division interval , wherein the condition r=s applies, where r and s are integers in which s>r.

6. The position measurement system according to claim 5, wherein the plurality of markings of the material measure form a random number sequence, any arbitrary selection of a number m of directly adjacent markings of the plurality of markings being different from any other arbitrary selection of a number m of directly adjacent markings of the plurality of markings, at least one selection of m1 directly adjacent markings of the plurality of markings occurring in at least two positions of the random number sequence, wherein e1.2msr applies, where e is a number of receiver coils in the plurality of receiver coils.

7. The position measurement system according to claim 1, wherein all receiver coils of the plurality of receiver coils that are on a side facing away from an associated switching device of the at least one switching device are electrically connected to a same voltage level.

8. The position measurement system according to claim 1, the scanning device further comprising: an actuation device configured to actuate the plurality of switching devices, the actuation device having a plurality of D flip-flops that are interconnected in the form of a shift register having a clock input and a plurality taps, each of the plurality of taps being configured to actuate a corresponding switching device of the plurality of switching devices.

9. A method for operating a position measurement system comprising a material measure having a plurality of markings arranged in a row with respect to a measurement direction, and a scanning device that is configured to move relative to the material measure in the measurement direction, the scanning device comprising a transmitter winding arrangement having a plurality of transmitter areas arranged in a row with respect to the measurement direction, a plurality of receiver coils arranged in a row with respect to the measurement direction, a maximum of one single receiver coil of the plurality of receiver coils being situated in each of the transmitter areas, an inductive coupling between the transmitter winding arrangement and the plurality of receiver coils being a function of a position of the scanning device with respect to the material measure, and at least one switching device configured to differentially interconnect at least two adjacent receiver coils of the plurality of receiver coils, the method comprising differentially interconnecting in succession different pairs of receiver coils of the plurality of receiver coils via an associated switching device of the at least one switching device; and using at least one receiver coil of the plurality of receiver coils to read two different markings of the plurality of markings of the material measure in one position of the position measurement system.

10. A position measurement system comprising: a material measure having a plurality of markings arranged in a row with respect to a measurement direction; and a scanning device that is configured to move relative to the material measure in the measurement direction, the scanning device comprising: a transmitter winding arrangement having a plurality of transmitter areas arranged in a row with respect to the measurement direction; a plurality of receiver coils arranged in a row with respect to the measurement direction, a maximum of one single receiver coil of the plurality of receiver coils being situated in each of the transmitter areas, an inductive coupling between the transmitter winding arrangement and the plurality of receiver coils being a function of a position of the scanning device with respect to the material measure; and at least one switching device configured to differentially interconnect at least two adjacent receiver coils of the plurality of receiver coils, wherein the plurality of markings of the material measure are formed by openings in a metal tape, the width and the spacing of each of the openings being an integer multiple of a first division interval , and wherein the plurality of receiver coils are each separated by a distance corresponding to a second division interval , wherein the condition r=s applies, where r and s are integers in which s>r.

11. The position measurement system according to claim 10, the scanning device further comprising: a differential amplifier connected to the at least one switching device to differentially connect the at least two adjacent receiver coils of the plurality of receiver coils.

12. The position measurement system according to claim 11, the at least one switching device further comprising: a plurality of switching devices having a separate switching device associated with each receiver coil of the plurality of receiver coils, the plurality of switching devices being configured to connect the plurality of receiver coils to a first signal line and a second signal line.

13. The position measurement system according to claim 12, the differential amplifier further comprising: a positive input connected to the first signal line; and a negative input connected to the second signal line.

14. The position measurement system according to claim 12, wherein the plurality of switching devices is configured to alternately connect the receiver coils of the plurality of receiver coils to the first signal line and the second signal line such that any two directly adjacent receiver coils of the plurality of receiver coils are connected to a different one of the first signal line and the second signal line.

15. The position measurement system according to claim 10, wherein the at least one switching device is configured to switch between a first state having a first electrical resistance and a second state having a second electrical resistance, the second electrical resistance being at least 1000 times greater than the first electrical resistance.

16. The position measurement system according to claim 10, wherein the plurality of markings of the material measure form a random number sequence, any arbitrary selection of a number m of directly adjacent markings of the plurality of markings being different from any other arbitrary selection of a number m of directly adjacent markings of the plurality of markings, at least one selection of m1 directly adjacent markings of the plurality of markings occurring in at least two positions of the random number sequence, wherein e1.2msr applies, where e is a number of receiver coils in the plurality of receiver coils.

17. The position measurement system according to claim 10, wherein all receiver coils of the plurality of receiver coils that are on a side facing away from an associated switching device of the at least one switching device are electrically connected to a same voltage level.

18. The position measurement system according to claim 10, the scanning device further comprising: an actuation device configured to actuate the at least one the switching device, the actuation device having a plurality of D flip-flops that are interconnected in the form of a shift register having a clock input and a plurality taps, each of the plurality of taps being configured to actuate a corresponding switching device of the at least one switching device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the disclosure are presented in the drawings an are explained in more detail in the description below.

(2) In the drawings:

(3) FIG. 1 shows a simplified schematic representation of the transmitter winding arrangement, the receiver coils, and the material measure of a position measurement system according to the present disclosure;

(4) FIG. 2 shows a schematic circuit diagram of the scanning device of the position measurement system according to FIG. 1;

(5) FIG. 3 shows a simplified schematic representation having different positions of the receiver coil with respect to the material measure; and

(6) FIG. 4 shows code examples which may occur during the operation of a position measurement system according to the present disclosure.

DETAILED DESCRIPTION

(7) FIG. 1 shows a simplified schematic representation of the transmitter winding arrangement 41, the receiver coils 51 to 54, and the material measure 20 of a position measurement system 10. For the sake of clarity, the transmitter winding arrangement 41, the receiver coils 51 to 54, and the material measure 20 are depicted adjacent to one another, transverse to the measurement direction 11, wherein they are actually situated one above the other in such a way that the plotted center lines 38 coincide. The proportions are correctly depicted in the measurement direction 11, which runs parallel to the aforementioned center line 38.

(8) The transmitter winding arrangement 41 and the receiver coils 51 to 54 are immovably arranged relative to one another in a scanning head. The scanning head is movable relative to the material measure 20 with respect to the measurement direction 11.

(9) The transmitter winding arrangement 41 comprises a first group and a second group 43a; 43b of serpentine conductor tracks 43. Contrary to the actual conditions, only one single conductor track 43 from each group 43a; 43b is shown in each case, whereas a plurality of conductor tracks 43 is actually present, wherein the conductor tracks 43 of one group 43a; 43b run essentially in parallel among each other. The conductor tracks 43 are arranged in different planes of a planar conductor track arrangement which are electrically insulated from each other, wherein vias (not depicted) are provided between the aforementioned planes in the vicinity of the boundary 44 and the connectors 45. The serpentine conductor tracks 43 of the two groups 43a; 43b intersect, wherein they are electrically connected to one another only via the aforementioned vias.

(10) Altogether, the transmitter winding arrangement defines multiple transmitter areas 42 which are identical to one another and arranged in a row with respect to the measurement direction 11. The magnitude of the electromagnetic field is the same in all transmitter areas 42 if the transmitter winding arrangement 41 is supplied with alternating current via an alternating current source (no. 46 in FIG. 2) at the connectors 45. The direction of the magnetic flux in directly adjacent transmitter areas is exactly opposite, wherein it is oriented essentially perpendicular to the drawing plane of FIG. 1 in each case.

(11) At most, one single receiver coil 51 to 54 is situated within the transmitter areas 42. No receiver coil is situated in the two transmitter areas 42 located on the end with respect to the measurement direction 11, since, because of edge effects, fields act there which are somewhat different from the ones in the inner transmitter areas.

(12) The receiver coils 51 to 54 each have a plurality of winding revolutions having a uniform winding direction, whereas only a single winding revolution is depicted in each case in FIG. 1. The receiver coils 51 to 54 are an integral part of the same planar conductor track arrangement as the transmitter winding arrangement 41.

(13) The material measure 20 is a metal tape which preferably has a constant thickness. Preferably, it is manufactured from a ferromagnetic material, for example, stainless steel, using a photochemical etching method. The metal tape 20 is provided with a plurality of rectangular openings 22 whose width and spacing are an integer multiple of a first division interval . The rectangular sides of the openings 22 run in parallel to or perpendicularly to the measurement direction 11. A continuous side web 23 continues in the measurement direction 11 on both sides, adjacent to the openings 22. Overall, the material measure 20 is designed mirror-symmetrically with respect to the center line 38, so that it does not warp if it is subjected to tensile stress for the purpose of setting an exact first division interval .

(14) The rectangular sides of the openings 22 running transverse to the measurement direction 11 are each arranged on an associated grid line 25-1 to 25-5 of the marking grid, wherein directly adjacent grid lines 25-1 to 25-5 each have the first division interval . The material measure 20 encodes the value 1 if a change occurs on a grid line 25-1 to 25-5 from material to free space, or vice-versa. The material measure 20 encodes the value 0 if no such change takes place, i.e., if either material or free space is present on both sides of the grid line 25-1 to 25-5. The corresponding code is designed in such a way that it is ensured that at least one pair of adjacent receiver coils 51 to 54 is able to detect a value of 1 in an optimal manner, regardless of the position of the position measurement system.

(15) The second division interval of the receiver coils 51 to 54 is constant, wherein the condition 2=3 is presently fulfilled, as the signal evaluation is then particularly simple. However, it is also conceivable to apply the condition 4=5. Fewer receiver coils 51 to 54 are then required, whereas the signal evaluation is more complex.

(16) FIG. 2 shows a schematic circuit diagram of the scanning device 30 of the position measurement system according to FIG. 1. The scanning device 30 comprises a sensor unit 40 and an evaluation unit 31. The evaluation unit 31 is preferably a separate printed circuit board on which the assemblies framed under the reference number 31 are arranged. The remaining components depicted in FIG. 2 are arranged in direct spatial proximity to one another, wherein the receiver coils 51 to 54 in turn are arranged on the material measure having a small distance from the markings. In the specific embodiment depicted in FIG. 2, particularly few connection lines 74; 75; 65c are required between the sensor unit 40 and the evaluation unit 31.

(17) A first terminal 55 of all receiver coils 51 to 54 is connected to a common voltage level 47. The common voltage level 47 may be the ground potential. If the differential amplifier 65 has an asymmetrical voltage supply, the common voltage level 47 may be the average voltage of this voltage supply. The common voltage level 47 may also be present at the evaluation unit 31, in particular at the analog-digital converter 32 there. The other, second terminal 56 of each of the receiver coils 51 to 54 is connected to a switching means 61 to 64 in the form of a switch based on semiconductors. Each of the switching means 61 to 64 is connected either to a first signal line or a second signal line 66; 67. The receiver coils 51 to 54 are alternately connected to the first signal line and the second signal line 66; 67 in such a way that two directly adjacent receiver coils 51 to 54 are connected to different signal lines 66; 67.

(18) Furthermore, a differential amplifier 65 is provided which has a positive input and a negative input 65a; 65b and an output 65c. The first signal line 66 is connected to the positive input 65a, and the second signal line 67 is connected to the negative input 65b. A state is considered below by way of example, in which the switching means 61 and 62, which are associated with the directly adjacent receiver coils 51; 52, are closed, whereas the remaining switching means 63; 64 are open. Therefore, the voltage which is induced in the first receiver coil 51 by the transmitter winding arrangement (no. 41 in FIG. 1) is present at the positive input 65a, and the voltage which is induced in the second receiver coil 52 by the transmitter winding arrangement is present at the negative input 65b. The differential amplifier 65 amplifies the difference between these voltages and passes the amplified voltage difference to the analog-digital converter 32 via its output 65c. Accordingly, in the presently described example, the first receiver coil and the adjacent second receiver coil 51; 52 are differentially interconnected via the first switching means and the second switching means 61; 62.

(19) The switching means 61 to 64 are actuated with the aid of an actuation device 70 which has a shift register 71. The shift register 71 is made up of multiple D flip-flops 72, a D flip-flop 72 being associated with each switching means 61 to 64. Each of the D flip-flops 72 has a clock input 72b, a data input 72a, and an output 72c. Each output 72c of a D flip-flop 72 is connected to the data input 72a of the D flip-flop 72 which is associated with the next receiver coil 51 to 54 with respect to the measurement direction 11. The clock inputs 72b of all D flip-flops are connected in parallel via a clock line 75 to a programmable digital computer 33 in the evaluation unit 31, so that they continue to be clocked simultaneously. Furthermore, the data input 72a of the first D flip-flop 72 in the series is connected to the aforementioned digital computer 33 via the data line 74. Each of the outputs 72c of the D flip-flops forms a tap 73 via which the associated switching means 61 to 64 is controlled. The switching means 61 to 64 is, for example, switched to a first state having a low electrical resistance if a logical 1 is present at the associated tap 73, whereas it is switched to a second state having a significantly higher electrical resistance if a logical 0 is present at the tap 73.

(20) The digital computer 33 initially applies a logical 0 to the data line, which is clocked into all D flip-flops 72 over four clock signals presently on the clock line. A logical 0 is then present at all taps 73, so that all switching means 61 to 64 are open. Subsequently, a logical 1 is applied to the data line 74 over two additional clocks, so that a logical 1 is present at the taps of the first two D flip-flops, whereas a logical 0 is present at all remaining taps. Thus, the first receiver coil and the second receiver coil 51; 52 are connected to the differential amplifier 65. With each additional clock, a logical 0 is now again present on the data line 74, so that the two aforementioned logical 1 values are advanced by one position of the shift register 71 with every clock pulse. Subsequently, each following adjacent pair of receiver coils 51 to 54 in the measurement direction 11 is connected to the differential amplifier 65 with each clock pulse.

(21) From the digital values output by the analog-digital converter 32, the digital computer 33 ascertains the absolute position which the scanning device assumes with respect to the material measure.

(22) It goes without saying that significantly more receiver coils are preferably used than the four receiver coils 51 to 54 depicted. For example, it is conceivable to use 40 receiver coils which have a second division interval of 0.667 mm, whereas the material measure has a first division interval of 1.000 mm. It is also conceivable to use 33 receiver coils which have into a second division interval of 0.800 mm, whereas the material measure has a first division interval of 1.000 mm.

(23) The circuit depicted in FIG. 2 may in principle be expanded by any number of receiver coils 51 to 54.

(24) FIG. 3 shows a simplified schematic representation having different positions of the receiver coils with respect to the material measure. Only the aforementioned grid lines 25-1 to 25-6 from the material measure are depicted as vertical dash-dotted lines. As already described, the change from material to free space used for the encoding takes place only at these positions. Any two directly adjacent grid lines 25-1 to 25-6 have the first division interval .

(25) Furthermore, the receiver coils 51 to 54 are depicted as rectangles whose width is equal to the second division interval , wherein the condition 2=3 is presently fulfilled. The aforementioned rectangles indicate the area of the material measure which has an influence on the voltage induced in the relevant receiver coil 51 to 54.

(26) Furthermore, FIG. 2 depicts four limit positions 81 to 84, one above the other, of the receiver coils 51 to 54 with respect to the material measure or the corresponding grid lines 25-1 to 25-6.

(27) In the first limit position 81, the pair made up of the first receiver coil and second receiver coil 51; 52 is influenced only by the conditions at the grid line 25-3. The pair made up of the second receiver coil and the third receiver coil 52; 53 is also influenced only by the conditions at the grid line 25-3. The pair made up of the third receiver coil and the fourth receiver coil 53; 54 is influenced only by the conditions at the grid line 25-4.

(28) Thus, the code at the grid line 25-4 may be ascertained only by evaluating the differentially interconnected pair made up of the third receiver coil and the fourth receiver coil 53; 54.

(29) If the receiver coils 51 to 54 are now shifted in the direction of the second limit position 82, it is seen that the pair made up of the second receiver coil and the third receiver coil 52; 53 reaches the area of influence of the two grid lines 25-3 and 25-4, while the pair made up of the first receiver coil 51 and the second receiver coil 52 remains only in the area of influence of the grid line 25-3. Thus, the code at the grid line 25-3 in this phase of movement may be ascertained only by evaluating the differentially interconnected pair made up of the first receiver coil and the second receiver coil 51; 52.

(30) The present reasoning may be easily applied to the phase of movement during the transition from the second limit position to the third limit position 82; 83. Here, the pair made up of the first receiver coil and the second receiver coil 51; 52 is influenced only by the conditions at the grid line 25-3, whereas the pair made up of the second receiver coil and the third receiver coil 52; 53 is influenced only by the conditions at the grid line 25-4.

(31) During the transition from the third limit position to the fourth limit position 83; 84, the pair made up of the second receiver coil and the third receiver coil 52; 53 is influenced only by the grid line 25-4, whereas the pair made up of the third receiver coil and the fourth receiver coil 53; 54 is influenced only by the conditions at the grid line 25-5.

(32) The fourth limit position 84 corresponds to the first limit position 81, wherein it is shifted exactly by a first division interval . Since the condition 2=3 is presently fulfilled, the present reasoning may be applied to a scanning device which has any number of receiver coils which are arranged in a row in the measurement direction 11. It is ensured that there is a sufficient number of pairs of receiver coils 51 to 54, each being influenced only by the conditions at a single grid line 25-1 to 25-6.

(33) FIG. 4 shows code examples which may occur during the operation of a position measurement system according to the present disclosure. The codes which were read off from the material measure using the receiver coils are indicated by the reference numeral 34. In the present example, 12 codes were read off, whereas the corresponding scanning device has 13 receiver coils. Since the condition 2=3 is presently fulfilled, a total of three groups G.sub.1; G.sub.2; G.sub.3 of codes result, each comprising 123=4 code bits. The code bits of a group G.sub.1; G.sub.2; G.sub.3 are spaced apart from each other by three code positions.

(34) The codes for which no code value was able to be unambiguously associated with the measured value ascertained by the analog-digital converter are indicated by the letter X. This is due to the fact that the corresponding codes were ascertained by a pair of adjacent receiver coils which is influenced by the conditions at two adjacent grid lines. The ambiguous codes 36 are all in the same group, presently in the group G.sub.2. The code values of the group G.sub.2 are thus presently discarded, so that the code values 35 which are used are taken only from the groups G.sub.1 and G.sub.2.

(35) The code values 35 which are used are now compared with the random number sequence which is applied to the material measure 20. This random number sequence is stored in the digital computer (no. 33 in FIG. 2) in a suitable form, so that the corresponding comparison may be easily carried out by the digital computer. The position 26 of the code 35 which was read off within the stored random number sequence corresponds to the absolute position which the scanning device assumes with respect to the material measure. Codes which differ from one another in only one position are presently considered to be equal.

(36) The aforementioned random number sequence is preferably ascertained using the method described in DE 10 2013 220 747 A1, so that at least a one-bit error correction is possible.

(37) Thus, in the present example, it is possible to compensate for the read error which has occurred at the position indicated by the reference numeral 37.

LIST OF REFERENCE NUMBERS

(38) G.sub.i Group of code bits First division interval Second division interval m Width of the random code 10 Position measurement system 11 Measurement direction 20 Material measure 21 Marking 22 Opening 23 Metal tape 24 Side web 25-1 to 25-6 Grid line of the marking grid 26 Position within the random code 30 Scanning device 31 Evaluation unit 32 Analog-digital converter 33 Programmable digital computer 34 Read-off code values 35 Code values used 36 Ambiguous bit 37 Erroneous bit 38 Center line 40 Sensor unit 41 Transmitter winding arrangement 42 Transmitter area 43 Serpentine conductor track 43a First group 43b Second group 44 Boundary between the two groups of serpentine conductor tracks 45 Terminal of the transmitter winding arrangement 46 Alternating current source 47 Common voltage level 51 First receiver coil 52 Second receiver coil 53 Third receiver coil 54 Fourth receiver coil 55 First terminal of a receiver coil 56 Second terminal of a receiver coil 61 First switching means 62 Second switching means 63 Third switching means 64 Fourth switching means 65 Differential amplifier 65a Positive input of the differential amplifier 65b Negative input of the differential amplifier 65c Output of the differential amplifier 66 First signal line 67 Second signal line 70 Actuation device 71 Shift register 72 D flip-flop 72a Data input 72b Clock input 72c Output 73 Tap 74 Data line 75 Clock line 81 First limit position 82 Second limit position 83 Third limit position 84 Fourth limit position