DE102011106941A1 - Measuring unit for measuring position of e.g. receiver coil, has receiver coil groups with receiver coils that are switched with output voltages in series in measuring direction, where distance of receiver coils amounts to specific equation - Google Patents

Abstract

The measuring unit (10) has a sampling unit (30) movable relative to a material measure (20) in a measuring direction (11). The sampling unit comprises a transmitter winding arrangement whose electromagnetic field is influenced by measuring marks (21) of the measure. The arrangement comprises non-overlapping effective transmitter coils that are periodically arranged along the measuring direction. Receiver coil groups include pairs of receiver coils that are switched with output voltages in series in the direction, where distance (delta) of the receiver coils amounts to specific equation.

Description

The invention relates to a position measuring device according to the preamble of claim 1.

From the EP 1 164 358 B1 is a position measuring device known. According to the 16 of the EP 1 164 358 B1 the position-measuring device comprises a material measure and a scanning device. The material measure comprises a multiplicity of mutually identical measuring markings, which are arranged distributed periodically along a measuring direction, wherein they have a pitch λ. The material measure may be, for example, a sheet-metal strip, wherein the measurement marks are formed by rectangular openings in the sheet-metal strip.

The scanning of the EP 1 164 358 B1 is movable in the measuring direction relative to the material measure. It comprises a transmitter winding arrangement, which consists of planar, non-overlapping coils EK1, Es1, Ec1, ..., Esn, Ecn, Ek2, which are connected in parallel. The material measure in this case influences the electromagnetic field of the transmitter winding arrangement in such a way that electrical voltages are induced in the receiver coil pairs S1- / S1 +,..., Cn + / Cn-1, by means of which it is possible to deduce the relative position between the material measure and the scanner. This is an incremental position-measuring device, ie it must be determined by counting the measuring markings at which point of the material measure the scanning device is located. By contrast, within the pitch λ, the position can be determined absolutely by interpolation.

In the context of this application, a printed conductor arrangement which generates substantially the same electromagnetic field as a coil-shaped or spiral-shaped printed conductor is referred to as an effective coil. This is particularly intended to an embodiment in which a plurality of effective coils are formed by a serpentine conductor track, as for example from the DE 10 2009 042 940 or the US 3 466 580 is known.

In the 10 of the EP 1 164 358 B1 the electromagnetic field of the transmitter winding arrangement is shown roughly schematically. It can be seen here that two adjacent transmitter coils have an opposite winding direction. Within each transmitter coil a receiver coil pair is arranged, which consists of two individual coils. The two individual coils have an opposite winding direction and are connected in series, wherein the distance is λ / 2. In this way induced voltages, which are generated by external interference fields, cancel each other out. On the other hand, the measuring voltages generated by the influence of the material measure add up. It is important that the field of the transmitter winding arrangement, which acts on a pair of receiver coils, is symmetrical with respect to the central axis of the receiver coil pair. If this is not the case, the measuring voltage has a so-called DC offset, which affects the measuring accuracy. It should be noted that the electromagnetic field which acts on a pair of receiver coils, is caused not only by the associated transmitter coil, but also by the adjacent transmitter coils. Within the outermost transmitter coils, therefore, an asymmetric field acts because they only have adjacent transmitter coils on one side. There are therefore no receiver coil pairs arranged.

It should also be noted that neither the individual coils of the receiver coil pairs nor the receiver coil pairs overlap with the transmitter coils. The corresponding conductor tracks are arranged in a plurality of mutually electrically insulated planar layers, wherein due to the lack of overlaps a minimum possible number of layers is required.

The different receiver coil pairs are connected in series to two receiver coil groups, namely a sine and a cosine group whose measurement voltages are 90 ° out of phase. The more receiver coil pairs a receiver coil group, the stronger the corresponding measurement voltage. In addition, as the number increases, so does the measurement error, since the measurement error of the entire receiver coil group by the series connection is always smaller than the largest measurement error of a single receiver coil pair. Due to manufacturing tolerances, the measurement error of each receiver coil pairs is significantly different, with larger outliers are averaged out by the series connection.

However, the averaging effect described above does not occur if the position measuring device has an error that repeats along the measuring direction with the graduation period λ when the scanning device moves. In this case, for example, thought of a material measure in which all the measurement marks have the same shape error. Such an error induces the same noise voltage in all receiver coil pairs of a receiver coil group, so that the averaging effect does not come into play.

From the US Pat. No. 5,804,963 A1 an inductive position measuring device is known, which instead of two receiver coil groups three Receiver coil groups has. It is clear that the above averaging effect occurs again in the evaluation of three measuring voltages, so that the largest signal error does not have the same effect as with only two measuring voltages. It goes without saying that this averaging effect increases with increasing number of receiver coil groups.

The object of the invention is, in a position measuring device according to the basic principle of EP 1 164 358 B1 to improve the measurement accuracy. For this purpose, more than two receiver coil groups should be provided in order to use the averaging effect. There should be no disadvantages in the compensation of interference voltages. In addition, the winding arrangement of the scanning device should have a small extent in the measuring direction. Furthermore, the measuring voltages of the different receiver coil pairs should add up to a strong overall voltage. In addition, there must be enough room for the transmitter coil arrangement between two receiver coil pairs.

According to the independent claim, this object is achieved in that the number n of receiver coil groups is three or larger, wherein a number n in the measuring direction successively arranged receiver coil pairs each belong to different receiver coil groups, the assignments of the receiver coil pairs to a receiver coil group in the measuring direction is periodic, the Distance δ of two immediately adjacent receiver coil pairs is always δ = (2 - 1 / (2n)) λ. The merit of the inventors is to have generalized the features relating to the assignment of the receiver coil pairs to the receiver coil groups from the case n = 2 to the cases n ≥ 3. They have recognized that the specification for the distance δ of the receiver coil pairs can not be easily generalized from the case n = 2 to the case n ≥ 3. For the case n = 2, the distance according to the invention would be δ = 7 / 4λ. When using the 14 of the EP 1 164 358 B1 The known formula (nλ + λ / 4) would optionally result in a distance of δ = 5 / 4λ or of δ = 9 / 4λ. However, the inventors have recognized that the first alternative can not be generalized to the cases for n ≥ 3 because there is no longer sufficient space available for the transmitter coil arrangement between the receiver coil pairs. Although the second alternative is basically generalizable to the cases n ≥ 3, the inventors have recognized that there is a shorter distance δ, which is also useful.

It should also be noted that the distance δ is always δ = (2 - 1 / (2n)) λ. It follows that transmitter coils, in which no receiver coil pair is arranged, can only be present at the two ends of the scanning device.

In the dependent claims advantageous refinements and improvements of the invention are given.

The transmitter winding arrangement can have a first and a second group of conductor tracks whose ends are connected to one another in an electrically conductive manner, wherein the conductor tracks of a group run in each case in a serpentine manner with a small distance parallel to one another, wherein the conductor tracks of the two groups intersect in such a way that they have a plurality of effective transmitter coils define. This ensures that all effective transmitter coils are encircled by the same stream and thus generate an identical transmission field. This ensures that the different receiver coil pairs are all exposed to an ideally symmetric field, so that optimal compensation takes place.

The receiver coil groups can be connected to an evaluation unit, wherein the evaluation unit a plurality of individual angles α _ij from the output voltages U _i ; U _{j can} each calculate two receiver coil groups, where they can calculate the position angle α as a weighted average of the individual angles α _ij . At the time of the EP 1 164 358 B1 known position measuring device are only two output voltages available from which the position angle α is calculated. This is done in a mathematically unique way by an ArcTan calculation, wherein the said output voltages are previously digitized with the A / D converter. In the position measuring device according to the invention, however, more output voltages are available than are required for calculating the position angle α. Mathematically speaking, an overdetermined system of equations must be solved.

Due to measurement errors, there is the problem that this system of equations in the mathematical sense is not solvable. From the 6 of the US 4,697,144 A1 It is known to convert a plurality of measurement voltages by analog circuitry into a pair of measurement voltages, from which the position angle can be calculated in a known manner by means of an ArcTan calculation. This is based on the assumption that the measurement voltages are pure sinusoidal signals, so that the addition theorems are valid. In this case, one can generate a new voltage from two measuring voltages which has a predetermined phase shift with respect to the original voltages. The mathematically necessary additions and multiplications with constant factors can be mapped electrically through a resistor network.

The problem here is that the output voltages of the present position measuring device are not ideal sinusoidal, they are only sine-like. The addition theorems are therefore only roughly approximated. In the proposed calculation method, the validity of the addition theorems is no longer presupposed. In addition, averaging effect minimizing the error is achieved by averaging, which is just to be achieved with the position-measuring device according to the invention.

The evaluation unit can use the individual angles α _ij as a solution of the equation f (φ _i -α _ij ) / U _i -k _ij * f (φ _j -α _ij ) / U _j = 0 where φ _i = (i-1) π / n where f (α) is a predetermined sine-like function that mimics the positional dependence of the output voltage of the coil groups, where k _{ij is} a predetermined correction factor representing the different sensitivities of the two coil groups S _i ; S _j compensated. The function f (α) must be determined beforehand by measurements. In particular, it must be determined how the output voltages of the receiver coil groups change when the scanning device is displaced relative to the material measure. Since the transmitter winding arrangement is preferably periodically and the receiver coil groups preferably identical, all receiver coil groups have the same function f (α). The correction factor k _ij is 1 if all receiver coil groups have the same number of receiver coil pairs. However, reference should be made to a co-pending application of the Applicant of the same filing date as the present application, the subject matter of which is a position-measuring device of the present type in which one receiver coil group has one more pair of receiver coils than the other receiver coil groups. Here a correction of the different sensitivity is required.

The solution of the above equation can be done in a known manner with the Newton iteration α _{n + 1} = α _n - f (α _n ) / f (α _n ) be determined. The values of f (α) and the corresponding derivative f (α) are preferably stored in a value table which is stored in the evaluation unit. Due to the sine similarity of f (α), it is sufficient if the value table is applied only for an angle quadrant. The functional values of the other angular quadrants agree with those of the first angle quadrant except for the sign. It should also be noted that the above equation has several solutions analogous to the ArcTan. The correct solution can be determined in a known manner by sign consideration with respect to the measured voltages.

All individual coils of the receiver coil pairs may consist of one or more planar spirals, which are preferably made substantially rectangular. With this design, the available sensor surface can be provided with the largest possible conductor track length, since almost the entire sensor surface can be covered with conductor tracks. The proposed scanner thus has the highest possible sensitivity.

The invention will be explained in more detail below with reference to the accompanying drawings. It shows:

1 a rough schematic side view of a position measuring device according to the invention;

2 a rough schematic plan view of the sender winding arrangement of the position measuring device according to 1 ; and

3 a rough schematic plan view of the receiver winding arrangement of the position measuring device according to 1 ,

1 shows a rough schematic side view of a position measuring device according to the invention 10 , The position measuring device 10 includes a material measure 20 and a scanner 30 , The measuring standard 20 consists of a large number of identical measuring marks 21 , which at a constant pitch λ periodically along the measuring direction 11 are arranged. The measuring standard 20 can be formed, for example, by a metal strip extending in the direction of measurement 11 extends, with the measurement marks 21 be defined by rectangular openings in the metal strip. The width of the openings and the width of the intermediate webs is the same size and is therefore λ / 2. Other conceivable embodiments are in the EP 1 164 358 B1 with reference to the local 2 explained.

The scanning device 30 is in measuring direction 11 opposite the measuring standard 20 movable, the position measuring device 10 a scanning signal U ₁ , U ₂ , U ₃ outputs, based on which the relative position of said components 20 . 30 can be determined. The measuring standard 20 is contrary to the representation in 1 considerably longer than the scanner 30 , so that the position measuring device 10 has a sufficiently large measuring path.

At this point it should be noted that the 1 to 3 with respect to the measuring direction 11 drawn to scale. In particular, the position of the various effective coils S _ij , E _ij with respect to the measurement marks 21 represented according to the actual conditions. It should be pointed out in particular that the first receiver coil pair E _{11 has} the same relative position with respect to the associated measuring markings 21 occupies like the last receiver coil pair E ₁₃ . In the direction perpendicular to the measuring direction 11 the size ratios are greatly exaggerated for the sake of clarity. The material measure has, for example, a pitch of 1.0 mm, the thickness of which is, for example, 0.3 mm. The thickness of the various planar trace assemblies in the scanner 30 is for example 0.3 mm.

In 1 is the constant pitch of the scanner 30 , namely the distance between two receiver _{coil pairs} E _ij denoted by δ. Between the pitch λ of the material measure 20 and the pitch δ of the scanner 30 applies in the embodiment according to the 1 to 3 the relationship 6 × δ = 11 × λ. In this selection, a scanning device is realized with three groups of receiver coil pairs, wherein between two adjacent pairs of receiver coils each sufficient distance for the transmitter coil arrangement is present, so that the transmitter and the receiver winding arrangement 40 ; 50 do not overlap. Corresponding to the above connection between the pitches δ and λ, three groups of receiver coil pairs E _{ij are} provided whose scanning signals U ₁ , U ₂ , U ₃ are phase-shifted by 120 °. It can easily be seen that the relationship δ = (2-1 / (2n)) λ according to the invention with n = 3 is fulfilled. Namely, δ = (12/6 - 1/6) λ = 11 / 6λ.

2 shows a rough schematic plan view of the transmitter winding arrangement 40 , The transmitter coil arrangement 40 consists of a first and a second group 41 ; 42 of printed conductors, being in 2 only one single trace of each group is shown. In fact, each track group includes 41 ; 42 a plurality of conductor tracks, which are arranged at a small distance parallel to each other. The tracks of each track group 41 ; 42 each extend in the form of a rectangular serpentine line, intersecting each other to define a plurality of effective transmitter coils S _ij . Contrary to the illustration in 2 the tracks run in the crossing area 43 exactly parallel so that the effective transmitter coils S _ij each have exactly the shape of a rectangle. The individual effective transmitter coils S _ij are all essentially identical, so that they all generate the same electromagnetic field. In this case, each effective transmitter coil S _{ij is} mirror-symmetrical to an associated central axis 31 executed. The transmitter winding arrangement thus also defines the pitch δ of the scanning device 30 , The two groups of tracks 41 ; 42 are each arranged in different, electrically isolated layers, so that in the crossing area 31 no electrically conductive connection between the two groups of conductors 41 ; 42 consists. Depending on a conductor track of the first and the second group is via a via 44 electrically conductively connected to each other so that all traces of a single voltage terminal U _S can be powered. The transmitter coil arrangement 40 is supplied during operation with AC voltage having, for example, a frequency of 100 kHz. The required frequency results from the maximum travel speed of the position-measuring device 10 and the pitch λ of the material measure 20 ,

The current direction of the individual effective transmitter coils S _ij is in 2 represented by circular arrows. It should be pointed out that the present interconnect arrangement inevitably has the consequence that two adjacent effective transmitter coils S _ij each have the opposite winding or current direction. The current intensity and thus the field strength of each effective transmitter coil S _ij can be set to any value by means of the number of parallel conductor track. As a rule, you will choose the highest possible transmitter field strength. Thus, the installation space between the receiver coil pairs E _{ij is provided} with the highest possible number of parallel conductor tracks, which can be manufactured with technical safety.

3 shows a rough schematic plan view of the receiver winding arrangement 50 , The receiver winding arrangement 50 comprises a plurality of receiver _{coil pairs} E _ij . Each receiver coil pair E _ij consists of two complementary individual coils En _ij , Ep _ij , ie, the individual coils are made essentially identical, wherein they have an opposite direction of winding. The two individual coils En _ij , Ep _ij have the shape of a rectangular spiral, wherein the distance is λ / 2. The rectangular spirals each have a plurality of Windungsumläufen on, in 3 only one single winding circulation is shown. The opposite winding direction of the individual coils En _ij , Ep _ij is in 3 indicated by rectangular arrows. In 1 For example, a minus sign denotes a winding direction in the counterclockwise direction and a plus sign indicates a winding direction in a clockwise direction. In the present embodiment, all receiver coil pairs have the same winding direction.

The receiver coil pairs E _ij are connected in series with receiver coil groups, respectively. The first receiver coil group includes the Receiver coil pairs E ₁₁ , E ₁₂ , E ₁₃ , the second receiver coil group, the receiver coil pairs E ₂₁ , E ₂₂ and the third receiver coil group, the receiver coil pairs E ₃₁ , E _32nd In the 3 Plotted connecting tracks represent the interconnection of the receiver coils in the sense of a circuit diagram correctly, with the rest, no relation to the actual trace course is present. The individual receiver _{coil pairs} E _{ij of} a receiver coil group each have the same relative position with respect to the associated measurement mark 21 or a 180 ° out of phase relative position. The distance of the receiver _{coil pairs} E _ij is accordingly an integer multiple of the pitch λ or of λ / 2. Insofar as there is a phase shift, the associated effective transmitter winding arrangement S _{ij has} a reverse winding sense, so that the measurement voltages induced in the receiver coil pairs add up and do not cancel out.

In the present embodiment, the receiver coil pairs E ₁₁ , E ₁₂ and E _{13 are} connected in series to a first group of receiver coil pairs. The receiver coil pairs E ₁₁ and E ₁₃ each have the same relative position to the associated measuring mark, wherein the associated effective transmitter coils S ₁₁ and S _{13 have} the same winding direction. By contrast, the receiver coil pair E ₁₂ is arranged 180 ° out of phase with respect to the associated measuring mark, the transmitter coil S ₁₂ having an opposite winding direction with respect to the transmitter coils S ₁₁ and S ₁₃ . At this point it should be pointed out again that all receiver coils have the same winding direction. The required polarity reversal of the receiver coil pair E ₁₂ could of course also be generated by reversing its winding direction. However, this is not contemplated in the present embodiment because of the present design of the transmitter coil assembly 40 the winding directions of the individual effective transmitter coils S _{ij is} fixed.

The evaluation unit is not shown in the figures. This is an assembly that is connected to the terminals U ₁ , U ₂ and U _{3 of} the receiver winding arrangement 50 connected to which the output voltages of the receiver coil groups are applied. These are also referred to as measuring voltages in the context of the present application. Preferably, the evaluation unit also generates the supply voltage U _{S of} the transmitter winding arrangement, so that the evaluation unit is also connected to its connection U _S.

LIST OF REFERENCE NUMBERS

λ

Pitch of the measuring graduation pitch of the scanner

S _ij

effective transmitter coil

U _S

Voltage connection of the transmitter winding arrangement

En _ij , Ep _ij

Single coil

E _ij

Receiver coil pair, consisting of the individual coils En _ij , Ep _ij

U _i

Voltage connection of the receiver winding arrangement

10

Position measuring device

11

measuring direction

20

Measuring standard

21

measurement mark

30

scanning

31

Center axis of a scanning element

40

Send Erwin extension arrangement

41

first group of tracks

42

second group of tracks

43

perpendicular to the direction of measurement extending section; crossing area

44

via

50

Empfängerwindungsanordnung

51

Distance between the first and last receiver coil pairs

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1164358 B1 [0002, 0003, 0005, 0010, 0011, 0015, 0025]
• EP 11643581 B1 [0002]
• DE 102009042940 [0004]
• US 3466580 [0004]
• US 5804963 A1 [0009]
• US 4697144 A1 [0016]

Claims (5)

Position measuring device ( 10 ) comprising a material measure ( 20 ) and a scanner ( 30 ), whereby at the material measure ( 20 ) along a measuring direction ( 11 ) periodically arranged, mutually identical measuring marks ( 21 ) are provided, which have a pitch λ, wherein the scanning device ( 30 ) relative to the material measure ( 20 ) in the measuring direction ( 11 ), the scanning device comprising a transmitter coil arrangement ( 40 ) whose electromagnetic field from the measuring markings ( 21 ) of the material measure ( 20 ), the transmitter winding arrangement ( 40 ) several along the measuring direction ( 11 ), periodically arranged, planar, non-overlapping effective transmitter coils (S _ij ), wherein two immediately adjacent transmitter coils (S _ij ) have an opposite winding direction, wherein within at least a portion of the transmitter coils (S _ij ) each a single planar receiver coil pair (E _ij ) is arranged, which in each case has two effective individual coils (En _ij , Ep _ij ), which are connected in series with opposite winding direction, whereby in the measuring direction ( 11 ) are spaced apart by a distance of λ / 2, wherein all the effective individual coils (En _ij , Ep _ij ) are made substantially the same except for the winding direction, wherein the receiver coil pairs (E _ij ) and the transmitter coil arrangement do not overlap, wherein a number n is provided at the receiver coil groups each comprising a plurality of receiver coil pairs (e _ij), which are so connected in series that add their output voltages, characterized in that the number n is at receiver coil groups of three or greater wherein a number of n in the measuring direction one behind the other arranged receiver _coil pairs (E _ij ) each belong to different receiver coil groups, wherein the assignments of the receiver coil pairs (E _ij ) to a receiver coil group in the measuring direction ( 11 ) is periodic, wherein the distance δ of two immediately adjacent receiver _{coil pairs} (E _ij ) is always δ = (2 - 1 / (2n)) λ. Position measuring device according to claim 1, characterized in that the transmitter winding arrangement ( 40 ) a first and a second group ( 41 ; 42 ) of interconnects whose ends are electrically conductively connected to each other ( 44 ), wherein the tracks of a group ( 41 ; 42 ) in each case run in a serpentine manner with a small distance parallel to one another, wherein the interconnects of the two groups ( 41 ; 42 ) such that they define a plurality of effective transmitter coils (S _ij ). Position measuring device according to one of the preceding claims, characterized in that the receiver coil groups are connected to an evaluation unit, wherein the evaluation unit a plurality of individual angles α _ij from the output voltages U _i ; U _{j can} each calculate two receiver coil groups, where they can calculate the position angle α as a weighted average of the individual angles. Position measuring device according to claim 3, characterized in that the evaluation unit, the individual angle α _ij as a solution of the equation f (φ _i -α _ij ) / U _i -k _ij * f (φ _j -α _ij ) / U _j = 0 where φ _i = (i-1) π / n where f (α) is a predetermined cosine-like function that replicates the positional dependence of the output voltage of the coil groups, where k _{ij is} a predetermined correction factor that compensates for the different sensitivities of the two coil groups. Position measuring device according to one of the preceding claims, characterized in that all individual coils (En _ij , Ep _ij ) of the receiver coil pairs (E _ij ) consist of one or more planar spirals, which are preferably made substantially rectangular.

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