DE19733885A1 - Measurement device for measuring travel and angle of rotation on moving objects with hard magnetic surface - Google Patents

Abstract

Time modulated coded magnetic tracks (31,32) are impressed upon the measurement surface (34) of the moving object by a recorder head. As the track passes magnetic sensors (M1,M2), they generate periodically changing signals which are processed electronically. A further coded magnetic track can be provided as a measurement reference track (33)

Description

The invention relates to a method for measuring paths and angles of rotation on moving Objects with a hard magnetic surface and a device for carrying them through of the procedure.

Such methods and devices are known from the patent literature.

The published patent application DE 44 24 633 A1 describes an electric position drive, described in particular for motor vehicle sunroofs, which is a ratchet wheel has permanent magnetic markings in different positions and in different expansion are applied. Each permanent magnetic marker is a Hall sensor assigned. The Hall sensor signals determine the position of the drive and are in electronics with the actuation signals together to form engine control signals processed. The permanent magnetic markings can consist of plastoferrite strips, which are glued into grooves.

In the published patent application DE 43 11 267 a position transmitter for monitoring the Radial angular position and / or the angular velocity and / or the direction of rotation of a described driven shaft, the one connected to the shaft, on the circumference Multi-pole laterally magnetized rotor with magnetic field sensors cooperates, which extends on a board perpendicular to the shaft axis are arranged and their output signals in corresponding evaluation circuits be evaluated.

From publication DE 35 10 651 A1 is an incremental encoder, in particular Rotation angle sensor known high resolution, in which an incremental wheel with broken Circumferential structure (serration) one on the structural change with a change of their Output voltage reacting sensor unit at a specified distance without contact opposite. The sensor unit comprises two sensor systems that are mutually one quarter period of the electrical output signals are spatially offset or the same Scan the circumferential position in accordance with spatially offset rotor structure areas, the in a square waveform converted output signals of the two sensor systems a gate circuit (exclusive OR) are linked together so that the twice the number of impulses with otherwise maintained spatial dimensions.  

From the published documents DE 39 40 505 A1 and DE 196 14 165 A1 Magnetic detectors are known in which a pulse gear on a magnetic field Magnetic field sensor changed and the position from the change in the sensor signal of the pulse gear is determined.

The object of the invention is to provide a method for measuring the displacement and angle of moving To create objects that are equally suitable for linear and rotational movements of hard magnetic workpieces is suitable for single and bulk items is inexpensive to implement.

The object of the invention is achieved by the method described below and by device based on the method solved.

A magnetic track is magnetized onto the surface of a permanent magnetic material, the field strength of which is modulated in a certain way. The modulation function F (x) is strictly periodic with the period length Lm. The description initially relates to a single magnetic track in a linear arrangement (hereinafter referred to as the measuring track). In addition, additional magnetic tracks can be applied to enable further position evaluation. A material measure for angles is achieved by developing the magnetic track (s) on the circumference of a circle. At least two magnetic field sensors scan the measurement track. They are mechanically arranged in a measuring head so that they scan the magnetic track offset. The spatial offset is chosen so that it is preferably 1/4 Lm, alternatively also (n + 1/4) Lm. If the measuring head is moved in the longitudinal direction of the magnetic track, the two magnetic field sensors deliver two periodic signals A and B. If the Modulation function is a sine function, and if both sensors are linear with the field strength, signals A and B are also sine functions that are out of phase with each other. If the magnetic sensors are offset by Lm / 4, the phase shift is just 90 °. Subsequent evaluation electronics obtain the information about the distance traveled in a known manner. A conventional counting method works with threshold discriminators and quadruple evaluation and delivers:

Xrel = (N.Lm / 4).

The fine position within the Lm / 4 gradation is obtained e.g. B. by

Xabs = Lm / 360 ° .arctan (A / B).

Here A and B is the sinusoidal signal from the two magnetic sensors. The path covered is made up of Xrel and Xabs.  

Most applications, e.g. B. in mechanical engineering, require a position or Angle specification in relation to a specified zero point or reference point. This The reference point is obtained by applying a second magnetic track, hereinafter referred to as the reference or auxiliary track. In the simplest case, the reference track is needed to contain only a single singularity (e.g. a change of sign), the position of a magnetic sensor is recognized and represents the reference point. The requirement for the The accuracy of this position is as follows:

According to the invention, the function F (x) is strictly periodic with the period length Lm After switching on, the measuring system initially does not provide any information about which Period the measuring heads are located. Therefore, the system is initially operated until the measuring head finds the singularity. The associated period should be called the zero period become. The quadrant and then Xabs are then determined within the zero period. The system is thus referenced.

The requirement for the position accuracy of the singularity and the adjustment accuracy of the Magnetic head only needs to go so far as to reliably detect the zero period he follows.

The invention is described in more detail with reference to the figures. Fig. 1 shows a section through a heavy duty roller bearings with an inventive Drehwinkelmeßkopf. A stator ring (23) is mounted on a bracket (22) on which is rotatably supported by rolling bodies (25) is a roller bearing ring (20). The roller bearing ring ( 20 ) carries a slewing ring ( 21 ). Magnetically coded tracks are attached to the outer circumferential surface of the roller bearing ring, opposite which is arranged a sheath measuring head ( 10 ) which is held on a measuring head holder ( 18 ) which is rigidly connected to the holder ( 22 ).

Fig. 2 shows a schematic representation of a rolling bearing ring ( 20 ). On the outer surface of the rolling bearing ring ( 20 ), a jacket measuring head ( 10 ) is arranged, which carries the sensors M1, M2, M11, M12, the reference sensor R and the interference field sensor S. The sensors M1 and M2 are assigned to the measuring track 1 ( 31 ), the sensors M11 and M12 to the measuring track 2 ( 32 ) and the reference sensor R to the reference track ( 33 ). All sensors except the interference field sensor ( 17 ) are arranged at a short distance from the measuring surface ( 34 ). The invention further provides that the measuring head is arranged on the end face of a rolling bearing ring. In this case, the end measuring head ( 11 ) with all sensors is assigned to the track ( 30 ) on the end face of the rolling bearing ring analogously to the jacket measuring head.

Fig. 3 shows the spatial arrangement of the magnetically coded tracks on the measuring surface ( 34 ). The measuring surface can be the outer surface of a rolling bearing ring, the end face of a rolling bearing ring or the surface of a linear scale. The areas of the same magnetization direction N and S are shown on a reference track R ( 33 ) and on measurement tracks 1 and 2 ( 31 , 32 ). the measuring tracks are characterized by different period lengths Lm.

In Fig. 4 the circuit arrangement of the rotation angle measuring system is shown in principle. The signals from the sensors ( 12 , 13 , 14 , 15 , 16 , 17 ) are fed to an electronic evaluation circuit via measuring amplifiers ( 42 , 43 , 44 , 45 ,...). In this evaluation circuit, the signal of the interference field sensor is subtracted from the signals of the measuring sensors and from the signal of the reference sensor and the amplitudes of the modulation signals are normalized. Analog voltages are either forwarded to a controller ( 41 ) via an interface or the position of the reference mark with respect to a fixed point of the measuring head is transferred using a known data protocol.

In FIG. 5, the output signals of the sensors M1 and M2 as a function of distance x on the measurement surface along the respective track shown. The phase-shifted sine curves A and B are overlaid by interference field Ss (x) (assumed here as constant). In practice, the amount of the interference field can exceed the amplitude of the modulation functions A and B, which is why the part of the magnetic field that does not originate from the magnetically coded tracks is measured in an interference field sensor. It is also possible to calibrate the measuring system by means of a calibration run and to mathematically eliminate the interference field. For this purpose, the signals SM1 (x) and SM2 (x) are measured over several periods Lm and the measurement curves are symmetrized to the zero line by determining the respective maxima and minima in the evaluation electronics ( 40 ).

In FIG. 6 embodiments are shown of the read heads. Fig. 6a) shows a cut core (53) having an air gap (52) which is guided at a distance of a few micrometers over the measurement surface (34). The magnetic field sensor ( 51 ) measures the magnetic flux in the cross section of the ferrite core. The width of the air gap must be chosen small compared to the period length Lm. Depending on the accuracy requirements, the period length Lm is 0.01 to 8 mm; with a period length of 0.5 mm, the angular position is accurate to 0.001 mm, provided that the distance between the reading head and the measuring surface is kept constant in the range of 0.03 mm and the analog-digital converter has a resolution of 8 bits.

In Fig. 6b), a read head arrangement is shown in which the magnetic flux is effected in a ribbon core of amorphous metal (54), wherein the flux in the tape core in the magnetic field sensor (51) is measured.

In Fig. 7a) a reading head is shown, which has a multi-cell magnetic circuit ( 55 ), which with the same period length Lm has formations which can be made to coincide with the areas of the same magnetization direction N. Another multi-cell magnetic circuit ( 56 ) which can be made to coincide with the areas S is arranged at a distance of at least one period Lm along the measuring surface. A yoke ( 57 ) is arranged on the multi-cell magnetic circuit ( 55 ) and forms a gap with the multi-cell magnetic circuit ( 56 ) in which the magnetic field sensor is arranged.

Fig. 7b) shows a simple arrangement of the reading head, in which a magnetic field sensor with a small active measuring volume is slidably arranged directly at a small distance above the measuring surface ( 34 ).

Fig. 8 shows an arrangement of the rotation angle measuring head holder, in which the jacket measuring head ( 10 ) carries the sensors M1, M2 and S on a sensor carrier plate ( 80 ). The sensor carrier plate is slidably supported on the measuring surface by means of support rollers ( 81 , 82 ). The mantle measuring head is attached to the measuring head holder ( 18 ) by means of compression springs ( 83 , 84 ) in such a way that the distance between the sensors and the measuring surface ( 34 ) always remains constant when there are changes in distance between a fixed reference point and the rolling bearing surface. Instead of the rollers, slide rails can also be provided. In the case of heavy-duty bearings with slewing ring diameters of over 0.5 m, the distance changes can be up to 0.3 mm in practice; however, the distance between the measuring sensors and the measuring surface must be kept constant between 0.01 and 0.03 mm, depending on the accuracy requirements for the measuring system.

By the z. Partly considerable deformations of the rolling bearing ring under load, structural changes in the area of the measuring surface ( 34 ) can occur, as a result of which the magnetization of the magnetically coded track can be changed. In order to reduce the influence of the flexing movement on the magnetization, a groove ( 26 ) is provided in the rolling bearing ring ( 20 ) in the vicinity of the outer circumference and the sensors M1 and M2 are arranged on the measuring surface in the area of the groove. In the cross section of the rolling bearing ring ( 20 ) shown, the measuring surface is not exposed to any mechanical loads, provided the rolling elements do not extend into the area of the groove.

An arrangement for applying the magnetic coding by means of a mastergoniometer is shown schematically in FIG. 9. A goniometer table / 1) is rotatably mounted on a goniometer base ( 70 ) and carries the roller bearing ring ( 20 ) to be coded. The goniometer table is driven by a drive motor, the respective angular position being transferred to an electronic coding control ( 47 ). If the angular position is transferred in digital form, the control ( 47 ) has a digital-to-analog converter with amplifier which controls the write current through the write coil in the write magnet ( 92 ) synchronously with the rotation of the goniometer. The write magnet for the reference track SMr ( 91 ) is also controlled. If an analog signal that is correlated with the angular position is transmitted by the goniometer, this is amplified in phase in the control ( 47 ) and fed to the writing coil. In an angle measuring system, the reference track is coded in such a way that the magnetization function R (x) has a sign change from minus to plus at the angle zero (more precisely: to the zero period), while a reverse sign change of another period, e.g. B. which is assigned at 180 °. The sign definition is arbitrary in that it can be assigned to both the north and south poles without violating the generality. The amount of the function R (x) is constant over the entire area of the track and generates a signal in the reference sensor, the amount of which can be used for diagnostic purposes.

In Fig. 10 a write head ( 90 ) is shown schematically, a write coil ( 94 ) being wound over a magnetic yoke ( 93 ) which has two tapered pole pieces in the area of the measuring surface ( 34 ) and separated by an air gap. The write current of the write head should be selected in such a way that the material to be encoded is magnetized on the measuring surface until saturation. Before each writing process, the measuring surface is demagnetized at least in the area of the tracks by means of an alternating magnetic field.

The tracks are usually encoded before the rolling bearing is assembled; However, it is also possible to make the coding on the built-in roller bearing, if this is the allow spatial conditions.

List of pictures:

Fig. 1 section through a heavy-duty roller bearing with rotation angle measuring head

Fig. 2 Schematic representation of a rolling bearing ring with rotation angle measuring heads

Fig. 3 spatial arrangement of the magnetically coded tracks on the measuring surface

Fig. 4 circuit arrangement for rotation angle measuring system

Fig. 5 waveforms at the magnetic field sensor outputs

Fig. 6 reading heads

• a) with ferrite core and Hall sensor  
• b) with amorphous metal band and Hall sensor

Fig. 7 read heads

• a) Magnetic connection across several similar magnetic areas
• b) without magnetic connection

Fig. 8

• a) View of the rotation angle measuring head holder
• b) Rolling ring with a grooved groove

Fig. 9 arrangement for applying the magnetic coding by means of a mastergoniometer

Fig. 10 Schematic representation of the print head

Reference list

10th

Coat measuring head

11

Forehead measuring head

12th

M1 sensor

13

M2 sensor

14

M11 sensor

15

M12 sensor

16

Reference sensor R

17th

Interference field sensor S

18th

Measuring head holder

20th

Rolling bearing ring

21

Slewing ring

22

bracket

23

Stator ring

24th

Rolling elements

25th

Rolling elements

26

Groove

30th

magnetically coded track

31

Measuring track 1

32

Measuring track 2

33

Reference track

34

Measuring surface

40

electronic evaluation circuit

41

control

42

Measuring amplifier

43

Measuring amplifier

45

Measuring amplifier

46

Measuring amplifier

47

electronic coding control

50

Read head

51

Magnetic field sensor (Hall sensor)

52

Air gap

53

Ferrite core

54

Band core made of amorphous metal

55

Multi-cell magnetic circuit

56

Multi-cell magnetic circuit

57

yoke

60

Limit of the direction of magnetization

61

Area of the same magnetization direction (S)

62

Area of the same magnetization direction (N)

70

Goniometer base

71

Goniometer table

80

Sensor carrier plate

81

Support roller

82

Support roller

83

Compression spring

84

Compression spring

90

Printhead

91

Writing magnet for reference track

92

Writing magnet for measuring track

93

Magnetic yoke

94

Writing coil
Lm period length.

Claims (33)

1. A method for measuring paths and angles of rotation on moving objects with a hard magnetic surface with a magnetically coded track in the measuring surface ( 34 ) and a measuring head arranged in the region of the magnetically coded track with at least two magnetic sensors ( 12 , 13 ), characterized that the magnetically coded track is magnetized directly onto the measuring surface ( 34 ) of the object demagnetized at least in the region of the track by means of a write head ( 90 ) and the track consists of at least one measuring track ( 31 ) with a magnetization that changes periodically with the period length Lm and that the measuring head is guided at a constant distance from the measuring surface ( 34 ), the distance being in the range between 0.01 mm and 0.05 mm and that the magnetic sensors ( 12 , 13 ) measure the static magnetic field of the coded track and which the signals of the Magnetic sensors ( 12 , 13 ) are fed to an electronic evaluation circuit. 2. A method for measuring paths and angles of rotation according to claim 1, characterized in that the magnetically coded track consists of at least two measurement tracks with different period lengths Lm. 3. A method for measuring paths and angles of rotation according to one of claims 1-2, characterized in that on the surface of a non-magnetizable material existing object a magnetizable layer in the area of the measuring surface optionally applied by vapor deposition, sputtering, gluing, electroplating or screen printing is and is magnetically encoded by means of a write head. 4. A method for measuring paths and angles of rotation according to one of claims 1-3, characterized in that on the surface of a soft magnetic material existing object optionally by alloying, diffusion and / or suitable Structural change, e.g. B. laser hardening a hard magnetic layer in the area of the measuring surface is produced. 5. A method for measuring paths and angles of rotation according to one of claims 1-4, characterized in that the track at least from a measuring track ( 31 ) with a periodic magnetic field F (x), which represents the measuring standard, and at least one reference track ( 33 ) consists. 6. A method for measuring paths and angles of rotation according to one of claims 1-, characterized in that the periodic course F (x) of the magnetic field strength along the measuring track ( 31 ) is a sine function. 7. A method for measuring paths and angles of rotation according to one of claims 1-6, characterized in that the periodic course F (x) of the magnetic field strength along the measuring track ( 31 ) is a triangular function. 8. A method for measuring paths and angles of rotation according to one of claims 1-7, characterized in that the measuring track ( 31 ) in the direction perpendicular to the direction of movement of the object has such an extent that the sensors M1 and M2 are preferably 90 ° out of phase with each other arranged and scan the measurement track with the field strength distribution F (x) out of phase. 9. A method for measuring paths and angles of rotation according to one of claims 1-8, characterized in that the measuring head contains at least two reading heads ( 50 ), each of which consists of a ferrite core ( 53 ) with two half-shells, which on the measuring surface ( 34 ) facing the side form a narrow air gap ( 52 ) and on the side facing away from the measuring surface ( 34 ) have a gap in which a magnetic field sensor ( 51 ) for measuring the magnetic flux is arranged. 10. A method for measuring paths and angles of rotation according to one of claims 1-9, characterized in that the measuring head contains at least two reading heads ( 50 ), each consisting of a band core made of amorphous metal ( 54 ) with two half-shells, which on the form a narrow air gap ( 52 ) on the side facing the measuring surface ( 34 ) and have a gap on the side facing away from the measuring surface ( 34 ) in which a magnetic field sensor ( 51 ) for measuring the magnetic flux is arranged. 11. A method for measuring paths and angles of rotation according to one of claims 1-10, characterized in that the magnetic field sensors magnetoresistive semiconductors (Field plates) and the magnetic field of the magnetically coded track are magnetic DC field is superimposed. 12. A method for measuring paths and angles of rotation according to one of claims 1-11, characterized in that the reading head ( 50 ) is constructed from a ferrite core ( 53 ) with two half-shells and that the width of the air gap corresponds to x times the length of the period Lm , where x is determined such that the measurement signal F (x) results in a function that is easy to evaluate. 13. A method for measuring paths and angles of rotation according to one of claims 1-, characterized in that the reading head has a multi-cell magnetic circuit ( 55 ) which has a number n (1 <n <15) magnetic poles with the width Lm / 2 on the the side facing the measuring surface and on the side facing away from the measuring surface carries a yoke ( 57 ) which forms a gap with a further, similarly designed multi-cell magnetic circuit ( 56 ) in which a magnetic field sensor ( 51 ) for measuring the magnetic flux is arranged and that the two multi-cell magnetic closures ( 55 , 56 ) are arranged at a distance which corresponds to an integral multiple of the period length Lm, along the magnetically coded track. 14. A method for measuring paths and angles of rotation according to any one of claims 1-13, characterized in that the width of the air gap of the reading head ( 50 ) is Lm / 4, and the magnetization function F (x) is a rectangular function with the period length Lm . 15. A method for measuring paths and angles of rotation according to any one of claims 1-14, characterized in that the width of the air gap of the reading head ( 50 ) is Lm / 4, and the magnetization function F (x) is a function with the period length Lm, the course of which is selected so that the measurement signal approximately results in a sine function. 16. A method for measuring paths and angles of rotation according to any one of claims 1-15, characterized in that the two sensors ( 12 , 13 ) for scanning the measuring track ( 31 ) are arranged slightly offset next to one another in the direction of movement, the two air gaps being a distance have just 1/4 of the period length F (x). 17. A method for measuring paths and angles of rotation according to one of claims 1-16, characterized in that the two sensors ( 12 , 13 ) for scanning the measuring track ( 31 ) are arranged one behind the other in the direction of movement, the two air gaps being at a distance, which is straight (n + 1/4) of the period length Lm. 18. A method for measuring paths and angles of rotation according to one of claims 1-17, characterized in that the reference track ( 33 ) carries a magnetization with the field strength R (x), which has a change of sign at a zero point and a further change of sign at further reference points may otherwise have a constant amount over the entire course of the reference track. 19. A method for measuring paths and angles of rotation according to one of claims 1-18, characterized in that the measurement signal of the reference sensor R ( 16 ) is used to compensate for the temperature dependence of the magnetization, in particular when approaching the Curie temperature. 20. A method for measuring paths and angles of rotation according to one of claims 1-19, characterized in that the signal of the reference sensor R ( 16 ) is used in the evaluation circuit for the drift caused by temperature and other influences from zero point and amplification of the magnetic field sensors or to detect and if necessary compensate their evaluation electronics, the sensors and the electronics of the evaluation circuit being thermally coupled and the evaluation circuits for the reference track and the measurement tracks being constructed identically. 21. A method for measuring paths and angles of rotation according to one of claims 1-20, characterized in that the reference track ( 33 ) has a plurality of singularities, for. B. change of sign - hereinafter referred to as "marks" - which allows several periods Lm to be marked at a reasonable distance, which can each be used as reference points. 22. A method for measuring paths and angles of rotation according to one of claims 1-, characterized in that the reference marks are attached at different distances are and the spacing is selected so that a different number of Lm's be included, for example in ascending order. Referencing is already done possible as soon as at least two marks have been swept over. The number of in between counted LM's allows a clear assignment to the current distance from the zero point. 23. A method for measuring paths and angles of rotation according to one of claims 1-22, characterized in that the reference marks are attached so that the distance represents a binary code that represents the absolute position. 24. A method for measuring paths and angles of rotation according to one of claims 1-23, characterized in that the track contains more than one measuring track which are coded such that an absolute path or angle position are calculated in the evaluation circuit ( 40 ) can. 25. A method for measuring paths and angles of rotation according to one of claims 1-24, characterized in that the object is demagnetized in the area of the measuring surface ( 34 ) with a high-frequency magnetic field. 26. Device for carrying out the method according to one of the above claims, characterized in that the measuring surface is the outer lateral surface of a rolling bearing ring ( 20 ) and that the jacket measuring head is guided at a constant distance from the measuring surface with support rollers ( 81 , 82 ) along this. 27. Device for carrying out the method according to one of the above claims, characterized in that the measuring surface is the outer lateral surface of a rolling bearing ring ( 20 ) and that the jacket measuring head is guided at a constant distance from the measuring surface with plain bearings along this. 28. Device for carrying out the method according to one of the above claims, characterized in that the measuring head with compression springs ( 83 , 84 ) between the holder ( 18 ) and the sensor carrier plate ( 80 ) is pressed onto the measuring surface. 29. Device for carrying out the method according to one of the above claims, characterized in that the measuring surface is the outer lateral surface of a rolling bearing ring and that the rolling bearing ring ( 20 ) has a groove ( 26 ) at a distance of 2-15 mm from the lateral surface, the depth of which exceeds the width of the magnetically encoded track. 30. Device for performing the method according to one of the above claims, characterized in that the measuring surface ( 34 ) is the end face of a rolling bearing ring ( 20 ) and the track ( 30 ) is scanned with an end measuring head ( 11 ). 31. Device for performing the method according to one of the above. Expectations, characterized in that the measuring surface is a mechanically unloaded part of a Is linear guide and an end measuring head on a displaceable along the linear guide Sledge is arranged. 32. Device for performing the method according to one of the above. Expectations, characterized in that the measuring surface is a mechanically unloaded part of a represents hardened shaft.   33. Device for performing the method according to one of the above. Expectations, characterized in that the material of the object is ball bearing steel.