Angle measuring system and method for producing an angle measuring system

An angle measuring system includes a first component group and a second component group, the first component group being mounted in a manner allowing rotation about an axis relative to the second component group. The first component group includes a ring having a running surface and an angle scaling. The second component group has a further ring having a further running surface, as well as a sensor for scanning the angle scaling. Rolling elements are arranged between the running surfaces, the angle scaling being applied such that a geometric pattern of the angle scaling in a first region differs from a geometric pattern of the angle scaling in a second region as a function of radial runouts of the running surfaces and/or of the rolling elements.

FIELD OF THE INVENTION

The present invention relates to an angle measuring system and a method for producing an angle measuring system.

BACKGROUND INFORMATION

Such angle measuring systems are used to measure rotary motions and rotational positions of a machine part, for instance, a shaft. The rotary motion is determined either incrementally or absolutely; the output measured value, for example, is a sequence of counting pulses, a counter value or a code word. Corresponding angle measuring systems are used particularly in what are referred to as pick-and-place machines in the manufacture of electronic components, or in machine tools for measuring rotary movements. The reproducibility or repeatability of the rotational angles of machine parts precisely to only a few angular seconds is very important when working with pick-and-place machines, for instance. In particular, the absolute accuracy of the measurement results of an angle measuring system is crucial in the case of machine tools. Certain conventional angle measuring systems have a separate bearing assembly of the component parts rotatable relative to each other.

The accuracy of an angle measurement is influenced by the quality of the angle scaling, its eccentricity and by the radial runouts of the bearing assembly or wobble errors.

German Published Patent Application No. 30 36 005 describes a method for producing an angle scaling for an angle measuring system in which code tracks are applied to a code disk by a laser beam. When being written on, the code disk is already connected to a shaft, so that the code disk is already centered relative to the shaft during the writing of the code pattern.

This method has the disadvantage that the angle measuring systems produced by it do not achieve the highest accuracy, are not sufficiently robust for many applications and moreover, require a relatively great amount of space.

SUMMARY

Example embodiments of the present invention provide a robust angle measuring system and a method for producing it, which provides a very precisely operating, compact angle measuring system in a simple type of construction.

According to example embodiments of the present invention, the angle measuring system includes a first component group, a second component group and a sensor, the first component group being mounted in a manner allowing rotation about an axis relative to the second component group. The first component group features a ring having a running surface and having an angle scaling. The second component group has a further ring having a further running surface and the sensor for scanning the angle scaling. Rolling elements are disposed between the running surfaces of the first and second component groups. The angle scaling is applied such that a geometric pattern of the angle scaling in a first region differs from a geometric pattern of the angle scaling in a second region as a function of radial runouts of the running surfaces and/or of the rolling elements.

The geometric patterns of the angle scaling in the angle measuring system are thus a function, inter alia, of the individual dimensions or dimensional deviations of the respective running surfaces and/or of the rolling elements provided in the angle measuring system.

The angle scaling is applied on a component of the first component group; the component may be connected as a separate component, for instance, as a graduation ring, in rotatably fixed manner to the ring, or else may be implemented as an integral part of the ring of the first component group. The latter is the case, for instance, when the angle scaling is applied directly on the ring.

The ring of the second component group may include a radially traversing opening, through which the angle scaling is able to be applied. The opening may be formed such that it has an axial extension which is less than ⅓, especially less than ⅕, of the axial outside dimension of the ring of the second component group.

Incidentally, the running surfaces are the surfaces or paths along which the rolling elements roll during operation of the angle measuring system. From the paraxial view, the running surfaces of the ring of the first component group may be convex, while the running surfaces of the ring of the second component group may be concave.

According to example embodiments of the angle measuring system, the ring of the first component group is located radially inside and may then also be denoted as inner ring, while the ring of the second component group in this case is located radially outside, and may be defined as outer ring.

For example, the angle scaling is disposed on a lateral side of the graduation ring. The term lateral side should be understood to refer to a cylindrical surface or peripheral area which is either closed around 360° or represents only a part of a peripheral area. The angle scaling may then be aligned with a directional component parallel to the axis.

The angle scaling frequently includes regions having different magnetic polarization. In this case, the magnetized regions are aligned with a directional component parallel to the axis, so that north poles and south poles quasi alternate with each other as magnetic graduation marks in the circumferential direction. In particular, the angle scaling may also include a plurality of tracks, for example, when the absolute angular position of a shaft to be measured is to be ascertainable directly by the angle scaling.

Alternatively or in addition to the substantially axial alignment of the angle scaling, the angle scaling may also be aligned with a radial directional component. In this case, at least a part of the angle scaling is applied on the face of the relevant component of the first component group.

The angle scaling may be applied on a component, particularly a graduation ring, of the first component group, which is made of a magnetizable material. The graduation ring may be made of a magnetically hard material having a coercive field strength of at least 1 kA/m. The coercive field strength is, for example, between 10 kA/m and 60 kA/m, e.g., between 25 kA/m and 45 kA/m.

For example, the sensor used may be an MR sensor or a Hall sensor.

Particularly good measuring accuracies of the angle measuring system are achieved if the first component group and the second component group as well as the rolling elements are arranged such that the first component group and the second component group are disposed so as to be axially and/or radially free from play with respect to each other.

For example, the first and the second component groups, respectively, may have two running surfaces, between which in each case rolling elements are disposed. The angle scaling as well as the opening through which the angle scaling is able to be applied may then be disposed axially between these running surfaces.

According to example embodiments, the ring of the second component group is solid, and in the circumferential direction, offset with respect to the opening, has a first recess for accommodating a printed circuit board having an electronic circuit.

The angle measuring system is implemented so that its maximum axial extension is less than 40%, e.g., less than 30% of the maximum outside radius of the angle measuring system. Furthermore, the angle measuring system may have a relatively large opening for accommodating a shaft to be measured, the radius of the opening being, for example, at least 50%, e.g., at least 60% of the maximum outside radius of the angle measuring system. For example, this opening is bounded by the inside diameter of the inner ring, while the outside radius of the outer ring then represents the outside radius of the angle measuring system.

In the method according to an example embodiment of the present invention, initially the rings of the two component groups are fabricated, in each case at least one finely machined running surface being produced on them. The angle measuring system is thereupon assembled in a manner that the running surface of the first ring is opposite the running surface of the second ring, and the rolling elements are disposed between both running surfaces such that the first component group and the second component group are situated so as to be axially free from play with respect to each other. The rings are later affixed to elements rotatable relative to each other—e.g., a stator block and a shaft—of a scaling machine. In a further operation, the angle scaling is applied on a component of the first component group, in this operation, the rings in the scaling machine being rotated around the axis relative to each other.

For example, an opening, especially radially oriented, is incorporated in the ring of the second component group. The angle scaling is then applied on the relevant component of the first component group using the opening.

The angle scaling may be provided such that only incremental angular-position information is able to be read through it, or else additionally or as an alternative to that, absolute angular positions, as well.

In order to apply an angle scaling which is made up of regions having different magnetic polarization, a magnetic writing head may be introduced into the opening, and the angle scaling may then be applied. For example, the component of the first component group on which the angle scaling is applied is made of a magnetically hard material.

The component, particularly a graduation ring, of the first component group on which the angle scaling is later applied may be mounted on the ring of the first component group during assembly, e.g., before the angle scaling is applied. In particular, the component may be mounted on the outer circumference of the ring.

The running surfaces may be machined with the aid of a grinding, honing or lapping process.

When assembling the first component group, the second component group and the rolling elements, an axial and/or radial prestress may be produced between the rings.

According to example embodiments of the present invention, the angle measuring system includes a first component group and a second component group, the first component group being mounted in a manner allowing rotation about an axis relative to the second component group. Furthermore, the first component group includes a ring having a running surface and an angle scaling. The second component group has a sensor for scanning the angle scaling as well as a printed circuit board having an electronic circuit for evaluating signals of the sensor able to be generated by the scanning. In addition, the second component group includes a solid ring on which a further running surface is situated, and has a first recess for accommodating the printed circuit board. The second component group further has a second recess for accommodating an electrical conductor. The electrical conductor is set apart from the sensor and electrically connects the sensor to the electronic circuit.

An extension of the first recess in the ring of the second component group in a direction parallel to the axis may be greater than an extension of the first recess in the circumferential direction. In particular, the greatest extension of the first recess in a direction parallel to the axis is greater than the greatest extension of the first recess in the circumferential direction.

The ring of the second component group has an axial outside dimension which is, for example, at least 1.5 times as great as the extension of the first recess in the ring of the second component group in a direction parallel to the axis. In particular, the axial outside dimension of the ring in question may be at least 1.75 times or at least 2 times as great as the extension of the first recess in the ring of the second component group in a direction parallel to the axis.

The ring of the second component group may have a third recess for accommodating the sensor. Prior to the assembly—in particular, exclusively prior to the assembly—of the first component group, the second component group and the rolling elements, the sensor may be mounted on the second component group. In particular, the electrical conductor may already also be mounted on the second component group prior to the assembly of the first component group, the second component group and the rolling elements.

Especially in view of a construction of the angle measuring system that is immune to disturbance, the ring of the second component group is implemented as a metallic ring, particularly as a steel ring.

The extension of the first recess may be greater than the extension of the second recess, in each case specific to a direction parallel to the axis. This holds true in particular for, in each instance, the greatest extensions of the second recess.

The electrical conductor may have a cross-section having different outside dimensions, e.g., a rectangular cross-section, that has two different edge lengths as the respective outside dimension. In this context, the larger outside dimension is in a direction parallel to the axis. For example, the same observation may be applied to conductors having an elliptical cross-section, as well.

The first recess may be formed such that the printed circuit board may be introduced into the first recess in the radial direction, especially in a direction toward the axis. In particular, the first recess then has an opening at the outer circumference of the ring of the second component group. Furthermore, the third recess may be formed such that the sensor may be introduced into the third recess in a direction leading away from the axis, radially to the outside. Accordingly, the third recess may have an opening at the inner circumference of the ring of the second component group.

Further features and aspects of example embodiments of the angle measuring system and the method are described below with reference to the attached figures.

DETAILED DESCRIPTION

According toFIG. 1, the angle measuring system of an example embodiment of the present invention includes a first component group1and a second component group2, in the exemplary embodiment presented, first component group1being used as a rotor and second component group2being used as a stator. First component group1includes a ring which, in the present exemplary embodiment, is designated as inner ring1.1. Correspondingly, a further ring, which is assigned to second component group2, is designated here as outer ring2.1.

In the method for producing an angle measuring system, first of all, inner ring1.1and outer ring2.1are fabricated. In so doing, in the beginning, the contours are brought out comparatively roughly by metal cutting. Axial outside dimension Z (seeFIG. 4b) of outer ring2.1is 70 mm in the present exemplary embodiment. Furthermore, a radially aligned opening2.15, here in the form of a cylindrical bore hole, is introduced into outer ring2.1. Axial extension z of opening2.15, that is, the diameter of the bore hole is 10 mm here, so that a ratio of z/Z=1/7 is thus obtained. In addition, in this manufacturing phase, a cavity which includes three chambers, i.e., three recesses2.11,2.12.2.13, is introduced into outer ring2.1. In this context, radially outermost recess2.11has the greatest volume. Recess2.12situated further inside connects the two adjacent recesses2.11and2.13.

In a further operation, in each case, finely machined running surfaces1.14,2.14are produced on inner ring1.1and outer ring2.1by a lapping process.

In the course of the further assembly, first of all a sensor2.2, e.g., an MR sensor, together with an electrical conductor2.4, here a flexible conductor, are then mounted in outer ring2.1. Electrical conductor2.4has a rectangular cross-section, and therefore has different outside dimensions B, d. Thickness d is relatively small in relation to width B. During assembly, electrical conductor2.4is introduced from the inner side of outer ring2.1into third recess2.13, with larger outside dimension B of electrical conductor2.4being in a direction parallel to axis A. After that, sensor2.2and electrical conductor2.4are moved radially outwardly until sensor2.2is positioned in third recess2.13, and electrical conductor2.4projects through second recess2.12into first recess2.11. Accordingly, third recess2.13is thus provided such that sensor2.2may be inserted into recess2.11in a direction leading away from axis A.

Next, the end of electrical conductor2.4is pulled radially outwardly, so that it is outside of outer ring2.1. In this position, this end of electrical conductor2.4is then connected to an electric coupling2.32on a printed circuit board2.3. A plurality of electronic components is situated on printed circuit board2.3, among others, one having an electronic circuit2.31for evaluating signals of sensor2.2.

First recess2.11is open radially to the outside, thus, is configured so that printed circuit board2.3may be introduced into recess2.11in a direction toward axis A. Printed circuit board2.3is thus inserted into first recess2.11accordingly, and is then fixed in position in first recess2.11. In so doing, printed circuit board2.3is oriented such that it is aligned parallel to axis A, thus, the plane of printed circuit board2.3is parallel to axis A.

In addition, a graduation ring1.2is mounted on the outer circumference of inner ring1.1. This graduation ring1.2is made of a magnetically hard material, here an iron-cobalt-chromium alloy having a coercive field strength of approximately 38 kA/m. In this phase, graduation ring1.2has no angle scaling1.21, i.e., no graduation pattern.

After that, inner ring1.1together with graduation ring1.2and outer ring2.1as well as rolling elements3are assembled such that rolling elements3are situated between both running surfaces1.14,2.14. As a result of the geometric dimensions of inner ring1.1, of rolling elements3and of outer ring2.1, a radial and axial prestress is produced between inner ring1.1and outer ring2.1. Thus, a system is produced in which first component group1is rotatable about an axis A relative to second component group2, component groups1,2being disposed so as to be axially and radially free from play with respect to each other due to the axial and radial prestress.

Because printed circuit board2.3having electronic circuit2.31in first recess2.11is surrounded by solid outer ring2.1, optimal protection is provided against electromagnetic disturbances. The same holds true for electrical conductor2.4in second recess2.12and for sensor2.2in third recess2.13, as well. In this connection, it should be noted that due to the precise fabrication of outer ring2.1, of rolling elements3and of inner ring1.1, a minimal gap is achieved between outer ring2.1and inner ring1.1, which takes effect positively in terms of immunity to electromagnetic disturbances. To further increase the immunity to electromagnetic disturbances, first recess2.11may be closed on the outside by a cover, especially by a metal cover. Furthermore, first recess2.11, and possibly also second and third recesses2.12,2.13, may be filled with a suitable potting material. For example, a cable outlet may be realized through a bore hole in the cover for the electrical connection between the angle measuring system and sequential electronics.

The unit assembled to this point is secured to a scaling machine. The scaling machine is used to apply an angle scaling1.21(FIG. 2) to graduation ring1.2. The scaling machine includes a shaft and a stator block, to which a magnetic writing head is attached. The stator block and the shaft are rotatable relative to each other using an air bearing. The scaling machine also includes an extremely exact angular-position measuring device, which is used to precisely determine the angular position of the shaft relative to the stator block.

Prior to applying angle scaling1.21, inner ring1.1is first secured in rotatably fixed manner to the shaft of the scaling machine. In the same manner, outer ring2.1is also affixed to the stator block. In this mounting state, a rotation of the shaft consequently brings about a rotation of inner ring1.1, and therefore of graduation ring1.2, as well.

After that, the magnetic writing head is inserted into opening2.15. Angle scaling1.21, made up of a plurality of magnetic (not visible) graduation marks, is thereupon applied directly onto the lateral side of graduation ring1.2. In so doing, graduation marks substantially parallel with respect to axis A are produced step-by-step as angle scaling1.21on the mantle side by suitable energizing of the writing head, north and south poles alternating with each other along the periphery. Each graduation mark is radially polarized. In the exemplary embodiment presented, the distance between the centers of the graduation marks in the circumferential direction is 200 μm. After each graduation mark is produced on the lateral side of graduation ring1.2, the shaft is further turned by a minimal amount, thereby permitting the next graduation mark to be applied. Thus, between the respective magnetizing steps, graduation ring1.2is further swiveled about axis A, controlled by the angular-position measuring device of the scaling machine. Despite the exceedingly precise production of inner ring1.1, outer ring2.1and rolling elements3, the system may still exhibit deviations from its ideal geometry.

Accordingly, radial runouts lead to different geometric patterns of angle scaling1.21in the circumferential direction, because angle scaling1.21is applied on graduation ring1.2in an add-on situation which corresponds to the final mounting, and in addition, the system is radially and axially prestressed. Thus, due to the indicated radial runouts, e.g., an eccentricity or a wobble error, the geometric pattern of angle scaling1.21in region U1may differ from the pattern in region U2, and specifically, as a function of the radial runout existing locally at the respective circumferential points. As a result, different patterns may be characterized by different spacings of the graduation marks or by different inclinations of the graduation marks relative to axis A. Because of the high degree of precision, these differences in the patterns of individual regions are comparatively small. Nevertheless, they contribute to the increase in the measuring accuracy of the angle measuring system.

After angle scaling1.21is applied, the unit preassembled to this point, made up of first and second component groups1,2, may be detached from the scaling machine.

Due to the exceedingly high mechanical stiffness of the angle measuring system, the measuring result is improved on one hand because of the minimal gap between outer ring2.1and inner ring1.1; on the other hand, a small and always constant scanning distance between sensor2.2and graduation ring1.2may be realized in this manner, as well, thereby making it possible to achieve an increased signal quality. Only by these measures is it possible to read magnetic angle scalings1.21, which have distances between the centers of the graduation marks in the circumferential direction of less than 300 μm, e.g., less than 250 μm or less than 200 μm, with high resolution.

The special form of recesses2.11,2.12,2.13and of opening2.15, as shown inFIGS. 4aand4b, contributes substantially to the achievement of the high mechanical stiffness of the angle measuring system. First of all, opening2.15is dimensioned such that its extension z is comparatively small relative to axial extension Z of outer ring2.1. In addition, first and second recesses2.11,2.12are formed so that their respective extensions in the circumferential direction U, u are smaller than their axial extensions H, h, thus U<H, u<h. In particular, first recess2.11of the outer ring has its greatest extension H in a direction parallel to axis A. Moreover, outer ring2.1is dimensioned such that extension H of first recess2.11is greater than extension h of second recess2.12(H>h), in each instance, specific to a direction parallel to axis A. In addition, extension U of first recess2.11is greater than extension u of second recess2.12(U>u), in each case specific to the circumferential direction.

The angle measuring system represents an autonomous unit which a user is able to mount easily on a shaft to be measured, but which supplies exceedingly exact angular positions. Because of the extremely precise arrangement of the angle measuring system, it is possible to dispense with an alignment coupling.

During operation of the angle measuring system, sensor2.2supplies position-dependent currents or voltages, corresponding to the poles of angle scaling1.21facing opposite sensor2.2. These currents or voltages are processed in electronic circuit2.31and ultimately digitized. The digital signals may then be passed on by the angle measuring system to sequential electronics, the digitizing permitting a data transmission largely immune to disturbances.

Moreover, due to the integrated type of construction, the angle measuring system is very compact in its outside dimensions, and in particular, has an extremely small maximum axial extension Z. In the exemplary embodiment shown, axial extension Z amounts to only approximately 25% of the maximum outside radius. In addition, due to the type of construction described, a high-quality angle measuring system is provided which is suitable for large diameters of shafts to be measured. Thus, the angle measuring system has an opening to this effect, whose inside radius comes to approximately 66% of the maximum outside radius.