WO2008138662A2

WO2008138662A2 - Two axes absolute linear positioning system

Info

Publication number: WO2008138662A2
Application number: PCT/EP2008/053153
Authority: WO
Inventors: Lutz May
Original assignee: Nctengineering Gmbh
Priority date: 2007-05-11
Filing date: 2008-03-17
Publication date: 2008-11-20
Also published as: WO2008138662A3

Abstract

The present invention discloses a two axes absolute linear positioning system (6), comprising a carrier (5), a first position sensor arrangement (1), a second position sensor arrangement (1), the first position sensor arrangement (1) and the second position sensor arrangement (1) each comprising a magnetic region (2) having a south pole and a north pole, and a magnetic field detector (3), wherein the first and the second magnetic regions (2) are arranged in a defined position with respect to the carrier (5), and wherein the orientation of the south pole and the north pole of the first magnetic region (2) is inclined to the orientation of the south pole and the north pole of the second magnetic region (2).

Description

Two axes absolute linear positioning system

The present invention relates to sensors in general. More particularly, it relates to a two axes absolute linear positioning system and to a bearing comprising a two axes absolute linear positioning system.

For many applications it is desirable to measure temporal and permanent loads with high precision and minimization of required measurement space. For example, it is advantageous to measure an occurring load on a bearing with a relatively compact sensor arrangement.

To measure loads acting on for example a bearing, it is known to measure a displacement, i.e. a change in distance, at two different points, each point located at one side of the bearing. Thus, with two according measurement results and taking into account the mechanical proportions of the bearing, one can determine loads acting on the bearing via the axes or the casing. However, this measurement requires two sensor arrangements placed at different positions on the bearing. Thus, individual space for each sensor arrangement is required at each side of the bearing.

It is an objective of the present invention to provide a two axes absolute linear positioning system and a bearing comprising a two axes absolute linear positioning system with reduced footprint to easily determine current loads acting on, for example, a bearing.

This object is achieved by providing provide a two axes absolute linear positioning system and a bearing comprising a two axes absolute linear positioning system according to the independent claims.

According to an exemplary embodiment of the present invention a two axes absolute linear positioning system is provided, comprising a carrier, a first position sensor arrangement and a second position sensor arrangement, the first position sensor arrangement and the second position sensor arrangement each comprising a magnetic region having a south pole and a north pole and a magnetic field detector, wherein the first and the second magnetic regions are arranged in a defined position with respect to the carrier and wherein the orientation of the south pole and the north pole of the first magnetic region is inclined to the orientation of the south pole and the north pole of the second magnetic region.

According to another exemplary embodiment of the present invention a bearing comprising a two axes absolute linear positioning system is provided,

In the context of the present invention, the following definitions are used:

Magnetic region: A magnetic region is any magnetic active region, which is changing/altering/influencing a least one magnetic (field) parameter in its vicinity. The magnetic region must not necessarily actively influence the magnetic field parameters, but can alter those parameters simply by its presence or simply withdraw energy from the field. The magnetic region may be something as simple as a permanent magnet or an actively magnetic encoded region. Alternatively, it may also be an active element, being powered by an energy source, subsequently influencing the magnetic field parameters. The influence may be predetermined, i.e. a calculated alteration, or may also be an undetermined, random, arbitrary alteration.

Magnetic field detector: A magnetic field detector is any device that is capable of detecting or perceiving an alteration, a change or another arbitrary influence on a magnetic field. The alteration may be either determined quantitatively or just qualitatively. The orientation of a magnetic field and a change thereof may also be detected.

With a two axes linear positioning system according to the present invention a simple and effective measurement of loads acting on a bearing may be possible. By combining two normally independent sensor arrangements within one single area the required space is significantly reduced. A two axis absolute linear positioning system according to the present invention may measure loads, like forces, acting for example parallel to the rotational axis of a bearing as well as perpendicular thereto, like gravitational forces. Such forces may be considered to act substantially independent from each other solely on the respective position sensor arrangement. However, that might only be the case if the orientation of the respective force is parallel to the main measurement orientation of the respective position sensor arrangement.

However, due to the inter-alignment of the two, electronically independent, position sensors arrangements, which constitute the two axis absolute linear positioning system, torque acting on a bearing may be measured as well. In this case, a torque may be determined due to a simultaneous change in position of both position sensor arrangements, thus generating a measurement signal in both position sensor arrangements.

In case of a linear force, as described above, two axis absolute linear positioning system, does not act parallel to a main measurement orientation of a position sensor arrangement, on in case the inclination between the main measurement orientations of the two position sensor arrangements in not substantially 90°, both position sensor arrangements may generate a measurement signal, even in case no torque is acting on the bearing. Furlher exemplary embodiments can be derived from the dependent claims.

Below, further embodiments of the two axes absolute linear positioning system according to the present invention will be described. However, it is denoted, that these preferred embodiments a!so apply to the bearing comprising a two axes absolute linear positioning system.

According Io a preferred embodiment, the at least one magnetic region may form part of the carrier. The magnetic region may be a substantially integral part of the carrier, which carrier was treated to obtain magnetic properties, for example a magnetized region of a magnetizeable carrier, i.e. a carrier, which carrier is made of a material, which material exhibits magnetically hard properties. With an according embodiment, the required installation space within a confined area may be minimized, thus resulting in a more compact design layout.

According to another preferred embodiment, the least one magnetic region, may be attached to the carrier. Thus, the magnetic region may be elevated when compared to the carrier. The magnetic region may be attached directly to the carrier by gluing, bonding, soldering or the like. The magnetic region may also be attached to another holding structure, like for example rubber, foam, metal etc., which in turn is attached to the carrier as described before. By this, is may be possible to significantly facilitate the installation of a position sensor arrangement or even the two axes linear positioning system as a whole. In an embodiment where magnetic treatment of the carrier itself is not possible, e.g. due to space or material constraints, the earlier or alternatively later attachment of the magnetic region may prove advantageous. By using, e.g. magnetic rubber, which may be in one case interpreted as rubber with any magnetic material insert (like magnetic particles), due to its plasticity, installation is significantly eased.

According to another preferred embodiment, the at least one position sensor arrangement may have a main measurement orientation, which main measurement orientation may be arranged substantially parallel to the orientation of the south pole and the north pole of the corresponding magnetic region. The orientation of the south pole and the north pole of the corresponding magnetic region may be derived as being a virtual straight connection between the respective south pole and north pole. The magnetic region may further be formed as a bar magnet or in other embodiments as a U-shaped magnet or yoke, while the main orientation may still be the straight line as described before. With an according parallel orientation, the maximum signal amplitude may be measured. Consequently, sensitivity is improved and it may even be possible to reduce the required magnetic fields thus resulting in a more compact embodiment.

According to another preferred embodiment, the at least one magnetic field detector may be adapted to measure a displacement of the corresponding magnetic region in a direction of the orientation of the south pole and the north pole of the corresponding magnetic region. That is, the at least one magnetic field detector may essentially be moved along the main measurement orientation, and thus may measure a offset displacement from the center of the magnetic region, i.e. the central point between the south pole and the north pole of the magnetic region. By an according measurement it may significantly case the required calculations to determine the exact movement of the magnetic regions vs. the respective magnetic field detectors, and thus the movement of the two axes absolute linear positioning system altogether.

According to another preferred embodiment, the at least one magnetic region may be one out of the group consisting of permanent magnet, magnetized region, magnetizable rubber, at least one coil, active element, passive element, RFID tag, LC oscillating circuit and LRC oscillating circuit.

According to another preferred embodiment, the at least one magnetic field detector may be one out of the group consisting of at least one coil, hall sensor, magneto resistance detector, giant magneto resistance detector and weak magnetic field detector.

According to another preferred embodiment, the at least one magnetic field detector may comprise at least two sub-sensors to form an automatic gain compensation type. For example, the magnetic field detector may comprise two independent coils each constituting a sub-sensor. Thus, for example, with one of the sub-sensors or coils being reversed, the magnetic field detector may only measure a difference in the magnetic field in an offset position regarding the central point of the magnetic region. Also, the signals of the two sub-sensors, e.g. independent coils, may be processed independently by, for example, one electronic circuits or also individual electronic circuits. Consequently, no signal may be measured by the magnetic field detector in the central or neutral position, which allows for automatic gain compensation. With an according symmetrical embodiment, output signals may only occur with the magnetic region is moved from the central position of the respective magnetic clement, that is only a difference or delta is measured. Thus, with no active output signal being generated in the central position, calibration of a zero point and thus taking into account the gain of the downstream signal processing circuitry may not be necessary at all. A sub-sensor may be any of the above-mentioned types of magnetic regions or a combination thereof.

According to another preferred embodiment, the system may further comprise electronic signal processing circuitry, wherein the electronic signal processing circuitry is adapted to compensate influences of the first sensor arrangement and the second sensor arrangement to each other to acquire true signals. Due to, for example, the close proximity of the two independent sensor arrangements, each magnetic region may also influence the magnetic field detector corresponding to the other magnetic region and thus the measured signal. To eliminate the mutual influences, an electronic signal processing circuitry may be employed. Thus, the system may measure true signals, i.e. signals that are compensated for the influence of the magnet region not relating to the respective magnetic field detector and thus sensor arrangement. Also, by using a electronic signal processing circuitry it may even be possible to reduce the required at least 4 sub-sensors of the at least two position sensor arrangements by combining the two inner sub-senors. According to another preferred embodiment, the bearing is a ball bearing or a roller bearing.

The above mentioned and further aspects, objects, objectives and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying figures. Identical or similar parts or elements are referred to with identical reference numbers.

The accompanying figures, which are included to provide a further understanding of the invention and constitute a part of the specifications, illustrate exemplary embodiments of the invention. These exemplary embodiments are not to be taken limiting the scope of the invention. The figures are not drawn to scale, however may depict qualitative dimensions.

It shows as follows:

Fig. I a and b show the functional principle of the sensor arrangement of the present invention. Fig. 2a to 2e show a two-dimensional sectional views of exemplary embodiments of the sensor arrangement of the present invention. Fig. 3 shows a two-dimensional sectional view of an exemplary embodiment of a bearing with a two axes absolute linear positioning system according to the present invention. Fig. 4a and b show exemplary electronic signal processing circuitry according to the present invention for acquiring true signals. Fig. 5 shows a two-dimensional sectional view of a second exemplary embodiment for a bearing Fig. 6 shows a two-dimensional sectional view of a third exemplary embodiment for a bearing

Below, exemplary embodiments of the two axes absolute linear positioning system according to the present invention will be described. However, it is denoted, that these preferred embodiments also apply to the bearing comprising a two axes absolute linear positioning system,

Fig. I a is used to explain the functional principle using an exemplary embodiment of a position sensor arrangement 1 , The magnetic region 2, here a permanent magnet, may influence a magnetic field detector 3, which may comprise two coils L 1,2. The magnetic field 4 may penetrate the two coils Ll, L2, which may be identical. L2 may be reveised in relation to Ll . The central point between the coils Ll ,L2 may also be the central point of the magnetic iegion 2, as illustrated by the dashed line. Due to the reversing of one coil with respect to the other coil, the magnetic field detector 3 may be in its neutral position when aligned with the central point, thus not producing any signal, as the magnetic field 4 may be acting eqυivalently on both coils.

Now referring to Fig. Ib, when the magnetic field detector 3 or equivalenlly the magnetic region 2 is moved from the central position, as indicated by the arrow, the respective effective part of the magnetic field 4 acting on Ll, L2 may not be equivalent any more, thus resulting in a signal that may be measured.

In Fig. 2a to 2e, different exemplary embodiments of the two axes linear position determining system 6 according to the present invention are shown. Two position sensor arrangements 1, each compiising a magnetic region 2 and a magnetic field detectoi 3, may be arranged on the carrier 5. In Fig. 2a, 2b and 2e, the magnetic region 2 may form part of the carrier 5, in Fig. 2c and 2d the magnetic region 2 may be attached to the surface of the carrier 5. The magnetic regions 2 may be positioned circumferentially on the circular carrier 5, thus allowing for rotation-independent measurements. The angle between the two position sensor arrangements 6 may be substantially 90°, however other angles may be realized as well, like 30°, 45° or 60° or any other arbitrary reasonable angle. In Fig. 2d, the displacement of the magnetic region 2 relative Io the respective magnetic field detector 3 along the main measurement orientation is indicated by the respective arrows. The position sensor arrangements 1 may be realized on either side of the carrier 5 or even on different sides. In Fig. 2d and 2e, the magnetic field detectors 3 are depicted on a printed circuit board (PCB). The orientation of the south pole and the north pole of a magnetic region with respect to the other magnetic region may be chosen arbitrarily or according to a special application or requirement.

In Fig. 3, a sectional view of a ball bearing 7 according to an exemplary embodiment of the present invention is shown. The ball bearing 7 may comprise an inner part 1 1 (with two halves 1 la,b) and an outer part 12 with two rows of balls 13 in between. The inner part 1 1 may be attached to a mounting portion 9. The two axes absolute linear positioning system 6 may be attached via a magnetic shielding 8 to the mounting portion 9. The magnetic shielding 8 may be necessary due to arbitrary objects with magnetic characteristics such as for example screw 10 within the vicinity of the rotational path of the two axes absolute linear positioning system 6. The dimensions of the two axes absolute linear positioning system 6 in relation to the ball bearing 7 may be exaggerated. With a load acting on the bearing 7, for example, via the mounting portion 9, the position sensor arrangements 1 may deliver a signal due to the displacement of the magnetic region 2 vs. the respective magnetic field detector 3. Again, the magnetic regions 2 may be positioned circumferentially on the circular carrier 5, thus allowing for rotation-independent measurements. In Fig. 4a and 4b, two exemplary embodiments of an electronic signal processing circuitry for acquiring true signals are shown. The respective signals from each of the two channels A and B may be processed subsequently and thus the influence of one magnetic region on the magnetic field detector of the other magnetic region may be removed or at least significantly reduced. By using an implementation with operational amplifiers as indicated in Fig. 4a and 4b feedback and thus oscillating behavior of the circuitry may be effectively prevented. Inverters may have to be implemented, here only indicated in Fig. 4a, depending on the actual implementation of the respective position sensor arrangement 1.

In Fig. 5 a two-dimensional cross section illustration of an exemplary embodiment of a second application is shown. Here, the application may be measuring the position of an outer part 12 vs. an inner part 1 1 (which may be assembled by two parts 1 Ia, 1 Ib) of a ball bearing 7. In a preferred embodiment, the outer part 12 may be static, the inner part 1 1 may be rotating. However, in different applications this may be reversed. In Fig. 5, the ball bearing 7 is shown in part (upper part of ball bearing 7) in a cross sectional view. Every component of the displayed ball bearing 7 may have magnetic properties, that is, a magnet may be attracted by each of the components. In this exemplary embodiment, the outer part 12 may remain static. As a consequence, all required sensor devices might have to be mounted or fixed to this part. The inner part 11 and the main shaft may be rotating. In this application, two linear position determining systems 14, i.e. a system comprising a magnetic region 2 and a TR-Pad 15 (transmitter-receiver pad), may be used. Each of the linear position determining systems 14 may be mounted at a side of the outer part 12. The application may be interpreted as a three-dimensional position determining system 14, however in this exemplary embodiment, the used coordinate system may be a rotational coordinate system or cylindrical coordinate system with the rotational axes or rotation angle being the one, main, referred axes or measured component. The left linear position determining system 14 may be measuring "upwards", which is why a physicai change in the targeted device, mainly the respective magnetic region 2, may be necessary. The measurement areas may be identical, however they may be different as well.

The angle sensor 16 according to this exemplary embodiment may require that one section of the left inner part 11 features a magnetic region 2. This may only be possible if the left inner part 1 1 is tooled from ferromagnetic material. Best angle sensor 16 results may be achieved when at least the left inner part 11 has been hardened by well-known measures. The sensor quality may thus improve by a factor up to ten. To prevent that the signal emanated by the magnetic region 2 will dissipate towards the left metallic body, i.e. the shaft carried by the bearing system, an air gap or stainless steel (non magnetic material) may be placed between the outer left wall of the left, inner part 1 1 and the adjacent shaft. For optimal effectiveness, the gap or non-magnetic material may be at least lmm in thickness. In another, even more preferred embodiment, it may be at least 1 ,5mm in thickness. If Mu-Metal is used the thickness may be reduced significantly. To prevent that the magnetic field detector 3 of the angle sensor will be distracted or confused by the movements of the adjacent bearing balls 13, the magnetic shielding may be placed between the magnetic field detector 3 and the bearing balls 13. In another preferred embodiment, only one magnetic region 2 in combination with a TR-Pad 15 may be implemented.

In Fig. 6 a two-dimensional illustration of a third exemplary embodiment is shown. Here, an alternative linear/angle position sensor 16 is shown. An arrangement of at least one magnetic field detector 3 in combination with a magnetic region 2 is displayed. This exemplary embodiment has been proven to be highly accurate and reliable. The present invention is not limited to the exemplary embodiments as shown in the accompanying figures. Rather, a plurality of embodiments are conceivable, which use the quintessence of the present invention even with deviant embodiments.

It should be noted, that the term "comprising" does not exclude other elements or steps and that "a" or "an" does not exclude a plurality. Also, elements described in association with different embodiments may be combined.

List of Reference Numbers

la,b Position sensor arrangement

2 Magnetic region

3 Magnetic field detector

4 Magnetic field

5 Carrier

6 Two axes absolute linear positioning system

7 Ball Bearing

8 Magnetic shielding

9 Mounting portion

10 Screw

I la,b Inner part

12 outer part

13 Bearing balls

14 Position determining system

15 TR-Pad

16 Angle sensor

Ll , 2 Coils

Claims

1. Two axes absolute linear positioning system (6), comprising: a carrier (5); a first position sensor arrangement ( 1 a); a second position sensor arrangement (Ib); the first position sensor arrangement (I a) and the second position sensor arrangement (Ib) each comprising: a magnetic region (2) having a south pole and a north pole, and a magnetic field detector (3); wherein the first magnetic region (2) and the second magnetic region (2) are arranged in a defined position with respect to the carrier (5), and wherein the orientation of the south pole and the north pole of the first magnetic region (2) is inclined to the orientation of the south pole and the north pole of the second magnetic region (2).

2. The system according to claim I₅ wherein at least one magnetic region (2) forms an integral part of the carrier (5).

3. The system according to one of the claims 1 and 2, wherein at least one magnetic region (2) is attached to the carrier (5).

4. The system according to one of the claims 1 to 3, wherein at least one position sensor arrangement (l a,b) has a main measurement orientation, which main measurement orientation is arranged substantially parallel to the orientation of the south pole and the north pole of the corresponding magnetic region (2),

5. The system according to one of the claims 1 to 4, wherein at least one magnetic field detector (3) is adapted to measure a displacement of the corresponding magnetic region (2) in a direction of the orientation of the south pole and the north pole of the corresponding magnetic region (2).

6. The system according to one of the claims 1 to 5, wherein at least one magnetic region (2) is one out of the group consisting of permanent magnet, magnetized region, magnetizable rubber, at least one coil, active element, passive element, RI¹ID tag, LC oscillating circuit and LRC oscillating circuit

7. The system according to one of the claims 1 to 6, wherein at least one magnetic field detector (3) is one out of the group consisting of at least one coil, hall sensor, magneto resistance detector, giant magneto resistance detector and weak magnetic field detector.

8. The system according to one of the claims 1 to 7, wherein at least one magnetic field detector (3) comprises at least two sub-sensors to form an automatic gain compensation type.

9. The system according to one of the claims 1 to 8, further comprising electronic signal processing circuitry, wherein the electronic signal processing circuitry is adapted to compensate influences of the first sensor arrangement (Ia) and the second sensor arrangement (Ib) to each other to acquire true signals.

10. A bearing comprising a system according to one of the preceding claims.

11. The bearing of claim 10, wherein the bearing is a bail bearing (7) or a roller bearing.