EP1360468A1

EP1360468A1 - Portable magnetic transducer

Info

Publication number: EP1360468A1
Application number: EP02718048A
Authority: EP
Inventors: Lutz Axel May
Original assignee: Fast Technology AG
Current assignee: Abas Inc
Priority date: 2001-01-25
Filing date: 2002-01-24
Publication date: 2003-11-12
Also published as: WO2002059555A1; GB0101981D0

Abstract

A hand-held unit for measuring torque has a magnetic structure (40) with two-spaced pole ends (44a:44b) of opposite polarity applicable at or adjacent to the surface of a portion (32) of a rotating shaft (30) of ferromagnetic material, the poles (44a:44b) being spaced in the direction of the shaft axis. An axially-directed, surface-adjacent magnetic flux (52) is induced in the local portion of the shaft (30) between the poles. A magnetic sensor device (60) intermediate the poles (44a:44b) is oriented to detect a torque-dependent component of the induced magnetic field external to the shaft surface. The magnetic structure incorporates a magnetic source (16) provided by a permanent magnet (46') or a D.C. or A.C. energised coil (50).

Description

Title: Portable Magnetic Transducer FIELD OF THE INVENTION

This invention relates to apparatus and method for sensing torque or force applied to a part. The invention has particular, though not exclusive, application to measuring torque applied about the longitudinal axis of a shaft. BACKGROUND TO THE INVENTION

It has been proposed to measure torque in a shaft by means of a magnetic transducer element formed integrally in a portion of the shaft. The transducer

portion is itself of a ferromagnetic material. One form of magnetisation proposed for a transducer element integral with a shaft is that known as circumferential magnetisation. The magnetisation in this case is generated in a closed circumferentially extending loop about the shaft axis, the material in which the circumferential magnetisation is induced being one exhibiting magnetoelasticity. The magnetised region generates axially-spaced North and South poles with the emanation of a torque-dependent field. Further discussion of circumferential magnetisation is disclosed, for example, in U.S. patents 5,351,555 and 5,520,059 (Garshelis) and the implementation of the integral transducer is more particularly addressed in published International patent applications WO99/21150, W099/21151 and WO99/56099. Another proposal for an integral transducer element is to induce an annulus of magnetisation about the axis of the shaft, the magnetisation being in the axial direction. Such a field emanates a torque-dependent component which can be sensed by a non-contacting sensor. This axially-directed magnetisation is referred to as longitudinal magnetisation. It has been more recently developed by FAST Technology AG. One form of longitudinal magnetisation is disclosed in published International Patent Application WO01/13081. Longitudinal magnetisation involves creating an annulus of magnetisation in a ferromagnetic transducer region. The magnetisation is axially-directed and establishes a toroid of magnetic flux extending about the axis of the shaft. The annular zone of longitudinal magnetisation referred to in the above-mentioned application is created by rotating a shaft relative to a magnet structure whose poles are axially separated as described with reference to Fig. 6 of WO01/13081. The annular zone of stored or remanent magnetisation is surface adjacent and a closed loop of flux is completed within the ferromagentic material interiorly of the annular zone. In addition a lesser flux path also exists exteriorly of the annular zone as shown, inter alia, in Figs. 7a and 7b of WO01/13081.

The region of the shaft in which the stored magnetisation is created thus provides a transducer element. The ferromagnetic material in which the stored magnetisation is created may or may not exhibit significant magnetoelasticity. The field detectable externally of the shaft is torque-dependent. The nature of the torque-dependent response has been found to depend on the width w (in the axial

direction) of the poles and the gap g between them. Further discussion of this is to be found in WO01/13081 above-mentioned which describes a form of longitudinal magnetisation whose torque-dependent response may be referred to as "circumferential sensing". Another form of annular longitudinal magnetisation known as "profile shift" is described in WO01/79801.

To detect the torque-dependent magnetic field component and provide a torque-representing signal, a non-contacting sensor arrangement of one or more sensor devices is associated with the transducer element. Such arrangements are disclosed and discussed in WO01/13081 and WO01/79801 previously mentioned.

Suitable sensor devices include saturating core, Hall effect and magnetoresistive types. A preferred sensor circuit incorporating one or more saturating core type devices is disclosed in WO98/52063.

It is to be noted that although the shaft whose magnetisation is discussed above is of solid cross-section, the shaft may be hollow provided the wall thickness is sufficient to sustain the described toroidal flux distribution.

In the various proposals mentioned above, the transducer element is a distinct item carried by or integral with the shaft. Consequently a pre-conceived process has to be performed to provide the transducer element together with the sensor arrangement cooperating with it to create the complete transducer assembly.

There are some circumstances in which it is highly desirable to make a measure of torque or other stress on a part which has not been subjected to a pre-conceived preparation for measurement. SUMMARY OF THE INVENTION

There will be described a portable, and preferably hand-held, unit capable of making measurements in the above desired manner. The present invention enables such a unit to be realised.

The invention is founded on the concept of applying a magnetic structure having a pair of spaced pole ends at a position in which the pole ends are on or adjacent a part which is of ferromagnetic material and torque in which is to be measured. The magnetic structure includes a magnetic source for magnetising the pole ends with opposite polarity to induce a magnetic flux in the portion of the part between the pole ends. A magnetic sensor device is located intermediate the pole ends to respond to a torque-dependent component of magnetic field emanated from the surface of the part. This concept may be extended to more generally measuring force in a part.

Aspects and features of the present invention for which protection is sought are set forth in the claims following this description.

The invention and its practice will be further described with reference to the

accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows one embodiment, of the invention in a hand-held sensor unit for measuring torque in a rotating shaft;

Fig. 2 illustrates the magnetic field induced in the shaft by the unit of Fig. 1 ;

Fig. 3 illustrates a potential problem with the unit of Fig. 1;

Fig. 4 shows the provision of magnetic shielding to at least mitigate the problem illustrated in Fig. 3; Fig. 5 shows another embodiment of Fig. 1 employing a permanent magnet source; and

Fig. 6 shows yet another embodiment of Fig. 1 utilizing two transducer regions.

Fig. 1 shows a unit embodying the invention applied to measuring torque in a shaft 30 rotating about an axis A-A. The shaft is of circular cross-section. The unit 40 comprises a magnetic structure 42 of ferromagnetic material. It has a pair of pole ends 44a and 44b between which a magnetic source 46 is provided. To this end the magnetic structure may be of U- or horseshoe shape the source being provided in the base 48 of the U-shape. In Fig. 1 the source is an electromagnet comprising a coil 50 wound about a core portion of base 48. Upon energising the coil with direct current I, one pole, 44a say, is made North the other 44b South, and the adjacent surface portion 32 of the shaft closes an axially-directed flux path 52 between the poles as is better seen in Fig. 2. The magnetic field induced in the shaft is longitudinal, that is extending in an axial direction. In contrast to the longitudinal magnetisations discussed above, it is, however, a localized magnetisation in the vicinity of the region between the poles. It is not intended to induce a remanent (permanent) magnetisation into the shaft. To this end it is presently considered that the fields used should not exceed about 30 Gauss. In order to magnetically engage the shaft the pole ends are co-planar in the embodiment shown, lying in a common plane tangential to the surface of the shaft 30 at portion 32. The pole end surfaces may be made concave to better engage the shaft surface and may be given a thin coating of a material having good tribological properties. The pole ends could be provided with means such as rollers in a low reluctance path to engage the shaft surface. It may also be desirable in some cases to de-gauss the region of the shaft in which the flux-path 52 is to be established.

Fig. 2 illustrates that associated with the internal, surface-adjacent, longitudinal flux induced in the shaft 30 is a component 58 external to the shaft adjacent the surface and capable of being sensed by a magnetic sensor device 60 comprising one or more sensors. Device 60 is adjacent to but not contacting the surface of shaft 30. The sensor device is located intermediate pole ends 44a and 44b and lies in or adjacent the common plane shared by the ends. Thus in a unit in which all the parts are mounted as described, the unit will provide magnetic access of the pole ends and the magnetic sensor(s) to the surface to which the unit is to be

applied for measurement.

The sensor device 60 is oriented to respond to the torque-dependent tangential or circumferential component of field. This arises by considering that when the shaft is under torque the longitudinal field direction is skewed from alignment with the axial direction in a direction and to an extent dependent on the direction and magnitude of the torque. The sensor device 60 may also comprise one or more sensors for detecting the axially-directed component of field. This component may be used as a reference against which the torque-dependent component is measured. It will be understood that because real magnetic flux lines extend in curved paths, other sensor orientations may be possible to sense any direction of flux, where the flux is torque-dependent.

One potential problem with the unit of Fig. 1 is shown in Fig. 3 which illustrates the possibility of stray fields 66 from the coil 50 affecting the magnetic sensor(s) such as 60. This problem can be obviated as illustrated in Fig. 4 by using a magnetic screen 70 which can be realised in the form of an enclosure for the coil and the core portion of the base 48 surrounded by it. For D.C. energisation mu- metal may be appropriate for the screening material. For A.C. energisation good electrically conductive materials generally are usable such as aluminium. The magnetisation source so far discussed uses a D.C. energised coil. The coil could be A.C. energised. The resultant alternating polarity flux in path 52 would be reflected in an A.C. output from the magnetic sensor(s). This can be employed to advantage by choosing the frequency of energisation and using a frequency- selective technique for detection. These measures can allow a better signal-to- noise ratio to be achieved than would otherwise be possible by discriminating from any local D.C. magnetic fields that may be present and local A.C. magnetic fields, e.g. at the mains (powerline) frequency.

Another form of magnetisation source is illustrated in Fig. 5. The unit of Fig. 5 is equivalent to a D.C. energised unit of Fig. 1 but a source in the form of permanent magnet 46' is provided between the pole ends in the U-shaped magnetic structure, the legs of the U-shape serving to guide the magnetic flux to the poles 44a, 44b.

Fig. 6 shows the provision of a unit in which two axially spaced transducer regions 32a, 32b are employed. Separate magnetic structures could be employed for inducing flux in each region but conveniently the regions are activated with opposite polarity using a double-U structure having a common pole 44'a and respective opposite poles 44'b and 44"b. To this end the coils must be energised appropriately and, for example, can be series connected with appropriate polarity as indicated in Fig. 5. The energisation can be D.C. or A.C. as already described.

The permanent magnet alternative of Fig. 5 may also be employed with a respective permanent magnet between poles 44'b and 44'a and between poles 44'a and 44"b with like poles directed toward common pole 44'a.

A respective sensor device 60' and 60" is provided intermediate pole ends 44'b and 44'a and pole ends 44'a and 44"b. In the embodiment shown all three pole ends are coplanar and colinear and the sensor devices lie in or adjacent the common plane. The sensor devices 60' and 60" are oriented for detecting the torque-dependent components of regions 32a, 32b. The sensor devices 60' and 60" can each comprise more than one sensor device, such as sensors 60a and 60b in Fig. 2a. The sensor devices 60' and 60" are connected in an additive manner as regards the wanted magnetic field components to be detected. This takes into account the opposite polarity of field induced in regions 32a and 32b by the connection of L1 and L2 as shown in Fig. 8. However, the sensor devices will be connected to cancel or nullify a common imposed extraneous field having the same polarity in regions 32a and 32b.

The magnetic sensor device(s) may be of the saturating core type connected in a sensor circuit as disclosed in WO98/52063.

The complete hand-held unit comprising the magnetic structure and sensor device can be realised as a unitary structure for example by potting or embedding the components in the operative working positions.

Claims

1. Apparatus for use in measuring torque or force in a part which is of a ferromagnetic material, comprising: a magnetic structure having a pair of spaced pole ends, said pole ends being configured for placement on or adjacent a surface portion of said part, said magnetic structure including a magnetic source for magnetising said pole ends with opposite polarity to induce a magnetic flux therebetween in a portion of a part adjacent a surface of the part on or adjacent which said pair of pole ends is placed, a magnetic sensor device located intermediate said pole ends in a predetermined position with respect thereto so as to be responsive to a torque- or force-dependent component of magnetic field emanated from a surface of a part on or adjacent which said pole ends are placed.

2. Apparatus for use in measuring torque or force in a part which is of ferromagnetic material, comprising: a magnetic structure having a pair of spaced pole ends magnetically engageable with a surface portion of a part, said magnetic structure including a magnetic source for magnetising said pole ends with opposite polarity; and a magnetic sensor device located intermediate said pole ends to provide a signal dependent on a torque- or force-dependent magnetic field component sensed by the sensor device.

3. Apparatus as claimed in Claim 1 or 2 in which said pole ends lie in a common plane and said magnetic sensor device lies on or adjacent said plane.

4. Apparatus as claimed in Claim 1 or 2 or 3 in which said magnetic source comprises a current energisable coil wound about a core magnetically connected to said pole ends.

5. Apparatus as claimed in Claim 4 in which said magnetic source further 5 includes means for supplying direct current or means for supplying alternating current to said coil.

6. Apparatus as claimed in Claim 1 , 2 or 3 in which said magnetic source comprises a permanent magnet.

7. Apparatus as claimed in Claim 4 or 5 comprising means for magnetically 0 screening said magnetic sensor device from the coil.

8. Apparatus for use in measuring torque or force in a part which is of ferromagnetic material, comprising a magnetic structure having first, second and third pole ends magnetically engageable with a surface portion of a part, 5 said magnetic structure including a first magnetic source acting between said first and second pole ends and a second magnetic source acting between said second and third pole ends for magnetising said second pole end with one polarity and said first and third pole ends with the opposite polarity, and a first magnetic sensor device located intermediate said first and second pole o ends to provide a first signal dependent on a magnetic field component sensed by the first sensor device, and a second magnetic sensor device located intermediate said second and third pole ends to provide a second signal dependent on a magnetic field component sensed by the second sensor device.

9. Apparatus as claimed in Claim 8 in which said first, second and third pole ends lie in a common plane and said first and second magnetic sensor devices are on or adjacent said common plane.

10. Apparatus as claimed in Claim 8 or 9 in which said first, second and third 5 pole ends are colinear.

11. Apparatus as claimed in Claim 8, 9 or 10 in which said first and second magnetic sources each comprises a respective current-energisable coil wound about a respective core portion.

12. Apparatus as claimed in Claim 11 in which the coils are connected together 0 for energisation to magnetise the second pole end with opposite polarity to the first and third pole ends.

13. Apparatus as claimed in Claim 12 further comprising means for supplying direct current or means for supplying alternating current to the coils.

14. Apparatus as claimed in Claim 8, 9 or 10 in which said first and second 5 magnetic sources each comprise a respective permanent magnet, the respective permanent magnets having poles of like polarity magnetically connected to said second pole end.

15. A method of measuring torque in a rotating part of ferromagnetic material, comprising: o applying a magnetic structure having a pair of spaced poles of opposite polarity on or adjacent a portion of the surface of said part with the poles spaced in the direction of the axis of rotation; inducing a magnetic flux in the surface portion between said poles; and locating a magnetic sensor device at or adjacent the surface portion intermediate said poles to detect a torque-dependent component of magnetic flux.