Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
  • G01L3/02—Rotary-transmission dynamometers
  • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
  • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
  • G01L3/101—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means
  • G01L3/102—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means involving magnetostrictive means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
  • G01L3/02—Rotary-transmission dynamometers
  • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
  • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
  • G01L3/101—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means
  • G01L3/104—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means involving permanent magnets

Definitions

• This invention relates to a transducer element and a transducer assembly. More particularly the invention is concerned with the measurement of torque or force using a magnetic transducer element with a non-contacting sensor arrangement.
• Magnetically-based transducers have come into widespread use.
• One particular application is in non-contacting measurement of torque in a rotatable shaft.
• a magnetised transducer element is carried with the shaft and emanates a torque-dependent magnetic field which is sensed by a sensor assembly not in contact with the shaft.
• One form of magnetisation used is a form of magnetisation known as circumferential magnetisation that extends in a closed loop about the axis of the shaft and is directed normally of the axis, that is in a circumferential direction. Examples of this form of magnetisation are disclosed in U.S. patents 5351555 and 5520059 (Garshelis).
• longitudinal magnetisation Another form of magnetisation more recently developed by the present applicant is one referred to as longitudinal magnetisation.
• 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 longitudinal annular zone of 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 WOO/13081.
• the annular zone of stored or remanent magnetisation is surface adjacent and a closed loop of flux is completed within the ferromagnetic material interiorly of the annular zone.
• a letter flux path also exists exteriorly of the annular zone as shown, inter alia, in Figs. 7a and 7b of Wo01/13081.
• the exterior magnetic field is detectable by an external sensor arrangement and is torque- sensitive.
• 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.
• a second annular zone of axial stored magnetisation is created radially inward of and of opposite polarity to, the surface-adjacent zone so that a toroid of magnetic flux is again established with each magnetised zone closing the flux path for the other zone. This is described with reference to Figs. 8a and 8b of WO01/13081.
• the magnetic 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 above-mentioned WO01/13081 and in published International Patent Application WO01/79801. WO01/13081 describes a form of longitudinal magnetisation whose torque- dependent response may be referred to as "circumferential sensing".
• WO01/79801 describes a form of longitudinal magnetisation whose torque- dependent response may be referred to as "profile shift" where the profile refers to the profile of the external field as plotted as a function of axial position for an axially-directed or a radial component of the external field
• a non-contacting sensor arrangement of one or more sensor devices is associated with the transducer element.
• the placement and orientation of the one or more sensor devices depends on which field component is to be sensed.
• 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.
• 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.
• the transducer element described above is created by subjecting a portion of the shaft to an externally impressed magnetic field (a procedure sometimes referred to as "programming"). Not only is there a magnetisation procedure to be undertaken which may involve non-uniformities as the shaft rotates, but the resultant magnetisation (strength of remanent magnetisation) of the transducer may change over the course of time.
• Patent Abstracts of Japan JPO and Japio relating to Japanese patent application 58066387 published under the number 59192930 discloses a magnetic torque transducer for a rotating shaft.
• the transducer element is provided by a film of anisotropic magnetic material adhered to the outer circumference of a region of the shaft.
• the film exhibits an easy axis of magnetisation that is axially-directed. Torsion in the shaft changes the direction of this easy axis.
• a permanent magnet is disposed within the shaft and interiorly of the film and oriented in an axial direction. According to the Abstract, the film is magnetised along its easy axis by the magnetic field generated by the interior permanent magnet to provide a detectable torque- sensitive field component.
• the film is spaced from the interior magnet. If the shaft is of non-magnetic material as appears to be the case, or of at least very low permeability material, the spacing between the magnet ends and the film provides a high reluctance path so that the flux in the film will be low. However, if the shaft were to be made of a high permeability material to provide a low reluctance magnetic connection between magnet and film, the material would then provide a shunt path closing the flux path for the magnet and again the flux in the film would be low.
• the prior transducer element also requires the step of providing a suitable magnetically-anisotropic film and adhering it to the shaft.
• the present invention is based on the concept of establishing a magnetic flux in an annular region of a ferromagnetic part, such as a shaft, using one or more magnets as the source of magnetic flux and without requiring a magnetisation procedure for the part which involves establishing a stored or remanent magnetisation within the ferromagnetic material.
• embodiments of the invention will be described by which the magnet or magnets are magnetically coupled to the annular region by a low reluctance connection.
• the annular region closes the flux path for the magnet(s) providing for an efficient generation of flux within the region with the efficient generation of a torque-sensitive external magnetic field.
• the magnetic flux path is established between the opposite polarity poles of two aligned but spaced magnets.
• the or each magnet used in the implementation of the invention may be a permanent magnet, such as a straight or bar form magnet, or it may be realised by means of an electromagnet.
• Fig. 1 shows an embodiment of the invention having a transducer element using a single permanent magnet as an internal source of magnetisation
• Fig. 2 illustrates the embodiment of Fig. 1 in a transducer assembly, and shows the flux distribution associated with the transducer element
• Fig. 3 shows an embodiment of the invention having three magnetised regions, at least the centre one of which is used as a transducer element;
• Fig. 4 shows a modification of the embodiment of Fig. 1
• Fig. 5 shows a transducer assembly using the modified embodiment of Fig. 2, and the flux distributions associated with the three regions;
• Fig. 6 shows another embodiment in which a transducer element region is created between two spaced permanent magnets.
• the present invention is applicable to a hollow part such as a tube, which may be referred to as a sensor host, in the hollow of which a permanent magnet accommodated and whose field extends to the outer surface of the part.
• a hollow part such as a tube
• a sensor host in the hollow of which a permanent magnet accommodated and whose field extends to the outer surface of the part.
• the invention will be described in relation to sensing torque applied about the axis of a shaft through which a bore extends or in which a blind bore extends so that the transducer region of the shaft is tubular.
• the shaft, or at least the transducer portion of it is of a ferromagnetic material.
• the axis of the hollow of the part and more specifically the axis of the tube or bore that has been mentioned lies on the axis about which torque is applied. Fig.
• FIG. 1 shows a shaft 30 of circular cross-section through which an axially-centred circular bore 32 extends so that the shaft is in the form of a tube.
• the shaft that is the tube wall 34, is of a ferromagnetic material.
• Inserted in the bore 32 is a permanent magnet 36 of straight or bar form whose magnetisation extends in the axial direction as shown by North and South poles, N and S.
• the permanent magnet 36 is also of circular cross-section and is snugly fitted within the bore 32.
• An important factor is the goodness of the magnetic connection of the magnet 36 with the section 40 of wall 34 that bounds the portion of bore 32 in which magnet 36 is received. The uniformity of this connection around the axis determines the rotational uniformity of the field established in the tube wall.
• the magnet in place by mounting it in a plastic tube so that the magnet is spaced from the interior tube wall and the tube can also serve to protect the magnet.
• High power magnets may well be of relatively brittle material.
• the strength of the permanent magnet can be selected as required. Too strong a magnet may result in the magnetic field continually overcoming the field distortion due to torsion in the shaft thereby masking the torque-dependent effect.
• the provision of a thin plastic liner between the permanent magnet and the tube wall may be used to control and moderate the effect of swamping of the wanted effects by an over- strong field from the central magnet.
• Fig. 2 is a view similar to Fig. 1 but more clearly shows the ferromagnetic tube 34 surrounding bore 32 and the flux distribution 38 (shown rather diagrammatically) due to the magnet 36.
• the section of the tube wall 34 surrounding the magnet 36 closes a flux path for the magnet, thereby providing magnetised transducer region 40.
• this flux distribution 38 forms an annulus.
• This toroidal flux distribution is akin to the flux distribution 26 disclosed in WO01/13081 but in that proposal the source of magnetism is the remanent magnetism stored in the outer part of the annulus with a flux path closed through the internal ferromagnetic material, whereas in Fig.
• the source of magnetism is the permanent magnet in the inner part of the annulus with the flux path closed by the outer ferromagnetic material adjacent the external surface of the shaft 30.
• Fig. 2 also shows the flux distribution also includes some axially-directed flux 42 emanated externally of the shaft 30. It is the external flux 42 which can be sensed by a non-contacting magnetic sensor device 44 to provide a transducer assembly for measuring the torque in the shaft which affects the flux 42.
• the placement and orientation of the sensor device 44 (which in practice may be an arrangement of sensor devices about the shaft axis) depends upon the precise nature of the torque-dependent field component to be sensed.
• the dimensions of the core magnet 36 and the surrounding tubular section of the shaft will result in a longitudinal magnetic flux which has a circumferential (tangential) magnetic field component that is dependent on torque.
• the sensor device(s) will be oriented accordingly.
• a sensor device or devices may also be oriented to detect the axially-directed magnetic field component to provide a measurement reference.
• Fig. 3 shows an extension of the embodiment of Figs. 1 and 2 to develop more than one magnetised region 40 in the shaft 30.
• Fig. 3 shows three such regions 40a, 40b, 40c generated by respective permanent magnets 36a, 36b, 36c.
• the magnets are poled so that adjacent magnets have like poles adjacent and the flux distributions alternate in polarity as indicated by arrows 38a, 38b, 38c.
• the adjacent like poles are spaced axially a Httle as is shown in Fig. 5 and denoted by reference numeral 46 to develop the toroidal flux distribution associated with each permanent magnet.
• An advantage of using a permanent magnet source in a hollow shaft or tube is that the magnet can be selected independently of the shaft material.
• the shaft material itself may need to be selected having regard to the mechanical requirements of the particular use and function to which the shaft is put, transmitting torque in a machine or mechanism for example.
• the permanent magnet can be selected primarily for its magnetic qualities rather than for mechanical performance.
• FIG. 2 Another embodiment of the invention will now be described which has two advantages over the embodiments thus far described.
• the need to dimension the magnet(s) to fit the bore can be avoided and the flux distribution into the wall of the tube can be enhanced.
• the flux distribution of Fig. 2 is diagrammatic to illustrate the principle of what is being done. Flux lines emerging from the poles, other than possibly at the outer circumference, enter what would normally be a high reluctance ambient medium in the bore, air for example.
• the embodiment now to be described provides a more guided flux path into the tube wall.
• Fig. 4 shows another embodiment in which the tube wall 34 of the hollow shaft 30 is provided with three annular magnetised regions 50a, 50b, 50c by use of three magnets 54a, 54b, 54c axially centred in bore 32 and aligned along tube axis A-A with alternating polarity.
• the three magnets are of significantly smaller diameter than the bore.
• Each pole (N,S)of each magnet is magnetically coupled to the tube wall by a respective disc of ferromagnetic material which is in contact with the pole and which has a diameter affording a close fit in the bore 32 and providing magnetic contact with the surrounding tube wall 34.
• This technique may be applied with the use of just one magnet or where plural magnets are used as seen in Fig. 4, a disc may be common to the facing like poles of adjacent magnets.
• the three magnets 54a, 54b, 54c are sandwiched between four discs 56a, 56b, 56c and 56d of a ferromagnetic metal, preferably a magnetically soft metal.
• the discs are a close fit in the tube bore.
• Discs 56b and 56c are each common to a respective pair of adjacent magnets.
• the discs can be considered to act as flux concentrators developing a low reluctance path with the tube wall section between the pair of discs co- operating with a given magnet. This configuration promotes a high magnetic field in the tube wall sections to create the transducer regions 50a, 50b, 50c. This is better illustrated in Fig.
• the annular region 50a, 50b, 50c of the wall 34 surrounding each magnet provides a flux path for establishing a toroidal flux distribution as already described.
• the inner region 50b is used as a transducer element
• the outer regions may be subject to flux leakage paths away from the regions as already discussed. They do, however, act as control or keeper regions enhancing the desired flux distribution of the inner region 50b.
• a torque transducer assembly is completed by suitable placement of one or more non-contacting magnetic field sensor devices 64 in association with the transducer element region 50b.
• a pair of devices 64 as is illustrated in Fig. 5 are placed diametrically opposite with respect to the shaft and are connected additively as regards the torque-dependent flux component sensed thereby.
• Fig. 5 is diagrammatic to illustrate the principle of providing a complete transducer assembly. Further discussion of sensor placement with respect to external field components to be detected is found in WO01/13081 and WO01/79801 above-mentioned.
• a support member such as a plastic tube, in which the magnet is seated and which in turn seats in the bore of the shaft.
• discs 56a-56d may be of circular shape as suggested above, it will be appreciated that the same function can be achieved by other shapes that fit within the bore 32, e.g. regular polygons. Such shapes, particularly if applied to the transducer element, can be expected to introduce a rotational non-uniformity into the sensed magnetic field, for example a regular ripple in the field for a rotating shaft which can be exploited for a speed measurement in addition to the torque. The same aim could be realised by a disc with a notch in its periphery providing a field perturbation used for speed measurement or indicating the angular position of the shaft.
• FIG. 6 Another approach to using a permanent magnet as the magnetic source for a transducer region of a hollow shaft is shown in the embodiment of Fig. 6.
• a hollow shaft 30 having an axial bore 32 therethrough has a single annular transducer region 70 formed in the wall section 34 of the tube between a pair of spaced magnets 72 and 74.
• the magnets are shown as being of a diameter to be a close fit in bore 32. They are separated by a significant distance appropriate to the axial length of the required transducer region and to this end may abut and be separated by a non-magnetic spacer member 76. It is to be noted that in the Fig.
• the two magnets are oriented in the bore with like polarity so that opposite poles face one another across spacer member 76 and magnetically connect to one and the other end of the section of wall 34 surrounding the spacer member 76.
• annular flux path 78 between the magnets is established in region 70, that is between the north pole of one and the south pole of the other.
• This annular flux path is longitudinally magnetised, though it is not a closed toroid as in the other embodiments.
• the flux path has an externally detectable component 80.
• magnets 72 and 74 of smaller diameter than the bore of the tube and interpose a respective ferromagnetic disc that is a close fit in the bore between each magnet and the spacer 76. This is to adopt the technique shown in Fig. 4. It will also be understood that by use of one or more additional magnets and spacers, the magnets all being oriented with the same polarity, more than one longitudinally magnetised region can be obtained.
• the use of electromagnet(s) enables the energisation level to be controlled and adjusted for a particular instance of use so that the torque-dependent effect on the magnetic flux in the shaft wall can be optimised.
• the energisation may be direct current but A.C. energisation is possible to generate an alternating magnetic flux for torque sensing. By selection of the energisation frequency a frequency-selective detection of the sensed component is achievable.
• a permanent magnet source or flux concentrator disc may have a cross-section which is not identical with that of the bore within which it fits so that the degree of magnetic connection with the bore or other hollow is a function of angle about the axis.
• the resultant non-uniform output signal can be dealt with by averaging techniques. Such techniques can also be applied in the circular cross-section cases specifically discussed above to smooth out any non-uniformities in the magnetic field about the axis of rotation.
• the deliberate introduction of non-uniformity can be also put to advantage in obtaining an output of rotational speed as well as the torque- dependent output.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• General Physics & Mathematics (AREA)
• Dynamo-Electric Clutches, Dynamo-Electric Brakes (AREA)

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• 2001
  • 2001-01-25 GB GB0101982A patent/GB0101982D0/en not_active Ceased
• 2002
  • 2002-01-24 EP EP02718049A patent/EP1356257A1/de not_active Withdrawn
  • 2002-01-24 WO PCT/EP2002/000786 patent/WO2002059556A1/en not_active Application Discontinuation

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