GB2256050A - Transducer using hall effect sensor - Google Patents

Abstract

One or more Hall effect sensors are used to sense displacement of magnet(s) and thus of a transducing element. As shown Hall device 20 attached to a housing 11 of a pressure sensor detects motion of magnet 19 attached to a rod 13. Uses in force and acceleration sensors, in rotary and linear displacement sensors, and in a joystick are described. <IMAGE>

Description

TRANSDUCER In British Patent Application No.9107915.2 of the present applicant, there is described a device for sensing and measuring torque applied to a shaft and, more particularly but not exclusively, a device for sensing and measuring torque in a power steering system. The device relies upon a magnetic field sensor, preferably a linear Hall effect (HE sensor).

The inventor has now recognised that the ideas underlying his pending patent application have much wider application than he first appreciated. The torque sensing device of his pending application was prompted by the need to improve the existing strain gauge torque sensors. Strain gauges are, however, used in a multitude of other applications, and the inventor has now developed ways of replacing strain gauges in a large number of these other applications.

According to the present invention there is provided a transducer device including a transducer element for generating an electrical output signal indicative of a magnitude and direction of a movement between a housing of the device and a sensing element mounted to the housing, characterised in that the transducer element is a Hall effect (HE) element and in that the HE element is mounted to one of the housing and the sensing element and a magnet is mounted to (or provides) the other of the housing and the sensing element so that what generates the output signal is relative movements between the magnet and the HE element, upon the imposition of a stress between the housing and the sensing element.

One embodiment of this invention is described in the earlier Patent Application, No.9107915.2. The specification of that earlier patent application does not state in terms that the electrical output signal is indicative of direction as well as magnitude of the movement in question, but those skilled in the art will recognise -that directional information is provided.

Indeed, as the embodiment in question is intended as the basis of a motor car power steering system, for mounting on the steering column of the vehicle, the generation of information as to the direction of rotation of the steering wheel is rather important.

Normally, a device in accordance with the present invention will include a magnetic shield around the magnet and sensor. The shield is conveniently of mu metal.

Normally, the magnet is mounted to the sensing element and the HE element is fixedly mounted to the housing of the device.

In a number of applications of the device of the invention, it will be preferable to provide more than one magnet and transducer element pair, and to duplex the outputs of the various pairs. Naturally, duplexing becomes more desirable as the importance of avoiding failure of the device increases. A good example is in the use of the invention to replace strain gauges in the so-called "force stick" (what used to be called "joy stick") of an aircraft, or a supplementary side stick of an aircraft.

For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: FIGURE 1 is longitudinal section of a pressure sensor of the invention; FIGURE 2 is front view of the device; FIGURE 3 is a longitudinal section of a translational force sensor of the invention; FIGURE 4 is an underneath plan view of the device; FIGURE 5 is a longitudinal section through an acceleration sensor of the invention; FIGURE 6 is an isometric view of the device; FIGURE 7 shows on its left hand side a longitudinal section through part of a rotary sensor in accordance with the invention and, on its right hand side, a perspective view of the sensor, with the HE element and magnet also shown in perspective on their own; FIGURE 8 is a front view of the device;; FIGURE 9 is a front view, partly in section, of a displacement sensor in accordance with the invention; FIGURE 10 is a plan view of the device; FIGURE 11 is a perspective view of a force stick in accordance with the invention; and FIGURE 12 is a longitudinal section through the Figure 11 device.

Referring to Figure 1, a low cost pressure sensor has a lower housing 10 and a mu metal upper housing 11, the housing halves engaging with each other by threads to retain between them a disc spring 12 which carries through an aperture at its centre a pressure sensing rod 13 which extends through a bore 14 in the lower housing 10 with an 0-ring seal 15, so that the lower end 16 of the rod may be receptive to externally imposed fluid pressure to urge the rod 13 upwardly, against the downward bias of the disc spring 12. The lower housing 10 is threaded at 17 for insertion in the wall of a vessel within which the pressure is to be monitored.

The upper end 18 of the rod 13 carries a magnet 19 and the upper housing 11 supports a Hall effect element 20 located alongside the magnet 19 so that it responds to upward movement of the magnet 19 relative to the housing 11, with increasing pressure applied to the lower end 16 of the rod 13. With a linear HE sensor, the output is proportional to magnitude of the upward movement. The sensor could be positioned directly above the magnet but this would probably give a lower magnitude electrical output for any given rod displacement.

In a more adaptable (but more expensive) construction, the HE sensor could be mounted on a bearing assembly such as has already been proposed in earlier Application No.9107915.2. This would allow, for example, disconnection of the threaded boss 17 without electrical disconnection of the sensor 20.

The lower housing 10 naturally includes means for its installation, in this instance, six flats 21 and a seal 22, these for co-operation with the thread 17 to secure the device in the wall of a pressure vessel.

Moving on to Figure 3 and 4, there is shown a device similar to the pressure sensor, but one which measures displacement in both directional senses. A control rod 13 is carried by a diaphragm 30 itself captivated between flanges of an upper housing 11 and lower housing 10, the housing halves being bolted together. The diaphragm 30 hermetically seals the interior 31 of the upper housing.

An annular recess 32 in the lower part of the control rod 13 accommodates the rim of the central circular aperture 34 of the lower housing 10 through which the control rod 13 passes, and this interaction provides mechanical stops to the extent of upward and downward movement of the control rod 13 relative to the housing 10 and 11, thereby to protect the diaphragm 30 from damage arising from excess movement, and to provide a safe failure mode in the unlikely event of diaphragm failure.

At the top of the rod 13, the magnet and sensor arrangements are the same as in the Figure 1 embodiment and so are described by the same reference numerals.

The device is used to measure displacement between first and second mechanical elements. The first mechanical element is secured to the boss 35 on the axis of the device above the upper housing 11, while the second element is secured to a threaded bore 36 in the flatted lower end of the control rod 13. The rod 13 carries a lock nut 37. The movemnet of the magnet 19 is detected by the sensor and its electrical output is proportional to the amount of movement. The direction of movement is indicated by the polarity of the voltage generated.

In both of the Figure 1 and Figure 3 embodiments, and in any other of the embodiments illustrated herein, it will be understood that the single illustrated HE sensor could be supplemented by one or more additional such sensors.

In Figures 5 and 6 is shown an acceleration sensor wherein a mu metal housing 50 accommodates a rectangular magnet 51 carried on a hub 52 itself mounted to the distal end of a flat-section elastically resilient sensing bar 53, the proximal end of which is secured to the housing 50.

Surrounding the bar 53 is a rectangular sleeve 54 which carries two HE sensors 55 in close proximity with the poles of the magnet 51, as indicated. On the radially inner surface of the rectangular sleeve 54, for interaction with the bar 53 is an soft stop ring 56 which cushions the movement of the bar 53 when accelerations suffered by the housing 50 are excessive. The housing 50 is of mu metal and has a pair of apertures 57 for mounting the housing to whatever element is to be monitored.

The weight of the hub 52 is carefully selected having regard to the deflection characteristics of the bar beam 53, and the mass of the magnet 51, to achieve the desired amounts of bending for the anticipated acceleration forces involved. Arrow 58 indicates the axis of directions of acceleration to which the device is most sensitive. With the illustrated arrangement of magnetic poles, the voltage output of the device will be either +ve or -ve in dependence upon which of the two directions of the axis 58 the acceleration is in.

The device shown is a duplex sensor.

Damping of the device can be achieved by the use of viscous fluid as is known in the art, this would of course require sealing of the HE sensor against fluid impregnation.

The principle of monitoring acceleration as shown could be readily modified to include other axis examples would be a X, Y and Z rate sensor also a "Yaw" sensor. Those skilled in the art will be able to produce other devices using the principle of monitoring the displacement of a magnet specific to certain axes, its magnitude and direction being indicated by the use of a linear HE sensor.

The rotary sensor of Figures 7 and 8 has much in common with the torque sensor of earlier Application No.9107915.2. A main housing 70 has mounting ring 71 for securing it to a first element and an upper housing 72 likewise has through apertures for fastening it to a second element so that rotational movement between the first and second elements can be monitored. The lower housing 70 has a shaft 73 fixed against rotation and with an external thread on which the upper housing 72 rotates threadably. This relative rotation is resisted by rings on the threaded shaft 73 and located tight against the housing 72, above it and below it.Each set of rings, above and below the housing 72, comprises a pair of locking rings and, captivated between the locking rings and the housing 72, an elastomeric resilient ring, deformation of which allows limited movement of the housing 72 up and down the shaft 73.

Mounted by a bearing 74 to the lower housing 70 is an annular transducer support 75 and mu metal transducer housing 76 which contains at least one HE sensor 77, directed radially inwardly to interact with a ring magnet 78 carried on the upper housing 72, so that relative rotational movement between the first and second elements causes the upper housing 72 to move up and down on the shaft 73 relative to the HE sensor 77, thereby to generate an output from the sensor 77 which is +ve or -ve in dependence upon the direction of axial movement of the magnet 78.

Figure 8 shows in more detail the sensor housing 76 and mounting ring 71 of the lower housing 70, and also the upper set of rings on the shaft 73, that is, upper 78 and lower 79 locking rings and rubber ring 80.

Conveniently, the bearing 74 is retained to the shaft 73 and support 75 by circlips, just visible in Figure 7. The shaft 73 can be provided at its upper end with a blind bore which is splined for its convenient external retention.

Of course, the angular displacement measured by the device is not limited to less than 3600 rotation.

In the displacement sensor of Figures 9 and 10, displacement between a housing 90 and a sensing rod 91 is achieved by providing a magnet 92 on the rod and a plurality of HE sensors 93 addressing the magnet 92 and arranged in a line within the housing 90. As the magnet 92 moves across the face of the line of sensors 93, the voltage output from each of these sensors 93 varies, to provide information indicative of the position of the rod 91 relative to the housing 90.

In the illustrated embodiment the outputs from the various sensors are summed. When the magnet 92 moves through the device past a sensor that sensor becomes saturated with magnetic flux, and the output from that sensor is added to the output of the next sensor as the magnet moves further through the device. This continues until all sensors are producing a voltage relative to the specific position of the magnet, these voltages being continually summed.

However, other wiring arrangements may suggest themselves to those skilled in the art, to meet particular applications and requirements of the device. Obviously, the number of sensors, their spacing, and the length of the magnet, will be selected in dependence upon the magnitude of the displacement to be measured, and the nature of the material of the magnets. The housing 90 preferably incorporates a mu metal shield. Of course the device will indicate the direction of movement of the magnet and those skilled in the art will see how easily the device can be duplexed with a minimal cost penalty.

Turning now to Figures 11 and 12, the force stick illustrated is intended to replace one currently used in aircraft and based on strain gauge technology. The strain gauges have to be duplexed. Not only is this expensive but there can also be a conflict between inherent safety and the requirements for "feel" in the stick which the pilot requires to feel comfortable using the stick. To allow enough strain in the stick for satisfactory measurement by strain gauges, the stick has to be significantly deformable, so much so that fatique problems in the stick cannot be entirely discounted. The serious consequences of fatique failure are therefore ensured against by using a mechanical fail-safe mechanism, and this adds to the expense. Not only should the illustrated device offer cost savings but it should also eliminate the compromises mentioned above.

The control rod 110 of the illustrated device has an upper end with a hand grip 111, mounted in a spherical bearing 112 and with a gaiter 113, all mounted to a generally cylindrical main housing 114. This main housing carries a sensor bush 115 itself carrying a plurality of HE sensors 116. The rod 110 extends through a large through aperture in the centre of the bush 115 to a lower end 117 which carries a substantial rubber bush ring 118 which is clamped to the housing 114. Thus, when the pilot executes pitch and roll movements of the hand grip 111, the rod 110 rotates in the spherical bearing 112 and this rotational movement is resisted by the deformation of the rubber bush 118. Obviously, the size and composition of the bush 118 is selected to give the desired feel to the hand grip 111.

Carried on the control column 110, beneath the spherical bearing 112 and adjacent to the sensors 116 is a magnet plate 120 which carries a number of magnets 121, one for each of the sensors 116. Each magnet 121 has a continuity plate 122. The magnet plate 120 is of non magnetic material and the continuity plates 122 are there to provide a consistent flux path for each magnet 121.

A mu metal shield 123 surrounds the magnet plate 120, and the sensor bush 115 is also of mu metal. The housing 114 has a mounting flange 124 with a plurality of mounting apertures 125 and the open lower end of the housing 114 is sealed threadably by an end cap 126. The magnet plate 120 is retained on the column 110 by a location sleeve 127 and threaded end cap 128, the rubber bush 118 fitting around the outside of the sleeve 127.

The stick assembly is mounted in the aircraft such that the magnet plate 120 is aligned with the roll axis 130 of the aircraft and the pitch axis 131 of the aircraft.

It will be obvious that resistance to movement of the force stick need not be provided by a rubber bush 118.

Those skilled in the art will be able to assess any likely alternatives.

Of course, such control sticks are useful in all sorts of applications besides real aircraft. Flight simulators is one application. Others which spring to mind are all sorts of industrial equipment, such as back hoe excavators, and consumer items such as electric wheel chairs and radio controlled model vehicles.

It will be apparent from the drawings that, in use of the device, movement of the hand grip 111 against the return bias of the rubber bush 118 causes movement of the magnet ring 120 and magnets 121 relative to the sensors 116, the amount of movement of the hand grip 111 being in proportion to the amount of movement of the magnets relative to their respective sensors. The movement is detected by the sensors and their electrical output is proportional to the amount of movement. The direction of movement is indicated by the polarity of the voltages generated by each of the sensors 116.

In pressure transducers, such as in Figure 1, the ordinary O ring 15 might be replaced by a more sophisticated low friction seal, say to allow the sensor to operate over a wide range of pressures with minimal seal stick/slip at low pressures.

For continuity of magnetic flux the opposite poles of each magnet should contact the same material (normally ambient air). Continuity plates can be used, however, such as those of Figure 12 or the locking rings 48,50 in the embodiment illustrated in Application 9107915.2.

But a non-linear sensor output, tailored as desired for specific applications, could be achieved by judicious use of dissimilar permeance materials at the opposed poles, or a keeper for squeezing flux lines into confined, pre-selected paths. Note, for example, the dissimilar treatment of the poles of the magnet 60 in Figure 3. This could be avoided, if considered necessary, by sandwiching the magnet 60 between surfaces of the alloy stem 13.

Claims (24)

1. A transducer device including a transducer element for generating an electrical output signal indicative of a magnitude and direction of a movement between a housing of the device and a sensing element mounted to the housing, characterised in that the transducer element is a Hall effect (HE) element and in that the HE element is mounted to one of the housing and the sensing element and a magnet is mounted to (or provides) the other of the housing and the sensing element so that what generates the output signal is relative movements between the magnet and the HE element, upon the imposition of a stress between the housing and the sensing element.

2. A transducer device as claimed in Claim 1 wherein the magnet is mounted to the sensing element and the HE element is fixedly mounted to the housing of the device.

3. A transducer device as claimed in Claim 1 or 2, incorporated in a force stick for an aircraft.

4. A transducer device as claimed in Claim 1 or 2 which is a pressure sensor.

5. A transducer device as claimed in Claim 1 or 2 which is an acceleration sensor.

6. A transducer device as claimed in Claim 1 or 2 which is a rotary movement sensor.

7. A transducer device as claimed in Claim 1 or 2 which is a translational displacement sensor.

8. A transducer device substantially as hereinbefore described with reference to, and shown in, any one of the accompanying figures of drawings.

Amendments to the clains have been fled as follows 1. A transducer device wherein at least one magnet is mounted to a sensing element and a polarity of Linear Hall Effect (LHE) sensors are fixedly mounted to at least one housing element of the device.

2. A transducer device as claimed in claim 1 whereupon the device measures pressure which has an upper and lower housing engaging with each other by threads to retain between them a disc spring internally clamped between a sensor rod, at the upper end of the rod is a permanent magnet with its North and or South pole uppermost and co-axial to the springs translational movement with a LHE sensor mounted at 90 degrees to that movement on the centreline of the magnet halfway between its North and or South pole end, upon a given force thereof enables the sensor to yield a signal proportional to the displacement and hence the pressure exerted on the device.

3. A pressure sensor as claimed in claim 2 that has a sensor rod which extends through a bore in the lower housing that holds an '0 ring which seals against the rod and hence seals the internal chamber housing the magnet and the sensor against pressurized fluids.

4. A pressure sensor as claimed in claim 2 wherein the upper housing which holds the sensor is also a mu-metal shield.

5. A pressure sensor as claimed in claimed 3 whereupon the 'o' ring is replaced by a low friction seal example stepseal to reduce seal stick/slip of course the seal material would be selected to suit the medium being measured.

6. A pressure sensor as claimed in the previous claims whereupon continuity plates (plates made from the same material and dimensions) are used at both ends of the magnet one end being attached the other end spaced to allow only movement through its measured range and then to be used as a mechanical safety stop the plates maintain continuity of magnetic flux and hence the accuracy of the device.

7. A pressure sensor as claimed in claimed 6 whereupon with judicious use of dissimilar permeance materials at the opposite poles of the magnet and or keeper used to squeeze flux lines into preselected paths that will yield nonlinear outputs which would be calibrated to suit specific applications.

8. A pressure sensor device substantially as hereinbefore described with reference to, and shown in Fig 1 and 2.

9. In the previous and forgoing claims it will be understood that in any of the embodiments illustrated herein that the single illustrated LHE sensor could be supplemented by one or more additional such sensors.

10. A transducer device as claimed in claim 1 whereupon the device measures translational movement using a control rod attached to a diaphragm which is itself captivated between an upper and lower housing, a magnet is attached to the upper end of the control rod, a LHE sensor is positioned so that its sensitive axis is at 90 degrees and on the centre line of the magnet halfway between its North and or South pole end, upward and downward movement of the control rod and hence the magnet past the LHE element yield both ( if calibrated ) the force applied and its direction indicated by the polarity of the voltage generated and whether the North or South pole of the magnet is uppermost.

11. A translational sensor as previously claimed whereupon the upper housing that contains the LHE sensor is also a mu-metal shield.

12. A translational sensor as claimed in claim 10 whereupon the upper and lower housings which contain the diaphragm are shaped to give mechanical stops at both ends of the devices stroke.

13. A translational sensor as previously claimed whereupon the upper and lower ends contain threads for external attachment.

14. A translational sensor device substantially as hereinbefore described with reference to Fig 3 and 4.

15. A transducer device as claimed in claimed 1 whereupon the device measures displacement using a housing and a magnet attached to the magnet is a sensing rod attached to the housing is a line of LHE sensors mounted along the magnets length, the sensitive axis of the sensors are at right angles and or 90 degrees to the North and or South pole end of the magnet.

16. A displacement sensor as claimed in claim 15 whereupon a line of LHE sensors are mounted directly to a printed circuit board (PCB) which is itself attached to a housing.

17. A displacement sensor as claimed in claim 15 and 16 whereupon the output of the sensors is continually summed as the magnet passes through the device until all sensors are producing a voltage relative to the specific position of the magnet.

18. A displacement sensor as claimed in claim 17 whereupon different sensor wiring circuit arrangements are used in dependence upon the nature of the output required.

19. A displacement sensor as claimed in claim 15 whereupon the number of sensors, their spacing, and the length of the magnet, will be selected in dependence upon the magnitude of the displacement to be measured and the nature of the material of the magnets.

20. A displacement sensor as claimed in claim 15 whereupon a second line of LHE sensors are placed in a suitable position to give a duplexed output, of course this device is not limited to duplexing.

21. A displacement sensor as claimed in claim 15 whereupon the outer housing and end caps preferably are, or can incorporate a mu-metal shield.

22. A displacement sensor as claimed in claim 15,16 and 17 whereupon the output polarity of the LHE sensors is indicative of the direction and amount of displacement of the magnet past the sensors or the sensors past the magnet.

23. A displacement sensor device substantially as hereinbefore described with reference to Fig 9 and 10.

24. A transducer device according to any one of the claims 1 to 23 and substantially as herein described with reference to and/or as illustrated in the figures of the accompanying drawings.