GB2067763A

GB2067763A - Position transducers

Info

Publication number: GB2067763A
Application number: GB8040131A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1980-01-19
Filing date: 1980-12-15
Publication date: 1981-07-30
Also published as: GB2067763B

Abstract

A transducer for providing signals representative of the axial setting of an angularly movable component comprises a cylindrical member 10 having a first series of zones 11 thereon, said zones having the same circumferential width and axial length and a capacitive sensing device 13 having a sensing surface 14 presented to the zones. As the area of the zones in turn presented to the surface of the device varies a fluctuating electrical signal is obtained which varies with the relative axial setting of the member and device. Calibration zones 12 of unequal width can be located between the zones 11. Alternatively the member can have a transverse slot and two further slots of unequal width cut into the surface at diametrically opposite positions, or axially spaced steps can be formed by cutting along different chords of the cross section of the member. <IMAGE>

Description

SPECIFICATION Transducers This invention relates to a transducer for providing signals representative of the axial setting of an angularly movable component.

The object of the invention is to provide a transducer for the purpose specified in a simple and convenient form.

According to the invention a transducer for the purpose specified comprises a generally cylindrical member coupled in use, to said component so as to be axially and angularly movable therewith, a plurality of circumferentially spaced zones on the periphery of said member, said zones being of substantially equal circumferential length, the zones extending from one end of the member and terminating in a generally radial plane disposed between the ends of the member, and a sensing device having a sensing surface presented to but spaced from the surface of the member, the sensing surface having a fixed area and the sensing device having a fixed axial position, the sensing surface being responsive to the nature of said zones whereby the sensing device provides a fluctuating electrical signal indicative of the areas of said zones which pass beneath the sensing surface, and hence the relative axial position of the member and the sensing device.

Examples of transducers in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a perspective view of one example of a transducer, Figure 2 is a developed view of a part of the transducer of Figure 1, Figure 3 is a graph showing the variation in a signal produced by the transducer of Figure 1, Figure 4 is a perspective view of another example of a transducer, Figure 5 is a view similar to Figure 2 of the transducer shown in Figure 4, Figure 6 is a graph similar to Figure 3 but relative to the example of Figure 5, and Figures 7 and 8 are views similar to Figures 1 and 2 showing another example of a transducer.

Referring to Figure 1 of the drawings, the transducer comprises a generally cylindrical elongated member 10 formed from metal and which is coupled to or forms part of a rotary component, the axial position of which can vary in use. The transducer is designed to provide signals from which can be determined the axial position of the component within a housing.

The surface of the member is provided with a plurality of raised zones, which for convenience are divided into two sets. The zones of the first set are referenced 11 and those of the second set 12.

Moreover, as will be seen from Figure 2 there are three zones in each set and each zone is provided with a respective reference letter.

The zones 11 extend from one end of the member and terminate in a radial plane between the ends of the member. They thus have the same axial length and in addition they have the same circumferential length. The circumferential spacing between the zones 11 is the same being in the example, 600.

The zones 12 are located in the gaps between the zones 11 respectively and extend the full axial length of the member. The circumferential lengths are however different.

Positioned adjacent the member 10 is sensing device 13 which in the example is a plate of a capacitor. The device defines a surface 14 presented to the surface of the member and which has substantially the same curvature as the surface of the member, but is spaced therefrom.

The device 13 in use is fixed within a housing containing the member in a position as shown in Figure 2, such that it partially overlaps the zones 11.

As the member rotates the capacitance value as measured between the member 10 and the device 13 will vary and ignoring for the moment, the zones 12, as the zones 11 pass beneath the surface 14 the capacitance value will rise from a minimum in practice, substantially zero, to a maximum when the surface 14 fully overlaps the zones 11 in the circumferential direction, i.e. as shown in dotted outline in Figure 2. These values will be the same for each of the zones 11 providing the distance between the zones 11 and the surface 14 does not vary. If the member is moved axially the capacitance value will change and the greater the overlap in the axial direction, the greater the capacitance value.By calibration the capacitance value can be related to the extent of overlap in the axial direction and hence the relative axial position of the device 1 3 and the member 10 and therefore the axial position of the component within the housing.

If the nature of the dielectric between the device 13 and the member 10 varies, there will be a change in the capacitance value and the calibration will be upset. Moreover, drift may occur in the electronic circuits which are utilised to measure and provide an indication of the capacitance value. The zones 12 are provided for the purpose of providing calibration points.

As mentioned above the zones 12 are of unequal circumferential length. The width of the zone 1 2 which is referenced B is arranged conveniently such that when under the surface 14, the capacitance value will be less than the minimum value which is possible when the surface 14 is overlapping the zones 1 The zone 12 referenced F is arranged to provide the maximum value of capacitance and conveniently it has a circumferential length substantially equal to that of the surface 14. The zone 12 which is referenced D has a circumferential length such that an intermediate value of capacitance is provided.

Figure 3 shows the variation of the capacitance value for one revolution of the member 10 and with a fixed relative axial setting of the member and device. The relative capacitance values will remain the same even if the dielectric between the device and the member changes. The capacitance values as provided by the zones 12 enable the electronic circuits utilised for measuring the capacitance value and providing the position signal, to be self calibrating.

Turning now to Figure 4, instead of forming the zones as projecting portions on the surface of the member as is the case with the example shown in Figure 1 , the spaces between the zones may be formed by slots. In Figure 4, the member 15 is of cylindrical construction and is provided with a transversely extending slot 1 6. This is readily formed using a milling cutter. The outer edges of the base wall of the slot 1 6 lie in the aforesaid common radial plane and the sensing device 1 7 is positioned accordingly, its circumferential length being less than that of the slot 1 6.Ignoring for the moment the remaining slots, the capacitance value between the device 1 7 and the member 1 5, will decrease from a maximum to a value which is determined by the axial position of the member 15 as when the device 1 7 extends partly over the slot 1 6. Two further slots 1 8, 1 9 are cut into the surface of the member and these slots as shown in Figure 4, are of unequal circumferential length.

The circumferential length of slot 18 is substantially less than that of the device 1 7 whilst the circumferential length of the slot 1 9 is only slightly less than that of the device 1 7. Moreover, the slots 18, 19 extend rearwardly beyond the base wall of the slot 1 6. As the member rotates the sensing device 1 7 will be exposed to the slots 18, 1 9 to give high and low values of capacitance respectively. The high capacitance value is attained when the device 1 7 lies over the slot 1 8 and the low value when the device lies over the slot 1 9. The measured value of capacitance is obtained as described earlier.

Figure 6 shows the variation in the capacitance value as the device 1 7 moves relative to the slots etc.

In the transducer shown in Figures 7 and 8 the member 20 is again of cylindrical form but it is provided with a pair of steps 22, 23. Again these can very readily be formed by a milling cutter, the end surface is referenced 25 and the same references are used on the developed view of Figure 8. The device 21 has a circumferential length which is less than that of the recess defined by the step 23 and also the portion disposed between the end surface 25 and the step 22. In this case therefore the capacitance value goes from a maximum value corresponding to the portion of the member between the end surface 25 and the step 22, through the measured value which depends upon the relative axial setting of the member in particular the step 22 and the device and to the minimum value corresponding to the device being in the position shown in Figure 8.

As described the devices 13, 17 and 21 are in effect plates of a capacitor and it is the capacitance value which is sensed. As an alternative the zones may be of a magnetic nature, in which case the devices will be responsive to the magnetic field produced by the zones remembering of course that the device must have a finite area in order to provide a signal representative of the relative axial position of the member and device. The devices may be of a light sensitive type in which case the zones will be of different density.

Claims

1. A transducer for providing signals representative of the axial setting of an angularly movable component comprising a generally cylindrical member coupled in use, to said component so as to be axially and angularly movable therewith, a plurality of circumferentially spaced zones on the periphery of said member, said zones being of substantially equal circumferential length, the zones extending from one end of the member and terminating in a generally radial plane disposed between the ends of the member, and a sensing device having a sensing surface presented to but spaced from the surface of the member, the sensing surface having a fixed area and the sensing device having a fixed axial position, the sensing surface being responsive to the nature of said zones whereby the sensing device provides a fluctuating electrical signal indicative of the areas of said zones which pass beneath the sensing surface, and hence the relative axial position of the member and the sensing device.

2. A transducer according to Claim 1 including further zones located between said first mentioned zones, said further zones each having areas presented to the sensing surface, the areas of said further zones presented to the sensing surface being substantially constant irrespective of the relative axial position of the component and sensing device.

3. A transducer according to Claim 2 in which said first mentioned zones and said further zones are defined by raised portions on the surface of said member, the first mentioned zones being equiangularly spaced and said further zones being located between said first mentioned zones respectively and having differing circumferential lengths.

4. A transducer according to Claim 2 in which said member is provided with a transverse slot extending through the member, and a pair of slots of differing circumferential width formed in the member substantially at right angles to the transverse slot, said pair of slots having a greater axial length than said transverse slot.

5. A transducer according to Claim 2 in which said member is provided with a pair of axially spaced steps.

6. A transducer according to Claim 1 in which said member is formed from metal and forms one plate of a capacitor, said sensing device forming the other plate of the capacitor.

7. A transducer for providing signals representative of the axial setting of an angularly movable component and comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 1,2 and 3 of the accompanying drawings.

8. A transducer for providing signals representative of the axial setting of an angularly movable component and comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 4, 5 and 6 of the accompanying drawings.

9. A transducer for providing signals representative of the axial setting of an angularly movable component and comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 7 and 8 of the accompanying drawings.