GB2040465A

GB2040465A - Lever Operated Control Unit

Info

Publication number: GB2040465A
Application number: GB7901767A
Authority: GB
Original assignee: BIDEFORD ELECTRONICS Ltd
Current assignee: BIDEFORD ELECTRONICS Ltd
Priority date: 1979-01-17
Filing date: 1979-01-17
Publication date: 1980-08-28
Also published as: GB2040465B

Abstract

A manual "joystick" control unit for controlling an invalid chair, has a drive coil 1 carried on a fixed support 2 and surrounded by symmetrically arranged pick-up coils 20. Drive coil 1 is supplied with a current of sinusoidal or triangular wave form and the coupling between coils 1 & 20 is determined by the angular displacement of a magnetic armature plate 17 on joystick lever 24, which is supported for universal tilting movement by a helical spring 12 & freely rotatable about its axis. Coils 20 have pole pins 22 with flat coplanar end faces & coil 1 has a pole piece 7. Lever movement is limited by roller 32 engaging stop lip 31 in plate 29 fixed to housing 4. Diametrically opposite pairs of coils 20 are connected to comparators. <IMAGE>

Description

SPECIFICATION Manual Control Unit This invention relates to a manual control unit of the kind which generates electrical signals in response to angular movements of a control lever in different directions, the output signals being dependent both upon the amptitude and direction of the angular movements of the control lever.

Such manual control units having a universally movable control lever or "joystick" are employed in many electrical servo-mechanisms including those in which movement of the lever controls corresponding movements of a vehicie, platform, or other device. For example, "joystick" type control units are used in some forms of electrically powered invalid chairs in which forward, backward and steering movements of the chair are controlled by manual movement of a single control lever.

The most common form of lever-operated control unit employs two potentiometers with respective wiper arms mounted on shafts which are mutually perpendicular and which are connected to the control lever so that rocking movement of the lever in one plane acts upon one potentiometer, while rocking movement of the lever in another, perpendicular, plane rotates the other potentiometer shaft, rocking movement in other planes resulting in a rotation of both potentiometer shafts. Such devices enable the rocking movement of the lever to be resolved directly into two electrical components representing the angular displacement of the shaft.

One of the disadvantages of manual control units employing potentiometers as described above is that the potentiometric devices are prone to wear after prolonged use, and their accuracy can moreover be affected in time by contamination. Furthermore, where such a potentiometric control unit is used by persons having limited muscular control, as for example in a motorised invalid chair, the control unit can be difficult to operate successfully since the resistance to movement of the control lever is not easily regulated. For some patients, who may be incapable of exerting fine manual control, the "joystick" lever should offer a reasonably stiff resistance to movement from its rest position, while for other patients, who may have little muscular power, the force required to displace the "joystick" lever should be small.

The present invention seeks to provide an improved manual control unit which is suitable for a wide range of practical applications, including use by invalids, and which is of robust construction, requiring little attention and having a long potential working life.

According to the present invention there is provided a manual control unit comprising a drive coil mounted on a fixed support, a number of pickup coils arranged symmetrically on the support around the axis of the drive coil, an armature member of magnetic material coupled magnetically to the drive coil and the pick-up coils, and a control lever movable angularly about a fulcrum which is located symmetrically with respect to the pick-up coils, the armature member being so arranged that angular movement of the lever in any direction results in a proportional change in the magnetic coupling between the drive coil and at least two of the pick-up coils.

Since the coupling to the pick-up coils is purely magnetic, there is no mechanical wear associated with the movement of the control lever, as compared with the known type of potentiometric control unit.

Preferably the control lever has a shaft which is supported by a resilient support member which maintains the shaft normally in a rest position in which the armature member carried by the control lever is equidistant from the pick-up coils.

The stiffness or resilience of the support member may be selected according to the intended use of the control unit so as to impart a desired resistance to movement or "feel" to the control lever.

The shaft of the control lever may be freely rotatable about its longitudinal axis. For example one end of the shaft may be rotatably supported in a bearing member to which the armature member is attached. This has the practical advantage that rotation of the control lever about its axis will not result in unscrewing of the control lever, so that the unit can to this extent be tamper-proof.

The resilient support member may comprise a helical spring anchored at one end to the bearing member and at its other end to the fixed support.

In a preferred embodiment of the invention the drive coil is arranged coaxially with the longitudinal axis of the control lever in the normal rest position of the latter, the pick-up coils being arranged with their axes parallel to the axis of the drive coil. The armature member is preferably in the form of a disc arranged between the control lever and the drive and pick-up coils, the plane of the disc being substantially perpendicular to the longitudinal axis of the control lever.

The control unit may have a housing attached to the fixed support and enclosing the pick-up coils, the housing having a cover plate with an aperture through which the control lever projects with clearance, the edge of said aperture defining the limits of angular movement of the control lever.

Various electrical circuits may be associated with the control unit. In one embodiment of the invention the drive coil is connectable to a cyclically alternating current source and the pickup coils are connected to a signal processing circuit which processes the signals detected by the pick-up coils to provide an output or outputs dependent upon the angular movement of the control lever from a rest position. For example there rnay be four symmetrically arranged pick-up coils diametrically opposite pairs of which are connected to respective comparator circuits which provide outputs representative of the angular displacement of the control lever in respective mutually perpendicular planes.

The invention will be further described, by way of example, with reference to the accompanying purely diagrammatic drawings, in which: Figure 1 is a longitudinal section through a manual control unit according to one embodiment of the invention; Figure 2 is a diagrammatic plan view showing the arrangement of the coits of the unit shown in Figure 1: Figure 3 illustrates the electrical arrangement of the coils shown in Figure 2; Figure 4 is a schematic circuit diagram illustrating part of one form of electrical circuit which may be associated with the coils of the control unit; Figure 5 is a schematic circuit diagram illustrating a signal processing circuit associated with the circuit of Figure 4:: Figure 6 is a schematic circuit diagram of part of an alternative form of electrical circuit which may be associated with the coils of the control unit, and Figure 7 represents graphically waveforms associated with the operation of the circuit shown in Figure 6.

The manual control unit illustrated in Figure 1 has a drive coil 1 mounted centrally upon a square base plate 2 which is located within a fixed support box 3. The support box 3 is fixed within a housing 4, part only of which is shown, by a support bracket 5 affixed to one wall of the housing by means of fixing screws 6.

A central polepiece 7 is supported on the base plate 2 by a central fixing screw 8 which passes through the base plate. The polepiece 7 has a core portion 9 which is disposed within the drive coil 2 and a pole portion 10 which covers the end of the drive coil 1 opposite the base plate 2 which has a frusto-conical pole face.

The polepiece 7 has a central counter-bore of larger diameter than the fixing bolt 8, extending into the polepiece from the end of the pole face 10. One end of a resilient support member in the form of a helical spring 1 2 is located in the annular space between the counter-bore and the fixing bolt 8 within the polepiece 7 and is anchored therein by a grub screw 1 3 passing through the pole portion 10. The other end of the helical support spring 12, shown uppermost in Figure 1, is located in a central cylindrical bore in a bearing member 14 and is anchored therein by a grub screw 1 5 which clamps a portion of the spring 12 against a spring support insert 1 6 located within the bore of the bearing member 14.

The bearing member 14 has an externally screw threaded integral collar through which the spring 12 passes, projecting towards the base plate 2. An armature disc 1 7 is located on the collar and clamped against an annular shoulder 18 of the bearing member 14 by a retaining nut 19 engaged with the screw threaded collar. The armature disc 17 is of magnetic material such as soft iron.

A number of, in this case, four, pick-up coils 20 are arranged symmetrically on the base plate 2 around the drive coil 1. In the illustrated embodiment the pick-up coils 20 are located at the four corners of the base plate 2, as shown diagrammatically in Figure 2 and are secured to the base plate 2 by fixing bolts 21 which pass through the base plate 2 and act as core elements for the respective pick-up coils 20. The fixing bolts 21 engage in screw threaded biind bores in respective pole pins 22 which extend coaxially from the face of the respective pick-up coil 20 opposite the base plate 2 and have the same external diameter as the respective pick-up coil 20. The four pole pins 22 have flat end faces which are coplanar with each other and which project beyond the upper edge of the support box 3.

The bearing member 1 4 supports a rotatable shaft 23 of a control lever 24. The shaft 23 passes through and is freely rotatable in a bore 25 in the free end of the bearing member 14, the end of the shaft 33 within the bearing member 14 having an enlarged flange 26 which adjoins the spring support insert 1 6 and which effectively anchors the shaft 23 in the bearing member 14 while permitting rotation of the shaft 23 about its longitudinal axis. The shaft 23 projects through a central aperture in a cover plate 27 forming part of the housing 4, the free end of the shaft 23 being surrounded by a knob 28.An annular stop plate 29 is affixed to the lower face of the cover plate 27 by fixing screws 30 permitting lateral adjustment of the stop plate 29, the latter having a bevelled stop lip 31 which projects into the aperture in the cover plate 27 and determines the limits of angular rocking movement of the control lever 24.

The entire assembly of the control lever 24, the bearing member 14 and the armature disc 17 is supported upon the helical support spring 12. In the normal undeflected condition of the support spring 1 2 the control lever 24 is coaxial with the fixing bolt 8 and with the axis of the drive coil 1, the armature plates 17 being parallel to and equidistant from the pole faces of the four pole pins 22 of the pick-up coils 20. The armature plate 1 7 forms part of the magnetic flux path between the drive coil 1 and the pick-up coil 20, and in the rest position of the control lever these flux paths are equal to each other so that the four pick-up coils 20 are equally coupled magnetically to the drive coil 1.

Displacement of the control lever 24 from its rest position by movement of the knob 28 will cause tilting of the armature plate 17, and will result in a proportional change in the magnetic coupling between the drive coil 1 and at least two of the pick-up coils 20. Various electrical circuits may be connected to the drive and pick-up coils for the purpose of providing electrical output signals which are influenced by such changes in the magnetic coupling and which, therefore, are proportional to the angular movement of the control lever 24. One circuit arrangement is described below with reference to Figures 3 to 6.

The permitted extent of angular movement of the control lever 24 is determined by the stop lip 31 on the stop plate 29. A cylindrical roller 32 is freely rotatably on the shaft 23 and rests on the bearing member 14, being retained in this position axially by a collar 33 secured to the shaft 23. The roller 32 comes into engagement with the stop lip 31 when the control lever 24 reaches the limit of its permitted angular movement.

Lateral movement of the control lever 24 when in this limit position will result in rolling movement of the roller 32 on the stop plate 29, minimising wear and potential damage.

In Figure 2 the inductance of the central drive coil 1 is denoted by Lx, and the inductances of the four pick-up coils 20 are denoted by L1-L4. The four pick-up coils are connected together as shown diagrammatically in Figure 3, the four coils being coupled magnetically to the drive coil 1 through a flux path which includes the armature disc 17.

Referring to Figure 4, the drive coil inductance Lx is supplied with a sinusoidal drive current from a wien bridge oscillator 35 through an amplifier Al. The signals induced in the two pick-up coil inductances L1, L2 will be in anti-phase and are amplified by respective amplifiers A2, A3, of which the amplifier A3 has variable gain to enable the outputs of the two amplifiers to be balanced in the neutral or rest position of the control lever 24. The two amplifier outputs are summed algebraically in a summer 36 which produces an error signal proportional to the difference in amplitude between the two signals picked up by L1 and L2, the error signal being amplified by a further amplifier A4.The signals picked up by the inductances L3, L4 of the remaining two pick-up coils 20 are amplified and combined to produce a further error signal in a manner similar to that described above for the inductances L1 and L2.

The two amplified error signals represent the amptitude of displacement of the control lever 24 in two mutually perpendicular planes and can be used to control respective electric motors, for example motors driving a vehicle in mutually perpendicular directions.

Each error signal may be processed to provide a digital control signal. A circuit for producing a pulse-form control signal from one of the error signals is shown diagrammatically in Figure 5.

The circuit shown in Figure 5 includes a step-up transformer 36 connected to a rectifier bridge 37 the full-wave-rectified output of which forms one input of a comparator 38 the other input to which is a reference input derived from a potentiometer 39. The reference input of the comparator 38 is set so that the mean voltage level at the reference input is greater than the rectified input from the rectifier bridge 37 when the control lever 24 is in its central rest position. When the control lever is moved the amptitude of the input error signal increases, and the comparator produces output pulses the width of which will be proportional to the height of the rectified sine wave half cycles above the threshold level set by the potentiometer 39. The output pulses may be used to drive a direct current motor of a vehicle such as an invalid wheel chair.There may be two such motors, each driven by a respective pulse output derived by the processing of the two error signals referred to above, the relative speeds of the two motors determining the direction of movement of the wheel chair.

The error signal output of each amplifier A4 may be used to resolve the direction of movement of the control lever 24. Thus each error signal may be passed through a squaring amplifier the output of which forms one input of an exclusive OR gate, the other input of which consists of the oscillator signal derived from the wien bridge oscillator 35 through a second squaring amplifier. The output of the exclusive OR gate will be low when the two squared inputs are in phase and high when the two inputs are anti-phase, similar outputs being obtained from the other error signal. The outputs from the two exclusive OR gates will represent uniquely the direction of movement of the control lever 24.

The drive coil LX may be supplied with a triangular current waveform instead of the sinusoidal waveform illustrated.

Figure 6 is a circuit diagram, corresponding to Figures 4 and 5, of an alternative electrical circuit for use with the control unit. In the circuit of Figure 6, the drive coil LX is supplied with a sinusoidal or triangular waveform drive current by a quadrature oscillator 35 through an amplifier Al. The signals detected in a pair of opposite pick-up coils L1 and L2 are applied to respective inputs of a differential amplifier DA1 which provides an output signal representative of the difference between the two pick-up coil signals, the null or balance point of the output of the differential amplifier DA1 being adjustable by a potentiometer 40.The output of the differential amplifier DA1 is further amplified and inverted by an inverting amplifier DA2, D.C. balanced, and then passed by a precision AC/DC convertor 41, which provides a rectified and smoothed DC output voltage signal L (Figure 7) proportional to the movement of the control lever 24 relative to the two pick-up coils L1 and L2.

The DC output signal L is fed to one input of a comparator 42 the other input of which is a triangle waveform signal T (Figure 7). The output of the comparator 42 will be at logic level 0 when the D.C. signal L is at a level lower than the base of the triangle waveform T, and will be at logic level 1 if the level of D.C. signal L exceeds the peak of the triangle waveform T. The output signal of the comparator 42 for intermediate levels of D.C. signal L will comprise pulses having a width which is proportional to the level of the D.C. signal L and, therefore, dependent upon the position of the control lever 24 relative to the two pick-up coils L1 and L2. These output pulses can be used for the energisation of an associated electric motor, as described with reference to the circuit of Figure 5.

In order to provide an indication of the direction of the displacement of the control lever 24 the amplified error signal from the amplifier DA2 forms one input of a Schmitt trigger A5 the output of which, proportional to the error signal, is compared with a quadrature (900 phase-shifted) output of the reference oscillator 35. When the outputs of the two coils L1 and L2 are almost equal, the error signal will be very small but phase shifted 900 with respect to the reference. This signal is squared and compared with the reference phase in a D type edge triggered bistable B1. The output of the bistable B1 will changeover depending on whether the data presented in the D input was at a logic 0 or a logic 1 during the rising edge of the check pulse (see Figure 7). A further refinement is to use a second D type bistable B2 with its D input connected in th Q output of the first bistable B 1. The clock input of the second bistable B2 is the final output pulse from the control system, and hence the rising edge of this pulse acts as a "data valid" request to confirm the direction signal, representing uniquely the direction of movement of the control lever 24.

Claims

Claims

1. A manual control unit comprising a drive coil mounted on a fixed support, a number of pick-up coils arranged symmetrically on the support around the axis of the drive coil, an armature member of magnetic material coupled magnetically to the drive coil and the pick-up coils, and a control lever movable angularly about a fulcrum which is located symmetrically with respect to the pick-up coils, the armature member being so arranged that angular movement of the lever in any direction results in a proportional change in the magnetic coupling between the drive coil and at least two of the pick-up coils.

2. A control unit as claimed in Claim 1, in which the control lever has a shaft which is supported by a resilient support member which maintains the shaft normally in a rest position in which the armature member carried by the control lever is equidistant from the pick-up coils.

3. A control unit as claimed in Claim 2, in which the shaft of the control lever is freely rotatable about its longitudinal axis.

4. A control unit as claimed in Claim 3, in which the shaft is rotatably supported at one end in a bearing member to which the armature member is attached.

5. A control unit as claimed in Claim 4, in whch the resilient support member comprises a helical spring anchored at one end to the bearing member and at its other end to the fixed support.

6. A control unit as claimed in any one of the preceding claims, in which the drive coil is arranged coaxially with the longitudinal axis of the control lever in the normal rest position of the latter, the pick-up coils being arranged with their axes parallel to the axis of the drive coil.

7. A control unit as claimed in Claim 6, in which the armature member is in the form of a disc arranged between the control lever and the drive and pick-up coils, the plane of the disc being substantially perpendicular to the longitudinal axis of the control lever.

8. A control unit as claimed in Claim 7, in which each pick-up coil has a core which projects beyond the coil towards the armature disc.

9. A control unit as claimed in any one of the preceding claims, in which a housing is attached to the fixed support and encloses the pick-up coils, the housing having a cover plate with an aperture through which the control lever projects with clearance, the edge of said aperture defining the limits of angular movement of the control lever.

10. A control unit as claimed in Claim 9, in which a bearing sleeve is freely rotatable upon the control lever and arranged to come into contact with the edge of the aperture in the cover plate upon displacement of the control lever to the limits of its angular movement.

11. A control unit as claimed in any one of the preceding claims, in which the drive coil is connectible to a cyclically alternating current source and the pick-up coils are connected to a signal processing circuit which processes the signals detected by the pick-up coils to provide an output or outputs dependent upon the angular movement of the control lever from a rest position.

12. A control unit as claimed in Claim 11, in which there are four symmetrically arranged pickup coils diametrically opposite pairs of which are connected to respective comparator circuits which provide outputs representative of the angular displacement of the control lever in respective mutually perpendicular planes.

13. A manual control unit substantially as herein described with reference to and as shown in the accompanying drawings.

New Claims or Amendments to Claims filed on 24th Sepa.1979.

Superseded Claim 1.

New or Amended Claims:

1. A manual control unit comprising a drive coil mounted on a fixed support, a number of pickup coils arranged symmetrically on the support around the axis of the drive coil, an armature member of magnetic material coupled magnetically to the drive coil and the pick-up coils, and a manually operable control lever movable angularly about a fulcrum which is located symmetrically with respect to the pick-up coils, the armature member being so arranged that angular movement of the lever in any direction results in a proportional change in the magnetic coupling, between the drive coil and at least two of the pick-up coils.