GB2049294A - Solenoid device with armature position detector - Google Patents

Abstract

A solenoid device includes an armature 11 slidable within a tube 10 which is closed by an end closure 13. The end closure is formed from radiation transmitting material and mounts in an unpressurised zone a radiation emitter 30 e.g. an LED 30 and a radiation detector e.g. a phototransistor. Movable with the armature is a flag member 26 which can vary the amount of radiation reaching the detector as the armature moves. The output of the detector can be used to provide a signal which indicates the position of the armature. <IMAGE>

Description

SPECIFICATION Solenoid devices This invention relates to solenoid devices of the kind comprising an armature slidable within a tube, a winding positioned outside the tube which when energised creates a magnetic field which effects axial movement of the armature within the tube, and an end closure for one end of the tube.

It is often the case that the fluid pressures on the outside and inside of the tube are different. For example where the solenoid device is utilised to determine the setting of a fluid control valve, the interior of the tube may be subject to the pressure at the inlet or outlet of the valve. Moreover, the solenoid device is designed so that there is little friction to impede the movement of the armature so that there is a low mechanical hysteresis. In some cases there is a need to provide an indication of the position of the armature and this can be achieved using a transducer. An external transducer raises problems because of the need to provide a transducer actuating member which passes through the end closure and which therefore needs some sort of fluid seal. The seal creates friction which impairs the operation of the device.

The object of the present invention is to provide a solenoid device of the kind specified in a simple and convenient form.

According to the invention a solenoid device of the kind specified comprises a radiation emitter and a radiation detector, said emitter and detector being mounted so that in use, radiation passes between the emitter and the detector along a path through the material forming the end closure, and a flag member movable with the armature for varying the amount of radiation which in use passes along said path.

One example of a solenoid device in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation of a portion of the device; Figure 2 is an end elevation of the device with parts removed for the sake of clarity; and Figure 3 is an electrical circuit diagram of the device.

With reference to the drawings the solenoid device comprises a tube 10 within which is slidably mounted an armature 11. The armature may be provided with special bearing arrangements to ensure that there is little frictional loss during movement of the armature within the tube 10. Surrounding the tube 10 is a magnetic core structure (not shown) which includes a winding and when the winding is energised, magnetic flux flows along a path which includes the armature, to effect axial movement of the armature.

An end closure member 12 is provided for the tube 10 and it is formed from a radiation transmitting material. By the term radiation we mean visible light together with radiation at both ends of the spectrum.

In the particular example the radiation is infra-red which is generated as will be described, by a light emitting diode (L.E.D.).

The end closure 12 comprises a first cylindrical portion 13 closely fitting within the tube 10 and having formed in its surface a circumferential groove which accommodates a seal member 14. The cylindrical portion is integrally formed with a portion 15 which is of cruciform section as best seen in Figure 2. A step is defined between the two portions and located against the step is a circlip 16 which is located within a groove formed in the internal peripheral surface of the tube 10. The circlip acts to retain the end closure in position against the higher pressure within the interior of the tube as compared with the exterior of the tube.

A hollow cover 17 is provided which acts to retain a mounting ring 18 in position against the end of the tube 10. Conveniently the cover is in screw thread engagement with threads formed on the periphery of the tube.

Formed within the two portions forming the end closure is an axial bore 19 and formed in the cover 17 is an aperture 20 in registration with the aforesaid bore. Passing through the aperture and into the position of the bore which is within the cruciform portion 15 is a manually operable push member 21.

The push member 21 is provided with a circlip 22 engageable with the interior surface of the cover to limit the extent of outward movement of the push member. In addition, the cruciform portion of the end closure member is provided with a fluid seal engageable with the push member 21.

At its inner end the push member is of reduced section and surrounding this portion of the push member is a coiled compression spring 23, one end of which engages against the step defined by the push member and the other end of which locates against the end of a plunger 24 slidable within the bore 19. The plunger extends through the end closure member 12 and mounts a collar 25 upon which is mounted a flag member 26. The flag member 26 as seen in Figure 2 is of plate like form and is located within a slot 27 formed in the portion 13 of the end closure member and its end portion remote from the armature 11 inclines towards the axis of the plunger 24.

In use, the pressure within the tube 10 maintains the push member 21 in its outermost position as determined by the circlip 22. The spring 23 however urges the plunger 24 into contact with the armature 11. Conveniently the end of the armature is provided with a recess 28 which accommodates the collar 25.

Movement of the armature 11 can be effected by moving the push member 21, such movement being imparted to the armature 11 by way of the plunger 24.

The portion 13 of the end closure defines a path for radiation as indicated by the arrows in Figure 2 which are referenced 29. The radiation is generated by an L.E.D. indicated at 30 which is positioned between two limbs of the cruciform section. At the other end of the radiation path 29 is a radiation detector in the form of a photo-transistor 31. Both the L.E.D. and the photo-transistor are mounted in an unpressurised zone and in recesses extending from the ledges defined by the cruciform section.

The radiation path traverses the groove 27 and the amount of radiation (infra-red) which passes along the path is determined by the position of the flag 26.

The transistor 31 is connected in a circuit whereby the varying conduction of the transistor 31 as a result of variations in the radiation reaching it, provides a signal indicative of the position of the armature.

Conveniently the L.E.D. and the transistor are surrounded by metal shields having slits formed therein respectively, the slits facing each other to minimise scatter of the radiation within the end closure.

Conveniently the end closure is formed from a polycarbonate but any other material capable of transmitting the chosen radiation may be utilised providing it also is able to withstand the mechanical stress to which it is subjected.

The mounting ring 18 conveniently acts to locate the L.E.D. and the transistor in the correct position and for this purpose it is provided with an aperture complementary to the section of the cruciform portion of the end closure member and furthermore with apertures through which the connecting leads to the L.E.D. and the transistor pass.

It is convenient to provide a further L.E.D. which is referenced 32 and a further photo-transistor 33 in association with the L.E.D. 30 and transistor 31 and a further radiation path is thus formed which is indicated at 34.

As seen in Figure 3, the two L.E.D.'s 30 and 32 are connected in series with the collecter-emitter path of a transistor 35 and a resistor 36 across a pair of supply lines 37,38. A potentiometer network is connected between the supply lines 37,38 and comprises a pair of series connected resistors 39,40.

The junction of the resistors 39,40 is connected to the base of transistor 35 and the conductive path of the transistor 32 is connected in parallel with the resistor 40. In use, the conduction of the transistor 35 is varied to compensate for variations in the voltage between the supply lines 37, so that the level of radiation of the L.E.D. 30 is maintained substantially constant. This circuit also compensates for variation in the ambient temperature. Moreover, the circuit also compensates for any variation in the translucence of the material forming the end closure such as may occur as the material ages.

In an alternative construction the end closure is formed from metal and has an end wall in which is formed a slot which accommodates the flag. The end wall defines a pair of aligned bores which break out onto the opposite sides of the slot, the bores and slot defining the radiation path. The light emitting diode and the photo transistor are disposed at the outer ends of the bores respectively conveniently in cylindrical recesses extending at right angles to the axes of the bores. Clamping plates are provided which engage the bodies of the light emitting diode and the photo transistor on the opposite sides of the bodies from the ends of the bores and retaining screws are provided which are located in threaded extensions of the bores.

As with the previous example a further light emitting diode and a further photo transistor may be provided for connection in a compensation circuit.

The leads to the diodes and transistors are conveniently led through an epoxy resin body which is cast within a tube engaged around the end closure, the end of the tube mounting an electrical connector.

Claims (16)

1. A solenoid device comprising an armature slidable within a tube, a winding positioned outside the tube and which when energised creates a magnetic field which effects axial movement of the armature within the tube, an end closure for one end of the tube, a radiation emitter and a radiation detector, said emitter and detector being mounted so that in use, radiation passes between the emitter and the detector along a path through the material forming the end closure and a flag member movable with the armature for varying the amount of radiation which in use passes along said path.

2. A device according to claim 1 in which said flag member is mounted for movement on a plunger slidable within a bore formed in the end closure.

3. A device according to claim 2 in which said plunger is spring loaded into contact with the armature.

4. A device according to claim 2 or claim 3 in which said flag member is of plate like form and is located within a slot formed in the end closure.

5. A device according to claim 4 in which said flag member is carried by a collar mounted upon the end of said plunger adjacent the armature, the flag member extending alongside the plunger and having an inclined portion.

6. A device according to claim 5 in which said bore extends through the end closure and there is located within the end portion of the bore remote from the armature a manually operable push member which can through the plunger be utilised to impart movement to the armature.

7. A device according to any one of the preceding claims in which said emitter is a light emitting diode and said detector comprises a phototransistor.

8. A device according to claim 7 in which said end closure is formed from a polycarbonate, the radiation passing through the material forming the end closure.

9. A device according to any one of the preceding claims in which said emitter and detector are located in recesses respectively formed in the end closure and in an unpressurised zone thereof.

10. A device according to claim 4 in which said flag is mounted at the end of the plunger.

11. A device according to any one of claims 1-3 and 10 in which said emitter is a light emitting diode and said detector comprises a photo-transistor.

12. A device according to claim 7 in which said end closure is formed from metal and said path is defined by a pair of aligned bores opening into said slot on the opposite walls thereof.

13. A device according to claim 12 in which said light emitting diode and said photo-transistor are situated at the outer ends of said bores respectively.

14. A device according to claim 13 in which said light emitting diode and said photo-transistor are located in an unpressurised zone, and are clamped against the ends of said bores.

15. A device according to any one of the preceding claims including a further radiation emitter and a further radiation detector mounted on the end closure said further emitter and further detector being connected in circuit with said first mentioned emitter whereby the level of radiation provided by said first mentioned emitter is maintained substan tially constant irrespective of electric supply varia tions and temperature variation.

16. A solenoid device of the kind specified com prising the combination and arrangement of parts substantially as hereinbefore described with refer ence to the accompanying drawings.