GB2284672A - Magnetically actuated switch assembly - Google Patents

Abstract

A switch assembly 11 for electrical or electronic use, has a main body 13 formed with a central aperture 15 which receives a button 31. The button supports a permanent magnet 43 and the main body supports a permanent magnet 19, the magnets being arranged with like poles facing each other to provide repulsion resulting in the button being biased outwardly from the main body. An aperture 45 is provided in the main body, offset from the central axis of the button and extending to a position alongside the space between the magnets. Located within the aperture is a semiconductor device in the form of a hall-effect sensor 47, which is soldered to a printed circuit board 25. The hall effect sensor is located at an appropriate depth within the aperture to sense the variation in the magnetic field due to movement of the magnets relative to each other. A circuit may be connected to the hall effect sensor to provide switching function in response to the button being pressed. A coil or a reed switch may be used in place of the hall effect device. <IMAGE>

Description

"SWITCH ASSENBLY" This invention relates to switches and in particular switch mechanisms.

Hitherto, known switches have included some mechanical arrangement such as a mechanical return spring, to provide resilience for returning the switch to its unoperated condition, after operation. Such an arrangement may be prone to failure, through wear of the spring and associated parts, particularly in harsh environments.

It is an object of this invention to provide a switch having a return mechanism which may overcome the aforementioned difficulty, or at least provide an alternative.

In accordance with one aspect of the present invention there is provided a switch assembly including a base supporting an actuator for movement between an operated position and an unoperated position, wherein said switch assembly includes magnetic repulsion means to bias said actuator away from said operated position, and sensing means to sense the change in magnetic field associated with said magnetic repulsion means, when said actuator is moved.

Preferably said magnetic repulsion means comprises a first magnet located in said actuator, and a second magnet located in said base in repulsive alignment with said first magnet, to repel said actuator.

Preferably said switch assembly includes control means having a sense input connected to said sensing means, and output means adapted to provide a change in status in response to movement of said actuator between said unoperated position and said operated position.

Preferably said sensing means and/or said control means is arranged to provide a change in status in response to said actuator being moved substantially to said operated position.

Preferably said sensing means comprises a hall effect sensor located in proximity to the first magnet, to sense movement thereof, when said actuator is moved.

Alternatively, said sensing means comprises a wound coil located in proximity to the first magnet, to sense movement thereof, when said actuator is moved.

As a further alternative, said sensing means comprises a switch responsive to the variation in magnetic field of said first magnet resulting from movement of said actuator between said unoperated position and said operated position.

Preferably said switch comprises a hermetically sealed reed switch located to switch in response to movement of said first magnet.

The invention will now be described with reference to the following description of one specific embodiment thereof, made with reference to the following drawings, in which: Fig. 1 is a cross-section of a switch assembly according to the embodiment; Fig. 2 is an orthographic projection of the switch assembly shown in Fig. 1; and Fig. 3 is a block circuit schematic of circuitry associated with the switch assembly of Figs. 1 and 2.

The embodiment is directed towards a switch assembly 11 as shown in Figs. 1 and 2. The switch assembly 11 includes a base in the form of a main body 13 formed with a central aperture 15 extending therethrough. The central aperture 15 includes an annular step 17 having a diameter sufficient to support, by friction fit, a circular permanent magnet 19.

The main body 13 is formed of polycarbonate plastic and includes a front face 21 and a rear face 23. Mounted to the rear face 23 of the main body 13 by any suitable means such as self tapping screws, is a printed circuit board 25. The rear face 23 includes a circular recess 27, for accommodating electronic components (not shown) mounted to the inner face of the printed circuit board 25.

Set in the front face 21 of the main body 13 is another circular recess 29 in which is received an actuator in the form of a press button 31 and an annular retaining insert 33. The annular retaining insert is secured in the circular recess 29 against the wall thereof as a friction fit, and is provided with a rear face 35, while the circular recess 29 is provided with an annular ledge 37. The press button 31 includes an annular step 39 which is arranged to contact the rear face 35 of the annular retaining insert 33, when the press button 31 is in the unoperated position, and on the other side, contact the annular ledge 37 in the circular recess 29, when the press button 31 is pushed to the operated position.

The press button includes a projecting portion 41 in which is supported a further permanent magnet 43. The two permanent magnets 19 and 43 are arranged with facing surfaces having like polarity, so as that they repel each other, and consequently bias the press button 31 outwardly to the unoperated position, as shown in Fig. 1. The permanent magnets 19 and 43 are shown with north poles in juxtaposition, although, as will be understood, the repulsion would be equally effective with south poles in juxtaposition. As will also be understood, the press button 31 has sufficient clearance within the main body 13, so as to be freely movable, with the application of force on the press button 31 to overcome the repulsion generated by the magnets 19 and 43.

An aperture 45 is provided in the main body 13, offset from the central axis of the actuator, extending to a position alongside the space between the permanent magnets 19 and 43. Located within the aperture 45 is a semiconductor device in the form of a hall-effect sensor 47, which is soldered to the printed circuit board 25. The hall effect sensor is located at an appropriate depth within the aperture 45 to provide sensitivity to the variation in the magnetic field due to movement of the magnets 19 and 43 relative to each other.

Referring to Fig. 3, a suitable schematic is shown, for interfacing between the hall-effect sensor 47 and a switching device. In the embodiment exemplified, the switching device is a relay 49, which is driven by a transistor 51. The hall-effect sensor 47 is connected via suitable interface circuitry (not shown) to an opamp 53. Also connected to the op-amp is a potentiometer 55, adjustment of which will allow for differing sensitivities inherent in different fieldeffect sensors 47. The polarity of input of the potentiometer 55 and the hall-effect sensor to the opamp 53 is not shown, as it is dependent on the manner in which the hall-effect sensor 47 is interfaced to the op-amp 53.In order to interface the hall-effect sensor 47 to the op-amp, the reader is assumed to have a basic knowledge of the operation of op-amps, and is also referred to data provided by the manufacturer of the hall-effect sensor to be utilised.

The other elements included in the circuit shown in Fig. 3 are a resistor 57, which provides current limiting of IBE of transistor 51, and a diode 59 for shunting "back-emf" from the coil of the relay 49, on de-energisation thereof.

Having described the invention, it should be clear how modifications may be made without departing from the spirit and scope of the invention. For example, the hall-effect sensor may be replaced with an electromagnetic coil, and a suitable interface circuitry provided on the printed circuit board 25, in order to detect magnetic field changes associated with movement of the permanent magnet 43.

Furthermore, the circuitry may be interfaced to more than merely a relay. For example, the outputs of the op-amps (or other interface if employed) in a system utilising a plurality of such switch assemblies made according to the invention may be scanned in a multiplex system for interface to a microprocessor or the like.

It will be noted that in the embodiment shown in Fig.

1, the relationship between the magnets 19 and 43 is such that they are separated from each other by an annulus extending from the projecting portion 41, as a result of the magnet 43 being recessed in the projecting portion 41. This prevents the repulsion between the magnets being overcome, as can occur in certain types of magnet. This recessing may not be necessary with some permanent magnets, as simple trials will show.

It will be understood that in applications where the switch is intended to be utilised in a dusty environment, it may be desirable to include a rubber boot between the actuator and the housing, to prevent the actuator from becoming jammed.

It should be appreciated that the scope of the invention is not limited to the description of the embodiment described herein.

Claims (9)

1A switch assembly including a base supporting an actuator for movement between an operated position and an unoperated position, wherein said switch assembly includes magnetic repulsion means to bias said actuator away from said operated position, and sensing a means to sense the change in magnetic field associated with said magnetic repulsion means, when said actuator is moved.

2 A switch assembly as claimed in Claim 1 wherein said magnetic repulsion means comprises a first magnet located in said actuator, and a second magnet located in said base in repulsive alignment with said first magnet, to repel said actuator.

3 A switch assembly as claimed in Claim 1 or 2 including control means having a sense input connected to said sensing means, and output means adapted to provide a change in status in response to movement of said actuator between said unoperated position and said operated position.

4 A switch assembly as claimed in Claim 3 wherein said control means is arranged to provide a change in status in response to said actuator being moved substantially to said operated position.

5 A switch assembly as claimed in any one of the preceding Claims wherein said sensing means comprises a hall effect sensor located in proximity to the first magnet, to sense movement thereof, when said actuator is moved.

6 A switch assembly as claimed in any one of Claims

1 to 4 wherein said sensing means comprises a wound coil located in proximity to the first magnet, to sense movement thereof, when said actuator is moved.

7 A switch assembly as claimed in any one of Claims

1 to 4 wherein said sensing means comprises a switch responsive to the variation in magnetic field of said first magnetic resulting from movement of said actuator between said unoperated position and said operated position.

8 A switch assembly as claimed in Claim 7 wherein said switch comprises a hermetically sealed reed switch located to switch in response to movement of said first magnet.

9 A switch assembly substantially as described herein, with reference to the description of the embodiment.