GB2030772A - Electro-mechanical interrupter with variable on/off ratio - Google Patents

Abstract

A timing device suitable for use in a microwave oven, for example to defrost food by a series of repeated bursts of microwave energy, comprises a microswitch 20 cyclically operated by a movable member 17 mounted on a pivoted lever 14. Timing cam 13 moves the lever 14 and member 17 back and forth in a fixed cycle to operate the switch and start and end the bursts of energy. A manually adjustable cam on shaft 22 can move the member 17 up and down on lever 14 so that the distance between surface 18, which is not parallel to lever 14, and the switch may be varied. This adjustment alters the time in the fixed cycle at which the microswitch is operated and therefore the lengths of the repeated bursts of microwave energy. More than one microswitch 20 may be provided for conjoint actuation by member 17. <IMAGE>

Description

SPECIFICATION Timing device This invention relates to an electro-mechani cal timing device providing a variable timed interval.

The invention provides an electro-mechani cal timing device having electrical switch means operable by a surface of a movable member, which member is movable in two senses, one being a cyclic movement towards and away from said switch means in a fixed timing cycle to operate said switch means, and the other being an adjusting movement along a line not parallel to said surface where by to vary the gap between said surface and the switch means and thereby the point of time in said cycle at which the switch means is operated.

Preferably said movable member is mounted to slide on a lever to provide said adjusting movement, and the lever is pivotally mounted to provide said cyclic movement.

The lever may at one end bear on a rotatable timing cam which drives the lever in said cyclic movement. The adjustment movement may be controlled manually via an adjustment cam bearing on said movable member. Said switch means may comprise a microswitch or a pair of microswitches both operated by said movable member.

The timing device may be intended for use in an electric oven (e.g. a microwave oven) to provide a defrost or cooking capability in which the oven is turned 'on' and 'off' in a cyclic manner, the time for which it is 'on' in each cycle being adjustable on a fixed time base.

A specific embodiment of the invention is shown in the accompanying drawings, in which Figure 1 is a plan view of a microwave oven timing device with a cover plate re moved, Figure 2 is a side view of the embodiment of Fig. 1, Figure 3 is a plan detail of a lever cam of Fig. 1, Figure 4 is an end view of the lever cam of Fig. 3, Figure 5 is a detail plan view of a timing cam of Fig. 1, and Figure 6 is a detail plan view of an adjust ing cam of Fig. 1.

Referring first to Figs. 1 and 2, the timing device comprises an electric motor 11 and gearbox 1 2 driving a shaft (not shown) having an axis A, the shaft carrying therewith a timing cam 13, seen best in Fig. 5. Timing cam 1 3 rotates continuously when the device is powered, and is followed by one end of a lever 14. The other end of lever 14 pivots about a slot in a housing for the device and a spring 1 5 urges the lever in the sense to remain in contact with the timing cam.

A lever cam 1 7 (Figs. 3 and 4) is mounted on lever 1 4 so as to take part in its pivotal movement, in which movement surfaces 1 8 of the lever cam contact the operating buttons of a pair of microswitches 20 mounted side by side. As the timing cam 1 3 rotates, the microswitches 20 are switched 'on' and 'off' once in each revolution. An appliance controlled by the microswitches is therefore turned on for a predetermined length of time once per revolution.

To adjust the predetermined length of 'on' time for different requirements, an adjustment cam 21 (Fig. 6) is mounted on a manually rotatable shaft 22, independently of the timing cam. The adjustment cam 21 bears on a top surface 22' of the lever cam 1 7. The mounting of the lever cam 1 7 on lever 14 provides for sliding movement of the lever in grooves 23. The lever cam is pushed along the lever by the rotation of adjustment cam 21 against the resistance of a spring 25 attached to a foot 26 on the lever cam and to an arm 27 cut out and bent over from the lever 14.

The lever cam 1 7 is of tapered shape, the switch operating surfaces 1 8 not being parallel to lever 14 so that its movement up and down lever 14 varies the distance between surfaces 1 8 and the buttons of the microswitches 20. Therefore the distance to be moved toward the buttons by lever cam 1 7 to operate the microswitches is also varied, and thus also the points in time in the unvarying cycle of timing cam 1 3 at which the switches are turned 'on' and 'off' can be altered.

Consequently the period of time for which the appliance is 'on' may be set by manually turning shaft 22 to a position selected against an index (not shown) to provide the required time interval.

The microswitches are mounted together on a plate 29, the position of which may be adjusted via slot 30 in order to calibrate the switching point. Although two microswitches are described here, of course the lever cam 1 7 could operate one switch only or more than two.

The timing device shown is specifically intended for use in a microwave oven for cooking and defrosting of food placed therein. It is found that defrosting and cooking of certain kinds of food is best carried out in a cyclic mode by separate repeated bursts of microwave energy, smaller articles of food requiring shorter bursts of energy. The manual selection made by turning shaft 22 may therefore be against an index marked from large to small articles, the selection of "large" corresponding to longer time intervals for which the oven is 'on'. The oven is then turned 'on' once in each revolution of the timing cam 13, the length of time for which it is 'on' having been selected by shaft 22.

The user must, therefore, select a cyclic mode via switches (not shown) which commence operation of the motor 11, and also select a suitable time interval through shaft 22.

While the timing device has been described particularly with reference to a microwave oven timer with provision for variable repeated bursts of energy, it may be used for any repeated operation where it is desired to vary the time for which an appliance is working, e.g. for a heating device.

Claims (8)

1. An electro-mechanical timing device having electrical switch means operable by a surface of a movable member, which member is movable in two senses, one being a cyclic movement towards and away from said switch means in a fixed timing cycle to operate said switch means, and the other being an adjusting movement along a line not parallel to said surface whereby to vary the distance between said surface and the switch means and thereby the points in time in said timing cycle at which said switch means is operated.

2. An electro-mechanical timing device as claimed in claim 1, wherein said movable member is mounted to slide in a linear path along a lever to provide said adjusting movement, the lever being pivotally mounted to provide the cyclic movement which consists in arcuate movement about a pivot point.

3. An electro-mechanical timing device as claimed in claim 2, wherein an adjustment cam rests against one end of said movable member and is rotatable to impart said linear adjustment movement to the movable member, a spring urging said movable member into contact with the cam.

4. An electro-mechanical timing device as claimed in claim 3, including means for manually rotating the cam to a selected position.

5. An electro-mechanical timing device as claimed in any of claims 2 to 4, wherein a rotatable timing cam bears on said lever to drive it back and forth about its pivot.

6. An electro-mechanical timing device as claimed in claim 5, including a motor connected to rotate said timing cam.

7. An electro-mechanical timing device as claimed in any of claims 1 to 6, wherein said switch means comprises one or more microswitches of which the or each operating button is located to be operated by the movable member.

8. An electro-mechanical microwave oven timing device substantially as described hereinbefore with reference to the accompanying drawings.