AU595424B2

AU595424B2 - Improvements to microwave ovens

Info

Publication number: AU595424B2
Application number: AU11647/88A
Authority: AU
Inventors: Maxwell Gervaise Maxwell
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-02-13
Filing date: 1988-02-11
Publication date: 1990-03-29
Anticipated expiration: 2008-02-11
Also published as: AU1164788A

Description

A 4 14 UBT tLIA <<4g P/00/0 1 Form PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE r Short Title: Int. Cl: CHEQUE TO VALUE OF AToAC'HED MAIL OFFICER 595424 Application Number: fl 0324; Lodged: 13 /2/87 SCmpete Specification-Lodged: Accepted:- Lapsed: Published: 1328 @:too: Related Art: Nam ofAplcat

MAUSTRALIAN

PATENT OFFICE TO BE COMPLETED BY APPLICANT MAXWELL GERVAISE MAXWELL 0 *Addtess of Applicant: Actual Inventor: Address for Service:, 40, WUNULLA ROAD, POINT PIPER, NSW 2027 PAMF1N F UTI1.

MAXWELL GERVAISE MAXWELL oOrof Pubic~ monor" 40, WUNULLA ROAD, POINT PIPER, NSW 2027 Complete Specification for the Invention entitled: IMPROVEMENTS TO MICROWAVE OVENS.

The following statement is a full description of this invention, Including the best method of performing It known to me.- Note:, The description Is to be typed In double spacing, pica type face, In an area not exceeding 250 mm In depth and 160 mm In width, on tough white paper of good quality and It Is to be Inserted Inside this form, 14599/78-L 14599/78-LPrinted by C. J.T~ommsN, Commonwealth Government Printer. Canberra.

1 A microwave oven consists basically of a metal box into which microwave frequency energy is injected to heat or cook food placed therein.

Because this energy produces radiation which may be injurious to health, steps must be taken to ensure that the generator cannot operate while the door of the oven is open and this is typically achieved by means of switches in the generator power supply circuit such that when the door is open the switches are open and power to the generator is cut off so that the generator cannot operate. When the door is closed the switches are closed and power is supplied to the generator enabling it to operate.

The electrical circuit of this switching arrangement as used in current designs of microwave oven is shown in Figure 1 where the switches above referred to are designated Sl and S2 and these are connected in series between the power supply and the microwave generator. Sl and S2 are mechanically linked to the door such that they are in their closed position when the door is closed and in their open position when the door is open or partly open. Two switches are used so that if either one fails with its contacts in the closed position the other switch performs the switching function. Because both switches may fail in the closed position a third switch, shown as S3, is also mechanically linked to the door so that when the door is closed switch S3 I is open.

*too o Operation of these three switches is so timed that when the oven door is closed S3 opens before SI and S2 close.

25 If both Sl and $2 fail in their closed position and the oven door *se is opened S3 closes and applies a short circuit across the microwave generator power supply causing fuse F to blow and cut off power to the generator.

The mechanical arrangement used to operate these switches in an oven e 30 of typical design is shown in Figure 2. This arrangement is complex e"0* and therefore costly to manufacture and costly to repair in the event of any failure. Moreover, the arrangement does not provide complete protection against hazardous radiation as all three switches can fail S. allowing the microwave generator to operate with the oven door open.

The invention described herein provides a means of eliminating the the three switch arrangement used in current design microwave ovens thereby reducing manufacturing and repair costs and it .provides a degree of protection against hazardous radiation higher than that of ovens employing the three switch system above described.

In Figure 3, Cl represents two contacts mounted on the body of the oven and C2 represents two contacts, connected together, mounted in a corresponding position on the oven door such that with the door closed the two pairs of contacts engage one with the other to form an electrical connection through which current from the power supply 'flows to the microwave generator. When. the door is opened, contacts Cl and C2 disengage to interrupt the power supply to the generator and the generator is thereupon switched off while the door is open.

Short circuit between contacts Cl and short circuit between the wires connected to Cl, which would negate the door switching function, is prevented by cogventional means not forming part of this invention.

2 A particular embodiment of the invention will now be described with reference to Figure 4 Two separate contacts Cl and C2 are fixed to the body of the oven at the side of the door aperture remote from the hinge, one contact adjacent to the top of the door aperture and the other contact adjacent to the bottom of the door aperture.

Two corresponding contacts are fixed to the door such that with the door closed each contact makes electrical connection with its corresponding oven body contact. The two door contacts are connected together within or at the door..

Closing the door completes the power supply circuit to the microwave generator allowing it to operate when power is applied to the microwave generator power supply circuit. Opening the door breaks the generator power supply circuit preventing operation of the generator while the door is open.

This embodiment of the invention, where the door/oven body contacts are adjacent to the extremities of the door aperture provides a means of complying with the international microwave oven safety standard International Electrotechnical Commission Publication 335-25 which re- 20 quires that opening of the door of a microwave oven operates a minimum of two interlocks (switches) and that these monitor two different parts o*o, of the door to minimise the effects of warping.

S

A second embodiment of the invention will now be described with reference to Figure 5 The oven door and oven body contacts above described are likely to to be damaged by arcing when the respective contacts make or break the microwave generator power supply circuit, particularly if the door is opend or closed slowly or left in a position where contact is not firmly maintained.

30 This embodiment provides a means of ensuring that the door cannot o be opened or closed slowly or left in a position where contact between door and oven body contacts is not positive.

Each door contact consists of a "finger" of springy metal, the end of •the finger being formed as shown in Fig. 5. The interior of each oven 35 body contact insulating moulding, in which the door contact finger moves, is formed to contain a depression such that when the door is being closed the tip of the finger locates firmly in the depression and further movement of the finger is resisted. To close the door fully, additional force is required and as this force is applied a point is reached where the resistance is suddenly overcome and the door and door/oven contacts close rapidly.

With the door fully closed the tip of the door contact finger seats in the moulding holding the door closed with door/oven contact firmly established.. When the door handle is pulled to open the door, movement of the door is resisted by the finger tip seated in the door contact moulding. As the pull is increased, the resistance is suddenly overcome and the door and door/oven contacts open rapidly, 1 3 The arrangemr it illustrated in Figure 5 ensures that the microwave generator cannot be activated by pushing one end of a wire into one oven body contact moulding and the other end of the wire into the other oven body contact moulding as each end of the wire will go through the moulding past and without touching the oven body contact.

END OF TEXT.

Claims and four drawings follow.

S e @es 0* 0 S* 9 s S 0 S o 6i 0 S e

I

II rl I