GB2084436A - Microwave Oven - Google Patents

Abstract

The oven has a shelf 26 for supporting articles to be cooked. The shelf is supported on four posts 28 at its corners and to which are attached for example knife edges 154 resting in V troughs attached to arms 158 pivotally mounted at 162 and acting on a leaf spring 94 terminating in a septum 46 which obturates the light reaching a photocell 42 from a light source 44 to an extent dependent upon the weight of the article on the shelf 26. Alternative embodiments employ variations in the mechanical structures operatively connecting the posts 28 to sensing means which may be mechanical rather than optical. The signal from the photocell 42 is converted to a digital signal indicative of the weight of the article and this signal is one of the input signals to a microprocessor determining the amount of time for cooking the article. The posts 28 are of small cross- section and pass through apertures in the bottom wall 24 of the oven cavity small enough to prevent the escape of microwave energy. <IMAGE>

Description

SPECIFICATION Microwave Oven Microwave ovens have used timing systems to control automatically the duration of time of application of microwave energy to a food body in the oven. In addition, the average level of mircrowave energy applied to the oven has been adjusted for different types of food. However, such systems have relied on an estimate of the weight of the food body or have required separately weighing the food body before putting it in the oven.

According to the present invention, there is provided a microwave oven comprising an enclosure and means for controlling the supply of microwave energy to the interior of the enclosure; means positioned in the enclosure for supporting a body to be processed with microwave energy in the enclosure; and weight sensing means positioned outside the enclosure and actuated by the body supporting means within the enclosure for supplying signals to the controlling means.

In the preferred embodiment a substantially microwave transparent shelf in the oven is supported on a plurality of low microwave loss posts, made for example of ceramic or plastics material, which extend through apertures in the bottom of the oven and rest on a weight sensing means outside the microwave enclosure. The weight sensing means supplies a signal through a variable frequency pulse oscillator to a digital processor through an interface which converts the measured weight to a digital data signal in accordance with well-known practice. The processor is also supplied with digital information from manual inputs such as touch pads to provide inputs of the kind of food body and the desired cooking conditions for the food body.Thus, the weight of the food body may be used to compute -the amount of microwave energy to be applied to the food body to achieve a given degree of cooking The apertures in the bottom of the microwave enclosure, through which the microwave transparent posts supporting the shelf extend, have traverse dimensions substantially less than an effective one-half wavelength at the microwave frequency so that substantially no microwave energy leaks from the microwave enclosure through these apertures. Sufficient support for the shelf with such support posts and apertures of a small size can be achieved by providing several spaced posts, sufficient to carry any desired load while still retaining microwave integrity of the enclosure.

The microwave transparent shelf supporting the food body within the enclosure is spaced from the metallic bottom of the microwave enclosure so that microwave energy is readily coupled through the microwave transparent support shelf into the under side of the food body.

The microwave oven enclosure can be supplied with microwave energy through a coaxial line energizing a rotating primary radiator within the oven. By positioning the primary radiator in the upper region of the oven and selectively producing radiation into the oven from a plurality of spaced regions having different polarization orientations, a uniform pattern of direct radiation toward the food body can be achieved so that coupling of the energy into the fobd body becomes substantially the same for different locations of the food body on the support shelf.

Thus, the cooking achieved by weight programming of the oven control is the same when the food body at substantially any location in the general central rigion of the support shelf and will produce substantially the same degree of cooking of a given food body. Preferably, the support posts for the shelf are positioned outside the central region of the shelf so that the shelf will be mechanically stable. Also, relatively inexpensive weight sensing means may be positioned beneath the lower surface of the microwave oven enclosure and can be used to produce reasonably accurate electrical signals for input to the data processor control system.

The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a diagram of a microwave oven embodying the invention; Fig. 2 is a vertical sectional view of the microwave oven taken along line 2-2 of Fig. 3; Fig. 3 is a vertical sectional view taken along line 3-3 of Fig. 2; Fig. 4 is a transverse sectional view taken along line 4- 4 of Fig. 2; Fig. 5 is a vertical sectional view of an alternative embodiment of the invention, taken along line 8-8 of Fig. 6; Fig. 6 is a transverse sectional view taken along line 6-6 of Fig. 5; Fig. 7 is a vertical sectional view taken along line 7-7 of Fig. 6;; Fig. 8 is a transverse sectional view taken along line 8-8 of Fig. 6; Fig. 9 is a vertical sectional view of an alternative embodiment of a microwave oven incorporating the invention taken along line 9-9 of Fig. 10; Fig.10 is a transverse sectional view taken along line 10-10 of Fig. 9; Fig. 11 is a vertical sectional view taken along line 11-11 1 of Fig. 10; Fig. 12 is a vertical section taken along line 12--12 of Fig. 10; and Fig. 1 3 is a vertical sectional view taken along line 13-13 of Fig. 10.

Referring now to Fig. 1, there is shown a microwave oven 10 of the type disclosed in Figs.

2-4. The microwave oven 10 has an enclosure 12 and a front control panel 50 which contains touch pads 52-62, 1 74 and 1 76 labelled heat units, power level, start, stop reset, zero, dish, weight and cook time respectively whose functions will be described presently. Touch pads 60, 62, 1 72 and 174 have individual lights 66, 68, 70 and 72 respectively which indicate when the particular touch pad is touched. A digital processor 74 contains a micro-processor 76, a read only memory 78, a random access memory 80 and an interface 82 is used to control the operation of a high voltage power supply 84 supplying the magnetron 22 whose microwave output is supplied via a waveguide 20 and a coaxial feed 16 to a rotating primary radiator 18.

The digital processor 74 may be, for example, the "Superkim" digital processor manufactured by microproducts of Redondo Beach, California.

However, for production economy, a special printed circuit board omitting the unused portions of the "superkim" may be used to save both space and cost. The touch pads of front panel keyboard 50 are connected to the interface 82 in a similar fashion to the conventional "superkim" keyboard and data for display of the lights on panel 50 is also supplied through the interface 82.

The support shelf 26 supporting a food body 40 in a dish 1 76 actuates weight sensor 32 whose output is derived via a photocell 42 responding to a light source 44. The intensity of the light from source 44 which falls on photocell 42 is determined by the amount of movement of a septum 46 actuated by the load on support shelf 26 by posts 28 which extend through apertures 30 in the bottom 24 of enclosure 12.

The amount of deflection of septum 46 depends upon the weights of the food body 40, the dish 176, and the shelf 26 acting on the weight sensor 32 against a leaf spring 94. The output of photocell 42 controls the free running pulse oscillator 92 whose pulse rate output varies between 1,000 and 2,000 pulses per second and preferably varies substantially as a linear function of the sensed weight. The output of the oscillator 92 is supplied to the digital processor 74 via the interface 82 which converts the pulse rate to a digital number and directs it to random access memory 80 to be stored.

Referring now to Figs. 2, 3 and 4 there is shown details of a microwave oven 10 which can be used in Fig. 1. Metallic microwave enclosure 12 has an access opening closed by a closure member 1 4 such as a door. Microwave energy is supplied to oven 10 through coaxial connection 1 6 extending through an aperture in the top of enclosure 12 and coupled to a rotating primary radiator 1 8. The central conductor of coaxial line 1 6 extends into waveguide 20 and supplies the radiator with microwave energy from magnetron 22 at a frequency, for example, of 2450 MHz in accordance with well-known practice. Air from a blower 86 is directed through waveguide 20 and into enclosure 12 to rotate radiator 1 8.

There is positioned above the bottom wall 24 of enclosure 12 a support shelf 26 made of substantially microwave transparent material such as Pyrex (Registered Trade Mark). Support shelf 26 is supported on four low microwave loss posts 28 which extend through apertures 30 in the bottom wall 24 of enclosure 12. Support posts 28 are rigidly attached to a weight sensing mechanism 32 supported on the bottom of microwave oven 10 while microwave enclosure 1 2 is supported, for example, by brackets 34 from the side and/or bottom walls of the cabinet 36 of microwave oven 10. Since the posts 28 are rigidly attached to the sensing structure 32 which is rigidly supported by the frame 36 of the oven, lateral motion of the members is prevented.The support shelf 26 is restricted laterally by ceramic washers 38 glued to the bottom surface of shelf 26 with the support posts 28 extending into the centers of the washers 38. The diameter of apertures 30 is made less than a half wavelength of the freqency of magnetron 22 and preferably is somewhat less than a quarter wavelength thereof so that substantially no microwave energy leaks out of enclosure 12 through apertures 30. Weight sensing element 32 may be a conventional scale element or may be specially designed to supply a digital output indicative of the weight of a load such as a food body 40 supported in enclosure 12 on shelf 26.

The weight sensor 32, as shown herein, has the frame 36 supported on the floor of the cabinet of oven 10. The posts 28 are rigidly connected to metal knife edge elements 1 54 which rest in V-shaped troughs 156 welded to arms 158. A pair of arms 1 58 is positioned on each side of the oven with their inner ends connected by a tension loop 1 32 and their outer ends resting via inverted trough portions 162 on knife edge bracket members 1 64 fixed to the frame 36.The inverted trough members 1 62 extend respectively at the front and rear of the oven between the arms 1 58 on each side of the weight sensor 32 so that weight pressure on any post is transferred equally to deflect all of the arms 1 58 via torsion of the inverted trough members 162 and the links 160.

A projection on one of the arms 1 58 presses a leaf spring 94, one end of which is attached to septum 46 and the other end of which is rigidly attached to a block 96 so that the projection 88 on the arm 1 58 forces the arms upwardly under the spring pressure of the leaf spring 94. When a weight is placed in the oven such as a dish or food body, motion of the posts 28 causes the arms 1 58 to move downward at their inner ends depressing leaf spring 94 and hence depressing septum 46 thereby reducing the light from light 44 which is intercepted by photocell 42. Since arms 1 58 and sensing mechanism 32 are removed from the center of oven floor 24, the floor 24 of the oven 10 can be beneath the actual tops of the arms 158 and torsion members 90 so that these members may be sufficiently rugged to transfer the weight to the sensor without interfering with the bottom 24 of the enclosure 12. Hence, the weight sensing mechanism 32 may be installed within the cabinet 36 of oven 10 for existing domestic microwave oven designs.

In the preferred mode of operation, the equipment, having been turned on, energizes weight sensor 32 and digital processor 74. The touch pad 60 is then touched with the oven empty to zero the equipment. Sensor 32 senses the weight of the shelf 26 in the enclosure 12 and stores a zero number in random access memory 80. During this process, the light 66 lights to indicate that this has been achieved. If a dish 1 76 is used for the food body 40, the weight of the dish may be separately stored in the memory 80 by pushing the pad 62 labelled "dish". This lights the light 68 and turns off the light 66. The food body 40 may be then placed in the oven with or without a dish since if no dish were used and the pad 62 labelled "dish" were touched, no additional weight would be stored in the memory 80.Weight pad 64 is then touched, and light 70 lights while light 68 goes out. The weight will appear at numerical display 98. Touching cook time pad 1 74 will light light 72 and the required cooking time will appear in the display units 98 for a preselected cook program in read only memory 78. This may be, for example, the reheat mode indicated by the lowest of the heat units 25 used for reheat or frozen pastry, as indicated by the light 100 and a power level of 100% as indicated by the light 1 02. Different heat units may be selected by sequentially pushing the heat unit pad 52 to cause lights 104-11 8 to be sequentially turned on one at a time extinguishing the previous lower light. If it is desired to reset these lights, touching reset pad 58 will cause the lights to return to their lowest or preset level.

Similarly, by touching power level pad 54, the lights 1 22-1 30 may be selected sequentially moving the cooking level from high or 100% power to warm or 10% power as indicated by light 128. If pad 50 is touched again, zero power light 1 30 lights in which case the display indicates time only. In all other locations, as indicated by lights 120-128, the display 98 indicates the computed time required to cook the food body 40 to the desired level. When the start pad 56 is then touched, the cooking proceeds at the selected heat unit level and power level until the appropriate time has elapsed with display 98 continuously showing the remaining cook time.

When the remaining cook time reaches zero, the magnetron 22 is deenergized by deenergizing the power supply 84. Also, an indicator such as an alarm bell, not shown, may be energized to give the operator an audible indication that the cooking program is completed.

This mode of operation of the unit eliminates cooking errors which might occur by programming in the weight of the food manually since the automatic control of the power supply by a food weight sensed in the oven at the time the start button is pressed prevents inadvertent manual insertion of erroneous data. Thus, it may be seen that any desired program may be stored in the read only memory 78 to provide necessary indications of the start and the stop.In addition, since the lights 100--130 indicate the input to the digital processor program and the computed function is indicated by the light 66-72, the computed result supplied by the microprocessor, as indicated by the display units 98, provides a simple substantially error-free checking mode in which the manually inputted data is indicated by the lights and the digitally processed result is indicated by the display 98.

Referring now to Figs 5-8, there is shown an alternative embodiment of an oven having a weight sensor 32 in which torsion members 90 transfer weight from the posts 28 to arms 1 58 which are connected by separate tension members 1 32 through a coil spring 134 to a bracket 136 connected to the enclosure 12.

When the food body 40 applies torque to the arms 158, their inner ends are depressed and the septum 46 moves between the photocell 42 and the light source 44 to cause changes in the output of photocell 42.

Referring now to Figs. 9-1 3, there is shown a still further embodiment of the invention wherein the posts 28 rest on movable frame members 138 which, in turn, are carried by the free ends of a pair of centre supported leaf springs 140.

Connection of the free ends of springs 1 40 to the frame members 138 is via adjustable screw members 1 42 which provide for levelling adjustment of the scale. A central channel member 144 is rigidly connected between the frame members 138 and carries the septum 46 which then moves between light 44 and photocell 42.

Zero adjustment of the unit is provided by supporting light 44 and photocell 42 on a separate support plate 146 which is adjustably attached to the oven cabinet 36 by screws 148 and springs 1 50 so that the weight sensor 32 may be zero adjusted.

Among many possible modifications, a strain gauge could be substituted for the light 44 and photocell element 42, various contours could be used for the edge of the septum 46 and any desired digital processing program could be used.

This application is one of four related applications tabulated as follows (including the present application): Reddie 8 Grose Application No. File No.

(1) 81/25743 24417 (2) 81/25744 24418 (3) 81/25745 24419 (4) 81/25746 24420 Applications (2), (3) and (4) have the same drawings and description thereof. The subject matter of each application can be indicated briefly as follows: (1 Microwave oven with external weighing mechanism for weighing article in oven cavity.

(2) Combination of weight information with user setting of kind of cooking or heating function to determine energy input.

(3) Non-linear relationship between energy input and weight.

(4) Microwave seal between external weighing mechanism and plate supported thereby inside the oven cavity.

Claims (8)

Claims

1. A microwave oven comprising an enclosure and means for controlling the supply of microwave energy to the interior of the enclosure; means positioned in the enclosure for supporting a body to be processed with microwave energy in the enclosure; and weight sensing means positioned outside the enclosure and actuated by the body supporting means within the enclosure for supplying signals to the controlling means.

2. A microwave oven according to claim 1, wherein the weight sensing means is actuated by a plurality of posts extending through apertures in a wail of the enclosure to the supporting means.

3. A microwave oven according to claim 2, wherein the maximum transverse dimensions of each said aperture is less than an effective onehalf a free space wavelength of the microwave energy.

4 A microwave oven according to claim 1,2 or 3, wherein the microwave energy is supplied by radiating means comprising a rotating primary radiator supplied by a coaxial line whose central conductor extends through a wall of the enclosure.

5. A microwave oven according to claim 4, wherein the central conductor extends through the upper wall of the enclosure.

6. A microwave oven according to claim 4 or 5, wherein the radiator radiates a plurality of different patterns of microwave energy toward a load positioned on the load supporting means.

7. A microwave oven according to any of claims 1 to 6, wherein the supporting means is substantially transparent to microwave energy.

8. A microwave oven according to any of claims 1 to 7, wherein the controlling means is means for supplying microwave energy to a rotating radiator in said enclosures comprising a source of a digitally controlled power supply whose digital control input is supplied by signals derived from the weight sensing means and supplying the microwave energy from a source of alternating current.