Method of controlling the driving of a tray of a microwave oven

Abstract: A microwave oven wherein at least a microwave cooking mode and an electric resistance heater cooking mode can be selected by a user. A tray (12) for supporting foodstuff can be raised and lowered and rotated about a vertical axis. A weight measuring mechanism (45) determines the weight of foodstuff on the tray. During a cooking sequence, an operator selects a cooking mode, and the weight of foodstuff is measured. A controller determines a desired cooking elevation as a function of the cooking mode and weight of the foodstuff. A rotation mechanism (42, 42a, 42b) begins to rotate the tray, and then the rotating tray is raised to the desired elevation, whereupon a cooking operation is performed while the tray is rotated at the desired elevation. At the end of the cooking operation, the tray is lowered to its initial position while still being rotated.

Description: The present invention relates to an oven comprising, a cooking chamber for cooking a foodstuff, a selector enabling a user to select from among various cooking modes, means disposed in the cooking chamber for supporting the foodstuff, elevating means for raising and lowering the supporting means, and control means for operating the elevating means, and to a method of operating an oven comprising a cooking chamber for cooking a foodstuff, a selector enabling a user to select from among various cooking modes, means disposed in the cooking chamber for supporting the foodstuff and elevating means for raising and lowering the supporting means, the method comprising obtaining one or more cooking parameters, including selecting one of the cooking modes Japanese Utility Model Publication (unexamined) No. 94-64013, filed on February 16 1993, discloses a microwave oven that includes a cooking chamber, a food supporting tray, a motor, and a reversible driving means. The driving means passes through the cooking chamber's middle section. The tray is mounted on the floor of the cooking chamber, and is connected to the motor so that it is elevated by the operation of the motor and then caused to rotate. If the motor is reversed, the driving means stops the rotation and moves the tray back down to the initial predetermined position so that it is ready for use. US Patent 4 615 405 and Japanese Laid-open Patent Publication 96-320123 disclose microwave ovens having a weight sensor for sensing the weight of food on a tray of a microwave oven. The US Patent discloses that the cooking time period is calculated as a function of the sensed food weight. Japanese Utility Model Publication (unexamined) No. 90-83891, filed on March 30 1990, discloses a microwave oven that includes a spin chuck table, a rotary tray located on the spin chuck table, and a tray elevating device which raises the tray to a prescribed height. When the tray elevating device goes into action, the tray is elevated and becomes disjoined from the spin chuck table. The tray then rotates, and microwaves generated by a magnetron are uniformly transferred, even to the bottom of the tray. US-A4757173 and US-A-4725703 provide additional background information which the reader may find useful in understanding the present invention. A conventional microwave oven depicted in Figure 7 includes: a metallic cabinet 10; a cooking chamber 11 within the cabinet; a magnetron (not illustrated) which feeds microwave radiation into the cooking chamber 11; a step up voltage transformer 13 which supplies high voltage, above mains voltage, to the magnetron; an electric resistance heater 17 that is mounted in the cooking chamber 11 to cook foodstuffs in the cooking chamber 11 by radiant and convective heat; and a food tray 12 at the bottom of the cooking chamber, which can be elevated and rotated about a vertical axis. In addition, a door (not illustrated) is provided on the front side of the cooking chamber 11, and a cooling fan is provided at the rear of the electrical component compartment 14. The heater 17 can be rotated between horizontal and vertical positions for different modes of cooking. The oven also includes a shaft 31 having an upper end connected with the bottom of the tray 12 and a lower end extending downward to the outside of the cooking chamber 11; an elevation guide member 34 positioned under the shaft 31 to elevate the shaft 31, a motor 32 that rotates the shaft 31 by means of a gear 32a; and a weight sensing unit 35 that is provided under the elevation guide member 34 to measure the weight of a foodstuff on the tray 12. The oven is a combination oven which has a cooking mode which employs radiant heat and convective heat produced by the electric heater 17. Alternatively, cooking can be performed using microwave energy. As is well known in the art, in use, the microwave radiation from the magnetron at a frequency of about 2,450 MHz produces rapid heating of food on the tray. Foodstuffs put on the tray 12 are to be cooked as the tray 12 rotates about a vertical axis and/or after the tray has been elevated. An elevator motor 33 is provided to move the elevation guide member 34 to the right and left between two positions in order to lower and raise the tray, respectively, in Figure 7. The microwave oven performs fast cooking of foods either by microwave energy or radiant/convective heat, and the movement of the tray can be performed during either of those cooking operations. If a user selects grill mode, barbecue mode or pizza-baking mode, by pressing appropriate buttons on an operation panel (not illustrated), the heater 17 is energised, and the guide member 34 is shifted to the position shown in Figure 7 to elevate the tray 12 to a predetermined height. Then, the tray 12 is rotated, and the cooking is performed. The tray 12, however, is always elevated to the same predetermined height without regard to the selected cooking mode. When the elevation of the tray 12 has been completed, the foodstuff on the tray 12 is cooked by microwave energy generated by the magnetron. Once the cooking operation stops, the tray stops rotating and then descends. The above-described conventional microwave oven always performs the cooking operation with the tray positioned at the same height regardless of the user selected cooking mode and the weight of the food. Thus, the heater does not vary the heating applied to the foodstuff according to the cooking mode, and this microwave oven will not therefore perform an optimum cooking function. Furthermore, where the tray has been elevated with the foodstuff offset to one side of the tray, rather than in the middle of the tray, the centre of gravity of the food is offset to that one side, so an imbalanced force is applied to the tray's shaft 31 as the tray moves vertically, which may cause a malfunction in the microwave oven, or may cause the oven to fail to operate. An oven, according to the present invention, is characterised in that the control means determines the desired elevation of the supporting means according to at least one cooking parameter, including the selected cooking mode. Preferably, the oven further includes weighing means for weighing the foodstuff on the supporting means, wherein the cooking parameters include the weight of the foodstuff on the supporting means. Preferably, the oven further includes means for rotating the supporting means about a vertical axis, wherein the elevating means is only operable to raise or lower the supporting means while the supporting means is rotating. Preferably, the oven comprises a microwave oven. More preferably, the microwave oven further includes an electric heater for generating convection heat and radiant heat. A method of operating an oven, according to the present invention, is characterised by determining a desired elevation of the supporting means as a function of at least one of the cooking parameters, and elevating the supporting means to the desired elevation. Preferably, the oven includes a weighing means for weighing the foodstuff on the supporting means, and the cooking parameters include the weight of the foodstuff on the supporting means. Preferably, the oven has a microwave generator for supplying microwaves to the cooking chamber and a weighing mechanism for weighing food disposed on the supporting means, the method comprising the steps of: A) obtaining a first cooking parameter by selecting one of the cooking modes; B) obtaining a second cooking parameter by measuring the weight of the foodstuff after an operation start signal has been input; C) determining a desired supporting means (12) elevation as a function of at least one of the parameters; and D) elevating the supporting means (12) to the desired elevation. More preferably, the microwave oven further includes an electric resistance heater for generating convection heat and radiant heat, step A comprising selecting from among the electric resistance heater and microwave generator to obtain the first parameter. Even more preferably, step C comprises determining the desired supporting means elevation as a function of both the first and second parameters. Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a general flow chart of a control sequence of a microwave oven in accordance with the present invention; Figure 2 is a general flow chart of a control sequence of a microwave oven in accordance with the present invention to avoid overloading of a tray's shaft during elevation and descent of the tray; Figure 3 is a front sectional view of a microwave oven in accordance with the present invention; Figure 3A is a vertical sectional view of an elevation mechanism in the oven according to the present invention; Figure 4 is a block diagram of a control circuit for a microwave oven in accordance with the present invention; Figure 5 is a flow chart of a control sequence of a microwave oven in accordance with the invention; Figure 6 is a flow chart of a control sequence of the microwave oven to avoid the overloading of a tray's shaft during elevation and descent of the tray in accordance with the invention; and Figure 7 is a front-sectional view of a conventional microwave oven. As shown in Figure 3, a microwave oven in accordance with the invention includes a cooking chamber 11, a magnetron 16 which is provided in an electrical component compartment 14 to feed microwave radiation into the cooking chamber 11, and a high voltage generator 13 which supplies high voltage, relative to mains voltage, to the magnetron 16. An electric resistance heater 20 is mounted on the upper side of the cooking chamber 11 to cook foodstuffs in the cooking chamber 11 by radiant and convective heat. A rotary tray 12 is provided at the bottom of the cooking chamber 11, which can be raised and lowered along its vertical rotation axis. To this end, the tray is mounted on a vertically extending shaft 43. A motor 42 delivers torque to a rotary gear 42a which meshes with a gear 42b so as to rotate the shaft 43 and the tray 12. An elevation mechanism 44, actuated by a motor 41, is positioned under the shaft 43, for moving the shaft 43 and the tray 12 up and down. The elevation mechanism 44 may correspond to that disclosed in our US application 08/664 665, filed on June 17 1996. That mechanism, depicted in vertical cross section in Figure 3A, includes a gear element 46b mounted for rotation about a vertical axis coinciding with the axis of the shaft 43. The gear element 46b includes gear teeth 46c which mesh with the teeth of gear 41a. An elevator guide member 44 is affixed to the gear element 46b to be rotated thereby about the axis of the shaft 43. The guide member 44 includes a cylindrical inner surface having a helical groove 44a formed therein. The outer edge of a non-rotatable elevator member 46a is mounted in the helical groove. Thus, when the guide member 44 is rotated about the axis of shaft 43 by means of the gear 41a, the elevator member 46a is caused to rise or descend, depending upon the direction of rotation of the gear 41a. A sleeve 43b is affixed to the lower end of the shaft 43. That sleeve includes an annular groove 43c in which the elevator member 43a is mounted, thereby connecting the shaft to the elevator member 46a for common vertical movement, while permitting the shaft 43 to rotate relative to the elevator member 46a. The shaft 43 includes a vertical slot 43a, and a steel ball 47c is disposed in the slot so as to be interposed between the gear 42b and the shaft 43. Thus, rotation of the gear 42b is transmitted to the shaft 43, and the shaft 43 is able to move vertically relative to the gear 42b. The sleeve 43b is able to travel through a hole formed in a bottom support plate 48a to engage a weight sensing mechanism 45. Any suitable conventional weight sensing mechanism can be utilised, such as that disclosed in the aforementioned US Patent 4 615 405 and Japanese Laid-Open Publication 96-320123. Referring to Figure 4, the main control circuit of the microwave oven includes a control portion 100 which controls the overall operation of the microwave oven from the start of cooking to completion, a power input portion 110 which furnishes the control portion 100 with the electric voltages and current appropriate for its operation, and a manually operable key operating portion 120 used to input to the oven a desired cooking mode and cooking time. A display portion 130 displays various messages and cooking conditions during operation, and a heater driving portion 150 controls the microwave oven's heater 20. The control circuit of the microwave oven also includes a magnetron driving portion 140 which controls the magnetron 16, an elevating motor driving portion 170 that controls the elevating motor 41 for elevating the tray 12 under the control of the control portion 100, a rotary motor driving portion 160 that controls the operation of the motor 42 for rotating the tray 12, and the weight sensing mechanism 45 which measures the weight of the foodstuff on the tray 12. Referring to Figure 1, the steps S1 to S4 give a general overview of a method of controlling the tray of an oven according to certain cooking parameters, including selecting the cooking mode (S1), detecting the weight of the food on the tray (S2), setting the desired tray height as a function of the cooking mode and food weight (S3) and elevating the tray to the desired height (S4). Referring to Figure 2, the steps S11 to S16 give a general overview of a method for avoiding the overloading of the shaft 43 during elevation or descent of the tray 12, including driving the rotating means (S11), raising the tray to the set height (S12), turning the elevating means off (S13), turning the magnetron and/or heater on (S14), lowering the tray to its initial height (S15) and turning the rotating, elevating and heating means off (S16). Figures 5 and 6 further illustrate the features of the invention shown in outline in Figures 1 and 2. Figure 5 shows a method of controlling the tray of an oven in accordance with the invention, including the steps of; selecting one of the cooking modes (S21); determining if a signal to start the operation of the oven has been input to the oven (S22); once the signal is detected, actuating the motor 42 to rotate the tray (S23); measuring the weight of a foodstuff disposed on the tray 12 (S24); setting an elevating height of the tray 12 in accordance with the selected cooking mode and the weight of the foodstuff (S25); operating the elevating motor 41 to raise the rotating tray (S26); determining if the rotating tray 12 has been elevated to the proper preset elevating height (S27); and, if so, de-energising the elevating motor 41 (S28). Cooking then proceeds as the tray continues to be rotated. Referring to Figure 6, a method according to the invention includes the steps of selecting one of the cooking modes (S31); determining if a signal to start the operation of the oven has been input to the oven (S32); once the signal is detected, actuating the motor 42 to rotate the tray (S33); measuring the weight of a foodstuff put on the tray 12 (S34); determining if a predetermined period of time has elapsed (S35); and once the predetermined period of time has elapsed, actuating the elevating motor 41 to elevate the rotating tray 12 to a prescribed height according to the cooking mode and food weight (S36). The method of Figure 6 also includes the steps of determining if the rotary tray 12 has been completely elevated to the prescribed height (S37); de-energising the motor 41 and performing a cooking operation using microwaves and/or heat once the tray 12 (which continues to rotate) has been completely elevated to the prescribed height (S38); determining if the cooking operation is over (S39); operating the elevating motor 41 so as to lower the rotating tray 12 when the cooking operation is over (S40); determining if the elevating motor 41 has returned the tray 12 to the initial position (S41); and de-energising the elevating motor 41 and the motor 42 once the tray has descended completely (S42). Foodstuffs to be cooked are placed on the tray 12. The weight sensing mechanism 45 measures the weight of a foodstuff on the tray by the weight transmitted to the sensing mechanism via the shaft 43. That is, when the shaft 43 is moved down to its lowest position, the weight sensing mechanism 45 compares a preset standard frequency with the frequency of an output signal currently produced by the weight sensing mechanism and determines a difference therebetween to measure the weight of the foodstuff on the tray 12. The motor 42 delivers torque to the rotary gears 42a, 42b to rotate the shaft 43 so as to turn the tray 12. The elevating motor 41 actuates the gear 41a to rotate the guide member 44 and thereby raise the elevator member 46a. The upward movement of the elevator member 46a is transmitted to the shaft 43 so that the shaft and tray, which are rotating relative to the elevator member, are raised. By rotating the tray as it is being raised or lowered, any unbalanced force applied to the tray and shaft due to the effective weight of the food being located at a distance from the centre of the tray, will be continually displaced about the axis of rotation, rather than being concentrated in a single location, so malfunctions which occur in the case of trays which do not rotate while being raised or lowered, can be avoided. The control sequence according to the embodiment of Figure 5 will now be described in detail. First, once power is applied to the microwave oven, a user puts a foodstuff to be cooked on the tray 12 inside the cooking chamber 11, and then selects one of the cooking modes (S21). Second, the control portion 100 determines (S22) if a signal indicating that oven operation is to be started has been input, i.e., if operation is "on". If the operation is "off", the control portion 100 returns to Step 21. Third, if the operation is "on", control portion 100 actuates the rotary motor 42 to rotate the tray 12. Simultaneously, the heater 20 and/or the magnetron 16 goes into action according to the selected cooking mode. For example, if the user selects a warming or thawing mode, the magnetron 16 goes into action, and if a baking or grill mode is selected, the heater 20 goes into action. In an oven-grill mode, the magnetron 16 and the heater 20 are actuated at the same time. Fourth, the weight of the foodstuff on the tray 12 is measured (S24). The load of the foodstuff is transmitted to the weight sensing mechanism 45 during operation of the rotary motor 42, for a period of, for example, 10 seconds. The output signal of the weight sending mechanism 45 changes frequency since the shaft 43 presses against a part of the weight sensing mechanism 45. At this point, the control portion 100 measures the weight of the foodstuff, using the difference between the preset standard frequency and the frequency of the output signal of the weight sensing mechanism 45. Fifth, a desired height of tray 12 is determined (S25) in accordance with the selected cooking mode and the weight of the foodstuff. The controller stores a preset cooking elevation of each cooking mode and then modifies that elevation depending upon the measured weight of food. For example, when it comes to baking a pizza, the tray 12 may be elevated by 10mm from its initial position so that the pizza is cooked to a highly delicious and palatable state. Sixth, the control portion 100 actuates the elevating motor 41, once the desired height of the tray 12 has been determined. The elevating motor 41 operates (S26) to rotate the guide member 44 and thereby raise the elevator member 46a, whereby the shaft 43 is elevated to raise the tray 12 to the set height. Seventh, the control portion 100 determines (S27) if the rotating tray 12 has been elevated to the preset height. If the tray 12 is not at the preset height, the control portion 100 returns to Step 26. If the tray 12 has been elevated to the preset height, the control portion 100 de-energises (S28) the elevating motor 41. The height to which the tray 12 is raised can be regulated by predetermining the distance by which the tray 12 is elevated per second during operation of the elevating motor 41 (i.e. by pre-calculating the linear speed of the shaft 43). For instance, if it is known that the shaft travels 1.41 mm/second, it can be calculated that in order to elevate the tray 12 by 10mm from its initial position, the elevating motor 41 must operate for 7.1 seconds. Accordingly, during the elevating step the control portion 100 determines if the elevating motor 41 has been operating for 7.1 seconds. If so, then the control portion 100 de-energises the elevating motor 41 to stop the elevation of the tray 12. Taking further examples, a tray can be elevated by 5mm to 15mm from its original position in other cooking modes, when an elevating motor 41 operates for 3.55 or 10.64 seconds respectively. Referring to Figure 6, the control sequence to avoid overloading the tray's shaft during elevation/descent of the tray 12 will be now described in detail. First, once power is applied to the microwave oven, a user puts a foodstuff to be cooked on the tray 12 inside of the cooking chamber 11, and then selects one of the cooking modes (S31). Second, the control portion 100 determines (S32) if a signal indicating that oven operation is to be started has been input to the microwave oven i.e. whether operation is "on". When operation is not "on", the control portion 100 returns to Step 31. Third, if operation is "on", the control portion 100 actuates the magnetron 16 and/or the heater 20 depending upon the selected cooking mode. Simultaneously, the control portion 100 outputs a control signal to the rotary motor driving portion 160 (S33) to thereby rotate the tray 12. Fourth, the weight of the foodstuff on the tray 12 is measured (S34). More specifically, the weight sensing portion 45 measures the weight of foodstuff on the tray 12 for a predetermined period of time after the initial rotation of the tray 12. The operating time of the magnetron 16 and/or the heater 20 is adjusted in accordance with the measured weight of the foodstuff and the selected cooking mode, as explained earlier. Fifth, the control portion 100 determines (S35) if a predetermined time period associated with the selected cooking mode has elapsed. If that time period has not elapsed, the control portion 100 returns to Step 34. When the control portion 100 determines (S35) that the time period has elapsed, the control portion 100 actuates the elevating motor 41 (S36) so that the rotating tray 12 is elevated to a predetermined height. The proper height of the tray 12 is calculated according to the cooking mode and the weight of the foodstuff as described above. The tray 12 continues rotating while rising to the calculated height. Sixth, the control portion 100 determines (S37) if the tray 12 has been elevated to the preset height by comparing the time period of operation of the motor 41 with a reference value, as explained earlier. When the tray 12 has not yet been elevated to the preset height, the control portion 100 returns to Step 36. When the tray 12 has been completely elevated to the preset height, the control portion de-energises the elevating motor 41 to stop the further elevation of the tray 12 (S38), and the cooking operation is carried out using the microwaves and/or heat. During the cooking operation, the tray continues to be rotated, so the magnetron's microwave energy and the heater's heat are evenly and thoroughly applied to the whole of the foodstuff on the tray 12. Seventh, the control portion 100 determines (S39) if a signal exists indicating that the cooking operation should be stopped. If so, then the control portion 100 actuates (S40) the elevating motor 41 to lower the rotating tray 12 to the initial positon. More specifically during step S39, once a signal for stopping the cooking operation is input to the oven during the operation of the magnetron 16 and/or heater, i.e. if either the cooking time has elapsed, or there is a keyboard input to cancel the cooking, the control portion 100 drives the elevating motor 41 in the opposite direction so as to move the tray 12 down. At this point, the tray 12 descends, while rotating, so the microwaves and/or convection or radiant heat are uniformly distributed to the food. Eighth, the control portion 100 determines (S41) whether or not the tray 12 has been completely lowered to the initial position. If the tray 12 has not descended completely to the initial position, the control portion 100 returns to Step 40. Ninth, when the elevating motor 41 has lowered the tray to the initial position, the control portion 100 de-energises (S42) the elevating motor 41, the rotary motor 42, the magnetron 16 and the heater 20. As described above, according to the present invention, the height of the tray is set in accordance with a user selected cooking mode and the weight of a foodstuff to be cooked, so that the microwave energy can be evenly and thoroughly applied to the foodstuff on the tray, thereby providing an improved cooking function. During the raising and lowering of the tray, the tray continues rotating, which tends to minimise the effect of overloading of the tray's shaft and motor and also applies the microwave energy evenly to the foodstuff, even when the weight of the food is offset from the centre of the tray. That is, the offset force is displaced around the axis of rotation rather than being concentrated at a single location as would occur if the shaft were raised or lowered without being rotated.

Claims: An oven comprising, a cooking chamber (11) for cooking a foodstuff, a selector enabling a user to select from among various cooking modes, means (12) disposed in the cooking chamber (11) for supporting the foodstuff, elevating means (44) for raising and lowering the supporting means (12), and control means for operating the elevating means (44), characterised in that the control means determines the desired elevation of the supporting means (12) according to at least one cooking parameter, including the selected cooking mode. An oven according to claim 1, further including weighing means (45) for weighing the foodstuff on the supporting means (12), wherein the cooking parameters include the weight of the foodstuff on the supporting means (12). An oven according to claim 1 or 2, further including means (42, 42a, 42b) for rotating the supporting means (12) about a vertical axis, wherein the elevating means (44) is only operable to raise or lower the supporting means (12) while the supporting means (12) is rotating. An oven according to any preceding claim, comprising a microwave oven. A microwave oven according to claim 4, further including an electric heater (20) for generating convection heat and radiant heat. A method of operating an oven comprising a cooking chamber (11) for cooking a foodstuff, a selector enabling a user to select from among various cooking modes, means (12) disposed in the cooking chamber for supporting the foodstuff and elevating means (44) for raising and lowering the supporting means (12), the method comprising obtaining one or more cooking parameters, including selecting one of the cooking modes, and characterised by determining a desired elevation of the supporting means (12) as a function of at least one of the cooking parameters, and elevating the supporting means (12) to the desired elevation. A method according to claim 6, wherein the oven includes a weighing means (45) for weighing the foodstuff on the supporting means (12), and the cooking parameters include the weight of the foodstuff on the supporting means (12). A method according to claim 6, the oven having a microwave generator (16) for supplying microwaves to the cooking chamber and a weighing mechanism (45) for weighing food disposed on the supporting means (12), the method comprising the steps of: A) obtaining a first cooking parameter by selecting one of the cooking modes; B) obtaining a second cooking parameter by measuring the weight of the foodstuff after an operation start signal has been input; C) determining a desired supporting means (12) elevation as a function of at least one of the parameters; and D) elevating the supporting means (12) to the desired elevation. The method according to claim 8 wherein the microwave oven further includes an electric resistance heater (20) for generating convection heat and radiant heat, step A comprising selecting from among the electric resistance heater (20) and microwave generator (16) to obtain the first parameter. The method according to claim 8 or 9 wherein step C comprises determining the desired supporting means (12) elevation as a function of both the first and second parameters.

Inventors: HAN DAE-SUNG, HONG SEOK-WEON, KANG KWANG-SEOK, HAN, DAE-SUNG, HONG, SEOK-WEON, KANG, KWANG-SEOK
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1997
Main classification: H05B6
IPC codes: F24C7, H05B6, F24C15, H05B11