GB2305093A

GB2305093A - Microwave oven turntable with vertical motion

Info

Publication number: GB2305093A
Application number: GB9618318A
Authority: GB
Inventors: Suk-Jin Han; Eung-Sup Lee
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1995-08-31
Filing date: 1996-09-02
Publication date: 1997-03-26
Anticipated expiration: 2016-09-02
Also published as: JPH09119651A; KR980003201A; JP2859586B2; KR100210066B1; GB2305093B; MY113875A; GB9618318D0; CN1085818C; CN1149689A

Abstract

A microwave oven includes a rotary turntable mounted on a shaft (70) which is rotated by a first motor (207). A first gear (209) is slidably splined on the shaft (7) and connected to the motor drive through a second gear (211). The turntable can also be raised and lowered. The lower end of the shaft (7) engages a rotary cam (221) driven by a second motor (215) through a third gear (217). In another embodiment cooperating lips 420B, 400A provided on the shaft (70) and the cam in order to positively draw the shaft (70) downwardly when the turntable is to be lowered.

Description

Turntable Driving Apparatus of Microwave Oven The present invention relates to a microwave oven with an improved turntable drive for rotating and vertically moving the turntable to enable more uniform and quicker cooking of food.

Conventionally a microwave oven as illustrated in Figure 1, has a heating chamber 2 for accommodating food to be cooked, and an external casing 1. A stirrer blade 5 is rotatably mounted in a stirrer cover 3 on a shaft 4, to disperse microwave radiation from a waveguide 6 so as to heat uniformly the food accommodated in the heating chamber 2. A magnetron 7 that receives high voltage power from power source (not shown), feeds microwave radiation into the waveguide 6. A cooling fran 8 is operative to cool the casing 1 during activation of the magnetron 7 and to rotate the stirrer blade 5.

The heating chamber 2 is provided with a turntable 9 to receive a plate or like vessel with food to be cooked. The turntable is rotated by driving means 10 on the underside of the chamber 2.

When the vessel containing food to be cooked is placed on the turntable 9 and power is switched on, the magnetron 7 generates microwave radiation, which is guided into the stirrer cover 3 along the waveguide 6, to the rotary stirrer blade 5. At this time, the stirrer blade 5 is rotated by the draft of the cooling fan 8, and serves to disperse uniformly the microwave energy and supply it into the heating chamber 2, so that the food on the turntable 9 can be dielectrically heated.

Also, the turntable 9 is rotated by the driving means 10, so that the food on the turntable 9 can be evenly irradiated thereby to enable the food to be dielectrically heated.

Additionally, it would be desirable to adjust the height of the turntable in order to adjust the vertical position in which food is cooked in the heating chamber 2. This cannot be achieved with the turntable configuration shown in Figure 1.

A way to solve this problem is described in Japanese laid open utility model application No. Hei 1-150396, which, as illustrated in Figure 2, includes a turntable rotary means 20 for rotating the turntable 9 and turntable vertical moving means 30 for vertically moving the turntable 9 through a mechanical linkage. A first motor 21 is mounted on the interior of the casing 1 and is connected to the turntable 9 through a longitudinal extendible coupling comprising slidable driving coupling parts 22, 23, which extend vertically through a hole in the floor of the heating chamber 2. The turntable vertical moving means 30 includes first and second slide rods 33 and 34 respectively guided by first and second guide members 31 and 32 formed under the heating chamber 2, so as to support and simultaneously move the turntable 9 vertically.The first and second slide rods 33 and 34 are coupled by hinges to a pair of first and second left link members 35a and 35b and a pair of first and second right link members 36a and 36b respectively. A horizontally movable conneaion link member 37 is coupled to the joints between the right link members 35a, b and the left link members 36a, b. The connection link member 37 is pivotally coupled to a driving link member 38 which is coupled through a cam 39 to a worm wheel 40 meshed to a worm 42 driven by a second motor 41.

A deteaor 50 deteas when the turntable is in its lowermost position.

When the second motor 41 is switched on, it drives worm 42, which in turn rotates the meshed worm wheel 40 and the cam 39, which reciprocates the driving link member 38 pivotally coupled thereto. As a result, the connection link member is moved horizontally back and forth, causing the turntable to be raised and lowered. Thus, the turntable 9 can be vertically adjusted to a predetermined height in the heating chamber 2 by operation of the motor 41. The rotary drive for the turntable 9 accommodates the raising or lowering of the turntable, by virtue of the slidable coupling members 22, 23. However, a problem with this prior art turntable driving configuration is that structure thereof is complicated and breakdowns often occur.

Furthermore, there is another problem in that frictional noise can be generated and the complex linkages tend to wear prematurely.

According to the present invention there is provided an oven including a turntable mounted on the upper end of a shaft, means for rotating the shaft whereby to rotate the turntable, and drive means for applying an actuating force to the lower end of the shaft so as to produce longitudinal axial movement thereof whereby to raise and lower the turntable.

The present invention thereby provides a turntable driving apparatus in a microwave oven of a simplified structure with a reduced number of parts thereby to reducing the manufacturing cost thereof.

The turntable shaft can be mounted such as to have an improved life and at the same time, provide a smooth operation to reduce noise and vibration therefrom.

For a fuller understanding of the invention, reference will be made to the following detailed description of embodiments thereof, taken in conjunaion with the accompanying drawings in which: Figure 1 is a schematic longitudinal seaional view of a conventional microwave oven; Figure 2 is a longitudinal sectional view of a conventional turntable driving apparatus for a microwave oven; Figure 3 is a plan view of a turntable driving apparatus in a microwave oven, in accordance with the present invention; Figures 4 and 5 are longitudinal sectional view illustrating a minimum and maximum vertical position of the turntable shaft respectively taken along line D-D in Figure 3; Figure 6 is a perspeaive view of the coupling between a first gear and the turntable shaft shown in Figure 3;; Figure 7 is a longitudinal sectional view of turntable driving apparatus in a second embodiment of the invention; Figure 8 is an enlarged sectional view of a principal part referenced E in Figure 7; Figure 9 is an exploded perspective view of a third embodiment according to the invention; Figure 10 is a plan view of principal couplings shown in Figure 9; Figure 11 is a partial sectional view of Figure 10; Figure 12 is a plan view of principal parts for explaining an operation of the third embodiment of the present invention; Figure 13 is a side view for illustrating how the turntable shaft is captured by traction member on rotation of the cam member; Figure 14 is a side view for illustrating how the turntable shaft is raised by the rotary cam member; and Figure 15 is a side view of principal parts for illustrating a state where the turntable shaft is forcibly lowered by a traction member.

Throughout the drawings, the same reference numerals and symbols are used to designate like or equivalent parts or portions for ease of illustration and explanation.

A first embodiment of the present invention will be described in detail with reference to Figures 3, 4, 5 and 6. The heating chamber 2 has a turntable shaft 70 protruding through its floor for axially rotating the turntable (not shown, but corresponding to turntable 9 of Figures 1 and 2). A casing that includes a cover member 205 is disposed on the underside of the chamber 2, containing a first electric motor 207 for rotating the shaft 70 and hence the turntable, through a first gear 209 on the shaft 70 that meshes with a second gear 211 driven by the motor 207.

The casing also includes a base plate 213 with a second elearic motor 215 for raising and lowering the shaft 70 axially, so as to raise and lower the turntable, by means of a third gear 217 coupled to the second motor, which meshes with a ring of teeth 221a formed around the perimeter of a cam 221 that is rotatably mounted on the base plate 213 by a screw 219, to rotate about an axis parallel to that of the shaft 70.

The turntable shaft 70 is formed with a "D" shaped seaion and the first gear 209 is slidably splined thereon. The gear 209 is formed with a through hole 209a (Figure 6) having a slightly larger "D" shape at an inner periphery thereof than the "D" shape of the turntable shaft 70 so that it can be both axially rotated and moved longitudinally. The lowermost end of the shaft 70 is semi-spherical in shape so as to be slidably point contacted in a correspondingly shaped track 221c formed in a slanted surface 221b on the rotary cam 221.

The turntable shaft 70 is mounted in a bearing 223, so that the shaft can be smoothly rotated without being swayed and can also be moved longitudinally, to allow the turntable to be both rotated and raised and lowered. The bearing 223 is supported by a holder member 227 coupled by a plurality of fastening members 225 to the cover member 205. The cover member 205 and the base plate 213 are integrally formed with respective outwardly directed flanges coupled together by a fastening member 229. A sensor 231 figure 3) is disposed on one side of the base plate 213 to detect the rotary position of the cam 221 in which the turntable shaft 70 is lowered to its lowermost level.

Vertical, longitudinal movement of the turntable shaft 70 will now be described for the first embodiment of the invention . When the sensor 231 detects that the turntable shaft 70 is lowered to its lowest level, in an initial waiting state, the second motor 215 is energised in order to rotate the third gear 217, which in turn rotates the cam 221. The cam track 221c in the slanted cam surface 221b is thus slidingly and cammingly engaged with the lowermost end of the shaft 70, which causes the shaft to be raised and lowered longitudinally of its axis, repeatedly for successive revolutions of the cam 221.

Positional control of the shaft 70 in the vertical direction is thus achieved by controlling the drive of the second motor 215.

Next, rotary operation of the turntable shaft 70 will be described. This is achieved by energising the first motor 207, which drives the second gear 221, that in turn rotates the first gear 209 and hence the turntable shift 70, thereby causing the turntable coupled to the upper end of the turntable shaft 70 to rotate. Accordingly, the turntable can be moved vertically and rotated axially, by shaft 70, simultaneously.

As apparent from the foregoing, the microwave oven turntable driving apparatus according to the first embodiment, has the advantage that the struaure thereof is substantially simplified and has a reduced number of parts as compared with the previously described prior art devices, and can be manufactured at reduced cost.

A second embodiment of the present invention will now be described with reference to Figures 7 and 8. As illustrated in Figure 7 and 8, turntable rotary means 300 is situated in space existing between the cover member 205 and the base plate 213 and is mounted on the cover member 205. Turntable vertical moving means 310 is located in a space existing between the cover member 205 and the base plate 213 and is mounted on the base plate 213.

Power transmission means 320 is positioned in a space between the cover member 205 and the base plate 213 and is mounted on the cover member 205.

The power transmission means 320 includes upper and lower journal member 324 and 326 on the turntable shaft 70.

In this embodiment, the first gear comprises a transmission gear 328 slidably splined on the shaft 70 in the space between the upper journal member 324 and the lower journal member 326, the gear 328 being meshed with second gear 221 that is driven by motor 207.

The transmission gear 328 has a central "D" shaped opening which fits onto the "D" shaped peripheral surface of the turntable shaft in order to transmit torque from the first motor to the shaft 70.

The upper and lower journal members 324 and 326 are received in a holder member 330 which is in turn connected to the cover member 205.

The upper and lower journal members 324 and 326 are each formed with a central through hole (no reference numeral designated) fitted onto a shaped peripheral surface of the turntable shaft 70, to slide smoothly thereon.

The lower journal member 326 is formed at its upper surface with a ringshaped groove 326a. Furthermore, the upper and lower journal members 324 and 326 are made of plastic or metal coated with Teflon (Registered Trade Mark). The transmission gear 328 is formed thereunder with a ring-shaped protuberance 328a that fits into groove 326a on the lower journal member 326. The holder member 330 has an external peripheral opening therein so as to allow the transmission gear 328 to mesh with the second gear 221.

When the first motor 207 of the second embodiment is activated, the second gear 211 drives the meshed transmission gear 328 thereby to rotate the turntable shaft 70 and the turntable. As the turntable shaft 70 is rotated, the upper and lower journal members 324 and 326, coupled around the transmission gear 328 to the turntable shaft 70, perform a rotary sliding movement in the holder member 330. Furthermore, the transmission gear 328 and the lower journal member 326 serve to perform a rotary guide function due to contact made by the protuberance 328a in the groove 326a, resulting in smooth rotation of the turntable shaft 70.

An advantage of the apparatus according to the second embodiment of the present invention, is that the bearing arrangement in the holder member 330 results in smooth operation of the turntable shaft 70 and can reduce noise and vibration, because, when rotary and vertically moving functions of the turntable shaft 70 are performed independently, the holder member 330 configuration offers low friaion due to the configuration of the upper and lower journal members 324 and 326 being rotatably mounted between the turntable shaft 70 and the holder member 330.

A third embodiment of the present invention will now be described with reference to Figures 9 to 15. Turntable shaft 70 for rotating a turntable 9 (not shown), is coupled through the floor of the microwave oven heating chamber 2 and the first motor 207 which is disposed on one side of the cover member 205. The second gear 209 is slidably splined onto the turntable shaft 70 and is meshed with second gear 211 coupled to the first motor 207.

The second motor 215 is disposed diametrically opposite the first motor 207 (relative to shaft 70) on base plate 213, and drives third gear 217, which meshes with teeth 410a around a rotary cam 410 rotatably mounted on the base plate 213 about an axis 219, so as to move the turntable shaft 70 vertically.

The turntable shaft 70 is "D" shaped in cross seaion and is slidably splined with a corresponding "D" shaped axial hole in the first gear 209, such that the first motor can rotate the shaft 70 via the first and second gears 209, 221.

The first gear 209 is held in a holder member 227 so that the turntable shaft 70 can be smoothly rotated without any sway, and also moved up and down vertically. The holder member 227 is mounted on the bottom surface of the cover member 205 by a plurality of fastening members 225, and is provided with an interior bearing 223 of high abrasion resistance, so that the turntable shaft 70 can be smoothly rotated and vertically moved therein. Furthermore, the turntable shaft 70 has a semi-spherical contact member 400 of plastics material fused to its lowermost end so that it can slide easily relative to a slanted track surface on the rotary cam 410 without significant abrasion.

The contact member 400 is formed with an integral protruding tripping lip 400a having a lager outer diameter than that of the shaft 70 so that the turntable shaft 70 can be forcibly lowered by means of a traction member (described later).

The rotary cam 410 is formed at a lower peripheral surface thereof with gear thread 410a that meshes with the third gear 217, driven by the second motor 215. The rotary cam 410 in this embodiment has a generally cylindrical side wall 410b with a slanted upper surface that includes a concave track 410c which cunningly engages with the contact member 400 on the lowermost end of the shaft 70, so that when the rotary cam 410 is rotated, the shaft 70 is moved vertically. The shaft is thus cammed upwardly by an upwardly inclined portion of the surface 410c, and falls downwardly when cammed by a downwardly inclined portion of the track surface 410c.

If the turntable is eccentrically loaded with food to be cooked, the shaft 70 may not readily fall downwardly. To overcome this problem, a traction member 420 is provided. In order to locate the traction member 420 on the cam 410, a plurality of locating grooves 410d are formed in the cam so that the traction member 420 can be snap-fitted within the cylindrical wall 410b.

To this end, the body 420 is formed at its lower edge with a plurality of lugs 420c that are snap fitted into the grooves 410d.

The traction member 420 has a cylindrical body 420a with a slanted upper edge, generally coextensive with the slanted upper edge of the wall 410b of the cam member. The body 420a is formed at its upper peripheral edge with a half ring-shaped traction lip 420b for engaging the tripping lip 400a of the contact member 400 on the end of the turntable shaft 70, so that the turntable shaft 70 can be forcibly lowered as the cam 410 is rotated. The traction lip 420b partially overlies the portion of the track 410c that is slanted downwardly, so that the tripping lip 400a of the contact member 400 on the shaft 70, becomes captured underneath the traction lip with the result that the shaft 70 is positively lowered in response to rotation of the cam 410, as illustrated in Figure 12. The cam 410 has a descent region R1 and an ascent region R2 for the shaft 70.The traction lip 420b is formed with extension regions L1 and L2 at opposite ends of predetermined lengths that extend from the descent region R1 into the ascent region R2, the extension regions being lipped upwards in order to facilitate entry of the tripping lip 400a into the descent region R1, as shown in Figure 13, beneath the traction lip.

A first sensor 231 is disposed on one side of the base plate 213 in order to detect the lowermost position of the turntable shaft 70. A second sensor 232 is disposed to one side of the cover member 205 in order to control revolution of the first motor 207 by being tripped by a protruding lug formed on the second gear 211, when the gear 211 is rotated.

Now, ascent and descent of the turntable shaft 70 will be described. When the first sensor 231 detects that the turntable shaft 70 has descended to its lowest position and is in an initial wait state, the second motor 215 is energised so as to drive the third gear 217, thereby rotating the rotary cam 410, in this example, in an anticlockwise direction. Rotation of the cam 410 causes the slanted track surface 410c to slide past the contact member 400 on the bottom of the shaft 70, to cammingly raise and lower the shaft axially, repeatedly, with each revolution of the cam member.

The turntable shaft 70, as illustrated in Figure 12, is in its highest position when the slant track surface 410c at section G passes thereunder on rotation of the rotary cam 410, and the turntable shaft 70 descends to its lowermost position when the turntable shaft descent region R1 extending from section G, through section H to section I on the slant track surface 410c, passes thereunder progressively. The turntable shaft 70 then ascends to its highest level as the turntable shaft ascent region R2 extending from section I, section J to section G on the slant track surface 410c passes thereunder.

When the slant track surface 410b of section G of the rotary cam 410 passes under the shaft 70 as illustrated in Figure 13, the tripping lip 400 a of the contact member 400 on the shaft 70 can readily enter between the traction lip 420b and the slant track surface 410 due to the lip 420b being bent upwardly at a predetermined angle in the extension region L1, so that on further rotation if the cam 410, the shaft 70 is forcibly drawn downwardly. This is illustrated in Figure 15. Thus, an eccentric load on the turntable need not cause the shaft 70 to jam in the bearing 223, because the shaft is positively drawn downwardly. When the cam 410 rotates further, into the ascent region R2, the turntable shaft 70, as illustrated in Figure 14, is cammed upwardly by the slanted track surface 410c on the cam 410 without the need for interaction with the traction member 420.Control of the height of the turntable shaft 70, and hence the turntable, is realised by control of the second motor 215.

Rotation of the turntable shaft 70 is achieved by operation of the first motor 207, which drives the gear 211, which in turn drives gear 209 that rotates the shaft 70. It will be understood that the shaft can be axially raised and lowered and rotated concurrently.

An advantage of the microwave oven according to the third embodiment of the present invention, is that because the first and second motors 205 and 215 are symmetrically disposed about the axis of the shaft 70, the driving force of the first motor 207 is transmitted to the first gear 209 to rotate the turntable shaft 70 and thereby to rotate the turntable, and the driving force of the second motor 215 is transmitted to the rotary cam 410 to raise and lower the turntable shaft 70 by means of the slant track surface 410c, so that the structure thereof is simple and the number of parts involved can be reduced, thereby saving costs.

Another advantage is that, when the first motor 207 is assembled to the cover member 205 the second gear 211 and the first gear 209 are caused to be meshed therebetween and, when the second motor 251 is assembled to the base plate 213, the third gear 217, and the rotary cam 410 are caused to be meshed therebetween, and when the cover member 205 and the base plate 213 are assembled by means of a plurality of the fastening members 229, the contact member 400 underneath the turntable shaft 70 is structured to be automatically set to the slanted track surface 410c of the rotary cam 410, so that operational assembly processes involved for gear setting can be eliminated to thereby improve manufaauring efficiency.

Claims

1. An oven including a turntable mounted on the upper end of a shaft, means for rotating the shaft whereby to rotate the turntable, and drive means for applying an actuating force to the lower end of the shaft so as to produce longitudinal axial movement thereof whereby to raise and lower the turntable.

2. An oven according to claim 1 wherein said drive means includes a rotary cam which cammingly engages the lower end of the shaft, and motor means for rotating the cam whereby to raise and lower the shaft.

3. An oven according to claim 2 wherein the cam includes a slanted surface with a track that receives the lower end of the shaft.

4. An oven according to claim 2 or 3 including means for holding the lower end of the shaft in contact with the cam during lowering of the shaft.

5. An oven according to any one of claims 2 to 4 including a first gear slidably splined to the shaft, a first motor that drives a second gear meshed with the first gear to rotate the shaft axially, and a second motor that drives a third gear meshed with teeth disposed around the periphery of the cam, to rotate the cam and thereby reciprocate the shaft.

6. An oven according to any one of claims 2 to 5 including sensor means for sensing the longitudinal position of the shaft.

7. An oven according to claim 6 wherein the sensor means is operative to sense a predetermined position of angular rotation of the cam corresponding to the lowermost longitudinal position of the shaft.

8. An oven according to any preceding claim wherein the shaft protrudes through an opening in the floor of a cooking chamber in the oven.

9. An oven according to claim 8 wherein the shaft rotating means and the drive means are mounted in a casing below the floor.

10. An oven according to any preceding claim, comprising a microwave oven.

11. A turntable driving apparatus of a microwave oven, the apparatus comprising: a turntable shaft for vertically moving and rotating a turntable; a first motor for rotating the turntable shaft; a first and second gear for being mutually meshed and respectively drivingly coupled to the turntable shaft and the first motor in order to have the turntable axis rotated by the torque of the first motor; a second motor for vertically moving the turntable shaft; and a third gear and a rotary cam for being respectively mounted to and mutually meshed with the second motor and the turntable shaft in order to have the turntable shaft vertically moved according to the power of the second motor.

12. The apparatus as defined in claim 11, wherein the rotary cam comprises: a gear thread formed to be meshed with the third gear at a periphery thereof; a slanted portion formed at a predetermined angle at an upper side thereof to allow the turntable shaft to ascend and descent thereon; and a slanted track surface of semi-spherical shape formed at an upper margin thereof to allow the turntable shaft to be rotated and at the same time to be vertically moved by way of contact according sliding movement.

13. The apparatus as defined in claim 11, wherein the turntable shaft is formed at one end thereof with a semi-spherical surface so as to be smoothly slid along a slanted track of the rotary cam.

14. The apparatus as defined in claim 11 or 12 wherein the first gear comprises a bearing formed at an external side thereof for rotating and at the same time vertically moving the turntable shaft, and a holder member for supporting the bearing and preventing the turntable axis from being swayed.

15. A turntable driving apparatus of a microwave oven, the apparatus comprising: a turntable shaft for rotating and vertically moving the turntable; a transmission gear for being fitted to the turntable shaft so as to receive power from a power source to rotate the turntable shaft; an upper side and a lower side journal member for being fitted to the turntable shaft and for being disposed at an upper side and a lower side of the transmission gear to thereafter be rotated; and a holder member for supporting the transmission gear and the upper and lower journal members.

16. The apparatus as defined in claim 15, wherein the transmission gear is disposed at an upper surface and a lower surface thereof with ring-shaped protruders to be inserted into the upper and lower side journal members.

17. The apparatus as defined in claim 15 or 16, wherein the upper and lower side journal members are disposed at upper surface and lower surfaces thereof with a groove into which protruders formed at upper and lower surfaces of the transmission gear can be respectively inserted.

18. The apparatus as defined in claim 15, 16 or 17 wherein the upper and lower side journal member are made of synthetic plastics material.

19. The apparatus as defined in claim 15, 16 or 17 wherein the upper and lower side journal members are made of metal with a low friction plastics coating thereon.

20. A turntable driving apparatus of a microwave oven, the apparatus comprising: a first motor disposed at a cover member in order to rotate a turntable shaft coupled to the turntable; a second motor disposed at a base plate in an opposite direction from the first motor; a rotary cam disposed on the base plate so as to receive power from the second motor to vertically move the turntable shaft; and a traction member disposed on the rotary cam in order to forcibly pull down the turntable shaft when not properly listed down due to eccentric load applied thereto.

21. The apparatus as defined in claim 20, wherein the turntable shaft is integrally fused thereunder with a contact member so as to descent the turntable shaft simultaneously when descended by tractive force of the traction member.

22. The apparatus as defined in claim 21, wherein the contact member is disposed at an upper periphery with a tripping lip having a larger outer diameter than that of the turntable shaft.

23. The apparatus as defined in claim 21, wherein the rotary cam comprises: a gear thread formed thereunder at peripheral surface; a slanted wall formed thereon at a periphery at a predetermined angle to vertically move the turntable shaft; and a slanted track surface of concave semi-spherical shape to vertically move the turntable shaft in a state of being constantly contacted with the contact member coupled underneath the turntable shaft when the rotary cam is rotated on an upper surface of the slanted wall.

24. The apparatus as defined in claim 21, wherein the traction member comprises: a ring-shaped body having a slant angle at an upper surface thereof corresponding to an upper height of the slant wall when the traction member is inserted through an upper area of the rotary cam to thereby be positioned at an inner periphery of the slant wall; and a traction jaw having an outwardly bent half-ring shape disposed at a periphery of the body against an upper surface thereof for forcibly lowering the turntable shaft when the rotary can is rotated.

25. The apparatus as defined in claim 24, wherein the traction lip is bent between a maximum slant region and a minimum slant region against a 360 degree distance of the slant track surface at the rotary cam.

26. The apparatus as defined in claim 14, wherein the turntable axis descent region of the traction lip is formed at both ends thereof with a predetermined length of extension unit so as to have a longer region than a turntable axis ascent region.

27. The apparatus as defined in claim 26, wherein the extension unit is upwardly bent at an entry thereof at a predetermined angle so that the tripping lip of the contact member coupled to a lower area of the turntable shaft can be easily entered into the turntable axis descent region.

28. A microwave oven substantially as herein described with reference to Figures 3 to 6 or Figures 7 and 8 or Figures 9 to 15 of the accompanying drawings.