BACKGROUND OF THE INVENTION
This invention deals generally with latching mechanism for doors employed in pressure vessels. Such doors find use, for instance, in steam cookers, ink supply tanks, surgical instrument sterilizers, and pressurized airplane cabins. In the particular embodiment the invention relates to latching mechanism for doors utilized in pressure vessels of the type shown in Vischer U.S. Pat. No. 2,904,212 and in Vischer U.S. Pat. No. 3,409,164. These pressure vessels are used for food preparation in restaurants and institutional kitchens and employ a generally circular access door which is structurally warped about one axis. During use the door is positioned inside the pressure vessel, which has a circular access opening slightly smaller in diameter than the non warped diameter of the door. The door warp facilitates insertion of the door through the access opening, and after insertion through the access opening the door is stressed against an interior rim of the access opening to achieve an air tight seal. As the stressing takes place the door is flexed to remove the warp and assume the configuration of a spherical section of circular outline.
For opening or closing of doors of the type shown in the Vischer patents, the door is mounted on a support arm, which in turn is attached to the exterior of the pressure vessel along a moveable hinge line. This hinge line is moveable between a first point enabling door passage through the access opening and a second point enabling centering of the door within the access opening. During a typical door closing sequence the hinge line is initially in its first position, and the door is manually inserted through the access opening until it is inside the pressure vessel and clear of the rim of the access opening. Thereafter the door and its hinge line are shifted until door centering within the access opening is accomplished. From this centered position the door is pulled outwardly toward the door support arm, thereby contacting the rim of the access opening and commencing the above mentioned flexing sequence. Means are provided for securing the door in its sealed position.
For accomplishing the above mentioned door sealing action, there may be provided a camming assembly as shown in Vischer U.S. Pat. No. 2,904,212 or a worm and crank arrangement as shown in Vischer U.S. Pat. No. 3,409,164. The assembly of Vischer U.S. Pat. No. 2,904,212 is best applied to fairly small doors, because the available mechanical advantage for door flexing is rather small. The arrangement of Vischer U.S. Pat. No. 3,409,164 provides a much larger mechanical advantage and is therefore better suited for usage with larger doors. In this latter arrangement the available mechanical advantage depends upon the pitch of the worm and this may be selected to meet the particular application. Doors built in accordance with Vischer U.S. Pat. No. 3,409,164 necessarily require a fairly large amount of handle turning and therefore are not as fast to operate as doors .[.build.]. .Iadd.built .Iaddend.in accordance with Vischer U.S. Pat. No. 2,904,212.
SUMMARY OF THE INVENTION
This invention enables sealing of a warped door for a pressure vessel with relatively little physical exertion and yet with a quick and simple sealing motion. For accomplishing the improved sealing action the door is supported by a stem which is urged inwardly or outwardly by rotation of a cooperatively configured cam arrangement. Preferably the cam comprises a hollow cylindrical member surrounding the door support stem, and the cam has a helical slot which mates with a projection on the door support stem to produce the above mentioned door movement when the cam is rotated.
The cam is mounted on a door support arm and is rotated by manual movement of an operating handle connected thereto. The helical slot, which functions as the camming surface has a variable pitch angle, so that when the door has been swung closed to a first position within the vessel, and rotation of the operating handle has commenced, a relatively small rotation of the handle produces rapid outward movement of the door to a second position in contact with the inside rim of the access opening. Thereafter a reduced pitch angle provides the necessary mechanical advantage for stressing the door sealingly against the inside rim of the access opening at the expense of relatively little physical effort. Preferably the helical slot has a short extent of zero degrees pitch in that region which is engaged by the stem projection when the door is fully latched. This prevents the door stresses from initiating an unlatching sequence.
The door support arm has a fixed hinge line and is provided with a shift plate which cooperates with a lug on the door closer cam to provide automatic rectilinear and angular door shifting. When the operating handle is rotated to unlatch the door, the door initially moves inwardly into a stress relieved position, which is the second position mentioned above. Thereafter during continued inward movement away from the inner rim of the access door, the cam lug cooperates with a first lip on the shift plate to shift the door laterally toward the hinge line of the door support arm while concomitantly causing an angular door movement as described in detail below in the description of the preferred embodiment. The door is then in the above mentioned first position, and there is no need for manual shifting of the hinge line prior to opening of the door.
During the latching sequence, when the door moves from its first to its second position, the lug on the door closer cam contacts a second lip on the shft plate to shift the door laterally and angularly into a position centered within the access opening. This door shifting during latching is a reversal of the shifting action which takes place during unlatching and is completed before the door comes into contact with the rim of the access opening.
It is therefore an object of this invention to provide an improved door sealing mechanism for a pressure vessel such as a steam cooker or the like.
It is another object of the invention to provide a steam cooker having a sealing mechanism of a type wherein an initially warped door may be inserted through an access opening and then pulled sealingly outwardly by a quick and easy rotation of an operating handle.
Still another object of the invention is to provide improved means for laterally centering and angularly positioning an interiorly situated access door against an access opening for sealing of said opening by the access door.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a steam cooker with a warped access door in the fully opened position;
FIG. 2 is a pictorial illustration of a portion of the cooker of FIG. 1 with the access door closed;
FIG. 3 is an exploded pictorial drawing of a door support assembly;
FIG. 3A illustrates a door support stem in a position which is rotated from the operating position as illustrated in FIG. 3;
FIGS. 4A through 4C illustrate the cooperative action by the door closer cam and the shift plate during the door unlatching sequence.
FIGS. 5A through 5C illustrate the cooperative action between the door closer cam and the shift plate during the door latching sequence;
FIG. 6 is a developed view of the helical slot in the door closing cam;
FIG. 7 is a downwardly looking sectional drawing showing a door in the fully latched position;
FIG. 8 is a further sectioned and somewhat enlarged view of a portion of FIG. 7; and
FIG. 9 is a view taken along lines 9--9 of FIG. 8.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a typical pressure cooker 10 having a door 11 which is warped about a horizontal axis. Door 11 is supported by a door support arm 12 which in turn is hinged along a fixed hinge line 15 (FIG. 2) to the front face of cooker 10. Door 11 is laterally movable toward and away from hinge line 15, and in the fully opened position as illustrated in FIG. 1, door 11 is normally in the lateral position nearest the hinge line. This position of door 11 enables the door to be swung closingly through access opening 13 of pressure cooker 10 as to the position of FIG. 2. The closing motion progresses as illustrated by positions A, B and C shown in phantom lines in FIG. 7. This closing action is similar to a prior art closing action as taught by Vischer U.S. Pat. No. 2,904,212. However, it is to be noted that in the Vischer patent the hinge line of the door support arm is movable to accomplish door closing and latching, whereas in this invention the door support arm has a fixed hinge line with the door being laterally and angularly movable relative to the door support arm.
After the door 11 has been swung inwardly through access opening 13 to position C of FIG. 7, operating handles 14 are rotated clockwise to align the door with the access opening and also to pull it longitudinally outward toward arm 12. This outward movement of door 11 first brings it into contact with the inside of rim 42 of access opening 13, and continued movement thereafter stresses the door against rim 42 to remove the warp therefrom. The door thus assumes a generally spherical configuration for sealing engagement against rim 42. The final sealed position of door 11 is shown in solid lines as position D of FIG. 7.
As shown in detail in FIG. 3, door 11 is supported by a stem 16, being attached thereto by a bolt 17, a washer 18 and a rubber seal 19. Stem 16 slides longitudinally in either the inward or outward directions, within a hollow cylindrical door closer cam 20. Door closer cam 20 is provided with a helical slot 21 for mating engagement with a roller 22 on stem 16. Roller 22 is attached to stem 16 as by nut 23 and follows slot 21, so that rotation of door closer cam 20 about a longitudinal axis causes inward or outward movement of stem 16. This movement of stem 16 necessarily produces a corresponding movement of door 11. As further shown in FIG. 3, door closer cam 20 is directly connected to operating handles 14, and may have a decorative cover 24.
There is an arc-shaped door base 25 which is attached to door support arm 12 as by an arrangement of bolts and tapped studs (not shown) and door base 25 supports a door slide 26 which is laterally slidable relative thereto. Door slide 26 has a circular aperture 27 for receiving stem 16, and there is a lug 28 in aperture 27 for engagement with a slot 29 on the left side of stem 16 (see FIG. 3A). Door base 25 has an aperture 30 through which stem 16 also passes, but aperture 30 is laterally elongated to accommodate lateral movement of the stem 16.
Door closer cam 20 is retained by a pair of retainers 31 which grasp a groove 32 near the end of cam 20. Cam retainers 31 hold cam 20 against a thrust washer 33 which fits into door slide 26 as shown in FIG. 8. Door slide 26 has a pair of bosses 43 shown in FIG. 8 which fit inside slots 34 and 35 of door base 25. These bosses are bored for receiving a pair of bolts 36. Thus it will be seen that door base 25 is fixed relative to door support arm 12 while door 11 and stem 16, are movable both longitudinally and laterally in relation thereto. Door slide 26 and cam 20 are movable laterally relative to door support arm 12, and cam 20 is rotatable about a longitudinal axis to produce all of the aforementioned longitudinal and lateral movement.
Lateral movement of door 11 is accomplished by means of a shift plate 37 which is welded to the top of a ledge 38 forming a part of door base 25. Shift plate 37 has a first downturned lip 39 and a somewhat shorter second downturned lip 40 which cooperate with a lug 41 on door closer cam 20 as best illustrated in FIGS. 4A through 4C and 5A through 5C.
Referring now to FIGS. 4 and 5, when door 11 is in the fully closed and latched position, lug 41 extends downwardly below door closer cam 20 as illustrated in FIG. 4A. As mentioned above, door 11 is centered within access opening 13 when in the closed and fully latched position. At this time the center line of door closer cam 20 is positioned as illustrated at point e of FIG. 4A. To unlatch the door, operating handles 14 are rotated in a door releading, counterclockwise direction, which causes rotation of door closer cam 20 as indicated by the arrow in FIG. 4A. This rotation of door closer cam 20 causes inward movement of stem 16 to relieve the stress on door 11, while allowing the door 11 to remain in the above mentioned "centered" lateral position. After door closer cam 20 has been rotated approximately 162°, lug 41 comes into contact with the lip 39 of shift plate 40 as shown in FIG. 4B. In reaching this position in contact with lip 39, lug 41 passes under the lower edge of lip 40 without contact thereagainst. Further, after this rotation of about 162°, stem 16 has been moved inwardly sufficiently far to relieve all stress on door 11 and push door 11 inwardly out of engagement with rim 42 of access opening 13. Continued counterclockwise motion of operating handles 14 causes further longitudinally inward movement of door 11, and also causes lateral motion of door closer cam 20 so that its centerline moves from point e to point f as illustrated in FIG. 4C. This causes lateral motion of door 11 toward hinge line 15 of door support arm 12, so that it occupies position C of FIG. 7. This lateral motion of door 11 occurs during about 33° of cam rotation, so that the total rotation of operating handles 14 from the fully latched to the fully unlatched and shifted door operation is about 195°.
FIGS. 5A through 5C illustrate the cooperation between door closer cam 20 and shift plate 37 during the closing and latching operation. When door support arm 12 is swung inwardly for insertion of door 11 through access opening 13, cam 20 and shift plate 37 occupy the relative positions shown in FIG. 4C with door 11 being shifted laterally to the right or toward hinge line 15. After door support arm 12 has been swung into the fully closed position, as shown in FIG. 2, then the latching operation is commenced by rotating operating handles 14 in a door engaging, clockwise direction. For approximately 3° of handle rotation the only result is a longitudinally outward movement of stem 16 and door 11. At the end of this 3° lug 41 is in the position shown in FIG. 5A, at which point it contacts lip 40 of shift plate 37. This contact then begins causing a laterally leftward movement to center cam 20 and door 11 within access opening 13. The combined clockwise rotation and lateral translation of cam 20 causes lug 41 to move downwardly relative to lip 40, so that when cam 20 reaches the position illustrated in FIG. 5B lug 41 clears lip 40. At this point door 11 has been shifted to a fully centered position within access opening 13 and is ready to be moved outwardly thereagainst.
The lateral shifting represented as occurring between the positions illustrated in FIGS. 5A and 5B takes place during about 31° of operating handle rotation. Door 11 moves outwardly toward the inside rim 42 of access opening 13 during this period of time, but has not yet come into engagement therewith. Such engagement begins after about 3 more degrees of operating handle rotation, which is a total of about 37° of rotation from the position illustrated in FIG. 4C. Thereafter operating handles 14 are rotated an additional 158° to cause cam 20 to achieve the orientation illustrated in FIG. 5C. At this point door 11 is fully latched. It will be observed that no lateral translation of cam 20 takes place during the rotation from the position of FIG. 5B to the position of FIG. 5C.
It will be appreciated that all lateral translation of cam 20 as illustrated by FIGS. 4A through 4C and FIGS. 5A through 5C is accompanied by lateral translation of cam retainers 31, door slide 26, and stem 16, as well as the door 11. Door slide 26 slides along the face of door base 25, as above described, and this causes movement along an arc, rather than pure rectilinear translation in the lateral direction. As a result stem 16, door 11, and other elements attached thereto are angularly shifted about an angle θ as best illustrated in FIG. 7. It has been found that this combination of lateral and angular shifting provides optimal positioning of door 11 for passage through access opening 13 during opening and closing of the door. In the illustrated embodiment the angle θ is about 4°.
The longitudinally inward and outwardly movement of stem 16 and door 11 may be better understood by reference to FIG. 9 which illustrates cam 20, cam slot 21, and roller 22 in detail. FIG. 9 shows the position which roller 22 occupies in slot 21 when door 11 is in the fully latched position. FIG. 6, which is a developed drawing of cam 20 shows the relative movement of roller 22 along slot 21 as cam 20 is rotated. For still further explanation a tabulation of longitudinal displacements which may accompany the angular rotation is included in Table I below:
TABLE I
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Cam Position
Cam Rotation
Longitudinal Movement
(Degrees) (Degrees) (Inches)
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0 -- --
37 37 .485
47 10 .104
57 10 .077
67 10 .061
77 10 .050
87 10 .040
97 10 .034
107 10 .030
117 10 .027
127 10 .025
137 10 .023
147 10 .023
157 10 .027
167 10 .034
175 8 .045
195 20 .000
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As indicated by Table I, and FIG. 6, the first 37° of latching rotation causes roller 22 to move longitudinally inward about 0.0485 inches, which is about 0.0138 inches per degree of rotation. This produces movement of door 11 outwardly from position C of FIG. 7 to a position of initial contact with rim 42. During this motion there are no door stresses to be overcome and thus cam slot 21 has a rather steep pitch.
At the end of the above mentioned 37° of rotation, the door stressing operation commences. For the next 138° of cam rotation the door will be stressed from its initially warped configuration to a spherical section of circular outline for sealing engagement against rim 42. In order to overcome the door stresses with a minimum of physical effort, cam slot 21 has a rather shallow pitch in the region engaged by roller 22 during stressing. At the point of greatest door stress this pitch produces only about 0.0023 inches of longitudinal advance per degree of cam rotation, which produces a mechanical advantage about six times greater than that available during the first 37° of rotation.
After completion of the above mentioned 138° of door stressing rotation, the pitch of slot 21 goes to zero, so that the last 20° of cam rotation produces no movement of roller 22 or door 11. This "flat spot" in the slot prevents door stresses from urging roller 22 inwardly toward the unlatched position. For the illustrated example, which has been quite successfully operated, the total longitudinal movement of roller is 1.085 inches and is accomplished concomitantly with the above described lateral and angular shifting.
While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus and that changes may be made therein without departing from the scope of the invention.