US3024838A

US3024838A - Door assembly

Info

Publication number: US3024838A
Authority: US
Inventors: Fred F Egleston; Leroy R Misner
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-02-24
Filing date: 1959-02-24
Publication date: 1962-03-13
Anticipated expiration: 1979-03-13

Description

March 13, 1962 F. F. EGLESTON ETAL 3,024,833

DOOR ASSEMBLY Filed Feb. 24, 1959 5 Sheets-Sheet 1 wri March 1962 F. F. EGLESTON ETAL 3,024,838

DOOR ASSEMBLY Filed Feb. 24, 1959 5 Sheets-Sheet 2 INVENTORS FRED F. EGLESTON BYLEROY R. MISNER MLIW March 13, 1962 F. F. EGLESTON ETAL DOOR ASSEMBLY Filed Feb. 24, 1959 5 SheetsSheet 3 FIG. FIG. 5

A I i 7K1 i i l? 43 f l r 2 I60 INVENTORS FRED F. EGLESTON LERO) R. MISNER MAIW ATTORNEY March 13, 1962 F. F. EGLESTON ETAL 9 3 DOOR ASSEMBLY Filed Feb. 24, 1959 5 Sheets-Sheet 4 58 J8 .IIW' HIM 74 7 550 55b 76 g 1 E m 2 INVENTORS FRED F. EGLESTON BY LEROY R MISNER Mz/W ATTORNE Y Mardl 1952 F. F. EGLESTON ETAL 3,024,838

DOOR ASSEMBLY 5 SheetsSheet 5 Filed Feb. 24, 1959 Fla.

FIG. 9

FIG. /0

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INVENTORS FRED F. EGLESTON LEROY R. MISNYER BY M 414% ATTORNEY ilnited Eit'ates Patent 3,024,333 DGGR ASSEMBLY Fred Egleston, Woriand, Wyo. (5539 Fertiie Sh, Qompton, Calif.}, and Leroy R. Misner, 1123 Big Horn Ave, Woriand, Wyn.

Filed Feb. 24, 1959, Ser. No. 795,237 23 Qiairns. (Cl. Mil-193) The present invention relates to new and useful im provements in folding overhead doors and particularly to such improvements in relatively large doors of this type, such as are employed in airplane hangars and other relatively large structures.

In general, the invention contemplates the provision of a folding door for hangars and the like including upper and lower door sections pivotally interconnected along their adjacent edges for pivotal movement along a horizontal axis, the upper edge of the uppermost door section being pivotally connected to the building structure for pivotal movement along a horizontal axis. There is provided a door actuating motor mechanism having cable connections with an appropriate door section to effect relative pivotal movement of the door sections in unison. There are also provided latching means operable in synchronism with the actuating motor mechanism for looking and unlocking the door sections.

With the above in mind, one of the principal objects of the present invention is to provide a hangar door structure wherein the mutually pivoted and interconnected door sections may be moved to an open position completely clearing the top edge of the hangar opening so as to provide the complete head room space of the opening.

Another object of the invention is to provide a multiple section hangar door inlcuding motor actuated cable means extending through an upper door section and connected to the lower door section in a manner such that the door sections will be folded into lapped substantially parallel relationship disposed entirely above the top edge of the hangar opening when the door sections are moved to open position.

A further object of the invention is to provide a hangar door substantially of the above type wherein the cable means is maintained in straight line connection with the lower door section throughout movement of the door section between open and closed positions.

A still further object of the invention is to provide mutually cooperating latching means between the side frame members of the hangar opening and one of the door sections and wherein the latching means on the frame members is latched and uniatched in synchronism with the motor actuating means so as to render locking and unlocking of the door substantially completely automatically.

A still further object of the invention is to provide a hangar door operable in substantially the above manner and wherein the door actuating motor is automatically conditioned for reverse movement in accordance with the position of the door sections in open and closed positions.

The invention still further aims to provide a hangar door construction and actuating mechanism which is extremely simple and reliable in operation and which can be conveniently installed and which may be also applied to ex- FIG. 2 is an enlarged fragmentary side section showing the door sections in a further opened position and showing, in fragmentary broken lines, the position of the two door sections when the door is completely open and the position of the door sections in an intermediate position clearing the latch;

FIG. 3 is a fragmentary plan view of a portion of the upper door section showing the elongated and substantially sealed cable-receiving slot;

FIG. 4 is a fragmentary sectional view showing the bottom edge of the door in sealed closed position;

FIG. 5 is an enlarged fragmentary front elevation showing the latching mechanism on the side door frame member in released position;

FIG. 6 is a fragmentary elevation, similar to FIG. 5, showing the latching member in latched position with re spect to the cooperating keeper member on the adjacent door section;

FIG. 7 is a fragmentary elevation, similar to FIG. 5, but showing the action of the bypass mechanism on the lower door section operating on the latching member to permit the door to bypass the latching member in its movement between open and closed positions;

FIG. 8 is a fragmentary plan view showing the door actuating mechanism with the cable connections and further showing the cable connecting means between the actuating mechanism and the latching members on the side frame members of the hangar opening;

FIG. 9 is a fragmentary plan view showing the position of the latch control drum with the door open;

FIG. 10 is a fragmentary plan view showing the position of the latch control drum with the door closed;

FIG. 11 is a reduced schematic view showing the open door sections opening the upper limit switch; and

FIG. 12 is a schematic Wiring diagram for the motor control.

Referring more in detail to the accompanying drawings, there is shown the front of a hangar or similar relatively large building structure including side walls 11, a pitched roof 19 and a front gable section 12. The hangar opening 14 is defined by side

frame angle members

16, 18 and a top horizontal frame member 26 see FIG. 2) along the base of the gable section. The door is illustrated as including upper and

lower sections

22, 24, respectively, of substantially identical dimensions and hinged, as at 23, along their adjacent edges for relative pivotal movement about a horizontal axis. The upper door section 22 is hinged to the top frame member, as at 25 (see FIG. 2), also for pivotal movement about a horizontal axis. The door sections are formed of vertical and horizontal steel pipes, generally designated by the

numerals

17, 19, and angle irons to form skeleton frames which are covered with galvanized corrugated sheet or the like.

There are provided three

cables

26, 26a, 26b connected at spaced points to substantially the mid-portion of the lower door section 24, as shown in FIG. 2 with the cable 26b connected, as at 27, to the lower door section 24. These cables extend through elongated slots 28, 2&1, 28b, respectively, in the upper door sections, as shown in FIG. 1. The cables pass over pulleys 29, 29a, 2912, re spectively, mounted substantially flush with the plane of the gable section and are then trained over additional pulleys for connection with a door actuating mechanism which will be described hereinafter. The slots through the upper door section may be covered by a suitable weather resistant flexible material 30, as shown in FIG. 3, which may be of rubber, plastic or the like, and this material is slit, as at 31, in line with the slots through the upper door section so that the cable may pass therethrough but in doing so, there is provided a substantial seal between the cables and the material 30.

Keeper members are mounted at the bottom of each

side frame member

16, 18 and these keepers include

upstanding keeper arms

32, 32a spcaed outwardly from the adjacent frame member to provide a slot. Each frame member includes a transversely extending web portion 16a, 18a, on which a roller 35 mounted adjacent the bottom of each side of the lower door section 2 travels throughout the major portion of the opening and closing movement of the door. There are

spur elements

36, 37 carried at the bottom of each side of the lower door section, as particularly shown in FIGS. 2 and 7. Each spur element has a short offset arm 36a, 37:: extending outwardly of the door and carrying at the end thereof a

roller

38, 39. Each of these rollers 33, 39 passes within a

corresponding keeper arm

32, 32a to wedge the door inwardly against the frame when the door sections are completely closed. Each spur element also includes an elongated arm 36b, 37b presenting an inwardly facing wedge or camming surface to cooperate with a latching mechanism which will be described below.

The mechanism for locking the door sections in closed position includes a pair of latching members 39, in the form of bell crank levers and a pair of

keeper members

42, 43. The latching member 3? is pivotally mounted on a plate 53 attached to the building structure substantially midway between the side frame member 16. The

keeper members

42, 43 are mounted at opposite sides of one of the door sections adjacent the pivotal connection 23 with the other door section and, as illustrated, these keepers are mounted at the lower edges of the upper door section 22.

With respect to FIG. 2, the bell crank latching lever 39 includes an inner arm 39a and an outer arm 3% and the lever is normally biased by spring means 46 to the unlatched position of FIG. 2 with the arm 3% projecting outwardly of the door opening. In similar manner, the bell crank lever 40 is biased to the unlocked position of FIG. 5 by spring means 47 connected to the plate and to the end of the inner arm 4611. Each of the outer arms 3%,

49b carrying rollers

48, 49 adjacent the ends thereof for cooperation with the

spurs

36, 37, respectively. Thus, referring to FIGS. 5, 6 and 7, the roller 49 on the end of the bell crank arm ebb is positioned so that the free end of the spur 37 will pass outside of the roller (see FIG. 5) during opening movement of the door sections. To pass the latching mechanism, the inclined camming surface 37b of the spur will engage the roller 4? and urge the bell crank 44} to pivot in a counterclockwise direction, as shown in FIG. 7, and against the action of the spring 47 so that the bell crank lever will be moved in that direction and permit the bottom of the lower door section to pass over the arm 46b after which bypassing movement, the bell crank 40 will be spring urged back to the unlocked position of FIG. 5. This counterclockwise movement of the bell crank lever is not of sufficient extent to actuate the switch arms 7d, 71 which will be referred to hereinafter. Closing movement of the door sections will effect similar movement of th bell crank levers to permit the lower door section to bypass the same.

As the door sections continue in their opening movement, the

rollers

38, 39 will engage the inclined surfaces 56 of outwardly projecting

wedge plates

51, 52 adjacent the upper ends of the side frame members i6, i8 respectively, and ride onto the wedge plates to maintain the lower edge of the lower door section spaced outwardly from the frame members as the upper and lower door sections approach make or break contact with one another during opening and closing movements of the door sections.

Referring to FIG. 8, the elevating and lowering mechanism for the door sections is illustrated as being mounted on a basic frame structure 52 which, in turn, is mounted on a skeleton frame 53 (see FIG. 2) within the hangar structure and clear of the door opening, Each of the

cables

26, 26a, 26b are trained around pulleys 55, 55a, 55b, respectively, mounted within the gable section and are attached to a winch drum 56 journaled in suitable bearings mounted on the frame structure 52. The winch drum is rotated by a chain 57 engaging a large sprocket 58 and a smaller sprocket 59 attached to the drive shaft 60 which is also journaled in suitable bearings mounted on the frame structure. The drive shaft includes a flexible coupling 61 and is driven from ratio gears within a gear box d2. The gears within the gear box 62 are in turn driven by a pulley and belt 63 from an electric motor 64. Within the box 65, there is a conventional motor reversing relay to control the motor 64 in a manner to be hereinafter described. Even with the relatively large door sections, a relatively small motor may be employed, as for instance, a /2 H.P., 110 volt, single phase electric motor.

In the closed position of the door sections, the bottom of the lower door section 24 may carry a suitable footing pad 67 for sealing purposes, as shown in FIG. 4, the latch assuming the position of FiG. 6. It is to be understood that the outer position of the latch levers 39, 4% is such that the cooperating keepers 42:, 43 will pass under the arms 3%, 40b during final closing of the door sections and during initial opening thereof. in the latched position of HG. 6, the arm 40b has been moved inwardly in predetermined time sequence to engage the keeper 43 and this is effected by a pulling effort exerted on the cable run 74a of cable 74, a similar pull having been exerted on the cable run 741) to bring the lever arm 3% into engagement with the keeper 42. The cable 74 is trained around a pair of guide pulleys 75 mounted on a bracket 76 projecting upwardly within the lower edge of the gable section and then around a floating equalizing pulley 77 which, in turn, is connected to cable 78 having its opposite end attached to a control drum 3% internally threaded to threadedly engage a right-hand threaded shaft 81 forming an extension of the drive shaft 60. Of course, the cable runs 74a, 74b are trained over suitable pulleys at the top and sides of the building structure around the opening so that the ends of these cable runs may be properly connected to arms 3%, 4th. The arms 79, 71 are pivotally mounted in suitable manner on the side of the building structure adjacent recesses 43a, 44a in the

latch mounting plates

43, 44 and each arm is biased to the lower position of FIGS. 2, 5 and 7 by tension springs 72, 73. The

cables

26, 26a, 26!) run from the bottom of the winch drum 56 and the cable 78 runs from the top of the control drum 80.

The control drum has a stop arm 82 projecting radially from one end thereof and adapted to cooperate with a stop projection 83 extending parallel to the threaded shaft 81 from the frame structure 52. When the motor shaft is driven in the normal right-hand direction for opening the door sections, the control drum St has a tendency to initially rotate with the shaft 81 but in doing so, the arm 32 will be brought into contact with the stop projection 83, thus preventing rotation of the drum so that it will traverse the extension shaft 81 and position itself adjacent the sprocket 59, as shown in FIG. 9. Obviously, the stop arm 32 will slide along the stop projection 83 with the linear traverse of the drum 80 along the shaft 81. During the initial slight rotation of the control drum 80, the cable 78 will have been unrolled for about one-half the circumference of the drum and this relaxes the cable runs 74a, 74b so that the springs 46, 47 will position the

latch arms

39, 49, respectively, in the unlocked positions of FIGS. 2 and 5 against

stops

68, 69. During this traverse of the control drum 80 on the threaded shaft 81, the door sections will have been elevated to the full open position shown by the upper dotted line position of the door sections in FIG. 2. In this position of the door sections, as diagrammatically shown in FIG. 11, the upper door section 22 will have forced the upper spring biased limit switch inwardly against its biasing spring to break the motor circuit and stop the motor. This upper limit switch projects through the gable section adjacent the bottom edge thereof in approximately the position shown in FIG. 1 with respect to the transverse extent of the gable section.

As shown in the wiring diagram of FIG. 12, the doublethrow main control switch has an intermediate off" or stop position and two operative positions, an up position for rotating the motor in one direction for elevating the door sections and a down position for rotating the motor in the opposite direction permitting the door sections to move to closed position. Assume the door to be in its open position with the control drum 80 positioned adjacent the sprocket 59, the main switch is thrown to the down position which starts the motor rotating in the reverse direction, thus permitting the door sections to descend and allowing the upper limit switch 90 to resume its spring biased outward position. With this direction of rotation of the threaded shaft 81, there would normally be a tendency for the control drum 80 to rotate in unison therewith but to prevent this rotation, the springs 46, 47 acting on the latch levers 39, 40 to maintain them in unlocking position exert sufficient force to prevent rotation of the control drum and thus maintain the stop arm 82 in position against the stop projection 83 to slide therealong. In other words, the control drum 8t), during closing movement of the door sections, will be caused to traverse the threaded shaft 81 in the direction of the lock nuts 85. When the drum 8t) strikes the lock nuts 85, the drum will be caused to rotate in a left-hand direction with the shaft extension 81 and this will throw the stop arm 82 to the position shown in FIG. 10. This partial rotation of the control drum 80 at the end of its traverse along the shaft extension 81 will give an upward pull to the cable runs 74a, 74b in proper timing with respect to the closing of the door sections after the keepers 4 2, 43 have passed beneath the latching arms 3%, 40b. This results in shifting the latching

arms

39, 40 to a locking position, as shown in FIG. 6, with the arms 3%, 40b engaging the

keepers

42, 43, respectively. Similarly, the comparable movement of the inner arms 39a, 40a will elevate the adjacent arms '70, 71. The arm 71 constitutes a switch arm for lower limit switch 91 mounted within the recess 44a of plate 44. When the latch arm 46a assumes the latching position of FIG. 6, it will shift switch arm 71 upwardly to open switch 91 and stop the motor with the door positions in closed and automatically locked position.

Briefly summarizing, to open the door sections, the main switch is thrown to the up position which will energize the motor circuit and through the relays rotate the motor in a right-hand direction. This, in turn, will result in similar rotation of the threaded shaft extension 81 and initial rotation of the control drum 80 to bring the stop arm 32 into engagement with the under-side of the stop projection 83. This partial rotation of the drum 8% will unwind the cable 78 about one-half the circumference of the drum and relax the cable runs 74a, 74b sufficient to permit the springs 46, 47 to immediately shift the latching arms 39, at to their outward unlocked positions clearing' the

keepers

42, 43. The winch drum 56 then winds the

cables

26, 26a, 26b thereon for elevating the door sections. As previously pointed out, and with brief further reference to FIGS. 5 and 7, the

spurs

36, 37 will cause the adjacent latching arms to move inwardly permitting the bottom of the lower door section to pass the same. Specifically, referring to the spur 37, the inner cam or wedging surface 37b thereof will engage the roller '49 on the bell crank arm 40b and shift the same inwardly against the spring 47. After the bot tom of the door has passed the latching position, the spring 47 will automatically return the bell crank lever 49 to its outward unlocked position. Thereafter, the roller 39 will engage the wedge plate 52 and shift the lower door section outwardly as the door sections are elevated by the cables to their completely open position above the door opening. In this position, the upper door section will force the upper limit switch inwardly and thus stop the motor. During this Winding movement of the winch drum 56, the control drum 84 will have moved to the position of FIG. 9 adjacent the sprocket $59, as pointed out above. In this position of the parts, the door is ready for closing by operation of the main control switch to its down" position.

From the foregoing description, it will be appreciated that the present invention provides an extremely reliable and easily operated hangar door structure which, in its open position, allows complete headroom through the hangar opening 14. Further, it will be appreciated that after throwing of the main control switch to either of its operative positions, the opening and closing of the door is completely automatic in that the latching mechanism is automatically controlled by the control drum for operation in predetermined timed relationship with re spect to the opening and closing movements of the door so that the latching mechanism is automatically locked and unlocked at the proper time with respect to the approach and withdrawal of the

keepers

42, 43.

While certain forms of the invention have been shown for purposes of illustration, it is to be clearly understood that various changes in the details of construction and arrangement of parts may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

We claim:

1. A door assembly for relatively large openings as in hangars and the like and movable between a closed position and an upper open position disposed above the door opening and clear of the headroom space; and comprising spaced vertical side frame members and a top horizontal frame member defining the door opening, upper and lower door sections controlling the door opening with the lower door section having a predetermined vertical extent permitting the bottom edge thereof to be positioned clear of the door opening when the door sections are in the open position, means pivotally supporting the upper edge of the upper door sections from the horizontal frame member for pivotal movement about a horizontal axis, means connecting the upper and lower door sections along their adjacent edges for relatively pivotal movement about a horizontal axis remaining in fixed position with respect to the door sections, door operating mechanism including cable means passing through the upper door section and connected to the lower door section intermediate the top and bottom edges thereof, and pulley means positioned above said horizontal frame member and relatively closely spaced to the vertical plane of said frame members and over which the cable means is trained for effecting outward movement of the adjacent ends of the upper and lower door sections with simultaneous upward movement of both sections toward the open position in which the upper and lower door sections approach substantially vertical parallel relationship with one another and pivot as a unit upwardly to the open position exteriorly above the horizontal frame member with the door attached end portion of the cable means approaching a horizontal position leaving the door opening wholly unobstructed with the door sections removed from headroom space within the horizontal frame member.

2. A door assembly as claimed in claim 1, wherein the upper door section is provided with elongated vertical slot means through which the cable means extends, said slot means being positioned so that the cable means is constantly maintained in straight line connection with the lower door section throughout opening and closing move ments of said door sections.

3. A door assembly as claimed in claim 1, wherein the lower door section includes roller means adjacent the lower end thereof cooperatively bearing on the side frame members during opening and closing movements of the door sections.

4. A door assembly as claimed in claim 3, wherein the side frame members are provided with outwardly extending wedge means adjacent the upper ends thereof for engaging roller means on the lower door section to maintain the lower edge of the lower door section spaced outwardly from the frame members as the upper and lower door sections make or break the substantially parallel relationship with one another during opening and closing movements, respectively, thereof.

5. A door assembly as claimed in claim 1, wherein at least one of the side frame members is provided with latching means cooperative with keeper means on one of the door sections adjacent the pivotal interconnection therebetween to lock the door sections in closed position.

6. A door assembly as claimed in claim 1, wherein the lower door section carries adjacent its lower end a latching mechanism cooperating with a fixed keeper device at the base of one of the side frame members.

7. A door assembly as claimed in claim 1, wherein there is provided a pivoted latching member adjacent the central portion of at least one of the side frame members and biased toward open position, and wherein one of the door sections adjacent the interconnection therebetween carries a keeper element with which the latching member cooperates in response to the door operating mechanism for positively holding the door sections in closed position.

8. A door assembly as claimed in claim 7, wherein the lower door section carries roller means at the bottom edge thereof engaging the side frame members during sub stantially the entire opening and closing movements of the door sections, and wherein there is provided an upwardly projecting wedge arm adjacent the lower edge of the lower door section cooperating with the latching member during opening and closing movements of the door sections to shift the latching member toward closed position permitting the roller means to by-pass the latching member during such movements of the door sections.

9. A door assembly as claimed in claim 1, wherein the door operating mechanism includes motor means for operating the cable means, and wherein latching means disposed intermediate at least one of said frame members for cooperation with a keeper on one of the door sections is operatively interconnected with and responsive to operation of the motor means for controlling the same.

107 A door assembly as claimed in claim 9, wherein a control cable interconnects the latching means and motor means and is operable by the motor means to shift the latching means into engagement with said keeper to substantially simultaneously lock the door and stop the motor.

11. A door assembly as claimed in claim 10, wherein the control cable is connected to a control drum shifted by the motor means between positions corresponding to the latching and unlatching positions of the latching means, and wherein said control drum is rotated by the motor means in one of said positions to positively shift the latching means to latching position when the door is closed.

l2. A door assembly for relatively large openings as in hangars and the like; and comprising spaced vertical side frame members and a top horizontal frame member defining the door opening, upper and lower door sections controlling the door opening, means pivotally supporting the upper door section from the horizontal frame member for pivotal movement about a horizontal axis, means connecting the upper and lower door sections along their adjacent edges for relative pivotal movement about a vertically shiftable horizontal axis, a reversible door operating mechanism operatively connected to one of said door sections for shifting the door sections to open position and permitting closing thereof, a latch member mounted adjacent one of said side frame members for cooperation with a keeper mounted on one of the door sections to lock the door sections in closed position, a latch controlling member associated with the door operating mechanism and shiftable thereby between predetermined positions corresponding to the latching and unlatching positions of said latch member and connected to said latch member for shifting said latch member to latching position exerting a closing force on the door sections and permitting movement of said latch member to unlatching position, and motor control means operable in response to positioning of said latch controlling member in the position corresponding to the latching position of said latch member for stopping said door operating mechanism.

13. A door assembly as claimed in claim 12, wherein the door operating mechanism comprises a reversible electric motor and circuit therefor, and the control means comprises a switch in said circuit biased to closed position and shiftable to open position by said latch member in its latching position for stopping the motor.

14. A door assembly as claimed in claim 13, wherein there is provided an additional switch in said circuit biased to closed position and shiftable to open position by one of said door sections to stop the motor when the door sections are in open position.

15. A door assembly as claimed in claim 12, wherein the latch member is spring urged to unlatching position upon movement of said control means to its position corresponding to the unlatching position of said latch member.

16. A door assembly as claimed in claim 12, wherein the latch controlling member comprises a control drum rotatable by the door operating mechanism and having a cable connection with said latch member, and wherein there are provide-d means limiting rotation of said control drum between predetermined positions slacking said cable in the unlatching position of said latch member and pulling said cable to shift the latch member to latching position.

17. A door assembly for relatively large openings as in hangars and the like; and comprising spaced vertical side frame members and a top horizontal frame member defining the door opening, upper and lower door sections controlling the door opening, means pivotally supporting the upper door section from the horizontal frame member, means connecting the upper and lower door sections along their adjacent edges for relative pivotal movement about a horizontal axis, a reversible motor operatively connected to one of said door sections for shifting the door sections to open position and permitting closing thereof, a latch lever mounted adjacent one of said side frame members for engagement with a keeper on one of the door sections to lock the door sections in closed position and having a predetermined throw between latching and unlatching positions, means biasing said latch lever to unlatching position, a latching operator for shifting said latch lever to latching position and operatively associated with said motor for movement thereby, a cable connecting said latching operator and said latch lever, means limiting the cable-control movement of said latching operator to substantially the throw of said latch lever, and stop means responsive to movement of said latch lever to latching position for stopping said motor, when the door sections are closed.

18. A door assembly as claimed in claim 17, wherein there are two latch levers, one at each side of the door opening, and the cable includes runs to each of said latch levers.

19. A door asembly as claimed in claim 17, wherein the latching operator comprises a drum threadedly mounted on a screw shaft rotated by said motor and traversing said shaft in opposite directions as the door sections are opened or closed, and wherein the means biasing the latch lever to unlatching position exerts sufiicient tension on said cable to prevent rotation of said drum in one direc- Lion beyond a position permitting movement of the latch lever to unlatching position.

20. A door assembly as claimed in claim 19, wherein the drum carries a stop arm slidably engageable with a fixed stop to limit rotation of the drum in the opposite direction as it traverses the screw shaft during closing of the door sections, and wherein stop means on the screw shaft engages the drum at the end of its traverse causing partial rotation of the drum and stop arm in cable-pulling direction to shift the latch member to latching position when the door sections are closed.

21. A door assembly as claimed in claim 17, wherein there are provided additional stop means engageable by one said door section in open position to stop the motor.

22. A door assembly as claimed in claim 17, wherein the motor comprises an electric motor with circuit means including lower switch means operable by the latch lever to stop the motor with the door sections closed and upper switch means operable by one of the door sections to stop the motor when the door sections are in open position.

23. A door assembly as claimed in claim 17, wherein the latching operator comprises a drum threaded on a screw shaft rotated by said motor to rectilinearly traverse the drum on the shaft during opening and closing of the door sections, with means limiting rotative movement of the drum to one end of its traverse for controlling the cable actuation of the latch lever.

References Cited in the tile of this patent UNITED STATES PATENTS 1,412,871 Johnson Apr. 18, 1922 2,274,216 Sanders 'Feb. 24, 1942 2,327,316 Michelman Aug. 17, 1943 2,393,052 Mehard Jan. 15, 1946 2,589,479 Curtis Mar. 18, 1952 2,827,114 Stroup Mar. 18, 1958 FOREIGN PATENTS 1,040,958 France Oct. 20, 1953