US3047096A - Control for an elevator closure - Google Patents

Description

July 31, 1962 1. E. MAGr-:E 3,047,096

CONTROL FOR AN ELEVATOR OLOsURE Filed Dec. 22, 195e ./HNEDWD #714655 INVENTOR BY g/M AT1-omar United States' Patent O New llersey Filed Dec. 22, 1958, Ser. No. 782,145 4 Claims. ((21.187-48) This invention relates to door control mechanism, especially for horizontally sliding elevator doors equipped with protective mechanism used extensively in installations operating without attendants.

It is common practice in present day elevator installations to effect the closing of the elevator car and hoistway doors automatically. In such installations, safety devices, or protective mechanisms, have been provided that are responsive to the presence `of a person in the closing path of the doors to stop their closing movement, thereby minimizing the possibilityof injuring Ethe person. Also, it is usual in such installations not only to stop the doors in closing yupon detection of a person in their path, but to reopen them either lfully or partially to allow the-person to enter or leave the carunimpeded. Prior safety devices utilized yto accomplish this include the light beam type which is responsive to the presence of a person in the closing path of the door yand any distance from the leading edge of the door, and the -mechanical safety shoe type, carried by the door and forming its leading edge to be actuated by a person coming into contact with it. Such safety `devices are described and disclosed in Ithe patent to Bruns No. 2,634,828, issued April 14, 1953.

Many installations are equipped with both these safety devices. In such `arrangements the light beam device detects the presence of a person in the entranceway and the mechanical `safety shoe device detects the contacting of a person with the leading edge of the door, both safety devices operating independently of each other to control the door movements. Since the light beam device detects a person in the doors closing path regardless of the distance from the leading edge of the door, ya door is often prevented from moving toward its closed position although the transferring passenger may have ample room to enter or leave the car. To overcome this defect, some prior art arrangements disable the light beam device if the beam remains interrupted continuously for a predetermined time. Such an yarrangement is disclosed in the patent to Santini No. 2,785,771, lwherein if the light beam is interrupted for less than four seconds the closing door is stopped and reopened, but if the light beam remains continuously interrupted for more than four seconds, the light beam device is disabled and lthe door is closed; reliance being placed on the mechanical Asafety shoe to prevent injury to transferring passengers. Frequently, if intending passengers `arrive at spaced intervals (intervals of less than four seconds in the Santini system), this stopping and reopening iof the `door to allow passenger transfer occurs repeatedly and requires -the elevator to stand at 'a landing fora considerable time.

With such prior art arrangements, the apparatus that effects the movements of the door is required to start, accelerate, stop and reverse the door movement many times each day as quickly las practicable. Wear and tear on the mechanism inevitably Kaccompanies such usage. Also, as a general proposition, the degree of this wear and ltear is somewhat proportional to the speed with which these operations are accomplished. Therefore, the desire to handle elevator door movements in the least practicable time imposes a heavy burden 'on the mechanism that effectuates their movements. Without unduly restricting passenger transfer, thisA desire can be realized and the wear and tear on -the equipment can Ibest be minimized, all else being equal, by limiting the door movements and 3,047,096 Patented July 31, 1962 performing the door movement operations with a minimum of abrupt changes in the forces that are applied to the operating equipment. Y

It is an object `of the invention to improve elevator operating efficiency by providing improved elevator door control mechanism.

Another object of the invention is to safeguard transferring passengers while minimizing unnecessary door movements.

It is still another Iobject of the invention to provide a control for elevator doors 'which passenger transfer time.

A further object of the invention is to provide a door control which permits the closing of the doors at hi-gh speed while minimizing wear and tear of the door operating equipment Iand safeguarding transferring passengers. I

The invention will be described Iby reference to one preferred embodiment in which a `car door and a hoistway door of the power operated, side opening type and door protective mechanisms of the light beam and mechanical safety shoe types similar to those shown and described in the aforementioned Bruns patent are utilized. Such a light beam device detects the presence `of a person in the elevator entranceway any distance `from the leading edge of the car door While the mechanical safety shoe, forming the leading edge of the car door, is yactuated as the vleading edge contacts a person in its path.

ln this preferred embodiment the doors are opened incident to the car stopping at a floor landing, and at ythe expiration of a predetermined time interval termed the door open dwell period, which is presetto allow normal passenger transfer to take place, the doors are moved toward their fully closed position. Incident to the closing of the doors, the light beam protective device becomes effective to detect a person in their closing path. If the closing path of the doors is not obstructed by a passenger arriving late, Ithe doors continue at normal closing speed to their fully closed position. Should the light beam be interrupted by a late transferring passenger, the closing speed of the doors is reduced below normal closing speed and the doors continue moving toward their fully closed position at this reduced speed. Oncey the closing speed is reduced by such an initial detection of a transferring passenger, it is so maintained so long as the doors continue moving toward their fully closed position, thereby allowing passengers to clear the entranceway. As the doors thus move toward their closed position at the reduced speed, should the leading edge of the car door meet an obstruction in its path the mechanical safety shoe is actuated, causing the door operating mechanism to stop the closing movement of the doors. As the obstruction to the closing movement of the doors is removed and the mechanical safety shoe is released, the doors resume moving in the closing direction at normal closing speed provided that the light beam is also unobstructed. However, if the light beam remains broken by a person inthe closing path or is again obstructed, the closing speed is again reduced below the normal closing speed and is so maintained until Ithe doors reach their fully closed position unless the doors are again stopped by actuation of the mechanical safety shoe. In this manner both 'the light beam and mechanical safety shoe devices cooperate to effect a persistent closing effort of the doors after the normal passenger transfer time has expired to expedite late passenger transfer While safeguarding transferring passengers, thus expediting elevator service and minimizing door movements.

An additional advantage of the cooperation of the safety devices in controlling door movements is that the light beam device detects lan obstructing passenger in the closing path of the door and reduces the speed of the door in approaching that obstructing passenger before it Yminimal force and the door operating mechanism quickly stops the closing door. Also, by merely stopping the door while it is closing at the reduced speed, door movemerits and wear and tear on the door operating equipment are minimized. s

Should the light lbeam safety device become disabled 'at the expiration of the normal door open dwell period, the` door is immediately moved toward its fully closed position at the reduced speed Ywithout waiting for the expiration of a predetermined failure time, as in prior art arrangements. s

Features and Aadvantages of the invention will be seen from the above and from the following description of operation of one preferred embodiment when considered embodying the invention, as applied to that portion of an elevator power and control system which relates to control of the elevator doors, including circuits for door protective mechanisms; and

FIGURE ls is a spindle sheet Yfor use in side-by-side alignment with FIGURE 1 for locating the coils and contacts in FIGURE l.

With reference to lthe drawing, to facilitate and simplify the disclosure, only certain portions of the elevator control circuits are shown and these relate to the control of elevator doors at a floor landing. Also for convenience, only the contacts of field and brake switch H are shown in the wiring diagram, this switch being operated in the usual mannerby any one of several elevator control systems incident to the car starting Iand stopping at a floor landing and only its contacts, as shown in the circuits of FIGURE l, being involved Vin the operation of the subject invention.

'Ihe electromagnetic switches employed in the system illustrated are designated `as follows:

B--Light beam switch DC--Door close switch DO--Door open switch VI n the wiring diagram, identifying letters are applied to the coils of the electromagnetic switches and, with reference numerals appended thereto, are applied to the vcontacts 'of the switches to differentiate between different sets of contacts on the same switch, al1 contacts being 'shown for the unoperated condition of the switches.

' Door close limit switch DCL and door open limit switch DOL are actuated by door movement and are illustrated -for the closed position of the door. Door zone switch DZ is actuated by car movement to establish a lzone at a floor Vlanding within which the door may be opened and is shown for the position'ofthe car at a oor landing. Mechanical safety shoe switch SSC is actuatableto open condition, as the leading edge of the car door encounters a person in its closing path and returns 'to unactuated condition `as the leading edge of the car door loses contact with that person.

I Supply lines W-land W- apply unidirectional powerto the circuits of FIGURE 1. Resistors and capacitors are designated generally as R Iand C, respectively. The circuits for the light beam type protective mechanism are illustrated in the upper portion of FIGURE 11 and include two photo tubes PHTI and PHTZ, such as the RCA 91S gas iilled type, positioned on one side of the car door entranceway; two sources of light L1 and L2 for the photo tubes, arranged on the opposite side of the v 4 AMT, such as the RCA 6Sl7 high gain, sharp cut of pentode, having its control grid connected to point X for amplifying the signal appearing across resistor R1. Coil B of the light beam switch is connected in the anode circuit of tube AMT. So long as the lightrbeam for each tube PHT is not obstructed, a positive potential exists at point X of a value to cause suflcient current iiow through tube AMT and coil B to ymaintain the light beam switch operated and in turn light beam switch contacts B1 separated. DMA andV DMF designate, respectively, the armature and iield of a reversible direct current driving motor lfor mechanisnrto operateV both the car and hoistway doors' at a floor landing.

An understanding of the invention can best be gained Y from a description of the sequences of voperations beginning with a door opening operation. Assume that the vcar is traveling between oor landings so that the iield and brake switch H is operated. Under such conditions the coil XNT of the hall time switch is maintained energized and condenser C1 is maintained in fully charged condition through engaged tield and brake switch contacts H2.

Next assume that the car arrives at a oor landing in response to a call lfor service at that landing and in so doing actuates door zone switch DZ to closed condition. Incident to the car stopping at the floor landing, tield and brake switch H releases, separating its contacts H2 to interrupt the circuit of coil XNT and condenser C1.

Switch XNT is delayed in releasing, by the discharge of` condenser C1 through its coil. Switch H also engages-its contacts H3 to complete a circuit for coil D0 of the door open switch, the circuit extending from supply line W-lthrough door open limit switch DOL, field and brake switch contacts H3, door zone switch DZ, hall time switch contacts XN'Dl and'coil DO to supply line W-. Door open switch DO, upon operation, engages its contacts D01, short circuiting the now separated contacts H2 of the field and brake switch, completing the circuit for coil XNT and condenser C1 to maintain switch XNT operated. Door open switch D0 also separates contacts D03, removing a short circuit from armature DMA and engages contacts D02, DD4, completing a circuit for door motor armature DMA, causing it to rotate in a di-V rection to move the door toward its fully opened position,

the latter circuit extending from supply line W throughy D02, DMA and D04 to supply line W.

As the door moves in the opening direction, door close` and D04, interrupting the circuit of armature DMA and engages contacts D03, short-'circuiting armature DMA to brake the door motor dynamically, stopping the opening movement of the door. This switch also separates its contacts D01, interrupting the circuit o-f coil XNT of the hall time switch andV condenser C1, which condenser starts to discharge through a portion of adjustable resistor R2 and coil XNT. 4Hall time switch XNT is delayed in releasing for a -time interval determined by the resistor R2 capacitor C1 timing circuit, which time interval is termed the door open dwell period, during which the doors are kept in their fully opened position to allow yfor normal passenger transfer at the landing and at the expiration of which a door closing operation is initiated, as will be described. Y

It may be noted that the duration of this door open dwell period may be preset to establish a time interval deemed suli'icient to allow for normal passenger transfer at a oor landing for a particular installation by changing the position of the adjustable tap on resistor R2 to vary the discharger time of condenser C1.

After condenser C1 has discharged to a value where the excitation of coil XNT is no longer sufficient to hold the hall time switch operated, switch XNT releases, engaging its contactsr XNTZ to complete a circuit for coil DC of the door close switch thereby initiating a door closing operation, the circuit extending from supply line W+ through DCL, SSC, XNTZ and DC to supply line W-. Switch XNT also separates its contacts XNTl, for purposes to be explained later.

Switch DC, upon operation, engages contacts DC1 preparing a circuit through contacts H1 for the coil DP of the door protective switch. Switch DC also separates contacts DCS removing the shortcircuit from armature DMA and engages contacts DC2, DC4, completing a circuit for armature DMA, causing the armature to rotate in a direction to move the door toward its closed position, the latter circuit extending from supply line W+ through DC4, DMA yand DC2 to supply line W-.

As the door begins to move in the closing direction, door open limit switch DOL is actuated by door movement to closed condition in preparation for a subsequent door opening operation, but without effect at this time since contacts XNTl are already separated, as has been previously stated.

Now assume that after the expiration of the normal door open dwell period and as the door begins moving in the closing direction, an intending passenger, arriving late, interrupts the light beam extending across the entranceway. As the light beam is thus interrupted, the potential existing at point X is lowered, reducing the magnitude of the current conducted by amplifying tube AMT and passing through coil B of the light beam switch, connected in the anode circuit of tube AMT, suficiently to cause switch B to release. Switch B engages its contacts B1, completing a circuit through contacts DCI and H1 for coil DP of the door protective switch, which becomes self holding through its contacts DPI thereby remaining in operated condition even if the light beam is reestablished to separate contacts B1 again.

Switch DP, upon operation, engages its contacts DP2, short circuiting la portion of resistor R3 to' reduce the amount of resistance -in parallel with `armature DMA thereby decreasing the -current ow through the armature to reduce the closing speed of the Vdoor a predetermined value below normal closing speed. In this manner late passenger transfer is detected before the leading edge of the door encounters a transferring passenger and las a result the closing speed of the door is reduced to allow such late passengers -to enter or leave the car.` At the same time, since the door `continues to close at reduced speed instead of reopening or stopping, as -in the aforementioned prior -art arrangements, late passengers tend to move quickly in or out of the car and the departure of the car is not unduly delayed. It may be noted that the adjustable tap on resistor R3 may be sopositioned as to obtain the most practicable reduction in speed to accomplish the foregoing benefits.

Next assume that while the door is thus closing at reduced speed, the leading edge of the door comes into contact with a personin its closing path, actuating mechanical safety shoe switch SSC to open condition to interrupt the circuit for coil DC of the door close switch. Switch DC, upon releasing, separates contacts DC2, DC4 interrupting the armature circuit :and engages contacts DCS, short circuiting armature DMA t-o stop the closing movement of the door thereby allowing lthe late transferring passenger to move out of the path of the door. Contacts DCI also separate, interrupting the circuit of coil DP of the door protective switch. Switch DP releases, separating its contacts DPZ to insert all of resistor R3 in parallel with armature DMA in preparation for a resumption of the door closing operation `at normal closing speed once the obstruction is removed, 'as will be described later.

It may be noted that should a person remain in the closing path of the door after initial detection by the light beam device, the safety devices cooperate irst to reduce the closing speed of the door, as the light beam is broken, and then `to stop the door as the leading edge of the door encounters the obstructingpassenger. In this manner the closing movement of the ldoor is stopped only when necessary. Also, inasmuch as the leading edge of thedoor encounters the obstructing passenger to stop the do-or while it is traveling at the reduced speed, the possibility of injury to that passenger is minimized. Furthermore, stopping the door while it is traveling at the reduced speed minimizes shock to the door operating mechanism.

Now assume -that the obstructing passenger moves out `of contact with the leading edge but remains in the closing path of the door thereby releasing 'the mechanical safety shoe switch SSC but maintaining the light beam interrupted. As the mechanical safety shoe switch SSC returns to closed condition, a circuit for coil DC of the door close switch is completed through contacts XNTZ and switch DCL. Switch DC operates, separating contacts D03 to remove the Vshort circuit from armature DMA, engaging its contacts DC2 and DC4 in the armature, circuit yand contacts DCI in series with coil DP, causing the door to resume moving in the closing direction at reduced speed. It should be understood that if the obstructing passenger not only moves out of contact with the leading edge but also moves entirely out of the closing path of the door, the light beam is then unobstructed and switch DP remains in released condition. in such a case, as switch DC operates, the door moves in the closing direction `at normal clos-ing speed, contacts DCl engaging merely to prepare a circuit for coil DP of the door protective switch for a subsequent interruption of the light beam. Should the light beam again be interrupted, contacts Bl engage causing switch DP to operate and Kreduce the closing speed of the door below normal, -as has been previously explained. It should be understood that once the closing speed yof the door is thus reduced, the reduction in speed is maintained unless the door is stopped by actuation of mechanical safety shoe switch SSC.

As the door approaches its fully closed position, door close limit switch DCL is actuated by door movement to open condition interrupting the circuit of coil DC. Switch DC releases, separating its contacts DC2, DC4 and engaging its contacts DCS in the larmature circuit to stop the closing movement of the door.

Incident to starting the car away from the oor landing, eld and brake switch H operates, engaging its contacts H2 to complete a circuit for coil XNT and condenser C1 in preparation for the next floor llanding stop. As the car leaves the floor landing, door Zone switch -DZ is actuated by car movement to open condition, disabling the door open switch DO, preventing it from opening the door between floor landings.

In summary, it may be noted that the safety devices cooperate to control the door movements after the normal passenger transfer time has expired by providing advanced detection of an obstruction in the closing path of the door and upon such detection, effecting a reduction in the closing speed to allow passenger transfer. However, should the leading edge of the door encounter an obstruction, the closing movement of the door is stopped. When the obstruction is removed from the leading edge of the door, the door resumes closing at normal speed provided that an obstruction is not detected in the entranceway by the light beam. If such an obstruction is so detected by the light beam, the door continues moving in the closing direction but at the reduced approach speed, enabling the obstructing person to move out of its path before the `door reaches him. In this manner unnecessary door movements 'are minimized, yet lateV 7 and :discourage passengers aniving after :the expiration of the normal door open dwell period from unduly interfering ywith the door closing operation. Since the -advanced detection mechanism reduces the speed of the door before the leading edge encounters theV obstruction, :the stopping of the door is effected Iat this reduced ap- {proach speed, minimizing shock to the door operating mechanism. Also when the leading edge of the door strikes an'obstruotion in its path, it does so while the door is traveling -at the reduced approach speed, minimizing the danger of injury -to the transferring passenger and making practicable the use of relatively higher than usual door closing speeds to obtain fas-ter door operation.

It should also be noted, that should the light beam safety device become disabled, such as by failure of the photo tubes PHT, lights L or amplifying tube AMT, the door will close at reduced speed upon expiration of the normal door open dwell period without waiting for the expiration of a certain failure Vtime, as in prior art arrangements, thereby maintaining the car in service while safeguarding transferring passengers.

By proper selection for a particular elevator installation of the duration of the door open dwell period during which normal passenger transfer may take place and of the amount by which the closing speed of the door is reduced upon an initial advance detection of a late transferring passenger, the subject door control appreciably expedites elevator service and minimizes maintenance of the door operating mechanism withoutrunduly hindering passenger transfer.

Although the invention has been described according to a preferred embodiment using light beam and mechanical safety shoe type safety devices, cooperating to control door movements, the invention is just as applicable to a combination using the light beam type safetyV device in conjunction and cooperating with a proximity type detector which detects a person within a predetermined distance in advance of the leading edge of the closing door. Such a proximity type detector is described and disclosed in the aforementioned Bruns patent with particular reference to the upper portion of FIGURE 4 therein. With such an arrangement, by substitutingV a pair of normally engaged contacts DPX of the auxiliary door protective relay DPX shown in the aforementioned FIGURE 4 .of the Bruns patent for the mechanical safety shoe switch SSC in the circuits Vof FIGURE 1 herein, substantially the same operation is obtained as that disclosed for the preferred embodiment.

As changes can be made in the above described system and many apparently different embodiments of this invention can be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown on the accompanying drawing be interpreted as illustrative only and not n a limiting sense. i

What is claimed is:

1. A control for a horizontally sliding type elevator door mounted for sidewise movement for opening and `closing an elevator entranceway to passenger transfer,

said control comprising, door operating means for opening` and closing operation of said door, object-sensing means including a/,transmitter of radiant energy positioned on one side of said `entranceway and directing a beam of radiant energy horizontally across said entranceway across the path of passengers transferring through said entranceway and a radiant energy receiver positioned on the other side of said entranceway in line with said beam of energy and responsive to said beam, said object-sensing means being operatively responsive to interruption of said beam by a transferring passenger during a door closing operation of said door operating means, means for reducing the speed of said door below normal closing speed in closing, said speed reducing means being actuated by operation of said object-sensing means and remaining so actuated notwithstanding that said beam is subsequently reestablished only so long as said door continues moving in the closing direction, object-detecting means for detecting the presenceA of an object adjacent the leading edge of said door in the closing path of said door, and swi-tching means operatively responsive to such detection by said object-detecting means for causing said door operating means to stop the closing movement ofsaid door and return said speed reducing means' to unactuated condition. v Y Y 2. A control for a horizontally sliding type elevator door mounted for sidewise movement for opening and` closing an elevator entranceway to passenger transfer, said control comprising, door operating means for opening and closing operation of said door, object-sensingv means including a transmitter of radiant energy Vpositioned on one side of said entranceway and directing a beam of radiant energyV horizontally across said entrancey way across the path of passengers transferring through said entranceway, and a radiant energy receiver positioned on the other side of said entranceway in line with said beam of energy and responsive to said beam, said object-sensing means being operatively responsive to interruption of said beam by a transferring passenger during a door closing operation of said door operating means, means for reducing the speed of said door below normal closing speed in closing, said speed reducing means being actuated by operation of said object-sensing means and remaining so actuated notwithstanding that said kbeam subsequently is reestablished only so long as Vsaid door continues moving in the closing direction, object-detecting means for detecting the presence of an object contiguous the leading edge of said door in the closing path of said door, and switching means operatively responsive to such detection by said object-detecting means for causing said door operating means to stop the closing movement of said door for only so long as said detection persists, said speedreducing means returning to unactuated condition as said door is stopped by said door operating means, said speed reducing means again being actuatable by operation of said object-sensing means after said detection ceases Ffor againreducing the closing speed of said door. Y

3. A control for a sliding type elevator door mounted for opening and closing an elevator entranceway to passenger transfer, said control comprising, proximity-detect-r ing means operatively responsive to the presence of an object in the closing path of said'door within a predetermined range in vadvance of the leading edge of said,

door, switching means operatively responsive to operation 0f said proximity-detecting means, said switching means being actuated from a lirst condition to .a second condition when said proximity-detecting means responds to the presence of an object within said range and being returned to unactuated condition when said object ceases to be within said range, door operating means'for opening and closing said door, said dooropera-ting means being operatively responsive to actuation of said switching means by said proximity-detecting means to stop the closing movement of said door upon actuation of said switching means to said second condition and to resume l Y movmg said door in a closing direction upon return ofsaid switching means to unactuated condition, objectsensing means lincluding a radiant energy ytransmitter positioned on one side of said entranceway and directing a beam. of energy across said entranceway across the path of passengers transferring through said entranceway and a control device positioned on the other side of said entranceway in line with said beam of energy and operatively responsive to interruption of said beam by a 11ansferring passenger during a door closing operation of said doer operating means, means for reducing the speed of said door below normal closing speed during closing movement of said door, said speed reducing means being actuatable by operation of said controlV device of said object-sensing means, and holding means responsive to said door operating means for maintaining said actuated speed reducing means actuated only so long as said door continues moving in the closing direction.

4. In an elevator system in which a car serves several oor landings of a building, a control for a sliding elevator door mounted on said car for sidewise movement to open and close an entranceway to said car, said control comprising, door operating means for opening and closing said doors; switching means operable from a first condition to a second condition and to a third condition, said switching means when in said rst condition being effective to maintain said door operating means in a door-closing condition, when in said second condition being etective to cause said door operating means to stop said door and when in said third condition being effective to maintain said door operating means in a door-opening condition; initiating means operable incident to the car stopping at a floor landing in response to a call for service to actuate said switching means from said second condition to said third condition for initiating a door opening operation of said door operating means and lbeing effective to return said switching means to said second condition as the door arrives at its fully opened position; timing means for actuating said switching means from said second condition to said first condition upon expiration of a predetermined time after said door reaches its fully opened position to initiate a closing operation of said door operating means, objectdetecting means for detecting the presence of an object against the leading edge of said door in the closing path of said door, said detecting means actuating said switching means to said second condition upon detection of such l l an object to stop the closing movement of said door and returning said switching means to said first condition when detection ceases to resume closing said door,

speed reducing means for `reducing the speed of said door in closing below normal closing speed, object-sensing means including a radiant energy transmitter positioned on one side of said entranceway and directing a beam of energy across said entranceway in the path of passengers transferring through said entranceway at said landings and a control device positioned on the side of said entranceway opposite to said transmitter and in the path of said energy beam, said control device being operatively responsive to interruption of said beam during a door closing operation of said door operating means, said control device of said object-sensing means when so responsive causing actuation of said speed reducing means to reduce the closing speed of said door, and holding means responsive to such actuation, of said speed reducing means by said object-sensing means for maintaining said speed reducing means actuated only so long as said door continues to move in a closing direction, said holding means also being responsive to said switching means for releasing said speed reducing Vmeans upon actuation of said switching means to said second condition by said object-detecting means for restoring the normal closing-speed of said door.

References Cited in the file of this patent UNITED STATES PATENTS 2,634,828 Bruns Apr. 14, 1953 V2,806,553 Eames Sept. 17, 1957 2,900,521 Eames Aug. 18, 1959

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