US3429073A

US3429073A - Compact door operator

Info

Publication number: US3429073A
Application number: US589964A
Authority: US
Inventors: Benjamin Whitehead Tucker Jr
Original assignee: Otis Elevator Co
Current assignee: Otis Elevator Co
Priority date: 1966-10-27
Filing date: 1966-10-27
Publication date: 1969-02-25
Anticipated expiration: 1986-02-25

Description

Feb.25, 1969 Filed Oct. 27, 1966 5,2 35 62 6! a. w. TUCKER, JR 3,429,073

COMPACT DOOR OPERATOR INVENTOR BENJAMIN WHITEHEAD TUCKER JR BY MZW ATTORNEY Feb. 25, 1969 a. w. TUCKER, JR 3,429,073

COMPACT DOOR OPERATOR Filed Oct. 27. 1966 L2 LLZIZCLOSE 56 TPEN.

Sheet 2 of3 I35 I54 I32 I I FIG. 6

INVENTOR I BY ATTORNEY Feb. 25, 1969 a.w 1'ucKER, JR 3,429,0

COMPACT DOOR OPERATOR Filed 001:. 27. 1966 Sheet INVENTOR BENJAMIN WHITEHEAD TUCKER JR.

United States Patent 13 Claims ABSTRACT OF THE DISCLOSURE A closure apparatus including a support structure, a sliding door mounted on the structure for lateral movement between open and closed positions, a motor for operating the door, switch means for controlling the motor, a locking plate rotatably mounted on the structure, a linkage interconnecting the door and the locking plate for rotating the locking plate in response to lateral movement of the door, and a locking arm pivotally mounted on the structure and ang-ularly displaceable relative thereto to three selected positions to operate the switch means for respectively unlocking and opening, unlocking and closing and locking and closing the door.

This invention relates generally to operators for sliding doors and particularly to a novel operator suitable for use where space is at a premium as it is in rapid transit cars.

A so-called sliding door, as the expression is usually used, denotes a door which is opened or closed by a lateral motion, as contrasted with a swinging motion, whether the door actually slides or whether it travels on wheels, balls, or rollers. The cars of railway rapid transit lines are usually equipped with several such doors on each side to permit quick passenger transfer at each station and also with one at each end to allow passage between cars. The end doors are normally arranged for manual operation, while the side doors are usually provided with power actuated mechanisms, called operators, for opening and closing them either automatically or under the control of an attendant. In service, the doors and operators should have certain characteristics. Efiicient operation requires that the doors open and close quickly. They should operate smoothly without jarring or banging when fully opened or the fully closed position is reached. Provision must be made for preventing injury to a passenger in the pathway of a closing door. The mechanism must not be damaged if door closing is prevented by the presence of an obstruction. When fully closed, the door should be mechanically locked and a signal indicative of this condition should be generated, which signal should persist only as long as the door remains mechanically locked. The operator should be compact because there is no room above the door for bulky machinery. It is preferred that the operator be located entirely within the walls of the car so as to leave the interior free for the use of passengers. And, of course, the operator should be simple and inexpensive.

Many kinds of operators have been proposed in the past. Some have been operated by fluid pressure, others by electricity. None has been entirely satisfactory.

It is a general object of the present invention to provide an improved operator for a sliding door.

Another object is to provide an operator having the desirable characteristics previously mentioned.

A more specific object is to provide a compact operator which can be mounted readily within the wall of the structure carrying the door.

Briefly stated, a preferred embodiment of the invention includes a sliding door which is opened and closed by a linear electric motor acting directly between the door 3,429,573 Patented Feb. 25, 1969 and its supporting structure. A shaft mounted on the structure is mechanically interconnected with the door so as to be rotated back and forth by the opening and closing of the door. This shaft serves as the operating shaft for a fluid cushioning device and also carries a locking plate which cooperates with a pivoted locking arm to lock the door in its closed position. The door may be unlocked by energizing an electromagnet which raises the locking arm out of locking position. The motion of the arm actuates suitable signal and control switches.

For a clearer understanding of the invention, reference may be made to the following detailed description and the accompanying drawing, in which:

FIGURE 1 is a fragmentary elevation view of one side wall of a rapid transit car taken from within the car with the interior panel removed and showing a sliding door equipped with an operator in accordance with the present invention;

FIGURE 2 is an elevation view of the operator of FIGURE 1;

FIGURE 3 is a cross section view taken on the plane 3-3 of FIGURE 2;

FIGURE 4 is a schematic diagram of the electric control circuit;

FIGURE 5 is a schematic diagram of the timing circuit;

FIGURE 6 is a fragmentary elevation view of one end wallcf a rapid transit car taken from within the car with the anterior panel removed and showing a sliding door equipped with an operator in accordance with the present inventlon;

FIGURE 7 is an elevation view of the operator of F IG- URE 6;

FIGURE 8 is a cross section view taken on line plane 8- 8 of FIGURE 7; and

FIGURE 9 is a schematic diagram of the control circuit for the operator of FIGURES 6, 7 and 8.

Referring first to FIGURE 1 there is shown a rapid transit car 21, the side of which is formed with an openmg which is alternatively covered or exposed by one or more sliding doors such as the door 22. These doors are mounted for lateral movement by a conventional hanger arrangement the details of which are not a part of the present invention.

A linear electric motor, designated generally by the reference character 23, is provided for opening and closing the door 22. The motor 23 comprises a magnetic assembly 24 fastened to the car and an elongated conductive element 25 fastened to the edge of the door 22. The motor 23 may be any of various kinds but in the specific embodiment being described it is a two phase linear induction motor which operates in a manner analogous tothat of the familiar squirrel cage motor. The magnetic assembly 24 includes appropriate energizing windings for generating a linearly moving magnetic field.

A shaft 26 is rotatably mounted on the car 21. A crank arm 27 has one end rigidly fastened to the shaft 26 and the other end pivotally fastened to one end of a connect ing rod 28 the other end of which is pivotally fastened to the door 22. Accordingly, as the door is opened and closed by the motor 23, the connecting rod 28 and the crank arm 27 cause the shaft 26 to rotate.

Referring now to FIGURES 2 and 3, there is shown a generally vertical mounting plate 31 which is formed with a vertically extending flange 32 and a horizontally extending flange 33. The plate 31 is mounted within the wall of the car 21. As best shown in FIGURE 3, the wall of the car includes an interior panel 34, an exterior panel 35 and a number of cross pieces such as the cross piece 36. The plate 31 is mounted along the inside surface of the exterior panel 35 and is bolted to the cross piece 36.

The previously mentioned magnetic assembly 24 is fastened to the horizontal flange 33. The conductive element 25 is fastened to an L-shaped bracket 37 which in turn is fastened to the door 22. A roller 38 is fastened to a bracket 39 which in turn is also fastened to the horizontal flange 33 of the mounting plate 31. The roller 38 is positoned to support and guide the conductive element 25.

A switch 41, sometimes referred to as the open limit switch (L) is also fastened to the flange 33 and includes an actuator 42. The switch is operated by an up-turned flange 43 of a bracket 44 which is fastened to the movable element 25 in such a position that the switch is actuated when the door 22 is in its fully open position as illustrated in FIGURE 2.

The previously mentioned shaft 26 is the operating shaft of a hydraulic cushioning device 46 which is mounted on the plate 31. The device 46 operates in a well-known manner to cushion the door 22 as it reaches its fully open and fully closed positions. A locking plate 47 is rigidly fastened to the shaft 26 and to the crank arm 27. The upper surface 48 of the plate 47 is arcuate in form and concentric with the shaft 26, The arcuate surface 48 is broader than the remainder of the plate in a direction parallel to the axis of the shaft, as best shown in FIGURE 3. The plate 47 is also formed with a radial abutment 49.

A locking arm 51 is pivotally mounted on the plate 31 by a shaft 52. One end of this arm, the right hand end, as viewed in FIGURE 2, has a lower corner cutaway to form an abutment 53. The arm 51 is positoned above the plate 47 so that gravity urges the right hand end downward towards engagement with the arcuate surface 48. A small roller 54 is mounted near this end of the arm and is the portion of the arm which actually rests on the surface 48.

An electromagnet 56 is mounted on the plate 31 just above the arm 51 and includes a movable element which is connected to a link 57 which in turn is pivotally connected to the arm 51 so that this arm is raised when the electromagnet 56 is energized. A switch 58, sometimes referred to as the close limit switch (CL) is mounted on the plate 31 near the locking arm 51. As best shown in FIGURE 3, the roller 54 is mounted on a stud 59 which projects in back of the arm 51 so as to engage the actuator of the switch 58. The opposite end of the locking arm 51, that is, the left hand end as viewed in FIGURE 2, is formed with an extension 61 which carries two

machine screws

62 and 63 which are positioned to engage the actuators of

switches

64 and 65 which are mounted on the plate 31.

FIGURES 2 and 3 show the door 22 in its fully opened position. In order to close the door, the magnetic assembly 24 is energized by a circuit to be fully described subsequently. As the door closes, the connecting rod 28 and the crank 27 rotate the shaft 26 and the locking plate 47 clockwise. When the door is fully closed, the plate 47 will have rotated to the dotted line position which is just far enough to allow the locking arm 51 to drop down so that the two

abutments

49 and 53 are juxtaposed. Rotation of the Plate 47 in the counterclockwise direction is prevented, thereby locking the door closed, To open the door, the electromagnet 56 is energized thereby raising the locking arm 51 above the surface 48 to a position higher than the position shown in FIGURE 2. Then the motor 23 may be energized and the door opened.

It is to be noted that the arm 51 can assume any one of three positons. The first, or raised position, occurs during the door opening when the electromagnet 56 is energized to bring the arm 51 entirely out of contact with the surface 48. The second, or intermediate position, occurs when the electromagnet 56 is de-energized and the door 22 is in any positon except its fully closed position. At this time, the roller 54 rests upon the surface 48 as shown in FIGURE 2. The third positon is a fully lowered position, which can occur only when the door 22 is fully closed and the electromagnet 56 is de-energized, so that the arm 51 can drop down to bring the abutment 53 opposite the abutment 49 so as to lock the door.

The

switches

58, 64 and 65 are each capable of assuming either a first or a second condition. The closed limit switch 58 is positioned and adjusted so that it assumes its first condition when and only when the arm 51 is in its third, lower position with the door locked. This switch is used in the control circuit as will be more fully explained.

The switch 64, although operated by the extension 61, is also positioned and adjusted so that it assumes its first condition when and only when the arm 51 is in its third position with the door locked. This switch is used as a signaling device and may be connected to either light or extinguish a lamp when the door is locked.

The switch 65 is positioned and adjusted so that it assumes its first condition when and only when the arm 51 is in its first or raised position. As soon as the electromagnet 56 is de-energized, dropping the arm 51 to its second position, the switch 65 assumes its second condition in which it remains as long as the arm 51 is in either its second or its third position.

Referring now to FIGURE 4, there is shown the elec tric circuit for opening and closing the door. Lines L1 and L2 are connected to a suitable alternating current source. The motor 23 is provided with

terminals

71 and 72, bridged by a capacitor 74, and with a common terminal 73 which is connected through a normally closed contact KIA to the line L2. An adjustable resistor 75 is connected between line L1 and the arm of the switch 65 which is a single pole double throw switch. A warning lamp 76 has one terminal connected through the switch 64 to the line L1 and the other terminal connected to the line L2. A switch 77 is provided to open and close the door. This switch may be operated either manually or automatically but for purposes of explanation it will be assumed that the switch is manually operated. A timing circuit 78 includes the operating winding of a relay K1 which controls the previously mentioned contact KIA.

The remainder of the circuit can best be explained by considering its mode of operation. FIGURE 4 shows the position of the parts when the door 22 is closed. The locking arm 51 is in its third position; the switch 64 is in its first condition which is open and the lamp '76 is extinguished; the closed limit switch S8 is in its first condition which is open; the open limit switch 41 is closed; and the switch 65 is in its second condition which corresponds to its upper position as shown in the drawing. In order to open the door the switch 77 is moved to its open position thereby energizing the electromagnet 56 and raising the locking arm 51 to its first position. This closes the

switches

58 and 64 and moves the switch 65 to its lower position. Accordingly, the terminal 72 is energized directly from the alternating current source while the terminal 71 is energized through the capacitor 74. The door 22 is opened, the switch 41 is opened, and the motor is de-energized.

In order to close the door the switch 77 is moved to its close position thereby de-energizing the electromagnet 56, thus allowing locking arm 51 to drop to its second position at which the roller 54 engages the surface 48 of the locking plate as shown in FIGURE 2. This movement of the arm 51 raises the switch 65 to its up per position and, since the switch 58 is closed at this time, the terminal 71 is energized directly while the terminal 72 is energized through the capacitor 74. The door starts to close. If no obstructions are encountered the door closes allowing the arm 51 to drop to its third position and lock the door thereby opening the switch 58 and de-energizing the motor.

If an obstruction, such as a person, is in the path of the door it will be prevented from closing. The torque of the motor has been limited by resistor 75 so that no injury to the passenger can result. However, continued energization of the motor may cause it to overheat. To prevent such overheating, timer 78 is provided. If the door 22 does not completely close within a predetermined time after closing has been initiated, the timing circuit 78 operates to energize the relay winding K1 thereby opening the contact KIA and de-energizing the motor. After another predetermined time, the winding K1 is de-energized thereby closing the contact K1A, whereupon the motor 23 is again energized so as to close the door. This cycle of alternate energization and de-energization continues until the door is closed.

Rapid transit cars are usually provided with doors at each side but it is seldom that doors on both sides are opened simultaneously. Therefore a single timing circuit 78 can be used for the doors on both sides of the cars. Assuming, for example, that the motor 23 and door 22 are installed on the right hand side of the car, the left hand side is provided with a motor 81 including

terminals

82, 83 and 84 similarly connected. However, the same timing circuit 78 is also connected to the terminal 82 while the terminal 84 is connected to the terminal 73 so that the timing circuit 78 is operative whenever either the right or the left door is closed.

The details of the timing circuit 78 are shown in FIG- URE 5. The terminal 71 and the line conductor L2 are connected to the input terminals of a conventional full wave rectifier circuit 91 comprising four rectifying elements connected to the familiar bridge circuit. The positive output terminal is connected to a conductor 92 and the negative output terminal is connected to a conductor 93. Two additional rectifying

elements

94 and 95 are connected to form alternative upper legs of the bridge and provide a second input which is connected to the terminal 82. Thus, when either the terminal 71 or the terminal 82 is energized with alternating current, a voltage appears on the conductor 92 which voltage is positive with respect to the conductor 93.

The voltage on conductor 92 causes a current to flow through the low valve resistor 96 so as to charge a capacitor 97 quickly. A voltage regulating element such as a tube 98 is connected across the capacitor 97 so as to hold the potential of the junction 101 substantially constant. A conductor 102 is connected to the junction 101 and assumes a positive potential whenever either the terminal 71 or 82 is energized. Similarly, the junction 103, which is connected to the junction 102 through a resistor 104, becomes positive with respect to conductor 93.

Three silicon controlled

rectifiers

106, 107 and 108 are all non-conducting initially because their gate electrodes are at the same potential as their cathodes. The

rectifiers

107 and 108 are connected in a conventional asymmetrical multivibrator circuit in which, when the circuit is enabled, the two rectifiers conduct alternately. The rectifier 106 is connected in a circuit which enables the multivibrator after a predetermined time.

Upon the appearance of a voltage at the junction 101, a current flows through the resistors 111 and 112 and starts to charge the capacitor 113. This circuit has a substantially longer time constant than the resistor 96 and capacitor 97 but eventually the potential of the capacitor 113 rises sufficiently to cause a current to flow through the neon tube 114 and to render the controlled rectifier 106 conductive. The junction 103 falls quickly to substantially ground potential. A capacitor 115 starts to charge through the resistors 116 and 117. Likewise a capacitor 121 starts to charge through the relay winding K1 and a resistor 122. The circuit of capacitor 115 has a shorter time constant so that presently the potential thereof rises sufiiciently to cause the neon tube 123 to conduct thereby turning on the controlled rectifier 107. The multivibrator action almost immediately removes any partial charge from the capacitor 121 through a resistor 124 and a rectifying element 125. However, the capacitor 121 immediately starts to charge again through the resistor 122.

Eventually the potential rises sufiiciently to cause the neon tube 126 to conduct therefore turning on the controlled rectifier 108. The relay winding K1 is energized, the contacts KIA (FIGURE 4) are opened, and the motor 23 is de-energized. At the same time the controlled rectifier 107 is cut off and the capacitor starts to re-charge. Eventually, the controlled rectifier 107 is again turned on thereby turning off the rectifier 108', de-energizing the relay K1 and closing the contact KIA. Thus the motor 23 is alternately de-energized and energized. The cycle repeats until the door closes.

Reviewing the operation of the timing circuit, the motor 23 is energized to close the door and if there is no obstruction it is de-energized by the opening of the closed limit switch 58. If not so de-energized in a predetermined time, namely, the time required to charge the

capacitors

113, 115 and 121 successively, the contact K1A is opened thereby de-energizing the motor. After another predetermined time, namely, the time required to charge the capacitor 115, the motor is re-energized. Then, after another predetermined time, namely, the time required to charge the capacitor 122, the motor is again de-energized and the cycle repeats until the door closes.

The operation has been described as occurring when the terminal 71 is energized to close the door and this is correct. The timing circuit 78 also starts to operate when the terminal 72 is energized to open the door. However, the door normally opens quickly and reaches its fully open position before the timing circuit 78 can operate. While it is not necessary that the timing circuit operate during the opening of the door, such operation does no harm and actually provides additional protection to the motor.

The invention may also be applied to the end doors of a rapid transit car, that is, to the doors through which one passes when going from one car to another. As shown in FIGURE 6, the car 21 is provided with sliding doors 131 and 132 at each end. A linear electric motor 133 comprising a magnetic assembly 134 including an energizing winding is fastened to the edge of the door 132. An elongated conductive element 135 is fastened to the structure of the car. A shaft 136 is also mounted on the car structure and a crank arm 137 is rigidly fastened thereto. A connecting rod 138 has opposite ends pivotally fastened to the crank arm 137 and to the door 132. Thus, the motor opens the door and the door rotates the shaft 136-.

As best shown in FIGURE 7, a bracket 141 is formed with a generally horizontally flange 142 which is fastened the bottom of the magnetic assembly 134. The bracket 141 is also formed with a generally vertical flange 143 which is fastened to the door 132. The conductive element 135 is fastened to the car structure by means of a rubber block 144 which also serves as a resilient stop for the assembly 134 in case it should overtravel. A switch 146, also fastened to the car structure, includes an actuator 147 which is operated by a strap 148 fastened to the bracket 141 in such a position as to actuate the switch 146 when the door is in its fully opened position as shown in FIG- URE 7.

As best shown in FIGURE 8, the end wall of the car 21 includes an interior panel 151, an exterior panel 152 and two frame members or braces 153 and 154. A rigid block 155 is fastened to the brace 153 and supports a strong rigid plate 156 which in turn supports a mounting plate 157. As shown in FIGURE 7, a cushioning device 159 is fastened to the plate 157 and carries the previously mentioned operating shaft 136 to which the crank arm 137 is rigidly fastened. A locking plate 161 similar to the plate 47 of FIGURES 2 and 3, is fastened to the shaft 136 and the arm 137. A locking arm 162 is similar to the arm 51 except that the extension 163 on the left side may be formed slightly differently so as to accept two

machine screws

164 and 165 side by side, which screws operate

switches

166 and 167 respectively. These switches are both actuated to their first condition when and only when the arm 162 is in its first, raised, position. A switch 168,

7 comparable to the switch 58 of FIGURE 2, is actuated to its first condition when and only When the arm 162 is in its third, lowered position with the door locked. An electromagnet 169 is operatively connected to the arm 162 so as to unlock the door when energized in the same way that the electromagnet 56 unlocks the door 22.

The end door 132 is operated a little differently from the side door 22. On the interior Wall of the car, adjacent to the door, is a push button. When this button is depressed, the door opens and remains open for a predetermined time after which it closes. The circuit for accomplishing this is shown in FIGURE 9.

In FIGURE 9, the parts are shown in the positions they are in when the doors are fully closed. When power is first applied to the alternating current lines L1 and L2, current flows from L1 through the switch 166 and the rectifier 171 to the line L2. The relay winding K2, which is connected to the output terminals of the rectifier 171, is energized thereby closing the contacts K2A. A capacitor 172 is charged by being connected in series with

resistors

173 and 174 and a rectifying element 175 across the output of the rectifier circuit 171. The two

resistors

173 and 174 are of comparatively low value so that capacitor 172 can charge quickly. The relay winding K2 is connected from one terminal of the capacitor 172 through a large resistor 176 to the junction of the

resistors

173 and 174.

To open the door, the push button 181 is depressed momentarily thereby energizing the electromagnet 169 and raising the arm 162 to its first position which closes the switch 168 and moves the

switches

166 and 167 to their first conidtion which is the opposite condition from that shown in FIGURE 9. The electromagnet 169 is maintained energized through a circuit including the switch 166 and the contacts K2A which are now closed. The operation of the switch 166 also removes the alternating voltage source from the rectifier 171, tending to de-energize the relay winding K2. However, the capacitor 172 discharges through the

resistors

173 and 176 and the winding IQ thereby holding it energized for a predetermined time. At the same time, the motor 133 is energized through an adjustable resistor 182 and the switch 147 so as to open the door. When the door is fully opened the switch 147 is opened thereby de-energizing the motor. Eventually the capacitor 172 becomes discharged to such an extent that the relay winding K2 becomes de-energized thereby opening the contacts K2A which de-energize the electromagnet 169. The switch 167 is thereby moved to its upper position so that the motor 133 is energized through the switch 168, which is now closed, thereby closing the door. The capacitor 172 recharges quickly through the rectifier 175 and the

low value resistors

173 and 174. The apparatus is now ready for another cycle of operation.

It is to be noted that in the embodiment described in connection with FIGURES 1, 2 and 3, the magnetic assembly of the motor is stationary while the conductive element moves. This arrangement is suitable when the hollow wall is very thin so that it is impossible to place the door and the conductive element side by side. However, this arrangement requires a substantial amount of clearance in the lateral direction. As is apparent from FIGURE 1, when the door opens, the element moves a substantial distance to the left but the door does not reach the magnetic assembly 24 which is in substantially the same plane as the door. In contrast, in the embodiment of FIG- URES 6, 7 and 8 there is more room between the panels of the end wall but much less room in the direction of door motion. These conditions lend themselves to the use of a stationary conductive element and a movable magnetic assembly. As shown in FIGURE 8, the door 132, when open, is behind both the conductive element 135 and the mounting plate 157.

From the foregoing description it is apparent that the present invention provides a simple operating mechanism for the doors of rapid transit cars which mechanism pro- 8 vides the necessary locking safeguards and which mechanism can be placed within the walls of the cars.

Although some preferred embodiments of the invention have been described in considerable detail for illustrative purposes, many modifications will occur to those skilled in the art.

What is claimed is:

1. Closure apparatus, comprising,

a structure,

a sliding door mounted on said structure for lateral movement between open and closed positions, motive means for moving said door between said open and closed positions,

switch means for controlling said motive means,

a locking plate rotatably mounted on said structure,

means interconnecting said door and said locking plate for rotating said locking plate about an axis of rotation in response to lateral movement of said door,

a locking arm pivotally mounted on said structure and angularly displaceable relative to said structure about a pivot axis to first, second and third angularly spaced positions, said locking arm being operative at said first position to operate said switch means to control said motive means for opening said door and said locking arm being operative at said second position to operate said switch means to control said motive means for closing said door and said locking arm being operative at said third position to cooperate with said locking plate for locking said door when said door is fully closed, and

means for angularly displacing said locking arm.

2. Apparatus according to claim 1 in which said locking plate is formed with an arcuate surface and is formed with a first abutment disposed at one end of said surface,

said locking arm is formed with a second abutment and said locking arm has a roller rotatably connected therto, said roller being disposed adjacent said second abutment, and

said locking arm is mounted in such position that the force of gravity acting thereon urges said second abutment toward a position opposite said first abutment when said door is closed and urges said roller into engagement with said arcuate surface while said door is being closed.

3. Apparatus according to claim 1 in which said means interconnecting said door and said locking plate includes a thrust member, and in which said door has a central portion disposed between the top and bottom edges of said door that is connected to said thrust member.

4. Apparatus according to claim 3 in which said means interconnecting said door and said locking plate includes a crank arm rigidly fastened to said plate, and in which said thrust member is a connecting rod pivotally connected at opposite ends to said crank arm and to the central portion of said door.

5. Apparatus according to claim 3 in which said motive means has a portion connected to and controlled by said switch means and a portion connected to said door for moving said door between open and closed positions.

6. Apparatus according to claim 5 in which said motive means is a linear electric motor including first and second relatively movable members, one of said members being connected to said door adjacent to said thrust member connection.

7. Apparatus according to claim 6 in which said first member is an assembly including energizing windings and said second member is an elongated conductive element, and in which said motive means has means for adjusting the driving force appled by said motive means to said door.

8. Apparatus according to claim 7 in which said first member is fastened to said door and said second member is fastened to said structure.

9. Apparatus according to claim 5 further comprising means jointly responsive to the elapse of a predetermined time after initiation of door closing and to the location of said locking arm in said second operative position and said door in at least a partly opened position for alternately deenergizing and re-energizing said motive means.

10. Apparatus according to claim 5 further comprising manually operable means for energizing said motive means to open said door, and

means jointly responsive to the elapse of a predetermined time after initiation of door opening and to the location of said locking arm in said second operative position for energizing said motive means to close said door.

11. Apparatus according to claim 6, including a rotary fluid cushioning device which has a shaft fixedly connected to said locking plate coaxially therewith and which serves to bring said door to a smooth stop as it approaches its fully opened and fully closed positions, and including an electromagnet having a movable element operatively connected to said locking arm, and including a mounting plate which supports said locking arm and cushioning device and electromagnet on one side thereof :and which is supported by said structure.

12. Apparatus according to claim 11 in which said structure includes a hollow Wall formed with an interior and an exterior panel, said panels forming a space therebetween in which said mounting plate is disposed,

said wall being formed with :an opening through both of said panels,

said door being mounted so as to at least partially cover said opening when in its closed position and so as to retract into said space between said panels :and to be disposed adjacent to said mounting plate when in its open position.

13. Apparatus according to claim 6 in which said switch means includes first, second and third electric switches, all mounted on said structure, each capable of assuming either a first or a second condition, the condition of each being controlled by the position of said locking arm in each of the three operative positions of said locking arm.

References Cited UNITED STATES PATENTS 1,715,505 6/1929 Klumpp 49-14 X 1,976,223 10/1934 Hedley et al 4928O X 2,893,506 7/1959 Daugirdas 49'13 X 2,895,728 7/1959 Edelman 49-30 X FOREIGN PATENTS 551,522 6/1932 Germany.

I. KARL BELL, Primary Examiner. I DAVID J. WILLIAMOWSKY, Assistant Examiner.

U.S. Cl. X.R.