US1745990A

US1745990A - Automatic stopping and reversal of electromechanically-operated doors and the like

Info

Publication number: US1745990A
Application number: US338683A
Authority: US
Inventors: Harry B Goldman
Original assignee: Individual
Current assignee: Individual
Priority date: 1929-02-09
Filing date: 1929-02-09
Publication date: 1930-02-04
Anticipated expiration: 1947-02-04

Description

Feb. 4, 1930. H, B, GOLDMAN 1,745,990

AUTOMATIC STOPPING AND REVERSAL OF ELECTROMECHANICALLY OPERATED DOORS AND THE LIKE Filed Feb. 9, 1929 2 Sheets-Sheet l BRA E SOLE/V010 56 54 3 j4/a5l 624 55 5 3/ 50 g Feb. 4, 1 930. GQLDMAN 1,745,990

AUTOMATIC STOPPING AND REVERSAL OF ELECTROMECHANICALLY OPERATED DOORS AND THE LIKE Filed Feb. 9, 1929 2 Sheets- Sheet 2 Patented Feb. 4, 1930 UNITED STATES PATENT OFFICE HARRY B. GOLDMAN, OF PITTSBURGH, PENNSYLVANIA I AUTOMATIC STOPPING AND REVEIiSAL F ELECTROMEGHANICALLY-OPERATED DOORS AND THE LIKE Application filed February 9, 1929. Serial No. 338,688.

My invention relates to a door-reversing guard as applied to motor-driven overhead doors, and it also relates to a non-jammlng mechanism as applied to automatically operated elevator doors, whereby the door will be automatically opened wide if it strikes an obstruction while closing.

As applied to overhead doors, my invention is particularly designed for the Door mechanisms, shown in a Patent No. 1,661,719, granted March 6, 1928, to Roy M. Edwards and Julius P. Poschen. Such doors vary, in size, from the smallest garage door, to doors Weighing several tons, and are made with a 5 number of narrow horizontal panels which are hinged together and are guided in channels which carrv the door back into a horizontal overhead position when the door is raised or opened. The operation of the door is ef fected by means of a motor.

If such a door should strike an obstruction, such as an automobile top, while it was closing, the only protection tained prior to my invention was to trip out a circuit breaker on the motor or to slip a clutch or other driving connection. In either event,

. the door would be more or less perfectly protected, (if an attendant were near enough at hand to remedy matters in time), but the 0b-- stacle might be crushed by the force back of the door, particularly if the door is very large and heavy.

As applied to the power-driven doors of a completely automatic elevator with push-button control, which I have invented, my reversing guards or non-jamming devices on the edges of the car door and the shaftway doors are of utmost importance, because without some such means for protecting passengers trol, including automatic door-movement, would be impossible.

My invention comprises a light-weight yieldably mounted bar or guard, on the advancing edge of the door, with a guard-actuated switch arranged not only to stop the door, on reaching an obstruction, but also to automatically reverse it, so as to open the door wide. The amount of yield of the guard, or the distance which it can be depressed before which could be obagainst injury a full-automatic elevator con- I it strikes the door, should be somewhat greater than the distance necessary to bring the door to a full stop, which is usually about two inches for overhead doors.

My invention further comprises means for 5 rendering the reversing-guard action effective only when the door is closing, and not when it is opening.

My invention further comprises means for preventing the automatic reversal of the door when the reversing guard comes intoc'ontact with the floor, in the case of overhead doors, or into contact with the door jamb, in the case of elevator doors, in the fully closed position.

As many houses are equipped only with single-phase power lines, and as induction motors are the most readily adaptable motors for door-driving purposes, it is necessary to overcome a difficulty which arises by reason of the fact that such motors cannot be reversed until their speed has been reduced a certain amount. This is because the teaser coils of such motors produce what is called an elliptical field which is not sufficient to reverse the motor from full-speed ahead to full-speed reverse. A repulsion-start, induction-running motor has the same defect.

With the foregoing difliculty in mind, I have further provided a simple centrifugal switch, which, at negligible additional expense, will reliably prevent the too rapid operation of the reversing control circuits when an obstruction comes into the path of the closing door, and thus I am able, with a singlephase motor, to reliably reverse the door in the quickest possible time, in response to a depression of my reversing guard, as soon as the motor speed has been reduced to a value which admits of reversal.

A still further feature of my invention is a provision against the possibility that the for a single-phase door-operating mechanism according to my invention;

Fig. 2 is a circuit diagram showing the same thing, with details of the motor, centrifugal switch, brake and driving connec- Fig. 3 is a simplified diagram of the motor connections alone;

Fig. 4 is a view similar to Fig. 2, showing a modification;

Fig. 5 is a longitudinal sectional view of the bottom portion of an overhead door, showing my reversing guard in place, the sectional 111 18.116 being indicated by the line 55 in Fig. 6 is a transverse sectional view of the same, on the line 6-6 of Fig. '5;

Figs. 7 and 8 are views similar to Figs. 1 and 2, respectively, showing a three-phase system, as applied to an elevator door mechanism; 7

Fig. 9 is a simplified diagram of the control connections of the systemv shown in Figs. 7 and 8; and

Fig. 10 is an elevation'al side view showing the edge of an elevator door embodying my non-j amming guard, with parts broken away to show the construction.

In the embodiment of my invention shown in Figs. 1 to 3, I utilize a single-phase line 1, 2, from which energy is supplied to a reversible single-phase motor 3, carrying, on its shaft, a worm drive 4 for driving the sprocket wheel 5 of the chain drive 6 for the overhead door, such as is shown in the above-mentioned.

ever the motor is energized.

The motor 3 is provided with four terminal leads, 9, 10, 11 and 12, whereby the motor can be energized in either the forward or the reverse direction. As illustrated in Fig. 2, the motor is provided with main and auxiliary primary windings 14: and 15, at right angles to each other, having the

terminals

9, 10 and 11,12, respectively. The motor 3 is also provided with a rotor member having a commutator cylinder 17 with which are associated a pair of permanently shortcircuited brushes 18.-

The motor 3 is what is commonly known as a repulsion-induction motor, starting as a repulsionmotor with the brushes 18 effective, and operating at full speed as an induction motor, which operation is secured by means device 21 is adaptedto cooperate with two stationary back-contacts 25 which are closed when the motor speed falls to a value somewhere around 7 5% of its full speed, or a somewhat lower figure. Thepurpose of these centrifugal switch contacts 25 is to prevent the motor connections from being reversed, when the door is closing, until the speed has dropped to such value that a reversal of the driving connections will actually effect a reversal of the motor. This is necessary because of the peculiar difliculties in reversing certain single-phase motors, and it is true in straight single-phase induction motors, as shown in Fig. 4, as well as in the repulsioninduction motor which is shown for illustrative purposes in Fig. 2.

Two other kinds of protective devices, in addition to the centrifugal switch contacts 25, are utilized in my control device; to wit, the usual up and down

limit switches

27 and 28 which are opened when the door reaches its respective limits of travel, and my novel reversing guard 30 which is mounted on the'advancing edge of the door and which, when it comes into engagement with an obstruction, opens the switch contacts 31.

The up limit switch 27 is provided with up limit contacts 33 which are opened when the door is in its extreme open position.

The down limit switch 28 is provided with main down limit contacts 35 and also auxiliary down contacts 37, both of which are closed except when the door is within one or two inches of its extreme closed position. It is further provided with normally open auxillary contacts 38 which are in shunt with the reversing-guard contacts 31 and shortcircuit the same when the door is within three or four inches of its extreme closed position, or before the reversing guard 30 comes into contact with the floor, which occurs when the door is about three inches from the floor.

The construction and operation of my controlling device for the main motor 3 may now be described.

The control is effected by two electrically operated main control elements or contactors, an up or backward contactor 40 having an actuating coil 41 for closing the same, being opened by gravity or its equivalent; and a down or forward contactor 43 having an actuating coil 44 for closing the same, being also opened by gravity or its equivalent. The two contactors are usually protected by a Wcll known mechanical interlock (not shown) having provision for a lost-motion connection which permits either one of the contactors to close freely while the other one is open, but does not permit both contractors to be closed at the same time.

The motor 3 is adapted to have its main and auxiliary windings connected in series, with the auxiliary windings reversed for reversed rotation. Thus, the current flows in the direction 910-1112 for forward or downward movement, and in the direction -91012-11 for reverse or upward movement. To this end, the down contactor 43 is provided with two

main contacts

45 and 46 for connecting the terminal 10 to the terminal 11 and the terminal 12 to the line 1. The up contactor 40 has

main contacts

47 and 48 for connecting the terminal 10 to the terminal 12 and the terminal 11 to the line 1. The motor-terminal 9 is permanently connected to the line-wire 2. The down and up

contactors

43 and 40 thus constitute forward and backward main control elements adapted, when energized, to cause the prime mover or motor 3 to be energized in either the forward direction to lower or close the door, or in the backward direction to raise or open the door.

The up and down

contactors

40 and 43 are each also provided with a third main contactor, numbered 49 and 50, respectively, both of said contactors 49 and 50 being connected, on one side, to the line-conductor 1, and on the other'side to a brake-terminal 51, the other brake-terminal 52 being permanently connected to the other line-conductor 2. Thus, the brake solenoid 8 is energized, to release the brake, whenever either the up contactor 40 or the down contactor 43 is energized; that is, whenever the door is to be raised or lowered.

The control system is provided with a snapswiteh 53 which is connected to the line 2 by a conductor 54 and to certain of the control apparatus by a conductor 55, as will now be described.

The up contactor 40 is ener ized by means of an up push button 56, which connects the control-conductor 55, through the push button 56, to an up contactor controlline 57 leading to the up contactor-coil 41, which is in turn connected by a conductor 58 to the up-limit contacts 33, and thence, by means of a conductor 59, to the linewire 1. As soon as the up contactor closes, a holding circuit is completed by an auxiliary contact 61, which joins the conductor 57 directly to the control-conductor 55, which is connected, through the snapswitch 53, to the line-wire 2, thus by-passing the push button 56, and holding the contactor closed until the door reaches its upper limit of travel, when the up limit switch 27 o ens its contacts 33, thus de-energizing the up contactor.

68, which joins the actuating coil 44 to the' control-conductor 55. which is connected to the snap-switch 53 and thence to the line-wire 2, thus by-passing the push button 63 and normally holding the contactor closed until the door reaches its lower limit of travel, at which time the down limit switch 28 opens its contacts 35, thus de-energizing the down contactor.

The reversing guard 30, as shown more clearly in Figs. 5 and 6, is set on the advancing edge of the door 73. It is made as light as possible, so that it will not itself injure any object which may be in the path of the closing door, and it is pressed outwardly by a very light spring 74, so that the slightest touch will break its contacts 31, thereby opening the holding circuit of the down contactor.

If the door should come into contact with any obstruction when it is closing, I not only stop it, by means of my reversing guard, as just described, but I also cause it to be automatically reversed and returned to its fully open position. This reversing operation is effected by my centrifugal switch 25 which is closed whenever the speed of the motor is under about 75% of its full speed, which occurs soon after the de-energization of the forward contactor 43 and the main motor 3 by the opening of the guard switch 31 while the door is closing. The centrifugal switch 25 thus constitutes auxiliary switching means which are closed when the forward main control element is de-energizcd. Immediate application of the reversing connections of the single phase motor 3 shown in Figs. 1 and 2 is not desired because a single-phase induction motor will ordinarily not reverse until its speed is reduced a certain amount. I have found that 75% of full forward speed is sufficiently low to assure reversal, in the motors which I have tested; however, I contemplate that the centrifugal switch shall be set to whatevervalue may be necessary for the particular motor used on any installation. In the, repulsion-induction motor which I prefer, and which is shown in Fig. 2, the commutator-short-circuiting means 19 is preferably moved away from the commutator, so that the motor acts purely as a repulsion motor, before reversing its connections.

If the reversing guard touches an obstruction in the path of the closing door, the down contactor 43 is immediately de-energized, thereby open-circuiting the motor 3 and applying the brake 7, rapidly decelerating the motor. At about 7 5% speed, the centrifugal switch 25 closes, thereby energizing the up contactor control-line 57 by means of a conductor 76, which connects the up contactor control-line 57 to the centrifugal switch 25, whence a conductor 77 leads to the auxiliary down contacts 37' of the down limit switch 28, and so connects on to the energized control-conductor 55, except when the door is at its. extreme down limit of travel. The circuit and apparatus just outlined constitute means for energizing the up contactor just as if the up push button 56 had been depressed, and it does it automatically, without any loss of time,

= as soon as the speed of the motor 3 is such that it may safely be reversed.

If the control-circuit snap-switch 53 is opened, while the door is either ascending or descending, the door will stop and will remain in its place until the snap-switch is again closed, at which time the door will instantly and automatically start up, through the circuit comprising the centrifugal switch contacts 25 and the auxiliary down contacts 37 of the limit switch 28.

Asia takes about two inches to stop a heavy garage door, and as the reversing guard 30 must not become fully depressed before the door reverses, it is usual to provide three inches of movement of the reversing guard, its switch contacts 31 being instantly opened by the first movement of the guard. On reaching its down position, the door would first be stopped by the reversing guard which wouldstrike the fioor at about three inches above it and would bring the door to a stop at about one inch from the floor. If the down limit-switch contacts 37 open before the motor slows sufficiently to close the centrifugal switch 25, the door will not be reversed and will come to rest within about one inch from the floor.

Where it is desired to bring the door to fully closed position, the auxiliary normally open SWltClPCOIltHCtS 38 may be provided on the down limit switch 28, for short-circuiting the reversing-guard switch 31 at between three and four inches of the floor. This is done by having the first movement ofthe clown switch close the contacts 38, and later on, when the door is two inches from the floor, the main down limit contacts 35, for stopping the motor, will open, thus bringing the door to rest in contact with the floor. The reversing guard switch 31 and its cirbuttons is depressed. i

In the modification shown in Fig. 4, ll'have cuit 66, together with the by=passing switch 38 on the down or forward limit swltch 28, thus constitute meansv responsive to the operation of said guard switch, when the door is closing and before it is fully closed, to automatica ly deenergize the down contactor 43, and through the circuit 37-77- 25-7657 to energize the reversing contactor 40, as previously described, but this does not occur after the door has reached with in three inches of its fully closed position, when the by-passing limit switch 38 closes and renders the guard switch 31 inoperative.

In the embodiment of my invention shown in Fig. 4, a straight induction motor 80 is shown, having a main primary coil 81 and two teaser coils 82 and 83 for forward and reverse operation, respectively. The up contractor 84 energizes coils 81 and 83; and the down contactor 85 energizes coils 81 and 82.

Instead'of using an-auxiliary down contact 37 on the down limit switch 28, I may, as shown in Fig. 4, use auxiliary back-com tacts 87 on the reversing guard 30, whereby the door is automatically returned to full open position,'on hitting an obstruction.

The order of arrangement of the various safeguard devices is somewhat different in Fig. 4 from that shown in Fig. 2, and will be very briefly traced, as follows, using the same reference numerals as in Fig; 2 wherever possible. The normal'push-button energizing circuit for the up contactor 84 is from the control line 55, through'the up limit contacts 33 to.the up push button 56, and thence through the centrifugal switch contacts 25 to the energizing coil 41. As soon as the up contactor 84 closes, a holding circuit is established through the auxiliary contact 61 and the up limit contacts 33. The automatic reversal of the motor is eifected by a control circuit from the control line .through the,down limit contacts 35, the

- push button being immediately by-passed by the auxiliary holding contacts 68.

In the apparatus shown in Fig. 4, if the control-circuit snap-switch 53 is opened while the door is inmotion, the door will stop in its place, as in Figs. 1 and 2, but when the snap-switch is again closed the door will not automatically open, as in Figs. 1 and 2, but will stay in its place until one of the push not utilized the auxiliary short-circuiting contacts 38 for enabling the door to close its last inch, or thereabouts, the reversing guard 30 being so constructed that it substantially bridges the space between the door and the floor, not-withstanding the fact that the guard is still able to move up into a groove in the bottom of the door, or some equivalent construction, until it is flush with the bottom surface of the door.

In the three-phase system shown in Figs. 7-9, a three-

phase line

91, 92, 93, supplies a three-phase induction motor94, through forward and reverse contactors 95 and 96, heretofore referred to as down and u contactors, respectively. In this case, al that is necessary to reverse the motor is to reverse the phase-sequence, no centrifugal switch being necessary. The three motor-

terminals

97, 98 and 99 are connected to the contactors in a way which is obvious and which is clearly shown in the drawing. I

In Fig. 8, the motor is shown as being provided with a friction clutch-100 for driving a threaded shaft carrying a nut 101 which is guided by a runway 102 and which trips the limit switches 27' and 28 at the extreme limit of travel. The nut 101 is also shown as operating a horizontally sliding door 104:, such as an elevator door, for closing a doorway 105. In this case, as shown in Fig. 10, the advancing edge of the door, as it closes, is a vertical surface, which is guarded by a light channelshaped guard 106 pressed outward by upper and

lower springs

107 and 108, the upper spring being preferably the heavier, so that the guard practicallypivots thereon, and the lower spring being very light, so that the guard yields to the slightest touch. The guard carries the normally closed contacts 31 previously described.

The control circuits shown in Figs. 79 are as follows. Instead of a mechanical interlock with a lost-motion connection for preventing both contactors from closing at once and short-circuiting the line, an electrical interlock is provided. The normal push button control circuit .for the door-opening or up contactor 96 is from the control-line 55, through the up push button 56 and conductor 57, to a normally closed interlock 110 on the down contactor 95, said interlock being closed when the contactor is in its normal open position, thence to the actuating coil 41 of the up contactor 96, thence through conductor 58, up limit contacts 33, and conductor 59, to the line-wire 91. A holding circuit is immediately formed around the push button 56, from control-wire 55, through the auxiliary holding contacts 61, to the conductor 57.

The normal push button circuit for the door-closing or down contactor 95 in Figs. 7-9 is from the control-line 55, through the down" push button 63 and conductor 64, to

. 100 when a normally closed interlock 112 on the up" contactor 96, thence to the actuating coil 44 ofthe down contactor 95, thence through conductor 66, down limit contacts 35, conductor 67, reversing-guard contacts 31 and conductor 71, to the line-wire 91. A holding circuit is immediately formed by the holding contacts 68 on the down contactor- 95.

The up push button 56 in Figs. 7-9, besides being by-passed by the holding. contacts 61, is also by-passed by the auxiliary down contacts 37 which are closed at all times except in the fully closed position of the door, said contacts 37 being connected to the up conductor 57 by the conductor 76 and being connected, on the other side, directly to the control-line 55. When the door is descending or closing, the up contactor circuit is interrupted by the interlock 110 on the open down contactor; when the door is fully closed, the auxiliary down

limit contacts

35 and 37 are open; when the door is fully open, the up contactor circuit is interrupted by the up limit contacts 33. If the door is stopped by the reversing guard, while descending or closing, the down con tactor 95 is opened, thus closing the interlock 110, and as the auxiliary down contacts 37 are already closed, the up contactor is immediately energized, reversing the motor 94. The interlock 110' thus constitutes auxiliary switching means which are closed when the forward main control element is de-energized.

In the form of my invention shown in Figs. 7 to 10, where my reversing guard 106 is used to protect an elevator door 104 operated by a threephase motor 94:, I do not need a brake on the driving shaft. When the reversing guard is depressed with a very slight pressure, the three-phase motor instantly reverses andopens the door.

When the doorv is nearly closed, the down limit switch 28 opens both of its normally closed

contacts

35 and 37, just before the reversing guard 106 comes into contact with the door jamb, and the motor is deenergized, permitting the door to drift into closed position, the motor being finally stopped by the slipping of the clutch the door is fully closed. It is thus seen that the auxiliary normally open contacts 38 for short-circuiting the reversingguard contacts at the down or closed limit of travel is not needed in this embodiment of my invention.

My novel application of the friction-clutch drive for the doors of full-automatic elevators is claimed in my application Serial No. 408.982, filed Nov. 22, 1929.

While I have described by invention with relation to overhead doors and elevator doors, I wish'the word door to be understood as applying to any power-driven object that may jeopardize life or property by crushing an interposed object. The terms down, forward or door-closing should in like manner be understood as referring broadly to movement in the direction which would crush an interposed object, and the terms up, reverse, backward or door-opening, the reverse direction. I

VVhile' I have illustrated two forms of my reversing guard, as applied to overhead and elevator doors, respectively. I do not wish to be altogether limited to either form. For elevator doors, the channel formation of the guard, as shown in Fig. 10, may sometimes be preferred for decorative reasons and its safety to fingers. For overhead doors, however, I very much prefer a light, three-eighths-inch rod, as shown at 30 in Figs. 5 and 6, pressed downward by light springs 7 4 and having strong hmit-motion devices 115 for limiting theoutward movement of the guard, away from the door, to three inches. The springs 7 4: allow the guard-rod 80 to be depressed fully against the door, or into a groove therein, as the case may be, thereby sealing the doorway as perfectly as 'is possible without a guard. Where the rod remains in contact with the floor, instead f the door, as shown in Figs. 5 and 6, the rod also presents a small rounded surface, of considerably less area than the bottom panel of the door, for the formation of snow and ice, which, in door-arrangements having no guards, would possibly hold the door immovable until the ice is thawed. Moreover, the three inches play of the guard permits my door-operating motor to get a good start, even if the guard is held down by ice, giving a powerful hammering jerk at the end of the three-inch movement, which, aided by the small area of, the frozen surface, will easily break the ice-formation and free the door for operation.

Itwill be understood, also, that anysuitable cable or extension cord may be utilized with my invention, or any suitable reeling device for the guard contact conductors on the door. In Figs. 1 and 7, I have shown the apparatus at the controller as being connected, by three

cables

118, 119 and 120, to the parts located, respectively, at the motor, at the push buttons and on the door, but such showing should be taken only as illustrative.

In like manner, my illustration of a centrifugal device in Figs. 2 and 4; is intended merely as typical or suggestive of this entire class of devices and not as limiting myself to any particular form or style of speed-responsive device.

I claim as my invention:

1. The combination with an object wh" is mov ble in a limited path in the forward and bac ward directions and which is so disposed that its forward edge may exert a crushing action on an obstruction interposed in its way when it is moving forward, of a reversible prime mover mechanically connected thereto to drive the same, protective devices for cutting ofl' the power to said prime mover when said object reaches either extreme limit of its travel, a guard yieldably disposed on in its way when it is moving forward, of a reversible power driving means for driving the same, protective devices for cutting off the power to said prime mover when said object reaches either extreme limit of its travel, a guard yieldably disposed on said forward edge, means operative in response to a depression of said guard for causing said reversible power driving means to be energized in a direction to drive said object backward, and means operative at the extreme forward limit of travel of said object to prevent the said action of said guard-responsive means.

3. The. combination with an object which is movable forward and backward in a limited space, one end of said space being accessible so that an obstruction may become interposed where it would cause damage by reason of the advancing forward edge of said object, of a reversible prime mover mechanically connected to said object to drive the same, a brake on said driving connection, means for energizing said prime-mover in either direction at will and for deenergizing the same, means for causing said brake to be released when said prime mover is energized in either direction and to be applied when said prime mover is deenergized, protective devices for deenergizing said prime mover whenever said object is at either extreme limit of its travel, a guard yieldably disposed on said forward edge of the object, means responsive to a displacement of said guard to deenergize said prime mover, and means operative, whenever said prime mover is deenergized, to reenergize the same in the direction necessary to move said object backward, except when either one of said protective devices is effective at either limit of travel.

4. .The combination as recited in claim 3, characterized by the fact that said guard-responsive means is effective to interrupt only the forward movement of said prime mover and not its backward movement.

5. The combination as recited in claim 3, characterized by having means, responsive to an operating condition of said prime mover, for delaying said re-energization of the prime is movable in a limited direction until a presaid operating condition mover in the backward determined value of has been obtained.

6. The combination as recited in claim 3, characterized by having means, responsive to the speed of said prime mover, for delaying said re-energization of the prime mover until it has been decelerated to a predetermined speed. a

7. The combination with an object which is movable forward and backward in a limited space, one end of said space being accessible so that an obstruction may become interposed where it would cause damage by reason of the advancing forward or ge of said object, of a reversible prime mover mechanically connected to said object to drive the same, a brake on said driving connection, means for energizing said prime mover in either direction at will and for deenergizing the same, means for causing said brake to be released when said prime mover is energized in either direction and to be applied when said prime mover is deenergized, protective devices for deenergizing said prime mover whenever said object is at either extreme limit of its travel,

means for automatically energizing the prime ,mover in a backward direction when the advance of the door is interrupted before it reaches its forward limit of travel, and means responsive to the speed of said prime mover to make it impossible to initiate the said automatic energization of the prime mover in a backward direction unless its speed is less than a predetermined minimum.

8. The combination with an object which path in the forward and backward directions and which is so disposed that its forward edge may exert a crushing action on an obstruction interposed in its way when it is moving forward, of a reversible prime mover mechanically connected to said object to drive the same, an electrically operated forward main control element adapted, when energized, to cause said prime mover to be energized in the forward direction, an electrically operated backward main control element-adapted, when energized, to cause said prime mover to be energized in the backward direction, each of said main control elements being adapted, when deenergized, to cause the energization of said prime mover to be discontinued, normally closed limit switches for deenergizing the respective main control elements when said object reaches its respective limits of travel, a guard yieldably disposed on said forward edge of the object, a normally closed switch operative by a depression of the guard, andmeans responsive to the operation of said guardswitch, when said object is moving forward before it reaches the limit of its travel, to automatically deenergize said forward main control element and energize said backward main control element.

9. The combination with an object which is movable in a limited path-in the forward and backward directions and which is so disposed that its forward edge may exert a crushing action on an obstruction interposed in its way when it is moving forward, of a reversible power driving means for driving the same, an electrically operated forward main control element adapted, when energized, to cause said power driving means to be disposed in the forward driving condition, an electrically operated backward main control element adapted, when energized, to cause said power driving means to be disposed in the backward driving condition, said main control ele ments, when both deenergi-zed, being adapted to cause said power driving means to be disposed in the non-driving condition and to cause said object to be stopped, normally closed limit switches for deenergizing the respective main control elements when said object reaches its respective limits of travel, a guardyieldablydisposed on said forwardedge of the object, a normally closed switch operative by a depression of said guard, and circuit connections whereby the operation of said guard switch, when said forward main control element is energized, deenergizes the same and energizes the backward main control element, the forward limit switch comprising means for preventing the reversing action of the guard switch when the guard switch is actuated by the engagement of the guard with the forward limit of travel of said object.

10. The combination with an object which is movable forward and backward in a limited space, one end of said space being accessible so that an obstruction may become interposed against the forward limit of said space, where it would be damaged by the advancing forward edge of said object, of a reversible prime mover mechanically connected to said object to drive the same, a brake on the driving connections from the prime-mover, an electrically operated forward main control element adapted, when energized, to cause said prime mover to be energized in the forward direction, an electrically operated backward main control elements adapted, when energized, to cause said prime n'iover to be energized in the backward direct-ion, each of said main control element being adapted, when dc energized, to discontinue its energization of said prime mover, means for causing the brake to be released when the prime mover is encrgized in either direction and to be applied when the prime mover is deenergized, forward and backward control circuits adapted, when energized, to control the respective n'ain control elements, and a switch responsive to the speed of said prime mover to place an open point in. anrtthus prevent the energization of. a :fbackward control circuit whenever said speed is over a predetermined percentage of full speed.

11. The combination with an object which is movable for aid and backward in a limited space, one end of said space being accessible so that an obstruction may become interposed against the forward limit of said space, where it would be damaged by the advancing forward edge of said object, of a reversible prime mover mechanically connected to said object to drive the same, an electrically operated forward main control element adapted, when energized, to cause said prime mover to be energized in the forward direction, an electrically operated backward main control element adapted, when energized, to cause said prime mover to be energized in the backward direction, each of said main control elements being adapted, when deenergized, to cause the energization of said prime mover to be discontinued, normally closed forward and backward limit switches in series with the respective main control elements for deenergizing the same at the respective limits of travel of said object, a guard yieldably disposed on the aforesaid forward edge of said object, a normally closed switch opened by said guard and connected in circuit with said forward main control element to deenergize the same-when the guard is depressed, an auxiliary switching means which is closed when said forward main control element is deencrgized, and an auxiliary contact, on said forward limit switch, which is closed when said forward limit switch is undisturbed, said auxiliary switching means and auxiliary contact being in series with said backward main control element to automatically energize the same whenever the forward main control element is deenergized after having been energized while said object is in some intermediate position between its extreme limits of travel.

12. The combination with an object which is movable forward and,v backward in a limited space, one end of said space being accessible so that an obstruction may become interposed against the forward limit of said space, where it would be damaged by the advancing forward edge of said object, of a reversible prime mover mechanically connected to said object to drive the same, an electrically operated forward main control element adapted, when energized, to cause said prime mover to be energized in the forward direction, anelectrically operated backward maincontrol element adapted, when energized, to cause said prime mover to be energized in. the backward direction, each of said main control elements being adapted, when deenergized, to cause the energization of said prime mover to be discontinued, normally closed forward and backward lmnt contact devlces operative at the extreme limits of travel of said object, a guard yieldably disposed on the aforesaid forward edge of said object, a. normally closed guard contact device actuated by a displacement of said guard, an electrical circuit responsive to said forward limit contact device for deenergizing said forward main controlelement at the forward limit of travel, an electrical circuit responsive to said backward limit contact device for deenergizing said backward main control element at the backward limit of travel, an electrical circuit responsive to said guard contact device for deenergizing said forward .main control element when the guard is depressed, and means including an electrical circuit responsive to both said guard contact device and said forward limitcontact device for automatically effecting the energization of said backward main control element when said guard is depressed before the forward limit contact device is depressed.

13. An automatically operated door comprising a reversible electric motor, a mechanical driving connection between the motor and the door, means for energizing the motor to either open or close the door, limit switch devices for stopping the motor when the door reaches either its fully open position or its fully closed position, a guard yieldably disposed on the closing edge of the door, a normally closed guard-actuated switch for stopping the motor when the advancing edge of the guard comes into contact with anything, and means responsive to the opening of said guard switch when the closed-position limit switch is disturbed for automatically energizing the motor in the opening direction.

14. The combination with an object which is movable in a limited path in the forward and backward directions and which is so disposed that its forward edge may exert a crushing action on an obstruction interposed in its way when it is moving forward, of a reversible prime mover mechanically connected to said object to drive'the same, an electrically operated forward main control element adapted, when energized, to cause said prime mover to be energized in the forward direction, an -electrically operated backward main control element adapted, when energized, to cause said prime mover to be energized in the backward direction, each of said main control elements being adapted, when deenergized, to cause the energization of said prime mover to be discontinued, normally closed limit switches for deenergizing the respective main control elements when said object reaches its respective limits of travel, a guard yieldably disposed on said forward edge of the object, a normally closed switch operative by a depression of the guard, connections for deenergizing said forward main control element when said guard switch is opened, and means responsive to the forward limit switch for rendering the guard switch inoperative just before the depression of the guard at the forward limit of travel.

15. A mechanically operated door or the like, comprising a reversible prime mover for operating the same, forward and backward main control elements for controlling said prime mover, and automatic means responsive to the de-energization of said forward main control element when said door is advancing and before it reaches its fully closed position, to automatically energize said backward control element.

In testimony whereof, I have hereunto subscribed my name this 21st day of January, 1929.

HARRY B. GOLDMAN.