US 2170014 A
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Description (OCR text may contain errors)
Aug. 22, 1939. c. A. ELLIS 2,370,014
DOOR OPERATING DEVICE Filed Nov. 23, 1937 2 Sheets-Sheet 1 Patented Aug. 22, 1939 UNITED STATES DOOR. OPERATING DEVICE Charles A. Ellis, Natick,
Mass, assignor, by direct and mesnc assignments, to Maseco Corporation, Hopkinton, Mass, a corporation of Massachusetts Application November 23, 1937, Serial No. 176,099
The present invention relates to a door operating device and particularly to an electrically actuated device by which a door may be automatically opened and closed. This application is a continuation-in-part of the copending application Serial No. 43,376.
In prior devices of this character the incorporation of an electrically actuated door closing mechanism has necessitated that the door in opening and closing pass through a predetermined cycle, that is to say, that from a closed position the door must open to its full extent and then return to a. completely closed position. No arrangement is provided for leaving the door in full open position, nor is there any arrangement by which the swinging movement of the door may be reversed before the door is completely open or by which the door may be re-opened before being completely closed. One of the principal objects of the invention is to avoid the above noted objections in a device which incorporates the advantages of automatic opening and closing of a door, and the invention involves the provision of an electrically actuated door closer incorporating the features above referred to in a compact structure.
Where a door is actuated directly from an electric motor there is no time interval between the opening and closing movements of the door. Although there is no objection to this arrangement in certain installations, it is frequently desirable to have the door remain open for a short period of time before being automatically closed. A further object of the invention is to provide for a time delay between the opening and the closing of the door.
In certain installations, the door on which the apparatus is mounted is used at certain periods of the day to a great enough extent so that it would be desirable for the door to remain open. Accordingly, one feature of the invention is a provision for automatically holding the door open for a relatively long period of time when, in normal operation, the door would be swinging practically continuously by reason of the amount of trafiic in and out of the doorway.
A further feature of the invention resides in the provision for opening and closing the door entirely automatically by a suitable mechanism which can be controlled from a point remote from the door.
Other and further objects and advantages of th invention will more fully appear from the following detailed description taken in connection with the accompanying drawings, in which Fig. 1 is a perspective view showing an application of the device.
Fig. 2 is a vertical section through the device I of the invention.
Fig. 3 is a vertical section substantially along the line 3-3 of Fig. 2.
Fig. 4 is a horizontal section substantially along the line 4-4 of Fig. 2.
Fig. 5 is a vertical section substantially along the line 55 of Fig. 4.
Fig. 6 is a horizontal section substantially along the line 65 of Fig. 2.
Fig. '7 is an elevation of a detail.
Fig. 8 is a wiring diagram.
Fig. 9 is a modified wiring diagram.
Like reference characters refer to like parts in the different figures.
Referring first to Fig. 1, the device I of the invention is shown to be mounted on a door 2 supported by hinges 3 on a door frame 4. The shaft 5 of the device is connected through a pair of links 6 and 'l to a bracket 8 on the door frame 4. Turning movement of the shaft 5 will procure a swinging movement of the door for opening and closing said door.
Referring now to Fig. 2, the device of the invention comprises a frame consisting of a bottom plate H] and a top plate 10', these plates being held in spaced relation to each other by vertical bars ll suitably secured to the plates. A casin 2 for the device may be provided in order to conceal the mechanism therein and to protect the mechanism from dust, said casing fitting over the frame and having a dust proof opening I3 in the top thereof for the shaft 5. A suitable bracket, not shown, is secured to the frame to support the device on the door.
The bottom plate It has a cup l4 positioned therein to provide a bearing for the lower end of the shaft 5, the latter having a recess l5 toreceive a ball l6 which engages with the upper surface of the cup i4, eliminating, to the greatest extent possible, friction between the shaft 5 and the bearing. A bearing ring I! supports the lower end of the shaft 5 substantially centrally of the cup l4 and forms a radial bearing for the lower end of the shaft. The upper end of the shaft 5 extends through an opening in the plate ill and is supported in predetermined relation thereto by a suitable anti-friction bearing [8.
Extending between opposite side bars ll of the frame is a bracket I9, Figs. 2 and 6, which supports a driving motor with the driven shaft 2! thereof positioned parallel to the shaft 5. The shaft 2i is preferably driven through a reduction gearing incorporated in a part of the motor housing. A small gear 22 on the upper end of the shaft 2! engages with a large gear 23 journalled on a sleeve 24 axially slidable on the shaft 5. Clutch disks 25 and 26 engage with opposite surfaces of the gear 23 to provide a releasable connection between the gear 23 and the shaft 5. The clutch disk 26 is secured against turning movement and. also against axial movement on a sleeve 24' secured against axial movement on the shaft 5. The clutch disk 25 beneath the gear 23 is carried by a sleeve 21 axially slidable on the shaft 5 but secured against turning movement thereon. A coil spring 28 surrounding the shaft 5 between the sleeve 21 and a collar 29, urges the disk 25 intoengagement with the face of the gear 23 and accordingly urges said gear into engagement with the disk 26 to provide for a rotation of the shaft 5 in response to operation of the motor 20. The pressure of the spring 28 is sufficient to provide, normally, for a positive drive of the shaft 5 from the motor.
As best shown in Figs. 2 and 4, the shaft 5 has secured thereto a sleeve 30 to which is secured one of a pair of disks 3| and 32 which are adjustable relative to each other. The disks have alined slots 33 and 34 respectively, through which extends a bolt 35 by which the plates may be clamped in adjusted position. The peripheries of the disks 3| and. 32 form a continuous arcuate cam surface 36 which engages with the depending endof a pivotally mounted link 31. The link is mounted on av screw 38 carried by a plug 39 secured to the plate l6 and said link carries an adjustable screw 46 engageable with the switch button 4| of a switch 42. The switch button 4|, when depressed, closes a circuit through the driving motor 20 for actuating the door. Notches 43 and 44 at opposite ends of the disks 3| and 32 respectively, allow the button 4| to be released by the link 37 when the door is in closed position or in extreme open position. A coil spring 45 holds the link 31 against the periphery of the cam plates 3| and 32 at all times.
Referring now to Fig. 8, the motor 26 in the construction shown has two field windings 46 and 41, either of which may be separately energized for procuring a rotation of the motor shaft in opposite directions. The armature of the motor is connected in series with the field windings and a switch 48 provides for reversing the supply of electrical energy through the armature for reversing the direction of rotation of the motor shaft. Power is supplied from supply leads 4S and 56, the latter being connected to one terminal of the switch 42. The other terminal of this. switch is connected to the movable element of a reversing switch hereinafter described in detail. The movable element of this switch engages selectively with the contact 52 connected by a lead 53 to the field winding 46 or with the contact 54 connected by a lead 55 to the fixed contact 56 of a temperature controlled switch 5l. The movable element of this switch 5i is connected by a lead 58 to the field winding 47.
A lead 53, common to both of the field windings 46 and 4?, is connected to one of the movable elements 48a and 48b of the switch 48, and the other movable element of this switch is connected directly to the supply lead 49. The movable elements 68a and 482) are shifted as a. unit and engage selectively with contacts 60a and Bid or 6622 and EH). The contacts 60a and 6|b are connected to one side of the armature of the motor 26 by a lead 62, and the contacts 60b and 6|a are connected by a lead 63 to the other side of the armature. The switch 42 is so located as to cut off the power supply to the driving motor whenever the switch is open, and the door is then held by the motor against swinging movement. The switch 42 is normally open when the door is fully closed or in extreme open position, so that the door may remain at rest in either of these positions.
The switch 42 is bypassed by a normally open switch 64 which may be located at a point remote from the door to provide for opening of the door from a distant point. Closure of the switch 64 completes a circuit through the motor for actuation of said motor independently of the cam controlled switch 42. The switch 64- may be actuated mechanically for completely automatic opening and closing of the door by any desired mechanism, such as a light responsive element or photoelectric cell operating through a relay, or in certain cases, a sound responsive means including a vacuum tube and a relay actuated thereby.
It will be understood that the switch 64 may be omitted and in this event the door is started from its normally closed position manually. As the door begins to be manually opened, the switch 42 is closed, as a result of the swinging movement of the arm 6, to close the circuit through the driving motor so that the door is moved the rest of the way to its normal open position automatically by the device. The switch 42 may thus be closed by a manual swinging of the door independently of the motor operation as the clutch may slip during this swinging movement.
The reversing switch 5| is automatically shifted to make contact with the terminal 52 in the lead 53 from said switch to the motor, or with the terminal 54 which is connected by the leads 55 and 58 through the time-controlled switch 5! to the second field winding 41 for the motor. Thus with the switch 5| engaging the terminal 52, the motor is rotated in a direction to open the door; reversal of the switch 5| when the door is in its normal open position closes a circuit through the opposite field 4'! for rotation of the motor in a direction to close the door.
For automatic reversal of the switch 5|, each of the disks 3| and 32, as best shown in Figs. 3 and 4, carries on the underside thereof a depending finger 65 (see also Fig. 2), which is normally held in the vertical position shown, being mounted for a swinging movement about a pin 66, Fig. '7, to permit said finger to resiliently engage upstanding lugs 61 carried by a plate 68. The latter is guided by screws 69 which engage in slots in said plate, the screws being mounted on studs 1|, Fig. 5, on the bottom plate in.
As the door swings into closed position, involving a counterclockwise turning movement of the arm 6, Fig. 1, the finger 65 carried by the underneath plate 3| engages with the right hand lug 61 and urges the plate 68 into the right hand position of Fig. 4. Said plate has a notch 12, Fig. 2, therein engaging with the upwardly extending end 73 of an arm 14 pivoted on a stud carried by the plate l6 and having a projecting screw 14, engageable with the actuating button 5| of the switch 5|. While the end of the arm engages the notch l2, the switch 5| is held in a position for directing the power supply through the motor field 46, thereby providing for rotation of said motor in a direction for opening the door Whenever the switch 42 or 64 is closed to complete a circuit through the motor.
In the position of the disks 3| and 32 in Fig. 4, the door being fully closed, the switch 42 is in open position and the driving motor is at rest. When the manually controlled switch 64 is closed at this time, the switch 42 being open, the power supply is directed through the motor by the reversing switch in such a direction as to open the door. Just before the door reaches normal open position, the depending finger 65 on the plate 32 engages the left hand lug 61, Fig. 5, thereby reversing the switch 5| when at normal open position to reverse the direction of rotation of the motor and cause the door to close automatically.
In order that the direction of movement of the door may be reversed at any time during the opening or closing movement thereof, the device of the invention incorporates the automatically reversing switch 48, the mechanism for which is best shown in Fig. 3, for reversing the direction of rotation of the motor in response to a quick manual movement of the door in either direction. Referring to Fig. 3, the vertically eX- tending side bars ll support a plate 76 in vertical position adjacent to the shaft 5. Said plate provides a support for the switch 48 and carries a pin H on which is pivoted a lever 18. The depending end of said lever has a relatively large weight 19 attached thereto and the upper end of said lever has a projecting pin 89 engageable with a horizontal bar 8| pivoted at 82 to the plate it. The bar 9! has an adjustable screw 83 engageable with the button 48' of the switch 48.
The lever 15 is normally in the vertical position of Fig. 3, its movement from this position being limited by adjustable screws 84 and 85 carried in lugs 85 and 9'! secured to the plate l6 on opposite sides of the weight. The underside of the weight has a projecting lug 88 provided with an arcuate lower surface 89, which is engageable with the end of a latch 99 pivoted on a pin 9! provided by the plate 16. When the door is given a quick movement in either direction, Fig. 1, the inertia of the weight 19 causes the lever 18 to swing to one side or the other, Fig. 3, about the pivot ll, bringing the weight into engagement with either screw 84 or 85, in which position the latch 99 engages the lug 8i at either end of the surface 99 to retain the weight against said screw. When the lever '99 is thus swung against either screw 54 or 95, the switch 48 is shifted to reverse the direction of rotation of the driving motor, thereby procuring a reversal of the movement of the door, regardless of the position hereof.
The latch 99 is released by the swinging movement of the door into either end position to allow the lever '68 to resume its normal vertical position. To this end, a lug 92 on the plate 32, engages with the end of the latch 90, the latter having a cam surface 93 for cooperation with the lug to release the latch in the normal open position of the door, and a similar lug 92' on the plate 9i releases the latch in the closed position of the door. As shown in Fig. 8, the switch :29 is normally in the position shown, and when the lever '18 swings to one side or the other from vertical position, the switch 48 is shifted to reverse the motor rotation. The switch 48 automatically resumes the position of Fig. 8 as soon as the lever '58 resumes its vertical position.
In order that the door may remain in open position for a short time before being closed, the time-controlled switch 5'! is located in series with the motor. This switch, as best shown in Fig. 8, comprises a heating coil 94 which surrounds a bi-metallic thermal element 95, adapted to change its shape as a result of the heat from the heating coil 94. When the element 95 is heated a predetermined amount, it engages the contact 56 and thereby closes a circuit through the driving motor for actuating the latter to return to closed position. The heating coil 94 is connected by the lead 55 to the terminal 54 of the switch 5|, and by a lead 96 to the supply 49. Thus, when the switch 51 is shifted as the door reaches normal open position, a circuit through said coil is completed. The element 95 is connected by the lead 59 to the field winding 47, and in response to heat, is bent into engagement with the contact 55 connected to the lead 55, thereby completing a circuit through the motor for closing the door.
When the door is to remain open for a long period, there is a provision for cutting off the supply of power to the motor when the door is opened to a point beyond its normal open position. During the normal swinging movement of the door, the disk 32 does not move far enough relative to the arm 31 to permit the switch 42 to be opened by the arm 3'! engaging the notch 44, and the door movement is thus reversed at the normal open position. When the door reaches normal open position however, a slight manual opening movement allows the notch 44 to engage with the arm 31, thereby opening the switch 42 and breaking the circuit through the motor. The door is then held in open position with the motor acting as a brake to hold the door from moving toward closed position. The door may be closed at any time by a short manual swinging of the door toward closed position far enough to bring the arm 31 out of engagement with the notch 44. The same eifect may be obtained in causing the door to close by closing the switch 64 which bypasses the switch 42.
The device may be so arranged that upon the outbreak of fire the first opening of the door thereafter will cause said door to swing into extreme open position and remain there. To this end a plurality of switches 91 are positioned in parallel with the switch 5|, and in series with the opening field 41, being connected by leads 98 and 99 to the lead 59 between the switches 42 and 5!, and to the lead 53 respectively. The switches 91 are normally open and are automatically closed when the temperature thereof reaches a predetermined point. This type of switch is well known and ordinarily incorporates the familiar fusible link which normally holds the switch in open position but allows said switch to close when said fusible link melts as a result of a temperature rise. The switches 91 may alternatively be automatically closed upon opening of any one of the sprinklers in a sprinkler system in the building in which the device of the invention is positioned, or by other automatic control devices. The mechanism by which this would be procured is well known and need not be described. When this feature is incorporated in the invention, the door closing device operates in the manner above described so long as the switches 91 are open, and when the switches 91, or any of them, are closed, no immediate operation of the device occurs. However, when the door is next opened by the door actuating mechanism, it continues to open beyond the normal open position, one of the switches 9! being closed, so that the door moves beyond normal open position, thereby opening switch 42 to shut 01f the power, and the door remains in full open position. A fuse I00 may be incorporated in the main circuit through the mo tor to protect the device.
In the operation of the device, and starting with the door in closed position, the switch 42 is open,
' the door still occurs in the usual manner.
the movable elementof the switch 5| is in engagement with the contact 52 and the switch 48 is in the position shown in the wiring diagram. Movement of the door out of closed position manually closes the switch 42 through the action of the cam disk 3i as soon as the door starts to open, thereby energizing the motor field 46 and causing a rotation of the motor in a direction to open the door to its normal open position. Just before the door reaches its normal open position, the finger 65 engages and shifts the bar 68, thereby reversing the switch 5!. The switch is shifted beforethe door opens to the full open position, so that the switch 42 remains closed, the door is reversed and the motor returns the door to its vclosed position. As the door reaches fully closed position, the cam disk allows the switch 42 to open, and at the same time the switch 5! is returned to its original position, in readiness for completing a circuit through the field Q6 when the door is next opened.
If the door is to be opened automatically from some exterior source, as by means of a photoelectric cell operating through a relay, the door is started from fully closed position by momentaryclosure of the switch 65, which by-passes the switch 42 and causes the motor field 46 to be energized, and thereby move the door into normal open position. As soon as the door has started to open, the disks 3! and 32 close and hold closed the switch 12, so that, the switch 6d may be released.
Where the door remains in normal open position for a predetermined time interval, prior to closing thereof, the time control switch 57 becomes operative. As the .door reaches normal open position, the switch 56 is reversed, as above stated, at a time when the cam disks 3! and 32 still keep the switch 42 closed. When this occurs, the power supp-1y through the field it is discontinued and the door comes to rest in the normal open position, the motor acting as a brake to prevent movement of the door. When the switch 5! is reversed, a circuit through the heating coil 94 is established and as soon as the bimetallic thermal element 95 is heated by the coil sufiiciently to engage the contact 56, a circuit through the field 41 is established for closing the door. The door thus remains open in its normal open position for the time interval required for heating of the element 95 to a sufficient extent to engage a the contact 56.
If either of the switches 91 is closed by a fire in the building, or through any other mechanism arranged to close these switches, the opening of is to say, closing of the switches 91 does not cause immediately any functioning of the door operating mechanism. However, when the door is next started from its fully closed position, either manually or through closing of the switch 64, the door operating mechanism functions in the usual manner to cause the door to open. to its normal open position. When the door reaches this position andthe switch 5| is shifted to en- 'gage the contact 54, the circuit through the opening field 46 is not broken by reason of one' of the switches Bl being closed, and the door accordingly is automatically moved beyond its normal open position to its extreme open position,
' where the switch 2 is opened by reason'of the notch 44 in the cam disk 32. the closing field 41 of the motor is not closed when the switch 5| is shifted since the timecontrolled switch 51 is not closed. When the That The circuit through switch'42 opens with the door in'extre'me open position, the door actuating device no longer functions for moving the door, and the driving motor acts as a brake to hold the door in its extreme open position.
Where the door is to remain open for an indefinite period, the door is moved manually from its normal open position to the full open position, where the notch 44 in the cam disk 32 releases the switch 42, allowing the latter to open so that the motor acts as a brake in holding the door in the full open position. Since the switch 42 is open, there is no power supplied to the driving motor, and the door remains in the full open position until it is moved manually toward closed position far enough to cause the cam disk 32 to close the switch 42, or until the switch 64 is closed, thereby closing a circuit which by-passes the switch 42 and directing power to the field winding 41, which causes the door to close. It will be apparent that as the door moves into its normal open position before being moved manually beyond this position into the full open position the switch 5| has been reversed in readiness for causing the door to close whenever the switch 42 is closed long enough to heat the thermal element 95 to close the switch 57. Obviously, the overload clutch, comprising the clutch disks 25 and 26, allows the door to be moved manually from the normal open position to the full open position, since the gear 23 slips relative to the clutch disks as soon as the torque on the motor exceeds a predetermined amount. The resiliently controlled fingers 65 allow the clutch disks 3! and 32 to turn with the shaft 5 into the full open position of the door without damaging either the fingers or the lug 67 engaged thereby.
When the door is either opening or closing and a person using the door wishes it to move in the opposite direction, the automatically controlled switch 48 is shifted through means of the inertia actuated mechanism of Fig. 3. When the door is moved normally by the device, the lever l8 hangs in the normal vertical position shown. If the door is given a slight quick manual swinging movement in either direction, the lever '38, by reason of the mass 19 on the end thereof, swingsagainst either of the screws 85 or 86, thereby shifting the switch 48 to its opposite position and causing the door to move in a direction opposite to its normal movement into either closed or normal open position, at which point the cam 92 or 92 becomes operative to release the lever 18 and allow it to return to its original vertical position, thereby restoring the switch 48 to the position of Fig. 8, so that from that point on the door operates in the normal manner. It will be apparent that the door may be swung in either direction to cause shifting of the lever 78; that is to say, the door may be moved readily in the same direction that it is normally moving, or it may be moved inv the opposite direction. In either event this abnormal movement is possible by reason of the overload clutch comprising the disks 25 and 26. This feature is especially useful if a person attempts to open the door during its normal closing movement.
With reference now to Fig. 9, the wiring diagram of this figure incorporates, in addition to the structures above described, an arrangement by which the door may remain in open position for a relatively long period at intervals when the door would normally be opening and closing practically continuously. It will be understood that this wiring diagram incorporates only the" portion of the wiring diagram of Fig. 8 that is necessary to show the additional structure. Otherwise the diagram is exactly the same and the device functions entirely in the manner above described.
For this structure a box |I is attached to the casing I2 for the device and within the box is a bimetallic thermal element I02 having one end held against movement within the box by a block I03. This end of the bimetallic element is connected by a lead I94 to the terminal of the field winding 41 to which the lead 58 is regularly connected. The free end of the bimetallic element is normally in engagement with a fixed contact I05 which is connected by a lead I86 to the lead 58, the latter, as shown in the diagram of Fig. 8, being connected through the switch 51 to the lead 55. The box IOI is insulated and has positioned therein a heating coil I0! which is in parallel with the field winding 46, and therefore tends to heat the thermal element I92 during the intervals when the door is being opened. Thus, if the door is opening and closing practically continuously, the element I02 becomes heated and, as a result, moves away from the contact I05, thereby braking the circuit through the field winding 41. When this occurs, the door reaches normal open position in the usual way, but when the switch 5I is shifted, at the normal open position of the door, to cause the door to close, the circuit through the field winding 41 is not completed and the door remains in its normal open position until the interior of the box IOI has cooled down sufficiently to allow the thermal element I02 to again engage the contact I05.
The abovestructure maybe furtherimproved by the addition of a second heating coil I08 which is connected by a lead I 09 to the lead 98 and by a lead I I 0 to the lead 59. This heating coil is thus energized during all of the time that the switch 42 is closed and aids the heating coil I01 in heating the interior of the box IOI. This differential heating coil I08 adds heat to the box IOI almost as fast as heat is dissipated from the box and thus provides for the door remaining open for a relatively long period of time when this feature of the device is in operation. That is to say, whenever the door reaches normal open position and is held in this position by the movement of the thermal element I02 away from the contact I05, the main heating coil I0! no longer supplies heat to the box I0l since the circuit through the field winding 40 is broken as soon as the door reaches its normal open position. However, the coil I08 continues to supply heat to the box I 0| almost as fast as the heat is dissipated from the box and thus prevents movement of the bimetallic element back into engagement with the contact I05 for a substantial period of time.
From the foregoing it will be apparent that the device provides for automatically opening and closing a door, together with mechanism for having the door remain open a predetermined time before each closing thereof, this timing element being under the control of the thermal element 95. Furthermore, in any opening or closing position of the door, the movement of the door may be automatically reversed by a slight manual swinging movement of the door by means of the mechanism best shown in Fig. 3. The door may also remain in full open position for an indefinite period merely by manually swinging the door from its normal open position into the full open position Where the switch 42, which controls the circuits through the motor, is automatically opened. A further feature of the device is the provision for causing the door to move automatically into full open position by reason of some abnormal circumstance which causes the switches 91, or either of them, to be closed. In addition, to prevent practically continuous swinging movement of the door at peak periods of use, the structure disclosed in Fig. 9 becomes operative and causes the door to remain in normal open position for a relatively long time interval by means of the thermal element I02 located in a chamber, or box, in which heating units are located. The thermal element I02 obviously provides for the door to remain open a much greater period than the door would remain open under the control of the thermal element 95. That is to say, where the thermal element 95 might allow the door to remain open for ten seconds, the thermal element I02 could be arranged to cause the door to remain in its normal open position for a period of fifteen minutes. Obviously, this period of time can be controlled by the size of the heating coils I07 and I08.
1. In an electrically actuated door operating device, a driving motor, a driven member actuated thereby for moving a door, means for causing said motor to automatically open and close said door, and means operative upon a substantially continuous use of the door which involves substantially continuous operation of the driving motor for opening the circuit through said motor when the door is, in normal open position and for maintaining said circuit open for a predetermined interval.
2. In an electrically actuated door operating device, a driving motor, a driven member actuated thereby for moving a door, said driving motor being reversible for the opening and closing movements of the door, a thermal element normally closing a part of the reversing circuit of the driving motor, and a heating coil in the circuit through the driving motor for heating the thermal element during a part at least of the opening and closing movements of the door, said thermal element operating to break the circuit through said motor when the door is in normal open position, said heating coil operating to cause the thermal element to break the circuit when the door is subjected to almost continual use, thereby causing the driving motor to operate substantially continuously.
3. In an electrically actuated door operating device, a driving motor, a driven member actuated thereby for moving a door, said driving motor being reversible for the opening and closing movements of the door, a thermal element normally closing a part of the reversing circuit through the driving motor, a heating coil for heating the thermal element to break the circuit through said element when. the driving motor would otherwise be operating substantially continuously as a result of practically continuous use of the door, said coil being energized during at least a portion of each opening and closing movement of the door, and a second heating coil functioning at least when the above circuit is broken for supplying heat to the thermal element almost as fast as it is radiated therefrom 70 for increasing the length of time that the circuit is broken.
CHARLES A. ELLIS.