US2752150A - Garage door operator - Google Patents

Description

June 1956 M. K. RICHMOND ET AL 2,752,150

GARAGE DOOR OPERATOR Filed Nov. 28, 1952 2 Sheets-Sheet l -J 47 INVENTORS Moscow I. file/mow 7 21671980 0. l/aLnss I B J fife/vie y J1me 1956 M. K. RICHMOND ET AL 2,752,150

GARAGE DOOR OPERATOR Filed Nov. 28, 1952 2 Sheets-Sheet 2 f 1 80 i f 85 i M g as g 22 INVENTORS 1 Moscow kf lelCA/MM L SI-GML BY Elm/4000. l/auvss 80\ RiCElVER I I 1 w I 4 I we (far/2 6% United States Patent GARAGE DOOR OPERATOR Moscow K. Richmond, Los Angeles, and Richard D. Holmes, Beverly Hills, Calif.

Application November 28, 1952, Serial No. 322,974

11 Claims. (Cl. 268-74) This invention relates to apparatus for automatically opening and closing a garage door.

In the past, automatic garage door operators have taken many forms, the most recent types employing a single elongated actuating member for swinging the garage door open or closed through a generally longitudinal movement of the member. In the case of the overhead type of garage door, for example, one end of the actuating member is pivotally secured at the center-top portion of the door and its other end fed between two or more rollers which frictionally drive the member in one direction or the other. A reversible motor can be used to drive the rollers and may be remotely controlled by a receiver-relay in turn responsive to a radio signal transmitted from an automobile.

In the event an obstruction is encountered while opening or closing the door, these systems rely on the fact that the friction driving rollers will merely slip on the actuating member. When the obstruction is cleared from the door, it will then continue to open or close as the case may be. It will be appreciated that this slipping action will cause considerable wear on the rollers. Moreover, if the rollers are urged against the actuating member with sufiicient force to drive a heavy door, a relatively large force will be necessary to stop the door and thus any obstruction may be damaged considerably, although the operating mechanism will not suffer save for the wear on the rollers.

Aside from the above noted difficulty and in spite of considerable work towards efiecting 'an economical and simple mechanism, these prior systems are also relatively bulky and expensive and usually require skilled personnel for their installation.

It is a primary object of the present invention to provide a vastly improved garage door operator whichis characterized by extreme simplicity in installation and operation, which contains a minimum of bulky and movable parts, and which is extremely economical to manufacture.

More particularly, it is an object of the invention to provide a simplified garage door operator which incorporates in combination, a novel safety switch means for stopping the door whenever it encounters an obstruction.

This switch means is designed to cut off the primary power source for the door and thus minimize any damage to such obstruction.

Another object is to provide a simple means whereby the apparatus may be adjusted for applying a force in accordance with that required to operate the particular door with which the system is to be used.

Another object is to provide an apparatus which may be readily installed by a single person using only conventional household tools.

These and further objects of the invention are attained by providing a single elongated channel member pivoted at one end to the door and adapted to be fed between a driving roller and an idler roller for longitudinal movement. The squeezing force exerted by these rollers is 2,752,150 Patented June 26, 1956 made adjustable. The driving roller is rotated by a reversible power source adapted to be energized by manual and/ or remote control means. A safety switch feature is incorporated and includes a portion of the motor circuit completed through movable terminals coupled to the rollers whereby either a change in the speed of rotation of one roller with respect to the other or the complete stopping of the idler roller will open the circuit and stop the motor. Such change in speed or stopping of the idler roller will occur whenever the door is slowed in its motion or encounters an immovable obstruction.

A better understanding of the invention and its additional features and advantages will be had by referring to the following description in conjunction with the accompanying drawings, in which:

Fig. 1 is a perspective view of the apparatus;

Fig. 2 shows partially in cross-section the apparatus as installed in an ordinary garage equipped with an overhead type door;

Fig. 3 is a perspective view of the attachment between the door and the elongated actuating member as seen looking in the direction of the arrow 3 in Fig. 2;

Fig. 4 is a rear view of the apparatus as seen looking in the direction of the arrow 4 of Fig. 3;

Fig. 5 is a side view of the apparatus shown in Fig. 4;

Fig. 6 is an enlarged sectional view of a portion of the apparatus as seen looking in the direction of the arrow 66 in Fig. 5;

Fig. 7 is an enlarged side view partly in section showing details of a reversing switch;

Fig. 8 is an electrical circuit diagram of the apparatus;

Fig. 9 is a perspective view of the safety switch means; and

Figs. 10, l1 and 12 are schematic drawings useful in explaining the operation of the switch shown in Fig. 9.

Referring to Fig. l, the garage door operator is shown in the form of a compact unit 10 secured to an overhead beam 11 by bolts 12. The unit 10 comprises a power source such as a motor 13 adapted to rotate a driving roller through a single reduction pulley 14 and belt 15. A door operating beam, preferably in the form of an elongated channel member 16, is pivotally attached at one end to the center-top portion 17 of a garage door 18,- its other end being fed between the driving roller and an idler roller for longitudinal movement as will become clear as the description proceeds. A light bulb 88 is connected to turn on automatically when the door is opened.

In Fig. 2 the door 18 is shown as mounted for pivotal movement about a pivot point 20 from a vertically closed position shown in solid lines to a substantially horizontally overhead open position shown in phantom lines. A bias spring 21 substantially dynamically balances the door about the pivot point so that it may be easily moved from one position to the other. It will be seen that longitudinal movement of the elongated channel member 16 will serve to open or close the door 18. A radio receiver 22 may be provided to close a relay 23 in response to a signal to energize motor 13, or this function may be accomplished by a manual push button switch 24.

Fig. 3 shows one simple means for securing the end of the channel member 16 to the center-top portion 17 of the door 18. As shown, a bracket 30 is secured to the door and has upwardly extending ends 31 embracing the end of the member 16, suitable holes being provided in the sides of the member 16 and ends 31 for journalling a pivot shaft 32.

Referring now to Fig. 4, it will be seen that the driving roller 40, preferably rubber (see Fig. '7), is mounted on a shaft 41 journalled in bearings 42 secured to L-shaped angle irons 43. The shaft 41 is directly coupled to be driven by the pulley 14. Driving roller 40 is adapted to engage the upper surface of the channel member 16 as shown. Disposed below roller 4% is an idler roller 44, also preferably of rubber, secured to an idler shaft 45 journalled in bearings 46. idler roller 44 is urged agalnst the opposite side of. the channel 16 towards the drivlng roller 4i whereby the channel member 16 is squeezed between the rollers.

This squeezing force is attained by means of a shaftr 47 mounting two bolts 43 and 49 projecting perpendicularly therefrom in like directions and arranged respectively to engage cam plates 56 and 51 secured to the ends of the shaft 45, upon rotation of the shaft 47.

' As shown more clearly in Figs. and 6, the idler roller shaft 45 is free tomove .in a vertical direction only within slots in the angle iron supports 43, one such slot 51 being clearly shown. A handle 52 fixed to shaft 47: permits the shaft to be manually rotated from the phantom line position to the solid line position, such action camming the idler roller shaft 45 upwardly to causethe roller 44 to engage the under surface ofthe channel 16 as shown. By increasing or decreasing the amount the bolts 48. and 49 project frornthe shaft 47, the amount of Vertical move. ment and thus the squeezing force of idler roller 44. may be adjusted. With the handle 52 in down position so that the. idler roller is free of the channel 16, the garage door. may be, operated manually since the channel member is free to move longitudinally.

As shown in Figs. 4 and 6, the channel member. 16. includes two laterally extending flanges 53 and 54 extending along its length. A slide abutment 55:as shown clearly in. Fig. 6 is secured to the flange 53 at acertain position along the channel member 16 and a similarslide abutment 59 (Fig. 4) is positioned on the other flange 54. As the channel member 16 is fed between the rollers 40-and 44 the slide abutment 55 will engage a downwardly depending rod 56 secured to a shaft 5'7. As seen best in Fig. 4, the opposite end of shaft 57 is provided with a similar rod 53 projecting in a direction at right angles to the. rod 56 substantially into the plane of the drawing. Rod 58 when in its downward position due to the rotation of'shaft 57 is adapted to be engaged by the slide abutment 59 onthe flange 54.

This operation can best be seen by referring to Fig. 7 which showsthe rod 56 in down position and about to be engaged by the slide abutment 55 as the channel member- 16.moves.to the left as indicated by the arrow. The

other. rod 58 is shown extending out horizontally and thusv clearof the slide abutment. Now as the channel member 16 moves to the left the slide abutment 55 will engage, rod 56 and swing it upwardly towards the phantom lineposition as indicated bythe arrow. The shaft 5716 which the rods 56 and 58 are secured will rotate tomove a lmk 7liclockwise. A compression spring actuated arm or link 71pivoted at one end to the link 76 and extending at its other end through a stationary perforated lug 72' will be thus swung to the right about the lug 72 as a pivot and serve .to throw a toggle switch 73. The link 71 extends through a perforation in the handles of the toggle switch, as indicated; and a snapaction is obtained by compression spring 71a surrounding link 71 between the toggle switch and a fixed abutment 71b on the link. The

action of the snap action link '71 and the toggle switch thus stop the motion of the channel member 16. This switch also connects the motor for operation in reverse. By properly positioning the slide abutments on the channel 16, the length of movement of the channel can be.

adjusted to accommodate the motion necessary for the operatingof any particular garage door.

In the operation of the overall mechanism as described thus far, the lower idler roller 54 is cammed up into squeezing engagement with the channel member 16 by manually pushing the handle 52 (Fig. 5) upwardly. This places the apparatus in operative condition and it is never necessary to move the handle 52 to release the idler roller unless the mechanism gets out of order and it is desired to close the garage door manualy.

Assuming the door is initially closed, the circuit to. the motor may be closed by either the push button 24 (Fig. 2) or the relay 23, if the receiver 22 is suitably energized by a radio signal from a transmitter disposed in the automobile. Starting of motor 13 turns the driving roller M) (Fig. 4) to frictionally drive the elongated channel member 16 to the right as viewed in Fig. 2. This action raises the door as shown by the arrow. When the door is fully open the channel member 16. has. assed through the rollers to apoint where the slide abutment 55 incounters the rod 56 pushing this rod up to stop the motorand connect it for reverse operation. This switch also turnson the light 83, (Fig. l). The motor, although now connected in reverse, will not start again until the button 24 is again, pressed or the relay 23 activated.

When either the button or relay are again actuated, however, themotor will now turn the driving roller 40 in the opposite direction and the channel member 16 will be moved to the left. When the door is completely closed, the other slide abutment 5 9 on thefar end of the channel is ina position to encounter the rod 58 which was placed in the down position when the motor was previously thrown in reverse, and push this rod up to stop the motorandalso throw. itfrom reverse to forward. This action also turns off the light 88.

Tounderstan-d how this reversing switch and the electrical system functions, reference is made to Fig. 8 which shows in schematic form various electrical components of As shown in Fig. 8, a source of A.-C. is"

the apparatus. supplied to two power leads Sit-and 81, the lead 80 cmnecting through a relay contact 82to one end of the runingwinding-83of motor 13; The other power lead 81 extends up through fuse84 to the other end of the coil 83. Also-connected across the power leads is the radio receiver 22-, althoughthis component may derive its power from any other convenient source if desired. The reversingtoggle switch 73 is shown as comprising a double pole, doubleth-rowswitch, its two positions beingindicated by the solidand dotted arrows respectively.

In-the-solidline position the switch connects the power leads 80 and 81 to two leads 85 and 86 which lead to thesta rting winding coil 87 of motor 13, the lead 85 including-in series, relay contact 82. In this position the light88-is-alsoconnected across the power circuit. The motoris--now-connectedso that it will'operate to close the-garage door.- In the dotted line position, the connection of the leads 85 and 86 to the, power leads 80'and' 81 is reversed and the light 88 shorted out of-the circuit. The reversal of polarity of the leads 85 and 86 goingto motor winding 87 reverses the direction of the motor;

Starting and holding circuits designated I and II re: spectively, areencrgized by transformers T1 and T2, the primaries of each being connected between the leads 85 and-86 but theconnection of the-primary of T2 to lead 85' beingeffectedabove the relay contact 82. Circuits! and'Il both contain relay coil 89in common. Also included in the circuit II is a safety switch device 96 which willbe describedyin detail later. For present purposes it will be assumed that the safety switch 90, is closed so.

that the circuit II is a closed circuit.v Thecircuit I includesthe push button starting switch 24, whichmay also be eifectiyely closed by the relay 23 in response to a-sig al romi e eiver z- Assume first thatthereversing switch 73 is ;in. the dotted,

line position. In this state the garage door is closed and the light 88 off. The motor 13 will not operate because the relay contacts 82 and 82' are open. When the button switch 24 or relay switch 23 is closed, however, circuit I will be closed and thus energized through the transformer T1. Relay coil 89 will then close the relay contacts 82 and 82, applying power to the field winding 83 and starting winding 87 of motor 13 and to the primary of transformer T2. Circuit II will thus be energized and hold relay coil 89 energized and the relay contacts 82, 82' closed even though button switch 24 is released and relay 23 de-energized.

With both the running winding and starting winding of the motor 13 energized the motor will operate to open the garage door until the reversing toggle switch 73 is thrown by action of the slide abutment. It will be noted in Fig. 8 that in throwing this switch from the dotted line position to the solid line position, the circuit to leads 85 and 86 is momentarily broken. When this occurs, transformers T1, T2 and the relay coil 89 are all de-energized, permitting relay contacts 82 and 82 to open. Then when the toggle switch completes its throw so that the primary of T1 is energized, no further action will take place until the button 24 or relay 23 closes circuit I again. It is also to be noted that the light 88 is now connected across the circuit and will go on.

In this instance of the operation, the garage door is now open and the leads to the starting coil of the motor reversed. The motor, however, will not operate until a further signal is received in the receiver 22 or until button switch 24 is again depressed, to close the door.

It is thus seen that circuit I acts as a starting circuit and circuit II acts as a holding circuit.

In the event the garage door encounters an obstruction during the period it is opening or closing, the safety switch 90 is caused to open the circuit II thereby de-energizing relay coil 89 permitting contacts 82 and 82 to open and stop the motor 13.

The action of this safety switch can best be understood by referring to Fig. 9 which shows an enlarged perspective view of the switch.

As shown in Fig. 9 the driving roller shaft 41 includes an off-center crank pin or eccentric which may take the simple form of a machine screw 91. On either side of pin 91 extend the legs of a Wobbler element 92 preferably formed of an insulative pulastic and loosely pivoted about the idler roller shaft 45. The Wobbler element 92 mounts a terminal 93 projecting perpendicularly therefrom a short distance below the legs of the element. With this arrangement, rotation of the shaft 41 will cause the Wobbler element 92 to swing back and forth over a small are due to the off-center camming action of the pin 91 on the legs of the Wobbler element. This motion causes the terminal 93 to reciprocate over a small given distance at a rate proportional to the rotational speed of the driving roller shaft 41.

The adjacent idler roller shaft 45 is provided with a substantially U-shaped conductive strip 94 whose loop end or bight is of something more than 180 of angular extent, and surrounds and is in frictional contact with something more than a 180 portion of an .insulative sleeve 95 in turn fixed to the shaft. The strip 94 is biased to frictionally grip this sleeve but, nevertheless, permit frictional slippage between itself and the sleeve. The legs of the strip 94 extend laterally from the shaft in general parallelism with one another on opposite sides of the terminal 93 as shown and are spaced a distance apart greater than that given distance necessary to accommodate the reciprocatory motion of the terminal 93 when Wobbler element 92 is in action.

The electrical circuit ll of Fig. 8 is completed through the conductive strip 94 and terminal 93 when either one leg or the other of the strip 94 is in contact with terminal 93.

Referring to Fig. 10, it will be seen that with the driving roller shaft 41 turning in a clockwise direction, the idler roller shaft 45 will be turning in a counterclockwise direction due to the motion of the elongated channel member 16 (Fig. 7). The conductive strip 94 is therefore continuously urged to the left due to the frictional forces exerted thereon by the insulative sleeve 95 turning with shaft 45. Its right-hand leg will therefore perpetually stay in contact with the terminal 93 throughout the reciprocatory motion of said terminal. Similarly, when the driving roller shaft 41 is turning in a counterclockwise direction, idler roller shaft 45 will be turning clockwise and the lefthand leg of the strip 94 will perpetually stay in contact with the terminal 93 as shown in Fig. 11. The sleeve 95 serves not only to insulate the strip 94 from the shaft 45 but also provides a suitable friction surface.

Now, if an obstruction is encountered by the garage door, the longitudinal movement of the channel member 16 will be slowed or even stopped. This will not affect the rotation of the driving roller shaft 41 because the shaft is motor driven and the roller itself will simply slip on the channel member. However, the speed of the idler roller shaft will depend on the decreased or stopped motion of the channel member since the idler roller is driven thereby. Thus when the rotational rate of the idler roller shaft slows or changes with respect to the driving roller shaft, the legs of the strip 94 will not stay in contact with the terminal 93 since the reciprocatory motion of the latter is greater than the rate of turning of shaft 45 which tends to urge one leg or the other of the strip 94 into contact with terminal 93. The terminal and strip thus become momentarily separated as shown in Fig. 12 and open circuit II. Opening of the circuit II de-energizes relay coil 89 and opens contacts 82 and 82 to stop motor 13.

However, it will be noted that the safety switch 90 is not in the starting circuit I and therefore pushing button switch 24 or actuating relay 23 will start the motor going again. If the garage door is cleared of the obstruction in the meantime, the channel member 16 is free to move and idler roller shaft 45 will again move the conductive strip 94 into contact with terminal 93 to close holding circuit II.

The above described contact strip 94 and oscillating contact or terminal 93 may be regarded as a sensing means whose behavior is governed by both the drive roller (through oscillation of the terminal 93 by the crank pin on the drive roller) and the idler roller (through friction drive from the sleeve 95 on the idler roller shaft), in such a way as to sense the ratio of idler roller speed to drive roller speed, and to maintain a closed circuit condition (Figs. 10 or 11) with normal ratio of idler roller speed to drive roller speed, and to effect an open circuit condition (Fig. 12) upon decrease in said ratio.

It is to be noted that the garage door apparatus of the present invention utilizes a minimum of mechanical parts. Thus there is only one reduction belt drive from the motor to the driving roller shaft. There are only two rollers located one above the other with the channel member in between. This arrangement together with the fact that the channel member is thin, although strong due to its channel shape in cross-section, permits the channel member to swing about a transverse axis to accommodate the arcuate path followed by the point of its attachment to the top of the garage door, when the door is being opened or closed.

It is also to be noted that the relative mechanical simplicity of the apparatus permits it to be readily packed and shipped in a carton weighing less than 40 lbs. Furthermore, the apparatus may be readily installed by one person.

Modifications within the spirit of the present invention will occur to those skilled in the art. Thus while the invention has been described as a device for operating garage doors, it clearly has application for opening or closing other type doors or closure means. Moreover,

while the elongated actuating member has, been described as a metallic channel member it may be any type of'actuating member. such as a flexible endless belt for example, looped. over an end pulley at the rear of the garage and a pulley on the garage door whereby pulling of the belt in one direction or the other by the rollers will pull the garage door open or closed. In the event the door is biased towards closing by gravity for example, only a single flexible belt need replace the channel member.

Furthermore, while the safety switch has been described as including part of an electrical circuit, the switch action may be accomplished by having one or bothv of the ends of the strip 94 bear against micro switches to hold the latter closed, and upon the stopping of rotation of the idler roller, the cessation of the bearing pressure permitting the micro switches to open and stop the motor. Other arrangements for stopping the channel member within the spirit of the principles of the friction means disclosed will occur to those skilled in the art. For example, the cessation of the bearing pressure may permit a mechanical system to disengage the idler roller from the, actuating member.

Accordingly, the various features of the invention are not to be thought of as limited to the precise embodiments disclosed.

We claim:

1. In an apparatus for operating a garage door, a beam having one end operatively connected to the door, a driving roller adapted to engage one side of said beam, an idler roller adapted to engage the: opposite side of said beam, means for urging said rollers towards one another whereby said beam is squeezed between said rollers with a given force, a power source for rotating said driving roller such rotation moving the beam longitudinally and causing said idler roller to rotate, an element frictionally coupled to said idler roller whereby the element is urged in a given direction with a force substantially proportional to the rate of rotation of said idler roller; and normally closed contact means cooperating with said. element and said power source, said contact means being adapted to open to shut oil the power means in response to a change in speed between said driving roller and said idler roller, for stopping the movement of said beam.

2. In an apparatus for operating a closure means, an elongated actuating member attached at one end of said closure means and adapted to be moved in a substantially longitudinal direction by a driving roller, an idler roller engaging said member and adapted for rotation by movement of said member, power means for rotating said driving roller, and an electrical circuit for actuating said power means including a safety switch adapted to close said circuit when said two rollers are both turning due to longitudinal movement of said member and toopen said circuit when the rate of rotation of said idler roller changes with respect to the rate of rotation of said driving roller, said safety switch including a terminal adapted to be reciprocated over a given distance in response to rotation of said driving roller, a shaft adapted to rotate with said idler roller and disposed adjacent to said terminal, an insulative sleeve secured to said shaft, and a conductive strip surrounding a portion of the circumference of said sleeve and spring biased to grip said circumferential portion, the ends of said strip projecting laterally on opposite sides of said terminal and being spaced from one another an adjustable distance greater than said given distance, whereby rotation of said idler roller and shaft will frictionally urge one end, of said strip into perpetual contact with said reciprocating terminal to thereby close saidcircuit, unless the rate of rotation of said idler roller shaft is decreased with respect to the rate of rotation of said driving roller shaft.

3. In an apparatus for actuating an elongated member by meansof frictionally driving said member. in a longitudinal direction by a driving roller, an idler roller adapted to rotate in response tomovement of said elongated member, a power source actuated through an electrical ci'rcuit for rotating said driving roller, safety switch means "insaid electrical circuit for stopping said power source comprising a terminal adapted to reciprocate in response to the rotation of said driving roller, and a conductive strip frictionally coupled to the idler roller whereby the strip is biased in. response to rotation of said idler roller into contact with said terminal to complete said circuit only so long as the rotational rate of said idler roller does not decrease with respect to the rotational rate of.

said. driving roller.

4. In an apparatus for operating a closure means ineluding. an elongated channel member adapted to be frictionally driven in a longitudinal direction between a driving roller and an idler roller, a power source for rotating said driving roller, and a reversing switch for said power source, means for operating said reversing switch comprising, a shaft transversely disposed across but spaced from said channel member and including a first rod vertically extending from one end of said shaft to pass perpendicularly to oneside of said channel member; a second rod extending at substantially right angles to said first rod from the other end of said shaft, said channel member having a laterally extending flange along each of its longitudinal edges; and first and second slide abutments secured to said flanges respectively whereby upon longitudinal movement of said channel member betweensaid rollers, said first slide abutment will eventually abut said first vertical rod to turn said shaft and operate said reversing switch and cause said second extending rod to assume a vertical position, whereby it may be eventually engaged by said second slide abutment upon movement of the channel member in an opposite direction.

5. In an-apparatus for actuating an elongated member intolongitudinal motion, a driving roller f'rictionally engaging said member, an idler roller adapted to engage frictionally said member, a strip element frictionally coupled to the idler roller whereby the strip is biased to apply pressure in a given direction in response to rotation of said idler roller, and means responsive to a cessation of said strip pressure to stop the longitudinal motion of said elongated member, whereby cessation of the rotation of said idler roller will stop said longitudinal motion.

6. In an apparatus including a source of power for moving a: member, an element adapted to rotate in response to movement of said member, a safety device responsive to a change in'the rotational rate of said element from its normal operating rotational rate, for stopping the movement of said member'including: a strip in frictional engagement with a portion of said element, whereby upon rotation of said element said strip is urged in a given direction to exert a forcewhich is a function of the rotational rate of said element, and an electrical circuit connected tooperate said power source and adapted to open upon a change in said force.

7, An apparatus according to claim 6 in which said circuit includes a terminal adapted to be reciprocated by saidpower source over a given distance at a substantially constant rate, said strip being urged in a direction to engage said terminal only so long as said element is rotating substantially at said normal operating rotational rate whereby upon a change in rotational rate of said element and thus a change in said urging force, said' strip will separate from said terminal and open said circuit.

8., In an apparatus for operating a garage door, a beam having one end operatively connected to the door, a drivingroller adapted to engage one side of said beam, an

idler roller adapted to engage the opposite side of said beam, means .for urging'said rollers towards one another whereby said beam is squeezed between said rollerswith a given force, an electric motor operatively geared to said drive roller for rotating the same, such rotation moving the beam longitudinally and causing said idler to rotate, a power circuit includ? lg a control switch for said motor, and safety means for opening said motor control switch in event of obstruction to movement of said door and consequent slow down or stoppage of said beam and idler roller while said driving roller continues to rotate, said safety means comprising sensing means continuously sensing the speed of rotation of said idler roller relative to speed of rotation of said driving roller and responsive to decrease in such ratio below that eXisting under normal running conditions for effecting opening of said motor control switch.

9. The subject matter of claim 8, wherein said control switch is biased to a normally open condition, and wherein said safety means includes a holding circuit adapted when energized to hold said control switch closed, said holding circuit including a pair of electric contacts, and wherein said sensing means includes means holding said contacts closed during normal running, and responsive to decrease in relative speed of rotation of said idler roller with respect to said driving roller to open said contacts.

10. The subject matter of claim 9, including a means for oscillating one of said holding circuit contacts through a fixed path of given length at a speed proportional to driving roller rotation, a friction drive member rotating with said idler roller, a frictionally driven switch operating member in friction drive contact with said friction drive member, the other of said holding circuit contacts comprising two branch contact elements of said frictionally driven switch operating member positioned on opposite sides of said oscillating contact and spaced apart by a distance greater than the length of said fixed path of It: said oscillating contact, whereby rotation of said idler roller and friction drive means holds one of said branch contact elements in contact with said oscillating contact, unless the rate of rotation of the idler roller is decreased with respect to the rate of rotation of the drive roller.

11. In an apparatus for operating a garage door, a beam having one end operatively connected to the door, a driving roller adapted to engage one side of said beam, an idler roller adapted to engage the opposite side of said beam, means for urging said rollers towards one another whereby said beam is squeezed between said rollers with a given force, whereby rotation of said drive roller moves the beam longitudinally and causes the idler roller to rotate, a means for interrupting the drive of said beam by said drive roller, and safety means for actuating said interrupting means in event of obstruction to movement of said door and consequent slow down or stoppage of said beam and idler roller while said driving roller continues to rotate, said safety means comprising a sensing means continuously sensing the speed of rotation of said idler roller relative to speed of rotation of said driving roller and responsive to decrease in such ratio below that existing under normal running conditions for actuating said interrupting means.

References Cited in the file of this patent UNITED STATES PATENTS 731,185 Horst et a1 June 16, 1903 835,362 Merrill Nov. 6, 1906 1,109,928 Jones Sept. 8, 1914 1,338,671 Burnham May 4, 1920 2,430,729 Negri Nov. 11, 1947

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