US2758835A

US2758835A - Automatic door operator

Info

Publication number: US2758835A
Application number: US301871A
Authority: US
Inventors: Lance A Wikkerink
Original assignee: TREADWAY CORP
Current assignee: TREADWAY CORP
Priority date: 1952-07-31
Filing date: 1952-07-31
Publication date: 1956-08-14
Anticipated expiration: 1973-08-14

Description

Aug. 14, 1956 A. WIKKERINK 2,758,835

' AUTOMATIC DooR oPERATOR v FiledAJuly 31, 1952 s sheets-sheet 1 IN V EN TOR.

OMMr-M Aug. 14, 1956 A. WIKKERINK 2,758,835

AUTOMATIC DOOR OPERATOR Filed July 51, 1952 s sheets-shew 2- 1N V N TOR.

A TTQE/VEYS Aug 14, 1956 1 A. WIKKERINK 2,758,835

AUTOMATIC DOOR OPERATOR Filed July 31, 1952 3 Sheets-Shea?l 3 AM/CE H. W/KKEe/N/c MLLM+MJA AUTOMATIC 'DOOR OPERATOR' Lance A. Wikkerink, Milwaukee, Wis., assigner, by mesne assignments, to Treadway Corp., Woodbridge, N. l., a corporation of New Jersey Application .luly 3'1, 1952, Serial No. 361,871

Ll?) Claims. (Cl. 268-34) This invention relates to an automatic door operator.

It is the object of the invention to provide an automatic door operator which exerts its greatest force on the door in the initial stages of door movement whereby to overcome the inertia of the door. Conversely, the force of the operator on the door at the end of door movement is reduced in the device of the present invention whereby to avoid slamming the door and conserve energy otherwise thus wasted. Accordingly, in the device of the present invention, the thrust of the door operator is directly related to the resistance of the door and is materially reduced at the end of door movement.

in the `device of this invention, differential door operator thrust is developed by progressively changing mechanical advantage of a transmission mechanism between a motor or motors (which may have relatively constant thrust) and a connection to the door. Because no change in thrust is required of the motor, a motor of relatively small capacity is all that is required to power the device of this invention. The relatively great inechanical advantage in the transmission mechanism at the beginning of motor operation more than makes up for the small size of the motor. This is in sharp contrast to prior art devices which do not take into account changes in door resistance. In such prior art devices the motor is made large enough to overcome maximum resistance of the door. After the initial inertia of the door is overcome the excess energy of the motor is wasted in slamming the door against its frame. Here, however, my novel transmission compensates for changes in door resistance and utilizes the full capacity of the motor throughout the range of door movement. As compressed air is commonly used to actuate a compressed air motor in devices of this type, my operator only requires an air compressor of materially smaller size than those of the prior art.

Another object of the invention is to provide a novel uid control valve for the fluid motors iny the door operator of this invention. This control valve provides for a time lag or dwell between door opening and door closing movements for purposes hereinafter explained.

I also provide a novel electric actuating circuit for my door operator. The circuit is provided with an interlock which locks the control valve in one position when the safety mat switch is closed before the approach mat switch is initially closed, thereby holding the door closed until the safety mat switch is opened.

The door operator consists of a shaft having motion transmitting connections to the door and a crank on the shaft, a powered actuator and means for guiding the actuator against the crank arm on a path which is eccentric with respect to the axis of rotation on the shaft. In the course of its eccentric path the point of contact of the actuator with the crank shifts along the crank to vary the moment arm of the crank. Moreover, in the initial movement of the actuator, the crank is in inclined position with respect to the path of movement of the actuator. Accordingly, in the initial movement of the actunited States Patent fs"le ator, the actuator acts against the crank in the manner of a wedge to increase the mechanical advantage of the actuator respecting the shaft. This combination of wedging action and shifting of the point of contact of the actuator with the crank increases the torque exerted on the shaft during the initial movement of the actuator. Near the end of its stroke the point of contact of the actuator with the crank has moved close to the axis of shaft rotation with corresponding reduction in mechanical advantage and torque.

Other objects and advantage of the invention will be more apparent to one skilled in the art upon examination of the following disclosure.

In the drawings:

Fig. l is a fragmentary View in perspective of a building wall showing a door and door operating mechanism according to the present invention.

Pig. 2 is a horizontal cross section through the door operator of the present invention.

Fig. 3 is a cross section through a fluid control valve according to the present invention. 'v

Fig. 4 is a cross sectional view taken along the lines lfll of Fig. 3.

Fig. 5 is a cross sectional View taken along the lines 5 5 of Fig. 4.

Fig. 6 is a cross sectional View taken along the lines 6--6 of Fig. 2.

Fig. 7 is a schematic circuit diagram of the electric circuit which controls the door operator according to the present invention.

Fig. 8 is a graph plot of shaft torque against door position.

The invention has particular utility in super markets and other public buildings where it is inconvenient for pedestrians to manually manipulate entry and exit doors. l have chosen to describe the present invention in an embodiment in which the weight of the pedestrian im.- posed on approach and safety mat switches actuates an electric control circuit for the door operator which opens and closes the door automatically depending on the position of the pedestrian respecting the switches. The invention does not reside in the specific mat switches disclosed, however, as electric eye devices etc. could be substituted within the scope of the invention. While mechanisms of the general type described are in use today the present invention constitutes an improvement thereover in the respects herein mentioned. I

Fig. l shows in fragmentary perspective a wall 10 provided with a door frame 1l and a door 12 hinged at 13 to the frame. The door opens in the direction of traic. The entrance side of the door is provided with a oor approach mat i4 and the exit side of the door is provided with a safety mat l5. A pressure approach switch 16 and a pressure safety switch i7 are concealed beneath the respective mats to be actuated by the weight of a person walking on the mat.

The upper rail 20 of the door is provided with a bracket 2i, a link 22. and an operating arm 23 pivoted to the end of link Z2 by pin 2d. The other end of arm 23 is adjustably fixed to the downwardly projecting end of a rock shaft 25 rotatably mounted in the casing which houses the opening mechanism. The shaft 25 and arm 23 are provided with complementary mating tapers 18 (Fig. 6) permitting adjustment in their fixed connection. Bolt 19, seating against washer 29, draws the tapered surfaces into frictional locking engagement.

The casing Sil in which shaft 25 is mounted has both inner and outer walls. Heavy metal

inner walls

26, 27, and 28 (see Fig. 2) enclose a chamber of generally trapezoidal configuration containing the transmission mechanism and support the entire structure from the door frame il.. A light metal shell 3l forms with

walls

26, 27

and`28 an outer chamber containing the fluid motors and control valve and conceals all operating mechanism.

Swinging movement of the lever arm 23 on the axis of rotation of shaft 25 is effective through the link 22 and bracket 2l to open and close the door. Within the casing the shaft 25 is provided with a crank 32 having inclined or wedging surfaces 33 and 3ft. Shaft 25, together with arm 23 and crank 32, comprises a bell crank.

The

walls

26 and 27 of the casing 3@ are in oblique connection with the end wall 2S and converge toward said end wall for reasons hereinafter appearing.

Walls

26 and 27 are .provided with openings 35 and 36 respectively through which operator or piston rods 37 and 33 respectively of pistons 41 and i2 project into the interior of the trapezoidal casing to exert thrust on the opposed inclined surfaces 33 and 34 respectively of crank 32. Pistons 41 and 42 are mounted in

motor cylinders

43 and 44 which have their inner ends seated in the openings and 36 and their outer ends supported on the bracing rods 45 threaded into the

walls

26 and 27 of the casing, as illustrated at 40 in Figs. 2 and 6. Rods 45 carry head caps 46 in which seat the outer ends of

cylinders

43 and 44.

As so positioned the cylinders are substantially at right angles to the

Walls

26 and 27 of the casing. However, as the

walls

26 and 27 are angularly related, the cylinders are also. The cylinder head caps 46 are thus disposed near the outer corners of casing 3l and

fluid connections

47, 48 extend beyond the plane of wall 2S and are laterally aligned for easy connection to the valve 62 mounted on casing wall 28 therebetween.

Cylinders 43 and d4 are supplied through

fluid connections

47 and 43 with pressurized fluid, usually air, to constitute the

cylinder

43 and 44 fluid motors which drive the pistons 41, 42 into thrust engagement with crank 32.

The inner ends of the

piston rods

37 and 38 are pinned respectively at Si and S2 to guide links 53 and 54 provided with pivots and 56 tixed to oor 57 of the casing. The pivotally connected ends of the

piston rods

37 and 38 and links 53 and 5drespectively are provided with antifriction rollers 53 and S9 which contact the inclined surfaces 33 and 34 of crank 32.

Fixed pivots 55 and S6 of links 53 and 54 are oiset from the axis of oscillation of the shaft 25. Accordingly, the paths of movement of rollers 53 and 59 under the thrust of pistons 4l and d2 will constitute arcs which are eccentric with respect to the axis of rotation of shaft 25. The pistons il and 42 are slightly tiltable in their cylinders to accommodate such movement. Thus the elfective moment arm of crank 32 changes throughout the stroke of the pistons. in the completely retracted position of the piston (shown at the right in Fig. 2), roller 53 bears at the extreme end of the inclined surface 33 of crank 32. In the extreme forward position of the piston (shown at the left in Fig. 2), rolier 53 bears against inclined surface 34 of crank 32 near the base of the crank and relatively near the axis of rotation of shaft 25. Accordingly, in the initial movement of the pistons, the moment arm of crank 32 is greater than towards the end of piston movement. Consequently greater mechanical advantage and torque is imposed on the shaft in the initial movements of the piston.

Moreover, in the initial movement of the piston, the rollers 56 and 59 act on the inclined surfaces 33 and 34 of the crank 32 in the manner of a Wedge whereby further mechanical advantage occurs in the initial driving movements of the pistons. Thus there is a complex action combining a wedging action and a change in moment arm resulting in greater mechanical advantage at the beginning of piston stroke than at the end. Accordingly, the torque on shaft 2S is greatest when the door is started from a position of rest. Conversely, at the end of piston stroke, the torque is greatly reduced thereby eliminating slamming of the door against the frame. As before noted all the energy of the motor is used for useful work and none is wasted. A graph in which shaft torque is plotted against door position is shown in Fig. 8 of the drawings. This graph clearly shows how torque is directly related to the inertia resistance of the door.

The plot in Fig, 8 is taken from actual measurements using a spring scale at the end of lever arm 23. In the test aforesaid the lever arm was 27 inches in length. The uid motor was under a constant pressure of 70 pounds per square inch. Measurements were taken of thrust at the end o-f `the lever at various degrees of door opening movement. As also indicated on the graph the following chart shows the relation between shaft torque and door position:

Shaft; torque in pounds Door position in dcat end of 27 inch lever grecs of door opening arm movement Because of this novel distribution of torque during the course of piston movement a much smaller air compressor than has heretofore been required is needed to power the device of the present invention. Heretofore, in prior art devices where increased mechanical advantage was not employed at the beginning of door opening movement, greater thrust had to be used to start the door. As the piston is part of a constant thrust motor, this excessive thrust was continuous throughout vthe range of door movemeut yonly -to be absorbed at the end ol` the stroke is ineffectively banging the door `against the frame. ln the present invention great mechanical advantage is employed to start the door. A correspondingly smaller air compressor is accordingly needed.

The bell cranks 23, 25, 32 and links 53, 542- vmay be regarded as a transmission mechanism between the iluid motors `and the door. Because the transmission mechanism is adapted to change mechanical advantage between the motor and the door a constant thrust motor can be used with all the advantage of a variable thrust motor.

Fluid motors 43 and 4,4 are supplied with fluid, preferably compressed air, 'through a liuid control valve mechanisni indicated generally as 62. As best shown in Fig. 3, valve 62 comprises a cylinder 63 in which piston 64 is slidable. Piston 64 is hollowcd at b5 to receive a compression coil spring 66 which seats against the end wall of cylinder 62 to bias the piston toward the leit in Fig. 3. The hollowed socket and interior of the cylinder 63 together comprise a liuid chamber 67 which varies in capacity depending on the ,position of the piston. The portion of the piston-64` beyond the spring 6b moves in fluid chamber 70 enclosed by the valve casing 62. Charnber 7i) is in constant communication with a source of compressed air through fluid pressure connection 7i and flexible line 72. Chamber 79 is closed by a substantially planiform cover member 73 connected by bolts 74 to the valve casing 62. Cover member 73 is provided with three

uid ports

75, 76, and 77, aligned in the direction `of piston movement, to coact with a valve block 78 mounted on the piston 64. Valve block 7S comprises a bearing face provided with an annular groove or air channel 79 of diameter sufficient to simultaneously span and connect the center port 77 with one or the other of

ports

75, 76. In Fig. 3, port 76 is exposed to the compressed air in chamber 7@ and valve ports 75 and "i7 are in communication through the annular groove 79 in the valve block.

Valve block 78 comprises a body portion 30 seated in a complementary vlateral socket 83 in piston 64. Body portion Si) is socketed at Si to receive compression coil spring '82 which is biased against the end of socket 83 to insure good sealing contact of the valve block 78 about the

ports

7S, 76 and 77.

vFor the purpose of this description, port 76 inay be regarded as connected through coupling 34 and fluid line 85 to coupling 47 (Fig. 2) which serves fluid motor 43. Port 75 is connected by means of the coupling 86 and fluid line 87 to coupling 48 which serves fluid motor 44. Port 77 communicates with the atmosphere through needle valve 88. The connections shown operate the door in the organization shown in Fig. l and in which the door operator mechanism is mounted on the same side of the frame as the door is hinged. Floor mat 14 is at the approach side of the door and floor mat 15 constitutes the safety imat. lf door swinging movement were to be reversed in Fig. l it would be simply necessary to reverse the connections of fluid lines 85 and S7 to couplings 47 and 48. In that case, of course, mat 15 would be the approach mat and mat 14 would be the safety mat. The control valve mechanism 62 is so mounted on wall 28 of the casing that reversal of these connections is accomplished simply by rotating the control valve 62 through 180 and making the indicated connections. For this puipose couplings 86 and 84 are equally laterally spaced from the means on which the valve 62 is mounted to casing wall 28.

In the position of the valve shown in Fig. 3, line 85 is under fluid pressure to actuate fluid motor 43 and connect cylinder 44 to the atmosphere. Motor 43 thus holds the door closed as in Fig. l. This is the normal position of the operator with both approach and safety mat switches open. Chamber 67 of the control valve, however, i-s provided with a pressure release line 91 cnntrolled by a rubber or other elastic valve pad 92 normally closed against the end of the tube 91. ln this condition air pressures in

control valve chambers

70 and 67 are equal because of a bypass between said chambers resultant from the relatively loose fit of the piston 64 in cylinder 63. The piston is then freely biased to the left by spring 66. Valve 92, however, is mounted on the armature 93 of solenoid 94. Armature 93 is pivoted on pin 96 to bracket 95 and has a rearward extension 97 under tension of spring 100 anchored on ear 101 to bias the valve pad 92 against the end of tube 91.

When solenoid 94 is electrically energized, it attracts the armature 93 from the position shown in Fig. 3 to the position shown in Fig. 2 to open valve 92 and release the compressed air in chamber 67. Thereupon, pressure of the compressed air in chamber 70 will force the piston 64 to the right as shown in Fig. 3 against the bias of spring 66, said bias being insuflicient to resist the air pressure in chamber 70. Piston 64 will move until its end 63 strikes cylinder shoulder 69 which iixes the extreme right hand position of the piston. Movement of the piston 64 to the right, of course, alters the position of valve block 70 and serves to connect port 76 to the release port 77 to inactivate and exhaust air pressure in fluid motor 43 and to connect port 75 through chamber 70 with the source of air pressure to energize motor 44. Motor 44 then opens the door through the transmission mechanism in the manner hereinbefore described.

Because safety switch 17 and approach switch 16 are connected in parallel, as hereinafter more fully explained, the person walking through the door from the approach mat to the safety niat will maintain the solenoid 94 energized until he steps oif of safety mat 15. Both switches 16 and 17 are thereby opened to cle-energize solenoid 94. Spring 160 then returns valve 92 to closed position whereupon compressed air leaking from chamber 70 to chamber 67 through the bypass aforesaid will gradually equalize pressure in said chambers and permit spring 66 to return piston 64 toits Fig. 3 position.

The strength of the spring 66 and fluid capacity of the bypass or air bleed between

chambers

70 and 67 establishes a time lag or dwell between closure `of valve 92 and return of piston 64 to the position in which line S5 is again under pressure to energize motor 43 for return of the door to closed position. This dwell is highly important in my device for safety reasons. By setting a definite time lag between release of switch 17 and activation of door closing motor 43, a person passing through the door is well away from the safety mat before the door closes. A construction in which air bleed can occur because of the loose lit of piston 64 in cylinder 63, is less expensive than provision of a separate and distinct bypass channel of limited capacity between

chambers

67 and 70.

The electric circuit for controlling the operation of control valve 62 through solenoid 94 will now be described. This circuit is shown schematically in Fig. 7. A 24 volt transformer 102 is preferred to energize the solenoid. Other power sources, of course, could be adapted for use with the disclosed circuit. The transformer receives current at volts through input lines 103 and 104, and supplies current at 24 volts through its output lines 105 and 106. Terminal 107 of the solenoid 94 is directly connected to output line 105 of the transformer and the other terminal 108 of solenoid 94 is connected through line 111 along two paths of current liow as hereinafter indicated. Common line 111 branches at 112 through approach mat switch 16, line 113 and output line 106 to complete one circuit with the transformer. Closure of switch 16 will normally energize the solenoid.

Line 111 has a second branch at 114 connected through safety mat switch 17, line 115 and single pole double throw switch 116. In its left hand position in Fig. 7 switch 116 completes the solenoid circuit through line 117 to output line 106. Thus, with switch 116 in left hand position, switches 16 and 17 are connected in parallel and switches 17 and 116 in series. Accordingly, even though switch 16 is open, if both switches 17 and 116 are closed, solenoid 94 will be energized. If, however, switch 116 is in its right hand position in Fig. 7, and safety mat switch 17 is closed, solenoid 94 is short circuited through series connected switches 17 and 116. In that condition closure of approach mat switch 16 is ineffective to energize the solenoid because of the short circuit aforesaid.

Switch 116 dcsirably comprises a microswitch as illustrated in Fig. 2. Switch 116 is provided with an operator button 120 actuated by lever arm 121 having a roller 122 mounted in the path of cam surface 123 on shaft 2S. Accordingly, switch 116 is automatically thrown from one position to the other on rotation of shaft 25. In the position of the piston shaft in Fig. 2, in which the door is open, the solenoid 94 is energized. Thus switch 116 is in its left hand position as shown in Fig. 7 so that as long as either switch 16 or switch 17 is closed solenoid 94 will be energized to hold the door open. When the door is in its closed position, however, cam 123 will have caused switch 116 to move to its right hand position shown in Fig. 7. As long as switch 17 is open, closure of switch 16 is effective to energize solenoid 94. As before explained, when solenoid 94 is energized, control valve 62 is actuated to energize lluid motor 44 to open the door. in the course of door opening movement cam roller 122 on microswitch lever 121 will be actuated to change the position of the switch 116 from its right hand to its left hand position as shown in Fig. 7, so that when the pedestrian steps from the approach switch to the safety switch, the closure of safety switch 17 maintains piston 44 energized to hold the door open.

Assume, however, that someone is standing on the safety mat when the door is closed, switch 17 is closed and switch 116 is in its right hand position. Solenoid 94 is thus short circuited. Now if someone closes switch 16 by stepping on the approach mat, current supplied by the transformer 102 is short circuited around the solenoid through series connected switches 17 and 116 and the door cannot change position. Thus the person standing on the safety mat is protected from door opening movement. As soon as the person on the safety mat switch steps aside, however, switch 17 opens to break the series connection around solenoid 94 and the door will open in normal sequence. Solenoid 94 would also be short circuited if during the eXtreme initial movement of the door from closed toward open position switch 17 is closed. Cam face 123 is so dimensioned that switch 116 is held in right hand position (Fig. 7) until the door has made substantial pro-gress in its opening movement. Thus one stepping on safety mat 1S after the door has just started to open is protected.

While both door opening and door closing movement is normally controlled at relatively fixed accelerating and decelerating rates depending upon the rate of fiuid feed through

lines

85 and 87 to the respective cylinders' 43 and 44 and the structure of the transmission mechanism, it is conceivable that in either door opening or closing movement a gust of wind or other force might seize the door and increase its speed in the direction of movement of the energized piston and bang the door against the frame or otherwise damage it. rlhis would be possible unless otherwise provided against because as so far described the only resistance offered to door movement is door inertia and the resistance of the inactive fluid motor. The rate of fluid exhaustion from the inactive motor is controlled only by needle valve 88 (see Fig. 3). This is normally set to exhaust at a relatively rapid rate so as not to interfere with the operation of the active motor. Normally the inactive motor does not provide sufficient damping if a sudden gust of wind were to seize the door.

To provide against this contingency, a snubbing cylinder 124 is mounted by means of its threaded nipple portion 125 in a suitable tapped aperture in wall 26 of the casing (see Fig. 2). Cylinder 124 is filled between

movable pistons

126 and 143 with hydraulic fluid. The free end 133 of outermost piston 126 is provided with a generally concave socket 122 to receive plunger arm 127 which is pinned at 12S to second crank 129 on shaft 25.

The space between

movable pistons

126 and 143 isl divided into opposed chambers 134 and 135 by valve seat member 136 seated against snap ring 137. Valve seat member 136 is provided with a bypass channel 140 of small capacity and with a central valve opening 141 of larger capacity. Check ball 142 alternately releases and closes valve opening 141 depending upon the direction of ow of hydraulic fluid (desirably oil) against the valve seat 137 as is well known in the art. Piston 143 is provided with a rearwardly open socket 144 in which is seated a compression spring 145 which bears against snap ring 146. Spring 145 normally biases piston 143 toward the valve seat member 136 to flow oil through both the bypass 140 and the main valve opening 141 to force movable pislton 126 toward plunger 127 and require the piston to follow the plunger in all withdrawal movement thereof.

During movement of plunger 127 against piston 126 check ball 142 closes passage 141 and the oil must ow through bypass 140 toward piston 143 and against the bias of spring 145. Bypass 140 is sufficiently large so that piston 126 does not offer material resistance to plunger 127 under normal conditions. Door movement is thus normally controlled solely by the

iiuid motors

43 and 44. However, if the door is seized by a gust of wind, out of control of the

motors

43 and 44, bypass 14@ is sufficiently small to meter oil flow therethrough and piston 126 will snub inward movement of the plunger 127 and in turn check the door. Both

pistons

126 and 143 are provided with suitable O-ring seals 130, and 131 respectively to prevent escape of hydraulic fluid from confinement between the pistons. The angle of connection of crank 129 to shaft 25 is such that plunger 127 tends to withdraw from its concave seat during initial movement of

themotors

43, 44, but bears against its seat during the latter part of such movement.

From the foregoing description taken in connection with the accompanying drawings, it is clear that I have provided a novel door operator in which the torque imposed on the shaft operating the door varies throughout the range of door movement to apply greatest torque in the initial movement of the door where inertia is to be overcome and reduced torque at the end of door movement. My novel fluid control valve provides for time lag or dwell after the pedestrian has stepped off the safety mat before the door closes. My novel electrical circuit provides for complete electrical control of the solenoid and includes novel circuit elements whereby closure of the safety mat switch before and during initial movement of the shaft 25 will short circuit the operating solenoid to preclude opening of the door. My novel snubber is effective only under abnormal circumstances and operates to check the door when the door is forceably removed from the control of the motors. My novel assembly of operator components provides for positioning the valve 62 physicaily between the air connections to 'the pistons. The couplings 8 i and 86 are symmetrical with respect to the mounting of valve 62. Accordingly, rotation of the valve through l is all that is required to change air connections where the operator is converted from use on an in opening door to use with an out opening door.

I claim:

l. An automatic door operating system comprising a door operator having fluid operated means for acting on the operator in at least one direction of door movement, a fluid circuit including a connection to said fiuid operated means and a uid control valve in said circuit, said control valve having electric control means, an electric circuit for said electric control means, said circuit including an approach switch at the approach side of the door, a safety switch at the opposite side of the door, a multiple position switch actuated in response to door operator movements and a source of electric current, said electric control means having one terminal directly connected to said source and another terminal connected to said source in series through said safety switch and said door operated switch in one position of the door operated switch, said door operated switch having another position in which both terminals of said electric control means are connected through said safety switch.

2. The device of claim l in which said door operated switch is normally in said another position when the door is ciosed whereby closure of the safety switch will short circuit the electric control means and render closure of the approach switch ineffective to actuate the electric control means, said door operating switch being actuated to said one position in door opening movement to place said safety switch in parallel with said approach switch.

3. The device of claim 2 in which said door operator comprises a shaft having a cam surface, said door operated switch being mounted proximate said shaft and being provided with a switch actuating lever projecting into the path of movement of the shaft cam whereby said switch is actuated from said another position to said one position on rotation of the shaft in a door opening direction.

4. The device of claim 2 in which said fluid control valve comprises a cylinder and a piston within the cylinder and dividing the cylinder into opposed chambers, fluid ports in one of said chambers, resilient means biasing said piston toward said one chamber and a fluid release connection in the other of said chambers, said piston being provided with a port covering member alternately covering and opening said ports in the movement of the piston from one chamber to the other, a control valve for said fluid release connection, huid bypass means between said chambers, whereby to permit equalization of fluid pressure in said chambers when said fluid release connection is closed by said control valve, said bypass means having fiuid carrying capacity less than that necessary to permit normal action of said resilient means whereby said resilient means will move the piston toward the said one chamber at a rate dictated by fluid bleed through the bypass.

5. An electric circuit for an operator having electrical actuating means, said actuating means being provided with terminals, a source of current having a connection to one of said terminals, another of said terminals being connected to said source through a plurality of switches in series connection whereby all said switches must be closed to complete the circuit through said switches, and another switch in parallel with said series switches, one of said series switches comprising a multiple position switch having one position completing the circuit to said source and another position to short circuit the control through the other said series switch.

6. An automatic door operator comprising a casing and a shaft projecting through the casing and having a lever arm for connection with a door, a crank on the shaft within the casing and a pair of fluid motors mounted at the exterior of the casing and having pistons and piston rods for which the casing wall is apertured whereby said piston rods extend into proximity to the crank, swing arm guide means pivoted to the piston rods, said swing arms having fixed pivots Within the casing offset from the axis of shaft rotation whereby said piston rods have arcuate paths of movement eccentric respecting the axis of rotation of the shaft, said piston rods having means bearing at opposite sides of the crank whereby to actuate the crank in both directions of shaft oscillation.

7. The device of claim 6 in which said shaft is provided with a second crank and a plunger pivotally mounted on said second crank, and a fluid damping cylinder mounted on said casing and having means of connection with said plunger, said fluid motors having fluid pressure connections including a valve by means of which said motors are alternately pressurized and exhausted to operate the door, said uid damping means having a rate of movement greater than the rate of fluid motor operation whereby to be normally inactive but to control door movement if said shaft is rotated at a rate in excess of that normally produced by motor action.

8. The device of claim 6 in which said casing comprises opposite walls obliquely related whereby said uid motors are inversely obliquely related, and control means mounted on a wall between said motors and within the included angle of said motors, said control means having uid connections to said motors.

9. The device of claim 8 in which said control means is provided with means mounting it on said wall and terminals for said fluid connections which are symmetrically disposed respecting said mounting means whereby the connections of said fluid connections to said terminals can be reversed by rotating the control valve through 180 on said mounting means.

10. In a door operating device of the character described, a substantially constant thrust fluid motor, motion transmitting door connections, and a transmission mechanism between said door connections and said motor, said transmission mechanism comprising means for connecting said motor to said door connections with great mechanical advantage in the initial movement of the motor and progressively decreasing mechanical advantage thereafter, said transmission mechanism comprises a 10 shaft having a lever arm, a crank on said shaft, a swing arm having a fixed pivot offset from the shaft, said motor comprising a reciprocating member pivoted to said swing arm and in bearing contact with said crank whereby the path of movement of said member as guided by said swing arm comprises an arc eccentric with respect to the shaft.

11. An automatic door operator for the powered movement of a door and for imposing greater thrust on said door at the beginning of its movement than at the end of its movement, said operator comprising a shaft, motion transmitting connections from the shaft to the door, a crank arm mounted on the shaft, ya power operator movable against said crank arm to turn said shaft, and a link having a iixed pivot olset from the axis of shaft rotation and having a pivoted connection lto said operator whereby the path of operator movement comprises an arc about said link pivot which is eccentric with respect to the axis of shaft rotation whereby to shift the point of contact of the operator along said crank arm and vary the moment arm of said operator with respect to said shaft depending on the position of the door.

12. The device of claim l1 provided with a second power operator mounted at the opposite side of said crank arm from said power operator and having a pivotal connection with a second link having a xed pivot oifset from the axis of shaft rotation and at the side thereof opposite the fixed pivot of the Erst link, said second power operator having a path of movement which comprises an arc eccentric with the axis of shaft rotation whereby said door is powered in both its opening and closing movement and the moment arm of both said power operators is varied with respect to the position of the door.

13. The device of claim 11 wherein said crank arm comprises a wedge surface disposed at an oblique angle to the path of the rst increments of power operator movement whereby to increase the mechanical advantage of the power operator with respect to the shaft in said rst increments of power operator movement.

References Cited in the le of this patent UNITED STATES PATENTS 182,184 Funk Sept. 12, 1876 400,565 Haney Apr. 2, 1889 1,054,417 Hutchison Feb. 25, 1913 1,200,826 Forman Oct. 10, 1916 1,292,430 Cady Jan. 28, 1919 1,397,987 Sheppy Nov. 22, 1921 1,486,278 Brady Mar. 11, 1924 l 1,578,678 Norton Mar. 30, 1926 1,859,364 Haskell May 24, 1932 2,009,081 Conklin et al July 23, 1935 2,011,652 Rowntree Aug. 20, 1935 2,283,577 Roby May 19, 1942 2,385,151 Miller Sept. 18, 1945 2,386,216 Hay Oct. 9, 1945 2,536,489 Burke Jan. 2, 1951 2,550,349 Helz Apr. 24, 1951