U.S. patent number 3,764,874 [Application Number 05/223,901] was granted by the patent office on 1973-10-09 for garage door opener with instant reverse mechanism.
Invention is credited to David Charles Geoffrey.
United States Patent |
3,764,874 |
Geoffrey |
October 9, 1973 |
GARAGE DOOR OPENER WITH INSTANT REVERSE MECHANISM
Abstract
An electrical operator assembly for garage doors and the like
includes a reversible electric motor, a belt member and means
deflecting the belt member from a straight line path. When the door
operated by the assembly encounters an obstruction, the belt member
overcomes the deflecting pressure and operates reversing switch
means to reverse the direction of operation of the electric motor.
The control circuitry includes a multiposition relay adapted to
reverse the direction of operation of the motor upon change of the
contacts closed therein when a signal is received from the
reversing switch which transmits its signal directly to the relay.
In addition, a disabling switch is directly responsive to operation
of the drive means after a preselected period of travel in one
direction to disable the reversing switch and prevent its
transmission of a signal to the motor when the door approaches the
end of its preselected period of travel in that direction. The
motor remains in closed circuit contact with the relay means during
reversal of direction by the reversing switch.
Inventors: |
Geoffrey; David Charles
(Warren, MI) |
Family
ID: |
22838446 |
Appl.
No.: |
05/223,901 |
Filed: |
February 7, 1972 |
Current U.S.
Class: |
318/266 |
Current CPC
Class: |
E05F
15/41 (20150115); E05Y 2400/445 (20130101); E05Y
2400/57 (20130101); E05Y 2900/106 (20130101); E05F
15/684 (20150115); E05Y 2201/656 (20130101); E05Y
2400/552 (20130101); E05Y 2800/00 (20130101); E05Y
2201/672 (20130101); E05Y 2600/322 (20130101); E05Y
2201/66 (20130101) |
Current International
Class: |
E05F
15/00 (20060101); E05F 15/16 (20060101); H02p
001/42 () |
Field of
Search: |
;318/265,266 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gilheany; Bernard A.
Assistant Examiner: Duncanson, Jr.; W. E.
Claims
Having thus described the invention, I claim:
1. In an electrical operator assembly for doors and the like, the
combination comprising:
a. a support;
b. a reversible electric motor on said support;
c. a belt member mounted for rotation on said support in either
direction of rotation;
d. drive means on said support interconnecting said motor and said
belt member to effect rotation thereof in either direction, said
belt member extending about said drive means to define a
substantially U-shaped portion with spaced legs to opposite sides
of said drive means;
e. means deflecting a leg portion of said belt member from a
straight line path towards the opposite leg and including an
elongated deflecting member pivoted at one end on said support and
having its opposite end portion slidably engaged with said belt
member and spring means biasing said opposite end portion of said
deflecting member towards said belt member, said belt member being
adapted to overcome the biasing force of said biasing means upon
movement over said deflecting member towards the pivoted end
thereof and the encountering of an obstruction by the associated
door operated thereby to return to a substantially straight line
path to pivot the elongated deflecting member away from said
opposite leg of said belt member, said biasing means being closely
adjustable to control the biasing force required to be overcome by
said belt member to effect movement of said belt member to a
straight line path;
f. reversing switch means engageable by said deflecting member upon
pivoting thereof and operable to generate a signal upon overcoming
of the biasing force of said biasing means; and
g. control circuitry for said motor including:
1. limit switch means responsive to operation of and directly
actuated by said drive means to discontinue operation of said motor
after a preselected period of travel of said belt member in either
direction of rotation;
2. disabling switch means directly actuated by said said drive
means after movement thereof for a preselected period of travel in
one direction, said preselected period of travel being less than
the preselected period of travel for the motor discontinuing limit
switch means in that direction; and
3. multiposition relay means controlling current flow to said motor
to reverse the direction of operation thereof upon change of the
contacts closed therein, said reversing switch means sending an
electrical signal directly to said relay to change the contacts
closed therein and thereby change the direction of rotation of said
motor upon the encountering of an obstruction by the associated
door, said motor remaining in closed circuit contact with said
relay means during reversal of direction by operation of said
reversing switch means, said disabling switch means opening the
circuit for said reversing switch means to prevent generation of a
signal thereby to said relay means when said drive means approaches
the end of its preselected period of travel in said one
direction.
2. The electrical operator assembly of claim 1 wherein said relay
means comprises a two-position relay having a member moveable
between said two positions, a solenoid coil, and an armature acted
upon by said solenoid coil to move said moveable member from one
position to the other, said moveable member being latched in
position until moved therefrom by action of said solenoid, and
wherein said motor comprises a reversible motor having two windings
and wherein the contacts of said relay in said positions thereof
are each connected directly to one of said coils whereby the
direction of rotation of said motor may be varied by changing the
position of said relay, and wherein there is included means
connecting said two windings of said motor to supply current
90.degree. out of phase to the winding of said motor not directly
receiving current through the contact of the relay in the operative
position thereof.
3. The electrical operator assembly of claim 2 wherein said limit
switch means in said control circuitry comprises separate limit
switches disposed in the circuits between the separate coils of
said motor and said contacts of said relay in the two positions
thereof, whereby opening of either of the limit switches in the
closed circuit will discontinue flow of current to said motor and
terminate operation of the assembly.
4. The electrical operator assembly of claim 1 wherein said biasing
means comprises a compression spring acting upon the opposite end
portion thereof to bias said opposite end portion toward said belt
member and threaded adjusting means to closely adjust the biasing
force exerted thereby.
5. The electrical operator assembly of claim 1 wherein said
disabling switch means and said reversing switch means are in
series with current flow to said reversing switch being through the
disabling switch in its normally closed position, said disabling
switch means opening to disable said reversing switch means.
6. The electrical operator assembly of claim 1 wherein said drive
means includes a shaft member having a threaded portion and a
threaded member mounted thereon, said support including means to
prevent rotation of said threaded member whereby rotation of said
shaft will produce movement of said threaded member along the
length thereof; and wherein said limit switch means is actuated by
said threaded member during movement thereof to a preselected
distance along the length of said threaded portion, wherein said
limit switch means comprises a pair of limit switches, and wherein
there are provided a pair of threaded members at spaced points
along the length of said threaded portion each acting upon one of
said pair of limit switches at either extreme of the preselected
period of travel.
7. The electrical operator assembly of claim 6 wherein said pair of
limit switches and said disabling switch are mounted adjacent each
other and each has an actuator arm, one of said threaded members
acting upon the actuator arm of said disabling switch means shortly
before acting upon the actuator arm of the limit switch in the same
direction of travel.
Description
BACKGROUND OF THE INVENTION
Electrically operated door units are conventionally employed for
moving garage doors between open and closed positions in response
to a signal from a manual switch or from a radio transmitter.
Generally, such door operators employ reversible electric motors
and it is customary for them to employ some form of adjustable
limit switches to discontinue flow of current to the motor when the
door has reached either preselected extreme in its path of
travel.
Generally such operators include clutches of some type to allow
slippage of the motor when an excessive strain is placed thereon,
particularly if some obstruction is encountered or if an excessive
weight is inadvertently placed upon the door. In some instances,
operation of such clutch means will result in termination of
current flow but the pressure for the door to move in the given
direction continues to the level required to effect clutch
slippage.
In some door operators, reversing mechanisms are provided which
will automatically reverse the direction of door operation in the
event that an obstruction is encountered. In this manner, injury to
persons or goods may be avoided. Frequently these automatic
reversing mechanisms tend to be unduly sensitive and cause spurious
reversal of door operation and even recycling from one position to
another. In other instances, the reversing mechanism does not
readily permit precise control of door operation so that reversal
may occur inadvertently as the door reaches either extreme of
travel. This is particularly a problem when snow, ice, leaves and
the like tend to accumulate at the bottom the door track to a level
sufficient to produce spurious or unwanted operation of the
reversing mechanism.
It is an object of the present invention to provide an electrical
operator assembly for garage doors and the like of novel
construction which is relatively simple and economical to fabricate
and which will effect substantially instantaneous reversal of the
door movement upon the encountering of an obstruction of
predetermined size.
It is also an object to provide such a door assembly in which the
sensitivity of the reversing mechanism may be adjusted readily and
its point of disablement may also be adjusted conveniently
depending upon the desired tolerance to minor obstructions at the
end of movement of the door.
Another object is to provide such door assembly employing a simple
lever action which is readily and economically manufactured and
assembled and which is relatively trouble-free and long-lasting in
operation.
Still another object is to provide such a door assembly in which
the number of electrical components is minimized and those
components are relatively simple and long-lived in construction to
ensure extended periods of trouble-free operation for the
electrical circuitry.
SUMMARY OF THE INVENTION
It has now been found that the foregoing and related objects can be
readily attained in an electrical operator assembly for garage
doors and the like which includes a support, a reversible electric
motor mounted on the support and a belt member mounted for rotation
on the support in either direction of rotation of the motor. Drive
means interconnects the motor and the belt member to effect its
rotation in either direction, thus enabling movement of the door
between open and closed positions. The belt member extends about
the drive means to define a substantially U-shaped portion with
spaced legs to opposite sides of the drive means.
There is provided means for deflecting a leg portion of the belt
member from a straight line path towards the opposite leg and that
deflecting means includes an elongated deflecting member pivoted at
one end on the support and having its opposite end portion slidably
engaged with the belt member and spring means biasing the opposite
end portion of the deflecting member to produce the deflection. The
belt member is adapted to overcome the biasing force of the biasing
means upon movement over the deflecting member towards the pivoted
end thereof and the encountering of an obstruction by the door
during operation and it will pivot away from the opposite leg of
the belt member and return to a substantially straight line path.
The biasing means is closely adjustable to control the biasing
force required to be overcome by the belt member to effect movement
of the belt member to a straight line path. This movement of the
belt member overcoming the biasing force of the biasing means will
act upon reversing switch means operable to generate a signal.
The control circuitry for the motor includes limit switch means
responsive to operation of and directly actuated by the drive means
to discontinue operation of the motor after a preselected period of
travel of the belt member in either direction of rotation.
Disabling switch means is directly actuated by the drive means
after movement thereof for a preselected period of travel of the
belt member in one direction, and this preselected period of travel
is less than the preselected period of travel for the motor
discontinuing limit switch means in that direction. Multiposition
relay means controls current flow to the motor to reverse the
direction of operation thereof upon change of the contacts closed
therein. The signal from the reversing switch means is transmitted
directly to the relay to change its position and the contacts
closed therein and thereby change the direction of rotation of the
motor upon the encountering of an obstruction by the door. The
motor remains in closed circuit contact with the relay means during
reversal of direction effected by operation of the reversing switch
means. The disabling switch means opens the circuit for the
reversing switch means to prevent generation of a signal thereby to
the relay means when the drive means approaches the end of its
preselected period of travel in the one direction, thus avoiding
unwanted operation.
In its most usual form, the relay means comprises a two-position
relay having a member moveable between the two positions, a
solenoid coil, and an armature acted upon by the solenoid coil to
drive the moveable member from one position to the other. The
moveable member is latched in its position until moved therefrom by
action of the solenoid. The motor is a reversible motor having two
windings and the contacts of said relay in the two positions
thereof are each connected directly to one of the windings whereby
the direction of rotation of the motor may be altered by changing
the position of said relay.
Preferably, the circuit includes means connecting the two windings
of the motor to supply current 90.degree. out of phase to the
winding of the motor which is not directly receiving current
through the contact of the relay in the then operative position
thereof. The limit switch means in the control circuitry comprises
separate limit switches disposed in the circuits between the
separate windings of the motor and the contacts of the relay in the
two positions thereof, whereby opening of either of the limit
switches in the operative or closed circuit will discontinue flow
of current to the motor and terminate operation of the
assembly.
The biasing means is adjustable to control the biasing force
required to be overcome by the belt member to effect operation of
the reversing switch. This is conveniently effected by use of
deflecting means comprising an elongated member pivoted at one end
on the support and biasing means comprising a compression spring
acting upon the opposite end of the elongated member to bias the
opposite end toward the belt member. The elongated member acts upon
the reversing switch means when it overcomes the biasing force.
The disabling switch means and the reversing switch means are in
series with current flow to the reversing switch being through the
disabling switch in its normally closed position. In this manner,
disabling switch means is opened to disable the reversing switch
means.
BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS
FIG. 1 is a perspective view of a door operator assembly embodying
the present invention;
FIG. 2 is a bottom perspective view of the motor end of the
assembly of FIG. 1 with the housing removed and with the boom and
chain assembly fragmentarily illustrated;
FIG. 3 is a fragmentary plan view to an enlarged scale of the boom,
endless chain and reversing mechanism components of the
assembly;
FIG. 4 is a fragmentary perspective view of the pressure bar and
reversing switch mechanism to a greatly enlarged scale and with the
adjusting knob removed for clarity of illustration;
FIG. 5 is a fragmentary end elevational view of the pulley end of
the assembly with the housing removed and with portions of the
components broken away for clarity of illustration and with one nut
shown in phantom line at the opposite extreme of the path of
travel;
FIG. 6 is a fragmentary sectional view along the line 6 -- 6 of
FIG. 5; and
FIG. 7 is a partially schematic wiring diagram for the electrical
circuitry of the door operating assembly.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
Turning now in detail to FIG. 1 of the attached drawings, a garage
door operator assembly embodying the present invention includes an
elongated channel-shaped boom member generally designated by the
numeral 10 and a housing generally designated by the numeral 12
having a body portion 14 and an end closure portion 16 releasably
engaged therewith by the latch 18. The connecting arm generally
designated by the numeral 20 extends downwardly from the channel of
the boom 10 and is engaged in its upper end in the carrier 22; its
other end has a coupling arm 24 for engagement in a pivot bracket
(not shown) on the garage door (not shown). In accordance with
conventional practice, this assembly is suspended in the garage or
other area by straps (not shown) or the like.
As is seen in FIGS. 2 and 3, the carrier 22 is mounted on sprocket
chain portion 26 of an endless drive member generally designated by
the numeral 28 and which also has a cable portion 30. The endless
drive member 28 is disposed within the channel of the boom member
10 and at one end (the left as viewed in FIGS. 1 - 3) has its chain
portion 26 in driving engagement with the sprocket gear 32 and its
other end extends about a pulley or idler roller (not shown) in the
channel of the boom member 10 at a point remote from the housing
12. As seen in FIG. 2, the housing 12 encloses a mounting plate 34
upon the upper surface of which the one end of the boom member 10
is secured and upon the lower surface of which are mounted a
reversible electric motor 36 with a drive shaft 38, an electrical
component module 40 and the shaft generally designated by the
numeral 42.
At its lower end the rotatably mounted shaft 42 has mounted thereon
the clutch pulley 44 and at its upper end the sprocket gear 32 is
mounted so that driving engagement is provided thereby. The shaft
38 of the motor 36 has a motor pulley 46 thereon and the belt 48
provides driving engagement between it and the clutch pulley 44 in
either direction of rotation of the motor and thus movement of the
endless drive member 28 and carrier 22 in either direction along
the length of the boom member 10.
Above the housing plate 34, a notch 50 extends through the portion
of the sidewall 52 and into the adjacent portion of the top wall 54
of the boom member 10. The sidewall 52 is also provided with a
vertically extending slot 56 at a point spaced therefrom towards
the sprocket gear 32 and an aperture 58 at a point spaced therefrom
away from the sprocket gear 32. Pivotably seated in the slot 58 is
the tongue 60 at one end of the elongated pressure bar generally
designated by the numeral 62. At its other end the pressure bar 62
has a longitudinally extending notch 64 in which is slidably seated
the shank 66 of the fastener 68 which extends through and is seated
in the aperture 58. Mounted on the shank of the fastener 68
outwardly of the bar 62 are a compression spring 70 and an
adjustment knob 72.
The pressure bar 62 has an arm 74 which extends inwardly through
the notch 50 in the sidewall 52 and bears against the chain portion
26 so as to deflect that portion inwardly from a straight line path
under the action of the compression spring 70, and the biasing
pressure may be adjusted by rotation of the adjusting knob 72 on
the threaded shank 66 of the fastener 68.
The outer surface of the free end of the pivoted pressure bar 62
will bear upon the elongated upstanding activator arm 76 or the
reversing limit switch generally designated by the numeral 78 when
it is pivoted outwardly from the sidewall 52 in the direction
indicated by the arrow A in FIG. 4 by pressure exerted by the chain
portion 26 and sufficient to overcome the biasing pressure of the
compression spring 70. As best seen in FIGS. 1 and 2, the limit
switch 78 is mounted on the bottom of the mounting plate 34 and has
its actuator arm 76 extending upwardly through a cutout 80 therein.
The actuator arm 76 will press against the switch bottom 82 when
the pressure bar 62 pivots sufficiently, thereby sending an impulse
to the control mechanism.
Turning now to FIGS. 5 and 6, the mechanism for limiting operation
or travel of the endless drive member or belt 28 is illustrated.
The shaft 42 is rotatably mounted in the bushings 84, 86 in the
bracket 88 and has a threaded intermediate portion 90 upon which
are threadably mounted a pair of nuts 92, 94 having a multiplicity
of radially extending arms 96, 98. The bracket 88 also supports an
elongated spring stop member 100 which is releasably engaged in the
spacing between arms 96, 98 so as to prevent rotation thereof.
When the motor 36 operates, the rotation of the shaft 42 will cause
the trapped nuts 92, 94 to move upwardly and downwardly along the
threaded portion 90 since they are prevented from rotating by the
stop member 100. As they move one direction or another, one of the
nuts 92, 94 will deflect one of the actuator arms 102, 104 of the
limit switches 106, 108 to open the circuit, thus stopping
operation of the motor 36 and movement of the endless drive member
28 and carrier 22. When the nut 92 moves to the right as seen in
FIG. 5 during movement of the door, it will strike the actuator arm
102 to open switch 106 although it also moves the actuator arm 104
of the switch 108. Shortly before it acts upon the actuator arm 102
sufficiently to open the switch 106, it will first act upon the
actuator arm 110 of the disabling limit switch 112 to open that
switch and disable the reversing circuit components.
Similarly, when the motor is reversed, the nut 94 will travel along
the threaded portion 90 until it strikes the actuator arm 104 at
the end of opening movement of the door, thus opening switch 108.
In this direction of movement, the disabling switch 112 is closed
throughout the cycle. It will be appreciated that the extent of
travel of the nuts 92, 94 may be adjusted by springing the stop
member 100 outwardly from the arms 96, 98 sufficiently to permit
rotation of the nuts 92, 94 along the length of the threaded
portion 90.
In normal operation of the door operator assembly, current flowing
to the motor 36 will cause the carrier 22 to move along the boom 10
in one direction or the other with the chain portion 26 distorted
from a straight line path by the biasing pressure of the
compression spring 70 acting upon the pivoted pressure bar 62. If
an obstruction is encountered, this will produce tensioning of the
endless drive member 28 and the chain portion 26 will strive to
overcome the biasing pressure of the spring 70 and straighten
itself out into a straight line path. If this tensioning is
sufficient to reach or exceed the value established by adjustment
of the biasing pressure through the adjustment knob 72, the
actuator arm 76 will be moved against the switch button 82 to close
the reversing switch 78 and send an impulse to the control
circuitry for the motor 36 which will reverse its direction of
operation, all as will be described hereinafter in detail.
Turning now to FIG. 7, the electrical circuitry of the present
embodiment may be more readily understood. As shown the motor 36
has two windings 150, 152 so that altering the phase of current
flow to the windings 150, 152 will alter the direction of rotation
of the shaft 38 and thus the direction of movement of the carrier
22 along the boom member 10. To prevent injury to the motor 36, a
thermal overload circuit protection device 154 is incorporated.
The path of current to the windings 150, 152 of the motor 36 is
controlled by the multipole relay 139 which has contacts 144 and
146 respectively in line with the windings 150 and 152 through the
normally closed limit switches 106 and 108. Current flowing through
either line to one of the windings 150, 152 will be directed by the
capacitor 148 to the other of the windings 90.degree. out of phase.
The relay clapper 142 is operated by the armature 141 in response
to current flowing in the coil 140 which will move the clapper 142
to the opposite position where it will latch until another impulse
occurs in the coil 140. Whenever the door operator assembly
receives a start signal from the manual switch or radio receiver
(both not shown) generally designated by the switch 79, current is
already flowing through the circuitry 120, 122 and through the
windings 126, 128 of the transformer generally designated by the
numeral 124 to the terminal 134 of the terminal box. The closing of
switch 79 energizes the relay coil 140 to operate the clapper 142
and close the circuit to the motor 136 through one of the limit
switches 106, 108. Current also is provided directly to the light
delay circuit schematically designated by the numeral 130 which
controls the lamp 132.
As seen, the reversing switch 78 is in series with the disabling
switch 112, through the terminal contacts 136, 138. The disabling
switch 112 is normally closed so as to allow current to flow
through the line to the normally open reversing switch 78, whereby
closing of the reversing switch 78 by tensioning of the chain
portion 26 sufficient to overcome the biasing pressure of the
compression spring 70 will cause an electrical impulse to travel to
the relay coil 140 and move the clapper 142 to the other of the
contacts 144, 146. This in turn will reverse the direction of
current flow to windings 150, 152 of the motor 36, thus reversing
the direction of motor operation and door movement.
However, during closing movement of the door, the nut 92 will
strike the actuator arm 110 of the disabling switch 112 shortly
before the limit of its downward travel and open the switch 112,
thus terminating current flow to the reversing switch 78 through
the terminal 138. As a result, snow or other small obstructions
under the door which might produce tensioning of the chain portion
26 will not cause reversing of the current flow and opening
movement of the door. The distance of travel during which the
reversing switch 78 is disabled may be readily varied by changing
the actuator arm 110 or by substituting a different switch.
As the door reaches its limit of travel in either direction, the
nut 92 will move the actuator arm 102, 104 of the appropriate limit
switch 106, 108 to open that switch. This will open the circuit and
terminate current flow to the windings 150, 152 of the motor 36.
However current continues to flow to the light delay circuit 130
and thence to the lamp 132 for the desired period of time. When the
next start impulse is received from the manual button, radio
receiver or the like 79, the impulse transmitted to the coil 140 of
the relay 139 through the start circuitry (not shown) will move the
clapper 142 to the other of the contacts 144, 146, the limit switch
106, 108 of which is closed to permit current to flow directly to
the respective winding 150, 152 of the motor 36 and cause its
operation in the reverse direction. As the motor operates, the
limit switch 106, 108 opened by the action of the nut 92, 94 will
return to its normally closed position. When the movement is in the
opening direction, the nut 92 will move away from the actuator arm
110 of the disabling switch 112 to allow it to return to its
normally closed position and return the reversing switch 79 to
operating condition.
In the illustrated embodiment the chain tensioning will normally
function only in closing movement of the door so that the pressure
bar will function to operate the reversing switch only during such
closing movement. It will be appreciated that the chain biasing
mechanism amy be duplicated or modified so as to permit operation
of the reversing switch during opening movement of the door as well
as during closing movement.
It will be appreciated that the limit switches employed in the
present invention may vary from those specifically illustrated and
that the circuitry may also vary from that specifically employed
herein with proper modification of the several components. However,
the illustrated circuitry is extremely advantageous in requiring a
limited number of components which are relatively inexpensive and
readily serviced.
In adjusting the reversing mechanism, the door operated by the
assembly is raised to its open position by a suitable signal to the
assembly. An obstruction such as a chair or basket is placed within
the door opening and a signal is transmitted to cause the mechanism
to drive the door in the closing direction. If the door reverses
upon contact with the obstruction, the biasing pressure provided by
the compression spring is correctly adjusted. If, however, the door
automatically reverses or cycles back and forth prior to contacting
the obstruction, the adjusting knob should be turned to move it
inwardly on the fastener and thereby increase the compression of
the spring; such adjustments should be made in small increments to
avoid ovecorrection. Conversely, if the door remains in contact
with the obstruction, the adjusting knob should be turned to
decrease the compression of the spring, again in small increments
to avoid overcorrection.
Normally, the disabling switch actuator arm should be set so as to
operate that switch about 1 - 4, or even up to 6, inches before the
door reaches the end of its closing movement. In this manner, small
amounts of snow, leaves or the like will not cause reversing of the
door mechanism even though the chain may be tensioned in the course
of completing its closing movement.
It will be appreciated that the length of travel of the nuts upon
the lead screw may be readily adjusted for varying heights of
doors. Most conveniently, the limit switch for discontinuing
current flow to the motor in either extreme of travel and the
disabling limit switch are mounted upon a common support plate.
Thus, it can be seen that the operating assembly of the present
invention provides a substantially instantaneously acting reverse
mechanism in the event that an obstruction is encountered. The
sensitivity of the reversing mechanism may be adjusted readily and
its point of disablement may also be adjusted readily depending
upon the desired tolerance to minor obstructions at the end of
closing movement of the door. The lever action for operating the
reversing mechanism is relatively simple and economical to
manufacture and assemble, and is relatively trouble free and long
lasting in operation. The number of electrical components is
minimized and these components are relatively simple long lived
switches and relays to assure extended periods of trouble free
operation.
* * * * *