US3223048A

US3223048A - Mono-rail track switch

Info

Publication number: US3223048A
Application number: US1543A
Authority: US
Inventors: Henry A Gorjanc
Original assignee: Cleveland Crane and Engineering Co
Current assignee: Cleveland Crane and Engineering Co
Priority date: 1960-01-11
Filing date: 1960-01-11
Publication date: 1965-12-14
Anticipated expiration: 1982-12-14

Description

H. A. GoRJANc v' 3,223,048

Mono

Dec. 14, 1965 -RAIL TRACK SWITCH 4 Sheets-Sheet 1 Filed Jan. 11. 1960 HENRY A GaRJA/vc IN V EN TOR.

Dec. 14, 1965 H. A. GoRJANc MONO-RAIL TRACK SWITCH 4 Sheets-Shea?I 2 Filed Jan. l1. 1960 m6 ,f A w m l Hw R. 9m wm. h NNW/.www1 E ...H Ezbw n 0 i, Il www L mv. u?- MLILWWHM -"WUFHMXUNMN y .Ih 4 O a N* ||l|u v1 ,will t|1 .IIFU Lal. L 1 I- .w1 IR k N Ei V i u f. N... %%& E E w Q mi# E Armer/ys Dec. 14, 1965 H. A. GoRJANc 3,223,043

` MONO-RAIL TRACK SWITCH Filed Jan. 11. 1960 4 Sheets-Sheet 3 IN VEN T OR. /NAY A. GOPJANC MM Bf #35% A 'r TOR/vf V5 3,223,048 Patented Dec. 14, 1965 3,223,048 MONU-RAIL TRACK SWITCH Henry A. Gorjanc, Wicklitfe, Ohio, assigner to The Cleveland Crane 8; Engineering Company, Wckliffe, Ohio, a corporation of hio Filed Jan. 11, 1960, Ser. No. 1,543 3 Claims. (Cl. 104-102) This invention relates to material handling systems of the overhead monorail type, and more particularly to such a system having a motor operated switch therein for selectively connecting a single rail on one side of the switch with any one of a plurality of rails on the other side of the switch for providing a plurality of courses for carriers traveling along the rails to follow.

A principal object of the invention is the provision of an improved material handling system including a monorail switch shiftable between at least two operative positions by a reversible electric motor, the motor being responsive to a switch control circuit which is conditioned upon actuation to energize the motor for shifting of the switch to a preselected position and which circuit will remain so conditioned even though there be a power failure so that upon a return of the power the motor will continue to shift the switch to its preselected position.

Another object of the invention is the provision of a material handling system of the above mentioned character which comprises conductor bars associated with the rails for providing electric current to carriers or the like traveling thereon, and in which the switch control circuit comprises means for controlling both the energization of the switch operating motor and the actuation of bathe or blocking contactors for de-energizing the conductor bars leading into the switch to thereby prevent a carrier from running into an open switch.

Still another object of the invention is the provision in an overhead monorail system of a switch including a switch operating and baffling control circuit which comprises latching type relay means for controlling both the energization of the switch Operating motor and the actuation of the baiiie contactors, and which circuit comprises a limit switch which acts directly to de-energize the motor and the baflie contactors when the switch moves into a selected operative position.

The invention may be further briefly described as residing in certain combinations and arrangements of parts and other advantages thereof will be apparent to those skilled in the art to which it pertains from the following description of a presently preferred embodiment described with reference to the accompanying sheets of drawings forming a part of this specification, and in which:

FIG. 1 is a fragmentary plan view of a material handling system embodying this invention and having a two position motor operated switch therein;

FIG. 2 is an enlarged sectional view of a portion of the switch of FIG. l taken along line 2-2 thereof;

FIG. 3 is an enlarged sectional view of a portion of the switch of FIG. 1 taken along line 3 3 thereof;

FIG. 4 is a top view on an enlarged scale of the locking mechanism of the switch of FIG. l;

FIG. 5 is a sectional view of the locking mechanism of FIG. 4 taken along line 5 5 thereof;

FIG. 6 is an end view of the locking mechanism;

FIG. 7a illustrates one operative position of the limit switch;

FIG. 7b illustrates another operative position of the limit switch; and

FIG. 8 is a schematic diagram of the switch and bale contactor control circuit.

Referring to the illustrated switch 10 embodying this invention, an outer or xed frame assembly 11 supports an inner or movable frame assembly 12 which is adaptable to use in switches of either the shifting tongue or shifting rail type and, for purposes of illustrating one embodiment of the invention, is here described as having two

movable rail sections

15 and 16 which may be shifted to either of two operative positions to determine which of two

rails

17 and 18 on one side of the switch will be connected with a single rail 19 on the other side of the switch to provide a continuous path for a carrier passing through the switch.

In the operative position illustrated in FIG. 1, the rail 19 and the rail 18 are connected or aligned by the movable rail section 16 which is curved, thereby providing a curved path of travel for a carrier. The inner frame 12 is shiftable in either direction by means of a reversible electric motor 22, and when shifted to the right assumes an operative position with the rail section 15, which is straight, connecting the rail 19 and the rail 17 to provide a straight path of travel for a carrier.

lt will be recognized that carriers may pass through the switch 1i) in either direction so that a carrier entering the switch on rail 19 may exit either on rail 17 or rail 18 depending upon the position of the inner frame 12, and a carrier may enter from either of

rails

17, 18 and exit on rail 19. For the purposes of this description the rail 19 will be considered an entering rail.

The reversible electric motor 22 is under the control of a circuit, more fully described hereafter, which includes a cam actuated limit switch 23 which is preferably mounted on the movable frame 12 and is adapted to be actuated by cam means such as

cam elements

24, 25 mounted on the fixed frame 11.

When the movable frame 12 is occupying one of the mentioned operative positions, it is held from moving therefrom by a solenoid operated locking means, indicated generally at 27. The solenoid actuated locking means 27 and the motor 22 are energizable by the above mentioned control circuit to release and shift the frame 12 to an operative position other than the one occupied, and the limit switch 23 will, at the proper point in the movement of the frame 12, de-energize the motor 22 and the solenoid actuated locking means to secure the frame 12 in the selected operative position.

The

rails

17, 18 and 19 and the

movable railsections

15, 16 are of conventional monorail construction and will not, therefore, be described in detail. Suice it to say that each includes a rail member having a web 30 terminating at its lower edge in

horizontal ange portions

31, 32 extending from the opposite sides of the web for supporting the wheels of the overhead monorail carriers (not shown), and having upper lange portions 33.

A plurality of `conductor bars 35 are associated with each of the

rails

17, 18, 19 and with the

rail sections

15, 16, and serve to supply electric power to self-propelled carriers through current collectors carried thereby. In order to prevent a carrier from running into an open switch, means are provided to de-energize portions of the conductor bars 35 associated with an entering rail such as 19 during shifting of the frame 12 from one of its operating positions to the other. The de-energization is referred to as blocking or baffling and is automatically effected by baffle contactors such as a contactor 37 forming part of the control circuit more fully described hereafter.

The outer frame assembly 11 is supported in any conventional manner above the

rails

17, 18 and 19 and comprises spaced horizontal inverted T-shaped members 40 and 41 extending transversely of the rails and having lower inwardly extending ange portions 42 for slidably supporting the inner or movable frame assembly 12. The members 40 and 41 are connected at their ends by left and

right side members

43, 44 having inwardly directed flange portions 45 and downwardly directed portions 46. In addition, the outer frame 11 comprises a transverse angle member 47 extending between and welded to the

side members

43, 44 midway between the members 40, 41. The angle member 47 serves as a latch abutment means and as a support for the limit switch operating cam means 24, 25.

The inner frame assembly 12, including the

rail sections

15, 16 comprises L-shaped or

angle members

50 and 51 parallel and adjacent to the T-shaped members 40, 41 respectively, and each having a horizontal portion 52 overlying one of the adjacent lange portions 42 of the T-shaped members, and each having a depending vertical portion 53 having angle members 55 secured thereto as by welding and itself welded, riveted, or otherwise secured to the upper ange portions 33 of the

rail sections

15, 16 for support thereof. Any suitable antifriction means such as roller bearings 57 may be interposed between the horizontal portions 52 of the

members

50, 51 and the adjacent horizontal flange portions 42 of the T-Shaped members 40, 41 to support the inner frame assembly 12 on the outer frame assembly 11 and to facilitate the shifting of the inner frame assembly. Movement of the inner frame assembly 12 relative .to the outer frame assembly 11 is limited by adjustable stops 58 carried by members 59 welded to the vertical anges of the T-shaped members 40, 41.

The reversible electric motor 22 is preferably a single phase A C. motor. A gear reduction means 61 is conveniently provided on the motor 22 and rotates a sprocket .62 in driving engagement with a flexible transmission means in the form of a chain 63 which leads around a sprocket 64 suitably supported Kon the frame member 43 through which `the chain passes in openings provided therefor.

The ends of the chain 63 are connected to opposite ends of a rod 66 forming part of a resilient or shock absorbing connection to the inner or movable frame assembly 12. A base plate 67 is suitably supported across the rail sections and 16 and serves as a support for the hereafter vdescribed shock absorbing connection and the locking means 27.

As is best illustrated in FIGS. 4, 5, and 6, the base plate 67 is provided with a pair of bifurcated

upright members

69 and 70 extending therefrom. A coil compression spring 72 surrounds the rod 66 and is confined between the

upright members

69 and 70 and between end washers 73. A Cotter pin 74 or the like passes through the rod 66 outside of each end washer 73 and is adapted to pass through the bifurcation in each of the

upright members

69, 70. It will be apparent that the movement of the chain 63 in a sense to shift the inner frame 12 in either direction will cause the rod 66 to shift compressing the spring 72 between a cotter pin held washer 73 and one of the

upright members

69, 70 until the frame begins to move.

The locking means 27, which is supported also by the plate 67, comprises a spring loaded plunger 80 which is adapted to be received in openings 81 and 82 in the angle member 47, and serves to secure the movable frame 12 in either of its operative positions. The plunger 80 is reciprocably carried in a tube 85 and has an extension 86 terminating in a threaded end.

The tube 85 has secured at one end an angle member 88, a depending leg 89 of which confines a compression spring 90 in the tube, and which spring biases or urges the plunger 80 into engagement with the abutment or angle member 47. A cross plate or bar 92 lying adjacent the angle leg 89 has an opening receiving the extension 86 of the plunger 80, and the extension has a retaining and adjusting nut thereon. The spring 90 acts to extend the plunger 80 and normally draws the cross bar 92 toward the leg 89 of the angle member 88.

An operating lever 93 is pivotally secured at 94 to the angle member 88 and has depending side ears 95 in engagement with the cross bar 92. The lever 93 is connected by a link 96 to the armature 97 of an actuating solenoid 98 forming a part of the locking means 27. When the solenoid is energized, upon pressing of a push button or'

control switch

100, 101 of the control circuit (FIG. 8) described hereafter, the armature pulls in, rocking the lever 93 and camming one of the ears 95 against the cross bar 92 as shown in dotted lines in FIG. 4, thereby retracting the plunger against the action of the spring 90 and releasing the frame 12 for shifting movement.

Referring now to the illustration of FIGS. 7a, 7b and FIG. 8, the control circuit and the operation of the switch 10 will be described. FIGS. 7a and 8 show the limit switch 23 in the position it would occupy relative to the

cams

24, 25 with the inner frame 12 in the position illustrated in FIG. l, that is with the curved rail section 16 connecting the

rails

18 and 19.

Assuming the switch is to be shifted to its other operative position, with the straight rail section 15 connecting the

rails

17 and 19, the push button or control switch 100 is depressed or momentarily closed completing a circuit which may be traced from a power line L1 through the closed contacts 104 of the limit switch 23, a conductor 105, switch 100, the latch coil 106 of a latching relay 107, and a conductor 108, to a power line L2.

The latching relay 107 has an unlatch coil 109 and has

contacts

110, 111, 112, and 113 which are held closed when the relay is in its unlatched condition as shown in FIG. 8, and

contacts

114, 115, 116, and 117 which are held open when the relay is in its unlatched condition.

Energization of the latch coil 106 opens the

contacts

110, 111, 112 and 113 and closes

contacts

114, 115, 116 and 117 in which case a circuit can be traced from the conductor 105 through contacts 115, a conductor 120, and the motor 22 to the power line L2 energizing the motor. The contacts 114 connect terminals T2 and T3 of the motor 22 through conductors 121 and 122 thereby determining the direction of rotation of the motor in a sense to shift the inner frame 12 to the right from the position illustrated in FIG. 1. The closing of contacts 116 completes a circuit from the conductor 105 through a conductor 123 and the solenoid 98 to retract the plunger 80 releasing the frame 12 for movement.

Opening of the contacts 113 upon latching of the relay 107 breaks a circuit from conductor 105 through a conductor 125, a jumper 126 and the actuating coil 127 of the baing contactor 37 and opening contacts 128 thereof. The contacts 128 control the supply of power to a portion of the conductor bars 35 associated with the rail 19 entering the switch 10 and it will be recognized that when the contacts 128 are open this portion of the conductor bars 35 will be de-energized preventing any likelihood of a carrier running into the switch 10 while the frame 12 thereof is being shifted.

The cam 25 actuates the limit switch 23 as the movement of the inner frame 12 brings the limit switch into the position illustrated in FIG. 7b closing the contacts 130 thereof and opening the contacts 104. Opening of the contacts 104 severs the supply of current from the power line L1 thereby directly de-energizing the motor 22, the solenoid 98, and energizing the baille contactor 37 from the power line L1 through contacts 130 of limit switch 23, conductor 132, contacts 117, and the coil 127 to the power line L2.

It will be observed that the latching relay and all of its contacts remain in their latched condition although the closing of switch is only momentary. This arrangement provides a measure of protection in the event of a power supply failure to lines L1, L2 during movement of the inner frame 12, because the circuit remains conditioned to complete the shifting of the switch 10 and to keep the conductor bars 35 of the entering rail de-energized upon a return of power until the switch 10 is in the selected operative position.

When it is desired to return the switch 10 to the curved position of FIG. l, the curve push button or switch 101 is depressed or closed momentarily and a circuit can then be trac`ed from the power line L1 through contacts 130 of the limit switch 23, a conductor 132, switch 101, the unlatch coil 109 of the latching relay 107, and a conductor 133, to the power line L2. The relay 107 is thereby unlatched returning the contacts 110-117 thereof to their FIG. 8 positions. The plunger 80 will thereupon be retracted by energization of the solenoid 98, a circuit being completed from the conductor 132 through contacts 112, conductor 123 and the solenoid 98, to the power line L2. The motor 22 will be energized through contacts 110 and the conductor 122, with the terminals T1 and T2 being connected through

conductors

120, 121 and contacts 111 to determine the direction of rotation in a sense to move the frame 12 to the left and into its FIG. 1 position.

The contacts 128 of the baflle contactor 37 will again be opened to de-energize the conductor bars 35 of the rail 19 upon the opening of the contacts 117 and until the frame 12 arrives at its FIG. 1 position closing the limit switch contacts 104 and energizing the coil 127 through the contacts 113 and the jumper 126.

If the straight push button or switch 100 is closed when the switch is in its straight through position, nothing will happen because the limit switch contacts 104 will then be open, and if the curve push button or switch 101 is closed when the switch 10 is already in the curved position, nothing will happen because the limit switch contacts 130 will then be open.

The circuit has been described with but one baille contactor 37 controlling the energization of the conductor bars 35 of the entering rail 19. In some instances it is necessary to have carriers enter the switch along

rails

17 and 18 and in such instances the conductor bars 35 of rail 17 should be de-energized or baflled at all times except when that rail is actually aligned with the rail section 15. Also, the bars 35 of the rail 18 should be de-energized at all times except when it is aligned with the rail section 16. The circuit described is readily adaptable to accomplish such alternate baffling, the modification being effected by removing the jumper conductor 126 and adding another baflle contactor, like contactor 37, to be energized through the contacts 113. The contactor 37 which is then only under the control of contacts 117 can be used to baille the conductor bars 35 of the rail 17 and the added baille contactor can be used to bafile the conductor bars of the rail 18. With the circuit so arranged, the

rails

17 and 18 will be baffled at all times that they are not in alignment with the rail sections and 16 respectively.

Although the control switches 100 and 101 are referred to as push buttons, it will berecognized that in the case of automatic systems these switches may be in the form of switches mounted on the rails such as 17, 18 to be actuated by carriers traveling along those rails toward the switch 10.

Indicator lights are sometimes desired to show the switch position, and it will be recognized that these may readily be wired into the circuit for operation by the latching relay without modification of the circuit.

From the foregoing description and from the accompanying sheets of drawings it will be apparent that there has been provided by this invention a material handling system including an improved motor operated two position switch having a control circuit by which the previously enumerated objects and advantages have been attained, and that the switch and control circuit embodying this invention may be economically manufactured and will operate smoothly and effectively for long periods of time, with a minimum of maintenance.

Although the invention has been described in a detailed manner and with reference to a specific embodiment of switch, it is understood that the invention is not limited thereto but rather the invention includes all changes, adaptations and modifications which are reasonably embraced by the scope of the claims hereof.

Having described my invention, I claim:

1. In an overhead monorail carrier system, a switch hav- 6 ing a first frame, a second frame supporting said first frame for horizontal movement transversely of a ra-il on one side of the switch, a reversible electric motor mounted on one of said frames land connected by transmission means to the other of said frames, circuit means for controlling said rnotor for effecting movement of said first frame between first and second positions for selectively connecting said rail with either of two rails on the other Iside of the switch to provide a continuous path of travel for a carrier, said circuit means including a limit switch mounted on one of said frames and having first and second contacts closed in response to said first frame reaching said first and second positions, respectively, said first contacts being closed when said first frame moves from said `first to said second position and opened when said frame reaches said second position and said second contacts being closed when said frame moves from said second -tosaid first position and opened when said frame re-aches said first position, first and `second control -switches electrically connected rby said first and second contacts, respectively, when closed to a power conductor, rel-ay means havin-g a latch coil electrically connected to said first control switch and an unlatch coil electrically connected to said second control switch, -said relay means having third contacts adapted to be closed upon energization of said la-tch coil and fourth contacts adapted to 'be closed upon energization of said unlatch coil, said fourth contacts being opened upon energization of said latch coil and said third contacts being opened upon energization of said unlatch coil, said reversi'b-le motor lbeing connected through said third and fourth contacts to said first and second contacts, respectively, so that closing of said first control switch with said first frame in said first position latches said relay thereby closing said third contacts and conditioning said circuit t-o energize said -motor in a sense to move said first frame toward said second position until said first contacts of the limit switch are opened disconnecting said motor and said first control switch from said power conductor and connecting said second control switch to said power conductor by closing said second contacts, and closing of said second control switch with said first frame in said second position unla-tches said relay closing said fourth contacts and conditioning said circuit to energize said motor in a sense to move said first frame toward said first lposition until the second contacts of said limit switch are opened disconnecting said m-otor from said power conductor and connecting said first control switch with said power conductor.

2. An overhead monorail system as defined in claim 1 and wherein said switch includes solenoid actuated locking means for releasably holding said first frame in said first and second positions, said locking means being connected through said third and fourth contacts to said first and second contacts, respectively, for releasing of said first frame upon energization of said motor and for locking of said first frame upon de-energization of said motor.

3. In an overhead monorail carrier system, a switch having a first frame; a second frame supporting said first frame for horizontal movement transversely of a rail on one side of the switch; a reversible electric motor mounted on one of said frames and connected by 4transmission means to the other of said frames; circuit means for contro-lling said motor for effecting movement of said first frame between said first and second positions for selectively connecting said rail with either of two rails on the other side of the switch to provide a continuous path of travel for a carrier; conductor :bars associated with said rails and connected to a power supply; said circuit means including a limit switch mounted on one of said frames and having first and second contacts closed in response to said first frame reaching said first and second positions, respectively; said first contacts being closed when said first frame moves from said first to said second position and opened when said frame reaches said second posit-ion and said second contacts being closed when said frame moves from said second to said -tirst position and opened when A said frame reaches said irst position; first and second conjtrol switches electrically connected by said irst and second contacts, respectively, when closed to a power conductor; relay means having a latch c-oil electrically connected to said first control switch and an unlatch coil electrically connected to said second control switch; said relay means having third contacts closed upon energization yof said latch coil and four-th contacts closed u-pon energization of said unlatch coil; said fourth contacts being opened upon energization of said latch coil and said third contacts bein-g opened Iupon energization of said unlatch coil; lbafiie contactor means adapted upon de-energization to interrupt said power supply to said conductor bars; solenoid actuated locking means for releasing and locking said lirst frame in said first and second positions; said baffle contactor means, said locking means and said reversible motor being connected lthrough said third and fourth contacts to said lfirst and second contacts, respectively, so that closing of said first control switch with said first frame in said first position latches said relay thereby closing said third contacts and -conditioning said circuit to energize said motor in a sense to move said iirst frame toward said second position, to de-energize said baffle contact'or means and to actuate said locking means to release said first frame until said first contacts of said limit switch are opened vdisconnecting said motor from said power conductor and connecting said second control switch to said power conductor :by clos-ing of said second contacts, and Closing of said second control switch with said first frame in said second position unlatches said relay closing said fourth contacts and conditioning said circuit to energize -said motor in a sense to move said first frame toward said first position, .to de-energize said baffle contactor means and -to release said locking means until said second contacts `of said limit switch are opened disconnecting said motor, and said locking means from said power conductor and connecting said baffle contactor means and said airst contro-l switch with said power conductor by closing said firs-t contacts.

References Cited by the Examiner UNITED STATES PATENTS 1,097,160 5/1914 IBalzer 246-32 1,286,707 12/1918 Michener 246-242 1,413,820 4/1922 Zabel 246-242 1,453,024 4/1923 Rybn 104-102 1,588,244 6/1926 -Libby 104-102 1,877,876 9/1932 Hoppe 246-242 2,688,931 9/1954 spafford 1,04-88 `2,688,932 9/1954 Heil '104-88 2,688,933 9/1954 spaiford 104-88 2,714,355 8/1955 Benson 104-88 2,902,945 9/1959 sim-on 104-88 2,996,017

8/19611 Gorjanc et al. 104-130 EUGENE G, BOT Z, Primary Examiner.

JAMES S. SHANK, LEO QUACKENBUSH, Examiners.

Claims

1. IN AN OVERHEAD MONORAIL CARRIER SYSTEM, A SWITCH HAVING A FIRST FRAME, A SECOND FRAME SUPPORTING SAID FIRST FRAME FOR HORIZONTAL MOVEMENT TRANSVERSELY OF A RAIL ON ONE SIDE OF THE SWITCH, A REVERSIBLE ELECTRIC MOTOR MOUNTED ON ONE OF SAID FRAMES AND CONNECTED BY TRANSMISSION MEANS TO THE OTHER OF SAID FRAME, CIRCUIT MEANS FOR CONTROLLING SAID MOTOR FOR EFFECTING MOVEMENT OF SAID FIRST FRAME BETWEEN FIRST AND SECOND POSITIONS FOR SELECTIVELY CONNECTING SAID RAIL WITH EITHER OF TWO RAILS ON THE OTHER SIDE OF THE SWITCH TO PROVIDE A CONTINUOUS PATH OF TRAVEL FOR A CARRIER, SAID CIRCUIT MEANS INCLUDING A LIMIT SWITCH MOUNTED ON ONE OF SAID FRAMES AND HAVING FIRST AND SECOND CONTACTS CLOSED IN RESPONSE TO SAID FIRST FRAME REACHING SAID FIRST AND SECOND POSITIONS, RESPECTIVELY, SAID FIRST CONTACTS BEING CLOSED WHEN SAID FIRST FRAME MOVES FROM SAID FIRST TO SAID SECOND POSITION AND OPENED WHEN SAID FRAME REACHES SAID SECOND POSITION AND SAID SECOND CONTACTS BEING CLOSED WHEN SAID FRAME MOVES FROM SAID SECOND TO SAID FIRST POSITION AND OPENED WHEN SAID FRAME REACHES SAID FIRST POSITION, FIRST AND SECOND CONTROL SWITCHES ELECTRICALLY CONNECTED BY SAID FIRST AND SECOND CONTACTS, RESPECTIVELY, WHEN CLOSED TO A POWER CONDUCTOR, RELAY MEANS HAVING A LATCH COIL ELECTRICALLY CONNECTED TO SAID FIRST CONTROL SWITCH AND AN UNLATCH COIL ELECTRICALLY CONNECTED TO SAID SECOND CONTROL SWITCH, SAID RELAY MEANS HAVING THIRD CONTACTS ADAPTED TO BE CLOSED UPON ENERGIZATION OF SAID LATCH COIL AND FOURTH CONTACTS ADAPTED TO BE CLOSED UPON ENERGIZATION OF SAID UNLATCH COIL, SAID FOURTH CONTACTS BEING OPENED UPON ENERGIZATION OF SAID LATCH COIL AND SAID THIRD CONTACTS BEING OPENED UPON ENERGIZATION OF SAID UNLATCH COIL, SAID REVERSIBLE MOTOR BEING CONNECTED THROUGH SAID THIRD AND FOURTH CONTACTS TO SAID FIRST AND SECOND CONTACTS, RESPECTIVELY, SO THAT CLOSING OF SAID FIRST CONTROL SWITCH WITH SAID FIRST FRAME IN SAID FIRST POSITION LATCHES SAID RELAY THEREBY CLOSING SAID THIRD CONTACTS AND CONDITIONING SAID CIRCUIT TO ENERGIZE SAID MOTOR IN A SENSE TO MOVE SAID FIRST FRAME TOWARD SAID SECOND POSITION UNTIL SAID FIRST CONTACTS OF THE LIMIT SWITCH ARE OPENED DISCONNECTING SAID MOTOR AND SAID FIRST CONTROL SWITCH FROM SAID POWER CONDUCTOR AND CONNECTING SAID SECOND CONTROL SWITCH TO SAID POWER CONDUCTOR BY CLOSING SAID SECOND CONTACTS, AND CLOSING OF SAID SECOND CONTROL SWITCH WITH SAID FIRST FRAME IN SAID SECOND POSITION UNLATCHES SAID RELAY CLOSING SAID FOURTH CONTACTS AND CONDITIONING SAID CIRCUIT TO ENERGIZE SAID MOTOR IN A SENSE TO MOVE SAID FIRST FRAME TOWARD SAID FIRST POSITION UNTIL THE SECOND CONTACTS OF SAID LIMIT SWITCH ARE OPENED DISCONNECTING SAID MOTOR FROM SAID POWER CONDUCTOR AND CONNECTING SAID FIRST CONTROL SWITCH WITH SAID POWER CONDUCTOR.