US2680524A - Transfer apparatus - Google Patents

Description

June a, 1954 w. J. sham-Ea ETAL 2,680,524

TRANSFER APPARATUS I Filed Sept. 6, 1950 v 2 Sheets-sheaf 1 A June 1954 w. J. SNYDER ETAL 2,680,524

' TRANSFER APPARATUS Filed Sept. 6, 195(1' 2 Sheets-Sheet 2 Patented June 8, 1954 UNITED STATES PATENT OFFICE TRANSFER APPARATUS W'esley J. Snyder, Robert G. Griffin, and Ernest E. Dominick, Wisconsin Rapids; Wis., assigno'rs 't0 Pi'ewa'y Inc., Wisconsin Rapids, Wis., a corporation of Wisconsin Application September 6, 1950, Serial No. 183,394

4 Glaims.

This invention relates toa' transfer apparatussuch'as may be used with advantagefor removing a load of suspended articles from "a wheeled storage rack, when positioned at a first station, to a treating rack at a second station, the treating rack then being. moved into a furnace or chamber where the articles "are subjected to the desired treatment; and thereafter, when the treating rack has been removedfrom the furnace or chamber; removing the lead back' again tothe first station where it is deposited once more on a storage rackon'which it is moved'to a selected workstation; An apparatus'of this kind; having the improvements hereinafter describeddn' detail, will expedite the transfer operations considerably, will localize thetransfer of articles to and'from the treating'rack'at a'point in the room where difficult atmospheric conditions may be satisfactorily controlled, andwill assure transport of each load safely and d'ep'enda'bly when moved back and forth between the two stations involved.

The 'exempli'ficati'on of our'inventionherein to be described is one that has been designedfor the handling of metallic'article's, objects orpla't'es which are to be 'given'a' porcelain 'fiii'ish'. This usually involves an initial spraying treatment crane having tandem trucks whichtravel on an overheadrail, an elongated lifting hea'd mounted on the underside of the-cranewlth a duplex hoist mechanism for imparting equalized vertical movements thereto, and means forming part of the head for engaging with a plurality of cross bars arranged crosswise upon a storage rack for suspending therein the articles which are to be treated. A transfer of the loaded cross bars from the storage rack on to the lifting headand later a transfer back from the lifting head of the loaded cross bar's tothesame (or another) storage rack takes place at a first transfer station. fhecrane-propels theliftin'g head, when loaded, from this transfer station to a second transfer station, and back again; "at a later stage, to the first "station. The second transfer "station is proximate to "the treating furnace where the loaded cross bars are transferred from the lifting head on to a burning rack which is then advanced into the furnace where the treating operation proceeds; when done, and the burning rack is removed from the furnace, the loaded cross bars containing the treated articles are again transferred to the lifting head which is thenpropelled by the crane back' to the first station for discharge of theload. The construction and'operation of the lifting head'isan important featureof our inventio'ninasm'uch as it is responsible for the safe and expeditious transfer of the loaded cross bars at each station.

A suggestive embodiment'of this invention is:

illustrated in'the accompanying drawings Wherell'l 'Figure l is a view in plan of a typical layout for the present'transfer apparatus;

Fig. 2 is an end elevation of the transfer apparatus in operative position above a storage rack, a burning rack upon the carriage in front of ajfurnace being also illustrated in this view;

Figs. 3 and 4 are side elevations of storage and burning racks, respectively, forming part of the equipment comprised in the present transfer apparatus;

Fig. 5' is a side el'evational view of the crane and its load-lifting head;

Fig. 6 is an end elevation thereof in which the head is 'shown'as supporting a load when free of one of the storage racks;

Fig; 7 'is a'viewin perspective of a load-lifting head of modified construction;

Fig. 8'is a detail in section, taken on line 8-8 of Fig. '7; and

Fig. 9 is a diagram of wiring connections and associated electricalunits for control of operation of the c'rane'and'the lifting head of Fig. 7.

Referring first to Figs. 1 and 2, the equipment advantageously comprised in the present transfer apparatus is a monorail M supported from a building roof (or floor) structure R, a crane C mounted on the 'rnonorail for self-propulsion lengthwise thereof, a load-lifting'head I-I mounted on the crane for vertical movement therebelow, a furnace F (or other treating unit) positioned oppositely of one end of the monorail, a pair'of wheeled'loa'ding forks each mounted upon a wheeled carriage W for movement separately into'and out of the furnace, the carriage being shuttled transversely of the furnace front'to positioneither loading fork operatively with respect thereto, a plurality of wheeled load-carrying racks S '(hereinafter termed storage racks) whereon the load is stored both before and after 6 operation of the present transfer apparatus, and at least two burning racks B, one for each burning fork, and each in turn receiving from the transfer apparatus a load which is then advanced into the furnace (or other treating unit) for the desired time, then removed therefrom, and then (perhaps after a few minutes required for cooling) lifted by the transfer apparatus and transported thereon to a transfer station where delivery of the load onto a storage rack takes place. The improvements which are special to this invention are concerned largely with the load-lifting head forming part of the crane and with the electrical controls for the operating means for both the crane and its load-carrying head.

The monorail M is supported, as by hangers 29 from a beam 2! whereon a roof (or floor) 22 is carried (see Fig. 2), it being noted that but very little head space is required for its accommodation and for that of the crane C which is mounted on the monorail to be self-propelled thereon. The monorail proceeds straight, or through one or more curved portions, according to the layout desired, to a transfer station directly in front of the furnace F from an initial transfer station where the lifting head is operated to take on or discharge a load. In front of the furnace is the wheeled carriage W movable transversely thereof on rails 23, and carrying two side-by-side burning forks 25 each comprising a wheeled load-sup porting frame that is powered pneumatically or otherwise for movement into and out of the furnace. In this operation, the carriage C is propelled to the position requisite for locating the loaded burning fork directly in front of the furnace whose door is then quickly opened to permit advance of the burning fork thereinto, then quickly closed for the period of treatment, and then opened to permit retraction of the loaded burning fork on to the carriage which is then (or later) shuttled to remove the burning fork with treated load thereon to an offset position with respect to the furnace and concurrently advance the other burning fork centerwise with respect thereto. The furnace door is held open only as long as necessary to receive or release each loaded burning fork, thereby the conserve heat and prevent a rise in temperature in the immediate vicinity to an uncomfortable point.

The load which each burning fork advances into and out of the furnace is carried by one of the burning racks B. When removed from the furnace to the offset position of the empty rack in Fig. 1, the load will start cooling. After a short interval, another load is brought by the crane to the other burning rack, then empty and standing directly in front of the furnace. The load is then transferred to the empty rack, the furnace door is opened and the burning fork operated to advance the loaded burning rack into the furnace, and the door is then closed so that treatment of the load may take place. At this stage the carriage is again shuttled to the position which brings the burning rack, with treated load now relatively cool, directly under the monorail so that the crane may be operated to lift the load and carry it away to a distant transfer station for discharge on to one of the wheeled storage racks S. In this manner the successive loads may be handled with dispatch and safety by the present transfer apparatus. Certain parts of the equipment thus far mentioned, via, the.

furnace, carriage and burning forks, are not disclosed in detail since they are well known and so are not per se comprisedin our invention.

Referring now to Figs. 5 and 6, the crane C which is elongated parallelly with the monorail comprises a pair of electrically-interconnected motor units in the form of trucks each having wheels 28 resting upon the bottom flange 2? of the monorail to be supported thereby while traveling thereupon. To each set of wheels 26 power is transmitted from a motor 30 in electrical connection, by a conductor 3! and shoe 32, with a channeled rail 33 wherein the shoe is slidably supported. Each rail which is insulated from the other is in connection with a source of electrical energy so as to complete through the two motors a power circuit by which to propel the crane. The motors together with any electrical equipment necessary therefor are carried upon an elongated platform 35 constituting a framework for the crane-a construction which, so far as described up to this point, has been known in the past.

Carried by the crane platform on its underside is a hoist mechanism for the present load-carrying head H, together with the guides and controls therefor. This mechanism comprises a reversible motor 31, and a reduction gear 36 through which power is transmitted therefrom to a shaft 30 which is extended lengthwise of the crane and journaled for rotation in bearings 4|, one near each end of the crane platform 35. Carried fast on this shaft, at points near its opposite ends, is a pair of winches A3 to each of which is anchored, for winding thereupon, a lifting cable M which is trained around a sheave amxed to the top side of the head H which is elongated in the same direction as the crane. Each cable after being trained around its associated sheave is extended upwardly for anchorage to the crane platform as at 16. These sheaves are positioned in substantially the longitudinal center line of the head, one toward each end thereof. The head, as shown, consists of an interbraced framework in the general form of a rectangular platform suspending along each of its opposite sides a plurality of hangers 48 which together support longitudinally extending angle iron as whose lower flange is extended inwardly. These two angle irons will be referred to hereinafter sometimes as grab bars. We provide also stabilizing means to prevent lateral swaying of the head H during vertical movements in response to conjoint operation of the duplex hoisting mechanism, and this may conveniently take the form of a pair of telescoping guides extended between the crane platform 35 and the head H therebelow. As shown, each guide comprises a plunger 5i reciprocable within a cylinder 52 and constrained thereby to move vertically in a straight line, the lunger and cylinder at their remote ends being flanged at 53, for rigid connection, as by bolts 53, one to the platform 35 and the other to the lifting head.

From the underside of the crane platform 35 are suspended such electrical units as may be necessary or desirable in connection with the reversible motor 31 which, when energized, operates the two winches 43 in unison. In one direction of rotation, the motor operates to lift the head H and, when reversed, permits a controlled gravity descent thereof. The lifting head between the grab bars is open for a purpose that will shortly appear.

Each storage rack S (see Figs. 1 and 2) comprises a rectangular platform 5? carried upon a plurality of swiveled casters 58 of ample size and strength to support the. intended load. Rising from the platform, adjacent each side thereof,

is. a plurality of :angle bars 60 (three being the number shown) interconnected at thetop by a longitudinal supporting bar 6|. .At opposite ends of the platform short braces 62 extend obliquely upwardly to connect with the proximate vertical bar 65. There is thus provided along each side of the platform a rack framework mounting a longitudinal supporting bar, with a clear space maintained between the two frameworks for the length of the rack.

The burning racks B also comprise in each case aipair of spaced longitudinal supporting bars 65 each interconnecting at theirtops a plurality of vertical bars 66 which rise from base fittings 8? each rigidly secured near one end of a transverse beam 68 of channeled cross section. A stringer E9 is also shown as interconnecting each set of vertical bars for bracing purposes, and other like stringers it may be employed to interconnect the beams 65. The two sets of vertical bars are interconnected by the transverse beams so that the entire rack constitutes a unitary structure that is open and clear from end to end. The overall dimensions of the burning racks correspond rather closely with those of each storage rack.

For all the racks used with the transfer a paratus of our invention there is provided a large number of load-suspending cross bars '52, all alike so as to be freely interchangeable. cross bars, which may be of angle, channel or other cross section, are cut to the same length which is slightly less than the distance between the spaced grab bars of the lifting head H. Desirably the cross bars are .nocthed or apertured at uniformly spaced distances apart, each to receive, and fix the longitudinal position of, a hook E3 of heavy wire or the like. Upon these hooks are hung the articles or objects to be treated, the spacing being ample to prevent fouling of one with another while permitting therebetween a free circulation of air or other treating medium. The cross bars, when loaded, are placed crosswise of a storage rack to rest freely upon the hori zontal supporting bars 6i thereof and be sustained thereby at points near opposite ends of the cross bars. It is important that opposite ends of the cross bars be aligned, and means for this purpose are accordingly provided. This may take the form of an upwardly ofiset end portion at each end of the bar to provide an elongated drop center portion from which the load is suspended. When placing the cross bars (loaded or unloaded) on the storage rack, these offset portions '85 will assure alignment of the opposite ends of all bars on the rack.

In operation, a loaded rack is wheeled to the transfer station where a guide rail 11 is anchored to the floor. The caster wheels on one side of the rack are run into a channel of this rail which is parallel with the monorail thereabove and slightly offset (vertically) therefrom. While the loaded storage rack is so positioned, the crane is advanced along the monorail with its lifting head adjusted vertically to clear the cross bars by the distance which is requisite for permitting the grab bar flanges to advance under the bar ends free of contact therewith. When the lifting platform is over all of the cross bars, power is supplied to the hoisting motor 3'1 to raise the platform a sufficient distance for the grab bars to engage the end portions of all the cross bars and lift them clear of the storage rack. When done, the rack is manually wheeled away from beneath the lifting head, and without liability of These 6 touching any of the articles comprised inthe suspended load since the guide rail 1.1 will constrain the rack to move in a direction which parallels the monorail thereabove until after it has advanced clear of the load-lifting head H thereabove.

The loaded head H is next propelled by the crane C to the other transfer station in front of the furnace F. Here one of the burning racks B. While positioned on a fork, is ready to receive the entire load when transferred from the lifting head. This operation involves a lowering of the lifting head so that the end portions of the cross bars will be rested on the top supporting bars 65 of the burning rack; when done, the cross bars will be free of contact with the grab bars to permit areverse travel of the crane and lifting head supported thereby. The entire load will have been transferred to the burning rack, and the crane is free to move away a safe distance from the furnace whose door is then operated to open position; the fork then advances the loaded burning rack into the furnace, and the door isclosed so that treatment of the articles or objects comprised in the load may take place for a desired period of time. Retraction from the furnace of the burning rack, transfer of its load to the crane and travel thereof back to the loading station, and discharge of the load on to one of the storage racks, involves merely a reversalor repetition of the operations already described, and so need not be detailed further.

The lifting head H is characterized by its capacity for vertical movements while maintaining its horizontality, and by the stabilizing means associated therewith to restrain lateral swaying thereof; it is also characterized by the fixed grab bars, one facing toward the other whereby the crane is required to advance the lifting head H endwise and in a horizontal direction when approaching the load to be transferred, or when separating thereon. The head may be otherwise constructed, however, so that its approach or separation may require only a vertical movement, the crane remaining at rest during this stage of the operation. A lifting head embodying this latter type of construction is illustrated in Figs. 7 and 8, it being understood that the crane unit and hoisting mechanism therefor may be the same as that already described in detail. The stabilizing and hoisting elements shown in Figs. '7 and 8 which are the same as those already described bear corresponding reference characters modified only by the addition of a prime The lifting head H of Figs. 7 and 8 is an elongated interbraced framework of generally re"- tangular form having along its opposite sides longitudinally extending angle irons 86 each provided with a lower flange 8| that is turned inwardly toward the other. Reinforcing bars 83 are extended vertically of each angle iron 30 at spaced points oppositely of bearing blocks 84 which are affixed to the inner faces of the angle irons adjacent their tops. In addition, other bearing blocks 85 may be affixed to the framework of the liftin head H at points in alignment with the blocks 34. Registering openings are provided in all of these blocks for reception of a pivot rod 81 whereby to provide a swinging support for each angle iron 88. These irons which serve as grab bars are thereby suspended so as to swing outwardly from a vertical position to an angular position as indicated by the dotted' lines in Figs. '7 and 8.

The framework of the lifting head H may be I covered over with a top 83 of sheet metal or the like which, at medial points lengthwise of the head on opposite sides thereof, is notched to accommodate a pair of angle irons 90 which are aflixed to the outer faces of the grab bars to extend thereabove. Each pair of angle bars 90 is interconnected near its top by a pin 9| to provide a pivotal mounting for a block 92 which is positioned substantially above the axis of the rod 87. The upwardly protruding portions of the two bars 90 constitute, in effect, radial arms for a special purpose shortly to be made plain. The two blocks 92 are provided with registering; holes having right and left threads therein for accommodation of the end portions of a cross shaft 95 which is journaled to rotate within bearings 95. The end portions 97 of this rod are provided with screw threads, one right and the other lef so as to engage with the threaded openings in the blocks 92.

A mounting bracket 98 upstands from the head H to support a motor 99 having a vertical shaft at whose lower end is a worm screw Hit in mesh with a worm wheel liil that is mounted fast on the cross shaft 95. This motor, which is reversible, operates through the cross shaft 95 and radial arms 90 to swing the two grab bars concurrently in opposite directions so that outward or inward movements thereof will take place in unison.

A lifting head having the grab bar mechanism just described is suspended from a traveling crane with duplex hoisting and stabilizing mechanism, the same as already described. When brought to position over a rack whereon a plurality of loaded cross bars are freely mounted, the grab bars are swung outwardly, the head is then lowered the requisite distance for the grab bars to lie oppositely of the ends of the cross bars, the grab bars are then swung inwardly toward the ends of the cross bars so as to position their flanges 8i therebelow, and the lifting head is then raised to lift in one operation the entire set of cross bars together with the loads carried thereon. The operation of discharging tions may be manually performed by the simple electrical system shown in Fig. 9, this same arrangement in large part being also applicable to the lifting head of Figs. and 6. A part of the electrical system is shown in Fig. '7.

A stationary panel m5 mounted on the lifting head carries a pair of spaced microswitches I66 and it? having opposed operating buttons IE6 and 91, respectively, each switch being adjustable toward and from the other to vary the distance therebetween. There is mounted on the block 92 an upstanding arm ii i which traverses a line extending between the two switch buttons Hi5 and Nil. When advanced either way, according to the direction in which the shaft 95 is rotated, the arm ill will alternately engage these buttons for operation of the associated switches.

A suggestive electrical system in which the crane motor 3%, hoist motor 3?, and grab bar operating motor 99 are interconnected with the switches I96 and it! is illustrated in Fig. 9. The crane motor is shown as grounded at H5, and provided with leads HS and H! connected with opposite poles of the two circuits which determine its direction of rotation. The lead i [8 connects with one side of a pair of two-point make switches having spaced cross bars H8 and H9 carried on a plunger I20, the two switches in this gang being series-connected with one side of an associated two-point make switch formed by cross bars I22 and I23 carried on a second plunger I24. Current from a source of electrical energy is conducted through a main lead I25 to the opposite sides of all four of the switches just noted, the arrangement being such that no current can flow to the crane motor 38 when the switches H8 and 122 are in the open positions shown. However, when so opened, the remaining switches Hi) and 623 are closed to carry current therefrom through a lead [2? to a pair of series-connected make switches I28 and I29 in connection through leads i3! and 32 with one side each of the switches H36 and Hi. Whenever the switches !28 and 129 are closed, a circuit is established to the two switches I06 and iii? thereby to cause operation of the grab bar motor 99 whenever either of these switches I05 and i0? is closed, provided, however, that the two control switches H3 and ['23 be also operated to closed posiiton. Since these control switches HQ and 123 are open and closed only when the crane motor 351 is in or out of operation, respectively, it follows that no operation of the grab bar motor can take place except when the crane is at rest.

The lead i2? also extends to two other seriesconnected make switches 134 and 535 from which leads 13S and it! connect with opposite poles of the two circuits in the reversible hoist motor 31. Either switch may be closed to carry current to one circuit of the motor, provided that the control switches H9 and I23 be also closed to assure a concurrent non-operation of the crane motor 3t. The circuit to the crane motor is thus the master in that it may be opened or closed at will, irrespective of the positions of the switches in the circuits leading to the motors 3'6 and 99. The arrangement of circuits and switches is suggessive of one that is simple and effective to permit operation of either the grab bar motor 99 or the hoist motor 3?, one or both at a time, but only when the crane is remaining at rest. The switches may be mounted conveniently on a near-by stand or wall, or be assembled into a single housing that-is designed to be carried in the hands of a walking attendant, with the necessary electrical connec tions extending from the switch housing through a protective cable his to the several motors that are carried by the crane.

A distinguishing feature of our transfer apparatus is its vertical compactness which permits its installation and operation where overhead space is limited. This is due in large part to the utilization of a crane which is suspended from a supporting monorail, to the small vertical dimension of the platform comprised in the load-carrying head H, to the suspension of the hoisting mechanism from the underside of the crane platform thereabove, and to the interlapping therebetween of the stabilizing means by which the head is laterally restrained in its vertical movements. There is also the further distinguishing feature of having the load-carrying head provided with a platform of considerable area elongated in the same direction as the crane, and with longitudinally extending confronting grab bars depending from opposite sides of such a platform. Such a construction makes it possible to lift, transport, and set down, in three sequential operations, a large number of parallelly arranged load-carrying bars from each of which are suspended quantities of articles that are to be treated. And finally, with such an elongated crane and-associated elongated lifting head whereon it may happen that the suspended load is unevenly distributed, we have provided duplex means whereby the head may be raised or lowered while maintaining its horizontality, and other means for stabilizing the head so that the suspended articles will be prevented from shifting during both vertical and horizontal movements, thereby oonducing to maintenance of the spaced relation between such articles during every stage of the transfer operation.

The transfer apparatus includes a crane that desirably travels on a monorail thereabove. This has the advantages (1) of flexibility in that the monorail may be extended through straight and curved sections, arranged as best suited to the layout in the plant where the apparatus is to be operated; and (2) of utilizing only overhead supports for the monorail so that a Wide clear space is maintained below the crane for accommodation of the lifting head H and of the load carried thereby. Such a crane which also travels on trucks arranged in tandem, is elongated parallelly with its supporting monorail and with the elongated lifting head which it supports. The fore and aft bearing points provided by the tandem trucks endow the crane with capacity for resisting any fore and aft tilting tendency of the lif ing head should the load that it is required to carry be concentrated toward either end to produce a condition of unbalance.

We claim:

1. In a transfer apparatus wherein is utilized a monorail-supported traveling crane mounting an electrically-operated duplex hoisting mechanism, the improvement which comprises a horizontal lifting head comprising a platform elongated in the direction of the monorail and positioned below the crane, opposed grab bars depending from the lifting head platform at points adjacent the elongated sides thereof and extending horizontally for substantially the full length thereof, means mounting the grab bars on the platform for movement toward and from each other, supporting means depending from the hoisting mechanism in connection with the lifting head at spaced points lengthwise thereof for imparting equalized vertical movements thereto, electrically-operated power means for propelling the crane, and switchcontrolled electrical circuits extended between a source of electrical energy and the power means for both the hoisting mechanism and the crane, said circuits having means to prevent operation of the hoisting mechanism when the circuit for operating the crane propelling means is closed.

2. In a transfer apparatus wherein is utilized a monorail-supported electrically-propelled traveling crane mounting an electrically-operated duplex hoisting mechanism, the improvement which comprises a horizontal lifting head having a platform elongated in the direction of the monorail and positioned below the crane, opposed grab bars depending from the lifting head platform at points adjacent the elongated sides thereof and extending horizontally for substantially the full length thereof, means mounting the grab bars on the framework for movement toward and from each other, supporting means depending from the hoisting mechanism in connection with the lifting head at spaced points lengthwise thereof for imparting equalized vertical movements (iii thereto, electrically-operated power means for moving the grab bars toward and from each other in unison, and switch-controlled electrical circuits extended between a source of electrical energy. and the several power means, said circuits having means to prevent operation of the hoisting mechanism and the means for moving the grab bars when the crane propelling means is in operation.

3. In a transfer apparatus wherein is utilized a monorail-supported, electrically propelled, elongated traveling crane mounting an electricallyoperated hoisting mechanism, the improvement which comprises a lifting head having a horizontal framework elongated in the same direction as the crane and positioned therebelow, horizontally extending, opposed grab bars arranged below the lifting head framework. adjacent opposite sides thereof, means mounting the grab bars on the framework for movement toward and from each other, supporting means depending from the hoisting mechanism in connection with the lifting head for imparting vertical movements thereto, electrically operated means carried by the lifting head for moving the grab bars in unison toward and from each other, and switch-controlled electrical circuits extended between a current source and the several power means, said circuits having means to prevent power actuation of said grab bars when said crane is underway and means to prevent operation of said crane when said grab bars are actuated.

4. A transfer apparatus for lifting and transporting articles between spaced article-receiving stations comprising a monorail-supported elongated traveling crane, an elongated lifting head positioned beneath the crane and depending therefrom for vertical movement with respect thereto and horizontal movement therewith, means for connecting the lifting head to the crane and for causing vertical movement therebetween including a pair of cables spaced along the length of the crane having one of their ends fixed to the crane and their other ends wound about winches rotatably mounted on the crane, said cables intermediate their ends passing through sheaves on the lifting head, motor means on the crane for rotating said winches in one direction to take up the cable and raise the lifting head and in the other direction to pay out the cable and lower the lifting head, extensible stabilizing means between the crane and lifting head comprising two sets of vertically disposed telescoping plunger and cylinder elements disposed between the crane and head and spaced apart lengthwise of the crane, means on the lifting head for holding articles to be transported including a pair of inwardly-facing L-shaped grab bars positioned at opposite sides of the lifting head, pivot rods secured to t -e lifting head on which the grab bars are pivotally mounted, a member extending upwardly from each grab bar and having, at its upper end, a pivotally mounted block provided with a threaded opening, a cross shaft extending between said blocks and having threaded engagement in said openings, the threads on the ends of said shaft being right and left handed respectively so that rotation of the cross shaft will cause equal and opposite movement of the grab bars between article holding and article release positions, means including a reversible motor for rotating the cross shaft to pivot the grab bars, a pair of switches in circuit with said reversible motor for controlling the operation thereof positioned adjacent one of said blocks, and a switch operating arm carried by said References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Libby Apr. 2, 1912 Dickinson Sept. 5, 1916 Pauly Nov. 5, 1918 Henricks Feb. 25, 1919 Number Name Date Bolgiano May 13, 1924 Fitch Sept. 23, 1924 Durhan Jan. 18, 1927 Grondahl June 17, 1930 Hofiman June 24, 1930 Richter Dec. 1, 1931 Frazer Sept. 12, 1933 Coburn June 11, 1940 Brightly Jan. 2, 1951 Smith Apr. 3, 1951

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