US3808967A

US3808967A - Trash compactor

Info

Publication number: US3808967A
Application number: US00278424A
Authority: US
Inventors: J Fair; J Griswold
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-08-07
Filing date: 1972-08-07
Publication date: 1974-05-07
Anticipated expiration: 1991-05-07

Abstract

A two-station trash compactor including a frame supported carriage movable in a longitudinal path of travel between a pair of longitudinally spaced, trash compacting stations, homing apparatus for guiding the carriage to the trash compacting station, a compacting ram vertically movable on the carriage between a raised position and a lowered trash compacting position for selectively compacting trash in either of a pair of longitudinally spaced, partible trash containers at the trash compacting stations, and ram driving apparatus on the carriage for moving the compacting ram in a to-and-fro vertical path of travel to compact the trash a predetermined amount and then automatically returning the compacting ram to a removed position.

Description

I Unrted States Patent [1 1 1111 3,808,967 Fair et al. May 7, 1974 TRASH COMPACTOR 3,589,277 6/1971 Gray l0O/2l s [75] Inventors: John Fair, Portage; James L. FOREIGN PATENTS OR APPLICATIONS Griswold, Highway M60, Union 195,610 6 1957 Austria 100 226 City, both of Mich.

[73] Assignee: said Griswold, by said Fair Primary miner-Billy J. Wilhite Attorney, Agent, or FzrmLearman & McCulloch [22] Filed: Aug. 7, 1972 [21] Appl. No.: 278,424 [57] ABSTRACT A two-station trash compactor including a frame sup- 52 us. (:1 100/221 100/52 100/53 Pwed carriage movable in a bngimdinal Path loo/218 loo/226 1007229 A '1OO/255 travel between a pair of longitudinally spaced, trash 100/26 R 100 /295 220/4 compacting stations, homing apparatus for guiding the 511 Int. Cl. Babb 15/16 carriage the COmPaCtmB Static)", a P [58] Field of Search loo/53 215 221 229 A ram vertically movable on the carriage between a l0O/224 218 295 226 2 55 52 26 269 aised position and a lowered trash compacting posi- 22O/4 tion for selectively compacting trash in either of a pair of longitudinally spaced, partible trash containers at 56] References Cited the trash compacting stations, and ram driving apparatus on the carriage for moving the compacting ram in UNITED STATES PATENTS a to-and-fro vertical path of travel to compact the 3,521,550 7/1970 Van Doom et al 100/26 trash a predetermined amount and then automatically 2 122 22: :11:22 21:25:;;;;;;;;;;;;;-;;; to a 3,495,376 2/1970 Lundgren 100/221 X 8 Claims, 8 Drawing Figures PATENTEMY 7 1974 3808967 saw 1 OF 4 a lino Eu? FIGI TRASH COMPACTOR FIELD OF THE INVENTION This invention relates to trash compactors and more particularly to two-station trash compacting apparatus having a manually movable carriage carrying a trash compacting ram which compacts trash in partible containers.

BACKGROUND OF THE INVENTION The disposal of trash from commercial establishments such as restaurants, hotels, and hospitals, is expensive because of the large volume of trash which must normally be removed from these facilities. If bulky trash is permitted to accumulate, it utilizes valuable floor space. Accordingly, it is an object of the present invention to provide new and improved apparatus for compacting trash into a small volume.

It is important that a trash compacting machine be economical to operate, and require minimum maintenance. Accordingly, it is another object of the present invention to provide trash compacting apparatus which is more economical to manufacture, operate, and maintain than known trash compactors of the same general capacity.

If trash is compacted at only one station, the operation must be interrupted until the trash container, which has been filled with compacted trash, is emptied. An advantage of a two-station compactor is that twice as much trash can be packed before any trash containers need be emptied and as trash is being packed into a container at one station, the other container can be simultaneously filled. A two-station compactor which merely doubles the equipment of a single station compactor would appreciably increase the cost of the compactor. Accordingly, it is still another object of the present invention to provide a two-station trash compactor including a carriage mounted compacting ram which is manually movable between two trash compacting stations, and homing apparatus for guiding the carriage along a portion of its path to the stations and for releasably retaining resisting movement of the carriage from the stations.

In some cases it may be desirable to pack trash in a flexible, heavy duty compactor bag and in other cases it may be desirable to compact the trash in rigid garbage cans. Accordingly, yet another object of the present invention is to provide a trash compactor which can selectively pack trash in either a flexible bag or a rigid container.

As sometimes occurs, liquid is included in the trash and will splash outwardly of the trash container during compaction. Accordingly, a further object of the present invention is to provide trash compacting ram apparatus including a resilient splash ring to inhibit such liquid from splashing out of the trash containers.

If in operation the trash compacting ram engages non-compressible material near its outer extremity, the ram will tend to undesirably cant. Accordingly, a still further object of the present invention is to provide a rotatable funnel-shaped trash compacting ram which will cam non-compressible objects toward the center of the ram and prevent them from causing the ram to cant.

In a two-station compactor, workers can be filling one container while the trash in the other is being compacted. Since the containers are closely spaced, it is important that the workers not be injured by the moving ram. Accordingly, it is an object of the present invention to provide a two-station trash compactor incorporating adequate shrouds, shields, and housings to prevent an operator from inadvertently placing a part of his body under the compacting ram.

When trash is compacted in a container, the compacted trash is relatively heavy and packed in place, and thus not easily removed from the container. Accordingly it is yet another object of the present invention toprovide a partible trash container which is designed to facilitate removal of the compacted material. Other objects and advantages of the present invention will become apparent as the description thereof proceeds.

THE SUMMARY OF THE INVENTION Apparatus for compacting trash in trash containers comprising a frame, a transfer carriage longitudinally movable on the frame between first and second longitudinally spaced trash compacting stations, ram means on the carriage reciprocably movable in a to-and-fro path between inoperative and operative positions to compress the trash in the containers, and homing means for guiding the carriage to the first and second trash compacting stations.

The present inventionmay more readily be described by reference to the accompanying drawings in which:

FIG. 1 is a fragmentary, rear perspective view of trash compacting apparatus constructed according to the present invention;

FIG. 2 is a front perspective view particularly illustrating the trash container carriage assembly;

FIG. 3 is a vertical sectional view taken along the line 3-3 of FIG. 1, the side wall of the container being broken away to more clearly illustrate the compacting ram;

FIG. 4 is a sectional top plan view taken along the line 4-4 of FIG. 3;

FIG. 5 is a fragmentary sectional front view taken along the line 5-5 of FIG. 4 and particularly illustrating the apparatus for forcing the carriage out-of the home positions;

FIG. 6 is a fragmentary sectional rear view taken along the line 6-6 of FIG. 3 and particularly illustrating the relation between the lower portion of the frame and the container dolly assembly;

FIG. 7 is an under plan view of the homing carriage and tracks, taken along the line 7-7 of FIG. 3; and

FIG. 8 is a schematic diagram of an electrical control circuit for operating the apparatus illustrated in FIGS. l7.

DESCRIPTION OF THE PREFERRED EMBODIMENT Apparatus constructed according to the present invention is mounted on a framework or housing, ge ner- Supported on the channels 18, for movement between a pair of trash compacting stations, generally designated and 22, is a carriage, generally designated 24, which includes a platform mounting a plurality of axles or pivot pins 25a journaling a plurality of casters 26 having annular V-grooves 27 received on laterally spaced V-shaped tracks 28 which are fixed to the top sides of the channel members 18. The carriage 24 moves on the rollers 26, between the solid line position, illustrated in FIG. 1, and the chain line position, illustrated in FIG. 1, at the

stations

22 and 20, respectively.

An aperture 281: is provided in the carriage platform 25 and is spanned by a plate 30 having holes 32 therein receiving mounting pins 34 which are connected to the base of a double-acting, fluid operated cylinder 36. A pair of compression springs 38 surround the mounting pins 34 and react between the plate 30 and the heads of the pins 34 for biasing the cylinder 36 upwardly to the raised position, illustrated in solid lines in FIG. 3, but permitting movement of the cylinder 36 to a lowered position, in a manner and for a purpose which will be more particularly described hereinafter.

The cylinder 36'includes a piston rod 44 rotatable about its axis and having an end 46 threadedly connected to an internally threaded steel insert 47 centrally provided in a trash compacting ram, generally designated 48, which may be constructed of a lightweight aluminum alloy, for example. The compacting ram 48, which is circular in plan, has an annular groove 52 in the side wall thereof receiving an annular, resilient splash rail or ring 54. The outside diameter of the splash rail 54 is slightly larger than the outside diameter of the ram 48 but is slightly less than theinside diameter of either of a pair of trash containers, generally designated C, in which trash T is compacted.

The ram 48 is provided with an upwardly convergent trash compacting lower face 48a which tends to direct radially outwardly disposed non-compressible objects radially inwardly toward the axis of the cylinder rod 44 when the trash is being compacted. The face 48a is sharply inclined to a plane perpendicular to the axis of piston rod 44.

Fixed to the ram actuating cylinder 36 and underlying the support rails 19 is a homing or locator platform 56 having longitudinally spaced apart pairs of

wheels

58 and 60 journaled on suitable shafts 58a at 60a, respectively, fixed to opposite ends of the platform 56. Fixed to the underside of each of the longitudinal frame rails 19 is a track member 62 including longitudinally extending, vertically recessed, downwardly opening, run portions 64a and 64b along the laterally opposite sides thereof separated by a longitudinal guide rib 66. The

rollers

58 and 60 are biased upwardly against the underside of the track 62 by the biasing springs 38 which react between the pins 34 at the upper side of the cylinder 36 and the carriage supported crosspiece 30. The laterally outer run portions 64a each includes a pair, of downwardly opening, homing recesses 70 so that the rollers 60 are received in the recesses 70 when the carriage 24 is at either of the

stations

20 and 22. The laterally inner run portions 64b each includes a pair of downwardly opening homing recesses 70a so that the rollers 58 are received in the recesses 70a when the carriage 24 is at either of the compacting

stations

20 or 22. When the

rollers

58 and 60 are received in the recesses 70a and 70, they are, of course, moved upwardly from the chain line position illustrated in FIG. 3 to the solid line position also illustrated in FlG. 3. Because the

rollers

58 and 60 ride along separate runs 64a and 64b, respectively, the rollers 58 will not be received in the recesses and the rollers 60 will not be received in the recesses 70a. Also, since the

rollers

60 and 58 will only enter one of the recesses as the carriage moves in its longitudinal path, the transition of the carriage 24 between the

stations

20 and 22 is smooth once the

rollers

58 and 60 have been removed from their associated recesses 70a and 70. The recesses 70a and 70 are positioned that the rollers 58 and 60' riding on each track 62 will be simultaneously received in its associated recess 70a and 70, respectively. When the

rollers

58 and 60 are received in their respective recesses, the biasing springs 38 atop the cylinder 36 yieldably urge the

rollers

58 and 60 to remain in their homing recesses 70:; and 70, respectively. After the

rollers

60 and 58 engaging the tracks 62 are longitudinally moved out of their respective homing, or locator,

recesses

70 and 700, at one of the

stations

20 and 22 in a manner to be particularly described hereinafter, the carriage 24 will be smoothly and easily transferred to the other of the

stations

20 and 22 where the

rollers

60 and 58 are received in the other pair of homing recesses 70 and 70a. Fixed to opposite ends of the homing platform 56 are mounting and guide brackets 76 (FIG. 5) which mount a protective shroud or shield 78 that is U-shaped in plan and travels with the carriage 24 to provide a barrier which prevents the operator from inadvertently placing his hand under the compacting ram 48 at the station while placing trash in the compactor at the other station.

A front half-door 88 covers the lower half of the machine and includes horizontal hinge or guide pins 87 received in a pair of vertical tracks provided along the forward edge of the end walls 14. The half-door 88 may be moved upwardly from the position illustrated in FIG. 1 to a raised position covering a start switch 89 mounted on the upper front wall section 16 so that the containers C can be removed, emptied and replaced, without any danger of inadvertently activating switch Lever apparatus for longitudinally forcing the carriage 24 out of either of its home positions at the

stations

20 and 22 is provided, and includes a handle 100 fixed to a yoke 90 which is pivotally mounted on the underside of the homing bracket 56 by a fulcrum or pivot pin 91. Opposite ends of the yoke 90 are pivotally connected by a pair of pivot pins 92, to a pair of links 94 which are also pivotally connected by pivot pins 95, to horizontal reaction bars 96 slidably mounted in sleeves 97 fixed to opposite legs of the U-shaped ram covering shroud 78.

A pair of wear plates 98, which are engageable by the bars 96 as the yoke 90 is swung about the fulcrum 91, is fixed to the side walls 14. The handle 106 and the yoke 90 constitute a lever swingable about the fulcrum 91 so as to axially move the bars 96 into engagement with their associated plates 98 and force the

rollers

60 and 58 out of their respective recesses 70 and 70a so that the carriage 24 can move away from one of the

stations

20 and 22 towards the other station. The bars 96 react with the plates 98 and apply a longitudinal force which causes the

rollers

58 and 60 to be cammed out of the homing recesses 70 and 70a against the vertical biasing force of springs 38. When the

rollers

58 and 60 are moved a predetermined distance-so as to be removed from the recesses 70 and 70a, the carriage 24 can be longitudinally moved between the

stations

20 and 22, with relatively little manual force on the handle 100 since the

rollers

58 and 60 roll on the smooth track portions 64a and 64b and the carriage rollers 26 freely roll along the V-tracks 28.

A horizontal track 102 is provided along the midportion of each end wall 14 for receiving the flange 103 of a trash apron 104 having funnel members 105 which direct trash into the containers C. The shroud 104 is removable from the track 102 to enhance the cleaning thereof.

Also fixed to the homing platform 56 is a bracket 108 mounting a continuously operated electric motor 110 driving a fluid pump 1 12 also supported on the bracket 108 and connected with a pair of fluid conduits 113 which supply fluid through a solenoid actuated, spring returned, 4-way, 2-position valve 37 to opposite ends of the ram actuating cylinder 36. The cylinder 36 may suitably develop 10,000 pounds of force to be used with a -inch diameter ram 48 to create a trash compacting pressure of approximately 50 pounds per square inch. A pressure sensing switch 114. is connected in the line 113 to sense the pressure of the fluid therein and may suitably comprise a Static-O-Ring type pressure switch manufactured by Mechiniarts Associates, 401 Wyandott, Kansas City, Missouri. The purpose of the switch 114 will become apparent when the operation is described.

THE CONTAINER ASSEMBLY The container assembly apparatus, generally designated A, includes a carriage platform 1 16 supported by a plurality of casters 1 18 having vertical swivel pins 119 slidably and rotatably received in apertures 117 provided in the platform 116 for permitting the platform 116 to move vertically relative to the casters 118 between the upper and lower positions, illustrated in solid and chain lines, respectively, in FIG. 6, against the force of biasing springs 120' which react between the pins 119 and the platform 116 to bias the platform 116 to the raised position illustrated in solid lines in FIG. 7. When the compacting ram 48 compresses trash in the containers C, the platform 116 is moved downwardly to engage and be supported by the side frame members The containers C, which may each suitably be of a 30-gallon capacity, each includes a fixed half-container side wall 122 fixed to the platform 1 l6,- and a movable half-container side wall 123 fixed to a horizontal pivot pin 126 (FIG. 3), journaled by a pair of ears 128 fixed to the platform 116 for swinging movement about the horizontal axis of the shaft 126 from a position adjacent the fixed half-container side wall 122 to the removed position, illustrated in FIG. 2. Fixed to the movable container side wall 123 is the bottom wall 130 of the container C which lifts the compacted trash T from a position adjacent the platform 116 to a raised position away from the fixed half-container side wall 122 when it is swung vertically so that it may be more easily removed by a pick-up man.

The

container half walls

122 and 123 include confronting flanges 132 which are locked together by a U- shaped arm member, generally designated 134, pivotally mounted on a bracket 136 fixed to the halfcontainer side wall 123 for movement between a locking position illustrated in FIG. 1 and an unlocked position illustrated in FIG. 2. In the locked position, the U- shaped arm 134 is received over the abutting flanges 132 and a pin 140 is passed through aligned apertures provided in the abutting flanges 132 and the U-shaped portion 138 to lock the arm 134 in position. A handle 140a is fixed to the U-shaped arm 134 to facilitate movement thereof. If desired, a liner bag L (FIG. 2) may be inserted into the containers C to receive the garbage collected. The bag can later be tied and removed.

TI-IE CIRCUIT Referring now more particularly to FIG. 8, a pair of lines L1 and L2 are connected across a suitable source of power such as 1 10 volt, 6O cycle alternating current. Connected in series in line L1 are the contacts 89a of the start switch 89, which is mounted on the front wall 16 of the machine, the normally closed door contacts a of a switch which is mounted on one of the sidewalls 14 andwhich is actuated by the door 88 being moved to the raised position to open the contacts 120a, and a parallel circuit including sets of contacts 122a and 121a which are respectively closed when the

switches

122 and 121, mounted on opposite ends of the frame, are engaged by the carriage 24 being moved to the

stations

22 and 20, respectively.

Connected in parallel across'the lines L1 and L2 in line L3 is the fluid pump drive motor Ml. A control relay R1 is connected in line L4 across the lines L1 and L2 and includes holding contacts Rla connected in series with the normally closed contacts 124a which open when the switch 124 (FIG. 1) is actuated as the ram 48 is returned to the raised inoperative position. Connected across the lines L1 and L2 in line L5 are the normally closed contacts 114a of the fluid pressure switch 114 located in fluid conduit 113 and the advance solenoid 37a of a spring returned, solenoid actuated valve 37 which, when energized, will direct fluid to the ram advance cylinder 36 so asto move the compacting ram 48 downwardly to compress the trash. Connected across the lines L1 and L2 in'line L6 are the normally open contacts 11412 of the fluid pressure switch 114 and the retract solenoid 37b, which when energized, will actuate the ram control valve 37 so as to direct fluid to the ram cylinder 36 in such a manner as to return theram 48 upwardly to the raised position illustrated in FIG. 1. Anti-bacterial lights 45a are provided at the compacting

stations

20 and 22, for eliminating any bacteria in or about the containers C. The lights 45a are serially connected in line L7 across the lines L1 and L2 and may suitably comprise ozone producing lights such as that manufactured by the General Electric Company, Cleveland, Ohio as Model FGl 1 19- E2.

THE OPERATION In order for the machine to operate, the door 88 must be moved to the lower position to actuate the switch mounted on the sidewall 14 and close contacts 120a (line L1), and the carriage 24 must be at either of the

trash compacting stations

20 or 22 so that one of the homing switches 121 or 122 is actuated to close one of the sets of contacts 121a and 122a. After a suitable amount of trash has been dropped in one of the trash containers C, the container at station 22, for example, the start switch 89 is acutated to close the contacts 89a (line L1) to energize relay R1 (line L4) to close the holding contacts Rla connected in parallel with the start switch Contacts 89a. The fluid pump driving motor M1 is connected across the lines L1 and L2 in line L3 and is continuously energized. When the switch contacts 89a are closed, the advance solenoid 37a is energized and operates the ram control valve 37 so that fluid is directed to the ram control cylinder 36 in such a manner as to advance the compacting ram 48 axially into the container C at station 22. As the ram engages the trash, the compacting force is transmitted to the platform 116 which is driven downwardly against the forceof the caster supported springs 120' so that the platform 1 16 engages and is braced by the frame braces 10, and the trash T and the container C will be tightly clamped between the frame braces and the compacting ram 48. If the springs 120' were not provided, the caster wheels would be crushed and the entire frame would merely raise off the floor as the compacting ram pressed against the trash.'As the trash is being compacted, the splash ring 54 inhibits liquid, and other fluid garbage included with the trash, from being expelled out of the container C.

If the ram 48, while being lowered, encounters a radially outwardly disposed non-compressible object, the non-compressible object will be camm'ed radially inwardly toward the axis of the piston rod 44 by the tapering surface face 480 of the compacting ram.

When the trash T has been compacted to a predetermined amount, the pressure in fluid line 113 communicating fluid to the advance side of ram control cylinder 36' will build until the pressure switch 114 is actuated to open the normally closed contacts 114a (line L5) to deenergize the advance solenoid 37a and close the contacts l14b (line L6) to energize the retract solenoid 37b to raise the ram 43.

After the container at station 22 is filled, the carriage shifting handle 100 is grasped and turned counterclockwi'sely, as illustrated in FIG. 5, to slide the bar 96 adjacent station 22, into engagement with the adjacent wear plate ,98. The bar 96 reacts with the plate 98 to cam the

rollers

58 and 60 riding on one of the tracks may then roll freely toward the chain line position at station where the pair of

rollers

58 and 60 will be received by their respective homing recesses70 and 70a at station 20 to halt the carriage 24 in the second home position 20. The start switch is again energized to repeat the cycle.

When a trash container C is full, the door 88 is raised to a position covering the start switch 89 and the trash container assembly A is removed from underneath the apron 104. The loaded trash container C is emptied by removing the pin 140 and swinging the handle 134 about the axis of the handle member 136 to free the confronting flanges 132, The movable container half portion. 123 is then swung about the horizontal axis 126 to lift the trash T to the position illustrated in FIG. 2 and the trash T is then removed. The container-half 123 and handle member 136 are returned to the positions shown in FIG. 1 and the container assembly is returned to a position underneath the apron 104. The door 88 is returned to its original position covering the We claim:

l. A two-station trash compactor comprising:

a frame;

a transfer carriage longitudinally movable on said frame between first and second longitudinally spaced trash compacting stations;

ram means movable on said carriage in a to-and-fro path of travel for selectively compacting trash at said first and second stations; and

locator means including means resisting movement of said carriage from each station until said carriage is moved a predetermined distance from said station and then permitting said carriage to freely move toward the other of said stations.

2. The apparatus of claim 1 wherein said locator means includes roller means on one of said frame and said carriage and cooperating socket means on the other of said frame and carriage for receiving said roller means, said socket means being positioned such that said roller means moves vertically to be received thereby.

3. The trash compactor of claim 1 wherein said ram means comprises a convergent axial end compressing face for camming relatively radially disposed trash toward the axis of said compacting ram means as said ram means moves axially forwardly to compress said trash.

4. The apparatus set forth in claim 1 including:

trash container means for receiving trash to be compressed; and

a dolly supporting said trash container means and being movable between a position remote from said frame and a frame engaging position in response to trash being compacted.

5. The apparatus of claim 4 wherein said trash container means includes a platform, first and second partible container side wall portions relatively movable between abutting trash receiving positions and spread apart trash emptying positions, said first side wall portion being mounted on said platform for swinging movement about a horizontal axis to relatively movesaid locator means including means yieldably urging said carriage toward said track to resist movement of said rollers out of said socket means. 7. The apparatus set forth in claim 6 including means reactable between said carriage and said frame for longitudinally moving said carriage out of said homing po- 9 sition at said first and second stations against the force of said yieldable means.

8. The apparatus set forth in claim 6 wherein said track means comprises at least one pair of laterally spaced longitudinal tracks, said socket means comprising at least one socket in one of said tracks adjacent said first station and at least another socket in the other track adjacent said other station; said roller means including at least one pair of rollers on said compacting said second station.

Claims

1. A two-station trash compactor comprising: a frame; a transfer carriage longitudinally movable on said frame between first and second longitudinally spaced trash compacting stations; ram means movable on said carriage in a to-and-fro path of travel for selectively compacting trash at said first and second stations; and locator means including means resisting movement of said carriage from each station until said carriage is moved a predetermined distance from said station and then permitting said carriage to freely move toward the other of said stations.

4. The apparatus set forth in claim 1 including: trash container means for receiving trash to be compressed; and a dolly supporting said trash container means and being movable between a position remote from said frame and a frame engaging position in response to trash being compacted.

5. The apparatus of claim 4 wherein said trash container means includes a platform, first and second partible container side wall portions relatively movable between abutting trash receiving positions and spread apart trash emptying positions, said first side wall portion being mounted on said platform for swinging movement about a horizontal axis to relatively move said side wall portions between said abutting and spread positions.

6. The compactor as set forth in claim 1 wherein said frame includes longitudinal track means having longitudinally spaced apart, socket means at said first and second stations, said carriage including laterally spaced rollers on said track meanS receivable in said socket means when said carriage is moved to said first and second stations; said locator means including means yieldably urging said carriage toward said track to resist movement of said rollers out of said socket means.

7. The apparatus set forth in claim 6 including means reactable between said carriage and said frame for longitudinally moving said carriage out of said homing position at said first and second stations against the force of said yieldable means.

8. The apparatus set forth in claim 6 wherein said track means comprises at least one pair of laterally spaced longitudinal tracks, said socket means comprising at least one socket in one of said tracks adjacent said first station and at least another socket in the other track adjacent said other station; said roller means including at least one pair of rollers on said compacting ram means and positioned such that one roller is in longitudinal alignment with said one track and receivable in the socket at said first station when the carriage is at said first station and a second roller in longitudinal alignment with said second track and receivable in the socket at said second station when said carriage is at said second station.