US3389804A

US3389804A - Supporting track and advancing pawls for article display and storage apparatus

Info

Publication number: US3389804A
Application number: US590381A
Authority: US
Inventors: Lyon William Brouson
Original assignee: William Bronson Lyon
Current assignee: WILLIAM BRONSON LYON
Priority date: 1966-10-28
Filing date: 1966-10-28
Publication date: 1968-06-25
Anticipated expiration: 1985-06-25

Description

June 25, 1968 w. B. LYON 3,389,894

SUPPORTING TRACK AND ADVANCING PAWLS FOR ARTICLE DISPLAY AND STORAGE APPARATUS 5 Sheets-Sheet 1 Filed Oct. 28, 1966 INVENTOR. W////0m 5. L700 ATTORNEY 3 Sheets-Sheet 2 7 W. B. LYON SUPPORTING TRACK AND ADVANCING PAWLS FOR ARTICLE DISPLAY AND STORAGE APPARATUS June 25, 1968 Filed Oct. 28, 1966 ATTORNEY June 25, 1968 w. B. LYON 3,389,804

SUPPORTING TRACK AND ADVANCING PAWLS FOR ARTICLE DISPLAY AND STORAGE APPARATUS Filed Oct. 28, 1966 5 Sheets-Sheet 7 2 25 6 66 52 Ff/ K! m l I H L III I] a 2 W a? 66 22 2a 66 jjg fi INVENTOR.

VIM/mm B. 170/? ATTORNEY BY A United States Patent 3,389,804 SUPPORTING TRACK AND ADVANCING PAWLS FOR ARTICLE DISPLAY AND STORAGE APPARATUS William Bronson Lyon, 6204 Charlotte Pike, Nashville, Tenn. 37209 Filed Oct. 28, 1966, Ser. No. 590,381 7 Claims. (Cl. 211-15) This invention relates to improvements in supporting track and advancing pawls for article display and storage apparatus. The invention is an improvement of the apparatus disclosed and claimed in Patent No. 2,836,303. The principal objects of the invention are:

First, to provide a track and coacting conveyor and pawls for advancing article supporting bars around a generally rectangular circuit with vertical front and back reaches, in which the bar supporting pawls are supported along both of their sides, and connected centrally to the pawl advancing conveyor chain, so that the weight of articles supported on the bars does not impart any twisting stress to the conveyor chain or the connections between the pawls and the chains.

Second, to provide a pawl and chain supporting track with a novel pivotal connection between the pawls and the chain, and a novel arrangement of pawl receiving slots in the track system that permits bar supporting pawls to swing out of bar engaging position at preselected posi tions along the track in order to pass article supporting bars in a predetermined sequence.

Other objects and advantages of the invention will be apparent from a consideration of the following description and claims. The drawings, of which there are three sheets, illustrate a practical form of the invention.

FIGURE 1 is a fragmentary inside elevational view of the supporting track and pawl conveyor for supporting and advancing one end of article supporting bars between article storage and article display positions, the bars and a drive for the conveyor being shown in section.

FIGURE 2 is a fragmentary vertical cross sectional view along the line 22 in FIGURE 1, but with the pawls advanced to the article support bar.

FIGURE 3 is a fragmentary vertical cross sec ional view taken along the plane of the line 3-3 in FIGURE 1, but with the pawls advanced to show the top pair in FIGURE 1 at the bottom.

FIGURE 4 is a fragmentary horizontal cross sectional view along the plane of the line 44 in FIGURE 1.

FIGURE 5 is a view taken along the plane of the line 5-5 in FIGURE 1, showing the top rail in plan.

FIGURE 6 is a fragmentary vertical cross sectional view taken along the plane of the line 66 in FIGURE 2.

FIGURE 7 is a fragmentary vertical cross sectional view through the bottom rail, on the plane of the line 77 in FIGURE 3, with the pawls advanced to the rear.

FIGURE 8 is a fragmentary plan view of the top rail.

FIGURE 9 is a fragmentary plan view of the bottom rail.

FIGURE 10 is a sectional view on line 10-10 in FIG- URE 1, looking up at the lower set of pawls.

The above identified Patent No. 2,836,303 discloses a cabinet with supporting and guiding rails in each end for supporting three article support rods for advancing motion through a generally rectangular circuit within the cabinet. The rods are supported and advanced in their circuit by two conveyors, associated one wih each guide rail system at each end of the cabinet. Each conveyor includes two pairs of a leading pawl and a trailing pawl connected in equally spaced positions along the chain. The two conveyor chains are driven simultaneously by a cross shaft to advance the article support bars between four positions located generally at the four corners of the cabinet. Thus there is always a vacant position around the circuit which is not occupied by a support bar. This permits articles of considerable length, such as garments on hangers, to hang freely at a forward display position and at two vertically displaced storage positions; and permits the articles on each bar to be advanced around the storage and display circuit without interference between each group of articles. The leading pawl of each pair of pawls on the chains must by-pass a support bar to be in position to support the bar in downward motion to the display position. The trailing pawl of each pair must by-pass support bars in some positions to be able to advance to bars in other positions, and must further be able to tilt out of bar engaging position to leave a bar in one position and pass on the next bar.

The arrangement of the bar positions, and the sequence of operation of the pawls on the conveyor chains is fully described in the patent identified and so is not disclosed in greater detail. Similarly, the arrangement of two simultaneously operated conveyors is fully disclosed, so the drawings herein illustrate only one conveyor, and supporting and guiding track and rail system. It will be appreciated that the structure illustrated is duplicated in symmetrical relation at the opposite end of the storage and display space. The apparatus may be enclosed in a suitable cabinet (not illustrated), or may be built into unused portions of a building.

The supporting and guiding track system includes a front supporting bar 1 and a rear support bar 2. The bars may be suspended from a suitable support above or extended downwardly to a lower support (not illustrated). The front and rear bars are of angle shaped cross section having laterally extending

guide flanges

3 and 4 respectively. The support bars are connected by a top cross strap 5 and a bottom cross strap 6 to provide a rigid rectangular frame. In addition, the straps S and 6 may be secured to a wall 7 by screws 8 for additional support of the frame if desired.

Connected to the top strap 5 is a top support rail 9 of folded metal. Connected to the bottom strap 6 is a bottom support rail 10, also of folded metal. The top and

bottom rails

9 and 10 are further connected by a front hanger strap or bar 11 and a rear hanger strap or bar 12. The front hanger bar 11 has an angled front guide rail 13 secured thereto as by rivets 14, while a rear angled guide rail 15 is secured to the rear hanger strap as by rivets 16. The direction of travel of the conveyor around the rectangularly arranged rails is counterclockwise as viewed in FIGURE 1 and as indicated by the arrows. A drive shaft for connecting the conveyors at each end of the apparatus is indicated at 17 with suitable journals in the bottom guide rails.

The top guide rail 9 is shown more clearly in FIG-

URES

2, 6 and 8 and consists of an upright flange 18 having a forwardly or inwardly turned roller supporting fian e 19 intermediate of its height. Below the roller supporting flange the rail is inclined laterally outwardly as at 20 to a lower portion 21 which is secured to the previously described

hanger straps

11 and 12. The lower edge of the lower portion 21 is turned laterally inwardly in a broad conveyor supporting rail 22 having a chain supporting rib 23 secured to its upper side as by screws 24.

The lower guide and support rail 10 has a flat upright side portion 25 with a laterally inwardly turned roller supporting track 26 formed near. its lower end. Theinner edge of the roller supporting track is folded downwardly and outwardly in an inclined position as at 27 to a lower connected edge 28 which is secured to the

hanger straps

11 and 12. A broad conveyor supporting and guiding rail 29 is turned laterally inwardly from the upper edge of the rail and has a conveyor chain guiding track 30 secured to its lower side as by screws 31.

The front guide rail 13 is of angled cross section and has a laterally inwardly projecting conveyor guiding flange 32 with a chain guiding track 33 secured to its outer edge. The ends of the guiding flange 32 of the front rail 13 are connected to the forward ends of the upper and lower rails by curving portions of the flange 32 rearwardly as at 34 and 35. Lapped connecting plates or clips 36 secure the ends of the curved flanges to the lateral flanges of the adjacent top and bottom rails.

The rear guide rail has a laterally turned supporting flange 37 with a chain supporting track 38 secured to its rear surface. The ends of the flange 37 are bent into curved corner connecting plates 39 to connect the upper end of the rear rail to the lateral flang 24 of the top rail and to connect the rear end of the lower rail to the lower end of the flange 37. Connecting clips 40 overlap and connect the abutting edges of the corner plates and the rails.

Supported at each corner of the rectangularly arranged guide rails is a shaft 41. The shaft 41 at the upper front corner supports a sprocket 42 and a sprocket 43 is supported at the junction of the lower end of the front guide rail and the front end of the bottom guide rail. Corresponding

sprockets

44 and 45 are supported at the rear end of the bottom rail and the upper end of the rear rail. A link chain loop 46 is trained around the sprockets 42 to 45 and one of the sprockets is driven from the cross shaft 17 by a connection not illustrated. The several reaches of the chain loop 46 are supported by the

chain supporting tracks

23, 30, 33 and 38 between the sprockets.

The roller supporting track 19 on the upper guide rail 9 is positioned above the chain supporting flange and is positioned laterally outwardly to support the rollers 47 mounted on the ends of three

article supporting bars

48, 49 and 50. The upper roller supporting track 19 has a forward depression or detent 51 and a rear depression or detent 52 for arresting the motion of the rollers at these points as will be described. In reference to FIGURES 2 and 4 it will be seen that the roller supporting track 19 is positioned behind the laterally turned

flanges

3 and 4 on the front and rear support bars 1 and 2.

The laterally projecting roller supporting track 26 on the lower rail has a similar forward detent or depression 53 and rear depression or detent 54 and the track 26 is positioned in the plane of the

flanges

3 and 4 of the support bars. The front hanger support bar 1 has the lower end of its flange 3 separated and bent inwardly as at 55 to form a continuous track with the front end of the track flange 26 and the flange 4 of the rear support bar to the lower roller supporting track is similarly curved at 56.

The article support bars 48, 49 and 50 are advanced around the circuit of the supporting and guiding rails and tracks by two pairs of leading and trailing pawls indicated generally at 57A and B in FIGURE 1 and connected to the chain loop 46 at diametrically opposite or equally spaced points around the chain loop. The pawls of each pair are identical, but are mounted differently as will be described. The leading pawl 58A is a U-shaped member having side flanges 59 that are inclined rearwardly and outwardly of the chain loop at their leading edges to a crosspiece 60. Secured to the inner sides of the side flanges 59 and along their inner free edges are reinforcing strips 61 which project slightly beyond the inner edges of the pawl flanges. The projecting inner edges of the reinforcing strips may be arcuately cut away as at 62 for clearance in passing around the corners of the conveyor. The trailing edges of the side flanges 59 are generally perpendicular to the inner edges as indicated at 63. The trailing pawls generally indicated at 64A are also inwardly concave U-shaped members having side flanges 65 which extend perpendicularly along their leading edges at 66 to crosspieces 67. The trailing edges of the side flanges are inclined rearwa'rdly and inwardly at 68 and reinforc- 4 ing strips 69 are secured to the inner sides of the side flanges and project therebeyond in the same manner as the reinforcing strips 61. The inner edges of the strips 69 may be similarly recessed as at 70 for clearance.

The leading pawl 58A of the first pair of pawls shown at 57A in FIGURES l, 2 and 6 is secured to the chain 46 by an elongated pin 71 which forms one of the connecting pins for the adjacent links 72 of the chain. The pawl is mounted in olf-center straddling relation to the chain 46 and laterally outwardly therefrom toward the bar supporting track 19 by a relatively long sleeve 73 positioned between the inner side of the reinforcing plate and the outer links of the chain. A set collar 74 secured to the pin at the opposite inner side of the chain keeps the pin and sleeve in position laterally relative to the chain and the inside of the pawl. One of the pins 75 of the chain positioned in trailing relation to the pin 71 is longer than the normal link connecting pins 76 of the chain but shorter than the pin 71 to be positioned freely between the side flanges 59 of the pawl. The pin 75 is spaced from the side of the chain 47 and secured in place by a collar 77. As appears more clearly from FIG. 6 the ends of the pin 75 overlie notches 78 formed in the upper edges of the reinforcing strips 61 so that the pawl may pivot downwardly or outwardly relative to the circuit of the conveyor but is prevented from tilting inwardly by engagement between the ends of the pin and the bottoms of the notches which form stops on the pawls.

The trailing pawl 64A of the top illustrated pair of pawls 57A is connected to a pin 79 of the chain in trailing relation to the leading pawl. Like the pin 71, the pin 79 projects through a sleeve or roller of the chain and extends through the side flanges of the trailing pawl. The pawl is positioned in off-center straddling relation to the chain 46 in inwardly or more widely spaced relation to the track 19. This is accomplished by a relatively long sleeve 80 positioned between the inner side of the chain and the inner flange of the pawl and held axially in place by a lock collar 81.

A trailing pin 32 of the chain is of intermediate length similar to pin 75 and is retained transversely of the chain by a lock collar 83. Pin 82 registers with notches 84 in strips 69 on the inner sides of the side flanges 65 to prevent swinging of the pawl outwardly of the chain loop while permitting inward swinging of the pawl.

. The leading and trailing pawls of the lower pair of pawls 57B as shown in FIGURES 1 and 10 are the same as the first pair of pawls and are secured to the chain 46 in a similar fashion except that the leading pawl 588 shown in FIGS. 1 and 10 is offset inwardly from the supporting track 26 while the trailing pawl 64B is offset oppositely and outwardly away from the track 26.

Similar spacing sleeves

73B and 80B and lock

collars

74B and 818 secure the pins 718 and 79B in correct longitudinal and transverse relation between the chain and the pawl. Likewise the intermediate length pins 75B and 82B are held in place by set collars 77B and 83 The upper pawl guiding and supporting rail 22 is provided adjacent its front end with a pair of slots or recesses 85 and 86 that are in outwardly olf-center relation to the chain supporting rail or rib 23 to receive the side flanges of outwardly offset leading pawl 64 of the first pair of pawls 57A and the side flanges of the outwardly offset trailing pawl 58B of the other pair of pawls 57B as these pawls are advanced forwardly along the top supporting rail 22. At its rear end the top rail 22 is provided with a second pair of

slots

87 and 88 which are offset inwardly to receive the flanges of the alternate pawls of each pair of pawls. Slots 89 in each end of the top rail provide clearance for the

sprockets

42 and 45. The bottom pawls supporting rail 29, as is shown in FIGURE 9, is provided with a pair of

slots

90 and 91 adjacent its forward end which are offset laterally inwardly away from the bar supporting track 26 while the opposite or rear end of the rail is provided with

slots

92 and 93 which are offset oppositely outwardly toward the track 26. The ends of the rail 29 have slots 94 formed therein to clear the peripheries of the

sprockets

43 and 44.

From the foregoing description of the oppositely staggered slots in the pawl support rails and the oppositely offset pawls in the two pairs of pawls, it will be apparent that the leading pawl 58A of the upper pair of pawls 57A will register with the slots 85 and 86 and tilt downwardly therethrough as shown in FIGURE 6 to pass underneath the article supporting bar 48 located in the detent 51 as the chain 46 is advanced to the left as shown in FIGURES l and 6. The ends of the slots 85 and 86 will cam the pawl 58A outwardly in a position for its trailing edge 63 to engage and support the bar 43 downwardly along the front support rail 32 as the trailing pawl 64A pushes the bar 43 out of the detent. The trailing pawl 64A being offset from the chain oppositely from its associated leading pawl, will not enter into the slots 85 and 86 and will push the bar and its roller forwardly out of the detent. The detent 51 and the space therebelow is thus vacated. The opposite pair of pawls 57B, shown at the bottom of FIGURE 1, will be moving article support bar 49 rearwardly from detent 53, clearing detent 53 to receive bar 48. When the trailing pawl 64B reaches detent 54- at the rear of the lower support rail, its outwardly offset side flanges register with

slots

92 and 93 to pass bar 49 as shown in FIG. 10, and leave bar 49 on detent 54. Inwardly offset trailing pawl 64A will later pick up and advance bar 49. The second pair of pawls 57B continues up to the top support track 19 and the support bar resting in the detent 52, the leading pawl 58B passes under bar 50 by reason of its flanges being in registering relation with respect to the

slots

87 and 88 but the outwardly off-set flanges of trailing pawl 648 do not register with the slots. One of the next advancing cycles of the chain article support bar 50 in the detent 52 is advanced to the then vacant front top detent 51 by trailing pawl 64B where it is left by reason of the outwardly off-set position of its side flanges registering with and falling into slots and 86.

The arrangement of the pairs of pawls 57A and 5713 in oppositely offset straddling relation to the chain 46 and the oppositely staggered relation of the slots 85 to 88 and 90 to 93 provides the same sequence of advancing motion of the three article support bars 48, 49 and 5% as the structure in Patent No. 2,836,303 referred to above. At the same time the bar advancing pawls are supported on opposite sides of the chain completely around the circuit of the chain to support the loads applied thereto in advancing the bars. The article supporting bars or rather their rollers 47 are retained laterally on the advancing pawls through the vertical reaches of the conveyor by the retaining

flanges

3 and 4, and the vertically moving pawls are oppositely supported by the

vertical flanges

32 and 37. In passing between the

vertical flanges

32 and 37 and the top roller supporting track 19, the rollers 57 are supported and guided by curved extensions 95 projecting from the ends of track 19. The ends of the

vertical flanges

32 and 37 are slotted as at 96 to clear the

sprockets

42, 43, 44 and 45.

No attempt has been made to illustrate the driving connection to the chain conveyor 46 as this is disclosed in the prior patent referred to.

What is claimed as new is:

1. In an article storage and display device having conveyor chains arranged in spaced, upright, generally rectangular loops, with pairs of leading and trailing pawls connected to the chains in two equally spaced positions around said loops, sprockets located in the corners of said loops, and three article support rods extending between said loops to be advanced by said pawls between four positions located adjacent the corners of the loops, chain and rod guiding and pawl supporting mechanism comprising:

top and bottom chain and pawl supporting rails extending laterally inwardly across the plane of said loops with the top rail below the top reach of the associated loop and the bottom rail above the bottom reach of the associated loop, with the chains engaged with laterally inwardly spaced central portions of the rails,

top and bottom bar support tracks positioned in laterally overlapping relation to the outer portions of said chain and pawl supporting rails with the top bar support track located above the top support rail and the bottom bar support track located below the bottom pawl supporting rail,

bar restraining detents on said bar supporting tracks adjacent the ends thereof,

front and rear upright bar retaining tracks extending between the ends of said top and bottom bar supporting tracks with curved means connecting the upright tracks to the ends of the bottom bar,

upright front and rear chain and pawl guiding rails disposed in spaced relation to the inner sides of said front and rear tracks and having their ends spaced from the ends of said top and bottom rails,

sprockets engaging said chain loop and positioned in chain transferring relation between the ends of the rails,

said pawls having U-shaped cross sections with side flanges projecting inwardly of said chain loop to engage said rails,

first pivot pins connecting the leading ends of said leading pawls to said chain in laterally opposite offcenter but straddling relation to the outside of said chain loop,

second pivot pins connecting the leading of said trailing pawls in spaced relation behind said leading pawls and in laterally opposite off-center but straddling relation to the outside of said chain loop with each trailing pawl off-set oppositely to its associated leading pawl,

means on the insides of the side flanges of said pawls forming stops displaced in trailing relation to pivot pins connected thereto, stop pins projecting from said chain in overlying relation to said stops outwardly of said chain loop,

first pairs of longitudinal recesses formed in said top and bottom support and guide rails and located near the front ends thereof to receive the trailing'edges of the side flanges on the leading pawl of one of said pairs and the side flanges of the trailing pawl of the other of said pairs of pawls to permit inward tilting of the pawls to pass support bars engaged with the detents in said front ends, and other pairs of longitudinal recesses formed in the rear ends of said top and bottom rails in laterally oppositely off-set relation to said first pairs of recesses to receive the trailing edges of the side flanges of the leading pawl of said other of said pairs of pawls and the side flanges of the trailing pawl of said one of said pairs of pawls. 2. A storage and display device as defined in claim 1 in which said pawls are of folded metal with opposed edges on the trailing ends of the leading pawls and the leading edges of the trailing pawls, said edges being generally perpendicular to the inner edges of the side flanges of the pawls, and

strips of metal secured to the inner sides of the side flanges of said pawl-s and receiving said pivot pins,

said strips of metal having notches formed in their outer edges forming said stops for coaction with said stop pins,

said pivot pins and said stop pins projecting axially from connecting pins of said link chain.

3. A storage and display device as defined in claim 2 in which said strip of metal on said pawls project beyond the inner edges of the side flanges of said pawls to form rail engaging surfaces on the pawls.

4. An article storage and display device as defined in claim 1 in which top and bottom chain and pawl supporting rails and said top and bottom bar supporting tracks are angled sheet metal members having vertically turned mounting flanges on their outer sides,

said front and rear guiding rails being of angled metal with mounting flanges turned parallel to the plane of said chain loop, and

front and rear upright connecting bars connected to the flanges on said rails and said top and bottom support tracks.

5. An article storage and display device as defined in claim 4 in which said front and rear upright bar retaining tracks are of angled cross section with laterally turned parallel flanges forming their bar retaining portions,

the lower ends of said laterally turned flanges being curved toward the ends of said top and bottom rails to form said curved connecting means, and

top and bottom cross bars connected to said front and rear upright connecting bars and to said front and rear bar retaining tracks.

6. An article storage and display device as defined in claim 4 in which said recess in said top and bottom pawl supporting rails are slots formed in the sheet metal of the rails, and

chain supporting and guiding ribs secured to said rails.

7. An article storage and display device as defined in claim 4 in which said pawl supporting rail and bar supporting track are integral pieces of folded metal at the top and bottom of the device.

References Cited UNITED STATES PATENTS 707,200 8 1902 Bollinger. 2,836,303 5/1958 Lyon 2lll.5

' FOREIGN PATENTS 25 9,709 10/ 1926 Great Britain.

ROY D. FRA ZIER, Prim ry Examiner. R. P. SEITTER, Assistant Examiner.

Claims

1. IN AN ARTICLE STORAGE AND DISPLAY DEVICE HAVING CONVEYOR CHAINS ARRANGED IN SPACED, UPRIGHT, GENERALLY RECTANGULAR LOOPS, WITH PAIRS OF LEADING AND TRAILING PAWLS CONNECTED TO THE CHAINS IN TWO EQUALLY SPACED POSITIONS AROUND SAID LOOPS, SPROCKETS LOCATED IN THE CORNERS OF SAID LOOPS, AND THREE ARTICLE SUPPORT RODS EXTENDING BETWEEN SAID LOOPS TO BE ADVANCED BY SAID PAWLS BETWEEN FOUR POSITIONS LOCATED ADJACENT THE CORNERS OF THE LOOPS, CHAIN AND ROD GUIDING AND PAWL SUPPORTING MECHANISM COMPRISING: TOP AND BOTTOM CHAIN AND PAWL SUPPORTING RAILS EXTENDING LATERALLY INWARDLY ACROSS THE PLANE OF SAID LOOPS WITH THE TOP RAIL BELOW THE TOP REACH OF THE ASSOCIATED LOOP AND THE BOTTOM RAIL ABOVE THE BOTTOM REACH OF THE ASSOCIATED LOOP, WITH THE CHAINS ENGAGED WITH LATERALLY INWARDLY SPACED CENTRAL PORTIONS OF THE RAILS, TOP AND BOTTOM BAR SUPPORT TRACKS POSITIONED IN LATERALLY OVERLAPPING RELATION TO THE OUTER PORTIONS OF SAID CHAIN AND PAWL SUPPORTING RAILS WITH THE TOP BAR SUPPORT TRACK LOCATED ABOVE THE TOP SUPPORT RAIL AND THE BOTTOM BAR SUPPORT TRACK LOCATED BELOW THE BOTTOM PAWL SUPPORTING RAIL, BAR RESTRAINING DETENTS ON SAID BAR SUPPORTING TRACKS ADJACENT THE ENDS THEREOF, FRONT AND REAR UPRIGHT BAR RETAINING TRACKS EXTENDING BETWEEN THE ENDS OF SAID TOP AND BOTTOM BAR SUPPORTING TRACKS WITH CURVED MEANS CONNECTING THE UPRIGHT TRACKS TO THE ENDS OF THE BOTTOM BAR, UPRIGHT FRONT AND REAR CHAIN AND PAWL GUIDING RAILS DISPOSED IN SPACED RELATION TO THE INNER SIDES OF SAID FRONT AND REAR TRACKS AND HAVING THEIR ENDS SPACED FROM THE ENDS OF SAID TOP AND BOTTOM RAILS, SPROCKETS ENGAGING SAID CHAIN LOOP AND POSITIONED IN CHAIN TRANSFERRING RELATION BETWEEN THE ENDS OF THE RAILS, SAID PAWLS HAVING U-SHAPED CROSS SECTIONS WITH SIDE FLANGES PROJECTING INWARDLY OF SAID CHAIN LOOP TO ENGAGE SAID RAILS, FIRST PIVOT PINS CONNECTING THE LEADING ENDS OF SAID LEADING PAWLS TO SAID CHAIN IN LATERALLY OPPOSITE OFFCENTER BUT STRADDING RELATION TO THE OUTSIDE OF SAID CHAIN LOOP, SECOND PIVOT PINS CONNECTING THE LEADING OF SAID TRAILING PAWLS IN SPACED RELATION BEHIND SAID LEADING PAWLS AND IN LATERALLY OPPOSITE OFF-CENTER BUT STRADDLING RELATION TO THE OUTSIDE OF SAID CHAIN LOOP WITH EACH TRAILING PAWL OFF-SET OPPOSITELY TO ITS ASSOCIATED LEADING PAWL, MEANS ON THE INSIDES OF THE SIDE FLANGES OF SAID PAWLS FORMING STOPS DISPLACED IN TRAILING RELATION TO PIVOT PINS CONNECTED THERETO, STOP PINS PROJECTING FROM SAID CHAIN IN OVERLYING RELATION TO SAID STOPS OUTWARDLY OF SAID CHAIN LOOP, FIRST PAIRS OF LONGITUDINAL RECESSES FORMED IN SAID TOP AND BOTTOM SUPPORT AND GUIDE RAILS AND LOCATED NEAR THE FRONT ENDS THEREOF TO RECEIVE THE TRAILING EDGES OF THE SIDE FLANGES ON THE LEADING PAWL OF ONE OF SAID PAIRS AND THE SIDE FLANGES OF THE TRAILING PAWL OF THE OTHER OF SAID PAIRS OF PAWLS TO PERMIT INWARD TILTING OF THE PAWLS TO PASS SUPPORT BARS ENGAGED WITH THE DETENTS IN SAID FRONT ENDS, AND OTHER PAIRS OF LONGITUDINAL RECESSES FORMED IN THE REAR ENDS OF SAID TOP AND BOTTOM RAILS IN LATERALLY OPPOSITELY OFF-SET RELATION TO SAID FIRST PAIRS OF RECESSES TO RECEIVE THE TRAILING EDGES OF THE SIDE FLANGES OF THE LEADING PAWL OF SAID OTHER OF SAID PAIRS OF PAWLS AND THE SIDE FLANGES OF THE TRAILING PAWL OF SAID ONE OF SAID PAIRS OF PAWLS.