Apparatus for racking sheet materials

This invention relates to an apparatus for racking sheet materials characterized by an open-sided generally box-like rack having opposed sets of horizontally-disposed guiderails arranged in stacked relation one above the other to define tray tracks along the inside of the front and rear walls thereof. Slat-bottomed double-ended trays are mounted on the tracks for independent movement from a retracted position essentially centered within the rack to either one of two extended positions overhanging a side of the latter. Tray transfer means are provided for each tray accessible in the center of one end of the rack operative upon actuation, to drive a particular tray in either direction between its retracted and extended positions. A tool carriage is mounted on vertically-disposed tracks on the end of the rack with access to the tray transfer means for movement therealong into alignment with any of the tray transfer means. A tray transfer drive is mounted on said tool carriage for relative movement between a disengaged position and an engaged position operatively coupled to a selected tray transfer means upon being aligned therewith. And, a control mechanism interconnecting said tray transfer drive and a tray responsive to movement of the tray into one of its fully-extended positions, and partially disabling said transfer means by preventing its being used to move the extended tray in the direction in which it is extended.

In our U.S. Pat. No. 4,073,382, the assignee hereof disclosed a 
steel-racking apparatus characterized by two tiers of open-sided 
drawer-like receptacles especially designed to receive and store elongate 
structural members like, for example, pipe, tubes, beams, rods and the 
like. Both tiers of drawers were arranged in back-to-back relation inside 
a common centrally-positioned rack. Each drawer moved independently of the 
others out only one side of the rack but nothing prevented two or more 
drawers of the same or other tier from being opened at the same time nor 
did it make much difference since the drawers did not open very far and 
the center of mass of the loads carried therein stayed in relatively close 
to the rack where it would become virtually impossible to create a 
condition of imbalance sufficient to tip the apparatus over even if all 
the drawers on one side were open while those in the other tier were left 
closed. A single elevator ran up and down the rack at one end thereof in 
the usual fashion but, in addition, it had the capability of shifting 
laterally to either side where the drawer-actuating controls for each tier 
were located. In fact, when used as the center racking apparatus in a set 
of three, only the middle one needed to be equipped with an elevator since 
the operator could use it to service the adjacent tiers in the units 
alongside thereof. 
Elongate structural shapes and the like are, of course, but one type of 
material handled in a steel warehousing or fabricating operation and, when 
the time came to adapt the principles of the aforementioned patented rack 
to sheet materials, it was found to be seriously deficient. To begin with, 
the loads were heavier and the horizontal area thereof was substantially 
greater thus necessitating the use of receptacles or other extendable 
supports which opened a great deal farther than the open-ended drawers of 
the earlier rack. Even the conventional equipment used around a warehouse 
for handling the two different types of material (sheets vs. beams, etc.) 
differed substantially and, for this reason, demanded specially designed 
receptacles to be compatible therewith. 
For these and other reasons it became apparent that, for all practical 
purposes, the sheet-racking apparatus had to be completely redesigned 
although, as will appear presently, certain concepts that proved 
successful in the earlier unit were carried over into the instant one in 
modified form. To begin with, back-to-back tiers of receptacles portended 
serious problems of imbalance, potentially dangerous overhanging loads, 
extra heavy structures, difficulties with the drive mechanism, etc.; 
therefore, the double-tiered concept was bypassed in favor of a novel 
single tier of trays extendable on either side of a central support 
structure that utilizes the load on one end of the tray to partially 
counterbalance the overhanging load on the other end thereof when 
extended. Then, instead of separate drawer-actuating mechanisms for each 
drawer of back-to-back tiers thereof, only a single set of tray transfer 
mechanisms were needed placed centrally in the rack. 
As far as the elevator is concerned, the overall much greater width of the 
sheet rack suggested that the single elevator of the earlier unit be 
replaced by a double-cage elevator, each cage being offset toward one side 
of the unit while retaining the capability of moving sidewise to better 
control the loading and unloading of an extended tray. Both cages, when 
retracted, lie offset alongside the center column in position to raise and 
lower the tray transfer drive mechanism as well as couple and decouple the 
latter from a particular one. 
One of the most novel features, however, was the design of a lock-out 
mechanism which uniquely combined a tray actuated switch with a reversible 
electric motor so as to effectively prevent a second tray from being 
extended until the first one was retracted thus, insuring that no more 
than one loaded tray overhangs the rack at a time. 
Running up and down the center of the rack on rails is a single tray 
transfer mechanism drive selectively coupleable to individual tray 
transfer mechanisms for the purpose of extending and retracting them. This 
drive is reversible and accessible from either of the two elevator cages. 
It is, therefore, the principal object of the present invention to provide 
a novel and improved racking apparatus for sheet materials and the like. 
A second objective is the provision of a device of the class described 
which is particularly well suited to the storage and retrieval of heavy 
sheet materials such as steel plate and the like that must be loaded and 
unloaded with overhead cranes. 
Another object of the within described invention is to provide a rack with 
extendable slat-bedded trays capable of supporting the sheets in position 
to be placed and retrieved by hooks hooked under opposite marginal edges 
thereof. 
Still another object is to provide a rack for sheet steel and the like 
using double-ended trays, half of which are loaded from one side and the 
other half from the opposite side with one loaded half effectively 
counterbalancing the other when the latter is extended. 
An additional object is the provision of a rack of the type aforementioned 
wherein the trays themselves in fully-extended position effectively 
program the tray actuator drive so that it cannot function to extend a 
second tray until the first tray is retracted. 
Further objects are to provide a sheet material racking apparatus which is 
versatile, safe, reliable, easy to operate, rugged, compact and even 
somewhat decorative.

Referring next to the drawings for a detailed description of the subject 
matter depicted therein and, initially, to FIGS. 1, 7, 14 and 15 thereof 
wherein the entire unit is shown, reference numeral 10 has been selected 
to broadly designate the racking apparatus in its entirety while numerals 
12 and 14 have been similarly used to refer to the trays and the box-like 
frame housing them, respectively. In like manner, numeral 16 broadly 
designates the double-cage elevator, the cage on the right being 16R and 
the one on the left 16L. Between these cages is located the drive that has 
been generally referred to by reference numeral 18 and which moves both 
vertically and from front to rear into selective and independent operative 
engagement with one of the tray transfer mechanisms that have also been 
indicated in a general way by reference numeral 20. 
The frame 14 includes, in the particular form shown, four open rectangular 
nearly-identical subframes 22 standing on edge and extending from front to 
rear in transversely-spaced parallel relation. Crosspieces 24 and 26 
connect these subframes together at the front while a single crosspiece 28 
does so along the bottom at the rear thereof. As illustrated, a short 
crosspiece 30 is used at the upper rear (FIG. 15) connecting only the two 
inboard subframes 22 together. Other transversely-extending elements also 
interconnect the subframes, these taken the form of tray guiderail 
subassemblies 32 which will be discussed in detail presently in connection 
with FIGS. 3, 4 and 5. 
The racking apparatus shown in essentially free standing although it can, 
of course, be fastened down to the warehouse floor and made a permanent 
installation. The vertical load at the upright posts is considerble, 
therefore, load-spreading pads (not shown) can be used at these and other 
points of maximum load concentration should the need for them arise. 
It becomes apparent that the frame 14 in its basic form is an open-sided 
box with a floor 34 (FIG. 1) laid over the bottom horizontal frame members 
36 of each subframe 22. It contains no partitions and the front and rear 
ends thereof that have been broadly designated with reference numerals 38 
and 40, respectively, carry the horizontally-disposed tray guiderail 
subassemblies 32 which support the individual trays 12 in tiered relation 
for independent horizontal rolling movement therealong between retracted 
and extended positions. Each of the several trays extends lengthwise 
approximately the full width of the rack and is accessible from both sides 
of the latter. The right elevator cage 16R when in the extended phantom 
line position of FIG. 7 services the trays when extended to the right and 
the left elevator cage does likewise when the trays are extended out in 
the opposite direction. With the elevator cages retracted into position 
alongside the center of the rack, both place the operator in position to 
operate the tray transfer mechanisms. One of these transfer mechansisms 
is, of course, actuated to extend a selected tray before the need arises 
to extend the elevator cage into position for monitoring the loading and 
unloading thereof. 
Next, with particular reference to FIGS. 2-6, inclusive, the trays together 
with the mountings and transfer mechanisms therefore will be described in 
detail. Each of the several trays in the particular form shown is bordered 
on both sides by I-beam-like members 42 from which the lower outboard 
flange has been removed and replaced by a length of sprocket chain 44 
connected between spaced connectors 46. The opposed channels 48 on the 
inside of these beam-like members are bridged by transversely-extending 
heavy metal ribs or slats 50 arranged in longitudinally-spaced essentially 
parallel relation beginning at points spaced inwardly slightly from the 
beam ends. While not illustrated, these slats are preferably removable so 
that they can be rearranged to provide different spacings to accommodate 
various size sheets and loads. The slatted tray bed 52 thus formed is 
ideally suited to accept a load 54 laid atop thereof by the conventional 
sheet loading and unloading apparatus that has been identified by numeral 
56 in FIG. 2. The opposed hooks 58 on opposite ends of the pick-up fingers 
60 can lay down the load on the slats and move into extended disengaged 
position without being interfered with by the latter. 
FIG. 3 most clearly reveals the guiderail subassemblies 32 upon which the 
trays move horizontally between their extended and retracted positions. In 
the particular form shown, these subassemblies each include a pair of 
angle iron rails 62 extending crosswise of the front and rear faces 38 and 
40 of the frame 14 so disposed relative to one another that a pair of 
their flanges 64 lie in spaced parallel track-forming relation. A series 
of rollers 66 fastened to the web 68 of frame elements 42 at spaced 
intervals throughout the length thereof roll within the track defined 
between these rails. A cover plate 70 bridges the gap between the 
track-forming flanges 64 of rails 62 in the particular form illustrated. 
In FIGS. 2 and 3, it can be seen that the vertically-disposed flange 72 of 
the upper rail 62 of each pair also defines a track along which roller 74 
depending from the upper outboard flange 76 of beam element 42 can roll. 
These rollers 74 are mounted for rotation about vertical axes and several 
of them lie spaced throughout the length of the beam. A like set of 
rollers is placed on both sides of each tray cooperating with one another 
to maintain the latter centered with respect to its tracks. 
FIGS. 2, 4, 5 and 6 to which detailed reference will now be made all reveal 
certain features of the tray transfer mechanism 20. Centered beneath each 
tray in the tier is a longitudinally-extending shaft 76 journalled for 
rotation within bearing blocks 78 fastened to an extension 80 of the 
downturned vertical flange 82 of the lower of the pair of guiderails 62. 
The tray guidance system already described as well as all but one element 
of the tray transfer mechanism 20 is duplicated on both the front 38 and 
the rear 40 of the rack. Thus, the drive sprockets 84 fixed to opposite 
ends of each drive shaft 76 are both operatively engaged in sprocket 
chains 44 running along the sides of the trays. Clockwise rotation of the 
drive shaft as viewed in FIG. 5 will, of course, result in the tray 
associated therewith extending to the left and vice versa. In the 
particular form shown, each of the sprocket chains is reaved over a pair 
of vertically-adjustable idler sprockets 86 (FIG. 5) spaced on opposite 
sides of the drive sprocket that cooperate with the latter to keep the 
driving connection tight. Turning of the drive shaft, therefore, 
simultaneously drives both sides of each tray in the same direction and, 
of course, at the same speed. The only difference between the tray 
transfer mechanisms on the rear of the rack and those on the front is the 
presence of an extension 88 on the front shaped to detachably receive a 
crank or other tray mechanism drive 18 which will be described presently. 
Before proceeding with a detailed look at the remaining figures of the 
drawings, mention should, perhaps, be made of the switch actuator kickers 
90 on each tray located spaced inwardly of each end thereof as shown most 
clearly in FIGS. 2, 4 and 15. These kickers are confined to the rear frame 
element 42 of each tray. They function in a manner to be explained 
presently to shut off and partially disable tray transfer drive 18 once a 
given tray has reached its fully-extended position. 
Looking next at FIGS. 1, 7, 8, 9, 10 and 14, it can be seen that each of 
the outboard front subframe uprights 92 cooperates with the corresponding 
upright of the inboard subframe adjacent thereto to define a pair of 
vertically-disposed parallel rails upon which one of the two elevator 
cages 16 rides up and down the box-like frame. As was previously 
mentioned, the four subframes 22 are almost exactly alike, but not quite, 
in that the front uprights 92 of the outboard subframes have marginal 
flanges 94 thereon that extend outwardly while the corresponding upright 
92m of the adjacent inboard subframe has its flange 96 extending inwardly. 
Now, each elevator subassembly has a rectangular cage-supporting frame 98 
with vertically-disposed angle irons 100 at each end having inturned 
flanges 102 extending at right angles across the edges of the flanges 94 
and 96 on the subframe uprights 92 and 92m as is most clearly revealed in 
FIG. 8. These inturned flanges are apertured as shown at 104 in FIG. 10 to 
receive the anti-friction rollers 106 that run along the edges of the 
subframe upright flanges. Other anti-friction rollers 108 and 110 carried 
by these same inturned flanges 102 roll along opposite faces of flanges 94 
or 96 as the case may be. Thus, rollers 106, one pair of which is located 
at the top of the frame 98 while a second pair is located at the bottom, 
cooperate to keep it from tilting or binding as it runs up and down the 
tracks defined by subframe upright flanges 94 and 96. Outside and inside 
roller pairs 108 and 110 are, likewise, located at all four corners of 
cage-supporting frame 98 and they cooperate to keep it from tilting 
outwardly as it rides up and down its tracks. 
FIGS. 1, 7, 8 and 14 all show the wire cages 112 that are attached to the 
cage-supporting frame 98 for movement between the full line retracted 
position of FIG. 7 and the phantom line extended one. Grooved rollers 114 
(FIG. 8) ride along the parallel top and bottom margins of the frame 98 
supporting the cage for transverse movement along the latter between its 
extended and retracted positions. Other features of the connection between 
the elevator cage and the supporting frame 98 therefore such as, the limit 
stops, latches, etc., remain essentially the same as the earlier patent 
already mentioned and no useful purpose would be served by going over them 
again. There are, however, certain differences in the elevator hoist 
mechanism and the controls therefor which will be set forth briefly in 
connection with FIGS. 1, 7, 14 and 15 to which reference will now be made. 
To begin with, a pair of driven shafts 116 are journalled for rotation 
between the track-forming subframe uprights 92 and 92m at the bottom 
thereof while a single drive shaft 118 extends all the way across the top 
in spaced parallel relation above the latter. The upper shaft 118 carries 
two pairs of transversely-spaced sprockets 120 over which are reaved 
lengths of sprocket chain 122. Shafts 116, on the other hand, carry simple 
pulleys 120m vertically aligned with the sprocket 120 thereabove. In the 
particular form shown, the cage drive comprises half cable 124 and half 
sprocket chain 122, the sprocket chain part running over the sprocket and 
down the front of the rack to its point of attachment to the top of the 
cage-carrying frame 98 while the cable part runs from the other end of the 
chain underneath by pulley 120m and up to its point of attachment to the 
bottom of the cage frame as shown most clearly in FIG. 14. The element 122 
could, of course, be all sprocket chain but to do so would entail extra 
expense since only a little over half ever reaches sprocket 120. 
The upper of the two shafts 118 comprises the drive shaft of cage-elevating 
reversible gear motor 128 suspended from the underside of the rack at the 
front thereof offset to one side of the tray transfer mechanisms and 
shafts 76 thereof. Mounting the elevator drive motor 128 in the top of the 
rack has certain advantages in terms of keeping the power cord 134 out of 
the way and eliminating the more complex and expensive sliding control of 
the earlier patent. 
Mounted in the front of the rack at the top and bottom as seen in FIG. 7 
are transversely-spaced pairs of vertically-aligned pulleys 136. 
Counterweights 132 move up and down the rack behind each elevator cage 
attached thereto by a cable 140 passing from the counterweight, up and 
over the top pulley 136 of the pair and down to a point of attachment 138 
(FIG. 7) atop the cage-supporting frame 98. A second length of cable 142 
attaches to the bottom of the counterweight 132 and is reaved around the 
lower pulley of each vertically-aligned pair to its point of attachment 
144 on the lower edge of the cage frame. 
Both elevator cages, of course, share the common drive motor 128 which is 
reversible and controlled by either one of the two switches 146 mounted on 
top of the cage-supporting frame for vertical movement therewith. This 
switch does not move from side to side with the cage because, once the 
elevator is at the proper height, it is not used while the cage is 
extended. Actually, elevator drive motor 128 is not controlled directly by 
switches 146, but instead by a more complex control circuit complete with 
limit switches, automatic reversing capabilities and other features well 
known in the elevator control art; however, no useful purpose would be 
served by detailing such circuitry since it forms no part of the instant 
invention. 
As previously noted, the sliding switch contact of the earlier patent has 
been done away with and replaced by a counterweighted power cord 
retraction subassembly that has been most clearly revealed in FIGS. 7, 14 
and 15 to which detailed reference will now be made. Power cord 134 is run 
from switch 146 up over yet another pulley 148 mounted in the top front of 
the rack and back over the top of the rack to a pulley 150 attached to 
rear upright 152 of the outboard subframes 22. After passing over the 
latter pulley, it is reaved through a running block 154 carrying a 
counterweight 156 and back up again to a junction box 158 mounted on the 
rear upright 160 of the adjacent inboard subframe 22. Thus, as the 
elevator moves up and down the front of the rack, the power cord 
controlling it has the slack taken out of it by counterweight 156 that 
rides up and down the back of the rack in a direction opposite that of the 
cage frame 98. From junction box 158, the power cord, of course, connects 
into the motor control circuit (not shown). 
The remaining features of the invention that require detailed examination 
all have to do with the tray transfer mechanism drive 18 for which purpose 
reference will be made to FIGS. 7, 9, 11, 12, 13, 15, 16 and 17. On the 
front of the rack centered between the inboard subframes 22 are a pair of 
spaced parallel rails 160 attached to the upper and lower crossframe 
elements 24 and 26, respectively. An open rectangular frame 162 rides up 
and down the track defined by these rails 160 on rollers 106m and 110m 
that are mounted and function in a similar manner to their counterparts in 
the cage-carrying frame 98 already described in detail. In other words, 
rollers 106m roll along the inside of the rails 160 in much the same way 
as rollers 106 ride along the edge of flange 96 while rollers 110m 
similarly roll along the front and rear faces of the aforementioned 
guiderails. Also, in a manner analogous to the previously-described 
counterweight systems, a cable 164 is attached to the top edge of frame 
162 intermediate the side margins thereof and reaved over pulleys 166 and 
168 onto the back side thereof where it is attached to counterweight 170. 
In FIGS. 12 and 13, it can be seen that side frame elements 172 each carry 
a vertically-spaced pair of fixed blocks 174 having opposed V-shaped 
grooves 176 therein that receive V-shaped slides 178 for horizontal 
slidable movement toward and away from the box-like frame 162. 
Particularly in FIG. 12, it can be seen that a rectangular tool carriage 
180 carries slide blocks 178 in the corners thereof and also mounts the 
reversible electric tray actuator drive motor 182. This drive includes a 
female chuck 184 adapted to mate and form a driving coupling with selected 
shaped extensions 88 (FIG. 6) used to drive the trays in and out. By 
pulling carriage 180 out toward the operator, chuck 184 disengages from 
the shaft to which it was operatively coupled thus enabling the 
rail-mounted frame 162 to be raised or lowered as desired to another level 
on tracks 160 preparatory to reconnecting it to another of the tray 
transfer mechanisms; whereupon, moving the carriage inwardly again and, 
perhaps, rotating the chuck a few degrees will accomplish the desired 
driving connection since not all the shafts will stop in a position for 
the chuck to receive them. It should, perhaps, be mentioned that the loads 
carried by the trays are usually so heavy that manual actuation of the 
trays becomes impractical; hence, the need for the electrically-powered 
unit. 
FIGS. 9, 11 and 12 show the junction box 186 with the power cord 188 
emerging therefrom. This box together with the three control switches 190 
are all mounted for movement with frame 162 on a bracket 192 attached to 
the latter. Thus, the tool carriage moves in and out independently of the 
switches controlling the drive carried thereby. 
Of the three switches 190, 190L and 190R, one 190 is an on/off switch while 
the other two 190R and 190L are directional control switches that are 
operative to arcuate the drive in a particular direction, i.e. right or 
left. With the on/off switch "on", at least one of the directional control 
switches, and perhaps both, become operative to rotate the chuck into 
position to receive the drive shaft coupling 88. Under certain conditions, 
however, one or the other of the directional control switches is disabled 
thus preventing its being used to extend a tray. One switch of the two 
always remains operative to retract a tray and, upon retraction of an 
extended tray, the companion directional control switch becomes operative 
again in a manner which will now be set forth in detail in connection with 
FIGS. 15, 16 and 17. 
Journalled for rotation in the back of the rack offset to one side of the 
counterweight 170 and its support cable 168 is a vertically-disposed shaft 
194. Fastened to this shaft normally extending straight forwardly out over 
the adjacent side margins of the trays in the path of the kickers 90 as 
shown in FIG. 16 are a series of arms 196. Each tray, as it moves into 
fully-extended position on either side of the rack, will cause one of its 
kickers 90 to engage the arm 196 aligned therewith and rotate the shaft 
one direction or the other, shaft 194 having been shown rotated to the 
left in FIG. 15. 
On the very top of shaft 194, it carries a plate 198 rotatable therewith. 
This plate is essentially horizontal and it has a notch 200 on one side of 
the shaft and a somewhat larger generally V-shaped notch 202 on the other. 
Underneath notch 200 and offset on the same side of shaft 194 is a 
three-position switch 204 mounted on a suitable bracket 206 fastened atop 
the uppermost tray guiderail 72. The switch is of a standard type having a 
rotatable post 208 movable from a centered position to either of two 
shifted positions on opposite sides of its centered position. As 
illustrated, a crank arm 210 is attached to the post extending out over 
notch 200 in plate 198 where it carries a roller 212 seated in the latter. 
Clockwise rotation of shaft 194 and plate 198 carried atop thereof into 
the phantom line position shown in FIG. 17 will, of course, shift the 
switch from its centered position rearwardly. This rearward actuation of 
switch 204 is, of course, the result of a tray moving into extended 
position out the left side of the rack as viewed by the operator (FIG. 7). 
Switch 204 is so connected in the circuit controlling tray drive 18 that 
the winding of the motor which functions to turn chuck 184 anti-clockwise 
is opened and disabled. Thus, as soon as switch 204 is actuated to its 
rear position shown in phantom lines by clockwise rotation of shaft 194, 
the tray being extended to the left stops since the electric motor driving 
chuck 184 has shut off. As such, switch 204 overrides the left direction 
control switch 190L by opening the circuit containing same. Now, in the 
rear position just described, switch 204 leaves the motor winding active 
which will turn chuck 184 clockwise upon actuation of right direction 
control ssitch 190R to its closed position. This means, of course, that 
once the extended tray is loaded or unloaded as the case may be, closure 
of the main on/off switch 190 along with right directional control switch 
190R will start the chuck drive motor through closed contacts of switch 
204 connected to the clockwise motor winding. 
Now, as soon as the extended tray starts to the right back into the rack, 
its kicker 90 on the right end leaves arm 196 and frees shaft 194 along 
with its plate 198 to return to its centered full line position. It is 
normally biased into this centered position by an arm 214 mounted for 
limited angular movement about a vertical axis 216 intermediate its ends 
located on the opposite side of shaft 194 from the switch 204. This arm 
214 also carries a roller 218 on one end that is received within the 
V-shaped notch 202 in plate 198. A tension spring 220 is attached to the 
opposite end of arm 214 and to a fixed abutment 222 forming a part of 
mounting bracket 224. Abutment 222, spring 220, and arm 214 are aligned 
with shaft 194 and the bottom of the V-shaped notch when plate 198 is 
positioned to place switch 204 in centered position, this being the full 
line relationship of the parts shown in FIG. 17. With these parts shifted 
into the phantom line position of FIG. 17, tension spring 220 is, of 
course, stretched and it acts to bias arm 214 back into its full line 
centered position to which it returns as soon as the tray kicker 90 
releases arm 196. It should be noted that there are many other 
arrangements for biasing the switch 204 into its centered position 
including springs within the switch itself; however, the particular 
mechanism shown is advantageous since it is positive, visible to the 
operator and powerful enough to insure that shaft 194 always returns to 
its neutral position in which the arms 196 carried thereby face directly 
to the front. 
While positive mechanical stops (not shown) are also used to insure that 
the trays can only extend out about one-third of their overall length, 
cut-off switch 204 is fully effective for this same purpose since as soon 
as the power to a particular winding of chuck drive motor 182 is cut-off, 
the tray coasts an inch or two to a complete stop. It should be apparent 
also that once a tray is extended fully, the tray drive cannot be actuated 
to extend a second tray out the same side of the rack. Conceivably, the 
tray transfer drive could be shifted to another tray and actuated to send 
a tray into extended position on the opposite side of the rack since the 
reverse direction drive remains active; however, as a practical matter, 
this is never done and all the operations on a given tray are completed 
before working with another. As a matter of fact, it is very often 
difficult to release the chuck from one shaft for placement on another 
when the chuck can only be turned in one direction as it not infrequently 
binds a bit on the shaft. On the other hand, with all the trays retracted 
and the tray actuator drive fully operative, it becomes a simple matter to 
align the chuck axially with a particular shaft and rotate it one way or 
the other a few degrees to make the driving coupling therebetween. This 
becomes possible as soon as the shaft 194 frees switch 204 to return to 
its centered position. 
Finally, a few words of further explanation need to be said concerning 
on/off switch 190 and the right and left direction control switches 190R 
and 190L associated therewith. Switch 190 is a simple two position switch 
that will remain in either its "on" or "off" positions without being held. 
Conversely, both the direction control switches are normally biased into 
open position and must be held closed. Accordingly, when the operator 
wishes to extend a tray to the left, he must first actuate the on/off 
switch to its "on" position and then hold left position switch 190L 
actuated until the tray reaches its fully-extended position, whereupon, 
the cut-off switch will function to cut-off the circuit rotating the chuck 
anti-clockwise. Once the chuck stops rotating and the tray coasts to a 
stop, switch 190L can be released to its open position since it is no 
longer a functional part of the motor control circuit. Following 
completion of the operations with the extended tray, right direction 
control switch 190R is held closed and the chuck turns clockwise through 
the circuit that remains complete across the closed contacts of switch 
204.