Stacking device for plate-like objects, in particular titer plates or the like

Disclosed is a stacking device for stacking and unstacking plate-shaped objects such as titer plates. A magazine is provided to hold the titer plates and a support plate is provided beneath the titer plates. A clamping device is provided to hold the bottom-most titer plate or second titer plate from the bottom. The clamping device preferably has two opposing, horizontal clamping beams which are forced by means of springs against the respective titer plate and which can be moved synchronously away from the titer plate by a motor via a linkage. The clamping beams can also be rotated about a vertical axis so as to adapt to titer plates having different shapes.

FIELD AND BACKGROUND OF THE INVENTION 
The invention relates to a stacking device for plate-like objects, and in 
particular for titer plates or the like, which includes a magazine for 
holding a stack of the titer plates, a support plate or the like which can 
be moved between an upper and a lower limit point, a clamping device for 
clamping the titer plates in the magazine, and at least one spring for 
biasing the clamping device against the titer plates. 
In medical laboratory technology, for example, the Elisa process is used to 
measure antigens and/or antibodies (enzyme linked immunosorbent assay). 
For example, in order to measure antigens, antibodies are first absorbed 
on the titer plate; the titer plate is then washed; and in a subsequent 
process step, a test liquid containing the antigen is admixed. The next 
step includes a washing after which enzyme-marked specific antibodies are 
put on the titer plate. The titer plate is washed again, whereafter a 
substrate for the enzyme is admixed. Actual measurement of the antigens 
and/or antibodies is performed in a photometer. 
For use of either the photometer or the washing device, it is necessary to 
have the titer plates unstacked and fed individually thereto. 
Once the titer plates leave either the photometer or washing device, it is 
then necessary for the titer plates to be stacked again. 
During the stacking and unstacking process, the fact that the dimensions of 
titer plates are not completely uniform, that is, that the individual 
plates may differ in thickness, in width or in the fact that a plate may 
or may not have an additional lateral edge, has been demonstrated to 
create a problem with respect to holding the plates. 
Prior art stacking devices have attempted to overcome this problem by 
adjusting the device to the specific dimensions of each titer plate. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a stacking device of the 
aforementioned kind with which it is possible to stack or unstack 
different kinds of titer plates without having to make special adjustments 
for each different titer plate. 
This object is achieved by the present invention by providing a stacking 
device for titer plates which comprises a clamping device having two 
opposing horizontal clamping beams or members which are adapted to be 
moved synchronously away from the titer plates by means of a motor and 
which are arranged so as to be rotatable around vertical axis-defining 
pins. 
Such an arrangement, according to the invention, allows the stack of titer 
plates to comprise different titer plates. The clamping beams are not 
forced against the titer plates by the motor but rather by means of 
springs. This allows the stacking device to accommodate titer plates 
having varying widths and to always uniformly hold them securely. 
Preferably, each clamping beam has two contact projections which contact 
the titer plates and are, for example, formed by flat ribs or flanges 
extending inwardly from the clamping beams. These contact projections 
facilitate the uniform and secure holding of the titer plates, even if the 
height of the titer plates is not uniform. Each contact projection is 
provided with a rough coating in order to improve the holding contact 
between the contact projections and the titer plates. Preferred coating 
materials for this purpose are tungsten carbide or diamond, since these 
will provide a hard and disinfectable surface. 
In order to prevent the stack of plates from sliding downwardly in case of 
an accident, inwardly biased pins may be movably mounted to the clamping 
beams below the position of the contact projections and can be moved 
relative to the clamping beam so as to extend and be biased inwardly from 
the clamping beams a distance further than the contact projections. The 
pins are preferably biased inwardly by extremely weak leaf springs so that 
when the clamping beams are clamped against the second titer plate from 
the bottom of the stack, the pins are biased inwardly against the 
bottom-most titer plate but do not exert a holding force thereagainst. 
While the spring force is weak, it is sufficient to cause the pins to 
extend inwardly to engage beneath a downwardly sliding titer plate. 
The motor is advantageously connected to the clamping beams via a linkage 
which provides sufficient play so as to allow the clamping beams to adapt 
to titer plates having varying widths. This play is possible because the 
contact between the clamping beams and the titer plates is caused by the 
springs rather than by the motor. The linkage includes two pairs of racks, 
each of which includes an outer and an inner rack. Each of the inner racks 
is connected to the clamping beam on one side of the titer plates and each 
of the outer racks is connected to the clamping beam on the opposite side 
of the titer plates. Gear wheels are mounted between the inner and outer 
racks of each rack pair and positively engage with teeth formed thereon 
such that when the inner racks are moved in one linear direction, the 
outer racks are caused to move in the opposite linear direction. The two 
inner racks are mutually connected by a cross rod which has a pin fixedly 
mounted thereon. The motor has an eccentric drive pin or shaft which is 
connected to the pin of the cross rod by a rod having apertures in each 
end which receive the eccentric drive pin and the cross rod pin, 
respectively. 
The play provided by the linkage can be provided by making each of the 
apertures at the ends of the rod, which connects the motor to the cross 
rod, sufficiently large to loosely encircle the respective pin which the 
aperture receives. Alternatively, the aperture which receives the 
eccentric drive pin can be of a size which causes it to rotatably but 
closely encircle the pin, and the aperture at the other end of the rod can 
be foremd as a longitudinal slot so as to slidably encircle the pin. The 
longitudinal slot is formed in such a manner that the perimeter of the 
longitudinal slot forms a stop which prevents any one of the titer plates 
from being clamped too tightly by the clamping beams. 
The invention may also provide for the clamping beams to be moved 
vertically from a bottom position of rest to a top position in which the 
titer plates held by the clamping beams are barely below an upper limit 
point of the support provided by a magazine which holds the stack of titer 
plates. This is an advantageous feature because it allows the titer plates 
to be stacked, unstacked and transferred with absolutely no vibrations 
induced in the titer plates by the support plate. Without such a feature, 
the support plate may jolt the titer plates when moved upwardly to support 
them due to lack of precision in positioning the support plate. Similarly, 
if the lack of precision causes the support plate to be positioned 
slightly below the bottom of the bottom-most titer plate, the titer plates 
will be jolted when released from the clamping beams because they will 
fall onto the support plate. The vertical adjustability of the clamping 
beams nullifies this problem such that vibrations are not induced in the 
titer plates. It is also contemplated that the clamping beams may be 
biased downwardly by a spring into their bottom rest position. 
Another embodiment of the invention provides that the clamping beams have 
preferably rib-like projections extending inwardly toward the titer plates 
from bottom edges of the clamping beams so as to extend beneath the titer 
plate which is being held by the clamping beams. These rib-like 
projections, like the inwardly biased pins, will prevent a sliding titer 
plate from falling through the clamping beams. These projections are 
shaped so as to allow the titer plates to be restacked. 
It is also contemplated that the invention may include a hangar-shaped 
carrier used for feeding a titer plate from one magazine to another. 
Preferably, the carrier has a center rib disposed parallel to one side of 
the titer plate and two slanted carrier ribs extending therefrom at like 
angles in a diverging manner such that they are adapted to contact front 
and rear corners of the titer plate. The carrier is thus arranged to 
position the titer plate such that it is always exactly centered in the 
desired position by the diverging carrier ribs. Thus, when positioned in a 
work area or below a stack of titer plates to which the titer plate is to 
be guided, the titer plate is always properly oriented for the purpose. 
When two stacking devices according to the present invention are used with 
an analysis device, the titer plates can be readily stacked, unstacked and 
restacked such that they are maintained in the same sequence and can be 
guided to a subsequent testing station without the need for an 
intermediate station. 
Note that the stacking device of the present invention is not limited to 
use with titer plates but can also be advantageously utilized for handling 
other types of plate-shaped objects or stackable members.

DETAILED DESCRIPTION OF THE INVENTION 
As shown in FIG. 1, a stacking device 1 of the invention can be arranged 
along a processing line longitudinally before and after a photometer 2. 
The main components of the stacking device of the invention are a magazine 
3, two elongated clamping members or beams 4, and a support plate 5. 
The support plate 5 which supports a stack of titer plates from below is, 
for example, movable vertically by means of a piston/cylinder unit 6 so 
that the respective bottom-most titer plate is lowered from position A in 
the magazine 3 to a level B (see FIG. 1). The support plate 5 is 
preferably formed such that the titer plates will be contacted from below 
by three remote points of the support plate and thus be supported in a 
stable manner. 
The clamping beams 4 are arranged on either longitudinal side of the 
magazine 3. The clamping beams 4 are mounted on pins 7 for rotation in the 
directions of the arrows shown in FIG. 5 about axes extending 
longitudinally through the centers of the pins 7. This ability to rotate 
allows the clamping beams 4 to be repositioned to compensate for 
irregularities on the edges of the titer plate 12. 
Flanges 8 extend inwardly from an upper portion of each end of each 
clamping beam 4 and act to clampingly contact the titer plates 12. Pins 9 
extend through each end of each beam 4 and are biased inwardly toward the 
titer plates by relatively weak leaf springs 10 and are adapted to extend 
beneath a downwardly sliding titer plate to prevent it from falling 
through the clamping beams. The flanges 8 are preferably coated with a 
coating material 8' such as, for example, tungsten carbide or diamond so 
as to improve the holding contact between flanges 8 and the titer plates. 
The clamping beams 4 on one side of the titer plates 12 are biased toward 
the plates 12, by two pressure springs to thereby provide a clamping force 
against the titer plates 12. 
The titer plate 12 can be selectively released from their clamped condition 
by a motor 13 which is connected to the clamping beams 4 by a linkage. The 
linkage includes two pairs of racks, each of which includes an outer rack 
15 and an inner rack 16. Each of the inner racks 16 is connected to the 
clamping beam 4 on one side of the magazine 3 and each of the outer racks 
15 is connected to the clamping beam 4 on the opposite side of the 
magazine 3. The inner and outer racks of each rack pair have gear teeth 
formed thereon on mutually facing surfaces. A gear wheel 17 is mounted 
about a fixed axis between the inner and outer rack and is positively 
engaged with the teeth of each rack. A cross rod 14 spans between and 
connects distal ends of each of the inner racks 16. The motor 13 includes 
an eccentrically driven pin or shaft 19 and an anchoring pin is fixed to 
the cross rod 14. A rod 18 which includes large holes 21 formed in end 
portions thereof connects between the eccentric pin 19 and the anchoring 
pin 20, such that when motor 13 causes eccentric motion of pin 19, the 
inner racks 16 are moved linearly toward or away from the magazine 3. The 
linear movement of the inner racks causes rotation of gear wheels 17 
which, in turn causes linear motion of the outer racks 15 in a direction 
opposite to the direction of the inner racks 16. 
The connections between the rod 18 and the motor 13 and cross rod 14, 
respectively, are formed by the large holes 21 loosely encircling the pins 
19 and 20, respectively. Having the holes 21 loosely encircle the pins 19 
and 20 does not result in there being play between the clamping beams 4 
and the titer plates 12 because springs 11 maintain the clamping beams 4 
in clamping relation to the titer plates 12. The loose connections between 
the holes 21 nd the pins 19 and 20 do, however, allow the clamping beams 4 
to adapt to titer plates of slightly varying widths because it provides 
the racks 15 and 16 with sufficient play to allow the clamping beams 4 to 
rotate slightly about pins 7. 
By using the stacking device of the present invention the titer plates 12 
can be unstacked in the following manner. While the stack of titer plates 
12 is being supported from below by the support plate 5 at such a height 
that the second titer plate from the bottom of the stack is aligned with 
the clamping beams 4, the two clamping beams 4 are caused to clamp against 
the second titer plate from the bottom by means of motor 13, linkage 
14-21, and springs 11 (see FIG. 4). The support plate 5 is then lowered to 
the level B (see FIGS. 1 and 2) by the piston cylinder unit 6, carrying 
with it the bottom most titer plate. The titer plate thus carried to level 
B can be further transported horizontally by conventional means of 
conveyance (not shown). 
The thus emptied support plate 5 is then returned to its upper position 
wherein it supports the stack of titer plates 12 from below. Next, the 
stacking device of the present invention is readied (see FIG. 3) to unload 
additional titer plates by energizing the motor to cause the clamping 
beams 4 to move laterally away from and thus unclamp the bottom-most titer 
plate 12 against inward bias of the springs 11. The support plate 5 is 
then moved downwardly a distance equal to the height of one titer plate 12 
so as to vertically align the second titer plate from the bottom of the 
stack with the clamping beams 4. The motor 13 can then be energized so as 
to cause the clamping beams 4 to again be biased against and in clamping 
relation to the second titer plate from the bottom of the stack to thus 
secure the entire stack of titer plates 12 (see FIG. 4). The process can 
be repeated as often as desired in order to unstack additional titer 
plates. 
The above process can, of course, be performed in reverse in order to stack 
the titer plates. That is, from the state in which the clamping beams 4 
are clamped against the second titer plate from the bottom of the stack, 
the clamping beams are first moved outwardly to unclamp the titer plates, 
the support plate 5 is moved upwardly a distance equal to the height of 
one titer plate, the clamping beams are clamped against the bottom most 
titer plate to thereby support the stack of titer plates 12, and the 
support plate is lowered to level B so as to be in position to receive an 
additional titer plate thereon. A titer plate is then moved onto the 
support plate by conventional means and the support plate is raised until 
the new titer plate comes in contact with the stack of titer plates. This 
process can be repeated as often as desired in order to stack additional 
titer plates. 
FIGS. 6 and 7 show an alternative type of clamping beam 4' which can be 
used in the present invention. These clamping beams 4' have two narrow 
rib-like projections 37 which extend laterally inwardly and are adapted to 
extend under one of the titer plates when the titer plate is clamped by 
the clamping beams 4' so that the projections 37, like the pins 9 of the 
embodiment of FIG. 1-5, will prevent a sliding titer plate 12 from falling 
through the clamping beams 4'. 
FIGS. 6 and 7 show that the clamping beams 4' can be moved vertically in 
the direction of the double arrow HA so that the height of the stack of 
titer plates can be adjusted by merely moving the clamping beams 4'. This 
vertical adjustment is advantageous because it is often difficult to 
vertically position the support plate 5 precisely relative to the 
bottom-most titer plate. This lack of precision can cause the support 
plate 5, when moved upwardly, to hit and thus vibrate the titer plates 12 
or can cause the support plate to be positioned slightly below the 
bottom-most titer plate such that when the clamping beams 4' are released 
from the titer plates, the titer plates drop onto the support plate 5 and 
are thus vibrated by the contact. It is also contemplated that the 
clamping beams can be biased downwardly by springs (schematically 
illustrated in FIG. 6 by arrows 38). 
This vertical adjustment is important for use during both stacking and 
unstacking to reduce vibrations imparted to the titer plates 12. 
FIG. 8 shows a hangar-shaped carrier 25 for use in the stacking device of 
the present invention. This carrier 25 is used to feed a titer plate 12 
from a first magazine 3 to a second magazine 3 via a work area 28. 
The carrier 25 can be moved in the direction of the double arrow V. It 
includes a rib 26 disposed parallel to the longitudinal side 12' of the 
titer plate 12 and two laterally diverging carrier ribs 27, each of which 
extends from the rib 26 at a like angle .alpha.. Each of the carrier ribs 
27 presses against a corner of the titer plate 12 such that, when the 
carrier 25 forces the titer plate 12 in the direction of the arrow D, 
against an opposing surface 22, the titer plate 12 is automatically 
centered in the carrier 25, and is thus properly oriented in the working 
area 28 situated beneath the magazines 3. FIG. 9 illustrates a rod 18' 
which is a modified form of the rod 18 shown in FIG. 5, which connects the 
motor 13 to the cross rod 14. Rather than providing large holes at each 
end of the rod to loosely encircle the pins 19 and 20, a hole 23 is 
provided at one end which tightly, but rotatably, receives pins 19 therein 
and a longitudinal slot 24 is provided at the other end which rotatably 
slidably receives anchoring pin 20. The length of the slot 24 is such that 
the perimeter of the slot 24 acts as a stop so that no titer plate 12 can 
be clamped too tightly. 
Although the stacking device of the present invention has been described 
particularly for use with titer plates, it is to be noted that the 
stacking device is equally operable for use with other plate-shaped 
objects and stackable members.