Sample transfer arm assembly

The assembly includes a horizontally disposed sample transfer arm which is mounted to and extends radially outwardly from a vertically positioned cylindrical support member. A drive shaft is coupled by a drive mechanism to the cylindrical member for rotating the cylindrical member a predetermined arcuate distance to move the transfer arm between a first position over a first receptacle and a second position over a second receptacle. Locating stops associated with the cylindrical support member define and limit the arcuate movement of the arm. The drive mechanism includes a lost motion clutch assembly including a flat cam member which has a generally rectangular cross-section, which is fixed to the top of the drive shaft and which is received in a slot in the cylindrical member that extends axially inwardly from one end of the cylindrical member and that has a generally rectangular cross-section greater than the rectangular cross section of the cam member. A wide, generally U-shaped spring clip has a flat bight portion situated within the slot at the inner end thereof and has two leg portions which extend toward each other and which have opposed outer ends which are spaced apart a distance less than the thickness of the cam member. The cam member is received between and engaged by the leg portions of the spring clip within the slot in the cylindrical support member. Overrotation of the drive shaft in excess of the predetermined arcuate distance will cause the cam to turn within the slot and spread the opposed leg portions of the spring clip as movement of the arm is blocked by engagement of the arm with one of the locating stops at one end of the arcuate path of travel of the arm thereby to prevent damage to the assembly.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an improved sample transfer arm assembly 
and more specifically to a lost motion clutch mechanism incorporated 
within the assembly for permitting overrotation of the drive shaft without 
damage to the assembly when arcuate movement of an arm of the assembly is 
limited by engagement with a locating stop. 
2. Description of the Prior Art 
In one type of centrifugal automatic chemical analysis apparatus, a 
transfer disc having a plurality of spoke like channels formed therein 
with each channel having at least three wells is utilized in mixing sample 
and reagent and transferring the mixture to a reaction chamber. Starting 
from the inner radial end of each channel, there are first and second 
wells each of which forms either a reagent receiving well or a sample 
receiving well. The outermost well forms a mixing well. Such transfer disc 
with, for example, 36 channels, has each of the first and second wells 
filled with sample and reagent with one channel being filled with water. 
Then the transfer disc is inserted in a centrifugal chemical analysis 
apparatus such as the Rotochem.sub.TM sold by American Instrument Company, 
a division of Baxter Travenol Laboratories, Inc. of Deerfield, Ill. The 
apparatus is then operated to rotate the transfer disc to cause sample to 
mix with reagent and then to be ejected from the mixing well by 
centrifugal force through an outer opening at the end of each channel in 
the transfer disc and into a reaction chamber or cuvette in an annular 
ring positioned around and rotatable with the transfer disc. 
Light transmitting windows are provided at the top and bottom of each 
reaction cuvette and the annular ring is positioned to rotate past a light 
beam located on one side of the annular ring. A photosensitive device 
located on the other side of the annular ring in the light path of the 
light beamed from the light source senses the amount of light transmitted 
to monitor thereby the reaction and, upon each rotation of a reaction 
chamber 360.degree., the rate of the reaction taking place in each 
reaction chamber. 
In preparing a plurality of samples for analysis in the centrifugal 
chemical analysis apparatus, the transfer disc is placed on an automatic 
reagent and sample filling device such as the Rotofill.sub.TM sold by 
American Instrument Company, a division of Travenol Laboratories, Inc., of 
Deerfield, Ill. The automatic sample and reagent filling device is 
provided with a turntable on which the transfer disc is positioned and an 
annular sample tray supporting a plurality of sample cuvettes in a ring is 
positioned around the transfer disc and on the turntable. Positioned above 
the turntable is a stationary reagent arm for dispensing reagent to one or 
the other of the first and second wells in each channel of the transfer 
disc. 
Additionally, a sample transfer arm is positioned over the turntable and is 
mounted to and extends radially outwardly from a cylindrical support 
mounted on a rotatable and reciprocal drive shaft so that the transfer arm 
can be rotated about one end thereof a predetermined arcuate extent. To 
insure proper positioning of the transfer arm at a first position over a 
sample containing cuvette in the same tray, a cylindrical sleeve with a 
generally rectangularly shaped window through which the arm extends is 
received over the cylindrical support with one side edge of the window 
forming a stop which is located and fixed in place to locate the outer end 
of the transfer arm, when it engages that side edge of the window, over a 
sample cuvette in the sample tray. Then, a second cylindrical sleeve 
having a similar generally rectangularly shaped window is positioned over 
the first sleeve with the window thereof in registry with the first window 
and with an edge thereof forming a stop to locate the outer end of the 
transfer arm at the other end of its arcuate path of travel over the 
innermost well of the transfer disc. Lastly, a third cylindrical sleeve is 
received over the first two sleeves and has a generally rectangularly 
shaped window which is in registry with the first two windows. The third 
sleeve is rotatable between one releasably fixed locating position where 
an edge of the window therein is radially in line with the locating edge 
of the window in the second sleeve and a second releasably fixed locating 
position where the stop forming edge of the window is now positioned to 
stop movement of the transfer arm with the outer end thereof positioned 
over the second well of a channel in the transfer disc. 
In operation of the automatic reagent and sample filling device, water is 
placed in the wells of one channel. Then the turntable is indexed a 
predetermined amount to rotate a first sample cuvette in the sample tray 
to a position under the outer end of the sample transfer arm. Then the 
drive shaft, cylindrical support and transfer arm are moved downwardly to 
bring an aspirating dip tube mounted on the outer end of the transfer arm 
into the sample cuvette for aspirating a predetermined amount of sample 
into the dip tube. Then the drive shaft, cylindrical support and transfer 
arm are moved upwardly and rotated counterclockwise to move the sample arm 
against the side edge of the window in the second sleeve to locate the 
outer end of the sample transfer arm over the innermost well, unless, of 
course, the third sleeve had been moved to locate the edge of the window 
thereof to stop movement of the transfer arm with the outer end thereof 
over the second well. In either event, the drive shaft, cylindrical 
support and transfer arm are lowered to lower the dip tube into the well 
and the predetermined amount of sample in the dip tube is ejected into the 
well. Then the sample transfer arm is raised and rotated clockwise to 
bring the transfer arm back to its first position and the turntable is 
indexed to position the next sample cuvette under the dip tube at the end 
of the sample transfer arm to repeat the above sequence of operations. 
Reagent, of course, is dispensed into the first or second well by dip 
tubes extending from the reagent arm each time a new channel is positioned 
under the reagent arm. 
In the operation of the automatic reagent and sample filling device, exact 
control of the rotational movement of the drive shaft is not readily 
obtainable. As a result, stress and a bending moment are placed on the 
transfer arm when it engages one of the stop forming side edges of one of 
the windows when the drive shaft rotates more than the predetermined 
arcuate extent. Also a torque is placed on the drive shaft and the 
cylindrical support for the transfer arm. These stresses, bending moments 
and torque forces have resulted in damage to the device and failure of the 
device to operate properly. 
As will be described in greater detail hereinafter, the present invention 
provides a solution to this problem of bending moments and torque forces 
being placed on the sample transfer arm assembly by providing a lost 
motion clutch assembly in a drive arrangement between the cylindrical 
support and the drive shaft. 
The lost motion clutch assembly permits overrotation of the drive shaft 
beyond the predetermined arcuate extent without damage to the transfer arm 
assembly when arcuate movement of the transfer arm is limited by 
engagement thereof with one of the locating stops defined by a side edge 
of one of the windows in one of the sleeves. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided an improved sample 
transfer arm assembly for use in a device for transferring liquid sample 
from a first receptacle to a second receptacle, said assembly including a 
sample transfer arm, support means for supporting said sample transfer arm 
with said arm extending normal to and from the axis of said support means, 
locating means for locating and limiting arcuate movement of said arm 
about said axis of said support means, drive means including a drive shaft 
for rotating said arm support means a predetermined arcuate extent between 
a first position where the outer end of said arm is located over the first 
receptacle and at least one other position where said outer end of said 
transfer arm is located over the second receptacle, and with drive means 
including lost motion clutch means between said drive shaft and said arm 
support means for permitting overrotation of said drive shaft beyond said 
predetermined arcuate extent without damage to said sample transfer arm 
when arcuate movement of said sample transfer arm is limited by engagement 
thereof with said locating means.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1 in greater detail, there is illustrated therein an 
automatic sample and reagent filling device 10 of the type sold by 
American Instrument Company of Silver Spring, Maryland, a division of 
Travenol Laboratories, Inc., of Deerfield, Ill. under the trademark 
"ROTOFILL". The device 10 is particularly adapted for filling a transfer 
disc 12 which has thirty six channels 13 each of which has a first or 
inner well 14, a second well 15 and a third or outer well 16 with reagent 
and sample. Reagent is placed in the well 14 or the well 15 by a dip tube 
17 located above the transfer disc 12 and depending from a reagent arm 
assembly 18. Positioned around the transfer disc 12 is an annular sample 
tray 19 containing a plurality, i.e., thirty six, of sample cuvettes 20. 
Although hidden from view it is to be understood that the transfer disc 12 
and the annular sample tray 19 are supported on a turntable of the device 
10. 
The automatic reagent and sample filling device 10 also includes a sample 
transfer arm assembly 22. The sample transfer arm assembly 22 includes a 
sample transfer arm 24 which has a tubing 26 supported at the outer end 27 
thereof with a dip tube portion 28 of the tubing 26 depending from the 
outer end 27 of the sample transfer arm 24. The inner end 29 of the sample 
transfer arm is mounted to and extends radially outwardly from a 
cylindrical arm support member 30 which is received within three 
cylindrical sleeves 31, 32, and 33, as best shown in FIG. 2, which are 
telescoped over each other. The sleeves 31-33 are supported on a base 
member 36 within which is located a drive shaft 38 which is coupled to the 
arm support member 30 by a drive arrangement 39 for rotating the 
cylindrical member 30 to rotate the transfer arm 24 as best shown in FIGS. 
2, 3 and 4. As will be explained in greater detail hereinafter, according 
to the teachings of the present invention, the drive arrangement 39 
includes a lost motion clutch assembly 40. 
As shown, the first sleeve 31 has a generally rectangularly shaped first 
window formed therein which is defined in part by one side edge 41 that 
forms a locating edge or stop and through which the arm 24 extends. 
Likewise the second sleeve 32 has a generally rectangularly shaped second 
window therein in registry with the first window and with one side edge 42 
thereof forming a locating edge or stop. Similarly, the third or outer 
cylindrical sleeve 33 has a generally rectangularly shaped third window 
therein in registry with the other windows and with one side edge 43 
thereof defining a locating edge or stop. 
Also as best shown in FIGS. 2 and 3, the cylindrical sleeve 31 has a larger 
diameter, lower, cylindrical shell portion 46 integral therewith. The 
shell portion 46 is received over a stationary sleeve 48 and fixed thereto 
by means of a set screw 50 (FIG. 3). The second sleeve 32 is fixed to the 
first sleeve 31 by means of a set screw 52. The outer sleeve 33 is 
received over the second sleeve 32 and has two ball bearing detents 54 and 
56 which are mounted on the inside top thereof and which are adapted to be 
received in one or the other of a pair of notches 58 and 60 formed on the 
top annular edge of the second sleeve 32. As shown in FIG. 2, the third 
sleeve 33 is fixed by a screw to the second sleeve 32. 
Before describing the remaining parts of the sample transfer arm assembly 
22, the arrangement and function of the three sleeves 31, 32 and 33 will 
now be described with particular reference to FIGS. 4, 5 and 6. In this 
respect, when the transfer sample arm assembly 22 is assembled for 
operation, the sample transfer arm extending through the aligned windows 
in the sleeves 31-33 is positioned with the outer end 27 thereof located 
above a sample cuvette 20 in the sample tray 14. This is best shown in 
FIG. 4. Then the inner or first sleeve 31 is rotated counterclockwise on 
the stationary cylinder 48 until the locating edge 41 bears against the 
sample transfer arm 24. Then the set screw 50 is tightened to lock the 
first sleeve 31 in that position where the side edge 41 provides and 
defines a locating stop for limiting clockwise arcuate movement of the arm 
24 where the outer end thereof is located over a sample cuvette 20 as 
shown in FIG. 4. 
The arcuate extent of the window in the first sleeve 31 from the one side 
edge 41 to a second side edge 71 is slightly greater than the arcuate 
travel required to rotate the sample transfer arm 24 from the first 
position over the sample cuvette 20 as shown in FIG. 4 to a second 
position where the sample transfer arm is located over the innermost well 
14 as shown in FIG. 5. The proper positioning of the arm 24 over is 
accomplished by locating the transfer arm 24 with the outer end 27 thereof 
located over the innermost well 14 in the channel 13. Then the second 
sleeve 32 is rotated clockwise until the side edge 42 of the window 
therein engages the sample transfer arm 24. Next the set screw 52 is 
tightened to lock the second or intermediate sleeve 32 to the first or 
inner sleeve 31 with the edge 42 of the window forming a locating stop for 
the innermost position of the end 27 of the arm 24 over the innermost well 
14 of a channel 13 in the transfer disc 12. In this position, the ball 
bearing detents 54 and 56 of the third sleeve 33 are located in the 
notches 58 so that the locating edge 43 of the window therein is radially 
aligned with the locating edge 42 of the window in the sleeve 32 on a line 
parallel to a radius extending outwardly from the axis 59 of rotation of 
the cylindrical arm support member 30 as shown in FIG. 5. 
Once these positions are determined and the sleeves 31 and 32 locked in 
place, the notches 60 in the top edge of the second sleeve 32 
automatically define a position for the sleeve 33 when the detents 54 and 
56 are received in the notches 60 where the locating edge 43 of the window 
therein will locate the outer end 27 of the arm 24 over the second well 15 
in one of the channels 13 when the arm 24 bears against the locating edge 
or stop 43 as best shown in FIG. 6. 
In the operation of the sample transfer arm assembly 22 so far described, 
the drive shaft 38 will be rotated a predetermined arcuate extent by a 
prime mover (not shown) which will ideally move the arm 24 to a position 
against the locating edge 41 in the window of the sleeve 31. Then a 
reciprocating mechanism (not shown) will be operated to lower the shaft 38 
thereby to lower the dip tube 28 into a sample cuvette 20. Next the shaft 
38 is raised and rotated by the prime mover, ideally the predetermined 
arcuate extent, sufficient to bring the arm 24 into engagement with the 
side edges 42 and 43 of the windows in the second and third sleeves 32 and 
33 to position the outer end 27 of the arm 24 over the innermost well 14. 
This is assuming, of course, that it is desired to place sample in the 
innermost well 14. Of course, if it is desired to place the sample in the 
second well 15, then the locating edge 43 would be positioned as shown in 
FIG. 6 and the prime mover would be set to rotate the arm support member 
30 a shorter arcuate extent sufficient to bring the arm 24 into contact 
with the locating stop 43 of the sleeve 33. 
It will be appreciated that control of the prime mover for rotating the 
shaft 38 to rotate such shaft 38 a very limited arcuate distance between 
the locating edges 41 and 42 is very difficult if at all possible. As a 
result, over-rotation of the shaft 38 is often encountered such that with 
the previously utilized drive arrangement, stress is placed on the arm 24 
when it engages one of the locating stops 41 or 42 (or 43) with the result 
that a bending moment would be placed on the arm 24 and a twisting torque 
would be placed on the shaft 38 and the cylindrical support member 30. 
In accordance with the teachings of the present invention, this problem is 
obviated by the provision of the drive arrangement 39 with the lost motion 
clutch assembly 40 which will now be described in detail with reference to 
FIGS. 2, 3, 7 and 8. 
The drive arrangement 39 between the drive shaft 38 and the cylindrical 
support member 30 includes a flat generally rectangular cam member 80, 
which has rounded sides 81 and 82 and flat sides 83 and 84 and is fixed to 
a pin 85. In turn, the pin 85 is received within an axial bore 86 in the 
top end 87 of the drive shaft 38. A set screw 88 is provided for fixing 
the pin 85 within the bore 86 to properly locate the cam 80. 
The drive arrangement 39 also includes a generally rectangular slot 90 
which extends axially inwardly of the cylindrical support member 30 from 
the lower end thereof with the slot 90 being defined between opposed 
sidewalls 91 and 92 and an inner bottom wall 93 in the lower end of the 
cylindrical support member 30. The width of the slot 90 between sidewalls 
91 and 92 is greater than the thickness of the cam 80 between the rounded 
sides 81 and 82 thereof thereby to permit rotation of the flat cam member 
80 within the slot 90. 
In accordance with the teachings of the present invention, the lost motion 
clutch assembly 40 is defined by a wide, generally U-shaped spring clip 
100 and the interaction thereof with the cam 80 and slot 90. As shown, in 
clip 100 has a generally rectangular bight portion 102 which is sized and 
arranged to fit within the slot 90 against the inner wall 93 between the 
sidewalls 91 and 92 of the slot 90. The spring clip 100 further includes 
two leg portions 104 and 106 which extend angularly from the bight portion 
102 and toward each other. Each leg portion 104 and 106 is flared at the 
outer end thereof to provide rounded bead formations 108, 110 and an outer 
edge 112, 114 which is located outwardly of the plane of the leg portion 
104, 106. The space between the bead formations 110 and 112 is less than 
the thickness of the flat cam member 80 between the flat sides 83 and 84 
thereof. As a result, when the cam member 80 is received within the slot 
90 and between the leg portions 104 and 106 of the spring clip 100, the 
rounded bead formations 112 and 114 resiliently and frictionally bear 
against the flat sides 83 and 84 of the cam member. 
The spring clip 100 is preferably made from, i.e., punched from, a flat 
piece of 0.020 thick phosphor bronze having a 510 spring tempered 
hardness. 
In the operation of the lost motion clutch assembly 40, when the drive 
shaft 38 is rotated, the pin 85 is also rotated to rotate the cam 80 and 
this rotary motion is transmitted to the spring clip 100 as a result of 
the bearing engagement between the leg portions 104 and 106 and the cam 
80. This motion transmitted to the spring clip 100 is transmitted by the 
bight portion 102, bearing against the sidewalls 91 and 92, to the 
cylindrical support member 30 to cause rotation of the support member 30. 
However, and as best shown in FIGS. 7, 8, and 9 when the drive shaft 38 is 
rotated a greater arcuate extent than the arcuate extent between the 
locating stops 41 and 42 or 43, i.e., to the position shown in FIG. 5 or 
6, movement of the cylindrical arm support member 30 is prevented as a 
result of engagement of arm 24 with the locating stop 42 or 43. In this 
situation, the cam member 80 is allowed to turn against the spring action 
of the leg portions 104 and 106 of the spring clip 100, to spread them 
apart and move them outwardly with the slot 90 as shown in FIG. 8. To 
facilitate this movement, the cam member 80 has the rounded edges 81 and 
82. 
With the lost motion movement described above, undesired stresses which 
could be brought about by the bearing engagement of the sample transfer 
arm 24 against a locating stop 42 (or 43 or 41) is prevented. Also, it 
will be appreciated that when the drive shaft 38 is rotated to rotate in 
the opposite direction, the cam 80 will first move from the position shown 
in FIG. 8 to the position shown in FIG. 7 and then rotate the arm 24 until 
the transfer arm 24 engages the locating stop 41. 
It will be noted that the lost motion clutch assembly 40 allows lost motion 
movement between the cam 80 and the cylindrical arm support member 30 
without damage to the sample transfer arm assembly 22 when the arcuate 
extent of movement of the drive shaft 38 is not set in precise registry 
with the positions of the locating stops 41 and 42 or 43. In this way, 
allowance for error in the settings of the movement of the drive shaft 38 
are compensated for with the lost motion clutch assembly 40. 
From the foregoing description it will be apparent that the lost motion 
clutch assembly 40 of the present invention has a number of advantages, 
particularly the advantage described above of preventing damage to the 
sample transfer arm assembly 22 while allowing for accurate positioning of 
the sample transfer arm 24 at and between two or three positions, and 
other advantages which are inherent in the invention. Also it will be 
apparent from the foregoing description that obvious modifications and 
variations can be made to the lost motion clutch assembly 40 of the 
present invention without departing from the teachings of the invention. 
Accordingly, the scope of the invention is only to be limited as 
necessitated by the accompanying claims.