Automatic distribution apparatus and method of distribution

In a method for distributing liquids, in which a distribution tip attached detachably to the lower end of a distribution nozzle can be replaced at any time necessary, a tip rack having a plurality of unused distribution tips lined up thereon is placed on a fitting stage to have the distribution tips fitted with a distribution nozzles. Then, the existence, or non-existence, of a distribution tip left behind on the tip rack without being attached to a distribution nozzle after the fitting operation is finished is detected by a detection section formed of an interrupting-type light sensor, the targeted place of detection by the light sensor being the lower end of the distribution tip. Under the above-described structure, misfitting of a distribution tip can be detected with a high certainty at an early stage before an operation for sucking/discharging liquids is started.

FIELD OF THE INVENTION
 The present invention relates to an automatic distribution apparatus and a
 method of distributing samples or reagents used in biochemical and the
 like fields.
 BACKGROUND OF THE INVENTION
 Distributing liquid samples or reagents to a plurality of sample vessels in
 small quantities is an indispensable operation during experiment or
 analysis activities in the biochemical field, for example. The
 distribution is performed by sucking/discharging liquid through a
 distribution nozzle. The distribution nozzle is normally fitted with a
 disposable distribution tip. The distribution tip is replaced with a new
 one at any time whenever necessary.
 A distribution tip is fitted to the distribution nozzle by inserting the
 lower end of the latter into a pipet-shaped distribution tip. The firmness
 of fitting depends solely on the elastic fastening force of a resin
 distribution tip surrounding the lower end portion of the distribution
 nozzle. Because of dimensional dispersions in the inner diameters of
 distribution tips, the fastening forces sometimes fall short of a level
 required to insure a normal fitting state. This invites a misfitted state
 with the distribution tip.
 During a distribution operation, if a distribution head proceeds without
 having a distribution tip perfectly fitted thereto, a receiving plate will
 have a portion void of sample liquid. For assuring reliability of the test
 result, misfitting of a distribution tip should be avoided by all means.
 In a conventional apparatus, where a single distribution tip is used, the
 existence, or non-existence, of a distribution tip may be checked upon
 through an electrical conductivity test using a conductive material for
 the distribution tip. Or, it may be confirmed indirectly by watching a
 pressure during a suction operation. The above-described checking methods,
 however, are hardly applicable to a distribution head that has multiple
 distribution tips. The problem with the conventional automatic
 distribution apparatus is that it is difficult to detect a misfitted
 distribution tip with a high certainty level.
 SUMMARY OF THE INVENTION
 An automatic distribution apparatus for distributing liquid is designed
 such that a distribution tip attached detachably to the lower end of a
 distribution nozzle can be replaced at any time whenever necessary. The
 automatic distribution apparatus comprises a fitting stage that supports a
 holding member holding a plurality of unused distribution tips lined up
 thereon to have the unused distribution tips fitted to respective
 distribution nozzles, and detection means for detecting, after a fitting
 operation is finished, whether or not there is a distribution tip left
 behind on the holding member without being attached to a distribution
 nozzle. In a distribution apparatus having the above-described structure,
 misfitting of a distribution tip can be detected with a high certainty
 level at an early stage before the apparatus proceeds to a
 suction/discharge operation.
 An invented distribution apparatus further comprises a light sensor, whose
 optical axis is in parallel with the aligning line of distribution tips
 disposed on the holding member. This further improves the accuracy of
 detection.

DESCRIPTION OF PREFERRED EMBODIMENTS
 Exemplary embodiments of the present invention are described below with
 reference to the drawings.
 The structure of an invented automatic distribution apparatus is described
 referring to FIG. 1. A nozzle holder 2 of a distribution head 1 comprises
 a plurality of distribution nozzles 3. Each of the distribution nozzles 3
 is fitted with a distribution tip 4. The distribution head 1 can be moved
 in horizontal directions (X Y directions) by transfer means, or an X Y
 table 5.
 Within a movement range of the distribution head 1, a distribution stage 6
 is provided. The distribution stage 6 has a reserver 7 and a microplate 9
 provided thereon. The distribution head 1 is shifted to a position so that
 the bottom end of the distribution tips 4 fitted to the distribution
 nozzles 3 can dip into in a small hollow 7a of the reserver 7, and liquid
 kept within the small hollows 7a is sucked up through the bottom ends of
 the distribution tips 4. Then, the distribution head 1 is shifted to a
 position above the microplate 9, at a place where the distribution nozzles
 3 face a small hollow 9a of the microplate 9, and then the distribution
 nozzle 3 is lowered so that the bottom ends of the distribution tips 4 dip
 into the small hollows 9a for discharging the liquid being sucked within
 the distribution tips 4 into the small hollows 9a.
 A fitting stage 10 for fitting the distribution tips 4 is provided at a
 place within the movement range of the distribution head 1. A tip rack 11
 for holding the distribution tips 4 is placed on the fitting stage 10. On
 the tip rack 11 are multiple distribution tips 4 disposed vertically,
 lined up in correspondence with the orientation of the distribution
 nozzles 3. The distribution head 1 is shifted to a place above the fitting
 stage 10, with the distribution nozzles 3 aligned with the distribution
 tips 4. By lowering the distribution head 1, the distribution nozzles 3
 are fitted at the lower ends an unused distribution tips 4.
 Now in the following, means for detecting the distribution tips is
 described referring to FIG. 1 and FIG. 2. As shown in FIG. 1, a light
 sensor 12 is provided beneath the tip rack 11 mounted on a table 13 of the
 fitting stage 10. The light sensor 12 is an interruption type light sensor
 comprising a light emitting section 12a and a light sensing section 12b.
 The height of an optical axis "a" has been adjusted so as to hit the
 bottom ends of the distribution tips 4 projecting downward from the lower
 edge of the tip rack 11, as shown in FIG. 2. The optical axis "a" of the
 light sensor 12 extends in parallel with the queue line formed of the
 distribution tips 4 being held on the tip rack 11. Whether any of the
 distribution tips 4 of each queue is in the optical axis "a", or not, can
 be detected at a detection section 16 by sensing the light emitted from
 the light emitting section 12a in the light sensing section 12b. The
 results of sensing are delivered to a control section 18. The control
 section 18 drives the X Y table 5, via a driving section 17, to perform
 specific operations, such as re-fitting, discarding, etc. of distribution
 tip 4, in accordance with the results of sensing.
 The light emitting section 12a and the light sensing section 12b have been
 installed on a bracket 14 mounted on a transfer mechanism, or a movable
 table 15. When the movable table 15 is moved, the optical axis "a" shifts
 relative to the tip rack 11 in a horizontal direction perpendicular to the
 optical axis "a", in order to detect the existence, or non-existence, of a
 distribution tip 4 in each of the queues of distribution tips 4 on the tip
 rack 11.
 The operation of an automatic distribution apparatus having the above
 structure is described in the following. As shown in FIG. 1, a tip rack 11
 carrying unused distribution tips 4 is brought from a stock section (not
 shown) to be placed on the fitting stage 10. Distribution head 1, from
 which the used distribution tips 4 have already been removed, is located
 in a place above the tip rack 11. The positions of distribution nozzles 3
 are aligned to be located just above the distribution tips 4. Then, as
 shown in FIG. 3(a), the distribution head 1 is lowered to have the bottom
 ends of distribution nozzles 3 inserted into the distribution tips 4. The
 distribution tip 4 are thus fitted to the distribution nozzles 3. After
 that, the distribution head 1 is raised upward, as illustrated in FIG.
 3(b). Due to dimensional dispersions among the distribution tips 4, there
 may be a case where one or more of the distribution tips 4 are not fitted
 firmly with the distribution nozzles 3 to establish a normal fitting
 state. Such a distribution tip remains on the tip rack 11.
 In order to detect such a remaining distribution tip 4, the location of the
 optical axis "a" of light sensor 12 is adjusted to coincide with each of
 the respective queues of the distribution tips 4. By measuring the amount
 of light emitted from the light emitting section 12a received at the light
 sensing section 12b, the existence, or non-existence, of a distribution
 tip 4 remaining in the optical axis "a", namely the one kept staying in
 the tip rack 11, can be detected at the detection section 16. Such a
 distribution tip 4 remaining in the tip rack 11 without being attached to
 the distribution nozzle 3 can be thoroughly detected by shifting, through
 driving of movable table 15, the location of optical axis "a" to check;
 one after another, all of the queues of the distribution tips 4.
 The targeted point of detection by the optical axis "a" is at the bottom
 end of the distribution tips 4 projecting downward from the lower edge of
 the tip rack 11. Therefore, as soon as the distribution head 1 starts
 making an upward motion, after having been fitted with the distribution
 tips; the misfitting of a distribution tip 4 with a distribution nozzle 3
 is immediately detected at each of the fitting operation cycles. The early
 detection of misfitting reduces lost time, which would have otherwise been
 consumed in vain in an unfruitful motion for starting a distribution
 operation without correcting the misfitting. Without wasting time, an
 appropriate correction measure that suits best to the general circumstance
 of respective cases can be selected among the choices exemplified below.
 In a case in which there is no problem in the dimensional accuracy and the
 quality of the distribution tip 4, and thus the misfitting is considered
 to have been caused by a reason outside the distribution tip 4, the
 distribution head 1 is lowered once again for fitting. The remaining
 distribution tip 4 may be attached to the distribution nozzle 3. If
 misfitting occurs repeatedly for a certain specified number of times, then
 the distribution tip is judged to be rejected, and the tip rack concerned
 is replaced with a new tip rack.
 In a case in which the dimensional dispersions among distribution tips 4
 are evident and the misfitting seems to occur at a certain frequency, then
 all the relevant distribution tips 4 are rejected as soon as misfitting
 first occurs. A new tip rack 11 is introduced. The above described may be
 another choice.
 As still another choice, a distribution head 1 that caused misfitting may
 be inspected by the hands of engineers for correcting the misfitting of
 the distribution tip 4. In any of the cases, countermeasures against the
 misfitting can be taken before the next operational step for
 sucking/discharging liquid starts. If a distribution head void of a
 distribution tip conducts a sucking/discharging operation, the relevant
 plate can not serve as a due sample. In accordance with the present
 invention, the time loss and/or material loss due to misfitting can be
 minimized.
 As described in the foregoing, the present invention has made it possible
 to detect the existence, or non existence, of a distribution tip left
 behind on a holding member (on tip rack) because it remains unattached to
 a distribution nozzle after a fitting operation is finished. Thus the
 misfitting of a distribution tip is detected with a high certainty level
 at an early stage before it proceeds to a step of suction/discharge
 operations. Possible losses to be caused by misfitting can be reduced to a
 minimum in terms of both the time and the material.