Abstract:
The invention relates to a device for dispensing powder, comprising at least one storage tank ( 1 ) provided with a cap ( 2 ) comprising a flow orifice ( 3 ) for the powder. According to the invention, the device comprises a shutter ( 8 ) provided with an aperture ( 9 ) and fitted so as to be able to move relative to the cap between a shut position preventing the powder from flowing and an open position allowing the powder to flow through the aperture of the shutter, a channel ( 12 ) passing through the shutter so as to extend on either side of the aperture of the shutter in a direction that is substantially transverse to the flow of the powder, and means for creating a relative motion between the cap and the shutter in order to move the shutter between its two positions, said means being connected to a control unit ( 20 ) that is connected to contactless means for detecting the flow of the powder, the detecting means comprising, at a first end of the channel of the shutter, at least one emitter ( 21 ) emitting a wave into the channel and, at a second end of the channel, at least one receiver ( 22 ) for detecting the emitted wave. The invention also relates to a workstation comprising such a device for dispensing powder.

Description:
[0001]    The invention relates to a device for dispensing powder, cap for such a device and workstation comprising such a device. 
       TECHNOLOGICAL BACKGROUND OF THE INVENTION 
       [0002]    In the chemical and pharmaceutical industry, it is often necessary to produce extremely precise doses of reagents or products in the form of a powder. This is the case, for example, in laboratories in which molecules are tested or compositions are processed by mixing products. Those products are taken from libraries of samples in which the samples are conserved in the form of small quantities of powder stored in small flasks or reservoirs. The product quantity per sample being limited, it is necessary to use only the smallest possible quantity of product in order not to bring about rapid exhaustion of the library. 
         [0003]    Some libraries of samples are provided with an automatic powder dispensing device. 
         [0004]    There are automatic dispensing devices which comprise a storage reservoir which is provided with a dosage cap whose opening is adjustable. In accordance with an instruction regarding the quantity of powder to be dispensed and an indication of the quantity of powder already dispensed, a control unit controls the dosage cap in order to increase or decrease the opening thereof. The indication of the quantity of powder is provided by a so-called precision balance, the resolution of such a balance being, for example, 1/10 th  of a milligram or 1/100 th  of a milligram. 
         [0005]    In the document FR 2846632, the indication of the quantity of powder already dispensed is provided in the same manner by weighing means, the weighing means being arranged under a flask receiving the powder. 
         [0006]    However, it is difficult to supply quantities of powder of a few tenths of a milligram in a precise and repetitive manner with such devices. This is because generally, when a balance indicates a first mass value of dispensed powder, the quantity of powder dispensed already exceeds the initial instruction. In fact, the balance detects the start of flow of the powder into the flask at the time the powder touches the bottom of the flask, introducing an excessively large discrepancy for the dispensing of very small quantities of powder, even if the balance has a very high level of precision. 
       OBJECT OF THE INVENTION 
       [0007]    An object of the invention is to provide a means which ensures more precise detection of the start of the flow of the powder than the devices of the prior art. 
       BRIEF STATEMENT OF INVENTION 
       [0008]    In order to achieve this object, there is proposed a powder dispensing device which comprises at least one storage reservoir which is provided with a cap comprising a flow hole for the powder. 
         [0009]    According to the invention, the device comprises:
       a closure member which is provided with an opening and which is mounted so as to be movable relative to the cap between a closed position which prevents a flow of the powder and an open position which allows the flow of the powder through the opening of the closure member, a bore extending through the closure member so as to extend at one side and the other of the opening of the closure member in a direction which is substantially transverse relative to the flow of the powder;   relative displacement means of the cap and the closure member in order to move the closure member into the two positions thereof, those means being connected to a control unit which is connected to contactless detection means of the flow of the powder, the detection means comprising, at a first end of the bore of the closure member, at least one transmitter of a wave in the bore and, at a second end of the bore, at least one receiver for detecting the wave transmitted.       
 
         [0012]    In this manner, the detection of the flow of the powder is ensured downstream of the flow hole substantially in the region of the hole which ensures very precise detection of the flow of the powder towards, for example, a flask to be filled and in particular very precise detection of the start of the flow. 
         [0013]    The inventor has thus been able to develop a prototype which detects the start of the flow of the powder with a time interval of approximately 50 microseconds. With a device of the prior art comprising weighing means, if the balance is arranged at a distance of 45 millimeters from the reservoir, the balance detects the start of the flow with a discrepancy which may be up to 100 milliseconds in relation to the device of the invention. 
         [0014]    The device of the invention thereby allows quantities of powder to be supplied in the order of a few tenths of a milligram in accordance with the fineness of the powder and the density of the product. 
         [0015]    In an advantageous manner, the wave transmitted interacts directly with the powder when the powder flows through the opening of the closure member. The detection of the start of the flow is further very precise. 
         [0016]    According to the invention, there is also proposed a cap for such a device and a workstation comprising such a device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention will be better understood in light of the following description of non-limiting embodiments of the invention. Reference will be made to the appended figures, in which: 
           [0018]      FIG. 1  is a schematic view of the powder dispensing device according to a first embodiment of the invention; 
           [0019]      FIGS. 2   a  and  2   b  are respectively a view from below and a side view of a closure member of the device illustrated in  FIG. 1 ; 
           [0020]      FIGS. 3   a  and  3   b  are respectively a front view and a side view of a cap of the device illustrated in  FIG. 1 ; 
           [0021]      FIGS. 4   a ,  4   b  and  4   c  are schematic views illustrating different powder dispensing steps by means of the device illustrated in  FIG. 1 ; 
           [0022]      FIGS. 5   a ,  5   b  and  5   c  are schematic bottom views of the closure member and the cap in the course of the different dispensing steps illustrated in  FIGS. 4   a ,  4   b  and  4   c , respectively; 
           [0023]      FIG. 6  is a schematic bottom view of the closure member and the cap in a construction variant of the invention; 
           [0024]      FIG. 7  is a view similar to  FIG. 1  of a device according to a second embodiment; 
           [0025]      FIG. 8  is a very schematic plan view of a workstation comprising a powder dispensing device according to the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    With reference to  FIG. 1 , the powder dispensing device according to the first embodiment of the invention comprises a storage reservoir  1  of the powder. The storage reservoir  1  is provided with a cap  2  which comprises a flow hole  3  for the powder. The reservoir  1  is, for example, a glass vial having a capacity of 4 milliliters. 
         [0027]    During operation, the reservoir  1  is arranged in such a manner that a flow of the powder towards the outer side of the reservoir is brought about by gravitational force. The reservoir is in this instance arranged vertically, with the cap at the bottom, so that the powder then flows in a flow direction having a first substantially vertical axis Z. 
         [0028]    According to a specific embodiment, the reservoir  1  comprises a neck  4  of which one external surface is threaded. 
         [0029]    Preferably, with reference to  FIGS. 3   a  and  3   b , the cap  2  comprises a tubular wall which has cylindrical internal and external surfaces having a centre axis parallel with the first axis Z and an end closed by a partition which is pierced by the hole  3 . The internal surface of the cap  2  is tapped in order to allow the engagement thereof with the neck  4 . The partition has an external perimeter forming a shoulder  5  which is capable of receiving a sealing washer  6  which is intended to be clamped between the neck  4  and the shoulder  5  (as can be seen more clearly in  FIG. 1 ). The partition comprises, at the side of the reservoir  1 , a frustoconical surface portion which extends from the shoulder  5  as far as the hole  3  in order to make it easier for the powder to flow towards the flow hole  3  which has a circular contour in this instance. 
         [0030]    According to a preferred embodiment, a face of the partition comprising the flow hole  3  comprises, opposite the reservoir, a groove  7  which extends substantially in accordance with a second axis X which is orthogonal to the first axis Z, the groove  7  being arranged in the face of the partition in such a manner that the flow hole  3  opens in the groove  7 . Preferably, the groove  7  is arranged in the face in such a manner that the flow hole  3  is centered in the groove  7 . Here, the groove  7  is arranged in the face of the partition so as to extend substantially at the centre of the face. 
         [0031]    According to the invention, with reference to  FIG. 1 , the device comprises a closure member  8  mounted on the cap  2 . 
         [0032]    With reference to  FIGS. 2   a  and  2   b , the closure member  8  comprises an opening  9  which extends through the closure member  8  substantially in a direction parallel with the first axis Z. 
         [0033]    Furthermore, the closure member  8  has opposite edges  10  which are slidingly engaged in the groove  7  of the cap  2 . According to a specific embodiment, the groove  7  and the edges  10  form a connection of the dovetail type. 
         [0034]    The closure member  8  is formed so as to be mounted in a movable manner relative to the cap  2  between a closure position which prevents flow of the powder, the opening  9  of the closure member not being aligned with the flow hole  3  of the cap  2 , and an open position which allows flow of the powder through the opening  9  of the closure member  8 , the opening  9  of the closure member  8  being at least partially aligned with the flow hole  3  of the cap  2 . According to a preferred embodiment, the opening  9  and the flow hole  3  are formed in such a manner that, in the open position, the opening  9  and the hole  3  are convergent. In the open position, the powder then flows at a maximum flow rate. 
         [0035]    According to a preferred embodiment, as can be seen more clearly in  FIGS. 2   a  and  2   b , the groove  7  of the cap is blind at one of the ends thereof so that, in the closure position, the edges  10  move into abutment against the end of the groove  7 . Preferably, the cap  2  comprises a stud  11  which is arranged in the other of the ends of the groove  7  so that, in the open position, one of the edges  10  moves into abutment against the stud  11 . 
         [0036]    Preferably, the opening  9  is formed substantially in the manner of a cone which widens from a first face of the closure member  8  which faces the cap  2  to a second face of the closure member  8  which is opposite the first face. In this manner, the powder flows more readily. That allows any risk of agglomeration of the grains of powder during passage in the opening  9  to be minimized. 
         [0037]    Preferably, in the region of the first face of the closure member  8 , the opening  9  has a circular cross-section which is identical to the flow hole  3  of the cap  2 . 
         [0038]    The closure member  8  further comprises a through-bore  12  which extends at one side and the other of the opening of the closure member  8  in a direction substantially transverse relative to the first axis Z. The direction in which the bore  12  extends thus intersects with the first axis Z when the closure member  8  is in the open position. 
         [0039]    In a preferred manner, the bore  12  extends substantially in a closure member displacement direction between the open position and the closure position, that is to say, here a direction substantially parallel with the second axis X. In this manner, the direction in which the bore  12  extends intersects with the first axis Z substantially when the opening  9  of the closure member  8  is tangential relative to the flow hole  3 . 
         [0040]    The device further comprises relative displacement means of the cap and the closure member in order to move the closure member  8  into the closure position or into the open position. With reference to  FIG. 1 , the displacement means in this instance displace the closure member  8  between the closure position and the open position. 
         [0041]    According to a specific embodiment, the displacement means comprise a set of pincers  15  having parallel jaws. Each jaw is intended to cooperate with an opposing lateral face of the closure member  8  so as to clamp the closure member  8  between the two jaws. 
         [0042]    The displacement means also comprise in this instance a movable plate  16 , on which the set of pincers  15  is arranged in such a manner that a displacement of the movable plate  16  brings about a corresponding displacement of the set of pincers  15  and thereby a displacement of the closure member  8  from the closure position to the open position (and vice versa) when the closure member  8  is clamped between the two jaws. A motor  17  allows, for example, the plate  16  to be displaced. 
         [0043]    The displacement means are connected to a control unit  20  which in this instance controls actuation of the set of pincers  15  and a displacement of the movable plate  16 . 
         [0044]    The control unit  20  is further connected to contactless detection means for the flow of the powder. The contactless detection means in this instance comprise luminous detection means which comprise, at a first end of the bore  12  of the closure member  8 , at least one transmitter  21  of a light beam into the bore  12  and, at a second end of the bore  12 , at least one receiver  22  for detecting the light beam. In this manner, the light beam passes through the closure member  8  via the bore  12  and necessarily intersects with the first axis Z when the closure member  8  is in an open position. 
         [0045]    The transmitter  21  and the receiver  22  are carried by the displacement means. Here, one of the jaws carries the transmitter  21  and the other of the jaws carries the receiver  22 , the set of pincers  15  clearly being arranged in such a manner that, when the jaws clamp the closure member  8 , the transmitter  21  and the receiver  22  extend at the opposite ends of the bore  12 . 
         [0046]    The device further comprises a precision balance  23  which is arranged under the storage reservoir  1  and which is also connected to the control unit  20  in order to assist in determining a quantity of powder dispensed. 
         [0047]    The device comprises tapping and/or vibration means  24  in order to assist the flow of the powder, which means are connected to the control unit  20 . Such means  24  are particularly suitable for dispensing adhesive powder or powder which has a tendency to agglomerate. Since tapping and/or vibration means  24  are well known in the prior art, they will not be described here in greater detail. 
         [0048]    A dispensing cycle of a powder dose will now be described in accordance with a specific, non-limiting embodiment of the first embodiment of the invention. 
         [0049]    In an initial situation, a flask F is arranged on the balance  23  below the storage reservoir  1 . With reference to  FIGS. 4   a  and  5   a , the closure member  8  is then in a closure position so that the light beam transmitted by the transmitter  21  is received in its entirety by the receiver  22 . 
         [0050]    Subsequently, an instruction regarding a quantity of powder to be dispensed is supplied to the control unit  20 . 
         [0051]    The control unit  20  then generates an instruction for displacing the closure member  8  and intended for the displacement means. The jaws clamp the closure member  8  then the movable plate  16  moves in order to bring about a translation of the closure member  8  from the closure position towards the open position in accordance with a first predetermined increment. 
         [0052]    With reference to  FIGS. 4   b  and  5   b , the closure member  8  is displaced in such a manner that the opening  9  is tangent to then aligned partially with the hole  3 . The first grains of powder begin to flow towards the flask F through the hole  3  and the opening  9 . The light beam received by the receiver  22  is then attenuated by the grains. It should be noted that it is important that the geometry of the opening  9  and the hole  3  is such that the first grains fall into the beam. 
         [0053]    By means of the signal which the control unit  20  receives from the luminous detection means, the control unit  20  thereby determines the start of the powder being dispensed. 
         [0054]    In an advantageous manner, as a result of the arrangement of the bore  12 , with relatively weak coincidence between the opening  9  and the hole  3 , the light beam necessarily passes through the first axis Z, which ensures a very precise detection of the start of the flow. 
         [0055]    If a start of flow of the powder is not detected after the opening of the closure member in accordance with the first increment, the control unit  20  generates an actuation instruction intended for the tapping and/or vibration means  24 . If a start of flow of the powder is still not detected after a tapping action, the control unit  20  generates an instruction for displacement in accordance with a second increment. 
         [0056]    This control procedure is carried out in an iterative manner until the start of the flow is detected. The number of increments corresponding to the position of the closure member  8  relative to the cap  2  when the start of the flow is detected is then stored and the closure member  8  is brought into a closure position. The quantity of powder supplied is then weighed by the balance  23  which generates a weighing signal intended for the control unit  20 . 
         [0057]    On the basis of the information supplied by the balance  23  and the detection means, the control unit  20  determines the conditions (position of the closure member  8  relative to the cap and/or tapping) which allow the desired dispensing of powder. 
         [0058]    With reference to  FIGS. 4   c  and  5   c , the closure member  8  is then, for example, displaced until it reaches an open position. The flow rate of the powder is then at a maximum. A greater quantity of grains interacts with the light beam which can thereby be completely cut off, at least intermittently. 
         [0059]    On the basis of the signal received from the balance  23 , the control unit  20  derives a quantity of powder which has already been dispensed which it compares with the instruction for a quantity of powder to be dispensed. 
         [0060]    During a final step, the control unit  20  generates an instruction for displacing the closure member and intended for the displacement means. The movable plate  16  is displaced so as to bring about a translation of the closure member  8  in order to bring the closure member  8  into the closure position. 
         [0061]    According to a preferred embodiment, once the closure member  8  is in the closure position, the control unit  20  compares the signal provided by the balance  23  with the instruction concerning a quantity of powder to be dispensed in order to verify whether the instruction has been complied with. 
         [0062]    In this manner, the device of the invention allows the flow of the powder to be controlled very precisely. 
         [0063]    In an advantageous manner, the device of the invention can be adapted to any type of reservoir and in particular the reservoirs already in use in combinatorial libraries. This is because it is simply necessary to adapt the tapped portion of the cap to the reservoir desired. 
         [0064]    With reference to  FIG. 7 , a second embodiment will now be described. The common elements with respect to the first embodiment illustrated in  FIG. 1  retain the same numbering. 
         [0065]    In the first embodiment, the relative displacement means of the cap and the closure member displaced the closure member  8  between the closure position and the open position. 
         [0066]    In the second embodiment, the relative displacement means of the cap and the closure member displace in this instance the cap  2  and therefore the reservoir  1  so as to bring the closure member  8  between the closure position and the open position. 
         [0067]    The relative displacement means of the cap and the closure member preferably comprise a first set of pincers  18  having parallel jaws, each jaw being intended to cooperate with an opposing lateral face of the closure member  8  so as to clamp the closure member  8  between the two jaws. The first set of pincers  18  thereby maintains the closure member  8  above the flask F in a given fixed position in relation to the flask F so that the opening  9  of the closure member  8  is centered relative to an open end of the flask F. As for the first embodiment, the first set of pincers  18  carries the transmitter  21  and the receiver  22 . One of the jaws of the first set of pincers  18  carries the transmitter  21  and the other of the jaws carries the receiver  22 , the first set of pincers  18  clearly being arranged so that, when the jaws surround the closure member  8 , the transmitter  21  and the receiver  22  extend at the opposite ends of the bore  12 . 
         [0068]    The relative displacement means of the cap and the closure member further comprise a second set of pincers  19  having parallel jaws, each jaw being intended to cooperate with diametrically opposite surfaces of the cap  2  so as to clamp the cap  2  between the two jaws. 
         [0069]    The displacement means also comprise here a movable plate  24  on which the second set of pincers  19  is arranged so that a displacement of the movable plate  24  brings about a corresponding displacement of the second set of pincers  19  and thereby a displacement of the cap  2 , and therefore of the reservoir  1 , in order to bring the closure member  8  from the closure position to the open position (and vice versa) when the cap  2  is clamped between the two jaws. A motor  25  allows, for example, the movable plate  24  to be displaced. 
         [0070]    The displacement means are connected to the control unit  20  which here controls actuation of the second set of pincers  19  and a displacement of the movable plate  24 . 
         [0071]    In an advantageous manner, as a result of the second embodiment, the opening  9  of the closure member  8  remains fixed with respect to the flask F and is preferably centered about the open end of the flask F. Grains of powder are thereby prevented from becoming deposited on the rim of the open end of the flask F and those grains are prevented from falling out of the flask F when the flask F is closed, thereby corrupting the quantity of powder dispensed. 
         [0072]    In this manner, the device of the invention allows the flow of the powder to be controlled very precisely. 
         [0073]    With reference to  FIG. 8 , there is described a workstation comprising a powder dispensing device according to the second embodiment. The common elements with respect to the second embodiment illustrated in  FIG. 7  retain the same numbering. 
         [0074]    The first set of pincers  18  is arranged in the workstation in order to extend above the balance  23  in a permanent manner. Except for the relative movement of one of the jaws of the first set of pincers  18  relative to the other of the jaws of the first set of pincers  18 , the first set of pincers  18  has a fixed position in the workstation relative to the balance  23 . 
         [0075]    The relative displacement means of the cap and the closure member are here arranged in the workstation in order also to displace, in the workstation, an assembly E which is formed by the reservoir  1 , the cap  2  and the closure member  8 . 
         [0076]    To this end, the displacement means comprise a rotation unit  33  to which the second set of pincers  19  is connected in order to allow the assembly E to rotate about a third axis Y which is orthogonal to the first axis Z and to the second axis X. The displacement means also comprise a lifting unit  34 , to which the rotation unit  33  is connected in order to allow the translation of the rotation unit  33 , and thereby of the assembly E, about the first axis Z. The displacement means also comprise a translation unit  35 , to which the lifting unit  34  is connected in order to allow the translation of the lifting unit  34 , and thereby of the assembly E, along the second axis X. 
         [0077]    The displacement means are connected to the control unit which in this instance controls in particular actuation of the first set of pincers  18 , the second set of pincers  19 , the rotation unit  33 , the lifting unit  34  and the translation unit  35 . 
         [0078]    In a preferred manner, the workstation further comprises a device for dispensing a solvent to the flask F in order to dispense a volume of solvent to the flask F once the desired quantity of powder has been poured into the flask F. Preferably, this volume is determined on the basis of a concentration instruction which the control unit  20  has received. 
         [0079]    To this end, the device for dispensing a solvent comprises a container  30  which comprises the solvent to be dispensed and means for dispensing the solvent which are connected to the container  30 . The means for dispensing the solvent comprise, for example, a digital syringe  29 . The dispensing means are connected to the control unit which in this instance controls actuation of the digital syringe  29  in accordance with a concentration instruction which the control unit  20  has received and information concerning the quantity of powder which has been supplied to the flask F, which information is supplied by the balance  23 . 
         [0080]    According to a preferred embodiment, one of the jaws of the second set of pincers  19  comprises a first arm  36  which preferably extends in a direction parallel with the second axis X. The first arm  36  in this instance comprises a cannula  26  and a dispensing pipe which connects the digital syringe  29  to the cannula  26 . 
         [0081]    In a preferred manner, the workstation further comprises a top dispensing device in order to close the flask F by one of those tops once the desired quantity of powder has been poured into the flask F or once the desired quantity of powder and the desired quantity of solvent have been poured into the flask F. 
         [0082]    To this end, the top dispensing device comprises means for introducing tops, which means comprise, for example, a vibrating bowl  31 , in which the tops are placed. In a manner known per se, the vibrating bowl  31  allows a single top to be brought to a given position P fixed relative to the workstation. 
         [0083]    According to a preferred embodiment, the other of the jaws of the second set of pincers  19  comprises a second arm  37  which preferably extends in the direction in which the first arm  36  extends. The second arm  37  in this instance comprises means for gripping the top which is positioned in a position P in the vibrating bowl  31 , the gripping means being at least partially arranged on the second arm  37 . 
         [0084]    For example, if the tops are composed of elastomer material, the gripping means comprise a rigid suction cup  27  which is arranged on the second arm  37 , the suction cup  27  being connected to a pressure reduction generation member such as a vacuum pump  28 . The gripping means are connected to the control unit which in this instance controls actuation of the vacuum pump  28 . 
         [0085]    A work cycle will now be described in accordance with a specific, non-limiting embodiment. 
         [0086]    In an initial situation, the flask F is provided on the balance  23 . The jaws of the first set of pincers  18  are open and surround the flask F. 
         [0087]    The assembly E is in a zero position in which the second set of pincers  19  clamps the cap  2  of the storage reservoir  1  between its jaws, the reservoir  1  not being in a position which is capable of supplying the powder by means of gravitational force. The closure member  8  is mounted on the cap  2  in the closure position. 
         [0088]    During a first step, the lifting unit  34  displaces the assembly E as far as a first position in which the assembly E is at a sufficient height to allow the assembly E to be inverted as described in the following paragraph. 
         [0089]    During a second step, the rotation unit  33  displaces the assembly E as far as a second position in which the reservoir  1  is inverted so as to be able to supply the powder by means of gravitational force, the reservoir extending in this instance along the axis Z. The closure member  8  is then substantially at the same height as the open end of the flask F, it being possible for an adjustment of the height of the assembly E by the lifting unit  34  to be necessary so that the closure member  8  is substantially at the height of the open end of the flask F. 
         [0090]    During a third step, the translation unit  35  displaces the assembly E as far as a third position in which the opening  9  of the closure member  8  is substantially centered about the open end of the flask F. 
         [0091]    During a fourth step, the first set of pincers  18  clamps the closure member  8  between the jaws thereof so that the transmitter  21  and the receiver  22  extend at opposite ends of the bore  12 . 
         [0092]    During a fifth step, in accordance with the instructions from the control unit, the translation unit displaces the second set of pincers  19  and the cap  2  in accordance with the second axis X in order to supply the desired quantity of powder to the flask F. Since the closure member  8  is clamped between the jaws of the first set of pincers  18 , the displacements of the second set of pincers  19  and the cap  2  do not affect it. 
         [0093]    During a sixth step, once the desired quantity of powder has been supplied to the flask F, the first set of pincers  18  releases the closure member  8  which is then in a closure position. 
         [0094]    During a seventh step, the lifting unit  34  displaces the assembly E as far as a fourth position in which the suction cup  27  is at a height greater than the height of a top  32  in a position P of the vibrating bowl. 
         [0095]    During an eighth step, the translation unit  25  displaces the assembly E as far as a fifth position in which the suction cup  27  is substantially centered about the top  32 . The second set of pincers  19  is formed so that the cannula  26  is then centered about the open end of the flask F. 
         [0096]    During a ninth step, the lifting unit  34  displaces the assembly E as far as a sixth position in which the suction cup  27  is substantially resting on the top  32 . 
         [0097]    During a tenth step, the control unit simultaneously generates an actuation instruction intended for the vacuum pump  28  and a dispensing instruction intended for the digital syringe  29  concerning a quantity of solvent to be dispensed. The suction cup  27  thus grips the top  32  and the digital syringe  29  dispenses a quantity of solvent to the flask F. Preferably, once the digital syringe  29  has dispensed the desired dose of solvent, the control unit compares the signal supplied by the balance  23  to the instruction concerning the quantity of solvent to be dispensed in order to verify whether the instruction has been complied with. It is thereby possible to control the quantity of solvent dispensed more finely than when considering only the indications of the digital syringe  29 . 
         [0098]    During an eleventh step, the lifting unit  34  displaces the assembly E as far as the fifth position. 
         [0099]    During a twelfth step, the translation unit  35  displaces the assembly E as far as a seventh position in which the suction cup  27  is substantially centered about the open end of the flask F so that the top  32  is also centered about that end. 
         [0100]    During a thirteenth step, the lifting unit  34  displaces the assembly E as far as an eighth position in which the top  32  is arranged on the free end of the flask F so as to be fitted to the free end. 
         [0101]    During a fourteenth step, the control unit generates a stop instruction intended for the vacuum pump  28 . The suction cup  27  then releases the top  32 . 
         [0102]    During a fifteenth step, the assembly E is brought into a zero position by the lifting unit  34 , the translation unit  35  and the rotation unit  33 . 
         [0103]    Naturally, the invention is not limited to the embodiments described and it is possible to apply construction variants thereto without departing from the scope of the invention as defined by the claims. 
         [0104]    In particular, although it has been indicated that the powder dispensing device according to the invention was suitable for dispensing quantities of powder in the order of a few tenths of a milligram, the device is also completely suitable for dispensing larger quantities of powder. 
         [0105]    Although it has been described that the storage reservoir  1  was a glass vial having a capacity of 4 milliliters, the storage reservoir  1  may be different. For example, the storage reservoir  1  may be an 8-milliliter vial or a  13 -milliliter vial. 
         [0106]    The cap  2  may cooperate differently with the storage reservoir  1 . The cap  2  may, for example, simply be pressed into the neck  4  of the storage reservoir  1 . 
         [0107]    Although here the relative movement of the closure member  8  and the cap is a translation movement, the device may be arranged so that the closure member  8  (or the cap  2 ) is displaced in accordance with another movement, for example, in accordance with a rotation movement. 
         [0108]    The groove  7  may be a T-like groove and not a groove which is intended for a dovetail type connection. The groove  7  may not comprise any stop studs for the edges  10  of the closure member  8  at each of the ends thereof. For example, the movable plate  16  will then be controlled so as to limit a displacement of the closure member  8  relative to the cap  2 . 
         [0109]    Although in this instance the flow hole  3  is circular and the opening  9  has a circular cross-section, the hole  3  and the opening  9  may be of different forms. With reference to  FIG. 6 , the hole  3  is thus of triangular shape and the opening  9  has a circular cross-section. The hole  3  is provided on the cap  2  so that it is one of the tips of the triangle which coincides firstly with the opening  9  of the closure member  8  which allows the start of the flow of the powder to be controlled very finely. 
         [0110]    The term “relative displacement means of the cap and the closure member” is intended to be understood to be means which act either on the closure member or on the cap. 
         [0111]    By way of a variant, the contactless detection means may be optical means which use a light beam and preferably an infrared beam or ultrasonic means. 
         [0112]    Although in this instance the workstation comprises a powder dispensing device according to the second embodiment, the workstation may comprise a powder dispensing device according to the first embodiment. The relative displacement means of the cap and the closure member will then comprise means for displacing the cap relative to the flask and means for displacing the closure member relative to the cap. 
         [0113]    The elements of the solvent dispensing devices and top dispensing devices may be different from those described. For example, the first arm may comprise a double cannula, one of the cannulae being connected to the dispensing pipe and the other of the cannulae being connected to means for dispensing inert gas such as argon. In this manner, once the desired quantity of solvent has been supplied to the flask, the control unit will send a signal to the means for dispensing inert gas so that some inert gas is introduced into the flask in order to purge the remaining air in the flask. 
         [0114]    The workstation may comprise a different number of devices or different devices from those described in addition to the powder dispensing device. For example, the workstation may comprise only one powder dispensing device or only one powder dispensing device and one solvent dispensing device, or only one powder dispensing device and one top dispensing device. The workstation may comprise only one powder dispensing device and one device comprising means for dispensing inert gas such as argon in order to purge the remaining air in the flask.