Patent Publication Number: US-2015086448-A1

Title: Joint for Device for Metering Liquids

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for metering liquids, in particular in a laboratory. It is more particularly related to the metering of liquids in relatively small but accurate quantities, for example of the order of the μl up to 100 ml. More particularly the invention relates to a pipette, a metering device for a bottle or a syringe. 
     STATE-OF-THE-ART AND PROBLEMS FROM WHICH THE INVENTION ORIGINATES 
     Document US 2002/0012613 describes, in the introduction thereof, the problems connected with the metering of liquids using a laboratory device, for example a pipette. When working in a research laboratory or during routine measuring in a biomedical or an industrial medium, the user of a pipette may have to execute a very large number of liquid sucking or expelling operations. As pipetting operations are repetitive, they entail tiredness for the user, then contractions and, according to document US 2002/0012613, even physical damages. As exemplary damages the upper limb disorder (ULD), the repetitive strain injury (RSI), musculoskeletal disorders of the hand and the wrist, tendonitis of the flexor and extensor muscles, osteoarthritis of the basal joint of thumb and the carpal tunnel syndrome can be mentioned. 
     Numerous efforts have been made to reduce tiredness during repetitive metering operations. Document US 2002/0012613 may be cited as an example of an approach relating to the ergonomy of the metering instrument composed of a pipette. Such approach aims at adapting the shape of the pipette to the user&#39;s hand, so that it can be held more easily by the hand and can be operated more easily. 
     Other approaches to reduce tiredness and the associated problems aim at reducing the force required to suck in and to expel the liquid. 
     Upon the metering with a manual pipette including a disposable nozzle positioned on the lower tip of the pipette, the user first pushes a piston by pressing with his/her thumb on a metering button against the force of a spring which is positioned inside the body of the pipette and plunges the nozzle into the liquid. Then the user slowly releases the pressure exerted on the metering button which returns to its initial position while sucking in the liquid into the disposable nozzle, as it is pushed by the action of the spring. 
     The liquid is sucked in using the vacuum which is created, when the piston, which is housed inside the pipette and pushed by the metering button, goes up back inside the body of the pipette towards the upper stop position thereof. To create a vacuum, a joint is generally used which forms the sealing between the internal wall of the pipette cylinder and the piston. 
     The sucking in and the expelling of the liquid using a piston sealingly housed inside the cylinder cause the forces required for metering the liquids. Firstly, the joint is arranged so as to exert a contact force N, normal to the piston or, if it is positioned on the piston, on the internal wall of the cylinder. As a result, the contact force generates a friction force (F=μN, with μ being the friction coefficient and N the normal contact force) created between the joint and the piston, with the friction being the resultant of N required for preserving the sealing. It depends on the mechanic and geometric characteristics of the joint. 
     One understands that the spring which is used for pushing back the piston to the original upper stop position thereof must be strong enough to overcome the friction exerted by the joint on the piston. The friction force parallel to the surface of the piston and resultant of the contact force necessary for the sealing opposes any movement of the piston. The stronger the spring, the more the user uses his/her force to activate the metering button and thus the more her/she gets tired. 
     Efforts have been made to reduce the force of the spring so that the metering button can be more easily pushed by a user. However, in order to use a less strong spring, the contact force N and thus the friction exerted by the joint should be reduced, which would consequently increase the risk of a leakage i.e. for example the risk that the vacuum might not be maintained during the suction of the liquid. 
     In the state of the art, an annular joint made of rubber and/or elastomer, called an O-ring, is often used to provide the sealing between the piston and the wall of the cylinder. Document U.S. Pat. No. 6,926,867 can be mentioned as an example. With an O-ring having a solid section, the resulting friction is relatively high on the plastic material even in the presence of a lubricant. In addition, the joint tolerances are proportionally all the more important since the dimensions are smaller. This results in variable compression rate and contact pressure which are sometimes high to provide the sealing. The reduction in the tolerances on the O-ring and the housing thereof is possible but entails increases in the manufacturing and control costs. Finally, controlling the resulting friction force F is difficult with the O-rings. A minimal constant value can hardly be reached by reducing the contact pressure without increasing the risk of a leakage. 
     Considering the above, the present invention aims at reducing the friction force exerted by the joint intended to provide the sealing between the piston and the internal wall of the cylinder of the device. The present invention also aims at providing a joint preserving the sealing comparable with the devices of the state of the art while reducing the friction forces. 
     More generally, the invention aims at reducing the tiredness undergone by the user upon the repetitive metering of liquids. 
     The invention also aims at implementing a solution which can be provided on devices with different dimensions. More particularly, the present invention aims at implementing a sealing system for small sized metering devices adapted to pistons having a small diameter, by reducing the friction force while preserving a good sealing. In this context, the state of the art often provides joints positioned on the piston. Such joints have the drawback of being difficult to produce and to mount in the device when the piston has a small diameter as is the case with small volume pipettes, for example pipettes for metering volumes of the order 1 to 200 microliters. 
     The present invention also aims at implementing a solution which can be used not only in the field of manual metering devices, but also in the field of electronic devices. With electronic pipettes, for example, a reduced friction force would make it possible to use a motor with a lower power and thus a more economical one, and thus to increase the autonomy of batteries as well as the total number of pipetting operations. The present invention also aims at implementing a solution which can be used with mono-channel pipettes or advantageously multi-channel pipettes to reduce the total resultant activation force. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a device comprising a cylinder and a piston housed inside the cylinder for manually metering liquids, the device being so arranged that, upon metering operations, the piston moves along its axis to suck in or to expel the liquid, with the device further comprising a joint housed in the cylinder and arranged so as to provide a sealing between the cylinder and the piston. 
     According to a preferred embodiment of the device according to the invention, upon metering operations, the joint remains fixed with respect to the movement of the piston and includes at least two parts formed of material parts specifically shaped to locally optimize the functions of sliding and sealing on the piston as well as a sealing fastening against the cylinder. 
     According to one embodiment of the device according to the invention, the joint comprises a first part which cooperates with the internal wall of the cylinder and provides the functions of sealing against the internal surface of the cylinder and fastening to the latter, and a second part which is in contact with the piston and which provides the sealing functions between the joint and the piston and the sliding functions between the latest two pieces. These two parts, which fulfill different functions, have different shapes and/or dimensions. 
     According to another aspect, the invention relates to the manual metering of liquids which comprises a cylinder, a piston sliding in the cylinder against and under the effect of the force of a spring, and a joint housed between an internal wall of the cylinder and an external wall of the piston, characterized in that the joint is an annular part conformed with distinct respectively peripheral and internal annular parts. 
     The peripheral part is preferably arranged for a stationary fastening to said internal wall of the cylinder and said internal part is arranged for a continuous and sealed sliding against the external wall of the piston, with the latter being cylindrical. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a joint for the metering device according to a first embodiment of the invention, with the joint being shown in perspective. 
         FIG. 2  shows the joint in  FIG. 1  in an axial cross-section. 
         FIG. 3  shows a top view of the joint in  FIG. 1 . 
         FIG. 4  shows, in axial cross-section, a cylinder, a piston, and a joint of a device according to the invention. 
         FIG. 5  is an enlarged view of detail C in  FIG. 4 . 
         FIG. 6  schematically shows an enlarged and axial cross-sectional view of the detail of the joint shown in  FIGS. 4 and 5 . 
         FIG. 7  is a perspective view of the joint according to a second embodiment of the invention. 
         FIG. 8  is an axial cross-sectional view of the joint in  FIG. 7 . 
         FIG. 9  is a top view of the joint in  FIG. 7 . 
         FIG. 10  is an enlarged view of the detail C in  FIG. 8   
         FIG. 11  is a partial axial cross-sectional view of a third embodiment of the device of the invention. 
         FIG. 12  is an enlarged view of detail C of the device shown in  FIG. 11 . 
         FIG. 13  is an axial cross-sectional view of a fourth embodiment of the device of the invention. 
         FIG. 14  is an enlarged view of detail C of the device in  FIG. 13 . 
         FIG. 15  is an axial cross-sectional view of a fourth embodiment of the device of the invention. 
         FIG. 16  is an enlarged view of detail C of the device in  FIG. 15 . 
         FIG. 17  is an axial cross-sectional view of a fifth embodiment of the device of the invention. 
         FIG. 18  is an enlarged view of detail C of the device in  FIG. 17 . 
         FIG. 19  is an axial cross-sectional view of a sixth embodiment of the device of the invention. 
         FIG. 20  is an enlarged view of detail C of the device of  FIG. 19 . 
         FIG. 21  is an axial cross-sectional view of a seventh embodiment of the device of the invention. 
         FIG. 22  is an enlarged view of detail C of the device in  FIG. 21 . 
         FIG. 23  is an axial cross-sectional view of a first embodiment of a second implementation of the device of the invention. 
         FIG. 24  is an enlarged view of detail C of the device in  FIG. 23 . 
         FIG. 25  is an axial cross-sectional view of a second embodiment of the second implementation of the device of the invention. 
         FIG. 26  is an enlarged view of detail C of the device in  FIG. 25 . 
         FIG. 27  is an axial cross-sectional view of a third embodiment of the second implementation of the device of the invention. 
         FIG. 28  is an enlarged view of the detail C of the device of  FIG. 27 . 
         FIG. 29  is an axial cross-sectional view of a fourth embodiment of the second implementation of the device of the invention. 
         FIG. 30  is an enlarged view of detail C of the device in  FIG. 29 . 
         FIG. 31  is an axial cross-sectional view of a fifth embodiment of the second implementation of the device of the invention. 
         FIG. 32  is an enlarged view of detail C of the device in  FIG. 31   
         FIG. 33  is an axial cross-sectional view of a sixth embodiment of the second implementation of the device of the invention. 
         FIG. 34  is an enlarged view of detail C of the device in  FIG. 33 . 
     
    
    
     DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS OF THE INVENTION 
     The following description is given as a non-limitative illustration and refers to the appended drawings which show examples of several implementations of the metering device according to the invention. 
     In the context of such description, the location indications such as “high”, “low”, “upper”, “lower”, “external”, “internal”, “horizontal” and “vertical” should be understood directly with respect to the drawing such as shown in a made-up Figure. In the Figures, the objects are shown with their natural orientation i.e. with the orientation they have if the metering device which they belong to is held in a position of utilization. For example, a mono-channel pipette comprising a main axis is oriented so that such axis is vertical. This is also the case with a metering device for a bottle positioned on a bottle, or a manual pipette in the pipette holder thereof. 
       FIGS. 1 to 3  show a joint provided for a pipette according to a first embodiment of the device of the invention, with such joint being shown respectively in perspective, in an axial cross-section and as a top view in  FIGS. 1 ,  2 , and  3 . The joint  1  includes several parts  2 ,  3 ,  4 ,  5 ,  6 ,  7  having different shapes and each fulfilling a specific function, as explained hereinafter. 
     The part  2 , the more voluminous one, forms an annular body which is rigid and which has a profile constant on its contour. It acts as a support for the other parts and enables the fixed anchoring of the joint  1  inside the cylinder of a pipette. Downwards and on the outside of the contour thereof, it includes a slightly enlarged rim  5  intended to create a sealing contact with the internal wall of the cylinder of the pipette, as is described with respect to the second implementation. Two diametrically opposed protruding fins,  6  and  6 ′ protrudingly extend from the cylindrical external surface of the body  2  of the joint  1  toward the upper edge thereof. Such fins cooperate in anchoring the joint in the cylinder of the pipette. 
     Parts  3 ,  4 ,  7  are surrounded by the body  2 . The part  4  includes a horizontal annular connection between the inner edge  9  of the body  2  and two lips  3  and  7  having a reduced thickness, intended to slide in contact with the external cylindrical face of a piston forming the active element of the pipette. The upper lip  3  is sloping upwards whereas the lower lip  7  is sloping downwards. 
     The extreme edges of both annular lips  3  and  7  define the dimension of an opening  8  at the center of the joint  1 , with such opening having a circular shape when seen from above. One understands that the joint  1  in  FIGS. 1 to 3  is intended to be housed and engaged inside the cylinder and that the piston going through the joint will also be housed in the cylinder of a pipette. The profile of the joint, in diametrical section according to  FIG. 2 , has an axis of symmetry  15  which coincides with the axis of symmetry of the pipette and includes two symmetrical halves a and b, each with a massive zone  2 , 5  fixed to the cylinder and a flexible zone  4 ,  3 ,  7  shaped to have a sliding contact with the external face of the piston of the pipette. It is important that the contact between the lip  3 ,  7  and the piston is sealed but with a resistance to friction as low as possible, whereas the body  2  must be rigidly fixed to the cylinder. As regards the material of the joint  1 , an appropriate elastomer will preferably be chosen, which enables a precise molded shaping. 
     The different functions dedicated to the various parts of the joints explain the asymmetrical shape of each one of the parts a and b, on either side of the axis of symmetry, and distinguishes the device according to the invention from the joints for pipettes of the O-ring or X-ring type of the state of the art. 
     Reference is now made to  FIGS. 4 to 10  which show a metering device according to a second implementation of the invention. 
       FIG. 4  shows an axial cross-section of the elements in a pipette intended to be manually activated. Such a pipette includes a piston  23  which is housed so as to be able to slide in a cylinder  20  composed of a lower part  22  separated by a joint  21  from a upper part  24 . The joint  21  creates the sealing between the lower part  22  and an upper part  24  and the cylinder  20 , so that the pipette is functional. Whereas  FIG. 4  shows the piston  23  in one piece, as it is obtained for example with a molding process, the cylinder  20  can be made of two different parts,  22 ,  24 , liable to be connected with a thread. The free space at the basis of the cylinder  20  enables the suction of the liquid when the piston  23  goes up in the cylinder, on the basis of which a nozzle is fixed and plunged in the liquid. The suction effort is maintained thanks to the sealing provided by the joint  21 , as explained at the beginning of the present document. 
       FIG. 5  shows, as an enlarged and axial cross-section similar to  FIG. 4 , the position of the joint  21  between the two upper and lower parts  22  and  24  of the cylinder  20 . The joint  21  is housed inside the cylinder  20  exactly at the passage between the lower  22  and upper  24  parts. If both parts are made of two separate parts, the joint can be housed in the lower part  22  or in the upper part  24 , the condition for this last possibility being that the connection (possibly by thread) between both parts  22  and  24  is also sealed. 
     In  FIG. 5 , the extract indicated with letter C in  FIG. 4  illustrates the housing of the joint  21  in the cylinder  20 . The axial cross-sectional view shows, as in  FIG. 2 , the profiles of both symmetrical sections (a) and (b) of the annular joint and a certain similarity can thus be seen between the joint  1  in  FIGS. 1-3 , the matching parts having the same reference signs. The joint  21  in  FIGS. 4 and 5  thus includes the body  2 , the plane connection  4 , and the circular lips  3  and  7 , wherein the smooth cylindrical face of the piston  23  slides by deforming these elastically. The plane annular part  4  is provided with a cylindrical rib  11  extending in the lower part of the body  2  of the joint, unlike  FIGS. 1 to 3 . It provides recesses and improves the functional separation between the fastening of the joint to the cylinder  20  and the flexible sealing zone against the piston  23 . 
     A recess (or an air pocket) is a notch and/or a bulge which creates zones with a reduced thickness, with such zones defining the transitions between the various parts, more particularly between the parts fulfilling different functions. 
     The lower part  22  of the cylinder  20  shows, at the upper end thereof, a flat bottom housing  26  which receives the joint  21  and prevents any vertical movement of the latter towards the bottom of the cylinder  20 . A vertical movement upwards is mainly prevented by the fins  6 ,  6 ′ having the shape of ring sections protruding from the body  2 . Such fins are engaged in the openings  27 , 27 ′ which go through the wall of the cylinder  20 . The body  2  is rigid enough to prevent the movement of the joint  21  when a force oriented vertically upwards is applied thereon. 
     In order to improve the sealing between the joint  21  and the internal wall of the cylinder  20 , the rim  5  of the joint defining a perimeter which is slightly greater than that of the body  2  exerts a pressure on the internal wall of the cylinder  20 . The force creating such a pressure may be relatively high because no relative movement between the joint and the cylinder is provided upon the operation of the metering device. According to the invention, and thanks to the shape of the joint, the force exerted thereby on the internal wall of the cylinder  20  is uncoupled of the contact force exerted by the same joint on the piston  23 . The latter is much smaller. 
       FIG. 5  also shows that the lips  3  and  7  surround the piston  23  and thus create a sealing contact with the piston. Thanks to the reduced thickness of the lips  3  and  7  with respect to the rigid part  2  of the joint, and thanks to the orientation of the lips, which includes a vertical part, humans skilled in the art will appreciate that the pressure exerted on the piston is smaller than, and even substantially smaller than the pressure and the force exerted by the joint  21  on the internal wall of the cylinder  20 . The humans skilled in the art will more particularly note that, compared with an O-ring, the joint  21  includes several recesses  31 ,  32 , which uncouple the various parts thereof and thus make it possible to obtain the advantages of the invention. In particular, it is possible to reduce the frictional force exerted by the joint on the piston  23 . 
     The lips  3  and  7  of the joint shown in  FIG. 5  form a closed space  30 , which can be used as a tank for a lubricant. Using a lubricant at this place makes it possible to reduce the friction force on starting up by breaking the adhesion between the joint  21  and the piston  23  further to an extended period of rest, during which the device would not have been used. The flexibility of the lips at the zones of contact with the piston causes micro-deformations which also make it possible to quickly create the lubricating intermediate film. 
     The closed space  30  is shown on a larger scale in  FIG. 6 , wherein the presence of a lubricant  33  is visible. The lubricant  33  can particularly be found in the contact zone between one lip  3  and  7  of the joint  21  and the piston  23 . The lubricating film prevents/postpones the creation of adhesion forces and reduces the friction between the joint and the piston  23 , which entails that the force required to move the piston  23  in a vertical direction is comparatively smaller. 
     While referring to  FIG. 6 , we mentioned the thickness c, c′ of the lips  3  and  7  of the joint  21 . Each one of such thicknesses is measured at a contact point between the lip and the piston in a direction perpendicular to the piston axis. Such thickness (or distance) is small when compared to the dimensions of the joint or body  2  of the joint (visible in  FIGS. 1 ,  2 ,  5 ). According to one embodiment of the joint according to the invention, the distance c (and/or c′) is less than 1 mm, preferably less than 0.7 mm, less than 0.5 mm and/or even than 0.5 mm. Such thickness is preferably applied to the whole or to the main part of the surface of the contact zone between the joint and the piston. The uncoupling of the various parts of the joint, as mentioned in detail hereabove, allows such a small “contact thickness” between the joint and the piston  23  and also makes it possible to reduce the contact force and the friction force imparted by the sealing contact between the joint  21  and the piston  23 . Consequently, the spring forces required for pipetting can be reduced and the repeated handling of the metering device according to the invention becomes less tiring, the risk of contraction, muscle stresses, tendonitis and/or muscular pains are generally reduced. 
     According to one embodiment, a connection zone between the part fulfilling the function of anchoring the joint in the seat thereof and/or sealing against the wall of the cylinder and the part fulfilling the function of sealing the piston, which includes a reduced thickness as mentioned above. In this case, the lip does not necessarily provide the uncoupling function itself, but the structure which connects the parts fulfilling the various functions. If we consider the example of the joint  1  as illustrated in  FIG. 2 , this can be the annular connection  4  which is characterized by a thickness such as defined with respect to the letters c and/or c′ above. It should be noted that in this case, the measured thickness is the minimum thickness between two parts, more particularly between the anchoring and the sealing part against the cylinder (for example, the part  2  in  FIG. 2 ) and the sealing part against the piston (for example the lips  3  and  7  in  FIG. 2  or  5 ). An example with a small thickness connection is shown in  FIG. 12 , where connections  58  and  59  are thinner than the lips providing the contact with the piston. In  FIG. 12 , the thickness of the connection between the functions is reduced thanks to a recess  53 . 
     The embodiments illustrated in the following Figures also make it possible to take advantage of the above-mentioned advantages, which will thus not be systematically repeated. 
       FIGS. 7 to 9  show in perspective, in an axial cross-section and in a top view as well as an enlarged partial cross-section in  FIG. 10 , a joint  40  which is different from the joint  1  shown in  FIGS. 1 to 3 , in that it further includes two cross-sectional and parallel cuts  35 ,  35 ′ which go through the joint in vertical directions from the top down to approximately the middle of the joint  40 , stopping at the level of the internal connection  4  between the body  2  and the lips  3  and  7 . The cuts  35 ,  35 ′ affect the upper parts of the massive body  2  and are provided so as to cut four recesses in the wall of the body  2 , out of but close to the ends of the fins  6 ,  6 ′. The cuts  35 ,  35 ′ are vertical slots which are positioned at equal distances from the central axis of symmetry  15  of the joint  40 . 
     The four recesses created by the cuts  35 ,  35 ′ facilitate the insertion of the joint  1  into the housing thereof, by providing the shifting of the fins  6 ,  6 ′ and the upper part of the body  2  associated towards the inside of the joint. That way, the fins  6 ,  6 ′ facilitate the insertion of the joint into the housing thereof inside the cylinder  20 . As a matter of fact, the joint must be inserted through an upper opening in the cylinder  20  and through a passage having an internal diameter which is almost identical with the diameter of the joint  40 , more particularly the diameter defined by the upper edge of the body  2 . As the cuts  35 ,  35 ′ do not go further in the direction of the bottom of the joint  40  than the internal plane connection  4  and do not reach the level of the rim  5 , the cuts  35 ,  35 ′ do not interfere with the sealing function against the internal wall of the cylinder  20 . The part of the joint  40  which is higher than the internal connection  4  then fulfils, in addition to the function of anchoring the joint in the housing thereof using the fins  6 ,  6 ′, a function of flexibility facilitating the insertion of the joint during the assembling of the pipette. 
       FIG. 10  is an enlarged partial cross-sectional view of  FIG. 8  and appears in the latter in a circle. The characteristics shown in  FIG. 10  are also present on the joint  1  in  FIGS. 1-3 , but are not mentioned in these Figures because of the small size of such characteristics. 
       FIG. 10  shows a contact zone  41 , formed by a part of the upper lip  3 , the surface of which is not very high and has the shape of a hollow cylinder. It should be noted that the small height of such contact surface  41  means that the whole contact surface is reduced. The humans skilled in the art would more particularly note that the reduction in the contact surface between the joint  40  and the piston  23  is equivalent to a reduction in the friction force by adhesion when at rest, and during a relative movement between such two elements.  FIG. 10  also shows more particularly a segment having an asymmetrical profile  43  of the lip  3 , curved so as to both determine and minimize the contact surface  41 . 
       FIG. 10  also shows a contact zone  42  of the lower lip  7  with the piston  23  (not shown). The profile of the lip  7  does not have the asymmetric concave shape  43  of the upper lip  3 , but the contact zone  42  is however clearly defined and limited with respect to the remainder of the lip  7 . 
       FIGS. 11 and 12  show a general axial cross-section and a partial enlarged axial cross-section of one embodiment of the invention comprising a joint  50 . The joint  50  is simpler than the joints  1 ,  40  mentioned above, but also includes two lips which are in contact with the piston  23 . If the profile of the joint is considered ( FIG. 12 ) in an axial cross-section limited to one-half of the assembly with respect to the axis of the piston, it appears that the joint  50  is less asymmetrical than the preceding joints  1 ,  40 . It clearly appears that the joint  50  in fact has a plane of symmetry perpendicular to the axis of the pipette which in the plane of  FIG. 12  is reduced to a particular axis of symmetry d with the profile shown in this Figure. Outside and in contact with the cylinder  20  of the pipette, the joint  50  includes two body segments  56  and  57 . Both segments are not symmetrical with respect to the axis d because of the presence of the rim  5  on the body segment  53  and of a slightly sloping structure on the opposite body segment  57 . The external cylindrical face of the body segments  56  and  57  is in contact with the cylinder  20 . Inside, i.e. in contact with the piston  23 , the joint has two lips equally symmetric with respect to the axis d. Between the support elements  56  and  57  extends a recess  53  which defines  2  junctions or flexible connections  58  and  59 . If the small differences existing in the parts  56  and  57  which are responsible for the anchoring of the joint in the housing thereof, are ignored, only one axis of symmetry d is identified. 
     The hollow support  2 , present in the joints  1  and  40 , is transformed into two parts of support  56  and  57 , one being arranged vertically above the other and separated by a recess  53 . Such recess  53  creates two junctions  58 ,  59  which are approximately horizontal and which join the parts of the support  56  and  57  with the lips. The fineness of the junctions  58 ,  59  determines the mechanical uncoupling between the rigidity of the support parts  56  and  57  with a relatively large volume and the flexible lips. 
     At this stage, it should be mentioned that the joint  1 ,  40  and  50  are composed in one part and manufactured in only one material, generally an elastomer. The different rigidity and/or flexibility of the various parts of the joints result from the various thicknesses of these parts or from the volume occupied by the material by and in such parts. 
     Embodiments shall be mentioned further down in which the differences in rigidity making it possible to fulfill different functions are obtained by different materials placed in different parts of the same joint. 
     Upwards, the joint  50  is retained in the housing thereof using a holding ring  55  which is placed in a notch  54  of the pipette body  20 . Upon assembling the metering device, the joint  50  is inserted through an upper opening in the cylinder  20  and engaged up to the lower rim  26 . Then, the holding ring  55  is inserted and stopped at the notch  54 . In this way, the supporting elements  56  and  57 , which are relatively rigid, provide the fixed and stationary positioning of the joint  50  inside the seating thereof in the cylinder  20 . 
       FIGS. 13 and 14  also show respectively in a general axial cross-section and an enlarged partial cross-section an embodiment of the invention including a joint  60  with only one lip  7  provided as the lower lip of the preceding embodiments (the joints  1 ,  40  and  50 ). The general structure of such joint  60  has several parts in common with the embodiment shown in  FIGS. 11 and 12  and the matching parts are mentioned with the same reference numbers. 
     Contrary to the notes above with respect to the symmetry of the joint shown in  FIGS. 11 and 12 , the semi-section of joint  60  shown in  FIG. 14  has no axis of symmetry. The single lip  7  has a smaller sealing function upon the return of the piston (suction=partial vacuum, extended air cushion ΔP−), whereas upon the metering operation (the piston moved downwards), it tends to be reinforced by the creation of an overpressure ΔP+ providing a complete expulsion. 
     According to an alternative embodiment of the invention (not shown in the drawings), the joint includes only one lip similar to the situation shown in  FIGS. 13 and 14 , with the difference that the single lip is turned upwards and matches an upper lip of one of the embodiments described above. Such embodiment also has advantages since the single lip turned upwards has a significant sealing function upon the return of the piston which is important. Upon the suction of the liquid, the reduction in the friction obtained by eliminating the upper lip is an advantage. 
     It is clear that in a two-lip joint, with an upper lip and a lower lip, as shown in  FIGS. 1-12 , both advantages mentioned in detail above are obtained. 
       FIGS. 15 and 16  show an embodiment according to the invention including a joint  70 , the supporting part of which  72  has the shape of a hollow cylinder and includes and surrounds the greatest part of the stabilizing element  78 , which is rigid and made up of a different material and thus is more rigid than the remainder of the joint  70 , for example a metal core. The latter is thus composed of 2 different materials. The more rigid material  78  buried in the parts of the joint  70  which plays the part of a support for the assembly of elements, provides the anchoring and the stable positioning thereof in the housing. 
     The lower lip  77  and the upper lip  73  of the joint  70  are symmetrical ( FIG. 16 : half section of an axial cross-section). On the contrary the external part of the half section  72  is massive and has a sealing rim  5  which is operated as mentioned above and contains the stabilizing element  78  having a unsymmetrical form. Such element includes several parts, which in the radial cross-sectional view of  FIG. 16 , are shown as the arms  79 ,  71 ,  78 , but compose a short tubular element  79  considering the three-dimensional shape of such element  75 , and two extensions having the shape of flat rings  71 ,  78  with different diameters, respectively connected to the center and to the upper end of the tube  79 , and directed one inwards and one outwards of the cylinder. The external ring  78  goes through the body made of a less rigid material of the joint  70  to engage into a groove  74  in the internal wall of the cylinder  20 , in order to further anchor the joint  70  in the hollow cylinder  20 . In this way, the upper extension  78  is operated similarly to the holding washer  55  in  FIG. 12 . In the embodiment according to  FIGS. 15 and 16 , this “holding washer  55 ” composed of the extension  78  is integral with the joint  70 . In this way, using an element  78  made of a second material more rigid than the basic material wherein the lips are formed, thus makes possible (a) to obtain a more rigid supporting function provided by the supporting cylinder  72  and (b) at least partially the anchoring the joint  70  inside the cylinder using the interaction between the elements  78  of the joint and  74  of the cylinder  20  wall. 
     In other words, contrary to the joints of the state of the art, the present invention also relates to joints manufactured in one piece in several materials having different rigidity. The different rigidity enables the main formation of the parts of the joint reinforcing the anchoring thereof in the cylinder, for example through the interaction thereof with stops, such as a groove or openings existing in the cylinder  20 . 
       FIGS. 17 and 18  show another embodiment of the object of invention, according to which, as per the embodiment shown in  FIGS. 15 and 16 , the joint  80  is made of one piece but includes parts made of different materials. Like in  FIGS. 15 and 16 , one of the materials is more rigid than the other. In  FIGS. 17 and 18 , the tube  85  which is surrounded by or mainly buried, and supports an elastic material providing the sealing functions against the piston  23  in the cylinder  20 . 
     As can be seen in  FIG. 18 , the rigid element  85  exhibits an upper crown bulge  88 , which overlaps the less rigid material which the lips  83  and  87  are made of, as well as other parts of the joint characterized by their flexibility. Such upper crown  85  is formed so as to be able to engage into a groove  84  of the cylinder  20  wall, so as to block or stop the joint in the cylinder. 
     The joints shown in  FIGS. 15 and 16  or  17  and  18  can be manufactured for example by overmolding, bi-injection or any other composite process. As an alternative, both elements can be manufactured separately, and the less rigid part can be engaged on the rigid parts for example. Of course other possible manufacturing exists and can be chosen by humans skilled in the art. 
       FIGS. 19 and 20  show an other embodiment of the present invention. The joint  90  includes a tubular supporting part  92  having a longer shape than the previous embodiments. The connection element  4  starts from a region close to the basis of the supporting tube  92  and opens onto both lips  93  and  97 , which in the embodiment shown in  FIGS. 19 and 20  have different shapes, with the lower lip  97  being a bit longer than the lip  93 . 
     In  FIGS. 19 and 20 , the supporting tube  92  is thinner than in the previous embodiments. This type of embodiment makes it possible to fix the elements in the cylinder wall without any openings. It is advantageous for example, for small sized joints positioned in “deep” seats of cylinder, for example for multi-channel pipettes. Because of unmolding constraints, a groove for the fastening in the upper part close to the inlet of the cylinder is privileged. The stability and the support function are provided partly by the length of the tubular part  92 , the peripheral contact zones in  5  and  94  are compressed. The same principle applies to the embodiment shown in  FIGS. 21-22 , described above. 
     Towards its upper end, the supporting cylinder  92  includes an external rim  98 , which cooperates with the groove  94  in the cylinder so as to reinforce the anchoring of the joint  90  in the cylinder  20  of the metering device. 
     The embodiment according to  FIGS. 19 and 20  is further characterized in that the connection zone  4  having the shape of an internal flange starts from the supporting tube  92 , then first curves down and contacts the internal rim  26  of the cylinder  20 . Then the flange  4  is parted into two lips  93  and  97 , as described above. Then a recess  95  is formed between the flange  4  and the lower end of the supporting tube  92 , thus ideally separating the supporting and sealing functions relative to the wall of the cylinder  20  from the sealing function on the edge  5  with the piston  23 . 
       FIGS. 21 and 22  show one embodiment with a joint  100  similar to that of  FIGS. 19 and 20  but different therefrom in that the internal flange  4  of the joint  100  leaves from the lower end of the supporting tube  102 . In addition, the joint  100  includes a plurality of sealing ribs  103 ,  104  and  105  on the external surface of the supporting tube  102 . Such compression sealing ribs replace the enlarged rim  5  of the previous embodiments and secure the sealing function against the internal wall of the cylinder  20 . 
       FIGS. 23 and 24 , as well as the following Figures, relate to embodiments which vary from the preceding embodiments in that the lips such as lips  93  and  97 , for example, are absent. The sealing function against the piston  23  is provided by a part which, according to the half-profile shown in  FIG. 24 , for example, is the shape of a curved line  112 ,  114  oriented towards the axis of the piston and the crowned proximal zone  114  which is in contact with the piston. As seen in three dimensions, this type of joint is a tubular element the central part of which has a sinusoidal shape similar to bellows. 
     The shape and the arrangement of the joint  110  in the housing of the cylinder  20  are such that a large air pocket  115  exists and fills a very large part of the annular volume between the cylinder and the joint opposite the piston. The humans skilled in the art will value that, through such recess, the pressure and consequently the friction force exerted on the piston is highly reduced with respect to a rigid body made of a polymer material, such as O-rings, while preserving a good sealing. 
     The embodiment shown in  FIGS. 23 and 24  shows a joint  110 , the central part  112 ,  114  of which is curved toward the center thereof and the middle  114  of the curve slightly touches the piston  23  thus providing a tight connection with low friction force or low contact pressure. The lower part and the upper part  113  and  111  of the tubular elements are arranged so as to fulfill the other functions of the joint, as described hereinafter. 
     The lower part of the joint  110  is arranged so as to form a sealing connection with the internal wall of the cylinder  20 . For this purpose, a rigid ring  116  made of a metal or a rigid polymer, for example, pushes the lower portion  113  towards the wall of the cylinder  20 . A groove or a hollow part  117  is found in the wall of the cylinder  20 , which stops or locks the rigid ring  116 . Thus the joint  110 , and more particularly the lower part  113  are immobilized in the cylinder. 
     The upper end  111  of the joint  110  is shaped in a cylindrical form the cylinder and is stopped by a halting ring  119 , locked as the holding washers described above. 
     It should also be noted that, according to the embodiment shown in  FIGS. 23 and 24 , the profile of the internal face of the cylinder  20  includes a narrow part  118  reducing the internal diameter thereof at the level of the joint housing. The zone of such rim  118  makes it possible to control, for example to position closer, the position of the lower part  113  and ring  116  with respect to the piston  23 . In this way, the friction force and the sliding provided by the joint on the piston can be better adjusted. 
       FIGS. 25 and 26  show a joint  120  based on the same concept as the one in  FIGS. 23 and 24  with a few differences in the embodiment however. More particularly, the holding washer  119  intended to lock the vertical displacement upwards of the joint  110  in  FIGS. 23 and 24  does not appear in  FIGS. 25 and 26 . It is replaced by a widened structure  121  of the upper end joint  120 , which characterizes such embodiment by giving a high rigidity, so that it can then fulfil the function of anchoring the joint  120  upward. For this purpose, the widened structure  121  is engaged in a groove  123  of the internal wall of the cylinder  20  thus preventing any vertical movement of the upper parts of the joint  120 . 
     The lower part  112  of the joint also includes a widened part  122  which cooperates with the groove  117  as described in the preceding paragraph for the upper end of the joint  120 . However, in order to provide a sealing connection between the joint  120  and the internal wall of the cylinder  20 , a rigid ring  116  is provided to press the lower part  122  of the joint towards the internal face of the cylinder  20 . 
       FIGS. 27 and 28  show other alternatives of the joint according to the concept described with reference to  FIGS. 23-26 . In principle, the sealing of the joint  130  against the piston  23  is embodied in  FIGS. 23-26 , but the anchoring in the housing of the cylinder  20  is modified by the modification in the ends of the joint  130 . 
     This is also the case in the embodiment of  FIGS. 29 and 30 , which shows a joint  140  with a lower end  141  sufficiently voluminous and thus rigid to provide both the anchoring of the joint in the housing thereof and the sealing against the internal wall of the cylinder  20 . A ring or a rigid ring like that in  FIGS. 23-26  is no longer necessary. 
       FIGS. 31 and 32  show an alternative of the concepts in  FIGS. 23-30  in that the curved shape oriented towards the axis of the piston and the proximal zone of which is in contact with the piston includes, in a view showing the semi-profile in  FIG. 32 , two summits which form rounded contact points  153  and  157 , and thus creating a closed space  154  limited by the joint  150  and the piston  23 . Considering the joint  150  cylinder  20  and piston  23  assembly in three dimensions, it clearly appears that the contact points  153  and  157  are hollow contact rings or cylinders coaxial with the piston  23  and located in parallel planes. Similarly a closed space  154  has a three-dimensional shape of a ring. 
     The closed space  154  of the joint  150  has the same function as the closed space  30  shown, for example, in  FIG. 5  or in greater details in  FIG. 6 . Such space is used as a tank for the lubricant and thus contributes to the correct sliding upon the vertical movement of the piston  23  along its axis, upon the metering. 
       FIGS. 33 and 34  show an extension of the principle shown in  FIGS. 31 and 32  with a joint  160  which includes, according to the half-profile in  FIG. 34 , three rounded points  161 ,  162 ,  163  of contact with the piston  23  enclosing two closed spaces  164  and  165 . As in both previous examples, the contact points are located in a central zone of the joint limited upwards and downwards by portions of the joint  160  having a shape of inverted conical walls  155  and  156 . 
     It should be noted that the joint  160  assembly is relatively rigid, inclusive of the curved zone, but that this fact is partially compensated by the rounded contact zones  161 ,  162 ,  163  which are small and easily deformable upon the starting-up of the piston, which enables the regeneration of a lubricant interface film and reduces the friction force per contact zone. 
     For producing the joints according to the invention, molded elastomers of the FPM type preferably resisting a temperature from 15 to 150° C. can be used, which makes the usual utilization/sterilization range for laboratory instruments. Examples of such elastomers are silicone, butyl rubber, ethylene copolymers and propylene copolymers, as well as fluoride vinylidene and hexachloropropylene copolymer, among others. 
     According to the invention, additional methods are proposed to further reduce the friction forces of an elastomer, more particularly the adhesion forces at rest (creation on a surface of repulsion-responsive groups). The peripheral treatment of the joint and/or the adjunction of internal lubricants (whether solid or liquid) are techniques according to the invention. One cites, among others, the creation of micro-tanks of lubricants by “sand-blasting/cryogenization”, the halogenization or the surface molecular structural transformation by plasma projection, as well as the incorporation of “alloy” elements in the matrix, with such elements being chosen for example, among fluorinated powders and/or lubricants. If a lubricant is used, it can be simply added or be grafted. It is preferably chosen with a high molecular weight. 
     In the case where the joint includes an elastomer including, in the matrix thereof, an alloy element, the proportion by volume of said alloy element will be chosen to be smaller than or equal to 30%, preferably smaller than or equal to 25% of the total volume of the elastomer. 
     According to one embodiment of the device according to the invention, at least a part of the joint is made of a material having a Shore A hardness of less than 75. Preferably, the Shore A hardness of the material will be between 30-75, or 40 to 70. Preferably, any part in sealing contact with the piston will be characterized by the Shore hardness values mentioned above. For example, the lips shown in  FIGS. 2 ,  4 - 6 ,  8 ,  10  and  11 - 22 , or the contact zones  114  in  FIGS. 23-30 , and  153 ,  157 ,  161 ,  162 ,  163  of  FIGS. 31 to 34 , are composed of a material having the Shore characteristics mentioned above. 
     As mentioned above, the device according to the invention is characterized by the utilization of joint including parts having different geometric characteristics and/or different volumes. Thanks to the characteristics of the joint, it is possible to reduce the friction force exerted by the joint on the piston. The friction force must be &lt;&lt;F spring  which pushes the piston back and the level of which is adjusted to guarantee the contact accuracy against the mechanic stops determining the correct volumetric performances. The friction force generally also depends on the size of the piston and/or the pipetted volume. According to the present invention, friction forces (F stat =μ stat ×N and/or F dyn =μ dyn ×N) of the order of 2-5 N are obtained from maximum volumes up to 100 ml. For smaller volumes, more particularly maximum volumes of approximately 10 to 20 ml, the friction force may be reduced to about 1N. Finally, for maximum volumes of ≦1,000 μl, the friction force is ≦0.6 N, preferably ≦0.5 N, ≦0.4 N and even ≦0.35 N. The reduced frictional forces enable the utilization of a spring having smaller forces. 
     The devices of the invention make it possible to meter volumes between 1 μl and 200 ml. For example, the device of the invention may be a pipette or a metering device for metering volumes of 1 to 1,000 μl, 0.1 or 0.2 to 2 ml, 0.1 or 0.5 to 5 ml, and/or 1 to 10 ml. 
     According to another example, the device of the invention may be an adjustable micropipette covering the volume selected within the ranges of 50-1,000 μl, 10-200 μl, 1-100 μl, 1-50 μl, and 0.5-10 μl. 
     Preferably, the material can be sterilized at temperatures of approximately 121 to approximately 134° C. 
     The diameter of the piston of the device may be, for example, of 1.5 to 10 mm. Preferably, the piston of the device has a diameter of less than 6 mm, preferably &lt;5 mm or even &lt;4 mm or even &lt;3.5 mm or even &lt;3 mm. 
     The pressure variations around the working pressure (atmospheric pressure of approximately 1 bar) generally do not exceed approximately ±0.2 bar, preferably 0.1 bar or even 0.05 bar, depending on the volume.