Abstract:
A pipetting system with a pipetting device and at least one pipette tip releasably fastenable thereon, at least one fastening element on the pipetting device, on which the pipette tip is fastened, an ejection means on the pipetting device, which has an axially movable ejection element for releasing the pipette tip from the fastening element with an axial movement of the ejection element and a drive means for driving the axial movement of the ejection element, and a pull-means gear, push-means gear or linkage gear which transmits an essentially axial drive movement of the drive means into an axial movement of the ejection element and with which the ejection element at least on releasing the pipette tip from the fastening element is axially movable over a smaller distance than the essentially axial drive movement covers and an ejection force exceeding the force for the essentially axial drive movement can be exerted onto the pipette tip.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a pipetting system with a pipetting device and at least one pipette tip releasably fastened thereto. 
     Such pipetting systems are above all used in the laboratory for metering fluid quantities. These fluids are suctioned into pipette tips and ejected therefrom. For this mostly pistons are displacably arranged in a cylinder. With air cushion systems the piston and cylinder are integrated into the pipetting device and communicate with the pipette tip so that the metering of the fluid is evaluated via an air cushion. With direct displacement systems the piston and the cylinder are integrated into the tip and act directly on the suctioned-in fluid. Such pipetting systems are also called syringes. Pistonless systems may in particular comprise a pipette tip with a balloon-like end section which expands for suctioning in fluid, and for expulsion is compressed. 
     The pipette tip is detachably connected to the pipetting device so that after usage it may be exchanged for a fresh pipette tip, by which means with subsequent meterings contaminations may be avoided. Pipette tips for one-off use are available inexpensively of plastic. 
     The pipetting devices have a fastening attachment for fastening pipette tips. Mostly this is a conical projection onto which is squeezed the pipette tip with a conical receiver. This may be effected without gripping the pipette tip by sticking the fastening attachment onto a pipette tip which is ready and waiting in a holder. 
     For avoiding contamination of the operating personnel it is furthermore desirable to release the pipette tip from the fastening attachment without grasping it. For this many pipetting devices are equipped with an ejection means which with an ejection sleeve is allocated to the upper edge region of the pipette tip and may be actuated on an ejection knob. With pipette tips which are stuck on particularly strongly or even “rammed on”, for the ejection of the tips however a high force effort is required which already with one-channel systems compromises the use or even makes it impossible. A particularly high force effort may result by way of the multiplied tip ejection forces with multi-channel pipetting systems which have several parallel pipette tips to be ejected. 
     From EP 0 566 039 B1 there is known a pipette with a tip remover which for simplifying the use by way of reduction of the ejection force comprises a lever mechanism. This lever mechanism projects laterally from a pipette housing and is to be pressed manually. It may have a toothed wheel which on an actuation arm for the pipette tip is rotatably coupled in a vertical plane. Further the inner flank of the toothed wheel meshes with a rack on the side of the elongate housing. On the outer side of the actuation arm on the side of the housing there is arranged a hollow push-rod which with a thread on its inner side meshes with the outer side of the gearwheel. If the push-rod is pressed down, the toothed wheel moves downwards and simultaneously takes with it the actuation arm and an ejection sleeve, by which means a pipette tip is pushed back from a fastening cone. With this the push-rod covers exactly double the distance as the actuation arm and the force exerted on the push-rod is half as large as the force used for pushing back the pipette tip. This system is expensive in its design and permits only a single transmission ratio of 1:2 so that it is limited in its usability. 
     BRIEF SUMMARY OF THE INVENTION 
     Proceeding from this it is the object of the invention to provide a pipetting system with an ejection means which apart from those mentioned previously also permits other transmission ratios and design simplifications. 
     This object is achieved by a pipetting system with the features of claim  1 . Advantageous formations of the pipetting system are specified in the dependent claims. 
     The pipetting system according to the invention has 
     a pipetting device and at least one pipette tip releasably fastenable thereon, 
     at least one fastening element on the pipetting device, on which the pipette tip is fastened, 
     an ejection means on the pipetting device, which has an axially movable ejection element for releasing the pipette tip from the fastening element with an axial movement of the ejection element and a drive means for driving the axial movement of the ejection element, and 
     a pull-means gear, push-means gear or linkage gear which transmits an essentially axial drive movement of the drive means into an axial movement of the ejection element and with which the ejection element at least on releasing the pipette tip from the fastening element is axially movable over a smaller distance than the essentially axial drive movement covers and a force exceeding the force for the essentially axial drive movement can be exerted onto the pipette tip. 
     The pipetting system according to the invention is an alternative to the known pipette with tip remover, which on account of the pull-means gear, push-means gear or linkage gear permits the known transmission ratio as well as other transmission ratios and thus an increased freedom of design and expanded application possibilities. With a pipetting system according to the invention also transmission ratios are possible which vary during the tip ejection. Furthermore the pipetting system permits the possibility of constructional variations. 
     With a pull-means gear embodiment the drive means and the ejection element may have end sections which engage over one another and the gear may have a deflection roller rotatably mounted on the end section of the ejection element and a cable which at one end is fixed with respect to the fastening element and at the other end is fastened to the end section of the drive means. With this is it preferred that the drive rod and the ejection element are aligned parallel to one another. With the essentially axial drive movement over a certain distance the ejection element moves only over half this distance. At the same time however on the ejection element there is available a force for releasing the pipette tip, which is roughly double as large as the force exerted for the drive movement. Other transmission ratios may be achieved when several deflection rollers are mounted on the ejection element. This gear permits solutions which are particularly simple with respect to design. 
     With a push-means gear embodiment the gear has a first piston which is connected to the drive means and is displaceable in a first cylinder, and a second piston which is connected to the ejection element and is displaceable in a second cylinder, wherein the two cylinders communicate with one another, this communicating cylinder system is sealed to the surroundings and is filled with hydraulic fluid and the first piston has a smaller cross sectional surface than the second piston. 
     With these hydraulic transmission systems there is effected a displacement of the first piston over a certain distance, a displacement of the second piston over a smaller distance, wherein the ratio of the distances is inversely proportional to the ratio of the cross sectional surfaces of the two pistons. However the force exerted by the second piston on the ejection element and thus onto the pipette tip is larger that the force exerted by the drive rod onto the first piston, wherein the ratio of these forces is proportional to the ratio of the cross sectional surface of the two pistons. 
     With a further push-means gear embodiment the gear has a first bellows connected to the drive means and a second bellows connected to the ejection element, wherein the bellows are connected to one another in a communicating manner, this communicating bellows system being filled with hydraulic fluid and the smaller bellows having a smaller cross section than the second bellows. 
     With this system by way of the bellows of different diameters there is achieved a result corresponding to the pistons of different diameters. However here a sealing of the pistons or piston rods is done away with. 
     With both push-means gear designs there exists a large freedom in the selection of the transmission ratios. Also very simple design embodiments are possible. 
     With a linkage gear embodiment the gear comprises a first linkage rod which is linked to the drive means, and a second linkage rod which is linked to the ejection element, wherein the two linkage rods at the other end are linked to one another and in the linking region are guided along a guide which with respect to the fastening element is stationary in position and which comprises a first guide section whose distance to a common axis of the drive movement and of the ejection element increases in the direction of the drive means to the ejection element and is arranged such that the linking region, with the releasing of a pipette tip, is movable along this first guide section. 
     If the drive rod for the ejection of a pipette tip is moved axially the lining region of the two linkage rods gets into the region of the first guide section in that it diverts laterally from the common axis of the drive movement and of the ejection element. With this on the one hand the drive movement covers a larger distance than the ejection element and on the other hand on the ejection element there is made available a larger force than is exerted onto the drive rod. This embodiment likewise permits an extensive variability of the transmission ratio and even variable transmission ratios during an ejection procedure. Also here very simple design embodiments are possible. 
     With all embodiments the ejection element may be an ejection rod. This in turn may be connected to at least one further element of an ejection means. The fastening element may be a fastening attachment, a fastening receiver or likewise. 
     The invention may be applied with all types of pipetting systems, in particular with piston stroke and direct displacement systems with single stroke and dispenser systems, with hand and stationary systems, with manual and motorically driven systems and with one-hand and multi-channel systems. 
     Further details and advantages of the invention are evident from the subsequent description of four embodiment examples. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is hereinafter described in more detail by way of the accompanying drawings of five embodiment examples. In the drawings there are shown: 
     FIG. 1 a hand pipetting system in a course schematic view; 
     FIG. 2 an ejection means with pull-means gear in a longitudinal section through a pipetting device; 
     FIG. 3 the same ejection means in a longitudinal section through the pipetting device rotated about 90°; 
     FIG. 4 an ejection means with push-means piston gear in a longitudinal section; 
     FIG. 5 an ejection means with push-means bellows gear in an unactuated condition in a longitudinal section; 
     FIG. 6 the same ejection device in an actuated condition in a longitudinal section; 
     FIG. 7 an ejection means with a linkage gear with two linkage chains in a longitudinal section; 
     FIG. 8 an ejection means with a linkage gear with only one linkage chain in longitudinal section; 
     FIG. 9 the same ejection means in a section along the line IX—IX of FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With the subsequent description of various embodiment examples for corresponding constructional elements the same reference numerals are used. The associated description has validity for all embodiment examples which have these reference numerals. 
     According to FIG. 1 a hand pipetting system according to the invention has a hand pipetting device  1  with a housing  2  and with a housing shank  3  which at the lower end comprises a fastening attachment in the form of an stick-on cone  4 . 
     Onto the stick-on cone  4  there is stuck a pipette tip  5  so that it sticks on, but however may be pushed off the stick-on cone  4 . 
     Above an actuation knob  6  protrodes from the housing  2 . By way of axial pressing-in of the actuation button  6  in the housing  2  between two abutments a piston may be displaced in a cylinder. The cylinder is connected via a channel to an opening at the lower end of the stick-on cone  4 . By way of displacement of the piston in the channel a column of air is moved. After pressing-in the piston  6  this may traverse back to its initial position supported by a spring, wherein the air column may aspirate fluid into the pipette tip  5 . Renewed pressing-in of the actuation knob  6  effects an expulsion of fluid from the pipette tip  5 . 
     For a subsequent releasing of the pipette tip  5  from the stick-on cone  4  the pipetting device comprises an ejection means  7 . This has an ejection sleeve  8  displaceably arranged on the housing shank  3 , with a lateral projection  9  on the upper edge within the housing  2 . For actuating the ejection sleeve  8 , on one longitudinal side in the housing  2  there is located a drive rod  10  which is parallel to the housing shank  3  and which is actuatable by way of an ejection knob  11  which above projects beyond the housing  2 . The lower end of the drive rod  10  via a gear  12  is connected to the upper end of an ejection rod  13  which likewise is parallel to the housing shank  3 . The lower end of the ejection rod  13  is in turn allocated to the lateral projection  9  of the ejection sleeve  8 . 
     The gear  12  is a pull-means, push-means or linkage gear. It has a gear reduction. As a result of this on actuation of the ejection device  7  the displacement distance of the ejection head  11  is larger than the displacement distance of the ejection sleeve  8 , however the force exerted by the ejection sleeve  8  onto the upper edge of the pipette tip  5  exceeds the force exerted on the ejection knob  11 . Thus pipette tips  5  which are stuck may be released more easily from the pipetting device  1 . 
     FIGS. 2 and 3 show an embodiment of the gear as a pull-means gear  12 ′. With this at the lower end section of the drive rod  10  there is present a guide block  14  in which there is formed an axially aligned guide groove  15  which has a lateral opening  16 . Bordering on the guide block  14  the drive rod  10  comprises an axial guide bore  17 . 
     The ejection rod  13  is guided through a transversely aligned housing wall  18 . The ejection rod  13  below the housing wall  18  carries a ring which secures it against being upwardly pulled out. Above the housing wall  18  a compression spring  20  is guided on the ejection rod  13  which at one end is supported on the housing wall  18  and at the other end on a further ring  21  on which the ejection rod  13  sits. 
     On an upper end section the ejection rod  13  carries a bearing block  22 . This is pushed onto the ejection rod  13  and by way of rings  23 ,  24  is secured on the ejection rod  13 . The ejection rod  13  with its upper end projects into the guide bore  17  and the bearing block  12  is guided in the guide groove  15  of the guide block  14 . Above the bearing block  22  on the ejection rod  13  there is guided a compression spring  25  which at one end is supported on the ring  24  and at the other end on a step  26  between the guide groove  15  and the guide bore  17 . 
     On a bearing journal  27  of the bearing block  22 , which protrudes from the opening  16 , there is mounted a deflection roller  28 . The deflection roller  28  on the circumference has a groove  29 . Around the deflection roller  28  there is applied a cable  30  which is guided in the groove  29 . The cable  30  may in particular be a steel or wire cable. It runs roughly over half the circumference of the deflection roller  28 . One end of the cable  50  is fastened below the bearing block  22  onto the housing  2  and thus with respect to a stick-on cone  4  for a pipette tip  5 . At the other end it is fastened below the deflection roller  28  on the guide block  14  at  32 . 
     The fastening of the end  31  onto the housing  2  is effected for example by way of a loop which sits on a journal. The fastening on the guide block  14  is effected for example by way of a cable-resistant ball or other thickening which is pushed from the side into a receiver which comprises a passage for the cable  30 . 
     The bearing block  22  comprises a ring  33  which is concentric to the bearing journal  27  and which secures the deflection roller  28  with a bulge  34  on the inner circumference and prevents the cable  30  from slipping out of the groove  29 . The ring  33  however comprises passage bores through which the ends of the cable  30  are guided to the outside. 
     With an unactuated ejection knob  11  the gear  12 ′ assumes the shown arrangement. If the ejection knob  11  is actuated then the drive rod  10  with the guide block  14  pulls the end of the cable  30  attached thereto downwards. At the same time the cable  30  is pulled downwards over the deflection roller  28  and simultaneously the deflection roller  28  and thus the bearing block  22  and the ejection rod  13  are pulled downwards. This pull-means gear  12 ′ has the effect that with this the ejection rod  13  is moved through an ejection distance which is only half as large as the displacement distance of the drive rod  10 . On the other hand the ejection force which can be exerted by the ejection rod  13  is double as large as the force bearing on the ejection knob  11 . The lower end of the ejection rod  13  may thus directly or via an ejection sleeve  8  exert an increased force onto a pipette tip  5 . 
     After unloading the ejection knob  11  the spring  20  presses the pull-means gear  12 ′ back into the drawn initial position. The spring  25  pushes the drive rod  10  with respect to the ejection rod  13  back into the initial position and therefore compensates the differences of displacements of the drive rod  10  and ejection rod  13  so that the cable  30  is held under tension. 
     By way of the attachment of two deflection rollers on the ejection rod and on a deflection roller mounted fixed to the housing and by way of a cable guide from the drive rod via the first deflection roller of the ejection rod to the deflection roller fixed to the housing and from here to the second deflection roller of the ejection rod, even a quartering of the force effort may be achieved. Further variations are possible by way of roller arrangements and cable guides, as is known with block and tackles. 
     The push-means piston gear  12 ″ shown in FIG. 4 may likewise be applied to a pipetting system according to FIG.  1 . In this case the drive rod  10  is connected to a first piston  33 . This is arranged axially displaceable in a cylinder  34 . The drive rod  10  which at the same time is the drive rod of the piston  33 , is sealingly guided through the upper opening of the cylinder  34 . For this on an inner shoulder of the cylinder  34  there is supported an O-ring  35  which by way of a screw ring  36  is pressed between cylinder  34  and ejection rod  10 , similar to a gland seal. 
     The maximum diameter D 1  of the piston  32  is clearly smaller than the inner diameter of the cylinder  34 . 
     On the upper end of the ejection rod  13  there is seated a second piston  37  which is guided into the other end of the cylinder  34 . At the end face of this end of the cylinder  34  there sits a further O-ring  38  which by way of a union nut  39  is sealingly pressed against the outer circumference of the piston  37 . The outer diameter D 2  of the piston  37  corresponds roughly to the inner diameter of the section of the cylinder  34  in which it is displaceable. 
     The spring guided on the ejection rod is supported at one end on the transversely aligned housing wall  18  and at the other end on a shoulder  40  on the lower side of the piston  37 . 
     The inner space of the cylinder  34 , which is limited by the piston  33 ,  37  is completely filled with hydraulic fluid  41 . 
     The gear  12 ″ is shown in an unactuated arrangement. For a tip ejection the ejection button  11  is pressed so that the piston  33  submerges deeper into the cylinder  34 . By way of this hydraulic fluid is displaced and the piston  37  is moved downwards against the action of the spring  20  so that the ejection rod  13  takes with it the ejection sleeve  8  and finally presses the pipette tip  5  from the stick-on cone  4 . With this the distance covered by the drive rod  10  is greater than the distance covered by the ejection rod  13  and the ejection force (F 2 ) exerted by the ejection rod  13  onto the ejection sleeve  8  is larger than the force (F 1 ) acting on the ejection knob  11 , since the diameter D 2  of the piston  37  is smaller that the diameter D 1  of the piston  33 . For the force transmission ratio r (=F 2 /F 1 ) of this hydraulic transmission system the following applies: 
     
       
         r=D 2   2 /D 1   2   
       
     
     With this gear embodiment with the choice of the transmission ratio r one is very free. 
     Instead of this a pipette system according to FIG. 1 may also be equipped with the pushmeans bellows gear  12 ′″ according to FIG. 5 and 6. This has a first bellows  42  which at the end face side is connected to the drive rod  10  so that it may be pressed together by this. Furthermore it has a second bellows  43  which on the end face side is connected to the ejection rod  13  so that on unfolding it axially displaces this. On end face sides which face one another the two bellows  42 ,  43  are connected to one another via a short tubing section  44  so that their inner spaces communicate with one another. In this region between the bellows  42 ,  43  there circulates a radially aligned groove  45  into which engages a transversely aligned housing wall  18 . This wall has a laterally open slot  46  for inserting the tubing section  44 . 
     The bellows  42 ,  43  and the tubing section  44  are filled with hydraulic fluid  41  or with another suitable fluid. They have a circular cross section, wherein the bellows  42  may have a roughly half as large diameter (D 1 ) as the bellows  43  (D 2 ). 
     The bellows  42 ,  43  may be manufactured of an elastic material such that unimpinged they have the desire to assume the initial shape shown in FIG.  5 . It is however also possible to achieve this initial shape by way of an additional spring means. 
     Assuming this the bellows  42  by way of displacing the drive rod  10  may be pressed together in the direction of the arrow, wherein the hydraulic fluid  41  is displaced into the bellows  43  and expands this. Finally the arrangement according to FIG. 6 is reached in which the bellows is maximally pressed together and the bellows  43  is maximally expanded. With this the compression path Y of the bellows  42  is considerably larger than the expansion path Z of the bellows  43 . However the bellows  43  presses on the ejection rod  13  with a considerably higher ejection force (F 2 ) than (F 1 ) introduced into the bellows  42  via the drive rod  10 . Also with this hydraulic transmission system the transmission ratio r(=F 2 /F 1 ) is given by: 
     
       
         r=D 2   2 /D 1   2   
       
     
     The pipetting system according to FIG. 1 may advantageously also be equipped with a linkage gear  12   IV  according to FIG.  7 . The drive rod  10  and the ejection rod  13  are coaxially guided in axial guides  47 ,  48  of the housing. Onto the lower end of the drive rod  10  at  49  there are linked two first linkage rods  50 ,  50 ′. To the upper end of the ejection rod  13  at  51  there are linked two second linkage rods  52 ,  52 ′. In each case a first linkage rod  50 ,  50 ′ and a second linkage rod  52 ,  52 ′ are linked to one another at the other end at  53 ,  53 ′. Here in each case a roller  54 ,  54 ′ is rotatably mounted. 
     Between the axial guides  47 ,  48  there is formed in the movement region of the rollers  54 ,  54 ′ on both sides of the axis of the drive rod  10  and of the ejection rod  13  a guide  55 ,  55 ′ with a certain contour. This disappears in a first guide section  56 ,  56 ′ from the previously mentioned axis and in a second guide section  57 ,  57 ′ is parallel to this axis. 
     On actuation of the ejection means  12   IV  by displacement of the drive rod  10  in the direction of the arrow firstly the rollers  54 ,  54 ′ may be located within the guide  47 . As soon as the rollers  54 ,  54 ′ get into the region of the guide  55 ,  55 ′ they follow the contour of the first guide section  56 ,  56 ′ and distance themselves from one another. This situation is shown in FIG.  7 . During the movement of the rollers  54 ,  54 ′ over the first guide section  56 ,  56 ′ as a result of this the ejection rod  13  is displaced over a shorter distance than the drive rod  10 . On the other hand the ejection rod  13  may exert a larger force onto an ejection sleeve  8  than is exerted onto the drive rod  10 . Thus advantageously the pipette tip  5  is pressed off the stick-on cone  4  whilst the rollers  54 ,  54 ′ are moved along the guide section  56 ,  56 ′. In the subsequent second guide section  57 ,  57 ′ the movement of the ejection rod  13  in turn corresponds to the movement of the drive rod  10 , by which means a pipette tip  5  may already be pressed off in an accelerated manner. 
     By way of the first guide section  56 ,  56 ′ a force amplifying transmission of e.g. 3.5:1 may be achieved. In the subsequent second guide section  57 ,  57 ′ the transmission ratio is 1:1. 
     Subsequent to the first guide section  56 ,  56  in which the pipette tip is released, or instead of this for “the last push” one may go over to a “path-amplifying” transmission (e.g. 1:2 or the like). Examples for such further guide sections  58 ,  58 ′ and  59 ,  59 ′ are drawn in dashed. 
     Of course also other contours in the region of the guide  55 ,  55 ′ are conceivable. 
     It is also interesting that in spite of force amplification on ejection of the pipette tip no total stroke shortening need occur, since the reduced stroke of the ejection rod  13  on ejection may be made up for at the end of the ejection procedure. 
     According to FIG. 8 and 9 a linkage gear with a corresponding function may also be realized in that the drive rod  10  and the ejection rod  13  are only connected to one another via two linkage rods  50 ,  52  and only on one side of the common movement axis of the drive rod  10  and of the ejection rod  13  is there formed a guide  55  with the various sections  56 ,  57  (or  58 ,  59 ). A wall  60  lying opposite the guide  55  may then be flush with the borders of the guides  47 ,  48 . By way of this a space-saving constructional manner is possible. 
     It is to be understood that linkage gears according to FIGS. 7 to  9  may cooperate with a spring means which act on the ejection rod  13  opposite to the direction of actuation, in order to restore this back to the original position