EP2415525A2 - Pipette for a pipette system with pipette and syringe - Google Patents

Abstract

The pipette has a volume setting unit arranged in a pipette housing for adjusting liquid volume pipetted during operation of an operation lever (5). A control slide (9) is arranged at an axially displaceable rack gear (7) and controls intervention of a latch (8) into a gearing. The control slide is more adjustable at the rack gear in a specific position via the setting unit. The rack gear comprises a carrier (7.2) and a gearing part (7.3). The carrier includes a receiver for the gearing part that bears the gearing, where the carrier and the gearing part are made of different materials.

Description

The invention relates to a pipette for a pipette system with pipette and syringe, namely a pipette having the features of the preamble of claim 1.

Pipettes are devices for measuring and transferring liquids. The present is a pipette that allows a gradual release of a liquid from a syringe (Repetierpipette). Such a pipette is for example from the DE 199 63 141 A1 In such a pipette, liquid is taken up in the syringe inserted in the pipette housing of the pipette in one go. The pipette is then moved to the place of use. At the place of use, the liquid taken up in the syringe is released again step by step by repeated actuation of the actuating lever located on the pipette housing in previously set portions. The repeating pipette known from practice (multiple dispensers "HandyStep", the BRAND GMBH + CO KG, Wertheim in the general catalog "GK800" from page 61) has a piston adjusting device in the form of a rack-pawl combination, the rack is in one piece of extremely dimensionally stable metal , in particular brass, machined. The cost of producing such a rack is relatively high in relation to the cost of the pipette as part of a large-scale production.

Specifically, the teaching of the present invention is based on a pipette with a one-piece rack in such a piston adjusting device. From the EP 0 143 796 B1 Although it is a two-piece rack out, but on each section has a different teeth with different tasks, On a rack part teeth in sawtooth shape is integrally formed. It can be assumed that this is also a metal rack. whose teeth have been produced by machining on the actual rack carcass.

The teaching is based on the problem to optimize the known pipette with axially displaceable rack while maintaining the precision in terms of manufacturing costs in particular under aspects of mass production.

The above-mentioned problem is in a pipette having the features of the preamble of claim 1 by the features of the characterizing part of Anspmch 1 solved. Preferred embodiments and further developments are the subject of the dependent claims.

In the prior art, it is continuous so that the rack together with the teeth is made in one piece of metal highly dimensionally accurate. This is expensive and not optimal for a modern, highly effective crusher technology. According to the invention, the rack is now made in several parts, namely at least two parts, preferably exactly two parts. It consists first of a carrier which has a receptacle for a toothing part. In or on the receptacle of the carrier sits the toothing part, which in turn has the toothing of the rack.

The carrier on the one hand and the toothing part on the other hand can be made of different materials. The material of the carrier can be adapted to the local requirements. The carrier must be dimensionally stable and fix the toothing part safely and correctly in the piston adjusting device. He does not have to be particularly well-suited and he does not have to meet the special requirements of a finely-illustrated gearing.

In contrast, the toothing part is highly dimensionally accurate to manufacture and must be highly precise executable especially in the teeth. This is usually a more expensive material to use. The outer shape of the toothing part, in particular what deflections or the like. does not have to be particularly precise, because here the carrier acts with its rigidity, the toothing part can be made in particular relatively thin. Its spatial orientation and fixation is experienced only in connection with the serving as a stiff backbone wearer,

Particularly preferred embodiments and further developments of the invention-βen teaching are the subject of the dependent claims.

For the choice of material of the toothing part, it is recommended in the first place that the toothing part consists of a high-quality, preferably fiber-reinforced plastic, in particular of a fiber-reinforced PEEK. Such a plastic part can be manufactured as a series part with high precision and excellent dimensional stability and low shrinkage. However, this toothing part is expediently made as small as possible in terms of volume, because the material used is relatively expensive. In this context, it is preferred that the Support made of steel, in particular stainless steel, or of a dimensionally stable plastic, preferably made of PPS exists.

The wearer can be quite voluminous and is designed so that it is as stiff as possible. It is less important for its dimensional accuracy in detail. The material to be used here can be significantly cheaper than the material of the toothing part. Each of the two parts are assigned the tasks that best suit them.

In order to realize the optimal connection of the carrier with the Verzabnungsteil, it is recommended that the toothing part has a longitudinal contour, which is adapted to a longitudinal counter contour on the carrier so that a positive, preferably axially straight guide results, wherein , Preferably, the contour and the mating contour are formed as a T-slot guide. By this guide, the flat and usually relatively thin toothing part is aligned.

The dimensional accuracy of the toothing part can be further improved by the fact that the toothed part seen in cross section has at least one longitudinal stiffening web on the side opposite the toothing. The filling behavior in the injection molding process in a plastic part is significantly smoother by such a bridge.

According to a preferred teaching, it is recommended that the toothing part including the toothing in cross section has a ratio of the width to the height greater than 1.5, preferably greater than 4.0. Over its length, such a relatively uniformly elongate toothing part hardly has a delay and only a relatively small deflection. Due to the low height in relation to the width, it can be aligned relatively easily when inserted into the carrier. The toothing part can thus be optimized for the dimensional accuracy of the tooth pitch of the toothing, the deflection over the entire length of the toothing part may have less importance.

The teaching of the invention is of particular importance with a relatively small tooth pitch, tooth pitches below 1 mm can be produced in metal racks only with great effort. In a high-quality plastic injection molding technique can be according to the teachings of the invention, smaller tooth pitches to reach. Accordingly, it is recommended according to preferred teaching that the toothing has a pitch of less than 1.0 mm, preferably less than 0.6 mm. It is obvious that a smaller pitch allows a greater number of steps and possible sub-volumes.

The toothing in the case of the pipette according to the invention can also be optimized in the tooth form and in the tooth height. It is recommended that the toothing is sawtooth-shaped and the tooth angle between the tooth back and the tooth flank is between 25 ° and 45 °.

At a low pitch of, for example, 0.6 mm, the teeth are very fine on both the gearing and the pawl. In particular, in this case, it may be recommended that the pawl, which preferably consists of fiber-reinforced plastic, having a plurality of ratchet teeth, preferably three ratchet teeth.

In a preferred constructive embodiment of a typical pipette of the type in question, it is recommended that the width of the pawl is greater than 4 mm, preferably greater than 5.5 mm.

Furthermore, it may be recommended that the ratchet teeth of the pawl have the sawtooth shape of the toothing and that, preferably, the pitch of the ratchet teeth is less than the pitch of the toothing. The ratchet teeth so fall even with appropriate inclination of the pawl in the teeth on the toothing part and achieve a safe, force-transmitting engagement

Already in the prior art, a rigidly arranged stop is present on the pipette housing, which limits the movement of the pawl in the direction of the syringe. Such a construction is also recommended in the case of the pipette according to the invention. Furthermore, it is recommended that the toothing part has a stroke stop for the absorption of liquid in the syringe. The stroke stop ensures dimensional accuracy when engaging the first stroke to dispense liquid after previously taking up liquid in the syringe.

If the still possible last discharge stroke is smaller than the stroke set by means of the volume setting device, then the last possible delivery stroke should be puzzled in order to avoid volume errors. For this purpose, it is recommended that the rack has a cam which cooperates with the spool and with the piston advanced into the syringe raises the spool so that the pawl is dug out of the gearing. To be able to set this residual stroke prevention and to create a tolerance compensation, it is recommended that the cam is mounted on the rack in the axial direction adjustable.

For the adjustment of the cam on the rack in the axial direction, there are various possibilities. A particularly preferred construction is that the cam is mounted in an adjustable manner in the axial direction on a sliding block arranged on the carrier of the rack. It is particularly useful in this case then that the carrier of the rack is designed in one piece with this sliding guide.

Incidentally, the piston adjusting device typically has a receptacle for a piston head of a syringe. It is particularly useful then that the carrier of the rack is made in one piece with this recording

If both aspects described above come together, then the carrier of the toothed rack at the lower end is made in one piece with the receptacle of the piston adjusting device and integrally formed at the upper end in one piece with the sliding guide for the cam.

Fig. 1

eine perspektivische Darstellung einer bekannten Pipette mit eingesetzter Spritze,

Fig. 2

im Längsschnitt, ausschnittweise im Bereich des Betätigungshebels, ein bevorzugtes Ausführungsbeispiel einer Pipette gemäß der Erfindung,

Fig. 3

in einem Fig, 2 ähnlichen Längsschnitt, die Pipette mit teilweise betätigtem Betätigungshebel und Klinke im Eingriff in die Zahnstange,

Fig. 4

in einem Fig. 2 ähnlichen Längsschnitt, die Pipette mit Betätigungshebel in Endstellung,

Fig. 5

in einem Fig. 2 ahnlichen Längsschnitt, die Pipette mit vorgeschobener Zahnstange und ausgehobener Klinke,

Fig. 6

in einem Fig. 2 ähnlichen Längsschnitt, die Pipette in einer Variante mit einer verstellbaren Nocke,

Fig. 7

in einem Fig. 2 ähnlichen Längsschnitt, die Pipette in einer weiteren Variante mit einer verstellbaren Nocke,

Fig. 8

im Querschnitt, ausschnittweise im Bereich der Zahnstange, ein bevorzugtes Ausführungsbeispiel einer Pipette gemäß der Erfindung,

Fig. 9

Detailansichten eines bevorzugten Ausführungsbeispiels einer Zahnstange einer Pipette gemäß der Erfindung,

Fig. 10

eine perspektivische Darstellung einer Baugruppe einer Pipette mit eingesetzter Spritze und

Fig. 11

eine perspektivische Darstellung einer Zahnstange eines bevorzugten Ausführungsbeispiels einer Pipette gemäß der Erfindung.

In the following, the invention will now be explained in more detail with reference to a drawing showing merely exemplary embodiments. In the drawings, the figures show the following:

Fig. 1

a perspective view of a known pipette with inserted syringe,

Fig. 2

in a longitudinal section, in sections in the region of the actuating lever, a preferred embodiment of a pipette according to the invention,

Fig. 3

in one Fig. 2 similar longitudinal section, the pipette with partially actuated lever and pawl in the rack,

Fig. 4

in one Fig. 2 similar longitudinal section, the pipette with actuating lever in the end position,

Fig. 5

in one Fig. 2 similar longitudinal section, the pipette with advanced rack and lifted pawl,

Fig. 6

in one Fig. 2 similar longitudinal section, the pipette in a variant with an adjustable cam,

Fig. 7

in one Fig. 2 similar longitudinal section, the pipette in another variant with an adjustable cam,

Fig. 8

in cross-section, in sections in the region of the rack, a preferred embodiment of a pipette according to the invention,

Fig. 9

Detailed views of a preferred embodiment of a rack of a pipette according to the invention,

Fig. 10

a perspective view of an assembly of a pipette with inserted syringe and

Fig. 11

a perspective view of a rack of a preferred embodiment of a pipette according to the invention.

Fig. 1 shows the basic design of a pipette 1 according to the invention with an inserted syringe 2. The syringe 2 has a cylinder 2.1 with a mounting portion 2.2, which is preferably designed as a flange, and with a piston which in Fig. 1 can not be seen because it is located in the pipette housing 3 of the pipette 1 shown there. The piston has a piston which is also pushed completely out of the cylinder 2.1 and out of this cylinder 2.1 on the end of the piston head 2.3. The pipette housing 3 defines a longitudinal axis which is coaxial with the rotationally symmetrical syringe (2).

One recognizes in Fig. 1 how the syringe 2 to be handled with the pipette 1 is inserted with its fastening section 2, 2 and the piston head 2. 3 into the pipette housing 3. The prior art knows here a radial coupling (so in Fig. 1 shown; see also DE 199 63 141 A1 ) and an axial coupling (see, eg DE 199 17 907 A1 ). In the teaching of the present invention, this distinction does not matter.

In Fig. 1 is indicated that in the pipette housing 3 in the direction of the longitudinal axis of the pipette housing 3, that is, axially displaceable piston adjusting device 4 for the piston head 2.3 of the syringe 2 is located. The piston adjusting device 4 is actuated by means of a movable in the pipette housing 3 and partially protruding from the pipette housing 3 for the purpose of manual operation operating lever 5.

On the pipette housing 3, a handle part 3.1 and a finger strap 3.2 are formed. If you hold the pipette housing 3 on the handle part 3.1 with the palm, so you can press the operating lever 5 with your thumb, ie in Fig. 1 Press down towards the syringe (2). Each actuation of the operating lever 5 has the delivery of a specific, precisely set amount of the previously recorded in the syringe 2 liquid (repetitive pipette). To adjust the volume delivered by each actuation of the actuating lever 5, a volume setting device 6 is provided on the pipette housing 3. This adjustment is known per se from the prior art and is realized in a similar manner also in the case of the pipette forming the starting point.

For the further features of the pipette according to the invention, reference must now be made to the additional figures.

The piston adjusting device 4 initially has a toothed rod 7 which is axially displaceably arranged in the pipette housing 3 and is coupled to the piston head 2, 3 of an inserted syringe 2, which toothing 7. 8 and 9 Is provided on the operating lever 5 is a pivotally mounted pawl 8 of the piston adjusting device 4, which engages upon actuation of the actuating lever 5 in the opposing toothing 7,1 of the rack 7, as can be seen from the episode of Fig. 2 to 4 good to take. If one actuates the actuating lever 5, the piston of the syringe 2 is displaced by this engagement via the piston head 2.3, regularly downwards into the cylinder 2.1, for the purpose of dispensing a certain set amount of liquid.

On the rack 7 is a spool 9, the in FIGS. 2 and 3 is particularly clear. He is executed here as a double-folded bent part. This control slide 9 holds the pawl when the actuating lever 5 is not actuated (FIG. Fig. 2 ) About the teeth 7.1 of the rack 7. This spool 9 is adjustable in its position on the rack 7, what it just the volume setting 6 there. Other embodiments of the spool 9 are known, the gruindsätzhich control the engagement of the pawl 8 in the toothing 7. If the operating lever 5 is actuated, it moves from the in Fig. 2 shown position to the left. The down to the teeth 7.1 biased by spring force pawl 8 leaves the spool 9, now applies to the teeth 7.1 and engages in this ( Fig. 3 The further movement of the actuating lever 5 now leads to a movement of the rack 7 in Fig. 3 to the left in the Fig. 4 shown position, the end of the actuating stroke. If you let go now the operating lever 5 again, so he moves himself under spring force back into the in Fig. 2 shown position back. The next actuation stroke can begin.

8 and 9 Now show the essence of the teaching of the invention, namely that the rack 7 is made of several parts and at least a support 7.2 and a toothing part 7.3, wherein the carrier has a receptacle 7.2 7.2 for the toothing part 7.3 and the Verzabnungsteil 7.3 Teeth 7.1 carries. The carrier 7.2 on the one hand and the toothing part 7.3. On the other hand, they are made of different materials, which can meet the respective requirements particularly well. This has the advantages already explained in detail in the general part of the description.

Normally, the rack 7 may be made in two parts, but in principle may include more parts to the rack 7, essential is the special task assignment to the carrier 7.2 on the one hand and to the physically separate from the carrier, but connected to him gearing part 7.3, the teeth. 7 on the other hand. According to the invention therefore no one-piece design of the rack 7 is provided, but a multi-part design.

It is particularly preferred that the toothing part 7, 3 consists of a high-strength material, which can be manufactured dimensionally accurate and with minimal shrinkage, and that the carrier 7.2 consists of a material that is more cost-effective compared to the material of the toothing part 7.3, which less good dimensionally accurate to manufacture.

In the illustrated and preferred embodiment already shows the hatching in 8 and 9 in that here the toothing part 7.3 is made of a high quality, preferably fiber reinforced plastic, in particular of a fiber reinforced PEEK, consists. Furthermore, it can be seen that in this case the carrier 7, 2 consists of steel, in particular stainless steel, or of a dimensionally stable plastic, preferably of PPS

Thus, a combination of fiber-reinforced PEEK for the toothing part 7.3 with dimensionally stable PPS for the carrier 7.2 is particularly preferred.

A particularly preferred mechanical construction of the pipette according to the invention also results 8 and 9 , It can be seen here that the toothing part 7.3 has a longitudinal contour 7.4, which is adapted to a longitudinally extending counter contour 7.5 on the carrier 7.2 in such a way that a form-fitting, axially straight guide results. Here and preferably, the contour 7.4 and the mating contour 7.5 are formed as a T-slot guide. The T-slot guide can be in Fig. 8 recognize very well.

In order to optimize the filling behavior in the injection molding process for an existing plastic toothing part 7.3 and thereby increase the dimensional stability, in particular in the area of the toothing 7.1 is in in Fig. 8 illustrated embodiment, that the toothing part 7.3 in cross-section at least one longitudinal stiffening web 7.6 relative to the toothing 7.1. More precisely, there are four equally spaced stiffening webs 7, 6.

Also off Fig. 8 can be the profiling of the toothing part 7.3 remove. Here, it is provided that the toothing part 7.3 including the toothing 7.1 in cross section has a ratio of the width 7.7 to the height 7.8 including the toothing 7.1 greater than 1.5, preferably greater than 4.0. In the illustrated and preferred embodiment, a ratio of the width of 7.7 to the height of 7.8, which is measured to the top of the teeth 7.1, results in a little more than 4. It can be seen that the outer contour of the toothing part 7.3 is basically rectangular although executed with a two-sided stage of the T-slot guide.

The illustrated and preferred embodiment shows for the teeth 7.1 a very fine pitch, in particular one of less than 1 mm, preferably less than 0.6 mm. This one looks especially good in Fig. 9 , It recognizes one that the teeth 7.1 is designed sawtooth-shaped and the tooth angle 7.10 between the tooth back and the tooth flank is between 25 ° and 45 °. One can see here, despite the fineness of the division 7.9 sufficient tooth height, which allows a safe engagement of the ratchet teeth of the pawl 8,

This brings us to another special feature of the construction according to the invention. Here it is namely provided that the pawl 8, which preferably consists of fiber-reinforced plastic, has a plurality of ratchet teeth, preferably three ratchet teeth. The three ratchet teeth provided here ensure a secure engagement of the pawl 8 in the fine toothing 7.1. According to a particularly preferred teaching is so far provided that the ratchet teeth of the pawl 8 have the sawtooth shape of the teeth 7.1 and the pitch of the ratchet teeth is less than the pitch of the teeth 7.1. This takes into account the peculiarity of the construction according to the invention with the pivotally mounted with the actuating lever 5 pivot bearing of the pawl 8 ( Fig. 2 to 4 ). Even with this arcuate displacement, the ratchet teeth fall securely into the toothing 7.1, because they have a slightly different pitch with respect to the toothing 7.1.

This in Fig. 8 illustrated and so far preferred embodiment shows a construction in which the width of the pawl 8 is greater than 4 mm, preferably greater than 5.5 mm, is. Ultimately, the width of the pawl 8 also depends on the lifting force to be transmitted, which then has to be introduced over the width into the toothing part 7.3 and thus into the rack 7 with a particularly fine pitch of the toothing 7.1. Considering that here Hubkräfte between 5 and 25 N must be transmitted, so you have to accept an acceptable width of the pawl 8 in total, the total support 7.2 has a total width, which is about 1.5 times to 2 times the Width of the pawl 8 is.

In Fig. 2 and 4 and in Fig. 9 is shown that in the illustrated embodiment, but this is known per se, a fixedly positioned stop 10 is provided which limits the movement of the pawl 8 in the direction of the syringe 2. This has the meaning explained in the general part of the description. The stop 10 may be assigned to the actuating lever 5 instead of the pawl 8 also directly. It is fixedly attached to the pipette housing 3. You can see in Fig. 9 the pawl 8 are immediately in front of the stop 10.

Already in the general part of the description, it has been pointed out that the dimensional stability during the first stroke after the previous suction of liquid into the syringe 2 is ensured by a further stop, namely a stroke stop 7.11 on the toothing part 7,3. This one recognizes in Fig. 9 He works with the stop 10 on the pipette housing 3 together.

Furthermore, in the general part of the description, the problem of Resthubverhinderung has been addressed in the last discharge stroke by operating the operating lever 5. Here according to the invention is provided according to the preferred teaching that the rack 7 has a cam 7.12, which cooperates with the spool 9 and raised in the syringe 2 advanced piston the spool 9, so that the pawl 8 is dug out of the "teeth 7.1.

The stop given by the cam 7.12 can be seen in Fig. 5 to 7 in different variants. In the embodiment of Fig. 2 to 5 the cam 7.12 is integrally formed on the carrier 7.2. In the embodiments of 6 and 7 on the other hand, the cam 7.12 on the rack 7, more precisely on the support 7.2, mounted adjustably in the axial direction, to make an adjustment and tolerance compensation here. In any case, the cam 7.12 acts so that the spool 9 is raised and with the pawl 8 lifts up and triggers their ratchet teeth from the gearing 7.1 on the gearing part 7.3. The pawl 8 then moves at idle It has, in order to allow this, even a raised contact surface 8.1, with which it rests on the spool 9.

In Fig. 10 is that assembly of the pipette 1 is shown, which is driven with the exception of the cylinder 2.1 of the syringe 2 during the actuating stroke. The piston adjusting device 4 may for example be constructed as in the DE 20 2010 009 747 U1 disclosed. It has at least one coupling for the piston head 2.3 and a button for its operation. This can also be used to move the piston with the piston head 2.3 in the syringe 2 and the rack 7 in the pipette housing 3.

As Fig. 11 shows, here has the coupling of the piston adjusting device 4 a receptacle 4.1, which is connected directly or indirectly with the piston head 2.3 in the pipette housing 3 when attaching the syringe 2. In Fig. 11 is an advantage Embodiment shown, in which the recording 4.1 with the carrier 7.2 of the rack 7 is made in one piece. In practice, for example, the carrier 7.2 of the rack 7 with the receptacle 4.1 of the piston adjusting device 4 may be designed as a one-piece injection-molded part made of plastic.

In Fig. 10 can be seen right behind the end of the carrier 7.2 of the rack 7, the aforementioned cam 7.12. This is plugged here on a sliding guide 7.13 and mounted adjustable on this in the axial direction. The cam 7.12 will be on the in Fig. 11 mounted on the top right sliding guide 7.13 and then brought into the axial position, which is to be provided for them. In this position, it is fixed on the sliding guide 7.13, for example by a fixing screw. Fig. 11 shows right above the displacement guide 7.13 for the cam 7.12. It can be seen here that the carrier 7.2 in this exemplary embodiment is also designed in one piece with this displacement guide 7.13. Again, it may be the one-piece molding in the form of a Spritzgussteüs.

This in Fig. 11 illustrated embodiment, therefore, the carrier 7.2 with the receptacle 4.1 integrally formed at one end and the sliding guide 7.13 integrally executed at the other end.

In Fig. 11 is finally the one above in connection with 8 and 9 already mentioned, longitudinal counter contour 7.5 shown on the carrier 7.2. It can be seen that the mating contour 7.5 is here arranged segmentally, in sections.

LIST OF REFERENCE NUMBERS

1

pipette

2

syringe

2.1

cylinder

2.2

attachment section

2.3

piston head

3

pipette housing

3.1

Handle part

3.2

finger rest

4

Enste piston device

4.1

admission

5

actuating lever

6

Volumeneinstelleinrichtung

7

rack

7.1

gearing

7.2

carrier

7.3

toothed piece

7.4

contour

7.5

mating contour

7.6

reinforcing web

7.7

width

7.8

height

7.9

division

7.10

tooth angle

7.11

stroke stop

7.12

cam

7.13

displacement guide

8th

pawl

8.1

contact surface

9

spool

10

attack

Claims (15)

pipette
for a pipette system consisting of a pipette (1) and a syringe (2),
in which the syringe (2) has a cylinder (2.1) with a fastening section (2.2), which is preferably designed as a flange, and a piston with a piston head (2.3) protruding endwise from the cylinder (2.1), even when the piston is completely pushed into the cylinder (2.1). having,
with a pipette housing (3) having a longitudinal axis, wherein a syringe (2) to be handled with the pipette (1) can be inserted and removed from the pipette housing (3) with its attachment section (2.2) and piston head (2.3),
in the pipette housing (3) in the direction of the longitudinal axis of the pipette housing (3), ie axially displaceable piston adjusting device (4) for the piston head (2.3) of the syringe (2),
with an actuating lever (5) movably mounted in the pipette housing (3) and protruding therefrom for actuating the piston adjusting device (4),
preferably with a volume setting device (6) arranged in the pipette housing (3) for adjusting the volume of liquid pipetted upon actuation of the actuating lever (5),
wherein the piston adjusting device (4) has a toothed rod (7) with a toothing (7.1) which is axially displaceable in the pipette housing (3) and is coupled to the piston head (2.3) of an inserted syringe (2).
on the actuating lever (5) a pivotally mounted pawl (8) is arranged, which engages upon actuation of the actuating lever (5) in the toothing (7.1) of the rack (7) and via the piston head (2.3) the piston of the syringe (2) shifts and
on the rack (7) a control slide (9) is arranged, which controls the engagement of the pawl (8) in the toothing (7.1) and, preferably, via the Volumeneinstelleinrichtung (6) in its position on the rack (7) adjustable is, characterized
in that the toothed rack (7) is designed in several parts and consists at least of a support (7.2) and a toothed part (7.3), wherein the support (7.2) has a receptacle for the toothed part (7.3) and the toothed part (7.3) has the toothing (7.1 ) and
that the carrier (7.2) on the one hand and the toothing part (7.3) on the other hand consist of different materials which are adapted to the respective requirements. Pipette according to claim 1, characterized in that
that the toothing part (7.3) consists of a high-strength material that can be made dimensionally stable with low shrinkage and
that the carrier (7.2) consists of a less expensive material compared with the material of the toothed part (7.3), which is if necessary to produce less dimensionally stable. Pipette according to claim 2, characterized
that the toothed part (7.3) of a high quality, preferably fiber-reinforced plastic, in particular a fiber-reinforced PEEK, and in that the support (7.2) made of steel, in particular stainless steel, or, made of a dimensionally stable plastic, preferably of PPS. Pipette according to one of the preceding claims, characterized
in that the toothing part (7.3) has a longitudinally extending contour (7.4) which is adapted to a longitudinal counter contour (7.5) on the carrier (7.2) in such a way that a positive, preferably axially straight guide results, preferably , the contour (7.4) and the mating contour (7.5) are designed as a T-slot guide. Pipette according to one of the preceding claims, characterized
that the toothing part (7.3) seen in cross-section on the toothing (7.1) opposite side at least one longitudinal stiffening web (7.6). Pipette according to one of the preceding claims, characterized
that the toothing part (7.3) including the toothing (7.1) in cross section has a ratio of the width (7.7) to the height (7.8) greater than 1.5, preferably greater than 4.0. Pipette according to one of the preceding claims, characterized
that the toothing (7.1) has a pitch (7.9) of less than 1.0 mm, preferably of less than 0.6 mm. Pipette according to one of the preceding claims, characterized
that the toothing (7.1) is designed saw-tooth and the tooth angle (7.10) between the tooth backs and the tooth flank between 25 ° and 45 °. Pipette according to one of the preceding claims, characterized in that the pawl (8), which preferably consists of fiber-reinforced plastic, meluere, preferably three, ratchet teeth, and / or that the width of the pawl (8) is greater than 4 mm, preferably greater than 5.5 mm, is. Pipette according to claim 9, characterized
that the ratchet teeth of the pawl (8) have the sawtooth shape of the toothing (7.1) and that, preferably, the pitch of the ratchet teeth is less than the pitch of the toothing (7.1). Pipette according to one of the preceding claims, characterized
in that a stop (10) is fixedly arranged on the pipette housing (3) and limits the movement of the pawl (8) or the actuating lever (5) in the direction of the syringe (2). Pipette according to one of the preceding claims, characterized in that the toothing part (7.3) has a stroke stop (7.11) for the suction of liquid into the syringe (2). Pipette according to one of the preceding claims, characterized in that the toothed rack (7) has a cam (7.12) which cooperates with the control slide (9) and raises the control slide (9) when the piston is advanced into the syringe (2), so that the pawl (8) from the toothing (7.1) is dug. Pipette according to claim 13, characterized in that
in that the cam (7.12) is adjustably mounted on the rack (7) in the axial direction. Pipette according to one of the preceding claims, characterized
in that the cam (7.12) is adjustably mounted in the axial direction on a sliding guide (7.13) arranged on the support (7.2) of the rack (7), and in that the carrier (7.2) of the rack (7) is integral with the sliding guide (7, 13) is executed and / or
in that the piston adjusting device (4) has a receptacle (4.1) for a piston head (2.3) of a syringe (2) and in that the carrier (7.2) of the toothed rack (7) with the receptacle (4.1) is made in one piece.

Images