Phase pipette

Abstract: The invention relates to a pipette used for dosing of liquids. The most characteristic feature of the pipette is that in order to remove the liquid as completely as possible, the dosing piston (18) is pressed first into a low position below the basic position, after which an additional removing phase is carried out using a separate removing piston (13), so that the piston area that affects the liquid container (3) is greater during the additional removing phase. This way, a pressure stroke is formed, which effectively and reliably removes even the droplet that easily remains at the tip of the container. Most preferably, both the removing piston and the dosing piston move in the additional removing phase.

Description: TECHNICAL FIELD This invention relates to piston-operated pipettes, which are used for handling liquids. Specifically, the invention relates to the complete removal of liquid from the pipette. The invention is especially suitable for pipettes which should enable exact dosing of relatively little amounts of liquid, such as in the order of one microlitre. BACKGROUND OF THE INVENTION Piston-operated pipettes usually have a function called secondary movement, due to which the movement of the piston is longer when the liquid is ejected than the movement of the piston when the liquid is drawn in. This improves the complete ejection of the liquid from the pipette as much as possible. In known hand-operated pipettes, the secondary movement is arranged using two springs, whereas in electrically operated pipettes, the secondary movement can be produced by a suitable arrangement controlling the motor. It is characteristic of both the prior art approaches, that both the primary movement and the secondary movement are carried out by the same piston. Patent specification US-3 646 817 proposes a pipette having two spring-operated pistons, one of which is inside the other. The inner piston is a dosing piston the stroke of which determines the volume of the dose. The stroke of the dosing piston when drawing the liquid in is of the same length as when ejecting the liquid. The outer piston is a secondary piston which does not begin to move before the dosing piston has completed its downward stroke. DESCRIPTION OF THE INVENTION General description A pipette according to Claim 1 has now been invented. Some of its preferred embodiments are presented in the other claims. The most characteristic feature of the pipette is that to remove the liquid as completely as possible, the dosing piston is first pressed into a low position below the basic position, after which an additional removing phase is performed using a separate removing piston, so that the piston area affecting the liquid container is greater in the additional removing phase, which effects the formation of more pressure in the container. This way, a pressure stroke that effectively and reliably removes even the droplet that tends to stay at the tip of the container is directed to the container. Most preferably, the removing piston and the dosing piston both move during the additional removing phase. The pipette can either be a hand-operated pipette or a motor-operated pipette. Detailed description of some embodiments of the invention In the accompanying figures, Figure 1 shows one pipette according to the invention, Figure 2 is an enlarged view of the distal part of the pipette of Figure 1, Figures 3a - 3d are enlarged views of the lower part of the distal part of Figure 2 in different phases of operation, and Figure 4 shows the lower part of the distal part of another pipette according to the invention. The casing of the pipette of Figures 1 - 3 is composed of a handle part 1 and at its low end a narrower distal part 2, in which there is positioned a distal container 3. On the distal container there is a slidable sleeve 4 for removing the distal container, and as an extension of the sleeve, on the side of the handle, arm 5 for operating the sleeve. The device for removing the distal container can, for example, be such as described in specification FI-C-92374. There is a bore through the distal part 2. The lower part of the bore comprises a narrower tip bore and the upper part comprises a wider shaft bore. At their point of contact, there is a treshold 6. Fitted into the tip bore there is a sleeve-like cylinder 7, which is longer than the tip bore. In the upper end of the cylinder, there is a flange 8. The hole in the lower end 9 of the cylinder is smaller than the inner diameter of the cylinder. The outer surface of the cylinder 7 is sealed against the distal part 2. For this, there is an O-ring 10 in the shaft bore. Around the cylinder, there are a support ring 11 and a cylinder spring 12, so that the spring, via the ring, presses the O-ring against the treshold 6. Above the cylinder 7 there is fitted a tubelike cylinder shaft 13. It comprises a lower part corresponding to the inner diameter of the cylinder and a broader upper part, there being a treshold 14 between them. The cylinder shaft is sealed against the part 2 using an O-ring 15, which is fitted into the lower part of the shaft. As an extension of the cylinder shaft 13, above it, there is a shaft sleeve 16. In the upper end of the shaft sleeve, there is a flange 17 resting on the upper flange of the distal part 2. Inside the cylinder 7 there is a piston 18 fitted tightly. As a fix extension of the piston, there is a broader shaft 19. Surrounding the piston rod, between the fastening ring 20 and the flange 17 of the shaft sleeve 16 of the cylinder shaft there is a primary spring 21 pushing the piston towards its upper position and holding the flange against the distal part 2. In the upper end of the piston rod there is a counter button 22. The piston 18 is sealed by an O-ring 15' between the O-ring 15 and the upper flange 8 of the cylinder 7, by the force of the cylinder spring 12. Above the piston rod 19 there is a button shaft 23. At its lower end there is a sleeve 24 surrounding the piston rod. There is an adjusting ring 26 fitted around the button shaft using the thread 25. The adjusting ring is fitted in the handle part 1 in such a way that it is vertically slidable, without screwing, along guides 27. Above the adjusting ring, on the casing, there is a stopper 28 and a calibrating sleeve 29. At the upper end of the sleeve, there is a protruding flange 30. Between the flange and the stopper, there is fitted a secondary spring 31, which pushes the calibrating sleeve upwards. The upper position of the sleeve is determined by a nut 33 fitted into the casing by thread 32. Inside the lower end of the sleeve there is a lower flange 34. At the upper end of the button shaft 23 there is a button 35, which is broader than the shaft and reaches above the casing. When the pipette is unstrained, the piston being in the initial position, the primary spring 21 pushes both the piston 18 against the button shaft 23, and the controlling ring 26 against the stopper 28. The secondary spring 31 pushes the calibrating sleeve 29 against the nut 33. When the button 35 is pressed, the piston moves downwards against the force of the primary spring 21. As the lower end of the button meets the lower flange 34 of the calibrating sleeve, the secondary spring 31 also begins to resist the movement of the button, whereupon a clear increase of resistance is felt. The piston is held in this position whilst the tip 3 of the distal container is placed into the liquid to be pipetted. The piston is then released to return to its upper position, whereupon it draws a certain amount of liquid into the container. The length of the primary movement, and thus also the volume of the incoming liquid, can be adjusted by turning the button 35. When the liquid that was drawn in is to be removed, the button 35 is pressed downwards. In the primary phase (Fig. 3a), the piston 18 moves downwards the same length as when drawing the liquid in. Therefore, at the end of the primary phase, the lower end of the button would be positioned in such a way that it touches the lower flange 34 of the calibrating sleeve 29. After that, as the pressing of the button is continued, the secondary spring 31 also resists the movement. The parts of the pipette are designed such that at the beginning of the secondary movement, the lower end of the piston rod 19 is above the treshold 14 of the cylinder shaft 13 (Fig. 3b). At the first stage of the secondary phase, the piston 18 moves downwards, until the lower end of the piston rod 19 meets the treshold 14 of the cylinder shaft (Fig. 3c). As the pressing of the button is continued, the cylinder shaft 13 and the cylinder 7 also start moving against the force of the cylinder spring 12 (Fig. 3d). The cylinder 7 is wider than the piston 18, and the additional pressure stroke that it directs to the distal container 3 removes even the droplet remaining at the tip of the container. A pipette usually includes some kind of a volume display system, such as the one described in specification FI-64752 (corresponds to, e.g., specification US-4 554 134). In the pipette of Figure 4, the distal part 2 functions as a dosing cylinder without having a separate cylinder piece. The broader upper part 2.1 of the tip functions as a removing cylinder. The upper end of the spring 12 pushes the support ring 8' against the O-rings 15' and 15.1. By this means, the piston 18 is sealed in relation to the end part.

Claims: A pipette, which comprises an oblong casing (1, 2) with an upper end and a lower end, in the lower end of the casing, a container (3) for liquid, in the casing, a dosing cylinder (7), which includes a movable dosing piston (18), which has a basic position, above the basic position an upper position and below the basic position a low position, so that as the dosing piston moves from its basic position towards its upper position, suction is created in the container, and as the dosing piston moves from its upper position towards its low position, pressure is created in the container, a removing cylinder which includes a movable removing piston (13), which has a basic position and a low position, so that as the removing piston moves from its basic position towards its low position, more pressure is created in the container than when the dosing piston moves from its basic position towards its low position, equipment (19, 23, 35) for moving the dosing piston, and equipment (13, 19, 23, 35) for moving the removing piston, the removing piston not being movable from its basic position until the dosing piston has been moved from its basic position to its low position. A pipette of Claim 1, characterized in that the removing piston (13) surrounds the dosing piston. A pipette of Claim 2, characterized in that the removing piston is the dosing cylinder (13) of the dosing piston. A pipette of any of Claims 1 - 3, characterized in that the dosing piston (18) has below its low position a lower additional removing position, so that as the removing piston moves from its basic position to its lower position, the dosing piston moves from its low position towards its lower additional removing position and pressure is created in the container. A pipette of any of Claims 1 - 4, characterized in that it includes a primary spring (21), which pushes the dosing piston from its basic position towards its upper position. A pipette of any of Claims 1 - 5, characterized in that it includes a secondary spring (31), which pushes the dosing piston from its low position towards its basic position. A pipette of any of Claims 4 - 6, characterized in that it includes an additional secondary spring (12), which pushes the removing piston from its low position to its basic position and thereby the dosing piston from its lower additional removing position towards its basic position. A pipette of Claim 7, characterized in that the additional secondary spring (12) presses an 0-ring (10, 15.1) to seal the removing piston (13) against the casing (2). A pipette of Claim 7 or of Claim 8, characterized in that the additional secondary spring (12) presses the 0-ring (15', 15.1) to seal the dosing piston against the dosing cylinder. A pipette of any of Claims 2 - 9, characterized in that the dosing piston (18) includes a wider rod part (19) and in that the removing piston includes a lower part, which is narrower than said rod part (19) of the dosing piston.

Inventors: HEINONEN MAUNO, HEINONEN, MAUNO
Applicants: THERMO LABSYSTEMS OY
Application year: 1996
Main classification: B01L3
IPC codes: B01L3, G01N1