1. Field of the Invention
The invention relates to a motorized pipette which has an electronic, programmable control. In particular, the invention relates to certain operating modes of such a pipette.
2. Description of Related Art
Motorized pipettes of the type under consideration are extensively used in processes for pipetting of relatively small amounts of liquid, and take various forms as shown in U.S. Pat. No. 5,187,990 A, U.S. Pat. No. 6,254,832 B1, U.S. Pat. No. 6,090,348 A2 and U.S. Pat. No. 6,540,964 B2.
The known motorized pipette is designed and suited for pipetting of relatively small amounts of liquid (for example 1 ml per dispensing cycle) as shown in U.S. Pat. No. 6,090,348 A. The motorized pipette can work in a standard operating mode in which a volume of sample liquid which is input beforehand is taken up and dispensed again, or it can also be operated as a repetition pipette with dispensing of a volume of liquid which has been taken up, in several stages.
There are motorized pipettes with interchangeable pipette tips which are slipped onto a tip receiving section (air cushion pipettes) or with complete syringes (plunger/cylinder arrangement) which are mounted on the tip receiving section (direct displacement pipettes). For the former see U.S. Pat. No. 5,187,990 A and U.S. Pat. No. 6,254,832 B2 as examples; while for the latter see for example U.S. Pat. No. 6,540,964 B2. The teaching is used especially in an air cushion pipette. Therefore, often only the pipette tip of an air cushion pipette is addressed, but such is not intended to preclude the fact that the corresponding features can also be implemented in a direct displacement pipette with a syringe.
The starting point for the teaching of the invention is a motorized pipette with an optionally multi-part housing which can be held in the hand, with a housing head, a grip part and pipette shaft with a tip holding section. In the housing, there are an electrical drive motor, especially a stepping motor, a positioning means which is driven by a drive motor for taking up and dispensing exactly defined, extremely small amounts of liquid, and an electronic control for the drive motor. In or on the housing there are at least one actuating element for actuating the control, at least one programming element for setting and/or programming different operating modes of the control, and an optical display means for display of operating modes, settings, etc. By means of the control, for example a certain take-up volume, a certain take-up rate, a certain dispensing volume, a certain dispensing rate and/or a certain expulsion overstroke for the sample liquid can be stipulated. A take-up cycle and/or a dispensing cycle for the sample liquid is started by actuating the actuating element and is automatically stopped by the control.
In a known motorized pipette for take-up and dispensing of defined amounts of liquid there is an actuating element for actuating the control. In addition, there are several programming elements (programming keys) and an optical display means in the form of a LCD display on which various unambiguous symbols, as well as letters and numbers, can be displayed. In this way operating modes, settings, etc. of the motorized pipette can be clearly communicated to the user.
In the known motorized pipette, the control is programmed such that a take-up cycle and/or a dispensing cycle for the sample liquid is started by actuating the actuating element, then proceeds automatically and is automatically stopped by the control itself at the end, i.e., specifically when a certain take-up volume has been reached, or when the complete, taken-up liquid volume has been expelled. In part, an expulsion overstroke is incorporated into the triggering of the positioning means by the control.
Other motorized pipettes allow an expulsion overstroke to be added after a waiting and collecting time of short duration, for example one second, as shown in U.S. Pat. No. 5,187,990 A which also shows a host of embodiments for programming the control of a motorized pipette of the type. This technology has been further developed in a later patent U.S. Pat. No. 6,254,832 B1; the entire disclosure of which is hereby incorporated by reference.
For special applications of motorized pipettes of the type under consideration in which a very small liquid volume, for example a liquid volume between 2 μl and 50 μl must be taken up and discharged in a concerted manner, it is recommended that a very low dispensing rate be set. This is relevant in the charging of electrophoresis gels because in such use turbulence must be prevented with the greatest possible consistency. The proper programming of the electronic control with a very low dispensing rate requires a high level of attentiveness of the user. Additionally, in applications involving very small liquid volumes, it would be desirable to know accurately the dispensed volume of sample liquid.
A known motorized pipette has provided an operating mode in which an especially low dispensing rate can be set and the dispensing cycle for the sample liquid can be interrupted. This is particularly advantageous for titration. This low dispensing rate is feasible for charging of electrophoresis gels.
The interruption of the dispensing cycle by actuating the actuating element can be accomplished by releasing the actuating element, which is held continuously pressed during the entire dispensing cycle, for interrupting the dispensing cycle. However, dispensing can proceed from a first actuation of the actuating element to start the dispensing cycle to a second actuation pointed in the same direction which interrupts the dispensing cycle.
With respect to the display in the display means, the display means works continuously; therefore the progressively dispensed volume of sample liquid is continuously displayed in the display means. A change of the display on the display means occurs when the dispensing cycle is interrupted. However, the display can also be such that during the current dispensing cycle for the sample liquid the display means does not display the dispensed volume, or any clearly recognizable display. Consequently, the volume of sample liquid which has been dispensed up to the interruption is clearly displayed in the display means only after the completed interruption.
This motorized pipette is already known for use in control engineering for charging of electrophoresis gels and for other applications with especially difficult boundary conditions of pipetting or titrating. Likewise, there are development possibilities for especially small volumes of liquid in a problematic environment.