Field of technology

The present invention relates to an electronic pipette for use in the dosage of liquids and comprising a piston movable in a cylinder for aspiration and dispensing of liquid, an electric motor for moving the piston in the cylinder, and an electronic operating system with a user interface for operating the electronic pipette.

Technological background Pipettes used for liquid dosage in laboratories comprise a piston movable in a cylinder for aspiration of liquid into a tip container connected with the cylinder. The volume is usually adjustable. There are also electronic pipettes whose piston is actuated by means of an electric motor and a control system associated with it. However, there are also electronic pipettes whose pistons are actuated by manual force and which comprise an electronic display only. Electronic pipettes have a user interface for selection of the desired pipette function (e.g . forward or reverse pipetting), setting of the volume and for giving commands for performing operations. The user interface has the necessary switches for input of the necessary settings and performance of the functions. The user in- terface is connected to a display, by means of which the volume and other necessary data can be displayed. The display can also show menus allowing data input in the control system.

Examples of known electronic pipettes are disclosed in publications WO 2005079989 and WO 2005079987, for example. Pipettes usually have a calibration function allowing the piston stroke or the volume indicated on the display to be set so that the dosed liquid volume equals the indicated volume with maximal accuracy. In practice, calibration comprises weighing the mass of the liquid amount dosed by the pipette with an indicated volume. The liquid is usually distilled water and the calibration is per- formed at room temperature (20-25 °C). Usually weighing is repeatedly carried out and the mean value of the results of the weighing operations is calculated. However, due to the use of pipette during its lifetime, the parts of the pipette experience mechanical wear causing play and backlash between different components of the pipette, which affect the actual volumes of liquid aspired and/or dispensed with the pipette. Publication US 5,187,990 discloses an electronic pipette that automatically goes through calibration process upon either powerup or restoration of power after power loss. In the calibration process, the digital linear actuator of the pipette undergoes full extension in order to properly position the piston of the pipette in its home position prior to starting the pipetting processes. For compen- sating air pressure and liquid surface tension, among others, the piston of the pipette is moved for additional distance during the aspiration and/or dispensing of a volume of liquid.

Summary of the invention

In the present invention the actual backlash affecting the movement of a piston of an electronic pipette is measured with a system located in the pipette, the measured backlash value is forwarded to a control system of the electronic pipette, and the movement of the piston is adjusted by the control system based on the measured backlash value. This way the actual backlash, which varies from pipette to pipette, and during the lifetime of the pipette, can be properly eliminated from the functioning of an electronic pipette. The backlash directly affects the amounts of liquid aspired and dispensed with an electronic pipette, so the present invention provides for more accurate pipetted amounts of liquid.

The measurement of backlash is advantageously carried out by defining the actual position of the piston in a first position, then moving the piston a set dis- tance to a second position, then returning the piston exactly to the fist position and measuring the returning distance, and then comparing the set distance from the first position to the second position and the measured distance from the second position to the first position. The difference of these distances is the actual backlash value of the pipette. Advantageously the backlash is measured in both movement directions of the piston of the electronic pipette. The backlash may be different for different movement directions of the piston, so by measuring the backlash in both movement directions proper measurement value can be used for aspiration and for dispensing. Further, the measurement of backlash in both directions also allows minimizing the effect of measurement inaccuracies, such as hysteresis for example.

When the backlash is measured in both movement directions, an average value of the measured backlash values from different movement directions is ad- vantageously used as the measured backlash value for adjustment of the movement of the piston.

The backlash measurement may advantageously be carried out each time the electronic pipette is powered up. Thus the correct backlash value is available for pipetting operations substantially continuously. Alternatively the backlash measurement may be carried out only during calibration process of the pipette, since the backlash value does not generally increase significantly during normal use of the pipette.

In the method of the invention the definition and positioning of a home position of the piston of the electronic pipette may advantageously be implemented with the same sensor system than the backlash measurement.

Advantageously the backlash measurement is carried out to an electronic pipette which is a handheld entity.

A method of the invention is advantageously carried out during repetitive pipetting, in manual pipetting or in step based pipetting. The invention also provides an electronic pipette, comprising a piston actuated in a cylinder by a motor, a control system for carrying out pipetting operations, and a user interface for operating the pipette, which pipette is equipped with a device for measuring actual backlash affecting the movement of the piston of the electronic pipette. Advantageously in the present invention the device for measuring the actual backlash of the piston comprises one or more suitable sensors or sensor systems, such as an optical fork sensor, a reflecting sensor system and/or a magnetic sensor system.

Further, the device for measuring the actual backlash of the piston may be lo- cated as a part of the fixed structure of the pipette or it may be located in the piston itself or in a part moving with the piston, or it may be located partially both at the fixed structure of the pipette and in the piston itself. Advantageously the electronic pipette of the invention is a handheld entity.

The features defining a method according to the invention are more precisely presented in claim 1 , and the features defining an electronic pipette according to the invention are more precisely presented in claim 8. Dependent claims disclose advantageous features and embodiments of the invention.

Drawings

An exemplifying embodiment of the invention and its advantages are explained in greater detail below in the sense of an example and with reference to the accompanying drawings, where Figure 1 shows schematically a cross-section of an electronic pipette according to the invention,

Figure 2 shows schematically a functional diagram of an electronic pipette according to the invention,

Figures 3A and 3B show schematically an example of the principle of the present invention for measuring the backlash of a piston in an electronic pipette,

Figure 4 shows schematically an example of motor driving of a piston of an electronic pipette according to the invention during repetitive pipetting,

Figure 5 shows schematically an example of motor driving of a piston of an electronic pipette according to the invention in manual pipetting, and

Figure 6 shows schematically an example of motor driving of a piston of an electronic pipette according to the invention in step based pipetting.

Detailed description of the embodiments

Figure 1 shows schematically a cross section of an electronic pipette 1 accord- ing to the invention, which is formed as a handheld entity and the body of which comprises handle portion 2, at upper end of the handle portion tilted display portion 3, and at lower end of the handle portion tip portion 4 of the pipette. When the pipette 1 is used it is gripped from the handle portion 2 so that middle finger of the user sets against finger support 5 at the upper part of the handle portion, which leaves index finger of the user free to operate the operating switch 6 of the pipette. To the tip portion 4 is attached detachable pipette tip 7, to which liquid is aspired and from which liquid is dispensed during the use of the pipette 1 .

The outer surface of the display portion 3 of the pipette 1 is equipped with a display 8 and operation keys 9, which form the user interface of operating system of the pipette together with the operating switch 6.

Inside the body of the pipette 1 , extending in the area of the handle portion 2 and the tip portion 4 of the pipette, is located a cylinder 10 and inside the cylinder piston 1 1 movable with respect to the cylinder, which both extend along or parallel with the central axis of the handle portion and/or tip portion of the pipette. From the lower end of the cylinder 1 1 extends a channel 12 at the bottom end surface of the tip portion 4 for obtaining aspiration or dispensing of liquid to and from the detachable pipette tip 7 by moving the piston 1 1 inside the cylinder 10. Between surfaces of the cylinder 10 and the piston 1 1 is located a spring member 13 extending in the length direction of the cylinder and piston for forcing the upper end of the piston against the means for moving the piston in the cylinder.

The means for moving the piston 1 1 comprises a linear actuator formed by a threaded rod 14, which extends along or parallel with the central axis of the handle portion 2, and an electric motor 15, which moves the threaded rod in its lengthwise direction through a threaded connection between the un-rotating threaded rod and a rotating member of the motor. By moving the threaded rod 14 the piston 1 1 moves accordingly inside the cylinder 10.

The pipette 1 also includes a device for measuring the actual backlash of the piston, which in this embodiment is an optical fork sensor 1 6 located on top of the motor 15 so that the top end of the threaded rod 14 can move between the brackets of the fork sensor. Alternatively in the present invention the device for measuring the actual backlash of the piston may be located in the piston 1 1 itself or in a part moving with the piston, or it may be comprise two or more parts where at least one part is located in the piston 1 1 itself or in a part moving to- gether with the piston and at least one part is located at other fixed parts of the pipette.

In the embodiment of figure 1 , the movement of the threaded rod 14, and thus the motion of the piston 1 1 , is controlled as step based movement. Thus the backlash affecting the piston can be measured so, that first the threaded rod 14 is moved to a starting position by moving it upwards until the light path between the brackets of the optical fork sensor 16 is cut for the first time. From this starting position the threaded rod 14 is moved upwards for a set amount of steps, and then downwards until unobstructed light path is obtained again in the optical fork sensor. The difference between the set amount of steps upwards and the measured amount of steps required for moving the threaded rod 14 downwards to the exact starting position defines the actual backlash of the piston. This actual backlash is automatically forwarded to the operating system of the pipette to be taken into account during different pipetting operations. In some cases there might also be need to take into account the possible hysteresis or other possible measurement inaccuracies of the device for measuring the actual backlash of the piston. This can be implemented so that the measurement of the backlash is carried out both for upwards movement and downwards movement of the piston. Since the mechanical backlash is gener- ally constant for both directions, the difference of the measured backlash values in different piston movement directions gives the actual value of these measurement inaccuracies. For taking account the effect of these measurement inaccuracies, the measured inaccuracy may be used as such to compensate the movement of the piston, or average value of the measured backlash values from different movement directions may be used for the set backlash value.

Figure 2 shows schematically an example of a functional diagram of an electronic pipette, like the pipette 1 of figure 1 . The operations of the pipette are controlled with a central processing unit (CPU), which is equipped with memory for storing pre-programmed operations and functions. The user gives commands to the CPU through operation keys and with help of a display of the pipette. The CPU is supplied with operating power by a battery and a voltage regulator, which can be recharged with a charger through charging connections when the pipette is placed in its stand. The CPU of the pipette can also be connected to external databases through data interface. The CPU receives information from a backlash sensor of the pipette and calculates the backlash value to be used in the pipetting operations and then compensates the actual backlash of the piston movement. In accordance with instructions received from the user through the operation keys, the CPU controls the motor of the pipette through a motor driver. The dashed line on figure 3 presents boundary surface between the pipette itself and the stand of the pipette in which the pipette is placed when not in use.

Figures 3A and 3B show schematically an example of the principle of the present invention for measuring the backlash of a piston in an electronic pipette. In figure 3A the backlash affecting downward movement of a piston of an electronic pipette is defined and measured, i.e. the backlash affecting dispensing pipetting actions. In figure 3B the backlash affecting upwards movement of a piston of an electronic pipette in defined and measured, i.e. the backlash affecting aspiration pipetting action. Before the definition and measurement of backlash is started, the position of the piston is precisely defined with a sensor. Next, as shown in figure 3A, the piston is moved upwards by controlling the motor to drive the piston upwards for set amount of steps (V-steps). After the piston is moved to its upward position, the motor is controlled to drive the piston downwards back to the starting position defined by the sensor, and the required steps of motor are counted (X- steps). Backlash b1 for downward movement of the piston is then defined by subtracting V-steps from X-steps.

For defining and measuring backlash of the piston for upward movement, as shown in figure 3B, first the position of the piston is precisely defined with the sensor. Then the piston is moved downwards by controlling the motor to drive the piston downwards for set amount of steps (Y-steps). After the piston is moved to its downward position, the motor is controlled to drive the piston upwards back to the starting position defined by the sensor, and the required steps of motor are counted (Z-steps). Backlash b2 for upward movement of the piston is then defined by subtracting Y-steps from Z-steps.

As can be seen from figures 3A and 3B, when the direction of the movement of the piston is changed, the motor will first cover the length of the backlash before the piston itself starts to move. Further, this definition and measurement of backlash is advantageously implemented for both directions of movement each time the backlash is defined. If the measured backlashes b1 and b2 are not equal, mean value of these two measured backlash values can be used.

Figure 4 shows schematically an example of motor driving of a piston of an electronic pipette according to the invention during repetitive pipetting . Repeti- tive pipetting technique is a commonly used technique which offers rapid and simple procedure for repeated delivery of the same liquid volume.

In repetitive pipetting technique liquid volume larger than the required liquid volume to be dispensed during the repetition is aspired into the pipette. Then the required amount of repetitions is carried out, and finally any remaining liq- uid is removed from the pipette through blowout phase. After blowout phase the motor moves the piston back at home position for any further pipetting actions.

In the example of figure 4, the motor moving the piston of the pipette is driven the measured backlash value extra, so that the piston itself will move only the user defined value and aspirate and dispense exactly the required liquid volume.

In figure 4, the "Sensor" position and the relating "Sensor check" are used to check and properly position the piston to its home position.

Figure 5 shows schematically an example of motor driving of a piston of an electronic pipette according to the invention in manual pipetting . The manual pipetting technique in an electronic pipette can be used in different applications. It can be used for example to measure the amount of remaining liquid in reservoir. In manual pipetting liquid is aspired as long as the pipetting trigger or operating switch is kept pressed. In such use the display of the pipette shows the amount of volume that has been aspired into the pipette tip. During manual pipetting it is generally also possible to change between aspiration and dispensing whenever needed, which requires an exact compensation of backlash.

In the example of figure 5, in the first aspiration phase the motor drives the piston from the start until the end without any backlash, and when the first dis- pensing phase is started, the motor will first drive downwards the distance of the measured backlash b, which will not actually move the piston itself and the aspired liquid volume will not change at the display of the pipette. When actual movement of the piston is obtained with motor driving, the displayed volume will start to change accordingly. In the next aspiration phase, which is after dispensing of the total liquid volume from the pipette tip as can be seen from the figure 5, the motor will first drive the distance of the measured backlash b during which the displayed volume remains zero, and only after the actual movement of the piston is obtained will the displayed liquid volume start to increase accordingly. And similarly, when the second dispensing phase is started, the motor drives first the measured backlash b before the actual movement of the piston is achieved and before the displayed volume will change accordingly. Figure 6 shows schematically an example of motor driving of a piston of an electronic pipette according to the invention in step based pipetting . In step based pipetting technique each pipetting step is generally input separately by the user in the sequence in which these pipetting steps will be performed. This allows the user to make individual and even complicated pipetting sequences. Thus a step based pipetting sequence can contain several phases where piston movement direction is changed and each piston movement direction change requires an exact compensation of backlash.

In the example of figure 6, the first fill 1 is implemented with motor driving the piston with any backlash, since locating the piston at the starting home position also removes the backlash for aspiration. After fill 1 , the pipette tip is emptied with two dispensing operations dispense 1 and dispense 2, wherein during dispense 1 the measured backlash b is removed by driving the motor defined amount before actual movement of the piston together with dispensing action is obtained. In fill 2 and dispense 3 phases the measured backlash b is similar- ly removed with motor drive before actual movement of the piston is obtained and thus also the actual aspiration or dispensing function.

In all three pipetting techniques discusses above the dispensing accuracy is dependent on how precisely the exact backlash value of a given pipette is known and then compensated. The present invention provides a solution for determining the actual backlash value with a measurement system integrated in the electronic pipette itself and by that also enables the renewal of the measurement and compensation throughout the life cycle of the pipette.

The specific exemplifying embodiments of the invention shown in figures and discussed above should not be construed as limiting. A person skilled in the art can amend and modify the exemplary embodiments described above in many evident ways within scope of attached claims. Thus the invention is not limited merely to the embodiments described above.