Electronic pipette

Abstract

The electronic pipette comprises at least one cylinder (11), a piston (12) protruding into said at least one cylinder (11) and configured to be moveable in a reciprocating manner for aspirating liquid into the pipette and dispensing liquid from the pipette, a motor (13) for moving the piston (12), and a control system (30) for controlling the operation of the pipette, wherein the control system (30) is configured to monitor the counter-electromotive force of the motor (13).

Description

[0001] Electronic pipette

[0002] Technical field of the invention

[0003] The present invention concerns an electronic pipette, as defined in claim 1 .

[0004] Background of the invention

[0005] Pipettes used for liquid dosage in laboratories comprise a piston movable in a cylinder and serving to aspire liquid into and to dispense liquid from a pipette tip according to a selected pipetting function. The liquid volume is usually adjustable. Many pipettes are electronic pipettes, in which the piston is actuated by means of an electric motor and an associated control system. The motor can also be used for detaching the pipette tip from the pipette. Electronic pipettes have a control system and an associated user interface for setting the liquid volume to be aspirated or dispensed, for setting and changing settings of different pipette functions and for giving commands for performing operations. The user interface can comprise keys for this. The user interface may also comprise a display, by means of which the volume and any other necessary data can be displayed. The display can also show menus allowing selection of functions and input of settings by means of the keys. The display can be a touch display functioning also as input means. When the desired function has been selected and the volume and other settings have been entered, depression of the actuation switch automatically carries out the following step of the function until the entire function has been completed.

[0006] Electronic pipettes can provide precise and repeatable aspiration and dispensing. However, the precision of a pipette is affected by, for instance, the properties of the pipetted liquid, wear of the pipette, the way of using the pipette and malfunction of the pipette. All these may lead to imprecise aspiration and dispensing.

[0007] In some electronic pipettes, the electric motor used for aspirating and dispensing liquid can also be used for removing the pipette tip. The pipette tip is typically retained by friction force. A challenge relating to removal of pipette tips is that different pipette tips can require from the electric motor different torque and different amount of rotary movement. The required torque and rotary movement also depend on the user of the pipette, as different users may attach the pipette tips with different force. It is thus difficult to optimize the operation of the electric motor for the removal of pipette tips in such a way that the reliable pipette tip removal is ensured while the power consumption of the motor is minimized.

[0008] Summary of the invention

[0009] An object of the invention is to provide an improved electronic pipette solving at least part of the problems mentioned above.

[0010] The pipette according to the invention comprises at least one cylinder, a piston protruding into said at least one cylinder and configured to be moveable in a reciprocating manner for aspirating liquid into the pipette and dispensing liquid from the pipette, a motor for moving the piston, and a control system for controlling the operation of the pipette. The control system of the pipette is configured to monitor the counter-electromotive force of the motor.

[0011] The monitoring of the counter-electromotive force (back EMF) of the motor allows various diagnostic, detection and analyzing functions and more precise control of the operation of the pipette.

[0012] According to an embodiment of the invention, the control system is configured to control the operation of the motor based on the monitored counter-electro- motive force. By controlling the operation of the motor based on the monitored back EMF, the functioning of the pipette, such as aspirating, dispensing and tip removal can be improved.

[0013] According to an embodiment of the invention, the control system is configured to detect sudden changes in the counter-electromotive force. Detection of sudden changes of the back EMF allows, for instance, fault diagnosis and determining the positions of different components of the pipette, such as the piston or pipette tips. Also, detaching of a pipette tip can be detected by detecting a sudden change in the counter-electromotive force. The pipette can be configured to display predetermined information to the user based on a detected sudden change of the counter-electromotive force. The displayed information can be different depending on during which function the sudden change has been detected.

[0014] According to an embodiment of the invention, the control system is configured to compare the monitored counter-electromotive force to a predetermined reference value or reference signal. This can allow, for instance, determining the viscosity of the pipetted liquid or clot detection.

[0015] According to an embodiment of the invention, the control system is configured to calculate an average value of the monitored counter-electromotive force and to compare the calculated average value to the predetermined reference value.

[0016] According to an embodiment of the invention, the control system is configured to detect abnormal operation of the pipette based on the difference between the monitored counter-electromotive force and said reference value or reference signal.

[0017] According to an embodiment of the invention, the control system is configured to adjust the control parameters of the motor based on the difference between the monitored counter-electromotive force and said reference value or reference signal. For example the operation of the motor during tip removal can be adjusted.

[0018] According to an embodiment of the invention, the pipette comprises pipette tip removal means that are configured to be moveable by the motor to detach the pipette tip from the pipette, and the control system is configured to monitor the counter-electromotive force during detaching of the pipette tip. By monitoring the back EMF during pipette tip removal, the type of the pipette tip and / or the force used for attaching the pipette tip can be determined.

[0019] According to an embodiment of the invention, the control system is configured to detect the position of the pipette tip or detaching of the pipette tip based on the monitored counter-electromotive force. The data can be used for displaying information to the user of the pipette or for adjusting the operation of the motor during pipette tip removal.

[0020] According to an embodiment of the invention, the control system is configured to adjust the operation of the motor during detaching of the pipette tip based on the counter-electromotive force detected before and / or during detaching of the pipette tip. By adjusting the operation of the motor, the operation can be optimized for different pipette tips or for different ways of attaching the pipette tips to the pipette. Oversizing of the motor can thus be avoided. Also, the power consumption of the pipette can be reduced. According to an embodiment of the invention, the control system is configured to adjust the moving range of the pipette tip removal means and / or the rotation speed and torque of the motor based on the counter-electromotive force.

[0021] According to an embodiment of the invention, the control system is configured to determine properties of the aspirated or dispensed liquid based on the monitored counter-electromotive force. The properties can include the viscosity of the liquid and possible clots in the liquid.

[0022] According to an embodiment of the invention, the control system is configured to detect reaching of a predetermined piston position based on the monitored counter-electromotive force. For instance, reaching of the lowermost or uppermost piston position can be detected by detecting sudden changes of the counter-electromotive force. This allows, for instance, detecting and determining changes in the clearances of the mechanical parts connecting the piston to the motor. Also, by detecting when the piston reaches a certain predetermined position, the correctness of the position information of the control system can be reviewed. If the pipette uses a stepper motor, in certain situations the rotor of the stepper motor may lose synchronization and skip steps. The actual position of the piston may thus differ from the position determined by the control system. The predetermined position of the piston can function as a reference point for ensuring that the actual position and the desired position of the piston match each other.

[0023] According to an embodiment of the invention, the operation of the motor during aspiration and / or dispensing is adjusted based on said detection of reaching of the predetermined piston position. For instance, increased clearances in the mechanical parts of the pipette can be compensated by increasing the amount of rotating movement of the motor during dispensing or aspiration.

[0024] According to an embodiment of the invention, the motor is a stepper motor.

[0025] Brief description of the drawings

[0026] Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which

[0027] Fig. 1 shows a perspective view of an electronic pipette according to an embodiment of the invention without a pipette tip, Fig. 2 shows a cross-sectional view of the pipette of figure 1 ,

[0028] Fig. 3 shows the electronic pipette of figure 1 with a pipette tip,

[0029] Fig. 4 shows a cross-sectional view of the electronic pipette of figure 3,

[0030] Fig. 5 shows a multichannel pipette according to an embodiment of the invention without pipette tips,

[0031] Fig. 6 shows the multichannel pipette of figure 5 with pipette tips,

[0032] Fig. 7 shows as a block diagram parts of a pipette according to an embodiment of the invention, and

[0033] Figs. 8A-8C show examples of the measured counter-electromotive force in different tip removing situations.

[0034] Detailed description of embodiments of the invention

[0035] Figures 1 to 4 show different views of an electronic pipette according to an embodiment of the invention. The pipette comprises a handle portion 1 , a tip portion 3 and a display portion 2. The electronic pipette is a handheld device. The handle portion 1 is configured to be gripped by a hand of a user of the pipette. In a use position of the pipette, the tip portion 3 is located below the handle portion 1 and the display portion 2 is located above the handle portion 1 . The handle portion 1 comprises a hook 8 that is configured to be supported against a finger of the user.

[0036] The pipette comprises an actuation switch 5 that can be used for operating the pipette, in particular for starting an aspiration or dispensing function or step. The display portion 2 is provided with a display 7 that is configured to show various information to the user. The display 7 can be a touch display that can be used for operating the pipette. In the embodiment of figures 1 to 4, the display portion 2 is further provided with operation keys 6 that can be used for operating the pipette.

[0037] Figures 3 and 4 show a pipette tip 4 attached to the tip portion 3. The pipette tip 4 is detachably attached to the pipette. The pipette can be configured to allow different pipette tips to be attached to the pipette. For instance, the pipette tips 4 may have different lengths and / or volumes and some pipette tips may be provided with a filter. In the embodiment of figures 1 to 4, the pipette tip 4 is attached to the tip portion 3 of the pipette by friction. The user of the pipette thus pushes the pipette tip 4 around the conical lower part of the tip portion 3 and the pipette tip 4 is retained in the tip portion 3 by friction force.

[0038] The pipette comprises a cylinder 11 and a piston 12 protruding into the cylinder 11. The piston 12 is configured to be moveable in a reciprocation manner for aspirating liquid into the pipette and dispensing liquid from the pipette. As the piston 12 moves upwards in the cylinder 11 when the open end of the detachable pipette tip 4 is immersed in liquid, a partial vacuum is generated and liquid is aspirated into the pipette tip 4. As the piston 12 moves downwards, the liquid is dispensed from the pipette tip 4.

[0039] The pipette comprises an electric motor 13 for moving the piston 12. The motor 13 can be a stepper motor. However, the motor 13 could also be some other type of motor. The motor 13 is mechanically coupled to the piston 12 such that rotational movement of the motor 13 can be converted into linear movement of the piston 12. The piston 12 is thus configured to be moved by the motor 13 for aspirating liquid into the pipette and for dispensing liquid from the pipette.

[0040] In the embodiment of figures 1 to 4, the piston 12 is coupled to the motor 13 by means of a threaded rod 14. The motor 13 is configured to rotate the threaded rod 14, and as the threaded rod 14 rotates, it moves in a direction that is parallel to the axial direction of the cylinder 11. The threaded rod 14 is coupled to the piston 12 by means of a piston coupler 15.

[0041] In the embodiment of figures 1 to 4, the motor 13 is further configured to be used for detaching the pipette tip 4 from the pipette after pipetting. The pipette comprises pipette tip removal means 20 that are configured to be moveable by the motor 13 for detaching the pipette tip 4. A pipette tip removal function can be activated for example by means of the actuation switch 5, one of the operation keys 6 or via a touch display.

[0042] In the embodiment of figures 1 to 4, the pipette tip removal means 20 comprise a tip ejector coupler 21 and a tip ejector part 22. The tip ejector coupler 21 is attached to the threaded rod 14. During dispensing movement, the piston coupler 15 and the tip ejector coupler 21 move together and also the piston 12 is thus moved. The tip ejector coupler 21 is releasably attached to the piston coupler 15. The pipette can be provided for example with a magnet and a metal part configured to cooperate with the metal part to attach the tip ejector coupler 21 and the piston coupler 15 together. However, also some other type of releasable connection means could be used.

[0043] As the piston 12 reaches the end of the dispensing movement, further movement of the piston 12 and the piston coupler 15 is prevented by a stopper surface 16, but the tip ejector coupler 21 is allowed to move further. When a tip removal sequence is started, the motor 13 is rotated to move the threaded rod 14 further in the dispensing direction. The threaded rod 14 moves the tip ejector coupler 21 further. The tip ejector coupler 21 is configured to mechanically connect to the tip ejector part 22 via an intermediate part 23. As the tip ejector part 22 moves downwards, it pushes the pipette tip 4 and detaches the pipette tip 4 from the tip portion 3 of the pipette.

[0044] The pipette tip 4 is attached to the tip portion 3 by friction. Both the pipette tip 4 and the lower end of the tip portion 3 are conical. The pipette tips 4 are typically made of a plastic material having some elasticity. The exact position of the pipette tip 4 relative to the tip portion 3 of the pipette thus depends on the type and material of the pipette tip 4 and on how hard the user of the pipette has pushed the pipette tip in place. Therefore, also the friction force keeping the pipette tip 4 retained in the tip portion 3 varies.

[0045] Figures 5 and 6 show a pipette according to another embodiment of the invention. In the embodiment of figures 5 and 6, the handle portion 1 and the display portion 2 are identical to the respective parts of the pipette shown in figures 1 to 4. The tip portion 3’, however, differs from the tip portion 3 of the pipette of figures 1 to 4. In the embodiment of figures 5 and 6, the pipette is a multichannel pipette. The pipette comprises a plurality of cylinders and an equal number of pistons. The motor of the pipette is configured to move simultaneously all the pistons of the pipette. For each cylinder of the pipette, one pipette tip 4 can be attached to the pipette. Also the pipette of figures 5 and 6 is provided with pipette tip removal means. The pipette tip removal means comprise a tip ejector part 22’ that can be moved by the motor 13 of the pipette. As the tip ejector part 22’ moves in the dispensing direction of the pistons of the pipette, the pipette tips 4 are detached from the tip portion 3’ of the pipette. The tip ejector part 22’ can be mechanically connected to the motor 13 in a similar way as in the embodiment of figures 1 to 4. The tip ejector part 22’ or force transmission means between the tip ejector coupler and the tip ejector part can be configured such that the pipette tips 4 are not detached simultaneously with each other. This reduces the force needed to remove the pipette tips 4. For instance, the tip ejector part 22’ can be shaped such that the tip ejector part 22’ contacts at least some of the pipette tips 4 at a slightly different time than the other pipette tips 4. In the embodiment of figures 5 and 6, the tip ejector part 22’ is shaped to contact the pipette tips 4 in the middle of the row of the cylinders before the pipette tips 4 at the ends of the row of cylinders.

[0046] Figure 7 shows as a block diagram parts of a pipette according to an embodiment of the invention. The pipette comprises a control system 30 for controlling the operation of the pipette. The control system is operatively connected to the motor 13 and to the user interface 40 of the pipette. The user interface 40 comprises at least input means that allow a user of the pipette to operate the pipette. The user interface can further comprise a display 7 for showing information to the user. The display 7 can be a touch display forming at least part of the input means. Instead of a touch display or in addition to it, the input means can comprise one or more push-buttons or other similar means, such as the actuation switch 5 and operating keys 6 shown in figures 1 to 6. The user interface 40 can comprise two or more displays. The user interface 40 could also comprise other signal means than the display 7 for transmitting information to the user of the pipette. For instance, the pipette can comprise one or more signal lights and / or audio means for informing the user. The control system 30 can comprise a main control unit 31 and a motor control unit 32. The main control unit 31 can comprise various components, such as a central processing unit (CPU), a non-volatile memory and a volatile memory. The nonvolatile memory can be used for storing a computer program configured to operate the pipette based on the commands given by the user of the pipette via the input means. The non-volatile memory can also be used for storing settings and functions inputted by the user. The pipette comprises a battery 50 that powers the control system 30, user interface 40 and the motor 13.

[0047] The main control unit 31 is operatively connected to the motor control unit 32. The motor control unit 32 can be an integral part of the motor 13. The motor control unit 32 is configured to receive operating commands from the main control unit 31 . Based on the operating commands received from the main control unit 31 , the motor control unit 32 controls the electric current fed to the motor 13. The motor control unit 32 can further control the voltage of the power supply to the motor 13.

[0048] When the rotor of the motor 13 is turned, the changing magnetic flux induces an electromotive force resisting the turning of the rotor. This electromotive force self-generated by the motor 13 is called back EMF or counter-electromotive force. The faster the rotor of the motor 13 rotates, the greater is the magnitude of the back EMF.

[0049] The motor control unit 32 is configured to monitor the counter-electromotive force of the motor 13. The monitoring of the counter-electromotive force provides various benefits by allowing, for instance, more efficient operation of the pipette and fault diagnostics.

[0050] The control system 30 of the pipette can be configured to detect sudden changes in the counter-electromotive force. The control system 30 can be configured to compare the monitored counter-electromotive force to a predetermined reference value or reference signal. For instance, the control system 30 can be configured to calculate an average value of the monitored counter-electromotive force during a certain pipetting function or step of a pipetting function and to compare the calculated average value to the predetermined reference value. The control system can be configured to detect abnormal operation of the pipette based on the difference between the monitored counter-electromotive force and the reference value or reference signal. The detected abnormal operation can be communicated to the user via the user interface.

[0051] The control system 30 can be configured to determine properties of the aspirated or dispensed liquid based on the monitored counter-electromotive force. For instance, the viscosity of the liquid can be determined, as dispensing and aspirating of liquids with different viscosities causes different resistances, which lead to different counter-electromotive forces. Also, clots in the liquid can be detected based on sudden changes in the counter-electromotive force. The pipette can be configured to display to the user information on the properties of the liquid.

[0052] The control system 30 can be further configured to control the operation of the motor 13 based on the monitored counter-electromotive force. For instance, the control system 30 can be configured to adjust the control parameters of the motor 13 based on the difference between the monitored counter-electromotive force and said reference value or reference signal.

[0053] Also, the control system 30 can be configured to detect reaching of a predetermined piston position based on the monitored counter-electromotive force. For instance, reaching of the lowermost or uppermost piston position can be detected by detecting sudden changes of the counter-electromotive force. This allows, for instance, detecting and determining changes in the clearances of the mechanical parts connecting the piston 12 to the motor 13. The operation of the motor 13 during aspiration and / or dispensing can be adjusted based on the detection of reaching of the predetermined piston position. For instance, increased clearances in the mechanical parts of the piston 12 can be compensated by increasing the amount of rotating movement of the motor 13 during dispensing or aspiration. In the embodiment of figures 1 to 4, the piston 12 is provided with a flange 12A. As the flange 12A of the piston 12 contacts during downward movement of the piston 12 a stopper surface 16 arranged in the body of the pipette, the movement of the piston 12 is stopped. This can be detected as a sudden drop in the counter-electromotive force of the motor. As the motor 13 continues turning, the tip ejector coupler 21 is released from the piston coupler 15, which can be detected as a sudden increase in the counter- electromotive force. If the clearances of the mechanical parts of the pipette increase, a different amount of steps may be needed by the motor 13 to reach the position where the flange 12A of the piston 12 contacts the stopper surface 16. This information can be used for adjusting the operation of the motor 13 to maintain the precision of dispensing and aspiration.

[0054] If a stepper motor is used for operating the piston 12, a certain number of steps of the motor 13 equals a certain movement of the piston 12. In principle, one pulse of electricity turns the motor 13 one step. However, if the torque of the motor 13 is too low for overcoming the resisting force, the rotor of the motor 13 may lose synchronization and skip steps. The actual position of the piston 12 may thus differ from the position determined by the control system 30. By detecting when the piston 12 reaches a certain predetermined position, the correctness of the position information of the control system 30 can be reviewed. The predetermined position of the piston 12 can function as a reference point for ensuring that the actual position and the desired position of the piston 12 match each other.

[0055] According to an embodiment of the invention, the control system 30 is configured to monitor the counter-electromotive force during detaching of the pipette tip 4. This allows determining the type of the pipette tip 4 or the position of the pipette tip 4. The pipette tip removing function can thus be optimized for different pipette tip types and for different retaining forces.

[0056] Based on the detected counter-electromotive force, the operation of the motor 13 during detaching of the pipette tip 4 can be adjusted. For instance, the control system 30 can be configured to adjust the moving range of the pipette tip removal means 20 and / or the rotation speed and torque of the motor 13 based on the counter-electromotive force.

[0057] Figures 8A to 8C show examples of the counter-electromotive force measured during pipette tip removal. The rapidly fluctuating curves of figures 8A to 8C show actual measured counter-electromotive forces and the smoother curves show filtered signals representing counter-electromotive forces. As the counter-electromotive force depends on the rotation speed of the motor 13, lower rotation speed caused by a greater resisting force can be detected as a smaller counter-electromotive force. Figure 8A shows the counter-electromotive force when no pipette tip is attached to the pipette. In the example of figure 8B, a pipette tip has been attached to the pipette with a typical force, and in the example of figure 8C the pipette tip has been attached to the pipette with a greater force.

[0058] The memory of the control system 30 of the pipette can store reference signals for different pipette tips and different retaining forces. By comparing the counter-electromotive force detected during the pipette tip removal to the reference signals, it can be determined what kind of pipette tip 4 is attached to the tip portion 3, 3’ of the pipette and how hard the pipette tip 4 has been pushed in place. Based on the data, suitable operating parameters can then be set for the motor 13.

[0059] As the operation of the motor 13 during pipette tip removal can be optimized, there is no need to oversize the motor 13 to ensure reliable detachment of the pipette tips 4. Also, the power consumption of the motor 13 can be reduced and the operating time of the pipette is thus increased.

Claims

Claims:1 . An electronic pipette comprising- at least one cylinder (11 ),- a piston (12) protruding into said at least one cylinder (11 ) and configured to be moveable in a reciprocating manner for aspirating liquid into the pipette and dispensing liquid from the pipette,- a motor (13) for moving the piston (12), and- a control system (30) for controlling the operation of the pipette, wherein the control system (30) is configured to monitor the counter-electromotive force of the motor (13).

2. An electronic pipette according to claim 1 , wherein the control system (30) is configured to control the operation of the motor (13) based on the monitored counter-electromotive force.

3. An electronic pipette according to claim 1 or 2, wherein the control system (30) is configured to detect sudden changes in the counter-electromotive force.

4. An electronic pipette according to any of claims 1-3, wherein the control system (30) is configured to compare the monitored counter-electromotive force to a predetermined reference value or reference signal.

5. An electronic pipette according to claim 4, wherein the control system (30) is configured to calculate an average value of the monitored counter- electromotive force and to compare the calculated average value to the predetermined reference value.

6. An electronic pipette according to claim 4 or 5, wherein the control system (30) is configured to detect abnormal operation of the pipette based on the difference between the monitored counter-electromotive force and said reference value or reference signal.

7. An electronic pipette according to any of claims 4 to 6, wherein the control system (30) is configured to adjust the control parameters of the motor (13) based on the difference between the monitored counter-electromotive force and said reference value or reference signal.

8. An electronic pipette according to any of the preceding claims, wherein the pipette comprises pipette tip removal means (20) that are configured to be moveable by the motor (13) to detach the pipette tip (4) from the pipette, and the control system (30) is configured to monitor the counter- electromotive force during detaching of the pipette tip (4).

9. An electronic pipette according to claim 8, wherein the control system (30) is configured to detect the position of the pipette tip (4) or detaching of the pipette tip (4) based on the monitored counter-electromotive force.

10. An electronic pipette according to claim 8 or 9, wherein the control system (30) is configured to adjust the operation of the motor (13) during detaching of the pipette tip (4) based on the counter-electromotive force detected before and / or during detaching of the pipette tip (4).

11. An electronic pipette according to claim 10, wherein the control system (30) is configured to adjust the moving range of the pipette tip removal means (20) and / or the rotation speed and torque of the motor (13) based on the counter-electromotive force.

12. An electronic pipette according to any of the preceding claims, wherein the control system (30) is configured to determine properties of the aspirated or dispensed liquid based on the monitored counter-electromotive force.

13. An electronic pipette according to any of the preceding claims, wherein the control system (30) is configured to detect reaching of a predetermined piston position based on the monitored counter-electromotive force.

14. An electronic pipette according to claim 13, wherein the operation of the motor (13) during aspiration and / or dispensing is adjusted based on said detection of reaching of the predetermined piston position.

15. An electronic pipette according to any of the preceding claims, wherein the motor (13) is a stepper motor.

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