Method for contactless determination of the position of a driven displacement part of an electric motor, electric motor and pipetting system for aspirating and dispensing pipetting liquids using said
阅读说明:本技术 用于电动机的从动移动部的位置的无接触判定方法、电动机和使用该电动机抽吸和分配移液液体的移液系统 (Method for contactless determination of the position of a driven displacement part of an electric motor, electric motor and pipetting system for aspirating and dispensing pipetting liquids using said ) 是由 雷托·埃廷格 于尔格·拉斯特 弗里多林·吉塞尔 于 2018-05-03 设计创作,主要内容包括:提供一种通过多个磁场传感器(8)用于电动机(2)的从动移动部(4)的位置的无接触判定方法,其中,移动部相对于定子(6)可移动地布置并且具有产生具有多个周期性间隔开的最大值的移动部磁场的多个永磁体(40),和其中,多个磁场传感器沿着移动部的移动路径(43)布置。该方法包括以下步骤:通过多个磁场传感器,判定由多个永磁体产生并取决于移动部位置的瞬时磁场的多个测量值(70),从多个测量值(70)判定特定频谱信号分量(74),特定频谱信号分量具有对应于移动部磁场的相邻相似最大值之间的距离的空间频率,和通过特定频谱信号分量判定从动移动部的位置。(A contactless determination method for the position of a driven moving part (4) of an electric motor (2) by means of a plurality of magnetic field sensors (8) is provided, wherein the moving part is movably arranged with respect to a stator (6) and has a plurality of permanent magnets (40) which generate a moving part magnetic field having a plurality of periodically spaced-apart maxima, and wherein the plurality of magnetic field sensors are arranged along a movement path (43) of the moving part. The method comprises the following steps: determining a plurality of measured values (70) of the instantaneous magnetic field generated by the plurality of permanent magnets and depending on the position of the moving part by means of the plurality of magnetic field sensors, determining a specific spectral signal component (74) from the plurality of measured values (70), the specific spectral signal component having a spatial frequency corresponding to the distance between adjacent similar maxima of the magnetic field of the moving part, and determining the position of the driven moving part by means of the specific spectral signal component.)
1. A contactless determination method for the position of a driven moving part (4) of an electric motor (2) by means of a plurality of magnetic field sensors (8), wherein the moving part is movably arranged with respect to a stator (6) and has a plurality of permanent magnets (40) which generate a moving part magnetic field having a plurality of periodically spaced maxima, and wherein the plurality of magnetic field sensors are arranged along a moving path (43) of the moving part;
the method comprises the following steps:
determining, by a plurality of magnetic field sensors, a plurality of measurements (70) of the instantaneous magnetic field generated by the plurality of permanent magnets and dependent on the position of the moving part;
determining from the plurality of measurements (70) a specific spectral signal component (74) having a spatial frequency corresponding to a distance between adjacent similar maxima of the moving part magnetic field; and
the position of the driven moving part is determined by the specific spectrum signal component.
2. The method according to claim 1, characterized in that the determination of the position of the driven mobile part (4) is performed by means of the phase angle of a specific spectral signal component (74).
3. A method according to claim 2, characterized in that the determination of the position of the driven mobile part (4) comprises converting the phase angle of a specific spectral signal component (74) into an offset of the driven mobile part relative to a known position.
4. The method according to any of the preceding claims, characterized in that the determination of the specific spectral signal component (74) is performed by applying a Goertzel algorithm to at least a part of a plurality of measurement values (70).
5. A method according to any one of claims 1 to 3, characterized in that the determination of the specific spectral signal component (74) is performed by applying a Fast Fourier Transform (FFT) to at least a part of the plurality of measurement values (70).
6. The method according to any of the preceding claims, further comprising the step of:
selecting a subset (72) of the plurality of measurements;
wherein in the step of determining the specific spectral signal component (74) from the plurality of measurement values (70), the specific spectral signal component is determined in a subset of the plurality of measurement values.
7. The method according to claim 6, characterized in that the subset (72) of the plurality of measurement values is taken from magnetic field sensors (8) arranged adjacent to each other.
8. The method according to any one of claims 6 and 7, characterized in that the subset (72) of the plurality of measurement values comprises 4 to 10 measurement values, in particular 5 to 8 measurement values, still more in particular 6 measurement values.
9. The method according to any one of claims 6 to 8, wherein the selecting a subset (72) of the plurality of measurement values comprises the steps of:
organizing the plurality of measurement values (70) according to a spatial arrangement of the magnetic field sensors (8) along a movement path (43) of the moving part (43);
determining a first measurement whose absolute value exceeds a predetermined threshold; and
selecting the first measurement value and an adjacent measurement value as a subset (72) of the plurality of measurement values.
10. Method according to claim 9, characterized in that the position of the driven mobile part (4) is calculated from the position of the magnetic field sensor providing the first measurement value and the offset of the driven mobile part shown by the phase angle of the specific spectral signal component (74).
11. The method according to any one of claims 6 to 8, wherein the selecting a subset (72) of the plurality of measurement values comprises the steps of:
a subset of the predetermined number of measured values of adjacent magnetic field sensors (8) is selected which has the largest absolute value of the sum.
12. The method according to any of the preceding claims, wherein the determination of the plurality of measurement values comprises the steps of:
providing measurement data by a plurality of magnetic field sensors (8) and generating a plurality of measurement values by calibrating the measurement data;
wherein the calibration comprises compensating a drive magnetic field component which is generated by a drive element of the electric motor, in particular a current-carrying coil (60) of the electric motor, during operation.
13. The method of claim 12, wherein the calibrating further comprises:
-compensation of the offset of the plurality of magnetic field sensors (8); and/or
To compensate for production inaccuracies, in particular for measurement errors caused by an inaccurate placement of the magnetic field sensor.
14. Method according to any of the preceding claims, characterized in that the steps of determining a plurality of measurement values (70), determining specific spectral signal components (74) and determining the position of the driven moving part (4) are repeatedly performed during the movement of the moving part, in particular at least once per millisecond, still more in particular at least once per 100 μ s.
15. A method of moving a driven moving part of an electric motor (2), comprising:
-determining the position of the driven mobile part (4) according to the method of any one of the preceding claims; and
the driven moving portion is moved based on the determined position of the driven moving portion.
16. The method according to claim 15, wherein the electric motor (2) comprises a plurality of coils (60) arranged along a movement path (43) of the moving part; and
wherein the step of moving the driven moving part includes controlled current supply to the plurality of coils.
17. Method according to claim 15 or 16, wherein the slave moving part (4) is a piston of the pipetting device (100) or wherein the slave moving part is connected to a piston of the pipetting device for moving the piston and wherein the pipetting liquid (32) is aspirated or dispensed by movement of the piston.
18. Electric motor (2) with contactless position determination, comprising:
a driven moving part (4) having a plurality of permanent magnets (40), the permanent magnets (40) generating a moving part magnetic field having a plurality of periodically spaced maxima;
a stator (6) with respect to which the driven moving portion is arranged to be movable;
a plurality of magnetic field sensors (8) for measuring a magnetic field present along the movement path and arranged along the movement path (43) of the moving part; and
a position determination unit (12) receiving measurement data from the plurality of magnetic field sensors and configured to:
providing a plurality of measurement values (70) from the measurement data, the plurality of measurement values (70) being sampling points of an instantaneous magnetic field generated by the plurality of permanent magnets and dependent on the position of the moving part;
determining from the plurality of measurements (70) a specific spectral signal component (74) having a spatial frequency corresponding to a distance between adjacent similar maxima of the moving part magnetic field; and
the position of the driven moving part is determined based on the specific spectrum signal component.
19. The electric motor (2) according to claim 18, characterized in that the plurality of magnetic field sensors (8) are a plurality of hall sensors.
20. Electric motor (2) according to claim 18 or 19, characterized in that a plurality of magnetic field sensors (8) are arranged substantially uniformly along the movement path (43) of the moving part.
21. The electric motor (2) according to any of claims 18 to 20, characterized in that adjacent permanent magnets (40) have opposite polarities.
22. The electric motor (2) according to any of claims 18 to 21, characterized in that a plurality of permanent magnets (40) are arranged in series and wherein adjacent permanent magnets are oriented with the same magnetic pole opposite each other.
23. The electric motor (2) according to any of claims 18 to 22, characterized in that the driven moving part (4) has 4 to 8 permanent magnets, in particular 5 or 6 permanent magnets.
24. The electric motor (2) according to any of claims 18 to 23, characterized in that a plurality of permanent magnets (40) are bonded to each other.
25. The electric motor (2) according to any of claims 18 to 24, characterized in that the distance between adjacent similar maxima of the moving part magnetic field is between 10mm and 20mm, in particular between 12mm and 15mm, still more in particular between 13mm and 14 mm.
26. The electric motor (2) according to any one of claims 18 to 25, characterized in that the position determination unit (12) is configured to determine the position of the driven moving part (4) by the phase angle of a specific spectral signal component (74).
27. The electric motor (2) according to claim 26, characterized in that the position determination unit (12) is configured to convert the phase angle of the specific spectral signal component (74) into a shift of the driven moving part (4) relative to a known position.
28. The electric motor (2) according to any one of claims 18 to 27, characterized in that the position determination unit (12) is configured to determine the specific spectral signal component (74) by applying a Goertzel algorithm to the sampling points.
29. An electric motor according to any one of claims 18 to 28, characterized in that the position determination unit (12) is configured to select a subset (72) of the plurality of measurement values and to determine a specific spectral signal component (74) in the subset of the plurality of measurement values.
30. The electric motor (2) according to claim 29, characterized in that the subset (72) of the plurality of measurement values comprises 4 to 10 measurement values, in particular 5 to 8 measurement values, still more in particular 6 measurement values.
31. The electric motor (2) according to any one of claims 18 to 30, characterized in that the position determination unit (12) comprises a microcontroller.
32. The electric motor (2) according to any of claims 18 to 31, characterized in that the stator (86) comprises a plurality of coils (60) arranged along the movement path (43) of the moving part (4), the driven moving part being moved by controlled current supply of the plurality of coils.
33. The electric motor (2) according to claim 32, further comprising a control unit (14), the control unit (14) being coupled to the position determination unit (12) and configured to adjust the current flowing through the plurality of coils (60) based on the determined position of the driven moving part (4).
34. The electric motor (2) according to any one of claims 18 to 33, characterized in that the electric motor is a linear motor, and wherein the driven moving part (4) moves linearly on the moving path.
35. The electric motor (2) according to any of claims 18 to 33, wherein the driven moving part (4) is a rotor that is rotationally movable relative to a stator, and wherein the moving path of the moving part is substantially circular.
36. The electric motor (2) according to claim 35, further comprising a reference point sensor (10) detecting passage of a predetermined portion of the rotor.
37. Pipetting system (100) for aspirating and dispensing a pipetting liquid (32), comprising:
a piston having a liquid-facing end and a liquid-remote end;
a pipetting channel in which a piston is arranged and at the end of which a pipette tip (26) is arranged, wherein by moving the piston pipetting liquid (32) can be aspirated and dispensed through the pipette tip; and
the electric motor (2) according to any of claims 18 to 36, wherein the driven moving part (4) is part of a piston, or wherein the driven moving part is drivingly connected with a piston.
38. Pipetting system (100) according to claim 37, characterized in that at least the liquid-facing end of the piston has a seal (41) with respect to the pipetting channel, whereby a sealed volume is present in the pipetting channel between the liquid-facing end of the piston and the pipette head (26).
39. A computer program comprising program instructions which, when executed on a data processing system, perform the method according to any one of claims 1 to 17.
Technical Field
The present invention relates to the field of electric motors. In particular, the present invention relates to determining the position of a moving part of a motor. More particularly, the present invention is in the field of pipetting systems driven by electric motors.
Background
Pipetting systems are an example of technical systems in which a moving element, usually a movable piston, can be moved with high precision. In pipetting systems, by movement of the piston, the pipetting liquid is aspirated and dispensed by the pipette tip, respectively. For many applications, in particular in the field of laboratory automation, the release and absorption of liquids, i.e. the dispensing and aspiration of liquids, must be done very precisely. This results in an overall effort to perform as accurate a movement as possible with the piston. Therefore, when the piston is driven by the motor, accurate movement of the moving portion of the motor is desired. In the prior art, there are methods of determining the position of a piston in a pipetting system and controlling the motor accordingly. However, such existing systems involving position determination are not satisfactory. In many other technical fields there are also technical systems in which the components driven by the motor should be moved accurately.
It is therefore desirable to provide an improved position determination method, an improved motor and an improved pipetting system.
Disclosure of Invention
Exemplary embodiments of the present invention include a contactless determination method for a position of a driven moving part of an electric motor by a plurality of magnetic field sensors, wherein the moving part is movably arranged with respect to a stator and has a plurality of permanent magnets generating a moving part magnetic field having a plurality of periodically spaced maxima, and wherein the plurality of magnetic field sensors are arranged along a moving path of the moving part. The method comprises the following steps: determining, by a plurality of magnetic field sensors, a plurality of measured values of instantaneous magnetic fields generated by a plurality of permanent magnets and depending on the position of the moving part; determining specific spectral signal components from the plurality of measured values, the specific spectral signal components having spatial frequencies corresponding to distances between adjacent similar maxima of the moving part magnetic field; and determining the position of the driven moving part by the specific spectrum signal component.
Exemplary embodiments of the present invention allow for a direct and efficient determination of the position of the moving part of the motor, i.e. a determination of the position directly at the source of the movement. Due to the contactless determination of the position of the moving part, there is no additional load acting on the electric motor in the form of an additional drive mass. The contactless determination of position can support more power, prevent component wear, and make the overall system more robust than previous methods where the moving part of the motor or downstream driven component mechanically actuated the sensor.
The method may use permanent magnets that are always present for driving the moving part for contactless position determination of the moving part. In this respect, the following facts are utilized: the magnetic field generated by the permanent magnet not only serves as a basis for the movement of the moving part, but also exists measurably along the movement path of the moving part. The magnetic field generated by the permanent magnet forms the basis for determining the position of the moving part. However, there may also be a permanent magnet that is present in addition to the driving magnet only for determining that the position is set, wherein its magnetic field is measured and used for position determination. In this case, the additional permanent magnet is also drivingly connected to the moving part, and the magnetic field sensor is arranged along the moving path of the additional permanent magnet.
A plurality of permanent magnets are arranged in the moving part so as to form a moving part magnetic field having a plurality of periodically spaced maxima. The expression "moving part magnetic field" refers to the magnetic field that is present in the reference system of the moving part and that is static in this system due to the fixed arrangement of the permanent magnets. The maxima are local maxima, i.e. local magnetic south and north poles, respectively, compared to a straight environment. The expression "periodically spaced maxima" clearly indicates that the moving part magnetic field has alternating south and north poles, the order and spacing of which is repeated at least for part of the moving part magnetic field. The permanent magnets thus generate a moving part magnetic field with alternating south and north poles and a strong oscillating component. The moving part magnetic field generates a momentary magnetic field in the reference system of the stator, the momentary form of which depends on the position of the moving part. Since the moving part magnetic field has a plurality of periodically spaced maxima, the instantaneous magnetic field generated by the plurality of permanent magnets and applied to the plurality of magnetic field sensors has a strong signal component with a spatial frequency corresponding to the distance between adjacent similar maxima of the moving part magnetic field. This signal component is referred to herein as a specific spectral signal component, which is determined by the measured value determined by the magnetic field sensor. The position of the driven moving part can be effectively determined by using the specific spectrum signal component. The strong periodic components of the specific spectral signal components present in the magnetic field, which are generated by the permanent magnets and are determined in a targeted manner using the spatial frequency, allow the position of the moving part of the electric motor to be determined directly and efficiently.
The method is applicable to linear motors and motors with rotating rotors, as well as any other type of motor. In the linear motor, the moving portion has a linear moving path. The path of movement of the rotor may be described by the sum of all points through which a particular component of the rotor (e.g. an assembly adjacent the air gap) passes during operation. Therefore, the moving path of the moving part in the motor having the rotating rotor may be described as a circular path. The arrangement of the magnetic field sensors along the movement path of the moving part may be such that the arrangement has the same geometrical basic structure, i.e. for example a linear or circular arrangement, whereas the arrangement is offset with respect to the movement path of the moving part. However, other arrangements are possible. For example, in a linear motor, the magnetic field sensors may be arranged in a spiral path around the moving path of the moving part.
In the linear motor, the moving part may include a plurality of bar magnets installed opposite to each other on a moving path of the moving part. In this case, the length of each permanent magnet may correspond to the distance between a local north pole and a local south pole, or to half the distance between adjacent similar maxima of the moving part magnetic field.
A plurality of permanent magnets are arranged to generate a moving part magnetic field having a plurality of periodically spaced maxima. It is neither necessary that periodically spaced maxima have equal amounts of magnetic field value nor that all maxima be equally spaced. For example, the moving part magnetic field may wear towards its ends, leaving other distances between maxima than in the middle of the moving part magnetic field. It is important that the moving part magnetic field has a plurality of uniformly spaced maxima. The distance between the two maxima of the magnetic field of the moving part can also be referred to as the pole pitch or the pitch. The pole pitch is related to the spatial arrangement of the permanent magnets and possibly also to the distance between the permanent magnets. It will be appreciated that the distance between the maxima of the magnetic field of the moving part is not a precise distance in a geometrical sense. The distance between the maxima of the magnetic field of the moving part may vary slightly due to production tolerances and other inaccuracies, in particular in the positioning of the permanent magnets. The distance between the plurality of periodically spaced maxima is a nominal distance.
The plurality of measurements are measurements that are measured substantially simultaneously. The plurality of measurement values thus represents the spatial distribution of the magnetic field generated by the plurality of permanent magnets at a particular measurement time. The plurality of measurements are samples of the instantaneous magnetic field. In particular, the plurality of measured values are sampled values of a magnetic field which is currently present in the reference system of the stator and which is generated by the permanent magnet of the moving part. The spatial distribution of the magnetic field at a particular measurement time is then analyzed with respect to the spatial frequencies of the particular spectral signal components discussed above. The spectrum-specific signal component is a signal component indicating the positions of the plurality of permanent magnets because its spatial frequency corresponds to the distance between adjacent maxima of the moving part magnetic field. In this respect, the expression "spatial frequency corresponds to the distance between adjacent similar maxima of the magnetic field of the mobile part" may mean that the sampling point is analyzed precisely for this spatial frequency. However, it is possible that a particular spectral signal component may also have a spatial frequency which, in addition to the distance between adjacent maxima, also takes into account the offset of the magnetic field sensor with respect to the permanent magnet. The spatial frequency is only matched to the geometry of the magnetic field sensor arrangement relative to the permanent magnet. The expression "substantially simultaneously taken measurements" indicates that the measurements represent as far as possible a snapshot of the magnetic field. However, the expression also includes that the measured values may have a certain time offset from each other. This may be the case, for example, when the measurement values belong to a series of consecutive measurements (e.g. when using an analog magnetic field sensor, the output of which is successively applied to an analog-to-digital converter, so that the digitized measurement data represents measurements taken at slightly different times). In general, there may be practical limitations in the signal processing chain, due to which, in certain application scenarios, due to the higher complexity/parallelism, it may not be possible or desirable to achieve a complete time synchronization of the measurement values.
The stator may be provided with a plurality of electromagnets by which a moving portion of the motor is driven. The electromagnet can be a coil or a coil with windings, by means of which a time-varying magnetic field can be generated by suitable control.
According to another embodiment, determining the position of the driven mobile part is performed by the phase angle of a specific spectral signal component. It is possible to determine by phase angle how far the maximum of the magnetic field generated by the plurality of permanent magnets is from a known position (e.g. starting from the position of a particular magnetic field sensor). In this way, the position of the driven moving part can be determined in a particularly accurate and efficient manner. The determination by the phase angle is more reliable than the determination of the position of the driven moving part by the amplitude of the specific spectral signal component. The amplitude changes very rapidly with respect to the distance between the permanent magnet and the magnetic field sensor, and the position of the maxima relative to one another can also be determined accurately and reliably at a certain distance from the permanent magnet. Also, acquiring a very precise position of the permanent magnet may take less effort in manufacturing the moving part than keeping the magnetization of the permanent magnet within very narrow limits. Thus, position determination by means of phase angle may allow a better trade-off between trial/complexity and accuracy.
According to another embodiment, determining the position of the driven mobile part includes converting the phase angle of the particular spectral signal component to an offset of the driven mobile part relative to a known position. In this respect, the known position can be known from the currently measured variables in combination with production data of the entire system. For example, the known position may be known by a determination of the magnetic field sensor closest to a particular point of the moving part in combination with production data revealing where the magnetic field sensor is arranged. Production-related tolerances related to the nominal position of the magnetic field sensor can be measured and included in the position calculation of the driven moving part. The known position can also be known from the control of the electromagnets of the stator. In other words, the position of the moving part, which is considered to be a known position, can be estimated by the control of the electromagnet, and the exact position of the moving part can be determined from the amount of shift based on the phase angle of the particular spectral signal component.
According to another embodiment, the operation of determining specific spectral signal components is performed by applying a Goertzel algorithm to at least a portion of the plurality of measurements. The Goertzel algorithm extracts a single spectral signal component from a sample point or a subset of sample points of the instantaneous magnetic field. Thus, specific spectral signal components can be determined without requiring a comprehensive analysis of the spectrum of the signal formed by the sample points. Thus, the Goertzel algorithm facilitates a very efficient, fast and resource-saving decision on a particular spectral signal component. The Goertzel algorithm is also known as the Goertzel function. A description of the Goertzel algorithm itself and a description of the use of the Goertzel algorithm to determine any spectral components can be found, for example, in the following publications: the Goertzel algorithm was generalized to non-integer multiples of the fundamental frequency (authors: Petr Sysel and Pavel Rajmic), EURASIP journal, 2012, on the evolution of signal processing. The content of this document is incorporated by reference in its entirety into the present patent application.
According to another embodiment, the operation of determining the particular spectral signal component is performed by applying a Fast Fourier Transform (FFT) to at least a portion of the plurality of measurements. The fast fourier transform is an efficient implementation of the discrete fourier transform, which allows a spectral analysis of the signal defined by the sample points. By spectral analysis, specific spectral signal components can be determined. Therefore, fast fourier transforms represent an alternative to the Goertzel algorithm described above for determining a particular spectral signal component from a sample point or a subset of sample points.
According to another embodiment, the method further comprises the steps of: a subset of the plurality of measurements is selected. In this case, the specific spectral signal component is determined in a subset of the plurality of measurements. In other words, only a subset of the sampling points of the instantaneous magnetic field are used to determine a particular spectral signal component. Selecting a subset of the plurality of measurements as sampling points allows the measurements to be limited to a subset of the relatively correlated measurements, thereby allowing for high accuracy in the subsequent determination of the particular spectral signal component and subsequent determination of the position of the driven mobile portion.
According to another embodiment, a subset of the plurality of measurements is taken from magnetic field sensors arranged adjacent to each other. In this way, a set of consecutive measurement values is selected from which a particular spectral signal component can be determined in a particularly reliable manner.
According to another embodiment, the subset of the plurality of measurements comprises 4 to 10 measurements, in particular 5 to 8 measurements, still more in particular 6 measurements. The mentioned number of measurements allows a particularly good compromise between high reliability and accuracy and complexity that is easy to control when deciding on a particular spectral signal component.
According to another embodiment, selecting a subset of the plurality of measurements comprises the steps of: organizing the plurality of measurement values according to a spatial arrangement of the magnetic field sensors along a movement path of the moving part; determining a first measurement whose absolute value exceeds a predetermined threshold; selecting the first measurement value and an adjacent measurement value as the subset of the plurality of measurement values. In this way it can be ensured that those measurement values which are as relevant as possible are used for determining the particular spectral signal component, so that a high degree of reliability is achieved by selecting adjacent measurement values. This selection is also made in a particularly efficient manner, since the first measurement is only sorted out by a specific analysis of the measurements and the other measurements of the subset are selected by association with the magnetic field sensor. In the step of deciding the first measurement value whose absolute value exceeds the predetermined threshold, the direction of searching for the first measurement value may be decided appropriately for a specific application.
According to another embodiment, the position of the driven mobile part is calculated from the position of the magnetic field sensor delivering the first measurement value and the offset of the driven mobile part represented by the phase angle of the specific spectral component. In other words, the precise position of the moving part is determined from the offset of the driven moving part relative to the "that" magnetic field sensor which delivers the first measurement. The position of the magnetic field sensor delivering the first measurement is an example of a known position to which an offset has been added or subtracted.
According to an alternative embodiment, the subset of the plurality of measurement values is selected as the subset of the predetermined number of measurement values of adjacent magnetic field sensors having the largest absolute value of the sum. In this way, those measurement values are selected which describe the region of the strongest magnetic field, thereby ensuring a high reliability of the position determination.
According to another embodiment, determining the plurality of measurements comprises the steps of: providing measurement data by a plurality of magnetic field sensors; and generating a plurality of measurement values by calibrating the measurement data, wherein the calibration comprises compensating a drive magnetic field component which is generated by a drive element of the electric motor, in particular a current-carrying coil of the electric motor, during operation. Therefore, the compensation of the driving magnetic field component can also be regarded as the elimination of the signal component generated by the electromagnet of the stator instead of the permanent magnet of the moving part. In this way, the specific spectral signal components can be determined in a particularly reliable manner. The compensation of the driving magnetic field component may be performed algorithmically, for example by means of a corresponding filter or by using a look-up table, it being possible to use as input the momentary control of the driving element of the motor, i.e. the control of the electromagnet of the motor.
According to another embodiment, the calibrating further comprises: compensation for offset of the plurality of magnetic field sensors; and/or to compensate for production inaccuracies, in particular for measurement errors caused by an inaccurate placement of the magnetic field sensor. In this way, the inaccurate measurement inherent to the magnetic field sensor can be compensated, whether by an inherent offset of the sensor of the magnetic field sensor or by positioning the inaccurate magnetic field sensor relative to the nominal position. In this way, in turn, the specific spectral signal components can be determined in a particularly reliable manner.
According to another embodiment, the steps of determining a plurality of measurement values, determining a specific spectral signal component and determining the position of the driven mobile part are repeatedly performed during the movement of the mobile part. By repeatedly performing the steps in operation, the position of the driven moving part can be determined at different times, so that updated positions of the moving part are preferably obtained at regular intervals. In a particular embodiment, the steps are performed at least once every millisecond. In other words, these steps are performed at least once a second, so that the updated position of the mobile part is available at least once a second. In another embodiment, the steps are performed at least once every 100 milliseconds. As a result, even more up-to-date position data is available for the mobile part. When the steps of selecting a subset of the plurality of measurements and/or calibrating the measurement data are performed in an embodiment, these steps or one of these steps may similarly be repeated. This also applies to all other steps or modifications of the methods described herein.
Exemplary embodiments of the present invention also include a method of moving a motor driven moving part, the method including the steps of: as in any of the above embodiments, the position of the driven moving part is determined according to the method of determining the position of the driven moving part without contact; and moving the driven moving part according to the determined position of the driven moving part. In this way, a controlled movement of the driven moving part is made possible, wherein said movement of the driven moving part depends on the determined position of the driven moving part. Thus, a closed control ring is provided, thanks to which the movement of the driven moving part can be performed with very high precision.
According to a further embodiment, the motor comprises a plurality of coils arranged along the movement path of the moving part, wherein the step of moving the driven moving part comprises a controlled current supply to the plurality of coils. In this way, the coils of the motor form a plurality of electromagnets by which the moving portion can be moved with high precision.
According to another embodiment, the driven moving part is a piston of the pipetting device, wherein the pipetting liquid is aspirated or dispensed by movement of the piston. In an alternative embodiment, the slave moving part is connected to the piston of the pipetting device such that movement of the slave moving part affects the movement of the piston. This connection can be realized with relatively little complexity, for example by a piston rod between the moving part of the linear motor and the piston of the pipetting device, or by a relatively complex coupling, for example a gear arrangement between the rotatably movable rotor and the piston of the pipetting device.
Exemplary embodiments of the present invention also include a motor with contactless position determination, comprising: a driven moving part having a plurality of permanent magnets that generate a moving part magnetic field having a plurality of periodically spaced apart maxima; a stator, the driven moving part being movably disposed with respect to the stator; a plurality of magnetic field sensors for measuring a magnetic field existing along the moving path and arranged along the moving path of the moving part; and a position determination unit that receives measurement data from the plurality of magnetic field sensors. The position determination unit is configured to: providing a plurality of measurement values from the measurement data, the plurality of measurement values being sampling points of an instantaneous magnetic field generated by the plurality of permanent magnets and depending on the position of the moving part; determining from the plurality of measurement values a specific spectral signal component having a spatial frequency corresponding to a distance between adjacent similar maxima of the moving part magnetic field; and determines the position of the driven moving part based on the specific spectral signal component.
The additional features, modifications and technical effects described above with respect to the method of contactlessly determining the position of the driven moving part of the motor may be similarly applied to a motor with contactlessly position determination. The position determination unit of the electric motor may in particular be configured to carry out modified and/or additional steps of the above-described method.
The driven moving part of the motor is movable relative to the stator and relative to the plurality of magnetic field sensors. In other words, the moving part moves in a system called a static state, which is defined by the stator and the plurality of magnetic field sensors. Again, the motor may be a linear motor, wherein the moving part moves linearly with respect to the plurality of magnetic field sensors. The electric motor may also have a rotatably movable rotor as a moving part, which rotates in a system formed by a stator and a plurality of magnetic field sensors.
According to another embodiment of the invention, adjacent permanent magnets have opposite polarity. The spacing of adjacent different maxima of the moving part magnetic field, i.e. the spatial distance between the magnetic south and north poles of the moving part magnetic field generated by the permanent magnet arrangement, may correspond to the length of the permanent magnets or the spacing between adjacent permanent magnets.
According to another embodiment, a plurality of permanent magnets are arranged in series, adjacent permanent magnets being oriented with the same magnetic poles opposite each other. In particular, the permanent magnet may be a bar magnet. The permanent magnets may be arranged in series on a moving path of the moving part. The distance between adjacent similar maxima may be twice the length of the permanent magnets. With this arrangement, on the one hand, high magnetic field density and high dynamics of the motor can be well taken into account, and on the other hand, the maximum value of the magnetic field of the moving part can be clearly determined so that the position can be determined very accurately.
In the linear motor, the moving part may have a plurality of permanent magnets each including a south pole and a north pole, and arranged with the same magnetic poles adjacent to each other. In other words, adjacent permanent magnets may each be arranged such that their north or south poles are adjacent to each other. In an electric motor with a rotatably movable rotor, the permanent magnets may be arranged such that adjacent permanent magnets have alternating polarity in a direction towards the air gap. The distance between the centers of adjacent permanent magnets is then the pole pitch or pitch of the moving part magnetic field. For rotors, the pole pitch may be specified as a geometric angular dimension. However, the pole pitch may also be specified as a geometric length dimension. The spatial frequency of the particular spectral signal component may be adjusted based on the radial offset between the magnetic field sensor and the permanent magnet relative to the spacing of the maxima of the magnetic field along the moving portion of the permanent magnet. This is an example of the above-described situation according to which the spatial frequency of a particular spectral signal component takes into account the geometry of the overall system, but still corresponds to the distance between the maximum moving part magnetic fields.
According to another embodiment, the plurality of magnetic field sensors is a plurality of hall sensors. In this way, the magnetic field present at the magnetic field sensor can be measured very directly.
According to a further embodiment, the plurality of magnetic field sensors are arranged substantially uniformly along the movement path of the moving part. The substantially uniform arrangement of the magnetic field sensors allows a regular spacing between the sampling points, thereby making particularly accurate and reliable determinations of specific spectral signal components possible. The regular arrangement of the magnetic field sensors also allows particularly good filtering out of the magnetic field components generated by the electromagnets. In a linear motor, the magnetic field sensors may be arranged along a straight line, which may enable a very clear and flat structure. They may also be arranged in a different way, for example in a spiral path around the movement path of the moving part. In an electric motor with a rotor that can be moved rotationally, the magnetic field sensors can be arranged on a circular path.
According to another embodiment, the driven moving part has 4 to 8 permanent magnets, in particular 5 or 6 permanent magnets. The specified number of permanent magnets is a good compromise between effective movement of the movable part by the stator electromagnet and good position determination. In particular, a specified number of permanent magnets allows a good compromise to be made between high accuracy and reliability and complexity of good control when deciding on specific spectral signal components.
According to another embodiment, a plurality of permanent magnets are adhered to each other. In this way, the definition of the pole pitch of the magnetic field of the moving part by the dimensions of the permanent magnets is achieved in a simple manner, which can be well controlled in terms of production technology.
According to another embodiment, the distance between adjacent similar maxima of the moving part magnetic field is between 10mm and 20mm, in particular between 12mm and 15mm, still more in particular between 13mm and 14 mm. The indicated values allow a good compromise to be achieved between the size of the moving part, obtaining a sufficient magnetic field density for the movement of the moving part, and the resolution that needs good processing when deciding on a particular spectral signal component.
According to another embodiment, the position determination unit is configured to determine the position of the driven moving part by the phase angle of the specific spectral signal component. In this regard, the position determination unit may be configured to convert the phase angle of the particular spectral signal component to an offset of the driven mobile portion relative to the known position.
According to another embodiment, the location determination unit is configured to determine the specific spectral signal component by applying a Goertzel algorithm to the sampling points. The specific spectral signal components may also be determined by applying a Fast Fourier Transform (FFT) or another suitable kind of signal processing.
According to another embodiment, the location determination unit is configured to select a subset of the plurality of measurement values and determine the specific spectral signal component in the subset of the plurality of measurement values.
According to another embodiment, the subset of the plurality of measurements comprises 4 to 10 measurements, in particular 5 to 8 measurements, still more in particular 6 measurements.
According to another embodiment, the position determination unit comprises a microcontroller. Using a microcontroller, the specific spectral signal components and the position of the driven mobile part can be determined very quickly and efficiently. The microcontroller can be optimized for these process steps, so that the slave can be provided almost in real timeThe position of the moving part. However, a general-purpose microcontroller may be used to determine the position of the moving part from the measurement data. In general, any kind of data processing device may be used, for example a computer with appropriate software. An exemplary microcontroller is suitable
RX71M andRX63T。according to another embodiment, the stator has a plurality of coils arranged along the moving path of the moving part, the driven moving part being moved by controlled current supply of the plurality of coils.
According to another embodiment, the arrangement of the plurality of magnetic field sensors matches the arrangement of the plurality of coils. In the linear motor, the magnetic field sensor and the coil may be arranged at the same regular interval along the moving path of the moving part. In the motor having the rotor, the magnetic field sensors and the coils may be arranged at the same regular angular intervals as viewed from the center of the rotor. This adaptation of the arrangement of the magnetic field sensor and the arrangement of the coil allows particularly reliable and accurate generation of measured values from raw measurement data, since the magnetic field of the coil is very regular from the perspective of the magnetic field sensor.
According to another embodiment, the motor further comprises a control unit coupled to the position determination unit and configured to control the current flowing through the plurality of coils based on the determined position of the driven moving part. In this way, a closed control loop is provided in which the position of the moving part is controlled via the plurality of coils based on the position of the moving part determined from the measurement data.
According to another embodiment, the motor is a linear motor, wherein the driven moving part is linearly movable in the moving path.
According to an alternative embodiment, the driven moving part is a rotor rotatably movable relative to the stator, and the moving path of the moving part is substantially circular. As described above, the moving path of the moving part may be defined as the sum of all points through which a specific part of the rotor passes during one revolution. In particular, the movement path of the moving part may be defined as a set of points through which points facing the air gap of the permanent magnet surface pass during a revolution.
According to another embodiment, the electric motor comprises a reference point sensor which detects the passage of a predetermined portion of the rotor. In this way, the number of revolutions of the rotor can be measured. Therefore, together with the position determination of the above-described moving portion (i.e., the rotor in the present case), the total rotation of the rotor can be determined.
Any of the above-described embodiments of the contactless determination method for the position of the driven moving part of the motor is applicable to the motors in all the above-described embodiments. All features of the embodiments of the method are disclosed herein, individually or in any combination, with all features of the embodiments of the device of the electric motor, individually or in any combination.
It is generally noted that the contactless determination of the position of the moving part may involve determining an absolute position of the moving part or may involve determining a relative position of the moving part. In other words, the result of the position determination may be an absolute position or a relative position with respect to a rough position of the moving part determined in some other manner.
Exemplary embodiments of the present invention also include a pipetting system for aspirating and dispensing pipetting liquids, the pipetting system comprising: a piston having a liquid-facing end and a liquid-remote end; a pipetting channel provided with a piston and with a pipette tip at the end of the pipetting channel, wherein by moving the piston pipetting and dispensing of pipetting liquids can be carried out through the pipette tip; and the electric motor according to any of the above exemplary embodiments, wherein the driven moving part is a piston or a part of a piston, or the driven moving part is drivingly connected to a piston. The additional features, modifications and technical effects described above in relation to the motor and in relation to the method for contactless determination of the position of the driven moving part of the motor are similarly applicable to pipetting systems for aspirating and dispensing pipetting liquids.
In pipetting systems, as indicated in the exemplary embodiments described above, electric motors with contactless position determination can be used particularly advantageously. The described position determination of the motor is carried out in a particularly fast and accurate manner. Thus, the piston of the pipetting system can be controlled with high dynamics. This is particularly advantageous in pipetting systems, since they are intended, for example, for use in laboratory automation, to perform a large number of pipetting operations with the highest accuracy in the shortest time. Such a motor can be used particularly advantageously in relatively new pipetting systems which move a piston back and forth at very high speeds for pipetting operations, wherein the stroke of the piston is many times higher than the volume of liquid aspirated or dispensed and the liquid aspiration or dispensing takes place by means of pressure waves which are built up with high dynamics. Particularly in such a system having high dynamic characteristics, it is very valuable to quickly and accurately determine the position of the moving part of the motor. Such a highly dynamic pipetting system is disclosed in WO 2017/0107084 a 1. The contents of the above-mentioned application are incorporated in full into the present patent application by reference. In particular, the pipetting system of the present patent application may further be realized with all features of the claims of WO 2017/0107084 a1, alone or in any combination.
According to another embodiment, at least the liquid-facing end of the piston has a seal with respect to the pipetting channel, whereby a sealed volume is present in the pipetting channel between the liquid-facing end of the piston and the pipette head. The end of the piston remote from the liquid can also have a seal with respect to the pipetting channel. By providing two seals at both ends of the piston it can be ensured that the piston has a substantially symmetrical behavior within the pipetting channel for both directions of movement.
Exemplary embodiments of the present invention also include a computer program or computer program product comprising program instructions which, when executed on a data processing system, perform a method according to any of the embodiments described above. In this regard, the various steps of the method may be initiated by program instructions and may be performed by other components or may be performed within the data processing system itself.
Drawings
Further exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.
Fig. 1 shows an electric motor according to an exemplary embodiment of the invention, partly in a schematic longitudinal sectional view and partly in a block diagram;
fig. 2 shows a motor according to another exemplary embodiment of the invention, partly in a schematic transverse sectional view and partly in a block diagram;
fig. 3 shows a block diagram of a signal processing chain in an electric motor according to an exemplary embodiment of the present invention;
FIG. 4 shows exemplary measurements of a magnetic field sensor and shows an example of the determination of specific spectral signal components;
FIG. 5 shows a pipetting system according to an exemplary embodiment of the invention, partly in a schematic longitudinal section and partly in a block diagram;
fig. 6 shows a moving part magnetic field of an exemplary moving part, as it may be used, for example, in the pipetting system of fig. 5.
Detailed Description
Fig. 1 shows an
The
The moving
The moving
In the exemplary embodiment of fig. 1, the
A plurality of
The
The operation of the
As described above, the
Fig. 2 shows an
The moving
The
The
Furthermore, the
In addition to determining the number of revolutions of the
The position determination by means of the
It is emphasized that fig. 1 and 2 only show an exemplary arrangement of the stator, the moving part and the magnetic field sensor. Many other arrangements are possible. For example, in addition to the permanent magnets shown for driving the moving part, there may be further permanent magnets which generate a moving part magnetic field for determining the position. These additional permanent magnets may be arranged at different intervals from the permanent magnet provided for driving in order to reliably determine the specific spectral signal component. For example, in the case of an electric motor having a rotatably movable rotor, such additional permanent magnets may be arranged over the entire circumference of the rotor, with the magnetic field sensors being arranged along only a part of the path of movement of the rotor. However, it is also possible that the additional permanent magnets are arranged around only a part of the circumference of the rotor and that the magnetic field sensors are arranged along the entire movement path of the rotor.
Fig. 3 shows a block diagram of a signal processing chain in an electric motor according to an exemplary embodiment of the present invention. The illustrated signal processing chain is also used to provide a detailed description of a contactless determination method for the position of a moving part of an electric motor according to an exemplary embodiment of the present invention. The illustrated signal processing chain may be used in the motor of fig. 1 and the motor of fig. 2.
Fig. 3 shows the connection of the plurality of
The
The
First, the measurement data is corrected by the offset value of the
Second, the signal components of the magnetic field generated by the coils of the stator are filtered out. For this purpose, a known voltage is applied to the coil in a test operation, and the magnetic field generated is measured and the measurement data of the test are stored. In normal operation, the
Thirdly, inaccurate placement of the
As an output, the calibration module provides a set of measurements for the instantaneous magnetic field generated by the plurality of permanent magnets and present in the reference system of the stator. It is emphasized that the calibration may be imperfect and that the measurement of the instantaneous magnetic field generated by the plurality of permanent magnets is an estimate. This may even be the normal case. Thus, the measured values of the instantaneous magnetic fields generated by the plurality of permanent magnets can also be described as estimated values based on actual measurements.
The measured values are sent to the
The
The
The six selected
The
The analysis of the sampling points for a specific spectral signal component is based on the consideration that a permanent magnet with a defined pole pitch will generate a magnetic field with a strong oscillating component at a spatial frequency twice the pole pitch. In other words, the described analysis is based on the consideration that a plurality of permanent magnets with a defined pole pitch also generate a magnetic field to a large extent, which varies with this defined pole pitch. The location of the magnetic field is determined by spectral analysis relative to specific spectral signal components.
The specific spectral signal component is provided with
The
Which part or which part of the moving part is established at the determined position of the moving part is due to the specific design of the motor and the specific implementation of the above-mentioned signal processing. In the examples of fig. 3 and 4, the position of the moving portion determined by the above-described signal processing is the position of the second pole along the moving path of the moving portion. The background to identifying the location of the second pole is to take into account that the second pole is easier to identify than the first pole, since the magnetic field generated by the first pole is further extended by the absence of the other poles and is therefore weaker. It can be seen from the measurements of fig. 4 that there is already a peak of smaller intensity in the other direction before the measurement of the magnetic field sensor at the position 3.7 cm. The predetermined threshold is selected such that the absolute value of the magnetic field of the second pole exceeds the predetermined threshold. Based on the known geometry of the mobile portion, the location of any portion of the mobile portion may then be determined. It is emphasized that there are other possibilities to determine the position of a specific part of the moving part than the position of the second pole as described herein. For a given system, one skilled in the art can select and decide on a case-by-case basis a component whose position is determined accurately and reliably.
Referring to fig. 3, the
Therefore, in the exemplary embodiment of fig. 4, the
FIG. 5 shows
The
In the present example, the moving
The end caps 41, 42 are preferably formed of a low friction material comprising graphite, as is known, for example, from pistons available from Airpot corporation of Norwalk, Connecticut, (US). In order to make maximum use of the low friction provided by this material, the
As described above with reference to fig. 1 to 4, the
At the filling side end of the pipetting channel, a
Between the moving
Based on the state shown in fig. 5, two dispensing processes of the
For both dispensing processes described, the moving part can be moved in a controlled manner as described above with reference to fig. 1 to 4. Particularly in the second embodiment, since the movement of the moving
Fig. 6 shows a plurality of
Fig. 6 shows a portion surrounded by a broken line from the moving part
It is emphasized that fig. 6 and the preceding figures are not drawn to scale. Which are intended to illustrate the functional principles of exemplary embodiments of the present invention. It can be seen that, for example, the strength of the magnetic field of the moving part and the distance between the permanent magnet and the magnetic field sensor can be matched to one another in order to achieve a particularly efficient and reliable position determination.
The pipetting system of fig. 5 may comprise any of the components and modifications shown in WO 2017/017084 a 1. The contents of said patent application are incorporated in their entirety by reference into the present patent application.
The described position determination method and the described motor are also applicable to pipetting systems in which the piston directly abuts the pipetting liquid.
Furthermore, the described position determination method and the described motor are applicable to any other technical system in which a component driven by the motor moves with high accuracy.
While the invention has been described with reference to exemplary embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. The invention should not be limited by the specific embodiments described. But that the disclosure will include all embodiments falling within the scope of the appended claims.
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