Method for determining balancing action for balancing electric machine

Abstract

A method of determining a balancing action for an electric machine (100) comprising a stator (101), a rotor (102), a shaft (103) fixed to the rotor, and at least one bearing (104, 105) supporting the shaft is disclosed. The method comprises:-collecting measurement data from the displacement sensor (110) during rotation of the motor (100), said data relating to a displacement of a shaft of the motor on a detection plane (P) perpendicular to a longitudinal axis (Z) of the shaft; estimating an unbalance force by predicting at least one displacement of the shaft on the at least one detection plane using a dynamic model of the motor, the at least one displacement being a function of the at least one potential unbalance force, and comparing the measured displacement with the predicted at least one displacement; a balancing action is determined based on the estimated unbalanced force.

Description

Technical Field

[0001] The techniques disclosed herein generally relate to the balancing of electric motors, and more particularly to apparatus and methods for determining balancing actions to balance the motor. Additionally, a motor assembly is also disclosed. Background Technology

[0002] Industrial motors and shaft systems are critical components that typically require continuous, uninterrupted operation. To maximize the lifespan of motors / electric motors, it is essential to detect and correct suboptimal operating conditions before they lead to mechanical failure. These suboptimal operating conditions include machine vibration, which can damage motors, shorten their lifespan, and ultimately cause, for example, bearing failure. Mechanical imbalance, present in almost all rotating machinery, has been found to be one of the most common causes of machine vibration.

[0003] Balancing electric motors is a time-consuming and labor-intensive task. For example, field balancing of motors often requires uncertain estimates and multiple tests with trial weights. It may be necessary to transport the motor to the workshop for balancing, resulting in extended downtime. Therefore, in practice, considerable imbalance may need to be tolerated before the motor is balanced, which can lead to excessive mechanical wear and shorten the motor's lifespan.

[0004] In view of the above, there is a need for improved methods and devices for on-site balancing of motors. Summary of the Invention

[0005] The primary objective of the embodiments described herein is to provide improved methods and apparatus for balancing motors in at least some aspects. Specifically, the objective is to provide apparatus and methods for determining balancing actions to balance the motor. In particular, the objective is to provide apparatus and suitable methods for balancing motors in the field.

[0006] According to the first aspect, at least this primary objective is achieved by a computer-implemented method for determining balancing actions to balance a motor in its installed state, the motor including a stator, a rotor, a shaft fixed to the rotor, and at least one bearing supporting the shaft, such as at least one rolling element bearing. The method is executed by a control unit communicatively connected to a displacement sensor. The method includes:

[0007] - With the motor installed, during shaft rotation, measurement data is collected from a displacement sensor, which is related to the measured displacement of the shaft on at least one detection plane perpendicular to the longitudinal axis of the shaft;

[0008] -Predict at least one displacement of the shaft on at least one detection plane by using a dynamic model of the motor, the at least one displacement being a function of at least one potential unbalanced force, and estimate the unbalanced force based on collected measurement data by comparing the measured displacement with the predicted at least one displacement.

[0009] - Determine the balancing action based on the estimated unbalanced force.

[0010] By combining displacement sensors with a dynamic model of the motor, unbalanced forces acting on motor components, such as radial loads on motor bearings, can be estimated relatively quickly and efficiently. This method can be performed on-site during motor installation, reducing the need to transport the motor to a workshop. Therefore, the overall uptime and service life of the motor can be increased. This method can also be used to assist maintenance engineers in selecting appropriate balancing actions, such as choosing the counterweights and their installation location on the motor.

[0011] Optionally, predicting at least one displacement of the shaft includes predicting a set of shaft center trajectories (orbits), wherein each predicted shaft center trajectory describes the displacement of the shaft in at least one detection plane relative to a particular rotor and / or shaft imbalance.

[0012] This allows for the rapid and accurate estimation of unbalanced forces.

[0013] Alternatively, the dynamic model of the motor models the rotor as a rigid body with flexible supports. This has proven sufficient for speeds below the motor's critical speed. For example, the dynamic model can model the motor as a modified Jeffcott rotor, where the shaft and bearings are modeled as a series spring connection. For more flexible rotors operating above the first critical speed, the dynamic model of the motor can model the rotor based on finite element method (FEM) calculations.

[0014] Optionally, the method further includes:

[0015] - Determine the motor speed.

[0016] The estimation of unbalanced forces also includes inputting rotational speed into a dynamic model, wherein the dynamic model predicts at least one displacement as a function of rotational speed.

[0017] Optionally, the balancing action includes adjusting the mass distribution of the rotor and / or the shaft. This can be achieved, for example, by adding counterweights to the rotor and / or shaft or removing material to compensate for any detected imbalance.

[0018] Optionally, determining the balancing action includes using a dynamic model to select the balancing action that minimizes the magnitude of the shaft displacement. This allows for the efficient determination of the balancing action.

[0019] Optionally, determining the balancing action includes identifying at least one correction plane along the shaft, in which at least one correction mass will be added or removed. A dynamic model of the motor can provide information about the shaft's orbit (i.e., motion trajectory) in different planes including the correction planes(s). Therefore, a clear relationship exists between the force acting on one plane and the shaft displacement occurring in another plane. Several correction planes can be selected. In this way, the mass distribution of the shaft can be quickly adjusted to achieve a more balanced motor.

[0020] Optionally, determining at least one correction plane includes determining the number of correction planes along the axis. Therefore, it can be determined how many correction planes are necessary to achieve proper balance.

[0021] Optionally, determining the balancing action also includes determining at least one angular position within at least one correction plane where at least one correction mass will be added or removed. This allows for better balancing.

[0022] Optionally, the measurement data collected by the displacement sensor will be correlated with the displacement of the shaft along at least two directions within at least one detection plane, such as along two normal directions within at least one detection plane. This helps to accurately estimate the unbalanced force.

[0023] Optionally, the dynamic model also uses known bearing stiffness and known shaft stiffness to predict at least one displacement of the shaft. Therefore, at least one displacement can be accurately predicted using a relatively simple dynamic model of the motor, where the bearing and shaft can be modeled as springs based on known bearing stiffness and shaft stiffness.

[0024] Optionally, measurement data is collected while the shaft rotates at subcritical speeds, such as 4000 rpm or lower, or 3000 rpm or lower, or 2000 rpm or lower, or 1500 rpm or lower, depending on the motor design. The motor's critical speed, or first resonant frequency, is a design attribute, and the operating speed is related to it. For subcritical speeds, simpler dynamic models can often be used, thus reducing the complexity of estimating unbalanced forces. The rotational speed can be measured or estimated.

[0025] According to a second aspect, an electronic control unit is provided, which includes a processing circuit system configured to perform the processing described in the first aspect.

[0026] According to a third aspect, a motor assembly is provided. The motor assembly includes a stator, a rotor, a shaft fixed to the rotor, at least one bearing (such as a rolling element bearing) supporting the shaft, a displacement sensor for measuring the displacement of the shaft in at least one detection plane perpendicular to the longitudinal axis of the shaft, and a control unit according to the second aspect.

[0027] The motor can be an electric motor, a generator, or a combination of electric motor and generator.

[0028] The shaft may include conductive components, and displacement sensors may be arranged around the conductive components. The entire shaft may be made of the same material.

[0029] Optionally, the displacement sensor is a capacitive displacement sensor, comprising multiple capacitive sensing elements arranged circumferentially around the shaft (i.e., around the conductive parts of the shaft). This sensor can have a printed circuit board including mounting holes through which the motor shaft passes. This enables high-resolution measurement of shaft position and movement at low cost. Furthermore, capacitive displacement sensors are insensitive to ultrasonic noise, humidity, etc. Surface roughness can be averaged out by using a larger sensing area.

[0030] According to a fourth aspect, a computer program including computer code is provided, which, when run on the processing circuitry of a control unit, causes the control unit to perform the method according to the first aspect.

[0031] According to a fifth aspect, a computer program product is provided, comprising the computer program according to the fourth aspect and a computer-readable storage medium storing the computer program.

[0032] Other objects, features, and advantages of the embodiments appended herein will become apparent from the following detailed disclosure, the appended dependent claims, and the accompanying drawings.

[0033] Generally, unless otherwise expressly defined herein, all terms used in the claims shall be interpreted according to their ordinary meaning in the art. Unless otherwise expressly stated, all references to “a / an / the element, device, component, apparatus, module, action, etc.” shall be publicly interpreted as referring to at least one instance of that element, device, component, apparatus, module, action, etc. Unless otherwise expressly stated, the actions of any method disclosed herein need not be performed in the strictly disclosed order. Attached Figure Description

[0034] The inventive concept will now be described by way of example, with reference to the accompanying drawings, wherein:

[0035] Figure 1 This is a schematic diagram of a motor according to an embodiment;

[0036] Figure 2 It is a flowchart illustrating the method according to an embodiment;

[0037] Figure 3 This is a schematic diagram of the motor model used according to the embodiment;

[0038] Figure 4 It is a graph that compares experimental data with the axis trajectory modeled using a dynamic model;

[0039] Figure 5 This is a schematic diagram showing the functional units of the control unit according to an embodiment;

[0040] Figure 6 This is a schematic diagram showing the functional modules of the control unit according to an embodiment;

[0041] Figure 7 An example of a computer program product including a computer-readable device according to an embodiment is shown.

[0042] The accompanying diagram is schematic and not drawn to scale. Detailed Implementation

[0043] The inventive concept will now be described more fully with reference to the accompanying drawings, which illustrate certain embodiments of the inventive concept. However, the inventive concept can be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided by way of example only to make this disclosure more comprehensive and to fully convey the scope of the inventive concept to those skilled in the art. Throughout the specification, the same numerals refer to the same elements.

[0044] In summary, this invention proposes determining a balancing action to balance a motor in its installed state by collecting measurement data related to shaft displacement during rotation, estimating unbalanced forces based on the measurement data, and determining balancing actions based on the estimated unbalanced forces. When estimating the unbalanced forces, this invention proposes using a dynamic model of the motor, which is used to predict shaft displacements such as the shaft center trajectory based on potential unbalanced forces. Therefore, the actual movement of the shaft during motor rotation is compared with the predicted shaft movement based on the unbalanced forces. Thus, a balancing action can be selected to mitigate the estimated unbalanced forces.

[0045] Figure 1 The diagram schematically illustrates an electrical assembly 150 including a rotating motor 100 (such as an electric motor and / or generator). Figure 1 The longitudinal section view of the motor 100 is shown in the figure.

[0046] The motor 100 includes a stator 101 and a rotor 102. The stator 101 and rotor 102 are configured to interact electromagnetically with each other. A shaft 103 extending along a longitudinal axis Z is fixed to the rotor 102. The shaft 103 and rotor 102 are configured to rotate about the longitudinal axis Z relative to the stator 101. Bearings 104 and 105 (such as rolling element bearings) are arranged to support the shaft on a fixed component (not shown), such as the housing of the motor 100, and to enable the shaft 103 to rotate relative to the fixed component. Bearing 105 includes an inner bearing race 105a attached to the shaft 103 and an outer bearing race 105b attached to the fixed component. Bearing 104 is similar to or the same as bearing 105.

[0047] The motor assembly 150 includes at least one shaft displacement sensor 110, which is arranged to measure the displacement of the shaft 103 in a detection plane P perpendicular to the longitudinal axis Z. The shaft displacement sensor 110 is arranged around the shaft 103. The shaft displacement sensor 110 may be mounted, for example, near a bearing 105. The shaft displacement sensor 110 may have a through-hole, and the shaft 103 may extend through the through-hole. The shaft displacement sensor 110 may be a capacitive sensor. The shaft displacement sensor 110 may be, for example, of the type disclosed in EP2918964A1.

[0048] The shaft displacement sensor 110 can be configured to detect shaft displacement along the X-axis and Y-axis, wherein the X-axis and Y-axis are axes extending in the detection plane P and perpendicular to each other. The shaft displacement signal may include X-axis displacement measurements and Y-axis displacement measurements of shaft 103.

[0049] The motor assembly 150 also includes an electronic control unit 1 that is communicatively connected to the shaft displacement sensor 110. The control unit 1 can be configured to receive shaft displacement signals from the shaft displacement sensor 110 via wireless communication, wired communication, or a combination of both.

[0050] Figure 2 The illustration shows a dynamic model of motor 100, which can be used to predict the displacement (such as the shaft center trajectory) of shaft 103 on the detection plane P at speeds ω below the critical speed of motor 100. In the illustrated example, the dynamic model is a modified Jeffcott model, where the rotor is modeled as a flexible supported mass, and shaft 103 and bearings 104 and 105, located at axial distances L1 and L2 from the rotor, are modeled as a series spring connection. When the center of mass m of the mass deviates from the radial distance e from the rotation axis, an amplitude of F will be generated. R =meω 2The sinusoidal resultant force, and reaction forces F1 and F2, act on bearings 104 and 105, respectively. The bearing reaction forces can be calculated by multiplying the bearing stiffness by the axial displacement (not the displacement of the rotating mass) in bearings 104 and 105. Therefore, the axial deflection D along the X-axis in plane P is measured. x It can be described as

[0051]

[0052] Where F 2,x This is the unbalanced force acting on bearing 105 in the x-direction, where k1 is the bearing stiffness and k2 is the shaft stiffness. The deflection in the y-direction can be calculated using the same formula.

[0053] Figure 2 The simple model illustrated in the figure has been shown to be sufficient to predict the shaft center trajectory of a rigid rotor operating at speeds below the first critical speed. However, for more flexible rotors and / or shafts, if the operating speed is above the first critical speed, more advanced dynamic models, such as those based on finite element calculations, can be used.

[0054] Now refer to Figure 3 This describes a method 200 for determining a balancing action to balance a motor 100 in its installed state. The method is executed in a control unit 1.

[0055] In the first action 210, with the motor 100 in its mounted state, measurement data is collected from the displacement sensor 110 during the rotation of the shaft 103. The measurement data relates to the measured displacement of the shaft 103 on the detection plane P, such as the measured displacement along the X and Y axes. Preferably, the measurement data is collected when the rotor 102 and the shaft 103 are rotating at subcritical speeds (such as 4000 rpm or lower, or 3000 rpm or lower, or 2000 rpm or lower, or 1500 rpm or lower, depending on the motor configuration) to enable the use of the simplified dynamic model described above.

[0056] In the second action 220, the unbalanced force is estimated based on the collected measurement data. This is performed by the following actions: action 221—using a dynamic model of motor 100 to predict at least one displacement of shaft 103 on at least one detection plane P based on the potential unbalanced force; and action 222—comparing the measured displacement with the predicted at least one displacement. The dynamic model can predict the shaft center trajectory of shaft 103 on the detection plane P based on at least one potential unbalanced force. This shaft center trajectory can be described as shaft displacement in at least one direction (such as radially, for example, in the x and y directions). For rotational speeds below the critical speed of motor 100, the dynamic model used to estimate the unbalanced force can be the relatively simple dynamic model described above. Therefore, for a given rotational speed below the critical speed, a matrix can be defined that associates the potential unbalanced force with the shaft displacement(s) on the detection plane.

[0057] In action 221, predicting at least one displacement of shaft 103 may include predicting a set of shaft center trajectories, wherein each predicted shaft center trajectory describes the displacement of shaft 103 on at least one detection plane P in response to a particular rotor and / or shaft imbalance.

[0058] In the third action 230, a balancing action is determined based on the estimated unbalanced force. For example, a balancing action that counteracts the unbalanced force can be selected, thus minimizing the resulting unbalanced force. A dynamic model can be used to select a balancing action that minimizes the shaft displacement amplitude, thereby minimizing the unbalanced force. Balancing actions typically include adjusting the mass distribution of rotor 102 and / or shaft 103, such as by determining at least one correction plane along shaft 103 (in which at least one correction mass will be added or removed). The number of correction planes can be determined. The number of correction planes may vary depending on the type of rotor. For example, a single correction plane may be sufficient for a rigid rotor with flexible support (e.g., a rotor in a fan), although in most applications, two correction planes may be necessary for a relatively rigid rotor. For a relatively flexible rotor, three or more correction planes may be necessary. The minimum number of correction planes is determined by the flexibility of the rotor, but a larger number of correction planes can be selected to achieve a more precise and / or convenient balanced mass distribution.

[0059] Furthermore, at least one angular location within at least one correction plane where at least one correction mass will be added or removed can be determined. This at least one angular location can be determined using calculations from a dynamic model.

[0060] The method may further include an action 215 to determine the rotational speed ω of the motor 100. An action 220 to estimate the unbalanced force may further include an action 223 to input the determined rotational speed ω into the dynamic model. Thus, the dynamic model can predict multiple displacements (such as shaft center trajectory) of the shaft 103 based on the rotational speed ω.

[0061] Using the dynamic model described above, the experimentally generated axis center trajectory is compared with the modeled axis center trajectory. The comparison results are... Figure 4 The experimental data are shown in the figure. The experimental data were generated using an electric motor 100, whose unbalanced force was induced by introducing one or more unbalanced counterweights at a radial distance of 65 mm from the longitudinal axis of the electric motor 100. This method was tested for a range of speeds from 500 rpm to 4500 rpm. Unbalanced counterweights were introduced at both the driving and non-driving ends of the rotor 102. With a bearing stiffness of 90 N / μm and a shaft stiffness of approximately 81 N / μm, good consistency was achieved between the experimental shaft center trajectory amplitude and the model shaft center trajectory amplitude across the entire speed range, as shown in the figure. Figure 4 The figure shows the following: Curve A is the model amplitude at the driven end, Curve B is the model amplitude at the non-driven end, Curve C is the experimentally determined amplitude at the non-driven end, and Curve D is the dynamic stiffness characteristic of the shaft.

[0062] Figure 5 The components of the control unit 1 according to an embodiment are schematically illustrated in the form of several functional units. The processing circuitry system 510 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., which are capable of executing computer program products 720 (such as...). Figure 7 The software instructions are stored (e.g., in the form of storage medium 530) in the system shown. The processing circuitry system 510 may also be provided as at least one application-specific integrated circuit (ASIC) or field-programmable gate array (FPGA).

[0063] Specifically, the processing circuitry 510 is configured to cause the control unit 1 to perform the set of operations or actions disclosed above. For example, the storage medium 530 may store the set of operations, and the processing circuitry 510 may be configured to retrieve the set of operations from the storage medium 530 so that the control unit 1 can perform the set of operations. The set of operations may be provided as a set of executable instructions. Therefore, the processing circuitry 510 is arranged to perform the methods disclosed herein.

[0064] The storage medium 530 may also include a persistent storage device, such as any one or a combination of magnetic storage, optical storage, solid-state storage, or remotely mounted storage.

[0065] The control unit 1 may also include a communication interface 520 for communicating with other entities, functions, nodes, and devices via a suitable interface. Therefore, the communication interface 520 may include one or more transmitters and receivers comprising analog and digital components.

[0066] For example, the processing circuit system 510 controls the routine operation of the control unit 1 by sending data and control signals to the communication interface 520 and the storage medium 530, retrieving data and reports from the communication interface 520, and retrieving data and instructions from the storage medium 530. To avoid confusion with the concepts presented herein, other components of the control unit 1 and their related functionalities are omitted.

[0067] Figure 6 The components of the control unit 1 according to the embodiment are schematically illustrated in the form of multiple functional modules. Figure 6 The control unit 1 includes several functional modules: a collection module 610 configured to collect measurement data from a displacement sensor 110 during rotation of the shaft 103, the measurement data relating to a measured displacement of the shaft 103 on at least one detection plane P; an estimation module 620 configured to predict at least one displacement of the shaft 103 on at least one detection plane P using a dynamic model of the motor based on at least one potential unbalanced force, and to estimate the unbalanced force based on the collected measurement data by comparing the measured displacement with the predicted at least one displacement; and a determination module 630 configured to determine a balancing action based on the estimated unbalanced force. The control unit 1 may also include several optional modules (not shown) configured to perform the functions described above. Figure 3 The operations described herein. Generally, each functional module 610-630 can be implemented in hardware or software. Preferably, one or more or all of the functional modules 610-630 can be implemented by the processing circuitry system 510, possibly in cooperation with the communication interface 520 and the storage medium 530. Thus, the processing circuitry system 510 can be arranged to retrieve instructions provided by the functional modules 610-630 from the storage medium 530 and execute those instructions to perform any action of the control unit 1 disclosed herein.

[0068] Figure 7 An example of a computer program product 720 including a computer-readable device 740 is shown. A computer program 730 may be stored on the computer-readable device 740, which may cause the processing circuitry system 510 and its operatively coupled entities and devices (such as a communication interface 520 and a storage medium 530) to perform the methods according to the embodiments described herein. Therefore, the computer program 730 and / or the computer program product 720 may provide means for performing any action of the control unit 1 as disclosed herein.

[0069] exist Figure 7 In the example, computer program product 720 is illustrated as an optical disc, such as a CD (Compact Disc), DVD (Digital Versatile Optical Disc), or Blu-ray disc. Computer program product 720 can also be embodied as memory, such as random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), or electrically erasable programmable read-only memory (EEPROM), and more particularly, as a non-volatile storage medium of a device in external memory, such as USB (Universal Serial Bus) memory or flash memory (such as compact flash memory). Therefore, although computer program 730 is schematically shown herein as a track on the depicted optical disc, computer program 730 can be stored in any manner suitable for computer program product 720.

[0070] The inventive concept has been described above primarily with reference to several embodiments. However, those skilled in the art will readily understand that other embodiments besides those described above are also possible within the scope of the inventive concept, as defined by the appended claims.

Claims

1. A computer-implemented method (200) for determining balancing actions to balance an electric machine (100) in an installed state, the electric machine comprising a stator (101), a rotor (102), a shaft (103) fixed to the rotor, and at least one bearing (104, 105) supporting the shaft, such as at least one rolling element bearing, the method (200) being performed by a control unit (1) in communication connection with a displacement sensor (110), the method comprising: - collecting (210) measurement data from the displacement sensor (110) during rotation of the shaft (103) in the installed state of the electric machine (100), the measurement data relating to a measured displacement of the shaft in at least one detection plane perpendicular to a longitudinal axis (Z) of the shaft; - estimating (220) unbalance forces based on the collected measurement data by predicting (221) at least one displacement of the shaft in the at least one detection plane using a dynamic model of the electric machine, the at least one displacement being a function of at least one potential unbalance force, and by comparing (222) the measured displacement with the predicted at least one displacement; - determining (230) the balancing actions based on the estimated unbalance forces.

2. The method according to claim 1, wherein the predicting (221) at least one displacement of the shaft comprises predicting a set of shaft center trajectories, wherein each predicted shaft center trajectory describes a displacement of the shaft in the at least one detection plane for a specific rotor and / or shaft unbalance.

3. The method according to any one of the preceding claims, wherein the dynamic model of the electric machine models the rotor as a rigid body with flexible support.

4. The method according to any one of the preceding claims, further comprising: - determining (215) a rotational speed (ω) of the electric machine (100), wherein the estimating (220) the unbalance forces further comprises inputting (223) the rotational speed (ω) to the dynamic model, and wherein the dynamic model predicts the at least one displacement as a function of the rotational speed (ω).

5. The method according to any one of the preceding claims, wherein the balancing actions comprise adjusting a mass distribution of the rotor (102) and / or a mass distribution of the shaft (103).

6. The method according to any one of the preceding claims, wherein the determining (230) the balancing actions comprises using the dynamic model to select balancing actions that will minimize an amplitude of the shaft displacement.

7. The method according to any one of the preceding claims, wherein the determining (230) the balancing actions comprises determining at least one correction plane along the shaft (103) in which at least one correction mass body is to be added or removed, preferably wherein the determining the at least one correction plane comprises determining a number of correction planes along the shaft (103).

8. The method according to any one of the preceding claims, wherein the measurement data collected by the displacement sensor (110) relates to displacements of the shaft (103) along at least two directions within the at least one detection plane (P), such as two normal directions within the at least one detection plane (P).

9. The method according to any one of the preceding claims, wherein the dynamic model further uses a known bearing stiffness and a known shaft stiffness to predict the at least one displacement of the shaft (103).

10. The method according to any one of the preceding claims, wherein the collecting (210) of the measurement data is performed during rotation of the shaft (103) at a subcritical speed, such as at a rotational speed of 4000 rpm or lower, or 3000 rpm or lower, or 2000 rpm or lower, or 1500 rpm or lower.

11. An electronic control unit (1) comprising processing circuitry (310) configured to perform the method according to any one of claims 1 to 10.

12. An electric machine assembly (150) comprising a stator (101), a rotor (102), a shaft (103) fixed to the rotor, at least one bearing (104, 105) supporting the shaft, such as a rolling element bearing, a displacement sensor (110) configured to measure displacements of the shaft on at least one detection plane (P) perpendicular to a longitudinal axis (Z) of the shaft, and a control unit (1) according to claim 11.

13. The electric machine assembly according to claim 12, wherein the displacement sensor (110) is a capacitive displacement sensor comprising a plurality of capacitive sensor elements arranged circumferentially around the shaft (103).

14. A computer program (730) comprising computer code which, when run on processing circuitry (510) of a control unit (1), causes the control unit (1) to perform the method according to any one of claims 1 to 10.

15. A computer program product (720) comprising a computer program according to claim 14, and a computer readable storage medium (740) on which the computer program (730) is stored.

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