Measuring device and method for geometric and magnetic field measurement of workpiece having rotational symmetry and having plurality of permanent magnets

Abstract

A measuring device for performing geometric and magnetic field measurements of a workpiece (2) such as a rotor of a permanent magnet motor, the measuring device comprising: a fixed first frame (3); a rotating base (4) which is mounted on the first frame and rotates around a rotating shaft (4a); the clamping system (6) is used for fixing a workpiece on the rotating base and enabling the workpiece to rotate; a second frame (7) movably mounted on the first frame so as to move in a direction parallel to the rotation axis; the optical detection system (13) is fixed on the second frame and is used for carrying out optical scanning on the workpiece; a slider (14) movably mounted on the second frame so as to move in a direction (14a) perpendicular to the rotation axis under operation of the actuator (15); a magnetic field sensor (16) is fixed on the sliding block so as to be positioned to face the side face (17) of the workpiece for magnetic field measurement; and a processing and control unit (21) configured to make geometric measurements based on the optical scans and to control the actuator to position the magnetic field sensor at an appropriate measurement distance (D0; d1; d2). The invention also relates to an associated method for geometric and magnetic field measurement of a workpiece.

Description

Technical Field

[0001] The invention relates to a device and a method for measuring the geometry and magnetic field of a workpiece with rotational symmetry, typically cylindrical symmetry, having a plurality of permanent magnets around its axis, such as a rotor of an electric motor.

[0002] In particular, the invention can be used advantageously, but not exclusively, for measuring rotors of permanent magnet motors, as will be described in detail below without thereby losing its generality. Background Art

[0003] With the growing use of permanent magnet motors (PMMs), such as in the automotive sector, there is a growing need for rapid quality testing of various motor components, particularly the motor rotor. A PMM rotor consists of multiple permanent magnets arranged in a circular pattern around the rotor shaft. The quality of the rotor is typically defined by its mechanical quality (e.g., adherence to tight tolerances for various dimensional features) and the quality of the PMs (i.e., the precise magnetic properties of each PM and their distribution around the rotor shaft).

[0004] Devices capable of geometrically measuring mechanical parts with cylindrical symmetry, or more generally mechanical parts capable of rotating about their own axes (e.g., crankshafts of internal combustion engines), are known. The devices include an apparatus capable of clamping the mechanical part and rotating it about its axis, and a sensing head or optical apparatus for acquiring its dimensional parameters as the mechanical part rotates. Such devices are suitable for measuring the mechanical properties of electric motor rotors. In addition, there are other devices suitable for measuring the overall magnetic properties of permanent magnets. This means that each motor needs to be measured twice, using two different devices to measure the geometric properties and magnetic field properties of the rotor, respectively. Therefore, quality control of the rotor is relatively slow and difficult. Summary of the Invention

[0005] The object of the present invention is to provide a device and a method for geometric and magnetic field measurements of an electric motor rotor which do not have the aforementioned disadvantages and which can be implemented in a simple and cost-effective manner.

[0006] According to the present invention, there is provided an apparatus and a method for geometrical and magnetic field measurements of a workpiece having rotational symmetry about its axis and having a plurality of permanent magnets arranged around its axis, as defined in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention will be described with reference to the accompanying drawings, which show non-limiting embodiments of the invention, in which:

[0008] - Figures 1 to 4 A device according to the invention for geometrical and magnetic field measurements of a workpiece in a corresponding number of operating phases is shown; and

[0009] - Figure 5 Is used based on Figures 1 to 4 The graph obtained by measuring the magnetic field of the workpiece using the device shown.

[0010] Best Mode for Carrying Out the Invention

[0011] exist Figures 1 to 4 1 generally denotes the entirety of a device according to the invention for geometric and magnetic field measurements on a workpiece 2, such as a rotor of a permanent magnet motor. The rotor 2 is also shown arranged within the device 1 during the measurement process.

[0012] The device 1 comprises a frame, or first frame, or first fixed frame 3, which can be placed on the ground, for example, a rotating base 4 mounted on the frame 3 so as to be rotated about a rotation axis 4a, for example substantially vertical, by the action of an actuator, or first actuator 5, a clamping system 6 for holding the rotor 2 on the rotating base 4 and coaxially with the latter so as to rotate the rotor 2, and another frame, or second frame 7, which is movably mounted on the first frame 3 so as to be movable parallel to the rotation axis 4a, driven by another actuator, or second actuator 8. In particular, the first frame 3 comprises a pair of guide rails 9 parallel to the rotation axis 4a, along which the second frame 7 is slidably mounted.

[0013] The clamping system 6 is preferably a live center / dead center system of known type. Specifically, the clamping system 6 includes a live center 10 coaxially fixed to the rotating base 4, a movable head 11 mounted on the first frame 3 to move parallel to the rotation axis 4a, and a dead center 12 fixed to the movable head 11 to be coaxial with the live center 10.

[0014] The device 1 includes an optical detection system 13 ( Figure 2-4 ), the system is fixed to a second frame 7 so as to focus on the rotation axis 4a and thereby acquire an image of the rotor 2, in particular by optically scanning the rotor 2 by movement of the frame 7 (typically when the rotating base 4 rotates).

[0015] Preferably, the optical detection system 13 comprises a first component 22, in particular a transmitter, for example an infrared transmitter, which is fixed to the frame 7, and a second component 23, in particular a receiver or sensor, which is fixed to the frame 7 on the opposite side of the rotation axis 4a so as to be opposite to the component 22. For example, the component 23 comprises a linear array of photodiodes (CCD).

[0016] According to a preferred embodiment, the optical detection system is a well-known projection optical system.

[0017] The device 1 comprises a slide 14, which is movably mounted on the second frame 7 and is driven by a further actuator (or a third actuator) 15 to move in a direction 14a substantially perpendicular to the axis of rotation 4a, and a magnetic field sensor 16 fixed to the slide 14 and, when in use, located in front of a side 17 of the rotor 2 to measure the magnetic field. In particular, a further frame 18 is fixed to the second frame 7, and the slide 14 slides along a guide rail (not shown) fixed to said further frame 18.

[0018] Preferably, the magnetic field sensor 16 is a Hall sensor.

[0019] Preferably, the second frame 7 has a C-shaped structure and is configured to be arranged around the rotor 2 when in use to enclose it, such as Figures 1 to 4 As shown, one of the two components of optical inspection system 13, for example, component 23, is mounted on first arm 19 of the C-shaped structure, while the other component of optical inspection system 13, for example, component 22, is mounted on the other arm 20 of the C-shaped structure, in a position radially symmetrical to the position of component 22 relative to rotation axis 4a. Therefore, the two components 22 and 23 are at approximately the same height along a direction parallel to rotation axis 4a.

[0020] The magnetic field sensor 16 is mounted on one of the two arms 19 and 20 of the C-shaped structure of the frame 7 at a height, in a direction parallel to the rotation axis 4 a, which is different from the arrangement height of the optical detection system 13. In this way, the magnetic field sensor 16 does not interfere with the optical scanning performed by the optical detection system 13.

[0021] For example, in the embodiment shown in the figures, the magnetic field sensor 16 is mounted on the arm 20 of the C-shaped structure of the frame 7 , so that the magnetic field sensor 16 is located above the optical detection system 13 relative to the frame 3 .

[0022] However, it is conceivable that the shape of the second frame 7 and / or the relative positions of the light detection system 13 and the magnetic field sensor 16 differ from what is shown in the figures.

[0023] The device 1 comprises a processing and control unit 21 configured to control the actuators 5, 8 and 15 to perform an optical scan of the rotor 2 and then to measure the magnetic field of the rotor 2 in a manner that will be described in detail below.

[0024] The processing and control unit 21 controls the actuators 5 and 8 to drive the rotor 2 to rotate relative to the rotation axis 4a, more specifically to rotate the rotating base 4 and to move the second frame 7 parallel to the rotation axis 4a, for example from the bottom ( Figure 1 )up( Figure 2 ) moves to optically scan the rotor 2 through the optical detection system 13.

[0025] The processing and control unit 21 is configured to perform geometric measurement of the rotor 2 based on the optical scanning, specifically to achieve the geometric measurement of the rotor 2 by processing the image of the rotor 2 acquired during the optical scanning process.

[0026] A preliminary step can be envisaged, which involves repositioning the optical detection system 13 relative to the actual position of the rotor 2. Based on the acquired image of the rotor 2, the processing and control unit 21 controls the actuator 8 to move the frame 7 so that the optical detection system 13 is moved in a direction parallel to the rotation axis 4a to a suitable height relative to the position of the rotor 2 in order to scan the rotor 2 and perform the correct geometric measurements.

[0027] Subsequently, regardless of whether the preliminary step of repositioning the optical detection system 13 is performed, the processing and control unit 21 controls the actuator 8 to move the frame 7 so that the magnetic field sensor 16 moves in a direction parallel to the rotation axis 4a to a suitable height, e.g. Figure 3 As shown, the frame 7 is moved downward and the magnetic field sensor 16 is adjusted to be located at Figure 1 and Figure 2 At an altitude between the altitudes shown.

[0028] Preferably, the magnetic field sensor 16 is located at a height parallel to the rotation axis 4a (e.g. Figure 3 ) is determined based on geometric measurements (or geometric measurement values) of the rotor 2 obtained by processing an image of the rotor 2 acquired by optical scanning performed by the optical detection system 13.

[0029] In short, the geometric measurements (or geometric measurement values) are processed to determine the actual position of the rotor 2 along the direction parallel to the rotation axis 4a, and the frame 7 is moved along the direction of the rotation axis 4a according to the actual position of the rotor 2, so that the optical detection system 13 and / or the magnetic field sensor 16 are located at their respective appropriate heights along the direction parallel to the rotation axis 4a, thereby correctly performing the geometric measurement and magnetic field measurement of the workpiece 2.

[0030] At this point, the processing and control unit 21 controls the third actuator 15 according to the geometric measurements performed, so as to move the slide 14 in the direction 14a during the magnetic field measurement and to position the magnetic field sensor 16 at a suitable measuring distance from the rotation axis 4a or the side 17 ( Figure 4 ).

[0031] The magnetic field measurement is performed by rotating the rotating base 4 by a certain angle to obtain the angular trend of the magnetic field radially emitted by the rotor 2 . Figure 5 An example of a trend of the magnetic field B measured around the rotor 2 as a function of the angular position a of the rotating base 4 is shown. The peaks in the trend of the magnetic field B correspond to the magnetic poles present at a given angular position of the rotor 2, said poles being defined by the respective permanent magnets.

[0032] Controlling the position of magnetic field sensor 16 along direction 14a serves to position the sensor at a certain distance (referred to as the measurement distance) from side 17 of rotor 2 so that the magnetic field can be accurately measured even when the dimensions of rotor 2 vary. Indeed, the strength of the magnetic field, and therefore the amplitude of the signal detected by magnetic field sensor 16, depends significantly on the distance from the source of the magnetic field. In other words, controlling the position of magnetic field sensor 16 along direction 14a allows for automatic adaptation of the magnetic field measurement to the lateral dimensions of rotor 2.

[0033] According to a first embodiment, the processing and control unit 21 is configured to calculate the measured distance D0 from the rotation axis 4 a from the nominal size value of the rotor 2 .

[0034] Controlling the position of the magnetic field sensor 16 along the direction 14a also compensates for magnetic field measurement errors that are primarily due to non-ideal aspects of the rotor 2 being inspected or its configuration that differ from theoretical, “ideal” aspects.

[0035] The first non-ideal aspect is the potential offset of rotor 2 relative to clamping system 6 , which is caused by insufficient mechanical precision of live center 10 and dead center 12 and / or insufficient mechanical precision of the clamping holes in rotor 2. These clamping holes are located on the longitudinal axis of rotor 2 and engage with live center 10 and dead center 12. This offset error causes slight fluctuations in the position of rotor 2 relative to axis of rotation 4 a as rotating base 4 rotates. In other words, during the rotation of rotating base 4, this offset error causes fluctuations (periodic variations) in the distance between magnetic field sensor 16 and side surface 17 of rotor 2 , and this distance variation introduces errors in magnetic field measurement.

[0036] Another non-ideal aspect is the difference between the nominal and actual dimensions of rotor 2. This difference often results in asymmetry of side 17 of rotor 2 relative to its longitudinal axis. This asymmetry causes the distance between magnetic field sensor 16 and side 17 of rotor 2 to change as rotating base 4 rotates. This distance change introduces errors in magnetic field measurement.

[0037] According to a second embodiment, the processing and control unit 21 is configured to determine the transverse dimensions of the rotor 2 and the offset of the rotor 2 relative to the rotation axis 4a (i.e., the arrangement of the longitudinal axis of the rotor 2 relative to the rotation axis 4a) based on geometric measurements (or geometric measurement values), and to compensate the magnetic field measurements (or magnetic field measurement values) based on the offsets by appropriate signal processing. Furthermore, the processing and control unit 21 is configured to calculate a measured distance D1 from the rotation axis 4a based on the transverse dimensions of the rotor 2 and to control the third actuator 15 to position and maintain the magnetic field sensor 16 stationary at the measured distance D1 from the rotation axis 4a along the direction 14a during the magnetic field measurement.

[0038] Specifically, the processing and control unit 21 is configured to process geometric measurements (or geometric measurement values) to determine the lateral dimensions of the rotor 2, reconstruct the longitudinal axis of the rotor 2, calculate the change in distance between the magnetic field sensor 16 and the side 17 when the angular position of the rotating base 4 changes based on the relative arrangement of the reconstructed longitudinal axis and the rotation axis 4a, and convert the distance change into a magnetic field fluctuation, which is added to the measured magnetic field (value) through algebraic operations.

[0039] Therefore, during the magnetic field measurement process, magnetic field sensor 16 is always maintained at a measurement distance D1 from rotation axis 4a, and the offset of rotor 2 is corrected, thereby compensating the magnetic field measurement (or magnetic field measurement value). Measurement distance D1 takes into account the lateral dimensions of rotor 2 and the predetermined distance between magnetic field sensor 16 and side surface 17 of rotor 2.

[0040] According to a third embodiment, the processing and control unit 21 is configured as follows:

[0041] - Determine the transverse dimensions of the rotor 2 , in particular at the height of the magnetic field sensor 16 , based on geometric measurements;

[0042] - determining, based on geometrical measurements, the offset of the rotor 2 relative to the axis of rotation 4 a , ie the arrangement of the longitudinal axis of the rotor 2 relative to the axis of rotation 4 a ; and

[0043] - dynamically controlling the actuator 15 during a complete rotation of the rotating base 4 according to the determined lateral dimensions and offset of the rotor 2 so as to keep the magnetic field sensor 16 at a predetermined measuring distance D2 from the side surface 17 in the direction 14a.

[0044] In this way, the difference between the nominal and actual values ​​of the dimensions of the rotor 2 is compensated, as well as any deflection of the rotor 2. In fact, if the magnetic field sensor 16 remains stationary, any deflection of the rotor 2 will also cause the distance between the magnetic field sensor 16 and the side surface 17 of the rotating base 4 to change during a complete rotation.

[0045] According to one embodiment (not shown), the device 1 further comprises a known contact detection probe for performing other measurements in addition to the ones described above. For example, the contact detection probe is mounted in the second frame 7 at a position facing the magnetic field sensor 16 relative to the axis of rotation 4 a and is particularly arranged in a housing of the frame and mounted on a slide movable in a direction parallel to the direction 14 a so as to be able to move out of the housing and re-enter it, towards and away from the rotor 2 . For example, the housing is arranged on the first arm 19 of the frame 7 above the assembly 23 .

[0046] One advantage of the above-described device 1 is that, by controlling the position of the magnetic field sensor 16 along the direction 14 a according to the geometrical measurement (or geometrical measurement value) of the rotor 2, the magnetic field sensor 16 is positioned at a certain distance from the side surface 17 of the rotor 17, thereby achieving accurate magnetic field measurement. Another advantage is that certain non-ideal aspects of the measurement environment, namely the offset of the rotor 2 and the difference between the nominal value and the actual value of the dimensions of the rotor 2, are automatically compensated.

[0047] It should be noted that the above device 1 can be used to measure the geometry and magnetic field of any component with rotational symmetry (such as cylindrical symmetry) and having multiple permanent magnets arranged around its axis (not necessarily the permanent magnet motor rotor as described above).

Claims

1. A measuring device for carrying out geometric and magnetic field measurements of a workpiece (2), said workpiece (2) having rotational symmetry, for example cylindrical symmetry, about its axis and having a plurality of permanent magnets arranged around said axis, said workpiece (2) being, for example, a rotor of an electric motor, said device (1) comprising: A first fixed frame (3); a rotating base (4), which is mounted on the first fixed frame (3) and driven to rotate around a rotation axis (4a) by a first actuator (5); a clamping system (6), which is used to hold the workpiece (2) on the rotating base (4) and is coaxial with the latter to drive the workpiece (2) to rotate; a second frame (7), which is movably mounted on the first frame (3) so as to be driven to move parallel to the rotation axis (4a) by a second actuator (8); an optical detection system (13), which is fixed on the second frame (7) and is used to optically scan the workpiece (2); a slider (14), which is movably mounted on the second frame (7) The invention relates to a frame (7) for moving in a direction (14a) substantially perpendicular to the rotation axis (4a) by being driven by a third actuator (15); a magnetic field sensor (16) fixed to the slider (14) so ​​as to be located in front of a side surface (17) of the workpiece (2) when in use for magnetic field measurement; and a processing and control unit (21) configured to perform geometric measurement based on the optical scanning and control the third actuator (15) to position the magnetic field sensor (16) in the direction (14a) at an appropriate measurement distance (D0; D1; D2) from the rotation axis (4a) or the side surface (17) during magnetic field measurement.

2. The measuring device according to claim 1 , wherein the processing and control unit ( 21 ) is configured to control the third actuator ( 15 ) based on geometric measurements in order to position and maintain the magnetic field sensor ( 16 ) at the measuring distance ( DI ; D2 ) during magnetic field measurement.

3. A measuring device according to claim 1 or 2, wherein the processing and control unit (21) is configured to determine the offset of the workpiece (2) relative to the rotation axis (4a) and the lateral dimension of the workpiece (2) based on the geometric measurement, calculate the measurement distance (D1) based on the lateral dimension of the workpiece (2), control the third actuator (15) to position the magnetic field sensor (16) and keep it stationary at the measurement distance (D1) from the rotation axis (4a), and compensate the magnetic field measurement based on the offset of the workpiece (2).

4. A measuring device according to claim 1 or claim 2, wherein the measuring distance (D2) is predetermined, and the processing and control unit (21) is configured to determine the offset of the workpiece (2) relative to the rotation axis (4a) and the lateral dimension of the workpiece (2) based on the geometric measurement, and dynamically control the third actuator (15) based on the offset and the lateral dimension of the workpiece (2) so that the magnetic field sensor (16) is maintained at the measuring distance (D2) from the side surface (17).

5. A measuring device according to any of the preceding claims, wherein the clamping system (6) comprises a live center (10) coaxially fixed to the rotating base (4), a movable head (11) mounted on the first frame (3) so as to move parallel to the rotation axis (4a), and a dead center (12) fixed to the movable head (11) so as to be coaxial with the live center (10).

6. The measuring device according to any of the preceding claims, wherein the magnetic field sensor (16) is a Hall sensor.

7. A measuring device according to any of the above claims, wherein the second frame (7) has a C-shaped structure and is configured to be arranged around the workpiece (2) when in use; the optical detection system (13) includes a first component (22) mounted on a first arm (19) of the C-shaped structure and a second component (23) mounted on the other arm (20) of the C-shaped structure, and the magnetic field sensor (16) is mounted on one of the two arms (19, 20) of the C-shaped structure of the second frame (7) and is located at a height in a direction parallel to the rotation axis (4a), which is different from the height at which the optical detection system (13) is arranged.

8. The measuring device according to claim 7, wherein the optical detection system (13) is a projection optical system, and the components are respectively an emitter (22) and a sensor (23).

9. A measurement method for carrying out geometric and magnetic field measurements of a workpiece (2), said workpiece (2) having rotational symmetry, for example cylindrical symmetry, about its axis and having a plurality of permanent magnets arranged around said axis of said workpiece (2), said workpiece (2) being, for example, a rotor of an electric motor, said method comprising the following steps: - rotating the workpiece (2) relative to the rotation axis (4a); - optically scanning the workpiece (2) by an optical detection system (13); - processing the images of the workpiece (2) acquired during the optical scanning process to perform geometric measurements of the workpiece (2); - during magnetic field measurement, positioning and maintaining a magnetic field sensor (16) in a direction (14a) perpendicular to the rotation axis (4a) at an appropriate measuring distance (D0; D1; D2) from the rotation axis (4a) or a side surface (17) of the workpiece (2); and - Obtaining the angular trend of the magnetic field radially emitted by the workpiece (2) to perform magnetic field measurement.

10. The method according to claim 9, further comprising the steps of: - processing the geometric measurements to determine the transverse dimensions of the workpiece (2) and the offset of the workpiece (2) relative to the rotation axis (4a); - calculating a measured distance (D1) from the rotation axis (4a) based on the transverse dimension of the workpiece (2); - during magnetic field measurement, keeping the magnetic field sensor (16) stationary at a measuring distance (D1) from the rotation axis (4a) along the direction (14a); and - Compensating the acquired magnetic field measurements according to the determined offset of the workpiece (2).

11. The method according to claim 9, wherein the measured distance (D2) is predetermined; the method comprising the steps of: - processing the geometric measurements to determine the transverse dimensions of the workpiece (2) and the offset of the workpiece (2) relative to the axis of rotation (4a); as well as - dynamically controlling the position of the magnetic field sensor (16) according to the offset and the lateral dimension of the workpiece (2) so as to keep the magnetic field sensor (16) at the measuring distance (D2) from the side surface (17) of the workpiece (2) along the direction (14a) during magnetic field measurement.

12. The measuring method according to any one of claims 9 to 11, further comprising the following steps: - processing the geometrical measurements to determine the actual position of the workpiece (2) relative to a direction parallel to the axis of rotation (4a); as well as - According to the actual position of the workpiece (2), the optical detection system (13) and / or the magnetic field sensor (16) are positioned at an appropriate height along the direction parallel to the rotation axis (4a) to perform geometric measurement and / or magnetic field measurement of the workpiece (2).

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