Apparatus and method for performing geometric and magnetic field measurements on rotationally symmetrical parts having multiple permanent magnets - Patent 7222262

Abstract

An apparatus for performing geometric shape measurements and magnetic field measurements of a part (2), such as the rotor of a permanent magnet electric motor, comprising a fixed first frame (3), a rotating base (4) mounted on the first frame for rotation about an axis of rotation (4a), a gripping system (6) for holding the part on the rotating base so as to cause rotation of the part, a second frame (7) movably mounted on the first frame for translation parallel to the axis of rotation, an optical detection system (13) fixed to the second frame for performing optical scanning of the part, and an actuator ( the apparatus comprising: a slide (14) movably mounted on the second frame so as to translate along a direction (14a) perpendicular to the axis of rotation by the action of an actuator (15), a magnetic field sensor (16) fixed to the slide so as to be positionable facing a side (17) of the part for performing magnetic field measurements, and a processing and control unit (21) configured to control the actuator to perform geometric shape measurements based on optical scanning and to position the magnetic field sensor at appropriate measurement distances (D0, D1, D2) from the axis of rotation or from the side along said direction during magnetic field measurements. The invention also relates to related methods for performing geometric shape measurements and magnetic field measurements of parts.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for performing geometric and magnetic field measurements on a part, the part having rotational symmetry, typically cylindrical symmetry, about its axis and comprising a plurality of permanent magnets arranged around the part axis, for example around the rotor of an electric motor.

[0002] In particular, but not exclusively, the present invention may be used to advantage for measuring the rotor of a permanent magnet electric motor, and the following description will make specific reference thereto without thereby losing its general character. [Background technology]

[0003] The increasing use of permanent magnet electric motors, for example in the automotive sector, has led to an increasing need for rapid quality inspection of various components of electric motors, particularly the rotors of electric motors. The rotors of permanent magnet electric motors comprise a plurality of permanent magnets arranged in a circle around the rotor axis. The quality of the rotor is generally defined by its mechanical quality, e.g., conformance to tight tolerances for various dimensional characteristics, as well as by the quality of the permanent magnets, i.e., the strictly magnetic properties of each permanent magnet and their distribution around the rotor axis.

[0004] Devices are known that can perform geometric measurements on mechanical components with cylindrical symmetry, or more generally, on mechanical components that can rotate around their own axis, such as crankshafts of internal combustion engines. The devices include a means for grasping the mechanical component and rotating it around its axis, as well as feeler or optical means for acquiring dimensional parameters of the component while it is rotating. Such devices are suitable for measuring the mechanical properties of rotors in electric motors. Furthermore, other devices exist that are suitable for measuring the overall magnetic properties of permanent magnets. This means that two measurement sessions are required for each motor to measure the rotor's geometric and magnetic properties separately, i.e., using two different devices. As a result, rotor quality control is relatively slow and difficult. Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide an apparatus and a method for carrying out geometry and magnetic field measurements of the rotor of an electric motor that do not have the above-mentioned drawbacks and that can at the same time be implemented simply and at low cost. [Means for solving the problem]

[0006] According to the present invention, there is provided an apparatus and method for performing geometry and magnetic field measurements on a part, the part having rotational symmetry about its axis and comprising a plurality of permanent magnets arranged around the part axis, as defined in the appended claims.

[0007] The invention will now be described with reference to the accompanying drawings, which show non-limiting examples of embodiments thereof. [Brief explanation of the drawings]

[0008] [Figure 1]1 shows a device according to the invention for carrying out geometrical shape measurements and magnetic field measurements of a part during a corresponding number of stages of its operation; [Figure 2] 1 shows a device according to the invention for carrying out geometrical shape measurements and magnetic field measurements of a part during a corresponding number of stages of its operation; [Figure 3] 1 shows a device according to the invention for carrying out geometrical shape measurements and magnetic field measurements of a part during a corresponding number of stages of its operation; [Figure 4] 1 shows a device according to the invention for carrying out geometrical shape measurements and magnetic field measurements of a part during a corresponding number of stages of its operation; [Figure 5] 5 is a graph showing measurements of the magnetic field of a part carried out using the device described in FIGS. 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1 to 4, 1 generally indicates in its entirety an apparatus according to the invention for carrying out geometric and magnetic field measurements of a part 2, such as the rotor of a permanent magnet electric motor. The rotor 2 is shown positioned within the apparatus 1 during its measurement.

[0010] The apparatus 1 comprises a frame, or first frame, or first fixed frame 3, for example resting on the ground, a rotating base 4 mounted on the frame 3 so as to rotate, for example about a substantially vertical rotation axis 4a, by the action of an actuator, or first actuator 5, a gripping system 6 for holding the rotor 2 coaxially on the rotating base 4 so as to effect rotation of the rotor 2, and another frame, or second frame 7, movably mounted on the first frame 3 so as to translate parallel to the rotation axis 4a as driven by another actuator, or second actuator 8. In particular, the first frame 3 comprises a pair of guides 9 parallel to the rotation axis 4a, and the second frame 7 is mounted slidably along the two guides 9.

[0011] The gripping system 6 is preferably a live center / dead center system of known type. In particular, the gripping system 6 comprises a live center 10 fixed coaxially to the rotating base 4, a movable head 11 mounted on the first frame 3 for translation 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.

[0012] The device 1 comprises an optical detection system 13 (Figures 2 to 4) fixed to the second frame 7 so as to be focused on the rotation axis 4a in order to acquire an image of the rotor 2, in particular to perform an optical scan of the rotor 2 as a result of translation of the frame 7, typically during rotation of the rotation base 4.

[0013] Preferably, the optical detection system 13 comprises a first component 22, more particularly an emitter, for example an infrared emitter, fixed to the frame 7, and a second component 23, more particularly a receiver or sensor, fixed to the frame 7 on the opposite side of the rotation axis 4a so as to face the component 22. For example, the component 23 comprises a linear array of photodiodes (CCDs).

[0014] According to a preferred embodiment, the optical detection system is a shadow-casting optical system known per se.

[0015] The apparatus 1 comprises a slide 14 movably mounted on the second frame 7 so as to be driven by a further or third actuator 15 to translate along a direction 14a substantially perpendicular to the axis of rotation 4a, and a magnetic field sensor 16 fixed to the slide 14 so as to be positioned in use in front of a side surface 17 of the rotor 2 for carrying out magnetic field measurements. In particular, a further frame 18 is fixed to the second frame 7, and the slide 14 slides along a guide (not shown) fixed to the further frame 18.

[0016] Advantageously, the magnetic field sensor 16 is a Hall sensor.

[0017] Advantageously, the second frame 7 has a C-shaped structure and is configured to be arranged around the rotor 2 in use so as to surround the rotor 2, as shown in Figures 1 to 4. One of the two components of the optical detection system 13, for example, component 23, is attached to a first branch 19 of the C-shaped structure, and the other component of the optical detection system 13, for example, component 22, is attached to the other branch 20 of the C-shaped structure at a position diametrically opposite the position of component 22 with respect to the rotation axis 4a. Thus, the two components 22, 23 are arranged at substantially the same height along a direction parallel to the rotation axis 4a.

[0018] The magnetic field sensor 16 is mounted on one of the two branches 19 and 20 of the C-shaped structure of the frame 7 at a height along a direction parallel to the rotation axis 4a that is different from the height at which the optical detection system 13 is located. In this way, the magnetic field sensor 16 does not interfere with the optical scanning performed by the optical detection system 13.

[0019] For example, in the illustrated embodiment, the magnetic field sensor 16 is mounted to a branch 20 of the C-shaped structure of the frame 7 so that it is positioned above the optical detection system 13 relative to the frame 3 .

[0020] However, it is possible to envisage a shape of the second frame 7 and / or a relative position of the optical detection system 13 and the magnetic field sensor 16 different from that shown here.

[0021] The apparatus 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 a magnetic field measurement of the rotor 2 in a manner described in detail herein below.

[0022] The processing and control unit 21 controls the actuators 5 and 8 to drive the rotor 2 in rotation about the axis of rotation 4a, more specifically to rotate the rotation base 4 and translate the second frame 7 parallel to the axis of rotation 4a, for example from the bottom (Figure 1) to the top (Figure 2), in a known manner to perform an optical scan of the rotor 2 by the optical detection system 13.

[0023] The processing and control unit 21 is configured to perform geometric shape measurements of the rotor 2 based on the optical scanning, more specifically by processing images of the rotor 2 acquired during the optical scanning to perform geometric shape measurements of the rotor 2.

[0024] A preliminary step can be envisaged which involves repositioning the optical detection system 13 relative to the actual position of the rotor 2. Depending on the acquired image of the rotor 2, the processing and control unit 21 controls the actuator 8 to move the frame 7 so as to position the optical detection system 13 at the appropriate height along a direction parallel to the rotation axis 4a relative to the position of the rotor 2 in order to scan the rotor 2 and perform the correct geometric measurement.

[0025] Thereafter, regardless of the execution of the preliminary step involving repositioning of the optical detection system 13, the processing and control unit 21 controls the actuator 8 to move the frame 7 downwards and bring the magnetic field sensor 16 to an appropriate height along a direction parallel to the rotation axis 4a, for example as shown in Figure 3, in order to bring the magnetic field sensor 16 to a height that is between the height shown in Figure 1 and the height shown in Figure 2.

[0026] Preferably, the height along a direction parallel to the rotation axis 4a (Figure 3) at which the magnetic field sensor 16 is positioned is determined according to geometric shape measurements of the rotor 2 obtained by processing images of the rotor 2 acquired by optical scanning performed by the optical detection system 13.

[0027] In short, the geometric shape measurements are processed to determine the actual position of the rotor 2 along a direction parallel to the rotation axis 4a, and the frame 7 is translated along 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 positioned at respective appropriate heights along said direction parallel to the rotation axis 4a to correctly perform the geometric shape measurements and magnetic field measurements of the part 2.

[0028] At this point, the processing and control unit 21 controls the third actuator 15 to translate the slide 14 and position the magnetic field sensor 16 at an appropriate measurement distance from the axis of rotation 4a or from the side surface 17 along the direction 14a during the magnetic field measurement (Figure 4), depending on the geometric measurement to be performed.

[0029] The magnetic field measurements are performed by rotating the rotating base 4 over a rotation angle to obtain the angular trend of the magnetic field emitted radially by the rotor 2. Figure 5 shows an example of the trend of the magnetic field B measured around the rotor 2, i.e., as the angular position α of the rotating base 4 varies. The peaks of the trend of the magnetic field B correspond to the presence of the magnetic poles defined by the respective permanent magnets at a given angular position of the rotor 2.

[0030] Controlling the position of the magnetic field sensor 16 along the direction 14a has the function of positioning the magnetic field sensor 16 at a distance, also called the measurement distance, from the side surface 17 of the rotor 2, to enable accurate magnetic field measurements, for example, when the dimensions of the rotor 2 vary. Indeed, the strength of the magnetic field, and therefore the amplitude of the signal detected by the magnetic field sensor 16, is highly dependent on the distance from the source of the magnetic field. In other words, controlling the position of the magnetic field sensor 16 along the direction 14a allows the magnetic field measurement to be automatically adapted to the lateral dimensions of the rotor 2.

[0031] According to a first embodiment, the processing and control unit 21 is configured to calculate the measured distance D0 from the axis of rotation 4a depending on the nominal dimensional values ​​of the rotor 2.

[0032] Controlling the position of the magnetic field sensor 16 along the direction 14a also makes it possible to compensate for errors in the measurement of the magnetic field that are primarily due to non-ideal aspects, i.e. aspects of the rotor 2 to be inspected and / or its arrangement that differ from the theoretically "ideal" aspects, as described below.

[0033] The first non-ideal aspect is the possible offset of the rotor 2 relative to the gripping system 6 due to mechanical inaccuracies of the live and dead centers 10 and 12 and / or of the gripping holes of the rotor 2 that are located on the longitudinal axis of the rotor 2 and engaged by the live and dead centers 10 and 12. The offset error results in slight vibrations of the rotor 2 relative to the rotation axis 4a during rotation of the rotating base 4. In other words, the offset error causes vibrations, i.e., periodic fluctuations, of the distance between the magnetic field sensor 16 and the side surface 17 of the rotor 2 during rotation of the rotating base 4, and the distance fluctuations result in errors in the magnetic field measurement.

[0034] Another non-ideal aspect is the difference between the nominal and actual dimensions of the rotor 2. Said difference often results in an asymmetry of the side surface 17 of the rotor 2 with respect to its longitudinal axis. Said asymmetry results in oscillations in the distance between the magnetic field sensor 16 and the side surface 17 of the rotor 2 during rotation of the rotating base 4, and the variation in distance results in errors in the magnetic field measurement.

[0035] According to the second embodiment, the processing and control unit 21 is configured to determine the lateral 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, in response to the geometry measurements, and to compensate the magnetic field measurements by appropriate signal processing in response to the offset. Furthermore, the processing and control unit 21 is configured to calculate the measurement distance D1 from the rotation axis 4a in response to the lateral dimensions of the rotor 2, and to position the magnetic field sensor 16 and control the third actuator 15 to keep the magnetic field sensor 16 fixed at the measurement distance D1 from the rotation axis 4a along the direction 14a during the magnetic field measurements.

[0036] More specifically, the processing and control unit 21 is configured to process the geometric shape measurements to determine the lateral dimensions of the rotor 2, reconstruct the longitudinal axis of the rotor 2, calculate the variation in distance between the magnetic field sensor 16 and the side surface 17 upon variation in the angular position of the rotating base 4 based on the alignment of the reconstructed longitudinal axis relative to the rotation axis 4a, and convert the variation in distance into magnetic field oscillations to be algebraically added to the measured magnetic field.

[0037] Thus, the magnetic field sensor 16 remains fixed at a measurement distance D1 from the rotation axis 4a during magnetic field measurement, and the offset of the rotor 2 is corrected, thus compensating the magnetic field measurement. The measurement distance D1 takes into account the lateral dimensions of the rotor 2 and the predetermined distance between the magnetic field sensor 16 and the side surface 17 of the rotor 2.

[0038] According to the third embodiment, the processing and control unit 21 - determining the lateral dimensions of the rotor 2 according to the geometrical shape measurement, in particular at the height at which the magnetic field sensors 16 are positioned; - determining the offset of the rotor 2 relative to the axis of rotation 4a, i.e. the arrangement of the longitudinal axis of the rotor 2 relative to the axis of rotation 4a, as a function of the geometric shape measurement; dynamically controlling the actuators 15 during a complete rotation of the rotary base 4 in accordance with the thus determined lateral dimensions and offsets of the rotor 2 so as to keep the magnetic field sensors 16 at a predetermined measuring distance D2 from the side surfaces 17 along the direction 14a; The device is configured to:

[0039] In this way, differences between nominal and actual dimensions of the rotor 2 and / or any offset of the rotor 2 are compensated for. Indeed, if the magnetic field sensor 16 remains fixed, any offset of the rotor 2 will also result in a variation in the distance between the magnetic field sensor 16 and the side surface 17 during a complete rotation of the rotating base 4.

[0040] According to an embodiment not shown, the device 1 comprises, in addition to those described above, a contact detection probe of a known type for carrying out measurements. For example, the contact detection probe is attached to the second frame 7 in a position facing the magnetic field sensor 16 relative to the rotation axis 4a, in particular arranged in a housing of the frame and mounted on a slide movable along a direction parallel to the direction 14a so as to move in and out of said housing and towards and away from the rotor 2. For example, said housing is arranged in the first branch 19 of the frame 7 above the component 23.

[0041] An advantage of the above described device 1 is the automatic positioning of the magnetic field sensor 16 at a distance from the side surface 17 of the rotor 2 to enable, for example, accurate magnetic field measurements, by controlling the position of the magnetic field sensor 16 along the direction 14a according to the geometrical shape measurement of the rotor 2. Another advantage is the automatic compensation of certain non-ideal aspects of the measurement environment, i.e., the offset of the rotor 2 and / or the difference between nominal and actual values ​​of the dimensions of the rotor 2.

[0042] It is pointed out that the above-described device 1 can be used for geometric shape measurement and magnetic field measurement of any component (not necessarily the rotor of the permanent magnet electric motor described above as an example) that has rotational symmetry about its axis, typically cylindrical symmetry, and that has a plurality of permanent magnets arranged around the component axis.

Claims

1. 1. An apparatus for carrying out geometrical shape measurements and magnetic field measurements of a part (2), said part (2) having rotational symmetry with respect to its axis, e.g. cylindrical, and having a plurality of permanent magnets arranged around said part axis, e.g. around the rotor of an electric motor, said apparatus (1) comprising: a first fixed frame (3); a rotating base (4) attached to the first fixed frame (3) and driven by a first actuator (5) to rotate about a rotation axis (4a); a gripping system (6) for holding said part (2) on said rotating base (4) coaxially with said rotating base (4) in order to drive said part (2) in rotation; a second frame (7) movably mounted on the first frame (3) so as to be driven by a second actuator (8) to translate parallel to the rotation axis (4a); an optical detection system (13) fixed to said second frame (7) for performing an optical scan of said part (2); a slide (14) movably mounted on the second frame (7) so as to be driven by a third actuator (15) to translate along a direction (14a) substantially perpendicular to the axis of rotation (4a); a magnetic field sensor (16) fixed to the slide (14) so ​​as to be positioned in front of a side (17) of the part (2) in use to perform the magnetic field measurements; a processing and control unit (21) configured to perform the geometric shape measurement based on the optical scanning and to control the third actuator (15) to position the magnetic field sensor (16) at an appropriate measurement distance (D0, D1, D2) from the rotation axis (4a) or from the side surface (17) along the direction (14a) during the magnetic field measurement.

2. 2. The apparatus of claim 1, wherein the processing and control unit (21) is configured to control the third actuator (15) in response to the geometric shape measurement to position and hold the magnetic field sensor (16) at the measurement distance (D1, D2) during the magnetic field measurement.

3. 3. The apparatus according to claim 1, wherein the processing and control unit is configured to: determine an offset of the part (2) relative to the axis of rotation (4 a) and a lateral dimension of the part (2) in response to the geometric shape measurement; calculate the measurement distance (D1) in response to the lateral dimension of the part (2); control the third actuator (15) to position the magnetic field sensor (16) and keep it fixed at the measurement distance (D1) from the axis of rotation (4 a); and compensate the magnetic field measurement in response to the offset of the part (2).

4. 3. The apparatus according to claim 1, wherein the measurement distance (D2) is predetermined, and the processing and control unit (21) is configured to determine an offset of the part (2) relative to the axis of rotation (4 a) and a lateral dimension of the part (2) in response to the geometric shape measurement, and to dynamically control the third actuator (15) in response to the offset and the lateral dimension of the part (2) so as to keep the magnetic field sensor (16) at the measurement distance (D2) from the side surface (17).

5. 5. The apparatus according to claim 1, wherein the gripping system (6) comprises a live center (10) fixed coaxially to the rotating base (4), a movable head (11) attached to the first frame (3) so as to translate 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. 6. The device according to any one of claims 1 to 5, wherein the magnetic field sensor (16) is a Hall sensor.

7. the second frame (7) has a C-shaped structure and is configured to be placed around the part (2) in use; 7. The apparatus according to claim 1, wherein the optical detection system (13) comprises a first component (22) attached to a first branch (19) of the C-shaped structure and a second component (23) attached to the other branch (20) of the C-shaped structure, and the magnetic field sensor (16) is attached to one of the two branches (19, 20) of the C-shaped structure of the second frame (7) at a height along a direction parallel to the rotation axis (4a) that is different from a height at which the optical detection system (13) is arranged.

8. 8. The apparatus of claim 7, wherein the optical detection system (13) is a shadow-casting optical system and the components are an emitter (22) and a sensor (23), respectively.

9. A method for carrying out geometric and magnetic field measurements of a part (2), said part (2) having rotational symmetry about its own axis, e.g. cylindrical, and comprising a plurality of permanent magnets arranged around the axis of said part (2), e.g. the rotor of an electric motor, said method comprising: - driving said part (2) in rotation about an axis of rotation (4a); - carrying out an optical scan of said part (2) by means of an optical detection system (13); - processing the images of said part (2) acquired during said optical scanning so as to perform a geometric measurement of said part (2); - positioning and holding a magnetic field sensor (16) along a direction (14a) perpendicular to the axis of rotation (4a) at appropriate measuring distances (D0, D1, D2) from the axis of rotation (4a) or from a side surface (17) of the part (2) during the magnetic field measurement; - obtaining the angular trend of the magnetic field emitted radially by said part (2) in order to perform a magnetic field measurement; A method comprising:

10. - processing said geometric measurements to determine the lateral dimensions of said part (2) and its offset relative to said axis of rotation (4a); - calculating said measured distance (D1) from said axis of rotation (4a) depending on said lateral dimension of said part (2); - keeping said magnetic field sensor (16) fixed at said measuring distance (D1) from said axis of rotation (4a) along said direction (14a) during said magnetic field measurement; - compensating the acquired magnetic field measurements as a function of the determined offset of the part (2); The method of claim 9 comprising:

11. The measurement distance (D2) is predetermined; The method comprises: - processing said geometric measurements to determine the lateral dimensions of said part (2) and its offset relative to said axis of rotation (4a); - dynamically controlling the position of the magnetic field sensor (16) according to the offset and the lateral dimension of the part (2) so as to maintain the magnetic field sensor (16) at the measurement distance (D2) from the side surface (17) of the part (2) along the direction (14a) during the magnetic field measurement; The method of claim 9 comprising:

12. - processing said geometric measurements to determine the actual position of said part (2) relative to a direction parallel to said axis of rotation (4a); - positioning the optical detection system (13) and / or the magnetic field sensor (16) at an appropriate height along the direction parallel to the axis of rotation (4a) depending on the actual position of the part (2) in order to perform the geometrical shape measurement and / or the magnetic field measurement of the part (2); 12. The method of claim 9, further comprising:

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