Position sensor for long linear permanent magnet motors

Abstract

To provide positioning performance of a linear permanent magnet motor which is more reliable, simpler, and therefore more cost effective, and does not affect performance of a linear motor.SOLUTION: According to the present invention, a mover is arranged to move along a motion direction. A position sensing device has a sensing element operable to sense a magnetic field of an array of permanent magnets. The sensing element is fixed to a stator unit. The array of the permanent magnets is arranged at a space from the stator unit by an air gap in which electromagnetic fields created by the array of the permanent magnets and at least one coil are configured to interact to thereby generate traction. The sensing element is arranged to be positioned within a magnetic leakage field of the array of the permanent magnets in a case where the array of the permanent magnets is arranged in correspondence to the sensing element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to linear permanent magnet motors, and more particularly to long linear permanent magnet motors having position sensors for detecting or determining the position of a mover relative to a stator. [Background technology]

[0002] Patent Document 1 discloses a linear motor capable of measuring the absolute position of a movable unit called a mover. A plurality of Hall sensors are provided in a stator unit. A reference part made of a material different from the permanent magnet is attached to the movable part equipped with the permanent magnet, so that the magnetic field can be changed in the vicinity of the reference part. The Hall sensors are positioned so as to be able to sense the changed magnetic field.

[0003] Therefore, the Hall sensor can detect when the reference portion of the mover passes and determine absolute position. However, one drawback is that the mover must have a reference portion made of a material with different magnetic properties than the adjacent permanent magnet. Therefore, such a reference portion reduces the motor's performance. Another drawback is that the Hall sensor is located within the permanent magnet's main magnetic field when the permanent magnet moves, causing sensor saturation in analog measurements. Analog measurement is necessary to obtain a position sensor with higher resolution without adding too many sensors. Another drawback is that the Hall sensor is mounted between the coils and / or adjacent to the coils, which heats up during operation, increasing the temperature of the Hall sensor. The sensitivity of the Hall sensor is temperature-dependent, which can make reliable measurements difficult. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent Application Publication No. 1020150145407 Summary of the Invention [Problem to be solved by the invention]

[0005] The objective of embodiments of the present invention is to overcome the above-mentioned drawbacks, and in particular to provide a more reliable and simpler linear permanent magnet motor positioning capability, which is therefore cost-effective and does not affect the linear motor's performance.

[0006] An object of embodiments of the present invention is to provide a linear permanent magnet motor that has more accurate positioning performance without using expensive components such as a linear encoder. An object of the present invention is to provide a linear permanent magnet motor that can be accurately positioned over a long stroke. [Means for solving the problem]

[0007] The present invention provides a linear (i.e., linear stroke) permanent magnet motor according to the claims. The motor comprises at least one, and preferably a plurality of, stator units and a mover or movers. Each stator unit comprises at least one coil for generating a magnetic field. The mover comprises an array of permanent magnets spaced apart from the stator unit. An air gap is interposed between the array of permanent magnets and the stator unit. An electromagnetic field of the permanent magnets of the array interacts with an electromagnetic field generated by the at least one coil within the air gap, causing the mover to generate traction relative to the stator unit. The mover is arranged to move along a direction of motion. Advantageously, the permanent magnets of the array are spaced apart from one another along the direction of motion by a predetermined distance. Advantageously, the array of permanent magnets has a surface exposed to the air gap. The surface is advantageously flat and parallel to the direction of motion. The motor comprises a position detection device operable to determine the position of the mover relative to the stator unit (respectively).

[0008] The position detector comprises a sensing element operable to sense the magnetic field of the mover (of the array of permanent magnets), the sensing element being fixed to the stator unit.

[0009] In a first embodiment of the present invention, the sensing element is positioned so that, when the permanent magnet array is arranged corresponding to the sensing element along the direction of motion, the sensing element is located within the leakage magnetic field of the permanent magnet array. The leakage magnetic field is the portion of the magnetic field generated by the mover that is not connected by the stator unit. In other words, the leakage magnetic field is formed by magnetic field lines that do not connect with the coils of the stator unit when the permanent magnet array passes through.

[0010] In a second embodiment of the present invention, which can be realized in combination with or independently of the first embodiment, the sensing element is positioned so that an orthogonal projection of the sensing element onto the median plane of the air gap, which is parallel to the exposed surface of the permanent magnet array, is located outside the band formed by the orthogonal projection (of the periphery) of the permanent magnet array onto the median plane when moving along the direction of motion. Advantageously, when the sensing element is positioned inside the leakage magnetic field of the permanent magnet array, the orthogonal projection of the sensing element's position onto the median plane of the air gap is located outside the band formed by the orthogonal projection of the permanent magnet array onto the median plane when moving along the direction of motion.

[0011] By arranging the sensing element in the first or second embodiment described above, the sensing element is positioned at a position where the magnetic field strength of the permanent magnet array is greatly reduced when the mover passes, thereby avoiding saturation of the sensing element. As a result, the sensing element provides an output that is continuously proportional to the sensed magnetic field strength, allowing the position of the mover relative to the stator unit to be accurately determined, and advantageously, the absolute position of the mover can be accurately determined based on the sensing element alone without relying on expensive encoders. This allows the sensing element to be used for accurate position detection, eliminating the need for a linear encoder.

[0012] At such a position, the leakage field is significantly weaker than the main field, which almost completely eliminates the risk of saturating sensing elements, e.g., Hall sensors or magnetoresistive sensors, and is therefore suitable for analog measurements, thereby increasing the resolution of the position measurement without the need for additional sensing elements.

[0013] Furthermore, at such a location distal to the permanent magnet, the sensing element is mounted further distal to the coil compared to prior art, which virtually eliminates the risk of the sensor overheating due to coil heating.

[0014] Furthermore, the possibility of an upper or lower position of the permanent magnets (when viewed in orthogonal projection) allows the coils of the stator units to be placed closer together, resulting in a motor with higher force density.

[0015] DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which like reference numerals refer to like features. [Additional note 1] a stator unit (11) having at least one coil (14); a mover (12) having an array of permanent magnets (131), the mover (12) being arranged to move along a direction of motion (101), the array of permanent magnets (131) being spaced apart from a stator unit (11) by an air gap (18) configured to generate traction by interaction of electromagnetic fields generated by the array of permanent magnets (131) and at least one of the coils (14); a position detection device (16) operable to determine the position of the mover (12) relative to the stator unit (11); A linear permanent magnet motor (10) comprising: the position detection device (16) comprises a sensing element (161) operable to sense a magnetic field of the array of permanent magnets (131), the sensing element being fixed to the stator unit (11); A linear permanent magnet motor characterized in that the sensing element (161) is arranged so that when the array of permanent magnets is arranged corresponding to the sensing element, the sensing element is located within the leakage magnetic field (134) of the array of permanent magnets (131). [Additional note 2] 2. The linear permanent magnet motor of claim 1, wherein the air gap (18) is interposed between the array of permanent magnets (131) and at least one of the coils (14). [Additional note 3] 3. A linear permanent magnet motor according to claim 1 or 2, characterized in that the array of permanent magnets (131) has a surface (133) exposed to the air gap (18), the surface (133) being flat and parallel to the direction of motion (101), and the air gap having a median plane (181) parallel to the surface (133). [Additional note 4] 4. The linear permanent magnet motor of claim 3, wherein the sensing elements (161) are arranged such that their orthogonal projections onto the median plane (181) are located outside a band (132) formed by the orthogonal projections of the array of permanent magnets (131) onto the median plane (181) when moving along the direction of motion (101). [Additional note 5] 5. The linear permanent magnet motor according to claim 3, wherein the sensing element (161) is positioned at a position corresponding to the air gap (18) along a direction perpendicular to the median plane (181). [Additional note 6] 5. The linear permanent magnet motor according to claim 3, wherein the sensing element (161) is positioned at a position corresponding to the mover (12) along a direction perpendicular to the median plane (181). [Additional note 7] 7. The linear permanent magnet motor according to claim 6, wherein the sensing element (161) is positioned at a position corresponding to the array of the permanent magnets (131) along a direction perpendicular to the median plane (181). [Additional note 8] A linear permanent magnet motor characterized in that the sensing element (161) is arranged at a position corresponding to the stator unit (11) along a direction perpendicular to the median plane (181). [Additional note 9] 9. The linear permanent magnet motor according to claim 1, wherein the sensing element (161) is positioned along the direction of motion (101) at a position corresponding to the position of at least one of the coils (14). [Additional Note 10] 10. The linear permanent magnet motor according to claim 1, wherein the sensing element (161) is embedded in a support (111) made of a non-magnetic material and fixed to the stator unit (11). [Additional Note 11] 11. A linear permanent magnet motor according to claim 10, characterized in that the support is positioned so that an orthogonal projection of the support relative to the median plane (181) is located outside the band (132). [Additional Note 12] The linear permanent magnet motor according to claim 10, which is characterized in that the support portion (111) protrudes from the stator unit (11) toward the air gap (18) along a direction perpendicular to the median plane (181). [Additional Note 13] 13. The linear permanent magnet motor according to claim 1, wherein the position detection device (16) comprises a plurality of the sensing elements (161) arranged on a first side of the array of the permanent magnets (131) facing the air gap (18) and on a second side of the array of the permanent magnets (131) opposite to the first side. [Additional Note 14] 14. A linear permanent magnet motor according to any one of claims 1 to 13, characterized in that the position detection device (16) comprises a plurality of the sensing elements (161) arranged on a first side of at least one of the coils (14) facing the air gap (18) and on a second side of at least one of the coils (14) opposite to the first side. [Additional Note 15] 15. A linear permanent magnet motor according to claim 13 or 14, characterized in that the position detection device (16) comprises a pair of the sensing elements and is operable to determine position by differential measurement between the pair of the sensing elements. [Additional Note 16] 4. The linear permanent magnet motor according to claim 1, wherein the stator units (11) are a plurality of stator units arranged side by side along the direction of motion (101). [Additional Note 17] 17. The linear permanent magnet motor according to claim 16, wherein the linear permanent magnet motor includes one position detection device (16) for each of a plurality of the stator units (11). [Additional Note 18] 10. A linear permanent magnet motor according to claim 9, wherein the mover (12) comprises a portal structure (122) and a set of arrays of the permanent magnets (131) attached to the portal structure at the same position along the direction of movement (101) and on either side of at least one coil (14). [Additional Note 19] the permanent magnets (131) of the array of permanent magnets are arranged side by side along the direction of movement (101) with alternating polarities and spaced apart at the same pitch; A linear permanent magnet motor as described in any one of claims 1 to 18, characterized in that the position detection device (16) has a plurality of the detection elements (161) arranged at intervals along the direction of movement at a distance equal to the pitch divided by the number of the detection elements. [Additional Note 20] 20. The linear permanent magnet motor according to claim 1, wherein the detection element (161) is a Hall effect sensor. [Additional Note 21] the linear permanent magnet motor includes a control unit (15) operable to read the output of the sensing element (161); 21. A linear permanent magnet motor according to any one of the preceding claims, characterized in that the control unit is operable to compensate the output of the magnetic field of at least one of the coils (14). [Additional Note 22] the linear permanent magnet motor includes a control unit (15) operable to read the output of the sensing element (161); 22. A linear permanent magnet motor as claimed in any one of claims 1 to 21, characterized in that the control unit is operable to determine the amplitude of a phase current to be applied to at least one of the coils (14) based on the output of the sensing element. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic plan view of a permanent magnet linear motor according to an embodiment of the present invention; [Figure 2] 2 is a cross-sectional view of the permanent magnet linear motor shown in FIG. 1 taken along the line AA. [Figure 3] 1 showing the zone of highest magnetic field of the magnet yoke. [Figure 4] 2 showing a strip such as that of FIG. 3. FIG. [Figure 5] 3 is a cross-sectional view of the permanent magnet linear motor shown in FIG. 2 with the position of the magnetic field sensor changed. [Figure 6] 10 shows an operating scheme of a drive for a stator unit with coil field compensation for a sensor. [Figure 7] 1 is a graph of the waveform of an approaching magnet yoke sensed by three Hall effect sensors positioned at equal distances τp / 3 from each other. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1 and 2, a linear motor 10 in an embodiment of the present invention includes at least one, and typically multiple, stator units 11 arranged to remain stationary, and at least one mover 12 arranged to move relative to the stator units. The embodiment depicted in Figure 1 shows two movers 12 arranged to move along the array of stator units 11. The illustrated system is useful in transportation systems such as elevators, conveyance lines, magnetic levitation trains, etc.

[0018] The mover includes a magnet yoke 13. The magnet yoke 13 typically includes a plurality of permanent magnets 131 arranged in one or more arrays. The permanent magnets 131 are oriented to create an alternating magnetic field pattern in the direction of motion 101, which is directed toward the coils 14 attached to the stator unit 11. As shown in Figure 2, the magnets 131 are attached to a backplate 121, which is optionally made of iron, to provide a low reluctance return path for the magnetic flux.

[0019] 2, the mover 12 comprises a portal structure 122 having a generally inverted U-shape, which is arranged over the stator unit 11. The permanent magnets 131 are arranged in two arrays, one on each leg of the U, with the coils 14 of the stator unit 11 interposed between the two arrays. Advantageously, it should be noted that the portal structure is only one possible example of a mover structure, and that other structures may also be used, such as a mover with a single array of permanent magnets arranged on only one side of the coils 14, or a double portal structure with two arrays of stator units.

[0020] The stator unit 11 and the mover 12 / magnet yoke 13 are separated by an air gap 18. The electromagnetic fields of the permanent magnets 131 and the electromagnetic fields generated by the coils 14 interact in the air gap 18 to generate traction of the mover 12 relative to the stator unit 11.

[0021] Typically, each stator unit 11 includes a plurality of coils 14 coupled to a drive unit 15. Referring to FIG. 1, the linear motor 10 includes individual / independent drive units 15 (151, 152, 153, ..., 15 N ) having a plurality of stator units 11 (111,...,11 N ). Each of the coils 14 of the stator unit 11 is divided into a predetermined number of phases (typically three phases). The drive unit 15 controls the current flowing through the coils 14 to generate a phase-shifted alternating magnetic field that interacts with the magnetic field generated by the magnet yoke 13. The current in each phase is adjusted by the drive unit 15 to obtain a substantially constant thrust force regardless of position. When the mover 12 moves at a constant speed relative to the stator unit 11, a sinusoidal voltage is induced in the coil by the alternating magnetic field of the magnet yoke 13. When a sinusoidal current in phase with the induced voltage is applied to each phase, positive forces with various amplitudes are obtained. When the minimum number of phases is three and each phase has a phase n2τ in the direction of motion, p If the force is physically displaced by τ / P, a nearly constant force is obtained regardless of position (τ p (where is the distance between the magnets in the north-south direction, known as the pole pitch, P is the number of phases, and n is an integer other than a multiple of P.) Controlling these currents to obtain a nearly constant force regardless of position is called commutation. The magnitude of the current adjusts the overall magnitude of the force.

[0022] In a typical application, the travel distance is much longer than the length of the magnet yoke 13, so the stator unit 11 must be much longer than the length of the magnet yoke. Since a coil not overlapping the magnet yoke only dissipates heat without generating any force, the coil is divided into several small stator units 11 that are switched on according to the approach of the magnet yoke. Also, when several movers are considered, the stator units 11 are controlled individually, advantageously by independent drive units 15, since the positions of the movers relative to the stator units are different.

[0023] Knowing when to activate the coils 14 of a particular stator unit 11 requires determining the position of the approaching mover 12. Position sensing is required for both commutation (controlling multiphase currents according to the relative positions of the coils and magnet yoke(s)) and for position control of the magnet yoke(s). For typical moving magnet applications such as those described above, accuracies on the order of 0.1 mm and large air gap variations (on the order of 1 mm or more) are generally required.

[0024] To this end, in an embodiment of the present invention, each stator unit 11 comprises a position detection device 16 operable to sense the position of the mover 12 relative to the stator unit 11. The position detection device 16 is configured to determine the position of the magnet yoke by sensing the magnetic field of the magnet yoke using a magnetic field sensor 161. Examples of suitable sensors include Hall effect sensors and magnetoresistive (MR) sensors. Advantageously, the magnetic field sensors 161 are arranged at the ends of the stator unit 11 in the direction of motion 101, thereby enabling detection as the mover 12 approaches the respective stator unit. Advantageously, each position detection device 16 comprises a plurality of sensors (e.g., three sensors), each operable to measure the magnetic field in the same direction or in different orthogonal directions, e.g., the X, Y, and Z directions as shown in FIG. 1 .

[0025] In this embodiment of the present invention, the sensor 161 is disposed at a position where the strength of the magnetic field of the magnet yoke 13 is reduced when the mover 12 passes by. In particular, the sensor 161 is disposed at a position corresponding to the leakage magnetic field of the magnet yoke 13 (permanent magnet 131). By doing so, saturation of the sensor 161 is avoided or significantly reduced, thereby improving the measurement accuracy and resolution.

[0026] Referring to FIG. 3 , a hatched band 132 obtained by orthogonally projecting the (periphery) of the magnet yoke 13 onto the XZ plane and translating it along the motion direction 101 represents the region of highest magnetic interaction between the permanent magnet 131 and the coil 14. Extending this band 132 parallel to the Y axis on the stator unit 11 indicates the area that receives the highest magnetic field strength when the permanent magnet 131 passes through. This area is indicated by the hatched band 132 in FIG. 4 . Combining the hatched bands in FIGS. 3 and 4 , a volume of high magnetic interaction can be obtained. Therefore, the sensor 161 needs to be positioned outside this volume. As can be seen from FIG. 4 , advantageously, by placing the sensor 161 outside the volume indicated by the band 132 so that the sensor 161 senses the passing magnet yoke 13, the sensor can measure the leakage magnetic field 134 of the permanent magnet. In this embodiment of the invention, the sensor 161 is positioned to sense the leakage field 134 of the magnet yoke 13 / permanent magnet 131 rather than the main magnetic field as the mover 12 passes along each of the stator units 11.

[0027] By projecting both the band 132 and the sensor 161 and checking whether they overlap, it can be determined whether the sensor 161 is positioned outside the band 132. Referring to FIG. 2, the open arrow indicates the direction of the magnetic axis of the permanent magnet 131, which runs from north to south. The magnetic field lines in the air gap 18 travel substantially parallel to the Y axis before deflecting inside the stator unit 11. The XZ plane substantially corresponds to a plane perpendicular to the magnetic field lines inside the air gap 18. The XZ plane is also parallel to the direction of motion 101. Therefore, a median plane 181 of the air gap 18 can be defined, which is parallel to the XZ plane. The median plane 181 is located midway between the surface 133 of the magnet yoke 13 that is exposed to the air gap 18 and faces the stator unit 11, and the surface 123 of the stator unit 11 that is exposed to the air gap. By orthogonally projecting the band 132 and the sensor 161 onto the median plane 181, or alternatively onto any other plane parallel to the XZ plane, it becomes possible to determine whether an overlapping region between the band 132 and the sensor 161 exists.

[0028] Advantageously, the sensor 161 is positioned in a position where the magnetic field strength of the magnet yoke 13 is 20% lower, advantageously 15% lower, advantageously 10% lower than the (average) magnetic field in the air gap 18 inside the strip 132 .

[0029] Outside the band 132, there are several advantageous positions for positioning the sensor 161. As shown in Figure 1, the sensor 161 is located directly below the coil 14 (or alternatively directly above the coil 14), i.e., the sensor 161 is located at approximately the same position as the coil 14 along the direction of motion 101 (i.e., along the X-axis). Compared to a case where the sensor is located in front of or behind the coil 14 along the direction of motion 101, a below or above position has the advantage that the stator units 11 (and therefore the coil 14) can be placed closer to each other, thereby increasing the force density of the linear motor, as the available volume is used more efficiently.

[0030] Referring to FIG. 2 , the sensor 161 is located at the same Y-direction position as the permanent magnet 131. That is, the sensor 161 is located directly below (or above) the permanent magnet. More generally, the sensor 161 can be located at the same Y-direction position as the mover 12. Alternatively, as shown in FIG. 5 , the sensor 161 can be located at the same Y-direction position as the coil 14, that is, directly below (or above) the coil. More generally, the sensor 161 can be located at the same Y-direction position as the stator unit 11. Alternatively, the sensor 161 can be located at the same Y-direction position as the air gap 18. At either of the above positions outside the band 132, the magnetic field generated by the coil 14 is weaker, making the sensor signal less susceptible to the coil magnetic field. Furthermore, at these positions, the sensor is located further away from the thermal hotspot of the linear motor, which typically corresponds to the area of the coil 14. Therefore, the sensor is less likely to be heated by heat generated by the current flowing through the coil.

[0031] The position detection device 16 comprises a printed circuit board (PCB) 162 on which the sensor 161 is arranged and may comprise corresponding electronics. Advantageously, the PCB 162 is fixed to the stator unit 11, while the electronics are integrated into the stator unit (PCB 162) or as an add-on module. Advantageously, the stator unit comprises a support 111, in which the sensor 161 is embedded. The support 111 is made of a non-magnetic material, for example aluminum. Advantageously, the support 111 is located outside the area of the band 132.

[0032] Advantageously, each of the position detection devices 16 has a rotational speed τ p At least two sensors 161 are positioned at equal distances of τ p is the pole pitch of the magnet yoke 13, and N is the number of sensors 161. With this arrangement, multiple displacement waveforms such as those shown in FIG. 7 can be obtained, so that not only the position of the mover 12 but also the direction of movement of the mover 12 can be determined. The amplitude of the sensor signal depends on the position of the sensor 161 relative to the magnet yoke 13, the size of the magnet yoke, the size of the permanent magnet, and the material of the permanent magnet. The frequency of the sensor signal is determined by the speed and the pole pitch τ p Depends on.

[0033] 6, the drive unit 15 comprises a calculation unit 154 for executing a position sensor algorithm configured to determine the position of the magnet yoke 13 based on the magnetic field measured by the sensor 161. The magnetic field B measured by the sensor 161 m,1 ,...,B m,N Based on this, an algorithm for calculating the position of the magnet yoke 13 can be derived as follows: Initially, there is no magnet yoke 13 above the stator unit, so no magnetic field is measured and therefore no position can be determined. The magnet yoke is considered "out of range" and r=0.

[0034] Since only the magnetic field due to the magnet yoke 13 is of interest, it is necessary to compensate for the magnetic field generated by the coil 14. To this end, the calculation unit 154 comprises a coil magnetic field compensation unit 155 operable as follows: The magnetic field of the coil 14 can be compensated by measuring the drive current flowing through the coil and multiplying it by a compensation gain matrix according to Equation (1).

[0035]

number

[0036] where B m,i is a vector containing the magnetic field measurements by the sensors 161, I is a vector of measured phase currents in the coils, and C is the compensation matrix. Since the measured magnetic field has an approximately linear dependence on the magnitude of the current, the compensated magnetic field measurements can be completely written for N sensors 161 and P phases as:

[0037]

number

[0038] In C, each element describes the coupling coefficient of the phase currents to each of the sensors 161, for example in Tesla / Ampere. The compensation matrix C is -Measure the magnetic field without the magnet yoke while passing current through each phase. - analytically derived, and / or -By conducting finite element analysis, Obtained. If the coil units are installed very close to each other, the current measurements of adjacent drivers can be shared with each other and reflected in a correction matrix to improve accuracy if necessary.

[0039] The presence of the magnet yoke 13 (mover 12) can be detected by one or a combination of various methods. Suitable methods include: - verifying that the amplitude of each of the sensor signals is greater than a predetermined threshold; - checking that the sum of the amplitudes of each of the sensor signals is greater than a predetermined threshold; - checking that the sum of the squares of each of the sensor signals is greater than a predetermined threshold; Contains: Depending on the method and thresholds, the magnet yoke can be detected quickly, at the cost of less accuracy, as the magnetic field is small and insufficient to extract accurate position information.

[0040] The calculation unit 154 includes a counting unit 156 that detects "in range." When the magnet yoke is located within the sensor's range, if the magnet yoke enters from the right, counter k is reset to zero, and if the magnet yoke enters from the left, counter k is reset to N. p / 2-1 (where N p is the number of poles of the magnet yoke). - checking and comparing the signals of each of the sensors 161, and / or By utilizing two sensor groups (left and right), as shown in FIG. 1, where N=3, In this case, the position information from both sets of sensors is combined using a windowing function.

[0041] In the following description, it is assumed that a single group of sensors 161 is used. When the magnet yoke 13 is detected, the phase information is calculated by the sensor measurement B c,i can be estimated from

[0042]

number

[0043] where atan2 is the arctangent function with two arguments taking into account the appropriate quadrant. si and K. ci is given as shown in [Number 4].

[0044]

number

[0045] Since this formula can only yield unique values within the range of 0 to 2π, a counter k is included that is reset the instant the magnet yoke is detected and counts the number of transitions between 2π and 0 or 0 and 2π. Therefore, absolute position information is obtained by [Equation 5].

[0046]

number

[0047] where x CU is the overall position of the coil unit relative to the reference point.

[0048] By using the atan2 function, the accuracy of the method becomes independent of the amplitude of the waveform shown in FIG. 7 and therefore becomes largely independent of the lateral displacement in the Y and Z directions. Lateral displacement in the Y and Z directions still slightly affects the harmonic content of the waveform shown in FIG. 7. To minimize this effect, double-sided measurement can be considered, as shown in FIG. 2. A dual set of sensors 161 is symmetrically positioned with respect to the coil array at the same Y position. Alternatively, a dual set of sensors 161, 161′ is symmetrically positioned with respect to the magnet yoke 13. Double-sided measurement can provide better robustness against lateral displacement in the Y direction. In this case, both measurements are combined as shown in Equation 6.

[0049]

number

[0050] where B ml,i is the signal sensed by the left sensor 161′, and B mr,i is the signal sensed by the right sensor 161. This is particularly useful when there are large variations in the air gap 18.

[0051] Referring to FIG. 7, sensor 161 can sense the end effects of approaching or receding magnet yoke 13 due to the finite length of the magnet yoke. The signals are represented in regions 71 and 72, respectively. These end effects allow the moment when the magnet yoke enters the sensing region to be detected, thereby measuring absolute position. In region 70, the magnet yoke is located within range, and relative measurements are performed as described above. Thus, such a sensor can integrate both absolute and relative position sensing functions into one and the same sensing element.

[0052] The above measurement procedure is only possible if sensor 161 is continuously operated below the saturation level, which is advantageously made possible by placing sensor 161 in the above-mentioned position. Advantageously, when sensor 161 is placed in the above-mentioned position, the magnetic field level sensed by sensor 161 is 100 mT or less, advantageously 90 mT or less. In the absence of saturation, the signal captured by sensor 161 is sinusoidal as shown in Figure 7, allowing a completely analog measurement of the yoke position to be performed. This eliminates the need for a linear encoder, further reducing the cost of the linear permanent magnet motor of the present invention.

[0053] 6, the drive 15 receives the outputs H1,...,H of the sensor 161 (related to the magnetic field of the passing magnet yoke 13). N and based on the output of the sensor 161, the phase currents I1, I2, ..., I PTo this end, the detecting and counting unit 156 is configured to determine the amplitude of the magnet yoke. To this end, the detecting and counting unit 156 outputs a binary indicator r indicating whether an "in-range" position of the magnet yoke has been detected (e.g., r=1 if the magnet yoke is located in-range, and r=0 if the magnet yoke is located out-of-range), and the absolute position information x obtained from the calculation unit 154. MY and the rectifier unit 158 and the phase currents I1, I2, ..., I P The signal is supplied to a motion control unit 157 which is coupled to an end stage 159 which outputs a [Explanation of symbols]

[0054] 10 Linear motor 11 Stator unit 12 Mover 13 Magnet yoke 14 coils 15 Drive unit 16 Position detection device 101 Direction of motion 111 Support 131 Permanent Magnets 132 Obi 161 Sensors 162 Printed Circuit Board (PCB)

Claims

1. a stator unit (11) comprising at least one coil (14); a mover (12) having an array of permanent magnets (131), the mover (12) being arranged to move along a direction of motion (101), the array of permanent magnets (131) being spaced apart from a stator unit (11) by an air gap (18) configured to generate traction by interaction of electromagnetic fields generated by the array of permanent magnets (131) and at least one of the coils (14); a position detection device (16) operable to determine the position of the mover (12) relative to the stator unit (11); A linear permanent magnet motor (10) comprising: the position detection device (16) comprises a sensing element (161) operable to sense a magnetic field of the array of permanent magnets (131), the sensing element being fixed to the stator unit (11); The sensing element (161) is arranged so that when the array of permanent magnets is arranged corresponding to the sensing element, the sensing element is located within a leakage magnetic field (134) of the array of permanent magnets (131); the linear permanent magnet motor further comprising a control unit (15) operable to read the output of the sensing element (161); the control unit is operable to compensate an output of the sensing element (161) for a magnetic field of at least one of the coils (14) based on a measurement of a drive current flowing through the at least one of the coils (14); The control unit is operable to compensate the output of the sensing element (161) for the magnetic field of at least one of the coils (14) based on the drive current multiplied by a compensation gain matrix.

2. 2. The linear permanent magnet motor of claim 1, wherein the air gap (18) is interposed between the array of permanent magnets (131) and at least one of the coils (14).

3. 3. A linear permanent magnet motor as described in claim 1 or 2, characterized in that the array of permanent magnets (131) has a surface (133) exposed to the air gap (18), the surface (133) is flat and parallel to the direction of motion (101), and the air gap has a median plane (181) parallel to the surface (133).

4. 4. The linear permanent magnet motor of claim 3, wherein the sensing elements (161) are arranged such that an orthogonal projection of the sensing elements onto the median plane (181) is located outside a band (132) formed by an orthogonal projection of the array of permanent magnets (131) onto the median plane (181) when moving along the direction of motion (101).

5. 5. The linear permanent magnet motor according to claim 3, wherein the sensing element (161) is positioned at a position corresponding to the air gap (18) along a direction perpendicular to the median plane (181).

6. The linear permanent magnet motor according to claim 3 or 4, characterized in that the sensing element (161) is positioned at a position corresponding to the mover (12) along a direction perpendicular to the median plane (181).

7. 7. The linear permanent magnet motor of claim 6, wherein the sensing element (161) is positioned along a direction perpendicular to the median plane (181) at a position corresponding to the array of the permanent magnets (131).

8. The linear permanent magnet motor according to claim 3 or 4, characterized in that the sensing element (161) is arranged at a position corresponding to the stator unit (11) along a direction perpendicular to the median plane (181).

9. A linear permanent magnet motor as described in any one of claims 1 to 8, characterized in that the sensing element (161) is positioned along the direction of motion (101) at a position corresponding to the position of at least one of the coils (14).

10. A linear permanent magnet motor according to any one of claims 1 to 9, characterized in that the sensing element (161) is embedded in a support (111) made of a non-magnetic material and fixed to the stator unit (11).

11. 11. A linear permanent magnet motor according to claim 10, characterised in that the support is positioned so that an orthogonal projection of the support relative to the median plane (181) is outside the band (132).

12. A linear permanent magnet motor according to claim 10, which is dependent on claim 4, characterized in that the support (111) protrudes from the stator unit (11) towards the air gap (18) along a direction perpendicular to the median plane (181).

13. A linear permanent magnet motor as described in any one of claims 1 to 12, characterized in that the position detection device (16) comprises a plurality of the sensing elements (161) arranged on a first side of the array of the permanent magnets (131) facing the air gap (18) and on a second side of the array of the permanent magnets (131) opposite to the first side.

14. A linear permanent magnet motor as described in any one of claims 1 to 13, characterized in that the position detection device (16) comprises a plurality of the sensing elements (161) arranged on a first side of at least one of the coils (14) facing the air gap (18) and on a second side of at least one of the coils (14) opposite to the first side.

15. 15. A linear permanent magnet motor according to claim 13 or 14, characterized in that the position detection device (16) comprises a pair of the sensing elements and is operable to determine position by differential measurement between the pair of the sensing elements.

16. The linear permanent magnet motor according to any one of claims 1 to 15, characterized in that the stator units (11) are a plurality of units arranged side by side along the direction of motion (101).

17. 17. The linear permanent magnet motor according to claim 16, wherein the linear permanent magnet motor comprises one position detection device (16) for each of a plurality of the stator units (11).

18. A linear permanent magnet motor, characterized in that the mover (12) comprises a portal structure (122) and a set of arrays of the permanent magnets (131) attached to the portal structure at the same position along the direction of motion (101) and on both sides of at least one coil (14). A linear permanent magnet motor according to any one of claims 1 to 17.

19. the permanent magnets (131) of the array of permanent magnets are arranged side by side along the direction of movement (101) with alternating polarities and spaced apart at the same pitch; A linear permanent magnet motor as described in any one of claims 1 to 18, characterized in that the position detection device (16) comprises a plurality of the sensing elements (161) arranged apart along the direction of motion at a distance equal to the pitch divided by the number of the sensing elements.

20. A linear permanent magnet motor according to any one of the preceding claims, characterized in that the sensing element (161) is a Hall effect sensor.

21. the linear permanent magnet motor includes a control unit (15) operable to read the output of the sensing element (161); 21. The linear permanent magnet motor of claim 1, wherein the control unit is operable to determine an amplitude of a phase current to be applied to at least one of the coils (14) based on an output of the sensing element.

Images