Position sensor for a mover in a long stroke linear permanent magnet motor
View Patent ↗A linear permanent magnet motor may include a stator unit having a coil, a mover including an array of permanent magnets, and a position sensing device operable to determine a position of the mover. The mover is arranged to move along a motion direction. The position sensing device has a sensing element operable to sense a magnetic field of the array of permanent magnets The sensing element is fixed to the stator unit. The array of permanent magnets is spaced apart from the stator unit by an air gap in which electromagnetic fields created by the array of permanent magnets and by coil are configured to interact thereby generating traction. The sensing element is positioned such that it is within a magnetic leakage field of the array of permanent magnets when the array of permanent magnets is positioned in correspondence with the sensing element.
1. A linear permanent magnet motor, comprising:
a stator unit comprising at least one coil;
a mover comprising an array of permanent magnets, wherein the mover is arranged to move along a motion direction, the array of permanent magnets being spaced apart from the stator unit by an air gap in which electromagnetic fields created by the array of permanent magnets and by the at least one coil are configured to interact to generate traction;
a position sensing device operable to determine a position of the mover relative to the stator unit,
wherein the position sensing device comprises a sensing element operable to sense a magnetic field of the array of permanent magnets, the sensing element being fixed to the stator unit,
wherein the sensing element is positioned such that the sensing element is within a magnetic leakage field of the array of permanent magnets when the array of permanent magnets is positioned in correspondence with the sensing element; and
a control unit operable to read an output of the sensing element,
wherein the control unit is operable to compensate the output for a magnetic field of the at least one coil based on a measurement of a drive current through the at least one coil.
2. The linear permanent magnet motor of claim 1 , wherein the air gap is interposed between the array of permanent magnets and the at least one coil.
3. The linear permanent magnet motor of claim 1 , wherein the sensing element is positioned along the motion direction at a position in correspondence of a position with the at least one coil.
4. The linear permanent magnet motor of claim 1 , wherein the position sensing device comprises a plurality of the sensing element arranged at a first side of the at least one coil towards the air gap and at a second side of the at least one coil opposite the first side.
5. The linear permanent magnet motor of claim 1 , wherein the mover comprises a portal structure and a pair of the array of permanent magnets mounted on the portal structure at a same position along the motion direction and at opposite sides relative to the at least one coil.
6. The linear permanent magnet motor of claim 1 , wherein the permanent magnets in the array of permanent magnets are arranged juxtaposed along the motion direction with alternating polarity and spaced apart with a same pitch, and wherein the position sensing device comprises a plurality of the sensing elements spaced apart along the motion direction at a distance equal to the pitch divided by a number of the plurality of sensing elements.
7. The linear permanent magnet motor of claim 1 , wherein the control unit is operable to determine an amplitude of a phase current applied to the at least one coil based on the output of the sensing element.
8. The linear permanent magnet motor of claim 1 , wherein the magnetic leakage field consists essentially of a portion of the electromagnetic field generated by the array of permanent magnets, wherein the portion does not interact with the electromagnetic field generated by the at least one coil.
9. The linear permanent magnet motor of claim 1 , wherein the control unit is configured to compensate the output of the sensing element for the magnetic field of the at least one coil based on the drive current multiplied by a compensation gain matrix.
10. The linear permanent magnet motor of claim 1 , wherein the position sensing device comprises a plurality of the sensing element arranged at a first side of the array of permanent magnets towards the air gap and at a second side of the array of permanent magnets opposite the first side.
11. The linear permanent magnet motor of claim 10 , wherein the position sensing device comprises a pair of the sensing element and is operable to determine a position by differential measurement between the pair of sensing elements.
12. The linear permanent magnet motor of claim 1 , comprising a plurality of the stator units arranged juxtaposed to one another along the motion direction.
13. The linear permanent magnet motor of claim 12 , comprising one of the position sensing devices for each of the plurality of stator units.
14. The linear permanent magnet motor of claim 1 , wherein the sensing element is embedded in a support made of a non-magnetic material and fixed to the stator unit.
15. The linear permanent magnet motor of claim 14 , wherein the array of permanent magnets has a surface exposed to the air gap, the surface being planar and parallel to the motion direction,
wherein the air gap has a median plane parallel to the surface,
wherein the sensing element is positioned such that an orthogonal projection of the sensing element on the median plane falls outside a band formed by an orthogonal projection of the array of permanent magnets on the median plane when moving along the motion direction, and
wherein the support is positioned such that an orthogonal projection of the support on the median plane falls outside the band.
16. The linear permanent magnet motor of claim 14 , wherein the array of permanent magnets has a surface exposed to the air gap, the surface being planar and parallel to the motion direction,
wherein the air gap has a median plane parallel to the surface,
wherein the sensing element is positioned such that an orthogonal projection of the sensing element on the median plane falls outside a band formed by an orthogonal projection of the array of permanent magnets on the median plane when moving along the motion direction, and
wherein the support projects from the stator unit along a direction perpendicular to the median plane towards the air gap.
17. The linear permanent magnet motor of claim 1 , wherein the array of permanent magnets has a surface exposed to the air gap, the surface being planar and parallel to the motion direction, wherein the air gap has a median plane parallel to the surface.
18. The linear permanent magnet motor of claim 17 , wherein the sensing element is positioned such that an orthogonal projection of the sensing element on the median plane falls outside a band formed by an orthogonal projection of the array of permanent magnets on the median plane when moving along the motion direction.
19. The linear permanent magnet motor of claim 17 , wherein the sensing element is positioned along a direction perpendicular to the median plane at a position in correspondence with one of the air gap, the stator unit, and the mover.
20. The linear permanent magnet motor of claim 17 , wherein the sensing element is positioned along a direction perpendicular to the median plane at a position in correspondence with the mover, wherein the sensing element is positioned along a direction perpendicular to the median plane at a position in correspondence with the array of permanent magnets.