Variable field magnetic couplers and methods for engaging a ferromagnetic workpiece

1. A fixture for holding a ferromagnetic workpiece, the fixture comprising:

a frame;

at least one magnetic coupling device supported by the frame and positioned to support a lower side of the ferromagnetic workpiece, each magnetic coupling device comprising:

a housing having a first side;

a plurality of workpiece contact interfaces supported by the housing and adapted to contact the ferromagnetic workpiece;

a first permanent magnet supported by the housing and having an active N-S pole pair;

a second permanent magnet supported by the housing and having an active N-S pole pair, the second permanent magnet being moveable relative to the first permanent magnet;

an actuator operatively coupled to the second permanent magnet to move the second permanent magnet relative to the first permanent magnet; and

an electronic controller operatively coupled to the actuator, the electronic controller including logic which actuates the actuator to position the second permanent magnet relative to the first permanent magnet in at least each of:

(a) a first state wherein the second permanent magnet has a first position relative to the first permanent magnet to provide a first level of magnetic flux available to the ferromagnetic workpiece at the workpiece contact interfaces, the first level of magnetic flux available to the ferromagnetic workpiece at the workpiece contact interfaces being insufficient to hold the ferromagnetic workpiece relative to the magnetic coupling device; and

(b) a second state wherein the second permanent magnet has a second position relative to the first permanent magnet to provide a second level of magnetic flux available to the ferromagnetic workpiece at the workpiece contact interfaces, the second level of magnetic flux available to the ferromagnetic workpiece at the workpiece contact interfaces being sufficient to hold the ferromagnetic workpiece relative to the magnetic coupling device, the second level of magnetic flux being greater than the first level of magnetic flux.

2. The fixture of claim 1 , wherein the at least one magnetic coupling device includes a plurality of magnetic coupling devices, each of the plurality of magnetic coupling devices has associated pole shoes with workpiece contact interfaces shaped to match a corresponding profile of the ferromagnetic workpiece.

3. The fixture of claim 2 , wherein the plurality of magnetic coupling devices are spaced apart.

4. The fixture of claim 2 , wherein at least one of the workpiece contact interfaces has a non-linear shape to match a non-linear profile of the ferromagnetic workpiece.

5. The fixture of claim 1 , wherein the plurality of workpiece contact interfaces are provided through a plurality of pole shoes which are coupled to the housing.

6. The fixture of claim 1 , wherein the fixture is an inspection fixture.

7. The fixture of claim 6 , further comprising a probe adapted to contact an upper side of the ferromagnetic workpiece to inspect the ferromagnetic workpiece, wherein the second state provides a level of magnetic flux available at the workpiece contact interfaces to hold the ferromagnetic workpiece relative to the fixture and low enough to not alter the operation of the probe inspecting the upper side of the ferromagnetic workpiece.

8. The fixture of claim 1 , wherein the electronic controller actuates the actuator to position the second permanent magnet relative to the first permanent magnet in (c) a third state wherein the second permanent magnet has a third position relative to the first permanent magnet to provide a third level of magnetic flux available to the ferromagnetic workpiece at the workpiece contact interfaces, the third level of magnetic flux being greater than each of the first level of magnetic flux and the second level of magnetic flux.

9. The fixture of claim 1 , further comprising a sensing system supported by the housing, the sensing system including at least one sensor which monitors a level of magnetic flux available to the ferromagnetic workpiece at the workpiece contact interfaces.

10. The fixture of claim 9 , wherein the at least one sensor monitors the level of magnetic flux available to the ferromagnetic workpiece at the workpiece contact interfaces by monitoring a first leakage magnetic flux associated with a first workpiece contact interface of the plurality of workpiece contact interfaces with a first magnetic flux sensor.

11. The fixture of claim 10 , wherein the at least one sensor monitors the level of magnetic flux available to the ferromagnetic workpiece at the workpiece contact interfaces by further monitoring a second leakage magnetic flux associated with a second workpiece contact interface of the plurality of workpiece contact interfaces with a second magnetic flux sensor.

12. The fixture of claim 1 , wherein the second permanent magnet is rotatable relative to the first permanent magnet about an axis intersecting with the second permanent magnet to alter a position of the second permanent magnet relative to the first permanent magnet.

13. The fixture of claim 1 , wherein the second permanent magnet is rotatable relative to the first permanent magnet about an axis in a non-intersecting relationship with the second permanent magnet to alter a position of the second permanent magnet relative to the first permanent magnet.

14. The fixture of claim 13 , further comprising a first platter supported by the housing and a second platter supported by housing, the second platter being moveable relative to the first platter to alter a position of the second permanent magnet relative to the first permanent magnet,

wherein the first platter comprising

a first plurality of spaced apart permanent magnets including the first permanent magnet, each of the first plurality of spaced apart permanent magnets has a north pole side and a south pole side, and

a first plurality of pole portions interposed between adjacent permanent magnets of the first plurality of permanent magnets, wherein the first plurality of permanent magnets are arranged so that each pole portion of the first plurality of pole portions is one of a north pole portion which is adjacent the north pole side of two permanent magnets of the first plurality of permanent magnets and a south pole portion which is adjacent the south pole side of two permanent magnets of the first plurality of permanent magnets;

the second platter comprising

a second plurality of spaced apart permanent magnets including the second permanent magnet, each of the second plurality of spaced apart permanent magnets has a north pole side and a south pole side, and

a second plurality of pole portions interposed between adjacent permanent magnets of the second plurality of permanent magnets, wherein the second plurality of permanent magnets are arranged so that each pole portion of the first plurality of pole portions is one of a north pole portion which is adjacent the north pole side of two permanent magnets of the second plurality of permanent magnets and a south pole portion which is adjacent the south pole side of two permanent magnets of the second plurality of permanent magnets.

15. The fixture of claim 13 , wherein the second permanent magnet is translatable relative to the first permanent magnet to alter a position of the second permanent magnet relative to the first permanent magnet.

16. The fixture of claim 9 , wherein the actuator is a fluid actuator and the at least one sensor monitors the level of magnetic flux available to the ferromagnetic workpiece at the workpiece contact interfaces by monitoring a fluid characteristic of a working fluid of the fluid actuator, the working fluid controls a position of the second permanent magnet relative to the first permanent magnet.

17. The fixture of claim 9 , wherein the actuator is a fluid actuator and the at least one sensor monitors a position of an output of the fluid actuator.