Clamp assembly including permanent magnets and coils for selectively magnetizing and demagnetizing the magnets
A clamp assembly comprises a first clamp including a plurality of magnet devices. Each magnet device includes a permanent magnet and a coil surrounding the permanent magnet. The clamp assembly further comprises a controller for pulsing the coils to selectively magnetize and demagnetize the permanent magnets.
1. A method of clamping a stack, the method comprising:
positioning permanent magnets against a first surface of the stack;
placing a flux-conducting structure against a second surface of the stack; and
applying external magnetic field pulses to the permanent magnets to magnetize and demagnetize the permanent magnets,
wherein applying external magnetic field pulses to the permanent magnets to magnetize the permanent magnets comprises promoting magnetic domain alignment within the permanent magnets sufficient to clamp the stack between the permanent magnets and the flux conducting structure;
wherein applying external magnetic field pulses to the permanent magnets to demagnetize the permanent magnets comprises demoting magnetic domain alignment within the permanent magnets sufficient to reduce a clamping force applied to the stack by the flux-conducting structure and the permanent magnets;
wherein applying external magnetic field pulses is performed in a first direction for magnetizing the permanent magnets; and
wherein applying external magnetic field pulses is performed in a second direction for demagnetizing the permanent magnets, the second direction being opposite the first direction.
2. The method of claim 1 , wherein the permanent magnets are positioned about a process axis.
3. The method of claim 1 , wherein pulse duration is on the order of milliseconds, and clamping cycle is at least ten seconds.
4. The method of claim 1 , wherein the flux-conducting structure includes a plate for providing a flux path.
5. The method of claim 1 , wherein the flux-conducting structure includes a plurality of second magnet devices aligned with the permanent magnets.
6. The method of claim 1 , wherein the permanent magnets are disposed in a robot end effector.
7. The method of claim 6 , wherein applying external magnetic field pulses to the permanent magnets is performed selectively by a controller.
8. The method of claim 6 , wherein positioning permanent magnets against a first surface of the stack is performed by at least one robot.
9. The method of claim 1 , wherein applying external magnetic field pulses comprises applying a single external magnetic field pulse.
10. The method of claim 1 , wherein applying external magnetic field pulses comprises applying at least two external magnetic field pulses.
11. The method of claim 1 further comprising modulating either magnitude or duration of the external magnetic field pulses during magnetization to alter a peak current attained by the pulse.
12. The method of claim 1 , wherein applying external magnetic field pulses to the permanent magnet comprises applying external magnetic field pulses to less than all of the permanent magnets.
13. The method of claim 1 , wherein applying external magnetic field pulses is performed simultaneously for all of the permanent magnets.
14. The method of claim 1 , wherein the permanent magnets are demagnetized prior to being positioned against a first surface of the stack.