Patent ID: 8913229

Claim:
A multi-stage system comprising: a stator extending substantially parallel to a first direction; a first stage that is moveable relative to the stator in the first direction; a second stage that is moveable relative to the stator in the first direction; wherein the first and second stage are each provided with a system of magnets to generate a magnetic field, wherein the stator is provided with a plurality of electric coils, said electric coils being configured to interact with the magnetic fields generated by the system of magnets of the first and second stage in order to generate forces on the first and second stage to position them relative to the stator, a sensor configured to determine the position of the first and second stage relative to the stator; a controller configured to position the first and second stage relative to the stator in the first direction, wherein the controller is configured to: determine the position of the first stage relative to the stator in the first direction based on an output of the sensor; select a first subset of electric coils that are capable of having a non-negligible interaction with the magnetic field of the system of magnets of the first stage in the determined position of the first stage; determine the position of the second stage relative to the stator in the first direction based on an output of the sensor; select a second subset of electric coils that are capable of having a non-negligible interaction with the magnetic field of the system of magnets of the second stage in the determined position of the second stage; and activate the electric coils of the first and the second subset in order to position the first and the second stage relative to the stator, wherein the controller is configured, prior to activating the electric coils of the first and second subset, to: determine the electric coils that are part of both the first and the second subset; and exclude at least one electric coil that is part of both the first and the second subset from activating.