Method for controlling the position of a movable object, a control system for controlling a positioning device, and a lithographic apparatus

A lithography apparatus comprising:

• an illumination system configured to condition a radiation beam;
• a patterning device stage constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
• a substrate stage constructed to hold a substrate;
• a projection system configured to project the patterned radiation beam onto a target portion of the substrate;
• and
• a positioning system configured to control a position of a short stroke module configured to hold one of the substrate or the patterning device in at least a first degree of freedom, the positioning system including
• a first motor assembly including one or more reluctance motors configured to move the short stroke module in the first degree of freedom;
• a second motor assembly including one or more motors of a second type configured to move the short stroke module in the first degree of freedom;
• and
• a control system for controlling at least the first motor assembly, the control system including:
• at least one force sensing element configured to sense an amount of force applied by a corresponding reluctance motor;
• and
• a controller configured to:
• apply a first adjustment to the amount of force applied by the corresponding reluctance motor based on output from a corresponding force sensing element, and
• apply a second adjustment to adjust a size of a gap between a core and a flux carrying bar of the corresponding reluctance motor,
• wherein the second adjustment sets the size of the gap to a first distance in accordance with a first acceleration of the positioning system and sets the size of the gap to a second distance in accordance with a second acceleration of the positioning system.

A method of positioning a movable object in a first degree of freedom, the method comprising:

• providing a motor assembly including one or more reluctance motors configured to accelerate the movable object in the first degree of freedom;
• providing at least one feedback signal representative of an amount of force applied by the motor assembly;
• providing a first control signal to adjust the amount of force applied by the motor assembly based on the at least one feedback signal;
• and
• providing a second control signal to adjust a size of a gap between a core and a flux carrying bar of a corresponding reluctance motor,
• wherein the second adjustment sets the size of the gap to a first distance in accordance with a first acceleration of the movable object and sets the size of the gap to a second distance in accordance with a second acceleration of the movable object.

A method of positioning a short stroke stage of a lithographic apparatus in a first degree of freedom, the method comprising:

• providing a motor assembly including one or more reluctance motors configured to accelerate the short stroke stage in the first degree of freedom, each reluctance motor having a core coupled to a long stroke stage associated with the short stroke stage, a flux carrier bar coupled to the short stroke stage, and a gap between the core and the flux carrier bar;
• providing a first adjustment to the acceleration applied by the corresponding reluctance motor;
• and
• providing a second adjustment to adjust a size of the gap to minimize parasitic effects of a corresponding reluctance motor, wherein the second adjustment sets the size of the gap to a first distance in accordance with a first acceleration of the short stroke stage and sets the size of the gap to a second distance in accordance with a second acceleration of the short stroke stage.

A method of positioning a short stroke stage of a lithographic apparatus in a first degree of freedom, the method comprising:

• accelerating the short stroke stage in a first direction with one or more reluctance motors at a first end of the short stroke stage and one or more additional motors of another type;
• driving the short stroke stage at an approximately constant velocity in the first direction with the one or more additional motors;
• accelerating the short stroke stage in a second direction opposite the first direction with one or more reluctance motors at a second end of the short stroke stage and the one or more additional motors;
• driving the short stroke stage at an approximately constant velocity in the second direction with the one or more additional motors;
• providing a first adjustment to respective amounts of force applied by the one or more reluctance motors at the first and second ends of the short stroke stage as needed based on output from one or more feedback sensors to sense an amount of force applied by a corresponding one of the one or more reluctance motors, and
• providing a second adjustment to adjust a size of a gap between a core and a flux carrying bar of a corresponding reluctance motor to minimize parasitic effects of a corresponding reluctance motor, wherein the second adjustment sets the size of the gap to a first distance in accordance with the acceleration of the short stroke stage in the first direction and sets the size of the gap to a second distance in accordance with the acceleration of the short stroke stage in the second direction.