Patent Number: 
Section: claims

1. A lithographic apparatus comprising:a projection system configured to project a patterned radiation beam onto a target portion of a substrate, said projection system including a movable optical element configured to change, by a displacement thereof, a position of the projected patterned radiation beam;an optical element actuator configured to move the optical element;a first sensor configured to provide a position signal representative of the position of the projected radiation beam;a second sensor configured to determine a position of the movable optical element; anda projection system controller, operationally connected to the optical element actuator and configured to drive the optical element actuator based on the position signal provided by the first sensor and an output of the second sensor so as to control the position of the projected radiation beam. 2. The lithographic apparatus of claim 1, wherein the first sensor is operationally connected to the projection system controller, and wherein the projection system controller is arranged to control the optical element actuator based on the position signal provided by the first sensor. 3. The lithographic apparatus of claim 2, wherein the first sensor comprises a line of sight sensor that is configured to determine a line of sight through the projection system. 4. The lithographic apparatus of claim 3, wherein the line of sight sensor is configured to provide a position signal representative of the position of the projected radiation beam with respect to a metrology frame. 5. The lithographic apparatus of claim 2, wherein the first sensor is configured to provide a position signal representative of the position of the projected radiation beam with respect to the projection system, a substrate table that holds the substrate, or a metrology frame. 6. The lithographic apparatus of claim 2, wherein the position of the projected patterned radiation beam is controlled by rotating said movable optical element. 7. The lithographic apparatus of claim 2, wherein the projection system controller comprises:(i) a control path extending from a setpoint input to the optical element actuator, the control path comprising a position controller,(ii) a first feedback path extending from the second sensor, configured to determine a position of the movable optical element, to the setpoint input, and(iii) a second feedback path extending from the first sensor to the setpoint input, the second feedback path comprising a translation gain function. 8. The lithographic apparatus of claim 7, wherein the first feedback path and the second feedback path each include a filter, a filter transfer function of the filter of one of the first and second feedback paths having a substantially complementary filter characteristic of the filter transfer function of the other one of the first and second feedback paths. 9. The lithographic apparatus of claim 7, wherein the first feedback path and the second feedback path comprise a common filter having a first feedback path input and a second feedback path input and a common output, a filter transfer function from the first and second feedback path inputs to the common output having a substantially complementary filter characteristic. 10. The lithographic apparatus of claim 1, further comprising a position detection system configured to detect a position of the substrate, wherein the projection system controller is adapted to drive the optical element actuator to position the movable optical element so as to irradiate the substrate substantially at a desired position, wherein the positioning of the moveable optical element is based on desired position information that include said desired position and on a position of the substrate detected by the position quantity detection system. 11. The lithographic apparatus of claim 10, wherein the desired position information comprises a desired position of the substrate table, wherein the projection system controller comprises a substrate table position control loop configured to control a position of the substrate table, and wherein the projection system controller is adapted to drive the optical element actuator based on an error signal of the substrate table position control loop so as to compensate for a difference between the position of the substrate table and the desired position of the substrate table. 12. The lithographic apparatus of claim 10, wherein the projection system controller comprises an actuator control loop configured to control displacements of said movable optical element and an actuator feed forward path that extends from said substrate table position control loop to the actuator control loop, said actuator feed forward path having a position error signal of the substrate table position control loop as input. 13. The lithographic apparatus of claim 12, wherein the controller further comprises a set point feed forward path that extends from the substrate table position control loop to the set point input of the actuator control loop, said set point feed forward path having said position error signal of the substrate table position control loop as input. 14. The lithographic apparatus of claim 13, further comprising a patterning device support constructed to support a patterning device, the patterning device capable of imparting the radiation beam with a pattern in its cross-section to form the patterned radiation beam, wherein the patterning device support is displaceable by a patterning device actuator which is drivable by the projection system controller, and wherein the projection system controller is arranged to drive the patterning device actuator to position the patterning device in an object plane of the projection system. 15. The lithographic apparatus of claim 10, wherein the desired position information comprises a desired position of the patterned radiation beam as projected by the projection system, wherein the projection system controller is adapted to drive the optical element actuator, based on the desired position of the patterned radiation beam as projected by the projection system, to position the radiation beam to irradiate the desired portion of the substrate. 16. The lithographic apparatus of claim 1, wherein the movable optical element comprises a mirror disposed along an optical path of the projection system. 17. The lithographic apparatus of claim 16, wherein, the mirror is located proximate a projection output of the projection system. 18. The lithographic apparatus of claim 1, wherein the optical element actuator includes a pneumatic motor, an electric motor or a piezo electric element. 19. A device manufacturing method comprising:projecting a patterned beam of radiation onto a target portion of a substrate via a projection system;generating a first position signal representative of a position of the projected patterned beam of radiation;generating a second position signal representative of a position of a movable optical element of the projection system; andcontrolling a position of the movable optical element of the projection system based on both position signals so as to control the position of the projected patterned beam of radiation. 20. The device manufacturing method of claim 19, comprising:detecting a position of the substrate,providing a desired position information representing a desired position at which the projected patterned beam of radiation is to irradiate the substrate,driving the optical element actuator, based on the desired position information and the detected position quantity of the substrate, to position the movable optical element so as to irradiate the substrate substantially at the desired position.