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POSITIONING APPARATUS

  • US 20100076586A1
  • Filed: 10/25/2007
  • Published: 03/25/2010
  • Est. Priority Date: 10/30/2006
  • Status: Abandoned Application
First Claim
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1. Positioning device (11), comprising:

  • a stationary frame (2);

    a displaceable platform (3), arranged for displacement with respect to the frame in at least one displacement direction (x);

    an actuator (4) for displacing the platform with respect to the frame;

    a controller (6) for controlling the actuator;

    a position measuring device (15) for measuring the location of the platform with respect to the frame, the position measuring device (15) comprising;

    a first scale (20) having first scale divisions with a first pitch (P1) fixed to one of the platform and the frame, and a first scanner (23) fixed to the other of the platform and the frame, the first scanner adapted for scanning the first scale and for providing a first scanner output signal (SM1) which depends on the relative position of the first scanner with respect to the first scale, is periodical with a period equal to the first pitch, and within one first pitch distance has a unique relationship with the said relative position;

    a second scale (30) having second scale divisions with a second pitch (P2) fixed to one of the platform and the frame, and a second scanner (33) fixed to the other of the platform and the frame, the second scanner adapted for scanning the second scale and for providing a second scanner output signal (SM2) which depends on the relative position of the second scanner with respect to the second scale, is periodical with a period equal to the second pitch, and within one second pitch distance has a unique relationship with the said relative position;

    wherein the second pitch differs from the first pitch;

    wherein the controller is coupled to receive the first scanner output signal from the first scanner and to receive the second scanner output signal from the second scanner;

    and wherein the controller is designed, on the basis of the received two scanner output signals, to uniquely calculate the position (X) of the platform with respect to the frame in a measuring range (MR) that is larger than the largest of said two pitches (P1;

    P2).

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