US 6,137,580 AGranted

Autofocus system

AssigneeCreo Inc.

InventorDaniel Gelbart

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Abstract

A method and apparatus for an improved autofocus in an optical system is presented. The improved autofocus system uses distinct optics from those of the primary optical system. Although optically distinct, physically, the autofocus optics are mechanically linked to the optical output stage of the primary optical system. The optical separation of the autofocus optics from those of the primary optical system overcomes the trade-offs associated with trying to combine the primary optical function and focus in the same beam. In particular, the autofocus beam is not blinded by a more powerful write beam. The physical integration of the autofocusing optics with the optical output stage of the primary optical system overcomes the difficulties associated with using external distance sensors. In particular, the autofocusing system is not susceptible to steady state error because the autofocus sensor is a true null detector.

Claims18

Dependent claims

An apparatus for maintaining a desired separation distance between an object and an optical output stage of a primary optical system, said apparatus comprising:

(a) a laser source operative to generate an incident laser beam;
(b) a pair of optical elements rigidly attached to said optical output stage on either side thereof,
a first of said pair of optical elements operative to deflect said incident laser beam towards said object,
said object reflecting the incident beam, creating a reflected beam traveling back towards said optical output stage,
a second of said pair of optical elements operative to deflect said reflected beam;
(c) a position sensitive detector operative to receive said reflected beam on an input surface thereof and to provide an output signal representative of a location of the reflected beam on said input surface,
said location of the reflected beam on said input surface being representative of an actual separation between said object and the optical output stage of said primary optical system;
(d) a control loop operative to interpret the output signal produced by said position sensitive detector and output a corresponding control signal;
said control signal being calculated in such a way so as to zero a difference between the desired separation and the actual separation, as measured by the position sensitive detector, of said object and said optical output stage;
and
(e) an output stage positioner operative to receive the control signal from said control loop and to move said optical output stage in proportion to said control signal so as to maintain the desired separation between said object and said optical output stage.

8 more elements

A method for maintaining a desired separation distance between an object and an optical output stage of a primary optical system, said method comprising the steps of:

(a) generating an incident laser beam from a laser source;
(b) deflecting said incident beam with a first optical element, which is rigidly attached to said optical output stage,
said incident beam then proceeding to impinge on said object and reflect off of it becoming a reflected beam;
(c) deflecting said reflected beam with a second optical element, which is rigidly attached to said optical output stage;
(d) measuring a location of said reflected beam when it impinges on an input surface of a position sensitive detector,
said location of the reflected beam on said input surface being representative of an actual separation between said object and the optical output stage of said primary optical system;
(e) calculating a feedback signal based on:
(i) the actual separation between said object and the optical output stage of said primary optical system as determined in said measuring step, and
(ii) the desired separation between said object and the optical output stage of said primary optical system,
said feedback signal being calculated in such a way as to zero a difference between the desired separation and the actual separation of said object and said optical output stage;
and
(f) using said feedback signal to control an output stage positioner,
said output stage positioner moving said optical output stage in proportion to said feedback signal, so as to maintain the desired separation between said object and said optical output stage.

10 more elements

Dependencies are inferred from the claim text.