Patent ID: 8040520

Claim:
A device for detecting the edges of a workpiece held horizontally on a chuck table of a processing machine, said device comprising: a beam oscillation means for oscillating a detection beam, an objective lens for focusing the detection beam oscillated from the beam oscillation means, and a reflected light detection means for detecting the reflected light of the detection beam applied through the objective lens, wherein the beam oscillation means oscillates the detection beam in such a manner that the optical axis of the detection beam becomes parallel to a center axis of the objective lens at a position offset from the center axis by a predetermined distance; the reflected light detection means detects the edge of the workpiece based on a horizontal positional difference between reflected light obtained when the detection beam oscillated from the beam oscillation means and applied through the objective lens is reflected on an area where the workpiece is not existent and refracted by the objective lens and reflected light obtained when the detection beam is reflected on the workpiece and refracted by the objective lens; and the reflected light detection means includes a line sensor as a position detector for receiving reflected light which is reflected on the area where the workpiece is not existent and refracted by the objective lens and reflected light which is reflected on the workpiece and refracted by the objective lens, wherein the edge portion of the workplace is detected by horizontal displacement of the position where the reflected light is received on the line sensor, and the beam oscillation means and the reflected light detecting means are arranged immediately above the area where the lens is placed, along axes parallel to the center of the objective lens.