SENSING POLYGON SPEED WITH CAPACITIVELY COUPLED TACHOMETER
Original Publication Date: 1993-Feb-28
Included in the Prior Art Database: 2004-Apr-06
Xerox Disclosure Journal
It is commonly known to use a rotating polygon for raster scanning in order to expose a photoresponsive surface. For example US. Patent No. 4,349,847 to Traino (Issued Sept. 14, 1982) discloses such a raster output scanner (ROS). The motors used to rotate the polygons in ROS systems require accurate and stable speed control to achieve the desired image quality. Typically, motor control is achieved using a speed or position sensor in a feedback control loop to phase-lock the polygon drive motor to an oscillating signal. The present disclosure, however, is directed toward the use of a capacitively coupled tachometer to sense the polygon rotation. The use of a capacitive tachometer to sense rotation is well-known and is described in U.S. Patent No. 4,779,094 to Lee et al. (Issued Oct. 18,19881, and in U.S. Patents 4,563,683 and 4,477,810 to Tanaka et al. (Issued Jan. 7,1986 and Oct. 16,1984, respectively).