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Browse Prior Art Database

TACHOMETER START OF SCAN DETECTOR

IP.com Disclosure Number: IPCOM000025292D
Original Publication Date: 1984-Jun-30
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 84K

Publishing Venue

Xerox Disclosure Journal

Abstract

The majority of laser scanning systems which exist today use one or more external photodetector circuits to determine the position of the laser spot for start of scan applications. There are several versions of these in use but all of them require the detector to be positioned somewhere in the path of the scanning beam at a reasonable throw from the scanning motor. There is proposed a method in which tachometers are incorporated into the motor housing and used to detect the position of the shaft (and thus the laser spot position) for a simple two facet scanning system. The cost savings in a production environment could be substantial by eliminating the handling and alignment of an external device during manu-facture and service of a printer.

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KEROX DISCLOSURE JOURNAL

TACHOMETER START OF SCAN

DETECTOR

Louis D. Mailloux

Charles H. Russell

The majority of laser scanning systems which exist today use one or more external photodetector circuits to determine the position of the laser spot for start of scan applications. There are several versions of these in use but all of them require the detector to be positioned somewhere in the path of the scanning beam at a reasonable throw from the scanning motor. There is proposed a method in which tachometers are incorporated into the motor housing and used to detect the position of the shaft (and thus the laser spot position) for a simple two facet scanning system. The cost savings in a production environment could be substantial by eliminating the handling and alignment of an external device during manu- facture and service of a printer.

It is already known in the art to use special motors with tachometers built into them. As an example, a cylindrical magnet is mounted on the motor shaft and rotated inside the tach assembly. This consists of many turns of wire in a simple coil configuration on a plastic form, with a two piece structure of steel surrounding it to direct the path of the magnetic field.

Tests of these tachometers have shown that a two pole magnet does not give the shaft position accurately enough. When a sixteen pole magnet was used, the positional information was much more precise. The voltage induced in the coil is the result of the sum of the magnetic coupling effects produced by the eight adjacent circumferential pole pairs....