Incremental encoder with direction-indicating shutter

Abstract

A light-transmission-type encoder usable in, e.g., an image scanner, and suitable for detecting both the amount of and the direction of rotation. An image scanner featuring the encoder is used to read an image on an original while utilizing the self-scanning direction of a self-scanning image sensor as the main scanning direction and a direction substantially perpendicular to the main scanning direction as the sub-scanning direction, then transfer a read-image signal to image memory of a host computer for recording and displaying. The encoder includes a rotary body having peripheral slits permitting light transmission therethrough, a shaft integrally supporting the rotary body, a shutter having a slit and being loosely and swingably fitted on the shaft, a spring for causing force of friction between either the shutter and the shaft or the shutter and the rotary body, a first light-emitter and a first light-receiver which are disposed with the rotary-body slits therebetween, and a second light-emitter and a second light-receiver which are disposed with the shutter slit therebetween. With this encoder, the image scanner detects the direction of rotation of the rotary body from the relation in position of the shutter slit with the second light-emitter and light-receiver, and adjusts, in accordance with the detected direction, the position in which the image signal is stored in the image memory.