Patent ID: 7012201

Claim:
A rotary encoder comprising: a roller of substantially cylindrical shape having a center hole; a tubular inner shaft inserted in and connected to the center hole, the inner shaft having a slit formed at one end along a direction parallel to the axis thereof; a translucent cylindrical light guide shaft inserted in the inner shaft in a manner that one end is surrounded by the slit, the light guide shaft having: a first plane formed at a lower side at one end and in parallel to the axis thereof; a second plane formed at a lower side at the other end in parallel to the axis; a first inclined plane formed above the first plane at an angle of 45 degrees to the axis; and a second inclined plane formed above the second plane at an angle of 45 degrees to the axis and substantially orthogonal to the first inclined plane; a pair of holders securely holding one end of the light guide shaft, and supporting the roller in a rotatable manner through the inner shaft; a light-detecting device disposed under one end of the light guide shaft; and a light-emitting device disposed under the other end of the light guide shaft, wherein light emitted by the light-emitting device enters the light guide shaft at the first plane, is reflected off the first inclined plane and the second inclined plane, led to an outside of the light guide shaft through the second plane, and detected by the light-detecting device when it passes through the slit.