Code wheel for a reflective type optical rotary encoder

• US 4,806,751 A
• Filed: 06/29/1988
• Issued: 02/21/1989
• Est. Priority Date: 09/30/1985
• Status: Expired due to Fees

• Current Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Original Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Inventors: Takahashi, Yoshihiro, Abe, Hiraku, Shimojima, Yoji
• Primary Examiner(s): Westin, Edward P.
• Application Number:
  US07/213,468
• Time in Patent Office: 237 Days
• Field of Search: 250/231 SE, 250/237 G, 340/347 P, 356/373-375, 29/572, 29/578
• US Class Current: 359/235
• CPC Class Codes: G01D 5/34707 Scales; Discs, e.g. fixation, fabrication, compensation

Abstract

A code wheel for use with a reflective type optical rotary encoder which can be produced easily and optically read efficiently. The code wheel includes a non-reflective plate, and a reflective plate having a suitable number of notches formed along a periphery thereof and mounted in an overlapping relationship on the non-reflective plate whereby a reflective portion of the code wheel is formed by a face of the reflective plate between each two adjacent notches while a non-reflective portion is formed by a face of the non-reflective plate exposed through the corresponding notch of the reflective plate.

Claims

1. In a code wheel for a reflective type optical rotary encoder in which information such as rotational speed and direction of rotation is determined using a beam of light of a light emitting and detecting means which is irradiated upon and reflected from reflective portions and absorbed by nonreflective portions provided on one side of the code wheel,

the improvement wherein said code wheel comprises:

a nonreflective plate having a light absorbing function;

a reflective plate of a predetermined thickness having a reflective surface on one side thereof and a plurality of notches formed though the thickness of said reflective plate circumferentially along a periphery thereof, said reflective plate being mounted overlappingly on said nonreflective plate, wherein said reflective portions are formed by portions of the reflective surface of said reflective plate between adjacent ones of said notches, while said nonreflective portions are formed by portions of said nonreflective plate exposed through said notches in said reflective plate, and wherein said nonreflective plate has formed around a center axis thereof a protrusion of a predetermined height on which said reflective plate is mounted so that a gap is formed between said nonreflective plate and said reflective plate, and said reflective portions have their light reflective surfaces lying in one plane closer to the light emitting and detecting means which is spaced by a selected spacing from said nonreflective portions in an axial direction of said code wheel, said selected spacing being formed by the thickness of said reflective plate added to the height of said protrusion,

whereby any light nominally reflected from said nonreflective portions is reduced due to said selected spacing in the axial direction provided between said reflective portions and said nonreflective portions, and the difference in light reflectivity between said portions is enhanced and the detecting sensitivity of the optical rotary encoder is improved.