Patent ID: 8287083

Claim:
A position detecting device for detecting a position of an object, comprising: a light emitting portion that emits light; a light receiving portion that receives the light from the light emitting portion; a scale that is arranged between the light emitting portion and the light receiving portion, and includes a position detecting pattern and a smear detecting pattern; a control portion which determines position from the position detecting pattern and determines smear from the smear detecting pattern; and a sensor position switching unit that moves a photosensor having the light emitting portion and the light receiving portion to switch a state of detecting the position detecting pattern and a state of detecting the smear detecting pattern, wherein the position detecting pattern has a first light transmitting portion for transmitting the light from the light emitting portion and a first light interception portion for intercepting the light from the light emitting portion which are alternately arranged in a detection range of the object, wherein the smear detecting pattern for detecting smear of the scale has a second light transmitting portion for transmitting the light from the light emitting portion and a second light interception portion for intercepting the light from the light emitting portion which are alternately arranged, wherein the scale is a liner scale having a long plate shape, and wherein the smear detecting pattern is arranged at an outer side of the position detecting pattern in a longitudinal direction of the linear scale.