Patent ID: 7710549

Claim:
A movable-body-speed-detecting apparatus comprising: a movable body capable of moving linearly and/or circularly; a plate fixed to the movable body, the plate having a predetermined length in a direction in which the movable body moves; and light emission/reception means arranged such that light output from a light-emitting element enters a light-receiving element, wherein the plate has a window section that passes between the light-emitting element and the light-receiving element in accordance with movement of the movable body and that blocks or allows passage of light to the light-receiving element, wherein the light-receiving element has a first light-receiving element and a second light-receiving element that are arranged adjacent to each other in a direction in which the plate moves, and wherein the apparatus comprises light-amount-correcting means for correcting the amount of light emitted from the light-emitting element on the basis of the sum of light-amount detection signals obtained by the first light-receiving element and the second light-receiving element, and speed calculation means for calculating the speed of the movable body by converting the amount of light received by the first light-receiving element or the second light-receiving element into a signal and measuring the signal.