Patent ID: 8675211

Claim:
A position detecting device comprising: a moving part provided with vanes (F 1 , F 2 ) alternating with windows (W 1 ) on no more than a single track of alternating vanes and windows along a single axis extending in a moving direction of the moving part, and a fork light barrier for detecting movement of the moving part, wherein the fork light barrier is arranged along the movement direction of the moving part, and wherein the fork light barrier comprises: at least one light-emitting element on a limb of the fork light barrier, said element emitting light to an opposing limb during operation; at least one first, one second and one third light sensor (FT 1 to FT 3 ) on the opposing limb, wherein the second light sensor (FT 2 ) is arranged between the first light sensor (FT 1 ) and the third light sensor (FT 3 ) in the movement direction, and wherein a separation (L 1 ) in the movement direction between the first light sensor (FT 1 ) and the second light sensor (FT 2 ) is smaller than a separation in the movement direction between the second light sensor (FT 2 ) and the third light sensor (FT 3 ), wherein the fork light barrier and the moving part are arranged such that the movement of the moving part causes the windows and vanes to move between the limbs, a first light incidence state from the at least one light-emitting element onto either only the first sensor (FT 1 ) or simultaneously onto the second and third light sensors (FT 2 , FT 3 ) signals at least one of a movement direction and an incremental movement of the moving part, and a second light incidence state from the at least one light-emitting element onto the first, second and third light sensor (FT 1 , FT 2 , FT 3 ) signals a reference position of the moving part, wherein the first incidence state is a light incidence interruption or a light incidence resumption, and the second incidence state is a simultaneous light incidence interruption or a simultaneous light incidence resumption.