Device for sensing side positioning of wafers

摘要

An apparatus is provided which determines whether a member is placed correctly on a base. The apparatus comprises an arm mounted for movement toward and away from the base which normally holds the member in place on the base. The arm has a projection which extends a distance beyond the surface of the arm and toward the base. When the member is in a first or third position relative to the base, the projection makes contact with the member. When the member is in a second position relative to the base, the projection clears the member and is positioned in close proximity to the side of the base. The apparatus determines the position of the member by sensing with a photosensor a corresponding position of the arm displaced from the base. The displacement distance of the arm relative to the base is due to the distance that the projection extends beyond the surface of the arm.