Apparatus and method for sensing position of non-orbital movable truck

There is provided a position sensing apparatus when a non-orbital movable truck moves over a spherical surface, a cylindrical surface, or a flat surface, which is capable of position sensing even when, e.g., the non-orbital movable truck circumferentially moves over the spherical surface or the cylindrical surface to be hidden from the position sensing apparatus. A second linear encoder is disposed which includes a wire in a main body thereof to output an amount by which the wire is withdrawn as an encoder value. The tip of the wire of the second linear encoder is fixed to a position at the non-orbital movable truck to which the tip of the wire of a linear encoder is fixed. From an amount by which the wire of the linear encoder is withdrawn and the amount by which the wire of the second linear encoder is withdrawn, the position of the non-orbital movable truck is calculated in a calculation device.