Linear transmission device

A linear transmission device comprising:

• an elongated shaft member extending along an axial direction and having a helical groove;
• a moving module movably sleeved onto the elongated shaft member and reciprocally displaceable along the axial direction, and having a rolling groove which is aligned with the helical groove to form a load path;
• a rolling unit disposed in the load path and having a plurality of rolling elements and a plurality of spacers, there is one said spacer between each two neighboring said rolling elements;
• a return assembly inserted in the moving module and in communication with the load path, having a first return pipe, a second return pipe communicating with the first return pipe, and a return passage which extends through the first return pipe and the second return pipe and is provided for the rolling unit to circulate;
• at least one sensor disposed on the moving module and located at a joint between the first return pipe and the second return pipe, when the rolling unit moves in the return passage, the at least one sensor is able to detect the change of a distance between the rolling elements and output a detecting signal;
• and
• a data receiving unit signal connected to the at least one sensor for receiving the detecting signal from the at least one sensor.