Abstract: A belt sander includes a main casing, a frame arm rotatably connected to the main casing, an abrasive belt mounted to the frame arm and adapted to be driven by electric power, a positioning member, a first sensor and a second sensor. The positioning member is movably mounted to the main casing and is movable relative to the main casing between a releasing position, where the first and second sensors are in a first sensor state, and where the second sensor generates a first signal for ceasing the electric power, and a first engaging position, where the first and second sensors are in the second sensor state, and where the second sensor generates a second signal for conducting the electric power.

Abstract: A self-sensing wafer holder in a robot blade is described which includes a holder body of generally elongated shape adapted for carrying a wafer on a top surface and at least three sensors positioned on the holder body sufficiently away from each other to form a plane that is covered by the wafer. The at least three sensors can be of the capacitive type, the optical type or the weight sensing type. The wafer holder is capable of determining whether a wafer is properly seated on top of the holder and automatically stopping the motion of the robot blade when a misplacement is detected by utilizing a sensing circuit including logic gates.