Detection system for substrate clamp

Abstract

The present invention provides a method and apparatus for determining whether a substrate is in a clamped or unclamped state on a robot blade and preferably allows the position of a properly clamped substrate to be compensated for misalignments due to substrates not at or very near to their nominal positions on the blade. A sensor unit comprising a radiation source and a detector and capable of transmitting and receiving a signal is mounted outside a transfer chamber and is positioned to direct the signal therein. A robot blade having a reflecting member is actuated through the transfer chamber and into the path of the signal. The reflecting member is preferably positioned on a clamp finger and causes the signal to be reflected to the detector of the sensor unit when the signal is incident on the reflecting member. As the reflecting member moves through the signal the output of the sensor unit switches states, thereby generating values corresponding to the position of the reflecting member. Positional information may be derived from these values by comparison to predetermined, nominal positional information. The substrate is determined to be either unclamped, in which case the system is halted for operator intervention, or clamped. If the substrate is clamped, the derived positional information can be used to make adjustments for deviations from a nominal position due to variations in the diameter of the substrate.