Abstract: According to a bolt tightening method and a bolt tightening apparatus of the invention, a bolt is tightened by using a bolt tightening device, in which torque gradients expressed in terms of the ratio of a tightening torque exerted on the bolt to its turning angle are calculated by successively detecting the tightening torque at intervals of a specific bolt turning angle and calculating an average of individual torque gradient values by first and second torque gradient calculators, and the amount of tightening of the bolt is controlled by a tightening amount controller based on the average of the individual torque gradient values calculated.

Abstract: A substrate center-finding method and apparatus, for determining the center of a substrate being passed through a substrate handling chamber of a substrate processing system, includes any number of sensors arranged in any configuration and permits the substrate to pass through any trajectory that triggers the sensors. The locations of the sensors are calibrated by homing in on the sensors using a point, the reference point, near the tip of an arm assembly on a substrate handler. The substrate handler has an encoder for sensing the pivot angles of links in the arm assembly, whereby the coordinates of the reference point can be calculated from the angles and lengths of the links. When the substrate triggers a sensor, the location of the reference point is again calculated, and the coordinates of the trigger point on the edge of the substrate is determined relative to the reference point.