Optical vernier positioning for robot arm

In a computer controlled robot arm system having an effector on the free end thereof and being able to position and hold the effector adjacent the work piece at coordinates within the first tolerance, the improvements to position and hold the effector within second, closer, tolerance limits, comprising:

• (a) means operably driven by the computer for directing a first collimated light beam through points associated with the desired locating coordinates;
• (b) detector means carried by the effector and operably connected to the computer for detecting such light beam and sending a signal indicating the position of said light beam on said detector means to the computer, said detector means having a central position thereon where when said light beam is passing therethrough, the effector is at the desired coordinates within the second tolerance limits;
• (c) means for holding the outer end of said robot arm substantially fixed relative to the workpiece;
• (d) vernier drive means operably connected to be driven by the computer and positioned between outer end of said robot arm and the effector for moving the effector in the X and Y directions relative to the end of the robot arm when it is substantially fixed in position by said holding means;
• (e) means for moving the effector toward said coordinates to a location where said light beam is positioned within the sensing limits of the detector means;
• (f) means for utilizing said holding means when said effector is located with its associated detector having said light beam within its sensing limits;
• and
• (g) means for energizing said vernier drive means in closed loop relationship with said detector means to place the effector with said light beam passing through said central position, whereby the effector is located at the desired coordinates within said second tolerance limits.