an apparatus for monitoring the z - axis position of a transfer blade on a wafer transfer robot which transfers wafers among multiple chambers in a semiconductor fabrication facility . the invention comprises a ccd laser displacement sensor which measures the height or z - axis position of the transfer blade and generates an analog voltage the value of which depends on the height of the transfer blade . an analog controller connected to the ccd laser displacement sensor converts the analog voltage signal to physical distance , which may be displayed on an lcd display on the analog controller . the analog controller may further be connected to a robot controller through an interface pcb , in which case a voltage signal corresponding to an abnormal position of the transfer blade is transmitted to the robot controller and the wafer transfer operation is terminated .