Co-Ordinated Motion Control of Gantry Systems

Abstract

Among the various configurations of long travel and high precision cartesian robotic systems, one of the most popular is the H-type which is more commonly known as the moving gantry system. In this configuration, two motors which are mounted on two parallel slides move a gantry simultaneously in tandem. This gantry configuration has been in use for large overhead travelling cranes in ports, rolling mills and flying shear. When positioning precision is of the primary concern, direct drive linear motors are usually used and fitted with aerostatic bearings for optimum performance. The moving gantry stage is usually designed to provide a high-speed, high-accuracy X, Y and Z motion to facilitate automated processes in flat panel display, printed circuit board manufacturing, precision metrology, and circuit assembly where high part placement accuracy for overhead access is necessary. The stage is equipped with a high power density due to the dual drives, and it can yield high speed motion with no significant lateral offset when the two drives are appropriately co-ordinated and synchronised in motion. In certain applications such as in wafer steppers, the dual drives can also be used to produce a small “theta” rotary motion, without any additional rotary actuators. The application domain of the moving gantry stage is rapidly expanding along with the increasingly stringent requirements arising from developments in precision engineering and nanotechnology.