Assembly of a miniature linear actuator using vision feedback

Abstract

The assembly of a miniature linear actuator is described. The actuator consists of a base plate including the stator, a runner and guides on both sides of the runner. Stator, runner and guides are micro machined, using silicon as base material. The overall dimensions of the complete actuator are approximately 9 mm x 3 mm. A parallel robot with 4-DOF and a resolution of less than 1µm is used to assemble the actuator. The robots high accuracy is reached as a result of the parallel structure of the robot in combination with linear piezo drives. In addition, an integrated vision system allows the exact positioning of the robot relative to a previously teached position. The accuracy of the vision system is about 0.25µm. Communication between the robot and the vision system takes place over a high-speed RS-422 serial link. As a first assembly step the guides, which are 8 mm long and 700µm wide, have to be mounted onto the base plate, right and left to the runners track. A special focus is laid on the exact maintenance of distance and parallelism of the guides, which is assured by the vision system. If the gap between the guides is too wide, the runner can tilt above the z-axis, which causes the actuator not to work. The opposite, a too small gap, causes the runner to be stuck between the guides. The guides are handled by a SMA-actuated miniature gripper. To keep the guides in place they are fixed by droplets of glue, which are dispensed by a micro dispenser.

Embedded 3D vision system for automated micro-assembly

“…Therefore, for closed-loop operation, a high-resolution, embedded vision system must be considered. This approach has been used for example in planar assembly tasks 7 , where a small camera provided vision feedback. For solving more general assembly tasks that require 3D vision, a universal 3D sensor is still missing.…”