Abstract
An automatic precision robot assembly system is established. The robot assembly system mainly consists of an industrial robot, three cameras, a micro force sensor, and a specific gripper. The industrial robot is a six-axis serial manipulator, which is used to conduct grasping and assembly subtasks. Two microscopic cameras are fixed on two high accuracy translational platforms to provide visual information in aligning stage for assembly. While one conventional camera is installed on the robotic end effector to guide the gripper to grasp component. The micro force sensor is installed on the robotic end effector to perceive the contacted forces in inserting stage. According to the characteristics of components, an adsorptive gripper is designed to pick up components. In addition, a three-stage “aligning–approaching–grasping” control strategy for grasping subtask and a two-stage “aligning–inserting” control strategy for assembly subtask are proposed. Position offset compensation is computed and introduced into aligning stage for assembly to make the grasped component in the microscopic cameras’ small field of view. Finally, based on the established robot assembly system and the proposed control strategies, the assembly tasks including grasping and assembly are carried out automatically. With 30 grasping experiments, the success rate is 100%. Besides, the position and orientation alignment errors of pose alignment for assembly are less than 20 μm and 0.1°.
Highlights
In recent years, with the wide application of microelectromechanism system in the fields of medicine, aerospace, and precision electronic engineering, precision assembly technology has received more and more attention.[1,2] Precision assembly is to package millimeter-size or less components with micrometer-level precision requirements.[3]
The robot assembly system mainly consists of an industrial robot, a gripper, three cameras, a micro force sensor, and a host computer
(ii) Control strategy for grasping subtask: According to the configuration of robot assembly system, the central axis of the gripper is approximately parallel to the optical axis of camera installed on robotic end effector
Summary
With the wide application of microelectromechanism system in the fields of medicine, aerospace, and precision electronic engineering, precision assembly technology has received more and more attention.[1,2] Precision assembly is to package millimeter-size or less components with micrometer-level precision requirements.[3]. (ii) Control strategy for grasping subtask: According to the configuration of robot assembly system, the central axis of the gripper is approximately parallel to the optical axis of camera installed on robotic end effector. If the image feature errors are larger than the designed thresholds, the corresponding position errors in the frame fEg are computed based on the image Jacobian matrix, and the robotic end effector moves according to the designed grasping controller (1). In aligning stage for assembly, the orientation adjustment of robotic end effector with respect to frame fRg will lead to the position offset of component A. Image Jacobian matrix Jr represents the relation between image line angle’s change and rotational increment of robotic end effector with respect to frame fRg. In position alignment control, the desired position of component A is computed based on the position and orientation of component B. Jacobian matrix J f represents the relation between the movement of robotic end effector and the change of contacted forces, which can be calibrated in advance
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