Implementation of An Iterative 6-DOF Pose Estimation Method for Grasping a Hexagonal Nut by a Multilink Robot Arm

Abstract

The capability to manipulate small objects is one of the important requirements for producing assembly work robots. Moreover, a robot that exhibits human-like skills could be used to reduce the high labor cost for complex tasks. Therefore, we propose a seven-link dual-arm robot with three-fingered hands for cooperative tasks to manipulate small parts like nuts and bolts. As a continuity from a previous work in [1], we have proposed a method for calculating the 3D target pose in [2] to solve the problem of inclined target during grasping and screwing tasks. The study in [2] has presented a different approach to identify the geometric feature points of a target using vector calculations and the estimation of 6-DOF posture based on a method that is defined as CER (Confirm-Estimate-Rotate). In this paper, the implementation of this method on a 7-link robot arm in a visual servoing structure that focuses on an M10 nut as the starting point for a grasping task is shown. The dynamical system requires attention in many aspects including control, sensor integration, image processing and trajectory planning strategies for manipulation of small nuts. Here, the required kinematics adjustments for the motion control, grasping paths and configuration for robot fingers for attending the target in real-time operation is presented. Experimental results indicate the capability of our method to change the robot’s posture safely to match the posture of a target in inclined positions. Furthermore, a statistical grasping result has shown a moderate performance for various poses of nuts. Thus, this shows the improvement of robot for object manipulation and its  applicability for more complex tasks in future.