1 A Hybrid Contact State Analysis Methodology for Robotic-Based Adjustment of Cylindrical Pair B. Shirinzadeh 1 , Y. Zhong 2 , P. D. W. Tilakaratna 1 , Y. Tian 3 , M. M. Dalvand 1 1 Robotics and Mechatronics Research Laboratory, Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia 2 Department of Mechanical Engineering, Curtin University of Technology, Perth, WA 6845, Australia 3 School of Mechanical Engineering, Tianjin University, Tianjin 300072, China Abstract The peg-in-hole insertion and adjustment operation is one of the most common tasks in the robotic and automatic assembly processes. Fine motion strategies associated with adjustment operations on a peg-in-hole are fundamental manipulations that can be utilised in dynamic assembly and reconfigurable workholding or fixturing systems. This paper presents a comprehensive study of robotic-based height adjustment of a cylindrical pair based on maintaining minimum contact forces between the links. The outer link is held by the end-effector of a 6-DOF (Degrees of freedom) serial articulated robot manipulator. The environment represented by the inner-link can be either static or dynamic. A force based approach and a d value approach are established to determine the type of contact that exists between the links of a cylindrical pair, and to extract control parameters. Based on the comparison and analysis of these two approaches, a hybrid methodology is established by combining a d value approach with a force based approach for contact state determination. Formulations capable of extracting necessary control parameters which ensure minimum contact forces between the links are established from both planar and spatial viewpoints under both static and dynamic environmental conditions. Experimental results demonstrate the effectiveness of the proposed methodology. Keywords: Lower pairs, dynamic adjustment, contact state determination, and robotic manipulations. 1. Introduction Lower pairs are the fundamental building blocks of many mechanisms and form the basis for all assembly operations. As an example, tightening a nut and a bolt is represented by a screw pair, where inserting a microchip into its slot can be regarded as the height adjustment of a prismatic pair [1]. General manufacturing/assembly tasks such as position adjustment of a sleeve in a shaft prior to welding are described by a cylindrical pair. Likewise, the adjustment of a hinge is described by a revolute pair. The research on lower pairs has received considerable attention [2-8]. Automated planning of robotic manipulation for sliding workpieces (i.e. planar pairs) on a surface has also been extensively studied [3, 5, 8, 9]. In qualitatively demonstrating the alignment of a workpiece under an open-loop control, a methodology was developed to determine the locus of centres of rotation for all pressure distributions at the contact surface [8]. Further, the notion of configuration maps was proposed and established to evaluate the sequence of operations required to align a sliding workpiece [9]. Pushing manipulations were investigated on a hinge with negligible effect due to inertia, and a numerical procedure to determine its instantaneous center of rotation was established [3]. Determining the orientation of a polygonal planar object using data from a force/torque sensor attached to a fence,