• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.1
• /
• pp.142-149
• /
• 1995

This paper presents a new kinematic control strategy for serial redundant manipulators which gives repeatability in the joint space when the end-effector undergoes some general cyclic motions. Theoretical development has been accomplished by deriving a new inverse kinematic equation that is based on springs being conceptually located in the joints of the manipulator. Although some inverse kinematic equations for serial redundant manipulators have been derived by many researchers, the new strategy is the first to include the free angles of torsional springs and the free lengths of the translational springs. This is important because it ensures repeatability in the joint space of a serial redundant manipulator whose end-effector undergoes a cyclic type motion. Numerical verification for repeatability is done in terms of Lie Bracket Condition. Choices for the free angle and torsional stiffness of a joint (or the free length and translational stiffness) are made based upon the mechanical limits of the joints.

• Journal of the Korean Society for Precision Engineering
• /
• v.20 no.3
• /
• pp.97-104
• /
• 2003

This paper proposes a new parallel manipulator fur plane motion, and then discusses on the workspace and kinematical characteristics of the manipulator. The conventional planar parallel manipulators have some disadvantages which are complex non-closed type direct kinematics, workspaces containing useless voids, and concave type border tines of workspaces. The proposed planar parallel manipulator overcomes the above disadvantages, that is, the manipulator has simple closed type direct kinematics, a void-free workspace, and a convex type borderline of a workspace. This paper shows the simulation result of the workspace as well as performances indices using a homogeneous inverse Jacobian.

• Journal of Navigation and Port Research
• /
• v.47 no.4
• /
• pp.256-270
• /
• 2023

In this study, a sliding mode (SM) controller for dynamic positioning (DP) was specifically designed for a turret connection operation of a ship or an offshore structure in which an arbitrary point on the structure could be controlled as the motion center instead of the center of mass. The SM controller allows control of the arbitrary point and provides capability to manage uncertainties in the dynamics of ships and offshore structures, external forces caused by unknown changing marine environments, and transient performance of DP systems. The Jacobian matrix included in kinematic equations of the controlled object was modified to design the SM controller to control based on an arbitrary point of ships or offshore structures. To ensure robustness of the controller, the Lyapunov stability theory was applied in the design of the SM controller. In general, for robustness in DP control, gain scheduling based on a proportional-derivative (PD) control algorithm is employed. However, finding appropriate gains for gain scheduling complicates the application of DP systems. Therefore, in this study, the SM control algorithm was considered to mitigate the complexity of the DP controller for ships and offshore structures. To validate the proposed SM control algorithm, time-domain simulations were conducted and utilized to evaluate the performance of the control algorithm. The effectiveness of the proposed SM controller was assessed by comparing simulation results with results of a conventional PD control algorithm applied in DP control.