Session: 08-03-01: Design and Control of Robots, Mechanisms and Structures I

Paper Number: 165764

Force and Motion Control for a Six Degree-of-Freedom Robotic Manipulator With Digital Twin Visualization 

Robotic manipulators are used in various industries such as automotive and aerospace for a vast amount of applications. These common applications, such as material handling and assembly, require the end effector to follow the reference trajectories. In addition to trajectory tracking, a safe collaborative robot must control the force that the end-effector exerts
upon contact with any obstacles during trajectory tracking.

This paper presents a unified algorithm for motion and force control of a six-degree-of-freedom (DOF) collaborative robotic manipulator. Unlike conventional hybrid motion-force controllers, the proposed approach integrates motion and force control within a single framework, eliminating the explicit separation between the two. Assuming a force sensor is equipped at the tip of the end-effector of the manipulator, the goal is to perform trajectory tracking from any direction in the 3-dimensional Cartesian space while navigate through obstacles in the task space with the force sensing mechanism. The controller dynamically adjusts the manipulator's end-effector motion based on the reference trajectory in free space and the reference force upon contact with an object. During trajectory tracking, the controller ensures precise maneuvering through desired positions, orientations, and velocities. Upon contact, the force control mechanism restricts manipulator movement using a contact force model that incorporates material properties such as Young’s modulus, friction, and damping characteristics. The interaction force is modeled as a compliant contact force, where deformation and resistance are determined based on the stiffness and damping properties of both the end-effector and the contacted object. This enables adaptive force regulation to prevent excessive force application, minimizing potential damage to the manipulator and the environment. The system maintains active force and motion control during contact, allowing the end-effector to navigate obstacles while ensuring compliant interaction. Once contact is lost, the motion control resumes full trajectory tracking. The core control strategy is formulated through linear acceleration design, ensuring both trajectory accuracy and controlled force exertion.

The proposed controller is analyzed in detail, with validation provided through numerical simulations and digital twin visualization. The digital twin, which is another distinct feature of the paper, integrated with a force sensor, accurately replicates contact conditions by accounting for material-dependent interaction forces. The force sensor utilizes a detector process module to determine intersections between objects, utilizing an advanced ray trace methodology to compute the distance from the end-effector to an obstacle and identify collisions. The desirable properties are illustrated via the digital twin simulation, demonstrating the controller’s effectiveness in complex 3-dimensional Cartesian space trajectories.  

 

Presenting Author: Tsehuai Wu University of Maryland, Baltimore County

Presenting Author Biography: Dr. Tse-Huai Wu is a Professor of the Practice at University of Maryland, Baltimore County (UMBC) in Mechanical
Engineering. He received his Ph.D. from the George Washington University in 2016. After working in the industry for almost 5 years, he joined UMBC in 2020. His main interest area includes robotics, mechatronics, and autonomous vehicle control.

Authors:

Sagar Ojha Dynamic Dimension Technologies, LLC
Karl Leodler Dynamic Dimension Technologies
Lou Barbieri Dynamic Dimension Technologies, LLC
Tsehuai Wu University of Maryland, Baltimore County