An introductory review of active compliant control

Nowadays, industrial robots have been widely applied for performing position-controlled tasks with minimum contact such as spot welding, spray painting, packing, and material handling; however, performing high-tolerance assembly tasks still poses a great challenge for robots because of various uncertainties of the parts to be assembled such as fixtures, end effector tools, or axes. From this perspective, the advancement of research and development has led to cutting-edge robotic technologies for industrial applications. To understand the technological trend of industrial robots, investigated the state-of-the-art robotic assembly technologies to identify the limitations of existing works and clarify future research directions in the field. This paper especially interested on typical peg-in-hole (PiH) assemblies, as PiH methods provide insights for further development of robot assemblies. The assembly control strategies for PiH operations is classified by based on the types and features of the assemblies, and the literature in terms of the contributions of these studies is compared to PiH assembly. Finally, the control strategies for robotic PiH assemblies are discussed in detail, and the limitations of the current robotic assembly technologies are discussed to identify the future direction of research for the control of robotic assembly.

State-of-the-Art control strategies for robotic PiH assembly

A seamless interaction requires two robotic behaviors: the leader role where the robot rejects the external perturbations and focuses on the autonomous execution of the task, and the follower role where the robot ignores the task and complies with human intentional forces. The goal of this work is to provide (1) a unified robotic architecture to produce these two roles, and (2) a human-guidance detection algorithm to switch across the two roles. In the absence of human-guidance, the robot performs its task autonomously and upon detection of such guidances the robot passively follows the human motions. We employ dynamical systems to generate task-specific motion and admittance control to generate reactive motions toward the human-guidance. This structure enables the robot to reject undesirable perturbations, track the motions precisely, react to human-guidance by providing proper compliant behavior, and re-plan the motion reactively. We provide analytical investigation of our method in terms of tracking and compliant behavior. Finally, we evaluate our method experimentally using a 6-DoF manipulator.

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A dynamical system approach for detection and reaction to human guidance in physical human–robot interaction

In most existing bolt assembling operations, the human-machine collaboration (HMC) is used to guarantee both the operational efficiency and the connection quality. However, the huge labor intensity and costs are still needed when there exist bolts with huge quantity and multiple models in some special working environments, for example locomotive maintenance and automobile assembly. Actually, the robotic application can better solve the above problem. The main reason why this application is limited in the bolt assembly is due to the technological barriers related to the intelligent control. This paper firstly introduces the HMC-based and the robot-guided bolt assembly processes in detail, then summarizes the latest researches related to the significant technologies needed in the robot-guided assembly to show their present status and future trends. Finally based on the technology limitations this paper further presents some suggestions for future studies of each technology, which attempts to help readers broaden their research thoughts and speed up the development of the robot-guided bolt assembly.

A Review on Significant Technologies Related to the Robot-Guided Intelligent Bolt Assembly Under Complex or Uncertain Working Conditions

The State of the Art of Search Strategies in Robotic Assembly

In this paper, we propose a closed-loop force sensor based nested admittance/impedance control strategy to actively estimate and minimize the effects of geometric misalignment that naturally occur during assembly tasks with compliant robots. The method allows the robot to be used with a stiff impedance control setting, which is beneficial for free air motion performance, yet allows to adjust for large misalignment errors between parts that need be assembled.

Nicky Mol

Papers

Nested compliant admittance control for robotic mechanical assembly of misaligned and tightly toleranced parts