A Multi-objective Optimization Approach for Trajectory Planning in a Safe and Ergonomic Human-Robot Collaboration

In today’s manufacturing companies that rely on Human-Robot Collaboration (HRC), ensuring a safe and ergonomic workplace is becoming of pivotal importance. In a collaborative assembly scenario, this paper aims at planning the trajectory of a collaborative robotic arm, guaranteeing safety and ergonomics for the operator without neglecting production requirements. In particular, a multi-objective optimization approach for the trajectory planning in safe and ergonomic HRC is defined, with the aim of finding the best trade-off between the total traversal time of the trajectory for the robot and ergonomics for the human worker, while respecting safety requirements. The proposed approach consists of three main steps. First, the Rapid Upper Limb Assessment (RULA) ergonomic index is evaluated on a manikin designed on a dedicated software. The aim is to ensure a high quality of work in the considered HRC scenario with a consequent decrease of the musculoskeletal disorders associated with highly repetitive and dangerous activities. Second, a time-optimal and safety-constrained trajectory planning problem is defined as a second-order cone programming problem. Finally, a multi-objective control problem is formulated and solved to compute the trajectory that ensures the best compromise between time end ergonomics. The method is tested on numerical simulations and the obtained results are discussed, proving the effectiveness of the approach.

I. Introduction

In the current highly competitive industrial scenario, Human-Robot Collaboration (HRC) is universally regarded as the key enabling technology of the Industry 4.0, where the new models of collaborative robots (i.e., cobots) are expected to work in the same environment together with humans, without renouncing to employees’ safety and well-being [1].