Enhancing fluency and productivity in human-robot collaboration through online scaling of dynamic safety zones

Abstract

Industrial collaborative robotics is promising for manufacturing activities where the presence of a robot alongside a human operator can improve operator’s working conditions, flexibility, and productivity. A collaborative robotic application has to guarantee not only safety of the human operator, but also fluency in the collaboration, as well as performance in terms of productivity and task time. In this paper, we present an approach to enhance fluency and productivity in human-robot collaboration through online scaling of dynamic safety zones. A supervisory controller runs online safety checks between bounding volumes enclosing robot and human to identify possible collision dangers. To optimize the sizes of safety zones enclosing the manipulator, the method minimizes the time of potential stop trajectories considering the robot dynamics and its torque constraints, and leverages the directed speed of the robot parts with respect to the human. Simulations and experimental tests on a seven-degree-of-freedom robotic arm verify the effectiveness of the proposed approach, and collaborative fluency metrics show the benefits of the method with respect to existing approaches.

An experimental evaluation of robot-stopping approaches for improving fluency in collaborative robotics

“…[32]. Furthermore, the results are also compared in terms of concurrent activity in the robot workspace, introduced in [31], as well as number of robot stops. These quantitative metrics are briefly recalled in the following:…”

“…In this paper, we analyze three collision avoidance strategies, proposed by the same authors and characterized by different approaches for the calculation of the robot stop time: Approach 1: optimal scaling of dynamic safety zones, as in refs. [30, 31]. Approach 2: scaling of dynamic safety zones with linear search of the stop time, as in ref.…”

“…All the three approaches are compliant with the technical specification, with no distinction made between humans in the collaborative workspace with or without mobility issues or prior experience. However, these strategies affect differently the fluency in the collaboration, which directly reflects on the productivity and cycle time of the robotic system [31, 32]. The three compared approaches are briefly recalled in the following.…”

“…Approach 1 corresponds to scaling online the dynamic safety zones, as proposed in refs. [30, 31]. The approach is centered on minimizing online the time that the robot requires to safely halt, starting from its current kinematic state.…”

Development of the “Quad-SCARA” platform and its collision avoidance based on Buffered Voronoi Cell

“…Increased robots and individual grasping points or areas in Quad-SCARA are beneficial for manipulation performance, but on the other hand they also result in a higher risk of collision because their workspaces partially overlap with each other for the consideration of collaborative operation. Strategies against robot collision and human-robot collision mainly include (1) Impact mitigation for unavoidable collisions, with an instance that utilizes elastic deformation of passive compliant joints [14] and (2) Collision avoidance by area assignment or division in space and avoiding area overlap such as dynamic safety zone [15, 16], reachable occupancy [17], and others. The strategy in this paper belongs to the latter, and a collision avoidance system for robot motion planning during multi-point grasping is developed and described.…”