Abstract
Robots are gaining a foothold day-by-day in different areas of people’s lives. Collaborative robots (cobots) need to display human-like dynamic performance. Thus, the question of safety during physical human–robot interaction (pHRI) arises. Herein, we propose making serial cobots intrinsically compliant to guarantee safe pHRI via our novel designed device, V2SOM (variable stiffness safety-oriented mechanism). Integrating this new device at each rotary joint of the serial cobot ensures a safe pHRI and reduces the drawbacks of making robots compliant. Thanks to its two continuously linked functional modes—high and low stiffness—V2SOM presents a high inertia decoupling capacity, which is a necessary condition for safe pHRI. The high stiffness mode eases the control without disturbing the safety aspect. Once a human–robot (HR) collision occurs, a spontaneous and smooth shift to low stiffness mode is passively triggered to safely absorb the impact. To highlight V2SOM’s effect in safety terms, we consider two complementary safety criteria: impact force (ImpF) criterion and head injury criterion (HIC) for external and internal damage evaluation of blunt shocks, respectively. A pre-established HR collision model is built in Matlab/Simulink (v2018, MathWorks, France) in order to evaluate the latter criterion. This paper presents the first V2SOM prototype, with quasi-static and dynamic experimental evaluations.
Highlights
The currently emerging manufacturing paradigm, known as Industry 4.0, is behind the rethinking of how industrial processes are designed in order to increase their efficiency and flexibility, together with higher levels of automatization [1]
Previous works on variable stiffness actuator (VSA) resulted in design concepts that differ in several aspects, such as mass to volume ratio, elastic energy to mass or volume ratios, working principal, etc
Figure shows that V2SOM presents more than 80% gains on an head injury criterion (HIC) basis compared 12 to ofCS
Summary
The currently emerging manufacturing paradigm, known as Industry 4.0, is behind the rethinking of how industrial processes are designed in order to increase their efficiency and flexibility, together with higher levels of automatization [1]. From a dynamic perspective, integrating passive mechanisms in robot joints decouples a certain colliding inertia from the rest of the robot This reduces the overall kinetic energy absorbed by the impacted human. To improve the safety of physical human–robot interaction (pHRI), Zinn et al presented [13] a distributed macro-mini (DM [2]) actuation system that puts forward low-inertia actuators to interact with the human subject This allows for both safety and a fast control reaction via the low inertia actuated part. Several VSAs have been proposed, as discussed in previous studies [3,14] Their design concepts resulted in different structural paradigms (e.g., serial or antagonistic), different stiffness profiles, and a wide range of power to mass ratios. The proposed approach, leading to prototype V2SOM (variable stiffness safety-oriented mechanism) [1], presents the following novelties compared to the literature:.
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