Performing Energy-Efficient Pick-and-Place Motions for High-Speed Robots by Using Variable Stiffness Springs

Abstract

Typically, for pick-and-place robots operating at high speeds, an enormous amount of energy is lost during the robot braking phase. This is due to the fact that, during such operational phase, most of the energy is dissipated as heat on the braking resistances of the motor drivers. In order to increase the energy-efficiency during the high-speed pick-and-place cycles, this paper investigates the use of variable stiffness springs (VSS) in parallel configuration with the motors. These springs store the energy during the braking phase, instead of dissipating it. The energy is then released to actuate the robot in a next displacement phase. This design approach is combined with a motion generator which seeks to optimize trajectories for input torques reduction (and thus of energy consumption), through solving a boundary value problem (BVP) based on the robot dynamics. Experimental results of the suggested approach on a five-bar mechanism show the drastic reduction of input torques, and therefore of energetic losses.

Time‐optimal trajectory planning of a redundantly actuated planar parallel robot driven with series elastic actuators

“…Differentiating 𝐪 0 twice w. r. t. time and inserting it in the upper part of (2), the actuation torques 𝐮 can be directly calculated, see ( 13)-( 15). This results in the TOCP min q,𝐳, ż,z,𝐳 (3) ,𝐯,𝐮,𝑇 ∫ 𝑇 0…”

“…𝐪 0 (𝐪 1 , 𝐪 2 , 𝐳, ż, z) = 𝐪 1 + 𝐊 −1 𝐇 −𝑇 a (𝐪)(𝐌 z (𝐪)z + 𝐠 z (𝐪, ż)) (13) q0 (𝐪 1 , 𝐪 2 , 𝐳, ż, z, 𝐳 (3) , 𝐯) = d 2 d𝑡 2 𝐪 0 (14)…”

“…The sum of mentioned components fully defines 𝐪 0 . The final TOCP for the redundantly-actuated planar PKM driven by SEA is then min Δ𝑞,Δ q, q,𝐳, ż,z,𝐳 (3) ,𝐯 z ,𝑣 Δ ,𝐮,𝑇 ∫ 𝑇 0…”

“…In this paper, the topics of redundant actuation and series elastic actuators (SEA) for a planar parallel robot are combined and exploited for time-optimal trajectory planning. Time-optimal motion planning for redundantly actuated robots driven by rigid drives has been addressed in [1,2], whereas research about motion planning of parallel robots equipped with SEA is directed towards energy-optimality ( [3]). The resulting dynamic model of a SEA-actuated PKM splits into two dynamical systems coupled by the elastic component of the SEA only.…”