Optimal Control for Articulated Soft Robots

Saroj Prasad Chhatoi, Michele Pierallini, Franco Angelini, Carlos Mastalli, Manolo Garabini

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Soft robots can execute tasks with safer interactions. However, control techniques that can effectively exploit the systems' capabilities are still missing. Differential dynamic programming (DDP) has emerged as a promising tool for achieving highly dynamic tasks. But most of the literature deals with applying the DDP to articulated soft robots by using numerical differentiation, in addition to using pure feed-forward control to perform explosive tasks. Further, underactuated compliant robots are known to be difficult to control and the use of DDP-based algorithms to control them is not yet addressed. We propose an efficient DDP-based algorithm for trajectory optimization of articulated soft robots that can optimize the state trajectory, input torques, and stiffness profile. We provide an efficient method to compute the forward dynamics and the analytical derivatives of series elastic actuators (SEA)/variable stiffness actuators (VSA) and underactuated compliant robots. We present a state-feedback controller that uses locally optimal feedback policies obtained from the DDP. We show through simulations and experiments that the use of feedback is crucial in improving the performance and stabilization properties of various tasks. We also show that the proposed method can be used to plan and control underactuated compliant robots with varying degrees of underactuation effectively.
Original languageEnglish
Pages (from-to)3671-3685
Number of pages15
JournalIEEE Transactions on Robotics
Issue number5
Early online date13 Jul 2023
Publication statusPublished - Oct 2023


  • Articulated soft robots (ASRs)
  • Dynamics
  • End effectors
  • Heuristic algorithms
  • Optimal control
  • Robots
  • Soft robotics
  • Task analysis
  • feasibility-driven differential dynamic programming
  • optimal and state-feedback control
  • underactuated compliant robots

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Computer Science Applications
  • Electrical and Electronic Engineering


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