Publications

Y. Chen, Y. Li and D.J. Braun, Learning Finite-Horizon Nonlinear Optimal Control Policies with Unknown Control-Affine Dynamics (under review). This paper introduces a model-free method for learning finite-horizon optimal control for systems with control-affine dynamics. We approximate the time- and state-dependent optimal control policy using model-free…

Y. Y. Fu, A.U. Kilic and D.J. Braun, Energy Minimization using Custom-Designed Magnetic-Spring Actuators, pp. 3534-3539, Abu Dhabi, United Arab Emirates, 2024. This study introduces an innovative actuator that resembles a motor with a non-uniform permanent magnetic field. We have developed a prototype of the…

A.U. Kilic and D.J. Braun, A Novel Approximation for the Spring Loaded Inverted Pendulum Model of Locomotion, Detroit, MI, USA, pp. 4315-4321, 2023. The Spring-Loaded Inverted Pendulum (SLIP) is a heuristic model of robot locomotion. SLIP is commonly used to predict center-of-mass motion and derive…

S.Y. Kim and D.J. Braun, Variable Stiffness Floating Spring Leg: Performing net-zero energy cost tasks not achievable using fixed stiffness springs, vol. 8, no. 9, pp. 5400-5407, 2023. Sitting down and standing up from a chair and, similarly, moving heavy objects up and down between factory…

S.Y. Kim and D.J. Braun, Controllable Mechanical-domain Energy Accumulators, IEEE International Conference on Robotics and Automation, London, United Kingdom, pp. 7359-7364, 2023. Springs are efficient in storing and returning elastic potential energy but are unable to hold the energy they store in the absence of an…

C. Mathews and D.J. Braun, Design of a Variable Stiffness Spring with Human-Selectable Stiffness, IEEE International Conference on Robotics and Automation, London, United Kingdom, pp. 7385-7390, 2023. Springs are commonly used in wearable robotic devices to provide assistive joint torque without the need for motors and…

C. Dempsey and D.J. Braun, Novel Spring Mechanism Enables Iterative Energy Accumulation under Force and Deformation Constraints, IEEE International Conference on Robotics and Automation, London, United Kingdom, pp. 7391-7397, 2023. Springs can provide force at zero net energy cost by recycling negative mechanical work to benefit…

D Braun, C. W Mathews, Method and apparatus for human augmentation and robot actuation, US Patent App. 17/872,164, 2023. The present disclosure relates to a parallel variable stiffness actuator. The parallel variable stiffness actuator can comprise a spring and a variable-stiffness mechanism. The variable-stiffness mechanism…

D Braun, A Sutrisno, and T Zhang, Method and Apparatus for Augmented Locomotion, US Patent 11,439,564, 2022. Provided are apparatuses for augmenting human speed, human-driven compliant mechanisms, artificial limbs to augment human movement, and the like. The apparatuses can include variable stiffness mechanisms including springs…

D Braun, S Kim, Variable Stiffness Mechanisms for low Energy Cost Stiffness Modulation, US Patent App. 17/506,164, 2022. Disclosed herein is a variable-stiffness floating spring mechanism. The variable-stiffness floating spring mechanism can change its stiffness without changing an energy stored by a spring. The variable-stiffness…

Y. Chen, Y. Li, and D.J. Braun, Data-Driven Iterative Optimal Control for Switched Dynamical Systems, IEEE Robotics and Automation Letters, vol. 8, no. 1, pp. 296-303, 2023. This article presents a data-driven algorithm to compute optimal control inputs for input-constrained nonlinear optimal control problems with…

C. Mathews and D.J. Braun, Design of Parallel Variable Stiffness Actuators, IEEE Transactions on Robotics, vol. 39, no. 1, pp. 768-782, 2023. Direct-drive motors (DDMs) have been increasingly used for robot actuation because they provide high-fidelity torque control, but they typically have low torque density. Gearing can be used…