Publications

Prosthesis Design and Control

Exoskeleton Design and Control

Modeling and Measuring Human Locomotion

Control of Autonomous Legged Robots

Actuator Design and Optimization


Prosthesis Design and Control


  • Design and Benchtop Validation of a Powered Knee-Ankle Prosthesis with High-Torque, Low-Impedance Actuators. T. Elery, S. Rezazadeh, C. Nesler, J. Doan, H. Zhu, and R. Gregg. To appear in IEEE Int. Conf. Robotics & Automation, Brisbane, Australia, 2018. (Abstract)

  • Continuous-Phase Control of a Powered Knee-Ankle Prosthesis: Amputee Experiments Across Speeds and Inclines. D. Quintero, D. Villarreal, D. Lambert, S. Kapp, and R. Gregg. IEEE Transactions on Robotics, 2018, in press. (Abstract, PDF, Video)

  • Automatic Tuning of Virtual Constraint-Based Control Algorithms for Powered Knee-Ankle Prostheses. S. Kumar, A. Mohammadi, N. Gans, and R. Gregg. In IEEE Conference on Control Technology and Applications (Invited Session on Robotic Locomotion Control), Hawaii, 2017. Best Student Paper Award Finalist. (Abstract, PDF, Video)

  • Piecewise and Unified Phase Variables in the Control of a Powered Prosthetic Leg. D. Villarreal, D. Quintero and R. Gregg. In IEEE International Conference on Rehabilitation Robotics, London, United Kingdom, 2017. (Abstract, PDF, Experiment Video)

  • Stable, Robust Hybrid Zero Dynamics Control of Powered Lower-Limb Prostheses. A. Martin and R. Gregg. IEEE Transactions on Automatic Control, 62(8): 3930-3942, 2017, doi: 10.1109/TAC.2017.2648040. (Abstract, PDF)

  • Toward Unified Control of a Powered Prosthetic Leg: A Simulation Study. D. Quintero, A. Martin, and R. Gregg. IEEE Transactions on Control Systems Technology, 26(1): 305-312, 2018, doi: 10.1109/TCST.2016.2643566. (Abstract, PDF)

  • Preliminary Experiments with a Unified Controller for a Powered Knee-Ankle Prosthetic Leg Across Walking Speeds. D. Quintero, D. Villarreal, and R. Gregg. In IEEE Int. Conf. Intelligent Robots & Systems, Daejeon, Korea, 2016. (Abstract, PDF, Experiment Video)

  • A Haptic Feedback System for Phase-Based Sensory Restoration in Above-Knee Prosthetic Leg Users. A. Plauche, D. Villarreal, and R. Gregg. IEEE Transactions on Haptics, 9(3): 421-426, 2016, doi: 10.1109/TOH.2016.2580507. (Abstract, PDF)

  • Prosthetic Leg Control in the Nullspace of Human Interaction. R. Gregg and A. Martin. In Invited Session on Control Theory in Legged Locomotion, American Control Conf., Boston, MA, 2016. (Abstract, PDF)

  • Evaluation of Transradial Body-Powered Prostheses Using a Robotic Simulator. R. Ayub, D. Villarreal, R. Gregg, and F. Gao. Prosthetics & Orthotics International, 2016, doi: 10.1177/0309364616650077. (Abstract, Full Text)

  • Unifying the Gait Cycle in the Control of a Powered Prosthetic Leg. D. Quintero, A. Martin, and R. Gregg. In IEEE Int. Conf. Rehabilitation Robotics, Singapore, 2015. (Abstract, PDF)

  • Hybrid Invariance and Stability of a Feedback Linearizing Controller for Powered Prostheses. A. Martin and R. Gregg. In American Control Conference, Chicago, IL, 2015. (Abstract, PDF)

  • Virtual Constraint Control of a Powered Prosthetic Leg: From Simulation to Experiments with Transfemoral Amputees. R. Gregg, T. Lenzi, L. Hargrove, and J. Sensinger. IEEE Transactions on Robotics, 30(6): 1455-1471, 2014, doi: 10.1109/TRO.2014.2361937.
    (Abstract, PDF, Experiment Video)

Exoskeleton Design and Control


  • On the Design and Control of Highly Backdrivable Lower-Limb Exoskeletons. G. Lv, H. Zhu, and R. Gregg. IEEE Control Systems Magazine, under review. (Abstract)

  • Towards Total Energy Shaping Control of Lower-Limb Exoskeletons. G. Lv and R. Gregg. In American Control Conference, Seattle, WA, 2017. (Abstract, PDF)

  • Design and Validation of a Torque Dense, Highly Backdrivable Powered Knee-Ankle Orthosis. H. Zhu, J. Doan, C. Stence, G. Lv, T. Elery, and R. Gregg. In IEEE Int. Conf. Robotics & Automation, Singapore, 2017. (Abstract, PDF, Experiment Video)

  • Underactuated Potential Energy Shaping with Contact Constraints: Application to a Powered Knee-Ankle Orthosis. G. Lv and R. Gregg. IEEE Transactions on Control Systems Technology, 26(1): 181-193, 2018, doi: 10.1109/TCST.2016.2646319. (Abstract, PDF)

  • Experimental Implementation of Underactuated Potential Energy Shaping on a Powered Ankle-Foot Orthosis. G. Lv, H. Zhu, T. Elery, L. Li, and R. Gregg. In IEEE Int. Conf. Robotics & Automation, Stockholm, Sweden, 2016. (Abstract, PDF, Experiment Video)

  • Orthotic Body-Weight Support Through Underactuated Potential Energy Shaping with Contact Constraints. G. Lv and R. Gregg. In IEEE Conf. Decision & Control, Osaka, Japan, 2015. Best Student Paper Award. (Abstract, PDF)

Modeling and Measuring Human Locomotion


  • Real-Time Continuous Gait Phase and Speed Estimation from a Single Sensor. D. Quintero, D. Lambert, D. Villarreal, and R. Gregg. In IEEE Conf. on Control Technology and Applications (Invited Session on Robotic Locomotion Control), Hawaii, 2017. (Abstract, PDF)

  • A Robust Parameterization of Human Gait Patterns Across Phase-Shifting Perturbations. D. Villarreal, H. Poonawala, and R. Gregg. IEEE Transactions on Neural Systems & Rehabilitation Engineering, 25(3): 265-278, 2017, doi: 10.1109/TNSRE.2016.2569019. (Abstract, PDF, Experiment Video)

  • Unified Phase Variables of Relative Degree Two for Human Locomotion. D. Villarreal and R. Gregg. In IEEE Engineering in Medicine and Biology Conference, Orlando, FL, 2016. (Abstract, PDF)

  • A Unified Parameterization of Human Gait Across Ambulation Modes. K. Embry, D. Villarreal, and R. Gregg. In IEEE Engineering in Medicine and Biology Conference, Orlando, FL, 2016. (Abstract, PDF)

  • A Perturbation Mechanism for Investigations of Phase-Dependent Behavior in Human Locomotion. D. Villarreal, D. Quintero, and R. Gregg. IEEE Access, 4: 893-904, 2016, doi: 10.1109/ACCESS.2016.2535661. (Abstract, Open Access, Data)

  • Incorporating Human-like Walking Variability in an HZD-Based Bipedal Model. A. Martin and R. Gregg. IEEE Transactions on Robotics, 32(4): 943-948, 2016, doi: 10.1109/TRO.2016.2572687. (Abstract, PDF)

  • Characterizing and Modeling the Joint-level Variability in Human Walking. A. Martin, D. Villarreal, and R. Gregg. Journal of Biomechanics, 49(14): 3298-3305, 2016, doi: 10.1016/j.jbiomech.2016.08.015. (Abstract, PDF)

  • A Perturbation Mechanism for Investigations of Phase Variables in Human Locomotion. D. Villarreal, D. Quintero, and R. Gregg. In IEEE Int. Conf. Robotics & Biomimetics (ROBIO), Zhuhai, China, 2015. (Abstract, PDF, Experiment Video)

  • A Survey of Phase Variable Candidates of Human Locomotion. D. Villarreal and R. Gregg. In IEEE Engineering in Medicine and Biology Conference, Chicago, IL, 2014. (PDF)

Control of Autonomous Legged Robots


  • Observer-Based Feedback Controllers for Exponential Stabilization of Periodic Orbits for Hybrid Dynamical Systems: Application to Underactuated 3D Bipedal Walking. K. Hamed and R. Gregg. International Journal of Robotics Research, under review. (Abstract)

  • Passivity-Based Control with a Generalized Energy Storage Function for Robust Bipedal Walking. M. Yeatman, G. Lv, and R. Gregg. To appear in American Control Conference, Milwaukee, WI, 2018. (Abstract, PDF)

  • Observer-Based Feedback Controllers for Exponential Stabilization of Hybrid Periodic Orbits: Application to Underactuated Bipedal Walking. K. Hamed, A. Ames, and R. Gregg. To appear in American Control Conference, Milwaukee, WI, 2018. (Abstract, PDF)

  • Exponentially Stabilizing Controllers for Multi-Contact 3D Bipedal Locomotion. K. Hamed, R. Gregg, and A. Ames. To appear in American Control Conference, Milwaukee, WI, 2018. (Abstract, PDF)

  • Decentralized Event-Based Controllers for Robust Stabilization of Hybrid Periodic Orbits: Application to Underactuated 3D Bipedal Walking. K. Hamed and R. Gregg. IEEE Transactions on Automatic Control, under review. (Abstract)

  • Removing Phase Variables from Biped Robot Parametric Gaits. A. Mohammadi, J. Horn, and R. Gregg. In IEEE Conference on Control Technology and Applications (Invited Session on Robotic Locomotion Control), Hawaii, 2017. (Abstract, PDF)

  • Decentralized Feedback Controllers for Robust Stabilization of Periodic Orbits of Hybrid Systems: Application to Bipedal Walking. K. A. Hamed and R. Gregg. IEEE Transactions on Control Systems Technology, 25(4): 1153-1167, 2017, doi: 10.1109/TCST.2016.2597741. (Abstract, PDF)

  • A Control Framework for Anthropomorphic Biped Walking Based on Stabilizing Feedforward Trajectories. S. Rezazadeh and R. Gregg. In ASME Dynamic Systems & Control Conference, Minneapolis, MN, 2016. (Abstract, PDF)

  • Decentralized Feedback Controllers for Exponential Stabilization of Hybrid Periodic Orbits: Application to Robotic Walking. K. Hamed and R. Gregg. In Invited Session on Control Theory in Legged Locomotion, American Control Conf., Boston, MA, 2016. (Abstract, PDF)

Actuator Design and Optimization


  • Minimizing Energy Consumption and Peak Power of Series Elastic Actuators: a Convex Optimization Framework for Elastic Element Design. E. Bolivar, S. Rezazadeh, and R. Gregg. IEEE/ASME Transactions on Mechatronics, under review. (Abstract)

  • A General Framework for Minimizing Energy Consumption of Series Elastic Actuators with Regeneration. E. Bolivar, S. Rezazadeh, and R. Gregg. In ASME Dynamic Systems & Control Conference, Virginia, 2017. Best Student Robotics Paper. (Abstract, PDF)

  • Towards a Series Elastic Actuator with Electrically Modulated Stiffness for Powered Ankle-Foot Orthoses. E. Bolivar, D. Allen, G. Ellson, J. Cossio, W. Voit, and R. Gregg. In IEEE Conf Automation Science & Engineering, Fort Worth, TX, 2016. (Abstract, PDF)

Unreviewed Magazine Articles


  • Challenges for Control Research: Control of Powered Prosthetic Legs. R. Gregg, L. Hargrove, and J. Sensinger. The Impact of Control Technology, 2nd ed., T. Samad and A.M. Annaswamy (eds.), IEEE Control Systems Society, 2014, available at www.ieeecss.org. (PDF)

Conference Abstracts


  • Giving Up the Finite State Machine in the Control of Lower-Limb Wearable Robots?. D. Quintero, A. Martin, and R. Gregg. In Workshop on Rehabilitation Robotics and Human-Robot Interaction, IEEE Int Conf Robotics & Automation, Seattle, WA 2015. (PDF)

  • Determining the Sagittal Plane Function for a Model Prosthetic Foot. A. Martin, J. Smith, R. Gregg, and J. Schmiedeler. In American Society of Biomechanics, Columbus, OH, 2015.

  • Virtual Constraint Control of a Powered Prosthetic Leg: Experiments with Transfemoral Amputees. R. Gregg. In Dynamic Locomotion Workshop, Robotics: Science & Systems, Berkeley, CA, 2014. (PDF)

Visit the PI's Google Scholar for past publications.