Jerry E. Pratt

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It is known that for a large magnitude push a human or a humanoid robot must take a step to avoid a fall. Despite some scattered results, a principled approach towards "when and where to take a step" has not yet emerged. Towards this goal, we present methods for computing capture points and the capture region, the region on the ground where a humanoid must(More)
Virtual model control is a motion control framework that uses virtual components to create virtual forces generated when the virtual components interact with a robot system. An algorithm derived based on the virtual model control framework is applied to a physical planar bipedal robot. It uses a simple set of virtual components that allows the robot to walk(More)
This two-part paper discusses the analysis and control of legged locomotion in terms of N -step capturability: the ability of a legged system to come to a stop without falling by taking N or fewer steps. We consider this ability to be crucial to legged locomotion and a useful, yet not overly restrictive criterion for stability. Part 1 introduces a(More)
Exoskeletons that enhance human strength, endurance, and speed while being transparent to the wearer are feasible. In order to be transparent, the exoskeleton must determine the user's intent, apply forces when and where appropriate, and present low impedance to the wearer. We present a one degree of freedom exoskeleton called the RoboKnee which achieves a(More)
the Control of Bipedal Walking Robots by Jerry E. Pratt M.Eng, Massachusetts Institute of Technology (1995) B.S., Massachusetts Institute of Technology (1994) Submitted to the Department of Electrical Engineering and Computer Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the MASSACHUSETTS INSTITUTE OF(More)
Series Elastic Actuators have linear springs intentionally placed in series between the motor and actuator output. The spring strain is measured to get an accurate estimate of force. Despite using a transmission to achieve high force/mass and high power/mass, the spring allows for good force control, high force fidelity, minimum impedance, and large dynamic(More)
Most robot designers make the mechanical interface between an actuator and its load as stiff as possible[9][10]. This makes sense in traditional position-controlled systems, because high interface stiffness maximizes bandwidth and, for non-collocated control, reduces instability. However, lower interface stiffness has advantages as well, including greater(More)
Natural dynamics can be exploited in the control of bipedal walking robots: the swing leg can swing freely once started; a kneecap can be used to prevent the leg from inverting; and a compliant ankle can be used to naturally transfer the center of pressure along the foot and help in toe off. Each of these mechanisms helps make control easier to achieve and(More)