Keith W. Wait

A Gas-Actuated Anthropomorphic Prosthesis for Transhumeral Amputees

This paper presents the design of a gas-actuated anthropomorphic arm prosthesis with 21 degrees of freedom and nine independent actuators. The prosthesis utilizes the monopropellant hydrogen peroxide as a gas generator to power nine pneumatic type actuators. Of the nine independent actuators, one provides direct- drive actuation of the elbow, three provide direct-drive actuation for the wrist, and the remaining five actuate an underactuated 17 degree of freedom hand. This paper describes the design of the prosthesis, including the design of small-scale high-performance servovalves, which enable the implementation of the monopropellant concept in a transhumeral prosthesis. Experimental results are given characterizing both the servovalve performance and the force and/or motion control of various joints under closed-loop control.

Self locomotion of a spherical rolling robot using a novel deformable pneumatic method

The authors have designed and constructed a new type of actuation for a spherical robot. The proposed actuation system consists of a large number of individually inflatable rubber bladders covering a sphere. Inflation of one or more of these bladders imparts a moment to the sphere and coordinated inflation results in a directed motion. Further, the authors introduce a scheme for steering the robot by correctly selecting the proper bladders to inflate so that motive force is developed in a specified direction. The control scheme utilizes a passively rolling inner vehicle with a directional, remotely positioned light source that causes valves housed within the sphere to inflate the designated bladders through optical commutation.

A Pneumatically Actuated Quadrupedal Walking Robot

This paper describes the mechanical design and control of a pneumatic quadrupedal robot. Additionally, the authors propose a method of joint control that combines stance/swing gain scheduling with open-loop damping, the combination of which provides stable joint level control, without the oscillatory behavior associated with pneumatically actuated walking robots. A set of joint trajectories are described to provide stable walking. The joint trajectories and joint-level controllers are implemented on the pneumatic quadruped and experimentally shown to provide stable walking without significant (unwanted) oscillations of the body or legs. Further, the robots normalized speed and payload capacity are experimentally characterized. The robots performance in these metrics is shown to be highly competitive within the published literature.

A Gas-Actuated Anthropomorphic Transhumeral Prosthesis

This paper presents the design of an anthropomorphic 21 degree-of-freedom, 9 degree-of-actuation arm prosthesis for use by transhumeral amputees. The design leverages the power density of pneumatic actuation with the energy density of liquid propellants to obtain a self-powered dexterous prosthesis in which all of the requisite power, actuation, and sensing is packaged within the volumetric envelope of a normal human arm. Specifically, the arm utilizes a monopropellant as a gas generator to power nine pneumatic-type actuators that drive an elbow, three wrist degrees-of-freedom, and a 17 degree-of-freedom compliant hand. The design considerations discussed in this work include the design of compact, low-power servovalves; the choice of actuators based on energetic requirements of a normal arm; the design of compact elbow and wrist joints with integrated position and force sensing; and the components of the compliant hand design. The liquid-fueled prosthesis is expected to approach the dexterity of an anatomical arm and is projected to deliver half of the force and power output of an average human arm.

Liquid-Fueled Actuation for an Anthropomorphic Upper Extremity Prosthesis

This paper describes the design of a 21 degree-of-freedom, nine degree-of-actuation, gas-actuated arm prosthesis for transhumeral amputees. The arm incorporates a direct-drive elbow and three degree-of-freedom wrist, in addition to a 17 degree-of-freedom underactuated hand effected by five actuators. The anthropomorphic device includes full position and force sensing capability for each actuated degree of freedom and integrates a monopropellant-powered gas generator to provide on-board power for untethered operation. Design considerations addressed in this paper include the sizing of pneumatic actuators based on the requisite output energy at each joint; the development of small low-power servovalves for use with hot/cold gases; the design of compact joints with integrated position sensing; and the packaging of the actuators, on-board power, and skeletal structure within the volumetric envelope of a normal human forearm and elbow. The resulting arm prototype approaches the dexterous manipulation capabilities of its anatomical counterpart while delivering approximately 50% of the force and power output of an average human arm

Enhanced Performance and Stability in Pneumatic Servosystems With Supplemental Mechanical Damping

The authors present a model-based analysis of a position-velocity-acceleration-controlled pneumatic actuator that indicates that supplementing the pneumatic actuator with mechanical damping can significantly increase the gain margin, tracking accuracy, and disturbance rejection of a closed-loop-controlled pneumatic servoactuator. In order to validate the model-based analysis and purported performance and stability benefits provided by supplemental damping, experiments were performed on a single-degree-of-freedom pneumatic servosystem. Measurements conducted on the experimental setup, which validate the respective improvements in stability margin, tracking accuracy, and disturbance rejection, are described.

A Biologically Inspired Approach to the Coordination of Hexapedal Gait

This paper presents a method for the control of locomotion in a robot hexapod. The approach is based on the WalkNet structure, which in turn is based on the neural control structure of the insect Carausius morosus. Though the WalkNet structure has been shown to function well in kinematic (i.e., non-dynamic) simulations, the authors found that the approach to coordinated control of hexapedal locomotion entailed several significant problems when simulated in the presence of dynamic effects, including gravitational effects, inertial dynamics, and ground contact dynamics. As such, the authors propose several variations on the WalkNet structure that provides stable and robust locomotion in the presence of dynamics, while still maintaining the attributes of WalkNet coordinated control, including self-selection of gait and associated emergent behaviors. The approach is simulated in the presence of dynamics and shown to provide stable gait with emergent characteristics.

Design and control of a biomimetic hexapedal walker

This paper describes progress towards the development of a monopropellant-powered, pneumatically-actuated, hexapod robot. Design of the robot is presented, and an optimization based on the dynamic simulation of locomotion is described that selects the kinematic configuration to evenly distribute joint torques in the leg during locomotion. A finite state controller and leg impedance controller are described, and the controller is experimentally implemented on a pair of the hexapod legs to (1) validate the effectiveness of the control approach and (2) verify that the joint torques are indeed evenly distributed within the legs. Another optimization based on the dynamic simulation of locomotion is described that selects weights for a coordination-level controller that best tracks a desired body velocity.

Design of an Anthropomorphic Upper Extremity Prosthesis

This paper describes the design of a 21 degree-of-freedom, nine degree-of-actuation, gas-actuated arm prosthesis for transhumeral amputees. The arm incorporates a direct-drive elbow and three degree-of-freedom wrist, in addition to a 17 degree-of-freedom underactuated hand effected by five actuators. The anthropomorphic device includes full position and force sensing capability for each actuated degree of freedom and integrates a monopropellant-powered gas generator to provide on-board power for untethered operation. Design considerations addressed in this paper include the sizing of pneumatic actuators based on the requisite output energy at each joint; the development of small low-power servovalves for use with hot/cold gases; the design of compact joints with integrated position sensing; and the packaging of the actuators, on-board power, and skeletal structure within the volumetric envelope of a normal human forearm and elbow. The resulting arm prototype is intended to approach the dexterous manipulation capabilities of its anatomical counterpart while delivering approximately 50% of the force and power output of an average human arm.Copyright

Design and control of a pneumatic quadrupedal walking robot

The mechanical and electronics design of a quadrupedal walking robot featuring 12 pneumatically actuated degrees of freedom is presented. Control of the robots joint motions incorporates open-loop damping into the actuation and uses a stance/swing gain scheduler in the joint position controller. The inclusion of these two attributes enables stable and robust joint-level control while attenuating the undesirable oscillatory modes that are commonly associated with pneumatically actuated walking robots. Joint motion trajectories that permit stable walking are developed and implemented in the robot. The combination of these features and techniques is experimentally shown to enable stable walking locomotion of the robot that is not inhibited by unwanted oscillations of significant magnitude.