Joseph K. Hitt

An Active Foot-Ankle Prosthesis With Biomechanical Energy Regeneration

A unique, robust, robotic transtibial prosthesis with regenerative kinetics was successfully built and a 6-month human subject trial was conducted on one male below-the-knee amputee under linear walking conditions. This paper presents the quasistatic system modeling, DC motor and transmission modeling and analyses, design methodology, and model verification. It also outlines an approach to the design and development of a robotic transtibial prosthesis. The test data will show that the true power and energy requirement predicted in the modeling and analyses is in good agreement with the measured data, verifying that the approach satisfactorily captures the physical system. The modeling and analyses in this paper describes a process to determine an optimal combination of motors, springs, gearboxes, and rotary to linear transmissions to significantly minimize the power and energy consumption. This kinetic minimization allows the downsizing of the actuation system and the battery required for daily use to a self-portable level.

Robotic transtibial prosthesis with biomechanical energy regeneration

Purpose – The purpose of this paper is to describe a project which seeks to develop a new generation of powered prostheses based on lightweight, uniquely tuned, energy‐storing elastic elements in series with optimal actuator systems that will significantly reduce the peak power requirement of the motor and the total system energy requirement while providing the amputee 100 percent of required “push‐off” power and ankle sagittal plane range‐of‐motion comparable to able‐bodied gait.Design/methodology/approach – This paper presents the design, power, and energy‐efficiency analyses, and the results of a five‐month trial with one trans‐tibial amputee subject as part of the first phase of the Spring Ankle with Regenerative Kinetics project.Findings – The data show that by leveraging uniquely tuned springs and transmission mechanisms, motor power is easily amplified more than four fold and the electric energy requirement is cut in half compared with traditional approaches.Originality/value – This paper describes...

The SPARKy (Spring Ankle With Regenerative Kinetics) Project: Design and Analysis of a Robotic Transtibial Prosthesis With Regenerative Kinetics

Even today’s most sophisticated microprocessor controlled ankle-foot prosthetic devices are passive. They lack internal elements that actively generate power, which is required during the “push-off” phase of normal able-bodied walking gait. Consequently, lower limb amputees expend 20–30% more metabolic power to walk at the same speed as able-bodied individuals. Key challenges in the development of an active ankle-foot prosthetic device are the lack of high power and energy densities in current actuator technology. Human gait requires 250W of peak power and 36 Joules of energy per step (80kg subject at 0.8Hz walking rate). Even a highly efficient motor such as the RE75 by Maxon Precision Motors, Inc. rated for 250W continuous power with an appropriate gearbox would weigh 6.6 Kg. This paper presents the first phase of the Spring Ankle with Regenerative Kinetics (SPARKy 1), a multi-phased project funded by the US Army Military Amputee Research Program, which seeks to develop a new generation of powered prosthetic devices based on the Robotic Tendon actuator, that significantly minimizes the peak power requirement of an electric motor and total system energy requirement while providing the amputee enhanced ankle motion and “push-off” power. This paper will present data to show the kinetic advantages of the Robotic Tendon and the electro-mechanical design and analysis of SPARKy 1 that will provide its users with 100% of required “push-off” power and ankle sagittal plane range of motion comparable to able-bodied gait.Copyright

Dynamically Controlled Ankle-Foot Orthosis (DCO) with Regenerative Kinetics: Incrementally Attaining User Portability

A portable wearable robotic device that can actively supplement locomotion of partially limited ambulators in their normal environment (variable terrain, weather, man made structures, etc.) seems highly desirable but currently short of attainment due to several key technology gaps. Low energy and power density in current actuation technology, inadequate control schemes and safety of use are leading challenges towards a portable, complementary device. This paper presents the dynamically controlled ankle-foot orthosis (DCO) with regenerative kinetics which seek to incrementally attain portability by solving the energy/power density issue in powered elements by harnessing elastic energy of uniquely tuned mechanical elements and reducing the control problem and increasing safety by introducing compliant elements between the human-machine-environment interfaces.

The SPARKy (Spring Ankle with Regenerative kinetics) project: Choosing a DC motor based actuation method

The design process of a powered robotic ankle prosthesis presents many obstacles that must be overcome. To be practically implemented, such a mechanism must not only run on batteries, but sustain a long running time between recharging. Using springs to passively and actively store and supply energy to the robotic ankle, small DC motors can be optimized to perform high peak power tasks without sacrificing efficiency and net energy usage. Additional techniques are explored with the potential of substantially reducing the energy requirements as well as the size and weight of the prosthesis. The benefits of adding a unidirectional parallel spring with a Robotic Tendon are weighed and the possibility of actively varying the lever arm at which the spring force is applied is analyzed. The different actuation methods are compared to determine which methods work best in different gait regimes.

Control of a Regenerative Braking Powered Ankle Foot Orthosis

Wearable robotic systems can be used to assist people suffering paralysis from stroke. This paper presents the mechanical design, electronics and control structure of a powered ankle foot orthosis for stroke survivors walking on a treadmill. the mechanical structure consists of a powered orthosis using a robotic tendon that uses a motor to correctly position a tuned spring in the gait pattern. During the gait cycle, the robotic tendon regenerates spring energy and uses that energy in order to assist the subject in push off and follow through into the swing phase of gait. Rather than using a motor and gearbox having several times the weight of the foot, which can supply the required peak power, a reduced energy robotic device is built with a 0.95 kg actuator that uses one third of the power and one half of the energy required by a standard motor/gearbox solution. This device controls the equilibrium position of the spring using a closed loop position controller. A real time embedded system was developed in the Matlab Simulink environment to form hardware in the loop simulations and allow rapid control prototyping. Not only direct-control is demonstrated using a predefined gait pattern but also State Logic is developed in order to determine the users desired gait pattern. Experimental data, gathered from able body subjects walking on a treadmill prove that the system can assist gait by decreasing the peak power that a subject should supply by 50%. It is also demonstrated that springs can apply regenerative braking and that the concept is feasible and applicable in developing lightweight, functional wearable robots.

Load carriage effects on a robotic transtibial prosthesis

The purpose of this study was to investigate the kinetic and kinematic effects of load carriage while wearing a robotic transtibial prosthesis. Nine separate tests were conducted with a unilateral transtibial amputee test subject wearing the robotic foot-ankle prosthesis. The subject walked on a treadmill at 1.3 m/s with a back pack weighing 0 kg, 4.5 kg and 9 kg. Direct measurement of the kinematics and kinetics of the robotic prosthesis at varying loads and ankle joint stiffness using embedded sensors is presented. The test data suggest that the coping strategy for load carriage is one of kinetic variance and kinematic invariance for subjects using a powered, computer controlled foot-ankle prosthesis. The finding suggests that modulation of the spring stiffness as a function of load condition may reduce system energy expenditure by 10%.

Dynamic Pace Controller for the Robotic Gait Trainer

With over 600, 000 people each year surviving a stroke, it has become the leading cause of serious long-term disability in the United States [1,2,3]. Studies have proven that through repetitive task training, neural networks can be re-mapped thus increasing the mobility of the patient [4–8]. This paper is a continuation of Kartik Bharadwaj’s and Arizona State University’s research on the Robotic Gait Trainer [9]. This work is funded in part by the National Institutes of Health (NIH), grant number - 1 R43 HD04067 01. Previously the gait cycle was fixed at two seconds. For a smooth gait the patient had to be trained to follow the frequency of the robot. Audible cues were sounded to help the patient keep rhythm with the robot. This device now has an updated control methodology based on a Matlab and Simulink platform that allows the robot to dynamically adjust to the patient’s pace of gait. Data collected from an able-bodied person walking with the new device showed that the device dynamically adjusted to any normal range of walking gait. This more flexible design will allow the patient to focus more on the therapy and walk at his/her natural pace.Copyright

Materials Considerations for Improved Flash/Flame Protection

To investigate the capabilities of protective clothing materials to withstand the initial radiant energy effects and secondary flame impingement from a blast and devise suggestions for new materials, better configuration designs, and manufacturability of those designs must be considered. This paper discusses results that will directly benefit soldiers and others with risk to exposure of flash/flames due to explosions. Dismounted soldiers need a material that has improved flash/flame protective qualities to better protect them in combat situations that may result in burn injuries from fires that originate from a blast. This paper investigates why the burns occurred, how the materials used in the current configuration of clothing could be improved upon, and what new materials choices can be made in other configurations to better protect dismounted soldiers. The causes of failure have been evaluated, and by way of reverse and forward engineering, alternative choice of materials and improved designs has been considered. As a result, a prototype can/will be built based on the design characteristics, tested, and potentially fielded for use by soldiers. The paper provides sufficient background information on the anatomy of explosions, physiology of burn injuries, and blast type and burn relationships. Current testing methods for testing burn-protection materials are discussed including both bench scales and full scale tests and the pros and cons of each. The engineering requirements for current fire resistant clothing are broken down. Then, a description of the assumptions is listed, and the engineering design process is applied to the problem to determine which characteristics are most important in this type of fire-resistant material. This process includes a survey and several design tools to narrow the design criteria to the most important engineering characteristics required for a successful application of the design. Another aspect is introduced by including an analysis of the heat transfer characteristics of fire-resistant materials to help narrow the criteria and better understand the problem.© 2009 ASME