Matthew Holgate

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.

SPARKy 3: Design of an active robotic ankle prosthesis with two actuated degrees of freedom using regenerative kinetics

The goal of modern prosthetics is to replicate the function of the replaced limb or organ in the most capable and discreet fashion possible. However, even the most advanced, commercial, transtibial prostheses available today only passively adjust the position of the ankle during the swing phase of gait and return a portion of the userpsilas own gravitational input. To greatly improve the quality of life of a transtibial amputee, new technologies and approaches must be used to create a cutting-edge robotic ankle prosthesis which can perform on par with, if not outperform, the equivalent able-bodied human ankle. Initial attempts by us and others have had great success in providing the natural gait power and motion through all ranges of walking speeds. A new design is presented which governs both the coronal and sagittal angles and moments of the ankle joint to potentially provide unprecedented levels of athleticism and agility among transtibial amputees.

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

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.

A novel control algorithm for wearable robotics using phase plane invariants

With microprocessing power greatly increasing, hardware is no longer a hurdle in the development of controllers for wearable robotic systems, specifically lower limb robots. The challenge remains in developing smart algorithms that are able to detect which task a person is about to perform and then determine the correct desired movements for the robotic system. This paper reflects on four existing control algorithms for the task of level ground walking, and then presents theory and test results of a novel control algorithm based on phase plane invariants. The goal of this paper is to produce the correct motor reference command in a continuous fashion rather than based on determining distinct states for a given task.

Control algorithms for ankle robots: A reflection on the state-of-the-art and presentation of two novel algorithms

With computer speeds greatly increasing, hardware is no longer a hurdle in the development of controllers for wearable lower limb robots. The challenge remains in developing smart algorithms that are able to detect which task a person is about to perform and then supply the robot with the correct desired movements. This paper reflects on some existing control algorithms and then presents theory and test results of two novel concepts. The goal of this paper is to show that the two new concepts are capable of producing the correct motor profile.

Limit Cycles to Enhance Human Performance Based on Phase Oscillators

Wearable robots including exoskeletons, powered prosthetics, and powered orthotics must add energy to the person at an appropriate time to enhance, augment, or supplement human performance. This “energy pumping” at resonance can reduce the metabolic cost of performing cyclic tasks. Many human tasks such as walking, running, and hopping are repeating or cyclic tasks where assistance is needed at a repeating rate at the correct time. By utilizing resonant energy pumping, a tiny amount of energy is added at an appropriate time that results in an amplified response. However, when the system dynamics is varying or uncertain, resonant boundaries are not clearly defined. We have developed a method to add energy at resonance so the system attains the limit cycle based on a phase oscillator. The oscillator is robust to disturbances and initial conditions and allows our robots to enhance running, reduce metabolic cost, and increase hop height. These methods are general and can be used in other areas such as energy harvesting.

Adding and Subtracting Energy to Body Motion: Phase Oscillator

We are developing methods to add a bounded amount of energy to assist body motion. Energy is added based on the phase angle of the limb to create a “phase oscillator.” The energy is added assisting motion creating an oscillatory behavior. An anti-phase angle can be used to subtract energy from body motion as well. Using a “phase oscillator” controller, a powered hip exoskeleton assisted a runner and demonstrated a reduction in metabolic cost.Copyright

Compliant mechanisms for robotic ankles

We have developed a compliant robotic tendon mechanism for a robotic ankle. In this paper, we analyze the differences between a stiff and compliant robotic tendon versus a stiff and compliant slider crank mechanism. The compliant, slider-crank mechanism reduces peak forces and speed required by an actuator at the ankle.Copyright