Kevin W. Hollander

Compliant actuator designs

In the growing fields of wearable robotics, rehabilitation robotics, prosthetics, and walking k robots, variable stiffness actuators (VSAs) or adjustable compliant actuators are being designed and implemented because of their ability to minimize large forces due to shocks, to safely interact with the user, and their ability to store and release energy in passive elastic elements. This review article describes the state of the art in the design of actuators with adaptable passive compliance. This new type of actuator is not preferred for classical position-controlled applications such as pick and place operations but is preferred in novel robots where safe human- robot interaction is required or in applications where energy efficiency must be increased by adapting the actuators resonance frequency. The working principles of the different existing designs are explained and compared. The designs are divided into four groups: equilibrium-controlled stiffness, antagonistic-controlled stiffness, structure-controlled stiffness (SCS), and mechanically controlled stiffness.

An Efficient Robotic Tendon for Gait Assistance

A robotic tendon is a spring based, linear actuator in which the stiffness of the spring is crucial for its successful use in a lightweight, energy efficient, powered ankle orthosis. Like its human analog, the robotic tendon uses its inherent elastic nature to reduce both peak power and energy requirements for its motor. In the ideal example, peak power required of the motor for ankle gait is reduced from 250 W to just 77 W. In addition, ideal energy requirements are reduced from nearly 36 J to just 21 J. Using this approach, an initial prototype has provided 100% of the power and energy necessary for ankle gait in a compact 0.95 kg package, seven times less than an equivalent motor/gearbox system.

Comparison of Mechanical Design and Energy Consumption of Adaptable, Passive-compliant Actuators

Different, adaptable, passive-compliant actuators have been developed recently such as the antagonistic setup of two Series Elastic Actuators, the Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator, the Actuator with Mechanically Adjustable Series Compliance, and the Variable Stiffness Actuator. The main purpose of these designs is to reduce the energy consumption of walking/running robots and prostheses. This paper presents a design formulation to link the different mechanical designs together, and a study on the power consumption of these actuators.

Adjustable robotic tendon using a 'Jack Spring'/spl trade/

An adjustable robotic tendon is a spring based linear actuator in which the properties of a spring are crucial to its successful use in a gait assistance device. Like its human analog, the adjustable robotic tendon uses its inherent elastic nature to both reduce peak power and energy requirements for its motor. In the ideal example, peak power required of the motor for ankle gait is reduced from 250 W to just 81 W. In addition, ideal energy requirements are reduced from nearly 36 Joules to just 25 Joules per step. Using this approach, an initial prototype is expected to provide 100% of the power and energy necessary for ankle gait in a compact 0.84 kg package. This weight is 8 times less than that predicted for an equivalent direct drive approach.

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.

Design, implementation and test results of a robust control method for a powered ankle foot orthosis (AFO)

There are various methods to control a powered AFO. As different as they are in their approach each of them has certain advantages as well as difficulties. What is still needed is a robust control concept that meets the requirements for ankle gait assistance. A new, stiffness-control model has been developed that divides the stance phase of gait into five zones using either velocity or stiffness control for each zone. The design and implementation of this new control algorithm as well as some first test results are presented.

A robotic 'jack spring'™for ankle gait assistance

A Robotic ‘Jack Spring’™ is a new type of mechanical actuator, which is based upon the concept of structure control. A Jack Spring™ mechanism is used to create an adjustable Robotic Tendon, which is a spring based linear actuator in which the properties of a spring are crucial to its successful use in gait assistance. Like its human analog, the adjustable Robotic Tendon uses its inherent elastic nature to reduce both peak power and energy requirements for its motor. In the ideal example, peak power required of the motor for ankle gait is reduced from 250W to just 81 W. In addition, ideal energy requirements are reduced from nearly 36 Joules to just 25 Joules per step. Using this approach, an initial prototype is expected to provide 100% of the power and energy neccessary for ankle gait in a compact 0.84kg package. This weight is 8 times less than that predicted for an equivalent direct drive approach.© 2005 ASME