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

Abstract

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.

Conceptual Design of a Powered Ankle-foot Prosthesis for Walking with Inversion and Eversion

“…The active planter flexion-dorsiflexion can decrease an amputees metabolic cost (COT), or the metabolic energy required to transport unit body weight to unit distance, compared to a conventional passive elastic feet. The most recent electrically driven ankle foot prosthesis has been developed by the Arizona State University Human Machine Integration Lab and is called SPARKy3 (Spring Ankle with Regenerative Kinetics) [7]. SPARKy 3 is two degrees of freedom (DOF) device incorporating active control of inversion and eversion, plantar flexion and dorsiflexion.…”

Advances in Propulsive Bionic Feet and Their Actuation Principles

“…The best device in this category is the SPARKy 2 prototype [55,57,58] which has shown to support these 3 tasks. Other devices have the potential to be highly adaptable but still need to prove it.…”

“…At the Arizona State University (ASU-United States), the SPARKy project (Spring Ankle with Regenerative Kinetics) [55] uses a robotic tendon actuator (including a 150 W Brushed DC motor-Maxon RE40) [56] to provide 100% of the push-off power required for walking while maintaining intact gait kinematics. The first prototype (SPARKy 1 shown in Figure 10(a)) [57] was shown to store and release approximately 16 J of energy per step, while an intact ankle of a 80 kg subject at 0.8 Hz walking rate needs approximately 36 J [58]. A second prototype (SPARKy 2- Figure 10(b)) was built with a lighter and more powerful roller screw transmission and brushless DC motor.…”

Case Study on Human Walking during Wearing a Powered Prosthetic Device: Effectiveness of the System “Human-Robot”

“…Their device employed a pneumatic actuation strategy with an off-board power supply. More recent work has focused on the design of energetically autonomous powered systems [12][13][14]. In the growing field of rehabilitation robotics, the use of compliant actuators is becoming a standard where accurate trajectory tracking is not required.…”