Stiffness adjustment of a series elastic actuator in a knee prosthesis for walking and running: The trade-off between energy and peak power optimization

Abstract

In ankle-foot prostheses a serial spring can assist the motor to reduce peak power (PP) and energy requirements (ER) during locomotion. Similar benefits can be expected for an active knee prosthesis. We compare the situation of a direct drive with a series elastic actuator optimized for minimal ER or for minimal PP. The simulations indicate that at the knee joint a serial spring can highly reduce ER and PP in running and fast walking. Around preferred walking speed (1.3m/s) only a reduction in ER is found. The optimal stiffness changes with speed and gait. Still it is possible to use one constant stiffness for a huge range of walking and running speeds with only moderate increases of ER and PP in comparison to speed and gait optimized values.

Analyzing and considering inertial effects in powered lower limb prosthetic design

“…Inverse dynamics simulations for stiffness optimization consider different types and velocities of gait as in [16]. To calculate the biomechanical loads on the knee joint during gait, human kinematic data acquired from participants without amputation for walking at 1.6 m s −1 and running at 2.6 m s −1 in [20] are utilized as trajectories representing gait of an average able-bodied person.…”

“…In the design process, biomechanical requirements regarding velocities, forces/torques, and powers/energies are usually determined from gait analysis and/or simulation considering able-bodied subjects, e. g., in [4], [5], [14]- [16]. Thus, the inertial influences of the prosthetic system are not considered.…”

“…Thus, the inertial influences of the prosthetic system are not considered. This is also the case in most approaches to the design and stiffness optimization of elastic actuators that are used due to their benefits in energy efficiency [4], [5], [14], [16]. A first consideration of the real inertial properties usually takes place in experiments with prototypes as in [3], [11], [12] and hence does not influence design before the prototype level.…”

“…Beyond the inertial properties of the prosthetic system itself, the inertia of the actuator has been shown to have significant impact on power consumption and energy balance of powered devices with variable stiffness actuation [7]. However, this effect is also not covered in powered lower limb prosthetics design, e. g., in an established method for stiffness optimization [4], [14], [16]. This paper describes and discusses a method to consider the inertial influences of the whole system and the actuator in powered lower limb prosthetic design based on [7].…”

The Energy Amplification Characteristic Research of a Multimodal Actuator

“…The SEA was first developed at MIT [10], involving springs attached to a motor in series to mimic many of the desirable properties of human muscles. SEAs have since been applied in humanoid robots [11][12], rehabilitation robots and power-assisted exoskeletons [13][14][15]. Power output is an important characteristic for evaluating the capacity of an SEA.…”