Mechanical and biomechanical analysis of a linear piston design for angular-velocity-based orthotic control

Abstract

Abstract-A linear piston hydraulic angular-velocity-based control knee joint was designed for people with knee-extensor weakness to engage knee-flexion resistance when knee-flexion angular velocity reaches a preset threshold, such as during a stumble, but to otherwise allow free knee motion. During mechanical testing at the lowest angular-velocity threshold, the device engaged within 2 degrees knee flexion and resisted moment loads of over 150 Nm. The device completed 400,000 loading cycles without mechanical failure or wear that would affect function. Gait patterns of nondisabled participants were similar to normal at walking speeds that produced belowthreshold knee angular velocities. Fast walking speeds, employed purposely to attain the angular-velocity threshold and cause knee-flexion resistance, reduced maximum knee flexion by approximately 25 degrees but did not lead to unsafe gait patterns in foot ground clearance during swing. In knee collapse tests, the device successfully engaged knee-flexion resistance and stopped knee flexion with peak knee moments of up to 235.6 Nm. The outcomes from this study support the potential for the linear piston hydraulic knee joint in knee and kneeankle-foot orthoses for people with lower-limb weakness.

Numerical Study of a Customized Transtibial Prosthesis Based on an Analytical Design under a Flex-Foot® Variflex® Architecture

“…Calculation of the strain energy generated in the curved zone, through the deformation of equations defined by the strain energy, produces the Castigliano theorem: (7) Using the first Castigliano theorem (Equation ( 7)):…”

“…The operating conditions are the reaction times and forces, as well as the angles between each joint during the running cycle. In terms of biomechanical design, the main factors to consider are the mechanical properties [4], the length of the prosthesis [5,6], and the weight of the prosthetic components [7]. Most studies in the literature have focused on assessments of the kinematic and kinetic gait [8] and foot plantar pressure [9].…”

Design, development, and evaluation of a local sensor-based gait phase recognition system using a logistic model decision tree for orthosis-control

“…Some designs use weighted/spring-loaded pawls or belt clamping [1, 2, 4] to lock the knee at initial contact and disengage at foot-off, based on leg position. Most mechanically-controlled SCKAFO require full knee extension to engage knee-lock [4, 5, 8]. This can present difficulties for individuals who cannot extend their leg at each step, making continuous and reliable stance-control more difficult.…”

“…This can present difficulties for individuals who cannot extend their leg at each step, making continuous and reliable stance-control more difficult. Persons with knee-extensor weakness that have sufficient hip-flexion control could also use angular velocity based stance-control [3, 8, 9], where mechanical components at the knee engage knee-flexion resistance at any knee angle once an angular velocity threshold is passed, such as during a knee collapse or fall event (i.e., body weight sensing not required).…”

“…Unfortunately, mechanically-controlled SCKAFO can have inconsistent stance/swing phase recognition, leading to unreliable locking and unlocking and poor functional versatility across different walking conditions. Mechanically-controlled SCKAFO can also have difficulty negotiating between different walking speeds, gait modes, terrains, and daily living environments (i.e., stairs, ramps, uneven ground) [3–5, 8, 10–12].…”