Variable Geometry Stair Ascent and Descent Controller for a Powered Lower Limb Exoskeleton

Abstract

This paper describes a control approach for a lower limb exoskeleton intended to enable stair ascent and descent of variable geometry staircases for individuals with paraplegia resulting from spinal cord injury (SCI). To assess the efficacy of ascent and descent functionality provided by the control approach, the controller was implemented in a lower limb exoskeleton and tested in experimental trials on three subjects with motor-complete SCI on three staircases of varying geometry. Results from the assessments indicate that subjects were able to capably ascend and descend step heights varying from 7.6 to 16.5 cm without changing control settings; the controller provided for step time consistency highly representative of healthy subjects (9.2% variation in exoskeleton step time, relative to 7.7% variation in healthy subjects); and the exoskeleton provided peak joint torques on average 110% and 74% of the healthy-subject peak joint torques during stair ascent and descent, respectively. Subject perceived exertion during the stair ascent and descent activities was rated between “light” and “very light.”

Exoskeleton robots for lower limb assistance: A review of materials, actuation, and manufacturing methods

“…Indgeo has both carbon polymeric parts manufactured by 3D printing and metallic parts made by conventional CNC machining methods. 34 Similarly, the mechanical frame of Lokomat has been manufactured by using CNC machining. The casings to hide the mechanical parts of Lokomat for improved appearance have been manufactured by using 3D printing as mentioned in Table 1.…”

“…An alternate promising solution has been proposed by the developers of the Indego robot exoskeleton at Vanderbilt University. 34 Indego is composed of carbon composites, while high strength aluminum is utilized at the joints for enhancing strength. This has helped in reducing the weight of Indego to 27 pounds without compromising the strength of the orthosis.…”

“…DC motors are broadly classified into two types: brushless DC motors and synchronous AC motors. Exoskeletons such as Indego, 34 Re Walk, HAL (Figure 1(a)), 23,55 Lokomat, 38,39 ALEX (Figure 1(b)), 24 SCUT robotic exoskeleton, 48 WPAL 56 used DC motors for actuation. The benefits of electric actuators lie in their high-power capacity, torque-to-weight ratio, precision, and the others.…”

Trajectory-Free Control of Lower-Limb Exoskeletons Through Underactuated Total Energy Shaping

“…This suggests that each "layer" of the matrix carries a different weight in the overall kinetic energy. Motivated by this fact, we definedM 4 ∈ R 5×5 as: (5,8) . .…”

“…For instance, the hip-knee exoskeletons ReWalk [1], Ekso Bionics [2], and ATLAS [3] enforce predetermined joint kinematics through a finite-state-machine structure. The control strategies of other exoskeletons, such as the Hybrid Assistive Limb [4] and the Indego exoskeleton [5], also fall into the category of trajectory tracking. Despite the fact that these exoskeletons have shown promising results in gait rehabilitation, critical barriers still exist in the control technology, which limits their overall adaptability.…”