FIGURE 5 - available via license: Creative Commons Attribution 4.0 International
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| Base of support (BoS) of the robot feet. The right foot (outer rectangle) is labeled OFL-Original Front Left, OFR-Original Front Right, OBL-Original Back Left, and OBR-Original Back Right. The inner rectangle is labeled in an identical manner, with A as an abbreviation for Actual (BoS). (A) shows the dimensions of both feet in blue, with a width of 14 cm (OFL-OFR) and a length of 21 cm (OBR-OFR). The blue area describes the convex hull of each foot which is equal to the foot contact surface. The origin of the left and right foot is shown as a circle. The actual BoS is depicted as a green inner rectangle and is significantly smaller than the convex hull, with a width of 10.6 cm (AFL-AFR) and a length of 15.5 cm (ABR-AFR). The BoS was determined by experiments in which the robot was tilted while in null pose during single support (on one leg) and double support (on both legs) along the lateral and longitudinal axis until the robot tipped over. The labels correspond to (B), which shows the right foot of REEM-C and relates the dimensions of both the actual BoS and the contact area, that is, the convex hull of the foot.
Source publication
To enable the application of humanoid robots outside of laboratory environments, the biped must meet certain requirements. These include, in particular, coping with dynamic motions such as climbing stairs or ramps or walking over irregular terrain. Sit-to-stand transitions also belong to this category. In addition to their actual application such a...
Contexts in source publication
Context 1
... BoS is located inside a convex hull which is spanned by the contact surfaces of both feet when the robot is standing. In the case of REEM-C, the convex hull of the feet does not correspond to the actual BoS while standing ( Figure 5A). While a foot is about 21 cm long and 14 cm wide, we determine the BoS over a range of 15.5 cm length by 10.6 cm width ( Figure 5B). ...
Context 2
... the case of REEM-C, the convex hull of the feet does not correspond to the actual BoS while standing ( Figure 5A). While a foot is about 21 cm long and 14 cm wide, we determine the BoS over a range of 15.5 cm length by 10.6 cm width ( Figure 5B). This significantly smaller BoS is determined based on tipping over experiments. ...
Citations
... The movement speed in the elderly is found to be slower than the younger population, suggesting that a stable STS does not solely rely on leg muscle strength, but also the ability to maintain stability (Yamada and Demura, 2009). Optimal control was utilized to determine the best way possible for external forces to support an elderly person doing STS (Mombaur and Ho Hoang, 2017) and the optimal trajectory for the REEM-C humanoid robot to perform unassisted STS (Aller et al., 2022). Recently, an impedance modulation control that accounts for balance reinforcement and impedance compensation is created to assist STS motion of a person wearing the Angeleg exoskeleton (Huo et al., 2022). ...
... Optimal control is an optimization-based approach to determine the control and state trajectories over a time period, such that an objective function related to said controls and states are minimized (Siciliano et al., 2009). Since it is able to determine the required joint actuation of a recorded motion (Koch and Mombaur, 2015) and also generate an optimal trajectory (Hu and Mombaur, 2017;Mombaur and Ho Hoang, 2017;Aller et al., 2022), this method is chosen for the computational STS investigation presented. The dynamic process of interest is a person, without using crutches, performing STS with and without the TWIN exoskeleton. ...
With the global geriatric population expected to reach 1.5 billion by 2050, different assistive technologies have been developed to tackle age-associated movement impairments. Lower-limb robotic exoskeletons have the potential to support frail older adults while promoting activities of daily living, but the need for crutches may be challenging for this population. Crutches aid safety and stability, but moving in an exoskeleton with them can be unnatural to human movements, and coordination can be difficult. Frail older adults may not have the sufficient arm strength to use them, or prolonged usage can lead to upper limb joint deterioration. The research presented in this paper makes a contribution to a more detailed study of crutch-less exoskeleton use, analyzing in particular the most challenging motion, sit-to-stand (STS). It combines motion capture and optimal control approaches to evaluate and compare the STS dynamics with the TWIN exoskeleton with and without crutches. The results show trajectories that are significantly faster than the exoskeleton's default trajectory, and identify the motor torques needed for full and partial STS assistance. With the TWIN exoskeleton's existing motors being able to support 112 Nm (hips) and 88 Nm (knees) total, assuming an ideal contribution from the device and user, the older adult would need to contribute a total of 8 Nm (hips) and 50 Nm (knees). For TWIN to provide full STS assistance, it would require new motors that can exert at least 121 Nm (hips) and 140 Nm (knees) total. The presented optimal control approaches can be replicated on other exoskeletons to determine the torques required with their mass distributions. Future improvements are discussed and the results presented lay groundwork for eliminating crutches when moving with an exoskeleton.
