Abstract
Augmenting the physical strength of a human operator during unpredictable human-directed (volitional) movements is a relevant capability for several proposed exoskeleton applications, including mobility augmentation, manual material handling, and tool operation. Unlike controllers and augmentation systems designed for repetitive tasks (e.g., walking), we approach physical strength augmentation by a task-agnostic method of force amplification—using force/torque sensors at the human–machine interface to estimate the human task force, and then amplifying it with the exoskeleton. We deploy an amplification controller that is integrated into a complete whole-body control framework for controlling exoskeletons that includes human-led foot transitions, inequality constraints, and a computationally efficient prioritization. A powered lower-body exoskeleton is used to demonstrate behavior of the control framework in a lab environment. This exoskeleton can assist the operator in lifting an unknown backpack payload while remaining fully backdrivable.
Highlights
Exoskeletons offer the potential to greatly augment the physical load carrying ability by placing the strength of machines under the dexterous control of people
Strength amplification can be illustrated using the example of an ideal fixed-base “exoskeleton” performing a forcefeedback behavior with an end effector in contact with both the human and some load
While the human term stays the same, every other term is reduced. We could say these closed-loop dynamics amplify the influence of the human force by a factor of α
Summary
Exoskeletons offer the potential to greatly augment the physical load carrying ability by placing the strength of machines under the dexterous control of people. Amplification control systems are designed to magnify the physical strength of the operator as he or she interacts with a load through the exoskeleton, while reducing the weight and inertia the operator feels from the exoskeleton itself This kind of control allows non-repetitive, unpredictable tasks with unknown payloads. Admittance control for exoskeletons Yu and Rosen (2013); Fontana et al (2014); Jacobsen and Olivier (2014); Lecours et al (2012) uses force sensor feedback at the human interface in order to increase the human-side closed-loop admittance, reduce sensitivity to the mass model, and lift unknown loads. The controller from Kazerooni and Guo (1993) was still not designed to improve the human-side admittance relative to the torque-controlled gravity compensation strategy It still used admittance control and a position-controlled robot. We demonstrate the deployed controller’s ability to reduce the human effort necessary to lift the robot itself and an unknown payload, as well as the operator’s ability to back-drive the system to walk around and climb some stairs (Sec. 6)
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