Bipedal walking design for energy-optimal locomotion in varying environments

Abstract
Energy-efficient locomotion is an important requirement in the development of biped robots. Due to the limited energy storage (battery), the energy consumption significantly determines the walking distance to be covered. The energy efficiency depends on the controller used for the motion as well as on the structural design and mechanical parameters of the walking system. In this case, the solution approach is the application of special compliant functional systems that, depending on the environmental conditions and the gait, achieve an always advantageous matching of mechanical system elements, resulting in high energy efficiency. Thus, researchers teach bipedal walkers to move in a highly energy-efficient manner in different situations and across gaits.

Motivation
In technical bipedal walking systems, the inherent dynamics of the system can be adjusted to achieve high energy efficiency by adjusting mechanical system elements such as springs and dampers. However, adjusting mechanical elements to one gait results in the disadvantage that other gaits can only be performed with suboptimal efficiency. When using special mechanical elements that change their compliance and qualitative behaviour, it is possible to adjust the system simultaneously to a changing gait as well as to a varying environment so that energy efficiency and robustness increase while the control effort remains low. Such mechanical elements are compliant functional systems - compliant multi-stable mechanisms in combination with functional materials capable of changing their compliance and deformation behaviour. Walking systems with such systems are not known from the state of the art and research. Therefore, this project aims at establishing a scientific basis for the use of compliant functional systems for an engineered running system.

Aim
Therefore, the goal of this research project is to develop and apply a method to systematically optimize a biped robot to maximize energy efficiency in varying environments and for different gaits. The method is based on the application of compliant functional systems with variable properties that are specifically designed, optimized, and applied for energy consumption minimization for biped robots in a model-based manner.

Project work
In the first step, an underactuated robot model consisting of five segments is considered. Its rigid segments are additionally connected by compliant functional systems. They are applied not only in the conventional way as connections between segments of a leg, but also as connections between legs, providing additional and advantageous possibilities in terms of energy efficiency. Due to model-based research work of walking movements, optimal characteristics for spring and damper properties of the compliant functional systems are to be sought. Such systems should be able to imitate preferably any characteristic corresponding to the different gaits and environments. Suitable synthesis methods are developed and applied to the design of compliant functional systems to design such compliant systems. The latter are then manufactured and tested for functionality. A walking robot with the compliant functional systems is built and tested to prove and demonstrate its energy efficiency.
This project is being carried out jointly by two research partners: the Compliant Systems Group (FG NSYS) at the Technische Universität Ilmenau (TU Ilmenau) and the Institute of Engineering Mechanics (ITM) at the Karlsruhe Institute of Technology (KIT).

Results to be expected
The first results already allow an energy saving of over 70% when moving a walking system with compliant functional systems compared to a conventional walker. The walking system adapts to its gait and to any changing surface to always walk energy-efficiently on any ground, be it sandy, stony, or flat. Unlike other walking and driving systems, this results in the ability to cover longer distances. Therefore, the system can penetrate dangerous or unknown environments, such as catastrophic areas, other planets, further than conventional robots and perform rescue as well as investigation and courier tasks or the like. The walker to be developed is more energy-efficient than a wheel-driven vehicle and can master obstacles better. Therefore, it can also be used in extremely poorly passable environments where wheeled solutions are unsuitable.
The methods developed during the project can theoretically be extended to other areas where clocked oscillating mechanical systems are to gain energy efficiency. Their oscillation behaviour is always kept in the resonance range under changing conditions using developed methods, which promises high efficiency. Examples are automated production chains.