Heidi Cuypers

Mechatronic design of a sit-to-stance exoskeleton

This paper describes the design and development of an exoskeleton that can deliver assistance-as-needed to patients or elderly with muscle weakness. Since the proof-of-concept is a first step towards the development of a final commercial prototype, the design had to be adaptable for patients with different heights, be comfortable for the patients, safe in use, energy-efficient and affordable in production. For this reason a modular system was built, using the same compliant actuator system in all joints. This paper describes the global design decisions made and the construction of the actual prototype.

Conceptual design of a novel variable stiffness actuator for use in lower limb exoskeletons

A novel modular variable stiffness actuator (VSA), for use in the knee joint of lower limb exoskeletons, is presented. The actuator consists of a combination of a spindle-driven MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) and a spring acting in parallel, (dis)engaged by means of a simple on/off mechanism depending on the phase of the gait cycle. Such design approach is inspired by two clearly distinctive gait phases of a knee joint, one with a high velocity and low torque, and another one with low velocity and high torque profiles. By tackling each of these two phases separately, energy consumption and torque requirements of an active part of the actuator have been decreased, while keeping the size and the weight of the actuator at a reasonable size for use in wearable robots (WR).

Design of a modular add-on compliant actuator to convert an orthosis into an assistive exoskeleton

In an ageing population many people with muscle weakness may benefit from an assisting exoskeleton to improve their mobility. Recent developments in research labs around the world are often complex, not modular and expensive. This paper introduces a novel modular compliant actuator for use in assistive lower limb exoskeletons. It is a low-cost, light-weight, compliant actuator unit that can be easily mounted on commercially available orthoses. It has the versatility to assist hip-, knee- and ankle flexion/extension individually and/or in sit-to-stance or walking activities. An adjustable passive compliance is achieved by a design based on the MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) principle. The assisting output torque and the rendered range of compliance are simulated and experimentally demonstrated.

Analysis and verification of the performance of sandwich panels with textile reinforced concrete faces

Textile-reinforced concrete (TRC) is a composite material that recently gained renewed interest. Due to an improved durability, the usage of this composite in lightweight constructions becomes possible. In this article, the behavior of sandwich panels with TRC faces is studied. In the first part, several models are used in a finite element analysis and their advantages and disadvantages are discussed. In the second part, the calculated nonlinear behavior of the panels is compared to experimental observations.

MEASUREMENT OF THE DURABILITY OF GLASS FIBRE REINFORCED CONCRETE AND INFLUENCE OF MATRIX ALKALINITY

ABSTRACT Even today, one main topic of consideration regarding glass-fibre reinforced cementitious composites is the durability. At RWTH-Aachen (Germany) the durability of AR-glass yarns in concrete is under investigation. The aim of these investigations is to build up a model, allowing prediction of the long-term behaviour of textile reinforced concrete. This model includes the influence of humidity, pH and temperature conditions, combined with stress (constant load). For glass-fibre reinforced cementitious composites, the pH of the matrix has a considerable influence on the durability, since glass fibres can be severely attacked by high alkalinity. To overcome this problem a new cementitious material has been developed at the VUB (Brussels, Belgium). This Inorganic Phosphate Cement (IPC) provides a non-alkaline environment after hardening. Since the IPC matrix provides a neutral environment, other effects (humidity, temperature, stress) can be studied. A more common concrete mixture (micro-concrete with Ordinary Portland Cement (OPC), pH 13.5 after hardening) is also tested as a comparison material. The evolution of the tensile strength of IPC composites and OPC composites with AR-glass and with E-glass is measured and discussed. It is shown that the IPC matrix has in comparison to OPC a good durability.

Modeling Of The Tensile Behaviour Of An E-glassFibre Reinforced Phosphate Cement

ACK theory is found feasible to model the tensile behaviour of laminates based on inorganic phosphate cement/E-glass fibre mat, although the moduli in elastic and multiple cracking zone need to be adapted in consideration of 2-D random fibre distribution. The good agreement between experimental and calculated tensile curve shows that the E-glass fiber used in the laminates functions very well as reinforcement in IPC matrix. A parameter K defined in this paper obtained in the post cracking zone appears to be a useful tool to evaluate the quality of the fibre/matrix interface. The result will be helpful in computer aided design of IPC composites.

Durability aspects of AR-glass-reinforcement in textile reinforced concrete, Part 1: Material behaviour

Textile reinforced concrete (TRC) is an innovative material for thin-walled, structural elements with a high load-bearing capacity. For a safe design of TRC load bearing structures ambitious investigations were carried out to predict the time-dependent loss of strength of the AR-glass reinforcement embedded in fine grained concrete as a consequence of weathering. In the present paper possible reasons for the loss of strength of state-of-the art AR-glass reinforcement in nowadays cementitious mixtures are described and their relative importance is discussed, based on new results. In the accompanying paper (part 2), these results are used to present a durability model under complex weathering conditions.

Prototype design of a novel modular two-degree-of-freedom variable stiffness actuator

In bio-inspired robotic applications, multiple-degree-of-freedom actuators are often desired. The current state of the art of variable stiffness actuators consist mostly of different concepts for single-degree-of-freedom joints. An innovative Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator (MACCEPA) concept is presented to specifically accommodate implementation in two-degree-of-freedom joints. A prototype design, based on this concept, is furthermore presented. The working principle and relevant design choices are explained, a zero-dynamic model is derived for future design iterations, and the implementation in a first prototype is discussed.

Durability aspects of AR-glass-reinforcement in textile reinforced concrete, Part 2: Modelling and exposure to outdoor weathering

For a safe design of TRC (Textile reinforced concrete) load bearing structures the loss of strength of TRC as a consequence of weathering should be modelled. In part 1, possible reasons for the loss of strength of a state-of-the art AR-glass textile reinforced concrete were discussed. These findings are first used in this paper as a base for a corrosion model, describing the loss of strength in lab conditions. Subsequently, temperature and humidity were continuously measured during outdoor weathering and implemented into the model.

Modular Grid-based Design Concept ForFibre Reinforced Composite Shells

When designing a modular system, two main aspects need to be considered: the aspect of one building stone and the aspect of the overall structure. Both will be studied here in function of geometry, mechanical behaviour and historical background (architectural design, engineering science,...). The state-of-the-art of design principles, used in architectural designs over the latest decades, will provide the basis knowledge for the generation of a new kind of modular constructions. Combining both the artistic point of view (aesthetics) and the engineering point of view (calculations, FEM), a new design-concept will be generated: a system with modular hyperbolic paraboloid building stones, connected to one another through hinged connections.