Hendrik Van Brussel

Open Controller Architecture – Past, Present and Future

Abstract Open Control Systems are the key enabler for the realization of modular and re-configurable manufacturing systems. The large number of special purpose machines and the high level of automation have led to an increasing importance of open control systems based on vendor neutral standards. This paper gives an overview on the past, present and future of Open Controller Architecture. After reflecting on the different criteria, categories and characteristics of open controllers in general, the CNC products in the market are evaluated and an overview on the world-wide research activities in Europe, North America and Japan is given. Subsequently the efforts to harmonize the different results are described in order to establish a common world-wide standard in the future. Due to the “mix-and-match” nature of open controllers concentrated attention must be paid to testing mechanisms in the form of conformance and interoperability tests.

Multi-agent coordination and control using stigmergy

This paper describes and discusses a novel design and a prototype implementation for manufacturing control systems, aimed at handling changes and disturbances. This novel design utilizes the concept of a multi-agent system. Agents in this system use an indirect coordination mechanism, called stigmergy. Stigmergy is a class of mechanisms that mediate animal-animal interactions. It consists of indirect communication that is taking place between individuals of an insect society by local modifications induced by these insects on their environment. The coordination mechanism in this paper is based on a technique used by food foraging ants. Food foraging ants provide the inspiration by the manner in which they spread information and make global information available locally; thus, an ant agent only needs to observe its local environment in order to account for nonlocal concerns in its decisions. A prototype was built to test the coordination technique. The prototype comprises a flexible manufacturing system model/emulation that has dynamic order arrival, probabilistic processing time, and some general perturbations such as machine breakdowns. The prototype served to investigate a specific research question: is it possible to create short-term forecasts based on the intentions of the agents. It has been intentionally kept simple to facilitate the understanding of what is happening in the system. Size and complexity of the prototype implementations are being augmented gradually in ongoing research.

A New Approach to Modeling Hysteresis in a Pneumatic Artificial Muscle Using The Maxwell-Slip Model

Two main challenges in using a pneumatic artificial muscle (PAM) actuator are the nonlinearity of pneumatic system and the nonlinearity of the PAM dynamics. The latter is complicated to characterize. In this paper, a Maxwell-slip model used as a lumped-parametric quasi-static model is proposed to capture the force/length hysteresis of a PAM. The intuitive selection of elements in this model interprets the unclear, but blended contributing causes of the hysteresis very well, which are assumed to originate from the dry friction of the double helix weaving of the PAM braided shell, the friction of the weaving and the bladder, the elasticity of the bladder and/or the deformation of the conical parts of a PAM close to the end caps. The obtained model is simple, but physically meaningful and easy to handle in terms of control.

Design aspects of shape memory actuators

Abstract The need for high performance and at the same time compact actuators has existed for a long time, especially for multi-degree-of-freedom devices like robot hands and walking robots. These devices mostly use electrical actuators. Also for the presented research, the interest in designing actuators based on shape Memory Alloys emerged from a study in the field of multi-fingered robot hands. Shape Memory Alloy actuation is very attractive because of the very high power density that can be obtained using these materials. When calculating the ratio of actuator output to actuator volume, also called power density, SMA actuators offer even higher values than hydraulic actuation. Nevertheless, controlling these actuators and implementing them in robotic systems is not so straightforward. This paper defines a number of design rules for shape memory alloy based robotic actuators. It is demonstrated that SMA actuation offers very attractive properties for example in space applications and especially in a zero-gravity environment. This paper also shows that, when using an appropriate cooling method, accurate position control for Shape Memory Alloy actuators can be obtained.

Context-based filtering for assisted brain-actuated wheelchair driving

Controlling a robotic device by using human brain signals is an interesting and challenging task. The device may be complicated to control and the nonstationary nature of the brain signals provides for a rather unstable input. With the use of intelligent processing algorithms adapted to the task at hand, however, the performance can be increased. This paper introduces a shared control system that helps the subject in driving an intelligent wheelchair with a noninvasive brain interface. The subjects steering intentions are estimated from electroencephalogram (EEG) signals and passed through to the shared control system before being sent to the wheelchair motors. Experimental results show a possibility for significant improvement in the overall driving performance when using the shared control system compared to driving without it. These results have been obtained with 2 healthy subjects during their first day of training with the brain-actuated wheelchair.

A conceptual framework for holonic manufacturing: Identification of manufacturing holons

Future manufacturing systems will need to cope with frequent process disturbances and changes in production orders. Therefore, their control will require constant adaptation and high flexibility. Holonic manufacturing is a highly distributed control paradigm that promises to handle these problems successfully. It is based on the concept of autonomous cooperating agents, called “holons”. This paper presents the conceptual framework that is needed for the development of holonic manufacturing systems (HMS). The paper defines the identification task of the manufacturing holons as the first task in the development process and shows the role of a holon taxonomy herein. The holon taxonomy is based on orders, products, and resources as basic building blocks. They are structured using object-oriented design concepts like aggregation and specialization. Additional staff holons provide the basic holons with specialized advice. The resulting architecture fulfills the requirements for holonic manufacturing, where the autonomy of the agents provides the system with the ability to react to disturbances, while the existence of hierarchical control elements provides the system with opportunities for global optimization. The resulting architecture remains flexible, allowing control strategies ranging from very hierarchical to very heterarchical. A case study is given featuring the PMA testbed HMS.

An implantable drug-delivery system based on shape memory alloy micro-actuation

Abstract Shape memory alloy actuators feature an extremely high power-to-volume ratio. This property is a major advantage for miniature applications. This paper describes implantable drug-delivery systems based on shape memory alloy micro-actuation. A first type is designed for use with solid drugs while a second design enables delivery of liquid drugs. The operating principle of the latter system is based on a precisely controlled discontinuous release from a pressurized reservoir. It is realized using a shape memory actuated microwave system. One dose can be controlled with an accuracy up to 5 μl. The system is remotely powered and controlled using a transcutaneous transformer. A refilling possibility based on transcutaneous injections is provided. The design of the valve is such that it can be mounted on a printed circuit board together with the other electrical components. Furthermore, the valve is optimized towards aspects like biocompatibility, low-cost production, lifetime, safety and minimal dimensions. The drug-delivery system is aiming at patients who need multiple injections each day over a long period of time. The current prototype could already reduce the number of injections by a factor of 200. By further miniaturization a reduction factor of 3000 could be obtained.

A self-learning automaton with variable resolution for high precision assembly by industrial robots

This paper reports on the use of the stochastic automaton theory to configure control algorithms for high precision assembly operations performed with a force-sensing robot. The basic principle of the stochastic automation, i.e., its variable structure, has been extended to the dimensionality of the automaton by gradually optimizing the resolution of the input variables.

Microstructuring of silicon by electro-discharge machining (EDM) — part I: theory

Abstract Currently, nearly all microcomponents are fabricated by micro-electronic production technologies like etching, deposition and other (photo) lithographic techniques. In this way, main emphasis has been put on surface micromechanics. The major challenge for the future will be the development of real three-dimensional microstructures. The main objective of the proposed research is the development of a production technology for three-dimensional micromechanical structures together with a study of the mechanical properties of these structures. Electrodischarge machining (EDM) is a versatile technique which is very well suited for machining complex microstructures. This paper starts with an overview of EDM technology, the current state-of-the-art of micro EDM, and a comparison of EDM with other micromachining technologies. Afterwards, the basic parameters for EDM of silicon are derived. It will be demonstrated that EDM of silicon is not only feasible, but also forms an interesting, powerful and complementary alternative to traditional silicon micromachining.

User-adapted plan recognition and user-adapted shared control: A Bayesian approach to semi-autonomous wheelchair driving

Abstract Many elderly and physically impaired people experience difficulties when maneuvering a powered wheelchair. In order to ease maneuvering, powered wheelchairs have been equipped with sensors, additional computing power and intelligence by various research groups. This paper presents a Bayesian approach to maneuvering assistance for wheelchair driving, which can be adapted to a specific user. The proposed framework is able to model and estimate even complex user intents, i.e. wheelchair maneuvers that the driver has in mind. Furthermore, it explicitly takes the uncertainty on the user’s intent into account. Besides during intent estimation, user-specific properties and uncertainty on the user’s intent are incorporated when taking assistive actions, such that assistance is tailored to the user’s driving skills. This decision making is modeled as a greedy Partially Observable Markov Decision Process (POMDP). Benefits of this approach are shown using experimental results in simulation and on our wheelchair platform Sharioto.