Biologically inspired kinematic synergies enable linear balance control of a humanoid robot

Despite many efforts, balance control of humanoid robots in the presence of unforeseen external or internal forces has remained an unsolved problem. The difficulty of this problem is a consequence of the high dimensionality of the action space of a humanoid robot, due to its large number of degrees of freedom (joints), and of non-linearities in its kinematic chains. Biped biological organisms face similar difficulties, but have nevertheless solved this problem. Experimental data reveal that many biological organisms reduce the high dimensionality of their action space by generating movements through linear superposition of a rather small number of stereotypical combinations of simultaneous movements of many joints, to which we refer as kinematic synergies in this paper. We show that by constructing two suitable non-linear kinematic synergies for the lower part of the body of a humanoid robot, balance control can in fact be reduced to a linear control problem, at least in the case of relatively slow movements. We demonstrate for a variety of tasks that the humanoid robot HOAP-2 acquires through this approach the capability to balance dynamically against unforeseen disturbances that may arise from external forces or from manipulating unknown loads.

Méthode systématique de conception de cinématiques parallèles

Parallel kinematics structures currently find increasing industrial applications, particularly in packaging and assembly. With very few exceptions, machine-tools with parallel kinematics are limited to mechanisms with three or six degrees of freedom. Moreover, the spindle tilt is limited to very small angles. The advantages of parallel kinematics structures are high precision, lower fabrication cost, good dynamics and high stiffness. This dissertation proposes a systematic configuration design method for the development of new parallel kinematics structures. The parallel structures obtained with this method combine large spindle tilt angles with the advantages of parallel kinematics structures. First, components and characteristic elements of parallel structures are defined and the description of a proposed systematic method for configuration design, the "Design Cube Method", follows. The method enables the design of a family of parallel structures with a specified number and arrangement of mobilities. Methods such as "Gruebler's Formula" and the "Method of Intersecting Trajectories" serve to quickly verify the desired number of degrees of freedom of the structure and the optimal arrangement of the kinematic chains. Several mechanisms are described, that once integrated in a parallel structure, significantly increase the range of tilt of the end-effector, while keeping the stiffness as constant and as high as possible. A new parallel kinematics structure for a five-axis machine-tool has been developed using the new design methods described above. The performance specifications are listed, the desired arrangement of the axis is described and the design cube method is used to generate a new family of parallel kinematics structures. The various structures are evaluated in terms of how suited they are for machine-tool applications, and of the ease of integration of a mechanism to improve the tilt of the end-effector. A laboratory mock-up, demonstrating the various principles, and an industrial prototype of the new machine, the Hita-PDR, have been developed and fabricated. The bar lengths of the structure were selected so as to avoid singularities of the structure in the desired workspace. The specified high stiffness of the industrial prototype required the development of a new type of joint, the simple and double spherical joints with line contact. The high performances of the industrial prototype confirm the machine concept and the relevant choice of the parallel kinematics structure. This dissertation gives a global vision, of the various stages in the design of parallel kinematics structures with large rotations of the end-effector and high stiffness, starting with initial specifications, all the way up to the detailed design and manufacturing of the machine.

EPFL2004

Haptic interface design and control with application to surgery simulation

Ulrich Spälter

This thesis proposes a framework for haptic devices interacting with virtual environments. As application of the theoretical results a haptic device for the surgical training of hysteroscopy, a gynecologic intervention, is presented. Surgery simulators, which can be described as 'flight simulators for surgeons', comprise a virtual reality for modeling and visualization of organs, and the haptic device: While the surgeon interactively follows the scene on the computer screen, he perceives the contact forces at the tool handle of the surgical instrument. The haptic device tracks the position of the surgery tool and transforms the virtual contact forces to real forces, which can be actually felt by the surgeon. This thesis treats haptic devices with application to surgery simulators for minimally-invasive surgery. Haptic interfaces are complex mechatronic systems and show inherent trade-offs between haptic realism and system stability. Human factors play an important role, as the human operator can both stabilize or destabilize the system. The haptic perception, which can vary between individuals, as a criterion for haptic rendering quality is still not formalized. The optimization of haptic interfaces, within focus of research since 15 years ago, has remained a complex task. However, with look at the emerging applications for haptics, it has become an even more important topic. For this reason it is necessary to integrate mechanical design, control design, mechatronic elements and human factors in a unifying approach. This thesis highlights the principal trade-offs of haptic interfaces and works out design guidelines for new developments and quantitative information on where and how to optimize haptic systems. As application example a haptic interface for the simulation of hysteroscopy, a gynecologic intervention on the female uterus, has been realized as prototype. The device takes the characteristics of hysteroscopy into account and introduces features like insertion and complete removal of the surgery tool from the haptic interface. A design methodology is proposed, which combines aspects of theoretical kinematics based on Lie-Groups with integrated product development – a systematic approach for engineering tasks. The result, a novel kinematic design, has been realized as haptic interface prototype. The well-known affine parameterization for all stabilizing controllers is shown to be a well-suited tool for haptic control synthesis. It provides insights into the control trade-offs and allows to integrate human factors at controller design stage. The resulting controller, demonstrated by experimental results, can reduce parasitic effects (friction, device dynamics) close to and below the human perception threshhold, thus making the device transparent within the specified bandwidth and suitable for real-time implementation. For numerical controller representation the δ-operator is discussed. It unifies continuous and discrete time domain and has beneficial numerical properties. As there is still no standardized procedure for technical performance evaluation of haptic interfaces methods proposed in literature are summarized. In the near future a large market for haptic technology can be expected with applications from surgery-assist devices and drive-by-wire interfaces in automobiles to entertainment, which highlights the relevance of the treated topic.

EPFL2006

A Multi-Lead ECG Classification Based on Random Projection Features

David Atienza Alonso, Iva Bogdanova Vandergheynst

This paper presents a novel method for classification of multilead electrocardiogram (ECG) signals. The feature extraction is based on the random projection (RP) concept for dimensionality reduction. Furthermore, the classification is performed by a neuro-fuzzy classifier. Such a model can be easily implemented on portable systems for practical applications in both health monitoring and diagnostic purposes. Moreover, the RP implementation on portable systems is very challenging featuring both energy efficiency and feasibility. The proposed method is tested on a 12-lead ECG database consisting of 20 beats during normal sinus rhythm, 20 beats with myocardial infarction and 20 beats showing cardiomyopathy for 60 different subjects. The experiments give a recognition rate of 100% for a small number of RP coefficients (only 25), i.e. after a considerable dimensionality reduction of the input ECG signal. The results are very promising, not only from the classification performance point of view, but also while targeting a low-complexity feature extraction in terms of computation requirements and memory usage for real-time operation on a wireless wearable sensor platform.

IEEE Press2012

Haptic interface design and control with application to surgery simulation

Ulrich Spälter

EPFL2006

Méthode systématique de conception de cinématiques parallèles

EPFL2004