I am currently employed as a Systems Analyst with Intuitive Surgical, designing control algorithms for surgical robotics systems. My career until December 2008 took place in various academic institutes in the Netherlands and the US, below are short descriptions of some of the projects I worked on. Feel free to contact me for more information.

Postdoc project — Robot-assisted minimally invasive surgery

Between 2006 and 2008, I worked as a postdoc at the University of California, Berkeley (USA), collaborating with Prof. Sastry on robotics-assisted beating-heart surgery, and with Prof. Ken Goldberg on robotic flexible needle steering. This research was sponsored by the Netherlands Organization for Scientific Research (NWO) and the National Institutes of Health (NIH).

The objective of the beating-heart surgery project was to develop models, sensors, actuators, and control algorithms to synchronize the motion of surgical tools to the motion of the operating area, e.g. a beating heart. If this were possible, the surgeon could perform operations on a virtually stabilized heart, only supplying the (slow) relative motion of the tool with respect to the heart surface, instead of trying to manually synchronize the surgical tool to the (fast) motion of the beating heart. Important issues are the development of sensors that can accurately measure the position and orientation of an area of interest on the heart, motion estimation algorithms that can filter and predict the quasi-periodic motion of the beating heart, and control algorithms and actuators that accomplish safe and accurate motion of the surgical tools.

In a related project, we studied the development and control of a robotic flexible needle with a beveled tip. Flexible needles have greater mobility than rigid symmetric needles, and can reach targets around corners or behind sensitive or impenetrable areas such as bone. The research problem was to develop a path planning algorithm and robotic driver that can drive the needle through human tissue, avoiding obstacles in its path and reaching pre-specified target locations with high accuracy and via a reasonably short path. Applications of this problem are in numerous areas, ranging from various diagnosis objectives, performing biopsies, and accurately delivering radioactive seeds for the treatment of tumors. From a robotic point of view, bevel-tip needles are nonholonomic kinematic systems, and path planning for such systems is not trivial. This project was a collaboration with Johns Hopkins University, see the project page for more information.

Ph.D. project — Efficient bipedal walking robots

In March 2006, I completed my Ph.D. research with Prof. Stefano Stramigioli at the University of Twente on Port-Based Modeling and Control for Efficient Bipedal Walking Robots. The research was part of the European sponsored project GeoPlex, in which geometric modeling and control of complex physical system was approached from a port-Hamiltonian point of view.

Research on walking robots has shown that the process of walking, in itself, requires little energy. Indeed, many robots have been built that walk with high efficiency (the so-called passive dynamic walkers). My research aims to provide a framework for modeling, analysis, and efficient control of walking robots. The framework uses a port-Hamiltonian system description to express the dynamics of rigid mechanisms and their interaction with the ground. The structure of the resulting models forms the basis for the development of general analysis and control techniques.

The proposed framework extends well-known modeling methods to a broad class of rigid mechanisms with a configuration space described by any combination of Euclidean components (e.g. linear joints), Lie group/algebra components (e.g. ball joints), and nonholonomic components (e.g. nonslipping wheels). Two different 3D contact models are presented: one for compliant contact, and one for rigid contact.

Using the structure of the models, the problem of finding efficient walking gaits is cast as a numerical optimization problem. This setting allows one to optimize not only the joint trajectories but also the mechanical structure of a walking robot. Finally, three control techniques for efficient walking are presented. The first technique uses the computed optimal trajectories to define a power-continuous asymptotic tracking controller. The second technique stabilizes an experimental kneed walking robot (see picture) by means of a single controller on the hip joint. The third technique uses foot placement to increase the robustness of a three-dimensional walking robot.

M.S. project — Passive compensation of nonlinear robot dynamics

In 2001, I graduated from the Delft University of Technology on a project in the field of robotics and nonlinear control. The objective of the project was to find a passive controller to compensate for nonlinear robot dynamics. The result of the project was a general, coordinate-free formulation of a controller that is able to steer the robot in the desired direction without supplying energy, regardless of modeling errors and external disturbances. Practical applications of such a controller include interactive devices, where safety (and hence also passivity) is very important. The results from this project may also form a basis for further research on passive controller design.