Patrick Helmer

The sigma.7 haptic interface for MiroSurge: A new bi-manual surgical console

This paper presents the design and control of the sigma.7 haptic device and the new surgical console of the MiroSurge robotic system. The console and the haptic devices are designed with respect to requirements in minimally invasive robotic surgery. Dedicated left and right handed devices are integrated in an operator console in an ergonomic configuration. The height of the whole console is adjustable, allowing the surgeon seated and standed operation. Each of the devices is fully actuated in seven degrees of freedom (DoF). A parallel mechanism with 3 DoF actuates the translational motion and an attached wrist with 3 intersecting axis drives the rotations of the grasping unit. This advantageous design leads to inherently decoupled kinematics and dynamics. Cartesian forces are 20 N within the translational workspace, which is a sphere of about 120 mm diameter for each device. The rotational wrist of the device covers the whole workspace of the human hand and provides maximum torques of about 0.4 Nm. The grasping unit can display forces up to 8 N. An integrated force/torque sensor is used to increase the transparency of the devices by reducing inertia and friction. It is theoretically shown that the non-linear closed loop system behaves like a passive system and experimental results validate the approach. The sigma.7 haptic devices are designed by Force Dimension in cooperation with the German Aerospace Center (DLR). DLR designed the surgical console and integrated the haptic devices in the MiroSurge system.

The Delta Haptic Device as a Nanomanipulator

At the EPFL, we have developed a force-feedback device and control architecture for high-end research and industrial applications. The Delta Haptic Device (DHD) consists of a 6 degrees-of-freedom (DOF) mecatronic device driven by a PC. Several experiments have been carried out in the fields of manipulation and simulation to assess the dramatic improvement haptic information brings to manipulation. This system is particularly well suited for scaled manipulation such as micro-, nano- and biomanipulation. Not only can it perform geometric and force scaling, but it can also include fairly complex physical models into the control loop to assist manipulation and enhance human understanding of the environment. To demonstrate this ability, we are currently interfacing our DHD with an atomic force microscope (AFM). In a first stage, we will be able to feel in real-time the topology of a given sample while visualizing it in 3D. The aim of the project is to make manipulation of carbon nanotubes possible by including physical models of such nanotubes behavior into the control loop, thus allowing humans to control complex structures. In this paper, we give a brief description of our device and present preliminary results of its interfacing with the AFM.

A haptic guidance tool for CT-directed percutaneous interventions

We have developed a new navigation approach for computer-assisted interventional radiology. Our system combines a virtual reality display with high-fidelity haptic rendering to provide assistance and guidance of the medical gesture. Specifically, the system is designed to improve the accuracy of blind needle placement within tissues. The proposed technique actively helps the surgeon while keeping him in control of the procedure. We have recently developed an experimental setup for CT-guided biopsy. The setup features a high-precision haptic device connected to the biopsy needle, combined with a graphical interface. The haptic system guides the surgeons hand to the target tissue based on CT data, whereas a real-time, graphical visualization of the tool trajectory provides navigation information. The setup requires rigid registration of the patient with respect to the haptic interface. Tests have been performed in the presence of radiologists to validate the proposed concept, and early results show that the system is easy to use and requires little training. We are planning to conduct clinical testing in the near future to quantitatively assess system performance.

Rotational force-feedback wrist

Force-feedback structures are mechanical structures that can generate forces to restore to the user a tactile feeling corresponding to the world in which he is manipulating an object. This paper presents the mechanical design of a 3-rotational-degrees-of-freedom (DOF) wrist able to produce force feedback. The wrist, plugged on an existing 3-translation-DOF Delta force-feedback structure (called Delta haptic device), yields a 6-DOF force-feedback structure. The wrist comprises a stylus which is the interface with the user. The kinematic chain of the wrist is serial and composed by a Cardan corresponding to the pitch and the yaw, followed by a rotational joint for the roll. The originality of the wrist comes from the parallel actuation of the Cardan. The advantage of such an actuation is to provide a torque with low inertia and low friction less depending on rotations. The direct geometrical model of the wrist has been implemented, as well as the management of torques and currents applied. Several tests performed show the limit of the actuation of the roll compared with the very promising parallel actuation of the Cardan.

A disturbance observer for the sigma.7 haptic device

This paper presents a disturbance observer for the sigma.7 haptic device. External torques on the haptic device links are observed to distinguish between intended user interaction and accidental collisions of the links. Collisions can be unintentional contact of the human operator, e.g. with his knee, other people accidentally getting in contact with the haptic device or objects falling on it. The observer is based on the dynamic model of the device and sensor measurements from the joints position sensors and an integrated force/torque sensor. Is is implemented concurrently with a control algorithm that uses the force/torque sensor to effectively reduce the inertia and friction of the sigma.7. Furthermore, forces and torques applied on the grasping unit by the human operator are observed. Experiments are done with the sigma.7 customized for the German Aerospace Center (DLR) by Force Dimension.