A method for 6-DOF haptic rendering of isosurface geometry embedded within sampled volume data is presented. The algorithm uses a quasi-static formulation of motion constrained by multiple contacts to simulate rigid-body interaction between a haptically controlled virtual tool (proxy), represented as a point-sampled surface, and volumetric isosurfaces. Unmodified volume data, such as computed tomography or magnetic resonance images, can be rendered directly with this approach, making it particularly suitable for applications in medical or surgical simulation. The algorithm was implemented and tested on a variety of volume data sets using several virtual tools with different geometry. As the constraint-based algorithm permits simulation of a massless proxy, no artificial mass or inertia were needed nor observed. The speed and transparency of the algorithm allowed motion to be responsive to extremely stiff contacts with complex virtualized geometry. Despite rendering stiffnesses that approach the physical limits of the interfaces used, the simulation remained stable through haptic interactions that typically present a challenge to other rendering methods, including wedging, prying, and hooking.

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.

This paper presents a new approach for estimating physical properties of deformable models from experimental measurements. In contrast to most previous work, we introduce a new method based on particle filters which identifies the different stiffness properties for spring-based models. This approach addresses some important limitations encountered with gradient descent techniques which often converge towards ill solutions or remain fixed in local minima conditions.

Mass-spring systems have widely and effectively been used for modeling in real-time deformable objects. Easier to implement and faster than finite elements, these systems, on the other side, suffer from several drawbacks when coming to render physically believable behaviors. Neither isotropic or anisotropic materials can be controlled easily and the large number of springs and mass points composing the model makes it fastidious to define parameters to control elongation, flexion and torsion at a macroscopic level. Another weakness is that most of the materials found in nature maintain a constant or quasi-constant volume during deformations; unfortunately, mass-spring models do not have this property. In this paper, we extend the current state-of-the-art in soft tissue simulation by introducing a six-degree of freedom macroscopic elastic sphere described by mass, inertia and volumetric properties. Spheres are placed along the medial axis transform of the object whose centers are connected by a skeleton composed of a set of three-dimensional elastic links. Spheres represent internal mass, volume and control the global deformation of the object. The surface is modeled by setting point masses on the mesh nodes and damped springs on the mesh edges. These nodes are connected to the skeleton by individual elastic links, which control volume conservation and transfer forces between the surface and volumetric model. Using this framework we also present an efficient method to approximate collision detection between multiple bodies in real-time.