Proxy chain method and its application to scientific visualization

Journal ArticleWe present a method for combining multiple point-based constraints in haptic programming environments. Instead of using a single proxy point for haptic feedback, the method maintains a separate proxy for each constraint. The reaction force is computed by linking the proxies in a chain. Constraints are applied in sequential order, such that the proxy found in the current step becomes the probe for the next step in the chain. The advantage of the method over previous approaches is that the constraints are maintained precisely and the output is well-defined. We illustrate the method with examples from the domain of 3D scientific data visualization. Finally, we present the results of an experiment conducted to quantify the contribution of haptic guidance in two representative vector field exploration tasks

Constraint-based technique for haptic volume exploration

Journal ArticleWe present a haptic rendering technique that uses directional constraints to facilitate enhanced exploration modes for volumetric datasets. The algorithm restricts user motion in certain directions by incrementally moving a proxy point along the axes of a local reference frame. Reaction forces are generated by a spring coupler between the proxy and the data probe, which can be tuned to the capabilities of the haptic interface. Secondary haptic effects including field forces, friction, and texture can be easily incorporated to convey information about additional characteristics of the data. We illustrate the technique with two examples: displaying fiber orientation in heart muscle layers and exploring diffusion tensor fiber tracts in brain white matter tissue. Initial evaluation of the approach indicates that haptic constraints provide an intuitive means for displaying directional information in volume data

Improved calibration Framework for electromagnetic tracking devices

Journal ArticleElectromagnetic trackers have many favorable characteristics but are notorious for their sensitivity to magnetic field distortions resulting from metal and electronic equipment in the environment. We categorize existing tracker calibration methods and present an improved technique for reducing static position and orientation errors inherent to these devices. A quaternion based formulation provides a simple and fast computational framework for representing orientation errors. Our experimental apparatus consists of a 6DOF mobile platform and an optical position measurement system, allowing collection of full pose data at nearly arbitrary orientations of the receiver. A polynomial correction technique is applied and evaluated using a Polhemus Fastrak resulting in a substantial improvement of tracking accuracy. Finally, we apply advanced visualization algorithms to give new insight into the nature of the magnetic distortion field

Coregistration of Pose Measurement Devices Using Nonlinear Least Squares Parameter Estimation

Multimodal visual haptic user interfaces can be made more effective by accurately colocating the workspaces of their components. We have developed a coregistration technique for pose measurement devices based on nonlinear least squares parameter estimation. A reduced quaternion parameterization is used for representing the orientation component of coordinate transformations, which avoids the numerical instability of traditional approaches. The method is illustrated with two examples: the colocation of a haptic device with a position tracker, and the coregistration of an optical and a magnetic tracking system

Kinematic Calibration Using a Plane Constraint

This work deals with closed-loop calibration methods where the robot endpoint is constrained to lie on a plane. Previously published calibration approaches are shown to have certain weaknesses. A new solution is given using DH and Hayati notations and standard nonlinear least squares optimization. The procedure is extended via the Implicit Loop Method, which takes input noise into account. Pose selection is guided by the Noise Amplification Index. Simu-lation and experimental results are presented for a PUMA 560 industrial manipulator; and are compared to those ob-tained from an open-loop calibration procedure.

22 The Visual Haptic Workbench

Haptic feedback is a promising interaction modality for a variety of applications. Successful examples include robot teleoperation [57], virtua