Ulrich Spaelter

A systematic characterization method for gravity-feed micro-hole drilling in glass with spark assisted chemical engraving (SACE)

Gravity-feed drilling is the most commonly used method for micro-hole drilling in glass with spark assisted chemical engraving (SACE). This paper proposes a method allowing the systematic characterization of this drilling method. The influences of voltage, tool shape and force are investigated. It is found that SACE gravity-feed drilling shows two regimes depending on the drilling depth. During the first 200–300 µm, the discharge regime, controlled by the number of discharges inside the gas film, allows fast drilling (up to about 100 µm s−1). For deeper depths, the drilling is controlled by the hydrodynamic regime in which the drilling speed is limited by the flow of the electrolyte inside the micro-hole resulting in slow drilling of typically 10 µm s−1. Furthermore, it is shown how the gas film build-up time is limiting the drilling speed.

The current signal in spark-assisted chemical engraving (SACE): what does it tell us?

Spark-assisted chemical engraving (SACE) is a promising micro-machining technology for the low-cost machining of holes and channels in non-conducting materials, such as glass and some ceramics. Despite the complexity of SACE due to the interdependency of thermal, electrochemical and mechanical effects, the key data of the machining process can be obtained from only a few signals. Possible process surveillance signals are analysed and discussed. In particular, the current flowing between the electrodes is analysed. It is shown that various information can be deduced from it, such as qualitative indications of the local electrolyte temperature, differentiation between machining and non-machining and the distinction between the presence and absence of a gas film. However, so far no direct link between the current and the instantaneous material removal rate could be found. Experimental results are presented and the possibility of active process control based on current measurement is discussed.

A Computer-Based Real-Time Simulation of Interventional Radiology

Interventional radiology is a minimally invasive procedure where thin instruments, guidewires and catheters or stents are steered through the patients vascular system under X-ray imaging for treatment of vascular diseases. The complexity of these procedures makes training in order to master hand-eye coordination, instrument manipulation and procedure protocols for each radiologist mandatory. In this paper, we present a computer-based real-time simulation of interventional radiology procedures, which deploys a very efficient physics-based thread model to simulate the elastic behavior of guidewires and catheters. A fast collision detection scheme provides continuous collision response, which reveals more details of arterial walls than a center/line approach. Furthermore rendering techniques for realistic X-ray effect have been implemented. Our simulation structure is updated at a haptic rate of 500 Hz, thus contributing to physical realism.

Generic and systematic evaluation of haptic interfaces based on testbeds

The purpose of evaluation procedures is to achieve both qualitative and quantitative statements on haptic rendering realism and performance. Since a haptic interface provides an interaction between a user and a virtual environment, fidelity of a haptic interface directly affects the performance. To our knowledge, a standard, generic and reusable validation method which comprehensively addresses all the attributes of haptic feedback has not been realized yet. Despite the large number of human factor studies, only few of them have been proposed as well for haptic interface performance measurements. For this reason, we review validation procedures for haptic rendering and propose an evaluation method based on testbeds to obtain a systematic haptic interface assessment. We integrated the approaches of human factor studies into the testbeds to obtain a simple and yet complete measure of human-machine interaction performance. The testbeds were tested on a haptic interface, the IHP of Xitact SA, and performance results are presented. In the testbeds, performance metrics for generic haptic interaction tasks are expressed in terms of information transfer (bits) and sensory thresholds which are indeed device specific benchmark metrics. Thus, the suitability of a haptic interface for a defined task can be verified, device comparisons become possible and the obtained information can be used to identify possible improvements.

Virtual reality based simulation of hysteroscopic interventions

Virtual reality based simulation is an appealing option to supplement traditional clinical education. However, the formal integration of training simulators into the medical curriculum is still lacking. Especially, the lack of a reasonable level of realism supposedly hinders the widespread use of this technology. Therefore, we try to tackle this situation with a reference surgical simulator of the highest possible fidelity for procedural training. This overview describes all elements that have been combined into our training system as well as first results of simulator validation. Our framework allows the rehearsal of several aspects of hysteroscopyfor instance, correct fluid management, handling of excessive bleeding, appropriate removal of intra-uterine tumors, or the use of the surgical instrument.

A 4-dof haptic device for hysteroscopy simulation

In minimal-invasive surgery surgeons are generally confronted with complex scenario and sometimes they have to overcome unexpected pathologies or life-threatening injuries. Therefore there is a demand for realistic training without risk to the patient. Since a decade ago there have been research activities on virtual reality surgery simulators with haptic feedback with the goal to provide an alternative to traditional training methods on animals or cadavers. Haptic feedback is a key feature for every surgery simulator for the training of hand-eye coordination. In this paper a 4-dof haptic device is presented for hysteroscopy, the examination and treatment of the uterine cavity through the vagina. Specifications are presented, and kinematics as well as force transmission are analyzed. The realized prototype, result of a systematic design process, is based on a 2-dof spherical manipulator with low inertia and a 2-dof serial extension, which allows the use of slightly adapted original instruments. With difference to common surgery simulators tool insertion and complete removal can be performed. The performance of the prototype is shortly discussed.

A Versatile MRI/fMRI Compatible Spherical 2-DOF Haptic Interface

Haptic devices compatible with functional magnetic resonance imaging (fMRI) could become an invaluable tool for the study of human brain functionality and motor learning. This paper presents a spherical two-degree-of-freedom (DOF) device made entirely from polymers and suitable for use within an MR environment. The design includes a 2-DOF force sensor for measurement and control of interaction forces. It can be actuated by wire transmission from a remote or well-shielded place. This paper presents the realized prototype and discusses its application as haptic joystick, and its extension for 2-DOF planar displacement for use as x-y-manipulandum as well as tactile stimulator for the fingertips

Control of a Haptic Interface and a Micromachining Setup with an Open Source Real-Time System

Open source software have evolved into powerful tools for real-time control of mechatronic systems. They are of interest for academic purposes, as they promise high flexibility at low cost. In this paper, we investigate the performance of an open source control architecture based on the Linux Real-Time Application Interface (RTAI) through two applications, a haptic interface for surgery simulation and a setup for the micromachining of glass. Both applications demand a compact real-time system with sufficient precision (i.e. low jitter) for online process control and data acquisition. The real-time control has been realized on a laptop with a USB-port data acquisition card. Performance measurement results show that high quality real-time control can be performed up to 2kHz via USB communication, which is sufficient for a large range of robotic or mechatronic applications. Drawbacks like the need for considerable knowledge of Linux internals for successful installation as well as the current limitations are discussed and strategies are proposed to overcome these. Both setups are currently being used for ongoing research as well as for educational purposes.

A 2-DOF friction drive for haptic surgery simulation of hysteroscopy

Abstract Haptic Devices are key elements of surgery simulators, as they allow surgeons to experience the contact forces during the manipulation of the virtual tissue in a training session. Friction drives add important features to surgery simulation, like tool insertion and complete removal during the training and thus add realism to the simulation. In this paper we present a 2-DOF friction drive for smooth and slip-free tool translation and rotation, which is part of a 4-DOF haptic device for training of a gynecologic intervention (hysteroscopy). We present a specially developed mechanical design and the control structure for efficient friction compensation and low force ripple in the context of high quality haptic (force feedback) systems. The prototype is presented and experimental results are discussed.