Christoph Ledermann

Tactile sensor on a magnetic basis using novel 3D Hall sensor - First prototypes and results

In this paper, a new operating principle for a tactile sensor for medical diagnostics is proposed based on the measurement of three-dimensional magnetic fields. A permanent magnet and the newly developed 3D-Hall sensor AS54xx of the Fraunhofer Institute for Integrated Circuits (IIS) in Erlangen, Germany, are embedded in one silicone pad. An external force changes the position of the magnet in relation to the AS54xx, thus changing the measured magnetic field in three dimensions. In contrast to conventional tactile sensors, one sensor cell provides three dimensional information about external forces, thus making it potentially possible to detect tumors by palpation with only this one sensor cell. Three prototypes of the tactile sensor with different silicones and permanent magnets have been fabricated, and the feasibility of the operating principle has been proven for axial forces with laboratory experiments. Hysteresis effects of the tactile sensor have turned out to be negligible.

Simulation tool for 3D shape sensors based on Fiber Bragg gratings and optimization of measurement points

3D shape sensing using Fiber Bragg gratings has attracted the interest of several research groups in recent years, but so far no possibility has been presented to optimize the sensing system by simulation. Almost always, the gratings (the points of strain measurement) are distributed equidistantly, and the reconstruction algorithm has not been verified by simulation. In this paper we present our simulation tool that works on a mathematical basis and includes two parts: the first part describes how to determine the strains of Fiber Bragg gratings mounted along a given shape. The second part describes our algorithm to reconstruct the shape from this strain data using theory of differential geometry. This reconstruction algorithm is evaluated within the simulation environment and can be adapted to different system behaviors like circular bending of the instrument, cubic bending or bending according to the Euler beam theory. Furthermore, the gratings can be optimized with respect to their position and designated Bragg wavelength. To demonstrate the effectiveness of the simulation tool, an optimization has been conducted for the grating positions along a shape with two independent bendable segments. For each configuration of the shape, the reconstruction results using the optimized grating positions were significantly better than when using equidistantly distributed gratings.

Combining shape sensor and haptic sensors for highly flexible single port system using Fiber Bragg sensor technology

Single port surgery is a promising approach to further optimize the benefits of robot assisted minimally invasive surgery. Advantages include further minimization of trauma and reduction of scars, but it also increases the need for flexible, high-end instruments and miniaturized sensors. This paper describes a new concept of a miniaturized sensor system which combines a kinesthetic sensor, a tactile sensor and a position sensor. Latter is realized as a shape sensor. The combination of the sensors is possible because they are all based on Fiber Bragg Grating technology. A concept for each sensor is also presented. They are improved compared to current research and adapted to our needs. The miniaturized sensor system is integrated into an innovative, highly flexible single port system.

Using ORMOCER®s as casting material for a 3D shape sensor based on Fiber Bragg gratings

In robot assisted minimally invasive surgery, flexible instruments are a highly interesting research topic, as they promise more flexibility and new possibilities for surgical interventions. Shape sensors are needed in order to retrieve information about the geometry and especially the tip position of the instrument. Those shape sensors are usually based on Fiber Bragg Gratings. In contrast to other research groups, which e.g. use nitinol wires as a core for their fibers, we follow the approach of casting the fibers in soft materials. For our latest prototype, a special ORMOCER® material has been used, which is an inorganic-organic hybridpolymer with adjustable properties. The fabrication of the sensor is described in detail. The reproducibility of the wavelength measurements has been validated for several shapes, proving the reasonableness of our approach.

Biomimetic tactile sensor based on Fiber Bragg Gratings for tumor detection — Prototype and results

Robot assisted minimally invasive surgery features many advantages, such as augmented reality or more comfort for the surgeon during the operation. On the downside, the surgeon loses all aspects of haptic perception from the operation situ. Tactile sensors are necessary to restore some of the haptic perception. In this paper, a tactile sensor is presented that mimics the human finger and is based on Fiber Bragg Gratings. The idea is a comparison of strain measurements of two materials of different stiffnesses. The principle is described in detail, as well as the fabrication of our first prototype. First experiments have been carried out, showing the potential of the tactile sensor to detect tumors within healthy tissue by looking at the progression of the strain-strain-curve.

Motivation of a new approach for shape reconstruction based on FBG-optical fibers: Considering of the Bragg-gratings composition as a sensornetwork

In various fields of application, the shape and the tip position of flexible, snakelike objects have to be reconstructed. For this, the considered objects are fitted with so-called shape sensors. This shape sensors are e.g. applied in medical technology to support minimally invasive surgical interventions by tracking flexible instruments; this way navigation systems can be considerably supported. The sensors consist of a solid snakelike body out of flexible carrier material, as silicone, with embedded FBG - optical glass fibers along the object-axis. Guided along the observed instruments, the sensor is supposed to detect the instruments shape by detecting its own ones. The fibers measure the strain at discrete points along the sensor body, which is caused by deformation of the sensor. From these values the shape is estimated. This estimation is performed using specific algorithms. Accordingly, certain requirements regarding the position, orientation and exact number of the measurement units are made. As part of the manufacturing process of the sensor, however, exact control of fiber positioning cannot be realized. To compensate this inaccuracy and also further occurring problems, a fundamentally new calculation approach is presented in this paper. The basic idea is, to consider the system of measurement units as a sensor network. The position and orientation of the units are not considered to be static, because they can only be detected after production but cannot be exactly implemented in a controlled way with a planned position and orientation. The idea is realized by initializing a tensor field on a manifold, representing the surface of the object. This allows to apply the algorithm to measurement values, measured at randomly distributed positions along the sensor body. The new approach is promising and more accuracy in shape sensing is expected do be achieved. The approach of surface characterization is developed in a way that it is transferable to other applications. In the future, also areas in general can be analysed by applying to adapted algorithms based on the same idea. Interpolation of e.g. temperature- and radiation fields can be done in an intelligent way by measuring discrete values by efficiently distributed measurement units.

Non-linear compensation of production inaccuracies and material drift by adjusting the sensor data fusion algorithms for shape sensing based on FBG-optical fibers

Shape sensing, where the shape of an object is estimated using fiber optical Fiber Bragg Grating (FBG) sensors, has gained increasing popularity in the last years. While the production process and the applications are different for the various research groups, the basic principle of shape sensing is the same: at certain cross-sections along the observed object, the information of three strain measurements is merged to one curvature information, and the information of these curvatures is then used to estimate the shape with various mathematical theories, depending on the application. Some effort has been made to calibrate and determine the accuracy of the shape sensor, but research on the influence of bad positioning of the Fiber Bragg Gratings seems relatively unattended. In this paper, one aspect of bad FBG positioning, namely inaccurate placement of the FBGs within one cross-section, and its influence on the reconstruction results is investigated. Furthermore, a modified approach for the reconstruction algorithm is presented, improving the reconstruction results for bad FBG placement compared to the conventional approach.

Fiber optical sensor system for shape and haptics for flexible instruments in minimally invasive surgery: overview and status quo

In minimally invasive surgery, exible mechatronic instruments promise to improve the overall performance of surgical interventions. However, those instruments require highly developed sensors in order to provide haptic feedback to the surgeon or to enable (semi-)autonomous tasks. Precisely, haptic sensors and a shape sensor are required. In this paper, we present our ber optical sensor system of Fiber Bragg Gratings, which consists of a shape sensor, a kinesthetic sensor and a tactile sensor. The status quo of each of the three sensors is described, as well as the concept to integrate them into one ber optical sensor system.

EndoSnake—A Single-Arm-Multi-Port MIRS System with Flexible Instruments

Recently, the use of robotic assisted systems for minimally invasive surgery has increased. This is due to the precise manipulation and miniaturisation of the used equipment. The systems can be divided into multi-port and single-port robots, both with the aim of trauma reduction but with different approaches. On the one hand there are multiple robots, one with each instrument or camera and on the other hand there are small flexible instruments and only one incision in the abdominal wall. In this paper, a novel robotic system is presented that combines in a hybrid way the prior described characteristics and continues the medical aims of trauma reduction and surgeon comfort. One single lightweight robot with three individual configurable flexible instruments is being researched. Additionally, the modular hardware and software architecture is based on the open-source idea and rapid-manufacturing processes.