Peter P. Pott

Zusammenfassung

Minimally invasive surgery (MIS) has been an essential tool in the surgical sector for many years due to its crucial advantages compared to open surgery. To overcome remaining limitations, teleoperated MIS experienced a strong emergence. However, the widespread usage of such systems is hindered by the enormous financial hurdle. The use of standard components and conventional tools for teleoperated MIS can facilitate integration into existing hospital workflows and can be a cost-efficient and versatile approach for research purposes. To compensate for the lack of haptic feedback, some teleoperation setups inherit a sensor system allowing them to record interaction forces and display them at the user interface. In research and in commercially available systems, different positions for the sensor can be found. In this paper, mechanical interfaces for the guidance and actuation of non-wristed and wristed standard instruments are presented. Furthermore, a method for the extracorporeal measurement of interaction forces is presented, characterized, and discussed. The overall mean relative error of the magnitude of the interaction force is 9.4%, while the overall mean absolute error of the force vector is 14.4 $^$ , both below the respective human differential perception threshold. The presented measurement method is a simple, yet sufficiently accurate approach to measure interaction forces in surgical telemanipulation.

Zusammenfassung

We tested the feasibility of ultrasound technology for generating pressurized intraperitoneal aerosol chemotherapy (usPIPAC) and compared its performance vs. comparator (PIPAC).

Zusammenfassung

In conventional laparoscopy, the field of view of the surgeon is limited. Angled laparoscopes enable the observation of surrounding structures, however, to change the viewing perspective on a specific object, permanent repositioning and rotation of the shaft is required. In this paper, a demonstrator of a steerable flexible laparoscope is presented, enabling the user to intuitively adjust the perspective onto an object by means of a single control element. The laparoscope provides a viewing angle of ± 50° at 50 mm working distance. In first tests, the presented laparoscope showed advantages regarding intuitiveness of the control, easier handling, and improved depth perception.

Zusammenfassung

During laparoscopic procedures, the surgeon's view of the situs, and thus her or his performance, is dependent on the skills of the camera assistant. The surgeon lacks control over his own field of view and there is a high potential for reducing mental load and workflow issues. In this paper, a research setup of a 360° laparoscopic imaging system is presented and evaluated. The system consists of a 360° camera and a head-mounted display, through which the surgeon can inspect the situs. In a user test, the system showed advantages over a conventional laparoscope regarding orientation in thesitus, intuitiveness of operation, and faster task completion.

Zusammenfassung

Accurate measurement of interaction forces during robot-assisted surgery requires compact force sensing modalities in the surgical tools, thus might add considerable cost to the setup. Measuring the motor current to estimate gripping forces, is an advantageous approach since no expensive force sensor is needed. In this paper, a mechanical interface is presented, which allows actuating conventional articulated instruments for robot-assisted surgery. The interface features the estimation of static gripping forces at the instrument’s tip based on the motor current. The evaluation shows reproducible results, and the current-based approach seems to be a cost-efficient way to estimate gripping forces.

Zusammenfassung

When manipulating tissue during medical interventions, high-accuracy movements are important to avoid injuries. However, feedback is limited and it is hard to establish control loops to ensure correct movements. We propose the use of a novel highly compact 6-axis force / torque sensor (Ø 10.5 mm x 11.0 mm) within a hand piece to determine low forces and torques during various small-scale procedures including gentle tool-tissue interaction. For a first validation of the system, different venepuncture cannulas were connected to the sensor top and driven into skinned fruits (toma-toes and grapes) as well as into a silicone block. During insertion of the needle tips, maximum forces of 74 – 158 mN (tomato) and 51 - 161 mN (grape) were recorded, and steadily increasing forces in the range of 0 – 250 mN when insert-ing needles 7.5 mm into silicone. For a 0.99 g screw nut (9.73 mN), the measured gravitational force was 10.6 ± 1.5 mN during ten measurement sets. During the insertion, needle torques of up to 9.5 mNm were observed. Different cutting phases were seen similar to the phases during needle penetration testing. We conclude that the compact measurement setup used is suitable to measure the low forces and torques occurring when cutting soft, aqueous human tissues with or without skin-like layers.

Zusammenfassung

In robotic telemanipulation for minimally-invasive surgery, lack of haptic sensation and non-congruent movement of input device and manipulator are major drawbacks. Input devices based on cable-driven parallel mechanisms have the potential to be a stiff alternative to input devices based on rigid parallel or serial kinematics by offering low inertia and a scalable workspace. In this paper, the haptic user interface of a cable-driven input device and its technical specifications are presented and assessed. The haptic user interface allows to intuitively control the gripping movement of the manipulator’s end effector by providing a two-finger precision grasp. By design, the interface allows to command input angles between 0° and 45°. Furthermore, interaction forces from the manipulator’s end effector can be displayed to the user’s two-finger grasp in a range from 0 N to 6 N with a frequency bandwidth of 17 Hz.

Zusammenfassung

In robotic telemanipulation for minimally-invasive surgery, lack of haptic sensation and non-congruent movement of input device and manipulator are major drawbacks. Input devices based on cable-driven parallel mechanisms have the potential to be a stiff alternative to input devices based on rigid parallel or serial kinematics by offering low inertia and a scalable workspace. In this paper, the haptic user interface of a cable-driven input device and its technical specifications are presented and assessed. The haptic user interface allows to intuitively control the gripping movement of the manipulator’s end effector by providing a two-finger precision grasp. By design, the interface allows to command input angles between 0° and 45°. Furthermore, interaction forces from the manipulator’s end effector can be displayed to the user’s two- finger grasp in a range from 0 N to 6 N with a frequency bandwidth of 17 Hz.

Zusammenfassung

The treatment of (partially) paralyzed hands continues to reach surgical and therapeutic limits in Germany, marking the supply of patients with mechanical devices becoming increasingly relevant. The aim of the presented work is the realization of a modular orthosis for paralyzed hands. In paresis, an active hand orthosis can be used as a training device to relax spastic paralysis and a support structure to restore flexion and extension. This presented orthosis is intended to functionally support paralyzed fingers regarding the range of motion and achievable force, based on modular mechanical components and drive unit. For the drive unit an actuator principle is required, that permits quiet, lightweight, and inexpensive force generation. The twisted string actuation (TSA) is based on the axial twisting of two polyethylene strings. The twisting reduces the initial length of the string by creating a helix and – given non-elastic behaviour of the material – generates a tensile force against the load. The operating principle requires no additional gears and produces minimal noise. In the first step, the development approach is validated by the movement of two (spastically) paralyzed fingers (index finger, and middle finger) with the orthosis. Two DC-motors of different power are used to move the paralyzed fingers with the required force of 20 N. Two Dyneema® strings are used for the twisted string. Various tests are carried out to characterise the parameters (initial length of the twisted string, pre-twisting of the strings, motor behaviour) for operation. The drive unit works according to an antagonistic principle. The motors for extending the fingers are located on the dorsal side of the forearm, the motor for flexion on the palmar side. The motors and the TSA are attached to an orthotic structure that extends from the forearm to the metacarpophalangeal joint. The basic material of this support structure is ORFIT ECO 2.4 mm, a thermoplastic material which can be deformed at 65°C and adapted to the specific needs of the patient. The TSA is connected to a two-stage mechanical linear guide, which implements the flexion and extension of the fingers. Linear cross roller bearings guide the two carts for movement of the distal and proximal interphalangeal joints in the first step and complete flexion or extension through the metacarpophalangeal joint in the second step. Mechanical pivot joints at the interphalangeal joints and a double joint at the metacarpophalangeal joint allow the flexion and extension of the individual fingers. The joints, the supports for the paralyzed fingers and the two-stage mechanism are printed with polylactide (PLA) using Fused Deposition Modelling (FDM). The constant speed movement of the fingers is triggered by an input from the user. The movement is controlled by limiting the motor current, with feedback from an encoder. If the fingers get in touch with an object, the reaction torque in the motor increases, resulting in the TSA needing to apply more force to bend the fingers. As soon as the motor torque is above a defined maximum, the motor stops and with it a further flexion of the fingers, so that the object is held. A reversal of the direction of rotation causes the fingers to open again. The functionality of the mechanism driven with a TSA and movement over the pivot joints is proven by the first prototype and the movements of the fingers. Currently tests have been performed on a healthy subject and will be extended to subjects with paralysis in the future.

Zusammenfassung

Standard microscopes designed for the direct view through oculars have a rather large footprint due to standardised distance between objective and ocular. Most parts in microscopes are made from cast aluminium and brass for reasons of mechanical strength and vibration damping. In the future, microscopes could be designed more compact if solely digital imaging is used as the optical path could be shorter and less optical elements would be needed. One crucial mechanical part of a microscope is the mechanism to adjust the relative position of objective and probe. This work focusses on the deployment of linkages with monolithic joints to provide high-precision linear motion. As a demonstrator, the prototype of a fully automatic compact light sheet microscope is presented. The Lambda-mechanism by Chebyshev has been selected as it allows a complete straight part of the coupler curve. By arranging two such mechanisms in parallel and two of such arrangements in two parallel planes, a three-dimensional linear guide with a vertical axis of motion is created. To allow easy manufacturing and precise motion, monolithic joints with low friction and backlash are used. Using the described mechanism, a prototype of a light-sheet microscope was built using fused-deposition modelling 3D-printing (FDM) of ABS plastics. The device consists of three subgroups: the probe conveyer, the laser adjustment unit, and the actual microscope. The probe conveyor holds 26 specimens in transparent tubes and positions each tube under the lens. This is then moved vertically by the described monolithic mechanism by a stepper motor. Image acquisition is done using a Raspberry V2.1 camera (8 megapixels) with an additional 2.1 mm lens forming a 4f-optics arrangement and a Raspberry Pi3 Model-B computer. The latter is also used to control the mechanics of the microscope. For validation a pappus of dandelion seed was assessed. It was possible to easily visualize the geometrical structure in different horizontal planes. Structures down to ~1.2 µm could be differentiated. It became clear that the vertical stiffness of the monolithic mechanism is sufficient as is the alignment of the axes. The tolerances of the FDM printing process lead to only a very small lateral and angle displacement. However, lateral stiffness of the mechanism is not yet sufficient. Future development will provide higher optical resolution by deploying higher quality lenses and interchangeable fluorescence filters for greater flexibility.

Zusammenfassung

Energy harvesting could make it possible to replace batteries of active electronic implants or at least extend the lifespan of the implant, which primarily depends on the capacity of the batteries used. This paper provides an overview of current energy harvesting modalities for medical devices. For each modality, energy harvesting systems are analysed in terms of provided power, size, and location (wearable/implanted). To allow easy comparison the available electrical power was normalized to the largest surface of the devices. During the research 42 energy harvesting systems have been identified. For wearable devices, a power range of 0,43 nW/cm2 up to 1,2 mW/cm2 can be expected. For implanted devices 26,76 nW/cm2 up to 39,5 mW/cm2. The provided power of wearable and implantable systems would usually be sufficient to operate a pacemaker, for example. Most devices are extended in only two dimensions, thus the power-to-surface-ratio is valid. For wide use in medical devices, the systems still need to be adapted, particularly in terms of reliability, size, and biocompatibility.

Zusammenfassung

Venipuncture is one of the most often performed invasive clinical procedure. Nevertheless, complications still occur. One opportunity to counteract these complications is to indicate the insertion by electrical impedance measurement, which bases on the various electrical properties of different tissues. This paper presents the evaluation and reproducible fabrication of simple tissue-mimicking phantoms for investigation of impedance sensing techniques. Three different tissue-mimicking phantoms, representing blood, fat, and skin, were made on water-based recipes, including agar and gelatin as gelling agents. For evaluation of the electrical properties an electrode probe, made of hypodermic needles, was fabricated and characterized using six sodium chloride (NaCl) solutions of defined concentrations. For characterization of the phantoms, conductances were measured over a frequency range from 20 Hz up to 1 MHz using the self-fabricated electrodes. The calculated conductivities of the tissue-mimicking phantoms showed sufficient agreement with corresponding electrical literature data of native tissue. Tests with a layered tissue structure proved usability for impedance-based venous entry tests. However, the method proposed was not suitable for investigation of relative permittivity, which would be required for full electrical characterization.

Zusammenfassung

A method for identification of tissue types using a handheld impedance measurement device is proposed. An impedance analyzer chip AD5933, driven by an Arduino Nano, is utilized for measurements of the electrical impedance. The electrodes interfacing the tissue consist of two concentric standard hypodermic needles, separated by an insulating layer of PTFE. The electrical contact is established by two-pole splicing connectors. By a prior determination of the cell constant, the conductivity of the penetrated tissue type can be inferred from impedance values. The cell constant determined for the self-fabricated needle electrode is 3.72 ∙ 10-3 m. For NaCl solutions, percental differences between the conductivities found in this work and literature values are between 0.8 % and 37.7 %. For a test frequency of 100 kHz, only small differences from expected conductivity values (2.1 % for muscle, and 5.8 % for fat) are found in porcine tissue samples, demonstrating the ability to identify unknown tissue types. However, miniaturization of the needle as well as the consideration of the tissue’s permittivity is desired to increase detection quality.

Zusammenfassung

To assist the insertion of a robot-aided endoscope during colonoscopy, a measuring system is required so that the endoscope tip can align automatically and thus find the curved pathway of the large intestine. To achieve this, a self-expanding nitinol wire basket is used to sense the contour of the intestine. As the wire basket touches the wall, it is deflected towards the center of the intestine. The relative position of the wire basket within the camera image is captured, which describes the desired direction to follow the organ. To identify the wire basket in the image, the original RGB image stream is converted into the HSV (hue, saturation, value) color space. Thus, a binary image can be created, in which only the neon-green color portion of the wire basket is visible as a cross. The Hough Transformation is used to search for straight lines in the binary image. Once two lines are found, the intersection point can be calculated and thus its position in the image. The evaluation of the execution time of the algorithm on a live stream was 45 ± 31 ms on average. The algorithm robustly recognizes the wire basket even if it was not visible to the human eye in the original RGB image due to deficient lighting.

Zusammenfassung

Localized impedance measurements at the needle tip identifying the present tissue type could aid clinicians in needle procedures. To assess the sensitivity field of a hollow, bipolar needle electrode, a 3D finite element approach using COMSOL Multiphysics was chosen. The simulated bipolar needle electrode consists of two hypodermic needles (17 G and 23 G) with an insulating layer of polytetrafluoro-ethylene (PTFE) in between. Impedance values were recorded while steadily increasing the insertion depth of the needle electrode in a layered tissue structure of skin (dermis), fat, and blood. Simulation results reveal a highly local sensitivity volume around the needle tip that can be approximated by half a tri-axial ellipsoid with elliptic radii of 0.735 mm, 2.886 mm, and 1.774 mm. A comparison with simulated and measured impedance values shows great correspondence.

Zusammenfassung

Teeth grinding is, due to its various impacts on the human body, a highly discussed issue in dentistry. It can damage the tooth structure or cause pain due to muscle tension. At the moment, there is neither a satisfactory diagnostic nor a comprehensive treatment option. This paper deals with the development of an app-controlled, small, portable sensor unit that can be used by patients to monitor their teeth grinding in everyday life. It also offers a treatment option due to an implemented biofeedback option. To achieve the most cost-effective device possible, only off-theshelf electronics and no proprietary software were used. In initial tests, the measuring device showed high level of measurement accuracy when performing measurements without feedback at rest (f_score=-0.025...0).

Zusammenfassung

A twisted string actuator (TSA) is a small, strong, lightweight, and low-cost gear, transforming rotation into a linear pulling movement. The TSA consists of two or more strings that are twisted along their common longitudinal axis. The helix formed in this process becomes shorter the further the bundle is twisted. A possible application is a tendon-based endoscopic robot. To control the movement of the endoscope, a precise contraction of the tendon is necessary. Since the strings of the TSA show an elastic behaviour, position feedback is needed to determine the exact movement of the TSA. In this paper, a TSA with a closed-loop position control by a low-cost displacement sensor is presented.

Zusammenfassung

Upper limb absence has an impact on both physical and mental health of a human being. Nowadays, the costs of commercial, externally powered prosthetic hands range between 25.000 € and 70.000 €. A first demonstrator of a lightweight low-cost prosthetic hand is produced with 3D-printing technology (Fused Deposition Modeling). Due to integration of single-axis solid-state joints the five fingers can be printed in one piece. Thermoplastic polyurethane is used for this purpose. The flexion of all fingers is achieved by moving cords which are positioned on the palmar side of each finger. Two twisted string actuators are integrated to allow the movement of the thumb and the remaining four fingers. These actuators consist of two polyethylene strands which are twisted along their main axis by a DC motor, providing a tensile force to bend the fingers. In order to achieve simultaneous but differential actuation of the four fingers (small finger, ring finger, middle finger and index finger), a differential mechanism is used. The thumb is driven by a separate unit. In order to open the hand, the elasticity of the joints’ material is taken advantage of. With the developed mechanics it is possible to perform precision and cylindrical grasps with an opposed thumb. Weights up to 260 g can be held according to the shape and size of an object. To increase the adaption to different sizes and weights of objects, the design should be modified. It can be concluded, that the presented device is a promising basis for a lightweight, lowcost prosthetic hand in the future.

Zusammenfassung

Venepuncture is one of the most common invasive procedures in medical healthcare worldwide, however failure rates are still relatively high, particularly for paediatric, geriatric, darker skinned, and obese patients. Visualisation of the veins has been shown to decrease failure rates and can be achieved through trans-illumination, near infrared reflectance, or sonography. However, these techniques are either not reliable or very expensive, resulting in them not being commonly used in the clinical workplace. This paper develops a proof of concept low-cost LED vein detection device using photocurrent generated by LEDs in reverse bias. The prototype uses two emitting LEDs and one detecting LED to identify the location of a vein via trans-illuminance and reflectance. Various light intensities and wavelengths of the LEDs are tested in regard to resolution, noise, and signal peaks. A balance between system noise and resolution is identified for each LED in relation to the emitted intensity. No significant difference was observed in relative peak height when different wavelengths were used to identify the same superficial veins. The initial proof of concept proves the LED vein detection method and provides the foundation for further low-cost LED vein detection devices to be developed.

Zusammenfassung

Venepuncture is one of the most often performed invasive clinical procedure. Nevertheless, complications still occur. One possibility to counteract these complications is to indicate the insertion by electrical impedance measurement, based on the various electrical properties of different tissues. This paper presents the evaluation and reproducible fabrication of simple tissue-mimicking phantoms for investigation of impedance sensing techniques. Three different tissue-mimicking phantoms, representing blood, fat, and skin, were made on water-based recipes, including agar and gelatin as gelling agents. For evaluation of the electrical properties an electrode probe, made of hypodermic needles, was fabricated and characterized using six sodium chloride (NaCl) solutions of defined concentrations. For characterization of the phantoms, conductances were measured over a frequency range from 20 Hz up to 1 MHz using the self-fabricated electrodes. The calculated conductivities of the tissue-mimicking phantoms show sufficient agreement with corresponding electrical literature data of native tissue. However, the method was not suitable for investigation of relative permittivity, which would be required for full electrical characterization.

Zusammenfassung

Microscopy is an essential tool in research and science. However, it is relatively resource consuming regarding cost, time of usage, and consumable supplies. Current low-cost approaches provide good imaging quality but struggle in terms of versatility or applicability to varying setups. In this paper, a Compact Microscope Module for versatile application in custom-made setups or research projects is presented. As a first application and proof of concept, the use of the module in a High-Throughput Microscope for screening of samples in microtiter plates is shown. The Compact Microscope Module allows for simple and resource-efficient microscopy in various applications while still enabling relatively good imaging qualities.

Zusammenfassung

Access to systems for robot-assisted surgery is limited due to high costs. To enable widespread use, numerous issues have to be addressed to improve and/or simplify their components. Current systems commonly use universal linkage-based input devices, and only a few application-oriented and specialized designs are used. A versatile virtual reality controller is proposed as an alternative input device for the control of a seven degree of freedom articulated robotic arm. The real-time capabilities of the setup, replicating a system for robot-assisted teleoperated surgery, are investigated to assess suitability. Image-based assessment showed a considerable system latency of 81.7 ± 27.7 ms. However, due to its versatility, the virtual reality controller is a promising alternative to current input devices for research around medical telemanipulation systems.

Zusammenfassung

Microscopy enables fast and effective diagnostics. However, in resource-limited regions microscopy is not accessible to everyone. Smartphone-based low-cost microscopes could be a powerful tool for diagnostic and educational purposes. In this paper, the imaging quality of a smartphone-based microscope with four different optical parameters is presented and a systematic overview of the resulting diagnostic applications is given. With the chosen configuration, aiming for a reasonable trade-off, an average resolution of 1.23 μm and a field of view of 1.12 mm2 was achieved. This enables a wide range of diagnostic applications such as the diagnosis of Malaria and other parasitic diseases.

Zusammenfassung

Many medical interventions in therapy and diagnostics require needle insertion into tissue. Common complications such as increased pain and formation of haematoma are caused by wrong needle positioning. It has been shown that pain experience and needle positioning can be improved by a reduction of insertion force, which can be achieved by vibrating the needle axially. An experimental setup has been designed to investigate the influences of different combinations of vibration frequencies (10, 100, and 200 Hz) and vibration amplitudes (20, 100, and 500 μm) during needle insertion into thin sheets of polyethylene terephthalate (PET). A customary 20 W loudspeaker was used to generate the vibration. The results indicate a maximum reduction of 73 % in puncture force and up to a 100 % reduction in shaft friction force. However, the additional vibration force generated by the vibration movement has to be high enough to generate positive effects in terms of force reduction.

Zusammenfassung

Venepuncture is one of the most common invasive procedures performed worldwide, however, complications still occur. Currently, commercial single layer silicone phantoms used for venepuncture training do not accurately imitate the geometry and mechanical properties seen in the various patient groups. This paper presents the development of a realistic artificial venepuncture phantom. Three multilayered tissue phantoms are developed simulating venepuncture sites of paediatric, adult and geriatric patients. Silicone materials of different stiffnesses were selected to imitate the epidermis, dermis, subcutaneous fat, muscle and superficial veins. Singleaxis indentation tests were carried out on silicone samples and the multi-layered phantom inserts to characterize the material properties. The measured Young's moduli for the artificial dermis, fat and muscle show sufficient agreement with corresponding literature values. However, characterization of the complete phantom inserts showed stiffnesses four times larger than prior in-vivo studies. Future studies will work on developing a more comparable in-vivo study.

Zusammenfassung

Recently, there has been a strong emergence of teleoperated minimally invasive surgery due to the potential benefits for both, the surgeon's performance and outcomes for the patient. However, due to high acquisition costs, no widespread use has been achieved so far. The use of low-cost components can help to address this issue. In this paper, a commercial handheld virtual reality controller as an unconventional and versatile approach for the input device, is presented and investigated. Assessment of the input device is done by performing an experimental study with 24 participants on two different fine motoric tasks. Additionally, motion scaling is investigated by using different transmission ratios for the user's movements. The large and unrestricted range of motion of the presented input device showed to be a promising alternative to conventional input devices. However, the tasks showed room for improvement regarding the controller's ergonomics and usability. For further comparative investigations, conventional input devices and mimetic input devices need to be considered.

Zusammenfassung

In developing countries airborne micro-organisms are one of the most common causes of surgical wound infection. In the operating room low-turbulence displacementflow has been shown to reduce the influence of airborne bacteria. However, due to complexity and cost, current systems are not accessible to all potential users. In this paper a low-cost ventilation system is presented that provides lowturbulence displacement-flow over a surgical operating environment. A stand-alone, simple to assemble, mobile airflow system was developed using the principle of speed compensation for laminar airflow. From visual inspection and measurements, the system was seen to generate a continuous downwards displacement of air over the protected area around the situs. The entire system can be assembled quickly with minimal standard tools, making it very suitable for mobile use, such as in disaster areas. Future work is required to achieve the vertical dimension of a laminar flow field required by the DIN 1946-4. Overall, the low-cost and simple system could provide many potential users access to the technology and thus improving hygiene conditions in their operating environment.

Zusammenfassung

Current Directions in Biomedical Engineering | Volume 5: Issue 1 Endoscopic Pan/Tilt Camera for Thorax Interventions – Design and first results Alexander Mrokon 1 , Peter P. Pott 1 , and Volker Steger 2 1 Institute of Medical Device Technology, University of Stuttgart, Pfaffenwaldring 9, 70569, Stuttgart, Germany 2 University Department of Thoracic and Cardiovascular Surgery, Hoppe-Seyler-Str. 3, 72076, Tübingen, Germany DOI: https://doi.org/10.1515/cdbme-2019-0130 Add to Citavi project by DOI | Published online: 18 Sep 2019 PDF Abstract PDF Recommendations Abstract Minimally invasive surgery in some cases suffers from a limited view because certain areas are obscured by others. In this paper, a system is described, which can be used in minimally invasive procedures as an addition to a standard endoscope to improve the range of view. Through FEM simulation a magnetic circuit was designed to position the camera head. Subsequently, a camera positioning system was set up that includes an extracorporeal and an intracorporeal unit. The first controls the intracorporeal system. The latter has a camera inclination angle of up to 65° and an additional vertically downward viewing angle when aligned in parallel (inclination angle 0°). The panning angle is 360°. The camera system was evaluated in lab and cadaver trials. It has been found that the size of the intracorporeal system (16 × 10 × 150 mm) represents a major problem. Future work will focus of the reduction of the system’s size, the improvement of the camera image quality, and design changes considering mechanical stability.

Zusammenfassung

Venous blood circulation can be restricted due to various conditions commonly indicating a related medical condition. However, current non-invasive methods for determining venous blood flow are limited to be either very inaccurate or expensive. Alternatively, a method to measure sap flow non-invasively in trees is through thermal mass measurement principles. This paper investigates applying the thermal mass flow measurement principle to determine venous blood flow. A simplified finite element model (FEM) and simulation are created to determine the operating behavior and expected response of a thermal mass flow meter with venous blood flow under the skin. An initial prototype of a thermal mass venous blood flow meter is designed using a Peltier-element and RTD thermistors. Initial tests were done on N = 8 subjects identifying the presence of blood flow and, testing the devices basic functionality and performance. The simplified FEM model of venous blood flow proved the thermal mass blood flow device is feasible, and determined the initial characteristics of the first prototype. The initial prototype proved to be functional detecting rises in temperature downstream of +1.4 K (0.8 - 1.8 inter- quartile range) when the blood flow was released (t = 90 s after release), compared to when blood was not flowing. The initial prototype proved to be able to detect the presence of blood flow in all subjects. However, further work is required to increase the differences in temperature values or gradient measured for a change in flow rate so the actual flow rate can be determined.

Zusammenfassung

The twisted-string actuation (TSA) principle provides simple, lightweight, silent yet powerful actuators well suited for human-machine interaction. This comprises of not only the use in orthotic and prosthetic systems for lower extremities, arms, and wrists but also exo-skeletons. A TSA consists of a bundle of at least two fiber components and an actuator to twist it along its main axis. This forms a helical structure, which shortens the axial length - given non-elastic behaviour of the material. In practice, an axial bearing compensates for the load force and a linear guide counters the motor torque. In cases where a bi-directional force is required, a passive spring return mechanism can be included. Our work focuses on the integration of the described TSA components into a single elastic tube. Three TSAs are arranged in series and six in parallel such that they form an array that can bend in three dimensions with muscle-like behaviour and elastic properties. By switching motor units on and off, the length and force of the array can be varied between zero and maximum force without the need of an internal feedback loop. A first experiment is carried out to validate the force control. A possible application of this technology is soft medical robots for diagnostic and therapeutic purposes. The first demonstrator consists of three motor units in series. Six of these serial arrangements are combined in parallel forming an array of 18 motors. Each TSA unit consists of a DC motor, a string coupling including the axial bearing, the string made of high-density polyethylene, a cylindrical housing that protects the motor against axial forces, houses the DC motor, and provides the support for the previous unit. The entire TSA unit is encapsulated inside a thermoplastic polyurethane (TPU) tube which takes over the counter-torque, acts as linear bearing, is the return spring, and provides the elastic base for the TSA array. Thus, by using these modular units an infinite chain of TSA can be built and arranged as desired. The TSA units can be current-controlled and independently activated. Experiments showed that a no-load stroke of 18 mm and a maximum pulling force of 11 N can be achieved by a single TSA module. The spatial arrangement of the tubes allows muscle-like use in larger and anthropomorphic systems and also 2-dimensional bending and torsion of the array for soft robotic systems. Further work will comprise the improvement of the module, their miniaturization, simplified axial bearings, and integrated control electronics.

Zusammenfassung

In this study a basic principle for the gas supply of a pneumatic actuation for a mobile active knee joint orthosis is described. Instead of using a compressor or a bulky pressure reservoir, the system is supplied with pressurized gas directly from a thermodynamic process to reduce size and weight of the device. To achieve this goal a literature search was performed identifying chemical processes. These options were then analysed and evaluated considering the aspects energy density, safety, eco-friendliness, and technical feasibility of the construction. The expansion of liquified carbon dioxide with phase change achieves the best result due to its high level of safety and the simple technical feasibility of the system. However, CO2cools down considerably during the expansion, so heating up again to room temperature is necessary. Therefore, the technical construction includes a passive and an active heat exchanger.

Zusammenfassung

The aging of humans induces muscle weakness. Muscle weakness results the inability to climb stairs or stand up from a chair and thus, is one of the first steps towards elderly having a less autonomous and self-sufficient life. Therefore, an accessible active knee orthosis, which especially supports these movements would be of great assistance. Recent research projects have focused on feasibility, perfection of motion control and imitation of human movement. For active knee orthoses to be accessible it must be affordable. Hence, this paper systematically evaluates the current research projects around active knee orthosis and discuss the possibilities of implementing a lowcost active knee orthosis.

Zusammenfassung

Microscopy enables fast and effective diagnostics. However, its functionality is not accessible to everyone. Smartphone-based low-cost microscopes could be a powerful tool for diagnostics and educational purposes. Current smartphone-based microscopy approaches struggle with high cost, poor image quality and/or insufficient smartphone compatibility. In this paper, a very feasible and effective lowcost microscope is presented which addresses these issues. To minimize cost, a monolithic foldable structure is designed for production by injection molding. The design has a high order of functional integration, minimizing the number of components, while still enabling a micrometer focusing accuracy.

Zusammenfassung

We present a new teleoperation setup for minimally invasive single-port surgery through natural orifices. The system consists of an intra-corporal parallel slave robot with two instrument arms and a corresponding master interface with four degrees of freedom and grasping. The master interface mimicks the slave robot kinematics to prevent non-achievable movements. With a workspace of ø 60 mm $\times$ 85 mm, interaction forces of up to 5 N and mean speeds of up to 327 mm/s the robot is designed to perform a rectum resection intervention, an operation hardly possible with conventional laparoscopic instruments. In this work, we address several ergonomic aspects of the setup, including surgeon's pose, movement scaling, visual feedback, and haptic feedback. Two experiments were performed to investigate the accuracy and dexterity of the robotic system compared to conventional single-port systems. We found a significant decrease of errors in a point-and-touch-task when using the robot, but no effect on the duration of the task. Surgeons were able to perform suturing and knotting tasks as well as a gall bladder extraction in a porcine model with the robot in an hands on experiment. These experiments showed a good intuitivity and a high instrument control precision as described by the participants.

Zusammenfassung

A prototype of a powered knee orthotic device was developed to determine whether fractional external torque and power support to the knee relieves the biomechanical loads and reduces the muscular demand for a subject performing sit-to-stand movements. With this demonstrator, consisting of the subsystems actuation, kinematics, sensors, and control, all relevant sensor data can be acquired and full control is maintained over actuator parameters. A series-elastic actuator based on a direct current motor provides up to 30 Nm torque to the knee via a hinge joint with an additional sliding degree of freedom. For reasons of feasibility under everyday conditions, user intention is monitored by employing a noninvasive, nonsticking muscle activity sensor to replace electromyographic sensors, which require skin preparation. Furthermore, foot plates with force sensors have been developed and included to derive ground reaction forces. The actual knee torque needed to provide the desired support is based on an inverse dynamics model using ground reaction forces signals and leg kinematics. A control algorithm including disturbance feed forward has been implemented. A demonstration experiment with two subjects showed that 23 % of moment support in fact leads to a similar reduction in activation of the main knee extensor muscle.

Zusammenfassung

This paper presents the development of a surgical instrument to measure interaction forces/torques with organic tissue during operation. The focus is on the design progress of the sensor element, consisting of a spoke wheel deformation element with a diameter of 12 mm and eight inhomogeneous doped piezoresistive silicon strain gauges on an integrated full-bridge assembly with an edge length of 500 ?m. The silicon chips are contacted to flex-circuits via flip chip and bonded on the substrate with a single component adhesive. A signal processing board with an 18 bit serial A/D converter is integrated into the sensor. The design concept of the handheld surgical sensor device consists of an instrument coupling, the six-axis sensor, a wireless communication interface and battery. The nominal force of the sensing element is 10 N and the nominal torque is 1 N?m in all spatial directions. A first characterization of the force sensor results in a maximal systematic error of 4.92 \% and random error of 1.13 \%.

Zusammenfassung

This paper presents a surgical navigation system with an upper limb exoskeleton. The robotic system consists of a real-time tracking camera with optical markers and a 7-DOF serial manipulator for positioning a tool on a preplanned path. The detection of the user?s movement intention is enabled with integrated torque sensors and an inverse dynamic model of the kinematic chain. Therefore, the cooperative system combines the human ability to take decisions with the precision and fatigue resistance of a robot.

Zusammenfassung

Well engineered piezoelectric actuators characteristically show a high energy density, but there is still potential for improvement in transferring the energy from the piezoelectric element to the moving component (e.g. rotor). This transfer is basically determined by the friction between stator structures and the rotor. In prior publications a cilia based piezoelectric actuator was proposed, which uses a microscopic friction layer in this transfer procedure. The cilia based piezoelectric actuator uses a layer of carbon fibres with a defined inclination as a friction layer for the anisotropic energy transfer from the stator to the rotor. The stator structure is formed by a piezoelectric ceramic element (piezo stack), the stator structure, and the fibre layer, which is attached to the surface of the stator structure. As the piezo stack is activated, the stator structure amplifies its stroke and the fibres, which now are perpendicularly pressed against the contact surface of the rotor, set the rotor in motion tangentially to the fiber?s motion axis. As this happens, the fibers are elastically bent. Through the anisotropic friction resulting from this contact, the energy is transferred from the stator structure to the rotor. Thus, the rotor is set in motion. The interaction between the layer of fibers and the contact surface is a distinctive mark of the cilia based piezoelectric actuator. The reliability of the actuator depends strongly on the friction layer. The layer has to show a high mechanical resistance against frequent load stresses and a good matching with the contact surface for a high friction coefficient. To fulfil these requirements carbon fibres were chosen. Carbon fibres have very low masses and excellent mechanical characteristics. The high tensile durability and short length allows achieving very high resonance frequencies. In order to exploit these properties, the fibres have to be aligned in a straight way with a defined inter-fibre space. Doing so, additional friction between fibers is avoided and their elastic deflection is assured. The matching between the fiber layer and the contact surface can be experimentally investigated by measuring the transmitted energy from the fibers to different contact surfaces. The fiber layer plays a very important role in the functionality, energetic efficiency and lifetime of the proposed actuator. Therefore, a reliable production of this layer has to be investigated. In this paper, a method for the arrangement of carbon fibers into a 2D array is presented. Nickel coated fibers are used as source material, which are mechanically aligned in a parallel way and embedded in a polymer matrix. At this point, the fibers are mechanically treated with conventional cutting methods in order to achieve fibers with a defined inclination and length. After chemical adhesion between this matrix and a stainless stell substrate an etching procedure is executed to eliminate the nickel coating and the polymer matrix without harming the fibers or the substrate. With these steps, a pillar 2D array of carbon fibers with a defined space between the fibers is achieved. This space depends directly from the fiber coating thickness, which in this case is about 0,5 \mum for a fiber diameter of 7 \mum. Thinner nickel coatings on carbon fibers are commercially avaiable. To increase the spaces between fibers, carbon fibers with a thicker nickel coating can be arranged by manufacturers. The length of the layers that were manufactured in this work, the fiber distribution and the inter-fiber space were analysed with SEM microscopy.

Zusammenfassung

The use of robots in a medical environment is a challenging task not only for system development but also for the actual application in this demanding environment. Robots are used to enhance surgery quality in terms of precision, application of new therapies, or to improve ergonomics - only to name a few reasons. The approach described in this paper is to provide an exoskeleton worn by the orthopedic surgeon. It is intended to be used during drilling tasks at the spine and to enhance precision as the surgeon is led by optic, acoustic, and haptic perception. The parallel flux of forces and the inherently mobile robot base allow the surgeon to directly maintain responsibility for surgery. Not only the mechanical design of the system but also the control is decomposed into several levels. To do so, a behavior-based approach is used. The system?s design criteria are briefly described and first results are presented. The exoskeleton is composed of an anthropomorphic arm actuated by twisted-string actuators. This leads to a lightweight construction. To provide sufficiently fast and precise information about the spatial position and its time derivations, optical and inertial tracking is used. A six DOF User Guidance Opto-Acoustic Display is utilized to provide the surgeon with information on position and orientation of the tool with respect to the desired trajectory. First experimental results derived that the intended workspace meets the surgical requirements and the user guidance system enables the surgeon to follow the desired trajectory by intuitive user guidance.

Zusammenfassung

This paper proposes a new perception-based concept for force sensing in haptic systems. By using two different sensing principles, a better adaption to the human sensory system can be achieved. Based on the tactile and kinesthetic parts of haptic perception, this is done using different sensing principles, nominal ranges, bandwidth and degrees of freedom for each part. The requirements of each part are described in detail and possible realizations are investigated. The proposed concept allows for a better quality of haptic feedback at lower costs.