Design Methodology for Magnetic Field-Based Soft Tri-Axis Tactile Sensors

Tactile sensors are essential if robots are to safely interact with the external world and to dexterously manipulate objects. Current tactile sensors have limitations restricting their use, notably being too fragile or having limited performance. Magnetic field-based soft tactile sensors offer a potential improvement, being durable, low cost, accurate and high bandwidth, but they are relatively undeveloped because of the complexities involved in design and calibration. This paper presents a general design methodology for magnetic field-based three-axis soft tactile sensors, enabling researchers to easily develop specific tactile sensors for a variety of applications. All aspects (design, fabrication, calibration and evaluation) of the development of tri-axis soft tactile sensors are presented and discussed. A moving least square approach is used to decouple and convert the magnetic field signal to force output to eliminate non-linearity and cross-talk effects. A case study of a tactile sensor prototype, MagOne, was developed. This achieved a resolution of 1.42 mN in normal force measurement (0.71 mN in shear force), good output repeatability and has a maximum hysteresis error of 3.4%. These results outperform comparable sensors reported previously, highlighting the efficacy of our methodology for sensor design

Normal Force Calibration for Optical Based Silicone Tactile Sensor

AbstractThe need for calibration is important as ancient humankind at B.C. age pioneered calibration for measurable items such as length, weight, frequency and other basic measurement. In the robotic application, the precision of movement and the sensitivity of reaction also based on the calibration of its sensors and actuators. Therefore it is vital for a newly developed sensor to be calibrated thoroughly before it can be used. In this paper, the authors proposed a calibration of a new optical based silicone tactile sensor developed in our lab. Measurable item which is normal force is relates to the blob area of image recorded in the inner side of optical based silicone tactile sensor. The normal force acquired from digital force sensor in experiment conducted. The experiment produced 9 images. The 9 images acquired is processed in WiT 8.2 image processing software to find the area of the specific spot as known as blob image. A blob area VS normal force graph is plotted using experimental data. The graph is then interpolated using suitable curve fitting technique to get the optimum relationship. The result shows that the quadratic plot is the best suit for the data with the force range from 0 to 3.79N

Visuotactile Sensors with Emphasis on GelSight Sensor: A Review

This review paper focuses on vision and touch-based sensors known as visuotactile. The study of visuotactile sensation and perception became a multidisciplinary field of study by philosophers, psychologists, biologists, engineers, technologists, and roboticists in the fields of haptics, machine vision, and artificial intelligence and it dates back centuries. To the best of our knowledge, the earliest records of visuotactile sensor was not applied to robotics and was not even for hand or finger imprint analysis yet for recording the foot pressure distribution of a walking or standing human known as pedobarograph. Our review paper presents the different literature related to visuotactile sensors that lead to a high-resolution miniature pedobarographlike sensor known as the GelSight sensor. Moreover, this review paper focuses on architecture, different techniques, hardware, and software development of GelSight sensor since 2009 with its applications in haptics, robotics, and computer vision

An Optical Sensor Design: Concurrent Multi-axis Force Measurement and Tactile Perception.

PhD ThesesForce and tactile sensing have experienced a surge of interest over recent decades, as they convey useful information about the direct physical interaction between the sensor and the external environment. A robot end effector is a device designed to interact with the environment. End effectors such as robotic hands and grippers can be used to pick up, place or generally manipulate objects. There is a clear need to equip such end effectors with appropriate sensing means to be able to measure tactile and force information. Work to date has explored these two modalities separately. Tactile sensors have been developed for integration with gripper fingertips or as skins embedded with the outer side of manipulators, mainly to measure normal force and its distribution across a surface patch. On the other hand, force sensors have commonly been integrated with the joints of robotic arms or fingers to measure external multi-axis forces and torques via the connected links. We observe that a force sensor cannot measure tactile information, and current tactile sensors cannot accurately measure force information. This can become a particular issue when integrating force sensors remotely to measure forces indirectly, especially if the connecting link is flexible or, generally, difficult to model potentially impacting negatively on the force estimates. We aim to provide a solution for an integrated sensor capable of measuring tactile and force information at the point of contact, i.e., on the fingertip of a robot hand or arm. In this thesis, we explore the idea of integrating the two sensing modalities, tactile and force sensing, in one sensor housing with the signal acquisition being performed by a single monocular camera acting as the transducer. The hypothesis is that an integrated force/tactile sensor will perform in a better way than having these sensor modalities separated. This thesis shows that an integrated sensor achieves a tactile sensing performance comparable to existing vision-based tactile sensors and at the same time proves to provide more accurate force sensor information whilst extending the field of similar vision-based sensors from 3 DoF to 6 DoF. In addition, the tactile sensing element of our sensor is not affected by the patterns superimposed on to the flexible element of comparable vision-based sensors used to infer force information. In this thesis, we have implemented several sensor prototypes; designs and experimental analyses for each prototype are being provided. The manufactured sensor prototypes prove the validity of the proposed vision-based dual-modality sensing approach, and the proposed sensing principle and structure shows high versatility and accuracy, as well as the potential for further miniaturization, making the proposed concept suitable for integration with standard robot end effectors

Multi-Axis force/torque sensor based on Simply-Supported beam and optoelectronics

© 2016 by the authors; licensee MDPI, Basel, Switzerland. This paper presents a multi-axis force/torque sensor based on simply-supported beam and optoelectronic technology. The sensor’s main advantages are: (1) Low power consumption, (2) low-level noise in comparison with conventional methods of force sensing (e.g., using strain gauges), (3) the ability to be embedded into different mechanical structures, (4) miniaturisation, (5) simple manufacture and customisation to fit a wide-range of robot systems, and (6) low-cost fabrication and assembly of sensor structure. For these reasons, the proposed multi-axis force/torque sensor can be used in a wide range of application areas including medical robotics, manufacturing, and areas involving human-robot interaction. This paper shows the application of our concept of a force/torque sensor to flexible continuum manipulators: A cylindrical MIS (Minimally Invasive Surgery) robot, and includes its design, fabrication, and evaluation tests.The research leading to these results has received funding from the European Commission’s Seventh Framework Programme; project STIFF-FLOP (Grant No. 287728), and has received funding from the Wellcome Trust IEH Award (Grant No. 102431)

Design, Modeling, Fabrication and Testing of a Piezoresistive-Based Tactile Sensor for Minimally Invasive Surgery Applications

Minimally invasive surgery (MIS) has become a preferred method for surgeons for the last two decades, thanks to its crucial advantages over classical open surgeries. Although MIS has some advantages, it has a few drawbacks. Since MIS technology includes performing surgery through small incisions using long slender tools, one of the main drawbacks of MIS becomes the loss of direct contact with the patient’s body in the site of operation. Therefore, the surgeon loses the sense of touch during the operation which is one of the important tools for safe manipulation of tissue and also to determine the hardness of contact tissue in order to investigate its health condition. This Thesis presents a novel piezoresistive-based multifunctional tactile sensor that is able to measure the contact force and the relative hardness of the contact object or tissue at the same time. A prototype of the designed sensor has been simulated, analyzed, fabricated, and tested both numerically and experimentally. The experiments have been performed on hyperelastic materials, which are silicone rubber samples with different hardness values that resemble different biological tissues. The ability of the sensor to measure the contact force and relative hardness of the contact objects is tested with several experiments. A finite element (FE) model has been built in COMSOL Multiphysics (v3.4) environment to simulate both the mechanical behavior of the silicone rubber samples, and the interaction between the sensor and the silicone rubbers. Both numerical and experimental analysis proved the capability of the sensor to measure the applied force and distinguish among different silicone-rubber samples. The sensor has the potential for integration with commercially available endoscopic grasper

Objekt-Manipulation und Steuerung der Greifkraft durch Verwendung von Taktilen Sensoren

This dissertation describes a new type of tactile sensor and an improved version of the dynamic tactile sensing approach that can provide a regularly updated and accurate estimate of minimum applied forces for use in the control of gripper manipulation. The pre-slip sensing algorithm is proposed and implemented into two-finger robot gripper. An algorithm that can discriminate between types of contact surface and recognize objects at the contact stage is also proposed. A technique for recognizing objects using tactile sensor arrays, and a method based on the quadric surface parameter for classifying grasped objects is described. Tactile arrays can recognize surface types on contact, making it possible for a tactile system to recognize translation, rotation, and scaling of an object independently.Diese Dissertation beschreibt eine neue Art von taktilen Sensoren und einen verbesserten Ansatz zur dynamischen Erfassung von taktilen daten, der in regelmäßigen Zeitabständen eine genaue Bewertung der minimalen Greifkraft liefert, die zur Steuerung des Greifers nötig ist. Ein Berechnungsverfahren zur Voraussage des Schlupfs, das in einen Zwei-Finger-Greifarm eines Roboters eingebaut wurde, wird vorgestellt. Auch ein Algorithmus zur Unterscheidung von verschiedenen Oberflächenarten und zur Erkennung von Objektformen bei der Berührung wird vorgestellt. Ein Verfahren zur Objekterkennung mit Hilfe einer Matrix aus taktilen Sensoren und eine Methode zur Klassifikation ergriffener Objekte, basierend auf den Daten einer rechteckigen Oberfläche, werden beschrieben. Mit Hilfe dieser Matrix können unter schiedliche Arten von Oberflächen bei Berührung erkannt werden, was es für das Tastsystem möglich macht, Verschiebung, Drehung und Größe eines Objektes unabhängig voneinander zu erkennen