Angled sensor configuration capable of measuring tri-axial forces for pHRI

© 2016 IEEE. This paper presents a new configuration for single axis tactile sensor arrays molded in rubber to enable tri-axial force measurement. The configuration requires the sensing axis of each sensor in the array to be rotated out of alignment with respect to external forces. This angled sensor array measures shear forces along axes in a way that is different to a planar sensor array. Three sensors using the angled configuration (22.5°, 45° and 67.5°) and a fourth sensor using the planar configuration (0°) have been fabricated for experimental comparison. Artificial neural networks were trained to interpret the external force applied along each axis (X, Y and Z) from raw pressure sensor values. The results show that the angled sensor configuration is capable of measuring tri-axial external forces with a root mean squared error of 1.79N, less error in comparison to the equivalent sensor utilizing the planar configuration (4.52N). The sensors are then implemented to control a robotic arm. Preliminary findings show angled sensor arrays to be a viable alternative to planar sensor arrays for shear force measurement; this has wide applications in physical Human Robot Interaction (pHRI)

Microfabricated pressure and shear stress sensors

A microfabricated pressure sensor. The pressure sensor comprises a raised diaphragm disposed on a substrate. The diaphragm is configured to bend in response to an applied pressure difference. A strain gauge of a conductive material is coupled to a surface of the raised diaphragm and to at least one of the substrate and a piece rigidly connected to the substrate

Microfabricated tactile sensors for biomedical applications: a review

During the last decades, tactile sensors based on different sensing principles have been developed due to the growing interest in robotics and, mainly, in medical applications. Several technological solutions have been employed to design tactile sensors; in particular, solutions based on microfabrication present several attractive features. Microfabrication technologies allow for developing miniaturized sensors with good performance in terms of metrological properties (e.g., accuracy, sensitivity, low power consumption, and frequency response). Small size and good metrological properties heighten the potential role of tactile sensors in medicine, making them especially attractive to be integrated in smart interfaces and microsurgical tools. This paper provides an overview of microfabricated tactile sensors, focusing on the mean principles of sensing, i.e., piezoresistive, piezoelectric and capacitive sensors. These sensors are employed for measuring contact properties, in particular force and pressure, in three main medical fields, i.e., prosthetics and artificial skin, minimal access surgery and smart interfaces for biomechanical analysis. The working principles and the metrological properties of the most promising tactile, microfabricated sensors are analyzed, together with their application in medicine. Finally, the new emerging technologies in these fields are briefly described

The Manufacture and Mechanical Analysis of the PVDF Flexible Sensors

Polyvinylidene fluoride (PVDF) is a widely used sensing material with piezoelectricity property. Applying microelectronic technology to this material could result in multifunctional sensing unit. Based on the previous researches, a manufacturing process and flexible structure are proposed to manufacture the PVDF film and the PVDF flexible sensor using stretchable electronic technology. The sensor is designed to be paved on the surface of airfoil to monitor the structural behaviors. Two systems are compared, one with a polydimethylsiloxane (PDMS) layer and the other without. The finite element results show that the Au electrodes films are harder to be destructed for the system with PDMS, because the PVDF flexible sensor can realize the strain-isolation, therefore the resistance to destruction of the sensors could be improved. However, the deformation of duralumin is increased, so the substrate that the flexible sensor paves on will undertake a majority portion of stresses and strains, and a substrate with reasonable stiffness will contribute to the structure integrity

Tactile Sensing for Robotic Applications

This chapter provides an overview of tactile sensing in robotics. This chapter is an attempt to answer three basic questions: \u2022 What is meant by Tactile Sensing? \u2022 Why Tactile Sensing is important? \u2022 How Tactile Sensing is achieved? The chapter is organized to sequentially provide the answers to above basic questions. Tactile sensing has often been considered as force sensing, which is not wholly true. In order to clarify such misconceptions about tactile sensing, it is defined in section 2. Why tactile section is important for robotics and what parameters are needed to be measured by tactile sensors to successfully perform various tasks, are discussed in section 3. An overview of `How tactile sensing has been achieved\u2019 is given in section 4, where a number of technologies and transduction methods, that have been used to improve the tactile sensing capability of robotic devices, are discussed. Lack of any tactile analog to Complementary Metal Oxide Semiconductor (CMOS) or Charge Coupled Devices (CCD) optical arrays has often been cited as one of the reasons for the slow development of tactile sensing vis-\ue0-vis other sense modalities like vision sensing. Our own contribution \u2013 development of tactile sensing arrays using piezoelectric polymers and involving silicon micromachining - is an attempt in the direction of achieving tactile analog of CMOS optical arrays. The first phase implementation of these tactile sensing arrays is discussed in section 5. Section 6 concludes the chapter with a brief discussion on the present status of tactile sensing and the challenges that remain to be solved

Force Sensing Surgical Grasper with Folding Capacitive Sensor

Minimally-invasive surgery (MIS) has brought many benefits to the operating room, however, MIS procedures result in an absence of force feedback, and surgeons cannot as accurately feel the tissue they are working on, or the forces that they are applying. One of the barriers to introducing MIS instruments with force feedback systems is the high cost of manufacturing and assembly. Instruments must also be sterilized before every use, a process that can destroy embedded sensing systems. An instrument that can be disposed of after a single use and produced in bulk at a low cost is desirable. Printed circuit micro-electro-mechanical systems (PCMEMS) is an emerging manufacturing technology that may represent an economically viable method of bulk manufacturing small, single-use medical devices, including surgical graspers. This thesis presents the design and realization of a PCMEMS surgical grasper that can fit within a 5 mm trocar, and can accurately measure forces in 3 axes, over a range of +/-4 N. The designed instrument is the first PCMEMS grasper to feature multi-axis sensing, and has a sensing range twice as large as current PCMEMS devices. Experimental results suggest that the performance of the sensing system is similar to conventionally-manufactured MIS instruments that use capacitive force transducers. The techniques applied in this thesis may be useful for developing a range of PCMEMS devices with capacitive sensors. Improvements to the design of the grasper and sensing system are suggested, and several points are presented to inform the direction of future work related to PCMEMS MIS instruments

A Polymer-Based Microfluidic Device with Electrolyte-Enabled Distributed Transducers (EEDT) for Distributed Load Detection

The capability of detecting distributed static and dynamic loads is indispensable in a wide variety of applications, such as examining anatomical structures of biological tissues in tissue health analysis and minimally invasive surgery (MIS) and determining the texture of an object in robotics. This dissertation presents a comprehensive study of a polymer-based microfluidic device with electrolyte-enabled distributed transducers and demonstrates a new concept on using a single microfluidic device for distributed-load detection, which takes advantage of the low-cost microfluidic fabrication technology and the low modulus and biocompatibility of polymer. The core of the device is a single deformable polymer microstructure integrated with electrolyte-enabled transducers. While distributed loads are converted to different levels of deflections by the polymer microstructure, the deflections of the microstructure are translated to resistance changes by the five pairs of distributed transducers underneath the microstructure. Firstly, the design and working principle of the device is described. Then, due to its simple but efficient configuration, a standard fabrication process well developed for polydimethylsiloxane(PDMS)-based microfluidic devices is detailed and employed to fabricate this device. After that, the experimental setups for characterizing the device performance in static, step and sinusoidal inputs are illustrated. The experimental data then are collected and processed by using custom-built electronic circuits and custom LabVIEW/Matlab program to characterize the device performance. Lastly, the performance analysis of the device is conducted to obtain the performance parameters such as device sensitivity and load resolution. In summary, this polymer-based microfluidic device not only demonstrates the new concept and the capability of detecting distributed static and dynamic loads with a single device, with a thorough experimental study on the performance and characterization of this PDMS-based microfluidic device to correlate the device performance to its design parameters, but also the potential application of directly adopting this experimental method to measure the elasticity/viscoelasticity of a soft tissue

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

Concurrent Spatial Mapping of the Viscoelastic Behavior of Heterogeneous Soft Materials Via a Polymer-Based Microfluidic Device

This dissertation presents a novel experimental technique, namely concurrent spatial mapping (CSM), for measuring the viscoelastic behavior of heterogeneous soft materials via a polymer-based microfluidic device. Comprised of a compliant polymer microstructure and an array of electrolyte-enabled distributed resistive transducers, the microfluidic device detects both static and dynamic distributed loads. Distributed loads deform the polymer microstructure and are recorded as resistance changes at the locations of the transducers. The CSM technique identifies the elastic modulus of soft materials by applying a precisely controlled indentation depth using a rigid probe to a sample placed on the device. The spatially-varying elastic modulus of the sample translates to a non-uniform load, causing a non-uniform deformation of the microstructure and variations in the recorded resistance changes. The CSM technique measures the loss modulus of soft materials through a dynamic measurement by applying varying sinusoidal loads to a sample placed on the device. The spatially-varying loss modulus of the sample causes the microstructure to respond with corresponding time delay. Consequently, the phase shift between the sinusoidal load and deflection of the sample along its length are captured by the distributed transducers. As the first step of the experimental protocol, control experiments are implemented on the device to determine its static performance and system-level dynamic parameters. Next, the CSM technique is applied to both homogeneous and heterogeneous synthetic soft materials to measure their elastic moduli by applying a precisely controlled indentation depth through a probe, and the recorded load and device deflection are the output. The data are processed to obtain the overall load and the deflection of the sample at each transducer location and are further used to extract the elastic modulus distribution of the sample. The CSM technique is then applied to measure the loss modulus of soft materials. The measurable sinusoidal loads are the input, and the sinusoidal deflections of the device are the output. By applying the Fast Fourier Transform (FFT) algorithm and the nonlinear regression method, the data are processed to obtain the phase shift between the applied load and the device response along its microchannel length as well as the system-level parameters, namely stiffness (K), damping coefficient (D), and mass (M). In conjunction with the system-level parameters of the system with the device, obtained from the control experiment, the stiffness and the damping coefficient of a sample are calculated, and the sample’s loss modulus distribution is estimated accordingly. This CSM technique successfully measures the spatially-varying elastic modulus and loss modulus of soft materials. As compared with the nanoindentation-based technique, the CSM technique demonstrates its efficiency in spatially mapping the viscoelastic behavior of a sample without excluding interactions among neighboring compositions in a sample