Javad Dargahi

A micromachined piezoelectric tactile sensor for an endoscopic grasper-theory, fabrication and experiments

Present-day commercial endoscopic graspers do not have any built-in sensors, thus, the surgeon does not have the necessary tactile feedback to manipulate the tissue safely. This paper presents the design, fabrication, testing, and experimental results of a micromachined tactile sensor, which can be integrated with the tips of commercial endoscopic graspers. The prototype sensor consists of three layers. The top layer is made of micromachined silicon with a rigid tooth-like structure similar to the present-day endoscopic grasper. The bottom layer is made of flat Plexiglass serving as a substrate. Packaged between the Plexiglass and the silicon is a patterned Polyvinglidene Fluoride (PVDF) film. The proposed sensor exhibits high sensitivity, a large dynamic range, and a high signal-to-noise ratio. Through experimental results, it is shown that the magnitude and position of an applied force can be determined from the magnitude and slope of the output signals from the PVDF sensing elements. Structural analysis is also performed using the finite-element method, and the results are compared with the experimental analysis. The advantages and limitations of this sensor are also reported. A discussion of how the design of the sensor can be integrated with the design of an endoscopic grasper is also presented.

Advances in tactile sensors design/manufacturing and its impact on robotics applications – a review

Purpose – Reviews the benefits and potential application of tactile sensors for use with robots.Design/methodology/approach – Includes the most recent advances in both the design/manufacturing of various tactile sensors and their applications in different industries. Although these types of sensors have been adopted in a considerable number of areas, the applications such as, medical, agricultural/livestock and food, grippers/manipulators design, prosthetic, and environmental studies have gained more popularity and are presented in this paper.Findings – Robots can perform very useful and repetitive tasks in controlled environments. However, when the robots are required to handle the unstructured and changing environments, there is a need for more elaborate means to improve their performance. In this scenario, tactile sensors can play a major role. In the unstructured environments, the robots must be able to grasp objects (or tissues, in the case of medical robots) and move objects from one location to ano...

A multifunctional PVDF-based tactile sensor for minimally invasive surgery

In this paper a multifunctional tactile sensor system using PVDF (polyvinylidene fluoride), is proposed, designed, analyzed, tested and validated. The working principle of the sensor is in such a way that it can be used in combination with almost any end-effectors. However, the sensor is particularly designed to be integrated with minimally invasive surgery (MIS) tools. In addition, the structural and transduction materials are selected to be compatible with micro-electro-mechanical systems (MEMS) technology, so that miniaturization would be possible. The corrugated shape of the sensor ensures the safe tissue grasping and compatibility with the traditional tooth-like end effectors of MIS tools. A unit of this sensor comprised of a base, a flexible beam and three PVDF sensing elements. Two PVDF sensing elements sandwiched at the end supports work in thickness mode to measure the magnitude and position of applied load. The third PVDF sensing element is attached to the beam and it works in the extensional mode to measure the softness of the contact object. The proposed sensor is modeled both analytically and numerically and a series of simulations are performed in order to estimate the characteristics of the sensor in measuring the magnitude and position of a point load, distributed load, and also the softness of the contact object. Furthermore, in order to validate the theoretical results, the prototyped sensor was tested and the results are compared. The results are very promising and proving the capability of the sensor for haptic sensing.

An Endoscopic and Robotic Tooth-like Compliance and Roughness Tactile Sensor

This paper reports on design, fabrication and testing of a prototype Polyvinylidene Fluoride (PVDF) tactile sensor for endoscopic and robotic applications. The sensor can measure both compliance and surface roughness. It consists of rigid and compliant elements. A relative deformation between adjacent parts of the contact object is used to measure the compliance, and the deformation of the compliant element of the sensor is used to measure the profile of a rough surface. The sensor in miniaturized form can be integrated with both endoscopic graspers and robotic end effectors. The theoretical analysis of the sensor is made and compared with experimental values. The advantages and limitations of the sensor are also discussed.

PVDF-Based Microfabricated Tactile Sensor for Minimally Invasive Surgery

This paper aimed to develop a miniaturized tactile sensor capable of measuring force and force position in minimally invasive surgery. The in situ measurement of tactile information is a step forward toward restoring the loss of the sense of touch that has occurred due to shift from traditional to minimally invasive surgeries. The sensor was designed such that it can sense low forces which could be comparable to those produced by pulsating delicate arteries, yet can withstand high forces comparable to grasping forces. The influence of some hidden anatomical features, such as lumps, voids, and arteries, on the stress distribution at the grasping surface was studied. In this paper, the capability of the sensor to determine and locate any point load was also investigated. The proposed sensor was designed and manufactured to be highly sensitive, using polyvinylidene fluoride (PVDF). The microfabrication procedure of the sensor, including corner compensation for toothlike projections and patterning of PVDF film, was discussed. The micromachined sensor was tested, and the experimental results were compared with the results of 3-D finite element modeling.

Discretely Loaded Beam-Type Optical Fiber Tactile Sensor for Tissue Manipulation and Palpation in Minimally Invasive Robotic Surgery

In traditional open surgery, surgeons use their fingertip palpation to investigate the hidden anatomical structures of tissue. However, in the current commercially available minimally invasive robotic surgery (MIRS) systems, while surgical instruments interact with tissues, surgeons do not sense any tactile information. Therefore, tactile sensors are required to be integrated into the tips of surgical instruments to mimic the perception of the surgeons fingertips. The electrically based tactile sensors that exist at present cannot usually operate under static loading conditions. In addition, they are not compatible with magnetic resonance imaging (MRI) devices. Therefore, this research was aimed at restoring tactile information by developing an MRI compatible optical fiber tactile sensor. The sensor consists of only one single moving part. Thanks to this novel design, the sensor does not require the use of an array of sensors to measure the distributed tactile information. This capability simplifies the integration of the sensor into any suitable space available at the tips of surgical instruments. In addition, the sensor performs under both static and dynamic loading conditions. A theoretical model of the sensor and a finite-element model of the sensor-tissue interaction were developed. To validate the sensor, a prototype of the sensor was fabricated and tested.

A New Approach for Modeling Piezoresistive Force Sensors Based on Semiconductive Polymer Composites

Semiconductive polymer composites are used in a wide range of sensors and measurement devices. This paper discusses the development of a model and a new theoretical formulation for predicting piezoresistive behavior in semiconductive polymer composites, including their creep behavior and contact resistance. The relationship between electrical resistance and force applied to the piezoresistive force sensor can be predicted by using the proposed theoretical formulation. In order to verify the proposed formulation, the piezoresistive behavior of Linqstat, a carbon-filled polyethylene, was modeled mathematically. In addition, some experimental tests, such as thermo gravitational analysis and SEM, have been performed on Linqstat to find the volume fraction and size of carbon particles, which are essential for modeling. In addition, on a fabricated force sensor using Linqstat, a force versus resistance curve was obtained experimentally, which verified the validity and reliability of the proposed formulation.

MEMS Endoscopic Tactile Sensor: Toward In-Situ and In-Vivo Tissue Softness Characterization

The superiority of endoscopic surgery over traditional open surgery in many areas has encouraged researchers to tackle a few shortcomings that are associated with the current state of minimally invasive surgical procedures. Among the shortcomings of minimally invasive surgery (MIS), the lack of sense of touch was the motive of the present work. Therefore, this research was aimed at restoring tactile sensing capabilities by developing a microelectromechanical systems (MEMS) tactile sensor for integration with existing MIS graspers. The tactile sensor is able to measure force, force position and also the softness of the grasped object. The transduction element, a uniaxial polyvinylidene fluoride (PVDF) film, was characterized before the microfabrication of the corrugated sensor. A finite-element model of the sensor system and soft material was also developed. The simulation results were compared with those of the experimental tests and the comparison showed good agreement.

Simultaneous measurement of acoustic and streaming velocities using synchronized PIV technique

Synchronized particle image velocimetry (PIV) technique has been applied to measure the acoustic and streaming velocity fields simultaneously, inside a standing-wave rectangular channel. In this technique, the velocity fields were sampled at a certain phase of the excitation waveform. The acoustic velocity fields were obtained by cross-correlating the two consecutive PIV images, whereas the streaming velocity fields were obtained by cross-correlating the alternative PIV images at the same phase. The experimental values of the mean acoustic velocity and RMS streaming velocities obtained from PIV are in good agreement with the theoretical values, showing that this novel approach can measure both acoustic and streaming velocities, accurately and simultaneously, in the presence of large amplitude acoustic wave.

Design and microfabrication of a hybrid piezoelectric‐capacitive tactile sensor

Purpose – To measure the force applied to the tissue, the traditional endoscopic graspers might be equipped with a kind of tactile force sensor.Design/methodology/approach – This paper presents the design, analysis, microfabrication and testing of a piezoelectric and capacitive endoscopic tactile sensor with four teeth. This tactile sensor, which is tooth‐like for safe grasping, comprises a Polyvinylidene Fluoride, PVDF film for high sensitivity and is silicon‐based for micromachinability. Being a hybrid sensor, employing both capacitive and piezoelectric techniques, it is possible to measure both the static and dynamic loads. Another feature, to be considered in its design, is the ability to detect pulse. The proposed sensor can be integrated with the tip of any current commercial endoscopic grasper without changing its original design. It is shown that using an array of sensor units, the position of the applied load can still be determined.Findings – The static response of the sensor is obtained by appl...