Force-sensing Capability Research Articles

A Magnetic Catheter with Force Sensing Capability toward Interventional Surgery

A Magnetic Catheter with Force Sensing Capability toward Interventional Surgery

A Redundant Parallel Continuum Manipulator With Stiffness-Varying and Force-Sensing Capability

A Redundant Parallel Continuum Manipulator With Stiffness-Varying and Force-Sensing Capability

Optical Millinewton Force Sensors Based on GaN Devices Integrated With Bionic-Structured PMDS Films

In this work, optical millinewton force sensors are developed by integrating GaN devices with bionic-structured polydimethylsiloxane (PDMS) films. The chip-scale GaN-on-sapphire devices incorporating light emitters and photodetectors are fabricated using wafer-level microfabrication. Large-area bionic microstructures of varying size scales are patterned on the PDMS films using four different types of plant leaves as molding templates. The deformable PDMS film can efficiently modulate the light coupled into the detector during force loading, which endows the GaN devices with high sensitivity to millinewton forces. The force-sensing capabilities of the sensors are thoroughly investigated and compared. The device integrated with optimized film exhibits sensing characteristics with a sensitivity of 0.145 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> A/mN in the range of 0–290 mN and a sub-millinewton resolution of 0.165 mN. The developed optical sensor provides the attractive features of low-cost fabrication, high compactness, fast response, and high stability, making it highly valuable for millinewton force detection in practical applications.

Closed cervical traction techniques: moving into the 21st century.

Closed cervical traction for reducing dislocating cervical injuries, deformity correction, or discectomy distraction has been implemented in its modern form since the 1930s. Cervical traction state of the art has not changed significantly since the 1960s, with most reductions performed by using Gardner-Wells tongs or halo traction; however, there are many limitations of traditional weight-pulley traction, including limited reduction efficacy and patient safety shortcomings. In this paper, the authors review the history of cervical traction in the 20th century and the limitations of current traction techniques and describe a novel traction device developed at the University of Utah with robotic actuator load or position control and real-time force-sensing capabilities. Preliminary biomechanical testing results using the novel device in an extension spring loading model, with intact cadavers, and in iatrogenic facet injury cadaveric models demonstrated preliminary safety and efficacy of the device. The authors believe this and future research efforts aimed toward improving the efficacy and safety of cervical traction will help advance the field into the 21st century.

Compliant gripper with force estimation for physical human–robot interaction

Despite the major interest in the field of Human–Robot Interaction (HRI) in recent years, not much work has been presented on physical HRI (pHRI), especially for robot-initiated contact. Although pHRI is a key skill in areas like assistive or rescue robots, advances are limited by hard constraints in safety and compliance that require specific hardware features and force estimation capabilities. This work presents a new compliant gripper with four underactuated fingers and force-sensing capabilities designed to manipulate a human forearm. Fingers are based on the rigid-link approach, where one of the links has been replaced by a compression spring. High-resolution angular sensors at the passive joints allow computing the spring compression and the actuator torque. Then grasping forces are estimated through the kinetostatic model of the fingers. The gripper has been built and tested. Compliance and grasping force estimation and control have been successfully evaluated. Results prove that the proposed finger arrangement offers good performance, making our design suitable for pHRI applications.

Origami-Inspired Structure with Pneumatic-Induced Variable Stiffness for Multi-DOF Force-Sensing.

With the emerging need for human–machine interactions, multi-modal sensory interaction is gradually pursued rather than satisfying common perception forms (visual or auditory), so developing flexible, adaptive, and stiffness-variable force-sensing devices is the key to further promoting human–machine fusion. However, current sensor sensitivity is fixed and nonadjustable after fabrication, limiting further development. To solve this problem, we propose an origami-inspired structure to achieve multiple degrees of freedom (DoFs) motions with variable stiffness for force-sensing, which combines the ductility and flexibility of origami structures. In combination with the pneumatic actuation, the structure can achieve and adapt the compression, pitch, roll, diagonal, and array motions (five motion modes), which significantly increase the force adaptability and sensing diversity. To achieve closed-loop control and avoid excessive gas injection, the ultra-flexible microfiber sensor is designed and seamlessly embedded with an approximately linear sensitivity of ∼0.35 /kPa at a relative pressure of 0–100 kPa, and an exponential sensitivity at a relative pressure of 100–350 kPa, which can render this device capable of working under various conditions. The final calibration experiment demonstrates that the pre-pressure value can affect the sensor’s sensitivity. With the increasing pre-pressure of 65–95 kPa, the average sensitivity curve shifts rightwards around 9 N intervals, which highly increases the force-sensing capability towards the range of 0–2 N. When the pre-pressure is at the relatively extreme air pressure of 100 kPa, the force sensitivity value is around 11.6 /N. Therefore, our proposed design (which has a low fabrication cost, high integration level, and a suitable sensing range) shows great potential for applications in flexible force-sensing development.

Modeling and validation of multifield coupled self-sensing characteristics of magnetorheological elastomer for vibration isolators

In this paper, a multifield coupled self-sensing model for magnetorheological elastomer (MRE) isolators is proposed. By dispersing carbonyl iron particles and multiwalled carbon nanotubes in polydimethylsiloxane, an MRE with improved force-sensing capability is fabricated as a further effort to explore its comprehensive sensing effect. Then, the model is developed based on magnetic dipole analysis and tunneling theory. In addition, the conductive mechanism and vibrational operating state of the MRE are analyzed, while the effects of input force and current are investigated. The experimental results show that the resistance of the MRE decreases with increasing force or current, which is consistent with the theoretical model. For instance, the resistance decreases from 1.55 kΩ to 0.55 kΩ as the force changes from 0 N to 160 N, and the dynamic resistance responses show a very good match with the force input curve and the response curve present continuous, stable, and perfectly reversible signals. The validation results demonstrate that the proposed model can reproduce experimental results well without causing significant differences. In summary, the proposed model provides an accurate approach to estimating the conductivity of MREs for self-sensing actuator applications.

Design of a compliant load cell with adjustable stiffness

Manipulation at the sub-micron scale often requires force-sensing capabilities of milli-to nanonewton forces. This article presents a novel design of a compliant load cell with mechanically adjustable stiffness. The system enables adapting force sensitivity to the requirements of a specific application. The principle of the stiffness adjustment is based on a preloaded spring, that stores the potential energy used to compensate the effort needed to deflect the compliant structure of the load cell. Unlike Micro-Electro-Mechanical Systems (MEMS), the new mechanism can be fabricated at the centimeter-scale. This reduces the fragility of the system and facilitates interchange of end-effectors. A main advantage of this solution is the possibility to use one common force sensing device for diverse applications at various scales, such as in biotechnology, semiconductor nanoprobing or microassembly. We describe the analytical model of the load cell and use it to simulate the performance of the stiffness adjustment mechanism. The analytical results are then validated by finite element method (FEM) and experiments performed on a large-scale stainless-steel prototype. Empirical results show that the overall stiffness can be tuned to near-zero and beyond, resulting in a bistable mode. The presented model brings freedom for designing the sensitivity adjustment, and the experimental part shows the ability to reduce the stiffness of the prototype by approximately 200-fold, achieving a force sensing resolution of 0.41 μN

Penetration-force estimation approach for a flexure-jointed micro-injection mechanism with Lorentz force actuation

This paper presents a novel linear-motion compliant mechanism with Lorentz force actuation and integrated force-sensing capability for automated cell micro-injection. A model-based force estimation approach is introduced such that no force sensor is required. Model identification is undertaken by applying a sinusoidal actuation signal while the mechanism contacts with objects of known stiffness. Displacement data is then used to calculate model coefficients via a least-squares optimization. By using an observer-based state estimation scheme with actuation and displacement signals as inputs, force sensing accuracy within 70 μN RMS error could be achieved within a sensing range of 0 - 5 mN. This sensing capability confirms the suitability of the system for penetration force measurement in certain cases of cell micro-injection.

High strain rate compression of epoxy micropillars

The study of the high strain rate mechanical behaviour of materials using micropillar compression tests has been hindered so far due to the lack of suitable instrumentation. In the present study, a novel high strain rate micropillar compression set-up is introduced. The high speed tests are carried out with the impact configuration of a pendulum-based nanoindentation device that was instrumented with force-sensing capability by means of a piezoelectric load cell. This is necessary due to the considerable inertia effects that make the actual applied force on the sample much higher than the actuated one. The proposed novel technique was successfully applied to study the mechanical behaviour of an epoxy resin over a wide range of strain rates. The results reveal a significant strain rate sensitivity that correlates well with that obtained for the same material at the macroscale, validating the novel set-up.

Automatic Light Pipe Actuating System for Bimanual Robot-Assisted Retinal Surgery.

Retinal surgery is a bimanual operation in which surgeons operate with an instrument in their dominant hand (more capable hand) and simultaneously hold a light pipe (illuminating pipe) with their non-dominant hand (less capable hand) to provide illumination inside the eye. Manually holding and adjusting the light pipe places an additional burden on the surgeon and increases the overall complexity of the procedure. To overcome these challenges, a robot-assisted automatic light pipe actuating system is proposed. A customized light pipe with force-sensing capability is mounted at the end effector of a follower robot and is actuated through a hybrid force-velocity controller to automatically illuminate the target area on the retinal surface by pivoting about the scleral port (incision on the sclera). Static following-accuracy evaluation and dynamic light tracking experiments are carried out. The results show that the proposed system can successfully illuminate the desired area with negligible offset (the average offset is 2.45 mm with standard deviation of 1.33 mm). The average scleral forces are also below a specified threshold (50 mN). The proposed system not only can allow for increased focus on dominant hand instrument control, but also could be extended to three-arm procedures (two surgical instruments held by surgeon plus a robot-holding light pipe) in retinal surgery, potentially improving surgical efficiency and outcome.

Towards Bimanual Vein Cannulation: Preliminary Study of a Bimanual Robotic System With a Dual Force Constraint Controller.

Retinal vein cannulation is a promising approach for treating retinal vein occlusion that involves injecting medicine into the occluded vessel to dissolve the clot. The approach remains largely unexploited clinically due to surgeon limitations in detecting interaction forces between surgical tools and retinal tissue. In this paper, a dual force constraint controller for robot-assisted retinal surgery was presented to keep the tool-to-vessel forces and tool-to-sclera forces below prescribed thresholds. A cannulation tool and forceps with dual force-sensing capability were developed and used to measure force information fed into the robot controller, which was implemented on existing Steady Hand Eye Robot platforms. The robotic system facilitates retinal vein cannulation by allowing a user to grasp the target vessel with the forceps and then enter the vessel with the cannula. The system was evaluated on an eye phantom. The results showed that, while the eyeball was subjected to rotational disturbances, the proposed controller actuates the robotic manipulators to maintain the average tool-to-vessel force at 10.9 mN and 13.1 mN and the average tool-to-sclera force at 38.1 mN and 41.2 mN for the cannula and the forcpes, respectively. Such small tool-to-tissue forces are acceptable to avoid retinal tissue injury. Additionally, two clinicians participated in a preliminary user study of the bimanual cannulation demonstrating that the operation time and tool-to-tissue forces are significantly decreased when using the bimanual robotic system as compared to freehand performance.

Feasibility Study of Force Measurement for Multi-digit Unconstrained Grasping via Fingernail Imaging and Visual Servoing

Abstract A fingernail imaging has been shown to be effective in estimating the finger pad forces along all three directions simultaneously in previous works. However, this method has never been used for the purpose of force measurement during a grasping task with multiple fingers. The objective of this paper is to demonstrate the grasp force-sensing capabilities of the fingernail imaging method integrated with a visual servoing robotic system. In this study, the fingernail imaging method has been used in both constrained and unconstrained multi-digit grasping studies. Visual servoing has been employed to solve the issue of keeping fingernail images in the field of view of the camera during grasping motions. Two grasping experiments have been designed and conducted to show the performance and accuracy of the fingernail imaging method to be used in grasping studies. The maximum value of root-mean-square (RMS) errors for estimated normal and shear forces during constrained grasping has been found to be 0.58 N (5.7%) and 0.49 N (9.2%), respectively. Moreover, a visual servoing system implemented on a 6-degrees-of-freedom (DOF) robot has been devised to ensure that all of the fingers remain in the camera frame at all times. Comparing unconstrained and constrained forces has shown that force collaboration among fingers could change based on the grasping condition.

New instrumentation and analysis methodology for nano-impact testing

The nano-impact test is a technique for high strain rate mechanical characterization of materials at the nano/microscale. However, its use has been limited so far due to the lack of appropriate methods to determine the dynamic hardness under impact conditions. The main limitation up to date has been the determination of the true applied force due to considerable inertia effects. For this reason, dynamic hardness from nano-impact tests has traditionally been computed using an energy-based approach. This work overcomes this limitation by instrumenting the test device with force-sensing capability by means of a piezoelectric load cell. The methodology was evaluated on six materials covering a wide spectrum of mechanical behaviour. The work shows that the energy-based approach used so far yields significant errors on the determination of dynamic hardness, explaining contradictory results existing in literature, and identifies the main sources of error with the aid of finite element simulations. As a result, a new energy-based approach to determine dynamic hardness that overcomes the current limitations is proposed.

Multi-modal Framework for Image-guided Trans-oral Surgery with Intraoperative Imaging and Deformation Modeling.

Treatment of throat cancers have improved due to minimally-invasive trans-oral approaches. Surgeons rely on preoperative imaging to guide their resection; however, large tissue deformations occur during trans-oral procedures due to placement of necessary retractors and laryngoscopes which hinders the surgeon's ability to accurately assess tumor extent and location of critical structures. We propose an image-guided framework utilizing intraoperative imaging and deformation modeling to improve surgeon accuracy and confidence. A CT-compatible laryngoscopy system previously developed was evaluated in this framework. Intraoperative images were acquired during laryngoscopy; force-sensing capabilities were enabled in the laryngoscope; and tracking of the scope and anatomic features was trialed. Tissue deformation and displacement were quantified and determined to be extensive, with values <; 4.6 cm in the tongue, <; 1.8 cm in bony structures, and <; 108.9 cm3 in airway volume change. Surgical navigation using intraoperative imaging and tracking was evaluated. Preliminary assessment of deformation modeling showed potential to supplement intraoperative imaging. Future work will involve streamlined integration of the components of this framework.

A Microforce-Sensing Mobile Microrobot for Automated Micromanipulation Tasks

This paper presents a microforce-sensing mobile microrobot ( $\mu $ FSMM) for use in automated micromanipulation tasks. The design consists of a planar vision-based microforce sensor end-effector, while the microrobot body is made of chemically etched nickel that is driven by an exterior magnetic field. With a known stiffness, the manipulation forces can be determined from observing the deformation of the end-effector through a camera attached to an optical microscope. After analyzing and calibrating the stiffness of a micromachined prototype, the mobility and in situ force-sensing capabilities are verified through real-time, closed loop, force controlled manipulation tests with automated path planning and navigation. The calibrated stiffness of the microforce sensor end-effectors fabricated is on the order of 10−3 N/m. The online (real time) force-sensing resolution is approximately $1.5~\mu \text{N}$ . The sensing range is 0–20 $\mu \text{N}$ along the two planar directions. In automated micromanipulation experiments with a microcomponent, the $\mu $ FSMM utilizes real-time force control to apply a prescribed force of $6~\mu \text{N}$ to a desired location on a fixed microobject. Similarly, in another automated micromanipulation experiment, the $\mu $ FSMM demonstrates the use of real-time force control to limit the manipulation forces experienced by the microobject to remain below a threshold of 12 $\mu \text{N}$ . Note to Practitioners —This paper was motivated by recent interest single-cell biological micromanipulation tasks that seek to understand the role of environmental forces on the mechanics of cell development (mechanobiology) and the biological mechanisms that control such behavior (mechanotransduction). In addition, tissue engineering applications require the safe micromanipulation of single cells to desired locations in the workspace for growing tissue scaffolds. The $\mu $ FSMM presented here can be easily inserted into existing biological testbeds to use for these aforementioned applications. The designed magnetic coil system is compatible with standard inverted optical microscopes, while a digital camera for real-time image processing is already standard in these testbeds. The developed software interface can be used to prescribe automated microforce controlled manipulations of single cells and tissues in the workspace to carry out these aforementioned tasks. This paper is also suitable for carrying out general automated micromanipulation and microassembly tasks with advanced manufacturing applications.

Refining How We Define Laparoscopic Expertise.

Traditional stratification of expertise in laparoscopic simulation assigns participants to novice, intermediate, or expert groups based on case numbers. We hypothesized that expert video assessment might refine this discrimination of psychomotor expertise, especially in light of new measurable parameters. One hundred five participants performed a defined intracorporeal suturing task in the pediatric laparoscopic surgery simulator armed with force-sensing capabilities. Participants were stratified into novice, intermediate, and expert groups via three classification schemes: (1) number of complex laparoscopic cases, (2) self-declared level of expertise, and (3) average expert rating of participants' videos. Precision, time to task completion, and force analysis parameters (FAP = total, maximum and mean forces in three axes) were compared using one-way analysis of variance tests. P < .05 was considered significant. Participants stratified on the basis of case numbers and on the basis of self-declared level of expertise had statistically significant differences in time to task completion, but no significant difference in FAP. When participants were restratified according to expert assessment of their video performance, time to task completion as well as total and mean forces in X, Y, and Z axes allowed discrimination between novices, intermediates, and experts, thus establishing construct validity for the latter. Precision did not allow discrimination in any stratification scheme. Compared with traditional stratification, video assessment allows refined discrimination of psychomotor expertise within a simulator. Assessment of FAP may become a relevant tool for teaching and assessing laparoscopic skills.

IPEG 2018The 27th Annual Congress for Endosurgery in ChildrenApril 11–14, 2018, Seattle, Washington

IPEG 2018The 27^th Annual Congress for Endosurgery in ChildrenApril 11–14, 2018, Seattle, Washington

A Monolithic Force-Sensitive 3D Microgripper Fabricated on the Tip of an Optical Fiber Using 2-Photon Polymerization.

Microscale robotic devices have myriad potential applications including drug delivery, biosensing, cell manipulation, and microsurgery. In this work, a tethered, 3D, compliant grasper with an integrated force sensor is presented, the entirety of which is fabricated on the tip of an optical fiber in a single-step process using 2-photon polymerization. This gripper can prove useful for the interrogation of biological microstructures such as alveoli, villi, or even individual cells. The position of the passively actuated grasper is controlled via micromanipulation of the optical fiber, and the microrobotic device measures approximately 100 µm in length and breadth. The force estimation is achieved using optical interferometry: high-dimensional spectral readings are used to train artificial neural networks to predict the axial force exerted on/by the gripper. The design, characterization, and testing of the grasper are described and its real-time force-sensing capability with an accuracy below 2.7% of the maximum calibrated force is demonstrated.

Robot Patient Design to Simulate Various Patients for Transfer Training

To improve the patient transfer skill of nursing education students, we developed a robot patient that can simulate three categories of patients: 1) patients whose movements are affected by paralysis; 2) patients whose movements are sensitive to pain with painful expression; and 3) patients whose movements are constrained by medical devices. By practicing with the robot patient, nursing students can learn the skills required for interacting with various patients. To simulate trunk movements of these different patients, novel waist and hip joints with hardware-inherent compliance and force-sensing capability were proposed. In addition, control methods were developed and the parameters were tuned based on actual patient videos. To evaluate the developed robot, nursing teachers performed trials of transferring the robot patient as they would transfer an actual patient. The nursing teachers scored the robot patients based on a checklist. Moreover, subjective evaluations of a questionnaire were performed by the nursing teachers. The results showed that the nursing teachers performed most of the required skills of the checklist and agreed regarding the learning effectiveness of the robot. They recommended training nursing students using the robot patient in the questionnaire. Finally, hugging speed comparison showed that the nurses slow down the speed when dealing with a robot patient with painful expression.