An Experimental Correction Method for Relative Indentation of Normal Contact

Although tendon-driven continuum manipulators have been extensively researched, how to realize tip contact force sensing in a more general and efficient way without increasing the diameter is still a challenge. Rather than use a complex modeling approach, this paper proposes a general tip contact force-sensing method based on a recurrent neural network that takes the tendons’ position and tension as the input of a recurrent neural network and the tip contact force of the continuum manipulator as the output and fits this static model by means of machine learning so that it may be used as a real-time contact force estimator. We also designed and built a corresponding three-degree-of-freedom contact force data acquisition platform based on the structure of a continuum manipulator designed in our previous studies. After obtaining training data, we built and compared the performances of a multi-layer perceptron-based contact force estimator as a baseline and three typical recurrent neural network-based contact force estimators through TensorFlow framework to verify the feasibility of this method. We also proposed a manually decoupled sub-estimators algorithm and evaluated the advantages and disadvantages of those two methods.

An investigation on the relationship between grip, push and contact forces applied to a tool handle

Achieving adequate catheter tip-tissue contact is essential for delivering robust radiofrequency (RF) ablation lesions. We measured the contact force generated by a remote magnetic-guided catheter navigation system. A plexiglass model with an integrated scale was fashioned to mimic transvenous and retrograde access to sites in the right atrium and right and left ventricles. An 8 Fr RF ablation catheter was steered by remote magnetic guidance at fields of 0.08 and 0.10 T, with and without a long sheath positioned at the entrance of the chamber. Ten contact force readings were taken at each setting, with the scale recalibrated prior to each measurement. Generalized estimating equations were used to compare contact force measurements while adjusting for the non-independent data structure. A total of 240 contact force measurements were taken. Without a long sheath, contact forces with magnetic fields of 0.10 T (n = 60) and 0.08 T (n = 60) were similar (6.1 ± 1.4 g vs. 6.0 ± 1.3 g, P = 0.089). Contact forces were not significantly different with simulated transvenous (n = 80) and retrograde aortic (n = 40) approaches (6.2 ± 1.4 g vs. 5.7 ± 1.2 g, P = 0.132). The contact force increased substantially with a long sheath (P < 0.001) and was significantly higher with 0.10 T (n = 60) vs. 0.08 T (n = 60) fields (20.4 ± 0.6 g vs. 18.0 ± 0.5 g, P < 0.001). Magnetic fields of 0.08 and 0.10 T provide stable catheter contact forces, as reflected by the small variability between measurements. The average contact force is approximately 6 g without a sheath and increases to 20 g with a long sheath positioned at the entrance of the chamber of interest.

In general, the contact force, which is used in controller design for robotic compliant motion, can be either explicitly calculated through complicated computation or measured by expensive force sensors. A force control strategy using the estimated contact force is proposed. The estimation of the contact force and states is primarily based on their previous observer design. It is shown that the controller achieves asymptotic stability.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The intrinsic cardiac nervous system consists of ganglionated plexuses (GPs) localized epicardially to specific regions of the left atrium (LA). The relation between voltage thresholds and endocardial contact force associated with autonomic effects during stimulation of GPs has not previously been evaluated. Sixteen patients with symptomatic atrial fibrillation (AF) underwent mapping of GPs prior to radiofrequency ablation of AF. Pre-acquired computed tomographic images were merged with 3D non-fluoroscopic electroanatomic mapping of the LA. Using high-frequency stimulation (HFS), the voltage thresholds of GPs was obtained while patients received conscious sedation. At each location, the contact force measurement from the catheter was correlated with the voltage applied during HFS at 5, 10, or 15 V to obtain an autonomic effect, usually associated with asystole, or marked bradycardia. There were 192 applications of HFS, resulting in GP identification in all patients (mean 3.4 per patient, range 1-5). During HFS, an autonomic response was significantly more likely to occur at 10 V as compared with 5 V (P < 0.008). There was no significant relation between the measured contact force and the likelihood of obtaining an autonomic response. When performing HFS at 15 V, a sudden overshoot with maximal values of contact force of up to 100 g was also observed. High-frequency stimulation was well tolerated, without associated adverse events. An autonomic response during HFS was significantly more likely to occur at 10 V as compared with 5 V. Although the GPs are epicardial structures, significant contact force was not required for their localization.

This paper presents a distributed soft contact sensing method based on a sensitivity mapping function, which relates the change in measured voltages to that in the elastomer conductivity due to contact force acting on its surface. The sensitivity-image-based sensing system uses a small number of boundary electrodes with a multiplexer to create different electric-field patterns to generate a series of sensitivity images for machine learning, significantly reducing the number of training data typically obtained with single-point indentation measurements. The mapping function, which does not rely on the knowledge of the electric and conductivity fields during online sensing, can be trained with only a small amount of measured data in the order of the square of electrode number. The proposed method has been experimentally evaluated on two 16-electrode prototypes trained with 129 and 80 data for two typical applications, which are tactile perception on a flat surface and contact force measurement in a model knee joint, respectively. The former verifies the measurement accuracy of the contact position and force magnitude while the latter demonstrates the application of this method for measuring the internal joint forces between two curved surfaces.

Contact behaviors of medical devices, such as guidewires and catheters, are critical in endovascular surgeries. In this work, a new method to predict adhesive contact force between catheter and vascular artery is presented. Multi-asperity adhesion on the surface of vascular artery, deformation of asperity and deformation of vascular substrate are all considered. The single asperity behavior is described with Johnson-Kendall-Roberts (JKR) contact model. The multi-asperity behavior is based on Greenwood-Williamson (GW) asperity model. Vascular substrate is considered as elastic bulk substrate and its deformation is determined with Hertzian pressure from asperity on a circular region on the elastic half space. The model shows that the deformation of vascular substrate accounts for the majority of the total contact deformation and significantly affects the predicted contact force. The model is verified with published experimental data. The comparison shows that the model produces very accurate prediction of contact force between catheter and vascular artery when the contact force is compressive. Parametric analysis based on asperity topography is carried out. The analysis shows that the diameter of the circular region of the interface between asperity and vascular substrate has more significant effect on the estimation of contact force than the radius of asperity. Further validation of prediction accuracy of the model under experiment is needed.

As the manipulation object of a patient transfer robot is a human, which can be considered a complex and time-varying system, motion adjustment of a patient transfer robot is inevitable and essential for ensuring patient safety and comfort. This paper proposes a motion adjustment method based on a two-level deep neural network (DNN) and a greedy algorithm. First, a dataset including information about human posture and contact forces is collected by experiment. Then, the DNN, which is used to estimate contact force, is established and trained with the collected datasets. Furthermore, the adjustment is conducted by comparing the estimated contact force of the next state and the real contact force of the current state by a greedy algorithm. To assess the validity, first, we employed the DNN to estimate contact force and obtained the accuracy and speed of 84% and 30 ms, respectively (implemented with an affordable processing unit). Then, we applied the greedy algorithm to a dual-arm transfer robot and found that the motion adjustment could reduce the contact force and improve human comfort efficiently; these validated the effectiveness of our proposal and provided a new approach to adjust the posture of the care receiver for improving their comfort through reducing the contact force between human and robot.

Cable-driven continuum robots are widely used for endoluminal intervention because of their dexterity and shape conforming steerability. However, body contact between the continuum robot and its surrounding anatomy is unavoidable, which imposes a potential safety risk, including vessel wall damage or even perforation. This paper presents an approach for body contact estimation of continuum robots with tension-profile sensing of actuation fibers. First, tension-sensing optical fibers with multiple inscribed fiber Bragg grating (FBG) sensors are used for both actuation and in-situ sensing of the continuum robot. Second, a beam theory-based mechanical model considering segmental differences, multiple fiber interactions and external force interactions is established, followed by robust estimation of contact positions and forces. Finally, detailed simulations are conducted to validate the accuracy and effectiveness of the proposed method. Experiments on a notched continuum robot are carried out, and the results show that the proposed approach can effectively recover in-situ segmental actuation forces without the need of explicit modeling of the friction between the fibers and guiding channels. The method enables the estimation of the number of contact points, as well as contact positions and contact forces along the body of the continuum robot.

Current electrophysiology signal recording and mapping systems have limited dynamic range (DR) and bandwidth, which causes loss of valuable information during acquisition of cardiac signals. We evaluated a novel advanced signal processing platform with the objective to obtain and assess additional information of clinical importance. Over 10 canines, we compared intracardiac recordings within all cardiac chambers, in various rhythms, in pacing and during radiofrequency (RF) ablation across two platforms; a conventional system and the PURE EP™ [(PEP); Bio Sig Technologies, Inc., Los Angeles, CA, USA]. Recording cardiac signals with varying amplitudes were consistently and reproducibly observed, without loss of detail or introduction of artefact. Further the amplitude of current of injury (COI) on the unipolar signals correlated with the instantaneous contact force (CF) recorded on the sensing catheter in all the animals (r2 = 0.94 in ventricle). The maximum change in the unipolar COI correlated with the change in local electrogram amplitude during non-irrigated RF ablation (r2 = 0.61 in atrium). Reduction in artefact attributable to pacing (20 sites) and noise during ablation (48 sites) was present on the PEP system. Within the PEP system, simultaneous display of identical signals, filtered differently, aided the visualization of discrete conduction tissue signals. Compared to current system, the PEP system provided incremental information including identifying conduction tissue signals, estimates of CF and a surrogate for lesion formation. This novel signal processing platform with increased DR and minimal front-end filtering may be useful in clinical practice.

A new measuring method introduced in this paper can measure contact forces between wheel and rail without special wheel-set with slip rings or telemeters. In this method the lateral contact force is measured from the lateral distortion of wheel measured directly by several non-contact gap sensors. Normal and longitudinal contact forces are also measured from the deflection of spring or the strain of parts of the bogies except special wheel-set. This new method, unlike the conventional method, is able to store the data everyday on every curve of commercial lines, which change according to friction coefficient and train running speed and so on. In this paper the authors describe the new measuring method without strain-gauge-equipped wheel-set, estimations of comparing the new method and the conventional method, and data analysis of measurements by commercial service trains. Practicable use of this new method enables us to easily obtain the statistical data of derailment coefficients with an on-board measuring method. Statistically analyzing the variation of rail-lubrication conditions and characteristics of wheel-rail contact force on every curve with this new system can help to improve track conditions for maintenance.

Low Pressure Turbine (LPT) blades encounter highly stressed forced vibrations driven by centrifugal force and steady/unsteady aerodynamic loads. To prevent the blades from failure due to high cycle fatigue (HCF), the amplitude of these vibrations must be estimated and reduced. Friction damping devices like under-platform dampers, shrouds and snubbers are usually implemented to lessen these blade vibration amplitudes. For adjacent shrouded blades coupled to each other at the blade tips, the blade vibration levels are strongly affected by the three-dimensional periodic contact forces at shrouds resulting in energy dissipation due to friction. Therefore, to experimentally validate the numerical contact models that predict nonlinear forced response of shrouded blades, it is equally important to measure the contact forces acting at the shrouds. This study outlines the development and commissioning of an experimental test rig that allows the measurement of three-dimensional shroud contact forces and the forced response of the shrouded blade simultaneously. Firstly, the design requirements of the experimental setup that were considered while deciding the test rig components, are highlighted. The test rig comprises of a pair of tri-directional contact force transducers in contact with the two shroud ends of a dummy blade and includes a blade twisting mechanism for the application of the normal preload. The employed tri-directional contact force transducers consist of three uniaxial strain gauge-based force sensors, arranged in a tripod configuration, and attached to a reference block that accommodates the shroud. The calibration and the decoupling procedure of the tri-directional contact force measurement system is then briefly described. This is followed by the details of the experimental process to acquire the forced response and three-dimensional shroud contact forces simultaneously for a specified frequency range determined by a prior experimental modal analysis of the blade and test rig. Subsequently, the effects of the variation in shroud normal preload and excitation force on measured response and shroud contact forces are also discussed. Finally, the results demonstrate how the proposed experimental test rig provides a thorough understanding of the dynamic response of the shrouded blade and shroud contact forces which will lead to a more reliable experimental validation of simulation tools and its effect on system dynamics.

In this paper, we propose the estimation of contact force in a collaborative robot without explicit force-sensing based on the adaptive third-order sliding mode observer. An adaptive third-order sliding mode observer was designed to estimate the contact force based only on the position measurement. The information from the observer was used for admittance control and emergent stop control when the robot interacts with a human. The experimental results with the emergent stop control and admittance control, using the proposed contact force estimation for the 3-DOF AT2-FARA robot manipulator, illustrate the capability of the proposed system in real-world application.

In this paper we extend our previous work concerning the regulation of the contact force in active train pantographs with wire-actuators. In particular, we consider the problem of estimating the contact force, instead of measuring it, by means of the measured displacements of the upper and lower pantograph frames. The estimation method, based on the algebraic observability theory, entails the use of real-time sliding-mode differentiators. It makes use explicitly of the upper frame mechanical characteristics, but does not require any other information concerning the system model. We consider our previously proposed second-order sliding mode control scheme, which also includes proper linear compensating cascade filters devoted to cope with the de-stabilizing effects of the resonant wire actuator. We show that such a control scheme can be effectively combined with the given contact force estimation method.

Continuum robots enable safe and adaptive interaction with complex, unstructured, or constrained environments through continuous deformation, making them particularly suitable for medical and industrial applications. Accurate contact force sensing is essential to ensure safe and effective physical interaction in such scenarios. Although various embedded force sensors have been developed, sensor‐free approaches offer advantages in miniaturization, cost‐effectiveness, and biocompatibility. This review provides a comprehensive overview of sensor‐free contact force estimation methods for continuum robots, with an emphasis on algorithmic principles rather than specific continuum robot designs or applications. First, contact forces reported in the literature are systematically classified according to their distribution, components, and dynamics. Next, existing force estimation methods are divided into three categories: actuation‐based, deflection‐based, and environment‐based. For each category, the underlying algorithmic principles are discussed, representative challenges are highlighted, and their typical application scenarios are outlined. Finally, emerging trends and potential directions for future research are outlined.