Constant Contact Force Research Articles

Impedance mapping with constant contact force on 3D electroanatomic map to characterize tissues at pulmonary veno-atrial junction.

Generator impedance (Im) mapping with constant contact force (CF) by tip catheter at PV isolation (PVI) was assessed for a proposal of tissue characterization at PV-LA junction (PV-LAJ). In this observational, prospective, single-center study, Im mapping at constant CF = 10g (± 2g) was performed before PVI at PV-LAJ. PV in-vein, PV ostium (PVos), and antrum (PVan) contours were manually traced based on the 3D electroanatomic map (3DEAM) integrating intracardiac echocardiography and computerized tomography. PVan contour-methods based on Im mapping was defined on 3DEAM as the atrial-like Im contour closest to PVos, and its distance from anatomical PVan contour > 5mm was assumed as the non-concordance marker between contour and methods. Sixty-two patients (62 ± 9years; 43 males) were enrolled, and 244 PV-LAJ were assessed. From in-vein PV to LA and, less prominently, from PVos to PVan and LA, Im showed a unidirectional decrease with highly variable individual-specific distribution and values. PVan non-concordance was found in 59/665 segments (8.8%), 18% of PV-LAJs, and 53% of pts; it prevailed in superior PV-LAJ and measured on average 7.2 ± 1.1mm. Im decrease patterns and non-concordance were not associated with any clinical or anatomical feature, including PV dimensions and shape. Im mapping of LA-PVJ at constant CF added to 3DEAM may consistently track the tissue transition from PV to LA. PVan identified by Im was often located more toward LA than the 3D anatomical PVan, particularly in LSPV, suggesting the potential advantage of avoiding ablation of venous-like tissue. Im mapping can deserve further investigation for target characterization at LA-PVJ.

Robotic grinding of complex components: A step towards efficient and intelligent machining – challenges, solutions, and applications

Abstract Robotic grinding is considered as an alternative towards the efficient and intelligent machining of complex components by virtue of its flexibility, intelligence and cost efficiency, particularly in comparison with the current mainstream manufacturing modes. The advances in robotic grinding during the past one to two decades present two extremes: one aims to solve the problem of precision machining of small-scale complex surfaces, the other emphasizes on the efficient machining of large-scale complex structures. To achieve efficient and intelligent grinding of these two different types of complex components, researchers have attempted to conquer key technologies and develop relevant machining system. The aim of this paper is to present a systematic, critical, and comprehensively review of all aspects of robotic grinding of complex components, especially focusing on three research objectives. For the first research objective, the problems and challenges arising out of robotic grinding of complex components are identified from three aspects of accuracy control, compliance control and cooperative control, and their impact on the machined workpiece geometrical accuracy, surface integrity and machining efficiency are also identified. For the second aim of this review, the relevant research work in the field of robotic grinding till the date are organized, and the various strategies and alternative solutions to overcome the challenges are provided. The research perspectives are concentrated primarily on the high-precision online measurement, grinding allowance control, constant contact force control, and surface integrity from robotic grinding, thereby potentially constructing the integration of “measurement – manipulation – machining” for the robotic grinding system. For the third objective, typical applications of this research work to implement successful robotic grinding of turbine blades and large-scale complex structures are discussed. Some research interests for future work to promote robotic grinding of complex components towards more intelligent and efficient in practical applications are also suggested.

Position-based impedance force controller with sensorless force estimation

Purpose This paper aims to purpose an improved sensorless position-based force controller in gravitational direction for applications including polishing, milling and deburring. Design/methodology/approach The first issue is the external force/torque estimation at end-effector. By using motor’s current information and Moore-Penrose generalized inverse matrix, it can be derived from the external torques of every joints for nonsingular cases. The second issue is the force control strategy which is based on position-based impedance control model. Two novel improvements were made to achieve a better performance. One is combination of impedance control and explicit force control. The other one is the real-time prediction of the surface’s shape allowing the controller adaptive to arbitrary surfaces. Findings The result of validation experiments indicates that the estimation of external force and prediction of surface’s shape are credible, and the position-based constant contact force controller in gravitational direction is functional. The accuracy of force tracking is adequate for targeted applications such as polishing, deburring and milling. Originality/value The value of this paper lies in three aspects which are sensorless external force estimation, the combination of impedance control and explicit force control and the independence of surface shape information achieved by real-time surface prediction.

Development of Flexible Fiber Conditioner in Chemical Mechanical Planarization

A flexible fiber pad conditioner, which conforms well to the pad surface, has been developed. Conventional disc-type conditioners have a potential concern of uniform conditioning across the entire pad surface in terms of intermittent contact by face-to-face contact. In the flexible fiber conditioner, each fiber tip functions independently with constant contact force on the pad, by utilizing the bending effect of the flexible fiber. Therefore, the conditioner performs uniform and fine conditioning, following the height variation in the pad surface. Uniform conditioning was verified by a unique method using surface coloration on a pad with height variation. In addition, it was shown that, using the developed conditioner, the chips generated by pad conditioning were very small, and the pad surface was finely scraped and roughened. It was further demonstrated that the developed flexible fiber conditioner shortened the pad break-in process. Moreover, compared with the conventional disk-type conditioner, the developed flexible fiber conditioner resulted in a uniform polishing profile even in the midst of the break-in process. The results indicate that it is important for the break-in of the polishing pad, to uniformly scrape and roughen the entire area of the pad while following the pad surface, rather than planarizing the surface.

Path Planning for Robotic Grinding on a Large Forged Workpiece

In this paper a robotic grinding system which can produce a finished workpiece that respects some product geometric specifications is proposed. It is composed of a 1 DoF active compliance actuator fixed between the grinder and the robot. The 1 DoF actuator associated to the tool can be mounted at existing robotic installations which make this solution very flexible and easy to use by the industrials. The grinding system composed of the robot and the actuator is able to apply a constant contact force between the workpiece and the grinding tool. A path planning method is also presented in this article. Using analytical calculations, the robot path is determined for grinding a rounded corner on a parallelepiped workpiece with a given precision of the surface shape.

Non-contacted Permanent Magnetic Absorbed Wall-climbing Robot for Ultrasonic Weld Inspection of Spherical Tank

A novel wall-climbing robot for the onsite weld inspecting of spherical tank with Time of Flight Diffraction (TOFD) method has been developed, in order to liberate operators from dangerous and heavy working environment. Patented non-contacted permanent magnetic absorbed technology was adopted to realize reliable and flexible all-position moving along the weld seam on the surface of spherical tank. To ensure stable coupling for TOFD test, a surface adaptive probe holder which can provide constant contact force, have been particularly designed. Equipped with a visual sensing based weld seam tracking unit and industrial PC station, the robot could perform automatic flaw detection remotely even in the darkness environment. Onsite ultrasonic weld inspections have been carried out on a 4000m3spherical tank with 28mm in thickness. It is verified that the robot could accomplish tasks in any position and the acquired TOFD images satisfy the requirements of engineering evaluation.

Robotic grinding of a blisk with two degrees of freedom contact force control

This paper presents a novel two degrees of freedom (DOFs) contact force control method for robotic blisk grinding. The grinding tool is controlled to automatically adapt to the curvity change of the blisk blade and maintain a constant contact force as expected. A smart end effector is used as the actuating device for contact force control. The proposed force controller includes a gravity compensation module, a force prediction module, and a force-position controller. The direction and amplitude of the contact force are predicted with the force prediction module and are controlled with the force-position controller. The tool path of the robotic blisk grinding process is generated and optimized so that the contact points between the tool tip and the workpiece are evenly distributed along the grinding path. Both simulations and experiments are carried out to validate the effectiveness of the proposed method. The results show that the proposed method provides a good contact force control performance, with less than 1 N force fluctuation. The surface finish and roughness are significantly improved compared to the case without force control. The grinding efficiency is raised by about sixfold compared to the case with one DOF force control.

Analysis and assessment of robotic belt grinding mechanisms by force modeling and force control experiments

Abstract A tentative work from the perspective of cutting forces is carried out in this paper to analyse and assess the robotic belt grinding mechanisms. Firstly, a microscopic scale of cutting force model consisting of sliding, ploughing and cutting components is introduced, then the effects of force components on the machined surface roughness are explored based on the force control experiments, and finally a typical case on the robotic belt grinding of aero-engine blade with constant contact force is conducted to validate the practicality and effectiveness of force control. The results reveal two significant findings with respect to the high sliding force percentage and low cutting efficiency in comparison with the robotic belt grinding without force control.

Design and Evaluation of a Catheter Contact-Force Controller for Cardiac Ablation Therapy.

Maintaining a constant contact force (CF) of an ablation catheter during cardiac catheter ablation therapy is clinically challenging due to inherent myocardial motion, often resulting in poor ablation of arrhythmogenic substrates. To enable a prescribed contact force to be applied during ablation, a catheter contact force controller (CCFC) was developed. The system includes a hand-held device attached to a commercial catheter and steerable sheath. A compact linear motor assembly attaches to an ablation catheter and autonomously controls its relative position within the shaft of the steerable sheath. A closed-loop control system is implemented within embedded electronics to enable real-time catheter-tissue contact force control. To evaluate the performance of the CCFC, a linear motion phantom was used to impose a series of physiological CF profiles; lesion CF was controlled at prescribed levels ranging from 15 to 40g. For a prescribed CF of 25g, the CCFC was able to regulate the CF with a root mean squared error of 3.7 ± 0.7g. The ability of the CCFC to retract the catheter upon sudden changes in tissue motion, which may have caused tissue damage, was also demonstrated. Finally, the device was able to regulate the CF for a predetermined amount of time according to a force-time integral model. The developed CCFC is capable of regulating catheter-tissue CF in a laboratory setting that mimics clinical ablation therapy. Catheter-tissue CF control promises to improve the precision and success of ablation lesion delivery.

Electrochemical buckling microfabrication.

Can isotropic wet chemical etching be controlled with a spatial resolution at the nanometer scale, especially, for the repetitive microfabrication of hierarchical 3D μ-nanostructures on the continuously curved surface of functional materials? We present an innovative wet chemical etching method called "electrochemical buckling microfabrication": first, a constant contact force is applied to generate a hierarchical 3D μ-nanostructure on a mold electrode surface through a buckling effect; then, the etchant is electrogenerated on-site and confined close to the mold electrode surface; finally, the buckled hierarchical 3D μ-nanostructures are transferred onto the surface of a Ga x In1-x P coated GaAs wafer through WCE. The concave microlens, with a Fresnel structure, has an enhanced photoluminescence at 630 nm. Comparing with energy beam direct writing techniques and nanoimprint lithography, this method provides an electrochemical microfabrication pathway for the semiconductor industry, with low cost and high throughput.

Active Control of Contact Force for a Pantograph-Catenary System

The performance of the high speed trains depends critically on the quality of the contact in the pantograph-catenary interaction. Maintaining a constant contact force needs taking special measures and one of the methods is to utilize active control to optimize the contact force. A number of active control methods have been proposed in the past decade. However, the primary objective of these methods has been to reduce the variation of the contact force in the pantograph-catenary system, ignoring the effects of locomotive vibrations on pantograph-catenary dynamics. Motivated by the problems in active control of vibration in large scale structures, the author has developed a geometric framework specifically targeting the remote vibration suppression problem based only on local control action. It is the intention of the paper to demonstrate its potential in the active control of the pantograph-catenary interaction, aiming to minimize the variation of the contact force while simultaneously suppressing the vibration disturbance from the train. A numerical study is provided through the application to a simplified pantograph-catenary model.

IDC장치에 대한 공압시스템의 모델링에 관한 연구

An intelligent deburring control (IDC) device is used to control the constant force for a deburring tool mounted on the end-effector of a robotic arm. This device maintains a constant contact force between the deburring tool and the workpiece in order to provide a good deburring performance. In this paper, we build a mathematical model in Matlab/Simulink to estimate the force control mechanism of the pneumatic system for the IDC device. The Simulink blocks are built for each separate part and are linked into an integrated simulation system. Such a model also relies on the effects of the flow rate through the valve, air compressibility in the cylinder, and time delay in the pressure valve. The results of the simulation are compared to a simple experiment in which convenient math modeling is performed. These results are then used to optimize the mechanical design and to develop a force control algorithm for the pneumatic cylinder.

Dynamic Modeling and Force Control of a Redundant Robot for Polishing Applications

AbstractFor many robotic applications with tasks such as cutting, assembly or polishing, it is necessary to get in contact with the surrounding. In this paper a redundant robot with seven degrees of freedom in a metal polishing task is considered. For simulation as well as for the controller design a dynamic model of the robot and a contact model are required. The equations of motion of the robot are calculated with the Projection Equation in subsystem representation and the contact model contains linear tool elasticities and work piece elasticities. In the case of a polishing task, a constant contact force during the process is required even if the robot moves along a trajectory. Thus some degrees of freedom of the robot tool center point have to be position controlled while the other ones have to be force controlled. The redundant robot offers the possibility to avoid singular positions or to maximize the available end‐effector forces within the inverse kinematics and is therefore best suited for polishing large objects. The actual process forces are measured with a six axis force‐torque‐sensor mounted at the tool center point. These forces are used in a parallel force/position control law to achieve the desired behavior. Results from measurements of a test arrangement are presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Disposable Fluidic Self-Propelling Robot for Colonoscopy

Disposable Fluidic Self-Propelling Robot for Colonoscopy

A Novel Texture Sensor for Fabric Texture Measurement and Classification

Surface texture is one of the important cues for human beings to identify different fabrics. This paper presents a novel design of a surface texture sensor by imitating human active texture perception by touch. A thin polyvinylidene fluoride (PVDF) film is used as the sensitive element to fabricate a high-accuracy, high-speed-response fabric surface texture sensor, and a mechanism is designed to produce the relative motion at a certain speed between the texture sensor and the surface of the perceived fabric with constant contact force. Thus, the surface texture property can be measured as the output charge of the PVDF film of the sensor induced by the small height/depth variation of the moving fabric surface. A texture feature extraction method by compressing the zero value spectral lines in frequency domain is proposed. In addition, a radial basis function (RBF) neural networks based on unsupervised K-means clustering algorithm is used as classifier for texture recognition. The experiments show that the proposed texture sensor is effective in detecting the feature signals of fabric surface textures, which are suitable for the RBF networks to classify the different fabrics.

Dipole-moment-induced effect on contact electrification for triboelectric nanogenerators

Triboelectric nanogenerators (TENGs) have been demonstrated as an effective way to harvest mechanical energy to drive small electronics. The density of triboelectric charges generated on contact surfaces between two distinct materials is a critical factor for dictating the output power. We demonstrate an approach to effectively tune the triboelectric properties of materials by taking advantage of the dipole moment in polarized polyvinylidene fluoride (PVDF), leading to substantial enhancement of the output power density of the TENG. The output voltage ranged from 72 V to 215 V under a constant contact force of 50 N. This work not only provides a new method of enhancing output power of TENGs, but also offers an insight into charge transfer in contact electrification by investigating dipole-moment-induced effects on the electrical output of TENGs.

A Constant-Force Compliant Gripper for Handling Objects of Various Sizes

This paper presents the design, simulation, and testing of a compliant gripper that can provide a constant gripping force to handle objects of various sizes. Maintaining a proper gripping force is challenging when manipulating delicate objects with uncertain sizes and stiffnesses. To avoid damage and provide a stable grip of an object, force feedback is often required so that the gripping force can be directly or indirectly regulated. Without using additional sensors and control, the proposed gripper passively maintains a constant prespecified contact force between fingertip and object. The gripper is designed to have a constant input force generated by a constant-force mechanism (CFM). Transmitted through a statically balanced (SB) mechanism, a constant gripping force is obtained at the fingertip. After a formulation to find the optimal gripper configuration, the design is verified through comparison with simulation results. Finally, a prototype of the constant-force gripper is demonstrated. The novel gripper is expected to serve as a reliable alternative for object manipulation.

A Finger-Shaped Tactile Sensor for Fabric Surfaces Evaluation by 2-Dimensional Active Sliding Touch

Sliding tactile perception is a basic function for human beings to determine the mechanical properties of object surfaces and recognize materials. Imitating this process, this paper proposes a novel finger-shaped tactile sensor based on a thin piezoelectric polyvinylidene fluoride (PVDF) film for surface texture measurement. A parallelogram mechanism is designed to ensure that the sensor applies a constant contact force perpendicular to the object surface, and a 2-dimensional movable mechanical structure is utilized to generate the relative motion at a certain speed between the sensor and the object surface. By controlling the 2-dimensional motion of the finger-shaped sensor along the object surface, small height/depth variation of surface texture changes the output charge of PVDF film then surface texture can be measured. In this paper, the finger-shaped tactile sensor is used to evaluate and classify five different kinds of linen. Fast Fourier Transformation (FFT) is utilized to get original attribute data of surface in the frequency domain, and principal component analysis (PCA) is used to compress the attribute data and extract feature information. Finally, low dimensional features are classified by Support Vector Machine (SVM). The experimental results show that this finger-shaped tactile sensor is effective and high accurate for discriminating the five textures.

Output Feedback Control of Pantograph-Catenary System

Controlling the contact force between the pantograph and the catenary has become a requirement for improving the performances and efficiency of high-speed train systems. Indeed, these performances may considerably be reduced because of the catenary equivalent stiffness variation. In addition, the contact force may also vary and could become null, which may cause the loss of contact. Then, in this paper, we present an active control of the pantograph-catenary system. The proposed control strategy implements an output feedback control, using a common approximation of the catenary equivalent stiffness. Namely, the proposed solution is based on backstepping techniques and takes benefit from the exponential convergence of a high-gain observer. All the synthesis steps of the control law are given and a formal analysis of the closed loop stability shows an asymptotic tracking of a nominal constant contact force. Then, using a simulation example, the contact force results to be practically equal to the its constant reference, meaning that the effects of the catenary equivalent stiffness variation have been cancelled and showing the effectiveness of this solution.

Precision tool setting for fabrication of a microstructure array

A method is proposed for setting a new diamond cutting tool when tool replacement is required during the fabrication of a microstructure array on the outer surface of a roll by a fast tool servo with a force sensor. The sectional profiles of a small reference area in the fabricated part by the replaced old tool are detected through scanning the tip of the new tool with a constant contact force controlled by the fast tool servo. The new tool can be set accurately based on the identified position of the tool tip with respect to the reference area.