End Contact Research Articles

Design and performance analysis of carbon brush collector ring end-face contact for hydro generator

Abstract In hydro generators, the conventional radial contact method often results in unstable contact between carbon brush collector rings due to collector ring deflection. This paper presents a novel end-face contact method designed to enhance stability. The trajectory equations of the brush/ring contact are established when the collector ring swings and the “loss of contact” gaps of the two contact methods are compared. Further comparative analysis is conducted on the current-carrying friction wear of carbon brushes and collector rings in two contact modes. The results show that compared with the radial contact method, the brush/ring in the end-face contact method has a smaller gap and shorter time, the carbon brushes are less susceptible to spark erosion, the increase in friction coefficient and wear rate is small, and the contact resistance is lower and more stable. Scanning electron microscope analysis also shows that the spark erosion on the surface of the carbon brushes in the end contact mode is significantly weaker than that in the radial contact mode.

Safety-Centric Precision Control of a Modified Duodenoscope Designed for Surgical Robotics

There is limited research on robotic systems designed for Endoscopic Retrograde Cholangiopancreatography (ERCP) procedures using a side-view duodenoscope. The unique structure of the duodenoscope presents challenges to safely and precisely control the distal end pose. Control methods applied can reduce potential medical risks. We have redesigned the control section of the duodenoscope to facilitate its manipulation by a robotic system. An orthogonal compensator is employed to rectify the motion planes to standard planes. A hysteresis compensator based on the Prandtl-Ishlinskii model enables precise control of the distal pose of the duodenoscope. Furthermore, we utilize a contact force prediction model to prevent excessive contact force at the distal end. The performance of the modified duodenoscope is comparable to that of the standard duodenoscope. Following orthogonal compensation, the deviation angles of the motion planes is reduced by 32% to 98%. Post-hysteresis compensation, the root mean square error (RMSE) of the output angle of the distal end is decreased from 8.347° to 4.826°. The accuracy of distal end contact force prediction was approximately ±25% under conditions of high contact force. In conclusion, the modification and control strategy we proposed can achieve relatively safe and precise control of bending section, laying the foundation for the subsequent roboticization of duodenoscope systems for ERCP procedures.

Design and application of bidirectional soft actuator with multiangle chambers

Purpose This study aims to introduce a novel bidirectional soft actuator as an enhancement to conventional pneumatic network actuators. This improvement involves integrating air chambers positioned at specific angles to improve stability, adaptability and grasping efficiency in various environments. Design/methodology/approach The design approach incorporates air chambers positioned at a 45° angle relative to the horizontal direction at the actuator's terminus, along with additional chambers at a 90° angle. Mathematical models are developed for longitudinal and transverse bending, as well as for obliquely connected cavities, based on the assumption of piecewise constant curvature. Analyses are conducted on output forces, bending characteristics and end contact areas for both transverse and longitudinal ends. Findings The proposed soft actuator surpasses traditional pneumatic network actuators in gripping area due to the inclusion of a diagonal air cavity and a transverse pneumatic network structure at the terminus. As a result, it provides torsion and gripping force in both directions. Testing on a dedicated platform with two variants of grippers demonstrates superior gripping force capability and performance in complex environments. Practical implications Through the design of multiangle chambers, the soft actuator exhibits diverse driving angles and morphological variations, offering innovative design perspectives for industrial grasping. Social implications The design of multiangle chambers facilitates personalized configurations of soft actuators by researchers, enabling tailored angles for specific interaction environments to achieve desired functionalities. This approach offers novel insights into soft actuator design, addressing more prevalent industrial grasping challenges. Originality/value This study introduces a novel soft actuator design that significantly enhances gripping capabilities in comparison to conventional pneumatic network actuators. The incorporation of specific air chamber configurations and mathematical modeling provides valuable insights for the development of adaptable and efficient robotic grippers for industrial and household applications.

Raman spectroscopic stress mapping of single high modulus carbon fibre composite fragmentation in compression

Fragmentation of high modulus carbon fibres is relevant to the failure mechanisms of advanced polymer matrix composites in compression. In situ spatially-resolved Raman spectroscopy during the fragmentation of model single fibre composites is used to map local stress distributions during failure events. The characteristic graphitic band (the G band) located around 1580 cm−1 is associated with the in-plane carbon-carbon bonds; this band shifts its position, and can be calibrated, with the local axial stress in the fibre. The analysis maps the evolution of local stresses with increasing overall composite compression strain, identifying a series of critical events, including fibre fracture, interfacial debonding, and the formation of inter-fragment ‘wedges’. Fitting shear lag models provides interfacial shear strength values. Multiple failure maps of two examples of high modulus PAN carbon fibres (M46J and M55J) demonstrate the possibility of local fragment bending due to fragment end contact. A timeline of potential fragmentation events is proposed for carbon fibres undergoing compression.

Evaluation of variability in performance and paw placement patterns by dogs completing the dog walk obstacle in an agility competition.

The objective of this study was to describe paw placement patterns for canine athletes completing the dog walk obstacle during canine agility trials. It was hypothesized that dogs would demonstrate defined sets of paw placement patterns as they complete the dog walk obstacle and that those could be classified based on end contact behavior. Videos of 296 dogs attempting the dog walk obstacle at the 2021 UK Agility International (UKI) US Open were reviewed online. Data observed from video evaluation included front and rear limb paw placement across the dog walk and time to complete the obstacle. Results showed a high variability in obstacle performance. Mean time to complete the entire obstacle was 2.26 seconds (sd = 1.03). Mean and median completion times were qualitatively similar across all height classes. A slight majority of dogs hit the up ramp with their right foot first indicating running on their left lead (n = 185, 63%) with some variation observed between heights. Likewise, a slight majority (58%) of dogs hit the down ramp with their right front foot first (151/262). Given the high variation in completion times and paw placements, we could not identify clear patterns of dog walk performance. The large amount of variation observed with the dog walk obstacle suggests a need for future studies to employ alternative methods for objective gait analysis and to strategically select dogs to reflect the large variety in obstacle performance observed here.

Wettability and/or shape gradient induced spontaneous droplet motion on solid surfaces

This research investigates the dynamics of spontaneous droplet motion induced by wettability and shape gradients on microscale substrates. The study compares and analyzes the effects of different driving sources, including wettability gradient, shape gradient, and their combination. Findings reveal that the combination of wettability and shape gradients on a wedge-shaped track produces unique droplet motion patterns. Results demonstrate that, despite a slower initial acceleration, the combined driving force on the wedge-shaped track leads to a larger peak velocity compared to tracks with individual gradients. Additionally, the study explores the impact of track end contact angle and wedge angle on droplet motion. It highlights the preference for uniform wettability tracks for faster droplet motion, emphasizing the role of overall contact angle and wetting area. The research concludes that track size influences droplet motion, with larger wedge angles promoting faster and more stable motion. Overall, the study provides valuable insights into controlling and understanding droplet dynamics on structured surfaces.

Experimental study on stress relaxation of rubber O-ring for mechanical seal

The stress relaxation process and its variation law under multiple stresses have an important impact on the performance of rubber O-rings. An O-ring experimental device was developed, the end contact forces of the O-ring under the conditions of the single and multiple stresses were tested, and the contact force retention rate was calculated based on the test results. The change processes and laws of the end face contact force and the retention rate were obtained by the analyses of the experimental data under the different impact factors. The experimental results indicated that the compression ratio of the O-ring can increase the end contact force, but the greater compression ratio results in greater attenuation of contact force and longer attenuation time. The medium temperature hurts the contact force retention rate, and the medium pressure is conducive to stabilizing the contact force retention rate.

Study on the Frontal Collision Safety of Trains Based on Collision Dynamics

The high-speed collision issue brought on by railway vehicles’ intensive and high-speed operation has become a critical concern for operational safety. Therefore, it is necessary to research the high-speed collision problem of trains. Firstly, a train collision dynamic model suitable for higher collision velocities is established. This model includes a 38-degree-of-freedom (DOF) three-dimensional vehicle model and a three-layered vibrating fixed-track model. Corresponding mathematical models are developed for nonlinear factors such as wheel–rail contact, car–end contact, and coupler overload representation in the model. Then, the Train Collision State Score (TCSS) is proposed, enabling quantitative safety evaluation under different collision conditions. Finally, the influence of the energy-absorbing device’s initial attitude and leading car parameters on collisions is studied. The results indicate that initial vertical height difference and pitching angle significantly increase TCSS. As the force level of the energy-absorbing device of the leading car increases, the effects of two intermediate coupler overload states on TCSS show opposite trends.

Validation of methodology to determine the contact resistivity of ECA-based bonds grounded on end–contact resistance measurements using redundant and modified TLM test structures

Accurate determination of the contact resistivity between electrically conductive adhesives (ECAs) and solar metallization paste is a key component of optimizing the electrical performance of bonds based on ECAs, such as shingled joints. This work proposed and validates a methodology that accounts for non–negligible inhomogeneities of test structures based on ECAs and silver screen-printed metallization, such as changes in width of the ECA, to improve the accuracy in the calculation of the contact resistivity. The proposed validation uses statistical theory based on the central limit theorem and the law of large numbers showing that the contact resistivity of bonds based on two different commercially available ECAs can be clearly differentiated with a minimum confidence level of 95% and a maximum error margin of 5%. Moreover, the necessary sample size to achieve such requirements is calculated and shown to be equal to 24 test structures. The validation was done using an acryl-based adhesive loaded with silver flakes (∼10−4 Ω cm), which was compared to an epoxide-based ECA filled with silver–coated copper particles (∼10−3 Ω cm). The validated methodology indicates that the contact resistivity when using the acrylic conductive adhesive is 0.1791 ± 0.0766 mΩ cm2 while when using the epoxide-based adhesive is 0.5025 ± 0.1218 mΩ cm2. Additionally, it is shown that the standard deviation of the contact resistivity is highly dependent on the composition of the conductive adhesive. Hence, the sample size varies depending on the ECA. It is expected that the presented methodology will be a powerful instrument for developers and researchers in the improvement and optimization of ECAs and ECA bonding processes.

Influence of micro– and macrostructure when determining the contact resistivity of interconnects based on electrically conductive adhesives

The contact resistivity of interfaces in solar module interconnects has a direct impact on the series resistance of the entire module and fill factor. Thus, this impacts the performance of entire photovoltaic systems. Accurate measurement of the contact resistance is a key component of optimizing the performance of such interconnects. However, this is difficult for electrically conductive adhesive (ECA) based interconnects. This work shows that transmission line method (TLM) test structures based on ECA display non–negligible inhomogeneities leading to inaccuracies when determining the contact resistivity. Seven methods based on two models — the front– and end–contact TLM models (or a combination of both) — were investigated for four commercially available ECAs used in solar modules and their impacts on the extrapolation of the contact resistivity were quantified. It was determined that even when macroscale inhomogeneities (e.g., variations in the thickness of the ECA) are not present, microscopic structural effects influence the sheet and contact resistance. In particular, variations in the distribution of fillers significantly alter the bulk resistivity of the composites and this variability is also clearly correlated with differences in the geometry of the fillers. It is concluded that the best approach to reduce inaccuracies in the determination of the contact resistivity of ECA–based interconnects is to calculate the sheet and contact resistance locally (using three consecutive contacts) employing a redundant and modified test structure. Afterwards, the contact resistivity ought to be computed using the end–contact TLM model and the median should be assigned as the contact resistivity of the sample.

Kinematic analysis of the axle box unit operation

The axle load acts on the box unit and has shock-pulse nature when the car is moving, that can lead to a mutual change in the surface positions of the roller ends with the edges of the bearing races. The ways are proposed to optimize the internal geometry of the radial and end contact elements of the roller bearing of the axle box unit. It is proposed to eliminate the occurrence of possible conditions that lead to the movement of bearing rollers into the thrust and locking of bearing rollers by increasing the minimum limit in the axle clearance of the axle box.

A novel kinematics and statics correction algorithm of semi-cylindrical foot end structure for 3-DOF LHDS of legged robots

In this paper, aiming at the problem that the ideal modeling point of the foot end deviates from the actual contact point due to the rolling effect of the semi-cylindrical foot end in leg hydraulics drive system (LHDS), a novel and relatively simple kinematics and statics correction algorithm is proposed. This algorithm can effectively improve the accuracy of LHDS kinematics and statics, and it is still applicable when the body and the contact surface are at different angles. Firstly, this paper deduces the kinematics and statics when the foot end of LHDS is regarded as the point foot, analyzes and calculates the deviation under common working conditions. Secondly, in view of this phenomenon, a kinematics correction algorithm based on virtual DOF and a statics correction algorithm based on translation theorem of forces are proposed respectively. Finally, the proposed algorithm is verified by LHDS performance test platform under various working conditions. The results show that after applying the kinematics correction algorithm, the trajectory deviation reduction rate of the hip joint is over 65%; after applying the statics correction algorithm, the deviation reduction rate of foot end contact force is over 43%. The related research results can be applied to any similar foot end, which has engineering application value.

Excellent heat transfer enhancement of CNT-metal interface by loading carbyne and metal nanowire into CNT

The carbon nanotube (CNT)-metal structure widely occurs in the CNT application, especially for the heat dissipation of electronic devices of various scales. However, the research on mechanism of interfacial heat transfer between CNT-metal lacks an accurate and complete research system, and the enhancement strategy of interfacial heat transfer lacks a systematic method. Therefore, in this work, CNT is in the end contact with metal substrate with four sizes of CNT and three types of metal. The interfacial thermal resistance of CNT-metal is calculated by the combination of Two Temperature Model and Molecular Dynamics, and its mechanism is analyzed by atomic vibration density of state, vibration overlap energy, interaction energy. In addition, carbyne and metal nanowire are loaded in the CNT to improve heat transfer and the variation of heat transfer as a function of the loading material length, structure size, type, movement and temperature are analyzed to reveal the enhancement strategy.

Verification of Characteristics of McKibben Type Artificial Rubber Muscle Considering Material Properties of Muscle End Contact Surface

Verification of Characteristics of McKibben Type Artificial Rubber Muscle Considering Material Properties of Muscle End Contact Surface

A novel one-dimensional force sensor calibration method to improve the contact force solution accuracy for legged robot

• This method can be carried out on LHDS without disassembling the force sensor. • This method can avoid the irregular variation of calibration coefficient. • This method can simply compensate for the influence of dynamics. Abstract In this paper, aiming at the phenomenon that the calibration coefficient deviation of the one-dimensional force sensor will lead to the deviation in measuring force, a novel method is proposed to recalibrate the one-dimensional force sensors of each joint directly on the leg hydraulic driving system (LHDS) of legged robot. This method has two main contributions. One is that it not only can be carried out directly on LHDS without disassembling the force sensor but also can avoid the irregular variation of calibration coefficient caused by the installation preloading force, friction, mechanical clearance, and other factors. The other is that the method can simply compensate for the influence of dynamics in the calibration process and avoid the complicated mathematical calculation. Under eight working conditions, the experimental results show that the proposed calibration method can decrease the foot end contact force deviation rate more than 20% in the whole cycle. The novel calibration method proposed in this paper can be extended to any leg structure equipped with the same kind of one-dimensional force sensor. It has practical value in engineering.

Mechanical strength of RNA knot in Zika virus protects against cellular defenses.

Unusual knot-like structures recently discovered in viral exoribonuclease-resistant RNAs (xrRNAs) prevent digestion by host RNases to create subgenomic RNAs enhancing infection and pathogenicity. xrRNAs are proposed to prevent digestion through mechanical resistance to unfolding. However, their unfolding force has not been measured, and the factors determining RNase resistance are unclear. Furthermore, how these knots fold remains unknown. Unfolding a Zika virus xrRNA with optical tweezers revealed that it was the most mechanically stable RNA yet observed. The knot formed by threading the 5' end into a three-helix junction before pseudoknot interactions closed a ring around it. The pseudoknot and tertiary contacts stabilizing the threaded 5' end were both required to generate extreme force resistance, whereas removing a 5'-end contact produced a low-force knot lacking RNase resistance. These results indicate mechanical resistance plays a central functional role, with the fraction of molecules forming extremely high-force knots determining the RNase resistance level.

Buckling behavior of AA6061 circular tube under axial compression by considering contact condition of tube end

When a circular tube is under axial compression, it can be developed into specific forming technologies (e.g., tube inversion). However buckling failure is prone to occurring and seriously restricts the successful realization of the forming process or service performance. In this paper the conical convex or concave dies with different semi-cone angles were adopted to change tube end contact conditions and the buckling process, critical buckling force and the buckling waves of AA6061 tube under axial compression were investigated by using finite element simulation combined with experiments. The results show that the buckling deformation, the position where initial buckling wave appears, and the distribution of axial stress in tube blank are quite different when axially compressed on a flat die or a conical convex die (semi-cone angle β = 60°). For the conical convex dies as semi-cone angle increases from 75° to 87.5°, or for concave dies as semi-cone angle decreases from 110° to 92.5°, the axial compressive stress, critical buckling force and critical reduction increase, while the peak of the buckled wave decreases, i.e., occurrence of buckling delays and the buckling becomes more difficult to occur. When β is 90° (flat die), the critical buckling force and reduction reach the peak values.

Motion Planning for a Bounding Quadruped Robot Using iLQG Based MPC

When tackling motion control problem of the quadruped bionic robot with traditional control method, it is more and more difficult to improve the control effect due to the uncertainty caused by the factors such as model mismatch, distortion, and interference. Therefore, the demand for utilizing advanced control method to realize the motion control for legged bionic robot is growing. Among various advanced control methods, the model prediction control (MPC) has low requirements on model accuracy, and the system has good robustness and stability, which provides a good prospect for solving the balance problem of dynamic robots. In this paper model predictive control is used to realize the bounding gait motion control for a quadruped bionic robot. The MPC planner automatically generates the foot end position and contact force trajectory of the robot, so that the robot can track the desired motion state. However, as the model of the quadruped bionic robot is nonlinear, the generated MPC algorithm may be difficult to meet the real-time requirements. In order to solve this problem, this paper uses the iLQG optimization algorithm in the design of a model prediction controller and adds heuristic-based reference input. The comparison between the simulation and the classical SQP algorithm shows that the MPC based on the iLQG optimization algorithm has good convergence and tracking effect for the quadruped robot running, and has fast real-time performance.

Influence of Disc Specimen Configuration on Its Three-Dimensional Dynamic Stress Balance

In order to investigate the dynamic stress balance of different configurations of rock specimens, three-dimensional finite element models of SHPB were established. Five types of configuration disc specimens with a diameter of 75 mm and a thickness of 30 mm were impacted at a speed of 5 m/s using a special-shaped bullet. The propagation laws of stress wave on the contact surface of the specimen-bar and the inside of the specimen were analyzed, and the time history of the stress balance factors at different positions of the specimen was obtained. The results show that the amplitudes of the transmitted waves corresponding to the five types of disc specimens with different configurations have obvious differences, and the stress propagation in the specimen has three-dimensional characteristics. According to the ease of achieving stress balance, the five configuration specimens are ordered by notched semicircular bending disc, flattened Brazilian disc, cracked straight-through flattened Brazilian disc, Brazilian disc, and cracked straight-through Brazilian disc specimen. Among them, only the first three configurations of the specimen reached the stress balance. The dynamic stress balance is affected by the disc loading mode, end contact conditions, the presence of prefabricated cracks, and disc thickness. In addition, as the disc loading end is a processed platform, it is beneficial to achieve stress balance. Prefabricated cracks are not conducive to achieving stress balance. The loading method of the notched semicircular bending disc is more conducive to achieving stress balance. This research has a certain guiding significance for selecting suitable specimen configuration and research methods to carry out rock dynamic fracture experiments.

Dynamic trajectory adjustment of lower limb exoskeleton in swing phase based on impedance control strategy

The lower limb exoskeleton provides assistance by following the lower limb joints’ desired motion trajectory. However, angle control is not enough to meet the requirements in some special circumstances such as encountering obstacles. In the swing phase of the attached leg with the exoskeleton, there is a different contact force between the sole and the road surface in different road conditions. Therefore, it is particularly important to control the joint angle and contact force simultaneously, that is, it is not only necessary to follow the desired angle but also to minimize the influence of external contact force. In this article, a novel scheme is proposed to adjust the trajectory dynamically in the swing phase. First of all, the physical model is streamlined and the Lagrangian principle is carried out to dynamic analysis and established a model of lower limb exoskeleton in the swing phase. Furthermore, the angle dynamics equation is transformed into a Cartesian coordinate system to calculate the end contact force for the impedance model. Finally, the impedance control strategy together with a disturbance observer is designed which is suitable for nonlinear and strong coupling characteristics. The simulation result shows that the control system can follow the angle accurately in the condition of minimizing external constraints. Hardware experiment shows that lower extremity exoskeleton can adjust motion trajectory actively when encountering obstacles and complete the movement trajectory tracking at the same time.