Discrete Joints Research Articles

Design and kinematics analysis of a cable-stayed notch manipulator for transluminal endoscopic surgery

The friction between the joints of the continuum manipulator with discrete joints brings great difficulties to kinematic modeling. The traditional driving wire arrangement limits the load capacity of the manipulator. A cable-stayed notch manipulator for transluminal endoscopic surgery is proposed, and a driving force coupling kinematic mode is established. The manipulator is fabricated from a superelastic Nitinol tube with bilaterally cut rectangular notches and is actuated by a stay cable. By applying the comprehensive elliptic integral solution (CEIS) for large deformation beams, the bending angle of each elastic beam is obtained, and the kinematics from the driving space to the joint space is formed. According to the bending angle of each elastic beam, the expression of the manipulator in Cartesian space can be obtained by geometric analysis. The kinematics from the joint space to the Cartesian space is established. The outer diameter of the manipulator is only 3.5 mm, and the inner diameter can reach 2 mm, allowing instruments to pass through. The maximum error of the manipulator movement is less than 5%. The load capacity of the manipulator has been verified through the stiffness experiments, and the maximum load of the manipulator can reach 400 g. The cable-stayed notch manipulator can be accurately modeled on the base of CEIS, and its motion accuracy can meet the needs of engineering applications. The compact size and excellent load capacity of the manipulator make it potential for application in transluminal endoscopic surgical robots.

Experimental study on the effects of complex discrete joints on the mechanical behavior of rock‐like material

AbstractThe strength and failure of rock masses are ambiguous due to their complex structure. Investigating the strength and failure of jointed rock mass remains a persistent concern in mining engineering. This study aims to investigate the effects of joint dip angles of complex discrete joints on the mechanical properties and fracture evolution of rock‐like material. Rock‐like specimens with complex joints were prepared using 3D printing technology and then tested under uniaxial compression loading. The experimental results reveal the following findings: (1) The anisotropy of rock‐like material with complex joints is lower compared to the rock‐like material with simple joints. (2) The ratio of long‐term strength to uniaxial compressive strength of rock‐like material remains consistent despite changes in the dip angle of the joints. (3) Differing from intact rocks, AE events of the rock‐like material with complex joints are obvious in the initial loading stage and elastic deformation stage. (4) When the dip angle of the joint sets is 0 and 90°, fractures progressively propagate, and the failure mode of the rock‐like material demonstrates tensile failure along the pre‐existing joints. Conversely, when the dip angle of the joint sets is 45° and 135°, fractures are simultaneously initiated at various locations within the rock‐like specimen, resulting in a failure mode of rotational failure by the newly generated block.

An Ergonomic Flexible Multi-Fire Clip Applier With Multiple Degrees-of-Freedom for Minimally Invasive Surgery to Improve Hemostatic Efficiency

Abstract Hemorrhage can lead to shock and even death of patients, making one of the main risks in surgical procedures. Most traditional clip appliers are rigid, have limited flexibility, and can only fire a single clip within each insertion, which cannot meet the needs of surgeons to efficiently and flexibly control bleeding vessels. In this study, a novel hand-held Hem-o-lok clip applier is proposed, which is designed to have a high flexibility and allow multiple fires of clips. The wrist at the end effector consists of discrete joints and a flexible shaft, allowing bending in two directions. The tong head at the end effector enables multiple fires of hemostats and can be delivered to different positions for clamping blood vessels and human tissues. It also can be driven to rotate by the flexible shaft. Additionally, an ergonomic handle is designed to control the multiple degrees-of-freedom (DOFs) movements of the instrument tip. Finally, the effectiveness of the entire system is evaluated through performance experiments. The bending angle of end effector was about ±70 deg in both directions (yaw and pitch), and the rotation angle was ±160 deg. The measured gripping forces of the applier ranged from 16.70 N to 24.93 N, and the average time to complete three consecutive clamping was 8.67 s. The proposed clip applier could improve the hemostatic efficiency and allow an intuitive and flexible operation in the meantime.

Stiffness Change for Reconfiguration of Inflated Beam Robots.

Abstract Active control of the shape of soft robots is challenging. Despite having an infinite number of passive degrees of freedom (DOFs), soft robots typically only have a few actively controllable DOFs, limited by the number of degrees of actuation (DOAs). The complexity of actuators restricts the number of DOAs that can be incorporated into soft robots. Active shape control is further complicated by the buckling of soft robots under compressive forces; this is particularly challenging for compliant continuum robots due to their long aspect ratios. In this study, we show how variable stiffness enables shape control of soft robots by addressing these challenges. Dynamically changing the stiffness of sections along a compliant continuum robot selectively "activates" discrete joints. By changing which joints are activated, the output of a single actuator can be reconfigured to actively control many different joints, thus decoupling the number of controllable DOFs from the number of DOAs. We demonstrate embedded positive pressure layer jamming as a simple method for stiffness change in inflated beam robots, its compatibility with growing robots, and its use as an "activating" technology. We experimentally characterize the stiffness change in a growing inflated beam robot and present finite element models that serve as guides for robot design and fabrication. We fabricate a multisegment everting inflated beam robot and demonstrate how stiffness change is compatible with growth through tip eversion, enables an increase in workspace, and achieves new actuation patterns not possible without stiffening.

Experimental and Numerical Investigation on the Mechanical Behavior of Rock-Like Material with Complex Discrete Joints

Experimental and Numerical Investigation on the Mechanical Behavior of Rock-Like Material with Complex Discrete Joints

Kinematics modeling method of continuum space manipulator based on virtual discrete-jointed manipulator models

Continuum space manipulators (CSMs) have key application prospects in the maintenance of spacecrafts in narrow environments and space debris removal. Similar to conventional articulated space manipulators (ASMs), CSMs encounter a number of kinematic, dynamic, and control problems caused by the dynamic coupling between the continuum manipulator and its microsatellite platform. However, the continuum manipulator has no obvious kinematic joints. In addition, its motion is generated by the continuum deformation of its elastic body; thus, the virtual manipulator (VM) model of ASM in the free-floating state becomes inappropriate for CSMs. In this study, we propose a kinematic equivalent method for a free-floating CSM, which is equivalent to a virtual discrete-jointed manipulator (VDJM) connected to a virtual ground. First, the constraint relationship is used to establish the virtual vector manipulator (VVM) model for the CSM such that its center of mass in the free-floating mode remains unchanged. Furthermore, on the basis of the VVM model and D-H parameters of the CSM, virtual discrete joints are introduced, and a VDJM model for the CSM is proposed. Compared with the VVM model, the developed VDJM model can more intuitively express the motion characteristics of the CSM. Finally, we demonstrate the application potential of the developed VDJM model in the inverse kinematics solution, workspace, and dynamic coupling of CSMs.

20-year incidence trends of anal squamous cell carcinoma.

e15503 Background: Anal Squamous Cell Carcinoma (SCCA) accounts for 90% of cases of anal cancer. ~95% of SCCAs are driven by Human Papilloma Virus (HPV). We did a follow-up population-based analysis to assess incidence trends of SCCA over 20 years (2000-2019) in era of HPV vaccination (available since 2006). Methods: Data was extracted from Surveillance, Epidemiology, and End Results (SEER) database for years 2000-2019. Joinpoint regression models were fitted to identify a discrete joints (year) that represented a statistically significant change in direction of the trend of overall SCCA incidence. The average annual percentage change (AAPC) in age-adjusted incidence rate in all subgroups pre- and post-2009 (statistically significant joinpoint year) was measured. (Table 1). Results: 30,294 new cases of SCCA were identified from 2000-2019, with majority in females (61.6%), white population (86.5%), and ages 40-79 years (84.1%). A significant joinpoint for SCCA incidence was observed in 2009, wherein APC of 2.8% (95% CI 2.0-3.6) in 2000-2009 was reduced to 0.5% (95% CI -0.1-1.2) in 2009-2019 (82% relative reduction [RR]). In subgroup analysis, evaluating the trends after identifying a discrete joint (2009), we found that APC for White population reduced from 3.1% (P < 0.0001) to 1.1% (P = 0.022) (65% RR), and for Black population, APC of 3.2% (P = 0.0015) seem to flatten out at 0.3% (P = 0.768) in post-2009 years (91% RR). Ages 20-39 had a -4.2% (P = 0.028) APC pre-2009 that showed increase to 1.3% (P = 0.214) post-2009, however, small sample size noted. In ages 40-59, APC of 4.7% (P < 0.0001) seem to flatten out at -0.5% (P = 0.393) (111% RR). Ages 60-79 had a similar APC (2.4% [P = 0.0011] and 2.5% [P = 0.0001], respectively). In males, APC of 2.8% (P = 0.002) flattened out to 0.5% (P = 0.249) and females reduced from 3.2% (P < 0.001) to 1.2% (P = 0.009). Conclusions: In this study, we found a trend of decrease in the rate of growth of SCCA incidence pre- and post-2009, overall and among various subgroups. Furthermore, our results suggest that widespread education and scaling up access to HPV vaccination can decrease and potentially reverse the SCCA incidence. [Table: see text]

Continuum Robots for Medical Interventions.

Continuum robots are not constructed with discrete joints but, instead, change shape and position their tip by flexing along their entire length. Their narrow curvilinear shape makes them well suited to passing through body lumens, natural orifices, or small surgical incisions to perform minimally invasive procedures. Modeling and controlling these robots are, however, substantially more complex than traditional robots comprised of rigid links connected by discrete joints. Furthermore, there are many approaches to achieving robot flexure. Each presents its own design and modeling challenges, and to date, each has been pursued largely independently of the others. This article attempts to provide a unified summary of the state of the art of continuum robot architectures with respect to design for specific clinical applications. It also describes a unifying framework for modeling and controlling these systems while additionally explaining the elements unique to each architecture. The major research accomplishments are described for each topic and directions for the future progress needed to achieve widespread clinical use are identified.

Dual-Stream Structured Graph Convolution Network for Skeleton-Based Action Recognition

In this work, we propose a dual-stream structured graph convolution network ( DS-SGCN ) to solve the skeleton-based action recognition problem. The spatio-temporal coordinates and appearance contexts of the skeletal joints are jointly integrated into the graph convolution learning process on both the video and skeleton modalities. To effectively represent the skeletal graph of discrete joints, we create a structured graph convolution module specifically designed to encode partitioned body parts along with their dynamic interactions in the spatio-temporal sequence. In more detail, we build a set of structured intra-part graphs, each of which can be adopted to represent a distinctive body part (e.g., left arm, right leg, head). The inter-part graph is then constructed to model the dynamic interactions across different body parts; here each node corresponds to an intra-part graph built above, while an edge between two nodes is used to express these internal relationships of human movement. We implement the graph convolution learning on both intra- and inter-part graphs in order to obtain the inherent characteristics and dynamic interactions, respectively, of human action. After integrating the intra- and inter-levels of spatial context/coordinate cues, a convolution filtering process is conducted on time slices to capture these temporal dynamics of human motion. Finally, we fuse two streams of graph convolution responses in order to predict the category information of human action in an end-to-end fashion. Comprehensive experiments on five single/multi-modal benchmark datasets (including NTU RGB+D 60, NTU RGB+D 120, MSR-Daily 3D, N-UCLA, and HDM05) demonstrate that the proposed DS-SGCN framework achieves encouraging performance on the skeleton-based action recognition task.

Tendon Actuated Continuous Structures in Planar Parallel Robots: A Kinematic Analysis

Abstract The use of continuous and flexible structures instead of rigid links and discrete joints is a growing field of robotics research. Recent work focuses on the inclusion of continuous segments in parallel robots to benefit from their structural advantages, such as a high dexterity and compliance. While some applications and designs of these novel parallel continuum robots have been presented, the field remains largely unexplored. Furthermore, an exact quantification of the kinematic advantages and disadvantages when using continuous structures in parallel robots is yet to be performed. In this paper, planar parallel robot designs using tendon actuated continuum robots instead of rigid links and discrete joints are proposed. Using the well-known 3-RRR manipulator as a reference design, two parallel continuum robots are derived. Inverse and differential kinematics of these designs are modeled using constant curvature assumptions, which can be adapted for other actuation mechanisms than tendons. Their kinematic performances are compared to the conventional parallel robot counterpart. On the basis of this comparison, the advantages and disadvantages of using continuous structures in parallel robots are quantified and analyzed. Results show that parallel continuum robots can be kinematic equivalent and exhibit similar kinematic performances in comparison to conventional parallel robots depending on the chosen design.

17-year incidence trends of anal squamous cell carcinoma.

4058 Background: Anal Cancer is a rare neoplasm with 9 out of 10 cases being Anal Squamous Cell Carcinoma (SCCA). We did a population-based analysis to assess the incidence trends in patients with SCCA and identify any significant change in the direction of trends using the Surveillance, Epidemiology, and End Results (SEER) database. Methods: Data was extracted from SEER database for the years 2000-2016 for the US population, across all gender, ages, and races. Joinpoint regression models of SCCA incidence were fitted to identify any discrete joints (year) that represent statistically significant changes in the direction of the trend. The average annual percentage change (APC) in the age-adjusted incidence rate in the pre- and post-joinpoint era were measured. Subgroup analysis for gender, ages, and races was also done. Results: 27,721 new adult cases of SCCA were identified from 2000 to 2016. The incidence was higher amongst females (62.44%) compared to males (37.56%) with the white population contributing 85.41% to incidence compared to black (11.84%) and other (2.75%) population. The age-based incidence rate for different groups has been mentioned in Table. A significant jointpoint for SCCA incidence was observed in 2009. The APC was 4.6% (3.5-5.6 95% CI) in 2000-2009 which reduced to 2.1% (0.7-3.4 95% CI) in 2009-2016 indicating a 54% relative reduction in the average annual APC in the US population after 2009. Subgroup analysis revealed significant joinpoints for incidence decrease in Ages 40-59, 80 and above and females of all ages. No significant changes in APC were seen when stratified by race (Refer to Table). Conclusions: Our study, in our knowledge, is the first study assessing incidence trends of SCCA over 17-years. The overall incidence of SCCA is increasing but a statistically significant trend towards decreasing rate of growth in incidence was observed in 2009 and later. Further studies are needed to analyze the causality of such changes in the trend of SCCA. [Table: see text]

X-Shells

We present X-shells , a new class of deployable structures formed by an ensemble of elastically deforming beams coupled through rotational joints. An X-shell can be assembled conveniently in a flat configuration from standard elastic beam elements and then deployed through force actuation into the desired 3D target state. During deployment, the coupling imposed by the joints will force the beams to twist and buckle out of plane to maintain a state of static equilibrium. This complex interaction of discrete joints and continuously deforming beams allows interesting 3D forms to emerge. Simulating X-shells is challenging, however, due to unstable equilibria at the onset of beam buckling. We propose an optimization-based simulation framework building on a discrete rod model that robustly handles such difficult scenarios by analyzing and appropriately modifying the elastic energy Hessian. This real-time simulation method forms the basis of a computational design tool for X-shells that enables interactive design space exploration by varying and optimizing design parameters to achieve a specific design intent. We jointly optimize the assembly state and the deployed configuration to ensure the geometric and structural integrity of the deployable X-shell. Once a design is finalized, we also optimize for a sparse distribution of actuation forces to efficiently deploy it from its flat assembly state to its 3D target state. We demonstrate the effectiveness of our design approach with a number of design studies that highlight the richness of the X-shell design space, enabling new forms not possible with existing approaches. We validate our computational model with several physical prototypes that show excellent agreement with the optimized digital models.

Experimental observation and numerical simulation of cement grout penetration in discrete joints

This paper presents a comparison between experimental measurements and numerical estimations of penetration length of a cement grout injected in discrete joints. In the experiment, a joint was generated by planar acryl plates with a certain separation distance (; aperture) and was designed in such a way to vary the separation distances. Since a cement grout was used, the grout viscosity can be varied by controlling water-cement (W/C) ratios. Throughout these experiments, the influence of joint aperture, cement grout viscosity, and injection rate on a penetration length in a discrete joint was investigated. During the experiments, we also measured the time-dependent variation of grout viscosity due to a hardening process. The time-dependent viscosity was included in our numerical simulations as a function of elapsed time to demonstrate its impact on the estimation of penetration length. In the numerical simulations, Bingham fluid model that has been known to be applicable to a viscous cement material, was employed. We showed that the estimations by the current numerical approach were well comparable to the experimental measurements only in limited conditions of lower injection rates and smaller joint apertures. The difference between two approaches resulted from the facts that material separation (; bleeding) of cement grout, which was noticeable in higher injection rate and there could be a significant surface friction between the grout and joint planes, which are not included in the numerical simulations. Our numerical simulation, meanwhile, could well demonstrate that penetration length can be significantly over-estimated without considering a time-dependency of viscosity in a cement grout.

The Problem of Consideration Torsion Emergence in Beams

The calculation of the steel unrestrained and partially restrained roof beams with initial imperfections main stages is discussed. Restraining can be done by structures attached to the steel beams, namely, profiled flooring and discrete joints. On the basis of the new approach to the internal forces analysis and the geometric properties specification, the purpose was to find and describe the differences in the beam work as the part of roofing, which distinguishes it from the work conditions of the free supported beam. The features of the beam operation with the joint flexural and torsion are singled out. The need to improve the existing theoretical model for present deficiencies elimination is indicated. The bearing capacity determining methods for the flexible elements stability exposed to bending and bending with torsion are compared. Their advantages and disadvantages are revealed. It is proposed to increase the material saving by applying calculations. At the end of the article, conclusions regarding the consideration of investigated factors are given.

Cervical Cancer Incidence in Young U.S. Females After Human Papillomavirus Vaccine Introduction

Since 2006, human papillomavirus vaccine has been recommended for young females in the U.S. This study aimed to compare cervical cancer incidence among young women before and after the human papillomavirus vaccine was introduced. This cross-sectional study used data from the National Program for Cancer Registries and Surveillance, Epidemiology, and End Results Incidence-U.S. Cancer Statistics 2001-2014 database for U.S. females aged 15-34 years. This study compared the 4-year average annual incidence of invasive cervical cancer in the 4 years before human papillomavirus vaccine was introduced (2003-2006) and the 4 most recent years in the vaccine era (2011-2014). Joinpoint regression models of cervical incidence from 2001 to 2014 were fitted to identify the discrete joints (year) that represent statistically significant changes in the direction of the trend after the introduction of human papillomavirus vaccination in 2006. Data were collected in 2001-2014, released, and analyzed in 2017. The 4-year average annual incidence rates for cervical cancer in 2011-2014 were 29% lower than that in 2003-2006 (6.0 vs 8.4 per 1,000,000 people, rate ratio=0.71, 95% CI=0.64, 0.80) among females aged 15-24 years, and 13.0% lower among females aged 25-34 years. Joinpoint analyses of cervical cancer incidence among females aged 15-24 years revealed a significant joint at 2009 for both squamous cell carcinoma and non-squamous cell carcinoma. Among females aged 25-34 years, there was no significant decrease in cervical cancer incidence after 2006. A significant decrease in the incidence of cervical cancer among young females after the introduction of human papillomavirus vaccine may indicate early effects of human papillomavirus vaccination.

A numerical study on the limitations of modal Iwan models for impulsive excitations

Structures with mechanical joints are difficult to model accurately. Even if the natural frequencies of the system remain essentially constant, the damping introduced by the joints is often observed to change dramatically with amplitude. Although models for individual joints have been employed with some success, accurately modeling a structure with many joints remains a significant obstacle. To this end, Segalman proposed a modal Iwan model, which simplifies the analysis by modeling a system with a linear superposition of weakly-nonlinear, uncoupled single degree-of-freedom systems or modes. Given a simulation model with discrete joints, one can identify the model for each mode by selectively exciting each mode one at a time and observing how the transient response decays. However, in the environment of interest several modes may be excited simultaneously, such as in an experiment when an impulse is applied at a discrete point. In this work, the modal Iwan model framework is assessed numerically to understand how well it captures the dynamic response of typical structures with joints when they are excited with impulsive forces applied at point locations. This is done by comparing the effective natural frequency and modal damping of the uncoupled modal models with those of truth models that include nonlinear modal coupling. These concepts are explored for two structures, a simple spring-mass system and a finite element model of a beam, both of which contain physical Iwan elements to model joint nonlinearity. The results show that modal Iwan models can effectively capture the variations in frequency and damping with amplitude, which, for damping, can increase by as much as two orders of magnitude in the microslip regime. However, even in the microslip regime the accuracy of a modal Iwan model is found to depend on whether the mode in question is dominant in the response; in some cases the effective damping that the uncoupled model predicts is found to be in error by tens of percent. Nonetheless, the modal model captures the response qualitatively and is still far superior to a linear model.

Load Sharing Between Discrete Solder Joints in Bending: Effect of Spacing and Joint Properties

The fracture loads of copper–solder–copper double cantilever beam (DCB) specimens containing two discrete solder joints were measured and found to be maximum at a certain characteristic joint spacing. A finite-element model (FEM) showed that this corresponded to a minimization of the solder peel stress and an optimal load sharing among the two joints. This behavior was also analytically modeled using both a continuous foundation model and a simplified discrete foundation model, which isolated the effects of joint geometry and the bending stiffness of the solder and substrates. The model predictions of the characteristic joint spacing for both DCB and three-point bending configurations were satisfactorily compared with the FEM and the experimental data. The proposed approach is useful in predicting the load sharing among the multiple solder joints typical of surface mount microelectronic devices and in designing joint with maximum strength.

Kinematics Modeling of a Notched Continuum Manipulator

In this paper, the kinematics modeling of a notched continuum manipulator is presented, which includes the mechanics-based forward kinematics and the curve-fitting-based inverse kinematics. In order to establish the forward kinematics model by using Denavit–Hartenberg (D–H) procedure, the compliant continuum manipulator featuring the hyper-redundant degrees of freedom (DOF) is simplified into finite discrete joints. Based on that hypothesis, the mapping from the discrete joints to the distal position of the continuum manipulator is built up via the mechanics model. On the other hand, to reduce the effect of the hyper-redundancy for the continuum manipulator's inverse kinematic model, the “curve-fitting” approach is utilized to map the end position to the deformation angle of the continuum manipulator. By the proposed strategy, the inverse kinematics of the hyper-redundant continuum manipulator can be solved by using the traditional geometric method. Finally, the proposed methodologies are validated experimentally on a triangular notched continuum manipulator which illustrates the capability and the effectiveness of our proposed kinematics for continuum manipulators and also can be used as a generic method for such notched continuum manipulators.

Lobopodians

Lobopodians

Kinematics modeling and performance optimization of a kinematic-mechanics coupled continuum manipulator

An optimization design of a notched continuum manipulator is proposed in this paper, which is based on our defined performance evaluation indices. By experimental testing the mechanics-based forward kinematics and the curve-fitting-based inverse kinematics, our proposed kinematic-mechanics coupled continuum manipulator is equivalent to a robot that features discrete joints and rigid links. Based on the mechanics and the kinematics models, two kinematic performance evaluation indices are developed to comprehensively describe the performance distribution characteristics in the workspace. Firstly, the global stiffness performance index of the proposed manipulator is established based on the 3-dimensional 2-node Timoshenko beam element. Secondly, the equivalent Jacobian matrix, a linear mapping from the joint space to the task space of the continuum manipulator, is analyzed, and equivalent dexterity performance index is determined. Finally, the optimal design for our proposed continuum manipulator considering the stiffness performance and kinematics performance simultaneously is implemented as a case study utilizing the NAGA-II genetic algorithm. The results demonstrate that the optimized geometric parameters can improve the kinematic performance evaluation indices simultaneously, and our proposed kinematic performance evaluation indices can be applied and extended to the kinematic evaluation and the kinematic optimization of this kind of notched continuum manipulator.