Prototype Joint Research Articles

Jam-free gear\u2013clutch mechanism for load-sensitive step transmission in robotic joint

This paper introduces a novel gear–clutch mechanism that takes advantage of the difference between the directions in the reaction forces that occur during meshing and jamming to ensure jam-free engagement of the gears. The proposed mechanism is a more compact advancement of the previously developed linear rack-tilting clutch used to provide a step change in the reduction ratio. Mathematical models of the jam-free and stable meshing condition of the proposed mechanism are developed and experimentally verified, along with a discussion and recommendations to be considered as design guidelines. Additionally, a singularly actuated robotic joint prototype is developed to examine the performance of the proposed clutch mechanism. The joint was driven by a small 2-W DC motor. The maximum output torque was 4 Nm with a maximum travel range of over 200^circ during the high-force phase, and the maximum speed was 252^circ/s with an infinite travel range during the high-speed phase. The mechanism exhibits potential for applications that benefit from a step transmission and long force-exerting travel range such as vices, grippers, and industrial punching and shearing machines, as well as robotic arms and power assist exoskeletons.

Design of a standalone joint module toward real EAST in-vessel operation use

The remote handling in-vessel inspection manipulator for China’s Experimental Advanced Superconducting Tokamak (EAST) has proven its survivability in 120°C high temperature environment and its kinematics feasibility in full-scale tokamak mock-up. To adapt this manipulator for real in-vessel operation use, most of its joint components, such as motors, reducers, and transmission structures must be considered for possible contamination to the tokamak in-vessel ambient. In order to verify the feasibility of combining vacuum sealing techniques with the previous in-vessel inspection manipulator solution, we have designed a standalone rotary joint module as prototype for relevant experimental tests. The joint module has a standard stainless steel metallic bellow to seal all its ordinary commercial joint components from tokamak environment, while the servo control wires, sensor wires and active cooling tubes inside the sealed chamber are led out by special vacuum feedthroughs. Basic mobility tests have been carried out under equivalent vacuum environment. This paper mainly presents the joint module design and related vacuum environment tests result of this prototype joint module. Further work will concentrate on adapting the whole in-vessel manipulator for vacuum environment operation based on this joint module design and tokamak environment tests result.

Development of three-dimensional prints of arthritic joints for supporting patients\u2019 awareness to structural damage

BackgroundRheumatoid arthritis (RA) and psoriatic arthritis (PsA) result in severe joint destruction and functional disability if left untreated. We aim to develop tools that help patients with RA and PsA to understand and experience the impact of inflammatory joint disease on the integrity of their (juxta-articular) bone and increase adherence to medical treatment. In this study, we used high-resolution peripheral quantitative computed tomography (HR-pQCT) to develop 3D prototypes of patients’ finger joints.MethodsHR-pQCT (XtremeCT, Scanco) measurements were performed in healthy individuals and patients with inflammatory joint disease, followed by a 3D print using the objet30 printer. Healthy participants (n = 10), and patients (n = 15 with RA and 15 with PsA) underwent a detailed, standardized interview with demonstration of printed joints.ResultsUtilizing HR-pQCT images of metacarpophalangeal (MCP) heads, high quality and exact 3D prints as prototypes were created. Erosions in different sizes and the trabecular network printed in detail were visualized, demonstrating structural reduction in arthritic vs. healthy bone. After demonstration of 3D prints (healthy vs. erosive joint, visual and haptic) 26/39 (66%) participants (including healthy volunteers) were deeply affected, often quoting “shock”. Of the patients with RA and PsA, 13/15 (86%) and 11/15 (73%), respectively, stated that they would rethink their attitude to medication adherence. More importantly, 21/24 patients with RA or PsA (87.5%) expressed that they would have wished to see such 3D prints during their first disease-specific conversations.ConclusionUsing arthro-haptic 3D printed prototypes of joints may help to better understand the impact of inflammatory arthritides on bone integrity and long-term damage.

Simple and robust feedforward compensation of quadrant glitches using a compliant joint

Quadrant glitches commonly occur when rolling/sliding bearings are used in precision motion stages. Compensating them accurately using feedforward control is challenging due to the need for complex friction models, and the variability of on-machine friction dynamics. This paper shows that quadrant glitches can be accurately and robustly compensated with simple friction models by attaching the bearing to the moving table using a joint that is very compliant in the motion direction. Design of a prototype joint that achieves high compliance by combining a positive-stiffness flexure with negative-stiffness permanent magnets is presented. Large reductions in quadrant glitches are demonstrated in experiments.

Computational modelling of the moment-rotation relationship for deconstructable flush end plate beam-to-column composite joints

This paper presents a three-dimensional finite element modelling of an innovative flush end plate semi-rigid beam-to-column composite joint comprising deconstructable post-installed friction-grip bolted shear connectors. The moment versus rotation relationship for these prototype joints subjected to a hogging bending moment with the influence of partial shear connection is investigated using ABAQUS software. This relationship is an indicator of the ductility of a composite joint and is a necessity for a semi-rigid frame analysis. A detailed finite element model of the connection region including the precast concrete slab, steel beam, flush end-plate, bolted shear connectors and the steel column is developed in the paper. Material and geometrical non-linearities as well as the non-linearity of the interfaces are incorporated in the model. The accuracy and reliability of the numerical formulation are verified against experimental data reported elsewhere. In addition, a composite joint with partial shear connection is constructed and tested in this study, and the numerical predictions are compared with the test results. An extensive parametric study is then conducted, using several parameters that include the degree of shear connection, reinforcement ratio, thickness of the precast concrete slab, spacing of bolted shear connectors, size of the bolts in the connection zone, thickness of the flush end plate, steel grade for the beam, column and end plate and the column flange thickness. Finally, moment versus rotation models for deconstructable flush end plate beam-to-column composite joint are proposed, and it is demonstrated that the design models developed can also be used for composite joints with high strength steel components.

Hydraulically driven joint for a force feedback manipulator

Recently, surgical manipulators have been widely used to support human operations, such as surgical operations. These manipulator systems are suitable for careful work, but they have a few problems. One problem is that the manipulators are not equipped with haptic sensing functions. When a manipulator does not employ haptic sensing functions, an operator can only conduct an operation using visual feedback. Therefore, to substitute for visual detection, it is necessary for the operator to use advanced techniques to determine physical contact during an operation. We have developed a new mechanism to solve this problem. A hydraulically driven joint is constructed in a spherical bearing and bellows tubes that enables a haptic sense display for the operator. This system can measure the small forces acting on the tips of the manipulator using Pascal’s principle. A model of the system is derived from the relationship between the internal pressure of the bellows tube and the refraction angles of the joint. In this study, we quantitatively investigated the relationship between the internal pressure of the bellows tubes and the refraction angles of the joint. To estimate the refraction angle, we measured the quantity of water that was provided from syringes. It was confirmed that the developed system allowed for an estimation of both the strength and direction of the external force applied to the manipulator by measuring the bellows tubes’ internal pressure. This report describes the prototype joint.

Numerical Study of Deconstructable Flush End Plate Composite Joints to Concrete-filled Steel Tubular Columns

This paper describes a three-dimensional finite element modelling of an innovative flush end plate semi-rigid composite joint, to a concrete-filled steel tubular column, using high strength blind bolts. This innovative composite joint is formed by connecting a precast concrete slab to the top flange of a steel beam using post-installed friction-grip bolted shear connectors to facilitate the deconstructability of the entire system. A finite element model is developed using ABAQUS software to study the structural behaviour and failure modes of these prototype joints. Both geometrical and material non-linearities, as well as the non-linearity of the contacts and interfaces, are incorporated in the model. Four full-scale laboratory test specimens having deconstructable flush end plate composite semi-rigid joint to CFST columns using bind bolts are tested, with the results then used for validation of the finite element model. The proposed numerical models developed are used for conducting an extensive parametric study, in which the effects of the reinforcement ratio, thickness of the precast concrete slab, degree of shear connection, number of bolted shear connectors, size of the blind bolts in the connection zone and thickness of the flush end plate on the structural behaviour of the composite joint to concrete-filled columns are investigated. A design recommendation in the form of an empirical equation is then formulated.

Joint prototype and metric learning for image set classification: Application to video face identification

In this paper, we address the problem of image set classification, where each set contains a different number of images acquired from the same subject. In most of the existing literature, each image set is modeled using all its available samples. As a result, the corresponding time and storage costs are high. To address this problem, we propose a joint prototype and metric learning approach. The prototypes are learned to represent each gallery image set using fewer samples without affecting the recognition performance. A Mahalanobis metric is learned simultaneously to measure the similarity between sets more accurately. In particular, each gallery set is represented as a regularized affine hull spanned by the learned prototypes. The set-to-set distance is optimized via updating the prototypes and the Mahalanobis metric in an alternating manner. To highlight the importance of representing image sets using fewer samples, we analyzed the corresponding test time complexity with respect to the number of images used per set. Experimental results using YouTube Celebrity, YouTube Faces, and ETH-80 datasets illustrate the efficiency on the task of video face recognition, and object categorization.

12-GHz Rotary Joint With Substrate Integrated Waveguide Feeder

In this paper, a rotary joint fed by the substrate integrated waveguide (SIW) feeder is presented. This structure is able to effectively convert the TE10 mode in the SIW with arbitrary input angle to the symmetrical TM01 mode in the circular waveguide. A good matching can be implemented by use of a tapered dual-side parallel strip line (DSPSL) between a SIW and a printed probe. After introducing the design principle, a rotary joint prototype with two controllable transmission poles is fabricated and measured. From 11.6 to 12.6 GHz, its insertion loss is always less than 1.09 dB and return loss is better than 11.22 dB when being rotated at different angles. Besides, a tapered slot antenna (TSA) is employed to realize a rotary antenna based on the rotary joint proposed above. Stable performance and different polarizations can be achieved at different rotary angles. Based on the rotary joint with the SIW feeder, it is much more convenient for designers to extend the application field of the SIW devices.

Development and Control of a Compliant Asymmetric Antagonistic Actuator for Energy Efficient Mobility

This paper presents the development and control of a novel asymmetric antagonistic actuation scheme characterized by large energy storage capacity that enables efficient execution of motions. The asymmetric design consists of two actuation branches that transfer their power to a single joint through two compliant elements with different stiffness and storage capacity properties. The guideline for selecting the stiffness of both elements is elaborated, given the design parameters and control requirements. We propose a novel control strategy that distributes the effort required to generate the motion using the two actuation branches of this novel hardware, to drive the prototype joint in an energy efficient manner. As a proof of concept, a single degree-of-freedom knee-actuated hopping robot is designed for experimental validation. The dynamics of the leg and actuators are rigorously modeled and formulated. The data from simulation and experimental studies demonstrate a significant improvement in electrical energy efficiency and reduction in torque requirements.

Mechanical and Electrical Characteristics of a Bridge-Type Mechanical Lap Joint of HTS STARS Conductors

Segmented fabrication of high-temperature superconducting (HTS) coils has been proposed for the helical fusion reactor FFHR-d1; the joint-winding and “remountable” (demountable) helical coils concept are the primary and advanced options, respectively. This paper introduces recent research activities on a bridge-type mechanical lap joint of HTS Stacked Tapes Assembled in Rigid Structure (STARS) conductors, particularly to be used for joint winding of the helical coils, and also discusses some technical issues to develop a reliable joint. First, the required joint performance is discussed from the viewpoints of operation cost and mechanical behavior, taking the present design of joint winding of the helical coils for the FFHR-d1 into consideration. Then, mechanical and electrical characteristics of a prototype STARS conductor joint, which achieved a joint resistance of 1.8 nΩ at a current of 100 kA, are analyzed based on small- and largescale joint tests. It is suggested that the joint performance of the prototype joint can be improved more, according to tests of small-scale conductor joints. Finally, the study introduces a fabrication procedure for a reliable joint. We need to develop nondestructive testing for a joint at room temperature. For this purpose, we also perform an X-ray computed tomography inspection as a first step. The inspection can roughly judge whether a fabricated joint is acceptable.

Rapid Development and Application of Prototype Test System of Prefabricated Metro Station Structure Joint

In the context of the proposed prefabricated metro station named Yuanjiadian Station for Changchun Metro Line 2 and based on the final purpose of studying the tenon and mortise grouting joint’s mechanical properties, prototype test system of joint was developed and staged test finished. The test system includes loading system, test and monitoring system, assembling and grouting system, lifting and installation system and so forth. The system can complete the fourpoint bending test and four-point shearing test under any axial force of the prototype joint. Afterward, destructive test of axial force combining with bending moment was carried out under different conditions (including grouting ranges, grouting materials and tenon lengths). Ultimately, the flexural capacity and flexural rigidity for some specific tenon and mortise joint was derived and the safe bending moment of the joint was shown, providing guidance for design and construction.

Shear Capacity of Exterior Beam-Column Joints Reinforced with GFRP Bars and Stirrups

The demand for sustainable concrete structures with longer service life and lower maintenance cost has been driving the use of glass fiber-reinforced polymer (GFRP) reinforcement in new concrete structures. The behavior of GFRP bars under seismic loading in reinforced concrete (RC) frame structures has not been widely investigated. Furthermore, the ability of FRP-RC frame structures to dissipate energy in seismic events is still questionable due to the elastic-linear behavior of the FRP reinforcement. Very few studies have been conducted on the seismic behavior of GFRP-RC exterior beam-column joints, and none studied the shear capacity of joints. Therefore, this study attempts to partially fill this gap by investigating the shear capacity of beam-column joints reinforced with GFRP bars and stirrups. Six full-scale exterior beam-column joint prototypes (T-shaped) were constructed and tested under simulated seismic load conditions. Test parameters in this study included the concrete strength and the shear stress level in the joint. Diagonal shear failure in the joint exhibited in some specimens showed the significance of evaluating the shear capacity in the joint.

DC Resistance Performance of the Low-Resistance <inline-formula> <tex-math notation="TeX">$\hbox{Nb}_{3}\hbox{Sn}$</tex-math></inline-formula> Joints for the CHMFL Hybrid Magnet

The superconducting coils of a 40-T hybrid magnet were designed with Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn cable-in-conduit conductors wound in layers or double pancakes, which are connected in series by joints. Two kinds of electrical joints have been designed for the different terminals of the superconducting coils. The “terminal joint” is for the joints between the terminals of the superconducting coils and the ends of NbTi buslines. The “interlayer joint” is for the joints between the layers of the coils. Two prototype joint samples have been manufactured, and their dc resistance tested. The joints' manufacturing process and test results are presented in this paper.

Strength Degeneration of SRUHSC Column to RC Beam Joint Subjected to Reversal Cycle Load

In order to investigate the strength degeneration of SRUHSC column to RC beam joint subjected to reversal cycle load, six interior joint specimens were designed basing on half-scale model of prototype joint used in high-rise buildings. A reversal cycle loading test was carried out and test parameters included various axial load ratio and volumetric stirrup ratio. Strength degeneration of SRUHSC column to RC beam joint was described. A discussion on relations between λj and applied axial load ratio or volumetric stirrup ratio was presented. It was found that strength of all the joints degenerated in every displacement and degenerated more quickly with the increment of displacement during the reversal cycle loading, and that the strength of all the joints degenerated fast with the increment of applied axial load ratio and slowly with the increment of volumetric stirrup ratio. The experimental results indicated that test parameters had obvious influence on the strength degeneration of SRUHSC column to RC beam joint subjected to reversal cycle load.

A bio-inspired condylar knee joint for knee prosthetics

This paper presents a novel bio-inspired condylar prosthetic knee joint developed at the University of Bristol. The bio-inspired condylar joint mimics the structure and biomechanics of the human knee joint. The joint contains an inverted parallelogram four-bar mechanism combined with a cam mechanism. The joint has a favourable mechanical advantage compared with a hinge joint. The joint is also compact and robust. An adultsized prototype joint has been designed and tested. The prototype joint contains a long cable for the ligaments with a mechanism for adjusting preload. Compared with other prosthetic joints, the condylar joint has the advantages that it is simple and closely mimics human biomechanics. This paper presents the design of the new artifi cial knee joint and some of the test results. The joint can be used in artifi cial legs and also for knee implants. A rapid prototyping procedure is also presented that enables a custom-sized prosthetic knee joint to be made very quickly and from just a few key dimensions. This process has the potential to improve the quality of surgical implants.

Experimental investigation of a DfD moment-resisting beam–column connection

DfD (Design for Disassembly) has been reported to be the most direct approach to increase material reusability in the construction industry. The aim of DfD is to reuse the structural components instead of demolition followed by recycling of the demolition debris. In this study, a DfD moment-resisting beam–column connection is proposed for application in typical multi-storey RC apartment blocks, and it was investigated through a two-series test programme. In Series-1 testing, four full-scale prototype joint specimens were tested up to failure. Subsequently, a two-stage test was conducted for the other seven specimens including service load test, deconstruction, strengthening, reconstruction and re-test in Series-2 testing. Based on the test results, the proposed DfD M-R beam–column connection was shown to be capable of providing an adequate amount of moment resistance and proved to be feasible for deconstruction and subsequent reconstruction.

Fabrication of new joints for SST-1 TF coil winding packs

The Toroidal Field (TF) magnet system of SST-1 has sixteen NbTi/Cu based coils with about one hundred Inter-Pancake (IP) and Inter-Coil (IC) joints. New box type helium leak tight, low DC resistance joints have been designed, fabricated and tested at 5K temperature and 10kA DC transport current. The prototype of this joint has been validated in laboratory as well as on spare TF coil winding pack. Moreover, the performance of these joints has been realised and validated on actual sixteen TF winding packs, the joint resistance of ∼0.5nΩ repeatedly measured on hundreds of IP joints. The quality of terminations and joints was ensured at various stages of fabrication. The quality of joint box material was ensured by visual inspection, chemical analysis, radiography test, ultrasonic test, eddy current test, etc. This paper describes joint design drivers, joint design detail, prototype joint fabrication processes, quality assurance (QA)/quality control (QC) adopted during prototype and actual joint fabrication process, joint resistance measurement on actual TF coils and analysis of measured joint resistance in detail.

AC Loss of $\hbox{Nb}_{3}\hbox{Sn}$ Butt Joint for JT-60SA Central Solenoid

The upgrading project of the JT-60 to the JT-60 Super Advanced (JT-60SA) at Japan Atomic Energy Agency has started as a joint effort between Japan and the EU. The coils of the JT60-SA are separately fabricated in Japan and EU. The CS and EF coils are fabricated in Japan. In this paper, we describe the butt joint of the JT-60SA CS and measured the ac loss under a time-varying external magnetic field, and analyzed the ac loss at the butt joint by using the FEM simulation software COMSOL Multiphysics. As a result, the measured ac loss of the butt joint were found to be the smallest of all joints (the CS butt joint, the EF pancake joint, the terminal EF joint and the EF prototype joint), and to strongly depend on the thickness of the copper sleeve in full-size coil joint.

Active Joint Mechanism Driven by Multiple Actuators Made of Flexible Bags: A Proposal of Dual Structural Actuator

An actuator is required to change its speed and force depending on the situation. Using multiple actuators for one driving axis is one of the possible solutions; however, there is an associated problem of output power matching. This study proposes a new active joint mechanism using multiple actuators. Because the actuator is made of a flexible bag, it does not interfere with other actuators when it is depressurized. The proposed joint achieved coordinated motion of multiple actuators. This report also discusses a new actuator which has dual cylindrical structure. The cylinders are composed of flexible bags with different diameters. The joint torque is estimated based on the following factors: empirical formula for the flexible actuator torque, geometric relationship between the joint and the actuator, and the principle of virtual work. The prototype joint mechanism achieves coordinated motion of multiple actuators for one axis. With this motion, small inner actuator contributes high speed motion, whereas large outer actuator generates high torque. The performance of the prototype joint is examined by speed and torque measurements. The joint showed about 30% efficiency at 2.0 Nm load torque under 0.15 MPa air input.