Torsional Joint Research Articles

Analysis of non-geometric accuracy effects of articulated robots

PurposeArticulated robots are widely used in industrial applications owing to their high repeatability accuracy. In terms of new applications such as robot-based inspection systems, the limitation is a lack of pose accuracy. Mostly, robot calibration approaches are used for the improvement of the pose accuracy. Such approaches however require a profound understanding of the determining effects. This paper aims to provide a non-destructive analysis method for the identification and characterisation of non-geometric accuracy effects in relation to the kinematic structure for the purpose of an accuracy enhancement.Design/methodology/approachThe analysis is realised by a non-destructive method for rotational, uncoupled robot axes with the use of a 3D lasertracker. For each robot axis, the lasertracker position data for multiple reflectors are merged with the joint angles given by the robot controller. Based on this, the joint characteristics are determined. Furthermore, the influence of the kinematic structure is investigated.FindingsThis paper analyses the influence of the kinematic structure and non-geometric effects on the pose accuracy of standard articulated robots. The provided method is shown for two different industrial robots and presented effects incorporate tilting of the robot, torsional joint stiffness, hysteresis, influence of counter balance systems, as well as wear and damage.Practical implicationsBased on these results, an improved robot model for a better match between the mathematical description and the real robot system can be achieved by characterising non-geometric effects. In addition, wear and damages can be identified without a disassembly of the system.Originality/valueThe presented method for the analysis of non-geometric effects can be used in general for rotational, uncoupled robot axes. Furthermore, the investigated accuracy influencing effects can be taken into account to realise high-accuracy applications.

Design and analysis of Outside-Deployed Lamina Emergent Joint (OD-LEJ)

Lamina emergent mechanisms (LEMs) can be fabricated in plane, while achieve motion that emerges out of fabrication plane. This paper presents a new flexure hinge called Outside-Deployed Lamina Emergent Joint (OD-LEJ) with a small equivalent spring constant and a large angular displacement. The closed-form model is given and a finite element analysis (FEA) model is created. The FEA results show that this joint can achieve nearly 170.17˚ of rotation without plastic deformation. Stress analysis is done and the results gotten from theoretical calculation and FEA coincide with each other very well. Safety analysis and fatigue analysis are done as well. An Inside-Deployed Lamina Emergent Joint (ID-LEJ) is also proposed. The joint is analyzed through FEA and theoretical calculation. The joint shows a similar bending property as OD-LEJ. Comparisons between these two joints and Lamina Emergent Torsional (LET) joint are made. OD-LEJ and ID-LEJ do better than LET joint in large angular displacement and have a smaller equivalent spring constant. Finally, the movement of the center of rotation and some other problems are discussed.

Cryogenic expansion joint for LNG service

Pipelines transporting cryogenic liquids, such as liquefied natural gas (LNG), are typically constructed with metal components with a relatively high thermal expansion coefficient. Pipelines contract in length due to the large temperature differential that occurs. To accommodate this thermal contraction, LNG plants, offloading jetties, and other facilities typically utilise expansion loops and/or conventional in-line expansion joints (e.g. bellows). However, expansion loops require a large amount of space and support platforms, which can be costly and/or disruptive to an LNG facility construction. Additionally, conventional bellows-type expansion joints offer very little torsional strength, which may lead to catastrophic failure in the joint. Engineers at Clough Limited have patented two unique embodiments of a cryogenic expansion joint: a sliding concentric pipe-in-pipe cryogenic expansion joint; and a torsional cryogenic expansion joint. Both designs utilise inherent material properties to seal sequential pipeline segments together at cryogenic conditions. The pipe-in-pipe expansion joint provides large axial and unlimited torsional movement. The torsional expansion joint provides unlimited radial and some axial movement. These embodiments eliminate the large conventional expansion loops and reduce project capital expenditure.

A torsional MRE joint for a C-shaped robotic leg

Serving to improve stability and energy efficiency during locomotion, in nature, animals modulate their leg stiffness to adapt to their terrain. Now incorporated into many locomotive robot designs, such compliance control can enable disturbance rejection and improved transition between changing ground conditions. This paper presents a novel design of a variable stiffness leg utilizing a magnetorheological elastomer joint in a literal rolling spring loaded inverted pendulum (R-SLIP) morphology. Through the semi-active control of this hybrid permanent-magnet and coil design, variable stiffness is realized, offering a design which is capable of both softening and stiffening in an adaptive sort of way, with a maximum stiffness change of 48.0%. Experimental characterization first serves to assess the stiffness variation capacity of the torsional joint, and through later comparison with force testing of the leg, the linear stiffness is characterized with the R-SLIP-like behavior of the leg being demonstrated. Through the force relationships applied, a generalized relationship for determining linear stiffness based on joint rotation angle is also proposed, further aiding experimental validation.

Ambulant cerebral palsy

Cerebral palsy (CP) is the result of a non-progressive lesion or injury to the developing brain and has multiple causes and manifestations. This non-progressive lesion leads to progressive limb problems due to imbalance in muscle tendon unit (MTU) structure and function across joints. This leads to dynamic problems during movement and with posture that may progress over time to become fixed. Abnormal movement and posture result from contractures, lengthening and problems with tone in MTUs. Torsional problems, contractures and joint instability lead to lever arm dysfunction that has a detrimental effect on gait.This article aims to summarize the aetiology and pathophysiology of cerebral palsy, improve understanding of gait in the context of muscle imbalance and lever arm dysfunction, and describe an approach to the assessment and management of these patients.

柔軟半球足を持つ二足歩行ロボットのバランス制御と歩容生成

In this paper, a new type bipedal robot which has soft hemispheric feet is proposed. It is able to realize an efficient bipedal locomotion by utilizing a rolling motion of hemispheric feet effectively. Furthermore, each hemispheric foot has an active torsional joint. Thus it is able to move as a wheeled vehicle using an infinite rolling motion by the torsional joint. It, however, is difficult to keep its balance more proper than a humanoid robot having normal flat feet. Therefore, firstly a balance control and gait generation method which consider the rolling effect of feet are proposed. After that, several numerical simulations are conducted to demonstrate the effectiveness of the proposed balance control and gait generation method.

Design of Passive Weight Compensation for a Robotic Manipulator

A serial link manipulator consist of various unbalanced bars (links) attached by torsional joints that are subjected to torque loads due to the weight and configuration of the manipulator. This paper proposes a solution to passive weight compensation for serial link manipulators, using torsional springs. A set of characteristic points is selected and evaluated through sensibility analysis to define the required maneuvers. A nonlinear optimization methodology is used to find the springs parameters to minimize the energy consumption during the execution of the defined maneuvers. The energy saving is estimated through simulation as well as the effect of the maximum preload allowed for the spring.

Modeling and testing miniature torsion specimens for SiC joining development studies for fusion

The international fusion community has designed a miniature torsion specimen for neutron irradiation studies of joined SiC and SiC/SiC composite materials. Miniature torsion joints based on this specimen design were fabricated using displacement reactions between Si and TiC to produce Ti3SiC2 + SiC joints with SiC and tested in torsion-shear prior to and after neutron irradiation. However, many miniature torsion specimens fail out-of-plane within the SiC specimen body, which makes it problematic to assign a shear strength value to the joints and makes it difficult to compare unirradiated and irradiated strengths to determine irradiation effects. Finite element elastic damage and elastic–plastic damage models of miniature torsion joints are developed that indicate shear fracture is more likely to occur within the body of the joined sample and cause out-of-plane failures for miniature torsion specimens when a certain modulus and strength ratio between the joint material and the joined material exists. The model results are compared and discussed with regard to unirradiated and irradiated test data for a variety of joint materials. The unirradiated data includes Ti3SiC2 + SiC/CVD-SiC joints with tailored joint moduli, and includes steel/epoxy and CVD-SiC/epoxy joints. The implications for joint data based on this sample design are discussed.

Low Cycle Fatigue Life Prediction of Ti-6Al-4V Titanium Alloy under Multi-Axial Non Proportional Cyclic Loading

A series multi-axial tension and torsion low cycle fatigue life experiments of Ti-6Al-4V alloy were conducted on the MTS tension and torsion joint testing machine, in which the torsional strain control and non proportional cyclic loading method under the loading paths of circular, rectangular, square, oval and diamond were successively used. The experimental results are compared and analyzed with the results that calculated by the equivalent strain model, the energy method model and the critical plane method model. The results show that the critical plane method is the accurate prediction model to predict the multi-axial low cycle fatigue life of Ti-6Al-4V alloy.

더블-액션 압출공정을 적용한 전동조향장치용 토션조인트 요크 개발

The yoke, a component of conventional motor-driven power steering system, often contains welding defects from its manufacturing process. To eliminate these defects, the precision cold forging process has been tried. In this study, the double-action complex forging has been used to manufacture a torsion joint yoke. The backward extrusion proved faster than the forward extrusion in forging of the product. The double-action complex forging process utilized an upper die composed of a punch, a punch guide, a disc spring and a coil spring. The forged material pushes up the punch guide, and then the disc spring and the coil spring balances the backward extrusion force. Consequently, the flow of material was essentially in the forward direction, resulting in a successful forging operation. The forging load of Al 6061-T6 was higher than that of the automotive structural hot rolled plate.

Introduction of planar compliant joints designed for combined bending and axial loading conditions in lamina emergent mechanisms

This work introduces three joints to allow motion in lamina emergent mechanisms (LEMs) that were designed to have minimal parasitic motion under tension, compression, and a combination of tension and compression loadings. Closed-form models of the joints were developed and combined with optimization algorithms for maximum flexibility in bending and then modeled using finite element analysis (FEA). The FEA results were used to predict the stiffnesses of the joints in bending, tension, and compression. As a baseline, Lamina Emergent Torsional (LET) joints were designed to match the bending stiffness of each of the joints, so that the tensile-compressive performance could be compared. The joints demonstrate improved off-axis stiffness in tensile and/or compressive stiffness, at the cost of limited bending flexibility compared to the LET joint and requiring more material area. The resulting joints provide a broad set of capabilities that can be used by designers in lamina emergent mechanism design.

Groove design for form fit joints made by electromagnetic pulse crimping

The electromagnetic pulse process can be an alternative for many conventional productionprocesses. It can be used for perforating, cutting, welding, forming and crimping. In this thesis, the latter willbe investigated in detail, with the emphasis on tubular joints bearing axial tension and/or torsion loading.To get acquainted with the subject, first a literature study was performed concerning the general principlesof electromagnetic pulse crimping. Because a new field shaper had to be designed, literature on this topicwas also consulted. Finally, the design and use of grooves in crimp joints was studied. It has been reportedthat an inner piece (mandrel) with additional grooves in the joining zone significantly increases the strengthof a crimped joint [1]. However, the information on electromagnetic pulse crimping with a mandrel with morethan one groove is very limited. Therefore one of the main goals of this thesis is to determine an optimaldesign for a mandrel with two grooves used for axially loaded joints. A combination of finite elementsimulations and experiments was used to draw preliminary conclusions involving the double groove design.In a later stage torsional joints will be designed and suitable filler materials to realize leak proof joints will beevaluated.

Torsion deformity and joint loading for medial knee osteoarthritis

PurposeThe consequences of lower limb torsion deformity on knee loading in knee osteoarthritis are poorly understood. The purpose of this study was to quantify the associations between the mechanical axis, tibial torsion and knee loading in subjects with medial knee OA and in controls. MethodsTwenty-four subjects: end-staged medial knee osteoarthritis (OA) with apparent torsion deformity (TKO, n=6) and without torsion deformity (KOA, n=8) and controls (CON, n=10) were imaged using long standing lower extremity (LSLE) radiographs and computed tomography (CT). Medial knee loading was assessed using the internal knee varus moment determined by gait analysis. The LSLE mechanical axis, CT tibial torsion and the foot progression angle were used to predict medial knee loading. ResultsThe TKOs had significantly greater mechanical axis varus and knee varus moment compared to KOAs and CONs. The regression model predicting medial knee loading using the mechanical axis (β=0.898), tibial torsion (β=0.264) and foot progression angle (β=−0.369) showed a goodness of fit of 0.774. ConclusionsMedial knee loading was predicted by the mechanical axis and the foot progression angle. Future longitudinal studies are needed to assess the role of tibial intorsion during disease progression and following total knee replacement surgery.

Contribution of Knee Flexor and Extensor Strength on Sex-Specific Energy Absorption and Torsional Joint Stiffness During Drop Jumping

Lower extremity injury often occurs during abrupt deceleration when attempting to change the body's direction. Although sex-specific biomechanics have been implicated in the greater risk of acute knee injury in women than in men, it is unknown if sex differences in thigh strength affect sex-specific energy absorption and torsional joint stiffness patterns. To determine sex differences in energy absorption patterns and joint stiffnesses of the lower extremity during a drop jump and to determine if these sex differences were predicted by knee extensor and flexor strength. Cross-sectional study. Laboratory environment. Recreationally active, college-aged students (41 women: age = 22.1 ± 2.9 years, height = 1.63 ± 0.07 m, mass = 59.3 ± 8.0 kg; 40 men: age = 22.4 ± 2.8 years, height = 1.77 ± 0.1 m, mass = 80.9 ± 14.1 kg). Participants performed knee flexor and extensor maximal voluntary isometric contractions followed by double-leg drop-jump landings. Lower extremity joint energetics (J × N(-1) × m(-1)) and torsional joint stiffnesses (Nm × N(-1) × m(-1) × degrees(-1)) were calculated for the hip, knee, and ankle during the initial landing phase. Body weight was measured in newtons and height was measured in meters. Sex comparisons were made and sex-specific regressions determined if thigh muscle strength (Nm/kg) predicted sagittal-plane landing energetics and stiffnesses. Women absorbed 69% more knee energy and had 36% less hip torsional stiffness than men. In women, greater knee extensor strength predicted greater knee energy absorption (R(2) = 0.11, P = .04), and greater knee flexor strength predicted greater hip torsional stiffness (R(2) = 0.12, P = .03). Sex-specific biomechanics during the deceleration phase of a drop jump revealed that women used a strategy to attempt to decrease system stiffness. Additionally, only female strength values were predictive of landing energetics and stiffnesses. These findings collectively demonstrated that the task may have been more difficult for women, resulting in a different movement strategy among those with different levels of thigh strength to safely complete the task. Future researchers should look at other predictive factors of observed sex differences.

Flexible end-effector based on flexible pneumatic actuator and its grasping model.

Taking into account the disadvantages of rigid grasping end-effectors for agricultural fruits,such as low complaisance and easy to hurt the grasping object,authors designed a type of flexible end-effector,which took three pneumatic flexible bending joints as its fingers and one flexible pneumatic torsion joint as its wrist.The mathematical models for fingers and wrist of the end-effector were presented.According to the shapes of grasping objects,the end-effector’s gripping model for grasping columniform objects and holding model for grasping spheroidal objects were analyzed in detail.Simulation and experiments were conducted to study the impact of weight and radius of the grasping object to the air pressure inside the end-effector.The results showed that the mathematical models can represent the essential characteristics of the end-effector.The flexible end-effector can be applied in agricultural fruits picking task.

Lamina Emergent Torsional (LET) Joint

Part of the challenge in designing compliant mechanisms is finding suitable joints that provide the needed motion and force–deflection characteristics. The Lamina Emergent Torsional (LET) Joint is presented as a compliant joint suited for applications where large angular rotation is desired, but high off-axis stiffness is not as critical. The joint is introduced and the equations necessary for determining the force–deflection characteristics are presented. Since the LET Joint can be fabricated from a single planar layer, it is well suited for macro and micro applications. Illustrative examples are provided with devices fabricated from materials as diverse as steel, polypropylene, and polycrystalline silicon.

A rare pentad of foot and ankle deformities in hyperlax children

The aim of this paper is to describe the clinical features and radiological appearance of a rare and complex lower leg and foot deformity in hyperlax children. Four children were included in the study; of these, two had bilateral feet involvement. All deformities were present since birth, comprising a pentad of conditions: (1) pathologic external tibia and fibula torsion, (2) ball and socket ankle joint with medial subluxation and talus medial subluxation, (3) excessive hindfoot valgus, (4) peroneal and Achilles tendon displacement anterior to the lateral malleolus and (5) generalized ligament laxity. All children had failed cast manipulation. Only two had undergone a minimal soft tissue procedure, but there had been no improvement. All patients were ambulatory and pain free at the mean age of 6.5 years. Conservative or minimal soft tissue procedures are not effective in restoring the anatomy of such feet.

Varus/Valgus and Internal/External Torsional Knee Joint Stiffness Differs between Sexes

Background Torsional joint stiffness is thought to play a role in the observed sex bias in noncontact anterior cruciate ligament injury rates. Hypothesis Women will exhibit lower torsional stiffness values of the knee in response to varus/valgus and internal/external rotations than will men. Study Design Controlled laboratory study. Methods Knee kinematics of 20 university students (10 men, 27.3 ± 3.4 years, 177.3 ± 6.8 cm, 81.1 ± 7.0 kg; 10 women, 22.9 ± 1.5 years, 169.0 ± 7.1 cm, 66.1 ±11.4 kg) were measured while 0 to 10 Nm of varus and valgus torques were applied with the subject nonweightbearing and while 0 to 5 N.m of internal and external torques were applied with the subject nonweightbearing and weightbearing with the use of a custom joint testing device. Joint stiffness values were calculated at 1-N.m increments. Results When low magnitudes of torque were applied to the knee, women had significantly lower stiffness values than did men-With the exception of applied external torque with the joint weightbearing and varus torque with the joint nonweightbearing, women demonstrated an increase in joint stiffness as the magnitude of torque increased from lower to higher magnitudes. In contrast, for the men, joint stiffness values remained unchanged as the magnitude of applied torque increased. Conclusion Women exhibited lower knee stiffness in response to low magnitudes of applied torque compared to men and demonstrated an increase of joint stiffness as the magnitude of applied torque increased. Clinical Relevance The decreased stiffness behavior of the knee in response to low torques that was observed for women may have a role in detrimentally affecting knee biomechanics and resulting neuromuscular function, particularly when an individual transitions from nonweightbearing to weightbearing.

Differences in Torsional Joint Stiffness of the Knee between Genders

Background In many sports, female athletes have a higher incidence of anterior cruciate ligament injury than do male athletes. Among many risk factors, the lower rotatory joint stiffness of female knees has been suggested for the increased rate of anterior cruciate ligament injuries. Hypothesis In response to combined rotatory loads, female knees have significantly lower torsional joint stiffness and higher rotatory joint laxity than do male knees at low flexion angles, despite the fact that no such gender differences would be found in response to an anterior tibial load. Study Design Comparative laboratory study. Methods Joint kinematics of 82 human cadaveric knees (38 female, 44 male) in response to (1) combined rotatory loads of 10 N·m valgus and ±5 N·m internal tibial torques and (2) a 134-N anterior-posterior tibial load were measured using a robotic/universal force-moment sensor testing system. Results In response to combined rotatory loads, female knees had as much as 25% lower torsional joint stiffness (female: 0.79 N·m/deg; 95% confidence interval, 0.67-0.91; male: 1.06 N·m/deg; 95% confidence interval, 0.95-1.17) and up to 35% higher rotatory joint laxity (female: 26.2°; 95% confidence interval, 24.5°-27.9°; male: 20.5°; 95% confidence interval, 18.8°-22.2°) than did male knees (P < .05), whereas there were no gender differences in response to the anterior tibial load (P > .05). Conclusion Female knees had lower torsional joint stiffness and higher rotatory joint laxity than did male knees in response to combined rotatory loads. Clinical Relevance Larger axial rotations of female knees in response to rotatory loads may affect the distribution of forces in soft tissues and the function of muscles that provide knee stability. Control algorithms used during the biomechanical testing of cadaveric knees and computational knee models might need to be gender specific.

Yield Behaviour of Rubber-Modified Epoxy Adhesives under Multiaxial Stress Conditions: Effect of Plastic Deformability of the Matrix Phase

In a previous study, the yield stress in the adhesive layer of scarf and torsional butt joints with a rubber-modified adhesive was measured, and the results agreed with those calculated by a finite element method, where Gurson's constitutive equations were applied to the adhesive layer. In this study, to investigate the effect of plastic deformability of the matrix phase on the yielding behaviour of rubber-modified epoxy adhesives, the yield behaviour was investigated by using scarf and torsional butt joints, where a reactive diluent was used to vary the plastic deformability of the matrix phase. The applicability of Gurson's model was examined in terms of the yield stresses calculated by a finite element method with a variety of the model parameters. As a result, it is confirmed that the yield stresses of the rubber-modified adhesives with different matrix phases can be approximately estimated by Gurson's model, and the model parameter's agreement with the experimental data increases with increasing the plastic deformability of the matrix phase.