Joint Clearance Research Articles

Dynamic Analysis of a Delta Parallel Robot with Flexible Links and Joint Clearances

Delta robot is a lightweight parallel manipulator capable of accurately moving heavy loads at high speed and acceleration along a spatial trajectory. This intensive dynamic process may have a significant impact on the end-effector trajectory precision and motor behavior. The paper highlights the influence on the dynamic behavior of a Delta robot by considering individual and combined effects of clearances and friction in the spherical joints, as well as the flexibility of the rod elements. The CAD modeling of the Delta robot and its motion simulation on a representative spatial trajectory where the maximum allowed values of speed and acceleration are reached were performed using the Catia and Adams software packages. The obtained results show that the methods used were successfully applied and the effects are mutually interconnected, but not cumulative.

Dynamic response and nonlinear characteristics of multi-link mechanism with clearance joints

Dynamic response and nonlinear characteristics of multi-link mechanism with clearance joints

Fabrication of precise non‐assembly mechanisms by multi‐material fused layer modeling and subsequent heat treatment

AbstractAdditive manufacturing techniques offer several potentials for future design and production. One of these potentials is non‐assembly mechanisms, movable mechanisms which need no assembly after production. Especially non‐assembly mechanisms consisting of kinematic pairs face major tolerance issues. This work advances into the new field of non‐assembly mechanisms consisting of kinematic pairs from multi‐materials. The research described in this article shows how tolerance issues can be overcome by the deliberate use of intrinsic and printing‐induced shrinkage processes. Therefore, non‐assembly mechanisms produced by multi‐material printing using fused layer modeling (FLM) are heat‐treated after the printing process to reduce and adjust the joint clearance. It was found that PLA was a suitable material for this process due to its relaxation and recrystallisation behavior during heat treatment. The printing techniques and relevant shrinkage mechanisms were analyzed and explained. Furthermore, it was found that relaxation of orientations and recrystallization could be separated in two different heat treatment steps creating a possibility for “induced self‐healing.” In addition, tribological aspects of such mechanisms will be discussed.

Tolerance analysis by static analogy on 2D assemblies with fits and fasteners

In tolerance analysis, the effect of clearance fits is especially difficult to estimate because the mating parts are not necessarily in actual contact and can take an infinite number of relative positions. The treatment of these situations is allowed in most of the available methods, possibly introducing additional elements in the dimension chains with appropriate statistical assumptions. The paper provides a similar extension for the static analogy, a previously proposed method that converts the tolerance analysis problem into an equivalent problem of force analysis. The procedure represents each fit, possibly between patterns of features (e.g., fasteners and holes), with a proper constraint in the equivalent static model. The ability of the constraint to transmit forces and torques is determined according to the types and directions of misalignments allowed by the joint clearance. With simple rules, this avoids complications in the static model, which must include only the constraint between parts rather than the geometric details of the mating features. The extended method, currently limited to 2D dimension chains, is demonstrated on examples involving both dimensional and geometric tolerances. The comparison with existing methods shows the correctness of the proposed procedure. The simplicity of the workflow confirms the possibility, already demonstrated for the static analogy, of avoiding numerical simulations or even the use of computer-based tools.

The discretization method and multi-contact force model on 3D cylindrical clearance joint for multibody dynamics of spatial mechanical system

The discretization method and multi-contact force model on 3D cylindrical clearance joint for multibody dynamics of spatial mechanical system

Targeting Synovial Lymphatic Function as a Novel Therapeutic Intervention for Age-Related Osteoarthritis in Mice.

The synovial lymphatic system (SLS) removes catabolic factors from the joint. Vascular endothelial growth factor C (VEGF-C) and its receptor, VEGFR-3, are crucial for lymphangiogenesis. However, their involvement in age-related osteoarthritis (OA) is unknown. This study was undertaken to determine whether the SLS and the VEGF-C/VEGFR-3 pathway contribute to the development and progression of age-related OA, using a murine model of naturally occurring joint disease. SLS function was assessed in the knees of young (3-month-old) and aged (19-24-month-old) male and female C57BL/6J mice via a newly established in vivo IVIS-dextran imaging approach, which, in addition to histology, was used to assess the effects of VEGF-C treatment on SLS function and OA pathology in aged mice. RNA-sequencing of synovial tissue was performed to explore molecular mechanisms of the disease in the mouse knee joints. Results showed that aged mice had impaired SLS function, including decreases in joint clearance (mean T1/2 of signal intensity clearance, 2.8 hours in aged mice versus 0.5 hours in young mice; P < 0.0001), synovial influx (mean ± SD 1.7 ± 0.8% in aged mice versus 4.1 ± 1.9% in young mice; P=0.0004), and lymph node draining capacity (mean ± SD epifluorescence total radiant intensity ([photons/second]/[μW/cm2 ]) 1.4 ± 0.8 in aged mice versus 3.7 ± 1.2 in young mice; P < 0.0001). RNA-sequencing of the synovial tissue showed that Vegf-c and Vegfr3 signaling genes were decreased in the synovium of aged mice. VEGF-C treatment resulted in improvements in SLS function in aged mice, including increased percentage of signal intensity joint clearance (mean ± SD 63 ± 9% in VEGF-C-treated aged mice versus 52 ± 15% in vehicle-treated aged mice; P=0.012), increased total articular cartilage cross-sectional area (mean ± SD 0.38 ± 0.07 mm2 in VEGF-C-treated aged mice versus 0.26 ± 0.07 mm2 in vehicle-treated aged mice; P < 0.0001), and decreased percentage of matrix metallopeptidase 13-positive staining area within total synovial area in 22-month-old VEGF-C-treated mice versus 22-month-old vehicle-treated mice (mean ± SD decrease 7 ± 2% versus 4 ± 1%; P=0.0004). SLS function is reduced in the knee joints of aged mice due to decreased VEGF-C/VEGFR-3 signaling. VEGF-C treatment attenuates OA joint damage and improves synovial lymphatic drainage in aged mice. The SLS and VEGF-C/VEGFR-3 signaling represent novel physiopathologic mechanisms that could potentially be used as therapeutic targets for age-related OA.

Synthesis of clearance for a kinematic pair to prevent an overconstrained linkage from becoming stuck

Abstract. Mechanisms are prone to stuttering or even jamming due to the deformation of components, especially for overconstrained linkages for which geometric conditions must be strictly satisfied. In this paper, joint clearance is actively introduced to release the local constraint so that the linkages can still achieve general movement under the deformation of components. And a joint clearance model with a revolute joint (R-joint) is built. Based on the model, the minimum joint clearance introduced, which keeps mechanisms moving smoothly, is found when the components of the linkages have a certain deformation. The correctness of the proposed method is verified with a numerical case, and the optimal position for clearance introducing is analyzed. It opens up an important way to solve the phenomenon of stuttering or jamming in overconstrained linkages.

Dynamic Analysis of Bidirectional Solar Arrays with Flexible Panels and Clearance Joints

The dynamic characteristics of a two-step deployable bidirectional solar array system with flexible panels and clearance joints are studied in this paper. Driving mechanisms, closed cable loop configurations, and latch mechanisms are considered in this system where normal contact force is established using a nonlinear spring damping model and the friction effect is determined by a modified Coulomb friction model. With the simulation strategy of activating different constraint states and applying latch torques, the multiple deployment and locking processes of the system are implemented. The results indicate that the second locking causes obvious vibration on the dynamic responses of the yoke and main panels and leads to a complex bidirectional vibration of the main panel connected to the side clearance joints. The equivalent suspension damping property produced by the coupling of the flexibility and clearances can reduce the vibration of the deployable components. Moreover, the attitude and orbital motion results reveal the effect of different deployment methods of the system on the spacecraft attitude. Finally, the trajectories of journal centers and contact forces are analyzed to indicate the foundation of the dynamic behavior of the system.

Modeling and dynamics characteristics analysis of six-bar rocking feeding mechanism with lubricated clearance joint

Modeling and dynamics characteristics analysis of six-bar rocking feeding mechanism with lubricated clearance joint

Dynamic characteristics and reliability analysis of parallel mechanism with clearance joints and parameter uncertainties

Dynamic characteristics and reliability analysis of parallel mechanism with clearance joints and parameter uncertainties

Optimal rigid-flexible dynamic of space slider-crank mechanism with clearance joints

Optimal rigid-flexible dynamic of space slider-crank mechanism with clearance joints

Error modelling and motion reliability analysis of a multi-DOF redundant parallel mechanism with hybrid uncertainties

Accuracy is one of the most important properties of mechanisms. However, the inherent uncertainties will cause an error between the actual motion and the desired motion, leading to a motion reliability problem. The error model and motion reliability of a type of multi-DOF (degrees of freedom) redundant parallel mechanism (MDRPM) with hybrid uncertainties are studied. Firstly, the error model of the mechanism is established and verified. Then, the motion inside the joints is analyzed, and the joint clearance is regarded as an interval variable, while the other variables are treated as random variables. On this basis, a hybrid motion reliability method based on the quasi-Monte Carlo simulation method (QMCSM) is developed for a mechanism with hybrid uncertainties. Compared with the traditional simulation method, the amount of computation required by the QMCSM is significantly reduced, and it is more suitable for solving the large-scale motion reliability problem of the MDRPM. A numerical simulation and experiments are performed. The simulation results show that the feasibility and adaptability of the motion reliability method in this paper are different. The experimental results demonstrate that the error model is effective, so the motion reliability analysis based on the error model is reliable.

Dynamic analysis for mechanical system with clearance joint considering dependent interval parameters

Uncertainties caused by measuring errors or incomplete knowledge affect the dynamic response and functional reliability of the mechanical system, particularly for the mechanisms with clearance joints. Considering that dependency between the interval parameters in the uncertain quantification of mechanical systems with clearance joints is prone to be ignored, in this article, a dynamic analysis procedure considering the correlation between interval parameters is presented. Firstly, the continuous contact force model and modified friction force model are embedded into the deterministic dynamic governing equations of the mechanical system with clearance joints derived by the Lagrangian method. To characterize the correlation between interval uncertainties, the convex ellipsoid model is employed, and a Chebyshev-based convex scanning method is developed to obtain the bounds of dynamic response. Finally, a robot manipulator with clearance joint considering dependent uncertainties is illustrated as an example to investigate the clearance effect and correlations between uncertainties on the dynamic behavior. In the numerical simulation, the geometrical parameters of the manipulator arm are regarded as dependent interval parameters. The results show that the dependence between interval uncertainties induces relatively conservative bounds and should be considered carefully in the case of a large clearance size existing in the mechanical system.

Robotic-assisted surgery training (RAST) program: module 1 of a three-module program. Assessment of patient cart docking skills and educational environment.

There is currently no standardized robotic surgery training program in General Surgery Residency. RAST involves three modules: ergonomics, psychomotor, and procedural. This study aimed to report the results of module 1, which assessed the responsiveness of 27 PGY (postgraduate year) 1-5 general surgery residents (GSRs) to simulated patient cart docking, and to evaluate the residents' perception of the educational environment from 2021 to 2022. GSRs prepared with pre-training educational video and multiple-choice questions test (MCQs). Faculty provided one-on-one resident hands-on training and testing. Nine proficiency criteria (deploy cart; boom control; driving cart; docking camera port; targeting anatomy; flex joints; clearance joints; port nozzles; emergency undocking) were assessed with five-point Likert scale. A validated 50-item Dundee Ready Educational Environment Measure (DREEM) inventory was used by GSRs to assess the educational environment. Mean MCQ scores: (90.6 ± 16.1 PGY1), (80.2 ± 18.1PGY2), (91.7 ± 16.5 PGY3) and (PGY4, 86.8 ± 18.1 PGY5) (ANOVA test; p = 0.885). Hands-on docking time decreased at testing when compared to base line: median 17.5 (range 15-20) min vs. 9.5 (range 8-11). Mean hands-on testing score was 4.75 ± 0.29 PGY1; 5.0 ± 0 PGY2 and PGY3, 4.78 ± 0.13 PGY4, and 4.93 ± 0.1 PGY5 (ANOVA test; p = 0.095). No correlation was found between pre-course MCQ score and hands-on training score (Pearson correlation coefficient = -0.359; p = 0.066). There was no difference in the hands-on scores stratified by PGY. The overall DREEM score was 167.1 ± 16.9 with CAC = 0.908 (excellent internal consistency). Patient cart training impacted the responsiveness of GSRs with 54% docking time reduction and no differences in hands-on testing scores among PGYs with a highly positive perception.

Dynamic analysis and wear calculation of space deployable mechanism considering spherical joints with clearance and coating

In the space deployable mechanism considering spherical joints with clearance, the kinematic stability and working life of will be seriously affected. To address this problem, this paper proposes a nonlinear stiffness coefficient expression and an improved viscous damping coefficient expression considering the wear reduction properties of coatings, so as to obtain a conformal contact force model based on the analysis and comparison of the existing common normal contact force models. The new contact force model is qualitatively analyzed from three aspects, namely clearance size, recovery coefficient, and material properties, so as to demonstrate the correctness and applicability of the model. In the prefabricated space deployable mechanism (RSSP) with spherical joint clearance, the acceleration variation of the actuator is analyzed and compared by using the new contact force model, and the wear quantity of the spherical joints with clearance and coating is predicted. The dynamic results show that spherical joints with clearance have a significant effect on the acceleration of the actuator, and the long working time will inevitably lead to increased vibration and reduce the motion accuracy and life of the mechanism. By comparing with the calculation results of wear, it is found that the wear of spherical joint clearance with coating decreases significantly in all vector directions, and the wear area of the Euler Angle increases slightly compared with that without coating because of the increase of contact collision frequency. Therefore, the wear calculation method and coating strategy proposed in our work can provide a theoretical basis for improving the kinematic accuracy and working life of space deployable mechanism system considering spherical joints with clearance.

Sustained intra-cartilage delivery of interleukin-1 receptor antagonist using cationic peptide and protein-based carriers

Blocking the interleukin-1 (IL-1) catabolic cascade following joint trauma can be achieved using its receptor antagonist, IL-1Ra. However, its clinical translation for osteoarthritis therapy has been unsuccessful due to its rapid joint clearance and lack of targeting and penetration into deep cartilage layers at therapeutic concentrations. Here, we target the high negative charge of cartilage aggrecan-glycosaminoglycans (GAGs) by attaching cationic carriers to IL-1Ra. IL-1Ra was conjugated to the cartilage targeting glycoprotein, Avidin, and a short length optimally charged cationic peptide carrier (CPC+14). It is hypothesized that electro-diffusive transport and binding properties of IL-1Ra-Avidin and IL-1Ra-CPC+14 will create intra-cartilage depots of IL-1Ra, resulting in long-term suppression of IL-1 catabolism with only a single administration. IL-1Ra was conjugated to Avidin or CPC+14 using site specific maleimide linkers, and confirmed using gel electrophoresis, high-performance liquid chromatography (HPLC), and mass spectrometry. Intra-cartilage transport and retention of conjugates was compared with native IL-1Ra. Attenuation of IL-1 catabolic signaling with one-time dose of IL-1Ra-CPC+14 and IL-1Ra-Avidin was assessed over 16 days using IL-1α challenged bovine cartilage and compared with unmodified IL-1Ra. Positively charged IL-1Ra penetrated through the full-thickness of cartilage, creating a drug depot. A single dose of unmodified IL-1Ra was not sufficient to attenuate IL-1-induced cartilage deterioration over 16 days. However, when delivered using Avidin, and to a greater extent CPC+14, IL-1Ra significantly suppressed cytokine induced GAG loss and nitrite release while improving cell metabolism and viability. Charge-based cartilage targeting drug delivery systems hold promise as they can enable long-term therapeutic benefit with only a single dose.

A practical method for the deformation of long‐stroke hydraulic manipulators in grasping‐handling tasks

AbstractLong‐stroke hydraulic manipulators are utilized in various grasping‐handling tasks, and the flexible deformation of these manipulators is the primary obstacle that affects precise position control of the end‐effectors in Cartesian space. This deformation is manifested in the following three aspects: joint deformation, structural deformation and clearance variation. Due to deformation uncertainty, methods that model the hydraulic manipulator as a combination of flexible multibody systems and hydraulic actuators are unsuitable. In this article, we propose an incremental inverse kinematics model (IIKM) as a new approach to solving the above deformation difficulties. The projection method is used to obtain the inverse kinematic analytical solution of long‐stroke hydraulic manipulators, which is based on the manipulator deformation in the current configuration (current configuration refers to the arrangement of the manipulator links when the manipulator starts to move to the target position). The proposed method avoids complex flexible multibody modeling and parameter identification, allowing long‐stroke hydraulic manipulators to be accurately controlled within a certain neighborhood. An evaluation coefficient is proposed to analyze the calculation accuracy of the IIKM in combination with the success rate obtained from 190 grasping experiments. Through these experiments, we determine the optimal calculation height range of the IIKM in the vertical direction and the optimal calculation position area in the horizontal direction and prove that the IIKM result can guarantee the success of grasping‐handling tasks when the end‐effector is within the optimal calculation height range.

Posture and Dynamics Analysis of Hydraulic Support with Joint Clearance under Impact Load

A hydraulic support is one of the key pieces of equipment in a fully mechanized coal-mining face. The shaft is seriously worn due to repeated support shifting in coal-mining operations, and the hydraulic support bears a large amount of impact load in the support process, leading to a threat to its dynamic stability. In order to study the impact load on the posture and dynamics of a hydraulic support, and considering the joint clearance of the hydraulic-support hinge point, based on the dynamics software Adams, the equivalent variable-stiffness damping system is used to replace the column, and the impact analysis model of the hydraulic support with joint clearance is established. The roof pressure is vertically applied to the load balance area of the top beam by static load, and the impact load is vertically applied to the top beam downward. Based on the above model, considering the different distributions of joint clearance, research about the influence of joint clearance on the posture and dynamic characteristics of the hydraulic support is carried out. The results show that when there is joint clearance on both sides of the hydraulic support, when the top beam bears the impact load, the X-axis PMR (position movement ratio) at different positions of the top beam is more than 80%, and the forward-tilt posture is obvious. When the hydraulic support has only unilateral clearance, the front end of the top beam bears the impact load, and the front end of the top beam moves laterally, while the rear end of the top beam mainly moves longitudinally. When the end of the top beam bears the impact load, the vertical PMR of the top beam is less than 1%. When the impact load acts on the side with joint clearance, the top beam has a certain degree of lateral offset, and the offset directions on both sides of the top beam are inconsistent. At this time, the top beam presents a torsional-bearing posture. When the front end of the top beam is loaded, the mechanical curve of each hinge point is higher than the rear-end load. For the hinge point on the side without clearance, the maximum load-fluctuation coefficient reaches 1.04, while for the hinge point on the side with clearance, the minimum load is 0 kN, which will mean some hinge points cannot to play a supporting role. The analysis results will be helpful to research hydraulic supports considering joint clearance.

Reliability modeling for dependent competing failure processes based on planar mechanism

Considering the influence of external random shock on the kinematic accuracy of mechanism, a new reliability model of dependent competing failure processes (DCFP) is proposed in this paper. The kinematic accuracy of the mechanism is limited by the original errors such as the dimension error and joint clearance error, and it is also affected by aging and wear-out during service life, thus eventually leading to functional failure. Meanwhile, according to the magnitude of the external random shock, the random shock has different effects on the degradation process of the mechanism. In this study, a DCFP model with accuracy degradation process and multi-type mixed shock is considered. The time-dependent kinematic accuracy reliability model of the planar mechanism is established based on the Gamma degradation theory, effective length model, mechanism kinematic error theory and the fourth moment technique. Moreover, the magnitude of random shock is divided into different regions when the extreme shock, cumulative shock, and δ-shock on mechanism reliability are considered. Finally, a numerical example of the pantograph mechanism is conducted to demonstrate the feasibility and effectiveness of the proposed model. The results show that the kinematic accuracy reliability of the pantograph mechanism reduces with the increasing of wearing capacity and external shocks. According to sensitivity analysis, an effective way to improve the reliability of the planar mechanism is to optimize its strength of the mechanism. The proposed method can be used to evaluate the reliability of planar mechanisms with dependent competing failure modes.

Dynamics Analysis of the Double Push Rod Limb-Leg Mechanism with Clearance Joint

Dynamics Analysis of the Double Push Rod Limb-Leg Mechanism with Clearance Joint