This paper describes an experimental investigation under laboratory controlled test conditions on a pair of worm gears in which simulative wear modes were intentionally allowed to occur. Moisture ...corrosion wear, acid attacked corrosion wear, hard contaminant-related three body abrasive wear and normal adhesive wear as a base line for comparison purpose were investigated. A brass worm and steel worm gear pair test rig was used throughout the test series. The test samples of wear particles were collected and assessed through the observation of an optical micrograph in order to correlate and compare the wear particle characteristics to each specific simulative wear mode of the worn worm gear pairs. In addition, weight losses from all tested worm gear pairs were assessed with utilization of full factorial statistical experimental design in a laboratory controlled test condition. Several interesting issues accrued, these included main and interaction effect of independent wear variables on weight losses, typical worn surface pattern analysis and wear particle morphological analysis. It can be deduced from the experimental results statistically and physically that weight losses and wear particles from worm gear pair tribosystem characteristics exhibited a direct relationship with different simulative wear modes. In addition, it should also be possible to detect and diagnose grease lubricated worm gear wear utilization from wear particle analysis when condition monitoring grease lubricated worm gear sets.
•Design of experiments were employed to analyze wear variables on the worm gear weight losses.•Microscopic analysis of worn surfaces and wear particles are presented.•The grease-lubricated worm gear wear modes correlate with the wear products’ characteristics.
Polyamide 66 is widely used for sliding parts, such as resin worm gear. Glass fibers are usually added to increase its strength. In this study, the tribological behavior of glass fiber ...reinforced-polyamide 66 composite in contact with carbon steel under high contact pressure, sliding, and grease lubricated conditions is studied. Measurement of mechanical properties and SEM observations of composite sliding surfaces after different sliding cycle numbers indicate that sliding induces characteristic damage of the surface (peeled off fibers and scratching of polyamide) and a degradation in mechanical properties. These lead to an increase in friction and creep of the composite. The wear effect increases with the increase in sliding cycles, and the initial orientation of the fibers in the composite sliding surface has significant effects on the wear of the steel counterpart. The contribution of each phenomenon to the tribological behavior is discussed. The damage to the composite surface and the increase in contact temperature due to sliding have great effects on the tribological properties compared to the presence of wear debris in grease and wear on the steel. The effects of the hardness of the steel on the tribological properties are investigated, and it is found that wear of the composite is reduced by using softer steels.
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•The tribological behavior of glass fiber reinforced PA66 in contact with steel under grease lubrication is studied.•Sliding induces damage of the surface, leading to an increase in wear and creep of the composite and friction.•The initial orientation of the fibers in the composite sliding surface has significant effects on the wear of the steel.•The damage to the composite surface and the increase in the temperature have great effects on the tribological properties.•Wear of the composite is reduced by using softer steels by the relation between the hardness of fibers and steel.
Aiming at the problem that the basic impedance control has great impact force and is difficult to cope with environmental changes when it contacts with the tooth surface of worm gear, an adaptive ...impedance control method based on genetic algorithm was proposed. The influence law of spindle speed, feed speed and grinding force on the surface quality of worm gear tooth surface is analyzed. With material removal rate as the optimization objective, an optimization model of grinding process parameters is established based on particle swarm optimization algorithm, and the optimal grinding process parameters for industrial robot grinding worm gear tooth surface knife marks are obtained: Spindle speed (n=3087.82r/min), Feed speed (vf=0.51mm/s), Normal grinding force (F=19.9N). The experimental results show that the roughness of worm gear tooth surface is increased from 0.941 to 0.719 by using the optimized grinding process parameters. Moreover, this method can effectively suppress the external force influence of industrial robots in the process from free space to constrained space, and the force fluctuation is significantly reduced after contact stabilization, and it has stronger environmental adaptability and force control performance.
Abstract
Based on the analysis of current office work status and office robots, this paper proposes a design scheme of intelligent mechanical gripper which can transfer data and move objects ...independently to assist daily office work. It is proposed to design mechanical structure, including mechanism motion design and part structure design, and to use Autodesk Inventor to design and simulate mechanical parts and components. Dimensional and strength checks are carried out on key components, and stress analysis is simulated by using stress analysis module included in Autodesk Inventor. Finally, the mechanical structure design scheme and control system design scheme for the mechanical gripper are proposed. The overall design mainly centers on the functions expected to be completed, and innovates different organizations in combination to achieve the intended objective.
•All in one system work was introduced for accuracy improvement of the double flank worm gear pair rolling tester (DFWGT).•Results were given for system calibration, positioning error compensation, ...sensitivity coefficients and expanded uncertainty for DFWGT.•The uncertainty was optimized based on the uncertainty budget for DFWGT.
To improve the measurement accuracy of the double flank worm gear pair rolling tester, the grating system is calibrated by laser interferometer and then compensation model using polynomial function is established, uncertainty budget is carried out based on the sensitivity test and error sources analysis, and some factors are adjusted to lower the measurement uncertainty. After compensation, the positioning error of worm gear moving slider, worm slider and worm gear measuring slider is reduced from 1.80 μm to 0.20 μm, 20.00 μm to 0.50 μm, and from 0.70 μm to 0.05 μm respectively. Related sensitivity coefficients for measurement results total radial composite deviation Fid, tooth-to-tooth radial composite deviation fid,andrunoutFr are within 0.01 to 0.04. According to GUM, three parts are considered in uncertainty evaluation including standard uncertainty of base unit, standard uncertainty of data acquisition & software system and standard uncertainty of measurement condition. After the optimization of the main error sources, the expanded uncertainty for measurement results Fid, fid,Fr is reduced from 5.4 μm, 4.6 μm and 2.5 μm to 2.6 μm, 2.1 μm and 1.5 μm respectively. The experimental results show that, the accuracy improvement method for double flank worm gear pair rolling tester can reduce measurement uncertainty, and the whole work can be a certain reference for the accuracy improvement of precision instruments.
This paper presents the design of a symmetric variable stiffness joint that employs worm gear and sliding helical transmissions to adjust the effective length of the leaf springs. Firstly, the design ...concept and working principle of the variable stiffness joint are presented, along with two different assembly methods. Secondly, the stiffness equations and characteristics of the variable stiffness joint are then derived and analyzed. Next, the dynamics of the variable stiffness joint are modeled and simulated visually using Simulink. Finally, a prototype of the variable stiffness joint is constructed and its stiffness characteristics are experimentally verified. The experimental results demonstrate that both assembly methods are capable of adjusting the stiffness and position of the joint within a certain range. This study contributes to the understanding and development of symmetric variable stiffness joints by presenting a comprehensive design, analysis, simulation, and experimental evaluation. The proposed joint has potential applications in various fields that require adaptability, adjustability, and safety.
•The memorizing characteristic of thermal errors is revealed.•The mapping between machining error and positioning error is established.•The machining error is reduced significantly with error ...compensation.•The self-recurrent wavelet neural network is applicable to error modeling.•The predictive ability is better than that of previous studies.
To increase the machining accuracy of worm gear machines, the thermal error compensation was carried out from the view of X-axis's error mechanism of worm gear machines. The spatial motion error of the worm hob caused by X-axis's positioning error is derived, and then the necessity for the reduction of the positioning error is proved. The memory behaviors of the thermal error are revealed, and finally, the applicability of self-recurrent wavelet (SRW) neural networks to the error modeling is demonstrated. Then the genetic algorithm (GA) is used to optimize the number of neurons in the wavelet and product layers and weights of SRW neural networks, and the error models are established with the GA-SRW, SRW, and back propagation (BP) neural networks. The results show that the predictive performance of the error models based on GA-SRW, SRW, and BP neural networks decreases in turn. Moreover, the precision improvement ratios for the average normal error of tooth surfaces of the GA-SRW neural network error model are more than 21.8% and 43.7% compared to the SRW and BP neural networks error models, respectively. Besides, the predictive performance of the GA-SRW neural network model is better than that of the regression models.
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This paper presents the fundamentals of the design and applications of new worm gear drive solutions, which enable the minimisation of backlash and are characterised by higher kinematic accuracy. ...Different types of worm surfaces are briefly outlined. Technological problems concerning the principles of achieving a high degree of precision in machining are also described. Special attention is paid to the shaping of conical helical surfaces. Increasing the manufacturing precision of drive components allows one to achieve both lower backlash values and lower levels of its dispersion. However, this does not ensure that backlash can be eliminated, with its value being kept low during longer periods of operation. This is important in positioning systems and during recurrent operations. Various design solutions for drives in which it is possible to reduce backlash are presented. Results of experiments of a worm gear drive with a worm axially adaptive only locally, in its central section, are presented. In this solution, it is possible to reduce backlash by introducing adjustment settings without disassembling the drive. An important scientific problem concerned defining the principles of achieving a compromise between the effectiveness of reducing backlash and the required load capacity of the drive. In this paper it has been shown that in worm gear drives with a locally axially adaptive worm, as well as with a worm wheel with a deformable rim, it is possible to achieve significant reduction of backlash. In high precision drives-for example, those with an average backlash value of <15 micrometers-this can enable more than a two-fold reduction of the average backlash value and more than a three-fold decrease of the standard deviation of local backlash values.
This study examined the geometric interference of cylindrical worm gear drives using an oversized hob to cut the worm gear. The instantaneous line contact of a fully conjugated gear set becomes an ...instantaneous point contact when an oversized hob is used. In this type of worm gear drive, however, an edge contact can occur between the worm and worm gear. The edge contact is caused by geometric interference, and it occurs regardless of the presence of elastic deformation, misalignment, and transmission error. Aspects of the interference are presented through graphical illustrations. For examining the interference based on the differential geometry, two methods are proposed. The first method is for determining the surface separation topology between the tooth surfaces of a worm and a worm gear for an entire meshing cycle, and the second method for determining the boundary of the initially occurring area of interference when the hob oversize changes from zero to a nonzero value. By using the presented methods, the influence of various design parameters, such as the lead angle of the worm, the oversize of the hob, and the normal pressure angle, on the interference are examined and discussed through numerical examples.
•We introduced geometric interference in cylindrical worm gear drives.•Examination of the interference by using surface separation topology is presented.•Examination of the boundary of the initially occurring area of interference is presented.•Characteristics of the interference were investigated through numerical examples.•The involute and Klingelnberg types of worm gear drives are chosen for the illustration.
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