Influence of controller parameters on the life of ball screw feed drives

The ball screws are the machine component most frequently used for transforming rotational into linear motion of a feed drive, to position the machine tool components carrying the cutting tool to the desired location. A failure of the ball screw usually leads to a total breakdown of the axis; therefore, the attainable life of this component is an important issue concerning the availability and productivity of modern machine tools. This article presents an approach to evaluate the influence of control parameters on the fatigue life of ball screws based on simulation, by means of a numerical model of a machine tool servo-axis. Ball screw life was evaluated with different conditions, varying the position loop main proportional gain and the kinematic limit conditions for trajectory generation. Furthermore, the mathematical model was used to evaluate optimal control gain and trajectory conditions for a machine tool based on the achievable life span of the ball screw feed drive system, with regard to the desirable performances, such as position accuracy, promptness, and cutoff frequency

A methodology for analyzing radial ball bearing vibrations

This paper presents the development of a methodology for calculating radial ball bearing vibrations. First, analytical and numerical models were developed and then, the obtained results were experimentally verified. In the experiment, a test rig for a dynamic testing of bearings subjected to an external load was used. Special attention was paid to the analysis of the total bearing deformations and stiffness, being the main parameters that define the dynamic behaviour of a bearing. In order to determine total deformations of a ball bearing as an assembly, a finite element model of the bearing was developed. The results obtained from the new methodology for a particular ball bearing type have been verified by experimental results. The obtained correlations of the experimental and the numerical results are about 2.5%. Based on the calculations and the experimental testing of the chosen ball bearing type, under conditions of a variable radial load, the analysis of the influence of the radial load on the dynamic behaviour of a ball bearing was performed. The analysis of the obtained results showed that the vibration amplitude increases with a similar multiple factor as loads increase

A Methodology for Analyzing Radial Ball Bearing Vibrations

This paper presents the development of a methodology for calculating radial ball bearing vibrations. First, analytical and numerical models were developed and then, the obtained results were experimentally verified. In the experiment, a test rig for a dynamic testing of bearings subjected to an external load was used. Special attention was paid to the analysis of the total bearing deformations and stiffness, being the main parameters that define the dynamic behaviour of a bearing. In order to determine total deformations of a ball bearing as an assembly, a finite element model of the bearing was developed. The results obtained from the new methodology for a particular ball bearing type have been verified by experimental results. The obtained correlations of the experimental and the numerical results are about 2.5%. Based on the calculations and the experimental testing of the chosen ball bearing type, under conditions of a variable radial load, the analysis of the influence of the radial load on the dynamic behaviour of a ball bearing was performed. The analysis of the obtained results showed that the vibration amplitude increases with a similar multiple factor as loads increase

DEVELOPMENT OF A NOVEL Z-AXIS PRECISION POSITIONING STAGE WITH MILLIMETER TRAVEL RANGE BASED ON A LINEAR PIEZOELECTRIC MOTOR

Piezoelectric-based positioners are incorporated into stereotaxic devices for microsurgery, scanning tunneling microscopes for the manipulation of atomic and molecular-scale structures, nanomanipulator systems for cell microinjection and machine tools for semiconductor-based manufacturing. Although several precision positioning systems have been developed for planar motion, most are not suitable to provide long travel range with large load capacity in vertical axis because of their weights, size, design and embedded actuators. This thesis develops a novel positioner which is being developed specifically for vertical axis motion based on a piezoworm arrangement in flexure frames. An improved estimation of the stiffness for Normally Clamped (NC) clamp is presented. Analytical calculations and finite element analysis are used to optimize the design of the lifting platform as well as the piezoworm actuator to provide maximum thrust force while maintaining a compact size. To make a stage frame more compact, the actuator is integrated into the stage body. The complementary clamps and the amplified piezoelectric actuators based extenders are designed such that no power is needed to maintain a fixed vertical position, holding the payload against the force of gravity. The design is extended to a piezoworm stage prototype and validated through several tests. Experiments on the prototype stage show that it is capable of a speed of 5.4 mm/s, a force capacity of 8 N and can travel over 16 mm

Integrated Power/Attitude Control System (IPACS) study. Volume 2: Conceptual designs

For abstract, see N74-22706

Versatile mass excited impact oscillator

Open Access via Springer Compact Agreement. Contributions of the technicians at the University of Aberdeen to the development of this experimental rig is gratefully acknowledged by the authors: in particular, Edward Stephen for creating the LabVIEW program controlling the excitation force parameter and recording the experimental data, Raymond Stephen for the electrical equipment provided, and the mechanical workshop for the improvements in the rig. The authors also acknowledge the support from and Chinese Scholarship Council (CSC Grant Number 11502161). A part of this project was funded by Coordenação de Aperfeiçoamento do Pessoal de Nível Superior (CAPES) under the Grant Number 88881.189487/2018-01.Peer reviewedPublisher PD

Effects of principal stress rotation and drainage on the resilient stiffness of railway foundations

Railway foundations play an integral role in controlling the stability of the overlying track structure and the maintenance of the overall track geometry. Premature failures of railway track foundation are likely to result in frequent maintenance, which may entail significant costs since railway track foundations are less easily accessible than the other layers of railway track. Premature failures of track foundations may arise if the service loads exceed the design specifications, but may also develop as a result of the shortcomings of the design codes to simulate in situ stress paths, which involve cyclic stress changes in the horizontal as well as vertical direction, which result in principal stress rotation (PSR). Laboratory investigations have suggested that cyclic changes in the horizontal as well as vertical direction may result in a higher rate of plastic strain accumulation than cycling the vertical stress only. The effect of PSR on the soil stiffness is less certain however. Furthermore little consideration has been given to how the gradation of different soils may affect in situ drainage conditions and therefore influence the rate of railway track deterioration during PSR. A knowledge gap exists as to how cyclic changes in the directions of principal stresses may affect the pore pressure and stiffness of soils under different drainage conditions.In order to improve our understanding of the effects of PSR on the long term performance of railway track foundations, a series of laboratory tests were conducted which investigated the effects of cyclic changes in the direction of principal stresses on the pore pressure, stiffness and susceptibility to failure of saturated railway track foundation soils under different drainage conditions. The investigated sand-clay mixes were selected so as to replicate the gradation of an in situ railway track foundation. It was found that even small additions of clay to the volume of a sand significantly affected the response of the mixes during cyclic changes in principal stress direction. Moderate additions of clay in the pore space of a sand reduced the susceptibility to principal stress rotation by reducing the tendency for excess pore pressure generation and by increasing the cyclic shear stress the mixes were able to sustain before rapid plastic strain accumulation occurred. Increases in principal stress rotation below the cyclic shear threshold increased the resilient stiffness of the sand-clay mixes, however once this threshold was exceeded rapid stiffness degradation occurred. Below the cyclic shear threshold, the response of the mixes was stable over a high number of loading cycles and no abrupt fatigue failures were observed. The sand-clay mixes were sensitive to even small changes in the magnitude of PSR near the cyclic shear threshold. Small increases in PSR could trigger the sudden collapse of a previously stable sand-clay mix. Under conditions where the rate of pore pressure dissipation was regulated by the permeability and the volumetric compressibility of the soil, the sand clay mixes with moderate additions of fines were stable over a range of cyclic increases in PSR which correspond to the maximum expected changes in magnitude within the depth of a ballasted railway track foundation

Weighing Vehicles in Motion [1964]

This report describes the construction, installation, testing and performance analysis of three types of dynamic electronic scales; the Taller-Cooper, a commercially developed four load cell scale, the Broke Bridge, an adaptation of a German prototype employing two load cells and the Bean Type Scale, an experimental prototype that uses a pair of instrumented aluminum beams as the weight sensors

Mechanical support design of analyzer for a diffraction enhanced x-ray imaging (DEI) system

Diffraction Enhanced X-ray Imaging (DEI) uses synchrotron X-ray beams prepared and analyzed by perfect single crystals to achieve imaging contrast from a number of phenomena taking place in an object under investigation. The crystals used in DEI for imaging requires high precision positioning due to a narrow rocking curve. Typically, the angular precision required should be on the order of tens of nanoradians.One of the problems associated with DEI is the inability to control, set, and fix the angle of the analyzer crystal in relation to the beam exiting the monochromator in the system. This angle is used to interpret the images acquired with an object present and the usual approach is to determine where the image was taken “after the fact”. If the angle is not correct, then the image is wasted and has to be retaken. If time or dose is not an issue, then retaking the image is not a serious problem. However, since the technique is to be developed for live animal or eventually human imaging, the lost images are no longer acceptable from either X-ray exposure or time perspectives.Therefore, a mechanical positioning system for the DEI system should be developed that allows a precise setting and measurement of the analyzer crystal angles. In this thesis, the fundamental principles of the DEI method, the DEI system at the National Synchrotron Light Source (NSLS) and the sensitivity of the DEI system to vibration and temperature has been briefly studied to gain a better understanding of the problem. The DEI design at the NSLS was analyzed using finite element analysis software (ANSYS) to determine the defects in the current design which were making the system dimensionally unstable. Using the results of this analysis, the new analyzer support was designed aiming to eliminate the problems with the current design. The new design is much stiffer with the natural frequency spectrum raised about eight times. This new design will improve the performance of the system at the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory, New York, USA and should assist in the development of a new DEI system for the Bio-Medical Imaging and Therapy (BMIT) beamline at the Canadian Light Source (CLS), Saskatoon, CANADA

Multi-objective design optimization of a mobile-bearing total disc arthroplasty considering spinal kinematics, facet joint loads, and metal-on-polyethylene contact mechanics

Total disc arthroplasty (TDA) is a motion-preserving surgical technique used to treat spinal disorders, when more conservative medical therapies fail. Unfortunately, a high incidence of revision surgery exists due to postoperative complications including abnormal kinematics, facet joint arthritis, and implant failures. However, TDA is still an attractive option, since an optimally designed artificial disc is expected to reproduce native segmental biomechanics. Correspondingly, it would mitigate the development of adjacent segment diseases (a major concern of spinal fusion) caused by altered segmental biomechanics. Design optimization is a process of finding the best design parameters for a component/system to satisfy one/multiple design requirements using optimization algorithms. The shape of a candidate design is parametrized using computer-aided design, such that design parameters are manipulated to minimize one/multiple objective functions subject to performance constraints and design space bounds. Optimization algorithms typically require the gradients of the objective/constraint functions with respect to each design variable. In the traditional design optimization, due to the high computational cost to calculate the gradients by performing finite element analysis in each optimization iteration, it often results in a slow process to seek the optimal solution. To address the problem, an artificial neural network (ANN) was implemented to derive the analytical expressions of the objective/constraint function and their gradients. By incorporating analytical gradients, we successfully developed a multiobjective optimization (MOO) framework considering three performance metrics simultaneously. Furthermore, a new mobile-bearing TDA design concept featuring a biconcave polyethylene (PE) core was proposed, to strengthen the PE rim, where a high risk of fracture exists. It was hypothesized that there is a trade-off relationship among postoperative performance metrics in terms of spinal kinematics, facet joint loading, and metal-on-polyethylene contact mechanics. We tested this hypothesis by refining the new TDA to match normal segmental biomechanics and alleviate PE core stress. After performing MOO, the best-trade-off TDA design was determined by the solved three-dimensional Pareto frontier. The novel MOO framework can be also used to improve existing TDA designs, as well as to push the cutting edge of surgical techniques for the treatment of spinal disorders