Tolerance Analysis Of Mechanism Research Articles

Effects of contact behaviors on tolerance analysis of mechanism based on skin model shapes and a boundary element method

Abstract Tolerance analysis plays an important role in predicting the quality of mechanical products in early design stage. However, previous researches on tolerance analysis have mostly ignored the effects of contact behaviors between mating surfaces. This may lead to unrealistic results, especially when analyzing products with kinematic pairs such as rotating mechanisms. In order to obtain more accurate and realistic analysis results, this paper proposes a tolerance analysis approach that considers the effects of contact behaviors between mating surfaces. Geometric features with machining and assembly errors are modeled based on the concept of Skin Model Shapes. Contact behaviors between mating surfaces are calculated by the Conjugate Gradient-Fast Fourier Transform (CG-FFT) method, a classic Boundary Element Method (BEM) for solving contact problems. On these bases, a cam mechanism is adopted as an example to illustrate the effects of contact behaviors on transmission performance. Through the tolerance analysis, not only the transmission error of cam mechanism is analyzed, but also the contact status and pressure distribution between kinematic pairs can be obtained, which provide references for other aspects such as reliability analysis.

Prospective motion correction using coil-mounted cameras: Cross-calibration considerations.

Optical prospective motion correction substantially reduces sensitivity to motion in neuroimaging of human subjects. However, a major barrier to clinical deployment has been the time-consuming cross-calibration between the camera and MRI scanner reference frames. This work addresses this challenge. A single camera was mounted onto the head coil for tracking head motion. Two new methods were developed: (1) a rapid calibration method for camera-to-scanner cross-calibration using a custom-made tool incorporating wireless active markers, and (2) a calibration adjustment method to compensate for table motion between scans. Both methods were tested at 1.5T and 3T in vivo. Simulations were performed to determine the required mechanical tolerance for repositioning of the camera. The rapid calibration method is completed in a short (<30 s) scan, which is carried out only once per installation. The calibration adjustment method requires no extra scan time and runs automatically whenever the system is used. The mechanical tolerance analysis indicates that most motion (90% reduction in voxel displacement) could be corrected even with far larger camera repositioning errors than are observed in practice. The methods presented here allow calibration of sufficient quality to be carried out and maintained with no additional technologist workload. Magn Reson Med 79:1911-1921, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

A discrete geometry approach for tolerance analysis of mechanism

Tolerance analysis aims at predicting the effects of inevitable geometric deviations on the quality and function of mechanical products and is therefore an import tool in the design and dimensioning of mechanism. Since geometric deviations have various sources, different simulation tools and computer-aided engineering applications must be applied to determine them. Most of these tools are based on a surface or volume discretization, which leads to a workpiece representation in discrete geometry. In this contribution, an approach for the tolerance analysis of mechanism employing these discrete geometry representations is proposed. It is based on the processing of non-ideal workpiece representatives and helps to incorporate results from different validation applications. The approach is applied to the tolerance analysis of spur gears by employing a Tooth Contact Analysis algorithm.

Statistical Tolerance Analysis of a Mechanism with Gaps based on System Reliability Methods

One of the aim of statistical tolerance analysis is to evaluate a predicted quality level in the design stage. A method consists in computing the defect probability P expressed in parts per million (ppm). It represents the probability that a functional requirement D will not be satisfied in mass production. This paper focuses on the statistical tolerance analysis of over-constrained mechanism with gaps. In this case, the values of the functional characteristics depend on the gap situations, and are not explicitly formulated as a function of part deviations. To compute P, two different methodologies will be presented and confronted. The first one is based on D an optimization algorithm and Monte Carlo simulations. The second methodology uses system reliability methods. The whole approach is illustrated on a basic academic problem inspired by industrial interests.

Recent Patents on Mechanical Tolerances

The focus of this paper is to survey recent patents related to mechanical tolerances. First, a general overview of tolerances is provided, followed by issues related to research in mechanical tolerances. Various research aspects of mechanical tolerances that are introduced are tolerance specification, analysis, allocation, synthesis, transfer and evaluation. Patents related to mechanical tolerances, issued since the beginning of the millennium, are selected for the survey. A comparison of the claims in the patents is provided, followed by the discussion of future research issues in mechanical tolerancing. Keywords: Mechanical tolerance analysis, tolerance allocation, tolerance evaluation and patents

Multibody approach for tolerance analysis and optimization of mechanical systems

A multibody approach is suitable for tolerance analysis of mechanical systems since multibody formulation can directly consider part-level tolerance variables. In this study, procedures for performing tolerance analysis and corresponding sensitivity analysis for spatial multibody systems are proposed. First, statistical formulation for performing multibody system tolerance analysis is developed to obtain system level tolerance for given part-level tolerances. One very useful aspect of the proposed formulation is that in the process of computing system tolerance, the sensitivity of system tolerance with respect to part-level tolerances can be additionally obtained. The kinematics of spatial multibody systems has been redefined in terms of both generalized coordinates and part-level tolerance variables. Tolerances in geometry of a body are specified in terms of the variations in relative locations of joint definition points and relative distance between them. Tolerances in the joint kinematics are defined through variations in vector closure equations and orthogonality equations that are two fundamental constraint equations for most kinematic joints. To demonstrate the validity and effectiveness of the proposed tolerance analysis procedure, tolerance analysis of a spatial 4-bar mechanism and tolerance optimization are performed.