The dimensional variation analysis of complex mechanical systems

Dimensional variation analysis (DVA) is a computer based simulation process used to identify potential assembly process issues due the effects of component part and assembly variation during manufacture. The sponsoring company has over a number of years developed a DVA process to simulate the variation behaviour of a wide range of static mechanical systems. This project considers whether the current DVA process used by the sponsoring company is suitable for the simulation of complex kinematic systems. The project, which consists of three case studies, identifies several issues that became apparent with the current DVA process when applied to three types of complex kinematic systems. The project goes on to develop solutions to the issues raised in the case studies in the form of new or enhanced methods of information acquisition, simulation modelling and the interpretation and presentation of the simulation output Development of these methods has enabled the sponsoring company to expand the range of system types that can be successfully simulated and significantly enhances the information flow between the DVA process and the wider product development process

The use of a kinematic contraint map to prepare the structure for a dimensional variation analysis model

Dimensional variation analysis (DVA) models are widely used in the automotive industry to predict how minor variations in the size, shape and location of the component parts are likely to propagate throughout a body structure, suspension, engine or transmission system and how this will affect the overall assembly, operation and performance. This paper is one of in series of four papers that describe how different techniques can be utilised to aid the creation and application of DVA models. This paper explains the development and use of the kinematic constraint map (KCM) method to prepare, in advance, the most appropriate structure for a DVA model. The KCM method provides a concise and comprehensive graphical method that, in one document, can identify all the physical constraints that govern the location and (where applicable) the motion of each component within a complete mechanical system. Once complete, the KCM for a mechanical system contains sufficient information to fully define the structure of the subsequent DVA model. The other three papers cover the use of virtual fixtures, jigs and gauges to achieve the necessary component location and the required variation measurements; the use of two stage DVA models to simulate interdependence between different model configurations and the use of 3D plots to display large numbers of DVA results as a single 3D shape

The use of a two stage dimensional variation analysis model to simulate the action of a hydraulic tappet adjustor in a car engine valve train system

Dimensional variation analysis (DVA) models have been used in the manufacturing industry for over 20 years to predict how minor variations in the size, shape and location of the components parts is likely to propagate throughout and affect the overall dimensions, operation and performance of a complete mechanical system. This paper is one of in series of four papers that describe how different techniques can be utilised to aid the creation and application of DVA models. This paper explains the development and use of a two stage DVA model to simulate the action of a hydraulic tappet adjuster and dimensional interdependence that exists between the adjustment of a hydraulic tappet and the actuation (opening & closing) of the cylinder valve. The three other papers cover the use of kinematic constraint maps to prepare the structure of a DVA model; the use of virtual fixtures, jigs and gauges to achieve the necessary component location and the required variation measurements, and the use of 3D plots to display large numbers of DVA results as a single 3D shape. A hydraulic tappet adjustor performs two functions; it is part of the valve train system that actuates (opens & closes) the cylinder valve and it also self adjusts to take up any free play in the valve train system. These two functions, tappet adjustment and valve actuation, are separate operations that occur at different times during the valve train operating cycle and so need to be modelled as different configurations in a DVA model. In a conventional multiple configuration DVA model, each configuration has to be fully constrained and mathematically closed independently of any other model configuration. This requirement makes it difficult to include the interdependence between tappet adjustment and valve actuation. The two stage approach overcomes this limitation by allowing the output variation from the tappet setting configuration to be carried over into the valve actuation configuration and can thereby fully account for the interdependence between the two operation

A method of visualising the 3D dimensional variation behaviour of kinematic systems

At present, the output from the dimensional variation of an assembly is often in the form of a statistical process control chart or histogram. Such output, while informative, is not particularly suited to the evaluation of dimensional variation behaviour in complex kinematic assembly systems. This paper presents a graphical method of visualising the 3D dimensional variation behaviour of any chosen point feature in a kinematic assembly system by the use of 3D bounding surfaces. The bounding surfaces describe a volume such that there is a known probability that the chosen point is contained within the volume. The bounding surfaces and the volume they describe visualise the dimensional variation behaviour of the chosen point feature as it traverses one or more of the kinematic assembly system's movement ranges. This paper demonstrates that the visualisation allows the dimensional variation behaviour of the chosen point to be presented in a compact and readily comprehensible manner that enables evaluation of the analysis output within the context of the original simulation model geometry. An example of the method applied to a simple kinematic system is also shown

The use of virtual fixtures, jigs and gauges in dimensional variation analysis simulation models.

This paper describes the use and deployment of, virtual fixtures, jigs and gauges to locate, align and measure features in simulation models used in the dimensional variation analysis (DVA) of assembly systems. The particular example chosen in this paper is a McPherson strut suspension. The correct use of virtual fixtures, jigs and gauges can significantly improve the accuracy and realism of the simulation model and thus the DVA output. In kinematic assembly systems, the use of virtual fixture, jigs and gauges is often essential to produce a working simulation model