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ASOM: A highly intuitive software for the Analysis, Synthesis and Optimization of Multi-bar systems

The need for solutions for kinematic systems in the automotive and engineering industry is present at a constantly high level. The requirements on the development of appropriate multi-bar systems are continuously increasing at the same time and have presently become so complex that even for experienced engineers it will take a lot of time to generate solutions using ordinary CAD software. With ASOM, a software is now available which makes it possible to reduce the necessary development time for multi-bar systems considerably. The design work is carried out in a highly interactive fashion by giving the developer full control over the synthesis process.

The Challenge

Multi-bar systems are used quite often in a very diverse spectrum of products in the automobile and engineering industry. The requirements regarding comfort, efficiency, weight, cost and robustness of moving systems like hoods, hatches, doors etc. are continuously increasing. Meeting these requirements has presently become a very serious task, consuming an ever greater part of the development resources. Just the simple fact that desired motions for multi-bar systems cannot be fully anticipated (and thus designed) even by experienced developers and engineers, already poses a serious challenge in and of itself. These requirements are increased further by the necessity to consider additional aspects like specifications for orientations of given planes, for motions, for restriction and collision zones, for energy storage elements or for drives, as well as a large variety of other ergonomic and functional aspects.

For these reasons, among others, in current multi-bar system developments a complete redevelopment is often avoided in favour of using or modifying pre-existing kinematic solutions – which in most cases do not represent optimal solutions. Sometimes the desired motion concept is even dropped completely when no pre-existing solutions are found.

The Solution

The development of the software ASOM was motivated heavily by the wish to free the developer from this dilemma. ASOM makes that possible by implementing an inverse approach. Usually the design engineers first define structures and then "combine" them to implement a certain desired motion. In an inverse approach, though, the functionality (in this case the desired motion) is fully defined first and from this the necessary structures are determined through special mathematical methods under consideration of all additional requirements and conditions. This is the same concept used by software-assisted optimization methods in other industries, where desired values for target parameters are defined first and then the corresponding values for all influencing parameters are determined in a subsequent computation step (inversely). Especially for problems with dependencies that cannot be inverted mathematically, where relations e.g. are not bijective, this cannot be solved easily or trivially.

For the problem of multi-bar system development, the software ASOM generates such solutions almost fully automatically. This is because here - in contrast to standard CAD solutions - not the kinematic system is entered as input, but the wishes and requirements of the engineers, based on their development goals. It is then the task of the software to generate appropriate multi-bar systems that implement these requirements. This approach is much easier for the user, more efficient, and considerably faster, particularly since it is possible to carry out this process in real time and in a highly interactive fashion in ASOM. The design process is no "black box" solution generator, but an open interactive process, where a knowledge transfer from the software to the user is possible, which is important for developers. This is because any generated solutions can only be accepted if the developer can comprehend and retrace all results in full detail. Thus, valuable know-how is generated during the redevelopment of multi-bar systems from scratch. Practical tests have shown that in this way development efforts can be reduced drastically (from weeks or even months down to minutes, or at least only a few hours). If under consideration of all given requirements it should happen that no optimal solution can be found, this will be made quite obvious. And even in this case, solutions will be generated that fulfill the requirements as well as is possible.

The development of ASOM was carried out in close and productive cooperation with the Volkswagen AG, while continuously ensuring an intuitive usability of the software in practical scenarios. The result of this is, besides the avoidance of a simple "black box" solution, the implementation of a number of powerful modules that have been integrated into the inverse design approach.

In the following, some of these ASOM modules are presented as examples:

Module: Design methods for energy storage elements

According to the need at hand, either specific pre-exisiting gas springs can be configured and added to a project or completely new gas springs can be designed. The use of real gas laws, the specification of certain mounting conditions and / or the definition of certain desired manual force conditions can optionally be included. They are then considered automatically.

Module: Holding force tool

Here as well, an inverse approach is implemented: the user defines desired manual force values for important positions and ASOM automatically adjusts the system to fit these conditions.

Module: Tolerance analysis tool

With the help of this tool it is also possible to check in real time whether the current design will also fulfill the set requirements if existing manufacturing tolerances are considered.

Module: Rule-bases and extensions

An integrated, easily usable programming language enables the user to integrate company-specific core know-how into ASOM, which can then automatically be considered as well.

Module: Optimizer

More complex individual wishes and requirements can be considered explicitly and intuitively (e.g. by graphical input for a merit function). The ASOM optimizer automatically generates several globally optimized solution variants.

Summary

Up to now, the design process for multi-bar systems was very time-consuming, due to the increasing complexity of the requirements, and thus characteristically relied heavily on heuristics. With ASOM this problem no longer exists, due to our highly consistent implementation of synthesis concepts. The designer can now generate in a very short time solutions that are fit for practical use, but which stay entirely comprehesible at the same time. The designer can thus concentrate fully on fulfilling customer wishes and requirements.

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