Abstract:

In recent years, there is an increasing interest in the use of simulation software in the teaching of Machine Theory. These computer programs help the student to understand deeply, and in a more visual way, the theoretical basis explained in the lectures. This is clear taking into account that more and more textbooks of Machine Theory include a CD-ROM with a simulation program to complement the book contents.

One possibility is the use of a commercial software package as, ADAMS® or DADS®. These kind of general-purpose programs have the advantage of their powerful capabilities and their reliability. However, it is necessary to spend a considerable time to train the student in the use of these programs that have been developed to be used by professionals and experts.

Consequently, in the Department of Mechanical Engineering of the University of the Basque Country, an educational computer software has been developed to help the students in the understanding of Machine Theory. This approach for teaching this subject is not new. Other universities as Dresden University or Aachen University have previously used these kind of software in the lectures.

In this paper is presented a new educational computer program for the analysis and simulation of planar and spatial mechanisms. Despite of its generality, the software is particularly useful for the analysis of parallel manipulators. Nowadays, planar and spatial mechanisms can be found in most industrial machines and processes. In order to design them, the students must be able to make different kinematic analysis, like the resolution of the position problem, velocity and acceleration analysis, identification of the different assembly configurations, workspace computation, singularity analysis, etc.

Commercial software is available to perform these complex kinematic calculations. However, the geometrical definition process is often difficult, especially in the case of spatial mechanisms. Generally, the geometrical modelling process implies two steps. In the first step the elements are modelled independently. In a second step these elements are assembled and the kinematic parameters of the joints are defined. This modelling phase requires the student quite a lost of time and effort before starting the kinematic analyses. Taking this into account, in the software presented in this paper, a new pre and post processor tool has been developed and implemented. It allows the modelling of complex spatial mechanisms in an easy and simple way.

Once the mechanism has been modelled, the student is able to simulate and visualise the mechanism motion. Also, the paths of the points selected by the user can be obtained. From the modelling data, the software is able to generate and solve the velocity equation of the mechanism. Consequently the student can obtain the instantaneous degrees of freedom for each position of the mechanism, the angular and linear velocity plots and other entities as the fixed or moving axodes. The analysis and visualisation of these results, helps the student in the understanding of the performances and capacities of a spatial mechanism from the kinematics point of view.

Keywords:

educational software, user-friendly interface, spatial mechanisms, geometrical modelling, kinematic.