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PROARC - An Integrated CAD/CAM System for Robotized Arc Welding

A CAD-Based Programming System for arc welding robots was developed in an international project with German and Hungarian participants. The basic goal of the system is to assist robotized arc welding in Small and Medium Size Enterprises (SME) mostly for small and medium lot sizes. The product of the development is such an interactive offline robot programming system that gives assistance to easily design and then perform arc welding tasks. Commercially available offline robot programming systems are either too expensive or cannot provide all required functionalities. The system (PROARC: EC COPERNICUS Project 7831) is implemented on the world-leading PC-based CAD system, AutoCAD, by using its new object-oriented interface ARX. However beside these platform related attributes of the system, PROARC provides a number of efficient functionalities for the seam programming. In order to allow the system to be integrated into a CIM environment, standardised OSI (Open System Interconnection) interfaces have been chosen.

1. Introduction A large number of industrial robots has been established in the field of arc welding over the last twenty years. The reliability of robots, their use in more than two shifts and the reproducible welding quality are arguments for the use of this technology.

However, the application of arc welding robots is mostly limited to the production of big lot sizes. The classical way to program a robot is still the teach-in method in which the robot has to be led to the various points, which afterward will be connected by a manually generated program. This programming method is highly insufficient and not economical for small or medium lot sizes. Therefore offline-programming systems have been developed to decouple the process of program generation from the actual robot in the workcell.

System objectives The target group are clearly SME companies, which consequently cannot afford so high investment costs as large companies do. The costs of the required computer type, additional hardware and software had to be kept low in order to encourage the companies to invest in new technologies. Personal computers and standard software are important preconditions for this goal. Furthermore, the use of well known software tools for the realisation of a new system enables the user to work with the new system effectively after a very short time of practising. The user will accept the system faster and the productivity will raise with the user's motivation.

Out of this motivation the AutoCAD system has been chosen as the development platform for the PROARC system. It meets the precondition of a frequently used software in SMEs and it provides the required functionalities to develop a user friendly programming environment. E.g. the user should be freed from complicated input sequences and should be able to provide his knowledge of a welding expert for the system in a simple way. There is a flexibility of the seamís programming in PROARC. No system is known, which allows a flexible restructuring of the welding sequence and the unconstrained back (modelling) and forth (simulation) stepping within a single programming session.

The basic requirements of the PROARC system defined by the consortium were the following, grouped in three categories:

Modelling

  • support of standard CAD interfaces (IGES, DXF);
  • 3D solid modelling of the entire workcell, including robot, positioner, torchstation, and cleaning device;
  • support of collision checking during simulation;
Programming
  • support of Fillet and Butt welds;
  • support of multiple layers with straight and circular weldlines as well as combination of those;
  • automatic generation of welding paths including
  • the appropriate welding data;
  • unconstrained programming of welding sequences;
Program generation and communication
  • support of a common interface between the programming and program generation part of the system to provide the use of different robot languages;
  • the DNC connection support of an MMS (Manufacturing Message Specification) (ISO 1989) interface between the programming system and the robot to provide more control over the welding process for the user;
3 Partners WZL of RWTH Aachen,
University of Veszprém,
MTA SzTAKI 4. Further readings Final report
Nacsa, J., Kovács G.L.: An Integrated CAD/CAM System for Robotized Arc Welding, Proceedings of the 27th International Symposium on Industrial Robots (ed. Prof. D. Fabrizi), 6-8 Oct. 1996, Milan, Italy pp. 287-292.
     
 
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