Valk Welding: 1999

A robot performs best when doing the same tasks all the time. The company Van Hool knew this all along, but now new Panasonic robots perform all sorts of different tasks.

Just as most automation tools, the robot seemed best suitable for standard operations. In production lines with many standard and repetitive jobs, the robot has long been introduced. It is often the robot's task to move workpieces from such production line over the same track over and over again. The finest example are the pick-and-place solutions in the electronic industry. The automotive sector too has long made use of the robot for the same standard and repetitive pick-and-place tasks and for cutting and welding.

Robot automation
The same goes for the Belgian coach constructor Van Hool. A short walk through the workplaces proof that there is a lot of welding here. According to Karel Vandersloten (public relations) that is no surprise: "A Van Hool coach consists of a metal construction and as long as we have no other connecting techniques, welding is one of the most important tasks."

Van Hool has many years of experience with welding robots. "Some years ago, we installed our FMS-system : first with one welding robot, later with a second. The FMS-system is an automated high-rise storage system with a robot continuously driving round with jigs that he takes from a rack and offers to the employees. In between, the robot takes filled jigs from the racks and presents them to the welding robots. Once welded, he goes the other way round and stores the jig with the welded profile in the racks. "This system too is efficient due to standardisation: workpieces and profiles have been made accurately to size beforehand, and stored in a specifically designed storage system.

The way to standardisation
For other production parts, the use of robots is less obvious. According to Jean De Wilde of the department Industrial Vehicles: "Because we cannot start from standardised workpieces, the use of robots is rarely efficient".

With Panasonic robots, Van Hool has found a solution to use robots in an efficient way, also to weld non-standardised workpieces. To optimise the welding job, we use three criteria regarding the workpieces for which there are jigs:

• How much time is needed for manual welding
• How many pieces must be welded at the same time and
• How frequently

The existence of jigs to clamp the pieces already implies a certain amount of standardisation. For such workpieces, that are being welded in relatively small series, we have to have more workstations per robot, two is not enough. Every jig has its own welding programme; the robot automatically loads and unloads the jig once this is recognised by the robot. When working with two or more workstations, off-line programming becomes important. With on-line programming, the robot cannot continue to weld and a number of workstations are not used. With our current system "off-line programming" we are able to programme welding tasks for these almost standardised products while the robot just continues welding.

Van Hool recently employed a new Panasonic robot installation for the automation of frame welding for tank containers. These frames form part of the supporting construction of the containers with a maximum size of 2.5 to 3 meter. The welding robot (supplied by Valk Welding) is mounted in hanging position to a longitudinal guide with a useful length of 23 meter. The production line has four workstations where the frames are positioned in a mould between two manipulators in all possible positions. "The advantage of this setting is that while a robot in a workstation is welding a frame, the frames can be changed in the other workstations. Such a flexibility normally requires a lot of programming time, because no two frames are the same. At first sight, the frames may seem the same (when it comes to size), but this is rarely the case considering the tolerances of the tubes. In addition, the tank supports always differ. The off-line programming system enables us to develop a number of basic programmes that can be adjusted rapidly off-line on the PC. In addition, programmes can be copied, for example from jig 1 to other workstations. The difference in tolerance is being handled by the measurement system of the robot. Based on the measured values, the PC repositions the robot and recalculates the welding track of the robot. Robot automation is only worthwhile when we can programme frames faster or when we can adjust changes for similar frames faster or have the robot deal with these changes."

The DTPS programming system
The Desktop Programming & Simulation-system (DTPS), that goes with the Panasonic robots, is a new software package that can be used under Windows on a PC. It is an off-line programming system whereby the robot can be programmed without having to stop the production. Managing, optimising, downloading and simulating programmes are also possible. This is a graphical programming environment with which all robot movements can be followed. Even zooming in is possible. The products can be loaded via DXF or IGES format directly from the CAD/CAM system.

The DTPS-system is designed as any other robot programming system. First, the parameters (robot type, tools, external axes…) are set. Once these basic parameters have been entered, the installation is set.

There is not further physical action required for teaching or for actual programming. The weld is selected, if need be the position of the welding torch is entered and the weld is programmed. A simulation can be used to check the quality of the programme (unnecessary movements, invalid spots…). Once the movements of the robot are set, some other parameters must be entered, such as the welding parameters (flux, voltage and progress speed) and the logic commands.

It seems incredible: a robot welding perfectly based on a design. The programme or the diagram only forms the ideal welding pattern for the robot. Thanks to sensors, the robot will measure the deviation of the setting compared with the ideal pattern and adjust its track. Of course, when the deviation is too large (for example the distance between 2 tubes is too large to apply a weld), the robot must be adjusted.

(Source: Belgian Business & Industrie - March 1999)