A solution of numerical control well polished

The company D.Grune Konstruktionen und Maschinenbau has made this integration with the help of the Generic Motion Control of B & R, combining various elements of the technology of drives in a single system. The result is a machine grinder for long steel pipes that subtracts the welds of the boards of these in an automated manner and with a precision up to a tenth of a millimeter.

Pipes are made of steel tubing, with longitudinal welds as a result of the own manufacture. In order to proceed with processing, this cord of welding should be eliminated. Explains Dieter Grune, owner of D. Grune Knostruktion and Maschinenbau: "A reason to delete it is its possible interference in ultrasonic measurement used to test the connections between the sections of tubes".

The objective of the grinding process is therefore used for removal of excess material from the cord of welding, acquiring a high precision without weakening the material, at the same time that takes into account the possible deviations that may arise from the productionsuch as irregular welds or deviations from the edges.

Before the sawing of the longitudinal seams was performed manually in the company of tubes using simple power tools. "An approximate typical output of 200 tubes per shift, quickly reaches up to 100 meters of cord of welding that need to be amolados." This work was very heavy and laborious. With workload processed manually, variations of quality lead to imprecise results virtually inevitable, and in the worst cases forced to shred tubes "highlights Grune."

Clearly, there is a need to mechanize the process of grinding of tubes. According to Dieter Grune, there are many difficulties before that mechanisation can become a reality. "One of the greatest challenges, on the basis that a pipe is cylindrical, is the process of sawing, as up to 20 parameters describe the geometry of a tube." "In addition the tube is not always well located with the cord in the same position". With a complete solution of automation, the machine would also have so that finding the cord in the initial position. Only then the grinding unit can position and make sure in the tube. To carry it out, Grune built a three-axis robot in a car on Rails. Laser sensors provide information to the driver with the identification of the position of the tube and the cord. Based on this information, the arm of the robot that contains the unit of sawing, remains a controlled motion and it is positioned directly above the Centre of the cord. In order to do so, it is not enough with the calculation of the positions of the engines for a specific slogan (transform) position, since in addition they should also obtain the current Cartesian coordinates (using the inverse).

This process of positioning using transforms is not a problem for a standard robot controller. "We do not use all the possibilities of a controller of a standard industrial robot, which add us additional costs;" "for that reason started to look for an alternative" explains Grune.

In principle, driver necessary CNC for sawing unit must be a powerful team. However, the curves and transforms should be then calculated in another device that exceed the capabilities of a CNC device. "The volume of resulting information could not be transferred to or from the CNC to fast enough using conventional methods." "For us this rule out the option of using a conventional CNC" highlight Grune.

GMC is more than a CNC

The solution Grune used in early machines, however, turned out to be effective. "One of the main disadvantages of hardware we chose at the beginning was the low speed which involved us the use of limited resources." "Other problems included a great time of development used by providers and ultimately the lack of solutions," says Grune, explaining the decision to seek a hardware to replace and its change to B & R.

With B & R, Grune is benefiting from the resources of a large very innovative supplier. Particularly the GMC (Generic Motion Control) solution of this Austrian company covers the needs of Grüne.

Whole machine, including the electrical part, and the hydraulic and pneumatic actuators of different manufacturers are controlled from a standard control composed of an automaton modular X 20 and a system of inputs/outputs, in addition to a servo of B & R and inverters connected by Powerlink. The features of SoftPLC and SoftCNC, are being carried out simultaneously from the CPU. Also the software needed to develop the transforms for the robot is also executed in the same control.

Combining all the control in the CPU makes the exchange of information between the functions of software really quickly, avoiding the typical bottlenecks in the exchange of information that would be with a conventional solution of CNC. Other benefits of this integration are the reduction of components and the simplification of the process engineering. The sequence of movements of the robot and the unity of sawing whose prototype was developed at the same time, makes the machine cycle times have been reduced.

And the CPU has still sufficient capacity in parallel with the integration of drives and the grinding machine to make other arrangements. "We are currently using Matlab to model our Core Module, a software model that we have developed for Windows that helps us calculate curves" reveals Grune. Laser sensors detect the path of the cord, and this software uses the information to calculate the necessary movements of the head of the grinding, which is moving tangentially to the pipe. "It requires complex calculations to provide CNC with the proper curve" explains Grune. Once the software has been imported, Grune engineers can simulate the sequence of movements, allowing them to perform optimizations and future developments of more quickly. At the same time, thanks to the interface Matlab / Simulink, the corresponding control code can be generated automatically, and run on the CPU X 20 together with the application of control.

"The industrial PC that were used for the Core program are no longer required, which again increases the efficiency of the system" says Grune satisfied with what has been achieved. "And the flexibility of the system, the transparent form of how to manage information and sophistication of our control will allow us to work with several projects at the same time satisfying demands of customers to measure, such as an integrated security."