Friday 12 July 2013

Game, set and match!

Rapid, reproducible automated testing of tennis balls

I suppose it was inevitable in the week that Scottish player, Andy Murray won the Wimbledon lawn tennis championship we get a story like this!

World-class tennis players rely on the tennis balls to be of championship quality. To ensure uniformity and consistency in performance during tennis tournaments, ball manufacturers are required to submit samples of their products to the International Tennis Federation (ITF) for testing and approval.

Mecmesin, a leading designer and supplier of force and torque measurement solutions, was tasked to design a cost-effective, yet leading-edge automated tennis ball testing machine for the ITF and was looking for a partner to advise on the most appropriate automation equipment. It turned to Festo who supplied Mecmesin with pneumatic components comprising linear axes and pneumatic grippers, together with a PLC based control system which Mecmesin programmed.

The ITF required a versatile test system that can accommodate a range of tennis ball sizes including the larger sized, slower foam balls which are designed for use by beginners. The system needed to reliably automatically load and unload the tennis balls on to the tester, and grip and rotate the balls while being tested. Many parameters are tested over three axes to ensure the uniformity and consistency of results necessary for the international standard required.

There were two additional requirements of the machine. First, the tester had to be monitored remotely, allowing staff to carry on with other tasks, and secondly, it had to be built in such a way that it could accept new tests in the future, without the system having to be re-designed.

Mecmesin has worked with Festo on previous projects and was keen to explore how Festo equipment could be used for this application.

“We worked closely with Mecmesin to fully understand the requirements of the testing machine and recommended our CPX integrated automation platform which includes a PLC,” says Bill Evans, Business Development Consultant at Festo. “This system enables the machine to be monitored remotely, which means staff do not need to be in attendance during the hour long test.”

“By using an automated sample handling system, testing is more reproducible and does not require constant attendance from technicians who are free to perform other duties,” says Simon Garland, Automation Engineer at Mecmesin. “The automated system can safely be left unattended to perform all the required tests, and on completion, a comprehensive test report is available with graphical display of the test results.”

On the previous system, balls were automatically loaded on to the machine, and the test set to run. However, if a ball became misaligned during the test, the testing process would stop until the technician came back later in the day. The test would need to be started again and a technician would need to stay with the machine to manually load the balls. Now, the testing is more rapid and by alerting the technicians to any problems in real-time, the system is more efficient.

“A CPX automation platform with CP string remote I/O capabilities was chosen as it allows Mecmesin to add further modules easily in the future without re-designing the entire control structure,” continues Bill.

To ensure consistent match performance, samples of the ball are tested by being compressed to a specified load, and the amount of movement measured. This is termed “forward deformation”. The load is then released and the “return deformation” is also measured. To make sure each ball behaves uniformly, precision grippers rotate the ball and the test is repeated on three perpendicular axes. In addition, the diameter of the ball and its weight are also recorded. Up to 12 balls can be loaded onto the sample carousel, and when testing is completed, the test report can include pass and fail criteria simplifying the interpretation of the results.

The sophisticated pneumatic ball handling mechanism is capable of locating and positioning the tennis balls on the force testing platform, a weighing scale or the 12 sample carousel. The system is driven by Mecmesin’s powerful Emperor™ software which has a simple user interface, allowing the operator to select which tests are to be made from a menu of options. Results can be stored within the system, or exported to other software applications for secure data storage.

The automated tennis ball tester contains a number of components from Festo including all operating cylinders, linear actuators, pneumatic grippers, PLC, valve terminals and a rotary table enabling it to reliably perform a wide range of tests.

The tennis ball tester was delivered to the ITF in the summer of 2012 and has been used heavily ever since. Mecmesin has been pleased with the reliability of the Festo solution and the two companies are continuing to work together on other projects.

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