Force and torque measurement specialist, Mecmesin was appointed by the ITF to design a machine to undertake these tests, cost-effectively and fully automatically. Seeking an automation partner for this project, the company turned to Festo for the necessary pneumatic actuators and grippers, plus a PLC based control system that Mecmesin could confidently programme.
The ITF wanted a versatile test system able to accommodate a range of tennis ball sizes, including the larger sized, slower foam balls which are designed for use by beginners. The system spec included reliable, automatic loading and unloading of test samples plus a facility for gripping and rotating the balls under test. A number of parameters are tested in three axes to ensure the uniformity and consistency of results required by the international standard.
Two additional requirements included a remote monitoring capability and the flexibility to accommodate new tests in the future without having to modify the machine. Mecmesin had worked with Festo on previous projects and was keen to seek the latter’s ideas about how its components might be used for this application. Festo’s Bill Evans takes up the story:
“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. This system enables the machine to be monitored remotely, which means an operator does not need to be in attendance during the hour long test. 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.”
As Mecmesin automation expert, Simon Garland points out, using an automated sample handling system ensures that the testing is more reproducible and does not require constant attendance from technicians who are free to perform other duties. “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,” he adds.
With the previous system, balls were automatically loaded to the machine, and the test set to run. However, if a ball became misaligned during the test, the testing process would stop and remain so until a technician attended to rectify the problem. The test had subsequently to be restarted and the technician remained onsite to manually load the balls. Now, the testing is more rapid and by alerting operators to any problems in real-time, the system is more efficient.
To ensure consistent match performance, samples of the ball are tested by compressing them to a specified load, and the amount of movement measure – a process 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. The diameter of the ball and its weight are also recorded.
In the new machine, up to 12 balls can be loaded on the sample carousel, and when testing is completed, a test report can be configured to include pass and fail criteria, simplifying the interpretation of the results.
The 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 Emperor software which has a simple user interface, allowing the operator to select which tests are to be undertaken from a menu of options. Results can be stored within the system, or exported to other software applications for secure data storage.
In addition to the CPX PLC platform, the machine includes a number of components from Festo, including all operating cylinders, linear actuators, pneumatic grippers, valve terminals and a rotary table. It was delivered to the ITF in the summer of 2012 and has operated reliably throughout its demanding testing timetable ever since.