As anyone living in Gauteng will attest, a hail storm can wreak havoc on gardens, car bodywork, windows and solar panels. With help from Festo, the South African Bureau of Standards (SABS), whose testing activities include a wide range of testing, calibration and inspection, have automated their Hail Gun for testing solar panels against hail damage.
Over the past couple of years, the province has been lashed by heavy hail storms raising interest in products that are resilient to nature’s bullets. Festo was asked to assist the SABS with a solution to automate the movement on their Hail Gun. This gun is designed to pick up an ice ball and shoot it at a solar panel, to establish it’s endurance to the impact.
“Our solution included both pneumatic and electric drives and a customised control panel for the system,” explains Johannes Ngwenya, Festo Sales Engineer. A pneumatic vacuum generator was used to suck an ice ball through a barrel canister. Once the ice ball was in place, the L-port valve is activated to switch the vacuum off and open positive air thus shooting the ice ball at the solar panel. “We required movement in 1mm increments” says Herman Strauss of the SABS, “Electric drives have proven to be best suited to this application as they provide the fine motion control we needed.”
The Hail Gun needed to be attached onto X, Y, Z positional drives so that the ice balls can be directed at any point on the solar panel. “The mass of the Hail Gun and the panel dimensions of 2m x 2m x 1.5m helped us to size the electric drives and the required stroke,” says Ngwenya. It was decided to use the ELGA toothed belt drive which is an ideal axis for linear gantries and cantilever axes. Additionally, this electric drive delivers speeds of up to 10 m/s, acceleration of up to 50 m/s2 and a repetition accuracy of up to ±0.08 mm.
Control to the system was provided by the compact CMMO-ST motor controller which serves as a closed-loop and open-loop position controllers. It offers quick easy parameterisation through the either the Festo Configuration Tool (FCT), as was done with this application, or via an Ethernet interface with integrated web server. The cost-effective CMMO-ST forms part of the Festo range of Optimised Motion Solutions products with ServoLite technology.
Installed on each drive is the versatile EMMS-AS servo motor, a dynamic, brushless, permanently excited synchronous servo motor with a choice of 3 feedback systems which allows for single- or three-phase motor controllers, torque optimised or speed optimised winding variants. This high performance series is designed for demanding drive and positioning tasks such as this application with such a small incremental movement required.
“The control panel was built at our Isando workshop and the entire system was delivered within 8 weeks” concludes Ngwenya.