Caution! Glass! Handle with care!
Photovoltaic panels are made of thin and extraordinarily fragile sheets of glass. To ensure their safe movement and precise positioning, the company Heckert-B.X.T. Solar, situated in the state of Saxony, puts its faith in the TSsolar transfer system made by Rexroth.
These are the characters in Jens Bonitz’ nightmares: splintered glass, ruined PV cells, littered transfer belts and laminators, tedious cleaning, downtime and production losses. Jens Bonitz, Technical Director of the Heckert-B.X.T. Solar GmbH in the eastern German town of Chemnitz, is responsible for process reliability in photovoltaic panel manufacturing operations.
Handling sheets of tempered glass, just four millimeters thick, and seven changes of direction within the system fully illustrate the extreme demands placed on the conveyor system. The Rexroth TSsolar transfer system is aligned with the special needs of the solar industry. Frequency inverters make for soft starts and stops while the lift and transverse motion sections form the basis for smooth directional changes. Grime is eliminated by low-wear, low-dust, toothed synchronization belts containing no silicone.
At Heckert Solar the transfer system achieves safe and sure component movement along the entire, fully automated manufacturing line. The thin, tempered sheets of glass are first cleaned at a washing station. Then the cells are positioned, cross-connected, soldered and laminated.
Washing, soldering, laminating
But there’s manual work at the start of the production process. Inspectors shake each and every cell received — microscopic fissures are audible! Scrupulous optical and technical checks follow, all in the interest of guaranteeing flawless quality. In the meantime the glass sheets are washed, laid on the TSsolar system and provided with a film. The sheets must never jam up, stop too quickly or touch anything during movement since, being tempered, they would shatter into thousands of tiny shards.
After installing stringers and cross-connections for the individual cells on the solar glass plate, the panels are moved to the laminator. Laminating takes longer and that is why it is done with two machines running in parallel.
Six conveyor belt modules transport the glass wafers between the washing station and the soldering machines. There the solar cells are connected by soldering, in individual rows, and then positioned exactly on the prepared pane. Two lift and transverse motion units divert the glass to the soldering machines. The conveyor belts with their toothed backs are augmented by roller conveyors to even out differences in the transport levels and keep the glass from bending under its own weight. The process then continues with the electrical cross-connections. At the following inspection section the panels are examined and then moved to two laminators that, given the extended processing time, operate in parallel.
Here the transfer system boasts a custom solution for Heckert Solar. The fixed stops are fitted with air jets. They create a cushion of air that lifts the film, which extends slightly over the edges of the glass. The stops grasp just the glass itself and align it at an accuracy of down to half a millimeter. This keeps the stops from shifting the film or even displacing it entirely. “Positioning exactness like this is important above all just ahead of the machines where the cells are laminated to the panel,” is how Bonitz explains the significance of this particular idea. The concept grew out of close cooperation among Heckert Solar, Mondragon Assembly — the system engineering company, and Rexroth.
A smooth journey
The shock-absorbing lift and traversing units have to offer the same degree of accuracy. They ensure jerk-free, trouble-free changes in direction. If individual cells were to be shifted due to abrupt stops or jerky motions of the lift and transverse units, then the resulting defect in the finished panel would be immediately apparent to the naked eye. The transfer system also avoids jerky movements by providing a separate drive for every element along the way. Frequency inverters are used to ensure gentle acceleration and deceleration.
The TSsolar system carefully maneuvers the glass through the seven directional changes within the processing plant — with complete synchronization of the two belts used at each conveyor module and at each lift and traversing unit. And with this concept the transfer system at Heckert Solar achieves the specified eighty percent efficiency. Jens Bonitz emphasizes that, “Without the transfer system, none of the automation concepts could have been implemented at all”.
More information:
www.boschrexroth.com/transfer_systems
www.boschrexroth.com/solar
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