To handle and store the wide variety of rolled products, an aluminum processing company utilized an overhead bridge crane together with a solid fixed mast extending from the bridge almost to floor level. This arrangement allowed the coils to be lifted vertically, moved, and relocated for storage. The company operated the handling of the coils manually, the operator riding around to pick up coils and move them to the storage area. However, this mode of operation led to the coils frequently making contact with a wall or racking structure, resulting in damage, not only to the product but also to the building and the fixtures therein. A more costly consequence of the frequent crashes was the damage to the gearbox that operated the overhead crane. The frequent replacing or repairing of gearboxes becoming a major capital expense. Furthermore, since gearboxes are long lead items to obtain, the company was forced to maintain an inventory of gearboxes, again at significant cost. It was recognized that this situation was untenable. Seeking a solution to the problem, the company approached Trutegra, who responded by designing an obstacle avoidance system (OAS), a system that today has become a standard product for Trutegra.
What is an Obstacle Avoidance System? It is a group of interacting components that together provide a means of preventing accidental contact with obstacles in the work area. The components include the “OA server,” connected to the cranes by Ethernet, real-time position sensors on each crane, and an operator interface program to give real-time viewing of the crane in the work environment. It also provides a live view of crane interactions from remote locations. The system records crane movements over extended periods of time, making the recorded data available for playback later. In operation, the system maintains constant communication between crane (or cranes) and the OA server. Position and velocity data are communicated from the crane to the OA server and warning information is sent from the server back to the crane. If there is a breakdown in the communication the PLC assumes that a collision is imminent and intervenes to stop the crane, making the system “fail-safe”. The OAS imports CAD drawings of the fixed obstacles in the area in which the crane is operating and translates them to a database for comparison to the position of the crane at all times. The operator display indicates proximity to an obstacle with green (safe distance), yellow (approaching obstacle), and red (imminent collision or stop) highlighting the moving crane. The crane is automatically slowed to a stop to avoid any collision. The system controls five-axes (hoist, bridge, trolley, rotate, and adjacent crane) to produce a velocity override factor for each speed reference, for real-time obstacle avoidance.
The OAS provides a hyper-accurate map of the operating area covered by the crane, including the presence or absence of a load, the size of the load if one is present, and what interference zones exist. The operator has retained manual control of the crane but as with automatic braking systems in automobiles, intervention occurs to avoid contact with an obstacle. The software for the OAS will interact with a standard CAD style drawing of the physical area so that it is a very easy product to teach. A DVR feature referred to as the flight recorder was designed into the system by Trutegra to record every single input and movement made by the operator during the workday. The information obtained allows calculation of efficiencies and it acts as a safety net, providing details of events leading to any crash that may occur.
With the introduction of the OAS, the plant significantly reduced the amount of money spent on replacing or repairing the gearboxes. In fact, in the first year of operation with the OAS, no gearboxes required attention. Furthermore, the changes to the way the operators worked resulted in increased productivity, a benefit that was entirely unexpected. Future projects may involve the full automation of the area, eliminating the need for an operator, yet maintaining the OAS should manual operation be required. The product mix would easily allow such a change to be made.