Precision Crane Control Material Handling

Eliminating the sway of huge payloads through state-of-the-art controls technology is one outcome of a research lab driven by a unique industry/university partnership.

Located in the heart of downtown Atlanta, Georgia, on the campus of the Georgia Institute of Technology (Georgia Tech), is one of the foremost multidisciplinary research centers focusing on next generation manufacturing technologies: the Manufacturing Research Center (MARC).

For nearly a decade, Siemens, through the Siemens Cooperates with Education (SCE) program, has worked with the university in supporting MARC with a substantial financial commitment, as well as donations of  equipment, software, and sometimes guidance. Each year it also funds two students from Europe to come to MARC and participate in its work.

The MARC team, typically consisting of graduate students and PhDs doing research, have turned the Siemens’ commitment into a series of challenging projects. The first one was an innovative realization of a full-sized gantry crane. Cranes are often considered rather simple devices, but the MARC team infused the tool with intelligence. It provides advanced zone control, whereby the operator, without touching a part, can direct the crane to any location using an advanced optics system. During this project, the MARC team also developed a new type of sway control. In a normal crane, the payload being positioned sways back and forth when the crane starts or stops moving. The MARC system incorporates sway dampening features that largely eliminate sway from motion along gantry cranes—a notable advance and one of the first highlights to emerge from the MARC projects affiliated with Siemens.

Ideas Taking Flight

MARC’s current project results from The Boeing Company’s recognition of Georgia Tech as a strategic university partner to investigate and develop innovative manufacturing technologies for potential application in the aerospace industry. To support this effort, an Aerospace Manufacturing Laboratory was established within MARC: 2,000 square feet configured to advance manufacturing techniques for aerospace structures, consistent with the technical and research talent available at Georgia Tech.

The lab is equipped so that large structures can be transported by mobile platform, lifted and located via an overhead crane system, and positioned within certain tolerances for further machining, fastening, or inspection via wireless communication.

To date, emphasis has been placed on incorporating technologies that would facilitate material handling with precision, including tight tolerance control and reduced performance variation.  One research project associated with overhead crane use focuses on input shaping, which has been shown to significantly reduce the residual swing that accompanies the hoisting and movement of payload.  Even when hoist distances are large, the shaping process reduces residual oscillation amplitude well below the level obtained with time-optimal, rigid-body commands.  An integrated control system within the laboratory— Siemens’ contribution to the project—is critical for this and other projects to succeed.

A control room is under development to house an electrical cabinet that supplies power to the crane and control cabinet. A Siemens S7-Embedded Controller, incorporating a touch screen, will be used to operate the motion system with an emergency stop. The crane bridge and each trolley will be equipped with aSiemens Motion Controller (i.e., Simotion) for precise movement. To locate position, several sensors—laser and vision systems—will be used. Communication with the control cabinet will be wireless (IWLAN).  A user will be able to control the crane via various input devices (e.g., laptop, mobile touch panel, or pendant). These devices will be connected to the embedded controller (EC31) over Wi-Fi (W788) with digital input (32 DI), Ethernet (Scalance X208), and/or Profibus (CP5603) capability.

The embedded controller will perform calculations based on signals from the input devices with the desired velocity command, including command shaping. These calculations can be done via WinAC (Soft PLC) or Windows XP, which communicates with the soft PLC over shared memory extension (SMX), custom code extension (CCX), or a controller management interface (CMI). It will also be possible to bypass the command shaping in the PLC and send the raw position or velocity commands to the bridge and trolleys so that they will calculate the command shaping.

The velocity commands are then sent via Wi-Fi to a Simotion controller.  Four Simotion controllers will be available, one for the bridge and one for each trolley.  With trolleys moving in the x-y plane, the bridge has two friction drives. The y-positions are measured via SICK laser sensors. The error between desired position and current position will be evaluated in the Simotion controller or in the PLC, whichever way the operator or crane maintainer wants it to be done. Each trolley will also incorporate a laser to measure the x-position with a camera to monitor sway and z-position locations.  All collected data measurements are sent to the embedded controller for processing.

“The innovative concept here is the redefining of the manufacturing process through dynamic tools deployed on mobile platforms and the automation technologies driving them,” says Robert Carper, training business developer and “Siemens Cooperates with Education” promoter at Siemens Industry.

In traditional manufacturing, particularly in the manufacturing of large items, a massive conveyor belt or a crane moves a part along a fixed trail or assembly line. People or robots then interject their value-add. “This system is unique in that other elements may come to the mobile platform or the platform can move to another piece of tooling,” explains Carper. “This allows dynamic scheduling of interactions between manufacturing elements, which maximizes manufacturing throughput.”

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