The retractable roof in Vancouver39s BC Place is powered by a hybrid inverter drive

The retractable roof in Vancouver's BC Place is powered by a hybrid inverter drive.

Robots Take Control of Material Handling

Thanks to a new breed of decentralized machine controls, warehouse operations are gaining in productivity and profitability.

Material handling requires the most reliable equipment and innovative automation technologies for demanding installations. The time for critical analysis and cost savings is before finalizing the drive train, gearing and motor drive for a material handling application. A number of strategies and tools can help operators and equipment manufacturers optimize machine and robotic productivity and profitability.

Hybrid Drives

Servo motors are ideal for applications requiring precision and dynamic performance, with recurring motion sequences and perfectly coordinated return systems. However, many positioning applications do not require the higher performance or higher cost of a servo motor. Dynamic speed, torque and precision motion control can be achieved with a hybrid option, such as a powerful inverter in combination with an asynchronous motor.

For example, BC Place—a 10-acre arena in Vancouver, BC, with a 55,000-seat capacity—needed automated partitions to block off seats when hosting events with smaller audiences. The initial project concept involved mounting a series of curtains or panels between the first and second decks of the stadium. The biggest challenge was not the enormous size of the facility, but the need to have the panels reference each other and deploy smoothly and simultaneously in order for the system to function properly.

The engineering team from Thern Stage Equipment, a manufacturer of customized engineered hoisting and rigging solutions for theaters, identified the need for ease of communication in the wireless control system for the proposed retractable structure in the stadium. Thern ruled out a servo motor, yet wanted the capability to handle a semi-complex series of commands. The company opted for a hybrid design that blends the simplicity of a conventional AC motor with electronic drive control technology. It gives the arena power and freedom in motion control with freely adjustable speeds, programmable I/O and integrated functions. A closed-loop system in both a positioning and a torque mode, the system uses a PROFINET plug-in network communication module.

Delivering up to 200% rated torque, the hybrid system served as the backbone of the retractable structure. The performance pushes into levels that would previously have required servo technology, with positioning accuracies of 0.1mm at 60 operations (120 movements) per second. The savings obtained by choosing an induction motor over a servo motor were significant, with a 20%-50% average price differential between the technologies.

Decentralized Machine Control

Machine builders have traditionally focused on optimization at the machine level. In the past, there have been cells with robotic functions that were distinct and separate from other machine functions. Within the industry, there is heightened interest in automation control, especially around the integration of robotic and machine functionality.

As more warehouses and distribution centers come online with decentralized control architectures, the right combination of technologies is critically important. Decentralized control allows a drive package to be part of an enclosure or mounted directly on the equipment, which puts the power at the motor shaft.

This provides numerous advantages, including smaller cabinet size, reduced heating within the cabinet, lower requirements for wiring, and faster commissioning. Moving high voltage out of a central cabinet also alleviates the need for service personnel and engineers to wear full protective equipment when working on the system.

Decentralized motion control can reduce and even eliminate the load on the machine control system. Inverter drives are capable of taking over decentralized control responsibilities. An I/O system can be incorporated into the system to evaluate the control signals. An end-to-end network can be established using EtherCAT or CANopen, with access via a scalable visualization concept.

The overall decentralized system can incorporate a range of high efficiency motors and gearboxes designed for automation tasks. Material handling operations are also yielding energy cost savings, as more machines come equipped with economy modes for improved efficiency during times when conveyors are not in operation or running lightly loaded.

Breaking Down Programming Barriers

Historically, developers used ladder logic and other classic programming languages to program machine tasks. That required extensive training and a comprehensive knowledge of the programming language. Despite the high bar, machine designs often re-created the wheel by relying on code from earlier versions of the machine. When it was time for installation, an engineer would have to go onsite with a laptop, identify the correct software needed for the specific machine, and load configuration files. These approaches yield multiple redundancies and incur unnecessary expenses at nearly every level.

Software can have a major impact on reducing programming time, which goes right to the bottom line of machine productivity and profitability. Within the industry there is clear need and demand to streamline machine and robotic design processes to better utilize engineering resources. Application software that enables design engineers to solve productivity challenges is an important new trend in material handling.

Machine design application software leverages known motion control functions and incorporates these proven movements into preconfigured blocks of control functionality. Replacing complex programming with uniform machine configuration software tools can significantly reduce engineering time and technical requirements, and eliminate redundancies that drive up cost. Rather than mastering programming languages, valuable engineering time can be strategically directed at enhancing a machine's exciting and value-added performance factors.

For example, AB Graphic International, a label converting manufacturer, operates multiple inspection rewind equipment, including RFID tag insertion, laser die cutting, booklet label machines and 100 percent camera inspection systems. Production runs are shrinking with rising demand for custom, localized services. Digital printing machines and PC-based systems are replacing conventional flexographic presses.

Yet, productivity still relies on motion control—winding quality, faster changeover times, easy maintenance and reliability. The company needed strategies to keep pace with the digital era.

In this case, servo technology offered the best solution with mechanical flexibility and precise tension control. The company chose to replace mechanical systems with servo inverter technology, which provided a straightforward topology with reduced wiring requirements. AB Graphic can now interlink the DC power supply bus and EtherCAT connections, without requiring circuit breakers or individual mains supplies.

Featuring double-axis and single-axis drives, the new inverters substantially reduced cabinet footprint by 15%-20%.

The software allows the company's design engineers to plug blocks of predesigned control function modules into a template with which they can create machine control functions. The modules are effectively programs that run autonomously, so they can be easily exchanged and independently tested. All of the variables, including I/O and HMI data, exist as structures within the module.

Approximately 80% of software developed for most new machines can be generated using code developed for previous generations. Leveraging this knowledge and field-tested function with technology modules for machine programming represents a leap forward from the days of copying lines of code from old projects to paste into new ones.

AB Graphic's new label converting system can hold prepress parameters, label sizes, slit width, quality and roll size. This information enables them to automatically configure machines without operator intervention for running smaller batches with faster changeover times. The new solution has also improved the quality of performance. The software and controller combination uses open network industry standards to streamline M2M communications. This gives them the benefit of a decentralized topography combined with the seamless integration and supervisory control of upstream and downstream equipment.  

Doug Burns is director of business development with Lenze Americas (www.lenze.com), a manufacturer of electrical and mechanical drives, motion control and automation technologies.

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