Overhead Handling: Handling Up High
April 01, 2010 - MMH Editorial
Using space overhead frees up the floor for safer, more efficient movement of products, work-in-process and associated tooling. In addition to decluttering the work zone, these systems offer enhanced ergonomics, plus a means to move items too large to be transported with a fork-based vehicle.
For moving products weighing 5 pounds to 1,500 pounds, overhead chain systems are the most common type of overhead handing. Evenly spaced pendants hanging along a single chain are pulled through a single enclosed track, or I-beam track, to carry the loads.
The next level of conveyance is dual-track power-and-free systems. These systems are comprised of a chain track on top, which provides the power, and the free track below, which contains the trolleys that move loads through the system.
Capable of carrying 25 pounds to 25,000 pound loads, power-and-free conveyors are used extensively in conveying materials to and from automation, manual workcells, and hostile environments like industrial washers, paint equipment and ovens, according to Brent Brosch, director of product sales for Jervis B. Webb (248-553-1000, http://www.jervisbwebb.com). “Power-and-free conveyors are extremely flexible, versatile and can be programmed to service a few work cells or an entire plant with proven reliability,” he says.
“From a new development perspective, lately there's been more emphasis put on noise reduction in chain and power-and-free conveyors, with use of non-metallic wheels to reduce the noise in a workplace,” says Brosch. And, to further reduce noise, other components are also being made of non-metallic materials, he adds.
Ideal for carrying a load from Point A to Point B, electrified monorail systems are best suited for moving high-value products across long distances with fewer stops. The system consists of a single rail or I-beam from which a hook or hoist hangs, providing lateral and vertical movements of loads weighing up to 30,000 pounds.
“Monorails have remained very similar in appearance over the past 30 years, but a lot of subtle improvements have been made,” Brosch says. “Previously, most I-beam systems were built for very heavy-duty cycle use, particularly in automotive manufacturing. Today, other industries with light- to medium-duty manufacturing applications, like appliances and warehousing, are installing lighter duty monorail systems appropriate for their needs.”
Workstation and overhead cranes
Offered in multiple types and load capacities, cranes are comprised of three components:
- a stationary or mobile bridge made of rails and carrying one or more trolleys,
- the unit that travels side to side and carries the hoist, and
- a lifting device that hooks onto and manipulates a load.
Cranes can be manual or power driven, depending on the application and the size of the load that has to be moved.
On the smaller scale, workstation cranes enable operators in a work cell to safely manipulate relatively light loads. These free-standing units handle product in a relatively limited area, like in production environments.
More workstation cranes are being installed as part of lean-driven manufacturing process changes, says Jeff McNeil, marketing manager for Gorbel (800-821-0086, http://www.gorbel.com). “To enhance the ability to produce multiple products in a single assembly area, companies are turning to flexible systems that maximize the productivity of their operators—installing more ergonomic workstation cranes and lifting devices to help users work smarter,” he says.
Some of the newest workstation cranes are intelligent devices that combine manual and servo-driven operations, McNeil says. The manual function allows workers to move at their own pace as they walk to a bin, select a part and guide the crane to a machining center process. The servo-driven function controls the positioning of the part on the machine, preventing damage to either, by slowing down for part placement and release.
Massive overhead cranes move heavy loads that are not practical to transport with a lift truck over long distances. Ceiling-mounted bridge cranes are often part of the building structure. Top-running, double-girder cranes mount the bridge on top of the runway and have two girders for the bridge. Always powered, these bridge cranes offer capacities up to 600 tons. Alternately, under-hung cranes have a trolley that runs on the bottom of the support I-beams. They're ideal for loads of 15 tons or less.
Gantry cranes look similar to overhead bridge cranes but are not part of the structure of a building. Instead, a gantry consists of two uprights connected by an I-beam that serves as a bridge for the trolley. They can be either powered or manually manipulated and handle capacities up to 5 tons.
Speed control continues to be refined in overhead cranes for better load handling, says John Paxton, president of Demag Cranes & Components North America (440-248-2400, http://www.demagcranes.us).
“The enhancements include smooth acceleration and deceleration of the hoist and even step-less control, similar to the gas pedal on a car,” Paxton says. “The more you push on the button, the faster you go, and as you let up, the slower you go. That gives the operator improved control for spotting and positioning.” This functionality results in improved productivity.
A bigger trend in 5-ton and above cranes, says Paxton, is the integration of smart controls to enhance safety and reduce downtime. “These controls monitor the hoist, store information including warnings and error codes, and allow the data to be retrieved. By monitoring the load spectrum, users know how the hoist is being used and can schedule maintenance as needed, both predictive and preventive.” This also improves safety and reduces downtime due to unexpected repairs, Paxton adds.
Driven by safety concerns, more and more overhead systems are being controlled by wireless radio remotes instead of wired pendant control. The wireless method permits the operator to run the crane from a safe distance, while pendants require the operator to be near the load as it moves.
Wireless systems include a radio receiver mounted on the crane and wired into the programmable logic controller (PLC) and motors that are turned on and off by the system. They also include a handheld transmitter that the operator uses to send a signal to the receiver.
“One of the emerging trends we see in crane controls is remote diagnostics,” says Haroon Inam, vice president of global engineering for Cattron Group International (724-962-3571, http://www.cattrongroup.com). “This and a multitude of other reports—including productivity monitoring and safety conformance—can be custom-created to examine crane behavior, as well as operator behavior.”
Reports are generated from the data collected by the machine control unit. “The information can be conveyed to a global help desk not only for condition-based monitoring, but also to enable remote upgrades of software without the need for a technician to visit each site individually,” says Inam.