Cranes are critical in a number of industries, including aircraft/aerospace, auto manufacturing, chemicals and minerals, pulp and paper, steel production, and utilities, as well as the grain industry, logging, rail yards, and ship loading.
Traditionally, industrial cranes have been operated by human operators sitting in cabs in the cranes. In such instances, the operator's actions are guided by the hand signals of a person outside of the crane. "In the past, cranes were operated by the cab operators," says Brad Robinson, president of Robinson Engineering, which has been offering remote control technologies since 1962. "The guy on the ground was hooking the chains, doing the loading, and having to wave his hands to direct the operator where to move the crane."
In other cases, rather than have an operator sitting in a cab, a person outside of the crane would operate the unit, using pendant pushbutton stations suspended from the crane.
In recent decades, technology has advanced to the point where cranes can be operated by remote control. While this technology has been around since the 1960s, it has continued to improve over the years, with newer systems providing more safety, reliability, efficiency, versatility, and cost savings than in the past.
The two standard technologies for remote control crane operation are radio frequency (RF) signals/waves and infrared light. While both continue to be available, the RF technology is the more popular of the two, having about 98 percent of the market, according to Magnetek Material Handling, because of its advantages over infrared technology. For example, infrared units have shorter operating ranges than RF units. In addition, infrared light can be deflected by dust or other airborne particles, and even blocked by larger objects in its path.
"Infrared was a neat idea," says Robinson. "However, in most plants, especially steel mills, there is too much dirt and dust, and all of the reflectors and lenses on the crane get covered in dirt and dust. As a result, you have to constantly clean off sensors and other surfaces."
A remote control system consists of two units. One is a portable transmitter that creates control signals. The other is a receiver that is permanently installed on the crane. The receiver is connected to the crane's control unit. Each switch on the transmitter creates a specified combination of "pulses" that is transmitted to the receiver, which then decodes the "pulses" and transmits them to the crane's motor controllers.
While remote control technology can be purchased already installed in new cranes, the technology can also, in many cases, be retrofitted onto existing cranes. One prerequisite for retrofitting is that the existing crane must be equipped with magnetic motor controllers, rather than drum controllers (the latter are common on many older models of cab-operated cranes). A second prerequisite is that the brakes must be equipped for emergency use and connected with the existing motor controls. For example, hydraulic brakes that are traditionally operated via foot pedal must be converted to allow for electronic actuation.
The technology has been keeping up the with the times. "A lot of smaller and inexpensive remotes are just two-step push-button units that provide direction plus high speed," says Robinson. "As such, they have always worked well for small cranes." However, with the introduction of variable frequency drives (VFDs) a few years ago, most large cranes now have five speeds: slow, slow-medium, medium, medium-high, and high. "This allows you to have more control over the motors and speeds," he says. With advances in technology, remote control units are also able to respond to the need for changes in speed (see Figure 1).
While Robinson Engineering offers a number of different models, its most popular model is the Crane Boss 400, which is custom-made for each crane and, according to Robinson, is primarily used in steel mills. "More than one crane in the same plant can be controlled by the Crane Boss 400," he says. "The system can be installed on existing cranes or can be installed on new cranes at the time of manufacture." The unit can handle as many as seven five-speed or stepless reversing motors with all motions simultaneous and in any combination. It can also control many auxiliary functions, such as magnet lift-drop, lights on-off, interlock latch-unlatch, signal sounding, and brakes.
Another manufacturer, Magnetek, offers a wide range of products, from the most basic to the most complex. "We have cost-effective off-the-shelf systems that would be appropriate for applications such as stick cranes," says Norm Davis, Magnetek radio controls business development manager. At the other end of the spectrum are very complex custom-engineered solutions that require a significant amount of in-house engineering. "A custom-engineered application is appropriate any time there is critical lift that requires a fine level of control or an increased awareness of what is going on with the systems during the lift," says Davis. "Another situation would be when the crane has a lot of different capabilities and requires a higher level of selection for the operator, who may need to control a number of different components of the crane at different times."