By Mike Bacidore, Managing Editor
The futuristic technology of the Star Trek macrocosm always has been centuries ahead of its time, both literally and figuratively.
"Gene Roddenberry had real buttons all over the place in the original 'Star Trek' series," notes T.J. McDermott, senior project engineer at Formost Fuji (www.formostfuji.com) in Woodinville, Wash. "Seventy-five years after that, they were replaced by touchscreens in 'Star Trek: The Next Generation.' In reality, software controls on touchscreens arrived centuries before Gene envisioned it."
Software continues to replace machine hardware for a variety of reasons, but some machine builders offer words of caution.
"Theoretically, the only real control necessary is an e-stop button," continues McDermott. "The rest can be touchscreen buttons. That said, there are instances where mechanical coupling of a system is better than electronic gearing; a mechanically coupled system can never be out-of-time under normal operating conditions."
Camco-Ferguson indexing drives used to be an important component of Formost Fuji's machines, explains McDermott. "They can be replaced by a servo drive and motor, along with software to create an equivalent cam profile," he says. "The servo drive and software solution allows for infinite flexibility over the mechanical drive; changing the cam profile table is easy, compared to changing out the indexing drive. Given a choice, I would much rather create a cam profile via software; if I want to fine-tune the motion profile—a polite way of saying I want to correct a mistake—changing numbers stored in RAM is easy. Cutting a new cam plate is a rather expensive way of creating a new profile."
Temperature controls now get integrated into the logic processor instead of being external devices, adds McDermott. "The on/off switches, dials and indicators now reside completely inside the logic processor and the display screen," he explains. "Again, given a choice, I'd rather have the software-driven temperature controls. When they're not needed, they're off-screen and out of the way."
However, software does not lend itself to intuitive troubleshooting, notes McDermott. "With a mechanical system, it's relatively easy to track the various chains, cams and gears to see how the motion is generated," he says. "With a software-generated cam profile, the education level of the troubleshooter must be much higher. The trade-off thus is flexibility vs. the skill level of the maintenance staff."
Nick Shea, project engineer at DMC (www.dmcinfo.com), Chicago, has worked with safety PLCs on several projects and seen some direct advantages of replacing hardware such as a safety relay with a safety program in the safety PLC. "Some benefits of going this direction are wiring advantages, flexibility and configuration," he explains. "By wiring only to a PLC, you get both safety functionality and monitoring and diagnostics. Plus, you have a single pair of contacts as PLC inputs, rather than wiring to both an input card and safety relay. It also simplifies wiring for construction and future wiring for troubleshooting."
Software also is more flexible, explains Shea. "Safety logic and conditions can usually be quickly modified programmatically without physical modifications to system," he says. "And custom variations to safety logic that are impossible or limited with hardware alternatives are possible in software. Also, machine guarding or manufacturing-line e-stop zoning can be done in software, rather than multiple safety relays. Safety zones also can be dynamically modified based on machine operating status. And intelligent devices such as laser scanners and light curtains usually are made to integrate smoothly into the software development environment of a safety PLC."
Rapid Conductor, a hot plate welder designed and built by Extol (www.extolinc.com) in Zeeland, Mich., is a good example of replacing mechanical systems' controls with electronic control, says Rob Bouws, product development engineer at Extol. "Traditional hot plate welding uses hydraulic cylinders with mechanical stops on the fixture and heated tooling," he explains. "Adjustment of melt depth and seal depth is time-consuming and difficult on these machines because shims need to be inserted under the hard stops in order to tune in the process."
Extol's Rapid Conductor uses coordinated servo control instead of cylinders. "The user can adjust melt and seal depth just by changing parameters on the HMI," says Bouws. "The machine is also much faster because the motors can move quickly with controlled accel/decel and it doesn't open farther than necessary to remove the heated tool. Servo motors also offer control features previously not possible on traditional hot plate welders. The speed at which parts contact and pull away from the heated tools can be controlled. Both parts can be loaded in the lower fixture, and the upper fixture can come down and pick up the upper part half before welding."
Pete Mansfield, engineering fellow hardware systems at Kiva Systems (www.kivasystems.com) in Woburn, Mass., recalls around the early '90s when multi-axis controller card vendors were starting to come out with packaged features with names related to "cam" or "gear," implying one could replace the mechanical linkages between different shafts with independent, though software-linked, direct drive control.
"The obvious benefit is you don't have to commit to one specific drive ratio or cam profile between axes, for example, but on the flip side, if you only have one drive ratio you care about, then the hardware solution would likely still be more cost-effective," he says. "My general approach to new machine design is to look for the mechanical linkage solution first. But there certainly are areas where independent control is needed to perform coordinated movements."