Integrating Safety and Control

Lekx-Toniolo had less than three months to design and develop all the software for the machine's control system. "Beckhoff's IEC 61131-compliant programming environment as well as TwinSafe/FSoE came together as an integrated package that helped reduce engineering and integration times," he says.

Having one common automation platform with one network that can handle standard and motion control as well as safety requirements is not only simpler, it also consumes much less cabinet space than more traditional designs that use safety relays or multiple control platforms.

"Benefits of the system included a reduction in wiring, complete modularity, and the ability to reuse system elements in the future with very little reengineering," Lekx-Toniolo explains. "The cabinet space was reduced to less than a quarter of that typically required for a weld cell of this size."

Because it's based on pre-programmed safety function blocks, a TwinSafe environment is easy to adopt, understand and use, Lekx-Toniolo says. "The performance of EtherCat and TwinSafe let us mount safety devices closer to the hazard, which in turn allows operators to be to closer to the work piece, lowering overafll machine cycle times."

Rod Brown, engineer at Kuka, says a single control system simplifies the job. Kuka used a Siemens Industry programmable safety controller in a robotic automobile body shop to control multiple doors, main control panels with auxiliary panels on the robots, roller tables and assorted remote devices. The Siemens controller acts as both the control processor for normal machine functions, and the safety processor to monitor and control all safety devices.

By working from one common programming environment, and using ladder logic for both process control and safety, Kuka substantially reduced its engineering efforts and increased flexibility. "We built the system in no time and commissioning was surprisingly easy," Brown says. "This approach saved us tens of thousands of dollars on the first installation alone."

CAMotion, based in Atlanta, faced a safety problem that probably couldn't have been solved with separate safety systems. CAMotion builds X, Y, Z, Theta machines for all types of motion, including overhead gantries, with many applications in the printing industry.

In one overhead gantry system, CAMotion had to integrate control and safety functions because its overhead robot worked in the presence of human operators on the ground.

What is particularly interesting about the application is that the safety I/O communicates with the PLC control system over a wireless safety-rated network. The gantry I/O communicates to the PLC on the ground, entrusting the safety of the system to wireless.

Figure 1. A combination of an integrated and distributed automaton system is used to provide control and safety for this robot weld assembly cell.

"We built a large-overhead-gantry-robot log-depalletizing system (Figure 2) that picks up heavy ‘logs' in the form of green strapped book pages on a pallet, and loads them onto a conveyor," says Steve Ross, control engineer at CAMotion. "The safety problem was that people could be in the area, which was not protected by safety barriers. The system had to use vision sensors mounted on the overhead gantry to detect the presence of people, and stop operations if anyone intruded."

People need to be in the area because, after the robot deposits a log onto the conveyor, operators have to remove a strap and end boards. The robot gantry actually operates in the presence of humans, who are free to move around. The safety system ensures that the robot and the humans never meet.

"Because the gantry is overhead and mobile, we had to use an integrated safety system with wireless transmission between the gantry I/O and the ground-based PLC," Ross adds. "We used a Siemens integrated safety PLC to control the robot and perform the safety functions, a single network for both control and safety I/O, and laser scanners mounted on the gantry to detect people, find the pallets, and help direct the robot to pick up the pallets and put them on conveyors."

Figure 2, camotion.jpg. This overhead gantry crane communicates wirelessly with the automation system on the ground, thus entrusting safety functions to a safety-rated wireless link.

One network and one PLC simplified the application, reduced the amount of wiring, and helped cut installation time by 30%, Ross says, adding that it enabled fast trouble-shooting and diagnostics, allowing deployment in two days.

"We think it's critical that all robotic systems be able to accommodate a human working with the robot," Ross says. "This becomes increasingly important for cost-effective machines. The more closely a system allows humans and robots to work, the more productive it can be."

A video of the installation can be viewed at www.ControlDesign.com/CAMotion.

Integrated safety applications are becoming more widespread, turning up in one industry after another. Diosna in Osnabrück, Germany, supplies a variety of custom-built machines to the food, pharmaceutical and chemical industries.

The company used a Rockwell Automation GuardLogix PAC to handle the batch control, process parameter control, and all of the automation needed for a compact granulator system for a tablet manufacturing plant in Puerto Rico. GuardLogix also handles the machine's safety infrastructure. Diosna likes the fact that a PAC can be used for both control and safety, particularly with respect to the programming environment.

"All of our machines are bespoke, custom-created to match the customer's application requirements," says Henning Falk, product manager at Diosna. "However, we can reuse blocks of code for standard operations, and we've found that program editing on the AB equipment has been nice and simple." Unlike older separate safety systems with their complex and specialized programming requirements, newer integrated safety systems feature programming methods and concepts similar to standard automation.