Since its founding, KEB has offered spring-set brakes, which are used to stop a motor shaft when power is cut. Brakes frequently went on products such as hoists, elevators, and presses where safety is a concern. “In the ’90s we started to incorporate safe-torque-off functionality into our VFDs,” says Jonathan Bullick, sales & marketing manager at KEB America. “At the time it was referred to as a Category 3 Safety Stop. That progressed into a certified SIL3 safe-torque-off function, which is now standard on all our new drive products. And we added other safety products and functionality as well."
KEB is now offering the safety components, as well as the motion control components, says Bullick. "This makes us a single-source control solution for machine automation," he says. "It's a strategic area of our products and where our customers are leading us. We can offer a complete safety solution, not just one product. And the safety is an obvious fit for our drives, controls and brake products."
A lot of KEB’s core applications involve motion control, continues Bullick. "This includes positioning for a machine tool or a packaging machine or tower crane," he says. "The natural progression was to include these safe motion functions such as safely limited speed (SLS) and safely limited position (SLP) into our drives. At the same time, we worked to develop a safety extension to our industrial PC product. This extension became our new Safe PLC and Safe I/O, which is based on Failsafe over EtherCAT (FSoE). The drives and Safe PLC are programmed in a single environment using Combivis Studio 6 Safety."
The Safe PLC works in parallel with the main PLC of a machine. "The machine PLC runs the machine functions, such as motion control, and, in addition to that, there would be a separate, self-contained safety processor that is handling safety I/O and monitoring the related functions and logic," says Bullick.
The KEB safety control products function on FSoE. "This provides the possibility for traditional discrete wired safety to move to a network cable," says Bullick. "We see this as a big advantage. It simplifies wiring, so there is a cost advantage in wiring time. Some of our customers have rental and mobile equipment that is frequently being moved and set up. The ability to put the safety on the network reduces commissioning time and possibly wiring errors.”
The new FSoE digital I/O block is a combined digital input and output module with four inputs and two outputs. This module works well for monitoring safety devices such as guard switches, light curtains and safety mats.
The safe-motion capability has moved well beyond safe-torque-off functionality. "With the addition of FSoE and scalable safety functions, both the logic and control can reside in either the PLC or the drive," says Bullick. "Safety often handled in a Safe PLC can be moved to the drive. In a decentralized topology, the drive manages the safe motion of the axis it is controlling. In large multi-axis type of applications, this structure has the advantage of spreading out the processing power to quickly react to an unsafe condition. At this time, many drives do not have this functionality."
Handling safe motion at the servo or variable frequency drive offers a number of advantages. "Safe motion allows the machine to operate in a limited safe state instead of completely shutting down," says Bullick. "For example, during safe-limited-speed operation, a user might be able to make adjustments on the machine while it is powered and operating at a slow speed. In another example and traditionally, it might have been required for a machine to be completely powered off before an operator lifted a protective gate or door. It now might be possible to keep high power to the drive but activate one of the safety functions. The benefit here is that the drive does not receive a power cycle, which requires some time for the capacitors to bleed before it can be started up again. Implementing these safety features also become efficiency gains."
The drive safety functionality scales for all new KEB drive products. The functionality available in the S6 Servo Drive will carry through to the upcoming F6 drive, which extends to 1,000 hp.
The Combivis Studio 6 development environment includes many modules, such as document database, drive commissioning, PLC programming and function block libraries. "For our new safety hardware and functions, we added a safety module in a new release called Combivis Studio 6 Safety,” says Bullick. "The Studio 6 Safety provides safety program development using a function block diagram (FBD) safety editor, which contains certified safety modules per PLCopen safety standards."