PC Control: Press manufacturer Schuler has integrated hydraulic control into PC-based logic where control can be easily modified as well as protected.
In an ambitious pilot installation, press manufacturer Schuler Hydrap (http://rbi.ims.ca/3855-526) is leveraging Ethernet for high-speed communications between a PC-based control system and the distributed I/O in its new Profilineฎ hydraulic presses. The product line runs on a network that is up to 500 percent faster than previous implementations, and has dramatically reduced cycle times.
With these new systems, Schuler implemented TwinCAT Automation software from Beckhoff (http://rbi.ims.ca/3855-527) so that all control tasks, including I/O, hydraulics, and drive control could be implemented on one uniform platform. Schuler's in-house HMI software called Basic-View, based on a Siemens protocol, provides operator interaction with the machine. Both the HMI and TwinCAT control run on a single industrial PC, replacing what had been separate controllers for HMI, PLC, as well as hydraulic control.
"The integration of the hydraulic control into the PLC software already allowed us to run an improved process and improve the quality of the manufactured parts," says Ralf Sohr, manager of electric design at Schuler.
But despite progress, the bus system was still seen as a bottleneck. Clement Peters, corporate manager, controls & drives design for Schuler, explains that by using numerical control tasks in the TwinCAT software, Schuler was "able to model transfer applications with high-quality motion control, utilizing 1 to 2 msec cycle times."
Reducing cycle times was critical to making use of a single control platform and meeting the requirements of the hydraulic control. Peters says that "fast (significantly less than 1 msec) reading, computation, and writing of analog signals and encoder positions is mandatory for the system."
New control architecture
By switching platforms, Schuler integrated the hydraulic control into PC-based logic where it could be easily modified as well as protected. Schuler's overall goal was a common, IEC-based control platform across all products, the ability to cover all demands for control tasks, and platform independence.
With the existing system that utilized a PLC, proprietary hydraulic control modules and Profibus communications, Schuler was unable to reduce the cycle time to lower than 5 msec due to the communications overhead of the system. The network bottleneck situation improved significantly when it started using Beckhoff's Ethernet-based EtherCATฎ system. According to Sohr, the speed of the system and its small overhead provides an ability to execute fast motion and hydraulic control for all of their applications.
Reduced cost, increased simplicity
User Friendly: Schuler is confident that customers will embrace press machinery with Ethernet-based control systems.
Despite technology advantages, Sohr clearly sees further potential as technology providers improve Ethernet connector technology. For example, the RJ45 connector does not require a shield and is simply and easily assembled with the help of a simple screwdriver.
Peters plans to expand applications into other areas. "We see the potential for application in the press transfer system," he says. "We expect to guide the transfer system with centralized command values for a virtual main shaft and synchronize modules, as well as components such as transfers, conveyors, feeders, or palletizers."
Today, the Profiline control also still needs additional bus systems, but Schuler is looking to eliminate those through the expanded use of Ethernet technologies due to the fact that maintaining multiple bus systems on machines requires extra effort in planning, configuration, and commissioning.
A future goal for Schuler is to use a uniform control platform throughout the Schuler group. After successfully implementing common practices in motion control applications and programming standards for the main control platforms, components are being uniformly selected. And with these activities, Schuler is creating a common look and feel for its machines and machining lines.
Along the work of standardizing PLC and motion control applications, a library for hydraulic control is in the making. In practice this means that, in the future, a mechanical cross bar transfer press from Schuler will be based on the same function blocks as a hydraulic press from Schuler SMG or Schuler Hydrap.