The rubber-coated rollers used in the printing and coating industries need to be accurately ground with a profile to suit their application. These profiles are parallel in some applications, but for most a precise convex or concave profile is needed. Designing a machine that will consistently and accurately grind these is not easy, especially when the machines are expected to handle rollers up to 5m long, 600mm in diameter and weighing up to a quarter of a tonne.
When developing its RG300 roll grinder, Halifax Numerical Controls (HNC) needed to produce a product that would set new standards for versatility, convenience and productivity. The engineers decided a CNC system may not offer the most flexible platform so instead decided to design a new control system based on Omron products, which would allow them to produce a fully customisable solution.
The resulting solution includes a four-axis machine controller, of which only two axes are currently used; two 600W servo axes with absolute encoders; two inverter drives, one for the workhead drive, the other for the grinding wheel drive; a colour touchscreen operator interface panel (HMI); a safety relay and a safety locking switch.
All of the major items are linked by EtherCAT, which offered several advantages, such as simplifying the control wiring and allowing direct access to the key operating parameters for all of the inverters and servo drives, which means that they can all be set up and controlled from the HMI panel. The panel can also be accessed via the network, allowing operation of the machine to be visualised remotely using the in-built web browser functionality.
The Ethernet support offered by the Omron NJ machine automation controller made it possible to connect a third-party wheel balancer direct to the control system via the controller’s built-in Ethernet/IP port. This enables the wheel balancer to be monitored and controlled from the machine’s main HMI panel, eliminating the need for a separate user interface.
The NJ301 machine controller also features a fast, powerful Intel processor, and full advantage was taken of this by using it to run specially written algorithms for calculating the cam profiles needed for specific types of roller. Whereas the calculations had taken around ten seconds for each profile, the controller executes them almost instantaneously.
For configuring and programming the control system, HNC made use of Omron’s powerful Sysmac Studio Integrated Motion and Logic programming platform, which makes developing even the most complex control programs a fast and easy task.
With the new control system, profiles for each type of roller are prepared off-line, and are loaded into the control system with the aid of a standard SD memory card. The operator then chooses the required recipe via a barcode scanner. The selected product is confirmed on the HMI’s display, and the control system does the rest.
The graphical display minimises the amount of text used in the operator interface. HNC has, in fact, programmed the interface so that the small amount of text it was essential to use can be displayed in any one of sixteen languages, with instant switching between languages. The operator interface can also be easily customised to suit user requirements.
In addition, the HMI unit has been programmed to provide powerful machine diagnostics and to log key machine operating parameters, both functions being facilitated by the unit’s ability to access all major operating parameters in all of the control devices via the EtherCAT network.
Of further benefit, to accommodate the need for a manual handwheel control option for the grinding operation, it was only necessary to add an encoder interface to connect the handwheel to the EtherCAT network. It was also possible to use a spare analogue input on one of the inverter drives as a general purpose analogue input instead of purchasing an additional analogue module.
The first machine has been operating for several months at a customer in Wales, and the company is also seeing a lot of interest both within the UK and worldwide, in particular due to how easy it is to operate.
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