Roll grinding made easy by control system from Omron

The first of the new HNC RG300 machines has now been operating for several months at a customer site in Wales, and its benefits have proved so convincing that HNC has already received orders for a further machine to be used in the UK, and no fewer than four machines that will be used in the Far East.

Rubber-coated rollers are used extensively in the printing and coating industries and must be accurately ground with a profile to suit their ultimate application. For some applications, the profiles are parallel, but for the majority a precise convex or concave profile is needed. Designing a machine that will consistently and accurately grind these profiles is no easy task, especially when end users typically expect the machines to handle rollers up to 5m long, 600mm in diameter and weighing up to a quarter of a tonne.

Halifax Numerical Controls has considerable experience in designing and manufacturing these machines, but when the company started development on its new RG300 machine, it was determined to come up with a product that would set new standards for versatility, convenience and productivity, thereby giving HNC and the RG300 a strong competitive edge in UK and world markets.

After carefully evaluating the available control technologies for the new roll grinder, HNC's engineers concluded that using a CNC system may not offer the most flexible and customisable platform for their machine. They felt that they needed an approach that would allow them to easily tailor the control system to suit the specific application.

After further investigating control options and after having detailed discussions with Omron, the HNC engineers decided that the best option would be to design a radically new control system based on Omron products, which would allow them to produce a fully customisable system.

There were several reasons why HNC selected Omron equipment for this important project. These included Omron's ability to supply all of the major control items needed, its ability and willingness to demonstrate Ethernet connectivity to third-party equipment, the global availability of service and support for its products, and HNC's previous excellent experience of working with Omron.

Linked by EtherCAT

The control system developed by HNC's engineers for the new RG300 roll grinder 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 these components are from the Omron range, and all of the major items are linked by EtherCAT, an Ethernet-based networking system specifically developed for use in high-speed, real-time control applications.

Using EtherCAT in this project delivered several important advantages. For example, the control wiring was simplified. This cut wiring time, saved space in the control panel and reduced the risk of wiring errors, which meant that testing and commissioning were faster and easier.

In addition, the EtherCAT network allows 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. In fact, the HMI panel can also be accessed via the network, allowing the operation of the machine to be visualised remotely using the in-built web browser functionality of the HMI.

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. As a result, the wheel balancer can be monitored and controlled from the machine's main HMI panel, eliminating the need for it to have its own separate user interface.

The NJ301 machine controller used in the project 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 previously taken as long as 10 seconds for each profile, the NJ301 controller executes them almost instantaneously.

For configuring and programming the control system, HNC made extensive 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 simply chooses the required recipe via a hand-held barcode scanner. The selected product is confirmed on the HMI's display, and the control system does the rest. This arrangement is very straightforward, which means the risk of costly errors is almost eliminated, and it also requires no CNC experience on the part of the operator. In addition, the graphical display minimises the amount of text used in the operator interface, making it readily adaptable to international markets. In fact, HNC has 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. In addition, the operator interface can be easily and inexpensively customised to suit specific user requirements.

The HMI unit has also 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.

Bonus benefits

During the development of the control system for the new RG300, the HNC engineers discovered many bonus benefits of using the Omron equipment. For example, 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 - no other hardware was needed. And 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.

Mike Diskin, Managing Director of Halifax Numerical Controls, says: "The Omron control solution gives us everything we were looking for in terms of performance, versatility and reliability, and it's also very good value. In fact, compared with other control systems we investigated it gives us much more functionality for our money.

"Our new RG300 machine is attracting a lot of interest both within the UK and worldwide, and much of that interest is because of how easy it is to operate, which, of course, is largely a function of the control system. Omron has made it possible for us to develop a powerful, flexible and cost-effective solution that our customers love, and that will grow with us as we further develop the capabilities of our machines in future."

Follow the link to view a video clip about Omron's work with Halifax Numerical Controls on the control system automating their roller grinding machines, and for further details go to www.industrial.omron.co.uk/.