Digital advantages for force measurement in printing presses: asset management with FDT containers and Device Type Managers
In a rotary printing press, the paper must always be held under as constant a tension as possible. This is the only way to prevent the paper getting folded or creased, or even torn. Not only that, but the only way to obtain optimum quality printing is if the paper web tension is in the right range. This is why the Koenig & Bauer corporate group, one of the biggest printing press manufacturers in the world, relies on HBM measurement technology.
Koenig & Bauer AG (KBA) manufactures rotary printing presses for newspaper and commercial printing, sheetfed offset presses and digital printing and special application presses. The KBA Group employs around 8,300 staff worldwide. At company HQ in Würzburg (Germany), the Development team works to continually improve existing printing press technology. As KBA supplies presses to the world, this continued development focuses on issues such as easier commissioning and the possibility of remote maintenance. It was only last year when KBA changed over from analog to digital measurement technology and now further optimization is taking place, with the introduction of the appropriate Device Type Manager (DTM) and an FDT frame application, to allow considerably more accurate monitoring of the presses and efficient asset management.
Principle of measurement
The tension of the paper web is measured at the so-called guide rollers within the printing press. To do this, HBM strain gages (SGs) are fitted to the bearing journals on which the guide roller is mounted. The strain gages generate a signal when the bearing journal is deformed by the force the paper web transmits to the guide roller. The strain gage connections are connected to a signal amplifier in parallel. This allows the strain gage signals of both the bearing journals to be determined and the signal amplifier supplies an output signal, that is used for subsequent control.
New digital amplifiers
HBM’s digital digiCLIP DF30DP amplifiers are used for this purpose. They supply an absolute force value which, together with the known geometric variables such as the width of the paper web and the wrap angle of the guide roller, can be directly converted to a web tension force that is related to the width of the paper web. “The greatest advantage of this new technology is that it can do away completely with the need for extensive mechanical calibration”, says Holger Engert, who is the Measurement Technology Manager responsible for development in web tension force measurement at KBA. This enables the company to save valuable time and therefore money, during commissioning. Holger Engert sums it up like this: “We were initially astounded that we were able to obtain fully assembled bearing journals from HBM with already calibrated strain gages, at a better price than from our previous supplier.”
Easy integration into the control concept
As the amplifiers have a Profibus DP interface available, it is very easy to integrate them into the primary control concept of the printing presses. Four measuring points are installed for each paper web. As one printing press can contain up to twelve webs, the maximum number of measuring points is 48. Communication with the control level, which is based on PC technology, takes place via Ethernet. This also makes remote printing press maintenance possible, via VPN, for example. Digital amplifiers are ideal for this concept. The primary control can read out the control parameters for paper web tension at any time. Control can also be accessed for remote maintenance, which had not been possible with conventional analog technology. “As we sell our machines throughout the world, being able to maintain them fully by remote control is a crucial advantage”, stresses Holger Engert. It is possible to save money again here if there is a problem, for example, and process parameters and process statuses have to be checked from Germany. Because the service engineer has access to full machine control via VPN, it only takes a few minutes to run diagnostics for the measurement and control components, so that any possible faults can be localized and eliminated. In the long term, this will help to reduce the amount of installation activity.
Device Type Manager
As mentioned at the beginning, the newly introduced Device Type Manager, specifically developed by HBM for digiCLIP amplifiers, also has a contribution to make. The DTM works in much the same way as a printer driver does for a PC. It includes all the requisite functions for parameterization, operation and diagnosis of digiCLIP amplifiers. A graphical user interface guarantees easy operation. KBA‘s IndraWorks from Bosch Rexroth is used as the FDT container (Field Device Tool) on which all the DTMs run. Now, just by double-clicking on the DTM, the service engineer will receive a status report on all the digiCLIP amplifiers that are installed, at a central point, so that an extended diagnosis can begin straight away. Tests with the FDT container and the DTM have almost been successfully completed and the printing press prototype has been working reliably.
Holger Engert has this to say about the advantages of DTM: “Without generating a single line of program code, we have been able to utilize in full the functionality of the HBM software’s ‘digiCLIP Assistant’ in a non manufacturer-dependent FDT frame application for parameterizing and monitoring our web tension measuring points.”
“The competent and uncomplicated advice we received from the responsible HBM team during the prototype phase was really helpful to us in making the changeover to the new technology trouble-free”, concludes Holger Engert.
HBM’s digiCLIP amplifiers are absolutely ideal for automation applications in an industrial environment. The noise-free and stable measurement technology is a feature of the modules, and provides outstanding measurement quality. The carrier-frequency modules provide reliable, noise-free measurements of variables such as force, strain, torque and pressure. It only takes a few seconds for users to faultlessly adapt the sensor technology to the amplifier. Each module has a Profibus DP interface for communication, which can be used for parameterization, measurement acquisition, remote diagnosis and backup. A separate Profibus adapter module is also available, to provide a standard connection for Profibus. The modules have an internal digital signal processor for calculating practical characteristic quantities such as limit values, instantaneous values or peak values from the measurement signals. This powerful signal conditioning is self-monitoring, thus relieving the burden on the subsequent automation systems. This is an easy way to realize distributed structures. This Device Type Manager (DTM) is now available free, and also has a graphical user interface for parameterization, operation and diagnosis of all the digiCLIP amplifiers that are installed, from a central point.