The aesthetic value of a picture in an advertisement, a high-quality brochure or an upscale catalogue is based on the quality of the print. Pure colours and colour gradients can only have their desired effect if every colour pixel is precisely positioned. The specialists at Heidelberger Druckmaschinen AG (Heidelberg) are building high-tech printing units at their factory in Wiesloch-Walldorf to master this challenge.
Heidelberger are relying on the measuring systems from Carl Zeiss , among others, to ensure the precision of the components. A modern printing machine is high-tech equipment. To print each colour separately, a printing press must consist of several up to 16 printing units and can be up to 27m long. Depending on the model, up to 18,000 pieces of paper pass through such a system per hour during printing operations.
The more precisely the pixels have to be placed, the higher the demands on the printing machine, and thus the designers and specialists in production, the assembly specialists and the metrologists. Current technology achieves pixel accuracy of 0.01mm. This precision can hardly be imagined, but the human eye still notices the slightest deviation in print.
The components of the printing unit must be manufactured and assembled with extreme accuracy in order to put the best quality on paper: axial and lifting curves, radial segments, and radial and multiple curves. Critical parts include the paper feeding cylinder, gear wheels and cam discs. For the printing machine to meet the high demands, the parts must display narrow tolerances in the range of a few micrometers.
The quality of the print is decided by the precision of the geometric values. Therefore, these components must be produced, measured and assembled with the utmost accuracy.
The equipment used by production personnel at Heidelberg for their production-integrated process monitoring includes a CenterMax coordinate measuring machine. With its special design and thermal stability, CenterMax is suitable for shopfloor.
With their new climate-controlled (20°C) precision measuring lab, Heidelberger are well-equipped to measure in extreme accuracy ranges. This is the location of the central entity that develops and defines measuring methods and ensures them in production.
Furthermore, this area of activity also includes arbitrary measurements, measurements on calibrated master gages, for example, impression cylinders, measurements on relevant, critical parts, and the inspection of operating equipment and selected delivered components.
According to Walter Siegmund, Head of Test Equipment Management, at their internal measuring centre, they have laid the foundation for seamless and precise measuring runs. The constant temperature and the optimised vibration insulation ensure lower measuring uncertainties.
Heidelberger can perform many measurements more efficiently and with fewer risks than in the past. Additionally, the climate-controlled preparation zone used to temper the test pieces leads to shorter throughput times. Heidelberger have to completely rely on the results from the precision measuring lab.
With complex structures such as printing machines, there is a high risk that defective parts or modules have an impact on the printing process. Therefore, highly precise measurements at the reference temperature of 20° are an important element of quality.
The measuring lab also contains a special version of the Zeiss Prismo 3D coordinate measuring machine as a precision measuring instrument. This machine was recently added to complement the UPMC 850 reference coordinate measuring machine that has been in operation for years. Equipped with a rotary table for large workpieces, the Prismo is a flexible measuring system that enables Heidelberger to meet the high demands on quality during production control.
Siegmund had two main requirements for a successor to the classic in precision measuring lab: first, it must have the same accuracy as the UPMC 850, and it must also have a measuring range large enough to measure with extreme accuracy the large impression cylinders that can weigh up to four tonnes.
Prismo, specified in accordance with ISO 10360, features MPEE of up to 0.8µm + L/400 for the three different measuring range rates. Acceptance testing was performed at the factory in Wiesloch with 20 gage block measurements in different positions. The straightness measurement on a 700mm long reference standard delivered a value better than 0.5µm.
Roundness deviation (MPERONt) throughout the measuring range was also less than 0.5µm with a 260mm long stylus. The scanning performance value (MPETHP) also delivered good measuring results. The CAA point grid was particularly narrow. The in-depth acceptance testing of guide way errors together with the new realtime correction of the table returned negligible CAA residual errors.
Special components and a special adjustment resulted in probing reproducibility of better than 0.15µm throughout the entire measuring range. The C99 controller permits speeds of up to 520mm per second despite the high resolution of 0.02µm. The stability of the guideway accuracy was verified using a variety of load tests – with weights up to four tonnes.