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LMS Test.Lab helps engineers tailor the machine dynamics of Heidelberg presses
When a slight shake becomes an earthquake
LMS Test.Lab helps engineers tailor the machine dynamics of Heidelberg precision printing presses, where alignment of high-speed parts is measured in microns and even small vibrations of crucial components cannot be tolerated.
 No performance-robbing vibrations are allowed in equipment from Germany-based Heidelberg Printing Machine Company, the leader in the global sheetfed offset printing press market. They are number one because of the speed and precision of their machines, and they stay top with some of the best designs, high-quality production, and most responsive customer service in the world. A critical part of excelling in each of these areas is fast-turnaround testing. They use a range of LMS Test.Lab tools to analyze tensional harmonics, vibration amplitudes, resonant frequencies and mode shapes in real time. With analysis and diagnostic software on their laptops and a data acquisition system in a suitcase-size unit, engineers travel on-demand with everything they need to pinpoint the root cause of vibrations and find optimal solutions at product development centers, manufacturing plants and customer sites. The system is quick, analysis is state-of-the art, and results are displayed immediately, enabling engineers to evaluate vibrations while the machine is running and immediately determine corrective actions. With these powerful vibration test and analysis capabilities on a single integrated and portable system, LMS Test. Lab is regarded by Heidelberg as an indispensable technology in maintaining their strong market position.
Imagine a machine longer than 30 meters, with the mechanical complexity of an aircraft and the precision of a fine watch movement. That’s an offset printing press, or at least the largest models. Every day you probably see material that’s been printed on this type of equipment including magazines, newspapers, posters, books, packaging, brochures, pamphlets, forms and labels. Offset presses account for almost 70% of production in the print media industry because of their speed, economy, and consistently high quality.
The speed and precision of these machines depend on the synchronized fast-action movement of thousands of intricate interconnected parts and assemblies. Sheets of paper (or cardboard, plastic or other material depending on the job) are fed in one by one by an automated feeder and travel at nearly five meters per second through a series of up to fifty rotating sheetguiding drums while dozens of rollers and cylinders apply different colored ink dots as small as 10 microns wide. Sets of mechanical grippers transfer the sheets from one drum to the next until finished printed material emerges from the end of the line and is automatically stacked.
Offset presses deliver near-perfect prints because of their ability to accurately align sheets fed onto each of the many drums. Variation in this "registration" must not exceed 30 microns – less than the width of the human hair. So even the slightest jitter, quiver, or shudder in critical parts of machine dynamics is like an earthquake that could interfere with the proper operation of these high-speed precision machines.
Disruptive vibrations not allowed
These disruptive vibrations are the enemy of Dr. Stefan Schreiber, Senior Manager of Mechanics and Measurement Technology at Heidelberg Printing Machine Company. The firm has 150 years of tradition under its belt and is a titan in the sheet-fed offset press industry with the lion’s share of the worldwide market for sheetfed offset presses and an annual sales volume far beyond its closest competitor. He works at company
headquarters in Heidelberg, Germany, just a few kilometers south of the city of Mainz where Johannes Gutenberg built the world’s fist moveable type printing press in 1460 from a converted wine press.
 Called "The Masters of Print Media," Heidelberg is tops in the offset press industry because they develop some of the most advanced and innovative printing systems in the world, including pre and post-press equipment. Schreiber clearly reflects the pride of the company in the high quality of its machines. "No vibrations that interfere with proper machine operation can be tolerated in our high-speed, precision presses," he affirms. "They must be tracked down and eliminated."
Stand next to an offset press and you can hear the smooth-running sound of the typical operation of this complex machine. Put your hand on a side panel and you can feel rhythmic pulsations and tremors. "These are normal, totally harmless vibrations of a high-speed offset press at work. The inherent mass and stiffness of interconnected moving parts always yields a dynamic system," explains Schreiber. "But print quality may be deteriorated by certain other vibrations: resonances of particular amplitudes in sensitive parts of the machine, for example where ink is applied and paper aligned. The engineering challenge is in tailoring machine dynamics so it is robust against excessive vibration and not susceptible to any harmful resonances at critical locations. If the dynamics are understood, you can reduce excitations, shift resonant frequencies out of the  operating area, and so on." Heidelberg’s unique ability to tailor machine dynamics comes from the experience of its highly skilled engineers and the advanced technology they use in getting their important work done accurately and efficiently. The company is a long-time user of LMS Test.Lab, which combines multi-channel data acquisition with a suite of integrated testing, analysis and report-generation capabilities. He explains that advanced technology is essential in quickly identifying and evaluating vibrations. "We don’t have time for trial-and-error, hit-or-miss guesses. The source of vibrations that might adversely affect print quality must be spotted and fixed in the shortest possible time."
Fast turnarounds
This level of quick problem solving is key to meeting Heidelberg’s demanding product development schedules, with the company rolling out new models and enhanced features one right after another at a rapid pace to stay ahead of competitors. Indeed, Schreiber says that the large majority of his group’s work is in prototype testing to study machine dynamics and recommend design changes to optimize press performance.
 "Fast-turnaround vibration testing is essential in maintaining this steady stream of innovations in our product development programs," says Schreiber. He adds that quick-response vibration testing is also required at times during manufacturing when a machine must be adjusted to meet Heidelberg’s high quality inspection standards. Also, immediate troubleshooting may be needed sometimes when vibration concerns arise during installation of a press at a customer site and cannot be resolved by installation technicians. "High quality standards and timely customer service are part of our brand value that sets us apart in our industry," says Schreiber. "In this business strategy, state-of-the-art testing technology is essential in our work in product development, manufacturing and customer service solving vibration difficulties efficiently and effectively."
Critical importance of testing
Schreiber notes that LMS Test.Lab enables his engineers to pinpoint which of the many rapidly moving parts in an offset press are possible sources of performance-robbing vibration. Mechanical grippers transferring media between drums are susceptible to resonance. Likewise, drums and other rotating parts are vulnerable to torsional vibrations. Sometimes vibrations may be transmitted to other parts of the structure so that their origin may be quite different from the place where we see an effect.
"Identifying vibration sources is key to determining how the equipment design can be changed to solve any problems uncovered during prototype testing," says Schreiber. The geometries of the cams, bars and pillars of a particular gripper assembly might be modified, for example. The addition of parts such as torque restriction devices are some of the changes made during development that might be made to reduce torsional vibrations. Vibrations found during manufacturing inspection generally are solved by a realignment or replacement of components or with various damping materials if appropriate. These methods also are used as vibration remedies at customer sites, where unique building conditions sometimes set up unexpected resonances.
"For our engineers to be able to meet this wide range of vibration challenges, measurements must be highly accurate, analysis must be thorough, and the entire process must be done quickly," explains Schreiber. He points out that portability of the test system is essential in achieving this speed in troubleshooting at any one
of Heidelberg’s twelve production site or in providing first-hand service to a large global customer base, with more than 85% of sales made in 170 countries."
"LMS Test.Lab meets our demanding requirements in quickly investigating vibration issues and modifying machine dynamics anywhere in the world," says Schreiber. "The technology is critical to achieving the high levels of product quality and customer service that continue to make us number one in the industry."
Real-time results from a portable system
The speed and mobility of the LMS test system is especially important to Christian Hieb. As a senior engineer in the Mechanics and Measurement group, he goes wherever needed to perform vibration testing on Heidelberg’s offset presses.
"The LMS system is like a portable vibration test lab. I carry everything with me, even to remote sites," Hieb explains. "LMS Test.Lab software is on my laptop with all the analysis and diagnostic tools I need for a wide range of tests, without having to jump back and forth between separate systems or perform cumbersome data translations and conversions. The LMS SCADAS mobile data acquisition front-end is a rugged suitcase-size unit. I go to the site, attach accelerometers to the press, cable up the system and I’m all set. Otherwise, lugging around large racks of equipment and a workstation would slow us down."
 "LMS Test.Lab meets our demanding requirements in quickly investigating vibration issues and modifying machine dynamics anywhere in the world." Dr. Stefan Schreiber, Senior Manager of Mechanics and Measurement Technology at Heidelberg Printing Machine Company
Sensor connections are made easily on the front panel of the 24-channel LMS SCADAS unit and built-in signal conditioning modules are interchangeable according to the type of measurements taken. Conditioned signals are fed into LMS Test.Lab, which analyzes the data in real-time and displays results on Hieb’s laptop screen almost immediately.
"This speed in acquiring and analyzing data is a powerful capability," he says. "We get tremendous insight into dynamic behavior when we can see results clearly as the machine is running. This allows me to evaluate noise and vibrations on the spot, show customers or our own designers the vibration characteristics of machine operation, and determine immediately what corrective actions are necessary. What the LMS system does in seconds would take some other systems hours or days."
In this extensive battery of tests, color maps indicate vibration amplitudes at various frequencies and readily show "hot spots" of excessive levels. Order analysis is used to identify which drums are vibrating most by their characteristic Eigen frequency. Torsional vibration analysis also may be used to pinpoint vibration contribution of individual parts in a rotating assembly such as bearings or gearboxes.
Modal analysis is used to study resonant behavior of machine dynamics. Animated mode shape displays show how parts bend and twist during operation. Impact testing analyzes the response of the system to show which frequencies excite the structure to resonance. In this way, engineers can track down the root cause of structural vibration at a given frequency.
One tool that Hieb finds particularly useful is the LMS PolyMAX modal parameter estimation algorithm that highlights these resonances as colored spikes called "posts" on an amplitude vs. frequency diagram. Automation of this task saves time and provides more consistent interpretation of results that otherwise could vary depending on the operator.
"With these powerful capabilities on a single integrated system, LMS Test.Lab is an indispensable tool in our work," says Hieb. "The technology enables us to maintain the high quality standards for which we are known. I cannot imagine how we would study vibrations and tailor machine dynamics faster and more effectively any other way."
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