Less is more

Illustration | Bosch Rexroth AG
Marginal Column

November 2012

 

PCMC’s flexographic press – named “Fusion” – scores points with shorter set-up times and less waste product, thanks in part to Bosch Rexroth technology.

 
 

The customer is far more likely to purchase perfume displayed in an attractive package. And chocolates in a gilt embossed box claim a premium position when compared with others in simpler boxes. Packaging has to protect the contents, of course, but it also has to leave an impression – no matter whether it is made of paper, cardboard, foil or plastic. It’s quite clear that attractive appearance is an important selling point for many products. For the print shop, this means achieving good results at the best possible price. After all, the frills and trimmings shouldn’t cost more than the contents.

With this challenge in mind, the Paper Converting Machine Company (PCMC) in Green Bay, Wisconsin, knuckled down and developed the “Fusion”. This is a flexographic press that works more efficiently than its predecessor, thanks to Rexroth’s drive, control and linear guide technology. “This sector began demanding shorter set-up times to lengthen productive printing cycles”, says David Wall, PCMC’s head of development for printing, coating and laminating. “Print shop owners want to save both material and time.”

A brief pit stop

The Fusion, equipped with the IndraMotion automation system and servo drives supplied by Rexroth, fulfills these require­ments. It utilizes either 17 or 20 shafts, depending on the number of inking units. Seven further shafts serve as paper guides and control web tension between the feed and take-up rolls at the beginning and end of the machine. Each “Fusion” consists of a central printing cylinder between 2.4 and three meters in diameter. It can be surrounded by eight or ten printing units, each with two cylinders. These transfer the image and the ink to the material being printed.

The cylinders are powered by IndraDrive M servo drives and gearless drive motors in the IndraDyn T series. Making things quicker and easier – that was the criterion for selecting the control unit. The MLC IndraMotion can synchronize machines with up to 64 shafts. Time-consuming manual adjustment for register and color for each individual deck is now a thing of the past. An integrated visual inspection system aligns the registration marks in no time at all, ensuring that in­dividual colors are exactly congruent.

Photo | Bosch Rexroth AG

The “Fusion” flexographic printing press shortens set-up times.

 

Algorithms kept in memory help the printer cope with complex jobs. The result: After a roll of paper has been changed, the flexo press is back in operation far more quickly. The control system determines whether the printing cylinders are perfectly positioned, on the basis of the data stored in the drive units. An operating mode called PrintSense, developed by PCMC, makes use of this mode. It brings together the printing cylinder and the applicator roll in each printing unit with great precision.

The press is then ready to roll. Integrated safety features and an energy recovery system pro­vide the “Fusion” with an additional competitive edge. Energy that used to be wasted when the shafts were braked is now recovered and returned to the system. A further positive factor:“While the printing plates are being changed, an IndraDrive function called ‘Safe Stop’ securely holds the shafts in their correct positions,” explains Wall. “In the past we had to incorporate a braking or locking mechanism, and that meant additional parts.”

An efficient modular system

Fewer components mean lower costs – the “Fusion” sets new standards in this regard, too. By using intelligent drive technology, PCMC has managed to whittle down the number of parts required by almost 60 percent when compared with the previous model. This is because only two different motor sizes are now needed to drive the eleven machine shafts. This is achieved by installing IndraDyn T gearless motors, available from Rexroth’s comprehensive range of off-the-shelf modular components.These liquid-cooled motors consist of separate stators and rotors and can achieve maximum torques of up to 13,800 Newton meters, accelerating the Fusion six times faster than in the past.

“The multitude of standard motors is one of Rexroth’s major strengths,” emphasizes Doug Anderson, a sales engineer at the CMA/Flodyne/Hydradyne group, which specializes in system integration. When selecting suitable parts for PCMC, the experts went for one motor to actuate the large printing cylinder, which has to come to a standstill within ten to fifteen seconds. They chose a different motor for the image and inking cylinders, which differ in width.

A safe frame

To ensure that the cylinders are solidly and accurately fixed in position in spite of the high acceleration forces involved, PCMC also asked Rexroth to supply the linear technology. The performance requirements are stringent here. Once a print job is fin­ished, the printing and inking units are moved back and forth, next printing cycle begins, they have to be firmly in place and must lock the printing and anilox rolls securely. This is the only way to print each color precisely, even at maximum rotation speeds.

Highly accurate ball screw assemblies and four ball track systems are used in the “Fusion” to provide the required flexibility and stability. These components are compact, with­stand high loads and function faultlessly for thousands of hours – with next to no maintenance. “Under no circumstances may the mechanical parts start moving randomly around the press, since this would have a negative effect on the print image,” says Wall.

“The ball screw assemblies and ball track systems supplied by Rexroth give us the stability we need to maintain the clearances and tolerances the Fusion requires.” PCMC has delivered the first of its new flexo presses to its customers – and they have met with an enthusiastic reception. Dave Wall knows why: “Improved set-up times and clearer system lay­out make it a lot easier to increase productive printing time. These benefits, in conjunction with the energy savings involved, contribute to the success of the new ‘Fusion’.” This concept lays the basis for attractive and appealing packaging that turns a stroll through the shops into a real shopping adventure.