This section includes papers written by Alan.
With modules that are added inline to an existing press configuration, often it may not be practical to utilise the existing mechanical drive system. This could be a due to a physical problem in alignment or because the mechanical upgrades prove too expensive to change. When you consider the addition of a high quality phase shifter gearbox and its associated mechanical linkages, it easy to appreciate the cost comparison to a servo package that offers so much more.
In the case of the standalone finishing line, servo motors are used to the their greatest advantage to provide a totally “shaftless” transmission system on the machine.
If we consider a typical finishing line that encompasses both rotary hot foiling and die cutting a total of six servo drives are used to accurately control all web transport and tooling functions. These six drives are utilised as follows:
Unwind System: This servo drive is used to accurately control web tension of the unwind and replaces the electro mechanical brake system often found on less advanced machines. The servo driven unwind feeds material into the machine rather than pulling material from a braked unwind roll. This big difference is especially important when considering thinner filmic materials that require light tension control. An added advantage of the servo unwind drive is an inbuilt function to accurately calculate the roll diameter without the need for a sensor or a reel follower arm.
Infeed & Outfeed: The most important feature of any web press is tension control, without good tension control all functions of register are made difficult. On the “Reflexion” machine both the infeed and outfeed rollers have independent servo drives. These drives are used to create a very accurate tension control by working together to form an electronic drive ratio. Changing web tension is made easy by making an adjustment from the colour touch screen, which in turn communicates with the servo drives to provide an exact web tension management system.
Hot Foil, Die Cutting & Printing stations: Once again these modules are driven by independent servo drives. These drives ensure a complete isolation from the web transport system. In normal operation, these two drives are electronically locked via an encoder that measure web transport. In the case of pre printed webs that require re-registration, these two servo motors also have the ability to accurately control registration by comparing their position to a printed mark on the web. This feature provides for fully automatic registration on a complete range of substrates. Additionally servo technology on a rotary die cutting station can be used to create a cam profile and give infinitly variable sheet lengths avoiding the need to use different tools for sheet change lengths.
Rewind Unit: As with the unwind, once again an independent servo package is used. In the case of the rewind the servo drive is used to provide accurate rewind tension control along with full winder calculations.
Conclusion: When consider your next finishing line, ask yourself where you want to be in five years time?. Servo drives are the way forward in providing a flexible and upgradeable platform for your equipment.
As with all technology, it’s usage is only relevant where it enhances both machine control and production output by minimising waste products. Listed below are some of the many advantages offered by a servo machine.
Isolated drive transmission.
Minimal mechanical components.
A proven technology widely used in industry to great success.
Improved tension control.
Improved registration stability throughout the speed range.
A fully upgradeable platform.