Nigel Steel, UK sales manager at Parker SSD Drives, looks at the benefits that the latest generation of variable speed drives are bringing to the converting sector
The complexity of machinery used in the converting sector has always placed significant demands on the drives used to control the multitude of motors employed. AC, DC and servomotor drives act as the primary control devices for the high speed rotating machinery at the heart of systems used for the coating, embossing, laminating, printing and slitting of paper and film.
Although drives technology has been in use for many years to control parameters such as web speed and tension, machine and systems builders have only recently started taking advantage of the latest advances in the performance and functionality of today’s drives.
Many of these advances stem directly from the seemingly unstoppable advances in microprocessor technology that are bringing benefits across the control sector. Smaller yet ever more powerful processors – with capabilities estimated to be doubling roughly every two years – mean drives, too, are becoming smaller while offering higher levels of accuracy and resolution.
This moves them from being just variable speed controllers to sophisticated devices that can precisely adjust the speed and torque of motors in response to the changing load characteristics imposed on the motor by the machine itself. For example, a fully loaded paper roll will require a high torque factor to keep it moving at fast speed, whereas at the start-up of a paper machine the web is moving at slow speed and requires low torque for the initial tension to be applied.
In addition to web based operations with their speed and tension controls, converting machinery also takes in ancillary equipment such as knives, slitters, accumulators, winders, extruders and metering pumps. All have motors and all need drives, be they AC, DC or, increasingly, servodrives.
At one time all the disparate elements of a converting process might have had their own individual control system, possibly distributed from a central control panel or in local controllers at the drives themselves. Today’s control systems, however, are expected to be easy to integrate, capable of communicating across easily installed and maintained networks, while offering the operator interfaces that are easy and intuitive to use.
At the basic level, motor drives might be in danger of becoming almost a commodity item, thanks largely to the selfsame trend in mass market microprocessors. At the systems level, however, there is still a demand for products that reflect a relatively high degree of specialized experience on the part of the drives supplier.
Many drive vendors can cover the spectrum from basic to specialist devices, with price essentially being proportional to performance, so specific application knowledge can be a determining factor at the systems level. This is especially important in the converting sector, where the challenge of applications such as web tension requires both precision hardware control and excellent software programming skills to ensure that line productivity is maintained at all times.
In any drives application today, software is increasingly the key to success and many of the latest products can have over a thousand different features configurable through software which vendors often update free of charge. This is another benefit stemming directly from the increased microprocessor power of modern drives. Software can be used to continually monitor drive performance, keeping a check on key motor parameters. This not only ensures safe operation but also can be used to maximize operating efficiency and help with preventative maintenance.
The latest drives also feature flexible communications options and seamless integration with other control technologies using industry standard protocols. Indeed, manufacturers such as Parker have taken the concept of integration a step further by using a common modular construction across different types of AC and DC drive with, for example, common keypad controls, communications interfaces and configuration software. This eliminates the problems that have in the past been caused by proprietary islands of automation and offers both OEMs and end users easily integrated controls that operate seamlessly together.
Perhaps as importantly, by taking the concept of integration even further these modular drive systems help to reduce installation time and costs for systems builders who require multiple drives for complex applications. Modern drive units can also easily handle both low and high power requirements up to 400kW, yet are extremely compact; even larger modular systems generally have a relatively small footprint and can be installed in tower frames that then incorporate common modules.
Parker Electromechanical and Drives
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