Simpler motion control

23 March 2007



David Greensmith, Baldor's Ethernet Powerlink product manager, offers guidance for converting machinery designers


The availability of three phase AC drives compatible with the deterministic Ethernet Powerlink network brings substantial flexibility to the higher power converting machinery sector. The drives complete the Ethernet Powerlink motion control choices, joining single phase drives, controllers and development software that have been available for some two years.

The advantages for machine builders can be considered in two ways: those that come with Ethernet Powerlink, and those connected to facets of the new drive.

The Ethernet Powerlink or EPL standard (www.ethernet-powerlink.org), is a deterministic extension of standard Ethernet, but one that will also co-exist with standard TCP/IP Ethernet - providing machine builders with the means to satisfy both machine and plant level automation requirements. Motion (and machine) control requirements are met with a real-time network that uses time slots for determinism. 100Mbits/s bandwidth means that large numbers of devices can be managed by a single controller.

Among the advantages this brings are: reduced hardware, as one controller can handle virtually any application; less cabling/assembly (elements can be connected by daisy-chain cable); and 'total network visibility' (EPL's sheer bandwidth merges fieldbus and motion bus functionality).

Baldor's new MotiFlex e100 EPL compatible drives simplify system architecture by a single, flexible drive and motion control platform. For example, control of linear, rotary, servo and vector motors is simply a software configuration task.

MotiFlex drives are designed to operate independently, or as part of a shared DC bus system. Unlike traditional shared DC bus systems, they do not require a separate power supply. Instead, the AC/DC converter stage in each drive is capable of supplying power not only to itself, but also to a combination of drives. For many multi axis applications, one drive can power the complete system.

This will often result in the need for fewer electrical components, and simpler system building - only one set of contactors, fuses or MCBs, terminal blocks, and one EMC filter for a multi axis system. Alternative approaches can require the same AC components for each drive, or the addition of separate power supplies and capacitor banks with fixed ratings that may not be ideal for the application.

Each drive incorporates a universal encoder input and built-in analog and digital I/O, plus CANopen and USB ports. Two 'option card' slots support further expansion that allows users to configure the local attributes of the drive, and/or provide an upgrade path. Expansion options include I/O, feedback devices, a plug-in machine controller card compatible with the Mint motion language, and fieldbus interfaces. Together, this combination of technologies offers a versatile platform for converting machinery design.

Architectural freedom is one key advantage. Unlike traditional motion networks, EPL does not force a machine builder to adopt any particular control architecture. Systems can still have the traditional central controller if preferred - co-ordinating all drives in profiled torque, speed or position modes. However, these axes can also be self controlled positioning devices which respond on command - and consume little central processing overhead.

In addition, intelligent, programmable, drives can be employed to implement more complex standalone axes, or the complete motion system.

With the MotiFlex AC drive, if the converting machine is large and has numerous axes, one 'central' controller is ideal (all of the drives and I/O can still be distributed physically around the machine for reduced cabling and assembly). However, for less complex systems, an intelligent drive scenario is possible by equipping a drive with a plug-in motion control card - saving hardware.

Such a card can control up to three further daisy chained three or single phase drives, providing a low cost solution for the mixed technology requirements of many converting machines. This card can accommodate the complex motion control required in many converting applications, such as registration control, or knives that dynamically change speed throughout a cycle to synchronize with the web (to cut to different lengths).

Support for different motor types is also key. In addition to main unwind/rewind axes - which might be powered by AC induction, vector or servo motor depending on the load and performance requirements - a converting machine builder will often need servo and stepper axes for automated slitters, pinch rollers, stackers and conveyors. The new AC drive can accommodate many motor types simply by software selection. The EPL controller adds further flexibility, supporting single phase drives, servo or stepper motor technology.

Energy saving is another attribute. When operating in a shared DC bus system, power regenerated back into any MotiFlex AC drive during the deceleration phase of an axis may be utilized by the other axes, saving energy. n



Contacts

Baldor
Tel: +44 (0) 1454 850000





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A range of Ethernet Powerlink compatible components offers design opportunities ... A range of Ethernet Powerlink compatible components offers design opportunities ...


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