WERFACING

DRIVING ACROSSTHE DIGITALINTERFACE

Compatibility is becoming increasingly important in CNCand drive technology. Robert P Brennan, marketing

manager of Indramat, Illinois, proposes a digital drivesinterface standard.

NOW IS THE PERFECT time to intro-duce a digital interface standard - justwhen CNC and drive technology haveadvanced to the point of needing astandard that handles a broad range ofcommunications and power require-ments.

Without an appropriate digital in-terface standard, manufacturers willsoon end up with spindle drives, servodrives, and CNCs that are incom-patible. Manufacturers will also belocked into proprietary standards thatlimit their interfacing options.

A uniform interface, incorporatedas a standard as soon as feasiblypossible, will alleviate those problems

Without an appropriatedigital interface standard,

manufacturers will soon endup with spindle drives, servo

drives, and CNCs that areincompatible.

before they occur - before manufac-turers install numerous incompatibledigital NC control systems in theirplants.

SERCOSThe proposed new SERCOS (serial

real-time communications system) in-terface is that standard. It is now beingreviewed and considered by the EIA(Electronic Industries Association) forpossible adoption as a standard in theUS.

The interface will allow any controlmanufacturer's SERCOS interface-compatible digital NC to talk to anymanufacturer's SERCOS interface-

Computerised Manufacturing April/May 1991

INTERFACING

compatible digital spindle or servodrive over a well-defined, fibre-opticlink.

With a common interface, the ma-chine builder or user will have the flex-ibility to configure multivendor con-trol systems, the best CNC and the bestservo and/or spindle drives for theoperation.

Controls and drives will be inde-pendently selected based on the re-quired performance criteria. No com-promises will be made by being lockedinto purchasing all digital system com-ponents from only one manufacturer;the user will have options.

The SERCOS interface facilitatescommunications flexibility with asingle coherent (or standardised) in-terface employed throughout a user'splant.

The proposed interface was in-itiated by European machine builderswho were concerned about the im-pending problems of multiple digitalinterfaces. They foresaw the benefitsof a digital standard that would allowmany manufacturers' drives and con-trols to talk together.

The SERCOS interface was de-veloped jointly by the VDW (GermanMachine Tool Builders Association)and ZVEI (German Central ElectronicsIndustry Association).

The VDW/ZVEI working commit-tee includes major manufacturers ofmachine tools, numerical controls, andmotors and drives. Numerous othercompanies have endorsed the stand-ard.

InterfacingThe interface is not a product to be

purchased. Rather it is a set of stand-ard specifications that may be incor-porated into any company's variedcontrol and drive products. Each con-trol/drive maintains its own functionsand features.

SERCOS interface compatibilityprovides additional capabilities be-cause the controls/drives comply withan industry-wide standard mediumtransmission, topology, connectiontechniques, signal levels, message

Flbar-optlc cable

Spindl* driv*

An NC and digital drive system using the SERCOS interface.

structure, timing, and data formats.The SERCOS interface will make it

possible for manufacturers to use anyproduct-specific features on their ma-chines, as long as the controls /drivesare SERCOS interface-compatible.

The interface will unlock the door togreat expansion potential as newmanufacturing challenges unfold. Inaddition to allowing widespread useof today's digital technology, it willalso allow communication with digi-tal drives that may be developed in thefuture.

The interface standard will equipmanufacturers with more flexibilitythan is possible with any other tech-nique of applying digital drives. It willalso open a standard window into themanufacturing process that is unavail-able from any other technology.

FeaturesWith the interface, one fibre-optic

ring exchanges data between NC con-trols and drives. The fibre optics pro-vide noise immunity and eliminate theextensive cabling and wiring betweenthe CNC and the drive.

Standardised message format isused for entry and display of any oper-ating data, parameters, or diagnostics.In addition, the interface allows exten-sive servo and machine real-time diag-nostics.

Precise timing and synchronisationof commands and interpolation formultiple drives is achieved with theinterface. All operating data (com-mand values, feedback values etc) aresimultaneously updated between thedrives and CNC in each cycle.

The interface monitors multipleclasses of errors and signals variouslevels of corrective action including ashutdown, if nccessarv.

The first 32 000 parameters are pre-defined for CNCs and drives, thoughthe control system does not have to useall of them. In addition, space is al-lotted for a second 32 000 parametersthat may be defined for any specificapplication.

The interface also provides savings inwiring, configuration and installationand hardware within the CNC. [ 2

For more information enter ME147

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