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Contents…Encoders for Linear MotorsDid You Know...

What’s New with TNCInfrared 3-D Touch ProbeSingle-Field Scanning Linear Encoder

Web Site Helps with Encoder Selection2005 Heidenhain Trade Show Schedule

Encoders for Linear Motors, cont.





New Catalogs

HEIDENHAIN Makes Impressionsat IMTS

Volume 10, Issue 2

Encoders for Linear Motors in the Electronics Industry

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Did You Know...

For more information circle # 2on the reader service card.

Linear motors are graduallybecoming more important in such highly dynamicapplications with one ormore feed axes. The benefitsof this direct-drive technologyare low wear, lowmaintenance, and higherproductivity. However, thisincrease in productivity ispossible only if the control,the motor, the machineframe, and the positionencoder are optimallyadjusted to one another.

Direct drives place rigorous demands on thequality of the measuring signals. Optimummeasuring signals:

n reduce vibration in the machine frame,

n stop excessive noise exposure fromvelocity-dependent motor sounds,

n prevent additional heat generation, and

n allow the motor to realize its maximummechanical power rating.

The efficiency of a linear motor in regard to accuracy, speed stability, and heatgeneration is therefore greatly influenced by the selection of the position encoder.

Design of direct drives The decisive advantage of direct-drivetechnology is the very stiff coupling of thedrive to the feed component without anyother mechanical transfer elements. Thisallows significantly higher gain in the controlloop than with a conventional drive.

Velocity measurement on direct drives On direct drives there is no additionalencoder for measuring the speed. Bothposition and speed are measured by theposition encoder: linear encoders for linearmotors, angle encoders for rotating axes.Since there is no mechanical transmissionbetween the speed encoder and the feedunit, the position encoder must have acorrespondingly high resolution in order to enable exact velocity control at slowtraversing speeds.

… a HEIDENHAIN linear scale is a vitalmeasurement component in a newmedical imaging machine introduced to the market just this past August?DMetrix, Inc., in Tucson, Arizona,manufactures this high-speed medicalscanner that is now offered for use in critical digital pathology applications.

Known as the DMetrix DX-40 scanner,this new ultra-precise medical microscopeslide scanner is based on DMetrix’exclusive array-microscope technologywhich results in the ability to digitally imageup to 40 slides per hour. One of the coretechnologies enabling the high-speedscanning is an innovative loader. “Ourslipstream™ slide loader is very unique,”explains DMetrix’ Director of EngineeringArtur Olszak. “We have developed andutilize a patent-pending solution that rapidlytransports slides on a cushion of air.”

“The LIDA 400 linear scale fromHEIDENHAIN Corporation is really at theheart of our system,” added Olszak, “as it is used on the main scanning stageof the DX-40 scanner. It helps us to veryprecisely control the speed and position of our transport component in this verydemanding closed-loop system. We choseto use HEIDENHAIN’s linear scale because,frankly, it was the only scale that fulfilledour demands.”

HEIDENHAIN’s LIDA 400 scale -- with itsvery small dimensions, grating pitch of 20microns, and generous mountingtolerances -- is often the ideal encoder foruse in applications where preciseequipment positioning in a small package isrequired.

With a scanning head height of only 12mm, the LIDA 400 can be installed in verytight spaces. And in spite of its size, thevery small scanning head features anextremely large scanning area of 14.5mm2. This large scanning area allows theencoder a huge tolerance to contamination,

The semiconductor industry and automationtechnology increasingly require more

precise and faster machines in order to satisfygrowing demands on miniaturization, quality,and manufacturing cost reduction.

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Introducing the New SmarT.NC User Interface from HEIDENHAIN In addition to G Code and classic conversational programming for TNCs, HEIDENHAIN Corporation is now offering smarT.NC,a brand new user interface for TNCs intended for use by both theNC beginner and the conversational expert. This new interfaceenables users to create executable NC programs faster, moresafely, simpler, and more conveniently than ever before. SmarT.NCwas shown for the first time in North America on HEIDENHAIN’siTNC 530 controls at the IMTS show in September.

This exciting newprogramming systemguides the user in a self-explanatory and intuitiveway through the completeNC programming tasks byusing straightforwardforms. SmarT.NC is souser-friendly that the usercan decide whether to useit or the plain languagelevel at any time. Even if aprogram has been createdwith smarT.NC, forexample, it can be editedas before with the plainlanguage editor, makingthis a very unique system.

This procedure is possible because both smarT.NC and the plainlanguage editor access the same file: the plain language program!SmarT.NC is a simple all-in-one system as it also enables programverification and execution. This system has an integrated patterngenerator as well.

HEIDENHAIN’s new TE 530B operating panel is highlyrecommended for the use with smarT.NC since it makes itpossible to conveniently use the advantages of this new userinterface. This operating panel comprises a touch pad as well asthree new keys for comfortable operation of the smarT.NC. n

HEIDENHAIN’s New Compact Infrared 3-D Touch Probe - The TS 440 The newest addition to HEIDENHAIN’s recently improved 3-Dtouch trigger probes is the compact TS 440 model. Its extremelysmall dimensions make the infrared TS 440 the ideal touch probefor machines that carry out repeated setup and inspectionprocedures and have limited working space.

The TS 440 is offered in as small a size as49 mm x 63 mm, and offers 360 degreestransmission. Its features are similar toHEIDENHAIN’s TS 640 Trigger Probe,and in conjunction with HEIDENHAIN’stransceivers, can be used on the iTNC530 control and higher.

HEIDENHAIN also offers another newtransceiver for the infrared touchprobes, the SE 540. It is designedfor installation in the headstockproviding the advantage ofmoving along with the touchprobe. This ensures a reliabletransmission of infrared signals atany position of the machine’sworking space and is an advantagewith very large machines and thosewhose spindles move in two separateworking spaces.

3-D touch probes are ideal for quickand exact workpiece alignment aswell as for automated workpiecemeasurement on the machine. MostCNC controls – especially the TNCcontrols from HEIDENHAIN – offernumerous measuring cycles to automaticallymeasure and determine common geometriessuch as bore holes, rectangular pockets, circular pockets, slots, studs, bolt hole circles, and planes. n

What’s New with TNC Infrared 3-D Touch Probe

Single-Field Scanning Linear Encoder Offers Increased Resistance toContaminationNow available to the North Americanmarketplace is HEIDENHAIN Corporation’sredesigned LC 400 absolute sealed linearencoder with Single-Field Scanning. Because ofits new design, this encoder is poised to offermany advantages over other encoders, such asits increased resistance to contamination, highertraversing speeds, increased natural frequencyand a variety of absolute output formats.

This compact LC 400 incorporates a new single-field scanning technology (versus a previousfour-field scanning method) that utilizes a muchlarger single scanning window therebymitigating the effects of contamination.

The LC 400 also boasts constant signal qualityover the entire measuring length, resolution ofup to 10 nm and with it’s maximum traversingspeed of up to 180 m/min, it is ideal for linearmotor and machine tool applications. n




Single-Field Scanning Linear Encoder

The HEIDENHAIN web site (www.heidenhain.com) is of muchassistance to its visitors every day, including the availability of itsinteractive selection guide for rotary encoders.

Featured here, this Rotary Encoder Selection Guide enables its usersto insert required rotary encoder specifics and come up with optionsto complete the job.

Click onto this site to obtain much more information on measurementcomponents and systems, as well as take a look at the largest list ofrelated products available in the industry today.

Sign on and let us help you meet your measurement needs! n

2005 HEIDENHAINTRADE SHOWSCHEDULEAs always, you have the opportunity to visit withHEIDENHAIN at many trade shows each year; 2005being no exception. Though the schedule is stilldeveloping, HEIDENHAIN expects to exhibit at thefollowing next year:

n Medical Design & Manufacturing Show -Electronics West

January 10-12Anaheim Convention CenterAnaheim, California

n APEX

February 22-24Anaheim Convention CenterAnaheim, California

n The National Design Show

March 7-10McCormick Place - SouthChicago, Illinois

n WESTEC

April 4-7Los Angeles Convention CenterLos Angeles, California

n Quality Show

April 19-21Rosemont Convention CenterRosemont, Illinois

n SPS Electric Automation American

May 24-26Rosemont Convention CenterRosemont, Illinois

n SEMICON

July 12-14- (Front End) - Moscone Center - North- (Back End) - Moscone Center - WestSan Francisco, California

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www.heidenhain.com/anglemeasure/rotary_std_guide.htm

Web Site Helps with Encoder Selection


The velocity is calculated from the distance traversed per unit of time. This method – which is also applied to conventional axes – represents a numerical differentiationthat amplifies periodic disturbances or noise in the signal.

The combination of significantly higher control loop gain,as is used particularly with direct drives, and insufficientencoder signal quality can result in a dramatic decline indrive performance.

Signal quality of position encoders Modern encoders feature either an incremental, whichmeans counting, or an absolute method of positionmeasurement. The path information is transformed in the encoder into two sinusoidal signals with 90° phaseshift. Both methods require that the sinusoidal scanningsignals be interpolated in order to attain a sufficientlyhigh resolution. Inadequate scanning, contamination of the measuring standard, and insufficient signalprocessing can lead to a deviation from the idealsinusoidal shape. As a consequence, during interpolationperiodic position error occurs within one signal period ofthe encoder’s output signals. This type of position errorwithin one signal period is referred to as “interpolationerror.” On high-quality encoders, it is typically 1% to 2%of the signal period.

Effects of interpolation error: Generation of heat and noise If the frequency of the interpolation error increases, the feed drive can no longer follow the error curve.However, the current components generated by theinterpolation error cause increased motor noises andadditional heating of the motor.

A comparison of the effects of linear encoders with low and high interpolation error on a linear motorillustrates the significance of high-quality position signals.The LIDA linear encoder used here generates only barelynoticeable disturbances in the motor current: the motoroperates normally and develops little heat.

If at the same controller setting, the interpolation errors of the same encoder are increased through pooradjustment, significant noise arises in the motor current.This causes an increased amount of noise and heatgenerated in the motor.

Dynamic behavior Digital filters are often used with direct drives to smooth the position signals. However, the loss of phase-association by filtering in the speed-control loopmust be kept to a minimum, otherwise the dynamicaccuracy decreases.

Position encoders with optimum signal quality help to reduce the use of filters, meaning that the controlbandwidth is maintained.

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Position error within one signal period

Heat generation of a linear motor controlled using an encoder:A: With low interpolation error B: With high interpolation error

A B

Motor current of a direct drive with position encoderA: With low interpolation error B: With high interpolation error

Encoders continued from cover

Position encoders for direct drives Linear encoders that generate a high-quality position signal with lowinterpolation errors are essential for optimal operation of direct drivesin the electronics industry. Encoders that use photoelectric scanningare ideally suited for this task, since very fine graduations can bescanned by this method.

Encoders with optical scanning therefore play a significant role in exploiting the potential of direct drives.

Exact graduations HEIDENHAIN encoders with optical scanning incorporate measuringstandards of periodic structures known as graduations. The substratematerial is glass, steel, or – for large measuring lengths – steel strips. These fine graduations – graduation periods from 40 µm to under1µm are typical – are manufactured in a photolithographic process.They are characterized by high-edge definition and excellenthomogeneity – a fundamental prerequisite for low interpolation error,and therefore for smooth operating performance and high-controlloop gain.

Durable measuring standards By the nature of its design, the measuring standards of exposedlinear encoders are less protected from their environment.HEIDENHAIN therefore always uses tough gratings manufactured in special processes.

In the DIADUR process, hard chrome structures are applied to a glass or steel carrier. The AURODUR process applies gold to a steel strip to produce a scale tape with hard gold graduation.

In the SUPRADUR process, a transparent layer is applied first overthe reflective primary layer. Then an extremely thin, hard chromelayer is applied to produce a grating. Scales with SUPRADURgraduations have proven to be particularly insensitive tocontamination because the low height of the structure leavespractically no surface for dust, dirt, or water particles to accumulate.

In this way, HEIDENHAIN production technologies ensure anenduringly high signal quality that promotes the use of direct drives for particularly demanding applications.

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DIADUR phase grating with approx. 0.25 µm grating height

SUPRADUR process: Optical three-dimensional graduation structure

Photoelectric scanning in accordance with the imaging principle with steel scaletape and single-field scanning (LIDA 400)

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Optimized scanning methodsThe scanning method and the high quality of the grating shareresponsibility for low interpolation error. An especially beneficialfeature is the single-field scanning with which the exposed linearencoders from HEIDENHAIN operate: The output signals aregenerated from only one scanning field. This large scanning field,and the special optical filtering through the structure of thescanning reticle and photosensor, generate scanning signals withconstant signal quality over the entire range of traverse. This isthe prerequisite for:

n Low signal noise

n Low interpolation error

n High traversing speed

n Good control loop performance for direct drives

n Low heat generation of the motor

Signal generation based on the imaging measuring principle (LIDA 400) To put it simply, the imaging scanning principle functions bymeans of projected light signal generation: two scale gratingswith equal grating periods are moved relative to each other – thescale and the scanning reticle. The carrier material of the scanningreticle is transparent, whereas the graduation on the measuringstandard may be applied to a transparent or reflective surface.

When parallel light passes through a grating, light and darksurfaces are projected at a certain distance. An index grating with the same grating period is located here. When the twogratings move in relation to each other, the incident light ismodulated: if the gaps are aligned, light passes through. If thelines of one grating coincide with the gaps of the other, no lightpasses through. Photocells convert these variations in lightintensity into electrical signals. The specially structured grating of the scanning reticle filters the light current to generate nearlysinusoidal output signals.

In the XY representation on an oscilloscope, the signals form a Lissajous figure. Ideal output signals appear as a concentricinner circle. Deviations in circular form and position are caused by position error within one signal period and therefore go directlyinto the result of measurement. The size of the circle, whichcorresponds with the amplitude of the output signal, can varywithin certain limits without influencing the measuring accuracy.

On direct drives, deviations from the circular form cause acousticnoise, reduce control quality, and increase heat generation.

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Lower sensitivity to contamination Production facilities and handling devices for thesemiconductor industry demand high acceleration andcompact designs. Such requirements call specifically forexposed measuring systems that operate without frictionand, because they can operate without their own housing,can be designed to be very small and therefore low inmass. Special scanning methods and productiontechniques are used to provide tough protection againstcontamination even without sealing the encoder.

Exposed linear encoders from HEIDENHAIN operate withsingle-field scanning. Only one scanning field is used togenerate the scanning signals. Local contamination on themeasuring standard (e.g., fingerprints from mounting or oilaccumulation from guideways) influences the light intensityof the signal components, and therefore of the scanningsignals, in equal measure. The output signals do change in their amplitude, but not in their offset and phase position.They stay highly interpolable, and the interpolation errorremains small. The large scanning field additionallyreduces sensitivity to contamination. In many cases thiscan prevent encoder failure. This is particularly clear withthe LIDA 400 and LIF 400, which in relation to the gratingperiod have a very large scanning surface of 14.5 mm2.Even with contamination with 3mm diameter, the encoderscontinue to provide high-quality signals. The position errorremains far below the values specified for the accuracygrade of the scale.

An essential prerequisite for optical encoders with lowsensitivity to contamination is therefore an optimizedscanning method, the large scanning field, and thecontamination-tolerant graduation.

Application-oriented mounting tolerancesVery small signal periods usually come with very narrowdistance tolerances between the scanning head and scaletape. Thanks to the interferential scanning principle of theLIF 400 and innovative index gratings in the LIF 400, it hasbecome possible to provide ample mounting tolerances in spite of the small signal periods. Within the mountingtolerances, therefore, changes in the signal amplituderemain negligible.

This behavior is substantially responsible for the highreliability of exposed linear encoders from HEIDENHAIN.

Reaction of the LIF 400 to contamination

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À

Á

Â

HEIDENHAIN position encoders for direct drives (selection): Maximum values of interpolation error with respect to the signal period

Linear encoders for linear motorsExposed linear encoders fromHEIDENHAIN are optimized for use on fast, precise machines as sought by the semiconductor industry andautomation technology. In spite of theexposed mechanical design they arehighly tolerant to contamination, ensurehigh long-term stability, and are fast andsimple to mount. Their low weight andcompact design suit encoders of the LIFÀ , LIP Á and LIDA Â series particularlyfor linear motors. n

IS INTERESTED IN YOUR FEEDBACK

©2004 HEIDENHAIN CORPORATION

For further information, circle the appropriate number.Article #1 #2 #3 #4 #5 #6 #7 #8 #9 #10

333 E. State Parkway, Schaumburg, IL 60173Phone: 847/490-1191 FAX: 847/490-3931

Please send me HEIDENHAIN’s most current catalog.

o General o NC Linear o Digital Readout o METRO/CERTO Gauges

o Measurement Inspection o Angular Rotary o Incremental Rotary o Absolute Rotary

o Contouring Controls o Point-to-Point Controls o Servo Drive

VOLUME 10, ISSUE 2

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IS INTERESTED IN YOUR FEEDBACK

Your comments about topics addressed in this issue and topics you’d like to see in future issues:

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E-mail

o Please add me to your mailing list. (Provide address above)

©2004 HEIDENHAIN CORPORATION

For further information, circle the appropriate number.Article #1 #2 #3 #4 #5 #6 #7 #8 #9 #10

333 E. State Parkway, Schaumburg, IL 60173Phone: 847/490-1191 FAX: 847/490-3931

Please send me HEIDENHAIN’s most current catalog.

o General o NC Linear o Digital Readout o METRO/CERTO Gauges

o Measurement Inspection o Angular Rotary o Incremental Rotary o Absolute Rotary

o Contouring Controls o Point-to-Point Controls o Servo Drive

VOLUME 10, ISSUE 2

BUSINESS REPLY INFORMATION

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Angle Encoders

This latest catalog gives an overview of all of HEIDENHAIN’s angle encodersdescribed as encoders that have an accuracy of better than ± 5” and a linecount of at least 10,000. These angle encoders, which are available in bothincremental and absolute output formats and come in a wide variety ofmechanical configurations, are typically found in applications requiringprecision angular measurement to accuracies within several arc seconds,such as in rotary tables and swivel heads on machine tools, C-axes on lathes,measuring machines for gears, spectrometers, and telescopes.

Position Encoders for Servo Drives

HEIDENHAIN’s position encoders for servo drives are extensively detailed inthis catalog. The descriptions of the technical features contain fundamentalinformation on the use of rotary, angular, and linear encoders on electricdrives. Details include selection tables, technical features and mountinginformation, specifications, and electrical connection information.

ITNC 530 Contouring Control

Showcasing the newest TNC from HEIDENHAIN, this catalog details the iTNC530, a versatile contouring control for milling, drilling, and boring machines andmachining centers. This TNC features a fast and extremely powerfulprocessor architecture. The catalog details the features and specifications forthe machine manufacturer.



New Catalogs Available


HEIDENHAIN CORPORATION 333 E. State Parkway, Schaumburg, IL 60173www.heidenhain.com

“Accuracy of Feed Drives” Display

“Angle Encoders for Rotary Tables” Display

HEIDENHAIN MakesImpressions at IMTSDuring IMTS (the International Manufacturing TechnologyShow) this past September, HEIDENHAIN was once againon hand to talk with the many attendees who came tothis world-renowned machine tool show that is held in Chicago on every even year. This year, besidesshowcasing the very newest in precision measurementcomponents and systems, HEIDENHAIN also highlightedtwo large motion control displays at the booth.

These motion control displays had been developedrecently by HEIDENHAIN’s Research & Developmentdepartment in Germany in order to demonstrate thethermal effects on motion and signal quality for speedcontrol, always important considerations in any machiningprocess. Their availability and actions at IMTS were oftenthe subject of conversation by the viewers who areinvolved with designing or utilizing machine tools.

HEIDENHAIN’s first display at the IMTS boothdemonstrated the difference in drive performanceassociated with different measuring technologies (“Angle Encoders for Rotary Tables”). Here a rotarytable fixture display was equipped with three differenttypes of angle encoders to measure position and speed:magnetic, incremental, and absolute. The motion of thetable and audible drive tuning deviations then clearlydemonstrated how resolution, signal quality, andinterpolation contribute to the stability of servo loop, and the benefits and drawbacks of each type ofmeasuring system.

The second display highlighted the linear versus rotaryargument (“Accuracy of Feed Drives”). Here, a linear(HEIDENHAIN’s current single-field scanning technologyfor the LC scales) versus traditional rotary encoder/ballscrew system was used to capture position. Thisdisplay clearly demonstrated where drift error due tothermal effects often takes place with a rotary system,and the advantage, including resistance to contamination,of linear encoder systems.

Both of these displays were based on technical whitepapers available to anyone for the asking. The title of thepaper of the first display is “Angle Encoders for RotaryTables” while the latter is titled “Accuracy of FeedDrives.” It was exciting to see these papers come to life at IMTS.


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