Heidenhain Diadur

Volume 10, Issue 2

Encoders for Linear Motors in the Electronics Industry

Did You Know...

Linear motors are gradually becoming more important in such highly dynamic applications with one or more feed axes. The benefits of this direct-drive technology are low wear, low maintenance, and higher productivity. However, this increase in productivity is possible only if the control, the motor, the machine frame, and the position encoder are optimally adjusted to one another. he semiconductor industry and automation technology increasingly require more precise and faster machines in order to satisfy growing demands on miniaturization, quality, and manufacturing cost reduction.

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Encoders for Linear Motors Did You Know... What’s New with TNC Infrared 3-D Touch Probe Single-Field Scanning Linear Encoder Web Site Helps with Encoder Selection 2005 Heidenhain Trade Show Schedule Encoders for Linear Motors, cont. Encoders for Linear Motors, cont. Encoders for Linear Motors, cont. Encoders for Linear Motors, cont. Encoders for Linear Motors, cont. New Catalogs

10 HEIDENHAIN Makes Impressions at IMTS

Direct drives place rigorous demands on the quality of the measuring signals. Optimum measuring signals: n reduce vibration in the machine frame, n stop excessive noise exposure from velocity-dependent motor sounds,

n prevent additional heat generation, and

n allow the motor to realize its maximum mechanical power rating. The efficiency of a linear motor in regard to accuracy, speed stability, and heat generation is therefore greatly influenced by the selection of the position encoder. Design of direct drives The decisive advantage of direct-drive technology is the very stiff coupling of the drive to the feed component without any other mechanical transfer elements. This allows significantly higher gain in the control loop than with a conventional drive. Velocity measurement on direct drives On direct drives there is no additional encoder for measuring the speed. Both position and speed are measured by the position encoder: linear encoders for linear motors, angle encoders for rotating axes. Since there is no mechanical transmission between the speed encoder and the feed unit, the position encoder must have a correspondingly high resolution in order to enable exact velocity control at slow traversing speeds.

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… a HEIDENHAIN linear scale is a vital measurement component in a new medical imaging machine introduced to the market just this past August? DMetrix, Inc., in Tucson, Arizona, manufactures this high-speed medical scanner that is now offered for use in critical digital pathology applications. Known as the DMetrix DX-40 scanner, this new ultra-precise medical microscope slide scanner is based on DMetrix’ exclusive array-microscope technology which results in the ability to digitally image up to 40 slides per hour. One of the core technologies enabling the high-speed scanning is an innovative loader. “Our slipstream™ slide loader is very unique,” explains DMetrix’ Director of Engineering Artur Olszak. “We have developed and utilize a patent-pending solution that rapidly transports slides on a cushion of air.” “The LIDA 400 linear scale from HEIDENHAIN Corporation is really at the heart of our system,” added Olszak, “as it is used on the main scanning stage of the DX-40 scanner. It helps us to very precisely control the speed and position of our transport component in this very demanding closed-loop system. We chose to use HEIDENHAIN’s linear scale because, frankly, it was the only scale that fulfilled our demands.” HEIDENHAIN’s LIDA 400 scale -- with its very small dimensions, grating pitch of 20 microns, and generous mounting tolerances -- is often the ideal encoder for use in applications where precise equipment positioning in a small package is required. With a scanning head height of only 12 mm, the LIDA 400 can be installed in very tight spaces. And in spite of its size, the very small scanning head features an extremely large scanning area of 14.5 mm2. This large scanning area allows the encoder a huge tolerance to contamination, For more information circle # 2 on the reader service card.

What’s New with TNC

Infrared 3-D Touch Probe

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 the NC beginner and the conversational expert. This new interface enables users to create executable NC programs faster, more safely, simpler, and more conveniently than ever before. SmarT.NC was shown for the first time in North America on HEIDENHAIN’s iTNC 530 controls at the IMTS show in September.

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

This exciting new programming system guides the user in a selfexplanatory and intuitive way through the complete NC programming tasks by using straightforward forms. SmarT.NC is so user-friendly that the user can decide whether to use it or the plain language level at any time. Even if a program has been created with smarT.NC, for example, it can be edited as before with the plain language editor, making this a very unique system. This procedure is possible because both smarT.NC and the plain language editor access the same file: the plain language program! SmarT.NC is a simple all-in-one system as it also enables program verification and execution. This system has an integrated pattern generator as well. HEIDENHAIN’s new TE 530B operating panel is highly recommended for the use with smarT.NC since it makes it possible to conveniently use the advantages of this new user interface. This operating panel comprises a touch pad as well as three new keys for comfortable operation of the smarT.NC. n For more information circle # 3 on the reader service card.

The TS 440 is offered in as small a size as 49 mm x 63 mm, and offers 360 degrees transmission. Its features are similar to HEIDENHAIN’s TS 640 Trigger Probe, and in conjunction with HEIDENHAIN’s transceivers, can be used on the iTNC 530 control and higher. HEIDENHAIN also offers another new transceiver for the infrared touch probes, the SE 540. It is designed for installation in the headstock providing the advantage of moving along with the touch probe. This ensures a reliable transmission of infrared signals at any position of the machine’s working space and is an advantage with very large machines and those whose spindles move in two separate working spaces. 3-D touch probes are ideal for quick and exact workpiece alignment as well as for automated workpiece measurement on the machine. Most CNC controls – especially the TNC controls from HEIDENHAIN – offer numerous measuring cycles to automatically measure and determine common geometries such as bore holes, rectangular pockets, circular pockets, slots, studs, bolt hole circles, and planes. n For more information circle # 4 on the reader service card.

Single-Field Scanning Linear Encoder Single-Field Scanning Linear Encoder Offers Increased Resistance to Contamination Now available to the North American marketplace is HEIDENHAIN Corporation’s redesigned LC 400 absolute sealed linear encoder with Single-Field Scanning. Because of its new design, this encoder is poised to offer many advantages over other encoders, such as its increased resistance to contamination, higher traversing speeds, increased natural frequency and a variety of absolute output formats.

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This compact LC 400 incorporates a new singlefield scanning technology (versus a previous four-field scanning method) that utilizes a much larger single scanning window thereby mitigating the effects of contamination. The LC 400 also boasts constant signal quality over the entire measuring length, resolution of up to 10 nm and with it’s maximum traversing speed of up to 180 m/min, it is ideal for linear motor and machine tool applications. n For more information circle # 5 on the reader service card.

Web Site Helps with Encoder Selection The HEIDENHAIN web site (www.heidenhain.com) is of much assistance to its visitors every day, including the availability of its interactive selection guide for rotary encoders. Featured here, this Rotary Encoder Selection Guide enables its users to insert required rotary encoder specifics and come up with options to complete the job.

2005 HEIDENHAIN TRADE SHOW SCHEDULE As always, you have the opportunity to visit with HEIDENHAIN at many trade shows each year; 2005 being no exception. Though the schedule is still developing, HEIDENHAIN expects to exhibit at the following next year:

n Medical Design & Manufacturing Show Electronics West January 10-12 Anaheim Convention Center Anaheim, California

n APEX

February 22-24 Anaheim Convention Center Anaheim, California

n The National Design Show March 7-10 McCormick Place - South Chicago, Illinois

n WESTEC

April 4-7 Los Angeles Convention Center Los Angeles, California

n Quality Show

April 19-21 Rosemont Convention Center Rosemont, Illinois

n SPS Electric Automation American

www.heidenhain.com/anglemeasure/rotary_std_guide.htm

Click onto this site to obtain much more information on measurement components and systems, as well as take a look at the largest list of related products available in the industry today. Sign on and let us help you meet your measurement needs! n

May 24-26 Rosemont Convention Center Rosemont, Illinois

n SEMICON

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

For more information circle # 6 on the reader service card.

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Encoders continued from cover

The velocity is calculated from the distance traversed per unit of time. This method – which is also applied to conventional axes – represents a numerical differentiation that amplifies periodic disturbances or noise in the signal. The combination of significantly higher control loop gain, as is used particularly with direct drives, and insufficient encoder signal quality can result in a dramatic decline in drive performance. Signal quality of position encoders Modern encoders feature either an incremental, which means counting, or an absolute method of position measurement. The path information is transformed in the encoder into two sinusoidal signals with 90° phase shift. Both methods require that the sinusoidal scanning signals be interpolated in order to attain a sufficiently high resolution. Inadequate scanning, contamination of the measuring standard, and insufficient signal processing can lead to a deviation from the ideal sinusoidal shape. As a consequence, during interpolation periodic position error occurs within one signal period of the encoder’s output signals. This type of position error within one signal period is referred to as “interpolation error.” On high-quality encoders, it is typically 1% to 2% of the signal period.

Position error within one 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 the interpolation error cause increased motor noises and additional heating of the motor. A comparison of the effects of linear encoders with low and high interpolation error on a linear motor illustrates the significance of high-quality position signals. The LIDA linear encoder used here generates only barely noticeable disturbances in the motor current: the motor operates normally and develops little heat.

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

If at the same controller setting, the interpolation errors of the same encoder are increased through poor adjustment, significant noise arises in the motor current. This causes an increased amount of noise and heat generated 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 loop must be kept to a minimum, otherwise the dynamic accuracy decreases. Position encoders with optimum signal quality help to reduce the use of filters, meaning that the control bandwidth is maintained.

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A

B

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

Position encoders for direct drives Linear encoders that generate a high-quality position signal with low interpolation errors are essential for optimal operation of direct drives in the electronics industry. Encoders that use photoelectric scanning are ideally suited for this task, since very fine graduations can be scanned 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 measuring standards of periodic structures known as graduations. The substrate material is glass, steel, or – for large measuring lengths – steel strips. These fine graduations – graduation periods from 40 µm to under 1µm are typical – are manufactured in a photolithographic process. They are characterized by high-edge definition and excellent homogeneity – a fundamental prerequisite for low interpolation error, and therefore for smooth operating performance and high-control loop gain.

DIADUR phase grating with approx. 0.25 µm grating height

Durable measuring standards By the nature of its design, the measuring standards of exposed linear 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 over the reflective primary layer. Then an extremely thin, hard chrome layer is applied to produce a grating. Scales with SUPRADUR graduations have proven to be particularly insensitive to contamination because the low height of the structure leaves practically no surface for dust, dirt, or water particles to accumulate. In this way, HEIDENHAIN production technologies ensure an enduringly high signal quality that promotes the use of direct drives for particularly demanding applications.

SUPRADUR process: Optical three-dimensional graduation structure

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Optimized scanning methods The scanning method and the high quality of the grating share responsibility for low interpolation error. An especially beneficial feature is the single-field scanning with which the exposed linear encoders from HEIDENHAIN operate: The output signals are generated from only one scanning field. This large scanning field, and the special optical filtering through the structure of the scanning reticle and photosensor, generate scanning signals with constant signal quality over the entire range of traverse. This is the 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 by means of projected light signal generation: two scale gratings with equal grating periods are moved relative to each other – the scale and the scanning reticle. The carrier material of the scanning reticle is transparent, whereas the graduation on the measuring standard may be applied to a transparent or reflective surface. When parallel light passes through a grating, light and dark surfaces are projected at a certain distance. An index grating with the same grating period is located here. When the two gratings move in relation to each other, the incident light is modulated: if the gaps are aligned, light passes through. If the lines of one grating coincide with the gaps of the other, no light passes through. Photocells convert these variations in light intensity into electrical signals. The specially structured grating of the scanning reticle filters the light current to generate nearly sinusoidal output signals. In the XY representation on an oscilloscope, the signals form a Lissajous figure. Ideal output signals appear as a concentric inner circle. Deviations in circular form and position are caused by position error within one signal period and therefore go directly into the result of measurement. The size of the circle, which corresponds with the amplitude of the output signal, can vary within certain limits without influencing the measuring accuracy. On direct drives, deviations from the circular form cause acoustic noise, reduce control quality, and increase heat generation.

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

Lower sensitivity to contamination Production facilities and handling devices for the semiconductor industry demand high acceleration and compact designs. Such requirements call specifically for exposed measuring systems that operate without friction and, because they can operate without their own housing, can be designed to be very small and therefore low in mass. Special scanning methods and production techniques are used to provide tough protection against contamination even without sealing the encoder.

Reaction of the LIF 400 to contamination

Exposed linear encoders from HEIDENHAIN operate with single-field scanning. Only one scanning field is used to generate the scanning signals. Local contamination on the measuring standard (e.g., fingerprints from mounting or oil accumulation from guideways) influences the light intensity of the signal components, and therefore of the scanning signals, 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 error remains small. The large scanning field additionally reduces sensitivity to contamination. In many cases this can prevent encoder failure. This is particularly clear with the LIDA 400 and LIF 400, which in relation to the grating period have a very large scanning surface of 14.5 mm2. Even with contamination with 3mm diameter, the encoders continue to provide high-quality signals. The position error remains far below the values specified for the accuracy grade of the scale. An essential prerequisite for optical encoders with low sensitivity to contamination is therefore an optimized scanning method, the large scanning field, and the contamination-tolerant graduation. Application-oriented mounting tolerances Very small signal periods usually come with very narrow distance tolerances between the scanning head and scale tape. Thanks to the interferential scanning principle of the LIF 400 and innovative index gratings in the LIF 400, it has become possible to provide ample mounting tolerances in spite of the small signal periods. Within the mounting tolerances, therefore, changes in the signal amplitude remain negligible. This behavior is substantially responsible for the high reliability of exposed linear encoders from HEIDENHAIN.

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

Linear encoders for linear motors Exposed linear encoders from HEIDENHAIN are optimized for use on fast, precise machines as sought by the semiconductor industry and automation technology. In spite of the exposed mechanical design they are highly tolerant to contamination, ensure high long-term stability, and are fast and simple to mount. Their low weight and compact design suit encoders of the LIF À , LIP Á and LIDA Â series particularly for linear motors. n

À

Á

Â

For more information circle # 1 on the reader service card.

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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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o Please add me to your mailing list. (Provide address above) Please send me HEIDENHAIN’s most current catalog.

o o o

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o Digital Readout o METRO/CERTO Gauges o Angular Rotary o Incremental Rotary o o Point-to-Point Controls o Servo Drive

NC Linear

Measurement Inspection Contouring Controls

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

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

#7

#8

Absolute Rotary

#9

#10

©2004 HEIDENHAIN CORPORATION

VOLUME 10, ISSUE 2

IS INTERESTED IN YOUR FEEDBACK

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

Name Company Title Address City Phone (

)

FAX (

State )

Zip

E-mail

o Please add me to your mailing list. (Provide address above) Please send me HEIDENHAIN’s most current catalog.

o o o

General

o

o Digital Readout o METRO/CERTO Gauges o Angular Rotary o Incremental Rotary o o Point-to-Point Controls o Servo Drive

NC Linear

Measurement Inspection Contouring Controls

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

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

#7

VOLUME 10, ISSUE 2

#8

Absolute Rotary

#9

#10

©2004 HEIDENHAIN CORPORATION

BUSINESS REPLY INFORMATION

New Catalogs Available

Angle Encoders This latest catalog gives an overview of all of HEIDENHAIN’s angle encoders described as encoders that have an accuracy of better than ± 5” and a line count of at least 10,000. These angle encoders, which are available in both incremental and absolute output formats and come in a wide variety of mechanical configurations, are typically found in applications requiring precision 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. For more information circle # 7 on the reader service card.

Position Encoders for Servo Drives HEIDENHAIN’s position encoders for servo drives are extensively detailed in this catalog. The descriptions of the technical features contain fundamental information on the use of rotary, angular, and linear encoders on electric drives. Details include selection tables, technical features and mounting information, specifications, and electrical connection information. For more information circle # 8 on the reader service card.

ITNC 530 Contouring Control Showcasing the newest TNC from HEIDENHAIN, this catalog details the iTNC 530, a versatile contouring control for milling, drilling, and boring machines and machining centers. This TNC features a fast and extremely powerful processor architecture. The catalog details the features and specifications for the machine manufacturer. For more information circle # 9 on the reader service card.

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HEIDENHAIN Makes Impressions at IMTS During IMTS (the International Manufacturing Technology Show) this past September, HEIDENHAIN was once again on hand to talk with the many attendees who came to this world-renowned machine tool show that is held in Chicago on every even year. This year, besides showcasing the very newest in precision measurement components and systems, HEIDENHAIN also highlighted two large motion control displays at the booth. These motion control displays had been developed recently by HEIDENHAIN’s Research & Development department in Germany in order to demonstrate the thermal effects on motion and signal quality for speed control, always important considerations in any machining process. Their availability and actions at IMTS were often the subject of conversation by the viewers who are involved with designing or utilizing machine tools. “Accuracy of Feed Drives” Display

HEIDENHAIN’s first display at the IMTS booth demonstrated the difference in drive performance associated with different measuring technologies (“Angle Encoders for Rotary Tables”). Here a rotary table fixture display was equipped with three different types of angle encoders to measure position and speed: magnetic, incremental, and absolute. The motion of the table and audible drive tuning deviations then clearly demonstrated how resolution, signal quality, and interpolation contribute to the stability of servo loop, and the benefits and drawbacks of each type of measuring system. The second display highlighted the linear versus rotary argument (“Accuracy of Feed Drives”). Here, a linear (HEIDENHAIN’s current single-field scanning technology for the LC scales) versus traditional rotary encoder/ ballscrew system was used to capture position. This display clearly demonstrated where drift error due to thermal effects often takes place with a rotary system, and the advantage, including resistance to contamination, of linear encoder systems.

“Angle Encoders for Rotary Tables” Display For more information circle # 10 on the reader service card.

Both of these displays were based on technical white papers available to anyone for the asking. The title of the paper of the first display is “Angle Encoders for Rotary Tables” while the latter is titled “Accuracy of Feed Drives.” It was exciting to see these papers come to life at IMTS.

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