March 2012

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Angle Encoders Used For The World's Most Powerful Telescope

The ALMA observatory in theAtacama Desert in northern Chileuses the NEW incremental ERA7480C angle encoder. A specialstrength of the encoder isoutstanding precision within onesignal period. The encoders areused to position 25 antennas toform a giant telescope. Exactpositioning of the antennas weighingseveral tons is of decisiveimportance because the slightestimprecision distorts the result andleads to blurred images. Read more »

PRODUCT SPOTLIGHT

NEW ERO 6000 High Accuracy Angle Encoder

The ERO 6000 is perfect for use inmany metrology systems, incompact rotary tables and highdynamic applications such as airbearing spindles, laser trackersand robot arms. Its flat design andvery small scanning head utilizesan extremely sturdy and highquality gradation resulting in agrating period of 20 µm.Read more »

Also in this issue:

Did You Know...

...that there is a source forplug-and-play metrologycomputer system solutionsthat come already equippedwith PC-based QUADRA-CHEK products.Read more »

Industry Pulse

HEIDENHAIN's bidirectionalprotocol EnDat 2.2 is a100% digital interface,allowing users to savemoney in a few key areas.Read more »

Technical Tidbit

Choosing an encoder forposition and speed control?How to consider speedversus resolution and howmuch speed error can betolerated. Read more »

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March 2012

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Maximum Precision for a New View of the Universe

Angle encoders from HEIDENHAIN for the world's most powerful telescope

DR. JOHANNES HEIDENHAIN GmbH,

Traunreut

The international ALMA project is a source of prestige for all those involved. Although the observatory is

to be completed in 2013, it was already supplying breathtaking images from the depths of the universe

on October 3, 2011. 25 of 66 antennas are from Europe, and equipped with angle encoders from

HEIDENHAIN. It is this alone that makes precise positioning of the antennas possible, each weighing

several tons, as maximum precision is needed for next-generation astronomical observations.

The ALMA observatory in the Atacama Desert in northern Chile is the most powerful radio telescope in the

world, and the world's most complex terrestrial observatory. With ALMA, short for "Atacama Large

Millimeter/Submillimeter Array," astronomers aim to investigate remote galaxies and search for the building

blocks of solar systems and inhabitable planets. Construction of the observatory is not yet complete, yet the

unexpectedly high level of precision has caused furor throughout the world.

Until now around a third of the 66 radio antennas planned have been set up on the desert plateau at a

height of 5,000 meters. ALMA does not use one single antenna to observe the cosmos but several receivers

positioned precisely and interconnected to become a single telescope. Alma Correlator, one of the most rapid

specialized supercomputers in the world, calculates the image data of the antennas to produce a general

overall view.

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Pinpoint accuracy, light years away

The coupling of the antennas to produce a giant telescope enables ALMA to capture images of celestial

bodies at a distance of many millions of light years. Exact positioning of the antennas weighing several tons

is of elementary importance, and the slightest imprecision distorts the result and lead to blurred images.

A decision was taken by those responsible for the 25 European radio antennas to order angle encoders from

HEIDENHAIN. The company from Traunreut in Upper Bavaria, Germany has been developing angle encoders

for almost 60 years and is thus a pioneer in this sector. With outstanding measurement precision and a high

level of long-term stability, these devices ensure the required accuracy for alignment of the ALMA antennas.

A special strength of the HEIDENHAIN angle encoders used in the project is outstanding precision within one

signal period. They function without contact and are thus especially suitable for use in precision devices.

Precise measurement of horizontal and vertical angles

To align the horizontal angle (azimuth) with precision, the European ALMA antennas use the new incremental

ERA 7480C angle encoder with 247,800 scale lines and a diameter of 3155 millimeters. The ERA 7480C was

specifically developed for use with the ALMA and the tape length was adapted precisely according to the

required diameter. Achievable precision was simulated beforehand as a part of project development. The

ERA 7000 angle encoders consist of a scanning unit and a one-piece steel scale tape as graduation carrier.

The vertical angle (elevation) is set by the researchers in Chile with the aid of the ERA 4282C angle encoder

from HEIDENHAIN. The especially precise angle encoder of the ERA 4000 series with steel scale drum has

32,786 scale lines and a diameter of 209 millimeters.

The interface electronics from HEIDENHAIN adapt the encoder signals to the interface of the subsequent

electronics. The new external EIB 749 interface box interpolates and compensates the output signals from

the scanning head, and position values are output via Ethernet to the antenna's control computer.

Angle Encoders

The term angle encoder is typically used to describe encoders that have an accuracy of

greater than ±5 angular seconds and a line count above 10,000. These angle encoders are

found in applications that require the highly accurate measurement of angles in the range

of a few angular seconds, e.g. in rotary tables and swivel heads on machine tools, C axes

on lathes, but also in measuring equipment and telescopes.

Measuring Principle

HEIDENHAIN encoders incorporate measuring standards of periodic structures known as

graduations. These graduations are applied to a carrier substrate of glass or steel. With

the incremental measuring method used for example for the ALMA space telescope, the

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graduation consists of a periodic grating structure. The position information is gained by

counting the individual increments (measuring steps) from a datum set to any location.

Since an absolute reference is required to ascertain positions, the measuring standard has

an additional track that bears distance-coded reference marks. The absolute position on

the scale, established by the reference mark, is gated with exactly one measuring step.

HEIDENHAIN improves productivity

Products from HEIDENHAIN ensure that machines and plants work productively and efficiently. DR. JOHANNES

HEIDENHAIN GmbH develops and manufactures linear and angle encoders, rotary encoders, digital readouts

and numerical controls for demanding positioning tasks. HEIDENHAIN products are used primarily in high-

precision machine tools as well as in plants for the production and processing of electronic components.

With extensive experience and expertise in the development and manufacture of measuring devices and

numerical controls, HEIDENHAIN creates the groundwork for the automation of tomorrow's plants and

production machines.

Schematic representation of a circular graduation with distance-coded reference marks

(ERA 4480 with 20,000 lines as example)

ALMA does not use one single antenna for observation purposes but rather 66 receivers, precisely controlled and

interconnected to form a giant telescope. Exact positioning of the antennas weighing several tons is of decisive

importance, and this is ensured by angle encoders from HEIDENHAIN among other factors.

Source: Photo credits: ESO/José Francisco Salgado (josefrancisco.org)

www.heidenhain.com ©HEIDENHAIN 2012

ERA 7480 and ERA 4282 angle encoders

The ERA 7480C angle encoder consists of a scanning unit and a one-piece steel scale tape as graduation

carrier. The steel scale tape is supplied by HEIDENHAIN as standard to a length of 30 meters and significantly

longer on request. Circle segments are available in applications with no full circle or if measurement is not

required over 360°. The ERA 4282C modular encoder consists of a scale drum and a highly compact scanning

head.

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March 2012

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New High Accuracy Angle Encoder from

HEIDENHAIN

Distinguishing itself by its flat design and very small scanning head,

HEIDENHAIN's newest angle encoder is now being introduced to

the marketplace. Called the ERO 6000, this new angle encoder is

perfect for use in many metrology systems, in compact rotary

tables and high dynamic applications such as air bearing spindles,

laser trackers and robot arms.

The compact scanning head of the ERO 6000 is made possible

primarily by the application of a divergent scanning principle that does not require lenses or other beam-

directing optics. The scale graduation inside is an extremely sturdy and high quality METALLUR graduation.

This scanning method is new in HEIDENHAIN angle encoders. The component's resulting grating period is 20

µm, regardless of diameter.

Small scanning heads usually require small scanning fields, which are more sensitive to contamination due to

the scanning principle. To counteract this characteristic, a signal error compensation function is integrated in

the encoder's scanning sensor, which compensates the amplitude size and amplitude ratio within certain

limits and thus increases the reliability of the device.

Two ERO 6000 design types with line counts of 9,000 and 18,000, respectively, are being introduced

currently. The encoders are available with 1 VPP and TTL interfaces. When it comes to mounting, the

disk/hub assembly can be centered mechanically via 3-point centering or electrically with a second scanning

head.

Index Pages

Automation eNewsletter

Semiconductor and Metrology

eNewsletter

Machine Tool eNewsletter

Application Question?

Find out how HEIDENHAIN technology

can be integrated into your high-

precision motor, motion control and

machining systems processes. Call us

or complete the form to get access to

other industry position feedback and

finishing applications.

*All fields required.

*First Name:

*Last Name:

*Company:

*Phone:

*Email:

*Zip:

Comments:

www.heidenhain.com ©HEIDENHAIN 2012

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