HEIDENHAIN Length Gauges User Manual

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Length Gauges

April 2015

Length gauges from HEIDEN HAIN offer

high accuracy over long measuring ranges. These sturdily made gauges are available in application-oriented versions.

They have a wide range of applications in production metrology, in multipoint inspection stations, measuring equipment monitoring, and as position measuring devices.

This catalog supersedes all previous editions, which thereby become invalid. The basis for ordering from HEIDENHAIN is always the catalog edition valid when the contract is made.

Standards (ISO, EN, etc.) apply only where explicitly stated in the catalog.

The Interfaces of HEIDENHAIN Encoders brochure, ID 1078628-xx,

includes comprehensive descriptions of all available interfaces as well as general electrical information.

Contents

Length gauges – applications and products

Technical features and mounting information

Speciﬁcations

Range of applications, application examples

Length gauges from HEIDENHAIN

Length gauge overview

Measuring principles

Measuring accuracy

Mounting

Setup

Gauging force and plunger actuation

HEIDENHAIN-ACANTO absolute length gauges

Accuracy Measuring range

± 2 µm 12 mm

30 mm

Accessories

Electrical connection

HEIDENHAIN-CERTO incremental length gauges

HEIDENHAIN-METRO incremental length gauges

HEIDENHAIN-SPECTO incremental length gauges

Measuring contacts, switch boxes, coupling

Gauge stands, ceramic suction plate, diaphragm compressor

Cable-type lifter, gauge stands

Interface electronics

Evaluation electronics units

± 0.1 µm; ± 0.03 µm* ± 0.1 µm; ± 0.05 µm*

± 0.2 µm 12 mm

± 0.5 µm ± 1 µm

± 1 µm 12 mm

For HEIDENHAIN-CERTO

For HEIDENHAIN-ACANTO, HEIDENHAIN-METRO and HEIDENHAIN-SPECTO

25 mm 60 mm

25 mm

60 mm 100 mm

30 mm

Interfaces

Cables and connecting elements

Service

Calibration according to DAkkS

* After linear length-error compensation in the evaluation electronics

Areas of application

In quality assurance

Metrology and production control

Length gauges from HEIDENHAIN play a role in incoming goods inspection, fast dimension checking during production, statistical process control in production or quality assurance, or in any application where fast, reliable and accurate length measurement is required. Their large measuring lengths are a particular advantage: whether the part measures 5 mm or 95 mm, it is measured immediately with one and the same length gauge.

Whatever the application, HEIDENHAIN has the appropriate length gauge for the required accuracy. The HEIDENHAIN- CERTO length gauges offer a very high accuracy of ± 0.1 µm/± 0.05 µm*/ ± 0.03 µm* for extremely precise measurement. Length gauges from the HEIDENHAIN-METRO program have accuracy grades as ﬁne as ± 0.2 µm, while the HEIDENHAIN-SPECTO length gauges, with ± 1 µm accuracy, offer particularly compact dimensions.

Gauge block calibration and measuring device inspection

The regular inspection of measuring equipment called for by standards, and the inspection of gauge blocks in particular, necessitate a large number of reference standard blocks if the comparative measurement is performed using inductive gauges. The problem is the small measuring range of inductive gauges: they can measure length differences of only up to 10 µm. Length gauges, which offer large measuring ranges together with high accuracy, greatly simplify the calibration of measuring devices required to ensure traceability.

The length gauges of the HEIDENHAIN- CERTO program with measuring ranges of 25 mm with ± 0.1 µm/± 0.03 µm* accuracy and 60 mm with ± 0.1 µm/± 0.05 µm* accuracy are especially well suited for this task. It permits a signiﬁcant reduction in the required number of reference standard blocks, and recalibrating becomes much simpler.

* After linear length-error compensation in

the evaluation electronics

Thickness gauging of silicon wafers

Inspection of styli

Calibration of gauge blocks

In production

Multipoint inspection apparatuses

Multipoint inspection apparatuses require durable length gauges with small dimensions. They should also have relatively large measuring ranges of several millimeters with consistent linear accuracy in order to simplify the construction of inspection devices—for example by enabling the construction of one device for several masters. A large measuring length also provides beneﬁts in master production, because simpler masters can be used.

Thanks to their small dimensions, the HEIDENHAIN-ACANTO absolute length gauges, like the HEIDENHAIN-SPECTO incremental length gauges, are specially designed for multi-point measuring stations. They feature accuracy grades up to ± 1 µm over measuring ranges up to 30 mm. Higher accuracy requirements up to ± 0.2 µm can be met with similarly compact HEIDENHAIN-METRO length gauges.

Unlike inductive gauges, HEIDENHAINSPECTO length gauges provide stable measurement over long periods— eliminating recalibration.

Position measurement

Length gauges from HEIDENHAIN are also ideal for position measurement on precision linear slides and X-Y tables. Working with measuring microscopes, for example, becomes much easier thanks to the digital readout and the ﬂexible datum setting.

Here, length gauges from the HEIDENHAIN-METRO and HEIDENHAIN-SPECTO program come into use with large measuring ranges of 30 mm, 60 mm or 100 mm at consistently high accuracy grades of ± 0.5 µm or ± 1 µm.

In this application as linear measuring device, the length gauge’s fast installation in accordance with the Abbe measuring principle by its clamping shank or planar mounting surface is of special beneﬁt.

Testing station for ﬂatness inspection

Position measurement on an X-Y table for lens mounting

Tolerance gauging of semiﬁnished products

Length gauges from HEIDENHAIN

A number of arguments speak for HEIDENHAIN length gauges. These include not only their technical features, but also their high quality standard and the worldwide presence of HEIDENHAIN.

Large measuring ranges

HEIDENHAIN length gauges are available with measuring lengths of 12 mm, 25 mm, 30 mm, 60 mm or 100 mm. so that you can measure very different parts in one measuring setup and avoid frequently changing setups with expensive gauge blocks or masters.

High accuracy

The high accuracy speciﬁ ed for HEIDENHAIN length gauges applies over the entire measuring length. Whether the part measures 10 mm or 100 mm, its actual dimension is always measured with the same high quality. The high repeatability of HEIDENHAIN length gauges comes into play during comparative measurements, for example in series production.

In particular HEIDENHAIN-CERTO length gauges provide high linear accuracy and offer resolution in the nanometer range.

Robust design

HEIDENHAIN length gauges are built for an industrial environment. They feature consistently high accuracy over a long period of time as well as high thermal stability. They can therefore be used in production equipment and machines.

Wide range of applications

HEIDENHAIN length gauges are suited for many applications. Automatic inspection equipment, manual measuring stations or positioning equipment—wherever lengths, spacing, thickness, height or linear motion are to be measured, HEIDENHAIN length gauges function quickly, reliably and accurately.

Absolute position measurement

HEIDENHAIN-ACANTO length gauges operate with absolute measurement over a range of 12 mm or 30 mm and with high repeatability. Its particular advantage is that the measured value is available immediately after switch-on.

Worldwide presence

HEIDENHAIN is represented in all important industrial countries—in most of them with wholly owned subsidiaries. Sales engineers and service technicians support the user on-site with technical information and servicing in the local language.

Know-how

The high quality of HEIDENHAIN length gauges is no coincidence. HEIDENHAIN has been manufacturing high-accuracy scales for over 70 years, and for many years it has developed measuring and testing devices for length and angle measurement for national standards laboratories. This know-how makes HEIDENHAIN an extraordinarily qualiﬁ ed partner for metrology questions.

Length gauge overview

Accuracy Measuring range

Plunger actuation

Absolute position measurement

± 2 µm HEIDENHAIN-ACANTO

By measured object

Pneumatic

Incremental linear measurement

± 0.1 µm ± 0.05 µm ± 0.03 µm

± 0.2 µm HEIDENHAIN-METRO

± 0.5 µm ± 1 µm

± 1 µm HEIDENHAIN-SPECTO

After linear length-error compensation in the evaluation electronics

*) *)

HEIDENHAIN-CERTO

By motor

By external coupling

By cable lifter

or measured object

Pneumatic

HEIDENHAIN-METRO

By motor

By external coupling

By measured object

Pneumatic

CT 6000 CT 2500MT 101 MT 60

AT 3000

AT 1200

12 mm 25 mm/

30 mm

60 mm 100 mm Page

AT 1218 EnDat

AT 1217 EnDat

AT 3018 EnDat

AT 3017 EnDat

CT 2501 » 11 µA

CT 2502 » 11 µA

CT 6001 » 11 µA

CT 6002 » 11 µA

MT 1271 « TTL MT 1281 » 1 V

MT 1287 » 1 V

MT 2571 « TTL MT 2581 » 1 V

MT 2587 » 1 V

MT 60 M » 11 µA

MT 60 K » 11 µA

MT 101 M » 11 µA

MT 101 K » 11 µA

ST 1278 « TTL ST 1288 » 1 V

ST 1277 « TTL ST 1287 » 1 V

ST 3078 « TTL ST 3088 » 1 V

ST 3077 « TTL ST 3087 » 1 V

ST 3000 ST 1200MT 2500 MT 1200

AT 3000

AT 1200

Measuring principles

Measuring standard

HEIDENHAIN length gauges are characterized by long measuring ranges and consistently high accuracy. The basis for both is the photoelectrical scanning principle.

HEIDENHAIN length gauges use material measuring standards consisting of absolute or incremental graduations on substrates of glass or glass ceramic. These measuring standards permit large measuring ranges, are insensitive to vibration and shock, and have a deﬁned thermal behavior. Changes in atmospheric pressure or relative humidity have no inﬂuence on the accuracy of the measuring standard— which is the prerequisite for the high long- term stability of HEIDENHAIN length gauges.

HEIDENHAIN manufactures the precision graduations in specially developed, photolithographic processes.

• AURODUR: matte-etched lines on goldplated steel tape with typical graduation period of 40 µm

• METALLUR: contamination-tolerant graduation of metal lines on gold, with typical graduation period of 20 µm

• DIADUR: extremely robust chromium lines on glass (typical graduation period of 20 µm) or three-dimensional chromium structures (typical graduation period of 8 µm) on glass

• SUPRADUR phase grating: optically three dimensional, planar structure; particularly tolerant to contamination; typical graduation period of 8 µm and ﬁner

• OPTODUR phase grating: optically three dimensional, planar structure with particularly high reﬂectance, typical graduation period of 2 µm and less

Measurement procedure

With the incremental measuring method, the graduation consists of a

periodic grating structure. The position information is obtained by counting the individual increments (measuring steps) from some point of origin. Since an absolute reference is required to ascertain positions, the measuring standard is provided with an additional track that bears a reference mark. The absolute position on the scale, established by the reference mark, is gated with exactly one signal period.

The reference mark must therefore be scanned to establish an absolute reference or to ﬁnd the last selected datum.

With the absolute measuring method, the position value is available from the encoder immediately upon switch-on and can be called at any time by the subsequent electronics. There is no need to move the axes to ﬁnd the reference position. The absolute position information is read from the graduated disk, which is formed from a serial absolute code structure. A separate incremental track is interpolated for the position value and at the same time—depending on the interface version—is used to generate an optional incremental signal.

DIADUR phase grating with approx. 0.25 µm grating height

Photoelectric scanning

Most HEIDENHAIN encoders operate using the principle of photoelectric scanning. Photoelectric scanning of a measuring standard is contact-free, and as such, free of wear. This method detects even very ﬁne lines, no more than a few microns wide, and generates output signals with very small signal periods.

The ﬁner the grating period of a measuring standard is, the greater the effect of diffraction on photoelectric scanning. HEIDENHAIN uses two scanning principles with linear encoders:

• The imaging scanning principle for grating periods of 20 µm and 40 µm

• The interferential scanning principle for very ﬁne graduations with grating periods of, for example, 8 µm

DIADUR graduation

Along with these very ﬁne grating periods, these processes permit a high deﬁnition and homogeneity of the line edges. Together with the photoelectric scanning method, this high edge deﬁnition is a precondition for the high quality of the output signals.

The master graduations are manufactured by HEIDENHAIN on custom-built highprecision dividing engines.

5 µm

Imaging principle

To put it simply, the imaging scanning principle functions by means of projected-light signal generation: two scale gratings with equal or similar 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 is located here. When the two gratings move relative to each other, the incident light is modulated. If the gaps in the gratings are aligned, light passes through. If the lines of one grating coincide with the gaps of the other, no light passes through. An array of photovoltaic cells converts these variations in light intensity into electrical signals. The specially structured grating of the scanning reticle ﬁlters the light to generate nearly sinusoidal output signals.

The smaller the period of the grating structure is, the closer and more tightly toleranced the gap must be between the scanning reticle and scale.

Interferential scanning principle

The interferential scanning principle exploits the diffraction and interference of light on a ﬁne graduation to produce signals used to measure displacement.

A step grating is used as the measuring standard: reﬂective lines 0.2 µm high are applied to a ﬂat, reﬂective surface. In front of that is the scanning reticle—a transparent phase grating with the same grating period as the scale.

When a light wave passes through the scanning reticle, it is diffracted into three partial waves of the orders –1, 0, and +1, with approximately equal luminous intensity. The waves are diffracted by the scale such that most of the luminous intensity is found in the reﬂected diffraction orders +1 and –1. These partial waves meet again at the phase grating of the scanning reticle where they are diffracted again and interfere. This produces essentially three waves that leave the scanning reticle at different angles. Photovoltaic cells convert this alternating light intensity into electrical signals.

A relative motion of the scanning reticle to the scale causes the diffracted wave fronts to undergo a phase shift: when the grating moves by one period, the wave front of the ﬁrst order is displaced by one wavelength in the positive direction, and the wavelength of diffraction order –1 is displaced by one wavelength in the negative direction. Since the two waves interfere with each other when exiting the grating, the waves are shifted relative to each other by two wavelengths. This results in two signal periods from the relative motion of just one grating period.

Interferential encoders function with grating periods of, for example, 8 µm, 4 µm and ﬁner. Their scanning signals are largely free of harmonics and can be highly interpolated. These encoders are therefore especially suited for high resolution and high accuracy.

The HEIDENHAIN-CERTO and the HEIDENHAIN-METRO length gauges of the MT 1200 and MT 2500 series operating according to the interferential principle.

The HEIDENHAIN-ACANTO, HEIDENHAINSPECTO and the HEIDENHAIN-METRO length gauges of the MT 60 and MT 100 series operating according to the imaging principle.

Imaging principle

LED light source

Measuring standard

Condenser lens

Scanning reticle

Photovoltaic cell array

Interferential scanning principle (optics schematics) C Grating period y Phase shift of the light wave when passing through the scanning reticle  Phase shift of the light wave due to motion X of the scale

Photocells

LED light source

Condenser lens

Scanning reticle

Measuring standard

Measuring accuracy

The accuracy of linear measurement is mainly determined by

• the quality of the graduation,

• the quality of the scanning process,

• the quality of the signal processing electronics,

• the eccentricity of the graduation to the bearing,

• the error from the scale guideway relative to the scanning unit, and

• the orthogonality of the length gauge to the bearing surface.

These factors of inﬂuence are comprised of encoder-speciﬁc error and applicationdependent issues. All individual factors of inﬂuence must be considered in order to assess the attainable overall accuracy.

Error speciﬁc to the measuring device

The error that is speciﬁc to the measuring device is shown in the Speciﬁcations as the system accuracy.

The extreme values of the total error F with reference to their mean value lie over the entire measuring length within the system accuracy ± a. They are measured during the ﬁnal inspection and documented in the calibration chart.

The system accuracy includes

• the homogeneity and period deﬁnition of the graduation,

• the alignment of the graduation,

• the error of the bearing, and

• the position error within one signal period.

Position error within one signal period

Position errors within one signal period already become apparent in very small motions and in repeated measurements. They are therefore considered separately.

The position error within one signal period ± u results from the quality of the scanning and—for encoders with integrated pulseshaping or counter electronics—the quality of the signal-processing electronics. For encoders with sinusoidal output signals, however, the errors of the signal processing electronics are determined by the subsequent electronics.

The following individual factors inﬂuence the result:

• The size of the signal period

• The homogeneity and period deﬁnition of the graduation

• The quality of scanning ﬁlter structures

• The characteristics of the sensors

• The stability and dynamics of further processing of the analog signals

These deviations are to be considered when specifying position error within one signal period.

Position error within one signal period ± u is speciﬁed in percent of the signal period. For length gauges, the value is typically better than ± 1% of the signal period. You will ﬁnd the speciﬁed values in the Speciﬁcations.

Short-range accuracy

The short-range accuracy describes an error that occurs within a distance of ± 100 µm from a measuring point. It includes electronic and mechanical inﬂuences of the gauge on the result of measurement. The values for short-range accuracy typically lie below the speciﬁed values.



Position error

Position error a over the measuring length ML

Position error within one signal period

Position

Position error u within one signal period



Position error



Signal level

Signal period

360 °elec.

Application-dependent error

Other factors besides the system accuracy also inﬂuence the attainable total accuracy of measurement. These include in particular the ambient temperature and temperature ﬂuctuations during measurement as well as a stable, orthogonal measuring setup.

All components included in the measuring loop, such as the holder for the measured object, the gauge stand with holder, and the length gauge itself, inﬂuence the result of measurement. Expansion or deformation of the measuring setup through mechanical or thermal inﬂuences adds directly to the error.

Mechanical design

A stable measuring assembly must be ensured. Long lateral elements within the measuring loop are to be avoided. HEIDENHAIN offers a stable gauge stand as an accessory. The force resulting from the measurement must not cause any measurable deformation of the measuring loop.

Length gauges from HEIDENHAIN operate with small gauging force and have very little inﬂuence on the measuring setup.

Orthogonal mounting

The length gauge is to be mounted so that its plunger is exactly orthogonal to the measured object or the surface on which it rests. Deviations result in measuring error.

The accessory HEIDENHAIN gauge stands with holders for an 8 mm clamping shank ensure orthogonal mounting. Length gauges that provide planar mounting surfaces are to be adjusted in the direction parallel to the mounting surface (Y) to be perpendicular to the measuring plate. A quick and reliable adjustment is possible with the aid of a gauge block or a parallel block. The perpendicularity to the measuring table (X) is already ensured by the gauge stand.

Thermal characteristics

Temperature variations during measurement cause changes in length or deformation of the measuring setup. After a change in temperature of 5 K, a steel bar of 200 mm length expands by 10 µm.

Length changes resulting from a uniform deviation from the reference temperature can largely be compensated by resetting the datum on the measuring plate or a master; only the expansion of the scale and measured object go into the result of measurement.

Temperature changes during measurement cannot be ascertained mathematically. For critical components, HEIDENHAIN therefore uses special materials with low coefﬁcients of expansion, such as are found in the HEIDENHAIN-CERTO gauge stand. This makes it possible to guarantee the high accuracy of HEIDENHAIN-CERTO even at ambient temperatures of 19 °C to 21 °C and variations of ± 0.1 K during measurement.

In order to measure with complete accuracy, the length gauge should be switched on approximately 15 minutes before the ﬁrst measurement.

The measuring loop: All components involved in the measuring assembly, including the length gauge

Orthogonal mounting

Thermally induced change in length:

Expansion of the measuring loop components as a result of heat

Calibration chart

All HEIDENHAIN length gauges are inspected before shipping for accuracy and proper function.

They are calibrated for accuracy during retraction and extension of the plunger. For HEIDENHAIN-CERTO gauges, the number of measuring positions is selected to ascertain very exactly not only the longrange error, but also the position error within one signal period.

The Quality Inspection Certiﬁ cate conﬁ rms the speciﬁ ed system accuracy of each length gauge. The calibration standards ensure the traceability—as required by EN ISO 9001—to recognized national or international standards.

For the HEIDENHAIN-METRO and HEIDENHAIN-CERTO series, a calibration chart documents the position error over the measuring range. It also shows the measuring step and the measuring uncertainty of the calibration measurement.

For HEIDENHAIN-METRO gauges the calibration chart shows the mean value of one forward and one backward measuring stroke.

The HEIDENHAIN-CERTO calibration chart shows the envelope curve of the measured error. The HEIDENHAIN-CERTO length gauges are supplied with two calibration charts, each for different operating attitudes.

Operating attitude for calibration chart 1

Example

Temperature range

The length gauges are inspected at a reference temperature of 20 °C. The system accuracy given in the calibration chart applies at this temperature.

Operating attitude for calibration chart 2

The operating temperature indicates the ambient temperature limits between which the length gauges will function properly. The storage temperature range of -20 °C to 60 °C applies for the device in its packaging.

Repeatability

Whereas the system accuracy applies over the entire measuring range, for some applications the repeatability is the decisive factor. It plays an important role in repeated measurements.

Repeatability is deﬁned in the standards DIN 32876 and DKD-R 4-3, and describes a length gauge’s capability to supply very similar measured values for identical measurands and conditions.

HEIDENHAIN ascertains the repeatability of the length gauges with ﬁve measurements near the lower plunger stop. The plunger is completely extended and retracted at medium speed. Since the length gauge was already in operation for at least 10 minutes before this, it is already in a stable thermal state.

The repeatability of the length gauges is usually better than the values listed in the table. The characteristic statistical distribution is shown in the diagram, using the ST 1200 as an example.

Repeatability depends on the

• combinations of materials used in the components,

• installed electronics,

• optomechanics used, and the

• bearing of the plunger.

Series Repeatability

< x

± 2s

AT 1200

AT 3000

CT 2500

CT 6000

MT 101

MT 1200

MT 2500

MT 60

ST 1200

ST 3000

0.4 µm

0.8 µm

0.02 µm

0.03 µm

0.04 µm

0.03 µm

0.09 µm

0.06 µm

0.25 µm

0.7 µm



Frequency

ST 1200: Statistical distribution of the repeatability

Repeatability



Mounting

Abbe principle

HEIDENHAIN length gauges enable you to work according to the Abbe measuring principle: The measured object and scale must be in alignment to avoid additional measuring error.

Fastening

The CT 6000, MT 60 and MT 101 length gauges are fastened by two screws onto a plane surface. This ensures a mechanically stable installation of even these large length gauges. Special holders are available for fastening the MT 60 and MT 101 to the MS 100 gauge stand for the HEIDENHAINMETRO (see Accessories).

The CT 2500 is mounted by its standard clamping shank with 16h8 diameter. A holder is available for fastening the HEIDENHAIN-CERTO to the gauge stand (see Accessories).

The AT, ST, MT 1200 and MT 2500 length gauges feature a standard clamping shank with 8h6 diameter. These HEIDENHAIN length gauges can therefore easily be used with existing measuring ﬁxtures and stands.

As an accessory, HEIDENHAIN offers a special clamping sleeve and screw. It facilitates fastening the length gauge securely without overstressing the clamping shank. Clamping sleeve ID 386811-01



CT 6000 MT 60 MT 101

 

CT 2500

 

 

–



Secured with clamping sleeve

Operating attitude for HEIDENHAINCERTO

The HEIDENHAIN-CERTO can be operated at any attitude. However, the mounting position with horizontal length gauge and upward facing mounting surface should be avoided because in such a case no guarantee can be made for accuracy.

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