Technical Information

Exposed linear encoders: permanently stable measuredvalues and detailed accuracy data
Exposed linear encoders are used wherever very high demands are placed on the accuracy of the measured value. This includes production
and measuring equipment in the semiconductor industry, PCB assembly machines and measuring machines. In order to ensure permanent
accuracy over the entire life cycle of the encoder, HEIDENHAIN has developed the signal processing ASIC HSP 1.0 for application in
exposed linear encoders with incremental position value acquisition.
The ASIC almost completely compensates fluctuations in signal amplitude due to interference. The underlying, significantly improved
signal stabilization is particularly effective against contamination of the measuring standard or scanning reticle. The result is a permanently
stable measuring signal almost entirely without impairment of interpolation accuracy or increased noise component.
HEIDENHAIN is also introducing new accuracy data for exposed linear encoders. They enable the design engineer to refer to detailed
information when selecting the appropriate encoder for his application. In addition to accuracy, he can find the following data:• Accuracy of the graduation over short intervals• Accuracy of the interpolation• Position noise

LIDA 400

LIF 400

LIP 6000
Figure 1: Exposed linear encoders with the HSP 1.0 ASICApril 2016

Greater reliability through stable measured values
Constantly high-quality signal through adaptation of illumination

In principle, HEIDENHAIN encoders
provide stable scanning signals that needno additional stabilization. However,contamination in the measuring standard
and scanning reticle can negatively affectthese scanning signals. Depending on theapplication, sooner or later it can causesignal quality problems because
contamination increases in the courseof time.

Scale

Contamination

Reliably high-quality measuring signals
The HEIDENHAIN HSP 1.0 signal processing
ASIC permanently monitors the scanningsignal. If contamination on the measuring
standard or scanning reticle result in signal
changes, the HSP 1.0 almost completelycompensates them.
In this way, this intelligent ASIC ensuresthat the scanning signal retains its highquality and stability for the long term.
Interpolation error and position noise do
not increase in normal operation fromcontamination.

Structured
detector

Permanently stable signalPosition measurement with an exposed
linear encoder equipped with the HSP 1.0
signal-processing ASIC therefore results ina very stable signal over the entire
measuring range—regardless of thetraversed contamination. The signal
amplitude stays nearly constant at 1 VPP(Fig. 3). Even if the ASIC’s control limit
were exceeded due to increasing,extremely heavy contamination, it would
not result in an abrupt signal failure.
Instead, the signal amplitude would only
slowly decrease.

With HSP 1.0 signal processing ASIC
Without HSP 1.0 signal processing ASIC

Index grating
LED light source

Figure 2: Single-field scanning with large scanning window—in this example the LIDA 400—works in combination with the HEIDENHAIN HSP 1.0 signal
processing ASIC to ensure a constantly high-quality scanning signal even with contamination on the measuring standard and scanning reticle.

2

No influence on the noise component
If the signal amplitude decreases, theHSP 1.0 readjusts it by increasing the LEDcurrent. The concomitant increase in lightintensity from the LED hardly worsens thenoise component in the scanning signals
even during heavy signal-stabilizing
intervention—quite unlike systems thatplace the amplification in the signal path,
which also increases the noise component.
Contamination does not influenceinterpolation error in practice
However, the HSP 1.0 signal processing
ASIC not only stabilizes the signal
amplitude. It also ensures that the signal
keeps it original, ideal signal shape undercontamination. In this way it keeps
interpolation error very small when themeasuring standard and scanning reticle
are contaminated.

Oil1)

WireFingerprint

Signal in VPP 

Without contamination, signal
stabilization is unnecessary
Among other things, exposed linear
encoders from HEIDENHAIN thank theirstable scanning signal to the large sensor
surface of the structured detector. It
ensures that interference has only a small
overall influence on signal scanning. The
signal stabilization does not have to work
quickly or aggressively, which provides
optimal conditions for a stable scanningsignal. If there is no contamination on themeasuring standard or scanning reticle,
such as after careful mounting, the signal
stabilization does not even start tofunction.

2)

Oil

1.2
1.0
0.8
0.6
0.4
0.2
0

Interpolation error
and noise in µm 0406080100120Position in mm 10–1100 nm
50 nm
0–50 nm–100 nmWith HSP 1.0 signal processing ASIC
Without HSP 1.0 signal processing ASIC1)2)1), 2) = Oil drop  2 mm—incremental track half or fully covered.

Figure 3: Measuring standard with contamination and the associated signal amplitudes withconventional scanning and scanning with the HSP 1.0 signal processing ASIC3

Detailed accuracy data
Exact information for better encoder selection

HEIDENHAIN has expanded its accuracy
data for exposed linear encoders. Up tonow, the encoder-specific error wasspecified rather generally as the accuracy
grade and the position error within one
signal period. In future, users will find thefollowing more detailed information:• Accuracy of the measuring standard• Accuracy of the interpolation• Position noise
The division of data into the accuracy ofthe measuring standard, the accuracy of
the interpolation, and the position noise
enables design engineers to make a much
more accurate prognosis of attainableaccuracy in the respective application.
This enables them to better and moreeasily select the encoder most appropriate
for their respective application.

Accuracy of the measuring standard
The accuracy of the measuring standard ismainly determined by• the homogeneity and period definition of
the graduation,• the alignment of the graduation on its
carrier,• the stability of the graduation carrier.
The accuracy of the measuring standard
is indicated by the uncompensatedmaximum value of the baseline error.
It is ascertained under ideal conditions byusing a series-produced scanning head tomeasure position error. The measuring
points are an integral multiple of the signal
period, so that interpolation errors have noinfluence (Fig. 4).
The accuracy grade a defines the upper
limit of the baseline error within any max.
one-meter section. For special encoders, abaseline error for defined intervals of themeasuring standard is additionally stated.
In addition to the accuracy grade of e.g.
±1 µm, this now provides the user with theinformation that in an interval of 5 mm theencoder concerned attains accuracy of ±0.125 µm (Tab. 1, model LIP 281).

Position error Baseline error

Position

Signal level Position errorThe accuracy of the interpolation is
ascertained with a series-produced
measuring standard, and is indicated bya typical maximum value u of theinterpolation error (Fig. 5). Encoders withanalog interface are tested using
HEIDENHAIN electronics (e.g. EIB 741).
The maximum values do not include
position noise and are indicated in theSpecifications.
The interpolation error has an effect withvery small traversing speeds and during
repeat measurements. In addition, it
increases the motor current and with it thetemperature of the motor.

Accuracy of the interpolation

Accuracy of the measuring standard

Figure 4

Accuracy of the interpolation
The accuracy of the interpolation is mainly
influenced by• the size of the signal period,• the homogeneity and period definitionof the graduation,• the quality of scanning filter structures,• the characteristics of the sensors, and• the quality of the signal processing.

Interpolation
error

Signal period
360° elec.

PositionFigure 54

The position noise depends on the signal
processing bandwidths necessary forforming the position values. It is ascertained
within a defined time period, and isindicated as a product-specific RMS value.
Position noise is primarily responsible forthe reproducibility of measurement results
and the repeatability of an encoder.
Position noise in the velocity control loop
influences running smoothness at low
traverse velocities.

Position noise

RMS

Position error 

Position noise
Position noise denotes all random
processes that result in unforeseeable
position error. The position values aregrouped around an expected value in theform of a frequency distribution.

Time 

Frequency density

Figure 6

Table 1Baseline error

LIPFor very high accuracyAccuracy
gradeInterval± 0.5 µm

 ±0.075 µm/5 mm

LIDA
For high traversing speeds
and large measuring lengths

SignalperiodMeasuring
lengthInterfaceModel±0.01 nm0.128 µm

70 mm to270 mm

 TTL

LIP 372

1VPPLIP 382± 1 µm± 3 µm±0.125µm/5mm±1 nm

0.512 µm

20 mm to3040 mm

 1 VPPLIP 281± 0.5 µm
± 1 µm ±0.175 µm/5 mm

±7 nm

2 µm

70 mm to420 mm

 TTL

LIP 471

 1 VPPLIP 481

 TTL

LIP 5711VPPLIP 581

 TTL

LIF 471

 1 VPPLIF 481 TTL

LIDA 473

 1 VPPLIDA 483± 1 µmLIF
For high accuracy

Interpolationerror± 1 µm± 3 µm± 1 µm± 3 µm± 5 µm ±0.175 µm/
5 mm

±0.225µm/
5mm

±0.275 µm/
10 mm±12 nm±12 nm±45 nm

4 µm

4 µm

20 µm

70 mm to1 440 mm

70 mm to1020 mm

240 mm to3040 mm

5Detailed accuracy data
Acquisition and documentation of data

Measurement of accuracy in one interval
While the accuracy grade is specified forone section of maximally 1 m, or with shorter
linear encoders for the entire measuring
length and therefore describes the minimum
accuracy of the system, the accuracy in
one interval permits direct conclusions on
the actually attainable accuracy of measured
values in small intervals.

Every exposed linear encoder manufactured
by HEIDENHAIN is individually inspected
and certified for its quality. For all highaccuracy exposed linear encoders, a Quality
Inspection Certificate with measurement
curve and detailed measuring log (Fig. 7)
documents the results of the measurements
performed. All other exposed linear encoders
are supplied with a Quality Inspection
Certificate that certifies the compliancewith the limit values specified for theindividual encoder.

To be able to state accuracy in one interval,
HEIDENHAIN first defines the interval
width for which the accuracy is to be stated.
With the LIP 200, for example, the interval
width is 5 mm. Then the scale is continually
measured over its entire measuring length
in defined, very small measuring steps
with the chosen interval width. Finally, theuncompensated baseline errors over theinterval width measured in this way for eachmeasuring step are evaluated. The worst
value, i.e. the greatest measured baseline
error over all measured intervals, is thenspecified as the maximum value ±FI.

Figure 8 illustrates an example of selected
measuring steps. The baseline error within
the selected interval width reaches its
maximum in the second measuring step.
This can then be listed in the documentation
as the accuracy of the measuring standard.
Advantages of specifying accuracy in
one interval
In many applications it is not the accuracy
over the entire measuring range that isdecisive, but rather the accuracy in a very
narrowly limited section. On PCB assemblymachines, for example, the last millimetersof the measuring path decide whether themounting process can be highly accurate.
In such applications, the user can canobtain substantially more precise informationfrom the accuracy in a defined interval thanfrom the accuracy grade.

Baseline error

Interval width

Qualitätsprüf-Zertiﬁkat

Quality Inspection Certiﬁcate

DIN 55 350-18-4.2.2

DIN 55 350-18-4.2.2

LIP 201 R
ID 631000-13
SN 44408260

Measuring stepMax FI

Positionsabweichung F [μm]Position error F [µm]Messposition PosE [mm] / Measured position PosE [mm]Die Messkurve zeigt die Mittelwerte der Positionsabweichungen
aus Vorwärts- und Rückwärtsmessung.

The error curve shows the mean values of the position errors frommeasurements in forward and backward direction.

Positionsabweichung F des Maßstab: F = PosM – PosE
PosM = Messposition der Messmaschine
PosE = Messposition des Maßstab

Position error F of the scale: F = PosM – PosE
PosM = position measured by the measuring machine
PosE = position measured by the scale

Maximale Positionsabweichung der Messkurve
innerhalb 670 mm

Maximum position error of the error curve± 0,30 μm

Unsicherheit der Messmaschine

within 670 mm± 0.30 µm

Uncertainty of measuring machine–6–6

U95% = 0,040 μm + 0,400 ·10 · L (L = Länge des Messintervalls)

U95% = 0.040 µm + 0.400 ·10 · L (L = measurement interval length)

Messparameter

Measurement parameters

Messschritt

1000 μm

Measurement step

1000 µm

Erster Referenzimpuls bei Messposition

335,0 mmFirst reference pulse at measured position

335.0 mmRelative Luftfeuchtigkeit

max. 50 %Relative humidity

max. 50 %Dieser Maßstab wurde unter den strengen
HEIDENHAIN-Qualitätsnormen hergestellt und geprüft.
Die Positionsabweichung liegt bei einer Bezugstemperatur
von 20 °C innerhalb der Genauigkeitsklasse ± 1,0 μm.

This scale has been manufactured and inspected in accordance withthe stringent quality standards of HEIDENHAIN.
The position error at a reference temperature of 20 °C lies within
the accuracy grade ± 1.0 µm.

Kalibriernormale

Kalibrierzeichen

Calibration standards

Calibration referencesJod-stabilisierter He-Ne Laser
Wasser-Tripelpunktzelle
Gallium-Schmelzpunktzelle
Barometer
Luftfeuchtemessgerät

40151 PTB 11
61 PTB 10
62 PTB 10
A6590 D-K-15092-01-00 2012-120230 DKD-K-30601 2012-11

Iodine-stabilized He-Ne Laser
Water triple point cell
Gallium melting point cellPressure gauge
Hygrometer

40151 PTB 11
61 PTB 10
62 PTB 10
A6590 D-K-15092-01-00 2012-120230 DKD-K-30601 2012-11= Single interval= Interval with maximum baseline error Max FI

Figure 8: Ascertainment of accuracy in one interval

28.01.2014
DR. JOHANNES HEIDENHAIN GmbH · 83301 Traunreut, Germany · www.heidenhain.de · Telefon: +49 8669 31-0 · Fax: +49 8669 5061

Figure 7

6Prüfer/Inspected byK. Sommerauer

Figure 9: For each scale of an exposed linear encoder, HEIDENHAIN uses a special measuring machine to ascertain the baseline error in a defined interval.

Figure 10: The interpolation deviation of each exposed linear encoder is measured on a special measuring station by measuring the scanning head.

7

Exposed linear encoders

Exposed linear encoders from HEIDENHAIN
are optimized for use on fast, precisemachines as sought by the semiconductor
industry and automation technology. In spiteof the exposed mechanical design, they arehighly tolerant to contamination, ensurehigh long-term stability, and are quickly andeasily mounted.

LIF 400

LIP 6000

LIDA 400

More information:• Catalog: Exposed Linear Encoders
DR. JOHANNES HEIDENHAIN GmbH
Dr.-Johannes-Heidenhain-Straße 583301 Traunreut, Germany{ +49 8669 31-0
| +49 8669 32-5061
E-mail: info@heidenhain.dewww.heidenhain.de1172234-20 · 1 · 4/2016 · H · Printed in Germany