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Linear encoders for linear drives

General information

Selection criteria for linear encoders

HEIDENHAIN recommends the use of

exposed linear encoders whenever the

severity of contamination inherent in a

particular machine environment does not

preclude the use of optical measuring

systems, and if relatively high accuracy is

desired, e.g. for high-precision machine

tools and measuring equipment, or for

production, testing and inspecting

equipment in the semiconductor industry.

Particularly for applications on machine

tools that release coolants and lubricants,

HEIDENHAIN recommends sealed linear

encoders. Here the requirements on the

mounting surface and on machine guide-

way accuracy are less stringent than for ex-

posed linear encoders, and therefore instal-

lation is faster.

Speed stability

To ensure smooth-running servo

performance, the linear encoder must

permit a resolution commensurate with

the given speed control range:

• On handling equipment, resolutions in

the range of several microns are

sufﬁ cient.

• Feed drives for machine tools need

resolutions of 0.1 μm and ﬁ ner.

• Production equipment in the

semiconductor industry requires

resolutions of a few nanometers.

At low traversing speeds, the position

error within one signal period has a

decisive inﬂ uence on the speed stability of

linear motors. (See also Measuring

Accuracy.)

Traversing speeds

Exposed linear encoders function without

contact between the scanning head and

the scale. The maximum permissible

traversing speed is limited only by the

cutoff frequency (–3 dB) of the output

signals.

On sealed linear encoders, the scanning

unit is guided along the scale on a ball

bearing. Sealing lips protect the scale and

scanning unit from contamination. The ball

bearing and sealing lips permit mechanical

traversing speeds up to 180 m/min.

Signal period and resulting measuring step as a function of the subdivision

factor

Subdivision factor

Signal period [μm]

Measuring step [μm]

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