Siemens SLI-5310 Instruções de Operação descarregar pdf (Página 26)

26

Measuring principles

Measuring standard

HEIDENHAIN encoders with optical scan-

ning incorporate measuring standards of

periodic structures known as graduations.

These graduations are applied to a carrier

substrate of glass or steel. The scale

substrate for large diameters is a steel

tape.

HEIDENHAIN manufactures the precision

graduations in specially developed, photo-

lithographic processes.

• AURODUR: matte-etched lines on gold-

plated 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

ﬁ ner

• OPTODUR phase grating: optically three

dimensional, planar structure with

particularly high reﬂ ectance, typical

graduation period of 2 μm and ﬁ ner

Magnetic encoders use a graduation carrier

of magnetizable steel alloy. A graduation

consisting of north poles and south poles is

formed with a grating period of 400 μm.

Due to the short distance of effect of

electromagnetic interaction, and the very

narrow scanning gaps required, ﬁ ner

magnetic graduations are not practical.

Encoders using the inductive scanning

principle work with graduation structures of

copper and nickel. The graduation is applied

to a carrier material for printed circuits.

With the absolute measuring method,

the position value is available from the en-

coder immediately upon switch-on and can

be called at any time by the subsequent

electronics. There is no need to move the

axes to ﬁ nd the reference position. The ab-

solute position information is read from the

grating on the circular scale, which is de-

signed as a serial code structure or con-

sists of several parallel graduation tracks.

A separate incremental track or the track

with the ﬁ nest grating period is interpolat-

ed for the position value and at the same

time is used to generate an optional incre-

mental signal.

In singleturn encoders, the absolute

position information repeats itself with

every revolution. Multiturn encoders can

also distinguish between revolutions.

Circular graduations of absolute rotary encoders

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 graduated disks are provided

with an additional track that bears a

reference mark.

The absolute position established by the

reference mark is gated with exactly one

measuring step.

The reference mark must therefore be

scanned to establish an absolute reference

or to ﬁ nd the last selected datum.

Circular graduations of incremental rotary encoders

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