singleturn encoders Multiturn encoders the absolute posi-tion information repeats itself with every revolution. can also distinguish between revolutions. Circular graduations of absolute rotary encodersWith 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 absolute position information is read from the grating on the circular scale, which is designed 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 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 by counting the individual incre-ments (measuring steps) from some point of origin. Since an absolute reference is required to ascertain positions, the circular scales are provided with an additional track that bears a incremental measuring method, reference mark. the graduation consists of a periodic grat- ing structure. The position information is obtained

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 sub- strate for large diameters is a steel tape.These precision graduations are manufac-tured in various photolithographic process- es. Graduations are fabricated from:extremely hard chromium lines on glass or gold-plated steel drums, matte-etched lines on gold-plated steel tape, or three-dimensional structures on glass or steel substrates.The photolithographic manufacturing pro-cesses developed by HEIDENHAIN pro- duce grating periods of typically 40 µm to 4 µm.These processes permit very fi ne grating periods and are characterized by a high def- inition and homogeneity of the line edges. Together with the photoelectric scanning method, this high edge defi nition is a pre-condition for the high quality of the output signals. The master graduations are manufactured by HEIDENHAIN on custom-built high- precision ruling machines. 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 elec- tromagnetic interaction, and the very nar- row scanning gaps required, fi ner magnetic graduations are not practical.Encoders using the inductive scanning prin-ciple have graduation structures of copper. The graduation is applied to a carrier mate-rial for printed circuits. ••• With the

22