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Rotary encoders and angle encoders

for three-phase AC and DC motors

General information

Speed stability

To ensure smooth drive performance, an

encoder must provide a large number of

measuring steps per revolution. The

encoders in the HEIDENHAIN product

program are therefore designed to supply

the necessary numbers of signal periods

per revolution to meet the speed stability

requirement.

HEIDENHAIN rotary and angular encoders

featuring integral bearing and stator

couplings provide very good performance:

shaft misalignment within certain

tolerances (see Speciﬁ cations) do not

cause any position error or impair speed

stability.

At low speeds, the position error of the

encoder within one signal period affects

speed stability. In encoders with purely

serial data transmission, the LSB (Least

Signiﬁ cant Bit) goes into the speed

stability. (See also Measuring Accuracy.)

Transmission of measuring signals

To ensure the best possible dynamic

performance with digitally controlled

motors, the sampling time of the speed

controller should not exceed approx.

256 μs. The feedback values for the

position and speed controller must

therefore be available in the controlling

system with the least possible delay.

High clock frequencies are needed to fulﬁ ll

such demanding time requirements on

position values transfer from the encoder

to the controlling system with a serial data

transmission (see also Interfaces; Absolute

Position Values). HEIDENHAIN encoders

for electric drives therefore provide the

position values via the fast, purely serial

EnDat 2.2 interface, or transmit additional

incremental signals, which are available

without delay for use in the subsequent

electronics for speed and position control.

For standard drives, manufacturers pri-

marily use the especially robust HEIDEN-

HAIN absolute encoders without integral

bearing ECI/EQI or rotary encoders with

TTL or HTL compatible output signals—

as well as additional commutation signals

for permanent-magnet DC drives.

For digital speed control on machines

with high requirements for dynamics, a

large number of measuring steps is

required—usually above 500 000 per

revolution. For applications with standard

drives, as with resolvers, approx. 60 000

measuring steps per revolution are

sufﬁ cient.

HEIDENHAIN encoders for drives with

digital position and speed control are

therefore equipped with the purely serial

EnDat22 interface, or they additionally

provide sinusoidal incremental signal

with signal periods of 1 V

(EnDat01).

The high internal resolution of the EnDat22

encoders permit resolutions greater than

19 bits (524 288 measuring steps) in

inductive systems and greater than 23 bits

(approx. 8 million measuring steps) in

photoelectric encoders.

Thanks to their high signal quality, the

sinusoidal incremental signals of the

EnDat01 encoders can be highly

subdivided in the subsequent electronics

(diagram 1). Even at shaft speeds of

12 000 min

–1

, the signal arrives at the input

circuit of the controlling system with a

frequency of only approx. 400 kHz

(Diagram 2). 1 V

incremental signals

permit cable lengths up to 150 meters.

(See also Incremental Signals – 1 V

)

Diagram 1:

Signal periods per revolution and the resulting number of measuring steps per revolution as a

function of the subdivision factor

Subdivision factor

Signal periods per revolution

Measuring steps per revolution

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