Siemens SLI-5310 Instruções de Operação descarregar pdf (Página 30)

30

Application-dependent error

Rotary encoders with

photoelectric scanning

In addition to the system accuracy, the

mounting and adjustment of the scanning

head normally have a signiﬁ cant effect on

the accuracy that can be achieved by rotary

encoders without integral bearings with

photoelectric scanning. Of particular

importance are the mounting eccentricity

of the graduation and the radial runout of

the measured shaft.

Example

ERO 1420 rotary encoder with a mean

graduation diameter of 24.85 mm:

A radial runout of the measured shaft of

0.02 mm results in a position error within

one revolution of ± 330 angular seconds.

To evaluate the accuracy of modular

rotary encoders without integral

bearing (ERO), each of the signiﬁ cant

errors must be considered individually.

1. Directional deviations of the

graduation

ERO: The extreme values of the directional

deviation with respect to their mean value

are shown in the Speciﬁ cations as the

graduation accuracy for each model. The

graduation accuracy and the position error

within a signal period comprise the system

accuracy.

2. Errors due to eccentricity of the

graduation to the bearing

Under normal circumstances, the bearing

will have a certain amount of radial

deviation or geometric error after the disk/

hub assembly is mounted. When centering

using the centering collar of the hub,

please note that, for the encoders listed in

this catalog, HEIDENHAIN guarantees an

eccentricity of the graduation to the

centering collar of under 5 μm. For the

modular rotary encoders, this accuracy

value presupposes a diameter deviation of

zero between the drive shaft and the

"master shaft."

If the centering collar is centered on the

bearing, then in a worst-case situation both

eccentricity vectors could be added

together.

Resultant measured

deviations M for various

eccentricity values e as a

function of graduation

diameter D

Eccentricity e [μm]

f

Measuring error M [angular seconds]

f

For rotary encoders with integral

bearing, the speciﬁ ed system accuracy

already includes the error of the bearing.

For angle encoders with separate shaft

coupling (ROD, ROC, ROQ, RIC, RIQ), the

angle error of the coupling must be added

(see Mechanical design types and

mounting). For angle encoders with stator

coupling (ERN, ECN, EQN), the system

accuracy already includes the error of the

shaft coupling.

In contrast, the mounting and adjustment

of the scanning head normally have a

signiﬁ cant effect on the accuracy that can

be achieved by encoders without integral

bearings. Of particular importance are the

mounting eccentricity of the graduation

and the radial runout of the measured

shaft. The application-dependent error

values for these encoders must be

measured and calculated individually in

order to evaluate the total accuracy.

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