Position Encoders for Servo Drives - DR. JOHANNES HEIDENHAIN GmbH - #29

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     29 The following relationship exists between the eccentricity e, the mean graduation diameter D and the measuring error ¹ (see illustration below): ¹ = ± 412 · ¹ = Measuring error in " (angular seconds) e = Eccentricity of the radial grating to the bearing in ìm D = Mean graduation diameter in mm Model Mean graduation diameter D Error per 1 ìm of eccentricity ERO 1420 ERO 1470 ERO 1480 D = 24.85 mm ± 16.5" ERO 1225 ERO 1285 D = 38.5 mm ± 10.7" e D 3. Error due to radial deviation of the bearing The equation for the measuring error ¹ is also valid for radial deviation of the bearing if the value e is replaced with the eccentricity value, i.e. half of the radial deviation (half of the displayed value). Bearing compliance to radial shaft loading causes similar errors. 4. Position error within one signal period ¹u The scanning units of all HEIDENHAIN encoders are adjusted so that without any further electrical adjustment being necessary while mounting, the maximum position error values within one signal period will not exceed the values listed below. Model Line count Position error within one signal period ¹u TTL 1 VPP ERO 2 048 1 500 1 024 1 000 512 † ± 19.0" † ± 26.0" † ± 38.0" † ± 40.0" † ± 76.0" † ± 6.5" † ± 8.7" † ± 13.0" † ± 14.0" † ± 25.0" The values for the position errors within one signal period are already included in the system accuracy. Larger errors can occur if the mounting tolerances are exceeded. Rotary Encoders with Inductive Scanning For rotary encoders without integrated bearing with inductive scanning, the attainable accuracy depends on the power supply, the temperature, the rotational speed, the working gap between the rotor and stator, and on the mounting conditions. Further information is available upon request. Measuring error ¹ as a function of the mean graduation diameter D and the eccentricity e M Center of graduation "True" angle ‘ Scanned angle Scanning unit