Design Types and Mounting. )On sealed linear encoders, the scanning unit is guided along the scale. A coupling connects the scanning carriage with the mounting block and compensates the mis- alignment between the scale and the machine guideways. This permits relatively large mounting tolerances. The coupling is very rigid in the measuring direction and is fl exible in the perpendicular direction. If the coupling is insuffi ciently rigid in the mea-suring direction, it could cause low natural frequencies in the position and velocity control loops and limit the bandwidth of the drive.The sealed linear encoders recommended by HEIDENHAIN for linear motors generally have a Bandwidth Linear encoders with sinusoidal output signals 1 V On linear motors, a coupling lacking in rigid- ity can limit the bandwidth of the position control loop. The manner in which the lin- ear encoder is mounted on the machine has a very signifi cant infl uence on the rigid-ity of the coupling. (See are therefore best suited for high traversing speeds and small measuring steps. Sinusoidal voltage signals with levels of natural frequency of coupling greater than 650 Hz or 2 kHz in the mea- suring direction, which in most applica-tions exceeds the mechanical natural fre- quency of the machine and the bandwidth of the velocity control loop by factors of at least 5 to 10. HEIDENHAIN linear encoders for linear motors therefore have practically no limiting effect on the position and speed control loops.Traversing speed and resulting output frequency as a function of the signal period Signal period Traversing speed [m/min] Transmission of measuring signals The information above on rotary and angu- lar encoder signal transmission essentially applies also for linear encoders. If, for ex- ample, one wishes to traverse at a mini- mum velocity of 0.01 m/min with a sam-pling time of 250 µs, and if one assumes that the measuring step should change by at least one measuring step per sampling cycle, then one needs a measuring step of approx. 0.04µm. To avoid the need for spe- cial measures in the subsequent electron- ics, input frequencies should be limited to less than 1 MHz.
PP attain a –3 dB cutoff frequency of approx. 200 kHz and more at a permissible cable length of up to 150 m.The fi gure below illustrates the relationship between output frequency, traversing speeds, and signal periods of linear encod-ers. Even at a signal period of 4 µm and a traversing velocity of 70 m/min, the fre- quency reaches only 300 kHz.
Output frequency [kHz] For more information on linear encoders for linear drives, refer to our Exposed Linear Encoders and Linear Encoders for Numerically Controlled Machine tools catalogs.

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