Computer Drive Installation Instructions

10 Axis and Spindle Installation 09.95

10.5.4 Curved acceleration characteristic (SW 4 and higher)

When induction motors are used (spindle operation), allowance must be made for their speed-

dependent acceleration capability in position-controlled operation:

Fig. 1 Torque characteristic of induction motor

TorqueM Constant

torque

Breakdown limit

M = const

Constant

power

M 1/n M 1/(n*n)

Rated speed Speed n

max

At speeds (n) above rated speed (n

), the drive acceleration capability decreases in relation to

the speed. Immediately above rated speed nn, there is a range of "constant power" in which

the torque (and thus also the acceleration capability) drop in proportion to 1/n. When speed n

increases further, there is a range ("breakdown limit") immediately above speed nk in which

the torque decreases in proportion to 1/(n*n).

The required parameters are selected and set in the MSD drive unit.

Fig. 2 Speed characteristic during acceleration (thick line)

Speed

Setpoint

The obtainable linear ramp-up time constants

increase out of proportion for higher speeds

T2 Time

SINUMERIK 840C (IA)