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ISP - Rev 6/95
Ip - Iop
Tp = 2.2ln ----------
Ip - Ic
Ic - Amplifier continuous current rating.
Ip - Peak demanded (not amplifier Ip)
Iop - Actual operating current before the peak demand.
Example:
A motor is driven by an ISP-15/65 amplifier at constant speed and constant
current of 5A. What is the maximum possible duration of a 20A peak ?
20 - 5
Tp = 2.2ln -------- = 2.42 seconds
20 - 15
4.5.2 Dynamic contouring of continuous and peak current limits
Most of the servo motors have reduced continuous current limits at high speeds
(Fig. 4.2). This phenomenon is due to commutation limits and iron looses which
become significantly high as speed increases and this leads to reduction of the
continuous current limit. The ISP amplifiers have the features which enable the
user to define the current limit envelope as closely as possible to the motor
operating envelope defined by the motor manufacturer.
Velocity
Torque
Cont.
zone
Interm.
zone
Fig. 4.2:
Typical operating envelope of a brush servo motor