Patent ID: 8738239

Claim:
A swing control system for a construction machine including a swing electric motor swinging an upper swing structure and a swing control unit, wherein the swing control unit comprises: a reference speed calculation means for calculating a reference swing speed and a maximum acceleration according to a manipulation signal of a control lever for a swing manipulation; a swing speed determination means for calculating a first speed change amount from a difference between the reference swing speed and an actual swing speed by the electric motor that is currently fed back, calculating a second speed change amount for a sampling time from the maximum acceleration, and determining a swing speed according to the manipulation signal by comparing the first speed change amount and the second speed change amount and adding a smaller amount between the first speed change amount and the second speed change amount obtained as the result of comparison to the actual swing speed currently fed back; and an output torque control means for controlling an output torque of the electric motor by generating a control signal for the determined swing speed; wherein the reference speed calculation means calculates the reference swing speed and the maximum acceleration according to the manipulation signal with limiting of absolute values of the reference swing speed and the maximum acceleration in a predetermined upper limit range, and the predetermined upper limit is the maximum value of the swing speed and the maximum acceleration according to pilot signal pressure as the maximum values of swing speed and acceleration would be if a hydraulic swing motor were used, instead of the swing electric motor, for swinging the upper swing structure; wherein the swing speed determination means determines the swing speed according to the manipulation signal by adding the first speed change amount to the actual swing speed currently fed back without comparing the first speed change amount and the second speed change amount if the pilot signal pressure when the hydraulic swing motor is used, which corresponds to the manipulation signal, is smaller than a predetermined value.