To rotate a rotary body at a constant velocity, a swing control device 50 of an electric rotary excavator controls the rotation of the rotary body with a small first torque command value T1. Thus, when inertia moment of the rotary body is changed due to extension or retraction of a boom and an arm, the...http://www.google.com.au/patents/US20080164832?utm_source=gb-gplus-sharePatent US20080164832 - Rotation Control Device and Construction Machine
