Abstract: A machine with a movable element, such as a machine tool and its spindle carrier, that is powered by a motive means to move the element is provided with a counterbalancing system having at least two counterforce means operably connected to the movable element for exerting a counterbalance force on the movable element in opposition to the first force and wherein a first one of the counterforce means has a controllable servomotor means. The control means controls the servomotor means so as to cause the counterbalancing system to exert a substantially constant counterbalance force on the movable element in opposition to the first force. The second one of the counterforce means may be a hydraulic means having a hydraulic cylinder operably connected to an accumulator and a hydraulic piston operably disposed in the cylinder and connected to the movable-element.

Abstract: A method and apparatus are disclosed for reducing the cross-coupled movement in a member of a CNC machine caused by movement in another member of the machine through the structural dynamics of the machine. The method includes receiving the discrete position commands for a member oriented in one axis of movement for the machine, transforming the discrete position commands to attenuate frequency components that contribute to the movement coupled through the structural dynamics of the machine, and generating velocity commands from the transformed discrete position commands to control the servos that drive the members. The discrete position command transform is preferably a second order filter that implements the transfer functions of a digital notch filter and digital low pass filter. The second order filter that transforms the discrete position commands is implemented in a digital computer by state variable difference equations.