Abstract: Imminent control instability is detected in a system that applies a stimulus to an object. The system provides a parameter signal that represents a system parameter indicating oscillation of the object while the stimulus is being applied to the object. The method comprises monitoring maximum amplitude of a dominant tone in a selected frequency band of the parameter signal; and taking an action to avoid imminent control instability if the maximum amplitude persists over a specified period of time.

Abstract: Imminent control instability is detected in a system that applies a stimulus to an object. The system provides a parameter signal that represents a system parameter indicating oscillation of the object while the stimulus is being applied to the object. The method comprises monitoring maximum amplitude of a dominant tone in a selected frequency band of the parameter signal; and taking an action to avoid imminent control instability if the maximum amplitude persists over a specified period of time.

Abstract: A method for reducing force and position control tracking errors caused by changes in hydraulic pressure at the actuator ports of a hydraulic servo valve. The method may use either the force command signal or the load cell signal in conjunction with a mathematical algorithm to compensate for changes in the flow capacity in the servo valve caused by changes in pressure at its ports. Good performance can be attained using the load cell signal. Alternatively, the algorithm can use the force command signal. The performance of the control loop with proper velocity feed-forward compensation keeps the feedback signal largely in phase with the command. Pressure sensors for detecting pressure changes at the actuator ports of the servo valve are not required for load droop compensation.

Abstract: A force compliant mechanism (750) for a force control system (600) includes a housing (752). A force compliant volute spring member (754) that has an input end (790) and an output end (792) is disposed within the housing (752). A force actuator input shaft (798) operates in response to a force induced thereon. An output shaft (800) is coupled to the output end (792) and to a test object (802). A force transducer (780) is in operative coupling with the force actuator input shaft (798) and generates a force signal in response to the induced force. A method of reducing force transients and increasing stability within a force control system (660) includes applying a force on a test object (666). A force actuator (669) is decoupled from the test object (666). The overall stiffness of the force control system is reduced and dynamic energy is absorbed via a force compliant member (662) coupled to the test object (666) and the force actuator (669).

Abstract: A controlled system (480) for application of force on a test object includes a force actuator (484) that is coupled to and applies a force on the test object. A velocity signal generator (482) is in a feedforward configuration relative to the force actuator (484) and generates a velocity signal (503) that is predictive of the velocity of the test object. A controller (482) is coupled to the force actuator (484) and to the velocity signal generator (482) and generates a desired applied force signal (546) compensated by the velocity signal (503).

Abstract: A force control system (50, 300) for actuation of a test object (54, 304) includes a force actuator (52, 356) that is coupled to and applies a force on the test object (54, 304). A velocity signal generator (124, 310) is in a feedback configuration relative to the force actuator and generates a velocity signal (150, 324) that is indicative of the velocity of the test object (54, 304). A controller (62, 302) is coupled to the force actuator (52, 356) and to the velocity signal generator (124, 310) and generates a desired applied force signal (130, 380) compensated by the velocity signal (150, 324).