Abstract: A novel digital servo valve system for use in controlling a displaceable actuator includes a valve body with ports, a valve spool displaceable within the valve body to regulate fluid flow through the ports, and a motor having a drive shaft which displaces the valve spool. The system is characterized by a null adjustment mechanism which makes a null rotational position of the drive shaft coincide with a null position of the valve spool, at which positions the valve spool cuts off fluid flow through the ports. The null adjustment mechanism provided in accordance with the present invention permits the null positions of the valve spool and stepper motor to be adjusted without having to disassemble the servo valve.

Abstract: A novel digital servo valve system for use in displacing an actuator is capable of operating either in closed or open loop mode. The system includes a controller that compares computed values of actuator parameters with preselected parameter values and iteratively determines therefrom command signals for the servo valve. The servo valve is characterized by a ball screw mechanism that eliminates mechanical backlash and a torsion bar which increases radial and angular compliance. A servo valve provided according to the present invention also displays reduced flow forces using a simple, inexpensive valve body in combination with a uniquely configured displaceable spool.

Abstract: A exercising machine has a pivotal lever and includes a passive electrohydraulic resistance system which provides controlled resistance to lever movement. Hydraulic fluid which may leak from a piston-cylinder assembly, which comprises part of the system, collects in a sump and is sucked into the piston-cylinder assembly during the normal operating cycle of the exercise machine.