The problem of causal selection

A positioning apparatus includes a master hydraulic positioning cylinder having a relatively long stroke capability and a train of additively connected, short-stroke pneumatic control cylinders for controlling the length of stroke of the master cylinder and thus the positioning of a variable-position tool such as a band saw. One end of the cylinder train is connected by a feedback rod to an extensible portion of the master cylinder. A connecting rod connects the opposite end of the train directly to the spool of a three-position servo valve which controls the flow of hydraulic fluid to and from opposite sides of the master cylinder. When air pressure is admitted to a selected side of a selected control cylinder, at least a portion of the train shifts initially in a direction to move the servo valve to an operating position to begin stroking the master cylinder in a desired direction. Stroking movement of the master cylinder is transmitted through the feedback rod to the train to stroke the selected control cylinder until its piston bottoms out, after which continued stroking of the master cylinder shifts the train to close the servo valve and stop the master cylinder when it has stroked through a distance corresponding to the full stroke of the selected control cylinder. The cylinder train includes a pair of "lost motion" cylinders enabling movement of the train beyond the limits of movement of the servo valve. This lost motion of the train activates a high-speed valve in the hydraulic circuit to stroke the master cylinder at high speed and a "final set" cylinder in the train to ensure that final stroking of the master cylinder to a selected setting always occurs from the same direction to eliminate setting errors from lost motion in the system. A lockout valve in the hydraulic system overrides the servo and high-speed valves when the controlled tool is in an operating condition to block flow to the master cylinder and prevent possible damage to the tool or positioning apparatus.