Hydraulic valve controls fixture's motion profile

Troy, MI--An automobile manufacturer loads several unfinished car doors into a fixture, and then rotates the doors and fixture through 180 degrees. With a full load of doors onboard, the rotating fixture weighs approximately 1,200 lbs on a ten-inch arm. Operations are performed on the doors in both positions. After the 180-degree rotation, the doors move off to another manufacturing step, and the empty fixture rotates back to its starting point to pick up more doors.

Engineers wanted to control the velocity of the fixture's rotation, especially after it went over the top, so to speak. At that point, gravity tries to accelerate the doors and fixture into the factory floor. The risk to nearby workers, and to the doors and fixture, is obvious. Less obvious is the affect that shock generated by uncontrolled fixture movement can have on hydraulic lines. Controlled deceleration of the rotating mass eliminates shocks that can damage fittings and produce leaks.

Applications Engineer Tim Beck and his colleagues at Parker Hannifin's Hydraulic Valve Div. developed a solution to this problem in motion control by using the company's D1FL proportional directional control valve. The four-way valve permits a user to control the acceleration, deceleration, and velocity of an actuator via discrete input signals. To rotate the door fixture, the engineers used the valve to control an actuator that consists of a rack and pinion driven by a hydraulic cylinder.

In the fixture rotation system, engineers use the valve to generate a two-tiered velocity profile. Acceleration and deceleration are adjustable at the valve using potentiometers. Surface-mounted electronics then vary spool position to control the flow of oil to the actuator. The fixture's rotation ramps up to a constant velocity, then slows to a halt after 180 degrees of movement. Reversing the flow carries the fixture back to its starting point, once again ramping up to a constant velocity, and then decelerating. At the constant-velocity stage, the valve is essentially wide open.

Traditional two-speed hydraulic traverse and feed circuits require solenoid-operated valves that need two input signals for each direction of motion. A single D1FL accepts the same signals and can control two speeds in each direction of actuator movement. This type of control valve provides a relatively low-cost, flexible hydraulic solution to factory-floor motion control problems.

Additional details...Contact Don Caputo, Parker Hannifin Corp., Hydraulic Valve Div., 520 Ternes Ave., Elyria, OH (216) 366-5100