Hydraulic Oscillating Actuator

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There are some applications in which continuous rotation is not needed. Two examples are industrial mechanisms performing pick-and-place operations and heavy-duty, large-payload robots.

Vane motors with one or two vanes are used for limited-rotation applications. The single-vane unit can rotate 280°, and the double-vane 150 to 160°. The direction of rotation is determined by a valve that directs fluid into one chamber or the other. As the chamber fills, it causes the moveable vane to rotate (Fig. 5.21). These motors can generate torque up 500,000 lbf-in.

limited-rotation-motor

Motors with a helical spline (Fig. 5.22) are available with 90, 180, 270, and 360° of rotation. Rotation is set by the length and pitch of the helix. Units with torque ratings up to 1,000,000 lbf-in are available.

limited-rotation-motor-helical-shaft

Two devices that convert linear motion to rotary motion are available, the skotch yoke (Fig. 5.23) and the rack-and-pinion actuator (Fig. 5.24). The skotch yoke is limited to 90° rotation or less, but torque output up to 45,000,000 lbf-in is available. Two cylinders can be used to power the rack in the rack-and-pinion actuator and produce torque output in excess of 50,000,000 lbf-in. Rotation is limited only by the cylinder stroke.

Skotch-yoke-rotary-actuator

Rack-and-pinion-rotary-actuator

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