Motion System
HANDBOOK
Common rigid chains have two rows of link plates and shoulders, whereas duplex chains have three. Other options abound. Image courtesy iwis Drive Systems
Basics of
RIGID CHAIN ACTUATORS RIGID-CHAIN
actuators work by pairing a drive (usually an electric motor) with a length of chain sporting shoulders on each link. The motor output shaft—fitted with a specialty sprocket or pinion—applies tangential force to the chain. Then the chain comes out and straightens, and its links’ shoulders lock to form a rigid series. When the motor runs in the opposite direction, the chain shoulders disengage and allow for coiling. Inside the actuator body, reaction plates and guides counter thrust resistance and keep the chain on track. Links travel around the pinion to exit the actuator body along the stroke path. Here, the motor’s torque comes to act as forward thrust via the link shoulder to the rest of the links’ shoulders. The last link in the chain before the load has geometry
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that puts the thrust higher than the articulation axis. This makes a moment that effectively locks the link shoulders. In reverse, pulling force acts along the links’ cross axes. Rigid-chain actuators have the mechanical benefits of conventional chain but can act in horizontal push setups or vertically as jacks. Plus they’re compact. In contrast, traditional chain drives can only pull, so need two drives for bidirectional motion. Traditional screw jacks for vertical power transmission need space for retraction that’s as long as the working stroke itself. Before specifying a rigid-chain actuator, determine the application’s total load, including the transported load, acceleration forces, external environmental forces, and that due to friction — with a coefficient between 0.05 and 0.5 for typical rigid-chain actuator setups. Next, determine what type of actuator body and chain-storage magazine the application can accommodate. Determine whether the chain will need to change direction on its way from the magazine to actuator body. Actuators usually feed chain around 90° or 180° turns. Note that rigid-chain actuators can work alone or in tandem. Twinchain setups deliver high positioning accuracy and stability where loads are large or bulky. Here, a pushing bar acts as a yoke to keep loads steady, with optional hooks for pulling as well. Optimized geometry has
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9/13/16 2:27 PM