| 摘要 |
A fluid pressure operated device comprises a body adapted for moving an article and carrying magnets coupled to other magnets on a piston movable by fluid pressure in a cylinder. The body also carries spaced magnets and another piston carries spaced magnets. In a start position, one of said body magnets and one of said piston magnets are coupled. During normal operation the body and pistons move to another position in which the one body magnet operates a return sensor to return the device to start position. If an obstacle is encountered, the piston moves to release another sensor to reverse the device for a short stroke where a timer again reverses the fluid pressure to complete the stroke. Engagement with a second obstacle or a repeat engagement with the first obstacle returns the device to the start position and a warning alerts an operator to remove the obstruction.
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