| 摘要 |
A backhoe ( 100 ) has a hydraulic cylinder ( 316, 317 ) with a piston ( 318, 319 ) that rotates a rotatable boom ( 108 ). A lockable slider block ( 322 ) slides on the piston. Movement of the lockable slider block in one direction is caused by a spring ( 328, 329 ) mounted around the piston, and in another direction is caused by the telescoping of the piston into the hydraulic cylinder. The backhoe includes a hydraulic valve ( 340 ) that controls hydraulic pressure to the hydraulic cylinder and a sensor ( 320 ) coupled to the hydraulic valve. Once locked to a position on the piston, the lockable slider block engages the sensor on each occasion the rotatable boom rotates beyond a preselected angle of rotation. Engagement of the sensor causes actuation of the hydraulic valve, thereby preventing further rotation of the boom by the hydraulic cylinder. Alternative embodiments have an encoder ( 120, 130 ) that digitizes the position of the boom, and a microcomputer ( 410 ) that is programmed to actuate the hydraulic valve.
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