| 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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