Title: Tractor hitch position control system

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Abstract: A control system is provided for a hydraulically operated tractor hitch assembly including a rockshaft operated by a main cylinder which is controlled through a spool valve operated by a pilot cylinder which is controlled, in turn, through a solenoid operated pilot valve. The pilot valve is selectively controlled from first and second detector circuits through a gating circuit which is controlled by a third detector circuit which responds to a first error signal developed by comparing a command signal which corresponds to a rockshaft target position and a first feedback signal which corresponds to the actual rockshaft position and which is generated by a potentiometer connected to the rockshaft. The first detector circuit is operative when the first error signal is of relatively high magnitude and responds to a second error signal developed by comparing the first error signal with a feedback signal derived through a signal modifying circuit from the potentiometer connected to the spool valve, with the signal modifying circuit being operative to compensate for a dead zone of the spool valve and with the operation being such that the rockshaft is rotated to a position within a zero target range without under-shoot, over-shoot or oscillation. The second detector circuit is operative when the first error signal is of low magnitude and responds directly to the second feedback signal to center the spool valve.


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