Patent ID: 7849685

Claim:
A control device for a hydraulic cylinder having a cylinder body and a piston that slides inside the cylinder body, the control device comprising: a supply source that supplies working oil to the hydraulic cylinder; decelerating means that decelerates the piston, wherein the decelerating means includes first flow-adjusting means for changing the supply rate of the working oil supplied to the hydraulic cylinder and the discharge rate of the working oil discharged from the hydraulic cylinder; and deceleration-setting means that sets a position at which the piston starts decelerating such that the position is set further from a stroke end as the moving speed of the piston becomes higher, wherein the deceleration-setting means includes detecting means for detecting the moving speed of the piston and flow-controlling means for reducing the piston speed by operating the first flow-adjusting means such that the supply rate and the discharge rate are reduced, wherein the control device decelerates the piston as the piston approaches the stroke end of the cylinder body by adjusting a supply rate of the working oil supplied from the supply source to the hydraulic cylinder by a second flow-adjusting means, wherein a pair of the supply source and the first flow-adjusting means comprises a plurality of such pairs; the working oil from these pairs is joined and supplied to the common hydraulic cylinder, and the working oil discharged from the hydraulic cylinder is distributed to the corresponding first flow-adjusting means such that the flow rate is adjusted; the decelerating means further includes operating means for operating the first flow-adjusting means and forced-operating means capable of forcedly operating at least one of the first flow-adjusting means independently of the operating status of the operating means; and the flow-controlling means reduces the supply rate of the working oil supplied to the hydraulic cylinder and the discharge rate of the working oil discharged from the hydraulic cylinder by controlling the forced-operating means during the deceleration control of the piston, wherein the flow-controlling means determines whether the detecting means or the forced-operating means is under an abnormal condition during the deceleration control of the piston; and when it is determined that the detecting means or the forced-operating means is under an abnormal condition, one of the second flow-adjusting means, which is related to the first flow-adjusting means not driven by the forced-operating means, is operated such that the supply rate of the working oil supplied to the hydraulic cylinder is minimized.