A hydraulic work machine is provided which can improve the finishing accuracy in a horizontally leveling work, a slope face shaping work and so forth by preventing sudden acceleration of an arm when the excavation load decreases suddenly. The hydraulic work machine includes an arm velocity-control valve device 22 capable of adjusting a meter-out opening of the arm cylinder independently of a first arm directional control valve 23. A controller 100 is configured to control, when correcting and increasing an operation amount instructed by the first arm directional control valve, the arm velocity-control valve device to decrease the meter-out opening of the arm cylinder in response to the increase of load pressure of the arm cylinder.

An example robot includes a hydraulic actuator cylinder controlling motion of a member of the robot. The hydraulic actuator cylinder comprises a piston, a first chamber, and a second chamber. A valve system controls hydraulic fluid flow between a hydraulic supply line of pressurized hydraulic fluid, the first and second chambers, and a return line. A controller may provide a first signal to the valve system so as to begin moving the piston based on a trajectory comprising moving in a forward direction, stopping, and moving in a reverse direction. The controller may provide a second signal to the valve system so as to cause the piston to override the trajectory as it moves in the forward direction and stop at a given position, and then provide a third signal to the valve system so as to resume moving the piston in the reverse direction based on the trajectory.

A stage assembly (10) includes a stage (14), and a fluid actuator assembly (24) that moves the stage (14). The fluid actuator assembly (24) includes a piston housing (32) that defines a piston chamber (34); (ii) a piston (36) that separates the piston chamber (34) into a first chamber (34A) and a second chamber (34B); (iii) a supply valve (38C) that controls the flow of the working fluid (40) into the first chamber (34A); and (iv) an exhaust valve (38D) that controls the flow of the working fluid (40) out of the first chamber (34A). The supply valve (38C) has a supply orifice (250G) having a supply orifice area, and the exhaust valve (38D) has an exhaust orifice (352G) having an exhaust orifice area. Moreover, the supply orifice area is different from the exhaust orifice area. Further multiple valves of different sizes can be used in combination for the supply and exhaust for each chamber (34A), (34B).

An implement includes a mechanical coupling component configured to removably couple the implement to a support machine, a hydraulic fluid supply line configured to receive a supply flow of hydraulic fluid under pressure from a hydraulic system associated with the support machine, and a hydraulically-powered component configured to be actuated using the hydraulic fluid. The implement also includes a hydraulic fluid recovery system comprising a hydraulic fluid return line configured to fluidically couple to the hydraulic system associated with the support machine and provide a return flow of hydraulic fluid to the hydraulic system. A hydraulic fluid reservoir is configured to, when the hydraulic fluid return line is decoupled from the hydraulic system associated with the support machine, receive a portion of the hydraulic fluid from the hydraulic fluid return line when a fluid pressure in the hydraulic fluid return line increases to a pressure threshold.

A hydraulic control system achieves a reduction in meter-out pressure loss in accordance with variation of a negative load acting on a hydraulic actuator. A hydraulic fluid discharged from the actuator flows through meter-out flow lines having variable restrictors. A load sensor detects the magnitude of a negative load applied to the actuator by an external force in the same direction as the operating direction of the actuator. A control device reduces the sum total of the opening areas of the variable restrictors in accordance with an increase in the magnitude of the negative load detected by the load sensor and the operation amount detected by the operation amount sensor when the load abnormality sensor does not detect any abnormality. When an abnormality is detected, it reduces the sum total of the opening areas to a predetermined value in accordance with the operation amount detected by the operation amount sensor.

To reduce the cost by reducing the number of parts and simplify the control of regeneration in the hydraulic actuator even though the meter-in control and the meter-out control can be performed separately while the supply and the discharge of hydraulic fluid is controlled. A meter-in valve that controls supply flow from a hydraulic pump into a hydraulic cylinder is provided, and meter-out switching valve that switches the direction of supply and discharge of the hydraulic oil into the hydraulic cylinder and controls the discharge flow from the hydraulic cylinder to the oil tank is installed on the down stream side of the meter-in valve, and further, a regeneration control valve is installed on the down stream side of the meter-out switching valve.

To avoid a large size of a direction change-over valve and enable accurate supply flow control when providing a flow control valve at an upstream side of the direction change-over valve to change the relationship between supply flow rate and discharge flow rate for a hydraulic actuator. The configuration is to control a supply flow rate to a stick cylinder based on an opening area of the stick's direction change-over valve and stick's flow control valve, calculate a target opening area of the stick's flow control valve based on a target supply flow rate from hydraulic pumps A, B to the stick cylinder, the opening area of the stick's direction change-over valve, and a target differential pressure between hydraulic pump A and a load pressure of stick cylinder, and control the stick's flow control valve so as to keep the target opening area calculated.

An energy regeneration device capable of controlling flow of a working fluid discharged from an actuator while regenerating energy from the working fluid, and a work machine including the foregoing device, include a boom cylinder, an inertial fluid container, an oil tank, an accumulator, a low-pressure-side opening/closing device, and a high-pressure-side opening/closing device. A calculation unit calculates a duty ratio for opening/closing the low-pressure-side opening/closing device and the high-pressure-side opening/closing device in accordance with a desired flow rate of a hydraulic fluid discharged from the boom cylinder. A regeneration control unit selects alternately the low-pressure-side opening/closing device and the high-pressure-side opening/closing device as a destination with which the inertial fluid container communicates in accordance with the calculated duty ratio, and supplies the discharged hydraulic fluid to an accumulator.

A hydraulic excavator drive system includes: first and second pumps; arm cylinder; arm first control valve connected to the cylinder by an arm crowding supply line and arm pushing supply line; arm second control valve connected to the supply lines by a first and second replenishment line; and arm operation device that outputs an operation signal corresponding to an inclination angle of an operating lever. The arm second control valve is configured so, when performing an arm crowding operation, an opening area at a meter-in side changes in accordance with the operation signal, and an opening area at a meter-out side is: kept to zero when a predetermined condition is not satisfied; and kept to zero until the operation signal becomes a setting value or greater, and when the operation signal has become the setting value or greater, increases to a maximum value when the predetermined condition is satisfied.

Provided is a hydraulic control system for a construction machine, including: a control valve (31) for controlling supply and discharge of hydraulic fluid to and from an arm cylinder (4); an operation lever (6) for controlling the position of a spool of the control valve (31); a meter-out flow passage (34) for passing therethrough hydraulic fluid discharged from the arm cylinder; a variable restrictor (23a) provided in the meter-out flow passage; pressure sensors (41, 42) for detecting a magnitude of a negative load applied by an external force to the arm cylinder in a same direction as an actuation direction of the arm cylinder; and a controller (45) for reducing an opening area of the variable restrictor (23a) according to an increase in the magnitude of the negative load calculated with a detection value from the pressure sensors (41, 42).