A chuck apparatus grips a workpiece by a gripping section having a pair of chuck members. The chuck apparatus is equipped with a cover member and pressing members. The cover member includes insertion holes through which fingers of the chuck members are inserted, and seal members that surround the insertion holes and abut against the fingers. The cover member is attached to a body so as to cover base portions of the chuck members, and is elastically deformable so as to follow displacement of the chuck members. The pressing members press the seal members against the fingers.

A drive system for driving a chuck device including a piston and a pair of fingers to be opened and closed according to the displacement of the piston, includes a controller, a detection sensor to detect an axial position of the piston, and three-port servo valves to switch a state of supply of the fluid to the chuck device. A degree of valve opening is controllable based on a control signal input from the controller, and an amount of displacement of the piston and an amount of opening and closing of the fingers are controlled by changing the degree of valve opening. One of the 3-port servo valves is connected to a first cylinder chamber of the chuck device, and another of the 3-port servo valves is connected to a second cylinder chamber of the chuck device.

A control method of controlling a chuck device in a drive system for driving the chuck device, comprising opening or closing fingers by opening a switching valve at a first degree of valve opening to supply the fluid to a first cylinder chamber of the chuck device and to discharge the fluid from a second cylinder chamber of the chuck device so that a piston moves in one direction, and stopping the fingers in an intermediate position between a fully open position and a fully closed position by opening the switching valve at a second degree of valve opening to stop supplying the fluid to the first cylinder chamber and to stop discharging the fluid from the second cylinder chamber when the axial position of the piston reaches a target position set in advance while the fingers are being opened or closed.