Fluid actuator arrangement

A method for controlling the motion of an elongated fluid actuator arrangement (1) including a first cylinder housing (3) encompassing a first piston body (7) comprising a first piston rod engagement and disengagement means (29′) and dividing the first cylinder housing (3) in a first and second cylinder chamber (11, 13) coupled to a fluid supply (17) via a valve member means (15);

• a second cylinder housing (5) encompassing a second piston body (9) comprising a second piston rod engagement and disengagement means (29″) and dividing the second cylinder housing (5) in a first and second cylinder chamber (11, 13) coupled to a fluid supply (17) via a valve member means (15);
• a control unit (CPU) is associated with a sensor device (201) of the arrangement (1) for determining an actual cylinder-piston feature value and is coupled to said valve member means (15) for regulating fluid flow to said first cylinder housing (3) and said second cylinder housing (5);
• a piston rod (19) extends through the first piston body(7), the method comprises the steps of:
• providing a first actual cylinder-piston feature value to the control unit (CPU);
• comparing the first actual cylinder-piston feature value with a first desired cylinder-piston feature value;
• regulating fluid flow to the respective first and second cylinder chamber (11, 13);
• repeating the preceding steps until the first actual cylinder-piston feature value corresponds with the first desired cylinder-piston feature value;
• pressurizing the first cylinder chamber (11) of the first cylinder housing (3) with a first fluid pressure, wherein the first piston body (7) comprises an elongated sleeve-shaped engagement and disengagement means extending in the longitudinal direction (X), the first engagement and disengagement means is arranged to engage and/or disengage with the piston rod (19) by means of a cavity that can be pressurized;
• driving the first piston body (7) with the piston rod (19) from a first start position (Si) to a first end position (El);
• retracting the second piston body (9) to a second start position (S2);
• pressurizing the first cylinder chamber (11) of the second cylinder housing (5) with the first fluid pressure feature, wherein the second piston body (9) comprises an elongated sleeve-shaped engagement and disengagement means extending in the longitudinal direction (X), the second engagement and disengagement means is arranged to engage and/or disengage with the piston rod (19) by means of a cavity that can be pressurized;
• and
• driving the second piston body (9) with the piston rod (19) from the second start position (S2) to a second end position (E2),
• wherein:
• said valve member means (15) is controlled to manage the second start position (S2) to precede said first end position (El) with an overlap time interval;
• and
• the time for retraction of the second piston body is shorter than the time for the working stroke of the first piston body from the first start position to the first end position.