Fluid actuator arrangement and a method for control of a fluid actuator arrangement

A control element for control of an elongated fluid actuator arrangement comprising a piston rod member, at least two cylinders, each cylinder having a piston body dividing an interior of the respective cylinder in a first and a second cylinder chamber, a clamping mechanism associated to each cylinder, each of said clamping mechanisms being arranged to engage the piston body of the cylinder to the piston rod member in a forward movement of the piston body to drive the piston rod member, and to disengage the piston body of the cylinder from the piston rod member in a backward movement of the piston body to allow sliding of the piston body in relation to the piston rod member,

• wherein the control element further comprises:
• a piston body movement control element arranged to control a back and forward movement of the respective piston body so that forward movement is slower than the backward movement and to control the movement of the respective piston bodies in relation to each other such that at least one piston body is always moving forward and such that an overlap exists wherein at least two of the piston bodies are moving forward simultaneously during a cycle;
• and
• a clamping mechanism control element arranged to control the respective clamping mechanism to engage the piston body to the piston rod member in the forward movement and to disengage the piston body from the piston rod member in the backward movement;
• and
• a sensor arrangement arranged to obtain position information related to a position of the piston body within the respective cylinder,
• wherein the elongated fluid actuator arrangement is further arranged to continuously obtain sensor data related to the position and the velocity and the acceleration of the rod member, wherein the respective clamping mechanism and/or the respective back and forward movement is controlled based on the obtained sensor data related to the position and the velocity and the acceleration of the rod member,
• wherein the piston body movement control element is arranged to compare obtained position information with a desired position of the respective piston body and to force the respective piston body to the desired position based on said comparison, thereby, achieving synchronisation between the operations of the cylinders,
• wherein the control element is arranged to activate a safety mode at least one of upon detection of a deviation from a normal behavior of the fluid actuator arrangement and upon detection of activation of an emergency brake, and
• wherein each of said clamping mechanisms is configured to engage the respective piston body to drive the piston rod member and is configured, in the safety mode, to clamp around the piston rod member to secure that the piston rod member is held in a fixed position.

A method for control of an elongated fluid actuator arrangement comprising a piston rod member, at least two cylinders each said cylinder having a piston body dividing an interior of the respective cylinder in a first and a second cylinder chamber, a clamping mechanism associated to each cylinder, each of said clamping mechanisms being arranged to engage the respective piston body of the cylinder to the piston rod member in a forward movement of the piston body to drive the piston rod member, and to disengage the piston body of the cylinder from the piston rod member in a backward movement of the piston body to allow sliding of the piston body in relation to the piston rod member,

• wherein the method comprises:
• obtaining sensor data related to the position of the respective piston body;
• controlling a back and forward movement of the respective piston body so that forward movement is slower than the backward movement and so that at least one piston body is always moving forward and such that for each cycle an overlap exists, wherein at least two of the piston bodies are moving forward simultaneously, based on the obtained sensor data related to the position of the respective piston body,
• controlling the respective clamping mechanism to engage its associated piston body to the piston rod member in the forward movement and to disengage the respective piston body from the piston rod member in the backward movement,
• wherein the elongated fluid actuator arrangement is further arranged to continuously obtain sensor data related to the position and the velocity and the acceleration of the rod member, wherein the respective clamping mechanism and/or the respective back and forward movement is controlled based on the obtained sensor data related to the position and the velocity and the acceleration of the rod member,
• wherein the controlling of the position of the respective piston body comprises comparing the obtained sensor data related to the position of the respective piston body with a desired position of the respective piston body and to force the respective piston body to the desired position based on said comparison, thereby achieving synchronisation between the operations of the cylinders,
• wherein the control element is arranged to activate a safety mode at least one of upon detection of a deviation from a normal behavior of the fluid actuator arrangement and upon detection of activation of an emergency brake, and
• wherein each of said clamping mechanisms is configured to engage the respective piston body to drive the piston rod member and is configured, in the safety mode, to clamp around the piston rod member to secure that the piston rod member is held in a fixed position.