WO2018190756A1

WO2018190756A1 - A fluid actuator arrangement and a method for control of a fluid actuator arrangement

Info

Publication number: WO2018190756A1
Application number: PCT/SE2017/050353
Authority: WO
Inventors: Magnus Landberg
Original assignee: Saab Ab
Priority date: 2017-04-11
Filing date: 2017-04-11
Publication date: 2018-10-18

Abstract

The present invention regards a fluid actuator arrangement and a method of moving a first piston rod of the fluid actuator arrangement comprising a first piston (P1) comprising a first clamping device (K1), the first piston (P1) is arranged movable in a first cylinder housing (C1) in a first axial direction (X), a second piston (P2) comprising a second clamping device (K2), the second piston (P2) is arranged movable in a second cylinder housing (C2) in the first axial direction (X). A first piston rod (R1) extending through the first clamping device (K1) and through the second clamping device (K2); the first piston (P1) is configured to clamp and move the first piston rod (R1) a first distance corresponding with a first piston stroke length that the first piston (P1) is configured to perform in the first cylinder housing (C1); the second piston (P2) is configured to clamp and move the first piston rod (R1) a second distance corresponding with a second piston stroke length that the second piston (P2) is configured to perform in the second cylinder housing (C2); wherein the first piston stroke length is longer than the second piston stroke length. The first piston stroke length that the first piston (P1) is configured to perform is selectively provided for achievement of a feeding mode and the second piston stroke length that the second piston (P2) is configured to perform is selectively provided for achievement of a fine tuning mode.

Description

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

TECHNICAL FIELD

The present invention relates to a fluid actuator arrangement.

The present invention concerns the industry using hydraulic and/or pneumatic actuators for different types of applications and also concerns the manufacture industry producing such arrangements.

The present invention may relate to a fluid actuator arrangement being operated with a step-wise motion.

BACKGROUND

There is a desire to provide efficient operation of a fluid actuator arrangement adapted for feeding and fine tuning of a piston rod.

There is a desire to provide cost-effective manufacture and service maintenance of a fluid actuator arrangement adapted for feeding and fine tuning of a piston rod. There is a desire to provide a fluid actuator arrangement that reliably could distribute proper control functionality regarding force and motion rate of the piston rod.

Current technology as published uses fluid actuator arrangements that are designed with specific features for achieving desired motion rates and/or feeding rates and adjustment motion and/or fine tuning rates of the piston rod. This may imply high production cost and complex control arrangement for providing feeding and fine tuning of the piston rod.

Current technology also often uses complex hydraulic valves (e.g. servo valves, proportinal valves etc.) for providing the feeding and fine tuning performance by means of regulating the fluid flow and pressure of the fluid supply device. Such controlled feeding and fine tuning of the piston rod may make such arrangement costly and complex.

Prior art advanced hydraulic servo hydraulic systems may accurately control the position, velocity and force of the piston. However, they require a servo controller, an electrohydraulic servo valve and may add complexity and cost to the hydraulic system. They are also sensitive to contamination. US 4 526 086 discloses a piston-cylinder housing assembly for displacing a load through a long strike. The assembly consists of a rod and a piston slideable on the rod and a cylinder housing in which the piston is contained. The piston is clamped to the rod by fluid pressure. By clamping the piston to the rod and introducing fluid into the cylinder housing, relative movement is caused between the piston and cylinder housing and the rod.

SUM MARY OF THE INVENTION

An object of the present invention is to provide a fluid actuator arrangement with reliability in functionality and a cost-effective production and operation. This has in different embodiments been achieved by means of a fluid actuator arrangement comprising, a first cylinder housing and a second cylinder housing, a first piston comprising a first clamping device, the first piston is arranged movable in the first cylinder housing in a first axial direction, a second piston comprising a second clamping device, the second piston is arranged movable in the second cylinder housing in the first axial direction, a first piston rod extending through the first clamping device and through the second clamping device, the first piston is configured to clamp and move the first piston rod a first distance corresponding with a first piston stroke length that the first piston is configured to perform in the first cylinder housing, the second piston is configured to clamp and move the first piston rod a second distance corresponding with a second piston stroke length that the second piston is configured to perform in the second cylinder housing, wherein the first piston stroke length is longer than the second piston stroke length.

In such way is achieved a fluid actuator arrangement that with small corrective steps provides a high positioning accuracy without expensive hydraulic valve solutions. Suitably, the fluid actuator arrangement is adapted to digital hydraulic technology.

Preferably, the first piston stroke length that the first piston is configured to perform is selectively provided for achievement of a (discrete) feeding mode. Suitably, the second piston stroke length that the second piston is configured to perform is selectively provided for achievement of a fine tuning mode. Preferably, the feeding mode and/or the fine tuning mode being selectively selected by a control circuit.

Suitably, a second piston rod extending through a third clamping device of the first piston and through a fourth clamping device of the second piston.

Preferably, the first piston is configured to clamp and move the second piston rod in the first axial direction a first distance corresponding with a first piston stroke length that the first piston is configured to perform in the first cylinder housing, wherein the second piston is configured to clamp and move the second piston rod in the first axial direction a second distance corresponding with a second piston stroke length that the second piston is configured to perform in the second cylinder housing, wherein the first piston stroke length is longer than the second piston stroke length.

Suitably, at least a further piston rod extends through at least a further clamping device of the first piston and through at least a further clamping device of the second piston.

Preferably, the fluid actuator arrangement comprises a third cylinder housing and a fourth cylinder housing, a third piston is arranged movable in the third cylinder housing in a second axial direction, a fourth piston is arranged movable in the fourth cylinder housing in the second axial direction, a third piston rod extending through a fifth clamping device of the third piston and through a sixth clamping device of the fourth piston, the third piston is configured to clamp and move the third piston rod a third distance corresponding with a third piston stroke length that the third piston is configured to perform in the third cylinder housing, the fourth piston is configured to clamp and move the third piston rod a fourth distance corresponding with a fourth piston stroke length that the fourth piston is configured to perform in the fourth cylinder housing, wherein the third piston stroke length is longer than the fourth piston stroke length.

Suitably, the first piston rod and the third piston rod are coupled to each other via a first pivot joint member.

Preferably, the first pivot joint member may comprise a holding member equipped with a universal joint linkage arrangement coupled to the respective end of the first and the second piston rod for providing a possible angular deviation between the first axial direction and the second axial direction. Suitably, the fluid actuator arrangement comprises a fourth piston rod extending through a seventh clamping device of the third piston and through an eight clamping device of the fourth piston.

Preferably, the third piston is configured to clamp and move the fourth piston rod in the second axial direction a third distance corresponding with a third piston stroke length that the third piston is configured to perform in the third cylinder housing, wherein the fourth piston is configured to clamp and move the forth piston rod in the second axial direction a fourth distance corresponding with a fourth piston stroke length that the fourth piston is configured to perform in the fourth cylinder housing, wherein the third piston stroke length is longer than the fourth piston stroke length.

Suitably, the second piston rod and the fourth piston rod are coupled to each other via a second pivot joint member.

Preferably, the second pivot joint member may comprise the holding member equipped with a universal joint linkage arrangement coupled to the respective end of the second and the fourth piston rod for providing a possible angular deviation between the first axial direction and the second axial direction.

Suitably, the fluid actuator arrangement comprises at least a further piston rod extending through at least a further clamping device of the third piston and through at least a further clamping device of the fourth piston.

Preferably, the fluid actuator arrangement comprises end position cushioning member configured for controlled deceleration of the stroke velocity in both end positions of the respective first and second piston in the respective first and second cylinder housing.

In such way is provided that the respective piston will not "bang" into hard-stops or jolt. This will eliminate stress on the actuator elements and the movements can be smoother.

This has also in different embodiments been achieved by means of a method of moving a first piston rod by means of a fluid actuator arrangement comprising; a first cylinder housing and a second cylinder housing, a first piston is arranged movable in the first cylinder housing in a first axial direction X, a second piston is arranged movable in the second cylinder housing in the first axial direction X, the first piston rod extending through a first clamping device of the first piston and through a second clamping device of the second piston, the first piston is configured to clamp and move the first piston rod a first distance corresponding with a first piston stroke length that the first piston is configured to perform in the first cylinder housing, and the second piston is configured to clamp and move the first piston rod a second distance corresponding with a second piston stroke length that the second piston is configured to perform in the second cylinder housing, wherein the first piston stroke length is longer than the second piston stroke length, the method is characterized by the steps of, engaging the first clamping device of the first piston to the first piston rod, disengaging the second clamping device of the second piston from the first piston rod, moving the first piston said first piston stroke length in a feeding mode, engaging the second clamping device of the second piston to the first piston rod, disengaging the first clamping device of the first piston from the first piston rod, and moving the second piston said second piston stroke length in a fine tuning mode.

Suitably, the first piston comprises a third clamping device and the second piston comprises a fourth clamping device, and at least one second piston rod extends through the third clamping device and through the fourth clamping device, the method is characterized by the steps of; engaging the third clamping device of the first piston to the second piston rod, disengaging the fourth clamping device of the second piston from the second piston rod, moving the first piston said first piston stroke length in a feeding mode; engaging the fourth clamping device of the second piston to the second piston rod, disengaging the first clamping device of the first piston from the first piston rod, and moving the second piston said second piston stroke length in a fine tuning mode.

Preferably, the fluid actuator arrangement further comprising; a third cylinder housing and a fourth cylinder housing, a third piston is arranged movable in the third cylinder housing in a second axial direction, a fourth piston is arranged movable in the fourth cylinder housing in the second axial direction, a third piston rod extending through a fifth clamping device of the third piston and through a sixth clamping device of the fourth piston, the third piston is configured to clamp and move the third piston rod a third distance corresponding with a third piston stroke length that the third piston is configured to perform in the third cylinder housing, and the fourth piston is configured to clamp and move the third piston rod a fourth distance corresponding with a fourth piston stroke length that the fourth piston is configured to perform in the fourth cylinder housing, wherein the third piston stroke length is longer than the fourth piston stroke length, the method is characterized by the steps of; engaging the fifth clamping device of the third piston to the third piston rod, disengaging the sixth clamping device of the fourth piston from the third piston rod, moving the third piston said third piston stroke length in a feeding mode, engaging the sixth clamping device of the fourth piston to the third piston rod, disengaging the fifth clamping device of the third piston from the third piston rod, and moving the fourth piston said fourth piston stroke length in a fine tuning mode.

Suitably, the method further comprises the steps of simultaneously engaging the first clamping device and the second clamping device to the first piston rod at the same time.

Preferably, the method further comprises the steps of simultaneously engaging the first clamping device and the second clamping device to the first piston rod and simultaneously engaging the third clamping device and the fourth clamping device to the second piston rod.

Suitably, the method further comprises the steps of simultaneously engaging the first clamping device and the second clamping device to the first piston rod and simultaneously engaging the fifth clamping device and the sixth clamping device to the third piston rod.

Suitably, moving the first piston said first piston stroke length is made in a first piston rod feeding mode by engaging the first clamping device of the first piston to the first piston rod.

Preferably, moving the second piston said second piston stroke length is made in a first piston rod fine tuning mode by engaging the second clamping device of the second piston to the first piston rod.

Suitably, moving the first piston said first piston stroke length is made in a second piston rod feeding mode by engaging the third clamping device of the first piston to the second piston rod.

Preferably, moving the second piston said second piston stroke length is made in a second piston rod fine tuning mode by engaging the fourth clamping device of the second piston to the second piston rod.

Preferably, the first cylinder housing comprises a first cap end located at a first end of the first cylinder housing.

Suitably, the first cylinder housing comprises a second cap end located at a second end of the first cylinder housing.

Preferably, the first cylinder housing comprises a first interior, in which the first piston is movable in X-direction dividing the first interior into a first cylinder housing chamber (the volume of which is variable) and a second cylinder housing chamber (the volume of which is variable). Suitably, by pressurizing the first cylinder housing chamber (being coupled to the fluid supply) of the first cylinder housing with a higher pressure than prevailing pressure in the second cylinder housing chamber of the first cylinder housing, the first piston moves from a first end position to a second end position.

Preferably, by pressurizing the second cylinder housing chamber (being coupled to the fluid supply) of the first cylinder housing with a higher pressure than prevailing pressure in the first cylinder housing chamber of the first cylinder housing, the first piston moves from the second end position to the first end position.

Suitably, by pressurizing a third cylinder housing chamber (being coupled to the fluid supply) of the second cylinder housing with a higher pressure than prevailing pressure in a fourth cylinder housing chamber of the second cylinder housing, the second piston moves from a third end position to a fourth end position.

Preferably, the distance in the first axial direction between the first end position and the second end position is larger than the distance in the second axial direction between the third end position and the fourth end position. Preferably, by pressurizing the fourth cylinder housing chamber (being coupled to the fluid supply) of the second cylinder housing with a higher pressure than prevailing pressure in the third cylinder housing chamber of the second cylinder housing, the second piston moves from the fourth end position to the third end position. Suitably, the fluid supply is coupled to a hydraulic valve member, e.g. a directional valve (controlling the motion of the piston in a first or second direction), a hydraulic logic valve and/or on/off-valve and/or spool type logic valve and/or 2 way-slip-in cartridge logic valve or other 2 way valve

(controlling the activation of the respective clamping device). Preferably, the first clamping device comprises a first expandable space (coupled for fluid communication to the fluid supply via a first hydraulic valve member controllable by a control unit) forming a first flexible wall segment surrounding the first piston rod, which first flexible wall segment upon pressurization of the first expandable space will be pressed toward the first piston rod envelope surface for clamping action. Preferably, the second clamping device comprises a second expandable space (coupled for fluid communication to the fluid supply via a second hydraulic valve member controllable by the control unit) forming a second flexible wall segment surrounding the first piston rod, which second flexible wall segment upon pressurization of the second expandable space will be pressed toward the first piston rod envelope surface for clamping action.

Preferably, the third clamping device comprises a third expandable space (coupled for fluid communication to the fluid supply via a third hydraulic valve member controllable by the control unit) forming a third flexible wall segment surrounding the second piston rod, which third flexible wall segment upon pressurization of the third expandable space will be pressed toward the second piston rod envelope surface for clamping action.

Preferably, the fourth clamping device comprises a fourth expandable space (coupled for fluid communication to the fluid supply via a fourth hydraulic valve member controllable by the control unit) forming a fourth flexible wall segment surrounding the second piston rod, which fourth flexible wall segment upon pressurization of the fourth expandable space will be pressed toward the second piston rod envelope surface for clamping action.

Preferably, the fifth clamping device comprises a fifth expandable space (coupled for fluid communication to the fluid supply via a fifth hydraulic valve member controllable by the control unit) forming a fifth flexible wall segment surrounding the first piston rod, which fifth flexible wall segment upon pressurization of the fifth expandable space will be pressed toward the first piston rod envelope surface for clamping action. Preferably, the sixth clamping device comprises a sixth expandable space (coupled for fluid communication to the fluid supply via a sixth hydraulic valve member controllable by the control unit) forming a sixth flexible wall segment surrounding a third piston rod, which sixth flexible wall segment upon pressurization of the sixth expandable space will be pressed toward the third piston rod envelope surface for clamping action.

Preferably, the seventh clamping device comprises a seventh expandable space (coupled for fluid communication to the fluid supply via a seventh hydraulic valve member controllable by the control unit) forming a seventh flexible wall segment surrounding a fourth piston rod, which seventh flexible wall segment upon pressurization of the seventh expandable space will be pressed toward the fourth piston rod envelope surface for clamping action. Preferably, the eight clamping device comprises an eight expandable space (coupled for fluid communication to the fluid supply via an eight hydraulic valve member controllable by the control unit) forming an eight flexible wall segment surrounding the fourth piston rod, which eight flexible wall segment upon pressurization of the eight expandable space will be pressed toward the fourth piston rod envelope surface for clamping action.

Preferably, the second cylinder housing comprises a first cap end located at a first end of the second cylinder housing.

Suitably, the second cylinder housing comprises a second cap end located at a second end of the second cylinder housing.

Suitably, the second cylinder housing comprises a second interior, in which the second piston is movable in axial direction dividing the second interior into a third cylinder housing chamber (the volume of which is variable) and a fourth cylinder housing chamber (the volume of which is variable).

Preferably, the first cap end of the first cylinder housing is provided with a first through bore extending in axial direction.

Suitably, the second cap end of the first cylinder housing is provided with a second through bore extending in axial direction.

Preferably, the first cap end of the second cylinder housing is provided with a third through bore extending in axial direction.

Suitably, the second cap end of the second cylinder housing is provided with a fourth through bore extending in axial direction.

Preferably, the first stroke length is defined in the first axial direction as a first piston length measure subtracted from a first distance measured from a first interior surface of the first cap end of the first cylinder housing to a second interior surface of the second cap end of the first cylinder housing.

Suitably, the first piston length measure is defined as a first measure measured, in the first axial direction, from a first effective piston surface of a first piston body of the first piston, which first effective piston area faces the first cap end of the first cylinder housing, to a second effective piston surface of the first piston body facing the second cap end of the first cylinder housing.

Preferably, the second stroke length is defined as a second piston length measure subtracted from a second distance measured from a first interior surface of the first cap end of the second cylinder housing to a second interior surface of the second cap end of the second cylinder housing.

Suitably, the second piston length measure is defined as a second measure measured, in the second axial direction, from a third effective piston area of a second piston body of the second piston, which third effective piston area faces the first cap end of the second cylinder housing, to a fourth effective piston area of the second piston body facing the second cap end of the second cylinder housing.

Preferably, the first, second, third and fourth effective piston areas may have different areas or similar areas or combinations thereof.

Suitably, the first piston is configured to be moved from a first end position to a second end position of the first cylinder housing, whereas when the first piston is positioned in the first end position, the first effective piston area will make a contact surface with the first interior surface of the first cap end of the first cylinder housing and when the first piston is positioned in the second end position, the second effective piston area will make a contact surface with the second interior surface of the second cap end of the first cylinder housing.

Suitably, the second piston is configured to be moved from a third end position to a fourth end position of the second cylinder housing, whereas when the second piston is positioned in the third end position, the third effective piston area will make a contact surface with the first interior surface of the first cap end of the second cylinder housing and when the second piston is positioned in the fourth end position, the fourth effective piston area will make a contact surface with the second interior surface of the second cap end of the second cylinder housing. Preferably, the first piston is formed with a first projection extending in the axial direction from the first effective piston area of the first piston body.

Suitably, the first piston is formed with a second projection extending in the axial direction from the second effective piston area of the first piston body. Preferably, the respective first and second projection being cylindrical shaped and being co-axially arranged to the first piston body and having a smaller diameter than that of the first piston body, which is slidably arranged in the first cylinder housing. Suitably, the first projection extends in the first axial direction though the first through bore of the first cap end of the first cylinder housing.

Preferably, the second projection extends in the first axial direction though the second through bore of the second cap end of the first cylinder housing.

Preferably, the second piston is formed with a first projection extending in the first axial direction from the third effective piston area of the second piston body.

Suitably, the second piston is formed with a second projection extending in the first axial direction from the fourth effective piston area of the second piston body.

Preferably, the respective first and second projection of the second piston being cylindrical shaped and being co-axially arranged to the second piston body and having a smaller diameter than that of the second piston body, which is slidably arranged in the second cylinder housing.

Suitably, the first projection of the second piston extends in the first axial direction through the third through bore of the first cap end of the second cylinder housing.

Preferably, the second projection of the second piston extends in the first axial direction through the fourth through bore of the second cap end of the second cylinder housing.

Preferably, the third piston is formed with a first projection extending in the first axial direction from a fifth effective piston area of the third piston body. Suitably, the third piston is formed with a second projection extending in the first axial direction from a sixth effective piston area of the third piston body.

Preferably, the respective first and second projection of the third piston being cylindrical shaped and being co-axially arranged to the third piston body and having a smaller diameter than that of the third piston body, which is slidably arranged in the third cylinder housing. Suitably, the first projection of the third piston extends in the second axial direction through a fifth through bore of a first cap end of the third cylinder housing.

Preferably, the second projection of the third piston extends in the second axial direction through a sixth through bore of a second cap end of the fourth cylinder housing.

Suitably, a first bearing is arranged in the first through bore of the respective first cap end for providing slidingly motion of the respective first projection and journaling the respective first projection.

Preferably, a second bearing is arranged in the second through bore of the respective second cap end for providing slidingly motion of the respective second projection and journaling the respective second projection. Suitably, the first cylinder housing and the second cylinder housing are rigidly coupled to each other directly or via a fundament member or via a junction device or frame or rack or exterior housing.

Preferably, the fluid actuator arrangement comprises a discrete feeding actuator unit and a fine tuning actuator unit.

Preferably, the discrete feeding actuator unit of the fluid actuator arrangement comprises a first piston comprising a first clamping device, wherein the first piston is arranged movable in the first cylinder housing in the first axial direction. Suitably, the fine tuning actuator unit of the fluid actuator arrangement comprises a second piston comprising a second clamping device, wherein the second piston is arranged movable in a second cylinder housing in the first axial direction.

Preferably, a first piston rod extends through the first clamping device and through the second clamping device in the first axial direction.

Suitably, the first piston is configured to clamp and move the first piston rod a first distance corresponding with a first piston stroke length that the first piston is configured to perform in the first cylinder housing; the second piston is configured to clamp and move the first piston rod a second distance corresponding with a second piston stroke length that the second piston is configured to perform in the second cylinder housing; wherein the first piston stroke length is longer than the second piston stroke length.

Preferably, the fluid actuator arrangement being adapted to a high lift system comprising Differential Flap Setting (DFS) including a trim functionality.

In such way is achieved optimization of the cruise aerodynamic efficiency and distributing loads by means of controlling of the aircraft wing centre and lift position by e.g. differentiating inner and outer flaps

Suitably, the fluid actuator arrangement is adapted to be operated in such way that the discrete feeding actuator unit moves the first piston rod for retracting or extracting the aircraft trailing edge flap (or leading edge slat or other secondary control surface) in discrete incremental steps of e.g. 2-4 degrees or of any desired amount, whereas the fine tuning actuator unit acts as a clamping unit clamping around the first piston rod when the first piston being disengaged from the first piston rod and is retracted to its starting position.

Suitably, the fine tuning actuator unit acts as a clamping unit when the first piston is retracted to its starting position.

In such way is a cost-effective control and mounting of a light-weight valve arrangement (comprising proven and robust ordinary on/off and directional valves) achieved.

Preferably, the fine tuning actuator unit is operated in discrete incremental steps during cruise for fuel saving by activating the trim functionality.

Suitably, the fluid actuator arrangement is adapted to be operated in such way that the fine tuning actuator unit moves the first piston rod for retracting or extracting the secondary control surface in small discrete incremental steps of e.g. 0,01-0,5 degrees or of any desired amount, whereas the discrete feeding actuator unit acts as a clamping unit clamping around the first piston rod when the second piston being disengaged from the first piston rod and is retracted to its starting position.

The fluid actuator arrangement provides a robust and cost-effective high lift flap system that is simple in its design and that provides both high-lift at start and landing and also trim of flap positions in cruise mode. This normally requires expensive, complex and maintenance intensive electrical or hydraulic actuation systems. The fluid actuator arrangement may of course be applied to other secondary control surfaces, such as leading edge slats, air brakes etc.

In such way is achieved weight saving, simplified wing design, no rotating and bending screw shafts along the wing spars.

In such way it is possible to provide energy transfer via electrical wires to remote positioned fluid actuator arrangement having a locally arranged fluid supply. In such way is achieved a compact and leak-free fluid actuator arrangement of a Flap Setting (DFS) including a trim functionality, permitting simple monitoring with detectable faults by means of Pre- Flight-Built-ln-Test and less demanding maintenance of the hydraulic system in comparison with electric ball screws. Furthermore, the operation of the fluid actuator arrangement is relatively simple to monitor and makes eventual faults easy detectable and the fluid actuator arrangement provides that a fail-safe position upon failure of the flap can be determined and elimination of flap asymmetries.

The fluid actuator arrangement provides a robust and cost-effective high lift flap system that is simple in its design and that provides both high-lift at start and landing and also trim of flap positions in cruise mode. This normally requires expensive, complex and maintenance intensive electrical or hydraulic actuation systems. The fluid actuator arrangement may of course be applied to other secondary control surfaces, such as leading edge slats, air brakes etc. The definition of the respective stroke length may be the distance that the respective piston moves from a first contact with a first interior cap end wall of the respective cylinder housing to a second contact with a second interior cap end wall of the cylinder housing, whereas a first effective piston surface of the respective piston in the first contact will be in contact with the first interior cap end wall and a second effective piston surface of the piston in the second contact will be in contact with the second interior cap end wall.

The definition of the respective stroke length may be the distance the respective piston moves from a first end position to a second end position, whereas in the first end position the respective piston abuts or is adjacent to the first cap end and in the second end position the respective piston abuts or is adjacent to the second cap end. Preferably, the entire volume of the interior of the respective cylinder housing is used by the piston moved between the first end position and the second end position.

Suitably, the respective stroke length can be regarded as a well-defined stroke length.

Preferably, the fine tuning motion and the descrete feeding motion of a single piston rod or the respective piston rod being performed in a stepwise manner (suitably with incremental steps).

Suitably, an incremental control technique is used for providing the fine tuning motion and the discrete feeding motion.

Preferably, the piston (e.g. second, fourth etc.) having the shortest stroke length determines the resolution (r) of the motion of the piston rod. Suitably, the next following piston stroke length is determined by a multiple value (m) raised to one (actuator number is determined as n=l) multiplied by the resolution (r).

Preferably, the next following piston stroke length is determined by the multiple value (m) raised to two (n) multiplied by the resolution (r).

Suitably, the next following piston stroke length is determined by the multiple value (m) raised to three (n) multiplied by the resolution (r) etc.

Preferably, the multiple value (m) is set to 2, 5, 10 or any other suitable value. The multiple value (m) can be varied depending on requirements on the total stroke length that is required and on time requirements, i.e the number of required discrete feeding and fine tuning iterations.

The total stroke length (the distance made by the piston rod) performed by the fluid actuator arrangement may be expressed by the following formula:

Total stroke length =∑ x_n · r · mⁿ wherein;

x_n: The number of strokes for each actuator in both direction (+/-)■ It can be negative number in order to minimize the number of strokes,

r: The resolution (the piston having the shortest stroke length)

m: The multiple value

n: The actuator number starting from zero

As an example: The number of strokes xo = - 1, xi = 1, x₂= - 1 , x₃ = 1 ; the resolution r = 1; the multiple value m = 5; the number of actuators n = 0-3 (four actuators). The total stroke length = -1-1-5⁰ (+) 1-1-5¹ (+) -1-1-5² (+) 1·1·5³ = -1 + 5 - 25 + 125 = 96 units. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of examples with references to the

accompanying schematic drawings, of which: Figs. la-Id illustrate a fluid actuator arrangement according to a first example;

Fig. 2 illustrates a fluid actuating unit according to a second example;

Figs. 3a-3b illustrate a fluid actuator arrangement according to a third example;

Fig. 4 illustrates a fluid actuator arrangement according to a fourth example;

Fig. 5 illustrates a fluid actuator arrangement according to a fifth example

Figs. 6-7 illustrate exemplary method flow charts according to further examples; and

Figs. 8a-8b illustrate fluid actuator arrangements according to a further examples.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings, wherein for the sake of clarity and understanding of the invention some details of no importance may be deleted from the drawings.

Figs. la-Id illustrate a fluid actuator arrangement 1 according to a first example. The fluid actuator arrangement 1 comprises a first cylinder housing CI and a second cylinder housing C2. A first piston PI is arranged movable in the first cylinder housing CI in a first axial direction X. A second piston P2 is arranged movable in the second cylinder housing C2 in the first axial direction X. A first piston rod Rl extends through a first clamping device Kl of the first piston PI and through a second clamping device K2 of the second piston P2. The first piston PI is configured to clamp and move the first piston rod Rl a first distance Al corresponding with a first piston stroke length SL1 that the first piston PI is configured to perform in the first cylinder housing CI. The second piston P2 is configured to clamp and move the first piston rod Rl a second distance A2 corresponding with a second piston stroke length SL2 that the second piston P2 is configured to perform in the second cylinder housing C2. The first piston stroke length SL1 is longer than the second piston stroke length SL2.

The first clamping device Kl and the second clamping device K2, each being coupled to a fluid supply (not shown) via a respective on/off-valve VI, V2.

Preferably, the respective on/off-valve VI, V2 or other logic valve may be an on/off-valve and/or a spool type logic valve and/or a 2 way-slip-in cartridge logic valve or other 2 way valves for providing clamping action. The first cylinder housing CI comprises a first interior il, in which the first piston PI is movable in X- direction dividing the first interior il into a first cylinder housing chamber (the volume of which is variable) CHI and a second cylinder housing chamber CH2 (the volume of which is variable). By pressurizing the first cylinder housing chamber CHI (coupled to the fluid supply 10) of the first cylinder housing CI with a higher pressure than prevailing pressure in the second cylinder housing chamber CH2 of the first cylinder housing CI, the first piston PI can move from a first end position El to a second end position E2 (see Fig. lb). By pressurizing the second cylinder housing chamber CH2 (being coupled to the fluid supply 10, see Fig. Id) of the first cylinder housing CI with a higher pressure than prevailing pressure in the first cylinder housing chamber CHI of the first cylinder housing CI, the first piston PI moves from the second end position E2 to the first end position El. By pressurizing a third cylinder housing chamber CH3 (being coupled to the fluid supply 10) of the second cylinder housing C2 with a higher pressure than prevailing pressure in a fourth cylinder housing chamber CH4 of the second cylinder housing C2, the second piston P2 moves from a third end position E3 to a fourth end position E4 (see Fig. lb).

Suitably, the fluid supply is coupled to the respective cylinder housing chamber via a hydraulic valve member 12 (see Fig. Id), e.g. a directional valve 12, a 3/2 valve or co-operating two on/off valves for moving of the respective piston PI, P2 in desired direction along the first axial direction X. The first stroke length SL1 is defined as a first piston body Bl length measure ml subtracted from a first distance dl measured from a first interior surface si of a first cap end CE1 of the first cylinder housing CI to a second interior surface s2 of a second cap end CE2 of the first cylinder housing CI. The first piston body Bl length measure ml is defined as a first measure, measured from a first effective piston area EA1 (see Fig. lb) of the first piston body Bl of the first piston (facing the first cap end CE1 of the first cylinder housing CI) to a second effective piston area EA2 (see Fig. lb) of the first piston body Bl (facing the second cap end CE2 of the first cylinder housing CI).

Correspondingly, the second stroke length SL2 is defined as a second piston body B2 length measure m2 (see Fig. lc) subtracted from a second distance d2 measured from a first interior surface si of the first cap end CE1 of the second cylinder housing C2 to a second interior surface s2 of the second cap end CE2 of the second cylinder housing C2. The second piston body B2 length measure m2 is defined as a second measure, measured from a third effective piston area EA3 of a second piston body B2 of the second piston P2 facing the first cap end CE1 of the second cylinder housing C2 to a fourth effective piston area EA4 of the second piston body B2 facing the second cap end CE2 of the second cylinder housing C2. The first piston PI is formed with a first projection PRl extending in X-direction from the first effective piston area EA1 of the first piston body Bl through a first through bore Tl. The first piston PI is formed with a second projection PR2 extending in X-direction from the second effective piston area EA2 of the first piston body Bl through a second through bore T2.

The respective first PRl and second PR2 projection being cylindrical shaped and being co-axially arranged to the first piston body Bl and having a smaller diameter than that of the first piston body Bl, which is slidably arranged in the first cylinder housing CI. The first projection PRl extends through the first through bore Tl of the first cap end CEl of the first cylinder housing CI. The second projection PR2 extends through a second through bore T2 of the second cap end CE2 of the first cylinder housing CI.

Preferably, the second piston P2 is also formed with a first projection PRl extending in X-direction from the third effective piston area EA3 of the second piston body B2. The second piston P2 is also formed with a second projection PR2 extending in X-direction from the fourth effective piston area EA4 of the second piston body B2 (see Fig. lc).

The respective first PRl and second PR2 projection being cylindrical shaped and being co-axially arranged to the second piston body B2 and having a smaller diameter than that of the second piston body B2, which is slidably arranged in the second cylinder housing C2.

The first projection PRl of the second piston P2 extends through a third through bore T3 of the first cap end CEl of the second cylinder housing C2. The second projection PR2 of the second piston P2 extends through a fourth through bore T4 of the second cap end CE2 of the second cylinder housing C2.

In Fig. la, the second clamping device K2 of the second piston P2 is engaged with the first piston rod Rl. The respective clamping device Kl, K2 comprises an expandable space coupled for fluid communication to the fluid supply via the respective logic valve member VI, V2 controllable by a control unit CPU (shown in Fig. Id). The respective expandable space forms a flexible wall segment (not shown) surrounding the first piston rod Rl, which flexible wall segment upon pressurization of the expandable space will be pressed toward the first piston rod Rl envelope surface for clamping action. In Fig. lb is shown that the second piston P2 has made a second piston stroke length SL2 to the third end position E3. In such way is achieved a fine tuning motion of the first piston rod l achieving a motion corresponding with the distance Al. In fig. lc is the second piston moved back to the fourth end position E3 (the second clamping device K2 is disengaged from the first piston rod Rl), meanwhile the first piston PI clamps and holds the first piston rod Rl.

In fig. Id is shown that the first clamping device Kl of the first piston PI is disengaged from the first piston rod Rl and the second piston P2 moves the second piston stroke length SL2 for providing a further fine tuning motion of the first piston rod Rl. By means of the control unit CPU efficient control of motion and operation of the first piston rod Rl can be achieved by controlling the respective hydraulic valve member 12 (e.g. hydraulic logic valve and/or on/off-valve and/or spool type logic valve and/or 2 way-slip-in cartridge logic valve or other 2 way valve) for providing a motion of the respective piston PI, P2 alternately clamped to the first piston rod Rl for providing fine tuning motion and feeding motion of the first piston rod Rl.

By means of using different piston stroke lengths and moving the first piston rod Rl a specific distance corresponding to the respective stroke length SLl, SL2, there can be achieved fine tuning motion of the first piston rod Rl and feeding motion of the first piston rod Rl, by simply using hydraulic logic valves (e.g. on/off-valves). The use of such hydraulic logic valves implies a non- complex solution for achieving fine tuning motion and feeding motion of the first piston rod Rl.

Fig. 2 illustrates a fluid actuating unit according to a second example. A fluid actuator arrangement 1 comprises a first cylinder housing CI and a second cylinder housing C2. A first piston PI comprises a first clamping device Kl. The first piston PI is arranged movable in the first cylinder housing CI in a first axial direction XI. A second piston P2 comprises a second clamping device K2. The second piston P2 is arranged movable in the second cylinder housing C2 in the first axial direction X. A first piston rod Rl extends through the first clamping device Kl and through the second clamping device K2. The first piston PI is configured to clamp and move the first piston rod Rl a first distance Al corresponding with a first piston stroke length SLl that the first piston PI is configured to perform in the first cylinder housing CI. The second piston P2 is configured to clamp and move the first piston rod Rl a further distance (same as Al) corresponding with the second piston stroke length SL2 that the second piston P2 is configured to perform in the second cylinder housing C2. The first piston stroke length SLl is longer than the second piston stroke length SL2. The first piston stroke length SLl that the first piston PI is configured to perform is selectively provided for achievement of a feeding mode. The second piston stroke length SL2 that the second piston P2 is configured to perform is selectively provided for achievement of a fine tuning mode. The feeding mode and/or the fine tuning mode being selectively selected by a control circuit 12 configured to control a respective first and second directional valve 17', 17" and a PLC (Programmable logic controller, not shown), whereby the clamping of the respective first and second piston to the first piston rod is achieved by engaging the respective clamping device Kl, K2 by controlling a respective first and second logic valve 15', 15". The respective logic valve may be a 3/2-valve or may be implemented in the form of two on/off valves.

A fluid supply 13 is coupled to the respective first and second clamping device Kl, K2 via the a respective first and second logic valve 15', 15", e.g. hydraulic logic valve and/or on/off-valve and/or spool type logic valve and/or 2 way-slip-in cartridge logic valve or other 2 way valve.

Preferably, the first clamping device Kl comprises a first expandable space coupled for fluid communication to the fluid supply 13 via the first logic valve 15' controllable by the control unit 12. The first expandable space formed by a first flexible wall segment (not shown) surrounding the first piston rod l, which first flexible wall segment upon pressurization of the first expandable space will be pressed toward the first piston rod Rl envelope surface for clamping action. The second clamping device K2 comprises a second expandable space also coupled for fluid communication to the fluid supply 13 via the second logic valve 15" controllable by the control unit 12. The respective first and second cylinder housing CI, C2 being coupled to the fluid supply 13 via directional logic valves 17. Figs. 3a-3b illustrate a fluid actuator arrangement according to a third example.

The definition of "stroke length" is regarded as the travelled length the respective piston makes in the respective cylinder housing in the axial direction between two end positions (where the piston reaches the respective inner cap end surfaces of the cylinder housing).

The stroke length of cylinder housing D is determined to d=5 cm. The stroke length of cylinder housing C is determined to c=l cm. The cylinder housing D and the cylinder housing C are regarded as first and second discrete feeding actuator units 1FAU and 2FAU. The respective cylinder housing B and the cylinder housing A being regarded as respective first 1FTU and second 2FTU fine tuning actuator units. The stroke length of cylinder housing B is determined to b=0,2 cm. The stroke length of cylinder housing A is determined to a=0,04 cm. The cylinder housings B and A are used for providing fine tuning of the motion of the piston rod R. The holding of the piston rod R is performed by the respective piston PD, PB, PA, PC. With small corrective steps a high positioning accuracy is enabled without expensive hydraulic valve solutions.

In fig. 3b is shown that the first 1FAU and the second discrete feeding actuator unit 2FAU moved the piston rod 7 cm. The first discrete feeding actuator unit 1FAU moves the piston rod 5 cm (d).

Subsequently, the second fine tuning actuator unit 2FTU holds the piston rod R. The second discrete feeding actuator unit 2FAU holds the piston rod R and, after releasing the second fine tuning actuator unit 2FTU from the piston rod R, moves the piston rod R the distance of 1 cm (c) (the stroke length of the second discrete feeding actuator unit 2FAU). In a next step the second fine tuning actuator unit 2FTU holds the piston rod R again and the second discrete feeding actuator unit 2FAU is released from the piston rod R and is retracted to a start position.

Subsequently, the second discrete feeding actuator unit 2FAU holds the piston rod R and, after releasing of the second fine tuning actuator unit 2FTU from the piston rod R, moves the piston rod R further 1 cm. The piston rod R is thus moved a distance of 5+1+1 cm in a "Discrete Feeding Mode" operation.

The characteristic feature of this design is that the discrete feeding actuator unit and the fine tuning actuator unit change functionality in the different phases. In the "Discrete Feeding Mode" the fine tuning actuator units 1FTU, 2FTU act as a static clamping units and the discrete feeding actuator units 1FAU, 2FAU move the piston rod R with incremental motion. That is, the first discrete feeding actuator unit 1FAU moved the piston rod 5 cm and the second discrete feeding actuator unit 2FAU moved the piston rod 1 cm two times.

For fine adjustment of the position of the piston rod R to be moved a distance of 7, 24 cm, the first and second fine tuning actuator units 1FTU, 2FTU are used for moving the piston rod R. Firstly, the first fine tuning actuator unit 1FTU clamps and moves the piston rod R a distance of 0, 2 cm (b) (corresponding with the stroke length of the first fine tuning actuator unit 1FTU).

In a next step the second discrete feeding actuator unit 2FAU holds the piston rod R. The second fine tuning actuator unit 2FTU initially holds the piston rod R and, after releasing the second discrete feeding actuator unit 2FAU from the piston rod R, clamps and moves the piston rod R a distance of further 0, 04 cm (a) (corresponding with the stroke length of the second fine tuning actuator unit 2FTU).

Thus, in a "Fine Tuning Mode" the respective discrete feeding actuator unit 1FAU, 2FAU acts as a static clamping unit and the respective fine tuning actuator unit 1FTU, 2FTU moves the piston rod , practicable with incremental motion if needed. That is, in this case, the first fine tuning actuator unit 1FTU moved the piston rod further 0, 2 cm (fine tuning) and the second fine tuning actuator unit 2FTU moved the piston rod further 0, 04 cm (fine tuning), i.e. the piston rod R has been moved totally 7, 24 cm (5+1+1+0,2+0,04).

The combinations of using the respective fine tuning actuator and the respective discrete feeding actuator are illustrated in following matrix:

Fine tuning actuator unit Discrete feeding actuator

action unit action

Static

Feeding Clamping Motion mode

Mode

Static

Fine tuning Motion mode Clamping

Mode

Static Static

Hold Clamping Clamping

Mode Mode

The fine tuning being performed in the "Fine Tuning Mode" can be done in both directions. And finally, when the required position is reached, all actuator units may enter the static clamping mode.

Fig. 4 illustrates a fluid actuator arrangement 1 according to a fourth example. The fluid actuator arrangement 1 comprising a first cylinder housing 401 and a second cylinder housing 403. It further comprises a first piston 411 comprising a first clamping device 421. The first piston 411 is arranged movable in the first cylinder housing 401 in a first axial direction XI. A second piston 413 comprises a second clamping device 422. The second piston 413 is arranged movable in the second cylinder housing 403 in the first axial direction XI. A first piston rod 431 extends through the first clamping device 421 and through the second clamping device 422. The first piston 411 is configured to clamp and move the first piston rod 431 a first distance corresponding with a first piston stroke length SL1 that the first piston 411 is configured to perform in the first cylinder housing 401. The second piston 413 is configured to clamp and move the first piston rod 431 a second distance corresponding with a second piston stroke length SL2 that the second piston 413 is configured to perform in the second cylinder housing 403. The first piston stroke length SL1 is longer than the second piston stroke length SL2.

The first piston 411 is formed with a first projection PI extending in X-direction from a first effective piston area PA1 of a first piston body 416, which is formed of a mid-section of the first piston 411 and which has a larger diameter than the first projection PI. The first piston 411 is formed with a second projection P2 extending in X-direction from a second effective piston area PA2 of the first piston body 416. The respective first and second projection being cylindrical shaped and being co- axially arranged to the first piston body 416 and having a smaller diameter than that of the first piston body 416, which is slidably arranged in the first cylinder housing 401. The first piston 411 further comprises a third clamping device 423 and the second piston 413 comprises a fourth clamping device 424. A second piston rod 432 extends through the third clamping device 423 and through the fourth clamping device 424.

Each clamping device 421, 422, 423 and 424 being coupled to a fluid supply 450 via a respective on/off hydraulic valve 461, 462, 463 and 464. A first 471 and a second 472 cylinder housing chamber of the first cylinder housing 401 being coupled to the fluid supply 450 via a first direction valve 465. A third 473 and a fourth 474 cylinder housing chamber of the second cylinder housing 403 being coupled to the fluid supply 450 via a second direction valve 467. The first piston stroke length SL1 that the first piston 411 is configured to perform is selectively provided for achievement of a feeding mode (Discrete Feeding Mode) and the second piston stroke length SL2 that the second piston 413 is configured to perform is selectively provided for achievement of a fine tuning mode. The feeding mode and/or the fine tuning mode being selectively selected by a control circuit (not shown) coupled to the respective on/off hydraulic valve 461, 462, 463 and 464 and coupled to the respective first and second direction valve 465, 467.

The fluid actuator arrangement comprises an end position cushioning member (not shown) configured for controlled deceleration of the stroke velocity in both end positions of the respective first 401 and second 403 cylinder housing.

Fig. 5 illustrates a fluid actuator arrangement 1 according to a fifth example. The fluid actuator arrangement 1 comprises a first cylinder housing 401, a second cylinder housing 403, a third cylinder housing 405 and a fourth 407 cylinder housing. It further comprises a first piston 411 comprising a first clamping device 421. A second piston 413 comprises a second clamping device 422. A first piston rod 431 extends through the first clamping device 421 and through the second clamping device 422 oriented in a first axial direction IX. The first piston 411 further comprises a third clamping device 423 and the second piston 413 comprises a fourth clamping device 424. A second piston rod 432 extends through the third clamping device 423 and through the fourth clamping device 424 oriented in a first axial direction IX.

A third piston 415 is arranged movable in the third cylinder housing 405 in a second axial direction 2X. A fourth piston 417 is arranged movable in the fourth cylinder housing 407 in the second axial direction 2X. A third piston rod 433 extends through a fifth clamping device 425 of the third piston 405 and through a sixth clamping device 426 of the fourth piston 407.

The third piston 405 is configured to clamp and move the third piston rod 433 a third

distance corresponding with a third piston stroke length that the third piston is configured to perform in the third cylinder housing 405. The fourth piston 417 is configured to clamp and move the third piston rod 433 a fourth distance corresponding with a fourth piston stroke length that the fourth piston 417 is configured to perform in the fourth cylinder housing 407. The third piston stroke length is longer than the fourth piston stroke length. A fourth piston rod 434 extends through a seventh clamping device 427 of the third piston 405 and through an eight clamping device 428 of the fourth piston 407. The third piston 405 is configured to clamp and move the fourth piston rod 434 the third distance corresponding with the third piston stroke length that the third piston is configured to perform in the third cylinder housing 405. The fourth piston 417 is configured to clamp and move the fourth piston rod 434 a fourth distance corresponding with a fourth piston stroke length that the fourth piston 417 is configured to perform in the fourth cylinder housing 407.

Preferably, the first piston rod 431 and the third piston rod 433 are coupled to each other via a first pivot joint member 480.

Suitably, the second piston rod 432 and the fourth piston rod 434 are coupled to each other via the first pivot joint member 480.

Fig. 6 illustrates a method flow chart according to a sixth example regarding a method of moving a first piston rod by means of a fluid actuator arrangement comprising; a first cylinder housing and a second cylinder housing, a first piston is arranged movable in the first cylinder housing in a first axial direction, a second piston is arranged movable in the second cylinder housing in the first axial direction, the first piston rod extending through a first clamping device of the first piston and through a second clamping device of the second piston; the first piston is configured to clamp and move the first piston rod a first distance corresponding with a first piston stroke length that the first piston is configured to perform in the first cylinder housing; and the second piston is configured to clamp and move the first piston rod a second distance corresponding with a second piston stroke length that the second piston is configured to perform in the second cylinder housing; wherein the first piston stroke length is longer than the second piston stroke length. The method is characterized by the step 601 comprising the start of the method. The step 602 regards the performance of the method and the step 603 regards the stop of the method.

The step 602 may comprise engaging the first clamping device of the first piston to the first piston rod; disengaging the second clamping device of the second piston from the first piston rod; moving the first piston said first piston stroke length in a feeding mode; engaging the second clamping device of the second piston to the first piston rod; disengaging the first clamping device of the first piston from the first piston rod; and moving the second piston said second piston stroke length in a fine tuning mode. Fig. 7 illustrates a method flow chart according to a seventh example. The fluid actuator arrangement may comprise the components of the sixth example and may further comprise a third cylinder housing and a fourth cylinder housing, a third piston is arranged movable in the third cylinder housing in a second axial direction, a fourth piston is arranged movable in the fourth cylinder housing in the second axial direction, a third piston rod extending through a fifth clamping device of the third piston and through a sixth clamping device of the fourth piston; the third piston is configured to clamp and move the third piston rod a third distance corresponding with a third piston stroke length that the third piston is configured to perform in the third cylinder housing; and the fourth piston is configured to clamp and move the third piston rod a fourth distance corresponding with a fourth piston stroke length that the fourth piston is configured to perform in the fourth cylinder housing; wherein the third piston stroke length is longer than the fourth piston stroke length.

The method may be characterized by the step 701 comprising the start of the method. The step 702 regards engaging the fifth clamping device of the third piston to the third piston rod. The step 703 regards disengaging the sixth clamping device of the fourth piston from the third piston rod. The step 704 regards moving the third piston said third piston stroke length in a feeding mode. The step 705 regards engaging the sixth clamping device of the fourth piston to the third piston rod. The step 706 regards disengaging the fifth clamping device of the third piston from the third piston rod. The step 707 regards moving the fourth piston said fourth piston stroke length in a fine tuning mode. The step 708 regards the stop of the method.

Fig. 8a shows an aircraft trailing edge flap 888 (secondary control) of a wing w, which aircraft trailing edge flap 888 is operated by a fluid actuator arrangement 1 according to a further example. The fluid actuator arrangement 1 comprises a discrete feeding actuator unit FAU and a fine tuning actuator unit FTU. The discrete feeding actuator unit FAU comprises a first piston PI comprising a first clamping device Kl, wherein the first piston PI is arranged movable in a first cylinder housing CI of the discrete feeding actuator unit FTU in a first axial direction X. The fine tuning actuator unit FTU comprises a second piston P2 comprising a second clamping device K2, wherein the second piston P2 is arranged movable in a second cylinder housing C2 of the fine tuning actuator unit FTU in the first axial direction X. A piston rod 890 (flap operating rod) extends through the first clamping device Kl and through the second clamping device K2 in the first axial direction X and is coupled to the aircraft trailing edge flap 888. The first piston PI is configured to clamp and move the piston rod 890 a first distance corresponding with a first piston stroke length SL1 that the first piston PI is configured to perform in the first cylinder housing CI. The second piston P2 is configured to clamp and move the piston rod 890 a second distance corresponding with a second piston stroke length SL2 that the second piston P2 is configured to perform in the second cylinder housing C2. The first piston stroke length SL1 is longer than the second piston stroke length SL2. The first piston PI is configured to perform, and is selectively provided for achievement of, a feeding mode. The second piston P2 is configured to perform, and is selectively provided for achievement of, a fine tuning mode. The piston rod 890 is coupled to a control horn and flap hinge bracket arrangement 886 of the aircraft trailing edge flap 888 for extension and extraction of the aircraft trailing edge flap 888. The feeding mode provides an angular motion of the aircraft trailing edge flap 888 step-wise, wherein the first piston PI clamps around the piston rod 890 and moves the piston rod 890 incrementally in steps

corresponding in length to the first piston stroke length SL1, each step corresponds to an angle of inclination v of the aircraft trailing edge flap 888. The fine tuning mode provides an angular motion of the aircraft trailing edge flap 888 step-wise, wherein the second piston P2 clamps around the piston rod 890 and moves the piston rod 890 incrementally in steps corresponding in length to the second piston stroke length SL2, each step corresponds to an angle of inclination y of the aircraft trailing edge flap 888. Fig. 8a shows a high lift system with Differential Flap Setting (DFS) including a trim functionality, which enables optimization of the cruise aerodynamic efficiency and loads by means of controlling of the aircraft wing centre and lift position by differentiating inner and outer flaps. During take-off and landing the fluid actuator arrangement 1 is operated in such way that the discrete feeding actuator unit FAU moves the piston rod 890 for retracting or extracting the aircraft trailing edge flap 888 in discrete incremental steps of e.g. 2-4 degrees or of any desired amount (the angle of inclination v), whereas the fine tuning actuator unit FTU acts as a clamping unit when the first piston PI is retracted to its starting position. This is made in a cost-effective manner by means of proven and robust ordinary on/off and directional valves (not shown). The fine tuning actuator unit FTU is operated during cruise for fuel saving by activating the trim functionality. The trim functionality is achieved by that the fine tuning actuator unit FTU moves the piston rod 890 for retracting or extracting the aircraft trailing edge flap 888 in trim discrete incremental steps of e.g. 0,01-0,5 degrees or of any desired amount (the angle of inclination y), whereas the discrete feeding actuator unit FAU acts as a clamping unit when the second piston P2 is retracted to its starting position. In such way is achieved a compact and leak-free fluid actuator arrangement of a Flap Setting (DFS) including the trim functionality, permitting simple monitoring with detectable faults by means of Pre- Flight-Built-in-Test and less demanding maintenance of the hydraulic system in comparison with electric ball screws. Furthermore, the operation of the fluid actuator arrangement is relatively simple to monitor and makes eventual faults easy detectable and the fluid actuator arrangement provides that a fail-safe position upon failure of the flap can be determined and elimination of flap asymmetries. The fluid actuator arrangement provides a robust and cost-effective high lift flap system that is simple in its design and that provides both high-lift at start and landing and also trim of flap positions in cruise mode. This normally requires expensive, complex and maintenance intensive electrical or hydraulic actuation systems. The fluid actuator arrangement may of course be applied to other secondary control surfaces, such as leading edge slats, air brakes etc. Fig. 8b shows an aircraft leading edge slat 894 (secondary control) of a wing w, which aircraft leading edge slat 894 is operated by a fluid actuator arrangement 1 according to a further example. The aircraft leading edge slat 894 is operated by and coupled to a piston rod 896, which extends through a discrete feeding actuator unit FAU and a fine tuning actuator unit FTU of the fluid actuator arrangement 1.

During take-off and landing the fluid actuator arrangement 1 is operated in such way that the discrete feeding actuator unit FAU moves the piston rod 896 for retracting or extracting the aircraft leading edge slat 894 in discrete incremental steps. The fine tuning actuator unit FTU is operated during cruise for fuel saving by activating a trim functionality by that the fine tuning actuator unit FTU moves the piston rod 896 in trim discrete incremental steps. A further example of the invention regards that the first piston comprises a third clamping device and the second piston comprises a fourth clamping device, and at least one second piston rod extends through the third clamping device and through the fourth clamping device; wherein the method is characterized by the steps of engaging the third clamping device of the first piston to the second piston rod; disengaging the fourth clamping device of the second piston from the second piston rod; moving the first piston said first piston stroke length in a feeding mode; engaging the fourth clamping device of the second piston to the second piston rod; disengaging the first clamping device of the first piston from the first piston rod; and moving the second piston said second piston stroke length in a fine tuning mode.

A further example of the invention regards the further method step of simultaneously engaging the first clamping device and the second clamping device to the first piston rod at the same time.

A yet further example of the invention regards the further method step of simultaneously engaging the first clamping device and the second clamping device to the first piston rod; and simultaneously engaging the third clamping device and the fourth clamping device to the second piston rod.

A yet further example of the invention regards the further method step of simultaneously engaging the first clamping device and the second clamping device to the first piston rod; and simultaneously engaging the fifth clamping device and the sixth clamping device to the third piston rod.

A yet further example of the fluid actuator arrangement according to the invention comprises at least a fifth piston rod extending through at least a ninth clamping device of the third piston and through at least a tenth clamping device of the fourth piston.

The present invention is of course not in any way restricted to the preferred embodiments described above, but many possibilities to modifications, or combinations of the described embodiments, thereof should be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims.

The fluid supply of the fluid actuator arrangement may advantageously be designed as an internal hydraulic supply including an electric motor and a hydraulic pump close associated with the fine tuning actuator unit and the discrete feeding actuator unit. This promotes a very compact system at the site where the fluid actuator arrangement is to be installed, wherein the power can be transmitted using an electrical cable instead of a long hydraulic hose or pipe.

Claims

1. A fluid actuator arrangement (1) comprising:

-a first cylinder housing (CI, 401) and a second cylinder housing (C2, 403),

-a first piston (PI, 411) comprising a first clamping device (Kl, 421), the first piston (PI, 411) is arranged movable in the first cylinder housing (CI, 401) in a first axial direction (X),

-a second piston (P2, 413) comprising a second clamping device (K2, 422), the second piston

(P2, 413) is arranged movable in the second cylinder housing (C2, 403) in the first axial direction (X),

-a first piston rod (Rl, 431) extending through the first clamping device (Kl, 421) and through the second clamping device (K2, 422); characterized by

-the first piston (PI, 411) is configured to clamp and move the first piston rod (Rl, 431) a first distance corresponding with a first piston stroke length (SLl) that the first piston (PI, 411) is configured to perform in the first cylinder housing (CI, 401);

-the second piston (P2, 413) is configured to clamp and move the first piston rod (Rl, 431) a second distance corresponding with a second piston stroke length (SL2) that the second piston (P2, 413) is configured to perform in the second cylinder housing (C2, 403); wherein -the first piston stroke length (SLl) is longer than the second piston stroke length (SL2).

2. The fluid actuator arrangement (1) according to claim 1, wherein

-the first piston stroke length (SLl) that the first piston (PI, 411) is configured to perform is selectively provided for achievement of a feeding mode; and

-the second piston stroke length (SL2) that the second piston (P2, 413) is configured to perform is selectively provided for achievement of a fine tuning mode.

3. The fluid actuator arrangement (1) according to claim 2, wherein

-the feeding mode and/or the fine tuning mode being selectively selected by a control circuit (CPU, 12).

The fluid actuator arrangement (1) according to any of claims 1 to 3, wherein

-the first piston (PI, 411) comprises a third clamping device (423) and the second piston (P2,

413) comprises a fourth clamping device (424), and

-at least one second piston rod (432) extends through the third clamping device (423) and through the fourth clamping device (424).

The fluid actuator arrangement (1) according to any of the preceding claims, further comprising:

-a third cylinder housing (405) and a fourth cylinder housing (407),

-a third piston (415) is arranged movable in the third cylinder housing (405) in a second axial direction (2X),

-a fourth piston (417) is arranged movable in the fourth cylinder housing (407) in the second axial direction (2X),

-a third piston rod (433) extending through a fifth clamping device (425) of the third piston (415) and through a sixth clamping device (426) of the fourth piston (417);

-the third piston (415) is configured to clamp and move the third piston rod (433) a third distance corresponding with a third piston stroke length that the third piston (415) is configured to perform in the third cylinder housing (405);

-the fourth piston (417) is configured to clamp and move the third piston rod (433) a fourth distance corresponding with a fourth piston stroke length that the fourth piston (417) is configured to perform in the fourth cylinder housing (407); wherein the third piston stroke length is longer than the fourth piston stroke length.

The fluid actuator arrangement according to claim 5, wherein the first piston rod (431) and th third piston rod (433) are coupled to each other via a first pivot joint member (480).

The fluid actuator arrangement (1) according to claim 5 or 6, further comprising:

-a fourth piston rod (434) extending through a seventh clamping device (427) of the third piston (415) and through an eight clamping device (428) of the fourth piston (417).

The fluid actuator arrangement (1) according to any of claims 5 to 7, further comprising: -at least a fifth piston rod extending through at least a ninth clamping device of the third piston and through at least a tenth clamping device of the fourth piston.

The fluid actuator arrangement (1) according to any of the preceding claims, further comprising end position cushioning member configured for controlled deceleration of the stroke velocity in both end positions (El, E2) for the respective first (PI, 411) and second piston (P2, 413) in the respective first (CI, 401) and second (C2, 403) cylinder housing.

10. The fluid actuator arrangement (1) according to any of the preceding claims, wherein the piston having the shortest stroke length determines a resolution (r) of the motion of the piston rod, and the next following piston stroke length is determined by a multiple value (m) raised to one multiplied by the resolution (r).

11. The fluid actuator arrangement (1) according to claim 10, wherein the next succeding piston stroke length is determined by the multiple value (m) raised to two (n) multiplied by the resolution (r), and the next subsequent piston stroke length is determined by the multiple value (m) raised to three (n) multiplied by the resolution (r).

12. The fluid actuator arrangement (1) according to claim 10 or 11, wherein the multiple value (m) is set to 2, 5, 10 or any other suitable value and may be varied depending on requirements on the total stroke length that is required and/or depending on time requirements.

13. A method of moving a first piston rod by means of a fluid actuator arrangement (1)

comprising:

-a first cylinder housing (CI, 401) and a second cylinder housing (C2, 403),

-a first piston (PI, 411) comprising a first clamping device (Kl, 421), the first piston (PI, 411) is arranged movable in the first cylinder housing (CI, 401) in a first axial direction (X), -a second piston (P2, 413) comprising a second clamping device (K2, 422), the second piston (P2, 413) is arranged movable in the second cylinder housing (C2, 403) in the first axial direction (X),

-a first piston rod ( l, 431) extending through the first clamping device (Kl, 421) and through the second clamping device (K2, 422);

-the first piston (PI, 411) is configured to clamp and move the first piston rod (Rl, 431) a first distance corresponding with a first piston stroke length (SL1) that the first piston (PI, 411) is configured to perform in the first cylinder housing (CI, 401);

-the second piston (P2, 413) is configured to clamp and move the first piston rod (Rl, 431) a second distance corresponding with a second piston stroke length (SL2) that the second piston (P2, 413) is configured to perform in the second cylinder housing (C2, 403); wherein -the first piston stroke length (SL1) is longer than the second piston stroke length (SL2); the method is characterized by the steps of:

-engaging the first clamping device (Kl, 421) of the first piston (PI, 411) to the first piston rod (Rl, 431);

-disengaging the second clamping device (K2, 422) of the second piston (P2, 413) from the first piston rod (Rl, 431);

-moving the first piston (PI, 411) said first piston stroke length (SL1) in a feeding mode; -engaging the second clamping device (K2, 422) of the second piston (P2, 413) to the first piston rod ( l, 431);

-disengaging the first clamping device (Kl, 421) of the first piston (PI, 411) from the first piston rod (Rl, 431); and

-moving the second piston (P2, 413) said second piston stroke length (SL2) in a fine tuning mode.

14. The method according to claim 13, wherein

-the first piston (PI) comprises a third clamping device (423) and the second piston (P2) comprises a fourth clamping device (424), and

-at least one second piston rod extends through the third clamping device (423) and through the fourth clamping device (424);

the method is characterized by the steps of:

-engaging the third clamping device (423) of the first piston (411) to the second piston rod (432);

-disengaging the fourth clamping device (424) of the second piston (413) from the second piston rod (432);

-moving the first piston (411) said first piston stroke length (SL1) in a feeding mode;

-engaging the fourth clamping device (424) of the second piston (413) to the second piston rod (432);

-disengaging the first clamping device (421) of the first piston (411) from the first piston rod (431); and

-moving the second piston (413) said second piston stroke length (SL2) in a fine tuning mode.

15. The method according to claim 13 or 14, wherein the fluid actuator arrangement (1) further comprising:

a third cylinder housing (405) and a fourth cylinder housing (407),

a third piston (415) is arranged movable in the third cylinder housing (405) in a second axial direction (2X),

a fourth piston (417) is arranged movable in the fourth cylinder housing (407) in the second axial direction (2X),

a third piston rod (433) extending through a fifth clamping device (425) of the third piston (415) and through a sixth clamping device (426) of the fourth piston (417); the third piston (415) is configured to clamp and move the third piston rod (433) a third distance corresponding with a third piston stroke length that the third piston (415) is configured to perform in the third cylinder housing (405); and the fourth piston (417) is configured to clamp and move the third piston rod (433) a fourth distance corresponding with a fourth piston stroke length that the fourth piston (417) is configured to perform in the fourth cylinder housing (407); wherein the third piston stroke length is longer than the fourth piston stroke length;

the method is characterized by the steps of:

-engaging the fifth clamping device (425) of the third piston (415) to the third piston rod (433);

-disengaging the sixth clamping device (426) of the fourth piston (417) from the third piston rod (433);

-moving the third piston (415) said third piston stroke length in a feeding mode;

-engaging the sixth clamping device (426) of the fourth piston (417) to the third piston rod (433);

-disengaging the fifth clamping device (425) of the third piston (415) from the third piston rod (433); and

-moving the fourth piston (417) said fourth piston stroke length in a fine tuning mode.

16. The method according to any of claim 13 to 15, wherein the method is characterized by the steps of:

-simultaneously engaging the first clamping device (Kl, 421) and the second clamping device (K2, 422) to the first piston rod (431) at the same time.

17. The method according to claim 14 or 15, wherein the method is characterized by the steps of:

-simultaneously engaging the first clamping device (421) and the second clamping device (422) to the first piston rod (431);

-simultaneously engaging the third clamping device (423) and the fourth clamping device (424) to the second piston rod (432).

18. The method according to claim 14, wherein the method is characterized by the steps of:

-simultaneously engaging the fifth clamping device (425) and the sixth clamping device (426) to the third piston rod (433).