The present invention relates to a fluid actuator arrangement according to the preamble of claim 1. The present invention also relates to a method according to claim 12 for raising and lowering a lifting member by means of the fluid actuator arrangement. The invention also regards a data medium storing program comprising a program code, which program when run on a computer executes the method according to claim 12. The invention also regards a lifting member of a lift fork truck comprising a fluid actuator arrangement according to claim 17.

The present invention especially belongs to the manufacture industry making lift fork trucks or similar. It may also concern other industries making use of different types of lifting apparatuses using hydraulic and/or pneumatic actuators.

BACKGROUND

Current fluid actuator arrangements used in different types of masts, such as duplex, triplex, quad masts for forklift trucks are often bulky and require large amount of energy for operation. The mast of a forklift truck is a vertical support that permits raising and lowering the lifting member comprising e.g. a forklift and a carriage. Especially in cases where the lifting member (e.g. a lift fork) is raised to the top of a lift fork truck mast and thus being fully extended, current arrangements limit the visibility for an operator or a driver of the truck. This is caused by bulky current lift cylinders hindering the view through the fully extended mast. The lift cylinders are provided to control the amount by which the mast, the lift fork and carriage being raised or lowered in the vertical.

US 5 190 435 discloses a lift fork truck having a lift fork, which is controlled by multistage hydraulic cylinders arranged in the mast. For providing a better view, the operator place is positioned in a cabin mounted on a pedestal being raised and lowered together with the forks.

SUM MARY OF THE INVENTION There is an object to provide a fluid actuator arrangement comprising a lifting member, which fluid actuator arrangement being defined in the introduction and which is light and compact.

There is also an object to achieve a fluid actuator arrangement that provides better view for an operator operating a lift fork truck. There is also an object to provide a compact fluid actuator arrangement that can produce energy- efficient drives for linear movements using as small number of components as possible.

There is an object to provide an energy saving fluid actuator arrangement.

There is an object to increase the lift capacity of a lifting member. There is furthermore an object to provide a fluid actuator arrangement having low centre of gravity.

This or at least one of said objects has been achieved by a fluid actuator arrangement comprising a first clamping unit coupled to a first actuating unit comprising a first and second cylinder in fluid communication with a fluid supply, wherein a first piston body of the first cylinder comprises a first rod engagement and disengagement device, a second piston body of the second cylinder comprises a second rod engagement and disengagement device, a second clamping unit is coupled to a lifting member; the first clamping unit is arranged around a first rod and the first actuating unit and the second clamping unit are arranged around a second rod.

Preferably, the first clamping unit is rigidly coupled to the first actuating unit via a link element linking the first clamping unit and the first actuating unit together. Suitably, the first clamping unit is bolted to the first actuating unit via a joining member.

Preferably, the first clamping unit is welded to the first actuating unit.

Suitably, the first rod constitutes a first lift mast and/or the second rod constitutes a second lift mast.

By means of the fluid actuator arrangement there is achieved a low center of gravity, especially of the mast, in order to raise the stability. The fluid actuator arrangement thus operates with low energy consumption.

In such way is achieved that synergies are obtained, such as extended working space.

Thereby is achieved a fluid supply having a small oil reservoir.

Preferably, the first engagement and disengagement device comprises a first expandable cavity coupled to the fluid supply. Suitably, the second engagement and disengagement device comprises a second expandable cavity coupled to the fluid supply. Preferably, the first clamping unit comprises a third expandable cavity coupled to the fluid supply.

Suitably, the second clamping unit comprises a fourth expandable cavity coupled to the fluid supply.

Preferably, the first piston body divides the first cylinder into a first and second chamber, at least one of which being coupled to a fluid supply via a valve arrangement.

Suitably, the arrangement comprises a control unit for controlling engagement and disengagement of the first actuation unit and the respective first and second clamping unit.

Preferably, the fluid supply comprises an electric motor and a fluid pump arranged adjacent to the first actuating unit.

In such way is achieved a fluid actuator arrangement that allows high system pressure and enables a compact hydraulic system. By this means is provided a local fluid supply for providing fluid to the fluid actuator arrangement.

Preferably, the fluid actuator arrangement further comprises a third clamping unit coupled to a second actuating unit comprising a third and fourth cylinder, wherein a third piston body of the third cylinder comprises third rod engagement and disengagement device, a fourth piston body of the third cylinder comprises a fourth rod engagement and disengagement device, a fourth clamping unit is coupled to said lifting member, the third clamping unit is arranged around a third rod, the second actuating unit and the fourth clamping unit being arranged around a fourth rod.

Preferably, the first and second mast each constitutes a hollow piston rod with an outer diameter of 60-120 mm, preferably 80-100 mm.

In such way the first rod can be used as both a first mast and a first piston rod. In such way is achieved that the design is light and compact.

Suitably, the fluid actuator arrangement is provided with a first and a second actuating unit arranged parallel with each other and each arranged around two parallel rods instead of one single actuator and rod.

Preferably, the first and/or second and/or further rods of the arrangement exhibit a diameter of 60- 120 mm, preferably 80-100 mm.

In such way the arrangement can manage a large loading force. Suitably, one single rod can be replaced by more than two parallel rods.

Preferably, the fluid supply provides a system pressure of 15 MPa to 45 MPa, preferably 20-30 MPa.

In such way is achieved high lift capacity of the fluid actuator arrangement.

Suitably, the lifting member comprises a lift fork. In such way is achieved a fluid actuator arrangement that provides a better view around for an operator operating a lift fork truck, to which the fluid actuator arrangement is arranged.

In such way is achieved excellent all-round visibility for a lift fork truck operator, especially when he controls the lift fork in high working positions.

In such way there is achieved a small, compact and light weight first actuating unit that can be used for all lifting modes and positions of the lift fork.

By means of the fluid actuator arrangement there is provided high lift force capacity.

Preferably, the first and/or second rod and/or additional rods exhibit an oval cross-section.

In such way is achieved that a large bending moment can be taken by the first and/or second rod.

Suitably, the major axis (longest symmetrical axis) of the oval cross section of the first and/or second rod is oriented in a direction corresponding with the extension of the lifting member extending from the first and/or second rod.

Preferably, the first and/or second rod and/or additional rods are hollow cylindrical rods. In such way is achieved a low-weight design.

This or at least one of said objects has also been achieved by a lift fork truck comprising the fluid actuator arrangement.

This type of design saves weight and provides a compact design with a lower center of gravity of a fork lift truck, which in turn implies outstanding stability.

In such way is achieved a lift fork truck having a very low center of gravity when the lifting member has been lowered to its lowest position. In such way is achieved that no bulky fork drive chains are needed. In such way the number of moving parts can be decreased, which promotes for less service and maintenance.

Preferably, the fluid actuator arrangement is provided for distributing control functionality regarding force and motion rate of the fluid actuator arrangement. Suitably, a control unit controls the valve arrangement to pressurize respective cylinder chamber and pressurize the engagement and disengagement devices in regard to detected features, detected by sensor members.

Preferably, the fluid actuator arrangement provides a first and a second mode of operation of the fluid actuator arrangement. Suitably, the first mode of operation includes that the control unit controls hauling of the first and second cylinder (and thus of the firsts actuating unit) relative the first rod. In such first mode of operation, the respective alternately clamped (to the second rod) first and second piston body -in a respective working stroke- are not moved relative the second rod.

Preferably, a retraction of the respective first and second piston body to a starting point within the respective first and second cylinder is also included in the first mode of operation.

Preferably, the second mode of operation includes that the first and second cylinder of the first actuating unit being locked in position relative the first rod by means of the first clamping unit (coupled to the first actuating unit).

Suitably, in the second mode of operation, the respective first and second piston body alternately clamps around and alternately moves the second rod relative the first rod and in such way thus also moves the second rod relative the first and second cylinder.

Preferably, in the second mode of operation, the lifting member is locked to the second rod by means of the second clamping unit.

Preferably, the first clamping unit features and is configured with the same functionality as the second clamping unit.

Suitably, a first chamber is pressurized with a first pressure, wherein a first piston body will be in engagement with the second rod by means of fluid transferred directly to the engagement and disengagement device via a channel system of the first piston body having an opening entering the first chamber. Preferably, the first engagement and disengagement device is controlled by the first pressure of the pressurized first chamber, wherein said first pressure also acts onto a first expandable inner wall (membrane) formed by a first expandable cavity of the first engagement and disengagement device of the first piston body, which first expandable inner wall thereby expands in radial direction inward toward the second rod envelope surface and clamps around the second rod.

Suitably, the second engagement and disengagement device is controlled by the first pressure of the pressurized third chamber, wherein said first pressure also acts onto a second expandable inner wall (membrane) formed by a second expandable cavity of the second engagement and disengagement device of the second piston body, which second expandable inner wall thereby expands in radial direction inward toward the second rod envelope surface and clamps around the second rod.

Suitably, the first expandable cavity is positioned in the first piston body so that it is coaxial with and parallel with (around) the first expandable inner wall and at a distance from the second rod envelope surface (i.e. coaxial with the second rod).

Preferably, the first engagement and disengagement device is rigidly fixed to the first piston body. Suitably, the second engagement and disengagement device is rigidly fixed to the second piston body.

Suitably, a first pressure of the pressurized first chamber acting onto a piston force area of the first piston body for moving the first piston body in the axial direction.

In such way is achieved that the pressurized fluid simultaneously will act on the expandable inner wall of the engagement and disengagement device engaging the second rod.

Preferably, a first pressure of the pressurized third chamber acting onto a piston force area of the second piston body for moving the second piston body in the axial direction.

Suitably, the second piston body comprises an engagement and disengagement device adapted to be able to engage or disengage the second piston body to/from the second rod arrangement. The engagement of the respective first and second engagement and disengagement device of the first and second piston body respectively is performed alternately.

In such way is achieved an optimal and secure functionality providing accurate performance of the lifting member. The speed and force of the first and second cylinder (relative the first rod in a first mode of operation) and/or of the rod (relative the first and second cylinders in a second mode of operation) can thus be controlled in an efficient way by varying the flow and pressure of the pressurized fluid in discrete steps. Preferably, multiple cylinders and piston bodies are combined in different ways in order to provide the most suitable speed-and-force solution for a specific application.

Suitably, a control unit is arranged to control the valve arrangement (controlling the direction of motion of the first and second cylinder relative the second rod) and to control a respective valve unit coupled to the respective first and second cylinder. Preferably, a valve unit is coupled via a fluid communication means to the respective first and second chamber and to the first and second expandable cavity.

Preferably, the control unit controls the valve arrangement for alternately pressurizing a first and second chamber of the respective first and second cylinder.

Thereby is achieved that the respective engagement and disengagement device alternately being pressurized for providing alternately engagement to the second rod (including an overlapping time period including that both engagement and disengagement devices being engaged with the second rod).

Preferably, the first and second piston body being controlled by the control unit to be clamped in turn on the second rod and being controlled to, substantially all times during an overlapping time period, both being clamped to the second rod wherein the first piston body is not disengaged (undamped) from the second piston rod until the second piston body has been clamped to the second rod during a pre-determined overlapping time period.

In such way is achieved smooth motion of the fluid actuator arrangement.

Suitably, the control unit is provided for controlling the valve arrangement alternately generating a second pressure (lower than the first pressure) to each chamber for retraction of the first and second piston body respectively.

Preferably, a first channel system arranged between the first expandable cavity and the fluid supply.

Suitable, the mass of material forming the expandable first inner wall exhibits a flexible material property providing that the first pressurized expandable cavity will expand the mass of material of the expandable first inner wall in a radial direction (inwardly) towards the second rod for engagement of the first piston body to the second rod.

Preferably, at the same time as the first piston body clamps against the second rod during a predetermined overlapping time period of 1ms - 100 ms, preferably 5ms - 75 ms, and thereafter only the second piston body is controlled to clamp against the second rod.

By alternately clamping the respective first and second piston body to the second rod with said overlapping time period and by alternately pressurizing the respective cylinder chambers of the first and second cylinders there is achieved a smooth motion of the first and second cylinders of the first actuating unit relative the second rod. Suitably, the first expandable cavity (or cavities) extends (extend) around the longitudinal axis of the first piston body and parallel and coaxially with the second rod at a predetermined distance. The first expandable cavity (or cavities) exhibits its prolongation (extends) in a direction corresponding with the cylinder axis and being formed coaxially with an X-axis of the first piston body corresponding with an X-axis of the second rod. Preferably, upon depressurization of the first expandable cavity, the mass of material forming the expandable first inner wall reverts to its original measure.

This or at least one of said objects has been achieved by a method for moving a lifting member of a fluid actuator arrangement, comprising a first clamping unit coupled to a first actuating unit comprising a first and second cylinder, wherein a first piston body of the first cylinder comprises a first engagement and disengagement device and a second piston body of the second cylinder comprises a second engagement and disengagement device, a second clamping unit is coupled to said lifting member; the first clamping unit is arranged around a first rod; the first actuating unit and the second clamping unit is arranged around a second rod, the method comprises the steps of: disengaging the first and second clamping unit; propelling said lifting member and the second clamping unit in motion relative the first and second rod by actuating the first actuating unit;

engaging the first and second clamping unit; and actuating the first actuating unit for propelling the lifting member in motion relative the first rod.

Preferably, the second rod constitutes an inner rod and the first rod constitutes an outer rod. Thereby is achieved that the inner rod is used for lifting the lifting member when the inner rod is positioned adjacent the outer rod and for that the inner rod also can be moved relative the outer rod.

Suitably, the inner rod is comprised of an inner rod arrangement comprising at least two inner rods and the outer rod is comprised of an outer rod arrangement comprising at least two outer rods.

Preferably, the inner rod arrangement comprises the first actuating unit and the second clamping unit and the outer rod arrangement comprises the first clamping unit.

Suitably, the outer rod arrangement comprises the first actuating unit and the second clamping unit and the inner rod arrangement comprises the first clamping unit. Preferably, in a first mode of operation the first rod is stationary with the second rod and in a second mode of operation the second rod is movable relative the first rod.

In such way the second rod can be used as a load-bearing beam and also as a mobile or fixed rod.

Suitably, the transition between the first mode of operation and the second mode of operation is made pulsation free. In such way is achieved a smooth motion of the lifting member.

Thereby is achieved a multiple use of the first and second rods enabling a light weight mast design.

Preferably, a shuttle valve sv is configured to guide the pressurized fluid to the respective cylinder chamber dependent upon which cylinder chamber being pressurized.

Suitably, the upper chambers (first and third cylinder chamber) alternately being pressurized and the respective piston being alternately clamped on the second rod.

In such way is achieved that the first and second cylinders are moved upward pushing the lifting member upward in said first mode of operation.

Preferably, in said second mode of operation, the lower chambers (second and fourth cylinder chambers) alternately being pressurized, the first and second cylinders being held still in position relative the first rod, and respective piston alternately being clamped on the second rod and by said alternately pressurization of the lower chambers the pistons alternately being moved relative the cylinders and propelling the second rod upward relative the first rod and bringing the lifting member upward. Alternatively, the guiding of the pressurized fluid to the respective engagement and disengagement devices may be configured to guide the pressurized fluid to the respective cavity chamber dependent upon which cylinder chamber being pressurized and which mode of operation being used.

Suitably, the fluid could be directed directly to the cavity or via the pressurized cylinder chamber or via a channel system provided in the cylinder wall being in contact with the piston.

Preferably, the method comprises the further step of disengaging the first clamping unit, the second clamping unit and the first actuating unit.

Suitably, the lifting member is lowered by means of gravity.

Preferably, the method comprises the further step of raising said lifting member and the second clamping unit relative the first and second piston rod by actuating the first actuating unit by pushing the lifting member and the second clamping unit upward.

Suitably, the method comprises the further step of lowering said lifting member and the second clamping unit relative the first and second piston rod by actuating the first actuating unit in motion downward and/or lowering the first actuating unit by means of gravity. Preferably, the method also comprises the step of propelling said lifting member and the second clamping unit in motion relative the first and second piston rod by actuating the first actuating unit in contact directly or indirectly with said lifting member and the second clamping unit by means of gravity.

Suitably, the method also comprises the step of raising the lifting member, wherein the second clamping unit rest directly or indirectly on the first actuating unit by means of gravity.

This is also achieved by a lifting member of a lift fork truck comprising a fluid actuator arrangement according to claim 17.

This is also achieved by a data medium storing program adapted for moving a lifting member, and a data medium storing program product according to claim 19.

Preferably, the first actuating unit constitutes a structural part of the lifting member.

Suitably, the first and second piston body being configured to take up bending forces. Further objects and advantages of the described invention will become apparent from a

consideration of the attached drawings and description.

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;

Figs. 2a-2f illustrate a first actuating unit of a second example of a fluid actuator arrangement; Figs. 3a-3b illustrate a fluid actuator arrangement according to a third example;

Figs. 4a-4b illustrate cross sections of exemplary rods of a fluid actuator arrangement according to a fourth and fifth example;

Fig. 5 illustrates a fluid actuator arrangement according to a sixth example;

Figs. 6a-6c illustrate a fluid actuator arrangement according to a seventh example;

Figs. 7a-7b illustrate a fluid actuator arrangement according to an eight example;

Fig. 8 illustrates a lift fork truck comprising a fluid actuator arrangement according to a ninth example;

Figs. 9a-9b illustrate flowcharts showing exemplary methods for controlling the motion of a fluid actuator arrangement according to different aspects; and

Fig. 10 illustrates a control unit according to one aspect of the invention.

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. Fig. la shows a fluid actuator arrangement 1 comprising a first clamping unit 3 coupled to an actuating unit 5 comprising a first 7 and second 9 cylinder (see e.g. Fig. 2) arranged in fluid communication with a fluid supply 11 (see e.g. Fig. 2). A first piston body 13 (see e.g. Fig. 2) of the first cylinder 7 comprises a first rod engagement and disengagement device (clamping device) 15 configured for controlled fluid communication by means of a control unit 61 (see Fig. 2a) with the fluid supply 17. A second piston body 17 of the second cylinder 9 comprises a second rod engagement and disengagement device (clamping device) 19 configured for controlled fluid communication by means of a control unit 61 (see Fig. 2a) with the fluid supply 17. Fig. la shows a second clamping unit 21 that is coupled to a lifting member 23. The first clamping unit 3 is arranged around a first rod 25. The actuating unit 5 and the second clamping unit 21 are arranged around a second rod 27. Fig. la shows that the lifting member 23 has been moved to its lowest position and the second clamping unit 21 rests on the actuating unit 5 by means of gravity. In Fig. lb is shown that the actuating unit 5 is activated (being hauled along the second rod 27), wherein the first 7 and second 9 cylinders (see e.g. Fig. 2) -by means of the alternate working strokes of the respective first and second piston 13, 17- haul the actuating unit 5 comprising the first and second cylinder 7, 9 and pushing the second clamping unit (being disengaged from the second rod 27) together with the lifting member 23 along the second rod 27 in a direction upward. At the same time, the actuating unit 5 (being rigidly coupled to the first clamping unit 3) also moves and/or brings the first clamping unit 3 along the first rod 25 in a direction upward. In Fig. lc is shown that the lifting member 23 has been moved to and has reached an uppermost position on the second rod 27. In this position, the first clamping unit 3 is engaged to the first rod 25 and secures the first actuating unit 5 to the uppermost position reached, in relation also to the first rod 25. The lifting member 23 is secured to the second rod 27 by means of actuating the second clamping unit 21 for clamping it to and around the second rod 27. In Fig. Id is shown that the first actuating unit 5 is activated for hauling the second rod 27 together with thereto secured (by means of the second clamping unit 21) lifting member 23. This is made by alternately clamping of respective first and second piston body (not shown) on the second rod 27 and pressurizing the first and second cylinders (not shown) providing a motion of the respective first and second piston body 13, 17 (see Fig. 2a) relative the cylinders.

Fig. 2a illustrates an example of how a first actuating unit 5 (coupled, rigidly and/or releasable, to a first clamping unit 3) may be configured. The first piston body 13 divides the first cylinder 7 into a first 31 and second 33 chamber, both of which being coupled to a fluid supply 11 via a valve arrangement 35. The first actuating unit 5 is coupled to the first clamping unit 3 via a bar 37. The first actuating unit 5 and the first clamping unit 3 are rigidly bolted to the bar 37. The first engagement and disengagement device 15 of the first actuating unit 5 comprises a first expandable cavity 41 as shown in Fig. 2b. The first expandable cavity 41 is coupled to the fluid supply 11 via the respective first and second cylinder chamber 31, 33 via the valve arrangement 35 in an alternately way controlled by a control unit 61. The second engagement and disengagement device 19 of the first actuating unit 5 comprises a second expandable cavity 43. The second expandable cavity 43 is coupled to the fluid supply 11 via a respective third 32 and fourth cylinder chamber 34 and also via the valve arrangement 35. The second clamping unit 21 (see Fig. 1 a) is preferably designed and configured in the same way as the first clamping unit 3. The first clamping unit 3 comprises a sleeve 71 having an expandable cavity 44 arranged for fluid communication with the fluid supply 11 and is actuated for clamping action on the first rod 25 via a valve device 40 by means of the control unit 61. The sleeve 71 further comprises an expandable inner wall 72 that expands in a direction radially inward toward the first rod 25 envelope surface for providing a clamping action on the rod 25 upon pressurization of the expandable cavity 44, thus locking the first actuating unit 5 in position relative the first rod 25, whereby the first actuating unit 5 is arranged to perform a second mode of operation; moving the second rod 27 by means of the first and second piston body 13, 17 relative the first rod 25. A first mode of operation of the first actuating unit 5 may be defined as "hauling" the first actuating unit 5 along the second rod 27 and thereby moving the lifting member 23 (see Fig. lb) by pushing the second clamping unit 21 in a direction upward and at the same time bringing the first clamping unit 3 in a direction upward along the first rod 25.

The first and second cylinder 7, 9 each comprises the respective first and second engagement and disengagement device 15, 19, each of which being adapted to engage or disengage the first piston body 13 and the second piston body 17 to the second rod 27 envelope surface. The first and second cylinder 7, 9 comprise a common cylinder sleeve 45 provided with a first 46, second 47, third 48 and fourth 49 flange member. The first and second cylinder 7, 9 being rigidly coupled to each other in axial direction along the cylinder axis X by means of bolts 51. The respective first and second piston body 13, 17 is each slidingly arranged in the respective first and second cylinder 7, 9. The respective engagement and disengagement device 15, 19 being controlled by the pressurized fluid (optionally fed from the highest pressurized cylinder chamber 31, 33; 32, 34 of the working cylinder 7, 9 or fed externally from outside). The pressurized fluid is preferably fed to the respective expandable cavity 41, 43 in an alternately way. The pressurizing of the respective expandable cavity 41, 43 implies that the fluid pressure, e.g. via a channel system 38 arranged in the respective piston body 13, 17 or via an external channel system, directly will expand the respective expandable cavity (by e.g. expanding an inner wall portion of the piston body to tightly clamp against the second rod 27 with an inward directed radial force). A shuttle valve sv is configured to guide the pressurized fluid to the respective cylinder chamber dependent upon which cylinder chamber being pressurized. I.e. the upper chambers (cylinder chamber 31, 32) alternately being pressurized and the respective piston being alternately clamped on the second rod 27 which implies that the first and second cylinders are moved upward pushing the lifting member upward in said first mode of operation. In said second mode of operation the lower chambers (cylinder chamber 33, 34) alternately being pressurized, the first and second cylinders are held still in position relative the first rod 25 and respective piston being alternately clamped on the second rod 27 and by said alternately pressurization of the lower chambers the pistons being moved relative the cylinders and propelling the second rod 27 upward relative the first rod 25. Of course, other examples of guiding the pressurized fluid to the respective engagement and disengagement devices are possible to be configured to guide the pressurized fluid to the respective cavity chamber dependent upon which cylinder chamber being pressurized and which mode of operation being present. The fluid could be directed directly to the cavity or via the pressurized cylinder chamber or via a channel system provided in the cylinder wall being in contact with the piston.

The alternately engagement of the first piston body 13 to the second rod 27 and the pressurized expandable first cavity 41 implies that the first piston body 13 propels the second rod 27 a first cylinder stroke length. The engagement of the first piston body 13 to the second rod 27 and the pressurized expandable first cavity 41 implies that the first piston body 13 propels the second rod 27 a first cylinder stroke length. Correspondingly, the second piston body 17 is pressurized and clamps against the second rod 27. This is made at the same time as the first piston body 13 clamps against the second rod 27 during an overlapping time period (under 1 ms - 100 ms, preferably 5 ms - 75 ms) and thereafter only the second piston body 17 is controlled to clamp against the second rod 27. By alternately clamping the respective first and second piston body 13, 17 to the second rod 27 and by alternately pressurizing the cylinder chambers 31, 33; 32, 34 there is achieved a smooth motion of the first and second cylinders 7, 9 of the first actuating unit 5 relative the second rod 27. A control unit 61 controls the valve arrangement 35 to pressurize respective cylinder chamber 31, 33; 32, 34 and the engagement and disengagement devices 15, 19 in regard to detected features (by sensors SI, S2, S3) and motion values of the cylinders 7, 9 plus the piston bodies 13, 17 relatively the second rod 27. This procedure is repeated for continuously moving (pushing) the lifting member 23 upward relatively first and second rod 25, 27 as shown in e.g. Fig. lb. Fig. 2b illustrates the first piston body 13 of the first actuating unit 5 in Fig. 2a. The expandable first cavity 41 of the first piston body 13 is in fluid communication with the respective cylinder chamber 31, 33; 32, 34 of the first cylinder 7. The first and second cylinder chamber 31, 33 are in turn coupled to a fluid supply (not shown). The first and second clamping unit 3, 21 are undamped in the first mode of operation. A fluid communication line 38' is coupled from the fluid supply to the first cavity for providing a clamping action in either first or second mode of operation.

Figs. 2c-2d schematically illustrate said first mode of operation wherein the first and second cylinders 7, 9 of the actuating unit 5 are moved upward relative the first and second rods 25, 27. The first piston body 13 is clamped on the second rod 27 by pressurizing its cavity as shown in Fig. 2c and the first cylinder chamber 31 is pressurised for raising the actuating unit 5 bringing along also the first and second clamping units 3, 21 and lifting member 23. In Fig. 2d is shown achieved full stroke of the first piston body 13 and by the motion upward of the first cylinder 7, and thus motion upward of the actuating unit 5, and the pushing of the undamped second clamping unit 21 coupled to the lifting member 23 upward.

Figs.2e-2f schematically illustrate said second mode of operation wherein the first and second clamping units 3, 21 are clamped on the respective rod. The first and second cylinders 7, 9 are being hold in position relative the first rod 25. The first piston body 13 and the second piston body alternately make working strokes in the first cylinder 7 and being controlled to be clamped on the second rod 27 thus moving the second rod 21 upward. As the lifting member 23 is rigidly coupled to the second clamping unit being clamped on the second rod 21, the lifting member 23 is moved upward. The second piston body is moved downward as a retraction stroke. A shifting between first and second piston body working stroke is performed and the second piston body performs the working stroke in a similar way. The transition between he working stroke of the first piston body and the second piston body is performed with an overlap wherein both piston bodies are clamped on the second rod and move it and will be performed in connection with Fig. 2f.

Fig. 3a illustrates a fluid actuator arrangement 201 according to a third example. In this example there is used a third rod 29 and a fourth rod 30 for lifting a lifting member 23. A second actuating unit 6 is arranged around the fourth rod 30. A second clamping unit 21 is arranged around the second rod 27, which second clamping unit 21 is rigidly (can be demounted) coupled to a lowest part of the third rod 29. A third clamping unit 22 is arranged around the third rod 29 and is rigidly coupled to the second actuating unit 6. The additional rods, actuator units and clamping units co-operate in a way similar to that described above. In Fig. 3b is illustrated that the first actuating unit 5 moves the second rod 27 upward at the same time as the second actuating unit 6 moves the fourth rod 30 upward relative the third rod 29. An example of an actuating unit and a clamping unit is shown in Fig. 2a and Fig. 2b.

Figs. 4a-4b illustrate cross sections of exemplary rods of a fluid actuator arrangement according to a fourth and fifth example. Fig. 4a shows a cross-section of the first rod 25 (and optionally also of the second rod 27) that is oval. The major axis mx (longest symmetrical axis) of the oval cross section of the first rod 25 is oriented in a direction corresponding with extension of the lifting member 23 (e.g. lift fork) extending from the first 25 and second rod 27. The first and second rod 25, 27 are hollow. In Fig. 4b is shown a first rod 25 that exhibits a circular cross-section.

Fig. 5 illustrates a fluid actuator arrangement 501 according to a sixth example. A first piston body 513 of an actuating unit 505 divides a first cylinder 507 into a first 531 and second chamber 533, both being coupled to a fluid supply 511 via a valve arrangement 535. A second piston body 517 of the actuating unit 505 divides a second cylinder 509 into a third 532 and fourth chamber 534, both being coupled to the fluid supply 511 via the valve arrangement 535. The actuating unit 505 is arranged around a second rod 527. The fluid actuator arrangement 501 comprises a control unit 561 for controlling engagement and disengagement of the actuation unit 505 and the respective first 503 and second 521 clamping unit. Optionally, the fluid actuator arrangement 501 may comprise a local electric motor (not shown) and a local fluid pump (not shown) arranged adjacent the first actuating unit 505 for feeding the respective cylinder 508, 509 with pressurized fluid. A first clamping unit 503 is rigidly coupled to the actuating unit 505 via a joining member 504. The first clamping unit 503 is arranged for clamping around a first rod 525. A lift fork 523 is coupled to a second clamping unit 521. The second clamping unit 521 is arranged for clamping around the second rod 527. Optionally, a dampener and/or spacing member 577 is arranged between the first actuating unit 505 and the second clamping unit 521. When the first actuating unit 505 hauls along the second rod 527 and it pushes the second clamping unit 521 (being disengaged from the second rod 527) and the lifting member 523 upward, the dampener 577 serves as a support on to which the second clamping unit 521 rests by means of gravity. The fluid actuator arrangement 501 is adapted to raise and lower the lift fork 523. In a first mode of operation, the actuating unit 505 operates by moving the cylinders 507, 509 (the cylinders are rigidly coupled to each other) along the second rod 527, pushing the lift fork 523 and undamped second clamping unit 521 upward and also bringing the first clamping unit 503 upward. When lowering the actuating unit 505, the lift fork 523 and the undamped second clamping unit 521 by means of gravity will be lowered and supported by the actuating unit 505 (via the dampener 577). During the first mode of operation, the first and second clamping units 503, 521 are disengaged for sliding performance along the respective first 525 and second 527 rod. The lift fork 523 is moved together with the second clamping unit 521 relatively the second rod 527 by actuating of the actuating unit 505. In a second mode of operation, the first and second cylinders

507, 509 being locked in position relative the first rod 525 by means of clamping of the first clamping unit 503 to the first rod 525. The first clamping unit 503 is rigidly coupled to the first actuating unit 505. This second mode of operation also comprises the step of locking the lift fork 523 to the second rod 527 by means of the second clamping unit 521 (preferably being rigidly coupled to the lift fork 523) clamping around the second rod 527. The second mode of operation comprises the positioning of the actuating unit 505 standing in position relatively the first rod 525. The first and second cylinders 507, 509 are thus locked relative the first rod 525. In this position, the actuating unit 505 is controlled by the control unit 561 to raise the second rod 527 by means of alternately clamping the piston bodies 513, 517 around the second rod 527. The lifting member 523 is locked in position relative the second rod 527 by clamping the second clamping unit 521 to the second rod 527. The lifting member 523 is fixedly coupled to the second clamping unit 521. In this second mode of operation the first and clamping unit 503, 521 are controlled by the control unit 561 to clamp or unclamp and to actuating the actuating unit 505 for propelling the lifting member 523 in motion relative the first rod 525. The first clamping unit 503 comprises a third expandable cavity C3 coupled to the fluid supply 511. The second clamping unit 521 comprises a fourth expandable cavity C4 coupled to the fluid supply 511. The respective cavity C3, C4 is configured to expand an inner wall of the respective clamping unit 503, 521 for clamping action on the respective rod upon pressurization of the respective cavity C3, C4, thereby locking the respective actuating unit 503 and the lifting member 523 to the respective rod.

Figs. 6a-6c illustrate a fluid actuator arrangement 601 according to a seventh example. This example shows a mast frame 691 comprising outer rods 625 and a centre rod 627. An actuating unit 605 is arranged around the centre rod 627 and is rigidly coupled to a respective outer clamping unit 603 being arranged on the respective outer rods 625. A centre clamping unit 621 is arranged on the centre rod 627 and is rigidly coupled to a forklift 623. In Fig. 6a is shown a first mode of operation managed by a control unit 660, wherein the actuating unit 605 is controlled to raise and push the centre clamping unit 621 upward together with the forklift 623. The actuating unit 605 also brings the outer clamping units 603 (being undamped) along the outer rods 625. In Fig. 6 b is shown the very last moment of the first mode of operation and the actuating unit 605 has reached the uppermost position. Thereafter a second mode of operation is managed by the control unit 660. The outer clamping units 603 are locked to the outer rods 625 as shown in Fig. 6b for locking the actuating unit 605 in fixed position relative the outer rods 625. The centre clamping unit 621 is controlled to clamp around the centre rod 627 for fixating the forklift 623 to the centre rod 627. The actuating unit 605 is in the second mode of operation activated to propel the centre rod 627 relative the outer rods 625. Inner guide frame stabilize the forklift 623 raising.

Figs. 7a-7b illustrate a fluid actuator arrangement 701 according to an eight example. Fig. 7a shows a mast arrangement 700 having outer rods 725 of an outer frame 780 and inner rods 727 of an inner frame 782. Outer clamping units 703 are releasable coupled to a pair of actuating units 705. Each inner rod 727 each comprises an inner clamping unit 721, both of which are releasable coupled to a forklift 723. A control unit 760 controls the raising and lowering of the forklift 723 by means of controlling the actuation of the outer clamping units 703, the inner clamping units 721 and the actuating units 705. Fig. 7b shows the fluid actuator arrangement 701 in a view from below. The forklift 723 comprises a first and second forklift prong 750, 751, which are controllable in motion by the control unit 760 (see Fig. 7a) relative each other in horizontal direction by means of an actuator arrangement similar in design and configuration to that of the actuating unit 705. Fig. 8 illustrates a lift fork truck 800 comprising a fluid actuator arrangement 801 according to a ninth example. A control unit 860 is arranged within the truck 800 for controlling the fluid actuator arrangement 801. A forklift 823, an actuating unit 805 and a first 803 and second clamping unit 821 are arranged to a mast device 870 of the lift fork truck 800 in a similar way as described above, wherein the upper position of the forklift 823, the actuating unit 805 and clamping units 803, 821 being marked with dashed lines.

Figs. 9a-9b illustrate flowcharts showing exemplary methods for controlling the motion of a fluid actuator arrangement according to different aspects. Fig. 9a illustrates a method for raising and lowering a lifting member of a fluid actuator arrangement, comprising a first clamping unit coupled to an actuating unit comprising a first and second cylinder, wherein a first piston body of the first cylinder comprises a first engagement and disengagement device and a second piston body of the second cylinder comprises a second engagement and disengagement device, a second clamping unit is coupled to said lifting member; the first clamping unit is arranged around a first rod; the actuating unit and the second clamping unit is arranged around a second rod. The method shown in Fig. 9a illustrates a first step 901 comprising the start of the method. A second step 902 illustrates the operating of the actuator arrangement. A third step 903 illustrates a stop of the method. The second step 902 may comprise the steps of; disengaging the first and second clamping unit; propelling said lifting member and the second clamping unit in motion relative the first and second piston rod by actuating the actuating unit; engaging the first and second clamping unit; and actuating the actuating unit for propelling the lifting member in motion relative the first piston rod.

Fig. 9b illustrates a further example of the method. Step 1001 illustrates start of the method. Step 1002 shows disengaging of the first and second clamping unit. Step 1003 shows propelling of said lifting member and the second clamping unit in motion relative the first and second piston rod by actuating the actuating unit. Step 1004 shows engaging of the first and second clamping unit. Step 1005 shows actuating of the actuating unit for propelling the lifting member in motion relative the first piston rod. Step 1006 shows disengaging of the first clamping unit, the second clamping unit and the actuating unit. Step 1007 shows propelling of said lifting member and the second clamping unit in motion relative the first and second piston rod by actuating the actuating unit in contact with said lifting member and the second clamping unit by means of gravity. In Step 1008 the method is fulfilled and stopped.

Fig. 10 illustrates a CPU device 2000 according to one aspect of the invention. The control unit 860 of the fluid actuator arrangement described in Fig. 8 may comprise the CPU device 2000 of a computer. The CPU device 2000 comprises a non-volatile memory NVM 2020, which is a computer memory that can retain stored information even when the computer is not powered. The CPU device 2000 further comprises a processing unit 2010 and a read/write memory 2050. The NVM 2020 comprises a first memory unit 2030. A computer program (which can be of any type suitable for any operational data) is stored in the first memory unit 2030 for controlling the functionality of the CPU device 2000.

Furthermore, the CPU device 2000 comprises a bus controller (not shown), a serial communication port (not shown) providing a physical interface, through which information transfers separately in two directions. The CPU device 2000 may comprise any suitable type of I/O module (not shown) providing input/output signal transfer, an A/D converter (not shown) for converting continuously varying signals from detectors (not shown) arranged to the fluid actuator arrangement and from other monitoring units (not shown) of the fluid actuator arrangement into binary code suitable for the computer.

The CPU device 2000 also comprises an input/output unit (not shown) for adaption to time and date. The CPU device 2000 also comprises an event counter (not shown) for counting the number of event multiples that occur from independent events in operation of the fluid actuator arrangement.

Furthermore, the CPU device 2000 includes interrupt units (not shown) associated with the computer for providing a multi-tasking performance and real time computing for operating a first and second mode of operation as described above. The NVM 2020 also includes a second memory unit 2040 for external controlled operation.

A data medium storing program P, comprising program routines, is adapted for controlling the valve arrangement and is provided for operating the CPU device 2000 for performing the method described. The data medium storing program P may comprise routines for providing smooth motion of the fluid actuator arrangement in an automatic or semi-automatic way. The data medium storing program P comprises a program code stored on a medium, which is readable on the computer, for causing the control unit (e.g. the control unit marked with reference number 860) to perform the operation of the fluid actuator arrangement by controlling the fluid actuator arrangement to raise and lower a lifting member of a fluid actuator arrangement, comprising a first clamping unit coupled to an actuating unit comprising a first and second cylinder, wherein a first piston body of the first cylinder comprises a first engagement and disengagement device and a second piston body of the second cylinder comprises a second engagement and disengagement device, a second clamping unit is coupled to said lifting member; the first clamping unit is arranged around a first rod; the actuating unit and the second clamping unit is arranged around a second rod, the method comprises the steps of; disengaging the first and second clamping unit; propelling said lifting member and the second clamping unit in motion relative the first and second piston rod by actuating the actuating unit; engaging the first and second clamping unit; and actuating the actuating unit for propelling the lifting member in motion relative the first piston rod; and repeating the steps for moving the piston rod further distance. The data medium storing program P further may be stored in a separate memory 2060 and/or in the read/write memory 2050. The data medium storing program P, in this embodiment, is stored in executable or compressed data format.

It is to be understood that when the processing unit 2010 is described to execute a specific function that involves that the processing unit 2010 may execute a certain part of the program stored in the separate memory 2060 or a certain part of the program stored in the read/write memory 2050.

The processing unit 2010 is associated with a data port 2099 for communication via a first data bus 2015. The non-volatile memory NVM 2020 is adapted for communication with the processing unit 2010 via a second data bus 2012. The separate memory 2060 is adapted for communication with the processing unit 2010 via a third data bus 2011. The read/write memory 2050 is adapted to communicate with the processing unit 2010 via a fourth data bus 2014. The data port 2099 is preferably connectable to data links of the fluid actuator arrangement.

When data is received by the data port 2099, the data will be stored temporary in the second memory unit 2040. After that the received data is temporary stored, the processing unit 2010 will be ready to execute the program code, according to the above-mentioned procedure. Preferably, the signals (received by the data port 2099) comprise information about operational status of the fluid actuator arrangement, such as operational status regarding the position of the first and second rod relative the first and second cylinder. It could also be operational data regarding the speed and brake performance of the fluid actuator arrangement. According to one aspect, signals received by the data port 2099 may contain information about actual positions of the lifting member by means of sensor members. The received signals at the data port 2099 can be used by the CPU device 2000 for controlling and monitoring of the first and second modes of operation in a cost-effective way. The signals received by the data port 2099 can be used for automatically moving the lifting member between two end positions. The signals can be used for different operations of the fluid actuator arrangement. The information is preferably measured by means of suitable sensor members of the fluid actuator arrangement. The information can also be manually fed to the control unit (e.g. the control unit marked with reference number 860) via a suitable communication device, such as a personal computer display.

The method can also partially be executed by the CPU device 2000 by means of the processing unit 2010, which processing unit 2010 runs the data medium storing program P being stored in the separate memory 2060 or the read/write memory 2050. When the CPU device 2000 runs the data medium storing program P, suitable method steps disclosed herein will be executed. A data medium storing program product comprising a program code stored on a medium is also provided, which product is readable on the computer, for performing the method steps according to claim 12, when the data medium storing program P according to claim 18 is run on a control unit (e.g. a control unit marked with reference number 61, 561, 660, 760, 860 above).

The arrangement may according to different aspects be adapted to one or several of various industrial segments; construction industry, transport industry, marine industry, liftfork manufacture industry, etc. The arrangement is not limited to be used in such segments, but also other industrial segments are possible.

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 valve arrangement may comprise a logic valve of suitable type. The valve arrangement may comprise a 3 ports/2 valve positions, so called 3/2 valve or others, or may comprise a two-way valve of any type suitable for control of the fluid actuator arrangement. The manoeuvring of the valve arrangement may be performed by means of a solenoid connected to a control unit adapted for controlling the valve arrangement and raising and lowering the lifting member. The fluid actuator arrangement may be adapted for fast and high clamp force engagement of the piston body for propelling the latter accurate also for acceleration of heavy loads. By control of the valve arrangement including e.g. a logical valve is provided that the fluid actuator arrangement is capable to optionally perform lower force and/or slower motion rate of the lifting member. A logical valve can be manoeuvred by the control unit to shut down the fluid flow to excluded cylinder/cylinders and direct fluid flow to only one cylinder. There are different types of valves that can be used for providing the above-mentioned aspects and other aspects. Electro- hydraulic controlled valves, other types of directly controlled electro-hydraulic logical valves, etc.