Method for lifting and / or lowering a mast assembly of a material handling vehicle and a material handling vehicle

Abstract

Method for operating a lifting and / or lowering movement of a mast assembly (2) comprised in a material handling vehicle (1), wherein a first element (3) of the mast assembly and a load carrier (7 are movable at the same time. There is also disclosed a material handling vehicle (1) comprising, a mast assembly(2), comprising at least a first element (3) and a second element (4), a hydraulic system (30), comprising a first hydraulic cylinder (5) and a second hydraulic cylinder (6), a load carrier (7) arranged movable along a length direction on the first section element (3) from a first lower end point (8) to a second upper endpoint (9), at the same time as the first element is moving.

Description

[0001] The present patent application is related to a method at a material handling vehicle according to the pre-characterizing part of Claim 1, and a material handling vehicle according to claim 8.BACKGROUND

[0002] It is known to adjust the decent speed of a material handling vehicle depending on the load, see for example EP 3 533 752 B1, which discloses an industrial truck with two different maximum lowering speeds.SHORT DESCRIPTION OF THE INVENTION

[0003] It is thus an improvement of current material handling vehicles, such that the lowering and / or lifting of any load may be increased effectively. It is thus proposed a method for operating a lifting and / or lowering movement of a mast assembly comprised in a material handling vehicle. The mast assembly comprising at least a first mast element and a second mast element. The first element is movable in relation to the second element to extend or contract the mast assembly. The first mast element comprises a load carrier arranged to be movable along the first mast element from a first lower endpoint to a second upper endpoint. The load carrier is powered by at least one first hydraulic cylinder. The first mast element is powered by at least one second hydraulic cylinder. The method comprises the steps of: extend or contract the mast assembly by moving the first mast element along the second mast element.

[0004] The movement of the load carrier is arranged such that the load carrier and the first mast element moves at the same time and in the same direction, for at least a predetermined portion of the load carrier's movement.

[0005] The advantages being, that an increased lowering speed may be achieved that will still be safe and have the possibility to increase the safety of the operation of the material handling vehicle as the time which a load needs to be lifted higher up, may be reduced. And in the same way an increased lifting speed may also be achieved, in a safe and reliable way.

[0006] In a further development a method according to claim 2 is proposed.

[0007] If the second mast element is a fixed mast element, in general the first mast element is the final element of the mast assembly. If the second mast element is not a fixed mast element a further mast element is included in the mast assembly. Thus, the second element will also be movable in relation to this further mast element.

[0008] In a further development a method according to claim 3 is proposed.

[0009] The advantage of controlling the specific hydraulic valves, is that this is safe and reliable solution.

[0010] In a further development a method according to claim 4 is proposed.

[0011] By also closing valves in the different lifting and lowering operations a much more effective method is achieved, for example in relation to valves only closed partly.

[0012] By controlling the hydraulic valves, a safe and reliable operation is achieved.

[0013] In a further development a method according to claim 5 is proposed.

[0014] The advantage is that the safe operation of the mast assembly and the load carrier is kept. I.e. for example the first element is in its lowest configuration, when the load carrier is still at a higher position, which allows for the operator of the material handling vehicle, to move the vehicle without the vehicle being higher than normal. I.e. the first element does not protrude higher up, which may lead to the first element to hit lower obstacles from roof, doorframes etc.

[0015] In a further development a method according to claim 6 is proposed.

[0016] By implementing a stopping of the load carrier before reaching a lower end point when lowering, the operation of the material handling vehicle is simplified. For example an operator may lower the cargo and then move with the vehicle, instead of needing to directly stop the load from reaching the ground / floor level. In a corresponding lifting operation a very good indication on when a lifted cargo from ground / floor level is sufficiently high for moving the vehicle is achieved.

[0017] In a further development a method according to claim 7 is proposed.

[0018] By adapting the speed of the load carrier and the first mast element a more precise and safer operation of the material handling vehicle is achieved.

[0019] There is also proposed a material handling vehicle comprising, a mast assembly, comprising at least a first mast element and a second mast element. Further the vehicle comprises a hydraulic system , comprising a first hydraulic cylinder and a second hydraulic cylinder. Further the vehicle comprises a load carrier arranged movable along a length direction on the first mast element from a first lower end point to a second upper endpoint by means of said first hydraulic cylinder. The first mast element is movable in longitudinal direction in relation to the second mast element, by means of the said second hydraulic cylinder. The material handling vehicle further comprises a control unit. The control unit is arranged to send and receive output and input from the hydraulic system. Thus, the control unit is arranged such that it controls the movements of the first and second hydraulic cylinders. Thus the control unit controls the movement of the load carrier and the movement of the first mast element in relation to the second section element. The control unit is arranged such that such that the movement of the load carrier along the first mast element is made at the same time as the first section element moves in relation to the second mast element, at least for a predetermined portion of said movement.

[0020] The advantage of the material handling vehicle is that the lifting and / or lowering operation is more effective. The time for lifting and / or lowering is reduced. Thus, the material handling vehicle is arranged, such that the vehicle will be controlled to have the increased speed of lifting and / or lowering.

[0021] In a further development a material handling vehicle according to claim 9 is proposed.

[0022] By controlling the hydraulic valves an effective and safe way of arranging the vehicle is achieved.

[0023] In a further development a material handling vehicle according to claim 10 is proposed.

[0024] The advantage is that the safe operation of the mast assembly and the load carrier is kept. I.e. for example the first element is in its lowest configuration, when the load carrier is still at a higher position, which allows for the operator of the material handling vehicle, to move the vehicle without the vehicle being higher than normal. I.e. the first element does not protrude higher up, which may lead to the first element to hit lower obstacles from roof, doorframes etc.

[0025] In a further development a material handling vehicle according to claim 11 is proposed.

[0026] By adding a predetermined distance from the lower end point of the load carriers movement range, there is a way to improve the operation of the material handling vehicle, such that the operator may immediately start moving with a lowered cargo. And also when lifting an improvement is that as the operator sees that the first mast element starts moving, he may easily start moving with the cargo he lifted from the ground or floor.

[0027] There is also proposed a computer program product according to claim 12 and there is also proposed a computer-readable storage medium according to claim 13.LIST OF DRAWINGS

[0028] Fig. 1 Discloses a material handling vehicle according to the disclosure. Fig. 2A discloses a mast assembly according to the disclosure with the load carrier at a first lower endpoint of a first section element. Fig. 2B discloses the load carrier after a movement along the first section element. Fig. 2C discloses the load carrier at the second upper endpoint. Fig. 3A discloses the first section element lifted to an upper endpoint. Fig. 3B discloses a movement of the load carrier and the first section element at the same time, in a lifting or lowering movement. Fig. 3C discloses the movement of Fig. 3B but at a lower point for both the load carrier and the first section element. Fig. 3 D discloses the stopped load carrier, when the first section moves. Fig. 3E discloses the first section being at the lower endpoint, with the load carrier at the predetermined stop distance from the lower end point. Fig. 4 discloses an hydraulic system used in the method of the disclosure and comprised in a material handling vehicle of the disclosure. Fig. 5 Method flowchart according to the disclosure. Fig. 6 discloses speed of the first mast element as a function of weight of a load according to one aspect. Fig. 7 discloses speed of the load carrier as a function of weight according to one aspect. Fig. 8 discloses speed of the load in relation to a fixed object, when both the load carrier is moving and the first mast element is moving. DETAILED DESCRIPTION

[0029] The present disclosure is related to material handling vehicles 1, see Fig. 1. The vehicle can also be named a truck, but not to be confused with a lorry. The material handling vehicle 1 has a load carrier 7 in most cases comprising two forks. The load carrier can also be a gripping device, a lifting module comprising an operator etc. The material handling vehicle 1 is powered by a drive motor 24 that provides the ability to move the material handling vehicle 1. The vehicle also has a hydraulic system 30, see Fig. 4. The hydraulic system comprises a pump 21 that is driven by a pump motor 23. The power source in the vehicle is in general a battery 25. The battery may be a lead acid battery or a Lithium Ion battery or any other type of battery. The battery is rechargeable. The material handling vehicle 1 is mainly designed to operate indoors. The vehicle 1 is preferred to not release any exhaust gas, such as CO 2 or the like. The vehicle 1 has the ability through the hydraulic system 30 to lift pallets, goods, material from floor level to a higher level.

[0030] The present disclosure is related to a material handling vehicle 1, as exemplified in Fig. 1 which discloses a high lifting material handling vehicle 1. However the material handling vehicle 1 can be any load lifting material handling vehicle, such as a stacker, an order picking truck with a stacking ability, a very narrow isle truck, etc. The material handling vehicle 1 has a mast assembly 2, as can be seen in Fig. 1. The mast assembly 2 is a telescopic mast assembly, comprising one or several mast elements 3 and 4 etc. One mast element 31 is in general a fixed mast element, the other further mast elements 3, 4 are movable in essentially vertical direction. Thus, the disclosed mast assembly 2 of Fig. 1 has a telescopic function that may extend the mast assembly 2 from a first height, to essentially a height of two, three times or more, the height of the mast assembly 2 as contracted. The material handling vehicle 1 has a load carrier 7. In the exemplified material handling vehicle 1, the load carrier 7 comprises a pair of forks 32, with an ability to rotate in a horizontal plane. However, for the disclosure the load carrier 7 may be a load carrier with forks 32 pointing in the line of the travel of the material handling vehicle 1, or in any other configuration. In particular Figures, 2A, 2B, 2C, 3A, 3B, 3C, 3D and 3E, the load carrier 7 is pointing out of the figures towards the viewer.

[0031] The first mast element 3 is essentially a frame of steel, that has a longitudinal or height direction that is longer than the width direction. The same is applicable for the second mast element 4. The first element 3 is slidable on the second element 4, preferably by rollers applied in tracks on the second mast element 4. Sliding motion is essentially in vertical direction. The exemplified fixed mast element 31 is in general the same steel frame as the other mast elements 3, 4 etc., but is attached to the chassis of the material handling vehicle 1.

[0032] The first mast element 3 comprises the load carrier 7. The load carrier 7 is slidable along the height direction of the first mast element 3, i.e. this slidable movement may be seen in Fig. 2A, 2B and 2C. The sliding movement has two endpoints, 8 and 9. The lower endpoint 8 is when the load carrier 7 is at the bottom of the first mast element 3. The higher endpoint 9 is when the load carrier 7 is at the top of the first mast element 3, Fig. 2A. To power the slide movement of the load carrier 7 there is a first hydraulic cylinder 5. As the first mast element 3 moves in relation to the second element 4, the hydraulic cylinder 5 moves with the third element, this can be seen in Fig. 2A and 2B. The first mast element 3 is movable along the second mast element 4, by means of a second hydraulic cylinder 6. The second hydraulic cylinder 6a is shown as attached at the bottom of the second mast element 4, this is merely an alternative, the second hydraulic cylinder 6a may for example be attached at the middle of the height of the second element 4. In general the second hydraulic cylinder 6 operates in a pair 6a and 6b. Such as disclosed in Fig. 4, where two second hydraulic cylinders 6a, 6b are disclosed. One may also call the second cylinders 6a, 6b the main lift cylinders 6a, 6b, which operates in order to extend the mast assembly 2. But it is thinkable to only have a single second cylinder 6 / 6a.

[0033] The second element 4 is movable also on the mast assembly 2, with a not shown hydraulic cylinder.

[0034] The material handling vehicle 1 thus, have an hydraulic system 30 as shown in Fig. 4. The main elements of the hydraulic systems is hydraulic valves 11, 12, 13 and 14, and hydraulic lines 15, 16, 18, 19, and 20. There is also comprised an hydraulic pump 21 driven by a motor 28. The hydraulic system further comprises one or several pressure compensators 38, 39, Fig. 5, that help the lifting / lowering speed of a load to be constant regardless of the weight of the load.

[0035] The material handling vehicle 1 further comprises a control unit 20. The control unit 20 is in general a computer comprising a processor, memory and the necessary interfaces to communicate with comprised sensors of the material handling vehicle. The control unit 20 is arranged such that it may send out control signals and receive input from the controlled devices of the material handling vehicle 1. In particular the control unit may store software that may control the hydraulic pump 21, but also each hydraulic valve.

[0036] The disclosure is related to a particular way of arranging the material handling vehicle 1, in that the material handling vehicle 1 is arranged such that the load carrier 7 and the first mast element 3 may move at the same time by being powered by the first and second hydraulic cylinders 5, 6a, at the same time. This, movement is in general to be understood to be in the same direction.

[0037] In order for this to take place it is necessary to open and close the hydraulic valves in a particular way, see Fig. 5. The hydraulic system 30 has a valve 11 that is related to allowing hydraulic fluid to move from the first hydraulic cylinder 5 to a reservoir 22 of the material handling vehicle 1. Thus, if the hydraulic valve 11 is open, the first hydraulic cylinder 5 will contract by means of gravity and in that hydraulic fluid moves out of hydraulic cylinder 5 and follows the hydraulic line 15 to the hydraulic line 18 and into the reservoir or tank 22, thus the load carrier 7 moves along mast element 3 in a lowering of the load carrier 7. Also, if valve 12 is open hydraulic fluid may in the same way flow out from the second hydraulic cylinder 6a through the line 16 and through hydraulic valve 12 to the line 18 and into the reservoir 22, thus mast element 3 moves along mast element 4 in a lowering of the mast element 3. This is of course also true if there are a third hydraulic cylinder 6b that works in pair with the second hydraulic cylinder 6a. As the exemplified hydraulic system 30 is disclosed with the second and the third hydraulic cylinders 6a, 6b on the same hydraulic line 40, opening of valve 12 will lead to that both the second and the exemplified third hydraulic cylinder 6b will have hydraulic fluid exiting. Thus, the material handling vehicle 1 is arranged to be able to open hydraulic valves 11 and 12 at the same time. Thus, the lowering movement from an elevated mast assembly 2 of the load carrier 7, may be made in a synchronized manner with both a moving first mast element 3 and a moving load carrier 7 in relation to the moving first mast element 3. It is thinkable to arrange this such that the synchronized movement of the load carrier 7 and the first mast element 3 is only made during a portion of the movement, for example as shown in Fig. 3A the load carrier and the first element 3 moves at the same time through Fig. 3A, 3B, and 3C, but it is thinkable to let the first mast element 3 move to an endpoint 17 first, and then thereafter move the load carrier 7 from position of Fig. 2B to the position of Fig. 2A. This is preferably made by stopping the load carrier 7 a predetermined distance X from the lower end point 8 of the load carrier 7, see Fig. 3D, 3E. Thus, as seen in Fig. 3D and 3E the load carrier 7 is stopped above the lower end point 8, but the first mast element 3 continues moving down to its respective lower endpoint 17. During the portion of synchronized movement there are preferably check valves 36, 37, that prevent the hydraulic fluid from going back to the pump 21. Even if the pump 21 is in general not in operation at a lowering movement, it is unnecessary to risk that hydraulic fluid under pressure is running in the backwards direction of the pump 21. The first mast element 3 has also a high endpoint 26 as shown in Fig. 3A.

[0038] The material handling vehicle 1 is also arranged to perform the same operation when lifting the load carrier 7. Thus, the load carrier and the first element 3 may move upwards by extending both the first hydraulic cylinder 5 and the second / third hydraulic cylinder / ers 6a and / or 6b at the same time.

[0039] This operation requires the opening of hydraulic valves 13 and 14, which will provide a hydraulic fluid flow from the reservoir 22 by the pump 21 through lines 19 and 20 to the respective first and second hydraulic cylinder 5 and 6, and exemplified second and third 6a, 6b cylinders. The hydraulic valves 11 and 12 are preferred to be closed in this operation, to avoid unnecessary circulation of hydraulic fluid to the reservoir through line 18.

[0040] The disclosure is thus related to a method operating a lifting and / or lowering movement of the mast assembly 2 of the material handling vehicle 1. The method steps being: extend that mast assembly 2 by moving the first mast element 3 along the second mast element 4.

[0041] Further, the movement of the load carrier 7 is arranged such that the load carrier 7and the first mast element 3 moves at the same time and in the same direction, for at least a predetermined portion of the load carrier's movement.

[0042] The method thus, resulting in an increased lifting and lowering speed as compared to the conventional way of lifting, i.e. that the load carrier first reaches the upper end point 9, and there after the first element 3 starts to move in relation to the second element 4.

[0043] The method also includes controlling the hydraulic valve assembly with a first valve 11, and a second valve 12, that are both used in the method when performing the steps of lowering. The method also includes closing valves 13 and 14 as mentioned above. And further the method includes the opening of valves 13 and 14 when performing a lifting operation, and also closing valves 11 and 12 in that operation.

[0044] The control unit 20 thus, comprises computer executable software that may perform the method steps. There are a bus system comprised on the material handling vehicle 1 for sending and receiving signals of the control unit 20. And there are not described actuators and switches that may control the hydraulic valves to be open or closed, as well as the pump 21 to operate or be at rest.

[0045] It has been found beneficial, set a condition for the synchronized movement of the load carrier 7 and the first element 3, such that before the load carrier 7 reaches the lower end point 8, the first element 3 has reached the lower end point 17. I.e. the first section element 3 is fully retracted in relation to the second element 4 and thus essentially parallel on all sides with the second element 4. In particular it will configure the mast assembly to be in its lowest configuration, thus making the material handling vehicle 1 low, and steady once the load carrier 7 is moving the final distance to the bottom end point 8.

[0046] The load carrier 7 may be configured to move at a slower pace than the first element 3. Thus, the load carrier 7 will never reach its lower endpoint 30 before the first element 3 reaches its lower endpoint 17.

[0047] The load carrier 7 may be configured to stop at a predetermined fixed distance X from the lower endpoint 30, and the first element 3 continues its movement to its respective lower endpoint 8, Fig. 3B, 3C, 3D and 3E. And then ensuing the stop of the first element 3 the load carrier 7 starts up its movement to towards its respective lower endpoint 30. This endpoint 30 would then be the same as what is needed for depositing a pallet on the floor, see Fig. 2A. Thus, this meaning that the load carrier 7 stops the predetermined distance X from the lower end point 8 of the load carriers movable range. The stop may occur both at lowering and lifting. Once the first element 3 is at its lower end point 17, the load carrier 7 may continue down to its respective lower end point 8.

[0048] As an alternative, the stopping of the load carrier 7 at the predetermined distance X and the start of the movement of the load carrier 7 again towards the lower endpoint 8 may be ramped to a slow stop, and then ramped up to a full movement, in order to soften the transition to a stop of the load carrier 7 and a stop of the movement of the first element 3.

[0049] The movement may also be reversed when lifting, in that first the load carrier 7 moves upwards from a floor position, or lower position, and then stops at the predetermined distance X from the lower end point 8. And then the first mast element 3 starts moving upwards a predetermined distance before the load carrier 7 starts moving along the first mast element 3 again.

[0050] Optionally, the hydraulic system 30 comprises pressure sensors 34, 35, Fig. 4. The pressure sensors 34, 35 are used in an optional Material handling vehicle 1 with the control unit 20 arranged to execute this alternative method for operating the lifting and / or lowering movement of a mast assembly. In this vehicle / method the lowering or lifting speed Vtot (total lowering or lifting speed of first mast element 3 and load carrier 7 as measure for example in relation to the floor) is controlled from a maximal speed Vx to a minimal speed VI based on the weight Mw, applied to the load carrier 7 of the material handling vehicle 1, Fig. 6, 7 and 8. By having knowledge of the surface area of the first hydraulic cylinder 5 and also the second hydraulic cylinder 6a or cylinders 6a and 6b, it is possible to determine the weight Mw of a load on the load carrier 7. If the weight Mw of the load is under a first predetermined value MI, the speed of the in the predetermined portion of the motion of the load carrier and first mast element may be Vtot = Vx, i.e. maximal, Fig. 8. I.e. Vx = Vf + Vc = Vtot, where Vc is the load carrier speed on the first element 3, and Vf is the speed of the first mast 3 element regardless of the speed of the load carrier 7, Fig. 6 and Fig. 7. Vx thus, means that the first and the second hydraulic cylinders are fully open, i.e. their respective valves 11 and 12 are fully open, and there load carrier 7 and the first mast element 3 moves down, at full speed or that they move up at full speed by opening of valves 13 and 14 in full, and at the same time keeping valves 11 and 12 closed. If the load is determined to be over the first predetermined value MI and under a maximal value Mx, the speed of the load carrier 7, through control of valve 11, is ramped down depending of weight, see Fig. 8. If the weight of the load is determined to be at Mx or more, the load carrier 7 is no longer moving at the same time as the first element 3. Instead the load carrier 7 is stopped at for example at a position according to Fig. 3A and does not move until the first element 3 has reached its lower endpoint 8 Fig 2C. The ramping is preferably made only on the load carriers 7 movement, i.e. valve 11 for lowering is involved, but valve 12 is always fully open, see Fig. 6.

[0051] Fig.6, 7 and 8 are all related to movement, during the predetermined portion of movement. I.e. there is still distance that both the load carrier 7 and the first mast element 3 may move. I.e. none of the load carrier 7 or the first mast element 3 is at its respective lower or high endpoints, 8, 9, 17, 26. Mxk in Fig. 6 designates a load weight that the material handling vehicle 1 maximally may lift or lower. Thus, maximal weight Mx is a fictive maximal weight, for when the load carrier 7 stops moving together with the first mast element 3 of the mast assembly 2. I.e. this is in the range Mx <=Mxk

[0052] There may optionally be so that there is ramping and lowering of the summarized speed of Vc + Vf at lowering, but not at lifting when the speed may always be set to maximal Vx.

Claims

1. Method for operating a lifting and / or lowering movement of a mast assembly (2) comprised in a material handling vehicle (1), said mast assembly (2) comprising at least a first mast element (3) and a second mast element (4; 31), wherein the first element (3) is movable in relation to the second element (4; 31) to extend or contract the mast assembly (2), wherein the first mast element (3) comprises a load carrier (7) arranged to be movable along the first mast element (3) from a first lower endpoint (8) to a second upper endpoint (9), wherein the load carrier (7) is powered by at least one first hydraulic cylinder (5), wherein the first mast element (3) is powered by at least one second hydraulic cylinder (6), wherein the method comprises the steps of: - extend or contract the mast assembly (2) by moving the first mast element (3) along the second mast element (4; 31), characterized in that the movement of the load carrier (7) is arranged such that the load carrier (7) and the first mast element (3) moves at the same time and in the same direction, for at least a predetermined portion of the load carrier's (7) movement.

2. Method according to claim 1, wherein the second mast element (31) is a fixed mast element, or wherein the second mast element is a movable mast element (4).

3. Method according to claim 1 or 2, wherein during the predetermined portion of the movement of the load carrier (7), the hydraulic cylinders (5, 6) are controlled to: - when the movement is a lowering movement: open a first hydraulic valve (11) associated with the first hydraulic cylinder (5) and, open second hydraulic valve (12) associated with the second hydraulic cylinder (6) at the same time, wherein the first hydraulic valve (11) is arranged to control hydraulic fluid flow in a hydraulic line (15) out from the first hydraulic cylinder (5), wherein the second hydraulic valve (12) is arranged to control hydraulic fluid flow in a hydraulic line (16) out from the second hydraulic cylinder (6), and / or - when the movement is a lifting movement: open a third hydraulic valve (13) associated with the first hydraulic cylinder (5) and, open a fourth hydraulic valve (14) associated with the second hydraulic cylinder (6) at the same time, wherein the third hydraulic valve (13) is arrange to control hydraulic fluid flow on a hydraulic line (15) to the first hydraulic cylinder (5), the fourth hydraulic valve (14) is arranged to control hydraulic fluid flow on a hydraulic line (16) to the second hydraulic cylinder (6).

4. Method according to claim 3, wherein the method comprises the following steps during the predetermined portion of the load carrier's movement: in a lifting movement: - close the first hydraulic valve (11) to prevent hydraulic fluid from diverting away from the first hydraulic cylinder (5), - close the second hydraulic valve (12) to prevent hydraulic fluid from diverting away from the second hydraulic cylinder (6), - open the third hydraulic valve (13) to allow hydraulic fluid to flow to the first hydraulic cylinder (3), - open the fourth hydraulic valve (14) to allow hydraulic fluid to flow to the second hydraulic cylinder (6), and / or in a lowering movement: - open the first hydraulic valve (11), to allow hydraulic fluid to flow from the first hydraulic cylinder (5) to a hydraulic fluid reservoir (22), - open the second hydraulic valve (12), to allow hydraulic fluid to flow from the second hydraulic cylinder (6) to the hydraulic fluid reservoir (22).

5. Method according to any of the above, wherein the method further comprises the step of: - control a lowering movement of the load carrier (7) and the first mast element (3) of the mast assembly (2), such that the first element (3) always reaches a lower end point (17) of the first mast element (3) on the second mast element (4; 31), before the load carrier (7) reaches its respective lower end point (8), wherein in the lower end point (17) of the first mast element (3) correspond to that the first element (3) retracted in relation to the second mast element (4; 31) and thus essentially parallel on all sides with the second mast element (4; 31), and / or - control a lifting movement of the load carrier (7) and the first mast element (3) of the mast assembly (2), such that the load carrier (7) is lifted on the first mast element (3) before the first mast element (3) leaves a lower end point (17) of the first mast element (3), and thus the predetermined portion of the lifting movement where both the load carrier (7) and the first mast element (3) moves at the same time, is not initiated at the start of a lifting movement if the load carrier (7) and the first mast element (3) are both being at their respective lower end points (8, 17), preferably up to a predetermined distance (X) of movement of the load carrier (7) on the first mast element (3).

6. Method according to any of the claims above, comprising the step of: - control a lowering movement by stopping the load carrier (7) at a predetermined distance (X) from the lower end point (30) of the load carrier (7), - continue with the lowering of the first element (3), until the first element (3) reaches its lower endpoint (30), optionally re-start the lowering of the load carrier (7) on the third element (3) until the load carrier (7) reaches its lower end point (30).

7. Method according to any of the claims above, comprising the steps of: - determine a load weight Mw that is carried on the load carrier (7), - compare the load weight Mw of the load with a predetermined weight MI, - determine if Mw < MI, and if the expression is fulfilled, allow lowering or lifting of first element (3) and load carrier (7) at a maximal speed (Vx) during the predetermined portion of the movement, - determine if Mw>Ml, and if expression is fulfilled, reduce the speed (Vc) of the load carrier (7) during the predetermined portion of movement, - determine if the load weight Mw is both above Ml and a predetermined maximal value of the load Mx, and if so, prevent the load carrier (7) from moving on the first element (3) before the first element (3) reaches its lower endpoint (17) and / or prevent the first element (3) to move before the load carrier has reached its higher endpoint (9).

8. Material handling vehicle (1) comprising: a mast assembly(2), comprising at least a first mast element (3) and a second mast element (4; 31), a hydraulic system (30), comprising a first hydraulic cylinder (5) and a second hydraulic cylinder (6), a load carrier (7) arranged movable along a length direction on the first mast element (3) from a first lower end point (8) to a second upper endpoint (9) by means of said first hydraulic cylinder (5), wherein the first mast element (3) is movable in longitudinal direction in relation to the second mast element (3), by means of the said second hydraulic cylinder (6), wherein the material handling vehicle (1) further comprises a control unit (20), wherein the control unit (20) is arranged to send and receive output and input from the hydraulic system (30), and thus the control unit (20) is arranged such that it controls the movements of the first and second hydraulic cylinders (5, 6), thus the control unit (20) controls the movement of the load carrier (7) and the movement of the first mast element (3) in relation to the second section element (4; 31), characterized in that the control unit (20) is arranged such that such that the movement of the load carrier (7) along the first mast element (3) is made at the same time as the first section element (3) moves in relation to the second mast element (4; 31), at least for a predetermined portion of said movement.

9. Material handling vehicle (1) according to claim 8, the vehicle (1) comprises: - a first hydraulic valve (11), a second hydraulic valve (12), a third hydraulic valve (13), and a fourth hydraulic valve (14), wherein the control unit (20) is arranged to control the opening and closing of the respective hydraulic valve (11 - 14), wherein, - the first hydraulic valve (11) is arranged to control hydraulic fluid flow in a hydraulic line (15) out from the first hydraulic cylinder (5), - the second hydraulic valve (12) is arranged to control the hydraulic fluid flow in a hydraulic line (16) out from the second hydraulic cylinder (6a; 6b), - the third hydraulic valve (13) is arranged to control the hydraulic flow on a hydraulic line (15) into the first hydraulic cylinder (5), - the fourth hydraulic valve (14) is arranged to control the hydraulic flow into the second hydraulic cylinder (6).

10. Material handling vehicle (1) according to any of the claims 8 or 9, wherein the material handling vehicle (1) is arranged such that it: controls a lowering movement during the predetermined portion of movement of the load carrier (7) and the first mast element (3) of the mast assembly (2), such that the first mast element (3) always reaches a lower end point (17), before the load carrier (7) reaches the lower end point (8), wherein in the lower end point (17) of the first mast element (3) is fully retracted in relation to the second mast element (4; 31) and thus essentially parallel on all sides with the second mast element (4; 31), and / or controls a lifting movement during the predetermined portion of movement of the load carrier (7) and the first mast element (3) of the mast assembly (2), such that the load carrier (7) is lifted on the first mast element (3) before the first mast element (3) leaves a lower end point (17) of the first mast element (3).

11. Material handling vehicle (1) according to any of the claims 8-10, wherein the material handling vehicle (1) is arranged by means of the control unit (20) such that it controls a lowering movement such that the load carrier (7) is stopped at a predetermined distance (X) from the lower end point (8), and in that the lowering movement of the load carrier (7) is continued when, the first mast element (3) reaches its respective lower end point (17), and / or controls the lifting movement such that the load carrier (7) stops at a predetermined distance (X) from its lower endpoint (8) and the first mast element (3) starts to move alone a predetermined distance from its respective lower end point (17), before both the load carrier (7) and the first mast element (3) moves together the predetermined portion.

12. Computer program product, comprising instructions which, when the program is executed by a computer, case the computer to carry out the steps of the method according to any of the claims 1-7.

13. A computer-readable storage medium comprising instructions which, when executed by a computer cause the computer to carry out the steps of the method of any of the claims 1-7.

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