SYSTEM AND METHOD FOR STACKING AND UNSTAFFLING LOAD CARRIERS

Description

[0001] The present invention relates to the technical field of handling load carriers for receiving goods in a conveyor system, in particular the handling of transport containers for baggage in airport baggage conveyor systems.

[0002] At airports, transport containers are used to transport baggage. These transport containers are loaded and unloaded after use. Empty transport containers must be stored when not in use. Stacking transport containers for storage reduces the space required. Stackers and destackers are used for this purpose. Empty transport containers are conveyed to a forklift, which builds stacks. These stacks are stored. When empty containers are needed, the stacks are moved to a destacker. This separates the transport containers for use.

[0003] Previous stackers and destackers used mechanisms that grip a stack from two sides. The stacker lifts the existing stack from both sides, and the next transport container moves underneath it. The existing stack is placed on top of the new transport container. The stacker reaches under the new transport container and lifts the stack. The process starts again from the beginning until the stack reaches its maximum height. The full stack is removed from the stacker, and the next stack can be built. The destacking process takes place in reverse.

[0004] Access from two sides requires the structure to be supported on both sides. Space is also required on both sides of the container conveyor lines, which increases the distance between container conveyor lines. At least one carrying or lifting element is used on each side, but in practice two are usually used to lift the transport containers. At least two carrying elements are required. If a stack is lowered onto a transport container, the carrying elements must be placed under the new, lowest transport container. In addition to the lifting movement, these carrying elements must be able to perform a grasping movement. The lifting elements must be guided around the transport container. Both sides must work synchronously. If separate motors are used, a control system for synchronization is required. Alternatively, mechanical synchronization can be used.Synchronization must be performed for both the lifting movement and the gripping movement.

[0005] Forklifts and destackers are positioned over a conveyor section. They are supported on either side of the conveyor or directly on the conveyor and have separate but synchronized lifting motors or a mechanical overdrive. The reloading movement is performed by the lifting motor and additional motors. These additional motors often rotate the lifting elements away from the transport container area.

[0006] The document FR 2 543 513 A1 discloses a system for stacking and / or unstacking load carriers, comprising a) a conveyor track on which the load carriers can be conveyed individually or stacked along a conveying direction; b) a lifting device for the load carriers arranged laterally of the conveyor track, wherein the lifting device comprises two engagement elements that can be brought into engagement with the load carriers; and c) a controller adapted to control the conveyor track and the lifting device such that the load carriers are stopped at a stop position relative to the lifting device and the engagement elements are brought into engagement, optionally with a stopped load carrier lying directly on the conveyor track or with a load carrier of a stack of load carriers that is not lying directly on the conveyor track; wherein the conveyor track has two interruptions for passing the engagement elements, wherein the interruptions are each dimensioned large enough to accommodate the engagement elements and lower them below the conveyor track;the system has a controllable lifting drive which is designed to change the height of the engagement elements, wherein the construction allows a vertical movement of the engagement elements; a horizontal distance between the engagement elements can be changed in order to bring the engagement elements into engagement with a load carrier, wherein the engagement elements have a rest position and an engagement position, wherein the engagement elements are positioned closer to one another in the engagement position than in the rest position, wherein the engagement elements in the rest position are arranged at a distance from one another which is greater than the extent of a load carrier, so that the engagement elements can be moved vertically around a load carrier in the stop position without hindrance; the system has a controllable drive which is designed to change the horizontal distance between the engagement elements.

[0007] The present invention is therefore based on the object of achieving an improvement over the prior art. This object is achieved by the solutions described in the independent claims.

[0008] The solution according to the invention provides a system for stacking and / or unstacking load carriers, for example transport containers, according to claim 1. The system comprises a conveyor track on which the load carriers can be conveyed individually or stacked along a conveying direction. The system comprises a lifting device for the load carriers arranged to the side of the conveyor track, wherein the lifting device comprises two engagement elements that can be brought into engagement with the load carriers. And the system comprises a controller that is adapted to control the conveyor track and / or the lifting device such that the load carriers are stopped at a stop position relative to the lifting device and the engagement elements are brought into engagement optionally with a stopped load carrier lying directly on the conveyor track and with a load carrier of a stack of load carriers that is not lying directly on the conveyor track.

[0009] If the load carrier engaged with the engagement elements is not the topmost load carrier in a stack of load carriers, one or more additional load carriers rest on top of the load carrier engaged with the engagement elements. The vertical positioning of the engagement elements to engage them with the load carrier is determined by the vertical positioning of the load carrier in question. The system can be used to stack and / or unstack a stack of load carriers. The lateral arrangement of the lifting device can be designed to save space.

[0010] A lateral arrangement should in particular be understood to mean a one-sided arrangement of the lifting device, i.e. the lifting device is located on a first side next to the conveyor track. This arrangement requires little space, as no installation space is needed on the second side of the conveyor track and also allows for a particularly simple design of the lifting device. In contrast to a lifting device arranged on two opposite sides of the conveyor track, no synchronization of the components on the opposite sides is required to carry out the vertical lifting movement. A lifting device arranged on one side next to the conveyor track can be easily anchored to the ground and / or mounted or constructed with a particularly heavy support foot to prevent it from tipping over, thus making it particularly stable.

[0011] A load carrier is understood to be a supporting device for holding one or more goods to form a loading unit. The load carriers are preferably transport containers. An advantageous application for the system is airport baggage handling units, as these often have an asymmetrical demand for load carriers and periods of high and low utilization alternate.

[0012] The system can, for example, be an airport baggage handling system or can be installed as a system for stacking and / or unstacking load carriers in an airport baggage handling system. The load carriers are loaded with baggage at check-in and unloaded at one end of the conveyor belt to be transported on a baggage transport trolley to an aircraft. Empty load carriers are loaded with baggage from arriving aircraft, but usually at another position on the airport baggage handling system. The demand for empty transport containers is usually asymmetrical, and the utilization of the airport baggage handling system often fluctuates greatly, so that empty load carriers must be transported from one end of the conveyor belt to the check-in or vice versa. The system can be designed for stacking and / or unstacking empty load carriers and / or load carriers filled with baggage or other goods.

[0013] The system can also be used in other areas of logistics, for example in mail sorting systems.

[0014] For the purposes of the invention, engagement elements are also understood to mean interconnected engagement elements that enable engagement with the load carrier. The engagement elements can, but do not have to, be similar in terms of design and their function during engagement. For example, it is possible for only one of the engagement elements to be movable.

[0015] The solution according to the invention can be further improved by various embodiments, each of which is advantageous in itself and, unless otherwise stated, can be combined with one another in any desired way. These embodiments and their associated advantages are discussed below.

[0016] To facilitate engagement, the engagement elements can be arranged such that they are aligned along an edge of a load carrier resting at the stop position on the conveyor track.

[0017] According to the invention, the engagement elements are arranged perpendicular to the conveying direction. Thus, the load carriers can be aligned perpendicularly or along the engagement elements by aligning the load carriers perpendicularly or along the conveying direction.

[0018] According to the invention, the horizontal distance between the engagement elements can be varied in order to engage the engagement elements with a load carrier. The engagement elements have a rest position and an engagement position, with the engagement elements being positioned closer to one another in the engagement position than in the rest position. In order to guide the engagement elements past a load carrier in the stop position, the distance between the engagement elements in the rest position is greater than the extent of the load carrier in the rest position.

[0019] The system has a controllable drive configured to change the horizontal distance between the engagement elements. The control system can be adapted to control the drive to move the engagement element(s) and thus change the horizontal distance between the engagement elements. Engaging thus requires only a single drive and no synchronization of multiple drives. Compared to multiple drives, a single drive is also more fail-safe.

[0020] In order to convey the load carriers along the conveyor track without being disturbed by the engagement elements and to position the engagement elements optimally in order to bring them into engagement with a load carrier, the engagement elements can be positioned below the load carriers resting on the conveyor track.

[0021] To easily lower the engagement elements beneath the conveyor track, the conveyor track has two gaps for the engagement elements to pass through. These gaps must be large enough to accommodate the corresponding engagement element.

[0022] According to the invention, the lifting device comprises a mast on which the engagement elements can be mounted vertically movable. The mast can simply be anchored to the ground and thus firmly positioned; however, if the conveyor track is designed to be stable, it can also be mounted on or at least directly on the conveyor track.

[0023] The system features a controllable lifting drive designed to change the height of the engagement elements. The control system can be adapted to control the lifting drive.

[0024] The system can also include a sensor unit configured to detect the load carriers on the system. To enable smooth engagement, the correct positioning of the load carriers in the stop position can be detected, particularly before engagement, and checked by the controller. Furthermore, the controller can be configured to perform stacking or unstacking depending on the detection result of the sensor unit.

[0025] According to one embodiment, the controller can be adapted to control the drive and the lifting drive in a synchronized manner depending on the load carriers in the system. This makes it possible to reduce the unnecessary transport of empty load carriers in the system. To enable efficient calculation, the controller can include a logic module for this purpose.

[0026] With regard to a method, the above-mentioned object is achieved by a method for stacking and / or unstacking load carriers, for example transport containers, with a system comprising a lifting device for the load carriers arranged laterally of the conveyor track, wherein the lifting device comprises two engagement elements that can be brought into engagement with the load carriers. The method comprises the following method steps: a) A load carrier lying directly on a conveyor track is conveyed individually or stacked along a conveying direction of the conveyor track. b) The conveyor track is stopped when the load carrier lying directly on the conveyor track is at a stop position. c) The engagement elements are brought into engagement either with the load carrier lying directly on the conveyor track or with a load carrier from a stack of load carriers that is not lying directly on the conveyor track. d) The lifting device moves the load carrier engaged with the engagement elements vertically. e) The lifting device stops the vertical movement of the load carrier engaged with the engagement elements. f) The engagement elements release the engagement with the load carrier.

[0027] To engage the engagement elements with the load carrier, the horizontal distance between the engagement elements can be reduced. Using a simple actuator system and movement of the engagement elements, a load carrier can be coupled to the lifting device.

[0028] According to a further embodiment, the engagement elements can be positioned below the load carriers resting on the conveyor track before the engagement elements are brought into engagement with the load carrier. This means that the engagement elements only need to overcome a short lifting distance, i.e., a minimal vertical movement, to be optimally positioned for engagement. This is particularly true when a load carrier resting directly on the conveyor track, i.e., the lowest-positioned load carrier in a stack, is to be brought into engagement with the engagement elements. Even with very high stack heights, stacking and unstacking thus involves covering a short lifting distance.

[0029] To further build up or dismantle the stack, another load carrier can be transported along the conveyor track, while the load carrier engaged with the engagement elements is held by the engagement elements. To further build up or dismantle the stack, the additional load carrier can be transported toward or away from the stop position.

[0030] Embodiments of the invention are explained in more detail below with reference to the figures. Figure 1a schematically shows a system not according to the invention from a bird's eye view; Figure 1b schematically shows a system according to the invention from a bird's eye view; Figure 2 an embodiment of the system with a load carrier in the stop position, engaged with the engagement elements from a bird's eye view; Figure 3 the system of Figure 2with a load carrier positioned in front of a break; Figure 4 shows the step-by-step formation of a stack of load carriers at the stop position; and Figure 5 shows the beginning of unstacking a stack.

[0031] Figure 1a shows schematically a system 2 not according to the invention from a bird’s eye view and Figure 1b shows a system according to the invention from a bird's eye view. System 2 shows a section of an airport baggage handling system. Individual load carriers 4 and a stack 18 of load carriers 4' are transported along a conveying direction 8 on a conveyor track 6. The conveyor track 6 is controllable and designed as a circulating conveyor belt, which allows conveying along and against the conveying direction 8. Three conveyor track sections 6a, 6b, 6c are shown, with a gap or interruption 20 between the conveyor track sections 6a, 6b and 6b, 6c.

[0032] Figure 1ashows how a lifting device 10 is arranged to the right of the conveyor track 6, i.e. only on one side. The lifting device 10 comprises a stationary mast 22, two engagement elements 12a, 12b, and two connecting elements 26 connecting the engagement elements 12a, 12b. The load carriers 12a, 12b are aligned along the lateral edges of the load carriers 4, with the load carriers 4 in turn being aligned along the conveying direction 8. The lifting device 10 acts as a lifting and lowering device; the first engagement element 12a is mounted directly and the second engagement element 12b is mounted indirectly on the mast 22, the construction allowing vertical movement of the engagement elements 12a, 12b and the connecting elements 26. Positioning and dimensioning of the lifting device 10 determine a stop position 16, which is determined on the middle conveyor track section 6b relative to the engagement elements 12a, 12b and the interruptions 20 or the connecting elements 26.The interruptions 20 are wider than the connecting elements 26, so that the connecting elements and the engagement elements 12a, 12b can be lowered below a conveying plane spanned by the conveyor track 6.

[0033] The system 2 comprises a sensor unit 24, for example comprising a camera and / or a light barrier, which is designed to detect the presence or absence of one and / or more load carriers 4 at different positions in the system 2, in particular in the stop position 16, and / or a movement of the load carriers 4. The system 2 also comprises a controller 14, which is connected to the conveyor track 6, in particular the central conveyor track section 6b, the sensor unit 24, and the lifting device 10.

[0034] Without one or more load carriers 4 at the stop position 16, the engagement elements 12a, 12b are in a rest position with a horizontal distance d max from one another. As soon as a load carrier 4 is conveyed to the predetermined stop position 16, the second engagement element 12b is moved horizontally towards the first engagement element 12a until a horizontal distance d min is achieved, which here is less than a lateral extension of the load carrier 4 transverse to the conveying direction 8. The horizontal distance d is changed here orthogonally to the conveying direction 8. The engagement elements 12a, 12b are now engaged with the load carrier 4. To carry out the vertical movement, the lifting device 10 comprises a drive (not shown here).

[0035] For vertically moving the engagement elements 12a, 12b, the lifting device 10 comprises a lifting drive (not shown in the drawing), which is driven as a motor on the mast 22 via a belt. After the engagement elements 12a, 12b have been brought into engagement with the load carrier 4, the engagement elements 12a, 12b are moved vertically, thus lifting the engaged load carrier 4.

[0036] Figure 1b shows a variation of the Figure 1a, wherein the two engagement elements 12 are arranged orthogonally to the conveying direction 8. The engagement elements 12 arranged orthogonally to the conveying direction 8 and the only one connecting element 26, which is fastened vertically movably to the mast 22 of the lifting device 10, form a U-shaped gripper. In the rest position, the engagement elements 12 are arranged at a distance d max from one another that is greater than the extension of a load carrier 4, so that the engagement elements 12 can be moved vertically around a load carrier 4 in the stopped position without obstruction. The interruptions 20 allow the engagement elements 12 to pass below the conveying plane and are therefore necessarily wider than the engagement elements 12. The engagement elements 12 can be moved horizontally and in or against the conveying direction 8 by a drive.In order to engage the engagement elements 12 with a load carrier 4 located in the stop position 16, the engagement elements 12 are positioned directly below the respective load carrier 4 and subsequently the engagement elements 12 are brought closer to each other by horizontal movement and thus the horizontal distance d min is set.

[0037] After the load carrier 4 has been brought into engagement with the engagement elements 12, it can be lifted by controlling the lifting drive by the control 14.

[0038] Figure 2According to a further embodiment, the system 2 shows two conveyor tracks 6, 6' arranged parallel to one another and lifting devices 10, 10' arranged in mirror images of one another. Between the conveyor tracks 6, 6' there is an access 28 dimensioned for people; for safety reasons, this has a minimum width of approximately 90 cm. The lateral arrangement of the lifting devices 10, 10' allows the moving components of the lifting devices 10, 10' to be located outside the danger zone for people. Since rectifying malfunctions often requires the presence of a person, the second conveyor track 6' does not have to be stopped to rectify a malfunction on the first conveyor track 6.

[0039] Figure 3 shows, according to yet another embodiment of the invention, the system 2 of Figure 2with a load carrier 4 positioned in front of an interruption 20. The engagement elements 12 are arranged in the rest position below the conveyor track 6.

[0040] The Figures 4a - 4k show step by step the formation of a stack 18 of load carriers 4 at the stop position 16 of a system 2 according to the invention using a lifting device 10. The system 2 is designed analogously to the system shown in Figure 3illustrated system 2. The conveyor track 6 is segmented in sections and comprises three conveyor track segments or conveyor track sections 6a, 6b, 6c, wherein between the conveyor track sections 6a, 6b and 6a, 6c there is a gap or interruption 20 which is wide enough to lower the engagement elements 12 below the conveyor track 6. The lifting device 10 is provided for stacking and unstacking load carriers 4, in particular empty airport transport containers. For stacking, the load carriers 4 lying directly on the conveyor track 6 are transported individually to the stop position 16 on the middle conveyor track section 6a, which represents a stacking position, are engaged with the engagement elements 12 and then the engagement elements 12, together with the load carrier 4 initially lying directly on the conveyor track 6, are lifted or unstashed by the lifting device 10.moved vertically so that a subsequent load carrier 4 can be transported along the conveying direction 8 into the stop position.

[0041] Figure 4ashows the engagement elements 12 in the rest position or open state below the conveying plane spanned by the conveyor track 6. In the rest position, the distance d max between the engagement elements is greater than the length of a load carrier 4. The distance d max between the engagement elements 12 in the rest position determines the distance between the two interruptions 20. With a constant distance d max and free interruptions, the engagement elements 12 can be moved vertically, i.e. raised and lowered, by the lifting device 10 without disruption and without stopping. Simple linear conveyors, for example conveyor belts, can be used as conveyor track sections 6a-6c; the decisive factor is the arrangement such that a gap is formed. From the first conveyor track section 6a, the load carrier 4 is conveyed along the conveying direction 8 to the stop position 16 on the middle conveyor track section 6b.

[0042] Figure 4bshows the load carrier 4 in the stop position 16 on the middle conveyor track section 6b, which has been stopped. The sensor unit 24 uses light barriers to check the correct positioning of the load carrier 4 resting centrally on the middle conveyor track section 6b. The engagement elements 12 remain in the rest position with an unchanged horizontal distance d max from each other. The two engagement elements 12 are now lifted by the lifting device 10 at a constant horizontal distance d max until the engagement elements 12 are, viewed vertically, in an engagement position directly below the load carrier 4 to be engaged.

[0043] Figure 4c shows the raised engagement elements 12 with the horizontal distance d max between them unchanged. Subsequently, the horizontal distance d between the engagement elements 12 is reduced in order to engage the engagement elements 12 with the load carrier 4.

[0044] Figure 4d shows the vertical engagement position of the engagement elements 12, which are already in Figure 4c The distance d between the engagement elements 12 was reduced to the reduced distance d min , which is smaller than the length l of the load carrier 4. The load carrier 4 is now also in a horizontal engagement position and is engaged with the engagement elements 12 and is thus clamped or held in place by them, but the load carrier 4 still rests directly on the conveyor track 6 or the central conveyor track section 6b. Subsequently, the engagement elements 12, together with the engaged load carrier 4, are lifted by the lifting device 10.

[0045] Figure 4e shows the first load carrier 4 lifted by the lifting device 10 via the engagement elements 12, which is lifted so far that space has been created at the stop position 16 for a further, subsequent load carrier 4' .

[0046] Figure 4f shows the subsequent load carrier 4', transported along the conveying direction 8, at the stop position 16 and thus pushed beneath the first load carrier 4. The first load carrier 4 remains engaged with the engagement elements. The lifting device 10 will subsequently lower the engagement elements 12 and thus the first load carrier 4.

[0047] Figure 4g shows the formation of a stack of the two load carriers 4, 4'. The lifting device 10 will lower the engagement elements 12 and thus the first load carrier 4 by approximately 2-3 mm before the clamped load carrier 4 is completely deposited on the other load carrier 4' resting directly on the conveyor track 6. The vertical distance d min between the engagement elements 12 remains unchanged.

[0048] Figure 4hshows a re-widening of the engagement elements 12 to the distance d max . The engagement between the engagement elements 12 and the first load carrier 4 is thus released.

[0049] The first load carrier 4 is stacked on the subsequent load carrier 4'.

[0050] Figure 4i shows a lowering of the engagement elements 12 until the engagement elements 12 are arranged in a vertical engagement position directly below the following load carrier 4'. Stacking with yet another load carrier 4" is now carried out analogously to the method described above, with the only difference that the engagement elements 12 hold the load of two load carriers 4, 4'. The additional load carrier 4', which is initially located at the bottom, engages with the engagement elements 12.

[0051] Figure 4jshows the result of the sequential stacking of three load carriers 4, 4', 4". Following the situation shown, another load carrier 4‴ is stacked from below.

[0052] Figure 4k shows how a stack of four load carriers 4, 4', 4", 4‴ was transported further along the conveying direction 8 by the middle conveyor track section 6b and the third conveyor track section 6c.

[0053] Figure 5 shows, according to yet another embodiment of the invention, a snapshot of a destacking of a stack 18 of four load carriers 4, 4', 4", 4‴. The destacking is carried out by the Figure 4The stacking process steps described in detail are carried out in reverse order. During unstacking, the bottommost load carrier 4‴ is separated from the remaining stack 18, comprising the three load carriers 4, 4', 4", wherein the bottommost load carrier 4‴ of the remaining stack 18 is brought into engagement with the engagement elements 12 and held by them. The three topmost load carriers 4, 4', 4" are lifted by bringing the second-bottommost load carrier 4" into engagement with the engagement elements 12. While when forming a stack 18 only a single load carrier 4 can be stacked from below, during unstacking it is in principle possible to transport two load carriers 4‴, 4" or even more load carriers 4 at the same time as a reduced stack 18 along the conveying direction 8. However, the prerequisite for this is that the lifting device 10 is designed to lift the engagement elements 12 sufficiently high.

[0054] According to a further embodiment, the load carriers 4 are designed to fit one another in a form-fitting manner, so that stacks 18 formed from them are stable enough to be conveyed along the conveyor track 6 without further securing. According to one embodiment, a system 2 can comprise two or more lifting devices 10a, 10b, wherein one lifting device 10a can be designed for stacking and the other lifting device 10b for unstacking. This assignment can be useful when there is always a similar, asymmetrically positioned need for empty load carriers 4 at one position and emptying of the load carriers 4 at another position. However, the task of stacking or unstacking can also be assigned dynamically and thus be interchangeable. A lifting device 10 can therefore be used for stacking and / or unstacking.

[0055] The load carriers 4 are coordinated with the system 2. The dimensioning and shape of the engagement elements 12, the width of the gaps 20 and their spacing from one another, as well as the design of the load capacity of the lifting device 10 and the stability and permissible load-bearing capacity of the engagement elements 12 are coordinated with the load carriers 4 used and the stacking height to be achieved. The use of other load carriers 4 requires an adaptation of the engagement elements 12 and / or the lifting device 10. The sensor unit 24 is designed not only to detect correct positioning of the load carriers 4, but also to detect faulty situations, for example incorrectly positioned / or incorrectly aligned and / or incorrectly stacked load carriers 14.

[0056] According to one embodiment, the sensor unit 24 is designed to detect the position and / or movement of the load carriers 4 on the entire system 2. The controller 14 is informed about the supply and demand for load carriers 4 at all positions of the entire system, so that the control of the conveyor track 6 and / or the lifting device 10 and the engagement elements 12, and thus the stacking and unstacking depending on the supply and demand of load carriers 4, is controlled in a particularly energy-efficient manner (fewer unnecessary stacking processes, as little unnecessary transport of unused load carriers 4 as possible) and space-efficient manner (stacks require less space than individual load carriers 4).

[0057] According to one embodiment, a lifting device 10 designed to form stacks 18 comprising four load carriers 4 can achieve a peak throughput of 1200 load carriers per hour. Figures 4a - 4kThe process steps shown can be carried out within seconds, sometimes even within tenths of a second.

[0058] According to the invention, the system 2 comprises a conveyor track 6, a lifting device 10 comprising a mast 22 fixedly mounted on at least one side of the conveyor track, for example, by anchoring it to the ground, a lifting drive, and engagement elements 12 mounted vertically movable directly on the mast 22 via a connecting element 26, wherein a vertical movement is driven by a lifting drive included in the lifting device 10. The system 2 further comprises a drive for changing the horizontal distance between the engagement elements 12. The system 2 also comprises electrical components.

[0059] According to the invention, the system 2 comprises two controllable drives. The first drive is a lifting drive designed to achieve a vertical movement of the engagement elements. The second drive is designed to achieve a horizontal movement of the engagement elements 12. The controller 14 is adapted to drive the drive and the lifting drive in a coordinated manner. The stacking and unstacking of load carriers 4 does not require simultaneous, but only sequential, execution of vertical and horizontal movements. The controller 14 is adapted to control the drive and the lifting drive in a synchronized manner depending on the load carriers 4 in the system 2, whereby the synchronized control here means sequential and not simultaneous control. Sequential control of two drives is easier to implement than simultaneous control.Since only two drives are required, system 2 is particularly wear-resistant and low-maintenance. According to a further embodiment, the controller 14 is designed as a control cabinet. The control cabinet comprises frequency converters for supplying the drives with the required frequency and at least one logic module for local control. The controller 14 controls the drive for the horizontal movement of the engagement elements 12 and the lifting drive for the vertical movement of the lifting device 10 or, resulting therefrom, of the engagement elements 12. The controller 14 detects the information detected by the sensor unit 24 and, depending on this information and taking into account further information, controls the conveyor track 6 and / or the lifting drive and / or the drive. List of reference symbols

[0060] 2System 4Load carrier 6Conveyor track 8Conveying direction 10Lifting device 12Interference elements 14Control 16Stop position 18Stack 20Interruption of the conveyor track 6 22Mast of the lifting device 10 24Sensor unit 26Connecting element 28Access dDistance of the intervention elements lLength of a load carrier

Claims

1. System (2) for stacking and / or unstacking load carriers (4), for instance transport carriers comprising a) a conveyor track (6) on which the load carriers (4) can be conveyed individually and stacked along a conveying direction (8) ; b) a lifting apparatus (10) arranged laterally with respect to the conveyor track (6) for the load carrier (4), wherein the lifting apparatus (10) comprises two engaging elements (12) which can mesh with the load carriers (4); and c) a controller (14) which is adapted to control the conveyor track (6) and the lifting apparatus (10) in such a way that the load carriers (4) are held on a stop position (16) relative to the lifting apparatus (10) and the engaging elements (12) are meshed optionally with a load carrier (4) retained so as to rest directly on the conveyor track (6) or a load carrier (4) of a stack (18) of load carriers (4) not resting directly on the conveyor track (6); wherein - the lifting apparatus (10) comprises a connecting element (26) which connects the engaging elements (12), wherein the two engaging elements (12) are arranged orthogonally to the conveying direction (8), and the engaging elements (12) and the connecting element (26) form a U-shaped gripper; - the conveyor track (6) has two interruptions (20) to allow the engaging elements (12) to pass, wherein the interruptions (20) are each dimensioned to be sufficiently large to receive the engaging elements 12 and to lower the same below the conveyor track (6); - the lifting apparatus (10) comprises a mast (22), on which the engaging elements (12) are mounted so as to be vertically movable by way of the connecting element (26) and the system (2) has a controllable lifting drive which is designed to change the height of the engaging elements (12), wherein the construction permits a vertical movement of the engaging elements (12); - a horizontal distance of the engaging elements (12) with respect to one another can be changed in order to mesh the engaging elements (12) with a load carrier (4), wherein the engaging elements have a rest position and an engaged position, wherein the engaging elements (12) are positioned closer to one another in the engaged position than in the rest position, wherein the engaging elements are arranged at a distance from one another in the rest position which is greater than the extent of a load carrier so that the engaging elements (12) can be moved vertically about a load carrier (4) located in the stop position in a manner free of obstacles; - the system (2) has a controllable drive, which is designed to change the horizontal distance of the engaging elements (12) from one another; - the engaging elements (12) can be positioned below the load carrier (4) which rests on the conveyor track (6) so that the load carrier can be conveyed along the conveyor track in a manner undisturbed by the engaging elements.

2. System (2) according to one of the preceding claims, characterised in that the engaging elements (12) can be positioned at the height and / or below and / or above the charge carrier (4) resting on the conveyor track (6).

3. System (2) according to one of the preceding claims, moreover comprising a sensor unit (24) which is designed to detect the charge carrier (4) on the system (2).

4. System (2) according to one of the preceding claims, characterised in that the controller (14) is adapted to control the drive and the lifting drive in synchrony as a function of the load carriers (4) in the system (2).

5. Method for stacking and / or unstacking load carriers (4), for instance transport containers, with a system (2) according to one of claims 1 - 4, comprising the method steps: a) a load carrier (4) resting directly on a conveyor track (6) is conveyed individually or in a stacked manner along a conveying direction (8) of the conveyor track (6); b) the conveyor track (6) is retained if the load carrier (4) resting directly on the conveyor track (6) is located on a stop position (16); c) the engaging elements (12) are meshed optionally with the load carrier (4) resting directly on the conveyor track (6) or a load carrier (4) of a stack (18) of load carriers not resting directly on the conveyor track (6); d) the lifting apparatus (10) moves the load carrier (4) meshed with the engaging elements (12) vertically; d) the lifting apparatus (10) stops the vertical movement of the load carrier (4) meshed with the engaging elements (12); f) the engaging elements (12) release the meshing with the load carrier (4).

6. Method according to claim 5, characterised in that the engaging elements are positioned below the load carrier (4) resting on the conveyor track (6) before the engaging elements are meshed with the load carrier (4).

7. Method according to one of claims 5 to 6, moreover comprising the method step a further load carrier (4) of the conveyor track (6) is conveyed while the load carrier (4) meshed with the engaging elements (12) is held by the engaging elements (12).