Self-propelled vehicle

Abstract

The invention relates to a self-propelled vehicle for lifting, transporting and setting down a load carrier, comprising: - a frame; - first wheel units with one or more first transport wheels embodied to support the frame on the ground surface and to displace it over the ground surface; - carrier units mounted on the frame for up and downward displacement; - a first actuator for displacing the one or more carrier units in up and downward direction between a lower position in which the carrier unit can be slid into or under the load carrier and an upper position in which a load carrier resting on the carrier unit is lifted off the ground surface; - second wheel units, mounted on the carrier units, with second transport wheels, wherein the second wheel unit is displaceable between a folded-out position in which at least the second transport wheels have been displaced to a lower position and a folded-in position in which the second transport wheels have been displaced to an upper position; - a second actuator coupled to a second wheel unit for the purpose of folding in and folding out the second wheel unit.

Description

[0001] SELF-PROPELLED VEHICLE

[0002] This description relates to a self-propelled vehicle, particularly an automated guided vehicle (AGV) or an autonomous mobile robot (AMR). The self-propelled vehicle can be configured to pick up a load carrier from a ground surface, transport it over the ground surface and set it down on the ground surface. The description also relates to the use of this vehicle and to a method for picking up, transporting and setting down a load carrier with this vehicle.

[0003] Automated guided vehicles (AGVs) are unmanned mobile robotic vehicles which are configured to displace goods in a determined space, such as a factory hall or distribution centre, or over a determined ground surface. An example of such an automated guided vehicle is described in the document WO 2019 / 009729 A2 in the name of the present applicant. The vehicle described in this document is suitable for transporting holders of a type provided with wheels, particularly for transporting shopping trolleys, vegetable carts or Danish trolleys. These latter trolleys, also referred to as CC trolleys or CC containers, are applied on a large scale, particularly in the horticultural industry.

[0004] Autonomous mobile robots (AMRs) are also unmanned mobile robotic vehicles for displacing goods in a determined space, such as a factory hall or distribution centre, or over a determined ground surface, although these robotic vehicles have been developed further relative to automated guided vehicles (AGVs) such that they can find their way around said spaces essentially autonomously. While an AGV typically has one or more fixed routes for moving from A to B in the space, an AMR can determine the most suitable route between A and B on its own.

[0005] The goods to be displaced are generally placed on a load carrier prior to transport. The load carriers are configured to support one or more objects or goods, optionally stacked, on for instance a ground surface. Transport of the goods generally takes place while the goods to be transported are loaded on a load carrier. Transportation of loaded (and also non-loaded) load carriers is often done by specially configured load carrier trucks. To transport the load carriers, the load carrier trucks lift the load carrier, optionally with load, off the ground surface and displace the lifted load carrier over the ground surface.

[0006] Other self-propelled automated guided vehicles are known for transporting carriers in the form of loading platforms, also known under the name pallets. These known vehicles are also known under the name pallet truck and are provided with a number of carrier units, often in the form of a lift fork, the outer ends of which slide into the passages between the beams of a pallet and can so be placed under the upper surface of the pallet.

[0007] The lift fork of many of the known pallet trucks is supported at only one end, i.e. the end with which the lift fork is attached to the mobile frame of the vehicle. In practice this means that use must be made of a counterweight to keep the vehicle stable when lifting the lift fork. This inevitably makes such a pallet truck relatively large and heavy. A great deal of energy is required to operate the pallet trucks, this limiting their maximum operating time before having to be charged again. Also known are pallet trucks of a type wherein the lift fork is supported not only at said first outer end but also at a second outer end, lying opposite the first outer end. Mobile pallet trucks are for instance known wherein second outer ends of the lift fork are supported by a number of wheels. Such pallet trucks with double-supported lift forks can take a much lighter form. Some examples even require no counterweight to be able to lift heavy loads.

[0008] In the known pallet trucks of this latter type (i.e. the double-supported type) it is however sometimes problematic to place the lift forks properly under or in the pallet and to support the pallet sufficiently to be able to lift it. One reason for this may be that a pallet sometimes has on its underside one or more lower support elements resting on the ground surface (for instance connecting boards or the like resting on the ground surface). These support elements often extend horizontally (when arranged on a horizontal ground surface), due to which reference is also made here to a horizontal support element. It will however be apparent that the support element can also extend at an incline, for instance when the support element is arranged on a sloping and / or irregular ground surface.

[0009] The lower support elements often form in said passages an obstacle to a lift fork with support wheels at the outer end, whereby the lift fork is unable to slide sufficiently into these passages of the load carrier. This is because the vehicle becomes stuck in the passage, with its wheels against the side of a lower support element. In other words, it is difficult and sometimes impossible to slide the lift fork of the pallet truck sufficiently into the passages of such a pallet, especially when the pallet truck has a relatively small mass relative to the mass of the pallet and / or when the pallet is empty and is arranged on a slippery ground surface. It may also occur, particularly when the pallet is empty or is only lightly loaded, that the lift fork of the vehicle shifts the pallet over the ground surface in that the wheels in the lift fork push against the support element.

[0010] The above stated problems are described inter alia in the document NL 2027243 Bl, the content of which can deemed as incorporated herein. The solution provided in this document is to provide the lift fork with a number of additional leading wheels.

[0011] Self-propelled vehicles for transporting load carriers and pallet trucks in particular are further generally less easy to manoeuvre and, when used in a small space, it is often difficult to turn the pallet trucks and position them correctly relative to a pallet so that this pallet can be lifted. Some of the known self-propelled vehicles also take up a great deal of space, for instance in vehicles in which use is made of extendable lift forks which can be extended relative to the rest of the vehicle so as to be placed under or in a load carrier.

[0012] It is an object to provide a self-propelled vehicle wherein at least one of the above stated drawbacks and / or other drawbacks is at least partially obviated. It is also an object to provide a self- propelled vehicle which has compact dimensions, is readily manoeuvrable and / or is light-weight, yet is still suitable for working with a variety of load carriers. It is a further object to provide a self- propelled vehicle with one or more double-supported carrier units whereby pallets, optionally pallets of a type with a lower support element, are easily transportable. According to a first aspect, at least one of the objects is achieved at least partially in a self- propelled vehicle, particularly an automated guided vehicle (AGV) or an autonomous mobile robot (AMR), for lifting off a ground surface, transporting over the ground surface and setting down on the ground surface a load carrier, particularly a pallet or cart, wherein the self-propelled vehicle comprises:

[0013] - a frame;

[0014] - one or more first wheel units, mounted on the frame, with one or more first transport wheels embodied to support the frame on the ground surface and to displace it over the ground surface;

[0015] - one or more drive motors for driving one or more first transport wheels of the first wheel units;

[0016] - one or more carrier units mounted on the frame for up and downward displacement, wherein each carrier unit has a support surface which is configured to support the load carrier;

[0017] - a first actuator for displacing the one or more carrier units in up and downward direction, transversely of the one or more carrying surfaces, between a lower position in which the carrier unit can be slid into or under the load carrier and an upper position in which a load carrier resting on the carrier unit is lifted off the ground surface;

[0018] - one or more second wheel units, mounted on each of the carrier units, with one or more second transport wheels; wherein the second wheel units are displaceable between a folded-out position in which at least the second transport wheels are in a lower position and a folded-in position in which the second transport wheels are in an upper position;

[0019] - a second actuator coupled to the one or more second wheel units for the purpose of folding in and folding out each of the second wheel units.

[0020] In the folded-out position in which the second transport wheels of the second wheel units have been displaced to a lower position the second wheel units can support the carrier units locally on the ground surface, this enhancing the stability of the vehicle, particularly while the vehicle travels over the ground surface (optionally provided with a load carrier which may or may not be provided with a load). In the folded-in position in which the second transport wheels of the second wheel units have been displaced to an upper position the carrier units can be slid into or under the load carrier in simple manner. If the upper position is chosen sufficiently high above the ground surface, the previously identified problem of the presence of an obstacle, for instance in the form of the presence of (horizontal) lower support elements of a load carrier such as the connecting boards of a (closed) pallet resting on a ground surface, can be obviated. The outer end of the carrier units can then simply pass these lower support elements without the carrier units or the second wheel units running the risk of running into such an obstacle.

[0021] In embodiments there is an option of travelling omnidirectionally with floating carrier units (also referred to as “prongs”). In determined embodiments each of the second wheel units comprises a part which is displaceable in up and downward direction relative to the relevant carrier unit. The second transport wheels can then be mounted (rotatably) on the relevant part. A second wheel unit is preferably embodied such that when the carrier unit is in the upper position and the second wheel unit is in the folded-out (lower) position, the second transport wheels of the second wheel unit support the relevant carrier unit on the ground surface. During use, the second transport wheels (in addition to the first transport wheels of the first wheel units) then make contact with the ground surface, and the carrier units are supported at two (or more) positions. The first and second wheel units thus make it possible to transport the carrier units over the ground surface in stable manner in the case of a (very) heavy load as well. There is in principle no need for counter-mass, or only a limited counter-mass is needed.

[0022] In a determined embodiment the second transport wheels in a folded-in position are in an upper position in which the second transport wheels lie clear of the ground surface over a predetermined distance. The transport wheels lying clear means they do not come into contact with the ground surface and they therefore extend at a determined distance above the ground surface. The upper position is here chosen such that at least a predetermined distance is always maintained between the upper side of the ground surface and the underside of the carrier units, for instance to ensure that each of the carrier units can be guided freely into or out of the (receiving) space above the lower support element and under the upper support element of the load carrier. This predetermined distance can for instance lie between 1 cm and 10 cm, preferably between 2 cm and 8 cm.

[0023] When the carrier unit is in the lower position and the one or more second wheel units are in folded-out position, the overall dimensions of carrier unit and second wheel unit amount to less than 20 cm in height direction in determined embodiments.

[0024] In the folded-in position the second wheel units are either wholly or partially folded in. The wheel unit and carrier unit can for instance be embodied such that, in folded-in state, the carrier unit has in principle a flat underside (thus minimizing the chances of the transport wheels becoming hooked behind a part of the load carrier (for instance a connecting part / support element of a pallet). In other embodiments the second wheel unit continues to protrude out from under the underside of the carrier unit to some extent.

[0025] In embodiments of the invention a second wheel unit is arranged inside the periphery of the relevant carrier unit, as seen in the horizontal plane. There are also embodiments wherein the carrier unit comprises at least one cavity and the second wheel unit is accommodated in this cavity of the carrier unit at least partially, preferably wholly, in the folded-in state. Such a construction provides in folded-in state a compact carrier unit, especially as seen in height direction, which is moreover relatively flush with the underside of the relevant carrier unit. This further reduces the risk of the carrier unit not being able to be slid properly into the receiving space of a load carrier and / or becoming wedged or stuck therein. The support surface of the carrier unit has a free outer end and an outer end directed toward the frame. In determined embodiments the second wheel unit is positioned closer to the free outer end than to the outer end directed toward the frame. This results in a relatively great mutual distance of the relevant second wheel unit and each of the first wheel units, this enhancing the travel properties and particularly the travel stability of the vehicle. In a determined embodiment the mutual distance (A) between a second wheel unit and each of the first wheel units amounts to at least 40 cm or at least 80 cm.

[0026] In a determined embodiment a control unit is provided for controlling at least the one or more drive motors, the first actuator and the second actuator (and any further actuators). The control unit can here be configured to control the folding in and out of the one or more second wheel units independently of the up or downward displacement of the one or more carrier units. In some cases the control unit will keep the second wheel units folded in while the carrier units are moved into or under the load carrier, are lifted up, travel, are set down and when the carrier units are moved out of the load carrier, in other cases the second wheel units will be folded out after the lifting up, the second wheel units are kept in the folded-out position during travel, and they will be folded in immediately before the load carrier is set back down onto the ground surface.

[0027] In a determined embodiment the control unit is configured to control the drive motors, first actuator and second actuator to:

[0028] - displace the carrier units to the lower position and optionally displace the second wheel units to the folded-in position, to displace the carrier units into or under a load carrier, and to then displace the carrier units from the lower position to the upper position and, optionally, to fold out the second wheel units during or after the upward displacement of the carrier units in order to prepare the vehicle for transportation; and / or

[0029] - fold in the second wheel units after transportation and then displace the carrier units from the upper position to the lower position in order to then move the carrier units out of the load carrier or out from under the load carrier.

[0030] In embodiments the first actuator is attached to at least one carrier unit and to the frame. The first actuator thus co-displaces when the frame is moved over the ground surface. The first actuator can displace all carrier units in height direction simultaneously during travel or standstill of the frame. In determined embodiments the second actuator is attached directly or indirectly to a carrier unit and to a second wheel unit. The second actuator is here preferably attached such that it co-displaces with the up and downward displacement of the relevant carrier unit. The second actuator can particularly be attached to a part of the first actuator, so that the second actuator co-displaces with the first actuator.

[0031] In determined embodiments the vehicle is configured to have the one or more carrier units support on the ground surface only via the frame and the first wheel units when all second wheel units are in the folded-in position. In determined embodiments the one or more second wheel units comprise one or more unidirectional second transport wheels. This is understood to mean that the wheels are embodied and suspended such that they enable travel in only one determined direction (whereby a reciprocal movement counts as one single direction). This direction is usually only the longitudinal direction of the vehicle, so that the vehicle is in fact most suitable to travel forward or rearward. In determined embodiments the second wheel units take a steerable form so that the direction of travel of the corresponding part of the carrier units can be adjusted and / or varied as desired, this enhancing the manoeuvrability of the vehicle.

[0032] A steerable second wheel unit is however complex and expensive. It has been found that such a complex wheel unit is not necessary. In order to be able to manoeuvre in small spaces it is most important that the carrier units are also able to move laterally (so in a direction transversely of the longitudinal direction of the vehicle). This is particularly important during the starting stage, in which the carrier units of the vehicle must be slid neatly into the receiving space of a load carrier, and in the final stage in which the carrier units must be moved back out from under the load carrier. During the transport stage between the starting and final stage the vehicle will generally require less rotating and turning, and will mainly travel in the longitudinal direction.

[0033] In a determined embodiment the one or more second wheel units therefore comprise one or more omnidirectional second transport wheels. Such omnidirectional wheels at least enable the vehicle to be positioned in a very small space.

[0034] In other embodiments the one or more of the second wheel units comprise both a unidirectional transport wheel oriented in a first direction and a unidirectional wheel oriented in a second direction, transversely of the first direction. The second wheel units particularly each comprise a first set of second transport wheels configured to move the relevant outer end of the carrier units in longitudinal direction and a second set of second transport wheels configured to move the relevant outer end of the carrier units in transverse direction. The first set of wheels and the second set of wheels travel alternately over the ground surface here.

[0035] In other further embodiments the second wheel unit is configured in the folded-out position to displace the transport wheel oriented in the first direction relative to the transport wheel oriented in the second direction in the height between a first support position, wherein the transport wheel oriented in the first direction supports on the ground surface, and a second support position wherein the transport wheel oriented in the second direction rests on the ground surface. In a determined embodiment one or more third actuators are provided for driving the displacement between the first and second support position. This third actuator can for instance once again be controlled by the above stated control unit. The control unit can here be embodied such that the vehicle can easily rotate and be driven by the first wheel units.

[0036] In a determined embodiment the carrier unit is mounted pivotally on the frame in order to enable it to tilt while lifting, transporting or setting down. This can be realized in determined embodiments by mounting the carrier units on a carriage which is mounted fixedly on a frame part which is arranged for tilting in forward and rearward direction. In principle, the tilting shaft forms part of a tilting mechanism which enables the pivoting through only a limited angular range, for instance a maximum of + / - 10 degrees or a maximum of + / - 5 degrees. This in order to allow the vehicle to support stably on the ground surface, also if the ground surface has irregularities (particularly height differences).

[0037] The pivotal mounting is important for distributing forces over the driven wheels in vehicles with and without load. It is also important that use is made of at least three (for instance four) driven omnidirectional wheels, so that omnidirectional travel with floating prongs is possible.

[0038] In determined embodiments a carriage coupled fixedly to a part of the first actuator is provided, this carriage forming part of the one or more carrier units. The carriage including the outer ends of the carrier units thus co-displace with the relevant part of the first actuator. The vehicle also comprises a rod system, for instance a rod system which extends in a parallelogram arrangement and which is structurally connected to at least one of the carrier units, preferably to each of the carrier units, and to the (fixed) frame. The parallelogram construction makes it possible to displace the (carriage with the) carrier units in upward and downward direction in a linear movement, wherein the orientation of the carrier units relative to the ground surface (usually the lying or even horizontal orientation) is preserved during the displacement. In other embodiments a linear guide construction is applied.

[0039] In a determined embodiment the second actuator is connected via a push rod construction to one or more of the second wheel units. The push rod construction transmits an extending or retracting movement of part of the second actuator to an up and downward movement of the second wheel units.

[0040] At least one of the first actuator and second actuator preferably extend in upward orientation relative to the frame, and the first and second actuator still more preferably extend adjacently of each other and / or parallel to each other. This makes it relatively easy to realize the up and downward movement of the carrier units and / or means that the dimensions of the vehicle in longitudinal and / or width direction can be limited. When use is made of a hydraulic cylinder, this can however also be realized in other embodiments by attaching the hydraulic cylinder directly to the (horizontal) push rods. In these embodiments the relevant actuator can otherwise also be in an orientation differing from an upright orientation.

[0041] In a determined embodiment two or more carrier units together form a fork for carrying the carrier unit on two or more support surfaces.

[0042] In advantageous embodiments of the invention the second wheel units are passive (i.e.) nondriven wheel units. The second transport wheels of the second wheel units further extend in a fixed direction relative to the longitudinal direction of the carrier units (i.e. in longitudinal direction and in transverse direction), and this direction cannot be adjusted. This allows the construction of the carrier units to be simple and light. In other embodiments the direction of the wheels can however be adjusted (so that the carrier units are steerable). It is for instance possible for one or more further actuators to be provided for driving and / or steering the second transport wheels.

[0043] In a determined embodiment at least one of the first wheel units is mounted on the frame with a tilting shaft. This in order to prevent static indeterminacy of the vehicle resting on a ground surface. This can for instance be the case when there are four driven wheels (when there are three wheels, this is not necessary under determined circumstances).

[0044] In a determined embodiment the one or more drive motors for the first wheel units comprise an electric motor and a battery, so that the vehicle can function wholly independently and without being connected to a mains electricity. In determined embodiments each wheel unit comprises its own battery, but in other embodiments a shared battery is provided for two or more of the wheel units - and preferably for all wheel units. It is noted here that when reference is made here to “battery”, this can mean that one single battery is provided or that a battery pack comprising more than one battery is provided.

[0045] A second aspect of the invention comprises the use of a self-propelled vehicle as described herein.

[0046] Further advantages, features and details of the present invention will be elucidated with reference to the following description of some embodiments thereof. Reference is made in the description to the figures.

[0047] Figure 1A shows a perspective side view of an embodiment of a self-propelled vehicle, the carrier units of which are in the lower position and the second wheel units of which are in the folded- in position;

[0048] Figure IB shows the side view of figure 1, provided with an example of a load carrier;

[0049] Figure 2 shows a more detailed side view of the embodiment of the self-propelled vehicle shown in figure 1 , with the carrier units in the upper position and the second wheel units in the folded- out position, wherein a load carrier in the form of a pallet is shown in broken lines;

[0050] Figure 3 shows a top view of the configuration of figure 2;

[0051] Figure 4 shows a partially cut-away view of the vehicle of figures 1 and 2;

[0052] Figure 5 shows an oblique rear view of the vehicle;

[0053] Figure 6 shows a partially cut-away side view of the rear part of the self-propelled vehicle, with the carrier units in the lower position and without a load carrier;

[0054] Figure 7 shows a bottom view of the self-propelled vehicle;

[0055] Figures 8-10 show in each case a partially cut-away side view of the embodiment of the foregoing figures, respectively in a first stage with the carrier units in the lower position and the second wheel units folded in (figure 6), in a second stage with the carrier units displaced to the upper position and the second wheel units still folded in (figure 7), and in a third stage with the carrier units in the upper position and the second wheel units folded out (figure 8); Figures 11 A-l 1C show partially cut-away views of the free outer end of a carrier unit according to a determined embodiment in respectively a folded-in position (figures 11 A and 1 IB) and a folded-out position (figure 11C);

[0056] Figure 12 shows a perspective view, as seen obliquely from below, of a cut-away free outer end of a carrier unit according to a further embodiment in which use is made of an omnidirectional second wheel unit according to a first embodiment, and an enlargement of the omnidirectional wheel unit in question;

[0057] Figure 13 shows a perspective view, as seen obliquely from below, of a cut-away free outer end of a carrier unit according to yet another embodiment in which use is made of an omnidirectional second wheel unit according to a second embodiment;

[0058] Figures 14A-14D show respective side views of the embodiment of figure 11, with the second wheel unit in a completely folded-up position (figure 14A), an intermediate position between a folded-out position and wholly folded-in position (figure 14B), a first folded-out position, also referred to here as the first support position for having the carrier unit be supported by a transport wheel extending in a first direction (figure 14C), and a second (even further) folded-out position, also referred to here as the second support position, for having the carrier unit be supported by a transport wheel extending in a second direction, transversely of the first direction (figure 14D).

[0059] The figures show a further embodiment of a self-propelled, automated guided vehicle (AGV) 1. It will be apparent that a vehicle in the form of an autonomous mobile robot (AMR) can also be applied in respect of this embodiment. Such AMRs are generally the same as AGVs, with the understanding that the control of the AMR is more developed than that of the AGV.

[0060] Referring to figures 1A-1B, 2-7, an embodiment of a self-propelled vehicle according to the invention is shown. In the shown embodiment the self-propelled vehicle 1 is a robot provided with sensors and control means whereby it can find its way (i.e. can navigate) essentially autonomously over a ground surface, for instance a ground surface of a warehouse, factory or similar location.

[0061] In the shown embodiment the vehicle 1 is constructed from at least an upright frame 2. Arranged around the frame 2 of vehicle 1 is a housing 5, for instance of plastic or light metal. Provided on the upper side of housing 5 is a control panel 10 whereby a user can operate the vehicle. In addition to this operating option via control panel 10, the vehicle can also be controlled remotely, for instance via a wireless communication unit of a control unit 7 which is provided on the underside of frame 2 (figure 7) or which is provided elsewhere (in other embodiments), for instance at a position above the above stated battery or the above stated battery pack.

[0062] The frame 2 can be advanced via a number of wheel units (first wheel units 12, to be described further) over a ground surface (O) such as a floor of a factory or warehouse. The vehicle also comprises two carrier units 19, 19’ positioned adjacently of each other. The carrier units 19, 19’ form as it were the elongate teeth of a fork 18 for lifting, transporting and setting down a load carrier (L, see figure IB). In the shown embodiment the two carrier units 19, 19’ also have a common part, also referred to hereinafter as the carrier carriage or carriage 70, whereby they are jointly connected to the frame 2, among other things. A carriage housing 11 is provided around the carriage 70. This housing is connected fixedly to the carrier units 19, 19’ and therefore co-displaces with the up and downward movement thereof. The carriage housing 11 has an upright, flat front side against which a load carrier and optionally the load arranged thereon can rest.

[0063] Figures IB, 2 and 3 show a random example of a load carrier (L) (without load) which can be lifted, transported and set down using the vehicle 1 according to the invention. In the shown version the load carrier (L) is a pallet 150 comprising a number of lower support elements 152 (more specifically, two parallel wooden lower boards on opposite outer ends of the pallet 150), a number of upper support elements 151 (more specifically, seven parallel wooden upper boards, parallel to the lower boards as well) which form a load arranging part, as well as connecting elements 153 arranged between the upper and lower support elements for mutually connecting the upper and lower support elements (more specifically, a number of wooden blocks and planks extending transversely of the upper and lower boards). Formed between the connecting elements is a receiving space 115 with two passages 154, 155, through which respectively a right-hand carrier unit 19 and a left-hand carrier unit 19’ must be moved in order to enable pallet 150 to be lifted and displaced. When the fork 18 consisting of carrier units 19, 19’ has been slid into the receiving space 115 of the load carrier (L), the support or carrying surfaces 20 of the carrier units 19, 19’ can engage on the underside of the load arranging part of the load carrier formed by the upper support elements 151.

[0064] The above stated frame 2 comprises a bottom frame part 4 and a top frame part 3. The bottom frame part 4 is a generally lying part on the underside of the vehicle 1. Arranged on the underside of the bottom frame part 4 of frame 2 is a number of first wheel units 12 provided with one or more (first) wheels, whereby frame 2 can travel over the ground surface. Such first wheel units can be embodied in diverse ways. The first wheel units 12 can for instance be embodied pivotally relative to respective upright shafts so that the running direction of the wheels can be varied. This means that these wheel units 12 are steerable.

[0065] One or more of the first wheel units 12 is driveable using one or more drive motors. These are powered via one or more batteries 72 (shown schematically in figures 4, 8 and 9).

[0066] Figures 6 and 7 show the first wheel units 12 and their relative arrangement in more detail. Each of the first wheel units 12 is rotatable around an upright shaft 12A (figure 7) and in the shown embodiment comprises at least two transport wheels which are positioned adjacently of each other on either side of the upright shaft and which can be controlled individually of each other. Controlling the transport wheels individually (i.e. having one transport wheel turn faster than the other) enables the wheel units 12 to be rotated relative to bottom frame part 4 so that the vehicle is movable in different directions.

[0067] In the shown embodiment the bottom frame part 4 is provided on the front side thereof with two first wheel units 12, each of which is positioned in or close to a corner of the bottom frame part 4, while a double first wheel unit 12 is realized on the rear side of the bottom frame part 4. The wheel units 12 of the double wheel unit are not mounted directly on the bottom frame part 4. The wheel units 12 are mutually connected via a connecting element 13 which is mounted pivotally on the bottom frame part 4 via a lying pivot shaft 14. This makes it possible to tilt the two wheel units 12 around the shaft 14, such that no static indeterminacy occurs and all transport wheels of all first wheel units 12 rest stably on the ground surface in principle.

[0068] The above stated top frame part 3 of frame 2 comprises an upright, outer frame part 9 (figure 5) which is mounted fixedly on the bottom frame part 4 and which supports the housing 5. A frame part 8 which is tiltable forward and rearward to some extent is provided inside the outer frame 9 and clear thereof. This tiltable frame part 8 is arranged on two tilting mechanisms 22 (figures 4 and 6) which are mounted on the upper side of the bottom frame part 4. The tilting mechanisms 22 enable the tiltable frame part 8 to be tilted in forward and rearward direction to some extent (through a limited stroke, so that the tilting movement is limited), so that any variations in the height of the ground surface can be accommodated and the carrier units do not drop to the ground when the wheel units are folded in.

[0069] A first actuator 50 is attached fixedly to the tiltable frame 8. In the shown embodiment this first actuator 50 is arranged vertically and comprises an electric extending cylinder 51. This extending cylinder 51 has a cylinder rod 52 extendable in longitudinal direction of the actuator, i.e. in up and downward direction in the shown configuration, and a cylinder housing 53. The extendable cylinder rod 52 is attached with its free outer end to the tiltable frame part 8 of frame 2, while the cylinder housing 51 is attached fixedly to the above stated carrier carriage or carriage 70 which is displaceable up and downward in height direction.

[0070] An embodiment of the carriage 70 is shown in detail in figure 6. The carriage 70 of this embodiment comprises an upright support part 76, on either side of which are arranged two flanges 75. As will be described below, the flanges 75 (see figure 6) are mounted fixedly on the cylinder housing 53 of first actuator 50, and also on a cylinder housing 63 of second actuator 60, with fastening elements 78 such as screws. This means that when actuator 50 is operated, it is not only the cylinder housing 53 of first actuator 50 that moves upward or downward, but the attached carriage 70 with the two carrier units 19, 19’ and second actuator 60 also moves upward or downward (direction Pi, figures 8, 9).

[0071] When the length of extending cylinder 51 is increased, i.e. when cylinder rod 52 is extended outward, the carriage 70 attached to the cylinder housing 53 of cylinder 51 will be displaced upward. When the length of cylinder 51 is however reduced by retracting cylinder rod 52, carriage 70 is displaced downward. Carriage 70 forms part of both carrier units 19, 19’. Therefore, when carriage 70 is displaced upward, the carrying surfaces 20 of the carrier units 19, 19’ are also displaced upward while, when carriage 70 is displaced downward, the carrying surfaces 20 of the two carrier units 19, 19’ are displaced downward. The above is shown inter alia in figures 8 and 9. Figure 8 shows the situation where the carrier units 19, 19’ are in the lower position and figure 9 shows the situation where they are in the upper position.

[0072] Also drawn in the figures is a rotatable rod system 23 which is used to guide the up and downward movement of carriage 70 of carrier units 19, 19’. Rod system 23 comprises two upper rods 24a mounted rotatably on either side of carriage 70 and two lower rods 24b mounted rotatably on either side of carriage 70. The upper and lower rods 24a, 24b are mounted via hinges 79 on the (stationary) tiltable frame part 8 of frame 2, while the upper and lower rods 24a and 24b are mounted via hinges 83 rotatably on the cheeks 75 of carriage 70. In the shown embodiment the rod system is a parallelogram construction, which ensures that carriage 70 remains neatly in an upright (particularly vertical) position during up and downward movement thereof. As a result, the carrier units 19, 19’ attached to carriage 70 will also remain in a correct, fixed orientation relative to the rest of the vehicle, when they are moved up and downward as well.

[0073] While figures 8 and 9 show that carrier units 19, 19’ of the fork 18 can be moved upward and downward (Pi), a second wheel unit 21 provided at the free outer end 100 of each of the carrier units 19, 19’ can be folded in or out independently of this up and downward movement of the carrier units. This is shown in figures 9 and 10. Figure 9 shows the vehicle in the upper position with folded-in wheel units 21, while figure 10 shows the vehicle in the same (upper) position with folded-out wheel units 21. Figures 11A and 11B show both positions of wheel units 21 in more detail according to a determined embodiment.

[0074] Figures 11 A and 1 IB show a rotatable first connecting part 35 which is mounted via one or more shafts 37 rotatably on downward hanging flanges 32 of carrier units 19, 19’. Provided on the outer end of first connecting part 35 lying opposite shaft 37 is a second connecting part 33. The second connecting part 33 is mounted via a (tilting) shaft 39 rotatably on the first connecting part 35. The (second) transport wheels 34 of the second wheel unit 21 are arranged rotatably on this second connecting part 33.

[0075] As shown inter alia in figure 11C, the second connecting part can rotate via the shaft 39, and this shaft therefore forms the tilting point for the connecting part and the wheels 34 mounted thereon. The position of shaft 39 (i.e. the tilting point) then lies some distance from the central axis 65 (figure 11C) between the respective shafts 66 of (transport) wheels 34. This distance (a) is chosen such that the wheels 24 remain in the same orientation (or, in other words, that the second connecting part 33 has a tendency to rotate toward the horizontal position of equilibrium under the influence of the force of gravity) when the wheels have come away from the ground, when the wheels have been lifted off the ground surface by the second actuator 60. This also makes the play of forces between wheels 34, the rod mechanism (with rod 38) and second actuator 60 substantially linear.

[0076] The (first) connecting part 35 can be swung upward and downward via an operating mechanism which is driven by the second actuator 60. The second actuator 60 comprises a cylinder housing 63 attached to carriage 70, and an extendable cylinder rod 62. The operating mechanism further comprises a push-pull rod 38 connected thereto via a connecting piece 39. The push-pull rod 38 is attached via a shaft 47 rotatably to a protrusion 48, provided on the (first) connecting part 35, of the second wheel unit. The push-pull rod 38 can be moved reciprocally (substantially horizontally) (in a translating, reciprocating movement, see direction P2, figures 11A-11C), wherein a movement in the direction of the second wheel unit 21 provides for the rotation of the first connecting part 33 (rotation Ri) from the upper position shown in figures 11 A and 1 IB to the lower position shown in figure 11C in order to fold out the relevant second wheel unit 21, while a movement of the push-pull rod in a direction away from the second wheel unit 21 results in rotation of the first connecting part 33 in opposite direction, from the lower position shown in figure 11C to the upper position shown in figures 11A and 11B.

[0077] As described above, the reciprocating movement of the push-pull rod 38 is driven by the second actuator 60. The rod 38 can be displaced to the left or to the right in a translating movement in that the rod is connected at the outer end opposite shaft 37 pivotally (via hinge 56, see figure 10) to the above stated intermediate part 39. This intermediate piece 39 is on one side connected rotatably via shaft 56 to rod 38 and is connected on the other side via shaft 58 to the displaceable cylinder rod 62, wherein the intermediate part 39 itself is coupled rotatably via a shaft 57 to the relevant carrier unit 19, 19’.

[0078] When the second actuator 60 is driven and the cylinder rod 62 is displaced downward, connecting piece 39 will begin to rotate (R2) about shaft 57 and the rotating movement will be converted into a translating movement of the push-pull rod 38 in the direction of the second wheel unit 21. This results in folding out of wheel unit 21. When the second actuator 60 is driven and the cylinder rod 62 is retracted and thus displaced upward, connecting piece 39 will begin to rotate about shaft 57 in opposite direction and the rotating movement will be converted into a translating movement of the push-pull rod 38 in a direction away from the second wheel unit 21. This results in folding in of wheel unit 21.

[0079] Figure 7 shows that the two wheels 34 of each of the second wheel unit 21 extend in one single direction, particularly the longitudinal direction of the carrier units. In many embodiments this configuration of the wheels 34 suffices to manoeuvre the vehicle under a load carrier, to transport the load carrier and finally set the load carrier down again at a different position. Situations can however be envisaged where there is for instance very little space for the vehicle to manoeuvre and particularly to slide the two elongate carrier units 19, 19’ into or out of the receiving space 115 of a load carrier (L). In some situations it is desirable to turn the vehicle with a short turning radius or even have the vehicle turn essentially about its own centre. In such situations it would be convenient for the carrier units to comprise wheels that not only extend in a first direction, i.e. the longitudinal direction of the carrier units, but also provide the option of moving the carrier units in a second direction, transversely of the first direction (i.e. the longitudinal direction of the carrier units). Embodiments of the vehicle in which this is possible are for instance shown in figures 12-14. In figure 12 there is a wheel unit 21, the construction of which correspond largely with the embodiment shown in figures 11 A-l 1C wherein use is made of unidirectional transport wheels 34. In the embodiment of figure 12 use is however made of a set of omnidirectional wheels 80. Each of the omnidirectional wheels 80 is constructed from a number of first wheel parts 81 extending at different positions along the periphery of the wheel and a number of second wheel parts 82 located between the first wheel parts 81. The first wheel parts 81 are fixed wheel parts and are mounted on or formed integrally with the centre (shaft) of the wheel, while the second wheel parts 82 are embodied for rotation relative to the rest of the wheel. More particularly, the second wheel parts 82 are rotatable about shafts (not shown) extending in principle in the peripheral direction of the relevant wheel 80. In other words, while the first wheel parts 81 have the result that the vehicle is able to move in longitudinal direction (PL) when wheels 80 turn, in that the wheels are able to rotate in a first rotation direction R3, the second wheel parts 82 have the result that the relevant wheel is also displaceable in transverse direction (PD) in that the second wheel parts 82 are embodied for rotation in a second rotation direction (R4).

[0080] Figure 13 shows a different embodiment of an omnidirectional wheel unit 21. Use is made here of unidirectional wheels which are arranged transversely of each other in order to make the relevant wheel unit omnidirectional. First connecting part 35 is connected via shaft 37 (and intermediate parts 30) rotatably to a respective flange 32 and connected via a shaft 45 rotatably to a second connecting part 61. The second connecting part 61 is in turn connected via shaft 59 rotatably to a third connecting part 44. Further provided is a spring 93 which is arranged between the first connecting part 35 and the second connecting part 61. The second connecting part 61 is held under tension of a spring 93, such that the second connecting part has a tendency to tilt relative to the first connecting part 35, as will be further elucidated below with reference to figures 14A-14D.

[0081] In the shown embodiment the omnidirectional wheel unit 21 comprises two unidirectional wheels 90, 91, wherein the one unidirectional wheel 90 can rotate around a shaft 45 perpendicularly of the longitudinal axis of carrier unit 19, 19’, whereby the carrier unit is able to move in longitudinal direction (PL) while the second unidirectional wheel 91 is able to rotate around a shaft 46 parallel to the longitudinal axis of the carrier unit, so that the carrier unit can be advanced in a direction (PD) transversely of the longitudinal direction thereof. It is important here to ensure that only one of the two wheels 90, 91 is resting on the ground surface (O) at any time. If both wheels 90, 91 were to make contact with the ground surface simultaneously, the vehicle cannot move, or cannot move as well.

[0082] In order to realize this one or more stop elements 49 are provided, behind which a corresponding protrusion 64 of the second connecting part 61 can hook so that the pivoting motion of the connecting part remains limited. When a wheel 91 rests on the ground surface (O), connecting part 61 will therefore pivot no further under the weight of the load. The push-pull rod 38 keeps the whole stable, and the second wheel 90 is thus prevented from making contact with the ground surface too. When the above stated push-pull rod or rod 38 is operated, connecting part 35 (based on the position of fig. 14A) begins to move downward into the position shown in fig. 14B. While the first connecting part 35 is being displaced downward by push rod 38, the second connecting part 33 will have a tendency to tilt slightly upward as a result of the presence of the spring 93. An upward-tilted position of the second connecting part 33 is shown in figure 14B. When push-pull rod 38 is pushed further, the first connecting part will tilt even further downward (until the situation shown in figure 14C occurs), wherein the second connecting part 33 will still keep extending upward to some extent. Hereby, the first transport wheel 90 will touch the ground surface (O), but the second transport wheel 91 will not. In this position it is thus only a wheel 90 of the second wheel unit 21 extending in longitudinal direction of the carrier units that touches the ground surface, and the vehicle can be advanced in longitudinal direction. When the carrier unit, particularly the free outer end thereof, must however be advanced in transverse direction, the push-pull rod 38 is pushed even further until the position shown in figure 14D is reached. The push-pull rod 38 tilts the first connecting part 35 further downward so that, finally, only wheels 91 touch the ground surface. Conversely, when push-pull rod 38 is moved in the opposite direction and the first connecting element 35 is thus pushed upward from the position shown in figure 14D to that of figure 14C, the spring action of spring 93 results in the second connecting part 61 tilting upward counter to the force of gravity. In the situation shown in figure 14D the outer end (particularly the free outer end 100) of carrier unit 19, 19’ can be displaced in transverse direction, for instance by correct control of one or more of the above stated first wheel units 12.

[0083] During use the vehicle can be manoeuvred in the lower position of the carrier unit, i.e. the position shown in figure 6, such that the carrier units 19 can be moved readily into the receiving space 115 of a load carrier. The whole of carriage 70 and carrier units 19, 19’ is then displaced upward by operation of first actuator 50 until the position shown in figure 9 is reached. Due to the absence of a counterweight in the vehicle, it is not advisable to begin displacing the load carrier with the heavy load that may be arranged thereon in this position, since in some cases the whole of load carrier and vehicle will become too unstable while travelling.

[0084] In most cases it will be decided to fold out the wheel units 21 of both carrier units 19, 19’ into the position shown in figure 10 before starting to move a load carrier which has been brought into the upper position shown in figure 9. In this position the load carrier with the load arranged thereon is supported by both all first wheel units 12 and all second wheel units 21. The distance A (figure 10) between the second wheel units 21 and the nearest first wheel unit 12 is further chosen such that the forces on the load carrier are distributed substantially uniformly over all the wheel units. The second wheel units 21 are preferably located in an area close to the free outer end 100 of the carrier units 19, 19’, so that said distance (A) is relatively great. In other embodiments (not shown) it is further possible to provide additional wheel units, for instance additional second wheel units at positions further away from the free outer end of the carrier units. In this way the downward forces on the vehicle caused by the load carrier can be distributed even more effectively. When the vehicle has reached its destination, the second wheel units can be folded in and the carrier units 19, 19’ can subsequently be displaced downward in order to set the load carrier down on the ground surface. With the second wheel units in the folded-in position, the carrier units 19, 19’ can be easily moved out of the receiving space of the load carrier without the possibility of the second transport wheels encountering an obstacle while travelling out.

[0085] Although folding out the second wheel units before travel is preferred in most cases, in determined other cases, for instance in cases where the load on load carrier L is relatively low, it is indeed possible to move the vehicle safely without the second wheel units being folded out.

[0086] It is further possible that the load carrier to be picked up is not resting on the ground surface over which the vehicle travels, but at a different (usually higher) position, for instance when the load carrier is arranged in a warehouse rack. In such a situation the load carriers are first displaced to the desired height (for instance different from the height shown in figure 9), the carrier units are moved into the receiving space of the load carrier, and the load carrier is lifted to some extent and moved out of the warehouse rack. As soon as there is space for the load carrier to be lowered, the carrier units of the machine are displaced downward. At the same time, the wheel units of the carrier units are folded out so that the load carrier is also supported by these wheel units in the lower position of the carrier units. When placing the load carrier in a warehouse, the above steps are performed in reverse order.

[0087] In the shown embodiments at least one of the first and second actuator 50, 60 (and preferably both actuators 50, 60) are of the electric type. The first and second actuator 50, 60 particularly comprise an electric extending cylinder. In other embodiments one or more of the actuators 50, 60 can for instance be embodied as a hydraulic extending cylinder. A hydraulic extending cylinder can be powered in usual manner via a hydraulic drive, which is not shown but is disposed in practice on a placing surface 6 or elsewhere in the vehicle.

[0088] Although in the embodiments described up to this point the transport wheels of the second wheel units 21 extend in a fixed direction, or at least enable a rotation in a single direction, in other embodiments the wheel units can be embodied such that the wheels are steerable. This steering can take place by mounting the wheels on a pivotable mounting part which can be pivoted around an upright shaft by means of a further actuator (not shown).

[0089] The invention is further defined by the following clauses.

[0090] 1. Self-propelled vehicle, particularly an automated guided vehicle (AGV) or an autonomous mobile robot (AMR), for lifting off a ground surface, transporting over the ground surface and setting down on the ground surface a load carrier, particularly a pallet or cart, wherein the self-propelled vehicle comprises:

[0091] - a frame;

[0092] - one or more first wheel units, mounted on the frame, with one or more first transport wheels embodied to support the frame on the ground surface and to displace it over the ground surface; - one or more drive motors for driving one or more first transport wheels of the first wheel units;

[0093] - one or more carrier units mounted on the frame for up and downward displacement, wherein each carrier unit has a support surface which is configured to support the load carrier;

[0094] - a first actuator for displacing the one or more carrier units in up and downward direction, transversely of the one or more carrying surfaces, between a lower position in which the carrier unit can be slid into or under the load carrier and an upper position in which a load carrier resting on the carrier unit is lifted off the ground surface;

[0095] - one or more second wheel units, mounted on each of the carrier units, with one or more second transport wheels, wherein the second wheel units are displaceable between a folded-out position in which at least the second transport wheels are in a lower position and a folded-in position in which the second transport wheels are in an upper position;

[0096] - a second actuator coupled to the one or more second wheel units for the purpose of folding in and folding out each of the second wheel units.

[0097] 2. Self-propelled vehicle according to clause 1, wherein each of the second wheel units comprises a part which is displaceable in up and downward direction relative to the relevant carrier unit.

[0098] 3. Self-propelled vehicle according to clause 1 or 2, wherein the second wheel unit is embodied such that when the carrier unit is in the upper position and the second wheel unit has been displaced to the folded-out position, the second wheel unit can support the relevant carrier unit on the ground surface.

[0099] 4. Self-propelled vehicle according to clause 1, 2 or 3, wherein the second transport wheels in a folded-in position are in an upper position in which the second transport wheels lie clear of the ground surface over a predetermined distance.

[0100] 5. Self-propelled vehicle according to any one of the foregoing clauses, wherein a wheel unit is arranged inside the periphery of the relevant carrier unit, as seen in the horizontal plane, and / or wherein the carrier unit comprises at least one cavity and the second wheel unit is accommodated in the cavity of the carrier unit at least partially, preferably wholly, in the folded-in state.

[0101] 6. Self-propelled vehicle according to any one of the foregoing clauses, wherein the support surface of the carrier unit has a free outer end and an outer end directed toward the frame, and wherein the second wheel unit is positioned closer to the free outer end than to the outer end directed toward the frame.

[0102] 7. Self-propelled vehicle according to any one of the foregoing clauses, wherein the mutual distance between a second wheel unit and each of the first wheel units amounts to at least 40 cm or, preferably, at least 80 cm.

[0103] 8. Self-propelled vehicle according to any one of the foregoing clauses, comprising a control unit for controlling the one or more drive motors, the first actuator and the second actuator, wherein the control unit is preferably configured to control the folding in and out of the one or more second wheel units independently of the up or downward displacement of the one or more carrier units.

[0104] 9. Self-propelled vehicle according to clause 8, wherein the control unit is configured to control the drive motors, first actuator and second actuator to:

[0105] - displace the carrier units to the lower position and optionally displace the second wheel units to the folded-in position, to displace the carrier units into or under a load carrier, and to then displace the carrier units from the lower position to the upper position and, optionally, to fold out the second wheel units during or after the upward displacement of the carrier units in order to prepare the vehicle for transportation; and / or

[0106] - fold in the second wheel units after transportation and then displace the carrier units from the upper position to the lower position in order to then move the carrier units out of the load carrier or out from under the load carrier.

[0107] 10. Self-propelled vehicle according to any one of the foregoing clauses, wherein the first actuator is attached to at least one carrier unit and to the frame.

[0108] 11. Self-propelled vehicle according to any one of the foregoing clauses, wherein the first actuator is configured to displace all carrier units simultaneously.

[0109] 12. Self-propelled vehicle according to any one of the foregoing clauses, wherein the second actuator is attached to a carrier unit and a second wheel unit and / or wherein the second actuator is attached to the first actuator for co-displacement with the up and downward displacement of the relevant carrier unit.

[0110] 13. Self-propelled vehicle according to any one of the foregoing clauses, which is configured to have the one or more carrier units support on the ground surface only via the frame and the first wheel units when all second wheel units are in the folded-in position.

[0111] 14. Self-propelled vehicle according to any one of the foregoing clauses, wherein the one or more second wheel units comprise one or more unidirectional second transport wheels.

[0112] 15. Self-propelled vehicle according to any one of the clauses 1-14, wherein the one or more second wheel units comprise one or more omnidirectional second transport wheels.

[0113] 16. Self-propelled vehicle according to any one of the clauses 1-14, wherein one or more of the second wheel units comprise both a unidirectional transport wheel oriented in a first direction and a unidirectional wheel oriented in a second direction, transversely of the first direction.

[0114] 17. Self-propelled vehicle according to clause 16, wherein the second wheel unit is configured in the folded-out position to displace the transport wheel oriented in the first direction relative to the transport wheel oriented in the second direction in the height between a first support position, wherein the transport wheel oriented in the first direction supports on the ground surface, and a second support position wherein the transport wheel oriented in the second direction rests on the ground surface.

[0115] 18. Self-propelled vehicle according to clause 18, comprising a third actuator for driving the displacement between the first and second support position. 19. Self-propelled vehicle according to any one of the foregoing clauses, wherein the carrier unit is mounted pivotally on the frame in order to enable it to tilt while lifting, transporting or setting down.

[0116] 20. Self-propelled vehicle according to any one of the foregoing clauses, wherein at least one of the first actuator and second actuator comprises an electric actuator.

[0117] 21. Self-propelled vehicle according to any one of the foregoing clauses, wherein at least one of the first actuator and second actuator comprises an electric actuator.

[0118] 22. Self-propelled vehicle according to any one of the foregoing clauses, comprising a rod system, for instance a rod system which extends in a parallelogram arrangement and which is structurally connected to at least one of the carrier units, preferably to each of the carrier units, and to the frame.

[0119] 23. Self-propelled vehicle according to any one of the foregoing clauses, wherein the second actuator is connected via a push rod construction to one or more of the second wheel units.

[0120] 24. Self-propelled vehicle according to any one of the foregoing clauses, wherein at least one of the first actuator and second actuator extend in upward orientation relative to the frame, wherein the first and second actuator preferably extend adjacently of each other and / or parallel to each other.

[0121] 25. Self-propelled vehicle according to any one of the foregoing clauses, wherein two or more carrier units together form a fork for carrying the carrier unit on two or more support surfaces.

[0122] 26. Self-propelled vehicle according to any one of the foregoing clauses, wherein the second wheel units are passive, non-driven wheel units.

[0123] 27. Self-propelled vehicle according to any one of the foregoing clauses, wherein a second wheel unit comprises a further actuator for driving and / or steering the second transport wheels.

[0124] 28. Self-propelled vehicle according to any one of the foregoing clauses, wherein at least one of the first wheel units is mounted on the frame with a tilting shaft.

[0125] 29. Self-propelled vehicle according to any one of the foregoing clauses, wherein a drive motor comprises an electric motor powered via a battery.

[0126] 30. Use of a self-propelled vehicle and / or a system according to any one of the foregoing clauses.

[0127] The invention is not limited to the embodiments thereof described herein. The rights sought are defined by the following claims, within the scope of which numerous modifications can be envisaged.

Claims

CLAIMS1. Self-propelled vehicle, particularly an automated guided vehicle (AGV) or an autonomous mobile robot (AMR), for lifting off a ground surface, transporting over the ground surface and setting down on the ground surface a load carrier, particularly a pallet or cart, wherein the self-propelled vehicle comprises:- a frame;- one or more first wheel units, mounted on the frame, with one or more first transport wheels embodied to support the frame on the ground surface and to displace it over the ground surface;- one or more drive motors for driving one or more first transport wheels of the first wheel units;- one or more carrier units mounted on the frame for up and downward displacement, wherein each carrier unit has a support surface which is configured to support the load carrier;- a first actuator for displacing the one or more carrier units in up and downward direction, transversely of the one or more carrying surfaces, between a lower position in which the carrier unit can be slid into or under the load carrier and an upper position in which a load carrier resting on the carrier unit is lifted off the ground surface;- one or more second wheel units, mounted on each of the carrier units, with one or more second transport wheels, wherein the second wheel units are displaceable between a folded-out position in which at least the second transport wheels are in a lower position and a folded-in position in which the second transport wheels are in an upper position;- a second actuator coupled to the one or more second wheel units for the purpose of folding in and folding out each of the second wheel units, wherein the second actuator is attached to the first actuator for co-displacement with the up and downward displacement of the relevant carrier unit; and- a control unit for controlling the one or more drive motors, the first actuator and the second actuator, wherein the control unit is configured to control the folding in and out of the one or more second wheel units independently of the up or downward displacement of the one or more carrier units.

2. Self-propelled vehicle according to claim 1, comprising a carriage mounted on the frame for up and downward displacement and comprising an upright support part and the one or more carrier units; and wherein the first actuator extends in upward orientation relative to the frame and is connected to the upright support part via a rod system, particularly a rod system extending in a parallelogram arrangement, or via a linear guide construction.

3. Self-propelled vehicle according to claim 1 or 2, wherein each of the second wheel units comprises a part which is displaceable in up and downward direction relative to the relevant carrier unit.

4. Self-propelled vehicle according to any one of the foregoing claims, wherein the second wheel unit is embodied such that when the carrier unit is in the upper position and the second wheel unit has been displaced to the folded-out position, the second wheel unit can support the relevant carrier unit on the ground surface.

5. Self-propelled vehicle according to any one of the foregoing claims, wherein the second transport wheels in a folded-in position are in an upper position in which the second transport wheels lie clear of the ground surface over a predetermined distance.

6. Self-propelled vehicle according to any one of the foregoing claims, wherein a wheel unit is arranged inside the periphery of the relevant carrier unit, as seen in the horizontal plane, and / or wherein the carrier unit comprises at least one cavity and the second wheel unit is accommodated in the cavity of the carrier unit at least partially, preferably wholly, in the folded-in state.

7. Self-propelled vehicle according to any one of the foregoing claims, wherein the support surface of the carrier unit has a free outer end and an outer end directed toward the frame, and wherein the second wheel unit is positioned closer to the free outer end than to the outer end directed toward the frame.

8. Self-propelled vehicle according to any one of the foregoing claims, wherein the mutual distance between a second wheel unit and each of the first wheel units amounts to at least 40 cm or, preferably, at least 80 cm.

9. Self-propelled vehicle according to any one of the foregoing claims, wherein the control unit is configured to control the drive motors, first actuator and second actuator to:- displace the carrier units to the lower position and optionally displace the second wheel units to the folded-in position, to displace the carrier units into or under a load carrier, and to then displace the carrier units from the lower position to the upper position and, optionally, to fold out the second wheel units during or after the upward displacement of the carrier units in order to prepare the vehicle for transportation; and / or- fold in the second wheel units after transportation and then displace the carrier units from the upper position to the lower position in order to then move the carrier units out of the load carrier or out from under the load carrier.

10. Self-propelled vehicle according to any one of the foregoing claims, wherein the first actuator is attached to at least one carrier unit and to the frame.

11. Self-propelled vehicle according to any one of the foregoing claims, wherein the first actuator is configured to displace all carrier units simultaneously.

12. Self-propelled vehicle according to any one of the foregoing claims, wherein the second actuator is attached to a carrier unit and a second wheel unit.

13. Self-propelled vehicle according to any one of the foregoing claims, which is configured to have the one or more carrier units support on the ground surface only via the frame and the first wheel units when all second wheel units are in the folded-in position.

14. Self-propelled vehicle according to any one of the foregoing claims, wherein the one or more second wheel units comprise one or more unidirectional second transport wheels.

15. Self-propelled vehicle according to any one of the claims 1-14, wherein the one or more second wheel units comprise one or more omnidirectional second transport wheels.

16. Self-propelled vehicle according to any one of the claims 1-14, wherein one or more of the second wheel units comprise both a unidirectional transport wheel oriented in a first direction and a unidirectional wheel oriented in a second direction, transversely of the first direction.

17. Self-propelled vehicle according to claim 16, wherein the second wheel unit is configured in the folded-out position to displace the transport wheel oriented in the first direction relative to the transport wheel oriented in the second direction in the height between a first support position, wherein the transport wheel oriented in the first direction supports on the ground surface, and a second support position wherein the transport wheel oriented in the second direction rests on the ground surface.

18. Self-propelled vehicle according to claim 17, comprising a third actuator for driving the displacement between the first and second support position.

19. Self-propelled vehicle according to any one of the foregoing claims, wherein the carrier unit is mounted pivotally on the frame in order to enable it to tilt while lifting, transporting or setting down.

20. Self-propelled vehicle according to any one of the foregoing claims, wherein at least one of the first actuator and the second actuator comprises an electric actuator.

21. Self-propelled vehicle according to any one of the foregoing claims, wherein at least one of the first actuator and the second actuator comprises a hydraulic actuator.

22. Self-propelled vehicle according to any one of the foregoing claims, wherein the second actuator is connected via a push rod construction to one or more of the second wheel units.

23. Self-propelled vehicle according to any one of the foregoing claims, wherein the second actuator extends in upright orientation relative to the frame.

24. Self-propelled vehicle according to any one of the foregoing claims, wherein the first and second actuator extend adjacently of each other and / or parallel to each other.

25. Self-propelled vehicle according to any one of the foregoing claims, wherein two or more carrier units together form a fork for carrying the carrier unit on two or more support surfaces.

26. Self-propelled vehicle according to any one of the foregoing claims, wherein the second wheel units are passive, non-driven wheel units.

27. Self-propelled vehicle according to any one of the foregoing claims, wherein a second wheel unit comprises a further actuator for driving and / or steering the second transport wheels.

28. Self-propelled vehicle according to any one of the foregoing claims, wherein at least one of the first wheel units is mounted on the frame with a tilting shaft.

29. Self-propelled vehicle according to any one of the foregoing claims, wherein a drive motor comprises an electric motor powered via a battery.

30. Self-propelled vehicle according to any one of the foregoing claims, comprising:- a rotatable first connecting part (35) which is mounted via one or more shafts (37) rotatably on a carrier unit (19, 19’);- a second connecting part (33) which is provided on the outer end of the first connecting part (35) lying opposite the one or more shafts (37) and which is mounted via a tilting shaft (39) rotatably on the first connecting part (35), wherein transport wheels (34) of the relevant second wheel unit (21) are arranged rotatably on the second connecting part (33); wherein the tilting shaft (39) is positioned some distance (a), for instance between 1 and 10 cm, preferably between 1 and 3 cm, from imaginary central axis 65 between the respective shafts 66 of said transport wheels 34.

31. Use of a self-propelled vehicle according to any one of the foregoing claims.

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