Pallet truck and method for use thereof

Abstract

Pallet truck for transporting a load carrier, comprising - a base unit (2) comprising - a number of running wheels (18), - an elongate carrier arm (4) with an elongate first carrier surface (8) on the top side of the carrier arm for supporting a load carrier thereon, wherein at least one running wheel of the number of running wheels is provided on the underside of the carrier arm, - a lifting unit (3) comprising - a lifting base body, - two elongate lifting arms (21) extending parallel to the length direction and on mutually opposite sides of the carrier arm, and with an elongate second carrier surface for supporting a load carrier thereon, - a vertical movement device (26) for moving the two lifting arms up and down relative to the lifting base body in the vertical direction between a pick-up state and a transfer state, and - a horizontal movement device (41) for moving the lifting unit to and fro relative to the base unit parallel to the length direction of the carrier arm, between a compact state and an extended state of the pallet truck.

Description

[0001] Title: Pallet truck and method for use thereof

[0002] Description

[0003] The present invention concerns a pallet truck for transporting a load carrier such as a pallet. Pallets exist in various designs and for example are standardized to International Standard ISO 6780 second edition 2003-12-01 “Flat pallets for intercontinental materials handling - Principal dimensions and tolerances”. On the top side, pallets always have a carrier surface for carrying a load thereon and, on the underside, a bottom surface with which the pallet can rest on a substrate such as a floor. Pallets are usually designed with insertion openings on at least two upright sides, so that, from the respective sides, it is possible to insert fork arms of a pallet truck via the insertion openings under the carrier surface of the pallet, and then raise the pallet and transport it. Some types of pallets have a bottom surface which is closed along the complete periphery. Such a closed periphery prevents the fork arms, which at their free ends are provided with fork wheels, from being inserted into the side openings of the pallet concerned because the fork wheels cannot pass through the closed periphery of the bottom surface. For such pallets, it is then also known to use pallet trucks with "floating" fork arms, which means that the fork arms concerned are not fitted with fork wheels at their free ends. Use of such pallet trucks may also be beneficial for lifting and transporting pallets admittedly in which the bottom surface is not closed around the complete periphery, but for which it is preferred or merely possible that a pallet truck approaches the pallet concerned from a side of the pallet where the bottom surface does have a closed periphery. These pallet trucks with floating fork arms are often provided with a counterweight in order to offer resistance against tilting of the pallet truck because of the weight of a pallet with a load thereon. Partly because of such a counterweight, such pallet trucks are relatively heavy and cumbersome and less manoeuvrable. Known pallet trucks which are fitted with a counterweight have a total weight which is substantially higher than the lifting capacity of the pallet trucks concerned.

[0004] European patent application EP 4421018 A1 describes a pallet truck with two extendable lifting arms and two carrier arms on the outsides of these lifting arms. The pallet truck concerned is suitable for picking up closed pallets, wherein, during use, successively the lifting arms are extended in floating fashion up to below thebottom surface of the pallet, the pallet is then raised using the lifting arms, wherein scissor arms are folded out below the lifting arms in order to contribute to the upward movement of the lifting arms, the lifting arms are then retracted again and lowered, wherein the pallet concerned comes to rest on the two carrier arms.

[0005] The invention now proposes an improved, at least in certain aspects, embodiment of a pallet truck which is structurally simpler and, partially as a result, has a relatively low cost price and can be used reliably. For this, the invention proposes a pallet truck according to Claim 1. Insofar as the present description uses the term 'vertical' or a term derived therefrom, this refers to the direction which extends perpendicularly to a flat horizontal substrate if the pallet truck is resting thereon. During use of the pallet truck, the lifting arms may be situated in the pick-up state at a level at which they can be inserted in the horizontal direction under the carrier surface of the pallet, while, in the transfer state, the underside of a pallet picked up by the lifting arms is situated higher than the first carrier surfaces. In contrast to the pallet truck described in EP 4421018 A1, a pallet truck according to the invention has a carrier arm which is provided between the two lifting arms and on the underside of which at least one running wheel of the number of running wheels is provided. This may achieve the advantage that the pallet truck comprises only one carrier arm and fewer running wheels. This can also simplify the control of the pallet truck and lower the risk of faults. A further advantage may lie in the limited space taken up by the pallet truck on the substrate on which the pallet truck rests, because there is no need to also provide carrier arms on sides of the lifting arms facing away from one another. The manoeuvrability and usability of the pallet truck can thereby be improved.

[0006] In an embodiment, the running wheels, in groups or otherwise, are provided at three positions which form the corners of a triangle. In such a triangular arrangement, a stable support can be achieved by the running wheels of the pallet truck.

[0007] In a further embodiment, the triangle is an isosceles triangle, wherein preferably the running wheel or the group of running wheels which is located at the site of the apex of the isosceles triangle is provided on the underside of the carrier arm. Running wheels positioned in this fashion can in particular contribute to a stable support of the pallet truck. In addition, it may offer structural advantages to arrange the running wheels in this manner. In general, it may be advantageous if at least the carrier arm, the lifting arms and the running wheels are arranged mirror-symmetricallyrelative to a vertical mirror plane which extends through the middle of the width of the carrier arm parallel to the length direction of the carrier arm.

[0008] The stability of support from the running wheels can in particular benefit if running wheels or groups of running wheels are provided on mutually opposing outer sides of the carrier arm. This can in particular reduce the risk of lateral tilting of the pallet truck, as may occur if the pallet truck is resting on a sideways sloping surface.

[0009] In particular if it is suitable for the pallet truck to be self-propelled, it is preferred if at least some of the number of running wheels, preferably all running wheels, are of the driven type. The respective drives for the running wheels may here be actuated by the controller of the pallet truck, for example on the basis of observations of sensors with which the pallet truck may be provided. A self-propelled pallet truck can to a large extent operate autonomously.

[0010] In particular if the pallet truck is designed to be self-propelled, it is further preferred if at least some of the number of running wheels, preferably all running wheels, which are pivotable about a vertical pivot axis belonging to a respective running wheel, are connected to the base unit. The running wheels concerned may thus be oriented in any arbitrary travel direction and for this reason may also be described as omnidirectional.

[0011] In a further embodiment, at least some of the number of running wheels, preferably all running wheels, are provided in groups of two coaxial running wheels, wherein, in yet a further embodiment, the vertical pivot axes belonging to running wheels which belong to a group of two coaxial running wheels coincide and extend between the two coaxial running wheels. By driving the two coaxial running wheels in suitable fashion, pivoting of the two running wheels about the common pivot axis can be achieved in order thus to orient the two running wheels in the desired direction.

[0012] In a further embodiment, the horizontal movement device comprises two, preferably no more and no fewer than two, horizontal guides which are provided on mutually opposite sides of the carrier arm, for guiding the horizontal movement of the lifting unit relative to the base unit between the compact state and the extended state. The horizontal guides thus extend parallel to the length direction of the carrier arms. Because the horizontal guides are provided on mutually opposite sides of the carrier arm, the carrier arm, during operation, because of the load acting on the carrier arm via the guides, is not torsionally loaded or only to a limited extent. This partlycontributes to the structural simplicity which can be achieved with such an embodiment.

[0013] In a further embodiment, the free end of the carrier arm protrudes relative to the free ends of the lifting arms at the rear of the pallet truck. The protrusion of the carrier arm here firstly need not restrict the turning circle of the pallet truck, and secondly offers the possibility of arranging the at least one running wheel, which is provided on the underside of the carrier arm, further in the direction of the rearmost free ends of the lifting arms, compared with the situation in which the carrier arm does not protrude, in order to improve the stability of the vehicle. Furthermore, the protrusion of the carrier arm offers the possibility of providing a sensor on the rearmost end, which sensor may be directed sideways and the observations of which are not blocked by the rearmost ends of the lifting arms.

[0014] In general, it may be suitable if the sides of the lifting arms facing away from one another are situated at a distance of between 50 cm and 100 cm, and / or if the width of the carrier arm which extends between the lifting arms is between 25 cm and 35 cm. With such distances, the pallet truck may be suitable for the pallets commonly used in practice, wherein the width of these pallets is between around 80 cm and around 120 cm.

[0015] More generally, it may be suitable if the height of each lifting arm is smaller than the height of each carrier arm, preferably wherein the height of each lifting arm is less than 9 cm or even less than 8 cm. Such a limited height makes the lifting arm suitable for picking up common pallets.

[0016] In a further suitable embodiment, the pallet truck has a width which is between 90 cm and 110 cm, and a length which is between 160 cm and 200 cm.

[0017] In a further embodiment, which may offer advantages in particular from a structural aspect, the vertical movement device comprises at least one vertical guide, preferably at least two vertical guides, further preferably precisely two vertical guides, for guiding the vertical movement of the two lifting arms relative to the lifting base body.

[0018] If the vertical movement device has a lifting mechanism for each of the two lifting arms, which lifting mechanisms are each provided below the second carrier surface of an associated lifting arm, for movement or at least for contributing to the movement of the two lifting arms between the pick-up state and the transfer state, theweight of a load carrier which can be lifted by the lifting arms can be increased. The lifting mechanisms can support the function of the vertical movement device.

[0019] Here, it may be advantageous in particular if each lifting mechanism, at least in the transfer state and preferably also in the pick-up state, extends completely within the rearmost half of the length of the associated lifting arm.

[0020] In an embodiment, each lifting mechanism comprises two scissor arms which are connected together in hinged fashion, and a supporting body is provided at the bottom end of at least one scissor arm. During lifting of a load carrier by the lifting arms, the lifting mechanism in use rests on the substrate via the support body. A support body may be configured for example as a fixed foot or as a rolling body such as a wheel.

[0021] In a further embodiment, the vertical movement device comprises a further lifting mechanism for contributing to the movement of the two lifting arms between the pick-up state and the transfer state, wherein the further lifting mechanism, during operation, exerts a vertical force on the two lifting arms at the front of the two lifting arms. The further lifting mechanism may here, in operation, cooperate with the above-mentioned lifting mechanisms, the vertical movement device of which may be provided for each lifting arm. The further lifting mechanism and the two lifting mechanisms may here be controlled in synchrony by a controller of the pallet truck.

[0022] In a further embodiment, the lifting unit comprises a lifting body via which the two lifting arms are connected to one another and which is connected to the lifting base body so as to be moveable up and down. Such a lifting body may be configured as a plate on which the lifting arms are suspended.

[0023] To promote a reliable transfer of a load carrier from the lifting arms to the carrier arm, in the pick-up state, the second carrier surfaces are situated at the same level as the first carrier surface, or preferably at a lower level than the first carrier surface.

[0024] The possible applications of a pallet truck can be increased if the vertical movement device is configured for moving the two lifting arms up and down relative to the lifting base body in the vertical direction between the pick-up state and a lifted state, wherein, in the lifted state, the second carrier surfaces are situated higher, preferably at least 20 cm higher, than in the transfer state. Thus, with the help of the lifting arms, a load carrier can not only be placed on the carrier arms but also at ahigher level, for example that of a table or roller conveyor which is often at least 45 cm above a substrate.

[0025] The abovementioned optional further lifting mechanism may advantageously be configured for moving the two lifting arms up and down between the pick-up state and the lifted state.

[0026] Here, the further lifting mechanism may be configured for performing a vertical stroke which is greater than the respective vertical strokes which can be performed by the two lifting mechanisms belonging to the two lifting arms. The control system of the pallet truck may here be such that the vertical movement of a load carrier between the pick-up state and the lifted state can only take place if the pallet truck is in the compact state, in order to prevent rearward tilting of the pallet truck.

[0027] In a further embodiment

[0028] the base unit comprises a base body, on the underside of which at least one running wheel of the number of running wheels is provided, and the carrier arm and the base body are movable to and fro relative to one another in the length direction of the carrier arm,

[0029] the lifting unit and the carrier arm are movable to and fro relative to one another in the length direction of the carrier arm, and

[0030] the pallet truck is provided with a transmission which is active between the base body, the carrier arm and the lifting unit so as, during operation of the transmission, because of movement of the carrier arm and the base body relative to one another, to cause movement of the lifting unit and the carrier arm relative to one another.

[0031] Such an embodiment may have the advantage that the horizontal movement device does not need to have a separate drive specifically for moving the lifting unit to and fro relative to the base unit between the compact state and the extended state of the pallet truck. This to-and-fro movement can in fact be eliminated by powering suitable running wheels and blocking further running wheels in targeted fashion so as to brake.

[0032] In a further embodiment, the transmission is configured, during operation, to cause the movement of the lifting unit and the carrier arm relative to one another to be greater than, preferably twice as great as, the movement of the base body and the carrier arm relative to one another.According to a further aspect, the invention also concerns a method for use of a pallet truck according to the invention as described above or as in optional embodiments. The method comprises the steps A to F as defined in Claim 25. The method is ideally suited for automated movement of in particular loaded load carriers intra-logistically such as within a warehouse, factory or distribution centre.

[0033] Specifically for use with a pallet truck of which the base unit comprises a base body and which comprises a transmission as described above, steps B and D are as defined in Claim 26. The blocking of the running wheels concerned may take place for example by orienting these transversely to the intended movement direction or by actively braking these running wheels.

[0034] In a further embodiment, during step D, the lifting unit is stationary and the base unit moves towards the lifting unit. Thus, during step D, the lifting arm can remain resting on the substrate via the above-mentioned lifting mechanisms which are each provided below the second carrier surface of an associated lifting arm.

[0035] Within the last-mentioned context, a further embodiment is distinguished in that, during step C, the respective lifting mechanisms are active in order to contribute to the lifting of the load carrier.

[0036] The invention will now be explained below with reference to the appended drawings which show two possible embodiments of the pallet truck according to the invention.

[0037] Figures 1a to 1c show three isometric rear views of a pallet truck in a first embodiment according to the invention, in a compact state;

[0038] Figure 1d shows the pallet truck from figures 1a to 1c in a top view; Figures 2a and 2b show the pallet truck in the isometric view of figure 1b, but in the extended state in which the lifting arms are in the pick-up state in figure 2a and in the transfer state in figure 2b;

[0039] Figures 3a to 8b show, respectively in an isometric view and in a side view, successive phases during use of the pallet truck;

[0040] Figure 9 shows an isometric view of the pallet truck during another use, in a phase which is comparable to the phase in figures 4a and 4b;

[0041] Figure 10 shows a side view of the pallet truck during another use, in the following phase which is comparable to the phase in figures 6a and 6b;

[0042] Figure 11a shows the pallet truck in a rear view;Figures 11 b and 11 c show a cross-section XI - XI in figure 11 a, while the pallet truck is respectively in the compact state and in the extended state;

[0043] Figures 12a and 12b show two isometric rear views of a pallet truck according to the invention in a second embodiment, in a compact state;

[0044] Figures 13a and 13b show the pallet truck from figures 12a and 12b but in extended state;

[0045] Figure 14 shows the pallet truck in a rear view;

[0046] Figures 15a and 15b show a cross section XV-XV while the pallet truck is respectively in the compact state and in the extended state.

[0047] Figures 1a to 1c show various views, cross sections, states and phases of use of a self-propelled pallet truck 1 according to the invention. The pallet truck 1 in this embodiment has a lifting capacity of 1200 kg and an own weight of around 750 kg. The pallet truck 1 comprises a base unit 2 and a lifting unit 3 (figure 2a). The pallet truck 1 is configured for transporting a load carrier such as a pallet 101 (figures 3a to 10) which in this example has a width of 100 cm. During such transport, the pallet truck 1 will move for at least the majority of the transport in the transport direction 11. Relative terms used such as 'front' and 'rear', 'before' and 'after', relate to this transport direction 11.

[0048] The base unit 2 is provided with a single, central, elongate carrier arm 4 which has a free end at the rear of the pallet truck 1 and at the front end opposite this adjoins the middle of a transverse frame part 7, which is provided on the underside of an upright main body 5 of the base unit 2. The flat, elongate, top side of the carrier arm 4 forms a carrier surface 8 for supporting a load carrier 101. Viewed from below, the frame part 7 and the carrier arm 4 together form a T shape.

[0049] The underside of the base unit 2 is provided with three pairs 18 of running wheels (figures 1b, 2a and 2b). Each of the running wheel pairs 18 is provided with two coaxial running wheels 19 which can be driven so as to be individually rotatable about horizontal rotational axes situated in line with one another, by means of electric motors which are not shown in detail and are provided for each running wheel 19. Each running wheel pair 18 is freely pivotable about a vertical pivot axis 20 which intersects the common rotational axis between the two running wheels 19 belonging to a running wheel pair 18. By driving the two running wheels 19 belonging to a running wheel pair 18 at different rotational speeds and / or in different rotational directions, the running wheel pair 18 concerned will pivot about the associated verticalpivot axis 20 relative to the rest of the base unit, and thus the pallet truck 1 can be steered to the left or right or move in a crabbing action, whereby sideways movement, such as perpendicularly to the transport direction 11, is possible. The pallet truck 1 is thus movable omnidirectionally.

[0050] Two of the three running wheel pairs 18 are situated at mutually opposite ends of the frame part 7, and the third running wheel pair is provided close to the rearmost free end of the carrier arm 4. The running wheel pairs 18 are here situated at the corners of an isosceles triangle which is depicted in dotted lines in figure 2b. The running wheel pair 18 provided under the carrier arm 4 is positioned at the site of the apex of the isosceles triangle. The two running wheel pairs 18 provided under the frame part 7 are situated outside the width a (figure 1a) of the carrier arm 4. The base unit 2, and also the pallet truck 1 as a whole, during movement of the pallet truck 1, rests via the running wheels 19 on a substrate configured as a floor 6, for example of a warehouse.

[0051] The main body 5 has a convex front side and forms a housing for batteries which amongst others supply the electric motors for driving the running wheels 19 and also other electrically driven components of the pallet truck 1 which will be described below. Also, the main body 5 forms a housing for the electronic controller of the pallet truck 1. This controller is configured to receive, during operation, wireless commands from a central control system. The commands concern the transport of a pallet 101, with or without a load 102 thereon, from one location to another location such as e.g. intra-logistically within the above-mentioned warehouse, including the loading of such a pallet 101 on the pallet truck 1 or the unloading of the pallet 101 from the pallet truck 1.

[0052] The controller is configured to be able to control the pallet truck 1 automatically. For this, the pallet truck 1 is also provided with various laser scanners which are each provided on the underside of the pallet truck 1 and can detect objects in the environment of the pallet truck 1 within their scanning field just above the floor 6. A front laser scanner 36 (figure 11 b), which is provided on the underside of the main body 5, observes the scanning field 14. Two sideways directed laser scanners 48, which are also provided on the underside of the main body 5, observe mirror-symmetrical scanning fields 15a, 15b. The base unit 2 comprises two short arms 49 directly above the laser scanners 48, which form a protection for the laser scanners 48. The top sides of the arms 49 are in line with the carrier surface 8, whereby theshort arms 48 can also contribute to the support of a pallet 101. A rear laser scanner 35, provided on the rearmost free end of the carrier arm 4, observes scanning field 16. The scanning fields 14 to 16, in top view around the pallet truck 1, form a closed common scanning field as visible in figure 1c. The laser scanners, including the laser scanner 37 yet to be described, of the pallet truck 1 are configured to communicate signals concerning their observations to the controller so that the controller is able for example to move the pallet truck 1 around obstacles, stop it temporarily to prevent a collision with a moving obstacle, and position it at a desired position relative to a pallet 101 in preparation for picking this up.

[0053] The lifting unit 3 is provided with two scoops 40. Each scoop 40 has a horizontal lifting arm 21 and a vertical suspension arm 39. The lifting arm 21 and the suspension arm 39 adjoin one another at right angles at the bottom end of the suspension arm 39 and at the front end of the lifting arm 21. The two lifting arms 21 extend parallel to one another and to the carrier arm 4. The flat, elongate, top sides of the lifting arms 21 form carrier surfaces 23 for supporting a load carrier such as a pallet 101. The suspension arms 39, close to their top ends, each have a hook-shaped part not shown in more detail, via which each of the associated scoops 40 is suspended on a scoop plate 38 of the lifting unit 3. The lifting unit 3 comprises a laser scanner 37, coupled to the controller of the pallet truck 1, which observes towards the rear and during operation can be used to observe a load carrier in order for the pallet truck 1 to be able to manipulate this correctly, namely if the load carrier concerned is situated at a distance above the floor 6, for example on a roller conveyor. The laser scanner 37 is provided on the underside in the middle of the width of the scoop plate 38, to which it is mechanically connected so that the laser scanner 37 moves together with the scoop plate 38.

[0054] The lifting unit 3 is furthermore provided with an upright lifting body 22 on the front side of the scoop plate 38 and scoops 40. On the rear side of the lifting body 22, opposite one another and directly opposite the two suspension arms 39, are two vertically oriented guides 24. On the front side of the scoop plate 38, for each guide 24, the scoop plate 38 is provided with two guide pieces 25 (figures 11b, 11c) which are configured to cooperate in guiding fashion with the guides 24 in order to contribute to the upward and downward movement, during operation, of the scoop plate 38 and scoops 40 relative to the main body 22. The guides 24 and the guide pieces 25 form part of a vertical lifting guide system 26, which also comprises anelectric actuator 27 which is active in operation in the vertical direction and with which a deflecting roller 28 can be moved up and down relative to the base body 22. A belt 29 is looped around the deflecting roller 28. The belt 29 is connected at a first end, at the site of reference sign 29a, to the scoop plate 38 and, at the site of reference sign 29b, to the lifting body 22 via a fixed part of actuator 27, which fixed part is rigidly connected to the lifting body. Powering the actuator 27, activated for this purpose by the controller of the pallet truck 1, leads to the pulley 28 moving over a distance x in the vertical direction and, because of the transmission via the belt 29, the scoop plate 38 and scoops 40 moving over a distance 2x in the same vertical direction.

[0055] The lifting body 22 also forms a housing for the actuator 27, deflecting roller 28 and belt 29. In the compact state of the pallet truck 1, the lifting body 22 extends within a recess, matched to the shape of the lifting body 22, inside the main body 5.

[0056] The lifting guide system 26 is configured to be active between the lifting body 22 and the scoop plate 38, more specifically to be able to move the scoop plate 38 up and down relative to the lifting body 22, between a low pick-up state, as shown amongst others in figures 1a to 1c, and a higher lifted state, in which the top guide pieces 25 are situated at the top ends of the guides 24. In the low pick-up state, in this embodiment, the carrier surfaces 23 of the lifting arms 21 extend at the same vertical level as the carrier surface 8 of the carrier arm 4. Alternatively, in the low pick-up state, the carrier surfaces 23 may also extend slightly lower than the carrier surface 8, for example 1 cm lower, and / or in the low pick-up state, the clearance between the floor 6 and the underside of the lifting arms 21 may be equal to 0 cm, wherein the lifting arms 21 in fact rest or almost rest on the floor 6. Thus, the lifting arms 21 may also be used for pallets of which the periphery on the underside is partially open, for use of lifting arms on the periphery. The pallet can be approached by the pallet truck while the lifting arms effectively scrape over the floor. A known example of such a pallet is a wooden Europallet.

[0057] In the lifted state, the carrier surfaces 23 of the lifting arms 21 are situated at least 110 cm higher than in the pick-up state. The stroke length of the actuator 27 is therefore at least 55 cm. For the purpose of the electrical supply to the actuator 27, supply cables run between batteries in the main body 5 and the actuator 27, via a cable guide (not shown in detail) as known from EP 4421018 A1.The distance between mutually facing sides of the lifting arms 21 corresponds to the width a of the carrier arm 4 and is 34 cm. The width b of each lifting arm 21 is 12 cm. The length of each of the lifting arms 21 is 120 cm. The carrier arm 4 protrudes at the rear of the pallet truck 1 by around 10 cm outside the length of the lifting arms 21. The turning circle 30 (figure 1d) of the pallet truck 1 is partially determined by the length of the carrier arm 4 and in this example is selected such that the turning circle of the pallet truck 1 , including the pallet 101 carried thereon, just fits within the turning circle 30. The radius of the convex form of the front side of the main body 5 is equal to that of the turning circle 30. The height of each of the lifting arms 21 is 7.5 cm, while the height of the carrier arm 4 is around 13 cm. The carrier arm 4 has a floor clearance of around 3 cm and the lifting arms 21 , in the low pick-up state, have a floor clearance of 0 cm. The carrier surface 8 of the carrier arm 4, like the top sides of the arms 49, is thus situated around 16 cm above the floor 6. The total width c and the total length d (in the compact state) of the pallet truck 1 are 100.5 cm and 183 cm respectively (figures 11 a and 11 b).

[0058] The lifting unit 3 is furthermore provided with a lifting mechanism 31 under each of the lifting arms 21, at the free rearmost end thereof. Each lifting mechanism 31 on the underside comprises a support foot 32, which is movable by means of the lifting mechanism 31 between a retracted state (figure 2a) and a deployed state (figure 2b). Each lifting mechanism 31 comprises a scissor mechanism, the arms of which at their top ends are moved towards or away from one another by means of a spindle, driveable by an electric motor (not shown in detail) actuated by the controller of the pallet truck 1, which spindle comprises screw threads oriented opposite one another. The spindle extends within the height of the associated lifting arm 21 parallel to its length direction. For a detailed description, reference is made to EP 4421018 A1. In the embodiment according to the present designs, the scissor arms are selected longer than in EP 4421018 A1, and the scissor hinge is situated above the bottom ends of the scissor arms, whereby a greater stroke can be performed by each lifting mechanism 31.

[0059] In the retracted state, each lifting mechanism 31 extends completely within the height of the associated lifting arm 21 , and the underside of the support foot 32 is situated in line with the underside of the lifting arm 21. In the extended state, the support foot 32 extends around 25 cm below the underside of the lifting arms 21. During use of the pallet truck 1, the support feet 32 can therefore rest on the floor 6while the pallet truck 1 is in a transfer state, as shown for example in figures 6a and 6b. The lifting mechanisms 31 then, in the transfer state, help support the lifting arms 21. In the transfer state, which is situated between the pick-up state and the lifted state, the carrier surfaces 23 of the lifting arms 21 are situated higher than the carrier surface 8 of carrier arm 4, as clearly visible in particular in figure 6b.

[0060] The lifting unit 3 is moved to and fro in the horizontal direction relative to the base unit 2 between a retracted compact state, as shown for example in figures 1a and 1b, and an extended elongated state, as shown for example in figures 2a and 2b. For the purpose of this movement, the base unit 2 is provided with two longitudinal guides 41 on mutually opposite long sides of the carrier arm 4, and the lifting unit 3 is provided with two mutually opposite guide pieces 42, which are each configured to cooperate in guiding fashion with one of the two longitudinal guides 41.

[0061] The lifting unit 3, as shown in figures 11b and 11c, furthermore comprises a drive device with a belt 43 which is situated largely on the carrier surface 8 of carrier arm 4 in a recessed part thereof 43, and is preferably configured as a toothed belt. The belt 43 is fixedly connected at a rear end to the carrier arm 4 close to the rear end thereof, at the site of reference sign 43a, and is fixedly connected by a front end to the carrier arm 4 close to the front end thereof, at the site of reference sign 43b, which position is situated on the front of the fork plate 38 and inside the housing formed by the lifting body 22. The belt 43 is looped around two pulleys 45 and a possibly toothed pulley 46 located in between, which is coupled for drive purposes to the electric motor 47. Powering the electric motor 47, activated by the controller of the pallet truck 1, because of the transmission via belt 43, leads to the lifting unit 3 moving forward or backward relative to the base unit 2 between the compact state and the extended state.

[0062] The pallet truck 1 may be used autonomously as follows for moving, in accordance with a command from the central control system, a load carrier such as a pallet 101 which may be loaded with a cargo 102 (figures 3a to 8b). In this example, the pallet 101 has a bottom surface which is closed around its complete periphery and has openings 110 in its upright side surfaces.

[0063] In the compact state in which the lifting arms 21 are in the low pick-up state, and the lifting mechanisms 31 are in the retracted state, the pallet truck 1 travels over the floor 6 to a position relative to the pallet 101, such that the two free ends of the lifting arms 21 extend directly opposite two openings 110 of the pallet 101 , and thefree ends of the carrier arms 4 are situated at a short distance, for example less than 5 cm, from the pallet 101 (figures 4a, 4b). This travel movement is typically backward, i.e. against the direction 11 and coming from the state shown in figures 3a and 3b, but initially may also be sideways, which is made possible because of the omnidirectional nature of the running wheel pairs 18.

[0064] Then, when the base unit 2 is stationary, the electric motor 47 is powered in order to move the lifting unit 3 backward and extend the lifting arms 21 from the compact state to the extended state (figures 5a and 5b). Here, the lifting arms 21 extend through the openings 110, wherein the lifting arms 21 come to extend over almost their complete length directly below the carrier surface of the pallet 101.

[0065] Then, in synchrony, both the actuator 27 and the drive motors belonging to the lifting mechanisms 31 are powered, in order to move the lifting arms 21 from the pick-up state to the higher transfer state (figures 6a and 6b). Here, firstly, the carrier surfaces 23 of the lifting arms 21 come into contact with the pallet 101, and secondly the support feet 32 inside openings of the open bottom surface of the pallet 101 come to rest on the floor 6, whereby pallet 101 is raised. The lifting mechanisms 31 thus prevent the pallet truck 1 from tilting backward because of the weight of the pallet 101 with load 102. In the transfer state, the bottom surface of the pallet 101 is higher than the carrier surfaces 8 of carrier arm 4.

[0066] Then, in synchrony, the running wheel pairs 18 and electric motor 47 are powered such that the pallet truck 1, from the extended state, assumes the compact state again, wherein the base unit 2 travels in a travel direction opposite direction 11 below the pallet 101, and the carrier arm 4 comes to extend directly below the pallet 101 (figures 7a and 7b).

[0067] The compact state may alternatively be assumed again from the situation shown in figures 6a and 6b if the base unit 2 remains stationary and the lifting arms 21 are retracted again by suitable powering of the electric motor 47. For such a process, it is preferred that the support feet 32 are replaced by roller bodies such as running wheels or running rollers. The two running wheels 19 belonging to the rearmost running wheel pair 18, i.e. those under the carrier arm 4, would then be powered while the front running wheels 19 belonging to the two front running wheel pairs are blocked or braked. The blocking of the running wheels 19 may take place for example by orienting these jointly in a V shape or transversely to the travel direction of the two front running wheels 19.Then, again in synchrony, both actuator 27 and the drive motors belonging to the lifting mechanisms 31 are powered in order to move the lifting arms 21 from the transfer state until the pallet 101 (also) comes to rest on the carrier surface 8 of carrier arm 4. Then, the pallet truck 1 can transport the pallet 101 with load 102 to another position by suitable actuation of the running wheels 19 of the three running wheel pairs 18.

[0068] For the purpose of unloading the pallet 1 , at the other position, the steps described above are performed in reverse order.

[0069] Figures 9 and 10 relate to another possible application of the pallet truck 1. Here, the pallet 101 with load 102 is situated on a roller conveyor 120 with a frame which is rectangular in top view and at its four corner points rests with four legs 121 on the floor 6. The pallet 101 can be raised from the roller conveyor 120, in the first instance by positioning the lifting arms 21 directly opposite the openings 110 (figure 9) via suitable powering of actuator 27, and by the pallet truck 1 then travelling backward in the direction of the roller conveyor 120, wherein the carrier arm 4 comes to extend between the legs 121 and thus directly below the pallet 101 and below the rollers of the roller conveyor 120. The lifting arms 21 are inserted through openings 110 to below the carrier surface of the pallet 101. Then actuator 27 is powered to move the lifting arms 21 upward so that the lifting arms 21 lift the pallet 101 from the roller conveyor 120 (figure 10). For the purpose of this lifting, no activity of the lifting mechanism 31 is thus used or necessary. After raising of the pallet 101 by the pallet truck 1, the pallet truck 1 moves the pallet 101 to a destination position where the pallet 101 can be deposited. For example, if this is directly on the floor 6, the activity of the lifting mechanisms 31 may be required here in order to give the carrier arm 4 the opportunity to withdraw from below the pallet 101.

[0070] With reference to figures 12a to 15b, a pallet truck 201 is now described. The pallet truck 201 differs from the pallet truck 1 in particular by the design of the base unit 202. The lifting unit 203 is almost identical to lifting unit 3.

[0071] Where the carrier arm 4 and upright main body 5 of the base unit 2 form a rigid whole, the carrier arm 204 of the base unit 202 is designed to be movable to and fro relative to the main body 205. During use, the to-and-fro movement of the carrier arm 204 relative to the main body 205 takes place by either driving the rearmost running wheels 219a under the carrier arm 204 and braking or blocking the front running wheels 219b under the main body 205, or by braking or blocking the rearrunning wheels 219a and driving the front running wheels 219b. For the purpose of the relative movement concerned, the carrier arm 204 is provided with two mirror-image guide grooves 241, in which extend guide bodies of the main body 205 (not shown in detail) extending into the guide grooves 241.

[0072] The pallet truck 201 further differs from the pallet truck 1 by a double belt transmission with endless belts 221 , preferably toothed belts, which extend on two mutually opposite long sides of the carrier arm 204 (figures 15a, 15b). Each belt 221 is looped around two rotatable deflecting bodies 222a, 222b which are situated at a fixed distance from one another at the ends of two parallel strips 223. The strips 223 extend parallel to the carrier arm 204 and are rigidly connected to the main body 205.

[0073] In the compact state shown in figure 15a, close to the rearmost deflecting body 222a in the top run of the belt 221 concerned, each of the belts 221 is connected to the central carrier arm 204 via a coupling piece 231. In the compact state, close to the front deflecting body in the bottom run of the belt 221 concerned, each of the belts 221 is furthermore connected to the lifting unit 203 via the coupling piece 232.

[0074] The pallet truck 201 can be brought from the compact state (figures 13a, 13b, 15a) into the extended state (figures 14a, 14b, 15b) by driving wheels 219b while wheels 219a are blocked or braked wheels, so that the main body moves backward (e.g. to a pallet 101). Because of the blocking or braking of the wheels 219a, the central carrier arm 204 remains stationary. The transmission with belts 221 ensures that the lifting body 203 also moves backward with the same speed relative to the main body 205 and with twice the speed relative to the carrier arm 204. Although in figures 12a to 15b, the lifting arms of the lifting body 203 are not illustrated with lifting mechanisms such as lifting mechanisms 31, in practice it is indeed possible to provide such lifting mechanisms also in pallet truck 201.

[0075] In a way similar to that described with reference to figures 3a to 8b, it is also possible using the pallet truck 201 to pick up a pallet 101, move this and deposit it at another position. An important advantage of pallet truck 201 compared with pallet truck 1 is that pallet truck 201 does not have or need a separate drive to be able to move the lifting unit 203 to and fro relative to the main body 205, or to bring the pallet truck 201 from the compact state into the extended state and vice versa. Moving the lifting arms of lifting unit 203 up and down also takes place in the same way as with lifting unit 3.

Claims

CLAIMS1. Pallet truck for transporting a load carrier, comprisinga base unit comprising- a number of running wheels which rest on a substrate during use of the pallet truck,- an elongate carrier arm with a free end directed towards the rear of the pallet truck and with an elongate first carrier surface on the top side of the carrier arm for supporting a load carrier thereon, wherein at least one running wheel of the number of running wheels is provided on the underside of the carrier arm,a lifting unit comprising- a lifting base body,- two elongate lifting arms extending parallel to the length direction and on mutually opposite sides of the carrier arm, each having a free end directed towards the rear of the pallet truck and an elongate second carrier surface for supporting a load carrier thereon, - a vertical movement device for moving the two lifting arms up and down relative to the lifting base body in the vertical direction between a pick-up state and a transfer state, wherein, in the transfer state, the second carrier surfaces are situated both higher than the first carrier surface and higher than the level of the second carrier surfaces in the pick-up state, anda horizontal movement device for moving the lifting unit to and fro relative to the base unit parallel to the length direction of the carrier arm, between a compact state and an extended state of the pallet truck.

2. Pallet truck according to Claim 1 , wherein the running wheels, in groups or otherwise, are provided at three positions which form the corners of a triangle.

3. Pallet truck according to Claim 2, wherein the triangle is an isosceles triangle.

4. Pallet truck according to Claim 3, wherein the running wheel or the group of running wheels which is located at the site of the apex of the isosceles triangle is provided on the underside of the carrier arm.

5. Pallet truck according to any one of the preceding claims, wherein running wheels or groups of running wheels are provided on mutually opposing outer sides of the carrier arm.

6. Pallet truck according to any one of the preceding claims, wherein at least some of the number of running wheels, preferably all running wheels, are of the driven type.

7. Pallet truck according to any one of the preceding claims, wherein the pallet truck is of the self-propelled type.

8. Pallet truck according to any one of the preceding claims, wherein at least some of the number of running wheels, preferably all running wheels, which are pivotable about a vertical pivot axis belonging to the respective running wheel, are connected to the base unit.

9. Pallet truck according to any one of the preceding claims, wherein at least some of the number of running wheels, preferably all running wheels, are provided in groups of two coaxial running wheels.

10. Pallet truck according to Claims 8 and 9, wherein the pivot axes belonging to running wheels which belong to a group of two coaxial running wheels coincide and extend between the two coaxial running wheels.

11. Pallet truck according to any one of the preceding claims, wherein the horizontal movement device comprises two horizontal guides which are provided on mutually opposite sides of the carrier arm, for guiding the horizontal movement of the lifting unit relative to the base unit between the compact state and the extended state.

12. Pallet truck according to any one of the preceding claims, wherein the free end of the carrier arm protrudes relative to the free ends of the lifting arms at the rear of the pallet truck.

13. Pallet truck according to any one of the preceding claims, wherein the vertical movement device comprises at least one vertical guide, preferably at least two vertical guides, further preferably precisely two vertical guides, for guiding the vertical movement of the two lifting arms relative to the lifting base body.

14. Pallet truck according to any one of the preceding claims, wherein the vertical movement device has a lifting mechanism for each of the two lifting arms, which lifting mechanisms are each provided below the second carrier surface of an associated lifting arm, for movement or at least for contributing to the movement of the two lifting arms between the pick-up state and the transfer state.

15. Pallet truck according to Claim 14, wherein each lifting mechanism, at least in the transfer state and preferably also in the pick-up state, extends completely within the rearmost half of the length of the associated lifting arm.

16. Pallet truck according to Claim 14 or 15, wherein each lifting mechanism comprises two scissor arms which are connected together in hinged fashion and wherein a supporting body is provided at the bottom end of at least one scissor arm.

17. Pallet truck according to Claim 14, 15 or 16, wherein the vertical movement device comprises a further lifting mechanism for contributing to the movement of the two lifting arms between the pick-up state and the transfer state, wherein the further lifting mechanism, during operation, exerts a vertical force on the two lifting arms at the front of the two lifting arms.

18. Pallet truck according to any one of the preceding claims, wherein the lifting unit comprises a lifting body via which the two lifting arms are connected to one another and which is connected to the lifting base body so as to be moveable up and down.

19. Pallet truck according to any one of the preceding claims, wherein, in the pick-up state, the second carrier surfaces are situated at the same level as the first carrier surface or preferably at a lower level than the first carrier surface.

20. Pallet truck according to any one of the preceding claims, wherein the vertical movement device is configured for moving the two lifting arms up and down relative to the lifting base body in the vertical direction between the pick-up state and a lifted state, wherein, in the lifted state, the second carrier surfaces are situated higher, preferably at least 20 cm higher, than in the transfer state.

21. Pallet truck according to Claims 17 and 20, wherein the further lifting mechanism is configured for moving the two lifting arms up and down between the pick-up state and the lifted state.

22. Pallet truck according to Claim 14 or a claim dependent thereon and according to Claim 21, wherein the further lifting mechanism is configured for performing a vertical stroke which is greater than the respective vertical strokes which can be performed by the two lifting mechanisms belonging to the two lifting arms.

23. Pallet truck according to any one of the preceding claims, wherein the base unit comprises a base body, on the underside of which at least one running wheel of the number of running wheels is provided, and the carrier arm and the base body are movable to and fro relative to one another in the length direction of the carrier arm,the lifting unit and the carrier arm are movable to and fro relative to one another in the length direction of the carrier arm, andwherein the pallet truck is provided with a transmission which is active between the base body, the carrier arm and the lifting unit so as, during operation of the transmission, because of movement of the carrier arm and the base body relative to one another, to cause movement of the lifting unit and the carrier arm relative to one another.

24. Pallet truck according to Claim 23, wherein the transmission is configured, during operation, to cause the movement of the lifting unit and the carrierarm relative to one another to be greater than, preferably twice as great as, the movement of the base body and the carrier arm relative to one another.

25. Method for use of the pallet truck according to any of the preceding claims, comprising the steps ofA moving the pallet truck to a position relative to a load carrier resting on a substrate, wherein, at this position, the pallet truck is in a compact state and the lifting arms are in the pick-up state and wherein free ends of the lifting arms are directed towards the load carrier,B after step A, moving the lifting unit by the horizontal movement device so that the pallet truck transfers from the compact state to or at least in the direction of the extended state, whereby the two lifting arms are positioned, at least with a part of their lengths, preferably with at least 80% of their lengths, under the load surface of the load carrier,C after step B, moving the lifting arms upward by the vertical movement device from the pick-up state to or at least in the direction of the transfer state, whereby the load carrier comes to rest on the second carrier surfaces of the lifting arms, and whereby the two lifting arms lift the load carrier from the substrate to a level at which the underside of the load carrier extends above the level of the first carrier surface of the carrier arm,D after step C, moving the lifting unit and the base unit towards one another in the horizontal direction by the horizontal movement device so that the pallet truck assumes the compact state again and the load carrier extends directly above the two first carrier surfaces of the carrier arms,E after step D, moving the lifting unit downward by the vertical movement device, whereby the load carrier comes to rest on the two first carrier surfaces, and F after step E, moving the load carrier by the pallet truck to a destination.

26. Method according to Claim 25 using a pallet truck according to Claim 23, whereinstep B comprises driving the running wheels provided on the underside of the base body while at least one running wheel on the underside of the carrier arm is blocked, such that the base body moves in the direction of the rearmost end of the carrier arm, and that, because of the operation of transmission, the lifting device isalso moved in the direction of the load carrier, wherein the two lifting arms are positioned with at least a part of their lengths, preferably with at least 80% of their lengths, below the load surface of the load carrier and the pallet truck assumes the extended state, andstep D comprises either driving the running wheels provided on the underside of the base body while at least one running wheel on the underside of the carrier arm is blocked, or driving at least one running wheel on the underside of the carrier arm while at least one running wheel on the underside of the base body is blocked, such that the rearmost end of the carrier arm and the base body are moved towards each other and, because of the operation of the transmission, the load carrier comes to extend directly above the first carrier surface of the carrier arm and the pallet truck assumes the compact state again.

27. Method according to Claim 26, wherein, during step D, the lifting unit is stationary and the base unit moves towards the lifting unit.

28. Method according to Claim 25, 26 or 27 using a pallet according to Claim 14, wherein, during step C, the lifting mechanisms are active in order to contribute to the lifting of the load carrier.

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