EP3543201B1

EP3543201B1 - Forklift comprising auxiliary wheel and method for stabilizing such a forklift

Info

Publication number: EP3543201B1
Application number: EP18163122.7A
Authority: EP
Inventors: Magnus Alveteg
Original assignee: Toyota Material Handling Manufacturing Sweden AB
Current assignee: Toyota Material Handling Manufacturing Sweden AB
Priority date: 2018-03-21
Filing date: 2018-03-21
Publication date: 2023-06-07
Anticipated expiration: 2038-03-21
Also published as: EP3543201A1

Description

TECHNICAL FIELD

The present disclosure relates to a forklift, to a method for stabilizing such a forklift and software for such a method according to the appended claims.

BACKGROUND ART

When performing material handling operations in facilities such as a warehouses or similar, speed of operation and efficiency is naturally of great importance. Other factors such as safety and a pleasant user experience are however also of significance, especially for certain types of forklifts which are designed to lift very heavy loads, perform operations at large heights, perform operation at various angles etc. One such type of forklift is a so called "very narrow aisle forklift" or VNA-forklift, which is designed to be able to be driven into narrow aisles intermediate shelves positioned at various vertical heights. Such forklifts may also be provided with a fork and a mast structure so as to be able to rotate the fork perpendicular to the driving direction of the forklift and place and/or retrieve objects at such an angle relative to the forklift. When the fork of such a forklift is moved outwards from the body of the forklift, to the left or right side of said forklift, the centre of gravity of the forklift and an object positioned at the fork will thus in turn also move to that direction, which in worst case scenario may cause the forklift to tip over.
GB 2 530 570 discloses a materials handling unit according to the preamble of claim 1, such as a forklift truck, for use in a very narrow aisle storage environment.
US 2016/340162 discloses a wheel assembly for a material handling vehicle.

SUMMARY OF THE INVENTION

The risk of a forklift tipping over is often higher for the case for a forklift if it only has three wheels, which is common so as to provide an improved manoeuvrability. Such three wheeled forklifts are commonly provided with auxiliary supports in the form of downwards directed pegs arranged at a lower portion of the chassis of said forklift. The auxiliary supports are arranged so as to be elevated from an underlying ground surface when the forklift is driven in a balanced manner. When the forklift performs an operation which may shift the centre of gravity and thus the balance of said forklift, the forklift may then tilt slightly until the auxiliary supports engage the surface below and balance is achieved. This may not always be very pleasant for a user as the initial tipping motion may be frightening when it occurs. Furthermore, as such an initial tipping motion must be performed in a controlled manner to avoid a situation wherein the forklift tips over due to a gained momentum; such auxiliary supports may thus also impair the speed and efficiency of such a forklift. There are other support systems used which attempt to solve these issues, wherein they may comprise movable auxiliary supports auxiliary supports and/or wheels in various shapes. However, such systems are often slow and cumbersome to use.
Despite prior art there is a need to develop an improved forklift which is safe and comfortable to use with regards to material handling operations. There is also a need to develop such a forklift which is fast and efficient to use for a plurality of material handling operations. Further, there is also a need to develop a method for stabilizing such a forklift prior to performing material handling operations.
An object of the invention is thus to provide an improved forklift which is safe and comfortable to use with regards to material handling operations. Another object is respectively to provide such a forklift which is fast and efficient to use for a plurality of material handling operations. An even further object is to provide a method for stabilizing such a forklift prior to performing material handling operations.
According to the invention a forklift is provided according to claim 1. The forklift comprises at least one auxiliary wheel, selectively movable between a lower position in which a resilient contact between an underlying floor surface and said at least one wheel is established, and an elevated position in which said at least one wheel is elevated from said floor surface. The control unit is arranged to receive an indication that a load carrier operation is initiated, wherein said load carrier operation is a vertical movement of the load carrier and detect that the at least one auxiliary wheel is in resilient contact with the underlying floor surface, wherein the control unit controls the at least one auxiliary wheel to shift from a resilient contact to a rigid contact with the underlying floor surface.
This has the advantage that such a forklift may be provided with an improved stability when performing material handling operations. It should be noted that the terms "resilient contact" and "rigid contact" are to be viewed respectively as; a flexible contact where a vertical movement of such a wheel does not translate movement to the forklift, and a non-flexible contact which may be perceived as a rigid extending element protruding from the forklift. This has the advantage that the resilient contact provides a sort of automatic alignment system for such a wheel, as such a wheel may conform to any potential irregular geometry of a floor or such on which it is in abutment with. Further, the rigid contact in turn provides the same effect as an auxiliary support or similar, which thus may counteract tilting of the forklift if the centre of gravity of the forklift and potential added load to the load carrier is moved in such a way that enough support is not provided to the truck by means of its regular wheels (the at least one support wheel and the at least one drive wheel). Such a forklift may thus exhibit an improved stability for material handling operations, while still have excellent handling capabilities when being driven and having the at least one auxiliary wheel in the elevated position.
According to an aspect the load carrier is arranged so as to be able to operate transversal to a driving direction of said forklift, and wherein a load carrier operation further comprises a transversal operation of the load carrier.
This has the advantage that such transversal operations may be performed in a much safer manner due to the increased stability of the forklift provided by the at least one auxiliary wheel. This is beneficial as transversal movements may shift the centre of gravity to a large extent wherein the at least one auxiliary wheel thus provides an increased stability in situations where it may be highly desirable.
According to an aspect the at least one auxiliary wheel is arranged to the forklift by means of a wheel suspension comprising a lifting device for moving the at least one auxiliary wheel between the lower position and the elevated position, a spring element, and a locking device for locking the at least one wheel in position.
This has the advantage that a wheel suspension may be provided, which suspension may provide the various functions to the at least one auxiliary wheel by means of distinct individual components, specially designed and modified for their specific usages.
According to an aspect the at least one auxiliary wheel may be automatically movable to the lower position by means of the lifting device when the at least one sensor device detects a specific predetermined guiding device.
This has the advantage that the at least one auxiliary wheel may be moved to its intended correct position prior to being utilized as a stabilizing wheel for a material handling operation. As forklifts are commonly used for material handling operations in combination with objects positioned at shelfs or similar, and wherein such shelfs may be arranged in aisles or the like, the at least one sensor device may detect such shelves and/or aisles when the forklift approaches such structures. The presence of such shelves and/or aisles may thus be perceived as specific guiding devices, wherein the at least one auxiliary wheel may be moved to the lower position when such a forklift approaches such structures. This further has the advantage that the at least one auxiliary wheel already is positioned correctly if a load carrier operation is initiated. Thus time is saved wherein such an at least one auxiliary wheel only needs to be locked in place before such a material handling operations may be performed. This may provide an amount of saved time for each such operation, which hence provides a fast and efficient forklift.
According to an aspect the locking device may comprise a piston having a cylinder in which a shaft is arranged and protrude therefrom, wherein the protrusion of the shaft can be locked relative the cylinder.
This has the advantage that the locking device may provide a fast and efficient locking mechanism, wherein the same mechanism may be incorporated into additional features of the wheel suspension as well, such as being used as a shock absorber or similar due to the piston cylinder interaction being a commonly used mechanism for such devices as wheel suspensions.
According to an aspect the at least one auxiliary wheel may be manually operated between the lower position and the elevated position by means of the control unit.
This has the advantage that the forklift may be able to utilize the stabilizing effect of the at least one auxiliary wheel at any given location, regardless of a presence of a guiding device. The forklift may hence be used in a semi-automatic, or fully automatic, manner when the at least one sensor device detects said specific guiding devices, but also be used at other separate locations which may not be provided with said specific guiding devices. An operator of the forklift may thus utilize the increased stability of such a forklift in a wider range of operational conditions.
According to an aspect the at least one auxiliary wheel may be laterally moved by means of the wheel suspension and the control unit when being positioned in the elevated position.
This has the advantage that the stabilizing system implemented by means of the at least one auxiliary wheel may be modified during use of such as forklift, which may increase the stabilizing effect provided to said forklift. If, for example, a material handling operation which requires a long transversal movement of the load carrier (for a forklift also comprising such capabilities), and/or the load applied to said load carrier during operation is considered to be a heavy load, an operator of the forklift may prior to such an operation move the at least one auxiliary wheel laterally, outwards from a centre of the forklift. By means of such an outwards directed movement, the contact points between the forklift and the underlying floor surface may be modified to be wider, which in turn allows for a larger transversal movement of the centre of gravity.
According to an aspect the forklift may comprise a warning system which may provide a warning signal by means of a warning device if the at least one auxiliary wheel is not in contact with the underlying floor surface and a load carrier operation is initiated.
This has the advantage that the safety and reliability of the forklift is enhanced, as load carrier operations which could lead to tipping of the forklift may be avoided. Such a warning system may be opted to be used as dictating or advisory depending on the material handling operation being performed, combined with the knowledge of an operator regarding the surroundings where the forklift is to be used..
According to an aspect the warning system further being arranged to restrict load carrier operations.
This has the advantage that it may be able to guarantee that the forklift may never perform operations deemed as unsafe in the regard that the added stability of the forklift due to the at least one auxiliary wheel is not in effect. This is beneficial as critical situations may be avoided to an extra degree which further enhances the safety and reliability of such a forklift. The restriction may comprise a full stop of the load carrier, wherein a potentially dangerous operation is impossible to perform.
According to an aspect the forklift may comprise two auxiliary wheels, arranged symmetrically about a centre line of said forklift, the centre line being parallel with a direction the forklift is directed when driving straight ahead.
This has the advantage that each individual auxiliary wheel may be utilized to increase stability for material handling operations on one side each of the forklift. Thus such a forklift may perform a transversal material handling operation to either side without any sort of input or pre-setting of a stabilizing system prior to said operation.
According to another aspect of the invention a method according to claim 11 is provided. The method comprises the steps of: a) driving the forklift to a position where the a load carrier operation is to be performed, b) lowering the at least one auxiliary wheel to the lower position, c) shifting the contact between the at least one auxiliary wheel and the floor surface from a resilient contact to a rigid contact, and d) performing the load carrier operation by means of the load carrier.
This has the advantage that a safe and reliable method is provided, which method may be used to improve the stability of such a forklift without altering its driving characteristics in a negative way. The method further provides the added advantage of not being reliant on auxiliary supports or similar which may cause a non-comfortable experience to an operator if said operator is positioned on the forklift when a load carrier operation is taking place.
According to an aspect the method further comprises a step e) monitoring the surroundings around the forklift by means of the at least one sensor device, said step e) being performed simultaneously as step a), and f) initiate step b) by means of the control unit when the at least one sensor device detects a specific predetermined guiding device.
This has the advantage that the at least one auxiliary wheel is aligned with the underlying floor surface during movement of the forklift, as soon as the specific predetermined a guiding device are detected. This in turn has the advantage that time is saved for each material handling operation performed utilizing the method, as the load carrier may be used as soon as the forklift has reached a location where such specific predetermined a guiding device are present. Unnecessary amounts of time is thus cut from such an operation, time which otherwise would be needed to move the at least one auxiliary wheel to the lower position before shifting it to the rigid contact. By means of controlling step f) and thus also step b) by means of the control unit the method may be used in a semi- or fully automatic mode, wherein an operator needs to perform less steps and operations him/her-self, which provides a fast and reliable method which at the same time is easy to perform.
According to another aspect of the invention a software according to claim 13 is provided.
This has the advantage that the method may be comprised in pre-programmed software which may be implemented into any forklift suitable for utilizing such a method.
Additional objectives, advantages and novel features of the invention will be apparent to one skilled in the art from the following details, and through exercising the invention. While the invention is described herein, it should be apparent that the invention may be not limited to the specifically described details. One skilled in the art, having access to the teachings herein, will recognize additional applications, modifications and incorporations in other areas, which are within the scope of the invention as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description of, as examples, embodiments with reference to the enclosed drawings, in which:

Fig. 1 shows a forklift in a top down view according to an embodiment,
Fig. 2 shows parts of a forklift in a side view from behind according to an embodiment,
Fig. 3a-c show an auxiliary wheel of a forklift in different positions and states according to an embodiment,
Fig. 4 shows parts of a forklift with an auxiliary wheel in a side view from behind according to an embodiment,
Fig. 5 shows a forklift in a side view according to an embodiment, and
Fig. 6 shows a flowchart of a method for stabilizing a forklift according to an embodiment.

DETAILED DESCRIPTION

According to a first aspect of the invention a forklift according to claim 1 is provided. The total number of wheels used for such a forklift may vary, and different combinations of drive wheels and support wheels are possible without deviating from the scope of protection. Depending on their intended usage, forklift having three wheels total and four wheels total are both common in the arts, wherein both such examples may provide different advantages for different types of material handling operations. The disclosure herein is mostly focused at a forklift having a total of three wheels for its driving operations; however any number of wheels may be used in combination with the inventive concept described herein. The forklift is operated in a free-range mode and at least a semi-automatic mode. In the free-range mode the forklift may be operated by means of a user interface, which may be provided to the forklift as part of an operator cabin, or a remote control, or a combination of the two. The forklift may further comprise docking means for docking to a guide system or similar, wherein the forklift may be either semi-automatically controlled when driven on such a guide system, where the guiding device in the form of a guide system provides for at least partly controlling of the forklift. Fully automatic operation may of course also be possible.
The elevated position provides clearance for driving operations wherein said at least one auxiliary wheel is not being in contact with the underlying floor surface. The at least one auxiliary wheel is thus also protected from damage and wear as it is not being used for driving and/or support when driving. When in the lower position and in resilient contact with the underlying floor surface, such an auxiliary wheel may initiate contact without providing support to the forklift by means of said contact. If such a wheel would be positioned at portion of an underlying floor surface, which portion is not perfectly aligned horizontally with the rest of the floor surface, the resilient contact may be kept without affecting the horizontal orientation of the forklift itself. When the at least one auxiliary wheel is in the resilient contact and a load carrier operation is to be performed, the initiation of such an operation will first shift the resilient contact into a rigid contact, wherein said rigid contact may be viewed as a load bearing and non-resilient contact with the underlying floor surface. This may be performed by means of the control unit being arranged to first shift said positions when an operation command is given, which command comprises a transversal direction. The at least one auxiliary wheel being in the rigid position may thus provide an increased stability to the forklift when performing such operations.
According to an aspect the load carrier is arranged so as to be able to operate transversal to a driving direction of said forklift, and wherein a load carrier operation further comprises a transversal operation of the load carrier. The load carrier is thus to be viewed as pivotally coupled to the forklift wherein a pivoting of said load carrier provides the possibility of material handling operations in a wide range of angles between two pivoted end positions. Such an angled operation may most commonly be at a right angle relative a driving direction of the forklift, but lower angles may of course also be possible within the disclosure, and may also benefit from the added stability of the forklift described herein. The term transversal operation is thus to be viewed as an operation which is performed with any amount of a transversal direction relative the driving direction of the forklift
According to an aspect the at least one auxiliary wheel is arranged to the forklift by means of a wheel suspension comprising a lifting device for moving the at least one auxiliary wheel between the lower position and the elevated position, a spring element, and a locking device for locking the at least one wheel in position. The spring element comprises a low spring force so as to provide the resilient contact when the at least one auxiliary wheel is in its lower position. The spring element may be a mechanical spring, a gas spring, or any other flexible type of element or device known in the arts. The lifting device and the locking device may be individual devices or incorporated into each other as a single device, and may also be any known devices known in the arts. Hence, it should be understood that the lifting device and the locking device may be provided to a forklift using a variety of commonly used devices such as mechanical link arm arrangements, hydraulics, pneumatics or a combination of such.
According to an aspect the at least one auxiliary wheel may be automatically movable to the lower position by means of the lifting device, when the at least one sensor device detects a specific predetermined guiding device. Such a specific predetermined guiding device may be parts of an aisle between shelves, wherein the sensor device may detect the structure of the construction of shelves positioned at sides of such an aisle. The specific predetermined guiding device may also be specifically positioned objects and/or materials arranged to be detected by the sensor device so as to indicate that the forklift at or in the vicinity of a position where material handling operations are to be performed, such as indication wires, a guide rail or similar. As an example magnetic material may be arranged at predetermined positions within and next to such an aisle, a shelf, a shelf arrangement or similar, wherein the sensor device is arranged to detect such magnetic material. The specific predetermined guiding device may even further be a guide system, or parts thereof, wherein when the forklift is used in combination of such a guide system the at least one auxiliary wheel may be lowered to the lower position automatically.
According to an aspect the locking device may comprise a piston having a cylinder in which a shaft is arranged and protrude therefrom, wherein the protrusion of the shaft can be locked relative the cylinder. An example of such a piston may be a hydraulic cylinder comprising controllable valves, wherein opening and closing of such valves may lock the shaft into position within the cylinder of said piston. Such a piston may further also provide a lifting mechanism and thus function as a lifting device as well. By means of controlling the amount of fluid within the piston, it may be used to control the protrusion of the shaft from the cylinder, wherein the flow of fluid from and to the cylinder may be controlled by means of a control valve, wherein the relative position of the piston may be locked in place. Such a piston may thus be utilized to lock the at least one auxiliary wheel both in the elevated position and the lower position, wherein the fluid flowing within the cylinder may be allowed to flow freely from and to the cylinder when the at least one auxiliary wheel is in the lower position and in resilient contact with an underlying floor surface.
According to an aspect the at least one auxiliary wheel may be manually operated between the lower position and the elevated position by means of the control unit. Such a feature may simply be a feature presented in a user interface for direct operative input to the control unit which may lower and elevate the at least one auxiliary wheel when deemed desirable by an operator. Furthermore, the forklift may be provided with the option of manually shifting the at least one auxiliary wheel between resilient contact and rigid contact so as to provide the forklift with a larger variety of option with regards to its usage. An operator may thus always have the added feature or manually shifting between all possible positions and states for such wheels, wherein the forklift may be used for a large plurality of different types of operations regardless of the surroundings.
According to an aspect the at least one auxiliary wheel may be laterally moved by means of the wheel suspension and the control unit when being positioned in the elevated position. The at least one auxiliary wheel may thus be arranged underneath the forklift in such a manner that it may be moved around when not in contact with an underlying surface. This may provide the possibility to enhance the stabilizing effect of such a wheel even further by moving it away from a centre of the forklift. The at least one auxiliary wheel may even be arranged in such a way that it may be moved out and extending past the chassis of the forklift. Such an arrangement may thus provide a paramount increase to stability of the forklift as the area defined by the contact points between the forklift and the underlying surface may be increased by a large portion. By means of arranging the at least one auxiliary wheel to the forklift by means of for example a telescopic arm or similar, comprised in the wheel suspension, the area defined by the contact points may be doubled or more.
According to an aspect the forklift may comprise a warning system which may provide a warning signal by means of a warning device if the at least one auxiliary wheel is not in contact with the underlying floor surface and a load carrier operation. Such a feature is easily provided to the forklift by means of arranging for example a pressure sensor coupled to the at least one auxiliary wheel, which sensor may detect if contact is initiated or not. Other types of sensor devices known in the arts may also be used. The warning system may then comprise a warning device which gives at least one warning signal, indicating to an operator of the forklift that no contact between the at least one auxiliary wheel and the underlying floor surface is achieved. Such a signal may be in the form of a blinking light, a warning sound, a vibration, or a combination of such warning signals. The operator will then immediately know that no additional support will be given by the at least one auxiliary wheel, wherein transversal operations may be deemed as unsafe to perform. Such a warning system may further be modified to include additional warning signals if the at least one auxiliary wheel is in contact with an underlying floor surface but the shift to a rigid contact for some reason fails. This may even further enhance the safety of using such a forklift.
According to an aspect the warning system further being arranged to restrict load carrier operations. The warning system may hence be arranged to enforce such a restriction by means of the control unit. Such a restriction may be in the form of reduced movement speed of the load carrier, wherein an operation will be saferto perform as the momentum generated by such a movement may cause a tipping motion is not performed in a controlled manner. Such a restriction may also be in the form of a full stop of the load carrier making operations temporarily not possible to perform at all.
According to an aspect the forklift may comprise two auxiliary wheels, arranged symmetrically about a centre line of said forklift, the centre line being parallel with a direction the forklift is directed when driving straight ahead. Having the forklift comprising two such wheels may thus provide the same added stability to the forklift in both side directions without any sort of movement or alteration of the forklift. The two auxiliary wheels may be operated simultaneously but individually so as to provide the same function to the forklift but not be dependent on each other. Hence, if both such wheels are in resilient contact with the underlying floor surface, and said floor surface is not completely level, both wheels may individually align with a portion of said floor surface underneath each wheel, wherein rigid contact may be initiated without changing the horizontal orientation of the forklift, but still provide an added stability in all directions around said forklift. As should be obvious, the forklift may be provided with any number of auxiliary wheels deemed necessary, wherein the total number of wheels may be modified depending on a specific usage which such a forklift is designed to perform.
According to an aspect of the invention a method according to claim 11 is provided.
According to an aspect the method further comprises a step e) monitoring the surroundings around the forklift by means of the at least one sensor device, said step e) being performed simultaneously as step a), and f) initiate step b) by means of the control unit when the at least one sensor device detects a specific predetermined guiding device. The control unit may thus activate at least parts of the steps of the method in an automatic manner.
As should be obvious, the forklift used for performing the different embodiments of the method as described above may be modified and exhibit any possible combination of the different features described with reference to the forklift and its different features as presented within the disclosure. The method may thus be performed manually, semi-automatically or fully automatically, with respect to the method in part or the entirety of the method, depending on the forklift and the type of operation to be performed.
According to an aspect a software according to claim 13 is provided. Such software may be stored on a computer readable storage medium which may be provided to the control unit of the forklift. It may also be provided directly to the control unit and/or an external user interface such as a tablet, a remote control or similar. Such software may thus be run to perform the entirety of, or parts of, the method when the method is performed in a semi-automatic or fully automatic manner.

DETAILED DESCRIPTION OF THE DRAWINGS

The detailed description with reference to the embodiments depicted are to be viewed as exemplary embodiments comprising a combination of certain features, which features have been described in detail above. It is thus to be understood that additional embodiments may be achieved by combining other features into embodiments not depicted herein. The figures are to be viewed as examples and not mutually exclusive combinations. It should also be noted that all figures shown and described are schematically represented, wherein generic parts of machinery is not depicted for the sake of simplicity.
Fig. 1 shows a forklift 1 in a top down view according to an embodiment. The forklift 1 is shown to be operated in an aisle 3 intermediate two rows of pallets 5 placed on shelf arrangements 7. As is seen said aisle 3 is narrow, wherein the forklift 1 may not turn so as to face a pallet 5 for a retrieval operation. The forklift 1 may thus be perceived as a "VNA-forklift". The forklift 1 may perform transversal operations by means of the load carrier 9 being arranged to pivot and perform transversal operation, and thus be operated in directions separate from a driving direction 11 of the forklift 1. The forklift 1 shown in fig. 1 comprises two support wheels 13, arranged at a front portion 15 of a chassis of the forklift 1. The forklift further comprises a drive wheel 17, arranged at a back portion 19 of the chassis, arranged as a swivel wheel and being coupled to a drive motor (not shown). Such a combination of wheels 13, 17 provides a very responsive and versatile manoeuvrability for the forklift 1 when operated in a free-range mode. When operated in a narrow aisle 3 as shown in fig. 1, the forklift 1 may be operated in various manners. It may be operated fully manually in free-range mode, however this may not always be practical and/or desirable. More common, and being the case herein, it may be operated in a semi-automatic mode in which as an example the drive wheel 17 is locked to driving straight ahead and an operator may control the moving speed. There is also the possibility that it may be operated in a fully automatic mode in which all operations performed are done so automatically according to a pre-set or chosen scheme of movement and handling operations. Such semi-automatic and fully automatic may be activated by an operator, or be automatically switched to when the forklift 1 is exposed to certain conditions. The forklift 1 comprises a plurality of sensor devices 21, wherein said sensor devices 21 may detect a guiding device 23. Such a guiding device23 may be an object such as parts 23' of the shelf system in the aisle 3, or be a specific element arranged for the purpose of being detected by the sensor devices 21 of the forklift 1. In fig. 1 a plurality of detection elements 23" are shown, which elements 23" may be of a specific material, such as a magnetic or a ferromagnetic material, wherein the sensor device 21 may detect such a material. The sensor devices 21 may also comprise optical sensors for detection of parts 23' of the shelf system for example. The forklift 1 may thus be driven to the aisle 3 and when at least one sensor device 21 detects specific a guiding device 23, the control unit (not shown) may engage a semi-automatic or a fully automatic mode for operation within the aisle 3.
The forklift as shown in fig. 1 further comprises two auxiliary wheels 35, arranged at the back portion 19 of the chassis of the forklift 1. These two auxiliary wheels 25 are elevated from the floor when the forklift 1 is operated in its free-range mode. When the forklift 1 enter the aisle 3 as shown, and engages a semi-automatic mode, the auxiliary wheels 25 will be lowered so as to engage the underlying floor surface 27 in a resilient contact with said floor surface 27. The resilient contact allows the auxiliary wheels 25 to establish a contact with said underlying floor surface 27 without affecting the horizontal orientation of the forklift 1. When the forklift 1 reaches a destination where a material handling operation is to be performed, the auxiliary wheels 25 are already in their correct position and no time is wasted aligning them. When a command is given to initiate a load carrier operation, the control unit will first shift the resilient contact of the auxiliary wheels 25 to a rigid contact, in which rigid contact the auxiliary wheels 25 may assist in take up load from the forklift 2 and potential load at the load carrier 9, which thus adds stability to the forklift 1. If the load carrier 9 is moved in a transversal direction (in fig. 1 forklift is set up to move the load carrier 9 left in the picture), the centre of gravity of the forklift with or without load will naturally also be moved left. If the centre of gravity would move outside of a base area defined by the contact points between the forklift 1 and the underlying floor surface 27, the forklift 1 would tip over, which of course is not desirable. Said base area without the auxiliary wheels 25 in rigid contact is shown in fig. 1 by a triangle 29 drawn with dashed lines. An increased base area, achieved by using the auxiliary wheels 25 is shown in fig. 1 drawn as a rectangle 31 with dotted lines. As is clearly seen, the usage of the auxiliary wheels 25 adds stability to the forklift wherein it may be used for transversal operations reaching further out from a centre line 33 of the forklift 1, in its driving direction 11. The detection of specific a guiding device 23 may also be utilized for automatic lowering of the auxiliary wheels 25, even if the forklift 1 would be operated in free-range mode within the aisle 3.
Fig. 2 shows parts of a forklift 1 in a side view from behind according to an embodiment. For the sake of simplicity only the drive wheel 17 and parts of the chassis of the forklift 1 is shown, as well as two auxiliary wheels 25 arranged to the chassis of the forklift 1 by means of a wheel suspension 35. The wheel suspension 35 comprises a lifting device for moving each auxiliary wheel 25 between their elevated position and the lower position 37. The wheel suspension 35 further comprises a spring element 39 and a locking device 41 for locking the auxiliary wheels 25 in their current positions. In the embodiment depicted the locking device 41 is in the form of a piston 43, having a cylinder in which a shaft is arranged and protrude therefrom, wherein the protrusion of the shaft may be locked relative the cylinder. When the shaft and cylinder are not locked relative each other, the auxiliary wheel 25 may thus move up and down freely, and be flexibly in contact with the underlying floor surface 27 by means of the spring element 39. When the shaft and cylinder is locked relative each other, rigid contact is instead achieved. The lifting device may be incorporated in the piston 43, wherein movement up and down may be performed by means of controlling the displacement of the shaft so as to achieve said movement, and then lock the piston 43 in the respective positions. The lifting device may also be arranged as an angular movement of an arm element 45 arranged between the auxiliary wheels 25 and the chassis of the forklift 1.
Fig. 3a-c shows an auxiliary wheel 25 of a forklift 1 in different positions and states, according to an embodiment. Fig. 3a shows the auxiliary wheel in its elevated position 47, wherein it is locked thereto by means of the piston 43 being prevented from displacing the shaft by means of a control valve 49 comprised in the piston 43, which control valve 49 may allow or prevent a hydraulic fluid to flow from and to the cylinder of the piston 43. Fig. 3b shows the auxiliary wheel 25 being in the lower position 37 and in resilient contact with the underlying floor surface 27. This is achieved by means of having the control valve 49 being completely open wherein the displacement of the shaft relative the cylinder of the piston 43 is un-restricted. The resilient contact is thus achieved by means of the spring element 39 biasing the auxiliary wheel 25 towards said floor surface 27. In fig. 3c, the auxiliary wheel 25 also is in the lower position 37, but is here shown to be locked in rigid contact with the underlying floor surface 27. This is again achieved by means of closing the control valve 49 which restricts relative movement of the shaft and the cylinder. The embodiment shown in fig. 3a-3c is to be viewed as an example, and it should be noted that the described features and functions may be achieved in alternate designs as well. The lifting device and the locking device may also be achieved by means of strictly mechanical means as well without deviating from the disclosure.
Fig. 4 shows parts of a forklift 1 with an auxiliary wheel 25 in a side view from behind according to an embodiment. For the sake of simplicity only the auxiliary wheel 25 is shown together with part of a forklift 1 and its drive wheel 17. The focus of fig. 4 is to exhibit the feature of the auxiliary wheel 25 being movable laterally when being in the elevated position as shown in the figure. The auxiliary wheel 25 drawn with solid lines may be perceived as an example of a default position, wherein the auxiliary wheel 25' drawn with dotted lines are present to represent a possible lateral movement of the same. This feature may be performed manually by an operator if he/she knows additional support and stability may be needed for a specific operation. Lateral movement for an increased stability may also be programmed into the control unit as part of a semi-automatic or a fully automatic operation of such a forklift, wherein the at least one the auxiliary wheel 25 may be moved outwards automatically for certain specific material handling operations in need of additional stability due to factors such as an extra heavy load, a need for a longer than normal reach of the load carrier or similar. As should be obvious, any type of wheel suspension by which the auxiliary wheel is arranged to the chassis of the forklift 1 may be arranged to accommodate for this specific feature when desired. This may be solved by hydraulics, pneumatics, mechanical devices or other known constructions known in the arts.
Fig. 5 shows a forklift 1 in a side view according to an embodiment. The forklift 1 according to this embodiment comprises a warning system as previously described. The forklift 1 is perceived to be in a situation in which an operational command for the load carrier 9 have been given, but for some reason the auxiliary wheel 25 is its elevated position 47. This may in such a case be detected by means of an additional sensor arrangement (not shown) wherein the control unit restricts the movement of the load carrier 9 and provides a warning signal 51 by means of a warning device 53. The warning device 53 is herein shown in a simple schematic form wherein the warning signal 51 may be perceived as a light, a sound, a vibration or any combination of such signals. The control unit may also send a wireless signal to additional warning devices, provided to a remote control, a facility in which the forklift is used or other.
Fig. 6 shows a flowchart of a method for stabilizing a forklift according to an embodiment. As is seen in the flowchart the method may be performed at least in part in both a manual and a semi or fully automatic manner. Whichever way the method is performed, the at least one auxiliary wheel may be lowered to the lower position and be in resilient contact with an underlying floor surface ahead of being shifted to a rigid contact in which a stabilizing support is provided to the forklift. Step a) comprises driving the forklift to a position where the load carrier operation is to be performed. This step may thus be either a manual operation in a free-range mode, or be a semi or fully automatic driving of the forklift to said position. Step b) comprises lowering the at least one auxiliary wheel to the lower position. This step may be performed manually at any point if deemed suitable to an operator operating the forklift, but is to be understood to be performed well ahead in time prior to the following material handling operation. As the forklift most commonly have a better manoeuvrability in free-range mode without the at least one auxiliary wheel lowered, it may be suitable to lower said wheel or wheels when the forklift when the forklift is moving straight towards the intended position. Step c) comprises shifting the contact between the at least one auxiliary wheel and the floor surface from a resilient contact to a rigid contact. This may be performed by means of the control unit of the forklift being configured to perform said shift when a load carrier command comprising a transversal portion of movement is given by an operator, wherein step d) comprises performing the material handling operation by means of the load carrier.
As is shown in the flowchart the method may be further expanded to comprise the step e) which comprises monitoring the surroundings around the forklift by means of the at least one sensor device, wherein step e) may be performed continuously so as to guarantee that it is performed during any sort of driving operation of the forklift. Hence, step f) then comprises to initiate step b) when the at least one sensor device detects a specific predetermined guiding device. The steps e) and f) thus allows for automating at least parts of the method so as to provide a stabilizing effect to a forklift in a fast and efficient manner.
The foregoing description of the embodiments has been furnished for illustrative and descriptive purposes. It is not intended to be exhaustive, or to limit the embodiments to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order to best explicate principles and practical applications, and to thereby enable one skilled in the art to understand the invention in terms of its various embodiments and with the various modifications that are applicable to its intended use, the scope of the invention being solely defined by the appended claims. The components and features specified above may, within the framework of the embodiments, be combined between different embodiments specified.

Claims

A forklift (1) comprising a load carrier (9), movably coupled to a mast, a control unit, at least one drive wheel (17), at least one support wheel (13), and at least one sensor device (21) for detection of a guiding device (23), wherein the forklift (1) may be operated in a free-range mode and at least a semi-automatic mode where the guiding device (23) provides for at least partly controlling of the forklift (1),
characterized in that
it comprises at least one auxiliary wheel (25), selectively movable between a lower position (37) in which a resilient contact between an underlying floor surface (27) and said at least one auxiliary wheel (25) is established, and an elevated position (47) in which said at least one auxiliary wheel (25) is elevated from said floor surface (27), wherein the control unit is arranged to receive an indication that a load carrier operation is initiated, wherein said load carrier operation is a vertical movement of the load carrier (9) and detect that the at least one auxiliary wheel (25) is in resilient contact with the underlying floor surface (27), wherein the control unit is arranged to control the at least one auxiliary wheel (25) to shift from a resilient contact to a rigid contact with the underlying floor surface (27).
The forklift (1) according to claim 1, wherein the load carrier (9) is arranged so as to be able to operate transversal to a driving direction (11) of said forklift (1), and wherein a load carrier operation further comprises a transversal operation of the load carrier (9).
The forklift (1) according to any of the preceding claims, wherein the at least one auxiliary wheel (25) is arranged to the forklift (1) by means of a wheel suspension (35) comprising a lifting device for moving the at least one auxiliary wheel (25) between the lower position (37) and the elevated position (47), a spring element (39), and a locking device for locking the at least one auxiliary wheel (25) in position.
The forklift (1) according to claim 3, wherein the at least one auxiliary wheel (25) is automatically movable to the lower position (37) in which the resilient contact between the underlying floor surface (27) and said at least one auxiliary wheel (25) is established, by means of the lifting device when the at least one sensor device (21) detects specific predetermined guiding devices (23, 23', 23").
The forklift (1) according to claim 3 or 4, wherein the locking device comprises a piston (43) having a cylinder in which a shaft is arranged and protrude therefrom, wherein the protrusion of the shaft can be locked relative the cylinder.
The forklift (1) according to any of the preceding claims, wherein the at least one auxiliary wheel (25) can be manually operated between the lower position (37) and the elevated position (47) by means of the control unit.
The forklift (1) according to claim 3, wherein the at least one auxiliary wheel (25) can be laterally moved by means of the wheel suspension by means of the control unit when being positioned in the elevated position (47).
The forklift (1) according to any of the preceding claims, wherein it comprises a warning system which provides a warning signal (51) by means of a warning device (53) if the at least one auxiliary wheel (25) is not in contact with the underlying floor surface (27) and a load carrier operation is initiated.
The forklift (1) according to claim 8, wherein the warning system further being arranged to restrict load carrier operations.
The forklift (1) according to any of the preceding claims, wherein the forklift (1) comprises two auxiliary wheels (25), arranged symmetrically about a centre line (33) of said forklift (1), the centre line (33) being parallel with the driving direction (11) of the forklift (1) when driving straight ahead.
A method for performing a material handling operation with a forklift according to claim 1, the method comprising the steps of:
a) driving the forklift (1) to a position where a load carrier operation is to be performed,

b) lowering the at least one auxiliary wheel (25) to the lower position (37),

c) shifting the contact between the at least one auxiliary wheel (25) and the floor surface (27) from a resilient contact to a rigid contact, and

d) performing the load carrier operation by means of the load carrier.
The method according to claim 11, wherein the method further comprises a step e) monitoring the surroundings around the forklift by means of the at least one sensor device, said step e) being performed simultaneously as step a), and f) initiate step b) by means of the control unit when the at least one sensor device detects a specific predetermined guiding device.
Software that when stored in the control unit of the forklift of claim 1 and is executed causes the forklift to perform the method according to any of claims 11 or 12.