WO2017151051A1

WO2017151051A1 - Transfer device, conveyor system comprising a transfer device, method for grouping objects by using a transfer device

Info

Publication number: WO2017151051A1
Application number: PCT/SE2017/050200
Authority: WO
Inventors: Marko Salmi
Original assignee: Flexlink Ab
Priority date: 2016-03-04
Filing date: 2017-03-03
Publication date: 2017-09-08

Abstract

Transfer device adapted to receive objects from a horizontal infeed conveyor belt and to forward the objects to a second horizontal outfeed conveyor belt, where the transfer device comprises a first conveyor belt and a second conveyor belt interconnected by a first upper carriage and a second lower carriage, where the transfer device is adapted to group the objects into spaced apart longitudinal groups comprising at least one object, and where the transfer device is adapted to temporarily increase the speed of an upper carriage until a leading edge of an object is aligned with a predefined position of an upper carriage. The advantage of the invention is that objects can be grouped in spaced-apart groups in a secure way at a high speed. The invention also concerns a conveyor system comprising a transfer device and a method for grouping objects from an infeed conveyor belt into a group comprising at least one object by using a transfer device.

Description

TRANSFER DEVICE, CONVEYOR SYSTEM COMPRISING A TRANSFER DEVICE, METHOD FOR GROUPING OBJECTS BY

USING A TRANSFER DEVICE

TECHNICAL FIELD

The present invention relates to a method and an arrangement for grouping objects in predefined groups, where a group comprises a predefined number of objects. The arrangement is adapted to be used in a conveyor system.

BACKGROUND ART

Conveyor systems are known, which handles, diverts, rotates, pushes and/or accumulates products in the manufacturing processes. Such systems can for instance be used in packaging, filling, machining or assembly processes. Particular conveyor systems can comprise diverters designed to distribute products from one to several lanes. Such diverters preferably enable distribution in a continuous motion flow from the incoming lane to the outgoing lanes. A diverter preferably distributes products to the outgoing lanes following a given ratio such as an equal amount of products to each outgoing lane or the distribution may be controlled by external signals such as the actual consumption or the status of surrounding machinery. Other conveyor systems may comprise mergers which are adapted to merge the flow of products from two or more product flows into one product flow. Such a system may e.g. be a system comprising two production units where each production unit produces objects with a rate of e.g. 200 objects per minute. The packing unit has a capacity of 400 objects per minute, such that the product flow from the two production units must be merged to feed the packing unit. One problem when merging two product flows into one product flow is the synchronization between the infeed product flows. If two objects enter the merger at the same time, they will collide and block the merger, such that the whole system has to be stopped. This will both damage the products and will lead to a reduced production of the system.

One common method of merging two or more product flows into one product flow is to use stop members of some kind, which stops the objects and releases one or more objects in a controlled and synchronized way, such that it is ensured that only one object at the time enters the merger point. Such stop members may be mechanical gates or brakes that stops or slows down the incoming objects in a controlled manner. One problem with this method is that the incoming flow of a product flow must be restricted or stopped in order to provide space for objects from other product flows, which limits the throughput of the system.

US 4843799 A discloses a system for separating and aligning several parallel flows of cookies, where cookies are stopped and released by holding fingers. This and similar systems may work fine for medium speed systems and for some types of objects, but are nevertheless depending on a limited speed of the incoming objects of the infeed conveyors. There is thus still room for improvements.

DISCLOSURE OF INVENTION An object of the invention is therefore to provide a transfer device that is adapted to group incoming objects in groups in a secure way. Another object of the invention is to provide a method that can group incoming objects in groups in a secure way.

The solution to the problem according to the invention is described in the characterizing part of claim 1 with regards to the transfer device and in claim 1 1 regarding the method. The other claims contain advantageous embodiments and further developments of the transfer device and method. In a transfer device adapted to receive objects from a horizontal infeed conveyor belt and to forward the objects to a second horizontal outfeed conveyor belt, where the transfer device comprises a first conveyor belt and a second conveyor belt interconnected by a first upper carriage and a second lower carriage, where the transfer device is adapted to group the objects into spaced apart longitudinal groups comprising at least one object, the object of the invention is achieved in that the transfer device is adapted to temporarily increase the speed of the upper carriage in a forwarding direction until a leading edge of an object is aligned with a predefined position of the upper carriage, that the upper carriage is adapted to reduce the speed to the previous speed when the leading edge of the object is aligned with the predefined position of the upper carriage, and that the upper carriage is adapted to return to a start position when a group has been formed. By this first embodiment of the transfer device according to the invention, the transfer device will ensure that all objects in each group are grouped together and that there is a well-defined spacing between each group. In this way, it is possible to group objects at a high speed with a high reliability. The transfer device can be used for different purposes. In one case, the transfer device is used to group objects in groups having a predefined number of objects, e.g. grouping the objects for a packing machine. In another case, two transfer devices are used with a merger device, such that the product flow of two conveyors is merged into one product flow. In this case, it is not important that each group contains a specified number of objects, but that the spacing between two groups of one transfer device corresponds to the length of a group of the other transfer device, such that the groups can be merged into one product flow without interfering with each other. This will secure that one group can fit within the spacing of two other groups. The transfer device will thus ensure that the spacing between the objects in a group is relatively equal, and that the last object in a group is not trailing behind with a greater spacing. If a group of one transfer device would comprise one object that is spaced apart with a greater distance than the other objects in a group, the length of that group would be longer than the spacing between two groups of the other transfer device. This could result in a collision between two groups, e.g. two groups that are being merged into one product flow or two groups entering a packing station.

The transfer device may also be used to arrange incoming objects one by one with a predefined distance. In this case, a group contains only one object. In this way, it is possible to arrange objects with a predefined spacing with a high speed, such that the handling of the objects in a later stage is simplified. This may e.g. be relevant when single objects are to be merged or diverted or when the incoming objects are equally spaced apart.

During the grouping of objects, the objects do not have to stop which allows a high throughput. The spacing of the incoming objects may either be equal or may vary, or the incoming objects may also bear on each other. The transfer device will group the objects into groups having at least one object in a non-stationary fashion, i.e. the objects are not stopped or grouped using a stop member where the objects in the group bear against each other. In this way, a high throughput and a smooth transfer of the objects is provided. The number of objects that can be comprised in a group depends e.g. on the length of the transfer device, the size of the objects and the speed of the infeed conveyor belt. A suitable number of objects in a group is preferably in the range of 2 - 15. The speed of the infeed conveyor belt is preferably in the range between 50 - 150 meters per minute, but may vary depending on the size of the objects.

In high speed systems, stop members cannot be used to group objects since the acceleration and deceleration of the objects must be very high, which affects the objects in a negative way and leads to higher energy consumption. A smooth transfer of the objects is especially important if the objects are to be aligned in a specific way, since the precision of the positioning of the objects decrease with every start and stop.

The transfer device comprises two conveyor belts interconnected by two carriages. Each conveyor belt is driven by an individual motor such that each conveyor belt may be driven by a different speed. The speed of the first conveyor belt can thus e.g. be adapted to the speed of the infeed conveyor belt. The speed of the second conveyor belt can e.g. be adapted to the outfeed conveyor belt. A third motor is arranged to position the carriage that interconnects the conveying surfaces of the first and second conveyor belt in a horizontal direction. In this way, the ratio of the conveying surfaces of the first and second conveyor belt can be changed. By selecting the speeds of the first and second conveyor belt and the horizontal speed and direction of the carriage, the transfer device can be used to group e.g. a selected number of objects into a group having a predefined number of objects. The distance between two groups can also be set to a predefined distance or time.

In a group, the objects must not bear against each other, but they are preferably arranged close to each other. The distance between the objects may be dependent on the type of object. For some rigid products, a small distance may be preferred in order to prevent the products from touching each other. For softer products, such as frozen vegetables packed in bags, the bags may even extend over each other to some extent without interfering with the product flow. Soft or sensitive products are preferably also arranged with a small spacing between them in a group. Especially, sensitive products that cannot be pushed, squeezed or handled roughly can be groped without bearing against each other.

BRIEF DESCRIPTION OF DRAWINGS The invention will be described in greater detail in the following, with reference to the embodiments that are shown in the attached drawings, in which

Fig. 1 shows a schematic side view of a transfer device according to the invention,

Fig. 2 shows an infeed flow and a grouping action by the transfer device according to the invention, and

Fig. 3 shows a system comprising two transfer devices according to the invention and a merger. MODES FOR CARRYING OUT THE INVENTION

The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way to limit the scope of the protection provided by the patent claims.

Fig. 1 and 2 show a first embodiment of a transfer device according to the invention. The transfer device 1 is arranged between an infeed conveyor belt 2 and an outfeed conveyor belt 3. The speed of the infeed conveyor belt may be constant or may vary depending on the requirements on the total system. The speed may vary if e.g. the objects on the infeed conveyor belt are spaced apart with a varying distance such that the objects can be delivered to the transfer device at a constant pace. The speed is also dependent on the number of objects that is to be handled during a specific time period. The speed of the outfeed conveyor belts may also be constant or may vary depending on the requirements on the total system. The speed of the conveyor belts is however preferably substantially constant during the grouping and transfer of objects from the infeed conveyor belt to the outfeed conveyor belts. The infeed conveyor belt transports objects 4 with a first speed v₀ from a production line or the like. The invention is especially suitable for high capacity production lines, where a transfer device is adapted to handle a product rate of 200 objects per minute or more. The invention is suitable for sensitive or soft objects that should not bear against each other or against a stop member of some kind, and for irregular objects which cannot bear against each other. However, the invention is also suitable for more rigid and regularly shaped objects such as e.g. cardboard boxes, poly-wrapped packs or bags. The objects travelling on the infeed conveyor belt are supplied with a first flow rate, which may be constant or may vary and the spacing between the objects may either be constant or may vary.

The transfer device 1 is adapted to receive the objects from the infeed conveyor belt and to group the objects into groups comprising at least one object and with a specified distance between each group. The number of objects in a group may be a constant, predefined number of objects corresponding to e.g. a specific packing size. The number of objects in a group may also vary depending e.g. on a time gap for a merger station positioned downstream of the transfer device, such that the product flow of two infeed conveyors can be merged into a single outfeed conveyor. The distance between two groups, i.e. the time interval between two groups for a given speed, may be selected such that the time interval between two groups matches the size of a group of another conveyor when two product flows are to be merged into a single conveyor.

The transfer device 1 comprises in one example a first conveyor belt 9 and a second conveyor belt 10 which are interconnected by a first, upper carriage 1 1 and a second, lower carriage 12. Each carriage comprises two rollers around which the first and the second conveyor belt runs. The first conveyor belt is driven by a first powered roller 13 and the first conveyor belt also runs around a first deflection roller 14. The first powered roller and the first deflection roller are stationery. The first conveyor belt 9 may be powered by a separate motor which enables the first conveyor belt to run at an individual speed if required. Preferably, the first conveyor belt is run at substantially the same speed as the infeed conveyor belt in order to reduce the strain on the conveyed objects.

The second conveyor belt 10 is driven by a second powered roller 15 and the second conveyor belt also runs around a second deflection roller 16. The second conveyor belt is powered by a separate motor which enables the second conveyor belt to run at an individual speed if required. The speed of the second conveyor belt is varied such that the objects can be grouped. The second powered roller and the second deflection roller are stationery.

The upper carriage 1 1 is driven in the horizontal direction by a separate motor. The upper carriage 1 1 is provided with a centre plane 7 which runs vertically through the centre of the upper carriage, between the two rollers. The upper carriage is preferably arranged on a rail or similar that allows the upper carriage to slide or roll only in the horizontal direction. The motor may drive the upper carriage by e.g. a toothed wheel or a chain, but other solutions such as a linear motor or a threaded shaft would also be possible to use. The lower carriage is also arranged in a similar way on a passive rail and is not driven by a separate motor. The lower carriage will follow the upper carriage such that the first and the second conveyor belts have the same tension at all times. The lower carriage is preferably attached to the upper carriage by one or two wire cables or the like running over pulleys, such that the upper and lower carriage can move in opposite directions simultaneously. When the upper carriage moves in one direction, the lower carriage will move in the opposite direction. The support surfaces of the first and the second conveyor belts may be supported by a sliding surface if the objects are relatively heavy or the conveyor belts are relatively long. The upper carriage 1 1 has a start position 8 close to the infeed conveyor, at the first deflection roller 14. Further, the upper carriage has an end position close to the outfeed conveyor, at the second deflection roller 16. The upper carriage can move between these two positions, but not further. This means that the grouping action performed by the upper carriage must be completed before the upper carriage reaches the end position. The upper carriage will always be returned to the start position but will rarely or never reach the end position.

By moving the upper carriage in one direction, the gap between the first and the second conveyor belt is moved in that direction. Depending on the speed of the first conveyor belt, the second conveyor belt and the speed of the upper carriage, the transfer device can be used to either separate objects or to group objects. In the described example, the transfer device is used to group the incoming objects into groups. This can be seen in Fig. 2, where a grouping action of the transfer device is shown. In this described example, the objects on the infeed conveyor belt are spaced apart with an equal distance. The speed v₀ of the infeed conveyor belt 2 is constant with a speed of 2 m/s, the speed v₃ of the outfeed conveyor belt 3 is constant at 3 m/s. Further, the speed vi of the first conveyor belt 9 of the transfer device is set to a constant speed of 2 m/s which corresponds to the speed of the infeed conveyor belt.

In Fig. 2a, the forming of a first group 23 with a first leading object 20 is completed. The objects of the first group are separated from the incoming flow and the objects have been transferred from the first conveyor to the second conveyor, and there is a specified distance between the trailing object of the first group 23 and the leading object 21 of the second group 24. The objects in the first group are in this moment all conveyed by the second conveyor belt 10 of the transfer device and the distance between the objects of the first group has not been changed, since the speed v₂ of the second conveyor belt is the same as the speed of the first conveyor belt. By setting the speed v₂ of the second conveyor to a lower speed than the speed of the first conveyor belt, the distance between the objects in the first group 23 would be somewhat reduced. The distance between the objects in the first group can be set in dependency of the speeds of the first and second conveyor belt and the speed of the upper carriage. The leading object 20 of the first group is about to enter the outfeed conveyor belt. The upper carriage has been returned to its start position 8, which is close to the infeed conveyor at the first deflection roller 14.

The leading object 21 of the second group has left the infeed conveyor and is now conveyed by the first conveyor belt. The leading object 21 is provided with a leading edge 5. When the upper carriage is returned to the start position, it is difficult to synchronize the position of the leading object with the start position of the upper carriage. This is mainly due to the high speed of the objects and the high speed of the upper carriage. One reason for returning the upper carriage to the start position is to be able to use the complete length of the transfer device. Another advantage of returning the upper carriage to the start position is that the number of required sensors and the required resolution of the sensors are reduced in order to simplify the system. Due to this, an object may be positioned randomly at the upper carriage when the upper carriage is returned to the start position. It is preferred to position the leading edge of a leading object in a predefined position 19 at the upper carriage. The predefined position may either be aligned with the centre plane 7 of the upper carriage, or may be offset from the centre plane by a specified length. It is however important that the leading object bears only on the first conveyor belt when it is positioned in the predefined position. In this example, the centre plane 7 of the upper carriage 1 1 will be used as the predefined position 19. This means that the leading edge 5 of an object and the centre plane 7 of the upper carriage will most probably not be aligned with each other. In order for the system to work properly, the leading object should only be positioned on the first conveyor, i.e. with the leading edge 5 positioned aligned with or upstream of the centre plane 7. In this example, the first group 23 will comprise five objects, the second group 24 will comprise four objects and the third group 25 will comprise five objects.

It would be possible to determine an exact stop position of the upper carriage, i.e. to stop the upper carriage before it reaches the start position, such that the leading edge of the leading object could be positioned in a predefined position, e.g. at the centre plane of the upper carriage. This would however require a fast camera system and image processing capacity and would also require a more powerful conveyor motors.

In this example, the speed v_t of the upper carriage 1 1 is now set to 2 m/s which correspond to the speed of the infeed conveyor belt and the first conveyor belt. The speed of the second conveyor belt is set to a speed that is higher than the speed of the outfeed conveyor belt. In this way, the distance between the objects transferred from the second conveyor belt to the outfeed conveyor belt will be reduced. The speed of the outfeed conveyor belt can be selected such that the distance between the objects corresponds to a predefined distance. Hard or solid objects may bear on each other while softer objects may require a short distance between them.

In Fig. 2b, the speed of the upper carriage is raised temporarily such that the leading edge 5 of the leading object 21 will move backwards relative the centre plane 7, i.e. the predefined position, of the upper carriage. The temporarily raised speed continues until the leading edge 5 of the leading object 21 and the centre plane 7 of the upper carriage are aligned with each other. One way to control this is e.g. to use an optical sensor 6 mounted on the upper carriage, at the position of the centre plane 7. When the sensor is covered by an object, the speed is temporarily raised until the sensor is not covered. When the sensor is not covered any more, the leading edge 5 of the leading object 21 and the centre plane 7 of the upper carriage are aligned, and the upper carriage resumes 1 1 its previous speed, in this example 2 m/s. It would also be possible to mount an optical sensor at any suitable position, and e.g. use a pulse sensor at one roller to determine the exact position of the object.

In Fig. 2c, the objects of the first group 23 have entered the outfeed conveyor belt and bear on each other. The distance between the objects that will form the second group 24 has not changed. The second leading object 21 and some of the other objects of the second group are conveyed on the first conveyor belt.

In Fig. 2d, the first group 23 is conveyed on the outfeed conveyor belt, where it will be forwarded to a further handling station, such as a merger, diverter or packing station. When all objects of the first group have left the second conveyor belt, the speed v₂ is set to the same speed as the speed vi of the first conveyor belt. In this example, the speed v₂ is set to 2 m/s. At the same time, the speed v_t of the upper carriage is set to -1 m/s, i.e. to a speed of 1 m/s in the opposite direction. The objects that belong to the second group are now conveyed by the first conveyor belt, and the leading object 22 of a third group 25 is about to enter the first conveyor.

A result of the upper carriage travelling in the opposite direction can be seen in Fig. 2e, where the objects of the second group 24 have entered the second conveyor belt. The upper carriage continues backwards to the start position close to the infeed conveyor belt, which can be seen in Fig. 2f. Here, the objects belonging to the second group 24 are now being transferred to the outfeed conveyor belt. This situation resembles Fig. 2a, but with the second group 24 ready to be compressed and to be transferred to the outfeed conveyor belt. At the same time, the leading object 22 of the third group 25 has entered the first conveyor belt. The upper carriage is in the start position and the leading object of the third group has entered the first conveyor. Here, the third leading object 22 partly overlaps the upper carriage and bears on both the first and the second conveyor belt. It will thus be necessary to temporarily raise the speed of the upper carriage until the leading edge of the third leading object 22 is aligned to the centre plane 7, i.e. the predefined position, as described above.

The shown system can be used to group objects into groups having the same size in order to prepare the objects for a packing station or for a diverter. The system can also be used to arrange single objects with a predefined spacing. The system can also be used to form differently sized groups, e.g. to allow objects from two or more infeed conveyors to be merged into one outfeed converter. In such a case, it is of advantage to be able to form groups of different sizes in order to be able to merge the objects into one outfeed conveyor, regardless of the distance of the objects on the infeed conveyors. The size of a group is in this case adapted to the available time gaps of the merger.

It is also possible to vary the design of the transfer device. It is e.g. possible to drive the powered rollers in other ways. In one example, the first and the second powered rollers are connected with a mechanical transmission driven by one motor. In this case, the speed ratio between the first and the second conveyor belt of the transfer device is fixed and predefined. It is also be possible to e.g. let the first conveyor belt be powered by the first infeed conveyor belt, if these are to be driven at the same speed. It is also possible to connect the second powered roller of the second conveyor belt and the movement of the upper carriage with a mechanical transmission that drives both at the same time. In such a case, the speed ratio between the two is predefined and fixed. Such solutions that require less drive motors may be utilized when the product flow is predefined and stable, when the transition device must not be adaptable to different product flow rates and/or different products.

In Fig. 3, a system comprising a merger 18 is used to merge two separate product flows. The system comprises two transfer devices, a first transfer device 1 and a second transfer device 17, which are positioned in two parallel product flows. In the shown example, each product flow comprises the same objects 4 which are transported with a relatively high first speed by two infeed conveyors, a first infeed conveyor 27 and a second infeed conveyor 28. The speed of the first and the second infeed conveyor may be the same or may differ. The objects 4 may e.g. come from two production stations that each produce objects at a given production rate. A typical infeed rate of the first and the second infeed conveyor is 0 - 200 objects per minute. The infeed rate of the first and the second infeed conveyor may be the same, or the infeed rate may differ between the two conveyors, depending e.g. on the production capacity of the upstream production or feeding stations. The two infeed flows are merged by the merger 18 to a third outfeed conveyor 29 that will transport all the merged objects in one product flow. The speed of the third conveyor is at least twice the speed of the infeed conveyors, depending e.g. on the required spacing of the objects on the third conveyor. A detector at each infeed conveyor detects the objects and the distance or time gap between each object.

The objects that are transported on the infeed conveyors may have a constant spacing between them or may bear against each other, or the spacing may vary somewhat. Each transfer device 1 , 17 will receive objects at a high rate. Each transfer device will group a number of objects as described above into a group of objects, comprising one or more objects. The size of the group will depend on the number of object on each infeed conveyor, and on the distance between the objects. In the shown example, the first transfer device 1 has grouped a first group 23 comprising five objects, which is about to enter the merger after a group of objects grouped by the second transfer device has just left the second transfer device. At the same time, the second transfer device has just formed a fourth group 26 comprising two objects. The fourth group will arrive at the merger just after the first group 23. A second group 24 comprising four objects will thereafter be formed by the first transfer device. The distance or time gap between the first group of objects and the second group of objects will correspond to the size of the fourth group, i.e. will be somewhat greater than two objects.

Due to the high infeed speed of the objects, it is important that a transfer device can group the objects in a specified manner. It is thus important that the transfer device can position a leading object of a group of objects upstream of an upper carriage. If an object is positioned over an upper carriage, bearing on both the first and the second conveyor belt, it will in some cases be drawn to the second conveyor belt, accidently forming a separate group comprising a single object. This group will not fit in the predicted flow of groups and will inevitable cause a collision in the merger, which will lead to a stop of the whole system. By using an inventive transfer device, it can be ensured that each group comprises the determined objects and that each group is spaced apart by a sufficient distance.

The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims.

REFERENCE SIGNS

1 : Transfer device

2: Infeed conveyor belt

3: Outfeed conveyor belt

4: Object

5: Leading edge

6: Sensor

7: Centre plane

8: Start position

9: First conveyor belt

10: Second conveyor belt

1 1 : Upper carriage

12: Lower carriage

13: First powered roller

14: First deflection roller

15: Second powered roller

16: Second deflection roller

17: Second transfer device

18: Merger

19: Predefined position

20: First leading object

21 : Second leading object

22: Third leading object

23: First group

24: Second group

25: Third group

26: Fourth group

27: First infeed conveyor

28: Second infeed conveyor

29: Outfeed conveyor

Claims

Transfer device, where the transfer device (1) is adapted to receive objects (4) from a horizontal infeed conveyor belt

(2) and to forward the objects to a second horizontal outfeed conveyor belt

(3), where the transfer device (1) comprises a first conveyor belt (9) and a second conveyor belt (10) interconnected by a first upper carriage (11) and a second lower carriage (12), where the transfer device (1) is adapted to group the objects (4) into spaced apart longitudinal groups (23, 24, 25, 26) comprising at least one object, characterized in that the transfer device (1 ) is adapted to temporarily increase the speed of the upper carriage (11) in the forwarding direction until a leading edge (5) of an object (4) is aligned with a predefined position (19) of the upper carriage (11), where the upper carriage (11 ) is adapted to reduce the speed to the previous speed when the leading edge (5) of the object (4) is aligned with the predefined position (19) of the upper carriage (11 ), and where the upper carriage (11) is adapted to return to a start position (8) when a group has been formed.

Transfer device according to claim 1, characterized in that the predefined position (19) is a centre plane (7) which runs vertically through the centre of the upper carriage (11 ) between two rollers of the upper carriage (11 ).

Transfer device according to claim 1, characterized in that the predefined position (19) is offset with a distance from a centre plane (7) in an upstream direction, where the centre plane (7) runs vertically through the centre of the upper carriage (11), between two rollers of the upper carriage (11 ).

4. Transfer device according to any of claims 1 to 3, characterized in that the transfer device (1 ) is adapted to group the objects (4) into groups comprising a predefined number of objects.

5. Transfer device according to any of claims 1 to 4, characterized in that the transfer device (1 ) is adapted to handle over 200 objects per minute.

6. Transfer device according to any of claims 1 to 5, characterized in that the transfer device (1) comprises three motors, where the first motor drives the first conveyor belt (9), the second motor drives the second conveyor belt (10) and the third motor drives one carriage (11; 12) in a horizontal direction.

7. Transfer device according to any of claims 1 to 6, characterized in that the transfer device (1) comprises a sensor (6) arranged at the upper carriage (11 ).

8. Transfer device according to claim 7, characterized in that the sensor (6) is adapted to detect an object (4) overlapping the centre plane (7) of the upper carriage (11 ).

9. Conveyor system comprising a transfer device according to any of claims 1 to 8.

10. Conveyor system according to claim 9, characterized in that the conveyor system comprises a plurality of transfer devices (1, 17) arranged in parallel.

11. Conveyor system according to claim 10, characterized in that the conveyor system further comprises a merger (18) adapted to merge the flow of products from the two product flows.

12. Method for grouping objects from an infeed conveyor belt into a group comprising at least one object by using a transfer device, comprising the steps of: - receiving objects from an infeed conveyor to the transfer device,

- returning an upper carriage of the transfer device to a start position of the upper carriage,

- setting the speed of the upper carriage to a predetermined speed in a forwarding direction,

- aligning a leading edge of a leading object with a predefined position of the transfer device by temporarily raising the speed of the upper carriage,

- reducing the speed of the upper carriage to the predetermined speed when the leading edge of a leading object is aligned with the predefined position of the upper carriage, and

- returning the upper carriage to the start position when a group has been formed.

13. Method according to claim 12, where the predefined position is a centre plane which runs vertically through the centre of the upper carriage, between two rollers of the upper carriage.

14. Method according to claim 12, where the predefined position is offset from a centre plane of the upper carriage in an upstream direction, where the centre plane runs vertically through the centre of the upper carriage, between two rollers of the upper carriage.

15. Method according to any of claims 12 to 14, wherein the method is adapted to group the objects into groups comprising a predefined number of objects.