WO1998047797A1

WO1998047797A1 - A conveyor unit for use in a closed loop conveyor system and a conveyor system

Info

Publication number: WO1998047797A1
Application number: PCT/DK1998/000165
Authority: WO
Inventors: Niels Lomborg Nielsen; Bent Lindrup Nielsen; Thomas BRO-JØRGENSEN; Uffe Edslev-Christensen; Steen Kibsgaard; Ole Prydtz; Urban Henriksen
Original assignee: Crisplant A/S
Priority date: 1997-04-24
Filing date: 1998-04-24
Publication date: 1998-10-29
Also published as: AU6919798A

Abstract

A conveyor unit for use in a closed loop conveyor system for transportation and/or sorting of goods comprises a frame structure (2, 3) having at least two pairs of caster wheels (4). Each pair of wheels is mounted on a wheel mounting member (5), at least one of which is connected to another part of the frame structure pivotally around a substantially vertical axis (6), so as to allow mutual displacement of two or more sub-trolleys or sub-wagons comprised in each conveyor unit. One or more receptacles comprising tiltable trays or cross-belts for carrying articles may be comprised in the conveyor unit. The conveyor unit may have a relatively long receptacle and/or relatively long common goods supporting surfaces constituted by a plurality of receptacles. Improved track-holding qualities and high capacity and/or flexibility may be achieved.

Description

A CONVEYOR UNIT FOR USE IN A CLOSED LOOP CONVEYOR SYSTEM AND A CONVEYOR SYSTEM

TECHNICAL FIELD

The present invention relates to a conveyor unit for use in a closed loop conveyor system for transportation and/or sorting of goods and to a closed loop conveyor system for transportation and/or sorting of goods.

BACKGROUND OF THE INVENTION

Closed loop conveyor systems of the above mentioned type comprising a plurality of conveyor units or conveyor trucks are widely used in factories, at mail offices, airports, railway stations and at other locations where transportation and/or sorting of piece goods such as mail, postage packages, luggage, fruit, machinery components or other items is carried out.

The conveyor units are provided with receptacles for carrying goods, such as tiltable trays and/or conveyor belts, e.g., cross belts or other means. The units drive along tracks which form a closed loop, e.g., inside an airport building, in a railway station or in a factory. In order to save space and reduce costs, it is usually desired to build these buildings as small as possible and to make use of the available space in an as efficient way as possible. Thus, it is desired to reduce the space occupied by a conveyor system to a mini- mum, while still allowing a high capacity and/or efficiency of the system together with a high degree of flexibility as far as the size and weight of items to be sorted is concerned.

One way of reducing the spatial extent of conveyor systems is to reduce the radius of curvature of the tracks forming the closed loop. However, the forces created in a transversal direction caused by centrifugal acceleration when moving along a curved track put a lower limit on the radius of curvature. Furthermore, the dimensions of the conveyor units and/or trucks and the receptacles mounted thereon limit the radius of curvature to a lower limit, beyond which the con- veyor units comprised in the conveyor system are not able to move through the curves .

Conveyor trucks and conveyor systems dealing with some of the problems outlined above have been proposed in the prior art. EP 0 540 464 Bl discloses a conveyor truck comprising two tiltable trays mounted on the truck and defining a common support surface. In one embodiment, the truck comprises four rollers or wheels which are rotatably mounted on the truck. In a second embodiment, the truck comprises at all four corners thereof two wheels which are mounted on a boogie which is pivotable around a vertical axis. According to EP 0 540 464 Bl, such an embodiment is suitable for trucks with larger distance between the axles.

WO 95/33669 discloses a conveyor system comprising a number of trolleys which are coupled together so as to form a train of trolleys. Each trolley comprises two wheels for running along a pair of tracks, each wheel being mounted pivotally around a vertical axis.

US 5,267,514 discloses a material handling car and track assembly comprising a car having a chassis with four wheel assemblies mounted on the chassis.

DESCRIPTION OF THE INVENTION

It has been found that the track-holding qualities of the conveyor units or trucks when moving along curved tracks is a major parameter which puts a lower limit on the radius of curvature of a conveyor system. Furthermore, the track-holding qualities limit the life time of a conveyor system as the wear on the wheels of the conveyor unit or truck increases with decreasing track-holding qualities. The impor- tance of this parameter increases with increasing velocity of transportation. In addition, the noise created by a conveyor system due to friction and/or slip between the tracks and the wheels under certain circumstances, e.g., when the conveyor system is installed at or near a place of work of humans, constitutes a major problem.

It has further been found that, in cases where relatively long trucks are desired, the track holding qualities and the associated problems related to wear and noise generation put restrictions on the maximum length of the trucks. Such long trucks may be desired for a number of reasons: the more receptacles for carrying goods are provided on each truck, the longer goods may be handled by the conveyor system; in case more than one receptacle is provided on each truck, a relatively long truck is desired in order to increase the flexibility and capacity of the conveyor and/or sorting system in which the truck is comprised; the longer the trucks of a conveyor system are, the fewer wheels and coupling devices for coupling trucks to one another are needed, and thus the conveyor system is cheaper to manufacture; long trucks allow for long substantially continuous supporting surfaces for supporting goods being transported by the conveyor system, and thereby the risk of goods being clamped or squeezed between truck parts may be eliminated or at least reduced as compared to conveyor systems wherein relatively long goods are being supported by two or more goods supporting surface which are mutually displaceable.

An object of the present invention is therefore to provide a conveyor unit for use in a closed loop conveyor system and having a frame structure which eliminates the problems concerning track-holding qualities and associated wear and noise generation as mentioned above. A further object of the present invention is to provide a conveyor unit which allows for a comparatively long receptacle or for a plurality of recep- tacles so as to achieve relatively high flexibility and a relatively high capacity of the conveyor system comprising a plurality of such conveyor units. A still further object of the present invention is to provide a conveyor system which occupies less space and allows for reduced radii of curvature in comparison to known systems and which is consequently operable with at least the same capacity as prior art systems while occupying less space than such prior art systems .

Thus, the present invention provides a conveyor unit for use in a closed loop conveyor system for transportation and/or sorting of goods, said system comprising a pair of mutually transversely spaced tracks, said conveyor unit comprising

a frame structure,

at least two pairs of caster wheels, each pair of wheels being mounted on a wheel mounting member constituting part of the frame structure, so that each wheel of said pair of wheels may move along each respective one of said tracks, at least one of the wheel mounting members being connected to the another part of the frame structure pivotally around a substantially vertical axis, and

means for unloading goods carried by the conveyor unit .

In the present context, the term "caster wheel" should be understood as a wheel which is pivotally mounted around an axis which is substantially perpendicular to the axis of rotation of the wheel, caster wheels being known per se from the prior art.

In the present context, a "vertical axis" should be understood as an axis which is perpendicular to a plane defined by the tracks of the conveyor system. As the plane defined by the tracks may be parallel to a horisontal plane at some locations along the conveyor system and tilted in relation to the horisontal plane at other locations, the vertical axis at one location along the conveyor system is not necessarily parallel to the vertical axis at another location along the conveyor system.

A conveyor unit according to the invention having a frame con iguration as described above provides improved track- holding qualities as compared to prior art systems while allowing for relatively long trucks and relatively low radii of curvature of the tracks of the conveyor system. The conveyor unit according to the invention is in particular useful in embodiments wherein one or more goods carrying means/receptacles are provided, and wherein all of the one or more goods carrying means of a conveyor unit are rigidly mounted on a first one of the wheel holding members of the conveyor unit or rigidly connected to a first one of the wheel holding members. In such embodiments, the one or more goods carrying means constitute a substantially continuous and common surface for supporting goods while the fact that a second one of the wheel holding members is pivotally mounted on the frame structure allows conveyor units having such long supporting surfaces for goods to pass through relatively narrow curves. As discussed in detail below, the goods carrying means may comprise tiltable trays, cross-belts or other devices .

The frame structure is preferably made from profiles which are assembled by way of welding, gluing, screwing and/or by other suitable processes of assembling. The profiles are preferably made from light-weight metallic materials such as aluminium or its alloys or from fiber materials. However, at least parts of the frame structure may be made from other materials such as steel or steel alloys, or where appropriate from plastic materials.

The caster wheels are preferably pivotally mounted around a substantially vertical axis. Wheels of this type are known, e.g., from furniture and mobile shopping baskets. A pair of caster wheels is mounted on a wheel mounting member which preferably extends in a substantially transversal direction in relation to the longitudinal direction of the conveyor unit which is substantially identical to the longitudinal direction of the tracks. The wheel mounting member may be fixed to the frame structure or pivotally mounted thereon and may be made from the same materials and profiles as the frame structure. The conveyor unit comprises at least two pairs of caster wheels mounted on associated wheel mounting members, at least one of which is pivotally connected to the frame structure. This configuration allows that when the conveyor unit moves along a curved track, the longitudinal/circumferential distance between two wheels on the outer radius may be different from the longitudinal/circumferential distance between two wheels on the inner radius. At the same time, as each wheel is a caster wheel, this wheel automati- cally takes the position in which the rolling resistance is the lowest possible. This position is per definition the position in which the axis of revolution of the wheel is perpendicular to the tangent of the track, i.e. the position wherein no slip between the wheel and the track is present. This is made possible by a frame structure which is not stiff. The at least one of the wheel mounting members which is pivotally connected to the frame structure is connected to said frame structure around a substantially vertical axis, such that the pivoting movement of said wheel holding member in relation to the frame structure takes place in a plane which is substantially parallel to the tracks.

The conveyor unit further comprises means for unloading goods carried by the unit. These means may be mechanical, electrical, magnetic and/or electromagnetic. In preferred embodi- ments of the invention, the unloading means are mechanical means comprising, e.g., one or more actuating rods. The unloading means are preferably activated by activating means arranged at unloading positions along the tracks. Preferably, loading and unloading of goods is controlled by control means, such as, e.g., electronic control means which may also control the velocity of the conveyor units comprised in a closed loop conveyor system according to the invention. Preferably, in a conveyor unit according to the invention, the frame structure comprises a first and a second subframe which are pivotally interconnected in tandem around said vertical axis, each of the subframes having a wheel mounting member with a pair of caster wheels.

As each subframe has a pair of caster wheels associated thereto, only the two subframes together define a bearing structure. This way of segmentating the frame structure improves the track-holding qualities of a conveyor unit when used together with caster wheels. This will be further illustrated in the following description of the drawings.

The invention makes it possible to considerably reduce radii of curvature in a conveyor system when relatively long goods- carrying surfaces of the conveyor unit are desired, as com- pared to prior art systems. In such cases, it is preferred that all receptacles of the conveyor unit are mounted on the first subframe, and that the length of the first subframe is not equal to the length of the second subframe, the first subframe in this case being the longer. For a conveyor unit wherein the length of the first subframe is 1550 mm and the length of the second subframe may be 400 mm, the minimum curvature radius is approximately 4.25 m which clearly illustrates the benefit of segmentating the frame structure into a first and a second subframe. A prior art conveyor unit having a single subframe with an overall length of approximately 1950 mm typically has a minimum curvature radius of approximately 6 m. There is no lower limit on the total length of the goods-carrying surface of the conveyor unit. For applications wherein a relatively long goods-carrying surface of a single receptacle or a relatively long common or substantially continuous goods-carrying surface of a number of receptacles comprised in a single conveyor unit is desired, the total length of the goods-carrying surface of the conveyor unit is preferably at least 800 mm, more prefer- ably at least 1000 mm, such as at least 1200 mm, for some applications preferably at least 1400 mm, such as at least 1500 mm, or at least 1600 mm, at least 1700 mm or at least 1800 mm, or at least 2000 mm or even more such as at least 2500 mm. With each of these lengths of goods-carrying surfaces, the tracks of the conveyor system may be designed such that their radii of curvature is preferably at the most 10 m, such as less than or equal to 8 m or 7 m, such as less than or equal to 6.5 m or 6 m, for goods-carrying surface lengths of less than or equal to 1550 mm, the radii of curvature may be less than or equal to 5.5 m, such as less than or equal to 5 m, such as less than or equal to 4.5 , such as less than or equal to 4 m, for goods-carrying surface lengths of less than or equal to 1200 mm, the radii of curvature may be less than or equal to 4 m, such as less than or equal to 3.5 m or less than or equal to 3 m. The length of the first subframe is usually at least 1.25 times the length of the second subframe, such as 1.5 to 6 times, such as 2 to 6 times, such as 2.5 to 5 times, such as 3 to 4.5 times, such as 3.5 to 4.25 times, such as approximately 4 times.

A further advantage of a segmentated frame structure having two or more subframes is that the length of the main profile beam span between the wheel bases is much shorter than compared with the main profile beam span of the frame of a conveyor unit having a single subframe with an equal overall length. This yields a stiffer structure with smaller deflec- tion and lower stresses which makes it possible to keep the dimensions of the profiles at a minimum. Furthermore, wear of the wheel bandages of the caster wheel and of a substantially vertical shaft, on which the caster wheel may be mounted, and an associated bearing is reduced.

In a preferred embodiment of the invention, the first sub- frame has a cross-shaped outline when seen in a top view. The second subframe preferably has a T-shaped outline when seen in a top view. A particular advantage of this configuration is that the length of the turn spanned by the conveyor unit having such a configuration may be identical or almost identical to the actual length of the conveyor unit when moving along a curved track. This is desirable, as the sum of the lengths of the cords formed by the conveyor units in a curve varies, depending on the circumferential position of the conveyor units in the turn, thereby imposing severe fluc- tuating longitudinal forces in a chain of conveyor units. This problem may be completely or at least partly solved by optimizing the main lengths of the frame structure, namely the longer main profile of the first subframe, the shorter transversal profile of the first subframe and the main pro- file of the second subframe, and combining these lengths properly. The cross-shaped outline of the first subframe is normally formed by the main profile and the one of the wheel mounting members of the conveyor unit, whereas the T-shaped outline is normally formed by the main profile of the second subframe and the another wheel mounting member of the conveyor unit. A possibility of such a configuration which is a further advantage of a conveyor unit and a conveyor system according to the present invention is that the wheel mounting members may be arranged at substantially equidistant spacings therebetween. Thus, a first distance between the wheel mounting member of the first subframe and the wheel mounting member of the second subframe of a first conveyor unit in a conveyor system may be substantially equal to a second distance between the wheel mounting member of the second sub- frame of the first conveyor unit and the wheel mounting member of the first subframe of a second conveyor unit, the first subframe of the second conveyor unit being connected to the second subframe of the first conveyor unit. Preferably the ratio between the first and second distance is in the range between 0.2 and 5, such as between 0.3 and 4, such as between 0.4 and 3 , such as between 0.5 and 2.5, such as between 0.5 and 2 , such as between 0.6 and 1.7, such as between 0.6 and 1.6, such as approximately 1.5 or 0.67, or between 0.8 and 1.2, such as approximately 1. The wheel mounting member of the first subframe may be positioned at any position along the main profile of the first subframe, such as at a position of 1/10 of the total length of the main profile, or at 1/8, 1/6, 1/5, 1/4, 1/3, 1/2 from one or the other end of the main profile. The position of the wheel mounting member of the first subframe along the main profile may be variable, so that the position may be adjusted according to a specific application of the conveyor unit.

Preferably, each wheel mounting member is an integral part of a subframe. In preferred embodiments of the invention, each subframe has a T-shaped outline. It is further preferred that the first subframe of a conveyor unit is pivotally connected to the second subframe of a preceding conveyor unit, and that the second subframe of a conveyor unit is pivotally connected to the first subframe of a following conveyor unit.

A conveyor unit according to the invention may further comprise guiding means for stabilizing the conveyor unit in a transverse direction perpendicular to said tracks. These guiding means may comprise a profiled, e.g., corrugated cross-sectional profile of at least one of the wheels and preferably more of the wheels, which profile engages with a corresponding cross-sectional profile formed in or on of the tracks. Additionally or alternatively, the guiding means may be located above or below the tracks and may comprise mechanical guiding means, such as rollers being in physical contact with guiding tracks, or magnetic guiding means.

Preferably, the guiding means comprise at least one guiding wheel rotatably mounted on at least one of the wheel mounting members around a substantially vertical axis, the guiding wheel rolling along a side portion of one of said tracks. In preferred embodiments of the invention, a guiding wheel for each track is provided, so as to efficiently absorb forces in the transversal direction. In more preferred embodiments of the invention, a pair of guiding wheels is mounted on each wheel mounting member, said pair of guiding wheels rolling along the side portion of opposite tracks. Preferably, the guiding wheels roll along the inner side portion of the tracks . A conveyor unit according to the invention may further comprise means for carrying goods/receptacles mounted on the first subframe. In preferred embodiments of the invention, no means for carrying goods are provided on the second subframe. However, in other embodiments of the invention, goods carrying means may be provided on both subframes or only on one of the subframes.

The means for carrying goods may comprise at least one tilt- able tray or at least one conveyor belt which is preferably a cross belt. The conveyor unit may comprise both one or more tiltable trays and one or more conveyor belts.

The conveyor unit may comprise at least two tiltable trays arranged one behind the other in the transport direction, the support surfaces of the trays being substantially aligned. By allowing independently or simultaneously tilting of the trays, the capacity and/or efficiency^" of a conveyor system is increased in relation to a system in which each conveyor unit comprises one tiltable tray having the same length as two tiltable trays with aligned support surfaces. As the conveyor unit may selectively carry one item occupying both trays of a conveyor unit, or two items each occupying one tray, or one item occupying one tray, the capacity and/or efficiency of the system is improved, provided a control system which is able to handle the independent or simultaneously tilting of the trays is present. A preferred embodiment of a conveyor unit according to the invention comprises three tiltable trays mounted on each conveyor unit. Other embodiments of the invention comprise four or more tiltable trays on each conveyor unit. One major advantage of having three or more trays per conveyor unit as compared to two trays per unit is the considerable increase in transportation/sorting capacity, especially in systems in which the majority of items to be transported occupy less than half of the total length of the trays of a unit, and hence also less than half of the recep- tacles. Thus, a configuration having three or more trays per conveyor unit provides a considerably increased capacity and/or efficiency if a substantial part of the items to be transported are items occupying a single receptacle.

Preferably, the aligned support surface of the trays and/or conveyor belts of a unit should be at least as long as the longest items to be transported and/or sorted in a given application, so as to prevent goods from being squeezed between trays of adjacent conveyor units. This is in particular relevant in applications where the items often are soft mail bags and/or fragile goods .

In order to prevent trays mounted on adjacent units from colliding when the conveyor unit moves along a curved path, adjacent opposite tray end portions of adjacent opposite conveyor units may have a convex outline. In other embodiments of the invention, trays mounted on adjacent tracks may overlap. However, this allows piece goods on the trays to displace relative to the trays which for some applications is not desirable.

In alternative embodiments of the invention, thin trays mounted on adjacent conveyor units may be tilted slightly forwards or backwards, so as to allow the trays to overlap in curves in one side and to separate in the other side. The trays may then have a rectangular outline. To some extent this configuration prevents soft and/or flexible items, e.g., bags to fall into the gap between two adjacent trays on different conveyor units, as in one side, the gap is minimal, and in the other side, trays of adjacent conveyor units overlap .

By pivotally interconnecting succeeding conveyor units near one side, instead of interconnecting them near the center axis of a unit, it may be achieved that the trays do always overlap, provided all curves of a conveyor system are curved in the same angular direction. In other embodiments of the invention, adjacent trays on succeeding conveyor units may be interconnected by a flexible construction, e.g., a pillow, a stretched elastomer film, a foam, overlapping fingers of plates or other suitable means, so as to thereby prevent adjacent trays on succeeding conveyor units from separating in turns. In alternative embodiments of the invention, the trays may be prevented from separating by applying mechanical or electric actuators, which may move the tray or trays relative to the frame structure of adjacent conveyor units. In still further embodiments of the invention, the size of the trays is adjustable, e.g. by telescopic means which are actuated by mechanical or electric actuators. Thereby the size of a tray may be adjusted to the size of a given item to be transported. Consequently, the size of adjacent trays are mutually adjustable. The actuating device or devices for tilting a tray may be activated by an activating device associated to that tray or by an activating device associated to another tray.

In alternative embodiments of the invention, the trays are releasably connected to the frame structure of a conveyor unit. Items to be transported may then be arranged on a tray prior to connecting the tray to a conveyor. The conveyor unit may initially have no trays connected thereto, or it may already carry one or more trays additional to the one which becomes connected thereto. The trays may have various dimensions, suited for different items. In case a tray is con- nected to a conveyor unit having no trays, the tray may engage with a single actuating device and may be supported by other actuating devices, or the tray may engage with the first and the last actuating device of a series of actuating devices, while intermediate actuating devices may be used for additional support. In some cases it might happen that the trays separate in curves. However, as an item is carried by a properly sized tray, this item does not risk to drop into a gap between two trays and/or to be squeezed thereinbetween, and it does not risk to displace in curves or at level changes. Preferably, each tiltable tray of a conveyor unit according to the invention is pivotally mounted around an axis extending in the transport direction of the conveyor unit, and preferably the conveyor unit is substantially symmetrical around this axis. In preferred embodiments of the invention the pivoting axes of all trays mounted on one conveyor unit are aligned. For special applications, it might be useful that the pivoting axis of the trays is not positioned in the center of a conveyor unit and/or that the axes of the trays of one conveyor unit are not aligned.

Preferably, the means for unloading goods comprise at least one actuating device connected to each tiltable tray. The actuating device transmits the unloading impulse or signal to the tiltable tray, and it may comprise only mechanical parts, or it may additionally/alternatively comprise electric and/or electromagnetic parts. In preferred embodiments of the invention, at least a right hand and a left hand actuating device is connected to each tray for selectively tilting said tray to the right or to the left, respectively. In other embodi- ments of the invention, only one actuating device may be connected to switching means for switching between the right hand side and the left hand side. This switching may be controlled by a control system comprised in the conveyor system.

As mentioned above, the control system is preferably able to cause simultaneous or independent tilting of the trays to the right or to the left, respectively. The capacity and flexibility of a conveyor unit and a conveyor system according to the present invention may be further optimized by employing a control algorithm for the allocation of items to be transported and/or sorted, which control algorithm allocate single tray items to the first or the last tray of an empty conveyor unit, so as to allow subsequent multiple-tray items to be allocated to previous or following trays on that conveyor unit. The control algorithm may further comprise that single tray items are preferably allocated to unoccupied trays of conveyor units wherein one or more trays are already occupied.

In order to activate the actuating device or devices, activating means arranged adjacent to the tracks at unloading positions along the tracks may be comprised in the conveyor system. Preferably, these activating means are controlled - preferably by means of electric signals - by the control system comprised in the conveyor system, such that when a given tray to be tilted passes the unloading position, the activating means will engage with an actuating member comprised in the actuating device, so as to tilt the tray. In a preferred embodiment of a conveyor unit according to the invention, the actuating member comprises a wheel or roller, and the activating means comprise a curved track. However, other mechanical configurations are possible, some of which are known from the prior art. It should be understood, that also electric and/or electromagnetic activating systems are possible within the scope of the invention.

In a preferred embodiment of the invention, a number of activating devices which is equal to the number of trays per conveyor unit, is arranged at both the right hand side and the left hand side at an unloading station. In this embodiment, the activating devices are arranged with a mutual distance equal to the corresponding distance between the actuating devices of a conveyor unit, so as to thereby allow simultaneously tilting of the trays. However, in other embodiments of the invention, the activating devices may be displaced in relation to the configuration outlined above, so as to thereby perform cascade tilting of the trays of a conveyor unit. Cascade tilting of the trays may also be achieved by arranging a single activating device at an unloading station which subsequently tilts the trays of a conveyor unit as these pass by the activating device. Inverse cascade tilting - i.e. tilting of the last tray of a conveyor unit first and tilting the first tray at last - may be achieved by arranging the activating devices with a mutual distance between them, which distance is larger than the mutual distance between the actuating devices of the trays . Obviously cascade tilting or inverse cascade tilting may be achieved in other ways. In other embodiments of the inven- tion, the control system controlling the conveyor system is able to handle cascade and inverse cascade tilting as well as simultaneous tilting of the trays.

An advantage of both the cascade tilting and the inverse cascade tilting of the trays is that it allows to reorient goods carried by the conveyor unit for proper orientation in a discharge chute, e.g., to reorient an item from being oriented in the longitudinal direction of the conveyor unit to being oriented in an at least partly transverse direction, i.e. at least partly parallel with the chute. Thereby nar- rower chutes may be employed, and a larger number of chutes may be employed for multiple- tray items.

For some applications of the invention it is preferred that the trays of a conveyor unit may have varying dimensions, in particular varying lengths. For instance, if the number of trays occupied by each item and the length of the item are known in advance, it is possible to allocate an item to one or more trays having substantially the same length as the item. This increases the capacity and efficiency of the conveyor system and provides increased functionality, as it is at least partly avoided to carry items over more than one tray. Examples of applications where this is useful, are manufacturing plants assembling assemblies of prefabricated parts where the exact number and size of the parts is known in advance.

For other applications, e.g., for postal order business, a number of predetermined trays in a conveyor system, e.g., every tenth tray, may carry a free gift or another predetermined item having known dimensions. Furthermore, for this and related kinds of applications, the tray dimensions may be employed as variable parameters when preparing logistic solutions for a conveyor system. For special applications, one or more trays may be equipped with special unloading means for unloading particular items .

In embodiments of the present invention, wherein the means for carrying goods comprise one or more tiltable trays, the tray or trays may be shaped and sized according to the kind of goods to be conveyed by the conveyor system and/or according to the path of the conveyor track, so as to assure safe transportation of goods during operation of the conveyor system. Thus, there may be provided large trays for large items, strong trays for heavy items, trays which prevent non- edged items from rolling over the side of the tray, or inclined trays for conveyor paths comprising level changes.

Whereas it is well-known per se to provide trays which sup- port goods in a substantially vertical direction, so as to establish a reaction force to gravity, the present invention provides, as an additional, individual and independent aspect, trays having means for supporting goods in other directions. Such means may comprise, for example, on or more barriers extending, e.g., along one or more edges of the tray, so as to prevent goods from sliding over such edges, e.g., in curves or at level changes of the conveyor system. In addition or as an alternative, tray surfaces may have non- planar configurations. Thus, the surface of a tray may be roughened or have a certain surface relief pattern. The tray may be shaped in such a way that a stable equilibrium point for goods, e.g., for non-edged goods and/or goods which tend to roll on the tray is provided. Thus, a tray may have a concave configuration which may be obtained, e.g., by a V- shaped cross section or by one or more cut-outs, depressions and/or grooves. The tray may be fortified or strengthened for special applications, e.g., applications where heavy goods are being transported in the conveyor system. For some applications, e.g., applications wherein the conveyor system comprises level changes or applications wherein the tracks are arranged in a non-horisontal plane, it may be useful to provide trays which are tilted in relation to the tracks.

The surface characteristics, such as, e.g., frictional properties, of trays may be adapted to particular applications of the conveyor system by adapting the material from which the tray is made and/or by providing a coating on the surface of the tray and/or by providing a certain roughness or surface relief pattern to the surface of the tray. In addition or as an alternative, a tray may, as an individual and inde- pendent aspect of the present invention, be provided with one or more bores or perforations allowing air to pass from below the tray, so as to control the sticking of goods to the surface due to suction. This is for example relevant when the goods being transported comprise articles being wrapped in, e.g., cellophane foil, such as, e.g., video or music cassettes, compact discs or books.

In other embodiments of the invention, the means for carrying and unloading goods may comprise at least one conveyor belt, e.g., a cross belt. The conveyor unit may comprise two or more -conveyor belts arranged one behind the other in the transport direction of the conveyor unit and/or side by side, and the upper runs of the conveyor belts may together define a substantially aligned support surface. The above remarks concerning the substantially aligned support surface and the controlling of unloading of goods do also apply for conveyor units having cross belts instead of or in addition to tiltable trays. Furthermore, the geometrical configurations and/or shapes of trays outlined above may also be adapted to cross-belts where applicable.

Besides tiltable trays and/or conveyor belts, a conveyor unit may comprise other kinds of receptacles, such as, e.g., trays with pushing devices, chain/rope/wire movements, roller surfaces, rotating and/or overlapping discs, any other known discharge means and/or any combinations thereof . It should be understood that all the above remarks and possible embodiments of conveyor units with tiltable trays and any combination thereof also apply to conveyor units with conveyor belts and/or to any other kinds of receptacles.

The conveyor unit according to the invention preferably further comprises driving means for driving the conveyor. These driving means may comprise any kind of force generating means, such as one or more fuel engines, one or more electromotors, linear induction motor or motors or any combinations thereof. The driving means are necessary in order to overcome rolling resistance between the caster wheels and the tracks and between the guiding wheels and the tracks, respectively, as well as aerodynamic resistance. Each conveyor unit may be provided with one or more fuel engines and/or one or more electromotors transmitting the generated force/torque to the wheels by mechanical transmission means. Alternatively/additionally, the conveyor unit according to the invention may be part of a magnetic track.

In a preferred embodiment of the invention, the driving means comprise a linear induction motor wherein the stationary parts preferably are positioned between the tracks below the conveyor units, and wherein at least parts of the conveyor units define moving parts of the driving means. Preferably, at least part of the conveyor units are provided with or made from magnetic material. This way of driving the units in a conveyor system eliminates losses caused by a mechanical transmission, as no mechanical transmission system is needed. Further, it eliminates noise caused by the driving means and causes no exhaust gasses.

A conveyor unit according to the invention may further comprise first control means for controlling unloading of goods carried by the conveyor unit, said control means communicating with second control means which are stationary and comprised in the closed loop conveyor system. The first control means may comprise electronic equipment or one or more bar codes or other means for identifying a specific conveyor unit in relation to other conveyor units and/or for measuring velocity of the unit, e.g., by means of photo cells or other sensing means arranged along the tracks. The first control means may further comprise processor means, though in a preferred embodiment of the invention, the first control means are inactive control means. The second, stationary control means comprise central control means controlling loading and unloading of goods, velocity of the conveyor units etc.

An alternative embodiment of a conveyor unit according to the invention relates to a conveyor unit wherein at least one of the subframes is mounted slidably in relation to at least one of the receptacles for carrying goods . Thereby it is obtained that a subframe supporting one or more receptacles may displace relative to the receptacles carried by the subframe itself, e.g., when the conveyor unit moves along a curved path. In a preferred embodiment, the receptacles of a unit are kept aligned under all conditions. An example of such a configuration is a conveyor unit according to the invention, further comprising a third subframe, the three subframes being arranged one behind the other in the transport direction of the conveyor unit wherein the subframes arranged at either end of the conveyor unit are pivotally connected to the middle subframe, and wherein the receptacles are mounted on and substantially aligned with the middle frame. In this embodiment, the three receptacles are aligned with the middle subframe, while in other embodiments the three receptacles may be mounted on other subframes than the middle one. Ob- viously, this configuration is also possible with more than three receptacles per conveyor unit. A plurality of receptacles may be arranged one behind the other and/or side by side on a conveyor unit. Other embodiments of the invention comprise a single or two receptacles mounted on one or more subframes. The invention further relates to a closed loop conveyor system for transportation and/or sorting of goods comprising

a pair of mutually transversely spaced tracks,

a plurality of conveyor units according to the invention,

- means for controlling unloading of goods carried by the conveyor unit, and

means for driving said conveyor units.

A closed loop conveyor system according to the invention wherein each of the conveyor units comprises at least one tiltable tray for carrying goods, preferably further comprises means for repositioning said trays after unloading. These means may be mechanical, electric and/or electromagnetic.

A closed loop conveyor system according to the invention may be substantially planar and it may comprise turns, it may comprise level changes and curves, or it may comprise return tracks located above or below the transportation and/or sorting portion of the tracks which may or may not comprise curves and/or level changes.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be further described with reference to the drawings in which:

Fig. 1 is a perspective view of a conveyor unit according to the invention, seen from above, Fig. 2 is a perspective view of two conveyor units of the type shown in fig. l which are coupled together, seen from above,

Fig. 3 is a perspective view of the conveyor unit of Fig. 1, seen from below, Fig. 4 is a perspective view of the conveyor units of Fig. 2, seen from below,

Fig. 5 is a schematic front view of a conveyor unit according to the invention, Fig. 6 is a schematic view of a conveyor unit according to the invention, seen from behind,

Fig. 7 is a schematic view of a conveyor unit according to the invention, seen from below,

Fig. 8 is a schematic view of two conveyor units accor- ding to the invention which are coupled together, seen from below,

Fig. 9 is a schematic side view of a conveyor unit according to the invention,

Fig. 10 is a schematic side view of two conveyor units of the type shown in Fig. 9 which are coupled together,

Fig. 11 is a schematic top view of a conveyor unit according to the invention,

Fig. 12 is a schematic top view of two conveyor units according to the invention which are coupled together, Fig. 13 is a side view of two conveyor units according to the invention which are coupled together,

Fig. 14 is a top view of the conveyor units of Fig. 13,

Fig. 15 is a view of a conveyor unit according to the invention, seen from behind, Fig. 16 is a perspective view of a subframe for a conveyor unit according to the invention,

Fig. 17 is a schematic top view of a chain of first prior art conveyor trucks moving along a curved path,

Fig. 18 is a detail of the first prior art conveyor truck of Fig. 17,

Fig. 19 is a schematic top view of a detail of a second prior art conveyor truck when moving along a straight path,

Fig. 20 is a partly cross-sectional view of the prior art truck of Fig. 19, Fig. 21 is a schematic view of the prior art truck of

Fig. 19 when moving along a straight path with an inaccurate distance between the tracks, Fig. 22 is a partly cross-sectional view of the second prior art truck of Fig. 21,

Fig. 23 is a schematic top view of a chain of conveyor units when moving along a curved path, Fig. 24 is a detail of Fig. 23,

Fig. 25 is a schematic front view of the conveyor unit of Fig. 23,

Fig. 26 is a schematic top view of an alternative embodiment of two conveyor units according to the invention which are coupled together,

Fig. 27 is a schematic top view of the conveyor units of Fig. 26, moving along a curved path,

Fig. 28 is a schematic top view of a detail of a conveyor unit of Fig. 26 when moving along a straight path, Fig. 29 is a schematic top view of a first detail of the conveyor unit of Fig. 26 when moving along a curved path,

Fig. 30 is a schematic top view of a second detail, of the conveyor unit of Fig. 26 when moving along a curved path,

Fig. 31 is a schematic top view of a first tray for a conveyor unit according to the invention,

Fig. 32 is a schematic end view of the tray of Fig. 31,

Fig. 33 is a schematic side view of the tray of Figs. 31 and 32,

Fig. 34 is a schematic top view of a second tray for a conveyor unit according to the invention,

Fig. 35 is a schematic end view of the tray of Fig. 34,

Fig. 36 is a schematic side view of the tray of Figs. 34 and 35 ,

Fig. 37 is a schematic top view of a third tray for a conveyor unit according to the invention,

Fig. 38 is a schematic end view of the tray of Fig. 37,

Fig. 39 is a schematic side view of the tray of Figs. 37 and 38,

Fig. 40 is a schematic top view of a fourth tray for a conveyor unit according to the invention,

Fig. 41 is a schematic end view of the tray of Fig. 40, and Fig. 42 is a schematic side view of the tray of Figs. 40 and 41.

DETAILED DESCRIPTION OF THE DRAWINGS

Figs . 1 and 3 show perspective views of a conveyor unit 1 according to the invention, while Figs. 2 and 4 show perspective views of two conveyor units 1 which are coupled together. Each conveyor unit 1 comprises a frame structure comprising a first sub rame 2 and a second subframe 3. A wheel mounting member 5 holding a pair of caster wheels 4 for moving along a pair of tracks is connected to each subframe. Each of the caster wheels 4 is pivotally mounted on the wheel mounting member 5 which is preferably an integral part of an associated subframe 2 or 3. The subframes 2 and 3 are pivotally interconnected around substantially vertical axes 6, so as to thereby connect each wheel mounting member 5 to the frame structure 2, 3. Each wheel mounting member 5 further comprises a pair of guiding wheels for stabilizing the conveyor unit 1 in a transversal direction. The guiding wheels 7 are rotatably mounted on the wheel mounting member 5 in a substantially horizontal plane, so as to roll along a side portion of the tracks. This is illustrated in Figs. 15 and 25 and will be described further below.

Each conveyor unit 1 comprises means for carrying goods . In a preferred embodiment of the invention, these means comprise tiltable trays 8a, 8b and 8c pivotally mounted around a substantially horizontal axis extending in the transport direction of the conveyor unit. For other applications of the invention, more than three trays per conveyor unit may be useful, and for yet other applications, less than three trays per unit may be useful. Preferably, the tiltable trays of a conveyor unit 1 define an aligned support surface, as illustrated in Figs. 10 and 13, and preferably each tray has a substantially concave cross section, as illustrated in Figs. 5, 6 and 15, so as to prevent goods carried by the tray to fall from the tray, e.g., when moving along a curved path. Fig. 15 illustrates a tray 8b which is tilted, and a non- tilted tray 8a.

The tilting of the trays may be controlled by a control system which allows the trays to be tilted simultaneously or individually, depending on the number and the length of piece goods carried by the trays. In a preferred embodiment of the invention, the number and size of goods carried by a conveyor unit is further registered by the control system.

The free end portions 8a' and 8c' of the trays 8a and 8c preferably have a convex shape when seen from above or below, cf . Figs. 7, 8, 11, 12 and 14, so as to prevent trays mounted on adjacent units from colliding when the conveyor unit moves along a curved track, or, so as to allow a chain of conveyor units to take narrower curves.

Each tiltable tray is connected to means for unloading goods carried by the conveyor unit 1. In a preferred embodiment of the invention, the means for unloading goods comprise a right hand and a left hand actuating device or actuating arm 9a and 9b, and an actuating wheel 10 mounted on the free end of each actuating arm, said wheel being suited for engaging with activating devices arranged at unloading stations along a closed loop conveyor system which comprises a chain of conveyor units according to the invention.

Fig. 15 shows a conveyor unit according to the invention, as seen from behind, with a pair of tracks 11a, lib, a track frame 12 and electric driving means 13 for driving the conveyor unit comprised in the track frame 12. One of the trays 8a is shown in its horizontal position, while another tray 8b is shown in its tilted position. The caster wheels 4 engage with the tracks 11a and lib, and the guiding wheels 7 engage with side portions 11a' and lib' of the tracks.

The second subframe 3 is shown in a perspective view in Fig. 16. The wheel mounting member 5 is an integral part of the subframe 3. The caster wheels 4 are mounted on the wheel mounting member around a substantially vertical axis 4' . Coupling means 6' are provided for pivotally connecting the second subframe to first subframes at both ends.

In order to illustrate a major advantage of a conveyor unit according to the invention, two prior art conveyor trucks are schematically illustrated in Figs. 17-22. Fig. 17 shows a schematic illustration of a first prior art conveyor chain comprising a chain of conveyor trucks 21 interconnected by connecting bars 22 which are pivotally connected to the trucks 21 around vertical axes 23. Each conveyor truck 21 comprises four wheels 24 which are unable to pivot around a vertical axis, and four guiding wheels 25 for rolling along side portions of a pair of tracks 26a, 26b. From Fig. 17 and from the detail in Fig. 18, it is seen clearly that when the chain of conveyor trucks moves along a curved path, the rotational direction of the wheels 24 will not coincide with the transport direction of the wheels which is the tangent to the curve of the tracks. This slip between the wheels 24 and the tracks 26a, 26b and the friction caused thereby result in high -resistance and considerable wear on the wheels. This again creates noise, reduces the lifetime of the wheels, creates tension in the truck and in the connecting bars and increases the force needed to overcome the friction between wheels and tracks which leads to increased energy consumption of the system. Further, this prior art conveyor truck will introduce vibrations due to the slip between wheels and tracks when driving along a curved path.

Figs. 19-22 show schematic illustrations of a second prior art conveyor truck 31 suggested in the prior art. The truck 31 comprises four wheels 34, each mounted on a boogie 38. Guiding wheels 35 for rolling along side portions of the tracks 36 are mounted on the boogie. The boogie may pivot in a horizontal plane around a vertical axis 37. Fig. 19 shows a schematic top view of this configuration in the optimal condition of use where the two guiding wheels are in contact with the track 36. Fig. 20 shows a partial cross sectional view of this configuration. If the lateral distance between two tracks varies in comparison with the lateral distance between two opposite boogies, the situation sketched in Figs. 21 and 22 might occur. When moving along the tracks, the conveyor truck might be thrown forth and back between the two tracks and thereby cause noise, wear on the wheels and vibrations in the truck. It may also happen that the truck 31 displaces by the distance o., thereby causing slip between the wheels 34 and the tracks 36 which again results in noise, reduced life time of the wheels and increased friction. These disadvantages may occur even if the lateral distance between two tracks in comparison with the lateral distance between two opposite boogies only varies within very small limits. The disadvantages may also occur when the conveyor truck moves along a curved path. When entering into a curve, the different transversal distance between the front boogies and the rear boogies may cause at least one of the guiding wheels to loose contact with the adjacent track. This may result in that the conveyor truck is thrown forth and back between the tracks .

Figs. 23-25 show schematic illustrations of a chain of conveyor units having T-shaped subframes and is intended to illustrate only the mutual arrangement of the wheels of a conveyor system in a curve. T-shaped conveyor trolleys or wagons are known per se from the prior art. As illustrated in Fig. 23, the subframes 2, 3 are pivotally interconnected around substantially vertical axes 6. When moving along a curved path, adjacent subframes will pivot relative to each other around the axis 6. At the same time, each caster wheel 4 will pivot around its vertical axis 4 ' , so as to thereby automatically position itself in the position causing the lowest resistance. This position is per definition the position in which the wheel 4 is parallel with the tangent of the track 11a, lib, respectively. This is illustrated clearly in Fig. 24. Thereby wear, noise generation and forces in the conveyor unit are reduced to a minimum. Fig. 25 shows a schematic end view of this configuration.

Figs. 26-30 illustrate an alternative embodiment of a conveyor unit according to the invention, comprising three tiltable trays 8a, 8b, 8c and three subframes 31, 32, 33. A wheel mounting member 35 is mounted on each subframe, and preferably a pair of caster wheels is mounted on each wheel mounting member, as described above in connection with Figs. 1-16 and Figs. 24, 25. The subframes 31, 32 and 32, 33, respectively, are pivotally interconnected around substantially vertical axes 36, while all three trays 8a, 8b, 8c are mounted on and substantially aligned with the subframe 32. Right hand and left hand activating members 9a and 9b are provided for activating tilting of the trays, cf. the above description. The tilting mechanism (not shown) may be mounted on the turn table 40 within an area 42 allocated thereto.

Two turn tables 40 are mounted on subframe 32. When the conveyor unit moves along a curved path, as illustrated in Figs. 27, 29 and 30, subframes 31 and 33, respectively, pivot around the axes 36 in relation to the subframe 32. Thereby a holding member 41 will slide along the outline 40' of the turn table 40. It is understood that the outline 40' of each turn table 40 is substantially circular, with the center of the circle located substantially on the axis 36. Since all three trays 8a, 8b, 8c are mounted on and substantially aligned with subframe 32, they do not displace in relation to subframe 32 when the conveyor unit moves along a curved path, and thus they will remain substantially aligned, their direction being defined by the direction of subframe 32.

In order to absorb longitudinal forces and to reduce longitudinal vibrations in the conveyor unit which may occur when moving along a curved path, resilient members 43 mounted on associated mounting members 43' may be applied for abutting the wheel holding member 5 or a support member 44, respec- tively. Other embodiments similar to the one shown in Figs. 26-30 may comprise a single or two subframes, wherein each of the subframes is associated to one or more receptacles.

Figs. 31-42 show various examples of suitable tiltable trays 8 which may be used as receptacles in a conveyor system according to the present invention. The trays of Figs. 31-42 further constitute embodiments of the individual and independent aspects of the invention related to tray configurations mentioned above.

The tray 8 shown in Figs. 31-33 is a substantially planar tray 8 with slightly elevated side portions 48 and a barrier 46 at one end of the tray. The tray 8 is particularly suitable for carrying well-defined items having planer surfaces, such as boxes.

The tray 8 shown in Figs. 34-36 has a V-shaped cross-section, as can be seen in Fig. 35, the tray 8 being particularly suitable for carrying, e.g., spherical or cylindrical items or other items, which tend to roll. The V-shape provides a stable equilibrium point for the items in a transverse direc- tion, thus ensuring that the items are kept in a position at or near a longitudinal center axis 45 of the tray 8. The items are thus prevented from rolling over the side of the tray 8 while being conveyed.

The tray 8 shown in Figs. 37-39 is particularly suited for carrying well-defined items, such as boxes. As shown in Fig. 39 the tray 8 is slightly inclined in the direction of movement, the tray 8 being particularly suitable for use in conveyor systems comprising level changes. The items will normally abut the barrier 46 provided at one end of the tray 8, thereby preventing items from sliding off the tray 8 at level changes. The tray configuration shown in Figs. 37-39 normally ensures that items are placed at equal positions on the trays in the conveyor system which may be useful, e.g., when items having identical shapes are being conveyed, as it allows for relatively narrow discharge stations which are usually comprised in the conveyor system. The angle of inclination of the tray in Figs. 37-39 is preferably 2-10°, such as 5° .

Figs. 40-42 show a tray 8 which is slightly inclined from both sides towards the center axis 45 of the tray.

It should be understood that the embodiment of a conveyor unit according to the invention shown in Figs. 1-16, 23-25 and 26-30 is not restricted to tiltable trays. As an example conveyor belts, e.g., cross belts may be mounted on the unit.

Claims

1. A conveyor unit for use in a closed loop conveyor system for transportation and/or sorting of goods, said system comprising a pair of mutually transversely spaced tracks, said conveyor unit comprising

a frame structure,

means for unloading goods carried by the conveyor unit .

2. A conveyor unit according to claim 1, wherein the frame structure comprises a first and a second subframe, which are pivotally interconnected in tandem around said vertical axis, each of the subframes having a wheel mounting member with a pair of caster wheels.

3. A conveyor unit according to claim 2, wherein each wheel mounting member is an integral part of a subframe.

4. A conveyor unit according to any of the preceding claims, further comprising guiding means for stabilizing the conveyor unit in a transverse direction perpendicular to said tracks.

5. A conveyor unit according to claim 4, wherein said guiding means comprise at least one guiding wheel rotatably mounted on at least one of the wheel mounting members around a substantially vertical axis for rolling along a side portion of one of said tracks .

6. A conveyor unit according to claim 5 , wherein a pair of guiding wheels is mounted on each wheel mounting member, said pair of guiding wheels rolling along the side portion of opposite tracks.

7. A conveyor unit according to any of claims 2-6, further comprising goods carrying means mounted on one or more of the subframes .

8. A conveyor unit according to claim 7, wherein the goods carrying means are mounted on the first subframe.

9. A conveyor unit according to any of claims 2-8, wherein the means for unloading goods are mounted on the first sub- frame.

10. A conveyor unit according to any of claims 7-9, wherein said means for carrying goods comprise at least one tiltable tray.

11. A conveyor unit according to claim 10, comprising at least two tiltable trays arranged one behind the other in the transport direction, the support surfaces of the trays being substantially aligned.

12. A conveyor unit according to claim 10 or 11, comprising three tiltable trays

13. A conveyor unit according to any of claims 10-12, comprising four or more tiltable trays.

14. A conveyor unit according to any of claims 10-13, wherein adjacent opposite tray end portions of adjacent opposite conveyor units have a convex outline, so as to prevent trays mounted on adjacent units to collide when the conveyor unit moves along a curved track.

15. A conveyor unit according to any of claims 10-14, wherein each tiltable tray is pivotally mounted around an axis extending in the transport direction of the conveyor unit.

16. A conveyor unit according to any of claims 10-15, wherein the means for unloading goods comprise at least one actuating device connected to each tiltable tray.

17. A conveyor unit according to claim 16, comprising at least a right hand and a left hand actuating device connected to each tray for selectively tilting said tray to the right or to the left, respectively.

18. A conveyor unit according to claim 16 or 17, wherein said actuating device is activated by activating means arranged adjacent to said tracks at unloading positions along the tracks .

19. A conveyor unit according to claim 18, wherein each actuating device comprises an actuating member for engaging with said activating means.

20. A conveyor unit according to claim 19, wherein the actuating member comprises a wheel or roller, and wherein the activating means comprise a curved track.

21. A conveyor unit according to any of claims 7-9, wherein said means for carrying and unloading goods comprise at least one conveyor belt.

22. A conveyor unit according to claim 21, comprising two or more conveyor belts arranged one behind the other in the transport direction of the conveyor unit and/or side by side.

23. A conveyor unit according to claim 22, wherein the upper runs of the conveyor belts together define a substantially aligned support surface.

24. A conveyor unit according to any of the preceding claims, further comprising driving means for driving the conveyor unit.

25. A conveyor unit according to claim 24, wherein the dri- ving means comprise a linear induction motor drive.

26. A conveyor unit according to any of the preceding claims, further comprising first control means for controlling unloading of goods carried by the conveyor unit, said control means communicating with second control means, which are stationary and comprised in the closed loop conveyor system.

27. A conveyor unit according to any of claims 2-26, wherein the length of the first subframe is not equal to the length of the second subframe.

28. A conveyor unit according to any of claims 10-27, wherein the dimensions of the trays or conveyor belts are variable.

29. A conveyor unit according to any of claims 10-28, wherein at least one of the subframes is mounted slidably in relation to at least one of the trays and/or conveyor belts for carrying goods .

30. A conveyor unit according to claim 29, comprising two subframes, the two subframes being arranged one behind the other in the transport direction of the conveyor unit, wherein subframes are pivotally interconnected, the trays and/or conveyor belts being mounted on and substantially aligned with one of the frames.

31. A conveyor unit according to claim 29, further comprising a third subframe, the three subframes being arranged one behind the other in the transport direction of the conveyor unit, wherein the subframes arranged at either end of the conveyor unit are pivotally connected to the middle subframe, the trays and/or conveyor belts being mounted on and substantially aligned with the middle frame.

32. A closed loop conveyor system for transportation and/or sorting of goods comprising

- a pair of mutually transversely spaced tracks,

a plurality of conveyor units according to any of the preceding claims,

means for controlling unloading of goods carried by the conveyor unit, and

- means for driving said conveyor units.

33. A closed loop conveyor system according to claim 32, wherein each of the conveyor units comprises at least one tiltable tray for carrying goods, said system further comprising means for repositioning said trays after unloading.