Patent Description:
The present invention generally relates to the technical field of moving mechanical devices. More particularly, the present invention relates to the field of omniwheel track systems and platforms using omniwheel track systems having full range of motion characteristics.

In recent years, mobile platforms have gradually played an important role in various industries, such as storage, manufacturing, transportation, military, and aerospace. According to their motion characteristics, mobile platforms can be divided into two types: full range track systems and non-full range track systems.

Conventionally, non-full range track systems have populated the market as there has been a lack of development of full range track systems. There are a number of drawbacks of non-full range track systems such as lack of convenience and an increased need for space to accomplish a task. Conversely, full range track systems offer many advantages such as the ability to operate in small and crowded spaces, the ability to freely travel, and the adaptability to situations requiring very precise positioning and high precision tracking.

Despite these advantages, the development of full range track systems has been lagging behind the development of non-full range track systems.

<CIT>) discloses a motor vehicle which may be moved in all directions in a directionally stable fashion. Such a vehicle comprises track plates, such as rollers, directly installed over sections of an endless band at an angle. The load of the vehicle is supported by sprockets and by endless band sections.

<CIT>) discloses a track type omnibearing moving platform. This platform comprises track assemblies having rollers mounted on a chain-liked endless band driven by sprocket wheels and rolling wheels. The load is thus supported by both the sprocket wheels and the rolling wheels. Some of the drawbacks of such a system are obvious. As an example, the direction of the load wheels of such a system tends to have reduced efficiency for horizontal loads.

European patent publication <CIT>) discloses a tracked vehicle comprising a track system having rollers installed at an angle on the endless track belt. The system comprises a controller adapted to control the movement of the endless track belts to move the vehicle in different directions.

There is thus a need for an improved omniwheel track system to overcome the drawbacks of the prior art systems.

There is also a need for an improved omniwheel track system allowing the splitting or dividing of the force created by the load to at least reduce the height of the resulting endless track system.

In order to overcome the above and other shortcomings, there is provided an omniwheel track system comprising a frame comprising at least one supporting plate, an endless drive mechanism mounted to the frame, and a plurality of segment assemblies mounted to the frame and drivable by the endless drive mechanism, the plurality of segment assemblies forming an endless track rotatable about the frame, each segment assembly comprising a housing adapted to receive at least one load wheel, each load wheel mounted to a corresponding segment assembly and rotatable about an axis, each axis forming an angle with a side of the housing.

In an embodiment, the endless drive mechanism comprises a motor, at least one drive wheel drivable by the motor via a rotating shaft, and at least one idler wheel drivable by the at least one drive wheel via an endless belt.

In an embodiment, each of the at least one drive wheel and at least one idler wheel is a sprocket and the endless belt is a chain.

In an embodiment, each of the at least one drive wheel and at least one idler wheel is a pulley and the endless belt is a belt.

In an embodiment, each segment assembly comprises at least three load wheels.

In an embodiment, at least one load wheel on each segment assembly is mounted to the segment assembly at an attachment point that is vertically offset from the remaining load wheels on the segment assembly.

Furthermore each segment assembly comprises a rotatably-mounted horizontal idling wheel configured to roll on a side of the endless drive mechanism.

In an embodiment, each segment assembly comprises a rotatably-mounted vertical idling wheel configured to roll on a side of the frame.

In an embodiment, the frame comprises a first supporting plate and a second supporting plate.

In an embodiment, each axis forms an angle of approximately <NUM> degrees with the side of the housing.

There is also provided an omniwheel track system platform comprising a plurality of the omniwheel track systems described above arranged on a main frame such that the omniwheel track system platform is movable omnidirectionally.

Other and further aspects and advantages of the present invention will be obvious upon an understanding of the illustrative embodiments about to be described or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

A novel omniwheel track system and platform using the same will be described hereinafter. Although the invention is described in terms of specific illustrative embodiments, it is to be understood that the embodiments described herein are by way of example only and that the scope of the invention is not intended to be limited thereby.

Referring first to <FIG>, a first embodiment of an omniwheel track system <NUM> is illustrated. The omniwheel track system <NUM> includes a housing or frame <NUM> adapted to receive an endless track <NUM>. The endless track <NUM> includes a plurality of segment assemblies or load links <NUM> driven by an endless driving mechanism <NUM>, typically embodied as a belt or chain and two wheels or sprockets. In some embodiments, the segment assemblies <NUM> are connected to the driving mechanism <NUM> and are driven by a motor <NUM>, such as an electric motor or a gear motor. As will be discussed in further detail below, a platform (not shown) including a plurality of omniwheel track systems <NUM> arranged on a main frame (not shown) can permit omnidirectional movement in a small area. In an embodiment, the system <NUM> is configured to be used without any motorization, which allows the system <NUM> to support a heavier load, without any constraints based on quantity or position.

Referring now to <FIG>, in a typical embodiment, the driving mechanism <NUM> is shown as a sprocket-chain system. A drive wheel or sprocket <NUM> is pivotally connected to the frame <NUM> and is driven by the motor <NUM>, typically by a shaft <NUM>. Understandably, any other means to drive the drive wheel <NUM> may be used. The driving mechanism <NUM> further includes an idler wheel or sprocket <NUM> pivotally connected to the frame <NUM>. An endless belt or chain <NUM> surrounds the drive wheel <NUM> and the idler wheel <NUM>. The drive wheel <NUM> actuates the idler wheel <NUM> by the chain <NUM>. In an embodiment, each of the drive wheel <NUM> and idler wheel <NUM> is a pulley and the endless belt <NUM> is a belt.

Still referring to <FIG> and <FIG>, in a typical embodiment, the frame <NUM> includes two sides, each side receiving an endless driving mechanism <NUM>. In such an embodiment, each segment assembly <NUM> is attached at one end to a first of the endless chains <NUM> and at another end to second of the endless chains <NUM>. In the embodiment shown in <FIG> and <FIG>, each end of the segment assembly <NUM> is attached to the top of the endless chain <NUM>. In some embodiments, each drive wheel <NUM> is connected to the other drive wheel <NUM> via a shaft <NUM> driven by the motor <NUM>. Such a configuration synchronizes the movement of each chain <NUM>. In some embodiments, the idler wheels <NUM> may further be connected together via a shaft (not shown). A person of skill in the art would understand that any other known methods of driving the wheels may be used within the scope of the present invention. As an example, each omniwheel track assembly <NUM> may be driven by a motor <NUM> or all assemblies <NUM> could be driven by a single motor <NUM>.

Now referring to <FIG>, an embodiment of a segment assembly <NUM> is illustrated in more detail. In some embodiments, the segment assembly <NUM> includes a housing <NUM> having a hollow structure adapted to receive at least one load wheel or roller <NUM>. The housing <NUM> includes apertures each adapted to receive one or more load wheel <NUM>. The load wheel <NUM> is pivotally mounted to the housing <NUM> to pivot or rotate about the axis <NUM>. In some embodiments, the pivot axis <NUM> is mounted about the upper surface of the housing <NUM> so that a part of the load wheel <NUM> is within the housing <NUM> and the other part of the load wheel <NUM> protrudes out of the housing <NUM>. In a preferred embodiment, the pivot axis <NUM> forms an angle with the side of the housing <NUM> to create an omniwheel effect.

Any number of load wheels <NUM> may be mounted on a segment assembly <NUM> according to the desired load to be applied on each track system and/or according to the dimensions of the housing <NUM>. Preferably, each segment assembly <NUM> includes three load wheels <NUM> installed about a <NUM>-degree angle. Understandably, other configurations using any number of load wheels <NUM> installed at different angles could be used within the scope of the present invention.

Still referring to <FIG>, in an embodiment, the attachment points of one or more of the load wheels <NUM> to the segment assemblies <NUM> may be offset from the ground. Illustratively, on a segment assembly <NUM> with three load wheels <NUM>, the center load wheel <NUM> may be positioned closer to the ground than the surrounding outer load wheels <NUM>. As such, when a heavy load is applied to the load wheels <NUM>, the bending of the segment assembly <NUM> causes the load distribution to be more uniform than if the attachment points of each load wheel <NUM> on a given segment assembly <NUM> were at the same height.

In an embodiment, a plurality of omniwheel track systems <NUM> may be attached to a main frame to form an omniwheel track system platform (not shown). Preferably, four omniwheel track systems <NUM> are mounted to each corner of the main frame, similarly to the configuration of a four-wheeled vehicle. In addition, a main frame capable of receiving a multiple of four track systems <NUM> could be used, for example with more than one omniwheel track system at each corner. In other embodiments, a main frame capable of receiving a multiple of track systems <NUM> other than four, for example six. A system <NUM> may also be combined with other types of systems, for example mecanum wheels, standard wheels or caster wheels.

To achieve the function of omnidirectional movement in a small area, each load wheel <NUM> in a segment assembly or load link <NUM> has a fixed bias angle. In such an embodiment, each load wheel <NUM> may freely rotate about its axis <NUM>. In a preferred embodiment, each bias angle is in the range of (<NUM> °, <NUM> °) or (-<NUM> °, <NUM> °), typically ±<NUM>°. To ensure the ability to move in all directions, some track systems <NUM> of the platform may have positive bias angles while other track systems <NUM> may have negative bias angles. In a preferred embodiment, the bias angle of the first pair of track systems <NUM> have bias angles differing by about ±<NUM>° from the biasing angle of a second pair of track systems <NUM>. In a typical platform, s first pair of track systems <NUM> is located on one side of the platform while a second pair of track systems <NUM> is located on the opposite side of the platform. In such an embodiment, the bias angle of the first pair of track systems <NUM> is diagonally opposed to the bias angles of the other pair of track systems <NUM>. Thus, the angles of the opposing pairs of track systems <NUM> are inverted. For example, if the bias angle of the first pair of track systems <NUM> is <NUM>°, the bias angle of the other pair of track systems <NUM> is -<NUM>°.

Preferably, each segment assembly <NUM> may be mass produced. In practice, if a segment assembly <NUM> is broken or needs maintenance, it may be easily replaced by detaching each of its ends from the endless driving mechanism <NUM>. In some prior art systems, the presence of a complex endless belt typically requires the removal of the complete belt or chain to repair or maintain the system, requiring the track system platform to be stopped.

In a typical embodiment of the present invention, the housing <NUM> includes a top surface <NUM> and a bottom surface <NUM>. While any known method may be used to mount the segment assembly <NUM> to the endless driving mechanism <NUM>, in some embodiments, the wider portion of the top surface <NUM> includes at least one aperture <NUM> adapted to link or mount the top surface <NUM> to the endless drive mechanism <NUM> using a fastener or any other method known in the art, such as a bolt, nut or rivet. Understandably, one skilled in the art shall understand that any other known configuration of housing <NUM> may be used in the present invention.

In some embodiments, the bottom surface <NUM> of the housing <NUM> may include one or more apertures <NUM> adapted to receive or mount a support element (not shown). Such a support element is typically configured to allow for the installation of the load wheel <NUM>. Understandably, the number and the dimensions of apertures <NUM> may vary according the structure supported by the support element and/or the number of load wheels <NUM> used.

In other embodiments, the housing <NUM> may include a bottom surface <NUM> having no aperture or may even be open (without bottom surface <NUM>). In embodiments where the track system <NUM> is used to support lighter loads, housing <NUM> may simply include a single plate of an appropriate thickness.

In some exemplary embodiments, the bottom surface <NUM> may include three pairs of apertures <NUM>, each pair being adapted to receive a support element configured to install one load wheel <NUM>.

Referring now to <FIG>, in an exemplary embodiment, the housing <NUM> may further include two side surfaces <NUM>. The side surfaces <NUM> are generally maintained adjacent to the two chains or endless belts <NUM>. Each side surface <NUM> may include one or more vertical idling wheels <NUM> pivotally mounted to the housing <NUM>, typically pivoting about a substantially vertical axis (not shown). Such vertical idling wheels <NUM> are adapted to roll on one of the sides of the frame <NUM>. Thus, the lateral loads applied on each segment assembly <NUM> are supported in part by the frame <NUM> rather than the chain <NUM>. Understandably, the vertical idling wheels <NUM> may be mounted at other portions of the housing <NUM> as long as their positioning results in the same transfer of lateral forces. Understandably, the vertical wheels <NUM> and horizontal idling wheels <NUM> may be replaced by sliders or other low friction mechanisms that allow the load to be supported.

The housing <NUM> or side surfaces <NUM> thereof may further include one or more horizontal idling wheels <NUM>. Each horizontal idling wheel <NUM> is generally pivotally mounted to a side surface <NUM> of the housing <NUM> about a generally horizontal axis (not shown) being substantially perpendicular to the chains <NUM>. Such horizontal idling wheels <NUM> are generally adapted to roll on one of the top and/or bottom portions of a horizontal portion of the frame <NUM>. The loads applied to the segment assembly <NUM> are thus supported completely or in part by the frame <NUM> rather than the chain <NUM>.

An embodiment of a horizontal idling wheel <NUM> is shown in <FIG>. The horizontal idling wheel <NUM> may include a bolt <NUM>, a washer <NUM>, a roller or bearing <NUM> and a bushing <NUM>. Understandably, any other embodiment of a wheel or other known low friction mechanisms may be used without departing from the scope of the present invention.

The periphery of the vertical idling roller <NUM> is typically slightly protruding through the side surface <NUM> of the housing <NUM> of the segment assembly <NUM>. Referring additionally to <FIG>, such protuberance generally allows a periphery portion of the vertical idling roller <NUM> to contact the sidewall of supporting plates <NUM>, <NUM> of frame <NUM>. As such, when each segment assembly <NUM> is driven by the sprocket-chain system <NUM>, the vertical idling roller <NUM> may easily roll along the sidewalls of the supporting plates <NUM>, <NUM> (as shown in <FIG> and <FIG>). Preferably, each segment assembly <NUM> includes one vertical idling roller <NUM> and two horizontal idling wheels <NUM>.

Referring now to <FIG> and <FIG>, the internal structure of an embodiment of the frame <NUM> for the track assembly <NUM> is shown. The frame <NUM> may be adapted to form a housing around the track system <NUM>. In such embodiments, the frame <NUM> generally includes six plates <NUM>, <NUM>, <NUM> (top and bottom not shown). Understandably, any other configuration of the frame may be used or even configurations without a frame may be provided.

In a preferred embodiment, the frame <NUM> further includes one or more supporting elements or plates <NUM>, <NUM>. The dimensions and shape of the one or more supporting plates <NUM>, <NUM> generally depend on the length of the endless driving mechanism <NUM> formed by the segment assemblies <NUM>. The supporting plates <NUM>, <NUM> typically include sidewall portions <NUM> and periphery portions <NUM>. The sidewalls portions <NUM> are adapted to allow the vertical idling wheels <NUM> to roll on such a surface. The periphery portions <NUM> are adapted to allow the horizontal idling rollers <NUM> to roll on such a surface. Precisely, for installing each segment assembly <NUM> on the supporting plates <NUM>, <NUM>, the segment assembly <NUM> can be pressed so that it can been supported by the supporting plates <NUM>, <NUM>. In a preferred embodiment, the supporting plates <NUM>, <NUM> are shaped as a rounded rectangle or an elongated circle to allow the chains <NUM> to move around the supporting plates <NUM>, <NUM>. Understandably, in other embodiments, the frame <NUM> may comprise only one supporting plate or more than two supporting plates and such supporting plates may have other shapes adapted to the desired configuration.

In other embodiments, the supporting plates <NUM> and <NUM> may form an assembly (not shown). Such an assembly may include wearing plates on the rolling surface of the supporting plates <NUM>, <NUM>. The assembly may also include elements to improve load balancing on the supported members <NUM>, <NUM>.

When the track system <NUM> forms part of a track system platform, increased loads may be supported on the system <NUM>. The loads applied on the platform are divided between the horizontal idling wheels <NUM> and the vertical idling wheels <NUM> which are supported by contacting or rolling along the supporting plates <NUM>, <NUM>. The resulting lateral forces are supported by the vertical idling wheels <NUM> while the vertical forces are generally supported by the horizontal idling wheels <NUM>. Such distribution of the forces allows the track system to support greater loads than in some prior art systems using similarly-sized wheels. Advantageously, each track system <NUM> may have a low height while supporting important loads.

Referring back to <FIG> and <FIG>, each segment assembly <NUM> is connected to two adjacent segment assemblies <NUM> to form an endless track <NUM>. As explained above, in a typical embodiment, each end of each segment assembly <NUM> is attached to an endless belt or chain <NUM>. The resulting endless belt <NUM> surrounds the idler wheel <NUM> and driving wheel <NUM>. The endless belt <NUM> is also supported by the one or more supporting plates <NUM>, <NUM>, typically positioned in between a corresponding idler wheel <NUM> and driving wheel <NUM>. When being driven by the driving wheel <NUM>, the segment sections <NUM> are adapted to slide or roll along the supporting plates <NUM>, <NUM>. Such rolling or sliding aims to substantially increase the potential load capacity on the track assembly <NUM>. Understandably, the supporting plates <NUM>, <NUM> are solidly or rigidly mounted or attached to the frame of the vehicle. As a result, the load is supported by the driving and idler wheels <NUM> and <NUM> and the supporting plates <NUM>, <NUM>.

To limit the friction of the rolling or sliding of the segment assemblies <NUM> over the supporting plates <NUM>, <NUM>, each segment typically comprises a low friction mechanism, such as one or more idling wheels <NUM>, <NUM>. In embodiments having load wheels <NUM> pivotally mounted to the segment assembly <NUM>, the one or more horizontal idling wheels <NUM> is adapted to roll over or under the periphery of the supporting plates <NUM>, <NUM> and the one or more vertical idling wheels <NUM> are adapted to roll on the side or wall of the supporting plates <NUM>, <NUM>. Such idling wheels <NUM>, <NUM> are each typically adapted to support high loads.

In some embodiments, the supporting plates <NUM>, <NUM> are adapted to support loads on a bottom section only. In such an embodiment, the idling wheels <NUM>, <NUM> roll on the surface only when passing under the bottom section of the supporting plates <NUM>, <NUM>.

In other embodiments, the low friction element or idling wheels <NUM>, <NUM> may be located on the supporting plates <NUM>, <NUM> themselves. In such embodiments, the endless belt or chain <NUM> is adapted to slide or roll on the supporting plates <NUM>, <NUM> through the low-friction mechanism present on the supporting plates <NUM>, <NUM>.

Still referring to <FIG>, the endless driving mechanism <NUM> typically surrounds the supporting plates <NUM>, <NUM>. A driving wheel <NUM> is preferably pivotally mounted at a first extremity of each supporting plate <NUM>, <NUM> and an idler wheel <NUM> is preferably pivotally mounted at a second extremity of each supporting plate <NUM>, <NUM>. Such embodiments are adapted to receive loads on the segment assemblies <NUM> on the periphery <NUM> of the supporting plates <NUM>, <NUM> and on the sidewalls <NUM> of the supporting plates <NUM>, <NUM>.

Referring now to <FIG> and <FIG>, there is an embodiment of the system <NUM> using a chain having attachment portions. In such an embodiment, each link of the chain <NUM> includes a portion adapted to be mounted to a segment assembly <NUM>. In some an embodiment, this portion is typically in the form of a plate having apertures adapted to be welded or attached to corresponding apertures <NUM> of the side portions of each segment assembly <NUM>.

Referring again to <FIG> and <FIG>, in some embodiments, the frame <NUM> may include apertures or passages <NUM> adapted receive the shaft <NUM> driven by the motor <NUM>. Preferably, the side plates <NUM>, <NUM> and the supporting plates <NUM>, <NUM> include apertures or passages <NUM> being aligned to allow the mounting of the shaft <NUM>.

Referring to <FIG>, the height of the omniwheel track system generally depends on the diameter of the driving wheel or sprocket <NUM>.

Referring to <FIG>, an embodiment of a method to mount a segment assembly <NUM> to a chain <NUM> is illustrated. The method comprises the steps of surrounding a chain <NUM> having mounting portions around a drive wheel <NUM> and an idler wheel <NUM>. The method further comprises attaching an extremity of the segment assembly <NUM> to the mounting portions of the chain <NUM>. The previous steps may be repeated to install additional chains <NUM>.

Referring now to <FIG>, in an embodiment, the entire system <NUM> may be mounted on a double pivot <NUM> to ensure that the applied loads are distributed as evenly as possible on the load wheels <NUM>. In another embodiment, in order to reduce the impacts of the load wheels <NUM> on the running surface, each segment assembly <NUM> includes a modified oval profile whereby a lower section <NUM> (between the shaft <NUM> and the ground) has a distance greater than that of an upper section <NUM>. Such an arrangement allows the load wheels <NUM> smoothly contact the ground. In another embodiment, depending on the application and the environment of use, the load wheels <NUM> can be made from various materials. For example, if the system <NUM> is to be used indoors on a smooth surface, the load wheels <NUM> can be made of polyurethane, while if the system <NUM> is to be used outdoors, the load wheels <NUM> can be made of rubber. In yet another embodiment in which a chain <NUM> is used, a tensioner system <NUM> including a running surface <NUM> is also provided, which ensures that the load wheels <NUM> remain in contact with the support plate <NUM>, regardless of the configuration of the tensioner system <NUM>.

One or more omniwheel track systems <NUM> can be combined with a variety of different systems, such as motorization systems, automation systems, security systems, navigation systems, or modular systems. Such motorization systems may include electric systems (such as electric motor and drive, power supply with wires, wireless or batteries, wireless induction chargers, or wired chargers), combustion systems (such as gas systems), tanks or fuel containers, fuel supply systems, hydraulic systems (such as hydraulic motors with various sources of hydraulic power). Such automation systems may include industrial or personal computer (PC) and/or programmable logic controller (PLC) and/or multipoint control unit (MCU) systems (such as from inside/outside the vehicle and possibly connected to an enterprise resource planning (ERP) system and/or a vehicle fleet manager), human machine interface (HMI) systems (possibly connected to PC, PLC, MCU or ERP systems), battery management systems, voice recognition systems (micro and software), speaker systems, light emitting diode (LED) systems (addressable and configurable), electric transformer systems, industrial or other common communication networks and associated hardware (such as Ethernet, Ethernet IP, Ethercat, Profibus, Profinet, rs485, Bluetooth, ZigBee, Wi-Fi and Canbus), and in wiring to connect different systems (such as for power and control). Such security systems may include a safety scanner, safety PLC, safety encoders, laser safety, safety curtains, safety relays, or other safety industrial systems. Such navigation systems may include Lidar, cameras (such as for image or barcode recognition), industrial vision systems (such as a camera with an algorithm for recognizing a line and/or a tag, such as a QR tag, to obtain position information), stereoscopic camera, sensors (such as ultrasonic sensors, light and/or color sensors, infrared sensors, magnetic sensors and proximity sensors), remote control (physical/virtual remote such as for a computer, tablet or cellphone), or manual control (such as a steering wheel, joystick, or buttons on a vehicle). Such modular systems may include a quick connect system (such as mechanical or electrical), a custom central part, lift platforms, an extensible platform (length/width), a tie to take cars by the wheels, a crane, a robotic arm, specific tooling/worktable, or racking.

One or more omniwheel systems <NUM> may be used in various application sectors such as transportation (handling, industrial logistics indoors/outdoors), construction (lifting equipment such as a ceiling lift or cisolift), heavy machinery (tractor, excavator), the automotive industry (garage, dealer, show), the mining industry, the prefab house industry, the machining industry, or the metallurgical industry.

Referring to <FIG> and <FIG>, three omniwheel systems <NUM> may be mounted at <NUM> degrees from each other onto a platform P in a triangular configuration. As persons skilled in the art will understand, many other configurations may be achieved for different applications.

Referring to <FIG> and <FIG>, four omniwheel systems <NUM> are mounted at each corner of a platform P in rectangular configuration. As persons skilled in the art will understand, many changes to this configuration may be achieved for different applications.

In recent test results, embodiments of the present omniwheel system <NUM> have advantageously reduced the noise levels as compared to the noise levels produced by other known mobile platforms. For example, at a floor speed of <NUM>/h an embodiment having an oval shape produced noise levels of less than <NUM> dB-A while other embodiments of the invention with different profiles have produced noise levels of less than <NUM> dB-A.

Claim 1:
An omniwheel track system (<NUM>) comprising:
a frame (<NUM>) comprising at least one supporting plate (<NUM>);
an endless drive mechanism (<NUM>) mounted to said frame (<NUM>); and
a plurality of segment assemblies (<NUM>) mounted to said frame (<NUM>) and drivable by said endless drive mechanism (<NUM>), said plurality of segment assemblies (<NUM>) forming an endless track (<NUM>) rotatable about said frame (<NUM>), each said segment assembly (<NUM>) comprising a housing (<NUM>) adapted to receive at least one load wheel (<NUM>), each said load wheel (<NUM>) mounted to a corresponding said segment assembly (<NUM>) and rotatable about an axis (<NUM>), each said axis (<NUM>) forming an angle with a side of said housing (<NUM>), characterized in that, each said segment assembly (<NUM>) comprises a rotatably-mounted horizontal idling wheel (<NUM>) configured to roll on a side of said endless drive mechanism (<NUM>).