WO2003042077A1

WO2003042077A1 - A pallet type transport system

Info

Publication number: WO2003042077A1
Application number: PCT/SE2002/001953
Authority: WO
Inventors: Joakim Abrahamsson
Original assignee: Joakim Abrahamsson
Priority date: 2001-11-13
Filing date: 2002-10-28
Publication date: 2003-05-22
Also published as: SE0103808D0; SE0103808L; SE521239C2

Abstract

The present invention relates to a pallet type transport system for transporting parts and/or components along an assembly line, comprising a guide rail mounted on an essentially flat underlying support surface. The transport system includes a number of motor driven pallets. Each pallet includes two first guide members arranged in a front part of the pallet and two guide members arranged in a rear part of the pallet, said guide members following the guide rail pair-wise. Each pallet is steered with the aid of four wheels. Two movement transmission members are disposed between the guide members and the four wheels so that each wheel will be in line with the direction of pallet movement. The guide rail includes a suitable aperture or opening at each branch location of the assembly line for through passage of said wheels and said guide members. The system also includes an auxiliary guide rail at each branch location to assist the change of direction of a pallet at a branch location of the assembly line.

Description

A PALLET TYPE TRANSPORT SYSTEM

FIELD OF INVENTION

The present invention relates to a pallet type transport system for trans- porting parts and/or components along an assembly line.

DESCRIPTION OF THE BACKGROUND ART

A pallet type transport device is used to transport a product between different working stations, where assembly is effected either automatically or manually. The most typical types of pallet track is a driven track that transports pallets with the aid of belts that pull the pallet forwards.

Patent Application U.S. 4,987,834 illustrates a pallet type transport system, which extends at least between a first station and a second station. The pallet track includes two grooves along which pallet wheels run, in the same way as a train. Each pallet has its own electric drive motor, driven by a chargeable battery, for instance. This document illustrates solely straight grooves in the absence of branches along the track. Each pallet also includes a photoelectric non-contact type of switch that detects the presence of a structure immediately in front of the pallet in its movement direction. Patent Application U.S. 6,102,194 describes a pallet type transport device in which the pallets are driven by two parallel belts that run in complementary recesses on the underside of the pallets. Each pallet includes a front and a rear bumper which co-acts in a manner such that should an advancing pallet contact a stationary pallet, the advancing pallet is stopped in order to minimise or to elimi- nate wear on the belts or on the bottom surface of respective pallets.

A significant drawback with the aforedescribed transport systems is that track installation is a complicated affair. Moreover, it is troublesome or impossible to provide the assembly line with branch locations in the case of these illustrated solutions. In the case of U.S. Patent Specification 4,987,834 reference is made to the use of switches, meaning that these switches must also be controlled in some way or another.

Other drawbacks are that tracks driven by belts, straps or roller chains have a drive for each separate track section or cross-switch. Stops and cross- switches on the tracks involve movements that are most often effected pneumatically. Moreover, many pallet location sensors are disposed around the tracks. This makes the tracks expensive, complicated to install, and also requiring a great deal of programming. Furthermore, the track includes many breakable parts. If a belt, drive motor, valve or sensor should break or fail to function, the entire track section or cross-switch concerned will become non-functional and therewith fail to allow pallets to pass through.

Another drawback is that the tracks require a separate control system that is unique for each application. Further drawbacks reside in the fact that the tracks have a given speed that cannot normally be regulated. When it is possible to regulate the speed of a motor, then this applies to the entire track section, meaning that those pallets located on a common driven track section will always move at the same speed. When the pallets are mutually in line with each other, they are most often stopped by preceding pallets therewith causing the pallets to slow down quite violently. The acceleration of the pallets is also controlled by the friction between belt and pallet and cannot be influenced. Tracks that are driven by roller chains, however, have a more gentle acceleration.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the aforesaid problems.

In accordance with the present invention, there is provided a pallet type transport system for transporting parts and/or components along an assembly line that includes a guide rail mounted on a substantially flat supportive surface. The transport system includes a number of motor-driven pallets, wherein each pallet includes two first guide members mounted on a front part of the pallet and two second guide members mounted on a rear part of the pallet, said guide members following the guide rail in pairs. Each pallet is also guided on four wheels and includes two movement transmission elements mounted between the guide members and the four wheels, so that each wheel will be in line with the direction of movement of said pallet. The guide rail includes an appropriate aperture for passage of the wheels and the guide members, at each branch location ofthe assem- bly line. An auxiliary guide rail is provided at each branch location for assisting guiding of a pallet that changes direction at a branch location in the assembly line. This transport system is highly flexible, since it enables a track to be readily installed and also enables an existing track to be readily altered. For example, no switches are required in this transport system. Neither is it necessary to adapt the pallets to the track in the case of this system.

Another advantage is that the track has no movable parts, meaning that it is cheaper and simpler to install, requires no cabling, requires no pneumatics, and has few parts that can break. The track need have no special design, but can, for instance, consist of a flat supporting surface, such as a workbench, a surface in a robot cell. What is required, however, is the possibility of mounting a guide rail. The track may also slope in the transport direction. Because each pallet has its own drive and because each pallet is able to move at an optimised speed on different parts of the track, independently of each other. A further advantage is obtained in this regard, when each pallet includes a control system that functions to guide the pallet at the branch points of the assembly line and regulates the speed of the pallet, and when providing the transport system with a main control system that communicates with said control system on each pallet in a wireless fashion. One advantage afforded by this arrangement is that no changes in the control system other than programming are required when a track is changed. If a pallet breaks, the pallet can be plucked from the track and the entire transport system will function nevertheless. Because each pallet has its own control system and an inbuilt code system, the same main control system can be used regardless of application, with the exception of programming the track function.

A further advantage in this regard is obtained when each of said first and said second guide members of each pallet have the form of guide rollers, and when each of said movement transmission members is comprised of a link arm system, wherewith the two first guide rollers transmit movement direction to the two wheels mounted in the front part of the pallet, via a first link arm system, and the two second guide rollers transmit movement direction to the two wheels mounted in the rear part of the pallet, via a second link arm system.

A further advantage is obtained in this regard when each pallet includes at least one guide motor connected to the pallet control system and arranged adja- cent the guide rollers, wherein the drive motor can be driven to bias the guide rollers against the auxiliary guide rail when the pallet shall change direction at a branch point.

A further advantage is obtained in this regard when an auxiliary guide rail at a branch point in the assembly line is arranged adjacent at least one of said apertures and at least on the same side of the guide rail as that towards which the pallet swings when changing direction at a branch point.

A further advantage is obtained in this regard when each pallet includes a drive motor and at least one power supply battery. A further advantage is obtained in this regard when the drive motor of each pallet is connected to drive the two rear wheels, and when each pallet also includes a differential member connected to the drive wheels.

A further advantage is obtained in this regard when each link arm system is comprised of a link arm connected to the two pairs of guide rollers and also of two guide arms, wherein each of the guide arms is connected to a respective end of the link arms and to a respective wheel.

A further advantage is obtained in this regard when the assembly line also includes at least one station in which the pallet battery/batteries can be (re)charged. A further advantage is obtained in this regard when parts of the guide rail are comprised of live rails for charging the pallet battery/batteries during operation.

A further advantage is obtained in this regard when each pallet includes a distance detecting member mounted in the front part of the pallet and operable to detect when the pallet comes too close to a immediate preceding pallet, said dis- tance detecting member being coupled mechanically to the guide rollers and link arms in a manner such that the distance detecting member will be turned to an extent greater than the two first guide rollers.

This means that when the pallets queue one behind the other, the distance-detecting device on the pallet senses the preceding pallet, wherewith the pallet is able to slow down and stop in a controlled fashion without driving into the preceding pallet. This enables the pallet to accelerate and decelerate in a manner which will ensure that the parts or components carried by the pallet will not be subjected to any significant forces.

A further advantage is obtained in this regard when each pallet includes an upper and a lower plate for substantial encapsulation of the components carried by the pallet, said plates being provided with pallet positioning holes essentially at each corner.

A further advantage is obtained in this regard when each pallet also includes a code reader, and when the transport system includes codes disposed along the assembly line, said code reader reading said codes for indicating the position of the pallet.

A further advantage is obtained in this regard when the main control system functions to send to the pallet control system, in a wireless fashion, control commands, which indicate the codes at which the pallet shall swing, change speed or stop.

A further advantage is obtained in this regard when each pallet also includes an inductive sensor, and when the assembly line includes a ridge at which the pallet shall stop, said ridge being detected by the inductive sensor, causing the pallet to stop.

It will be noted that the term omprise-comprising" as used in the present description is intended to indicate the presence of characteristic features, steps or components, but is not intended to exclude the presence of one or more other characteristic features, parts, steps, components or groups thereof. The invention will now be described with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a side view of a pallet included in a transport system in accordance with the present invention. Figure 2 is a front side view of the pallet shown in Figure 1.

Figure 3 is an exploded top view of the pallet shown in Figure 1.

Figure 4 is a top view of an assembly line included in the transport system according to the present invention. Figure 5 is a top view of part of the assembly line at a branch location. Figure 6 is a top view of part of the assembly line at another branch location.

DETAILED DESCRIPTION OF EMBODIMENTS Figure 1 is a side view of a pallet 10 included in the transport system according to the present invention. As will be seen from Figure 1 , the pallet 10 includes a top plate 12, a bottom plate 14 and a side part 16. Also shown in Figure 1 are two of the total of four wheels 18 that run on a generally flat support surface 20, which may consist of a work table or a robot cell.

Figure 2 is a front side view of the pallet 10 shown in Figure 1. Corresponding parts of the pallets illustrated in Figures 1 and 2 have been provided with the same reference numbers and will not be described further in conjunction with Figure 2. Also shown in Figure 2 are the two first guide members 22 which follow pair-wise the guide rail 24 that forms the assembly path of the transport system. Also shown is a distance-detecting device 26 which is mounted in the front part of the pallet 10 and which can be driven to detect when the pallet 10 comes too close to the pallet 10 in front. This distance-detecting device 26 may consist of a photocell 26. In addition to sensing when the pallet 10 comes too close to the next ahead pallet 10, the photocell also functions to detect any other obstacle in the path of the pallet. In order to enable the photocell 26 to detect objects when the pallet 10 turns to change direction, the photocell 26 is rotated with the aid of mechanical means coupled to the guide rollers 22 and link arms in a manner such that the photocell will be turned to an extent greater than the two guide rollers 22 and therewith detect objects at an appropriate angle in the transport direction.

Figure 3 is an exploded top view of the pallet 10 shown in Figure 1. The top plate 12 of the pallet has been removed in this case, so as to illustrate the construction of the pallet 10. Corresponding parts of the illustrations in Figures 1-3 have been identified with similar reference signs in all of said figures. As will be evident from Figure 3, each pallet includes a drive motor 30 connected for driving the two rear wheels 18. In other regards, each pallet 10 is controlled by four wheels 18 driven with the aid of two movement transmission devices 32 mounted between the guide rollers 22 and the four wheels. Each movement transmission device 32 includes a link arm 34 connected to the two pairs of guide rollers 22 and two guide arms 36, wherein each of the guide arms 36 is connected to a respective end of the link arm 34 and to a respective wheel 18. As the guide rollers 22 follow the guide rail in the assembly line, the link arm 34 and the guide arms 36 transmit the movement direction to the wheels 18, such that each wheel will be in line with the direction of pallet movement. Each pallet 10 also includes a control system 38 for controlling the pallet 10 at a branch location of the assembly line and to regulate the speed of the pallet 10. The inventive transport system also includes a main control system (not shown) which communicates with said control system 38 in a wireless fashion, via a communications module 39 on each pallet. Each pallet 10 also carries at least one chargeable power supply battery 40. In addition, each pallet 10 includes a differential member 42 mounted on the pallet drive shaft 44. The differential member 42 functions to enable the two wheels 18 on the drive shaft 44 to rotate at different speeds (necessary when negotiating a curve, for instance) and also to equally distribute the driving force on the two wheels 18. The pallet 10 also includes pallet-positioning holes 46 on respective corners.

Each pallet 10 further includes a motor control means 41 , a battery charging regulator 43, a control motor 45 connected to the pallet control system 38 and arranged at the guide rollers 22, wherein the control motor 45 can be driven to bias the guide rollers 22 against an auxiliary guide rail when the pallet 10 shall change its movement direction at a branch location.

Figure 4 illustrates from above an assembly line 50 included in the transport system according to the present invention. The assembly line 50 includes a guide rail 52, which is mounted on a substantially flat support. The guide rollers 22 shown in Figures 2 and 3 are intended to run on a respective side of the guide rail 52. The illustrated assembly line 50 includes two branch locations 54 at which the pallet 10 can change direction. Such a change is effected without the aid of a switch in the guide rail 52. Figure 5 illustrates from above part of the assembly line 50 at a branch location 54. As will be seen from Figure 5, the guide rail 52 includes an opening or aperture 56 at appropriate positions, to allow passage of the wheels 18 and the guide rollers 22 depending on the direction in which the pallet 10 moves. The assembly line 50 also includes an auxiliary guide rail 58. This auxiliary guide rail 58 is placed on the same side of the guide rail 52 as that on which the pallet 10 swings as it changes its direction of movement at a branch location 54. In the case of the Figure 5 example, the pallet 10 shall swing from a straight part of the track into a curve, i.e. to the right. Thus, the auxiliary guide rail 58 is arranged on the right side of the branch location 54. The guide rollers 22 are spring biased towards the auxiliary guide rail 58, causing the pallet 10 to turn to the right.

Figure 6 is a top view of part of the assembly line 50 at another branch location 54. In this case, the alternative is for the pallet 10 to either continue in a left-hand curve or to turn out of the curve and continue in a straight part of the track, i.e. to turn to the right. The auxiliary guide rail 58 is thus to the right of the branch location 52. In this case, the guide rollers 22 are spring biased towards the auxiliary guide rail 58, therewith causing the pallet 10 to follow the straight part of the guide rail 52.

There follows a general description of the transport system in accordance with the present invention and also the function of said system. The transport system is referred to in the following as a pallet track.

The design is partially built on the principle of a typical car track where the cars, which correspond to the pallets in this instance, have their own drive and run on a track that includes a groove which keeps the cars on the track and ensures that they move in the correct direction. One difference is that the pallets do not require the supply of current from current conductors in the track, but are battery driven. On the other hand, certain lengths of the track may include live rails for battery charging purposes. Because the pallets have their own drive and power supply, the track becomes very simple. Instead of a car track in which the cars are guided by a groove, the pallets are guided by a rail that projects up from the track. The reason why a rail is chosen instead of a groove is because a rail can be readily mounted on a typical workbench or directly in a robot cell. The pallets can move on any support surface whatsoever in principle, the only requirement being that a guide rail is mounted for guiding the pallets. The pallets travel on the sup- port surface on four wheels, in the same way as a car.

In order to be able to transport the pallets around the track in a desired manner, it is necessary to have control over where respective pallets are located. It must also be possible to guide/control the pallets, so that the correct pallet is switched at the correct location and is able to stop with a high degree of precision. Each pallet has, therefore, its own guide/control system capable of guiding the pallet in a chosen path, and to control the speed on the basis of the capability of a main control system. Communication between the pallet control system and the main control system is effected in a wireless fashion. The pallet includes a code reader for indicating the position of the pallet, said reader reading codes disposed at different places around the track. The code may signify that the pallet shall move at a given speed, or control which path selection shall be made. The pallet receives control commands from a main control system that indicates at which codes the pallet control system shall cause the pallet to turn, change speed, or stop.

The track need not be comprised of special profiles or include a power supply, but may be made of any material whatsoever. The only requirements are that the track is essentially flat and that a guide rail can be firmly screwed down. The track requires no drifts with separate power supply. The pallets can be driven in any machine whatsoever, provided that a flat underlying support surface is available. Since the pallet itself reads its position, no cables are required around the track other than at battery charging stations, which may be integrated generally in a position that will most often already have both electric current and pneumatic connections. The batteries may also be charged via live rails in the track. The pallet is steered on all four wheels such that friction and then also current supply will be as low as possible. Pallet speed can be governed so that the pallet will have a high speed over long transport distances and a low speed in the curves or when the pallet arrives at a position in which it is stopped. The pallets can be accelerated and decelerated without the product carried being subjected to signifi- cant forces. When the pallet shall stop in order to be positioned, the pallet is stopped by actuation of an inductive sensor by a ridge in the track. Since the pallet contains its own control system and motor, the pallet track can be started-up directly after installation of the track mechanics. Because the pallet has a certain degree of ground clearance, the pallet can also travel on a track of varied inclina- tion in the transport direction.

Since the pallet is battery driven, it is necessary to be able to transport the pallet with very low friction, so that current consumption will be as low as possible. Accordingly, all pallet wheels are steered such that each wheel will constantly be in an exact line with the transport direction, regardless of the radius of the curves. The wheels are turned by means of a link system. The pallet follows a guide rail mounted on the support surface by guide rollers. When the track shall enable a pallet to be switched from the main groove, the guide rail is provided with an opening or an aperture and the guide rollers are biased towards the direction in which the pallet shall move. The pallet has a two wheel drive (see above) and a differential that causes the wheels to drive uniformly in curves. The pallet has four pallet positioning holes, possibly also a guide rail, on the side of the pallet for a selective positioning method. The pallet is built-up of two aluminium plates with the electronics encapsulated therebetween. Each pallet measures 250x400 mm and a height of 60 mm and is able to transport a load of 20 kg.

The pallet can be driven by a 24 volt D.C. motor controlled via a motor control. Reengagement of the motor is effected with the aid of a pulse emitter. There is sent to the motor control an analogue control signal or a pulse train, which indicates acceleration and the desired pallet speed. The motor control regulates the voltage to the motor and reads the pallet speed via the pulse emitter, so that the pallet is kept at the desired speed regardless of load. The pallet control system is based on a standard PLC. Connected to the control system is a communications module which, in turn, communicates with the main control system in a wireless fashion. The main control system is a PC which includes a communica- tions card and keeps a check on the status of all pallets. The pallet's own control system controls the speed of the pallet and reads codes distributed along the track by means of the code reader. The main control system sends control commands to the pallet control system depending on the status of the pallet, these commands indicating how the pallet shall react to codes and also what the pallet shall do when a code is read-off. This code may relate to information concerning speed, path selection or that the pallet shall be stopped. The pallet also sends battery status information and other alarm signals to the main control system. When the pallet shall stop in a working station, it does so in response to the detection of a ridge mounted on the track, through the medium of a pallet-mounted inductive sensor. When the pallet stops for positioning purposes, the repeater accuracy is greater than ± 0.5 mm.

The pallet power supply can be effected with a Lithium ion battery. The battery will have a life capacity of between 3 and 6 hours, depending on load. In the majority of cases, this capacity will be sufficient to enable the battery to be recharged when the pallet is located in a workstation. The pallets are charged in a workstation when they are stationary or on straight stretches during operation. Charging is effected through the medium of live rails on which the rear guide rollers of the pallet run.

It is necessary that the track is flat and that a guide rail measuring 10x10 mm, for instance, can be fitted. A track manufactured as an aluminium profile will be standard. The track will include pallet switching guide rails, which include different curve radii. It is also possible to drive the pallet up or down an incline, the maximum permitted angle of which will depend on pallet load.

It will be understood that the invention is not restricted to the afore- described exemplifying embodiments thereof and that many modifications are possible within the scope of the accompanying Claims.

Claims

1. A pallet type transport system for transporting parts and/or components along an assembly line, comprising a guide rail mounted on an essentially flat underlying support surface, and a number of motor driven pallets, characterised in that each pallet includes two first guide members arranged in a front part of the pallet and two guide members arranged in a rear part of the pallet, said guide members following the guide rail pair-wise; in that each pallet is steered with the aid of four wheels, in that two movement transmission members are disposed between the guide members and the four wheels so that each wheel will be in line with the direction of pallet movement, in that the guide rail includes an aperture or opening at each branch location of the assembly line for through passage of said wheels and said guide members; and in that the system includes an auxiliary guide rail at each branch location to assist the change of direction of a pallet at a branch location of the assembly line.

2. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with Claim 1 , characterised in that each pallet includes a control system for guiding the pallet at the branch locations of the assembly line and for regulating the speed of the pallet; and in that the transport system includes a main control system which communicates with said control system on each pallet in a wireless fashion.

3. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 1-2, characterised in that each of said first and said second guide members of each pallet is comprised of guide rollers; and in that each of said movement transmission elements is comprised of a link arm system, wherein the two first guide rollers transfer the movement direction to the two wheels mounted in a front part of the pallet, via a first link arm system, and the two second guide rollers transfer movement direction to the two wheels mounted in a rear part of the pallet via a second link arm system.

4. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with Claim 3, characterised in that each pallet includes at least one control motor located adjacent the guide rollers and connected to the pallet control system, wherein said motor can be driven to bias the guide rollers towards the auxiliary guide rail when the pallet shall change direction at a branch location.

5. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 1-4, characterised by an auxiliary guide rail arranged adjacent at least one of said openings or aper- tures at a branch location on the assembly line and at least on the same side of the guide rail as that towards which the pallet turns when changing direction at a branch location.

6. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 1-5, characterised in that each pallet includes a drive motor and at least one power supply battery.

7. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with Claim 6, characterised in that the drive motor of each pallet is connected for driving the two rear wheels; and in that each pallet also includes a differential device in connection with the drive wheels.

8. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 3-7, characterised in that each link arm system is comprised of a link arm connected to the two pair- wise arranged guide rollers, and is also comprised of two guide arms, wherein each guide arm is connected to its respective end of the link arm and to a respective wheel.

9. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 6-8, characterised in that the assembly line includes at least one battery charging station in which the pallet battery/batteries is/are charged.

10. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 6-8, characterised in that parts of the guide rail consist of live, electric current carrying rails for charging the pallet battery/batteries during operation.

11. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 3-10, characterised in that each pallet has mounted at its front part a distance detector which can be operated to detect when the pallet is too close to a preceding pallet, wherein said distance detector is coupled mechanically to the guide rollers and link arms in a manner to cause the distance detector to turn to a greater extent than the two first guide rollers.

12. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 1-11 , characterised in that each pallet includes a top and a bottom plate that function to generally encapsulate the pallet-carried components, wherein said plates are provided with pallet positioning holes substantially at each corner.

13. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 1-12, characterised in that each pallet also includes a code reader; and in that said system also includes codes disposed along the assembly line, said code reader functioning to read said codes and therewith indicate the position of the pallet.

14. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with Claim 13, characterised in that the main control system sends control commands to the pallet control system in a wireless fashion, said commands indicating the codes requiring the pallet to turn, change its speed, or to stop.

15. A pallet type transport system for transporting parts and/or components along an assembly line in accordance with any one of Claims 1-14, characterised in that each pallet also includes an inductive sensor; and in that said assembly line also includes a ridge at which the pallet shall stop, said inductive sensor detecting said ridge and resulting in stoppage of the pallet.