CA2184508A1

CA2184508A1 - Magnetically guided vehicle

Info

Publication number: CA2184508A1
Application number: CA002184508A
Authority: CA
Inventors: Masaru Maruyama; Tadashi Ike; Noriyasu Sugiura; Yukio Hisada; Motohiro Sugiyama
Original assignee: Yazaki Kako Corp
Current assignee: Yazaki Kako Corp
Priority date: 1996-07-25
Filing date: 1996-08-29
Publication date: 1998-03-01
Also published as: JPH1039925A

Abstract

All wheels of the vehicle are universal casters and one magnetic guide type steering drive unit is removably attached to each of the front and back of the lower surface of the chassis of the vehicle. Each of the two magnetically guided type steering units comprises sensors provided at the front and rear portions in order to detect a magnetic tape path.

Description

2I8~508 TITLE OF THE INVENTION
MAGNETICALLY GU~DE~ VEIIICIE

BACKGROUND OF THE INVENTION
The present invention relates to an unmanned, magnetically guided vehicle which carries various loads in a fully automated fashion, in a factory or a warehouse, along a guide path of magnetic tape provided on the floor.
Various kinds of unmanned magnetically guided vehicles W}liC}I carry various loads along preset guide paths in factories, warehouses and golf courses have been developed and put into practice both domestically and abroad. For example, U.S. Patent No.5,525,884, assigned to the assignee of this patent application, discloses such a magnetically guided vehicle.
The magnetically guided vehicle, disclosed in the above referenced U.S. patent, comprises a magnetic guide type steering drive unit (hereinafter referred to as a steering drive unit) 4 that is mounted on the underside of a trolley 7 adjacent to the front wheels 5, as shown in FIG. 6. This steering drive unit 4 comprises a magnetic sensor 10 fastened to the front portion of the steering drive unit, a single drive wheel 2, a motor 3 for driving the wheel 2 and an automatic steering device for the driving wheel 2 by which the magnetic sensor 10 detects magnetism (magnetic force lines) emitted from magnetic tape laid along a guide path. Four wheels are provided at the four corners of the trolley's underside: the front wheels 5 are universal casters having good steering properties and the rear wheels 6 are fixed type casters.

'. . , 218~508 The driving wheel 2 of the steering drive unit 4 is mounted on an elevation changeover mechanism 16 that changes the position of the drive wheel 2 between a first position where the wheel 2 touches the floor with a pressure sufficient for moving the vehicle and a second position where the wheel is suspended with clearance above the floor. A manually operated changeover handle 20 i9 msnipulated to control the up-and-down operation of the drive wheel 2. When it is necessary to take the magnetically guided vehicle 1 away from the magnetic tape 17 for maintenance or inspection, the drive wheel 2 is elevated by the changeover handle 20 so that the vehicle 1 can be moved manually easily.
The steering drive unit 4 is further discussed below.
The magnetic tape sensor 10 is mounted on the front portion of a holder 8 for the drive wheel 2 by a supporting device 9. A
bearing block 11 receives a steering shaft that extends vertically from the holder 8 for the dr-ive wheel 2. The changeover mechanism 16 is provided between the bearing block 11 and a movable plate 12 that is removably fixed to the carriage frame of the trolley 7 by accouplement. A steering motor 13 is suspended under the lower surface of the movable plate 12 at the rear portion. A pulley from the steering shaft is coupled with a drive pulley from the steering motor 13 by a timing belt such that the driving wheel 2 can be automatically steered by the steering motor 13. A control device 14 is mounted on the back lower surface of the trolley 7 and a battery 15 for a power supply is mounted on back upper surface of the trolley 7.
The magnetically guided vehicle is operated as follows:
The magnetically guided vehicle 1 is actuated when an 218i508 operator manipulates a start buttorl. Software incorporated in the control device 14 controls the unllla[lrled operation of the vehicle continuously until a stop button is manipulated, as is discussed below. The magnetically guided vehicle 1 is controlled automatically without the aid of an operator because the magnetic tape sensor 10 senses the force and direction of the magnetic flux emitted from the magnetic tape laid along the guide path and the steering motor 13 is automatically controlled so that the magnetic tape sensor 10 traces the right or left edge of the magnetic tape. Automatic magnetic guide operation is thus accomplished. The vehicle decelerates rapidly and stops when detecting a loading position (or stop position) by a sensor or the like when moving. The detection signal from the magnetic sensor 10 is applied to the control device 14 so as to be processed. The control device 14 controls the steering motor 13 and the drive motor 3 in response to the processed output signal (namely, control signal). Therefore, the magnetically guided vehicle can automatically move and stop along the magnetic tape repeatedy in an unmanned operation.
The magnetically guided vehicle 1 can be disassembled into the steering drive unit 4, which is the main element of the vehicle, and the trolley 7, thereby allowing the trolley to be used for its original purposes. Since the position of the drive wheel 20 of the steering drive unit 4 can be changed by using the changeover handle 20, moving between the grounded position and the floating position, even if resistance from the driving device (especially, magnetic reluctance of the motor) is great, the magnetically guided vehicle can be easily manipulated by manually 218~5û8 pushing the vehicle when (1) the vehicle is moved to an area where the magnetic tape is not provided in order to perform maintenance or inspection of the vehicle or in order to the modify the guide path, or (2) the vehicle is moved to an area having no guide path in order to charge the battery and the like.
There are no particular problems in carrying loads using the above-described conventional vehicle 1 as long as it moves along a linear path. However, when the vehicle moves along a curved path, such as the corner shown in FIG. 7, problems arise.
The drive wheel 2 of the steering drive unit 4 is mounted at the front side of the trolley 7 adjacent to the front wheels (universal casters) 5, 5, so that the front wheels can be controlled but the rear wheels (fixed type casters) merely follow the movement direction of the steering drive unit 4 and are apt to move along the shortest path. Therefore, the front portion of the vehicle moves along the magnetic tape 17 but the rear portion is apt to move inside the corner along the shortest path. This causes a dangerous possibility that the vehicle passes closely by a structure or the like positioned inside the corner and hits it.
It is necessary to provide a space between the corner of the structure and the magnetic tape 17 large enough to avoid a collision. This requires the widening of the guide path and may result in problems with space. This kind of problem is exacerbated with a larger size vehicle.
After moving along the curved path past the corner, the vehicle must move along the straight path a certain distance before it is again fully parallel with the guide path. Thus, it is difficult to locate a loading position adjacent to a corner . 2I8~o8 and freedom is limited when designing a whole conveyer system.
One of the ways to resolve the above problem is to divert the course of the guide tape to the outside at a corner, as shown in FIG. 8, in consideratiorl of the difference between the paths of the front and rear wheels. In this way, the vehicle is prevented from hitting a structure at the corner, but, it is technically difficult to design such route with reference to the actual route difference and to lay the guide tape on the floor.
In addition, this method does not solve the problems of making the guide path wider or of the impossibility of locating a loading position adjacent to the corner.
Commonly the magnetically guided vehicle moves along a loop path in only one direction. However, according to specific conditions, it may be useful for the vehicle to move along a non-loop guide path in both directions, namely, forward and backward. Since, with the conventional type magnetically guided vehicle 1, the drive wheel 2 of the steering drive unit 4 is positioned at the front side of the chassis of the trolley 7 with respect to the center of mass (or the center of the drawing), it is actually impossible to steer the rear wheels of the trolley 7 in the same direction as or in a direction opposite to the direction of the front wheels 5 of the trolley 7. Therefore, the vehicle cannot move in both the forward and backward directions merely by reversing the switch connection and use of such vehicle is thus limited. Moreover, the prior art has a disadvantage in that more space is required for a looped guide path.
It is therefore an object of the present invention to provide an improved magnetically guided vehicle that can smoothly '. 218~508 move along a curved path and can move in both the forward and backward directions.

SUMMARY OF THE INVENTION
According to a magnetically guided vehicle of the present invention, a steering drive unit is mounted on the underside of a chassis of a trolley having wheels provided at least four corners of the trolley and the vehicle is guided to move along a magnetic tape laid on the floor, wherein all the wheels of the trolley are universal casters, two sets of magnetic guide type steering drive units are detachably mounted, one each on the front and back portions of the lower surface of the chassis for the trolley, and sènsors are provided at each of the front and rear portions of the magnetic guide type steering drive units for detecting the magnetic tape.
The two magnetic guide type steering drive units independently detect the magnetic tape and operate to move and stop in synchrony.
These two magnetic guide type steering drive units operate in synchrony at least while moving along the curved portion of the path.
The magnetically guided vehicle according to the present invention moves along the magnetic tape by using the frorlt and rear steering drive units, each detecting the magnetic tape, allowing the vehicle to move along the curved portion of the magnetic tape, moving and stopping in synchrony. Therefore, it is not necessary to consider the difference of movement of the front and rear wheels, even for a larger size vehicle. A vehicle - " 218~508 according to the present invention moves not only along the looped path in one direction but can also move both forward and backward. Therefore, it is not necessary to desigrl a closed loop guide path and the vehicle can be utilized ror marly load;rlg applications.

BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a front view of the magnetically guided vehicle according to the present invention;
FIG. 2 is a plan view of the magnetically guided vehicle according to the present invention;
FIG. 3 is a plan view for explaining the forward movement over time of the magnetically guided vehicle according to the present invention;
FIG. 4 is a plan view for explaining another example of the guide path to which the present invention may be applied;
FIG. 5 is a plan view for explaining an additional example of the guide path to which the present invention may be applied;
FIG. 6 is a front view of a magnetically guided vehicle of the prior art;
FIG. 7 is a plan view for explaining the forward movement over time of a magnetically guided vehicle of the prior art; and FIG. 8 is a plan view for explaining another example of a guide path to which the conventional vehicle may be applied.

DETAILED DESCRIPTION
Preferred embodiments of the present invention are discussed below.

~ _ 218~508 As shown in FlGs. 1 and 2, a magnetically guided type vehicle 21 comprises universal casters 5, 5', having good steering characteristics, provided at all four corners of the lower surface of the chassis 24 of the trolley 23. Two steering drive units 4, 4 are removably mounted on the lower surface of the chassis 24 so that they are positioned at the front and back portions of the chassis 24 symmetrically with respect to the center of mass (center of the drawing) of the chassis 24 and one of the units is adjacent to the front wheels 5, 6 and the other unit is adjacent to the rear wheels 5', 5'. The configuration and function of the steering drive unit 4 are the same as those discussed in the "Detailed Description" in the above-referenced U.S. Patent No. 5,525,884. In other words, each steering drive unit 4 comprises a drive wheel 2, a motor 3 for driving the wheel 2 and an automatic steering device for controlling the drive wheel 2. However, magnetic sensor lOa is fixed to a holder 18 for the drive motor 3 by a supporter 19 and magnetic sensor lOb is fixed to a holder 8 for the drive wheel 2 by a supporter 9, in order to detect magnetism (magnetic force lines) emitted from a magnetic tape 17 laid along the path on the floor. The drive motor 3 is a DC motor that rotates in the forward and reverse directions. The drive wheel 2 of the steering drive unit 4 is mounted on an up-and-down changeover mechanism 16 the position of which can be switched between the wheel touching the ground applying a pressure to provide for the moving of the vehicle and a floating condition where the drive wheel 2 is separated completely from the floor. A changeover handle 20 is coupled with the changeover mechanism 16 for manually lowering and 218~ o8 raising the drive wheel 2. Such a control may be performed remotely by a remote controller instead of the changeover harldle 20. Bumpers 22 may be provided if necessary at the front and rear portions of the magnetically guided vehicle 21 in order to soften any shock that may occur if the vehicle 21 hits a structure. The size of the chassis 24 of the trolley 23 may be about 800 x 2700 mm and there may be a space of about 230 mm between the floor and the chassis 24.
FIG. 3 illustrates how the front and rear steering drive units 4, 4 of the magnetically guided vehicle 21 detect the magnetic tape 17 independently and how they move forward along the linear and curved paths, moving and stopping in synchronY.
The magnetically guided vehicle 21 starts in response to the start button being pushed by the operator and the software incorporated in the control device 14 is programmed such that the unmanrled operation is repeated until the operator pushes the stop button as set forth below. In the two steering drive units 4, 4, the magnetic tape sensors lOa, lOa positioned at the fron-t side of the drive wheel 2 detect the intensity and direction of the magnetic force lines emitted from the magnetic tape 17 laid on the guide path. The steering motors 13, 13 are automatically actuated such that the positions of the magnetic tape sensors lOa, lOa correspond to the left (or right) edge of the magnetic tape 17. The magnetically guided operation is completed by driving the drive wheels 2, 2 and the magnetically ~uided vehicle can thus be controlled without an operator.
When the front and rear steering drive units 4, 4 are actuated synchronously, the magnetically guided vehicle 21 moves 2I8~508 in an automatic steering fashion so that the drive wheels 2, 2 follow the magnetic tape 17. Therefore, both the front wheels 5, 5 and the rear wheels 5', 5' of the vehicle 21 can be steered and the vehicle 21 can move smoothly along both linier and curved paths of the magnetic tape 17. This operation prevents the back portion (back wheels 5',5') of the vehicle 21 from colliding with a structure positioned inside the corner portion of the guide path. This invention does not have the problem of a difference between the paths taken by the front and rear wheels of the vehicle 21. Therefore, guide path can be formed by laying the magnetic tape 17 on the floor using a radius of curvature based on the radius of turn for the vehicle 21 and the width of the path used by the vehicle 21 along the magnetic tape 17.
After the magnetically guided vehicle 21 passes the curved portion of the path, it will quickly move linearly, substantially parallel with the magnetic tape 17. Therefore, it is possible to provide a loading position adjacent to the corner portion and the guide path can be designed with more freedom.
Since the front and back steering drive units 4, 4 drive the wheels 2, 2 in synchrony when the magnetically guided vehicle 21 moves along the curved portion of the path as well as the straight portion of the path, the total drive power of the two steering drive units will also provide large conveyance capability. This also means that the driving power of each of the steering drive unit 4 may be reduced and such steering drive unit can be manufactured in a compact and light body. In addition, the vehicle 21 moves more smoothly and stably without fishtailing. It is possible to use only the drive wheel of the 218~508 front side steering drive unit for the straight path and the soft curved path where the difference between the movement of the ~rOrlt atld back wlleels is solall. In suc~l ~ase, the drive wlleel 2 of the back steering drive unit 4 is elevated using the changeover handle 20.
The magnetically guided vehicle 21 can easily move in two directions, forward and backward, às shown in FIGs. 4 and 5. All the wheels 5, 5' of the trolley 23 are the universal casters with good steering properties. The steering drive units 4, 4 are mounted adjacent to the front and rear wheels, i.e., they are mounted at the front and r-ear sides symmetrically with respect to the center of mass tcenter of the drawing) of the chassis 24 (refer to FIG. 2) . The two magnetic sensors lOa, lOb are mounted at the front and rear portions of each the steering drive unit. Therefore, the vehicle 21 can move in both directions merely by switching the drive motors 3, 3 when the vehicle reaches the end point loading positions Al, A2. In such case, the system detects the intensity and direction of the magnetic force lines emitted from the magnetic tape 17 by using the proper magnetic tape sensors lOa, lOa or lOb, lOb that are positioned at the front side. In moving forward and backward, both drive wheels 2, 2 of the two steering drive units 4, 4 may be driven synchronously. Moreover, the drive wheel 2 of the single steering drive unit 4 positioned in front may be driven alone when moving along the straight path and the soft curved path where movement is not affected by the difference between the movement of the front and back wheels.

Claims

1. In a magnetically guided vehicle including a magnetic guide type steering drive unit mounted on a lower surface of a chassis for a trolley having wheels provided at no less than four corners thereof, said vehicle being guided to move along a path of a floor determined by magnetic tape laid thereon, said magnetically guided vehicle characterized in that all said wheels of said trolley are universal casters, two sets of said magnetic guide type steering drive units are detachably mounted, one each of said sets on front and back portions of said lower surface of said chassis for said trolley, and sensors are provided at said front and rear portions of the magnetic guide type steering drive units for detecting said magnetic tape.

2. A magnetically guided vehicle according to claim 1, wherein said two magnetic guide type steering drive units detect independently said magnetic tape and operate to move and stop in synchrony.

3. A magnetically guided vehicle according to claim 1 or 2, wherein said two magnetic guide type steering drive units operate synchronously during at least the time said vehicle is travelling on a curved portion of said magnetic tape.