GB2200477A - Bringing a load carrier to a given position - Google Patents

Description

C Q Z20 0 4 7 7 A method and arrangement for bringing a load carrier to a

given position.

1 The present invention relates to a method for bringing the load carrier of a high-lift materials handling vehicle to given position in relation to a given point, said vehicle being of the kind which is intended for handling goods in high-stand storage facility, preferably an automated facil ity, which incorporates tall structures fitted with shelving or pallet supports carried by vertical posts or like uprights, and in which method the extent of lateral or horizontal movement of the load carrier along the shelving or pallet support structures is measured by a distance meter, and pre-determined coordinates on the shelving or pallet support structure are detected by sensor means. The invention also relates to an arrangement of apparatus and devices for carrying out the method.

Vehicles or machines of the aforesaid kind are most often fully automatic and driverless and do not require constant attention or supervision. This means that the control systems by means of which the vehicle is guided to the correct position in front of a shelf compartment or pallet location into which an item of goods is to be deposited or from which an item of goods is to be collected must be highly reliable. In one known system the travel path of the vehicle is measured accurately with the aid of purely mechanical measuring devices which comprise a pinion wheel mounted on the chassis of the vehicle and a rack located on the floor of the pathway along which the vehicle moves. When such storage facilities are expanded, however, this known system becomes commensurately more expensive, both with regard to its mechanical construction and also to its maintenance. The system is also relatively slow. Another known vehicle positioning system of this kind operates with 1 the aid of a pulse counter or like device which is connected to a wheel axle of the vehicle, e.g. truck or crane, and which assists in calculating the approximitive position of a shelf compartment, whereafter the load carrier is brought to a precise position in relation to the shelf compartment or pallet location, with the aid of markings which are provided on each shelf or pallet location and which are detected, e.g., by a photocell mounted on the load carrier. This system enables the materials handling vehicle to be driven at a relatively high speed to a position in the near proximity of the shelf pallet location. The subsequent necessary fine adjustments to the position of the load carrier is more time consuming, however, since the markings must be searched for and detected over a relatively long path, in order to compensate for shelving or uprights which are out of true with the vertical or which bulge or lean outwardly, or to one side. Present day markings are normally provided in the form of reflective ribbon. Since a modern storage facility may incorporate as many as 30000 to 40000 pallet locations, the cost of marking each pallet location with the aid of such ribbon can be very costly. Furthermore, the ribbon can become dirty or simply fall off,thereby causing interruptions in operation.

one objective of the invention is therefore to provide a method and an arrangement of apparatus for bringing the load carrier of a materials handling vehicle to a given position in relation to a given location in a manner which will enable the vehicle to function independently of markings on the pallet locations. Another object is to enable fine adjustments to be made automatically to the position of the load carrier in correspondence with constant or temporary displacements in the shelving or pallet support structures. A third objective is to enable the speed of a transport cycle to be increased without detracting from the reliabil- p ity of the load-carrier positioning system. Further objectives of the invention and advantages afforded thereby will be apparent from the following description. These objectives are realized by the characterizing features set forth in the following claims.

5t The invention is based on the understanding that if it is to be possible to dispense with the use of reflective ribbon type markings or the like at each shelf or pallet location, then it must be possible to make compensatory calculations for misalignment of the uprights supporting the shelves or pallet locations and for outward bulging or sideways leaning of the uprights. If this compensating facility is not provided there is a risk of making positional errors, which can result in damage to both the transporting vehicle (machine) and the goods. These problems will, of course, become,progressively more serious.with progressively expanding storage systems. Some present day high-stand storage facilities already have shelving or stand heights in the order of 2530 m, and shelving heights are expected to increase still further in the future. It is impossible in practice to manufacture a pallet rack or shelving stand which can be erected in a truly vertical position. For example, the presence of small differences in the level of the floor supporting the rack or stand can result in pronounced deviations from the vertical in the case of very tall structures. Furthermore, the load often varies within different parts of the pal-let rack or stand and also throughout the rack as a whole. At the same time, it is highly desirable to be able to utilize all available storage space to the full, as far as is reasonably possible, which means that the pallets and goods carried thereby must be placed as close together as possible. Together this results in a tolerance requirement of ca + 5 mm, even when placing one- ton pallets at a height of 30 meters above floor level.

Vertical movement of the pallet rack is significantly smaller than the earlier mentioned horizontal or lateral movements, and it has also been found quite possible to effect the vertical adjustment with the aid of known techniques. For example, it is possible to apply a simple distance measuring technique, optionally with the aid of calibration at one or more levels.

According to the invention, the front surfaces of respective storage shelves or pallet locations are provided with gauge points which together form a system of coordinates and the positions of which are registered and compared with the position of fixed reference points located close to the floor of the shelving stand or rack. The position of respective points, or markings, is detected with the aid of sensors, such as photocells, mounted on the materials handling vehicle. The detected positions are registered in a computer which calculates the positional differences between the fixed reference points and the respective gauge points or coordinates located immediately thereabove. These differences are stored conveniently in the computer memory and since the uprights are firmly connected to one another by crosspieces, the positions of mutually different shelf compartments can be calculated by interpolation. This calculation is preferably not carried out until the computer receives a specific drive command. As a result of this storage of information in the computer memory, detection or sensing of the gauge points can be controlled to times when the storage facility is not being utilized or is only being utilized to a small extent, e.g. at night time. The sensor may also be caused to detect or sense gauge points which are passed during different transport cycles, thereby continually updating the aforesaid positional differences. According to another preferred embodiment of the invention a first sensor is fixedly mounted on the lower part of the vehicle in order to detect the reference points, while a second sensor is mounted on the movable load carrier in order to detect the gauge points or measuring points. The sensors are placed one above the other and enable the aforesaid difference calculations to be carried out quickly and reliably. The gauge points are preferably arranged in a diagonal diamond network over the front side of the storage shelves, preferably with an equidistant spacing in both the vertical and the horizontal directions. Because the uprights are connected rigidly together, it is often unnecessary to apply a gauge point to each upright. Depending on the construction of the shelving structure concerned and the various accuracy requirements placed on the system, a suitable spacing between the reflectors may be 5-15 m, and in order to achieve a uniform distribution of the gauge points, the gauge points of two mutually sequential uprights are preferably displaced vertically through a distance which is equal to half the distance between two mutually adjacent gauge points on one and the same upright. When these conditions are observed 100-500 pallet locations of a storage facility can be served by solely one reflector, which can be compared with present day storage facilities where only one pallet location is served by each reflector.

An embodiment of the invention will now be described in more detail with reference to the accompanying drawing, in which Figure 1 is a side view of the front side of storage shelving or a pallet rack provided with positional markings in accordance with the invention, and Figure 2 is a schematic side view of a materials handling vehicle provided with sensors in accordance with the invention.

The invention is intended primarily for application with automated materials handling systems in which goods are to be placed in high storage locations. Consequently, the goods transporter of the illustrated embodiment has the form of a materials handling railcrane 11. The railcrane comprises a chassis 12 which has mounted thereon, in a conventional manner, a tall vertical mast 13 and which is supported on wheels 14. A load carrier 15 equipped with a telescopic fork or tine assembly 16 is arranged for movement along the mast 13 in some suitable known manner. A first sensor 17 is mounted on a lower transporter part, and a second sensor 18 is mounted on the load carrier 15. The two sensors are located vertical one above the other and may conveniently consist of photocells, electron cameras or like instruments. In the illustrated embodiment the first sensor 17 is fixedly mounted to the chassis 12, whereas the second sensor 18 is arranged for movement along a vertical line which passes through the fixed sensor 17. The sensors are intended to detect various position markings 19 on the front surfaces of the different storage shelves or the racks carrying said shelves. The markings are preferably applied to the uprights 20 of the shelf racks or at least to rack parts that are firmly connected to the uprights, e.g. to the crosspieces 21 extending therebetween. The markings will preferably consist of reflective devices, e.g. strips of reflective tape gummed to the uprights or crosspieces. Alternatively, the uprights themselves, or some other suitable part of the shelving structure may serve as detection points for detection by the sensors 17, 18. Although the markings 19 may be applied, or incorporated, on, or in, each upright, as in the case of the illustrated embodiment, it is more convenient to space the markings more widely apart, commensurate with what has been said in the aforegoing, so that certain uprights will be devoid of markings. The illustrated markings are divided into reference marks or points 22 lo- 1 1 m cated close to the floor, and gauge markings or points 23, located at given mutual distances along the uprights. The reference points 22 are thus detected by the stationary sensor 17, whereas the gauge markings 23 are scanned and detected by the movable sensor 18. Each pair of mutually adjacent uprights 20 may have extending therebetween one or more shelves or pallet locations 24. A pulse-counting type distance meter 25 is connected to one of the wheel shafts of the chassis 12 and is operative in measuring the distance travelled by the railcrane, or transporter, from a given starting location. The reference markings 22 can be used for calibrating purposes in this case.

Described in the following is a method which can be applied beneficially for programming the necessary computer or data-processing apparatus and for handling the goods concerned. When updating differences inserted into the memory, the goods transporter 11 is ordered to move along a storage passageway with the load carrier adjusted to a given height above the floor. During travel of the transporter, the reference markings 22 are detected by the first sensor 17 and the gauge markings 23 located in register with the height setting of the second sensor 18 are detected thereby. The detection, or scanning, of the markings 22, 23, can be effected without stopping the transporter at respective gauge markings, although it may be considered convenient to introduce a facility which will enable the transporter to be slowed down slightly at the locations of respective gauge markings. A suitably located computer, microprocessor or the like in communication with the transporter 11 calculates the lateral differences between the detected value from the first, stationary sensor 17 and the second sensor 18, on the load carrier. These differences are then stored in the computer memory. The transporter is then ordered to repeat the procedure, along the next level of gauge markings and so on 1 until all markings have been detected and registered. In this way, the computer receives information concerning the actual facilities which are available in the shelving system. When the transporter is ordered to collect goods from or to deposit goods at a given pallet location 24, the computer first calculates the real position of the pallet location, or shelving compartment, on the basis of the aforesaid differences stored in the memory thereof, therewith enabling the transporter to be driven directly to the shelving compartment or pallet location concerned, without being delayed by the necessity to search for said compartment or location. Thus, the transporter can be driven at full speed until it almost reaches the shelving compartment in question, thereby minimizing the required braking distance. As beforementioned, other methods and arrangements can be used within the scope of the present invention.

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Claims (12)

1. Claims t,' 1. A method for bringing a load carrier to a given position,

   said load carrier forming part of a high-lift materials handling vehicle of the kind which is in tended to transport goods in a preferably automated high rise storage facility which includes shelving structures comprised of shelf compartments carried by uprights in which method horizontal movement of the load carrier past the storage shelves is measured with the aid of a distance meter and position markings on the shelving structures are detected by sensors, char acterized in that the position markings have the form of reference points located close to floor level and gauge points located at one or more height positions above respective reference points and are detected by a respective sensor in that the positional differ- ences between said reference points and gauge points are calculated; and in that the location of a given shelf com partment is calculated with the aid of said positional differences, so as to take into account any misalignment or outward bending of the. uprights
2. 2. A method according to Claim 1, characterized in that the positional differences or calculated positions of the gauge points are stored in a computer memory, and in that the gauge and reference points are detected at optional time points, preferably when the load carrier is not being used to transport goods.
3. 3. An arrangement for bringing a load carrier of a high-lift materials handling vehicle to a given posi tion, said vehicle being of the kind which is intended.to transport goods in a preferably automated high-stand storage facility which includes storage shelving structures having shelf compartments which are carried by uprights and which vehicle has arranged thereon a distance meter for measuring the distance moved by the load carrier hori zontally along the shelving structures, and sensors for detecting positional markings on the shelving structures, characterized in that the positional markings include reference points, which are located close to floor-level, and one or more gauge points, which are located at a given mutual distance above respective refer ence points; in that the sensor register the position of the points is intended to and in that a computer is programmed to calculate the horizontal differ ences between the positions of respective reference points and the overlying gauge points and, on the basis of these calculations, to control the horizontal movement of the vehicle along the shelving structures, so as to take into account any possible misalignment or outward bending of the uprights when positioning the load carrier in front of a given shelf compartment.
4. 4. An arrangement according to Claim 3, characterized in that the computer is programmed to store the differences or calculated abRolute values of the gauge points in a memory, wherewith detection of the positions of the gauge points can be effected at any desired moment in time.

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5. 5. An arrangement according to Claim 3 or 4, characterized in that the computer is programmed to calculate the positio,n of a particular shelf compartment prior to each mate rials handling cycle.
6. 6. An arrangement according to any of Claims 3-5, charac terized in that a first sensor is mounted stationarily on the lower part of the vehicle for the purpose of detect- ing the reference points; and in that a second sensor 11 v h h is mounted on the load carrier at a location above the first sensor for the purpsose of detecting the gauge points
7. 7. An arrangement according to any of Claims 3-6, characterized in that the reference and gauge points comprise reflective devices or parts of the uprights; and in that the sensors consist of photocells,kcameras or like devices.
8. 8. An arrangement according to any of the preceding Claims, characterized in that the gauge points are located in relation to one.another such as to build a diamond network over the front side of the shelving structures.
9. 9. An arrangement according to Claim 8, characterized in that the gauge points for two mutually sequential up- rights having gauge points are displaced vertically through a distance which is equal to half the distance between two mutually adjacent gauge points on one and the same upright.
10. 10. An arrangement according to Claim 8 or 9, characterized in that the gauge points have a mutual spacing of 5-15 M.
11. 11. A method for bringing a load carrier to a given position substantially as described herein with reference to the accompanying drawings.
12. 12. An arrangement for bringing a load carrier to a given position substantially as described herein with reference to the accompanying drawings.

    Published 1988 V The Patent Office, State House. 66"71 High Holborn, London WClR 4TP. Further copies may be obtained from The Patent Lnn0e, Sales Branch, St Mary Cray, Orpington, Kent J3R5 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Kent. Con. 1/87. Sales Branch. St Marv Crav. Omington. Kent J3R5 3RD. Printed by Multiplex techniques ita. bt mary uray. Aem, toli- -Lio 1 -