AU703606B2 - A crane positioning system - Google Patents

Description

P:\WPDOCS\AMD\SPECI\673947.EVA 29/1/98 -1- A CRANE POSITIONING SYSTEM FIELD OF THE INVENTION The present invention relates to a positioning system. In particular, the invention is directed to a method and apparatus for positioning an overhead crane in an x-y plane using a laser beam operating in the z direction, although the invention is not limited to this particular use.

DESCRIPTION OF THE PRIOR ART In a copper refinery, an electric overhead travelling crane is used to deliver anode and cathode elements from preparation machines, and place the anodes and cathodes in "cells".

The anodes and cathodes must be positioned accurately, as the distance between an anodecathode pair is crucial to the efficiency of the cell cycle. During the copper refining process, anodes and cathodes are repeatedly inserted in, and removed from, the cells.

Such cranes were originally operated manually. In order to reduce operating costs, the cranes have been automated. However, it has been found that automated cranes are unable to place the anodes and cathodes in an accurate and reliable manner on each insertion. There are two known positioning systems which seek to improve the accuracy of such cranes.

In one system, optical cameras are used to view the target and provide an indication of the accuracy of the positioning of the crane. In the other system, a flat target is used. The flat target comprises a series of engraved rings, and a hole in the middle. A laser beam generator is mounted on the crane, and an infrared laser beam is moved across the target to locate the hole and thereby position the crane.

The two known methods described above have proved to be expensive and not sufficiently reliable. Further, the apparatus used in these methods is prone to damage in the hazardous environment in which the crane operates. For these reasons, these methods have not achieved widespread popularity.

r_ P:\WPDOCS\AMD\SPFCI\673947.EVA 29/1/98 -2- SUMMARY OF THE INVENTION The present invention seeks to provide an improved method and apparatus for positioning a device or machine, such as a crane.

In one broad form, the present invention provides a method of positioning an object in an .x-y plane relative to a target spaced from that plane in the z direction, the target having a surface which has at least one transition in the z direction, the method comprising the steps of: transmitting a distance measuring beam in the z direction from a location whose spatial relationship to the object is fixed or known; moving the beam over the surface of the target in the x and/or y direction(s) to traverse the transition; and, ~positioning the object in the x and/or y direction(s) by reference to the x and/or y coordinate(s) of the transition as detected by the change in distance measurement in the z direction at the transition.

o *a .o Throughout this specification, references to the x, y and z axes are intended to refer to a'aorthogonal axes. Typically, the x-y plane is horizontal, and the z axis is vertical.

Typically, the transition is a step and the target surface on either side of the step is a sloping a surface, the two surfaces each sloping upwardly towards the step so that the step forms the junction of the crests of two surfaces of opposite slopes.

o aPreferably, a set of two aligned steps with associated sloping surfaces are provided on the target, the two steps facing in opposite directions.

More preferably, the target has two such sets of steps.

Typically, the beam is a laser beam generated from a location on the object. Once the position of the transition in the x-y plane is determined, it follows that the position of the object in the x-y plane can be determined and/or the object can be positioned at a desired x, y location P:\WPDOCS\AMD\SPECI\673947. EVA -29/1/98 -3relative to the transition.

In the preferred embodiment, the object to be positioned is a load guide for a crane and the target is situated adjacent a cell into which an anode-cathode pair is lowered from the load guide.

The invention also resides in the target for a ranging beam, the target being as described above.

In another form, the present invention provides apparatus for positioning an object in an x-y plane relative to a target spaced from that plane in the z direction, the apparatus comprising means for generating a distance measuring beam in the z direction from a location whose spatial relationship with the object is fixed or known, a target having a surface containing a transition, means for moving the beam in the x and/or y direction(s) over the target surface, 15 means for detecting the x and/or y position of the transition from change in the measured z distance at the transition, and electronic control means for positioning the object in the x S. and/or y direction(s) by reference to the respective x and/or y position of the transition.

Typically, the electronic control means includes a programmable logic controller or other 20 programmable device. The electronic control means is also able to control the positioning of the object.

In its preferred embodiment, the invention is in the form of crane apparatus comprising a gantry adapted to travel horizontally in the y direction, trolley means carried by the gantry and adapted to move horizontally in the x direction along the gantry, a load guide suspended from the trolley means, positioning means for moving the load guide in the x and/or y direction(s) relative to the trolley, laser beam distance measuring means mounted on the load guide, the laser beam distance measuring means generating a laser beam downwardly in the z distance, a target located below the load guide, the target having a surface containing a transition, and control means adapted to detect the x and/or y position of the transition from P:\WPDOCS\AMD\SPECI\673947EVA 29/11/98 -4change in the measured z distance at the transition, and to control the positioning means to position the load guide in the x and/or y direction(s) with reference to the respective x or y position of the transition.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully understood and put into practice, a preferred but non-limiting embodiment thereof will now be described by way of an example, with reference to the accompanying drawings, wherein: Fig. 1 is a schematic diagram of a crane positioning system according to one embodiment of the invention; Figs. 2 and 3 are perspective views of the target used in the system of Fig. 1; Fig. 4 is a plan view of the target of Fig. 1; Fig. 5 is an elevation of the target of Fig. 1; and Fig. 6 is an end elevation of the target of Fig. 1.

S. DETAILED DESCRIPTION OF PREFERRED

EMBODIMENT(S)

As shown in Fig. 1, an overhead crane comprises a crane trolley 10 mounted for travel along 20 a gantry 11 (in the direction). The gantry 11 itself is mounted for travel along a pair of spaced parallel rails 12 (in the direction). The crane trolley 10 carries a hoist mechanism which typically has one or more winch cables 13 from which anode-cathode pairs are suspended, in use.

The crane also includes a load guide in the form of a guide frame- 20 for accurate positioning of the anodes and cathodes. The guide frame 20 is suspended from the trolley 10, and may be moved in the x and y directions by linear actuators 21, 22 mounted between the trolley frame and the guide frame. The crane is an electric crane whose position is controlled by software, as described in more detail below.

P:\WPDOCS\AMD\SPECI\63947.EVA 29/1/98 The crane further comprises laser ranging apparatus. A laser beam generator 14 is mounted to the guide frame 20 and generates a laser beam 15 which is emitted downwardly (in the "z" direction). The beam 15 can be shifted in the x, y plane by linear actuators 21, 22 acting on the guide frame 20. From the reflection of the laser beam from a target surface, the ranging apparatus is able to calculate the vertical distance to the target. Such distance can be calculated in an accurate manner. However, the laser ranging apparatus is only able to calculate distances in the z direction, not in the x-y plane.

The preferred embodiment of this invention uses a target 16 with a stepped surface. As the laser beam traverses the step, there is an abrupt, and relatively large, change in the measured distance in the z direction. This sharp change in the z distance can be used to pinpoint the :'---location of the step, and hence to position of the guide frame 20 in the x or y direction, relative to the target.

S.

The preferred form of the reflective target 16 is shown in more detail in Figs. 2-6. The target 16 comprises a pair of oppositely inclined surfaces 17A, 17B whose crests are joined by a S step 17C. The target 16 also comprises a second pair of oppositely inclined surfaces 18A, 18B S. *joined by step 18C. The vertical faces of steps 17C and 18C are aligned in the x direction and orientated in different directions. The surfaces 17A, 17B, 18A, 18B slope in the y direction.

A step 19A in the x direction is provided between surfaces 17A and 18B. Similarly, a step 19B in the x direction, but facing the opposite way to step 19A, is provided between surfaces 17B :and 18A. The vertical faces of steps 19A and 19B are preferably aligned in the y direction.

The location (x and y coordinates) of all cells and machines to be accessed by the crane are stored as data in a "look up" table in a programmable logic controller (PLC) which controls the positioning of the crane. These coordinates are used for coarse horizontal positioning of the crane trolley For coarse positioning of the crane trolley 10 in the y direction, a distance measuring laser P:\WPDOCS\AMD\SPEC673947.EVA 29/1/98 -6is mounted at each end of the gantry 11. These lasers (not shown) are aimed at reflective targets mounted on the end wall of the building in which the overhead crane is located. The crane 10 is able to be positioned approximately at the y coordinate of a desired cell or machine by using the distance to the wall as measured by the laser ranging devices at each end of the gantry 11. (Angular misalignment of the gantry bridge 11 is accounted for by using both laser readings). The lasers typically provide a reading every 14ms, and have a resolution of 1mm with an accuracy of Coarse positioning of the crane trolley 10 in the x direction to a desired x coordinate is achieved by using an encoder driven by one of the non-powered trolley wheels on which the trolley 10 rolls across the gantry bridge 11. The encoder is calibrated at four positions across the bridge. The crane trolley 10 is driven until the correct reading is achieved. The readings are recorded and stored as location data, and corrected according to the load measured by the :hoisting load cells. Typically, the coarse positioning system can place the crane within 15 of its correct position.

".:"Once the crane trolley 10 has been positioned at a desired cell or machine, its laser ranging *apparatus is used for fine positioning. Preferably, two targets 16 are used for each cell (or machine) and a respective laser beam 15 is directed at each target. The laser beams typically each have a spot diameter of 3mm, and are aimed vertically at the targets 16 which are approximately 150mm square in plan. The lasers operate in a scanning mode, and have a resolution of 1mm. Each laser ranging device provides an output to an RS232 interface to the PLC every 29ms.

Each laser beam is scanned across its target 16 towards the apex of the sloping surface.

Typically, the beam is first moved in the y direction by linear actuator 22, then in the x direction by linear actuator 21. The laser beam is moved towards the crest of the particular sloping surface on which it impinges. The required direction of movement of the beam along the sloping surface in the y direction is detected by the increase or decrease in the laser reading of the z measurement. The position of the beam is measured by encoders on the linear P:\WPDOCS\AMD\SPECI\673947 EVA 29/1/98 -7actuators 21, 22.

When the beam moves in the y direction and traverses a step 17C or 18C, the sudden change in distance in the z direction detected by the laser ranging apparatus is recognised by the PLC software as indicating that the beam has traversed the step at the crest of the sloping surface, and the y coordinate is recorded by the PLC.

After the y coordinates have been aligned at both ends of the cell, the x direction actuator 21 moves the guide frame 20 until the laser beam 15 crosses the step (19A or 19B) in the x direction, indicating that the guide frame 20 is correctly positioned relative to the centre of the target cell.

As shown in the drawings, the steps 17C and 18C are reversed. That is, when traversed in the same direction along the y axis, one step goes up while the other goes down. This assists in positioning in the x direction. Since the direction of travel of the laser beam in the y direction to reach the step at the crest is known, the position of the laser beam relative to the centre of the target in the x direction is also known. That is, referring to Fig. 4, if the laser .**beam is travelling to the left in the y direction, a step up (18C) means that the beam has to move upwardly in x direction to find the centre of the target. Conversely, if the beam is travelling left along surface 17A and encounters a step down (17C), the beam must move downwardly in the x direction in order to find the centre of target.

O The beam is moved in the appropriate direction along the x axis until it crosses over step 19A or 19B at which point, the PLC software is able to determine that the guide frame is correctly positioned relative to the centre of the target.

The data stored in the "look up" table is updated by automatically recording the x and y coordinates from the fine positioning system when the guide frame is correctly positioned at the desired cell.

P:\WPDOCS\AMD\SPEC\673947VA 29/1/98 -8- Target cells and machines do not need to be at the same (vertical) level as the fine positioning system uses differential readings only. The height of each cell and machine loading point is stored as data in the "look upon table and referenced for vertical positioning using the laser distance measuring apparatus. The hoisting load cells are also used to supply data to enable the PLC to compensate for girder deflection.

A programmable limit switch is used to set the overall hoist motion limits while the actual level is measured by an encoder on the hoist drum shaft. The readings at which the load changes are noted and recorded by the PLC. Hence, the hoist position, and the z coordinate of the cells and machines are always known.

•The foregoing describes only one embodiment of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention.

For example, although the positioning system has been described with reference to its use on an overhead crane, it can also be used for positioning other devices and machines.

In an alternative embodiment, the target surface comprises two adjoining sloping surfaces of ooo 0 different slopes, the x or y position of the beam relative to the target being able to be determined from the transition in slope at the junction of the two surfaces.

*000 0The target may also comprise a single sloping surface have a transition in the vertical direction.

In yet another embodiment, the target consists of a stepped surface, preferably with steps arranged orthogonally in the x and y directions.

P:\WPDOCS\AMD\SPECM673947.EVA 29/1/98 -9- The present invention has been herein described with reference to a preferred but non-limiting embodiment. It should be understood that numerous variations and modifications will become apparent to persons skilled in the art. All such variations and modifications should be considered to fall within the scope of the invention as hereinbefore described and. as hereinafter claimed.

Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or comprising" or the term "includes" or variations thereof, will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers.

In this regard, in construing the claim scope, an embodiment where one or more features is *added to any of the claim is to be regarded as within the scope of the invention given that the essential features of the invention as claimed are included in such an embodiment.

9 9 oooo P:\WPDOCS\AMD\SPECI\673947.EVA 29/1/98 The claims defining the present invention are as follows: 1. A method of positioning an object in an x-y plane relative to a target spaced from that plane in the z direction, the target having a surface which has at least one transition in the z direction, the method comprising the steps of: transmitting a distance measuring beam in the z direction from a location whose spatial relationship to the object is fixed or known; moving the beam over the surface of the target in the x and/or y direction(s) to traverse the transition; and, positioning the object in the x and/or y direction(s) by reference to the x and/or y coordinate(s) of the transition as detected by the change in distance measurement in the z direction at the transition.

2. A method as claimed in claim 1, wherein the transition is a step, and the target surface has at least two portions of different slopes on either side of the step, each portion sloping upwardly towards the step so that the step forms the junction of the crests of the two portions.

3. A method as claimed in claim 1 or 2, further comprising the step of electronically storing the x and/or y coordinate(s) of the transition.

4. A method as claimed in any preceding claim, wherein the object to be positioned is a load guide for a crane, and the beam is a laser beam transmitted from a location on the load guide, the beam being moved in the x and/or y directions by moving the load guide in those directions.

5. A target adapted to be scanned by a distance measuring beam of an object positioning system, the target having at least two surface portions with a transition therebetween.

6. A target as claimed in claim 5 wherein the two surface portions are sloping.

7. A target as claimed in claim 5 or 6, wherein the transition is a step.

Claims (9)

1. 8. A target as claimed in claim 7, wherein the two portions have opposite slopes, each portion sloping upwardly towards the step so that the step forms the junction of the crests of the two portions.
2. 9. A target as claimed in claim 7 or 8, wherein the target comprises a set of two steps which are orientated in opposite directions. A target as claimed in claim 9, wherein the target comprises two sets of two steps, the sets being orientated orthogonally to each other.
3. 11. An apparatus for positioning an object in an x-y plane relative to a target spaced from I' that plane in the z direction, the apparatus comprising means for generating a distance measuring beam in the z direction from a location whose spatial relationship with the object is fixed or known, a target having a surface containing a transition, means for moving the beam in the x and/or y direction(s) over the target surface, means for detecting the x and/or y position of the transition from change in the measured z distance at the transition, and electronic control means for positioning the object in the x and/or y direction(s) by reference to the respective x and/or y position of the transition. oooto
4. 12. An apparatus as claimed in claim 11, wherein the electronic control means includes a programmable logic controller. o 13. An apparatus as claimed in claim 11 or 12, wherein the object is a load guide of a crane.
5. 14. An apparatus as claimed in claim 13, wherein the beam is a laser beam, and the beam generating means is mounted on the load guide. An apparatus as claimed in any one of claims 11 to 14 wherein the target is as claimed in any one of claims 5 to P:\WPDOCS\AMD\SPECI\673947.EVA 29/1/98 -12-
6. 16. A crane apparatus comprising a gantry adapted to travel horizontally in the y direction, trolley means carried by the gantry and adapted to move horizontally in the x direction along the gantry, a load guide suspended from the trolley means, positioning means for moving the load guide in the x and/or y direction(s) relative to the trolley, laser beam distance measuring means mounted on the load guide, the laser beam distance measuring means generating a laser beam downwardly in the z distance, a target located below the load guide, the target having a surface containing a transition, and control means adapted to detect the x and/or y position of the transition from change in the measured z distance at the transition, and to control the positioning means to position the load guide in the x and/or y direction(s) with reference to the respective x or y position of the transition.
7. 17. A crane apparatus as claimed in claim 16 wherein the target is as claimed in any one of claims 5 to 15 18. A crane apparatus as claimed in claim 16 or 17, wherein the positioning means comprises a pair of linear actuators, and the control means includes a programmable logic controller.
8. 19. A crane positioning system substantially as hereinbefore described with reference to 20 the drawings.
9. 20. A method of positioning a crane, substantially as hereinbefore described. *O DATED this 29th day of January, 1998. EVANS DEAKIN INDUSTRIES LIMITED By Their Patent Attorney DAVIES COLLISON CAVE P:\WPDOCS\AMD\SpECI\673947.EVA -29/1/98 ABSTRACT A crane has a load guide (20) which is able to be positioned in the x, y plane by reference to a target (16) spaced from the load guide in the z direction. The load guide (20) is suspended from a trolley (10) which moves in the x direction along a gantry (11) which travels in the y direction. A laser beam generator (14) is mounted on the load guide (20) and transmits a ranging beam (15) downwardly towards the target The load guide (20) and beam can be moved in the x and y directions by linear actuators (21, 22) acting on the load guide The target (16) has two pairs of sloping surfaces (17A, 17B; 18A, 18B), the crests of 10 the sloping surfaces of each pair being joined by a step (17C, 18C). Additional steps 19A, 19B are provided orthogonally to steps (17A, 17C). As the beam traverses the steps, the x or y coordinate of the step can be determined from the sudden change in the measured z distance at the step. The load guide (20) can therefore be positioned accurately relative to the target (16). ftof *l *foft