Load control device for a crane

Abstract

A control device and system for controlling a suspended load of a container crane with a trolley, a spreader and load lines arranged in a four point suspension for lifting a load and an optical sensor for sensing a deflection position of an orthogonal axis of a container suspended under the spreader. Two or more actuators are arranged attached to at least one load for moving at least one said suspension point closer to or farther away from an imaginary center line by shortening and/or lengthening the at least one load line.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the method and system of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:

FIG. 1 shows in a schematic diagram a simplified arrangement for a ship-to-shore (STS) crane.

FIG. 2 shows a diagram of positional error of skew, trim and list with respect to the orthogonal axes of a container,

FIG. 3 shows a layout for a load control device according to an embodiment of the invention,

FIG. 4 shows schematically an optical target, such as an optical transmitter comprising two or more light sources,

FIG. 5 shows the arrangement of the optical target on a container and in relation to a skew-type position error,

FIG. 6 shows a development of the optical target according to another embodiment of the invention, and

FIG. 7 shows an arrangement of the developed optical target on a container and in relation to a list error,

FIG. 8 shows show schematically a flowchart for a computer program to carry out a method according to an embodiment of the invention to rectify a skew-type error,

FIG. 9 a flowchart for a computer program to operate a method to rectify a list error and

FIG. 10 a flowchart for a computer program to operate a method to rectify a trim error.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a simplified schematic diagram of a ship-to-shore (STS) crane 1 arranged on a quayside for loading or unloading containers from a ship. The motor house mounted on the boom of the crane is arranged with main lifting motors and winding drums 2 which reel in or reel out ropes or load lines for lifting or lowering a container 20. The main lifting action takes place between the sheaves nearest the motor house and the boom tip 3 indicated as one end of the boom. Container 20 is held by a spreader 15 suspended from a trolley 21 which moves in the direction of arrow X forward (+ve) and back (−ve) along the boom. The load lines arranged on trolley 21 are also connected to actuators A (16-19) arranged at or near the tip 3 of the boom. The actuators, spreader, trolley and load lines are shown in more detail in FIG. 2.

FIG. 2 shows an arrangement according to an embodiment of the invention. The figure shows the container 20 held by a spreader 15 suspended from a trolley 21. The container is lifted and lowered by main winding drums 2, housed in the motor house (FIG. 1). On the other side of the container nearest the tip of the boom the load lines are arranged with actuators 16-19 which lengthen or shorten the load lines at that point. The spreader 15 is suspended from the trolley by load lines arranged at four points generally corresponding with the corners of the spreader 4a-4d. Trolley 21 is arranged with a sensor 5, preferably a CCD camera, which is aimed down at an optical target 7, which comprises two or more targets 8, 9 which preferably are light sources.

FIG. 3 shows three principal orthogonal axes with respect to a container 20, and shows three imaginary centre lines for the container with respect to the orthogonal axes. The figure also shows diagrammatically a skew error S as a rotation about a vertical axis V_H, a list error L with which a container tends to list around its long axis and rotate about the axis Y_W, and a trim error T with which one of the ends of the container along the long axis hangs lower, shown as a rotation about the imaginary centre line axis X_L.

FIG. 4 shows a light source 7. This comprises at least two light sources, which are preferably arranged as two large light sources 8, and two smaller sources 9. Measurements of two smaller light sources may be discarded when the spreader is very low, ie is at a great distance from the trolley. Correspondingly measurements of two larger light sources may be discarded when the spreader is close to the trolley (when the spreader is high).

The load control equipment consists of one CCD camera 5 and at least two of a plurality of optical transmitters 8, and/or 9. Optical transmitters 8 and 9 are of different size or light intensity. The CCD camera 5 is mounted under the boom preferably on the trolley, and the optical targets are mounted on the spreader. Thus an optical target (comprising at least two optical targets) aligned with the spreader moves as the container moves, and is arranged in a clear line of sight from camera 5. Measurements from camera 5 are taken continuously and distances calculated between the trolley and the spreader. For example when the spreader has a skew error and is rotated around its vertical axis V in the direction S of FIGS. 2, 3, then the spreader is positioned at an angle to orthogonal direction Y which, in concrete terms, means that at least one corner 4a-4d of the container has a distance error and is positioned too far from the boom tip and at least one other corner has a position error and is to close to the boom tip. To correct a distance error one or more actuators 16-19 are controlled so as to drive a load line, and thus a corner of the spreader 4a-4d, towards or away from the boom tip. In the case of a skew error a pair of actuators arranged on load lines and corresponding to the same X-direction side of the container are applied. For example actuator 18 can reel out a load line and 19 reel in to move corner 4a nearer to the tip of the boom. Similarly or as well, 16 could be reeled out and 17 reeled in to move corner 4c further away from the boom tip.

Preferably in of a pair of actuators 16 and 17, (or 19 and 18) the load line is reeled in by one actuator and reeled out by the other actuator by the same amount, same distance, to correct a linear error due to skew. The distance from the trolley to each of the optical targets on the spreader is measured, and the position of the optical targets relative an orthogonal axis is measured, so that one or more linear errors of position in an X or Y direction are calculated. When a linear error, such as a skew-type error, has been determined by measurement the actuators are moved a calculated distance in a linear direction to lengthen and/or shorten load lines arranged at one or more corners 4a-4d of the spreader. In this way the spreader is directly moved in a chosen linear direction by a measured amount by controlling the actuators, in order to minimize a measured or a measured and calculated linear error of spreader position.

In order to provide accurate error and fast correction the relative position of the spreader must be determined accurately and continuously. A continuous measurement means on one or more actuators is used to determine the position of each actuator at all times. An optical absolute encoder is preferred, such as the type in which the measuring system consists of a light source, a code disc mounted in a precision bearing and an opto-electronic scanning device. A light source, preferably an LED, illuminates the code disc and projects a pattern known as a track on the code disk onto the opto-array. At every position as the code disk rotates disk the opto-electronic array is partially covered by the dark track markings on the code disk. The light source transmitted through the code disk is interrupted and the code on the disc is transformed in the opto array into electronic signals. If necessary, fluctuations in the intensity of the light source may measured by additional components and/or photo-transistors. The electronic signals are then amplified, converted and output for evaluation. One or more single turn encoder suitably positioned may be used, and a best mode may be practiced using a multi-turn encoder. The multi-turn encoder may be used because more than one turn of the actuator shaft may be expected during an adjustment of the length of the load rope or load line. A multi-turn encoder may comprise several single turn encoders coupled together using a means such as a reduction gear.

FIG. 8 shows a flowchart or block diagram describing the steps that a computer program may execute in order to make a computer or processor carry out a method for load control according to an embodiment of the invention. Distance from the trolley to the spreader is measured 70, preferably continuously. When spreader position deviates from a predetermined position under the trolley, a linear deviation is calculated. If the linear deviation is determined to be a skew error, e_s then the present positions of the actuators is checked and at least one pair of actuators, such as 18 and 19, or 17 and 16, is moved 78. Which is to say that in the case or a rotated error, a skew error, one actuator of each pair reels out and the other one reels in. This pulls at least one corner of the spreader in a linear direction to reduce the error. This is best achieved by sending a signal of the same magnitude to each actuator of the selected pair, but of a different sign. Thus each actuator is driven over the same distance but in opposite directions. Measurements by the camera continue and when the present skew error has gone to zero, or another predetermined value, the movement by actuators for load control position stops. The combination of actuators used to correct a linear error in a skew direction is as described that each actuator pair parallel with the same long side moves, but in opposite directions. This may be summarized in a table form as:

	Pair	Pair	Skew error
	18, 16	19, 17	Error direction
	Reel out	Reel in	+
	Reel in	Reel out	−

In contrast to the opposed movement of specific actuators for a skew error, above, a list error for a container is corrected by application of each actuator pair parallel with the same long side moving (reeling out or reeling in) in the same direction:

	Pair	Pair	List error
	19, 16	18, 17	Error direction
	Reel in	Reel out	+
	Reel out	Reel in	−

A trim error is remedied by applying each actuator pair corresponding to each short side moving (reeling out or reeling in) in the same direction:

	Pair	Pair	Trim error
	17, 16	18, 19	Error direction
	Reel in	Reel out	+
	Reel out	Reel in	−

FIG. 7 shows a list error, in which one side of the container is rotated below the centre line by a linear distance of e_L

The corrections for errors of any of a skew, trim or list type may be applied together of subsequently. Preferably the trim or list correction is applied at a slower rate, using a lesser signal amplification in a proportional P-type loop.

FIG. 9 and FIG. 10 each show a similar flowchart for a computer program to control as that shown in FIG. 8, for skew correction. FIG. 9 for correcting a trim error specifies in contrast to the skew method shown in FIG. 8 that the at least two actuators corresponding to the same long side of a spreader, eg 4a-4c or 4b-4d, both of them move in the same direction, +ve or −ve. The skew correction method mapped in FIG. 8 points out that actuators move in opposition, ie one +ve and the other of the pair −ve. FIG. 10 shows a flowchart for correcting a list error. The actuator pairs also move in the same direction, in this case each pair corresponding to the short sides, ie 4a-4b and/or 4c-4d.

In the preferred embodiment, at least one camera member is a CCD camera. However other optical instruments may also be used, such as a laser scanner or laser range finder. In the preferred embodiment at least one optical target is an Infra Red (IR) transmitter. However other optical targets may be provided, such as: LCD diodes, fluorescent lamps or reflective targets such as reflectors, markings, patterns or high contrast surfaces on the spreader.

In another preferred embodiment the light source 7 comprises optical targets arranged in two directions. A T-shaped or even cross shaped arrangement of light sources may be used. In particular for measuring a list error, one part of the arrangement, such as 7′ of FIG. 4, 6 has a part T which may be arranged at a different height to the main linear part, as shown by the side elevation elements of FIG. 6. The difference in height between the main light sources and the light sources of the T part enable the CCD camera scanning to measure the list error more accurately because the vertical distance between the first light sources and the light sources of the T shape are already known, and deviations

In another embodiment an incremental encoder may be used as a simpler and cheaper sensor for finding actuator position. Preferably an incremental encoder or a combination of incremental encoders are used in situations where re-starts or re-configurations due, for example, to unexpected power loss or error situations are extremely rare.

One or more microprocessors (or processors or computers) comprise a central processing unit CPU performing the steps of the methods according to one or more aspects of the invention, as described for example with reference to FIGS. 3-7. The comparator may be comprised as a processor, or it may be comprised as a standard computer or processor or other device or a dedicated analogue or digital device or on one or more specially adapted computers or processors, FPGAs (field programmable gate arrays) or ASICs (application specific integrated circuits) or other devices such as simple programmable logic devices (SPLDs), complex programmable logic devices (CPLDs), field programmable system chips (FPSCs). The method or methods, such as those described in relation to the figures, especially to FIGS. 4-7, are performed with the aid of one or more computer programs, which are stored at least in part in memory accessible by the one or more processors.

The computer program comprises computer program code elements or software code portions that make the computer, processor or other device perform the methods using equations, algorithms, recursive algorithms, wireless communications parameter data, stored values, calculations and statistical or pattern recognition methods previously described, for example in relation to FIGS. 1 and FIGS. 8-10.

A part of the program may be stored in a processor, but also or instead in a ROM, RAM, PROM, EPROM or EEPROM chip or similar memory means. The program in part or in whole may also be stored locally (or centrally) on, or in, other suitable computer readable medium such as a magnetic disk, CD-ROM or DVD disk, hard disk, magneto-optical memory storage means, in volatile memory, in flash memory, as firmware, or stored on a data server. Other known and suitable media, including removable memory media such as Sony memory stick (TM) and other removable flash memories, hard drives etc. may also be used. The program may also in part be supplied from a data network, including a public network such as the Internet. The computer programs described may also be arranged in part as a distributed application capable of running on several different computers or computer systems at more or less the same time.

A graphical user interface (GUI) may be used to display one or more of the values obtained using the system and methods described above during the calculation of the position of the load of the crane. In a simple form, one or more readouts of parameters for the present container load such as speed in an X (or Y) horizontal direction, speed in a vertical direction are displayed on a screen in numerical and/or graphical representations. In particular, one or more such GUIs may be used to display relative positions of crane 1, load 15 and landing or lifting target relative to a real or graphical representation of the crane, load, landing position, truck etc in a part of a freight yard or container port. A selection action such as right-click with a computer mouse, or other computer input/selection member, on parts of the representation of the GUI may result in a display of any of: live real-time values for displacement errors of trim, list or skew type, or list or trim or visual representation of container orientation; stored values for errors in load position; configuration screens where it is possible to set or change predetermined values used in the determination of a position error, determination of a skew or list or trim error, calculation of load position. In one development of the GUI, one or more parts of the GUI may be combined on a screen together with a display of part of the operations provided by a video camera. Thus one or more parts of the GUI may be provided to give a visual readout which is superimposed over live pictures of the lifting or landing operations. In other words one or more graphical and/or numerical values for load position, trim error, list or skew error etc. may be superimposed on a live video picture while the load is being handled.

It should be noted that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention as defined in the appended claims.

Claims

1. A load control device for controlling movement of a suspended load of a container crane, said crane comprising a trolley, a spreader and load lines arranged in a four point suspension for lifting a load and an optical sensor for sensing a deflection position of an orthogonal axis of a container suspended under the spreader with reference to an imaginary center line of a said orthogonal axis of the container, the load control device comprising: two or more actuators are arranged attached to at least one load line, wherein two or more said actuators are arranged for moving at least one said suspension point closer to or farther away from said imaginary center line by shortening and/or lengthening the at least one load line, anda sensor means is arranged on at least one said actuator for detecting actuator position, and thereby any change of length of the at least one load line.

2. The device according to claim 1, wherein at least one first actuator is arranged to reel in one first part of a first load line and, at the same time, at least one second actuator is arranged to let out one second part of the first load line.

3. The device according to claim 1, wherein at least one said actuator comprises a device arranged for movement in a forward or reverse direction for reeling in or letting out part of a load line.

4. The device according to claim 3, wherein at least one said actuator comprises a device arranged for movement in a straight line in a forward or reverse direction.

5. The device according to claim 1, wherein at least one actuator comprises a screw drive powered by a motor for moving at least one load line in a substantially straight line.

6. The device according to claim 5, with at least one said actuator that comprises a screw device arranged for extending or withdrawing a shaft.

7. The device according to claim 1, further comprising: means for comparing a first actuator position and movement limits with a second actuator position and movement limits and determining which actuator shall be moved.

8. The device according to claim 1, further comprising: a control unit with a control loop for adjusting a detected deflection error to a given reference using a loop comprising input from a sensed position of at least one said actuator.

9. The device according to claim 8, wherein which control unit comprises an input for a continuous value for a position of at least one actuator.

10. The device according to claim 8, wherein which control unit comprises an input for a value for an actuator position sampled with respect to a time period or a movement increment.

11. The device according to claim 1, wherein said load control device comprises four said actuators arranged on the same side of a spreader.

12. The device according to claim 1, wherein said load control device comprises four said actuators arranged on the boom-tip side of a spreader.

13. The device according to claim 1, wherein said load control device comprises at least one rotary electric motor arranged as drive means for at least one actuator to lengthen or shorten a load line.

14. The device according to claim 1, wherein at least one actuator is powered by a motor and comprises a transmission or drive for moving a load line from any of the list of: worm gear, bevel drive, rack-and-pinion.

15. The device according to claim 1, wherein one or more hydraulically powered devices are arranged as drive means or as an actuator for moving a load line and by doing so thus lengthening or shortening the load line.

16. The device according to claim 1, wherein said load control device comprises an optical sensor arranged in line-of-sight of two or more light sources arranged on the spreader in a first straight line relative to an orthogonal axis of the container.

17. The device according to claim 16, wherein the optical sensor is also arranged in line of sight of at least one third light source arranged on a line which is perpendicular to the first straight line.

18. The device according to claim 17, wherein the at least one third light source is arranged at a different height to the light source of the first straight line.

19. The device according to claim 16, wherein the optical sensor is any from the list of CCD camera, laser scanner, laser rangefinder.

20. A method for controlling a container crane with a suspended load by means of a load control device, said crane comprising a spreader and load lines arranged in a four point suspension for lifting a load, the method comprising: sensing with an optical sensor a deflection position of an orthogonal axis of a container (or spreader) about an imaginary center line of a said orthogonal axis,optically sensing a deflection,determining a linear position of at least one said actuator, andsending a signal to at least two said actuators to move at least one said suspension point closer to or farther away from a said imaginary center line.

21. The method according to claim 20, further comprising: comparing a first actuator position and actuator movement limits with at least one second actuator position and movement limits anddetermining which actuator or actuators shall be moved.

22. The method according to claim 20, further comprising: reeling in one first part of a first load line and, at the same time, letting out one second part of the first load line and so shortening or lengthening a part of the first load line.

23. A The method according to claim 22, further comprising: reeling in in the same positive or negative direction two actuators of a pair of actuators corresponding to one same side of the spreader.

24. A The method according to claim 23, further comprising letting out a load line both in the same positive or negative direction two actuators of a pair of actuators corresponding to one same side of the spreader.

25. A The method according to claim 20, further comprising: driving at least one actuator with a motor arranged with a screw device.

26. The method according to claim 25, further comprising: driving at least one actuator with a motor arranged with a screw device for extending, withdrawing a shaft arranged attached to a load line.

27. A The method according to claim 20, further comprising: continuously determining a position of at least one actuator.

28. A The method according to claim 20, further comprising: determining a position of at least one actuator by means of samples dependent on a time period or a movement increment.

29. A The method according to claim 20, further comprising: measuring with the optical sensor a distance to two or more light sources arranged on the spreader in a first straight line relative to an orthogonal axis of the container.

30. The method according to claim 20, further comprising first straight line on the spreader and measuring any linear deviation from the orthogonal axis in an X or Y direction.

31. The method according to claim 30, further comprising: measuring with the optical sensor a distance to at least one third light source arranged on a line perpendicular to the first straight line and determining a list error.

32. The method according to claim 31, further comprising: determining a distance to the at least one third light source,calculating a list deflection of the container, anddetermining a common movement of a pair one or more said suspension points to correct the list error.

33. The method according to claim 15, further comprising: measuring a distance to each of the light sources from the optical sensor,measuring a linear deflection, a trim error of the spreader, anddetermining a common movement of a pair of one or more said suspension points to correct the trim error.

34. The method according to claim 20, further comprising: controlling said container crane by means of running one or more computer programs in at least one computer or processor.

35. A computer program product, comprising: a computer readable medium; andcomputer program instructions recorded on the computer readable medium and executable by a computer or processor to cause the computer or processor to carry out a method comprisingsensing with an optical sensor a deflection position of an orthogonal axis of a container or spreader about an imaginary center line of said orthogonal axis,optically sensing a deflection,determining a linear position of at least one said actuator, andsending a signal to at least two said actuators to move at least one suspension point closer to or farther away from said imaginary center line.

36. (canceled)

37. A system for controlling movement of a suspended load of a container crane, said crane comprising a trolley, a spreader and load lines arranged in a four point suspension for lifting a load, the system comprising: an optical sensor for sensing a deflection position of an orthogonal axis of a container suspended under the spreader with reference to an imaginary center line of a said orthogonal axis of the container,two or more actuators arranged attached to at least one load line, whereni the two or more actuators are arranged on the same side of the spreader andat least one actuator means is arranged with sensor means for measuring a linear movement of the actuator.

38. The system according to claim 37, further comprising: means for determining a linear position of at least one said actuator, andmeans for sending a signal to at least two said actuators to move at least one said suspension point closer to or farther away from a said imaginary center line.

39. The system according to claim 37, further comprising: means for comparing a first actuator position and actuator movement limits with at least one second actuator position and movement limits, andmeans for determining which actuator or actuators shall be moved.

40. The system according to claim 37, further comprising: one or more graphical user interfaces for displaying or manipulating data dependent on a linear position or movement of at least one said actuator.

41. The system according to claim 37, further comprising: at least two or more light sources are arranged in a first straight line on the spreader.

42. The system according to claim 41, wherein at least three light sources are arranged on the spreader or on the crane.

43. The system according to claim 37, wherein at least one sensor means is of the type known as an optical encoder.

44. The system according to claim 43, wherein at least one sensor means is of the type known as an incremental or an absolute encoder.

45. The system according to claim 43, further comprising: means for generating a signal for any pair of actuators such that each actuator receives a signal for linear movement which has the same value but is of opposite sign.

46. A graphical user interface of a human-machine interface for a user to monitor or control a suspended load of a container crane, said crane comprising a trolley a spreader and load lines arranged in a four point suspension for lifting a load and an optical sensor for sensing a deflection position of an orthogonal axis of a container suspended under the spreader with reference to an imaginary center line of a said orthogonal axis of the container, the graphical user interface comprising: means for displaying numerical data dependent on determining a linear position of at least one said actuator, and sending a signal to at least two said actuators to move at least one said suspension point closer to or farther away from a said imaginary center line.

47. A The graphical user interface according to claim 46, further comprising means for displaying the numerical data for speed, and/or position combined on the same display with any from the list of: real time video, graphic representations of the crane, graphic representations parts of the crane, graphic representations of speed and/or position.

48. The graphical user interface according to claim 46, further comprising: means for providing a display comprising representations of a position and/or speed of the suspended load for the current container comprising any from the group of: real time values, simulated values, previous values.

49. Use of a load control device according to claim 1 for controlling movement of a suspended load of a ship-to-shore container crane for handling freight containers.

50. Use of a system for load control according to claim 37 for controlling movement of a suspended load of a ship-to-shore container crane for handling freight containers.