WO2010109075A1 - Method for controlling a suspended load - Google Patents

Abstract

The invention relates to a method for controlling a crane when moving a load. According to the invention, image-numerical data on two differing load positions, created by a camera, is used, and the movements of the crane are controlled by comparing the said two data.

Description

Method for controlling a suspended load

The present invention relates to a method for controlling a suspended load and more specifically for controlling a load, in which the load is suspended on a cable or similar.

One typical example of the situation to which the invention relates is using it to control a crane. Cranes are generally controlled from a controller or a separate control cabin. A crane can be controlled using a pendant control panel, press- buttons, sidesticks, or some other devices, by means of which both direction and operating information and possibly, if necessary, speed information can be given simultaneously. The aim is generally to control one direction with one hand or finger.

In stepless transfers too, a minimum run speed is used, so that at even a slow transfer speed acceleration will always cause some degree of oscillation in the mass being moved. Attempts have been made to limit the oscillation of the load being moved with the aid of oscillation-damping methods. The methods can be mechanical, feedbackless, or with feedback implemented using power sources of various power systems, such as electrical, hydraulic, or pneumatic.

In the smallest devices, oscillation-damping systems are generally not used, due to their price, the small advantage obtained, and the complexity of the systems. The said system can also be relatively easily replaced by holding the load by hand or with other tools.

It is generally accepted that the oscillation of the mass being moved reduces accuracy and leads to time-consuming additional work, especially when during starting and arrival.

The present invention is intended to create a method that is easy to use, functional, and cost-effective. The characteristic features of the invention described are stated in the accompanying Claims. The method according to the invention now provides an arrangement, according to which a load to be moved can be controlled by damping the load, to create a situation, in which the load will not start to sway during the transfer, for example, using a two-speed transfer, or even using a nearly so-called stepless transfer.

In brief, the invention is based on a method, in which the load being moved, or the lifting device's hook, grab, or other element, which hangs from the lifting device, with the aid of a rope, chain, or other similar supporting element, is positioned by imaging. The movements of the load are followed in the form of images, so that guiding in a certain direction takes place by moving the load and drawing conclusions of the future control commands for the controlling element on the basis of this.

In terms of productivity and the available work time, it can be demonstrated that, in repeated transfer tasks, the savings accruing from the increased efficiency in a load's transfer movement will exceed the costs incurred by the method disclosed in the present invention, if the method according to the invention is used.

When moving products by hand, and setting them precisely in place, the movement in the device according to the invention takes place with the greatest control when the product being transferred is in the 'compression' arising to the horizontal force according to the rope angle (αx, αy).

Fx = g * tan(αx) = g * tan(Δ x / Δ h) Fy = g * tan(αy) = g * tan( Δy / Δh)

The said situation is illustrated in Figure 1 , which shows one schematic device envisaged for implementing the invention. This form of implementation has been envisaged as being implemented using an overhead crane.

In Figure 1, the side beams of the overhead crane are marked with the reference numbers 1 and 2. The beam drive motors 3 and 4 are intended for conventional transfers. The hoist 6 performs its own raising/lowering task according to the control and moves with the aid of drive motor 5 on a track 7. The aforementioned operations are conventional in crane technology. A camera system, described in greater detail hereinafter, is suitably located in association with the hoist, being at least almost directly above the load 8, the mass of which is g.

All movements are illustrated in a three-dimensional set of axes X-Y-Z. The letter X is used to mark the carriage transfer direction, Y signifies the beam transfer direction while for its part Z is used to mark the lifting direction, parallel to which the camera is installed. Following conventional marking, Δx is used to mark a horizontal deviation in the direction of the X axis from the vertical Z position. Δy is used to mark a horizontal deviation in the direction of the Y axis from the vertical Z position. For its part, Δh marks the distance of the load's centre of gravity from the attachment point of the lifting rope, αx and αy signify deviation angles.

Imaging positioning is performed using a camera, the real-time view (image) taken of the object being through the camera's optics from a photosensitive CCD cell to the image-processing system of a computer. In the image-processing system, analyses are created of the image, with the aid of which various analyses can be made of the image information of the real-time view.

In the system according to the invention, the camera on a) is below the hoisting device or the device carrying the load, and is aimed at the hoisting device or the load to be lifted, or b) located in the hoisting element or the load itself to be transferred and is aimed at the lifting device or the structures carrying the load. From either position, a similar image showing relative movement can be obtained.

All in all, the important thing is that the mutual position of the load and the structures from which the load hangs can be determined.

The person performing the transfer grips the buttons of the controller handle, or the controller intended for the transfer of the load attached to the lower end of the lifting rope carrying the load. When the transfer start and continue buttons are pressed, and the load is still suspended in place in a stable state of equilibrium, the image-processing system models the image according to the relevant real-time situation. The sub-area of the load being moved is delimited automatically, experientially, or in some other manner, as a sub-area of the image area depicting the carrying hoisting element or the entire load, to form a model in the computer's memory. When the load is moved, the computer retrieves the modeled image area, calculates the deviation of the direction and magnitude relative to the initial situation, and creates from the result control commands for instructing opposite- direction transfer movements, for the control system operating the control of the crane.

When the load being moved is pushed away from the state of equilibrium, the force increases, by which the load is made to deviate from the state of equilibrium, relative to the angle of the supporting rope. On the other hand, when the supporting structure receives a speed and direction control message according to the corresponding direction, the angle of the rope correspondingly continuously tends towards its state of equilibrium and, because the angle decreases, the magnitude of the speed instruction also decreases as the state of equilibrium is approached, at which the control is stopped in a controlled manner.

By means of the method, the forces required to control the load remain smaller and more easily controlled than be performing traditional control methods while the transfer movement is terminated in a controlled manner and precisely from above the load being moved.

The system is particularly useful in work stages, in which the mass of the hoisting device supporting the load is fairly large relative to the mass being moved.

In a case in which the modeled image area cannot be found from the continuous image flow, the measurement result will correspond to a zero result and the transfer speed will begin to decrease, finally stopping the transfer movement within the set time of the transfer device's slowing ramp. In this situation, the supporting structures of the transfer device are, however, only lagging behind and the unpredicted stopping takes place at the correct time in terms of the operations of the person performing the work, though not necessarily at the desired position.

There may be many reasons for not finding the taught image area, but in a building crane upper-storey structures may come surprisingly between the camera and the object being imaged, so that stopping will exactly the correct operation.

A problem with existing control systems in a corresponding situation would be the load lagging behind while the supporting structures would continue to move forward relative to the position of the load being moved and the angle error between the supporting structures are the load would only increase, despite the obstacle, which could lead to an increased danger.

Thus, by using a camera, which monitors the position of the hoisting element of the transfer device, it would also be possible to check that a) the lifting rope or similar has not struck an obstacle, or b) that the sway of the hoisting element has not grown too large (Close Loop Anti Sway).

The sensitivity of the load transfer can easily be adjusted by the camera optics and control-technology methods, so that small changes in the mass point of even a heavy mass can be detected precisely.

To make it possible to eliminate the effect of bending in the supporting structures and similar forces, the camera used for positioning the load should be suspended in the opposite direction to the direction of viewing, so that it will remain parallel to the original neutral axis of the object. The camera for a vertically suspended load should be allowed to rotate on bearings relative to both the X and Y axes.

The free mounting in bearings of the camera is particularly important when controlling a boom-crane type device, in which the boom can typically have pre- rising and the end of which bends down to a greater extent than the base of the boom, depending in addition on the boom's supporting structures. Because the movement correction can take place on the horizontal plane (X/Y), both axes of the camera according to the image area should be mounted in bearings and attenuated against the effects of, for instance, wind and deformations in the supporting structure.

The sensitivity of the bearings can be attenuated hydraulically, electrically using servo motors controlled by a modern gyroscope, or using an electric motor and the gyroscopic effect of a flywheel, to mention a few attenuation methods used to maintain the vertical attitude of the camera.

A drawback in a servo apparatus based on a gyroscope is the device's own slowness, its fault susceptibility, and its need of electricity.

The operating principle of both a gyroscope and a flywheel is based on the law of inertia. The inertia of the rotating mass resists changes from a vertical attitude according to gravity, in the velocity and direction of cameras suspended in bearings. Attenuation of the oscillation of the camera to correspond to the motion being studies is of very great importance precisely in the acceleration and deceleration stages.

Above, the emphasis has mainly been on systems, in which the camera is located facing downwards in the crane boom. Another alternative is naturally that the mutual positions of the load and crane are detected by placing the camera, for example, on a grip and orienting it permanently upwards to the load-bearing structures.

By using standard electronic solutions, the system according to the invention will be very precise. Of course, many procedures exist, by which precision can be increased, but in usual crane operation, for example, conventional precision will suffice.

The invention is described above with reference to crane operation the whole time. However, it is obvious that the fields of application of the invention are very much wider that crane operation. For example, it is possible to take any load whatever, for instance a heavy tool, the suspension and transfer of which in the work area could easily be arranged with the aid of the method according to the invention. Instead of proceeding in the traditional manner, i.e. controlling the transfer motors using separate switches, according to the invention it would be enough for the work machine that is the load to be moved towards the desired location and the operation would be automatic. However, for safety reasons there should be one operating switch in the system according to the invention, which could be pressed to prevent the control from being implemented at all. This is so that accidental movement of the load would not cause it to be moved under control.

Though the system is depicted in a 'natural' scale above, it is quite possible to upscale or downscale it. This also means new dimensions for it, in that the method could also be used in very small or large applications.

If the use of the invention is contemplated in different conditions, there will quite often be a need to move the load on essentially a horizontal plane. In that case, the three-axis observation described above could be reduced to observation on a two-axis plane. In such a situation, the system would be simplified considerably, as one axis of the system could be left out of account. Two-axis observation would be clearly easier and cheaper to implement than three-axis observation.

Claims

Claims

1. Method for controlling a hoisting device lifting a load, in which hoisting device there is a bridge, boom, or similar, to which the a grab element for gripping the load is attached movably by means of a lifting arm, rope, or similar, in which case at least one detector connected to a computer, for monitoring the movements of the grab element and the load attached to it, is located, with the aid of which information on the area observed by the detector is created, characterized in that the detector is a camera, with the aid of which a first image numerical datum of the initial state is created, the load is moved by hand or with the aid of a tool to move in a desired direction, a second image numerical datum is created of the new position of the load, from the data obtained the direction and magnitude of the movement of the load is calculated, and the hoisting device is controlled on the basis of the information obtained.

2. Method according to Claim 1 , characterized in that the hoisting device is controlled by seeking to restore the second datum position to be same as the position of the first image numerical datum.

3. Method according to Claim 1, characterized in that a CCD or RGB camera is used as the detector.

4. Method according to Claim 3, characterized in that a camera, in which there is zoom optics, is used as the detector.

5. Method according to Claim 1 , characterized in that the detector is located on the boom of a crane in a manner stabilizing in a vertical attitude.

6. Method according to Claim 1 , characterized in that, from the said second image numberical datum, the angles ( αx, αy) of the load/gripper are determined relative to the position in the initial situation, and the said data are given to the control system of the crane or similar, in order to guide it in the desired direction at the desired speed.

7. Method according to any of the above Claims, characterized in that the transfer device, such as a crane, is instructed to stop automatically, if the second image numerical datum cannot be detected.

8. Method according to any of the above Claims, characterized in that the stability of the camera is ensured by means of hydraulic methods based on a gyroscopic effect, or with the aid of a gyroscope.

9. Method according to any of the above Claims, characterized in that the control of the method starts only after an 'enable' command permitting its operation.