EP3169618B2 - Fill degree control for a bulk material gripper of a crane - Google Patents

Description

The invention relates to a method for filling a gripper for bulk material according to the preamble of claim 1.

It is common knowledge that grabs are used to handle bulk materials such as ore, coal, grain, gravel or sand. These grabs, also known as two- or multiple-shell grabs, have a size, shape and number of shells that are optimized for the bulk material to be handled. This ensures that the grabs penetrate the bulk material well, fill with the bulk material and can be easily emptied by it. The grabs are usually placed on the bulk material in an open position, sink into the bulk material under their own weight and during a closing movement the grabs grasp the bulk material and fill themselves with it. The grabs are closed hydraulically or via cable drives.

From the German patent DE 199 55 750 B4 is a crane with a grab for bulk material. The grab is designed as a so-called four-rope grab. Accordingly, there are two holding ropes and two closing ropes that can be moved independently of one another in order to open, close, raise and lower the grab. The holding and closing ropes are driven separately via two rope drums. To open the grab, the closing ropes are relieved and the grab only hangs on the holding ropes. The holding ropes engage a lever mechanism on the grab and, in conjunction with the grab's own weight, cause the grab to open. To fill the grab, the open grab with the closing rope slack is placed on the bulk material over the holding ropes. The holding rope is then released in order to allow the grab to sink into the bulk material under the effect of its own weight. The holding rope is then released. The grab is then closed by tightening the closing ropes, which fills it and is then lifted by the closing ropes after the grab has closed. In parallel, the holding ropes must be tightened to avoid slack ropes. In the area where the gripper is being lifted, the forces in the holding and closing ropes are then adjusted to one another again using appropriate controls, so that the subsequent lifting takes place together with the holding and closing ropes.

Usually, data on the bulk material density, the grab volume and the grab's own weight are not included in the crane control system. Under the rough operating conditions of the grab, the grab's fill level is only taken into account indirectly using empirical values.

From the DD288138A5 A method for preventing overloading of a gripper suspended from holding ropes and closing ropes is already known. During the closing process, a tensile force acting in the closing ropes and in the holding ropes is measured and the difference is compared with a target value for the tensile force acting in the closing ropes. If the difference exceeds a specified value for the target closing force, the holding motor is activated, which raises the gripper, which is not yet fully closed, and closes it further. In this way, the effect of the gripper's own weight, with which the gripper acts on the bulk material during closing and filling, is reduced and the fill level of the gripper is influenced.

Furthermore, the EP 0 458 994 A1 A tension control for the gripper ropes of a bulk material handling device, which comprise holding ropes and closing ropes, is known. In order to avoid a jolt caused by slack holding ropes when closing the gripper, the holding tension is regulated accordingly. However, the holding tension is regulated in such a way that the effect of the dead weight on the bulk material is not reduced during the closing process, since the gripper is only raised when it is completely closed. The tension control therefore does not influence the level of filling of the gripper.

In the DD 244 962 A1 A method for controlling the material pick-up for an automated gripper operation is described. During the gripper closing process, a gripper opening angle and a closing time of the gripper placed on the bulk material are monitored. If the gripper cannot be closed to a specified extent within a specified time during the closing process, the closing process is interrupted and a lifting mechanism is activated to lift the gripper from the bulk material. The closing process is then started again and checked to see whether it can be carried out as specified.

From the European patent specification EP 2 226 287 B1 A method is known for filling a gripper suspended from holding ropes, the gripper filling volume of which is influenced by regulating a holding torque of a holding mechanism for the gripper in such a way that a gripping curve of the gripper is raised during the closing process.

The invention is based on the object of creating a method for the optimal filling of a gripper for bulk material, which is raised and lowered by a crane via a control system and which acts on the bulk material with its own weight during closing and filling.

The object is achieved by a method for filling a gripper for bulk material with the features of claim 1. Advantageous embodiments of the invention and a use of the invention are specified in the subclaims.

According to the invention, in a method for filling a gripper for bulk material, which is suspended on holding ropes, is raised and lowered by a crane via a control system and which acts on the bulk material with its own weight during closing and filling, wherein a filling level of the gripper is influenced by reducing the effect of the gripper's own weight on the bulk material by influencing a tensile force acting in the holding ropes, an optimized filling level of the gripper is achieved by determining a tensile force target value for the holding ropes via the control system, the tensile force target value is output as an input variable to a tensile force controller, the tensile force controller controls an electric motor for raising and lowering the gripper and a determined tensile force actual value of the holding ropes is fed to the tensile force controller as an input variable. This also avoids overload shutdowns.

This invention advantageously makes it possible to control the filling level of a bulk material grab. This means that an excessive number of overload shutdowns are avoided when a crane with a bulk material grab is in operation, thus increasing the crane's handling capacity. Such overload shutdowns occur when the grab penetrates very deeply into the bulk material to be lifted during grab operation, thus taking too much bulk material into the grab. This alone can lead to an overload shutdown of the crane if the grab takes in more bulk material than the crane can lift. In combination with a large crane radius, this effect is intensified because the crane's permitted load capacity decreases, making overload even easier to reach, and in turn leading to an overload shutdown of the crane. If the grab is undersized in relation to the crane, such overload shutdowns of the crane can only occur if the crane radius is large. Since the handling capacity of the crane is always optimized from an economic point of view, a crane is more likely to be operated within the range of its permitted load capacity and thus with a grab that can achieve an optimal filling level over the entire outreach range. In other words, one that is slightly oversized in relation to the load capacity of the crane or optimally dimensioned in relation to small outreaches. This means that a grab used is more likely to be overfilled in relation to the crane and thus the method according to the invention, which aims to specifically reduce the effect of the grab's own weight, can intervene. It is also possible to use grabs that are too large in relation to the load capacity of the crane and the bulk density of the bulk material to be conveyed, since these are only partially filled using the invention. The influence on the tensile force acting in the holding ropes, which is carried out in order to reduce the effect of the gripper's own weight on the bulk material, in particular during the closing process of the gripper, is therefore carried out to such an extent that the gripper penetrates less deeply into the bulk material than it would do under its own weight alone.

In practice, the control system according to the invention made it possible to reduce the number of overload shutdowns by 90%, while increasing handling capacity.

A load capacity within the meaning of the invention consists of the dead weight of the grab, the bulk material picked up and, in the case of a rope grab, the dead weight of the rope between the boom tip and the grab.

According to the invention, it is also provided that a point in time of a change in the tensile force target value and a step size of a change in the tensile force target value are fed into the control system via a trend module based on the progression of the determined loads. By integrating the trend module, Based on stored empirical values - such as handling a comparable bulk material with the current grab - and the filling levels recorded during the crane's handling operation, an optimal filling level can be achieved more quickly and overloads can be safely avoided. The changes in the target tensile force value are dynamically adjusted during the closing process so that the load curve is used optimally in the entire radius range or outreach range and overloads are avoided or at least minimized.

In an advantageous embodiment, it is provided that the tensile force target value is increased via the trend module if the frequency of overload shutdowns exceeds a preselected value related to the load cycles and/or if the frequency of exceedances of the maximum permissible load exceeds a preselected value related to the maximum permissible load for a given radius.

In an advantageous embodiment, it is provided that the tensile force target value is reduced via the trend module if the frequency of overload shutdowns falls below a preselected value related to the load cycles and/or if the frequency of exceedances of the maximum permissible load falls below a preselected value related to the maximum permissible load for a given radius.

In a particularly advantageous embodiment, it is provided that the gripper is subjected to the actual tensile force value directed in a lifting direction via the crane by means of the control during closing and filling.

In order to avoid any overloading of the crane, the control system determines the filling level of the grab from a load determined immediately after the filled grab is lifted and the known dead weight of the grab.

The determination of the filling level is made more precise by the fact that a length of a free rope starting from the gripper and in the lifting direction is fed to the control system via a rope length module as an input variable, in the control system when calculating the filling level of the gripper, the gripper's own weight is also taken into account. a dead weight of the free rope is added.

Cranes for handling bulk materials usually have a luffing boom, so that the crane's reach changes during handling and the corresponding luffing of the boom. To take this into account, it is advantageous to provide the control system with a maximum permissible load dependent on the reach of the grab via a load curve module as an input variable for the crane. The control system therefore has the maximum permissible load in order to detect overload cases and determine the level of filling of the grab.

It is also advantageous that a nominal tensile force value is manually entered into the control system as an input value via a start value module. In particular, after a gripper has been changed or when starting a new handling task with bulk material of a different density, the start value can be entered based on experience. This allows the control system to reach an optimal filling level of the gripper more quickly.

In a preferred embodiment, the tensile force target value is iteratively reduced or increased in the control system based on the input variables from the load curve module, the rope length module and the determined load until the filling level of the gripper is in the range of 100%.

The use of the above-described method according to the invention is particularly advantageous for a crane with a gripper that is raised, lowered, opened and closed via holding ropes and locking ropes.

The control underlying the method according to the invention is also considered to be independently inventive and its use is accompanied by the advantages described above for the method.

• Figur 1 eine Ansicht eines Hafenkrans mit einem Greifer für Schüttgut,
• Figur 2 eine Traglastkurve eines Hafenkrans gemäß Figur 1,
• Figur 3 eine vergrößerte Ansicht des Greifers für Schüttgut von Figur 1 und
• Figur 4 eine schematische Darstellung einer Steuerung zur Optimierung des Füllgrads des Greifers für Schüttgut.

The invention is explained in more detail below using an embodiment shown in a drawing.

• Figure 1 a view of a harbor crane with a grab for bulk goods,
• Figure 2 a load curve of a harbour crane according to Figure 1 ,
• Figure 3 an enlarged view of the bulk material grab from Figure 1 and
• Figure 4 a schematic representation of a control system for optimizing the filling level of the grab for bulk material.

The Figure 1 shows a view of a mobile harbor crane 1 for handling bulk goods 14, such as ore, coal, grain, gravel or sand, between land and water or within handling terminals. The mobile harbor crane 1 is equipped with a gripper 2 for handling bulk goods and essentially consists of a tubular base 3 and an upper carriage 4 with a tower 5 and a boom 6. The base 3 is firmly mounted on a floating pontoon 7. Instead of the base 3, an undercarriage can also be provided, which rests on a quay for the handling process and can be moved on the quay via rubber tires or on rails. The upper carriage 4 is rotatably mounted on the base 3 and can be pivoted about a vertical axis of rotation d via a slewing gear (not shown). The upper carriage 4 also carries a lifting gear 8 in a rear area of the upper carriage 4, in which a counterweight 9 is also located. The tower 5, which extends in the vertical direction, is also supported on the upper carriage 4, to the top of which a roller head 10 with cable pulleys is attached. Furthermore, the boom 5 is articulated on the tower 5 approximately in the area of its half length and on the side facing away from the counterweight 9. The boom 5 is connected to the tower 4 at one end so that it can pivot about a horizontal luffing axis W. The boom 6 can be pivoted by a luffing angle w from its multitude of laterally projecting operating positions into an upright rest position via a luffing mechanism 11, which is articulated on the boom 6 and at the bottom of the upper carriage 4 and is usually designed as a hydraulic cylinder. The boom 6 is also usually designed as a lattice mast. Further cable pulleys are rotatably mounted on the boom tip 6a of the boom 6 facing away from the tower 4, via which holding cables 12 and closing cables 13 are guided to the gripper 2, starting from the hoist h, via the roller head 10 and the boom tip 6a.

The luffing angle w is enclosed between a vertical V that runs through the luffing axis W and a straight line G that runs in the area of an upper chord of the boom 6 and through the luffing axis W. Typically, a change in the luffing angle w is accompanied by a change in the outreach a of the crane 1, which is related to the maximum load of the crane 1. The outreach a corresponds to a horizontal distance between the vertical V through the luffing axis W and a rope direction S that is also vertical. The rope direction S coincides with the free holding and closing ropes 12, 13 that run from the boom tip 6a and swing out. In addition, the rope length I indicates a dimension for the freely hanging section of the holding and closing ropes 12, 13 between the boom sprayer 6a and the grab 2.

In addition, the Figure 1 It can be seen that a ship 15 loaded with bulk goods 14, in particular a lighter, a barge or a skiff, can be loaded or unloaded by the crane 1.

In the Figure 2 a so-called load curve of the port crane 1 is shown. The load curve shows the maximum permitted load of the crane 1 in tons over the outreach a in meters. Here, two load ranges I and II can be roughly distinguished. In the first load range I, due to the dimensioning of the crane 1 in the range of a outreach of 0m to about 38m, no reduction in the maximum permitted load capacity of around 63t. From a radius a of around 38m up to a maximum radius of around 51m, the maximum permitted load capacity decreases with increasing radius a. This area is defined as the second load capacity area II. In connection with the control system according to the invention, the second load capacity area II has been divided into a first load capacity sub-area II1, second load capacity sub-area II2, third load capacity sub-area II3 and fourth load capacity sub-area II4. Based on this load capacity curve, an overload is defined as exceeding the maximum permitted load capacity by around 10%.

In the Figure 3 is an enlarged view of the grab 2 for bulk material from Figure 1 shown. The gripper 2 has two shells 2a and is designed as a four-rope gripper which is suspended from two holding ropes 12 and two closing ropes 13. The holding and closing ropes 12, 13 can be wound up and unwound independently of one another from two rope drums arranged within the lifting mechanism 8, which are separate from one another and driven separately via holding and closing winches, in order to open, close, raise and lower the gripper 2. In order to open the gripper 2, the closing ropes 13 are relieved and the gripper 2 only hangs from the holding ropes 12. The holding ropes 12 engage a lever mechanism 16 of the gripper 2 and, in conjunction with the weight of the gripper 2, cause the gripper 2 to open. For filling, the opened gripper 2 with the closing rope 13 slack is placed onto the bulk material 14 via the holding ropes 12. In order to allow the gripper 2 to sink into the bulk material 14 under the effect of its own weight, the holding cable 12 is then released. The gripper 2 is closed by pulling the closing cables 13 in the lifting direction h. By closing the shells 2a of the gripper 2, the gripper fills with the bulk material 14 and can also dig into the bulk material 14. When digging in, a tension regulator 18 for the holding cables 12, which also serves as a slack cable regulator and is part of a control system 17 (see Figure 4 ), only the holding cables 12 are held under tension so that the gripper 2 can sink into the bulk material 14 under its own weight. The holding cables 12 are only held under tension as long as the closing cables 13 are closing the gripper 2. The gripper 2 also fills with bulk material 14 as a result of the closing process. After the gripper 2 has been closed, it is lifted by the closing cables 13. In parallel, the holding cables 12 are then tightened to prevent slack in the cable. In the area where the gripper 2 is lifted, the forces in the holding and closing cables 12, 13 are then adjusted to one another again using an appropriate control system so that the subsequent lifting takes place together with the holding and closing cables 12, 13.

If too much bulk material 14 is picked up during the gripping process, the total load may be too high in relation to the maximum permissible load, taking into account the current radius a. This total load is essentially made up of the weight of the bulk material 14 picked up, the weight of the gripper 2 and the weight of the free rope length I of the holding and closing ropes 12, 13. If the total load is too high, a load moment limiter 20 (see Figure 4 ) further lifting of the load is stopped in order to protect the crane. This total load can be determined, for example, in the form of a load force FLast via strain gauges on a cable drum of the hoist 8 and is available to the load moment limitation 20 as an input variable. This overload shutdown is logged in a crane database 21. As described at the beginning, overload shutdowns can occur more frequently during crane operation if the load capacity of the crane 1, bulk material density, grab volume and grab weight are not coordinated with one another. This is often the case if grabs 2 with too large a grab volume are used in relation to the bulk material 14 to be conveyed. When the crane 1 is in operation, however, the choice of grab 2 used is not always optimal.

If so much bulk material 14 is picked up by the gripper 2 during the gripping process that the measured total load is below the maximum permissible load, a payload and the total load when opening the gripper 2 at the target position are recorded in the crane database 21. The payload in terms of the weight of the bulk material 14 picked up is calculated from the total load minus the dead weight of the gripper 2 and the weight of the free rope length I of the holding and closing ropes 12, 13. A completed load cycle without an overload is then also recorded in the crane database 21.

The Figure 4 shows a schematic representation of a control 17, in particular a programmable logic controller, for optimizing the filling level of the gripper 2 for bulk material 14, based on which the function of the control 17 is explained in more detail. With the help of the control 17, the goal is achieved of independently adjusting the filling level of the gripper 2 with bulk material 14 depending on the load curve of the crane 1. The filling level of the gripper 2 is optimally utilized without overloading the crane 1 with regard to its load curve.

The controller 17 outputs a tensile force target value Fsoll for the holding cables 12 as a control variable, which serves as an input variable for the tensile force controller 18. Using this tensile force target value Fsoll, the tensile force controller 18 controls an electric motor 19, which drives a cable drum (not shown) for the holding cables 12. As a further input variable, the tensile force controller 18 is fed an ACTUAL tensile force value Fist, which corresponds to a measured tensile force in the holding cables 12. The ACTUAL tensile force value Fist is determined from the current data of the electric motor 19, in particular the motor current.

The input variables of the control 17, which is represented as an addition module and works, are a crane database 21, a rope length module 22a, a load curve module 22b, a start value module 22c and a 22d tendency module 22d is assigned. Within the rope length module 22a, the rope length I is determined which is present between the gripper 2 and the boom tip 6a shortly before the gripper 2 is placed on the bulk material 14. This can then be used to determine the dead weight of the holding and closing ropes 12, 13. The control 17 receives data on the maximum permissible load (SWL, safe working load) as a function of the radius a via the load curve module 22b. The radius a is determined in the usual way via the measured luffing angle w. The start value module 22c serves as an additional input variable, via which a start value for the tensile force DESIRED value Fdesired can be entered manually. This is helpful after a gripper change in order to reach an optimal filling of the gripper 2 more quickly. There is also the trend module 22d, in which trends are determined from determined utilizations in relation to the maximum permissible load, which lead to an increase or decrease in the nominal tensile force value Fsoll. The trends can be set on the basis of empirical values. In particular, the trend module 22d determines the number of overload shutdowns, which correspond approximately to a utilization of more than 110% of the maximum permissible load.

The control system 17 represents an iterative process in which the filling level of the gripper 2 adjusts to the load-bearing capacity curve. Starting with an overload shutdown due to an excessive load in the gripper 2, the outreach a and load-bearing capacity are saved. When the gripper 2 penetrates the bulk material 14 again, its holding cables 12 are subjected to a preselected tension load corresponding to the outreach a in order to achieve a less deep penetration of the gripper 2 into the bulk material 14 due to its own weight. In this way, the gripper 2 picks up less material and the crane 1 can be operated without an overload shutdown depending on the size of the preselected amount. Since the penetration of the gripper into the material depends on various factors, the preselected amount is recalculated for each gripping process.

During handling operations, trends are formed in the control system 17 on the basis of the data recorded in the crane database 21 on the current handling operation regarding the number of overload shutdowns and the number of load cycles. If these trends result in a frequency of overload shutdowns that exceeds a preselected value in relation to the load cycles, the tensile force target value Fsoll is increased in the control system 17. These trends can be related to an exceedance of the maximum permissible load for the given radius a, so that an increase in the tensile force target value Fsoll can occur even if the maximum permissible load is exceeded one or more times within a predefined number of load cycles, without overload shutdowns having already occurred. If this increase is not sufficient because the frequency of overload shutdowns or exceedances of the maximum permissible load, which exceeds a preselected value in relation to the load cycles, still exists, the tensile force target value Fsoll is increased further. As a result, the tensile force target value Fsoll is incremented until the frequency of overload shutdowns or exceedances of the maximum permissible load, which no longer exceeds the preselected value in relation to the load cycles.

If, during the handling operation, the trends formed in the control system 17 result in a frequency of overload shutdowns or exceedances that does not reach a preselected value in relation to the load cycles, i.e. in other words, corresponding undershoots, the traction force target value Fsoll is reduced in the control system. If this reduction is not sufficient because the frequency of overload shutdowns has not yet reached a preselected value in relation to the load cycles, the traction force target value Fsoll is further reduced. As a result, the traction force target value Fsoll is incremented downwards until the frequency of overload shutdowns reaches the preselected value in relation to the load cycles.

The extent to which the tensile force target value Ftarget is increased or decreased in the control system 17 and how quickly the system reacts to the change in trend can be parameterized in the control system 17. This allows the control system 17 to be adapted to the crane 1, the load curve of the crane 1, the bulk material density, the grab volume and the grab's own weight.

The tensile force target value Fsoll is also increased when the selected load curve is sufficiently utilized. This prevents the overload limit values from being exceeded. This is done via a corresponding fuzzy logic in the control system 17. This increase in the tensile force target value Fsoll also serves to sufficiently pre-tension the holding ropes 12 at the end of the closing process of the gripper 2 so that when the gripper 2 is almost closed, the load is distributed across all four ropes 12, 13 and thus no "dead time" occurs when the gripper 2 is raised.

In addition, the tensile force target values Fsoll are automatically adjusted to take into account the free rope length I of the holding and closing ropes 12, 13. The tensile force target values Fsoll are increased proportionally depending on the rope length I as the rope length I increases and decreased as the rope length I decreases. This proportional adjustment of the tensile force target values Fsoll leads to a compensation of the tensile forces that arise due to the dead weight of the holding and closing ropes 12, 13.

A further automatic adjustment of the nominal pulling force values Fsoll occurs when the radius changes and thus the maximum permissible load changes.

It is also possible for the crane driver to manually enter a nominal pulling force value Fsoll into the control 17, which is then saved and used as a starting value for the control 17. This manual value supports the crane driver when heavy loads are to be handled by pre-setting the nominal pulling force value Fsoll to a value without first determining the overload tendency or the tendency to exceed the limit.

With regard to the evaluation of the trends in the control system 17, which leads to a calculation of the nominal tensile force value Fsoll, it is intended that this takes place taking into account the load curve with the first load range I, the first load sub-range II1, the second load sub-range II2, the third load sub-range II3 and the fourth load sub-range II4. In the first load range I, the maximum permissible load is not dependent on the outreach. A correction of the nominal tensile force value Fsoll therefore does not take place. The non-linear second load range II is divided into the load sub-ranges II1, II2, II3 and II4. In the control system 17, the determined trends are assigned to the various load or sub-ranges I, II1, II2, II3 and II4. In this way, optimal filling of the grab 2 can be achieved more quickly depending on the outreach. This is useful when, for example, the crane 1 switches between different ship hatches on a ship 15. Crane 1 therefore always operates with the maximum permissible load during the first load cycle without unwanted

Overload shutdowns.

In the control unit 17, the individual increases or decreases in the desired traction force value Fsoll are added together and transmitted to the traction force controller 18.

• Anzahl an Lastzyklen bis eine Erhöhung des Zugsollwertes durchgeführt wird (Default = 1,0) Beispiel: Ist 1,0 vorgegeben, wird der Sollwert erhöht, wenn eine Überlastabschaltung erfolgt.
• Wert für die prozentuale Erhöhung des Zugsollwertes (Default = 5,0)
• Anzahl an Lastzyklen bis eine Reduzierung des Zugsollwertes durchgeführt wird (Default = 2,0), Beispiel: Ist 2,0 vorgegeben wird der Zugsollwert reduziert, wenn ein zweiter Lastzyklus mit einem Füllgrad kleiner 80% erfolgt.
• Wert für die prozentuale Reduzierung des Zugsollwertes (Default = 3,0)

In order to adapt the control 17 to the crane 1, the load curve of the crane 1, the bulk material density, the grab volume and the grab weight, the control 17 can be parameterized with the following values:

• Number of load cycles until the tension setpoint is increased (default = 1.0) Example: If 1.0 is specified, the setpoint is increased when an overload shutdown occurs.
• Value for the percentage increase of the tension setpoint (default = 5.0)
• Number of load cycles until a reduction of the tension setpoint is carried out (default = 2.0). Example: If 2.0 is specified, the tension setpoint is reduced if a second load cycle occurs with a filling level of less than 80%.
• Value for the percentage reduction of the tension setpoint (default = 3.0)

These values are entered when commissioning the crane 1 with different grippers 2. When commissioning the crane 1, a basic tensile force target value is also determined for different grippers 2 or at least for the lightest gripper 2, which is manually entered into the control system 17 as an initial value when changing to a gripper. During commissioning, the parameters are optimized in order to quickly achieve optimal filling behavior of the gripper 2. If, for example, very large and very heavy grippers are used, the tensile force target value Ftarget is set in % of the nominal torque of the electric motor 19 so that the gripper 2 no longer sinks into the bulk material 14. The electric motor 19 then applies such a high torque that the gripper weight is maintained.

After commissioning, it is checked whether the settings have proven themselves in practice and adjusted if necessary.

In the event that overload shutdowns occur, the frequency of shutdowns must be reduced after approximately 3 consecutive shutdowns by changing the parameters or by manually specifying the tensile force target value Fsoll. The parameters that influence the change in the tensile force target value Fsoll can be set within the control system 17. An adjustment is made when the crane is put into operation depending on the crane and the gripper used. Since the aim of the control system 17 according to the invention is to optimally fill the gripper 2 with bulk material 14, each optimized handling process will take place at approximately 100% of the permissible load, i.e. close to an overload, so that the incremental increase and decrease of the tensile force target value Fsoll still leads to overload shutdowns but with a significantly reduced frequency. In the context of handling operations, 10% overload shutdowns are not disruptive in relation to the load cycles per hour and are considered a good control result within the context of the present control system 17. This means that with, for example, 50 to 60 load cycles per hour, 5 to 6 overload shutdowns can still occur. In this case, an overload shutdown is also counted as a load cycle. Without the control 17 according to the invention, overload shutdowns can occur up to over 50% of the load cycles per hour, especially if the crane is used for a heavy bulk material 14 with a gripper 2 that is too large in relation to the bulk material density.

Every overload shutdown causes a longer cycle time during operation, which has a negative effect on the handling performance. Thanks to the control system 17 according to the invention, the grab 2 is always completely full over time, even when work is being carried out on different load hatches, since the grab is always automatically loaded to capacity depending on the outreach a, without the crane driver having to intervene.

Since the tensile forces acting in the holding ropes 12 are proportional to a force applied to the rope drum for the Holding cables 12 are the torque applied by the electric motor 19, the invention described above includes not only a determination and control of tensile forces, but also of corresponding moments.

List of reference symbols

1

Mobile harbour crane

2

Gripper

2a

Peel

3

Stand base

4

Uppercarriage

5

Tower

6

boom

6a

Boom tip

7

Floating pontoon

8th

Hoist

9

Counterweight

10

Roller head

11

luffing gear

12

Holding ropes

13

Locking ropes

14

Bulk goods

15

Ship

16

Lever mechanism

17

steering

18

Traction controller

19

Electric motor

20

Load torque limitation

21

Crane database

22a

Rope length module

22b

Load curve module

22c

Start value module

22d

Trend module

a

Discharge

d

Rotation axis

H

Direction lifting

l

free rope length

s

Direction lowering

w

Rocking angle

Fist

Actual traction force value

FLast

Load capacity

Ftarget

Tensile force target value

G

Straight

I

first load range

II

second load range

II1

first load sub-range

II2

second load sub-range

II3

third load sub-range

II4

fourth load sub-range

S

Rope direction

V

vertical

W

Rocker axle

Claims (10)

1. Method for filling a gripper (2) for bulk material (14), said gripper being suspended on holding cables (12), raised and lowered by a crane (1) via a controller (17) and acting on the bulk material (14) with its own weight during the closing and filling procedure, wherein by reducing the effect of the weight of the gripper (2) on the bulk material (14), a fill degree of the gripper (2) is influenced via the controller (17) in that a tensile force acting on the holding cables (12) is influenced, characterised in that a tensile force TARGET value (Fsoll) is determined for the holding cables (12) via the controller (17), the tensile force TARGET value (Fsoll) is output to a tensile force controller (18) as an input variable, an electric motor (19) for lifting and lowering the gripper (2) is controlled by the tensile force controller (18) and an ascertained tensile force ACTUAL value (Fist) of the holding cables (12) is supplied to the tensile force controller (18) as an input variable, wherein a time of a change in the tensile force TARGET value (Fsoll) and an increment of a change in the tensile force TARGET value (Fsoll) is supplied in the controller (17) via a tendency module (22d) with reference to progressions of ascertained working loads.
2. Method as claimed in claim 1, characterised in that the tensile force TARGET value (Fsoll) is increased via the tendency module (22d) if the frequency of overload cut-offs exceeds a preselected value related to the load cycles and/or if the frequency at which the maximum permissible working load is exceeded exceeds a value preselected in relation to the maximum permissible working load for a given working radius (a).
3. Method as claimed in claim 1 or 2, characterised in that the tensile force TARGET value (Fsoll) is decreased via the tendency module (22d) if the frequency of overload cut-offs is less than a preselected value related to the load cycles and/or if the frequency at which the maximum permissible working load is exceeded is less than a value preselected in relation to the maximum permissible working load for a given working radius (a).
4. Method as claimed in any one of claims 1 to 3, characterised in that during the closing and filling procedure the gripper (2) is influenced with the tensile force ACTUAL value (Fist), which is directed in a direction of lifting (h), via the crane (1) by means of the controller (17).
5. Method as claimed in any one of claims 1 to 4, characterised in that in the controller (17) the fill degree of the gripper (2) is determined from a working load (TL), which is ascertained after the filled gripper is raised, and the known weight of the gripper (2).
6. Method as claimed in claim 5, characterised in that that a length (l) of a free cable (12, 13) starting from the gripper (2) and in the direction of lifting (h) is supplied as an input variable to the controller (17) via a cable length module (22a), and in the controller (17) a weight of the free cable (12, 13) is also assigned to the weight of the gripper (2) during the calculation of the fill degree of the gripper (2).
7. Method as claimed in any one of claims 1 to 6, characterised in that in dependence upon a working radius of the gripper (2) a maximum permissible working load is supplied to the controller (17) via a working load curve module (22b) as an input variable for the crane (1).
8. Method as claimed in claims 5 to 7, characterised in that in the controller (17) the tensile force TARGET value (Fsoll) is iteratively decreased or increased using the input variables from the working load curve module (22b), the cable length module (22a) and the ascertained working load (TL), until the fill degree of the gripper (2) is in the region of 100%.
9. Method as claimed in any one of claims 1 to 8, characterised in that a tensile force TARGET value (Fsoll) as a start variable is manually input into the controller (17) via a start value module (22c) as an input variable.
10. Use of a method as claimed in any one of claims 1 to 9 for a crane (1) comprising a gripper (2) which is raised, lowered, opened and closed by means of holding cables (12) and closing cables (13).

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