KR20110044268A - Early overload detection for a load lifting device - Google Patents

Abstract

The present invention provides a method for dynamically detecting a malfunction of a cargo lift device comprising a force sensor, the method comprising: monitoring a signal of a force sensor in connection with an increase; Defining a time period necessary for raising the cargo holding means; Monitoring the signal in association with exceeding an overload threshold; Determining a weight force within a defined time period from the signal if the overload threshold is not exceeded for a defined time period and confirming the determined weight force as a base load; Determining a dynamic jump threshold higher than the base load but lower than the previous overload threshold as a nominal overload threshold; Monitoring the signal in relation to whether the signal is above or equal to the jump threshold and generating a block signal if the signal is above or equal to the jump threshold; It relates to the dynamic detection method comprising.

Description

EARLY OVERLOAD DETECTION FOR A LOAD LIFTING DEVICE}

The present invention relates to a method for dynamically detecting dangerous operation of a cargo lift device, in particular a container crane, comprising at least one force sensor interacting with the cargo containment means. The invention also relates to a crane comprising an overload safety device according to the invention.

Conventional overload safety devices monitor the weight force of a load suspended on a crane, but the load can be configured with the crane's cargo receiving means and the object to be raised. Cranes used for unloading container ships at docks include so-called "spreaders" as a means of receiving cargo. Spreaders are typically multi-jib type grabs, which each include locking pins at their ends. The locking pins can then be inserted and fixed respectively in corresponding container portions located on or within the surface of the corner portions of the top or bottom surface of the container. The locking pins can be integrated with so-called measuring axes depending on the situation. The measuring axis consists of a cylindrical force transducer with an electrical measuring system, for example a strain gauge strip (SGS). As soon as the locking pins engage the container and the container is raised by an elevating mechanism (e.g. rope hoist), the measuring area of the measuring axis is deformed, which in turn generates a corresponding measuring signal.

The greater the force on the measuring axis, the higher the measuring signal. Since cranes typically have to elevate the maximum nominal load, an overload safety device is provided which causes an emergency shutdown of the crane, in particular an interruption of the elevating process, when the nominal load is exceeded.

The present invention provides a method for dynamically detecting a malfunction of a cargo lift device comprising a force sensor, the method comprising: monitoring a signal of a force sensor in connection with an increase; Defining a time period necessary for raising the cargo holding means; Monitoring the signal in association with exceeding an overload threshold; Determining a weight force within a defined time period from the signal if the overload threshold is not exceeded for a defined time period and confirming the determined weight force as a base load; Determining a dynamic jump threshold higher than the base load but lower than the previous overload threshold as a nominal overload threshold; Monitoring the signal in relation to whether the signal is above or equal to the jump threshold and generating a block signal if the signal is above or equal to the jump threshold; Include.

1 is a load / time graph depicting an overload threshold, in particular a dynamic overload threshold, in accordance with the present invention.
2 is a flow chart illustrating a method according to the present invention.
3 is a load / time graph that appears when a load is applied to the spreader according to the prior art.
4 is a load / time graph that appears when no load is applied to the spreader according to the prior art.

Hereinafter, with reference to the accompanying drawings an embodiment according to the present invention will be described in detail. However, the present invention is not limited or limited by the embodiments. Like reference numerals in the drawings denote like elements.

Container spreaders are described by way of example in WO 02/10056 A1. Container cranes are described by way of example in DE 102 33 875 A1. These two applications are expressly incorporated herein by reference only to the general construction of the spreader and container crane respectively.

Conventional overload safety devices are also commonly used for the prevention of so-called "snag load" conditions. "Snag load" means that the load of the crane increases in an unintended manner, for example by entangling of a cargo or spreader on a ship to be unloaded or shipped. The load can thereby increase to almost infinity, specifically until the maximum overload shutdown is achieved. When throwing the spreader from the interior of the belly, the spreader or a container suspended from the spreader may be caught, for example, by another container protruding against the container to be further raised. As a result, when the additional raised container is tilted, the overload safety device only reacts when the nominal load of the crane (eg 60t) is exceeded. In other words, in this case, the crane will tow the vessel with a force of up to 60 t (when the container is not hung on the spreader) before the point where the spreader is caught on the ship is recorded. The force generated at this time must be supported by the steel structure of the crane or ship. There is a significant risk of damage to cranes, ships, spreaders and / or containers to be raised.

If starting from an empty spreader, ie a suspended cargo free spreader can be elevated at a maximum lifting rope speed of 280 m / min, for example, this corresponds to a lifting rope length of 2.5 cm when the reaction time is 5 ms. The response time of 30 ms thus corresponds to a lifting rope length of already 15 cm. In short, when operation with conventional overload safety devices is achieved, such theoretical lifting rope lengths must be supported by the steel structure of the crane and / or the ship. Therefore, efforts have been made to keep the reaction time as short as possible.

The problem with this goal setting is the fact that the two lift cases must be distinguished. In other words, it is to distinguish whether the spreader is raised under the conditions including the cargo and whether the spreader is raised alone. 3 shows a load / time graph, but the left portion of the graph indicated by the circle number 1 shows a normal ascending and lowering process when the overload is cut off. The right part of the graph, indicated by the circle number 2, shows such a lift process in which the "snag load" condition actually occurs.

In the normal case (see the left part of the graph), after raising the load, an overshoot occurs in the measurement signal of the force sensors which are typically arranged such that the load or load distribution can be preferably measured in the corner region. This overshoot stabilizes after a predetermined time. While the measurement signal vibrates, the average load can be calculated. This is illustrated by the horizontal line called "average load" in the graph of FIG. At the end of the normal hoisting process the cargo is put back down, whereby the measuring signal drops to zero.

In the right part of Fig. 3 is shown a lifting process in which an unintended load increase (“snag load”) occurs. After the cargo has risen (normal load cases parallel to the increase edge of the normal lift process), the load or the corresponding measuring signal again increases abruptly. The cargo may be jammed, for example, during operation of the container crane. Since the additional load increase does not occur in the normal operating mode, the control device finally starts in that the operation is carried out without further lifting, which further increase must be caused by an error. This is only detected by a conventional control device when the measurement signal exceeds a preset overload threshold. In this case, it usually takes some time for the measurement signal to reach the overload threshold, so that the actual reaction time is delayed relatively long, thereby avoiding personal injury and machine damage, since the crane is towed at full force. Can cause.

Further situations are shown in FIG. 4. This additional situation arises when the spreader is raised and / or moved under conditions where the cargo is not suspended. The spreader may be fixed alone, for example, inside the ship when moving. In the load / time graph of FIG. 4, the left side of the graph shows normal operation of the spreader, but the measurement signal corresponds to the weight of the spreader alone. The right part of the graph shows the operating situation indicating the "snag load" state.

If the load increase of the right curve 2 of FIG. 4 is compared with the load increase of the left curve 1 of FIG. 3, it can be seen that it is particularly difficult for the control device to distinguish between a normal load state and a “snag load” state. have. In other words, in the case of the right curve of FIG. 4, the crane may be loaded until it detects that the overload safety device has reached the overload threshold. At that moment, however, the crane pulls the spreader at its maximum nominal force, thereby causing significant damage.

Therefore, the objective of this invention is to aim at solving the said problem.

To this end, the present invention proposes the following steps: defining a time period required to raise the cargo receiving means regardless of whether or not the additional load is suspended; Monitoring the signal during an increase for a period of time defined in relation to exceeding an overload threshold; If the overload threshold is not exceeded for a defined period of time, determining an averaged weight force from the signal and determining this averaged weight force as a base load; Determining a dynamic jump threshold above the base load and below the nominal overload threshold as an overload threshold; And monitoring the signal with respect to whether the signal is above or equal to the jump threshold and generating a block signal if the signal is above or equal to the jump threshold.

In the prior art, the nominal overload threshold is defined as static, ie no adaptation of the overload threshold to each dominant situation. This can result in significant damage to the crane or ship, especially if the load is not suspended on the spreader, since it takes a relatively long time to reach the overload threshold and start blocking.

In contrast, in the present invention, the threshold value is determined to be dynamic, that is, the threshold value varies with time and can take a value adapted to the dominant situation. Upon completion of the rising transient process on rise, an average value is determined in accordance with the present invention, which corresponds to the weight of the spreader with or without cargo hanging. This determined value is increased by 30%, for example, to define a dynamic "jump threshold". If the signal from the force sensor exceeds this threshold, then clearly the spreader is jammed or fixed and an emergency shutoff should be made accordingly. This is usually done before the crane pulls the spreader at full force. Such situations may not only occur when the cargo is raised, but also during horizontal operation of the crane, or horizontal movement of the crane trolley, with the spreader suspended below it.

Also for this purpose, according to the present invention, since the jump threshold is dynamically adapted, the spreader lift in which the cargo is suspended and the spreader lift or "snag load" state in which the cargo is not suspended are distinguished. If no load is hanging on the spreader, the absolute value of the jump threshold is lower than when the load is hanging on the spreader.

In all cases, the point where the absolute overload threshold (nominal load threshold) is exceeded can be avoided.

In addition, a preferred case is when, during the intended ascending process, the signal passes through a transient phase that is included in the defined period, and the base load corresponds to the averaged value of the signal during the defined period.

In this way, an ascending transient process can be considered. The base value for determining the dynamic jump threshold represents the mean value, so that the jump threshold is not determined based on the extreme value during the ascending transient.

According to a preferred embodiment, a query is made as to whether the lifting mechanism of the cargo lifting device, in particular the rope winch, is activated during signal increase.

There are additional sources of information through these queries. If the elevating mechanism is not activated and the load is nevertheless increased, it can be deduced therefrom that the spreader and / or suspended cargo (e.g. container) has been jammed, for example during horizontal operation of the crane.

Thus, if the elevating mechanism is actuated, the rise of the cargo (from the ground) and the further rise of the cargo (with the cargo lifted up in the air together with the spreader) can be distinguished. In the first case where the cargo rises from the ground, an increase in the measurement signal of the force sensor is expected because the weight of the cargo must be increased in addition to the weight of the spreader. In the second case, where the cargo rises further, no further increase in weight is expected because the crane already holds the spreader and cargo.

Further preferably, for each force sensor it is checked whether the overload threshold inherent in the force sensor lower than the overload threshold of the overall system is exceeded.

In particular when using the spreader to lift the container, for each corner of the container a force sensor is mounted which does not necessarily have to be placed inside the spreader. Therefore, four force sensors (one force sensor for each lifting rope) are typically used when using a container. The sum of the measurement signals of the four force sensors corresponds to the total load (spreader and container). Therefore, each of the force sensors contributes to the determination of the total load, so for each force sensor individual overload values lower than the overall system overload value can be determined. Based on these individual overload values and the duration of the ascent transient, in the load / time graph, a window is defined that corresponds to the range in which the measurement signal must be moved during the ascent during the load transient. If the signal deviates from the range defined by this area, the emergency shutdown can be made at a relatively early point in time, as compared to conventional overload shutdown at the nominal overload value.

In addition, a preferable case is when the monitoring of the jump threshold is made continuously.

In this way the absolute value of the jump threshold can be adapted continuously, in other words dynamically.

According to a further preferred embodiment, the cargo receiving means is operated at a speed of up to 300 m / min and the detection reaction time is preferably 5 ms or less.

In this case the lifting rope length is 2.5 cm, which is the extent to which the lifting rope is further moved, even if an emergency shutoff occurs. This lifting rope length is supported by the steel structure of the crane or ship, and generally does not cause damage to the ship or crane.

Also, preferably, the dynamic jump threshold is newly determined every time the lifting process is made.

The calculation associated with the determination of the dynamic jump threshold can be performed permanently. This increases safety.

Obviously, the above mentioned and later described features may be used alone or in combination with each other as well as with the combination method specified, respectively, without departing from the scope of the present invention.

Embodiments of the present invention are shown in the drawings and described in more detail in the following detailed description.

The invention is implemented by software and / or hardware. The inventors have recognized that an emergency interruption through the definition of a dynamic overload threshold can be carried out more quickly and desirably than a conventional emergency interruption, which functions as a static overload threshold at the time of lifting or moving of the cargo. When referred to as a "dynamic" overload threshold, it is considered to be such a variable that, in the following, an emergency shutdown is initiated when exceeded. This may occur regardless of whether the value of the system is measured or whether the value is due to an external source. Each of these values is adapted to the dominant situation. In this case it is not distinguished whether the spreader is moved alone, ie without cargo, or whether the spreader is moved with the cargo suspended. However, the rise of the spreader made in the state in which the cargo is suspended and the spreader is to be raised, and the further rise of the spreader made in the state in which the cargo has already been suspended can be clearly distinguished.

The invention is applicable to cargo lifting devices such as, for example, container cranes or other types of cranes.

Force sensors are used to measure the load suspended on the crane. The force sensor typically consists of a force transducer and an electrical measurement system that interacts with the force transducer, which converts the weight force into an electrical signal. As the force sensor, for example, a measuring axis, a measuring tongue, a pressure cell, or the like can be used. As an electrical measurement system, for example, a strain gauge strip (SGS) can be used. This SGS can be adhesively fixed on the force transducer or provided by a "sputtering" technique.

The invention is used in particular in connection with so-called spreaders in the case of container cranes. The spreader is used, for example, as a gripping device for lifting the container. Force transducers, such as measuring axes, are used to measure the force acting on the lifting rope of the spreader. These measuring axes make measurements at the edges of the spreader which will normally be raised through the lifting rope. The sum of all measurement signals represents the total load.

The force sensors generate measurement signals that are sent to the control device for calculating the total weight. Based on such signals, side loads, overloads, slack signals, specific load signals, or side or slope load errors may also be determined. In order to produce such various information or signals, the individual measurement signals of the force sensors are combined in various ways as is known to those skilled in the art.

Obviously, only one force sensor may be provided.

1 shows a load / time graph for an ascending process. In the ascension process, the spreader is combined with the container. Meanwhile, the container is placed on the underlay (bottom surface / another container). As soon as the spreader is engaged with the container, the lifting process is started by the lifting mechanism of the crane. In doing so, the measurement signal is increased from zero to the first (limited) maximum. The first maximum value then represents a first measure of the weight force of the container. This is illustrated in the left part of the measurement curve indicated by circle number 1 in FIG. 1. As soon as the container is raised, ie ascended from the bottom or its underlay, the ascending transient process begins, which is manifested by the vibration of the signal by the average load value shown by the horizontal auxiliary line in FIG. After a certain time the ascent transient process is attenuated. The measurement signal then becomes nearly constant. The container can be moved and put back down later. When the container is down, the measurement signal drops to zero.

Depending on the value of the weight to be lifted and the speed of the lift process, the ascending transient is attenuated relatively slower or faster. In general, the maximum weight of the object to be elevated is already known. Knowing the weight of the object to be elevated, the duration of the ascending process may be presented in advance at least approximately. In the right half of FIG. 1 an additional ascent process is shown. The duration of the ascending process is bounded by two vertical auxiliary lines in the measurement curve indicated by the circle number 2.

The duration of the ascending process can be input in accordance with the invention to the control device according to the value of the load to be raised for each ascending process. However, the duration of the ascending process may be preset in the form of parameters previously stored in the storage of the control device. Numerous different parameters can be stored in order to be able to adapt to different loads.

According to the invention, a time window for the ascending process is triggered at the beginning of the ascending process. This triggering point corresponds in particular to such a point that the measurement signal is higher than zero. The measurement signal is detected over the period of the ascending process. After the end of the defined period, an average value corresponding to the average load is obtained. The average load is also shown by the horizontal auxiliary line in the right part of FIG.

Then, based on the averaged value, a dynamic jump threshold is defined in FIG. 1, referred to as " dynamic snag load threshold " in accordance with the present invention. The jump threshold is, for example, 30% higher than the averaged load in the graph.

In addition, it can be seen from FIG. 1 that the dynamic threshold is located below the overload threshold of the total load. In the example of FIG. 1 the dynamic load is even below the total overload threshold.

1 shows an additional horizontal auxiliary line called "overload threshold of edge points". This auxiliary line preferably represents the overload threshold of the individual force sensors which take measurements at the corners of the spreader via the lifting rope. Obviously, the individual overload thresholds appear lower than the total overload threshold.

During the duration of the ascent process, the load is monitored in accordance with the overload threshold of the corner points as well as the load increasing aspects.

Also shown in FIG. 1 is the “snag load” state at the end of the right measurement curve. A container suspended on a spreader may be stuck in another container that is still stored in the vessel, for example during the further lifting process (if the container is raised further after it is raised). Therefore, the measurement curve increases as if it leaps again. Since the dynamic threshold is much lower than the total overload threshold, the "snag load" state can be detected much earlier than the conventional approach. The "snag load" condition is always detected before the total overload threshold is reached and the lifting process is interrupted by generating an emergency stop signal. In this case, the load never damaging the crane or the ship.

2, the method according to the invention is described by way of example in the form of a flowchart.

In step S1, it is basically queried whether there is a signal increase. In such queries it is not distinguished whether the spreader is lifted alone or in the state of loading the cargo. If there is no load increase, the procedure returns to step S1. If there is an increase in load, the process proceeds to step S2 and inquires whether a predetermined period has elapsed. The predetermined time period can be entered manually or can be preset by querying the parameter data bank. If the query of step S2 confirms that the predetermined period has not yet elapsed, the process returns to step S2. Such queries should include the ascent transients shown in FIG.

If the predetermined period has elapsed in step S2, the flow proceeds to step S3 and is queried whether the overload threshold has been exceeded during this period. In addition, the query of step S3 can also be made in parallel with step S2.

If the overload threshold, in particular the total overload threshold or the individual overload thresholds inherent in the force sensor, has been exceeded, an emergency shutdown is initiated by the generation of a corresponding signal by the higher control device in step S4.

If the overload threshold has not been exceeded during the step S3 (measurement signal is located inside the area), the average load (spreader / spreader and container) is determined, and from this determined average load, the "dynamic" jump threshold is again determined. This is all done in step S5.

If the dynamic jump threshold has not yet been specified earlier, the jump threshold is established as a "new" transient threshold in step S6. If a jump threshold has already been specified, the new value is established as a "new" transient threshold.

In the query step S7, it is checked whether the lifting process is finished. If the lifting process is finished, the overload monitoring according to the present invention is also terminated. If the elevating process has not yet finished, the procedure returns to step S1.

Embodiments according to the present invention can be implemented in the form of program instructions that can be executed by various computer means can be recorded on a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of the computer-readable recording medium include magnetic media such as a hard disk, a floppy disk, and a magnetic tape; optical media such as CD-ROM and DVD; magnetic recording media such as a floppy disk; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

Claims (8)

A method for dynamically detecting a malfunction of a cargo lift device, in particular a container crane, comprising at least one force sensor interacting with a cargo containment means,
Monitoring a signal of the force sensor relative to a signal increase, proportional to the force exerted by the load receiving means;
If an increase is detected, checking whether the nominal overload threshold is exceeded; And
If the nominal overload threshold is exceeded, generating a shutoff signal to shut down the load elevating device within a shortest period of time;
In the dynamic detection method comprising a,
Defining a period of time necessary to raise the cargo holding means whether or not additional loads are suspended;
If an increase is detected, monitoring the signal for a period of time defined in relation to exceeding an overload threshold;
If the overload threshold is not exceeded for the defined period, determining an averaged weight force from the signal and determining the averaged weight force as a base load;
Determining a dynamic jump threshold above the base load and below the nominal overload threshold as the overload threshold; And
Monitoring a signal as to whether the signal is above the jump threshold or equal to the jump threshold and generating a block signal if the signal is above the jump threshold or equal to the jump threshold;
Dynamic detection method comprising a. The method of claim 1,
The signal passes an ascending transient stage covered by a defined time period during the intended ascent process;
Wherein the base load corresponds to an averaged value of the signal. The method according to claim 1 or 2,
The lifting mechanism of the cargo lifting device, in particular the rope hoist, is operated during signal increase. 4. The method according to any one of claims 1 to 3,
A plurality of force sensors are provided, comprising checking for each force sensor whether an overload threshold inherent in the force sensor that is lower than the nominal overload threshold of the overall system is exceeded. The method according to any one of claims 1 to 4,
And monitoring the jump threshold continuously. The method according to any one of claims 1 to 5,
The dynamic jump threshold is newly determined each time a lifting process is performed. A crane comprising an overload safety device with a control device adapted accordingly to carry out the dynamic detection method according to any one of claims 1 to 7. 8. A method according to claim 7, comprising force sensors for making measurements at the corners of the spreader so as to be able to measure each corner point load that can be used for the induction of the total load at the corner points of the cargo, in particular the container. Crane with spreader.

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