Patent Description:
When operating the jib of a crane having a jib mounted hoist, the motion of the jib will often affect the hoist in an undesired manner. When the jib is articulated, or parts of the jib are being telescopically displaced relative to each other the distance between a load carried by the hoist and the tip of the jib will change because the length of the uncoiled cable remains constant.

<CIT> discloses a method, by which this undesired effect can be avoided by installing a measuring device arranged and configured to send movement specific feedback to a regulator. Accordingly, the regulation loop can adjust the distance by sending a control signal to the hoist. When applying this regulation loop, one needs to measure the undesired effect continuously and correcting it by using the regulator. This means that the method has a limited speed of correction and requires that accurate measurements are carried out on a continuous basis.

<CIT> discloses a method according to the preamble of claim <NUM> and a system according to the preamble of claim <NUM> for controlling a crane by applying sensor measurements to introduce correction movements when the sensor data reveals that the motion that the crane experienced has an undesired component. This solution is capable of carrying out corrections. However, the corrections can only be carried out after the undesired components of the motion has been realized. Accordingly, it would be desirable to provide a solution, in which this drawback could be avoided.

Thus, there is a need for a method and a control system that reduces or even eliminates the above-mentioned disadvantages of the prior art.

The object of the present invention can be achieved by a method as defined in claim <NUM>, a control system as defined in claim <NUM> and a crane as defined in claim <NUM>. Preferred embodiments are defined in the dependent subclaims, explained in the following description and illustrated in the accompanying drawings.

The method according to the invention is a method for controlling a crane comprising a jib having a crane tip and a hoist comprising a load connection structure, wherein the crane is configured to carry a load attached to the load connection structure and comprises:.

wherein the method comprises the step of providing a command to the control unit to activate the one or more jib actuators, wherein the method comprises the following steps:.

Hereby, it is possible to provide a method, by which a correction is made before undesired motion actually occurs.

The method suggests application of a feedforward approach. In this manner it is possible to generate a correcting signal and activate the one or more hoist actuators by using the determined correcting signal at that point in time, at which the operator selects and executes a command causing a motion of the jib.

Accordingly, the errors that has to be corrected by the method according to the invention are smaller than the errors needed to be corrected by using prior at systems. At the same time, the method according to the invention is capable of providing a faster and more precise system than the prior art systems.

If the jib is extending, the hoist will release wire at the same time, hereby minimising the errors to be adjusted by the feedback.

The method according to the invention provides a simple, faster and more accurate regulation because it is proactive eliminating majority of the side-effect before it appears instead of allowing it to appear and then react.

The hoist is sometimes known as a cable winch used for lowering and hoisting a load.

In one embodiment, the one or more of jib actuators comprise one or more hydraulic cylinders.

In one embodiment, the one or more hoist actuators comprise one or more motors. In one embodiment, the one or more hoist actuators comprise one or more hydraulically driven motors. In one embodiment, the one or more hoist actuators comprise one or more electrically driven motors.

The control unit configured control the one or more jib actuators and the one or more hoist actuators configured to change the distance between the load and the crane tip. By the term "control" is meant activate and/or deactivate and/or turning on and/or turning off.

Providing a command to the control unit to activate the one or more jib actuators means that the control unit is applied to initiate activation of the one or more jib actuators. This step may comprise application of a regulator connected to the one or more jib actuators.

Determining the expected change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command may be calculated by using the control system and kinematics of the jib. In one embodiment, one or more sensor output may be used to carry out the determination of the change of the distance between the load and the crane tip caused by motion of the jib when executing the command.

Determining a correcting signal suitable for at least partly counteracting the change of the distance between the load connection structure and the crane tip may be done in several ways.

The correcting signal is a feedback in the form of a linear or angular position or derivative thereof (e.g. linear or angular velocity or acceleration). This feedback is sent to the control unit which through a closed loop path regulates the error from an operator-defined setpoint. When a command is provided, the control unit will through the feedforward path calculate a proactive response.

The activation of the one or more hoist actuators by using the determined correcting signal may be carried out in several ways.

In one embodiment, the command is forwarded to a control valve.

In one embodiment, the term "determining" includes that one or more calculations are carried out.

By the phrase "determining the change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command" is meant that the "expected" change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command is determined".

In one embodiment, the control unit comprises a single control device configured to control the one or more jib actuators and the one or more hoist actuators.

In one embodiment, the control unit comprises a first control device configured to control the jib actuators and a second control device configured to control the hoist actuator(s).

By the term "determining a correcting signal suitable for at least partly counteracting the change of the distance between the load connection structure and the crane tip" is meant determining a correcting signal that at reduces the magnitude of the change of the distance between the load connection structure and the crane tip.

In one embodiment, the load connection structure is a hook.

In one embodiment, the load connection structure is an eye (ringshaped structure).

In one embodiment, the crane is a lorry crane (truck-mounted).

It may be an advantage, that the correcting signal is selected in such a manner that activating the one or more hoist actuators by using the determined correcting signal, when not considering the effect of the jib, will cause a hoist induced change of the distance between the load connection structure and the crane tip that is smaller than the jib induced change of the distance between the load connection structure and the crane tip.

This can be expressed as in the following equation: <MAT>.

Hereby, the method can take into consideration that the speed of the hoist is faster than the speed of the displacement of telescopic extensions of the jib. It provides a simple way to implement the system.

In one embodiment, the command is forwarded to a control valve in a scale from +<NUM> to -<NUM>. If the operator of the crane commands +<NUM> straight away this is reached through a first order filter. In this situation it may be advantageous that the correcting signal is decreased by a factor in the rage -<NUM> to -<NUM>,<NUM>. It may be preferred that the correcting signal is decreased by a factor in the range -<NUM> to -<NUM> such as -<NUM>. This is a very simple way to execute the correction.

Other ways to calculate the feedforward, apart from a factor, includes a filter, a table and an interval.

In one embodiment, the feedforward is only activated by the extensions of the jib and fly-jib. The feedforward is, however, carried out in such a manner that the feedback does correct all other movements detected in the tip of the crane.

In one embodiment, the method and control system according to the invention comprises a filter is a system that performs mathematical operations to reduce or enhance certain aspects of a signal.

In one embodiment, the filter is a recursive filter.

In one embodiment, the filter is a non-recursive filter.

In one embodiment, the method and control system according to the invention comprises both a recursive and a non-recursive filter.

The filter may include the current value or a combination of the current and previously values. Filters can be simple or complex, of lower or higher order.

In one embodiment, the feedforward calculation is carried out by using a table. This may be accomplished in a manner, in which the table is applied by the control system to look up the current value in the table to see the expected reaction.

In one embodiment, one column in the table would be inputs, whereas another column would be outputs. The control system would therefore for each command be able to select a counter-command from the table.

In one embodiment, the control system carries out the feedforward calculation by using intervals. The idea of intervals allows the system to react different to an input depending on its value. In many systems, a threshold exists. Accordingly, a certain value acts as a threshold. Therefore, the system should react different on each side of the threshold. In one embodiment, there can be multiple intervals.

In one embodiment, the control system carries out the feedforward calculation by using an equation of a line. The equation of a line is another option. Here an input value gets multiplied by a factor before a constant is subtracted or added on. In this way the line can be lifted over a threshold. This is our current implementation of the feedforward: <MAT>.

In one embodiment, the control system carries out the feedforward calculation by using transfer functions. A transfer function is a mathematical expression of an action. It allows the control system to calculate an output if we know the input or vice versa. It transfers the input to an output. In this case the action is the action of a crane's dynamic actions. In order to make the operation in the controller faster this mathematical expression is simplified. It is a balance between accuracy and efficiency. It is possible to calculate an action from its command to the extensions and hence calculate another command to the hoist to counter this action. When a transfer function is modelled a regulator can be found mathematical. It is therefore both used for the feedforward and the feedback.

If several commends are selected simultaneously by the operator, the method comprises the following steps:.

The basic idea is to control the hoist in such a manner that, which allow us to keep the distance between the load and the crane tip constant.

It may be beneficial that the method is configured to be used to control a crane that comprises one or more sensors and wherein a sensor output is provided from one or more of the sensors, wherein the sensor output is used by the control unit to determine the change of the distance between the load and the crane tip caused by motion of the jib when executing the command.

It may be an advantage that the one or more sensors are configured and arranged to measure one or more of the following:.

It may be advantageous that the one or more sensors are configured and arranged to measure a position of structure with respect to a predefined coordinate system.

It may be beneficial that the one or more sensors are configured and arranged to measure a velocity of structure with respect to a predefined coordinate system.

It may be advantageous that the one or more sensors are configured and arranged to measure an acceleration of structure with respect to a predefined coordinate system.

It may be beneficial that the one or more sensors are configured and arranged to measure an angular position of structure with respect to a predefined coordinate system.

It may be advantageous that the one or more sensors are configured and arranged to measure an angular velocity of structure with respect to a predefined coordinate system.

It may be beneficial that the one or more sensors are configured and arranged to measure an angular acceleration of structure with respect to a predefined coordinate system.

It may be an advantage that the step of:.

are carried out on a continuous basis, wherein the sampling frequency of the determination of the change of the distance between the load connection structure caused by motion of the jib when executing the command is at least <NUM>.

Hereby, it is possible to provide a method that automatically compensates for the undesired effects of the motion of the jib on a continuous manner.

In one embodiment, the sampling frequency is at least <NUM>.

In one embodiment, the sampling frequency is <NUM>.

In a preferred embodiment, the method comprises the step of applying a regulator to regulate the one or more hoist actuator(s).

In one embodiment, the regulator is in fluid communication with the one or more hoist actuator(s), wherein the one or more hoist actuator(s) are hydraulically driven.

In one embodiment, the regulator is electrically connected with the one or more hoist actuator(s), wherein the one or more hoist actuator(s) are electrically driven.

In one embodiment, the crane comprises a manual hoist control element, wherein the method comprises the following steps.

when the manual hoist activator control element is not activated, wherein no automatic correction signal is executed by the hoist actuator when the manual hoist control element is activated (by the user).

Accordingly, the operator may control the hoist manually if the operator desires. If the operator does not activate the manual hoist control element. This allows (experienced) operators to operate the crane in the same way as they are used to.

In one embodiment, the manual hoist control element is an operating lever.

In one embodiment, the manual hoist control element is a J-stick.

It may be an advantage that the method comprises the step of determining the acceleration of the load and selecting:.

wherein the way by which the one or more hoist actuators are activated by using the determined correcting signal depends on the mode.

Hereby, it is possible to provide a more accurate way of compensating for the undesired effects of the motion of the jib.

In one embodiment, the sampling frequency depends on the mode.

In one embodiment, the acceleration of the load is determined by using a position sensor or an accelerometer arranged on a structure, to which the load is mechanically connected.

In one embodiment, the acceleration of the load is determined by using a position sensor or an accelerometer arranged on the tip of the jib.

In one embodiment, the control system is primarily activated. This means that the system is constantly activated in order to keep the distance between the load connection structure and the crane tip constant.

In one embodiment, the control system is configured to allow the operator to use the hoist to temporarily disable the control system.

In one embodiment, the control system is primarily deactivated.

This means that the system is deactivated. In this way the operator can activate control system to maintain the distance between the load connection structure and the crane tip at a fixed level when needed.

In one embodiment, the control system is primarily activated. This means that the system is constantly activated in order to keep the distance between the load and the crane tip constant.

In one embodiment, the method is configured to allow the operator to use the hoist to temporarily disable the control system.

This means that the system is deactivated. In this way the operator can activate control system to maintain the distance at a fixed level when needed.

The control system according to the invention is a control system for a crane comprising a jib having a crane tip and a hoist comprising a load connection structure, wherein the crane is configured to carry a load attached to the load connection structure and comprises:.

wherein the control system comprises a control unit configured to activate the one or more jib actuators, wherein the control system is configured to:.

Hereby, it is possible to provide a control system enabling that a correction is made before undesired motion actually occurs.

The control system method is based on application of a feedforward approach. In this manner it is possible to generate a correcting signal and activate the one or more hoist actuators by using the determined correcting signal at that point in time, at which the operator selects and executes a command causing a motion of the jib. Accordingly, the errors that has to be corrected when using the invention are smaller than the errors needed to be corrected by using prior at systems. At the same time, the invention provides a faster and more precise system than the prior art systems.

The control system according to the invention provides a simple, faster and more accurate regulation because it is proactive eliminating majority of the side-effect before it appears instead of allowing it to appear and then react.

The control unit configured control the one or more jib actuators and the one or more hoist actuators configured to change the distance between the load connection structure and the crane tip. By the term "control" is meant activate and/or deactivate and/or turning on and/or turning off.

It may be an advantage, that the control system is configured to select the correcting signal in such a manner that activating the one or more hoist actuators by using the determined correcting signal when not considering the effect of the jib will cause a hoist induced change of the distance between the load connection structure and the crane tip that is smaller than the jib induced change of the distance between the load connection structure and the crane tip.

Hereby, the control system can take into consideration that the speed of the hoist is faster than the speed of the displacement of telescopic extensions of the jib. It provides a simple way to implement the system.

If several commends are selected simultaneously by the operator, the control system is configured to:.

The basic idea is to control the hoist in such a manner that, which allow us to keep the distance between the load connection structure and the crane tip constant.

It may be beneficial that the control system is configured to be used to control a crane that comprises one or more sensors configured to provide sensor output, wherein control unit is configured to apply the sensor output to determine the change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command.

It may be advantageous that the one or more sensors are configured and arranged to measure one or more of the following:.

In one embodiment, the control system is configured to:.

on a continuous basis, wherein the sampling frequency of the determination of the change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command is at least <NUM>.

Hereby, it is possible to provide a control system that automatically compensates for the undesired effects of the motion of the jib on a continuous manner.

In one embodiment, the sampling frequency is least <NUM>.

In one embodiment, the crane comprises a manual hoist control element, wherein the control system is configured to:.

when the manual hoist activator control element is not activated, wherein the control system is configured to operate the crane in a manner, in which no automatic correction signal is executed by the hoist actuator when the manual hoist control element is activated (by the user).

This allows the operator to control the hoist manually by using the manual hoist control element.

As soon as the operator does not activate the manual hoist control element, the automatic correction of the hoist will be carried out by the control system. The invention allows the operator to operate the crane in the same way as the operator is used to.

It may be advantageous that the control system is configured to determine the acceleration of the load and select:.

In one embodiment, the control system is primarily activated. The system is constantly activated keeping the distance between the load connection structure and the crane tip constant at all time. When needed the operator will use the hoist to temporarily disable the system and in rare cases disable the system from the controller.

The system is deactivated. In this way the operator can activate to maintain the distance between the load connection structure and the crane tip constant when needed from the controller.

The crane according to the invention is a crane comprising a control system according to the invention.

The control system is suitable for operating a lorry crane (truck mounted crane) having at least one boom configured to carry a load.

The jib may be a telescopic, or fixed arm that is used to move objects.

The jib may be of any suitable type and size.

In one embodiment, the jib is a multi-segment telescopic jib.

In one embodiment, the jib is a fixed arm.

In one embodiment, the jib comprises a pair of sections and hinge members pivotally connecting one section to the other for swinging movement with respect thereto.

The control system is configured to be integrated with the hoist. The control system is activated when the hoist is activated. If the distance between the tip of the crane and the load connection structure be changed it can be done by adjusting with the hoist on the controller. This operation will yield a new setpoint with the new distance and the system will continue to keep this distance until another is chosen by the operator. The invention makes it possible to activate the system when the operator activates the hoist because they work together. If the operator does not want the system active, he can simply use the system to lock a certain position and disable the system afterwards.

The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention, which is defined by the appended claims.

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a crane <NUM> of the present invention is illustrated in <FIG>.

<FIG> is a schematic, perspective side view of a crane <NUM> according to the invention. The crane <NUM> is a truck-mounted crane (lorry crane) that comprises a crane base, onto which a telescopic and articulated jib <NUM> is mounted. The jib <NUM> comprises a first telescopic segment S<NUM> and a second segment S<NUM> rotatably attached to the first segment S<NUM>. The first telescopic segment S<NUM> is rotatably attached to the crane base and a jib actuator <NUM> formed as a hydraulic cylinder <NUM> is arranged to rotate the first telescopic segment S<NUM> with respect to the crane base. Another jib actuator <NUM>" is arranged to telescopically extend (lengthen) and shorten the first telescopic segment S<NUM>. The second segment S<NUM> can be rotated relative to the first segment S<NUM> by means of a hydraulic cylinder <NUM>'.

The crane <NUM> comprises a hoist comprising a cable <NUM> guided by rotatably mounted cable rollers <NUM>. The hoist comprises a hoist actuator <NUM>. The hoist actuator <NUM> is arranged at the crane base but may be arranged in a different position.

The crane <NUM> carries a load <NUM> fixed to a load connection structure (a hook) <NUM> provided in the distal end of the cable <NUM>. A sensor <NUM> configured to detect the distance D between the load connection structure <NUM> and the crane tip <NUM>. When the distance D is changed, the distance between the load <NUM> and the crane tip <NUM> will change equally. Accordingly, the sensor can monitor any change distance D between the load connection structure <NUM> and the crane tip <NUM> in order to keep the distance D constant. In one embodiment, the sensor is a wire sensor. In one embodiment, the sensor is an optical sensor.

<FIG> illustrates a block diagram of a crane according to the invention. The crane <NUM> comprises a jib <NUM> having three segments S<NUM>, S<NUM>, S<NUM> and a crane tip <NUM>. The jib <NUM> is telescopic and articulated. The jib <NUM> is mounted on a column <NUM> placed on a crane base <NUM>.

The crane <NUM> is equipped with at hoist (cable winch) <NUM> driven by a hoist actuator <NUM> arranged to coil and uncoil a cable <NUM> (indicated with a dotted line). The cable <NUM> is wound on the hoist <NUM> and is guided along the jib <NUM> by means of a plurality of cable rollers <NUM> to the tip <NUM> of the jib <NUM>. An attachment structure (for instance a hook like shown in <FIG> and <FIG>), may arranged at the free end of the cable <NUM> hereby enabling attachment to a load <NUM>.

The direction and magnitude of movements of the cable <NUM> is measured by a sensor <NUM> arranged at the roller <NUM> that is closest to the load <NUM>. The sensor signals are fed to a control unit <NUM> preferably on a continuous basis.

The jib <NUM> carries a load <NUM> attached to a load connection structure <NUM> arranged in a distance D from the crane tip <NUM>. The crane <NUM> comprises one or more of jib actuators (not shown) arranged to activate the jib <NUM> and hereby achieve articulation of the segments S<NUM>, S<NUM>, S<NUM>. Moreover, the crane <NUM> comprises one or more of jib actuators (not shown) arranged to activate the jib <NUM> and hereby achieve thrust movements B<NUM> (jib extension) and/or B<NUM> (fly-jib extension).

It is indicated that the jib <NUM> of the crane <NUM> can perform both articulation movements A<NUM> (boom movement), A<NUM> (jib movement), A<NUM> (fly-jib movement) and also thrust movements B<NUM> (jib extension), B<NUM>. (fly-jib extension).

The control unit <NUM> is configured control the one or more jib actuators (see <FIG> og <FIG>) and the hoist actuators <NUM>. The hoist actuator <NUM> is configured to change the distance D between the load connection structure <NUM> and the crane tip <NUM>.

The control unit <NUM> is adapted to maintain distance D relative constant by carrying out a feedforward approach. This means that the control unit <NUM> configured to ensure that change ΔD of the distance D between the load connection structure <NUM> and the crane tip <NUM> remains close to zero (within a predefined range so that the change ΔD of the distance D is smaller than a predefined level). This can be expressed as: <MAT> wherein L is a predefined allowable level (e.g. <NUM>).

The control system <NUM> is configured to execute commands. These commands may be inserted by operator of the crane <NUM> by means og a human-machine interface (HMI) device <NUM> of suitable type. In <FIG> the HMI device <NUM> is a remote control <NUM> configured to communicate with the control unit <NUM>.

When the operator <NUM> by means of the remote control <NUM> inputs a command CA (for performing an articulation A<NUM>, A<NUM>, A<NUM>) and/or CB (for performing a thrust movement B<NUM>, B<NUM>) and/or CH (for activating the hoist actuator <NUM>), the command CA, CB will be received by the control unit <NUM>. The control unit <NUM> will determine the change ΔDjib of the distance D between the load connection structure <NUM> and the crane tip <NUM> caused by motion of the jib <NUM> when executing the command CA, CB.

Hereafter the control unit <NUM> will determine a correcting signal CS suitable for at least partly counteracting the change ΔDjib of the distance D between the load connection structure <NUM> and the crane tip <NUM> caused by the motion of the jib <NUM>. The control unit <NUM> will immediately activate the hoist actuator <NUM> by using the determined correcting signal CS. Accordingly, the hoist actuator <NUM> and the jib actuators are activated simultaneously. In this manner it is possible to achieve that the change ΔD of the distance D between the load connection structure <NUM> and the crane tip <NUM> remains close to zero so that the load <NUM> can be manipulated with the highest possible accuracy by the crane <NUM>.

The control unit <NUM> is connected to a hydraulic valve <NUM> that is in fluid communication with the hoist actuator <NUM> and the jib actuators (not shown). The hydraulic valve <NUM> is configured to generating actuating signals C'A, C'B, C'S to the hoist actuator <NUM> and the jib actuators, respectively. The actuating signal C'A is applied to actuate the jib actuators responsible for articulation A<NUM>, A<NUM>, A<NUM> of the jib <NUM>. The actuating signal C'B is applied to actuate the jib actuators responsible for trust movements B<NUM>, B<NUM> of the jib <NUM>. The actuating signal C'S is applied to actuate the hoist actuator <NUM>.

The sensor <NUM> configured to detect the distance D between the load <NUM> and the crane tip <NUM> on the basis of one or more sensor signals X. The sensor signals X may include an angular position θ an, an angular velocity ω, an angular acceleration α, a position y, a velocity v or an acceleration a. Since the sensor <NUM> monitors the distance D, the control unit <NUM> has updated information about the distance D. Accordingly, the control unit <NUM> can determine the most optimum correcting signal CS for remain a constant distance D between the load connection structure <NUM> and the crane tip <NUM>.

If the control system <NUM> is deactivated, it would be possible to raise or lower the load <NUM> relative to the crane tip <NUM>. In <FIG> a lowered load <NUM> is indicated with a dotted line. When the control system <NUM> is activated, the control system <NUM> would use a feedforward approach to keep the distance D constant.

When the operator <NUM> gives a command CA and/or CB the control unit <NUM> will immediately generate a correcting signal CS that causes the hoist actuator <NUM> to counteract the expected change ΔDjib of the distance D between the load connection structure <NUM> and the crane tip <NUM> caused by the motion of the jib <NUM>.

In this way the hydraulic valve <NUM> only has to correct relative small errors. Accordingly, the control system <NUM> is capable of providing a faster and more precise regulation of the distance D than the prior art systems.

If for example, the jib <NUM> is extending, then the hoist actuator <NUM> will release cable <NUM> at the same time, leaving a small error to be adjusted by the feedback.

Therefore, the system and method according to the invention, provides a simple, fast and more accurate regulation by proactively eliminating majority of the side-effect before it appears instead of allowing it to appear and then react afterwards.

In one embodiment, the following formula is used or corrections of commands where extensions are included.

where CS is the correcting signal, CS_feedforward is the part of the correcting signal which comes from the feedforward signal and CS_feedback is the part from the feedback loop. In other words, a proactive part that corrects the current movement and a part that correct last cycles error.

If extensions are not part of the command the following equations can be used: <MAT> <MAT> <MAT>.

<FIG> illustrates a flowchart illustrating the workflow of a method according to the invention. The method comprises four steps I, II, III, IV.

In the first step I, a command CA or CB is selected. The selection may be accomplished by an operator as shown in and explained with reference to <FIG>. Using a remote control <NUM> to select the command CA or CB is a practical solution. However, in one embodiment, the command CA or CB may be inputted directly to the control unit <NUM>.

In the second step II, the expected change of the distance D between the load connection structure <NUM> and the crane tip <NUM> caused by executing the command CA and/or CB is determined. This may be done by using the control unit <NUM> to perform a calculation taking into account parameters indicative of the kinematic of the crane jib <NUM>. Such parameters may be measured by sensors arranged at the jib <NUM>.

In the third step III, a correcting signal CS to be sent to the hoist actuator <NUM> is determined. The determination may be based on a calculation of the expected change of the distance D between the load <NUM> and the crane tip <NUM> caused by motion of the jib <NUM> when executing the command CA and/or CB referred to in the second step II.

In the fourth step IV , the command CA and/or CB are executed by the jib actuator(s) <NUM> and the correcting signal CS is simultaneously executed by the hoist actuator <NUM>.

This sequence (step I-IV) is repeated in an ongoing manner as long as the control is suitable (as long as the distance D is intended to remain zero or close thereto).

<FIG> illustrates a perspective view of a crane <NUM> according to the invention. The crane <NUM> is a lorry crane (truck-mounted crane) equipped with a telescopic and articulated jib <NUM>. The jib <NUM> comprises a first segment S<NUM> and a second segment S<NUM> rotatably attached to the first segment S<NUM>. The jib <NUM> comprises a third telescopic segment S<NUM> that is rotatably attached to the second segment S<NUM>.

The first segment S<NUM> is attached to a crane base. A first jib actuator <NUM> formed as a hydraulic cylinder <NUM> is arranged to rotate the second segment S<NUM> with respect to the first segment S<NUM>. A second jib actuator <NUM>' formed as a hydraulic cylinder <NUM>' is arranged to rotate the second segment S<NUM> with respect to the third segment S<NUM>. A third jib actuator <NUM>" is arranged to telescopically extend (lengthen) and shorten the third telescopic segment S<NUM>. The second segment S<NUM> can be rotated relative to the first segment S<NUM> by means of a hydraulic cylinder <NUM>'.

The crane <NUM> carries a load <NUM> fixed to a load connection structure formed as hook <NUM> attached to the free end of the cable <NUM>. A sensor adapted to detect the distance between the load connection structure <NUM> and the crane tip is arranged at the crane tip. Accordingly, the sensor can monitor any change distance D between the load connection structure <NUM> and the crane tip.

<FIG> illustrates a flowchart illustrating the workflow of a method according to the invention. The method comprises five steps V, VI, VII, IIX, XI.

In the first step V, it is determined if the manual hoist control element is activated. The manual hoist control element may for example be an operating lever or a J-stick.

If the manual hoist control element is activated nor correcting signal is executed by the hoist actuator <NUM> as indicated in step X. This means that the operator operates the hoist manually. This manual control mode continues as long as the operator activates the manual hoist control element.

If, however, the manual hoist control element is not active (this is the case when the operator does not activate the manual hoist control element). The steps VI, VII, IIX and IX corresponding to the steps I, II, III, IV (shown in and explained with reference to <FIG>), respectively, are carried out.

Claim 1:
A method for controlling a crane (<NUM>) comprising a jib (<NUM>) having a crane tip (<NUM>) and a hoist (<NUM>) comprising a load connection structure (<NUM>), wherein the crane (<NUM>) is configured to carry a load (<NUM>) attached to the load connection structure (<NUM>) and comprises:
- one or more of jib actuators (<NUM>, <NUM>', <NUM>") arranged to activate the jib (<NUM>);
- one or more hoist actuators (<NUM>) arranged to activate the hoist (<NUM>);
- a control unit (<NUM>) configured control the one or more jib actuators (<NUM>) and the one or more hoist actuators (<NUM>) configured to change the distance (D) between the load connection structure (<NUM>) and the crane tip (<NUM>),
wherein the method comprises the step of providing a command (CA, CB) to the control unit (<NUM>) to activate the one or more jib actuators (<NUM>, <NUM>', <NUM>"), characterised in that the method comprises the following steps:
- determining the expected change (ΔDjib) of the distance (D) between the load connection structure (<NUM>) and the crane tip (<NUM>) caused by motion of the jib (<NUM>) when executing the command (CA, CB);
- determining a correcting signal (CS) suitable for at least partly counteracting the change (ΔDjib) of the distance (D) between the load connection structure (<NUM>) and the crane tip (<NUM>);
- activating the one or more hoist actuators (<NUM>) by using the determined correcting signal (CS).