Snag detection system

Abstract

The present invention relates to a crane system (2) comprising a trolley (7) to support a load and movable about a horizontal direction to provide movement of the load in a horizontal direction accordingly and a carrying member (10) supported by the trolley (7) and configured to carrying the load in use. A sensor (22,24) to measures the angle of the carrying member (10) relative to the trolley (7) and a controller (20) is configured to provide a dynamic model of the trolley (7) to determine an estimated angle of the carrying member (10) during movement of the trolley (7). The controller (20) is configured to compare to the estimated angle and the measured angle and control horizontal movement of trolley (7) in accordance with said comparison.

Description

[0001]Snag detection system The present disclose relates to a snag detection system and method for a crane system. Background of the Invention In overhead or bridge cranes, a hoist mechanism is movable along a bridge member. A rope or cable is suspended from the hoist mechanism to support a load. During use, the load may snag on another object. This may cause damage to the load, the rope or cable, the object and / or the user (for example, if the load becomes unsnagged and moves uncontrollably). A prior art solution is found WO 2013 / 041770. In this document, the system measures the oscillation or “sway” of the rope in use. This sway value is compared against a predetermined threshold value that is experimentally derived. The inventor has found numerous problems with prior art solution. As the predetermined threshold is derived by experiment, the system is prone to errors and may only be used within systems upon which parameters have been calculated. For example, each crane system comprises different dynamic properties, and so the experimental threshold must be determined for each system accordingly. Determining such experimental values is time consuming. The prior art system is therefore not universal and difficult to adapt for different crane system. There present invention aims to overcome or ameliorate one or more of the above problems. Statement of Invention According to a first aspect of the invention, there is provided: a crane system comprising: a trolley or hoist to support a load and movable about a horizontal direction to provide movement of the load in a horizontal direction accordingly; a carrying member supported by the trolley / hoist and configured to carrying the load in use; a sensor to measure the angle of the carrying member relative to the trolley / hoist; a controller configured to provide a dynamic model of the trolley / hoist to determine an estimated angle of the carrying member during movement of the trolley / hoist; and where the controller is configured to compare to the estimated angle and the measured angle and control horizontal movement of trolley / hoist in accordance with said comparison. The controller may be configured to determine a difference between said estimated angle and the measured angle. The controller may be configured to determine if said difference exceeds a threshold. The difference between said estimated angle and the measured angle may a define an error value. The controller may be configured to decelerate the trolley (i.e. reduce the speed thereof) when said threshold is exceeded. When the threshold is exceeded, the controller may be configured to drive the trolley at a lower speed. The speed may be a non-zero speed. The speed may be maintained (i.e. trolley is still actively driven). The speed may be decelerated towards zero speed. The threshold may comprise a first threshold. When the threshold is exceeded, the controller may be configured to stop the trolley. The threshold may comprise a second threshold. The second threshold may be greater than the first threshold. The controller may be configured to activate a brake. The controller may reduce power to the motor until the trolley reaches a zero speed. When threshold is exceeded, the controller may be configured to drive the trolley in a direction to reduce said angle difference. When threshold is exceeded, the controller may be configured to prevent travel in first direction, and permit travel in a second direction. The second direction may be an opposing direction to the first direction. The first direction may be direction of travel preceding before said threshold is exceeded. The trolley may be configured to move in the second direction a speed lower than a normal or maximum speed of the trolley. When said threshold is exceeded (e.g. the third threshold), the controller may be configured to automatically move the trolley in the second direction. The controller may be configured to move the trolley until the difference between said estimated angle and the measured angle reaches a threshold value. The threshold value may be when the difference between said estimated angle and the measured angle is less than or equal to zero and / or when the measured angle is indicative of when the carrying member extends in a vertical direction. The controller may be configured to move the trolley until the measured angle reaches a threshold value. The threshold value may be when the measured angle is less than or equal to zero and / or when the measured angle is indicative of when the carrying member extends in a vertical direction. When said difference between said estimated angle and the measured angle is outside a predetermined range or below / above a predetermined threshold, the controller may be configured to maintain normal operation of the trolley (i.e. no deceleration or stopping is applied). In normal operation any determination of angle difference may be disregarded. The further threshold may greater than the first and / or second threshold. The further threshold may indicate an angle difference indicative of erroneous or unrealistic angle difference. When the trolley moves in given direction and said measured angle is indicative that the carrying in angled toward the given direction relative to the estimated angle, the controller is configured to maintain normal operation of the trolley. The trolley may be configured to vary the effective length of the carrying member to provide vertical movement of the load in use (e.g. via a hoist mechanism). If said threshold or range of vertical position is exceeded, the controller may be configured to disregard any determination of angle difference. The controller may prevent variation the length of the carrying member in one or more direction. The dynamic model may be a function of one or more of: the length of the carrying member; or the acceleration or speed of the trolley. The acceleration or speed may be the vertical and / or horizontal speed of the hoist / trolley. The dynamic model may comprise a pendulum model. The dynamic model may comprise a state observer. The system may comprise an acceleration sensor. The controller may determine acceleration of the trolley via operating parameters of a motor (e.g. a speed command) configured to drive the trolley. The crane system may comprise a sensor configured to measure the effective length of the carrying member. The length sensor may comprise a rotary encoder (e.g. on the motor or drum of the hoist system). The effective length may be calculated periodically (e.g. between 0.1 and 1 second). The effective length may be determined when the carrying member has changed length by a predetermined threshold (e.g. every 10cm). The angle sensor and / or the length sensor comprises a laser, optical, time-of- flight or radio-based system to determine the effective position the carrying member. The sensor may determine a virtual length and / or angle. The angle sensor may comprise one or more inclinometer. The angle sensor may comprise a rotary encoder. The trolley may be mounted to a bridge or gantry. The bridge or gantry may be movable about one or more axis. The trolley may be movable in two horizontal directions. The dimensions may be provided in the horizontal plane. The controller may measure the angle of carrying member in the respective dimensions. Said estimated angle and / or measured angle are determined in two-dimensions accordingly. The controller may be configured to drive the trolley in the respective dimensions. The controller may be configured to continually monitor the carrying member angle and / or length. The controller may operate in real time. The controller may comprise a proportional controller to control said speed. According to a further aspect of the invention, there is provided: a method of operating a crane system comprising: providing a trolley or hoist to support a load and movable about a horizontal direction to provide movement of the load in a horizontal direction accordingly; providing a carrying member supported by the trolley / hoist and configured to carry the load in use; measuring the angle of the carrying member relative to the trolley / hoist; providing a dynamic model of the trolley / hoist to determine an estimated angle of the carrying member during movement of the trolley / hoist; and comparing the estimated angle and the measured angle and controlling movement of trolley / hoist in accordance with said comparison. The carrying member may comprise a motor to vary the length thereof. The hoist / trolley may comprise a motor to effect movement of the horizontal position thereof. The bridge or gantry may comprise a motor to effect movement of the horizontal position thereof. The crane may comprise an overhead and / or jib crane. According to a further aspect, there is provided: a computer program or computer readable medium comprising program instructions which, when executed by the computer, cause the computer to carry out a computer process implementing the method according to claim 15. Any aspect of the invention may be combined with any other aspect of the invention where practicable. Description Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings: Figure 1A shows a schematic view of a first crane system; Figure 1B shows a schematic view of a second crane system; Figure 2 shows a schematic view of a dynamic pendulum model; Figure 3 shows a schematic view of a control regime; Figure 4 shows a schematic view of a control system. A crane system 2 is shown schematically in figure 1. The crane comprises a bridge or overhead crane. The crane 2 comprises bridge portion 4. A hoist mechanism 6 is mounted to the bridge portion 4 and is movable along the length thereof. The bridge 4 may comprise a girder, beam, rail, jib or the like. The hoist 6 comprises a carriage or trolley 7 movably mounted to the bridge 4. The carriage may comprise a wheel, bearing or roller to provide movement thereof. Movement may be effected by a motor 8 provided on the trolley 7. The motor may comprise a gearbox or the like. The gearbox may then be operatively connected to the wheel / bearing / roller. In other embodiments, the trolley 7 may be effected via external driving means (e.g. via a screw drive or endless loop). A motor may be provided to effect movement of the gantry / bridge portion, where the gantry / bridge 4 is movable. The motor may comprise a gearbox. The gearbox may be connected to wheel or the like to drive the gantry / bridge. The gantry / bridge 4 may be mounted to gantry, rail, guide or support structure to allow horizontal movement thereof. The gantry / bridge 4 may be movable along a rail 9 or pair or rails. The bridge may comprise one or more wheel 11 configured to engage the ground, rail or the support structure where provided. The bridge may comprise a plurality of legs 13. The wheels 11 are provided on the legs 13. This provides a gantry crane like arrangement. In the embodiment shown in figure 1A, the rail 9 may be provided on fixed structure. The wheels 11 are therefore mounted directly to the bridge 4. This provides an overhead crane like arrangement. A carrying member 10 is provided on the hoist 6 to allow connection to a load in use. The carrying member 10 is typically flexible. For example, the carrying member may comprise a rope, cable or chain. The rope may comprise a metallic (e.g. steel) or polymeric / synthetic rope. In some embodiments, the carrying member may be rigid or comprise rigid portions. A connector 12 is provided at an end of the carrying member 10 for connection to a load. The connector 12 may comprise a hook, eyelet, carabiner or the like. The carrying member 10 is presented in a schematic manner in figure 1, and it can be appreciated that the carrying member 10 may be looped over a pulley (e.g. to form a pulley system) and / or comprises a plurality of parallel members. The “end” of the carrying member 10 may comprise a lowermost point of the carrying member 10 in use. The crane 2 may be configured to raise / lower the load. For example, the hoist 6 may comprise a winch, pulley system and / or other hoisting mechanism for effecting movement of the load in a vertical direction in use. The winch / pulley may pay-out or pay-in the carrying member 10. A drum (e.g. a rope drum) or spindle may be provided to store the carrying member 10. A motor may be provided to effect movement in the vertical direction (i.e. to rotate the drum). The motor may comprise a gearbox. A remote controller 14 may be provided to provide operation of the crane 2. The remote controller 14 may allow adjustment of the position of the trolley 7 along the bridge 4 and / or the vertical position of the load. The remote controller 14 may be wired or wireless. The remote controller 14 may comprise a pendant or radio controller. It can be appreciated that the exact form of the crane is not pertinent to the invention at hand, and in generally terms, the system comprises a hoist movable in a horizontal direction. The crane may comprise any suitable type of crane, for example one or more of: an overhead / bridge crane; a tower crane; a gantry crane (e.g. the bridge portions is movable); deck crane; jib crane; or hammerhead crane. Typically, any of the aforementioned driving motors are electric motors. In normal operation, the connector 12 lags behind movement of the trolley 7 due to the inertia of the connector 12 and / or the load thereon and / or frictional forces. The carrying member 10 is therefore angled with respect the vertical direction 16 in use, at least for a portion of the travel of the trolley 7. The carrying member 10 may be angled by angle, ^. The present system is configured to estimate said angle and then compare the estimated with a measured angle of the carrying member. If the load or connector 12 is snagged on an object, then the angle will typically increase, as the trolley 7 moves forward whilst the load remains stationary. This increase in the measured angle relative to the estimated angle can therefore be used to determine if the load or connector 12 is snagged or is otherwise not moving in a desired fashion. The method of determining the estimated angle is described with reference to figure 2. The load on the crane may be approximated by a dynamic model of a pendulum, where the connector 12 acts as a pendulum. H is defined as the length of the pendulum (i.e. distance to center of mass of hook / load), ^ is defined as the angle of the rope and a is the acceleration of the hoist (or bridge). The model may therefore be defined as: where g ≈ 9.8 is constant of gravitational acceleration and ω is angular velocity. The acceleration, a, may be determined by any suitable means. For example, the acceleration can be determined by taking derivative of inverter speed command. Additionally or alternatively, the hoist may comprise a rotary encoder to determine speed thereof an acceleration accordingly. In some embodiments, the trolley 7 may comprise inertial and / or position sensors. The acceleration data may be low pass filtered, for example, to filter out erroneous or unrealistic data. Linearizing, assuming a constant pendulum length H (hoisting changes slowly compared to pendulum dynamics), and converting to state-space format with state A pendulum period is defined by: A “state observer” is provided by the system. The state observer provides an estimate of a state of a physical system to provide model or control regime thereof. The state observer for the pendulum system is defined by: where are observer gains. The gains can be calculated by setting the characteristic polynomial of the system to the desired polynomial. As a desired polynomial we select where p is the location of the pole. In the present example, as the system is an oscillating system, and we want no oscillations, we set p on the real axis. Other selections may be possible (e.g. some values may be negative on the complex plane). L can then be solved by: Since the system is modelled as a pendulum, in the present example, the observer poles are set in relation to the pendulum period. The relation between the pole and settling time of the system is given by If the settling time is set to half the pendulum period is defined by: where is a tuning parameter that can be used to tune the observer settling time in relation to the pendulum period. The amount of correction the observer performs based on angle error can be set by another tuning parameter, The tuning parameter is defined that such that the parameter scales the observer gains. For snag detection, the observer state should typically only be corrected by a small amount for detecting pendulum behavior differing from normal sway. Typically, the error gain is The observer gains are thus as a function of pendulum length, as defined below: The observer gains are a function of rope length. This length may change as the hoist mechanism 6 is used to move the load in the vertical direction. A sensor is used to determine the effective length of the carrying member 10. The length sensor may comprise an external encoder (e.g. pulse or absolute) on the hoist motor, gear or rope drum axis (e.g. to monitor number of axle / drum rotations). Alternatively, the length may be determined via an inverter which monitors hoisting position from (e.g. motor encoder or motor speed feedback). The effective length is updated at regular intervals (for instance every 0.1 seconds or 1 seconds) and / or when rope length changes by certain threshold (for instance 10 cm). The observer is therefore updated in accordance with the current operation point. The observer typically operates in real-time or near real-time. It can be appreciated that above regime is one example of a state observer for determining the dynamic movement of the pendulum. Observer dynamics can be derived with other methods, and the other observer feedback gains L can be selected differently accordingly. Concurrently or in parallel, the system is configured to determine the actual angle, ^, of carrying member 10 / connecter 12. An angle sensor is used to measure said actual angle. The system runs the pendulum observer model and compares the measured rope angle to the observer estimate angle, ^^. If the angles differ by a predetermine amount, a snag is detected accordingly. In the present embodiment, the hoist is movable in 2-dimensions in the horizontal plane. For example, the hoist moves in both “trolley” and “bridge” directions. As such, two pendulum observers are used, one for each direction. Similarly, a two-axis rope angle sensor is needed. A variety of methods may be used to determine the angle or inclination of the carrying member, for example, one or more of: ^ An inclinometer attached to a portion of carrying member 10 and / or the connector 12. The inclinometer may be attached near a terminal end of the carrying member 10 (the end adjacent the trolley 7 and / or the connector 12). Multiple inclinometers may be provided. The inclinometers may be spaced along the axis of the carrying member 10. The angle may be determined as an average of the inclinometers. The sensor(s) may be provided at or adjacent a fixed end of the carrying member 10 (i.e. the end not configured to be reeled in). This ensures the sensor is not fed into a drum etc. ^ A potentiometer or encoder on fixed end joints or pivots connecting the carrying member 10 to the trolley 7. ^ Using an optical sensor. For example, one or more camera may be provided to determine the position of the carrying member 10 and / or connector 12. Two or more cameras may be used to capture a stereo image of the carrying member / connector, thereby allowing determination of the position thereof. The system may use machine learning or AI to allow accurate detection. ^ Using time-of-flight (ToF) type systems. For example, RADAR, LIDAR, laser range finding systems may be used. This allows passive detection of the position of the carrying member / connector ^ Using active tracking systems. The carrying member / connector is configured to emit a signal allowing determination of the position thereof. For example, the system may use one or more of: ultrasound; a radio beacon; or an ultra wide band (UWB) radio. It can be appreciated that where laser, optical, ToF, or active tracking systems are used to determine the position of the carrying member / connector, a virtual angle may be determined (i.e. rather than calculating the physical angle, a virtual angle is calculated given a known length and position of the carrying member 10 / connector 12). In some embodiments, the angle need not be determined at all, as the position or displacement, can be determined in absolute terms. Similarly, such systems can be used to determine the effective rope length, H, or other variable in the state observer. An angle error is defined as a function of the difference between the estimated angle, , and the measured angle, : where is the measured angle in a first dimension, is the measured angle in a second dimension, and are the respective angle estimates. and may relate to the angles measured in the trolley movement direction (i.e. along the axis of the bridge) and the bridge movement direction respectively. In other embodiments, the trolley 7 moves about a single axis. The angle error is defined as: where is the measured angle in the first dimension, and is the respective angle estimate. A snag is detected when magnitude of angle error ̅ exceeds a threshold, ^ The snag detection system is activated when said threshold, is exceeded accordingly Since an excess angle in the travelling direction, typically does not indicate snagging or other undesirable movement, angle errors exceeding threshold when angle is in the travelling direction can be ignored from snag detection. Typically, the angle difference used in the above may be limited to within a predetermined parameter. The angle difference may be limited to within a predetermined range or threshold. For example, if the difference exceeds a threshold value, then the measurements may be disregarded. This may help to eliminate large noise spikes or large angle tracking errors which can cause instability in the system. It can be appreciated that such a system may simply disregard measured angles, that are outside a predetermined parameter. For example, if the measured angle is above 90 degrees from vertical, then it is unlikely to represent a real-world value. In the event a snag is detected, the system acts to prevent further entanglement or damage to the system or load. This is achieved by decelerating and / or stopping of the hoist. In the present embodiment, when error, exceeds first threshold value, the trolley 7 is configured to decelerate. The trolley 7 may decelerate to predetermined speed. The predetermined speed may be less than or equal to 50%; preferably less than or equal to 30% of the maximum speed of the trolley 7. This may allow the load or carrying member 10 to untangle or unsnag itself. The system continues to monitor the angle of the rrying member 10 and determine the error, If the error, | | exceeds second threshold value, the trolley 7 is configured to stop completely. Brakes or other retarding force (e.g. reverse motion) may be activated. Alternatively, the power to the motor 6 may be denied and frictional forces cause the trolley 7 to stop. This allows the user to manually intervene. Typically, the user moves the trolley 7 in the reverse direction, for example, using the remote control 14. The trolley 7 can moved until the carrying member 10 is in a vertical direction 16 or until the load has become untangled. The system may be configured to prevent movement in the forward direction to prevent further entanglement. For example, the system is configured to deactivate or ignore commands to drive in the forward direction and only allow driving in the reverse direction. In some embodiments, the system may automatically reverse the trolley 7. The system may be configured to reverse the trolley 7 until error, |^|, or the absolute angle, is less than a predetermined threshold. For example, the system may drive the trolley 7 until the carrying member 10 is angled less than 0-5 degrees from the vertical direction. Once a snag is detected, the detection system may become inactive when the absolute angle: is below a predetermined threshold, Typically, such a threshold, is close to zero, and significantly less than the activation threshold, The system then allows the user to move the trolley 7 in forward direction. The system than continues to monitor the angle error, | | as previously described during operation thereof. In other embodiments, the user may manually reset the system. The control regime is shown in detail in figure 3. Each action is shown for a respective measured angle, , with indicating the angle away from the movement of the direction (e.g. toward left side of figure 1) and − indicating the angle away from the movement of the direction (e.g. toward right side of figure 1). The system determines the estimated angle, and measures the actual angle, Where the angle is negative or less than the estimated angle, the error, is disregarded as the carrying member 10 is travelling forward of the estimated angle. Where the measured angled, is greater than the estimated angle, but less than a threshold angle, the error, is less than threshold value and so no action is taken and the error, , can be disregarded. Once, the measured angled, exceeds the threshold angle, the error, is greater than threshold value and so the snag detection system is activated If the measured angled, is less than a second threshold angle, the trolley 7 is simply decelerated. The trolley 7 may continue to move at a predetermined speed. It can be appreciated that the predetermined speed may vary in proportion to the detected angle. For example, a plurality of thresholds of increasing measured angle may be provided, and the speed may decrease with each threshold. Alternatively, the speed may ramp down in a continuous fashion. If the measured angled, then exceeds the second threshold angle, (e.g. because the load is still snagged) the trolley 7 is stopped completely. The user then manually moves back the trolley 7, until the carrying member 10 is near vertical and the system deactivates The trolley 7 is moved such that that the measured angle, decreases. The speed at which the trolley 7 moves may be limited to a predetermined value. Said value will typically be lower than a normal or maximum operating speed of the trolley. In some embodiments, the trolley 7 may be configured to automatically move backwards until the error, reaches a certain threshold value. Said value may indicative of when the trolley 7 is vertically above the load (i.e. and / or when the angle is close to and / or less than the estimate value, If at any time, the measured angle, is greater than a first threshold angle, the error, may be disregard. This avoids obvious errors or introducing instability in the state observer. When the snag detection system is activated hoisting (i.e. vertical movement) is prevented. This prevents the user using the hoisting movement to further increase entanglement. In the present embodiment, hoisting up (i.e. decreasing the length of the carrying member 10) is prevented. Hoisting down (i.e. increasing the length of the carrying member 10) may be allowed to help untangled or unsnag the load. In some embodiments, all hoisting may be prevented, for example, to prevent the load hitting the ground if the hoist 6 is reversed. Although, the above system is described with reference to moving in a single direction / dimension, it can be appreciated that such an arrangement can be used in any travel direction or dimension accordingly. It can be appreciated that the above system can act to move the bridge / gantry to effect movement of the trolley. When the direction of travel incorporates trolley and bridge movement, then the system will operate in on both the trolley and bridge accordingly. Thus, in general terms, the system moves the trolley 7 about a horizontal plane by either driving the trolley 7 directly, or driving the bridge / gantry 4 upon which it is placed. The snag detection system 18 is shown schematically in figure 4. The system comprises a controller 20. The controller 20 comprises any suitable processing system. The controller 20 may comprise one or more of: a processor; microprocessor; microcontroller; volatile and / or non-volatile memory; SoC etc. The controller 20 may comprise an analog and / or digital computing device. The controller 20 may comprises an embedded or industrial PLC. Any of the above parameters (e.g. thresholds) and / or pendulum model parameters may be stored in non-volatile memory. The parameters can be input and / or configured to match crane and crane operator desired snag detection threshold. The angle sensor 22, length sensor 24, and optical / ToF / active tracking system 26 (where provided) are configured to operatively communicate with a controller 20. Acceleration data 28 is provided to the controller (e.g. by a separate sensor or as part of the driving system) The controller 20 is operatively connected to an inverter 30. The controller 28 can provide appropriate frequencies to the inverter to drive the motor 8 accordingly. Where the trolley 7 is not driven by an onboard motor 8, then controller 28 is operatively connected to offboard trolley driving means accordingly. In some embodiments, the controller 28 may be embedded or integrated with the inverter 30. The remote control 14 is operatively connected to the controller 28. The remote control 14 comprises one or more inputs to allow control of the trolley 7. The inputs may provide movement in the horizontal direction (i.e. along the bridge 4) and / or the vertical direction. This may allow the system 2 to act in a conventional manner. The controller 20 comprises a travel controller 32, state observer 34 and snag detection subsystem 36. The travel controller 32 is configured to drive the motor (to drive the trolley and / or bridge) in accordance with the instructions provided by the remote control 14 and / or the snag detection system 36 (e.g. to slow, reverse or stop the motor 8). The travel controller 32 may provide the acceleration data 28. The state observer 34 is configured to determine estimated angle as previously described. The snag detection module 36 is configured to compare the estimated value from the state observer 34 and compared this with measured angle from the angle sensor 22. The present system provides detection of the snagging of a load on a crane, helping to prevent accidents and / or damage to a load. The system uses a dynamic model to determine an estimate of an angle of normal operation. The threshold at which operation is considered abnormal (i.e. due to snagging), is thus determined by said dynamic model. This provides a more accurate and flexible system then those determined experimentally, such as in that provided in WO 2013 / 041770. The present system may therefore be used in a plurality of different crane types or arrangements with minimal configuration. Once snagging is detected, the system acts to automatically reduce the risk of further hazard. The system may automatically reverse the hoist to help with unsnagging.

Claims

Claims:

1. A crane system (2) comprising: a trolley (7) to support a load and movable about a horizontal direction to provide movement of the load in a horizontal direction accordingly; a carrying member (10) supported by the trolley (7) and configured to carrying the load in use; a sensor (22,24) to measure the angle of the carrying member (10) relative to the trolley (7); a controller (20) configured to provide a dynamic model of the trolley (7) to determine an estimated angle of the carrying member (10) during movement of the trolley (7); and where the controller (20) is configured to compare to the estimated angle and the measured angle and control horizontal movement of trolley (7) in accordance with said comparison.

2. A crane system according to claim 1, where the controller (20) is configured to determine a difference between said estimated angle and the measured angle and determine if said difference exceeds a threshold.

3. A crane system according to claim 2, where the controller (20) is configured to decelerate the trolley (7) when said threshold is exceeded.

4. A crane system according to claim 2 or 3, where when the threshold is exceeded, the controller (20) is configured to drive the trolley (7) at a lower, non-zero speed.

5. A crane system according to any of claims 2-4, where when the threshold is exceeded, the controller (20) is configured to stop the trolley (7).

6. A crane system according to any of claims 2-5, where when threshold is exceeded, the controller (20) is configured to prevent travel in a first direction, and permit travel in an opposing direction.

7. A crane system according to any of claims 2-5, where when said difference between said estimated angle and the measured angle is above a further threshold, the controller (20) is configured to maintain normal operation of the trolley (7).

8. A crane system according to claim 7, where the further threshold is greater than the first threshold.

9. A crane system according to any preceding claim, where when the trolley (7) moves in given direction and said measured angle is indicative that the carrying member (10) is angled toward the given direction relative to the estimated angle, the controller (20) is configured to maintain normal operation of the trolley (7).

10. A crane system according to any preceding claim, where the trolley (7) is configured to vary the effective length of the carrying member (10) to provide vertical movement of the load in use, and if said threshold is exceeded, the controller (20) is configured to prevent variation the length of the carrying member (10) in one or more direction.

11. A crane system according to any preceding claim, where the dynamic model is a function of one or more of: the length of the carrying member (10); or the acceleration or speed of the trolley (7).

12. A crane system according to any preceding claim, comprising a sensor (24) configured to measure the effective length of the carrying member (10).

13. A crane system according to claim 12, where the angle sensor (26) and / or the length sensor (24) comprises a laser, optical, time-of-flight or radio- based system to determine the effective position the carrying member (10) and determine a virtual length and / or angle.

14. A crane system according to any preceding claim, where the trolley (7) is movable about two dimensions in the horizontal plane, and saidestimated angle and / or measured angle are determined in two-dimensions accordingly.

15. A method of operating a crane system (2) comprising: providing a trolley (7) to support a load and movable about a horizontal direction to provide movement of the load in a horizontal direction accordingly; providing a carrying member (10) supported by the trolley (7) and configured to carry the load in use; measuring the angle of the carrying member relative to the trolley (7); providing a dynamic model of the trolley (7) to determine an estimated angle of the carrying member (10) during movement of the trolley (7); and comparing the estimated angle and the measured angle and controlling movement of trolley (7) in accordance with said comparison.

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