The present invention relates to a method and a system to detect the occurrence of a slack hoisting line of an operating winch, as appear in the preamble of the following claims 1 and 6, respectively.

In the present specification the term hoisting line is a generic term covering hawser, ropes, wire ropes, chains or bands used in the applications in question.

Cranes and submersible lifting systems, launch and recovery systems for survival craft and rescue boats, anchor mooring systems, elevator systems are examples of multi-layer spooling applications for which the invention applies.

In any multi-layer spooling application, such as in pedestal mounted marine crane systems, it is important to avoid any slack on inner line layers that can be crushed and nicked against the groove walls by outer layers or lead to improper spooling and entangled line. Improper spooling may cause uncontrolled movement of load in other end of the hoisting line during hoisting/lowering.

Stated scenarios could in worse case lead to personal injuries also, and therefore it is important to be able to detect slack hoisting line at winch as soon as possible and give an alarm to the operator or/and automatically stop the spooling.

Due to above stated consequences and to minimize the risk of any personal injuries by focus on health and safety, many of the independent classification regulations applicable for marine / offshore cranes as Det Norske Veritas (DNV), Lloyd ^' s

Register and American Bureau of Shipping together with international standards as NS EN 13852-1 are treating the subject and demand a device for detection of slack rope at drum. The state of art - existing devices.

One of the present devices for detecting slack hoisting line comprise mechanical device that may be mounted underneath the winch drum and work as a trigging device if the hoisting line is getting loose and hitting the device. Usually it is underneath the drum such device should be mounted due to gravity of the hoisting line. Within applications for example of cranes where the winch is mounted onto the jib where the direction of center of gravity of the rope will vary, this method is considered to be unstable. For a multi-layer spooling application where the inner diameter of the drum differs a lot from the outermost layer it is hard to calibrate the device and the method is considered to be unstable.

In another proposal, photoelectric sensors are mounted in suitable places on the winch to assure detection of slack hoisting line at drum. Within applications where the direction of center of gravity of the rope will vary, this method is considered to be unstable.

Yet another method includes means to monitor the actual load in hoisting line hook to trig an alarm if there is a rapid difference in load. Due to the wide range of load in the other end of the hoisting line of up to several hundreds of tons, the method becomes unstable, especially when there is no load except from loose gear attached in the other end. It is also normal to operate video camera(s) mounted in such position to allow an operator to constantly overview the winch and assure no slack of the hoisting line.

Regarding previous known embodiments, reference is made to the following US patent documents: US-3,462, 125A, US - 2010/0057279 and US-4,547,857A.

Objects of the present invention.

An object of the present invention is to present another, different and improved method and system to detect and monitor a slack hoisting line. A further object is to remedy the above mentioned disadvantages of the existing devices.

The present invention.

The method of the present invention appears in the characterising clause of the following claim 1 , in that the current rotating ratio VA / VB = Kx between the winch drum and the sheave is monitored to ensure that the ratio Kx is kept within a given range, and the detection of a rotating ratio outside the given range will trig an alarm to the winch operator and/or stop the winch operation.

According to a preferred embodiment the rotating ratio calculation is based on the diameter ratio Kx between the diameter DAX of the winch drum and the diameter DBO of the sheave, in that the sheave and drum rotate together.

According to a another preferred embodiment said ratio Kx is adjusted to change depending on the current hoisting line layer on the drum surface with the given hoisting line section diameter.

According to yet a preferred embodiment the rotating velocities of the winch drum and sheave, and the actual diameter DAX of the winch drum depending on the hoisting line layer are determined by means respective sensors units each generating pulse trains which are handled in a programmable logic controller (PLC) controlling the winch operation to trig said alarm and/or stop action.

Preferably the sensor used to determine the winch drum and sheave velocities is one of an encoder, a proximity sensor, a photoelectric sensor, and said velocities are determined by means of an angle encoder.

The system to detect the course of a hoisting line of an operating winch including a winch drum spooling on and off the hoisting line that extends over a sheave, is characterised in that it includes means to detect the actual rotating velocity VA and VB of the winch drum and sheave respectively, and

means to calculate the current rotating ratio VA / VB = Kx between the winch drum and the sheave, and

means to trig an alarm to the winch operator and/or stop the winch operation based on an deviating value of said rotating ratio Kx.

Preferably the rotating ratio calculation is based on the diameter ratio Kx between the diameter DAX of the winch drum and the diameter DBO of the sheave, in that the sheave and drum rotate together. According to a preferred solution, said ratio Kx is adjusted to change depending on the current hoisting line layer on the drum surface with the given hoisting line section diameter. According to a another preferred solution the system comprises sensors units to determine the rotating velocities of the winch drum and sheave, and the actual diameter DAX of the winch drum depending on the hoisting line layer and a programmable logic controller (PLC) to which generated pulse trains are transmitted, and said PLC controlling the winch operation to trig said alarm and/or stop action.

Preferably the sensor system used to determine the winch drum and sheave velocities is one of encoders, proximity sensors, photoelectric sensors, or

combinations thereof, and said velocities are determined by means of an angle encoder.

To obtain an extra degree of operational security for the winch system, more than two sensors given above, may be used to sense the rotational velocity of the same drum or sheave. It is also possible to combine two or more sensor systems to sense on the same drum or sheave.

Advantages of the present inventions.

With the present invention the following risk reductions are obtained: The operator does not need to manually monitor the winch and will therefore have a better overview of the total operation. He does not need to manually monitor the winch at all times and therefore the human factor of failure may be disregarded. Loss of signal from sheave sensor will instantly trig an alarm or/and stop the winch - fail safe. If the sheave will "jam" due to any reason, sensor will trig an alarm or/and stop the winch, being fail safe remedy.

In the invention, accuracy regarding detection of slack rope at drum is easy to adjust with aid of the predetermined ratios depending on application.

The inventive method that may be used in vary applications in that it may prevent severe system failure due to rapid alarm. Further it is a secure and stable method.

The structure of the invention may be successfully used in for winch systems operating for example davits, mooring systems, vessel anchor systems, cable cars, aerial cableways, lifts, and trolley tracks, in addition to operating different crane structures which are especially mentioned in the present text. The use of the present area within these technical fields, represents increasing operation security. Additionally it may prevent these structures to be exposed to fatal damages caused by malfunctions in a winch system. Drawing figures to be disclosed.

The present invention will be further explained with reference to use in a crane structure as a preferred use example, and to the following drawing figures, wherein.

Figure 1 shows in a perspective a crane using the invention for winch drums generally.

Figure 2 and 3 show in perspectives the details of the sheave and winch drum of said crane structures, respective. Figure 4 shows the principle of the present invention for detection of slack hoisting line, based on the winch line stretch from a winch drum and over a line sheave.

Figure 5 shows a section view of said multi-layer winch drum showing the different hoisting line layers around the winch drum surface, and to illustrate the diameter difference due to the numbers of hoisting line layers.

Figure 6 shows an elongated section of the multi layered -three layers D1 , D2, D3 - view seen along the rotating axis X-X of the winch drum. Figure 7 shows an enlarged detail of the three hoisting line layers D1 -D3 on the winch drum.

A disclosure of specific and preferred embodiments of the invention.

Initially the invention is explained with reference to Figure 1 which shows a pedestal mounted marine crane 10 of a vertical support 12 carrying a boom 14 hinged connected to the top section of the vertical support 12, and may pivot up and down by means of a hydraulic driven piston/cylinder-system system 16. The crane winch system includes a winch drum 22 including a driving element for operating a hoisting line 18 extending from the drum 22 along the topside of the boom and over a free running sheave 30 for holding a load (not shown) suspending at the end of the hoisting line 18. A second sheave 32 for an auxiliary winch may be connected to the same boom 14. Said sheave measured on does not need to be the boom peak Figures 2 and 3 show enlarged views of the winch drum 22, the sheave 30 and the hoisting line 18. As shown in figure 2, the surface of the winch drum 22 includes a continuous recess forming a spiral shape from one end of the drum to the other. With reference to figures 5, 6 and 7, when winding up the hoisting line 18 the inner drum surface spiral is first coiled up representing the diameter D1 as shown in figures 6 and 7. Then the line 18 is lifted one step upward to the layer representing the diameter D2, and in the next turn into the third layer of diameter D3. Figure 4 illustrates the principle of the present invention, as will be described more in detail in the following.

The length L of winch drum 22, in parallel to the rotational axis, is shown on figure 6, while and the hoisting line 18 diameter Dr is shown on figure 7. Both these figures (each may be denoted a "parameter") show the actual diameter for the three layers D1 , D2 and D3, while figure 5 also shows a fourth layer D4. The rotating axis X-X is also shown on figure 6

Each time there is a change in actual winding layer, the control system enters the new value for the actual winding diameter, one of D1 - D4 in sequence, for the winch drum 22. When unwinding the hoisting line 18 from the drum, said value KX for each layer, i.e. D4 - D1 , is registered in the opposite sequence.

Detection of slack hoisting line principle.

The main objective of the invention is to detect any possible occurring slack rope at winch drum 22 by controlling the ratio VA / VB = Kx between the rotation velocity VA of the winch drum 22 and the rotation velocity VB of the sheave 30.

In the system a range for the velocity ratio Kx is set to be within a range between a minimum value Ymin and a maximum value Ymax. When the system detects a Y- value outside this range the winch drum is arranged to stop in that the reason for the change may be due to some kind of damaging error in the winch operation. More precise the system and the winch operator is alarmed and or the winch operation is ceased.

This also implies to control that the tension of the line between the winch drum 22 and the sheave 30, is kept within a certain range. The invention of detecting slack hoisting line 18 at drum 22 is independent of multilayer spooling application and based on an already known technology "gear ratio", where below data must be known and used as input to monitor the difference in velocity between two rotating circular objects (drum 22 and sheave 30).

Current velocity of winch drum 22 (VA) [rpm]

Length of winch drum 22 (LW) [mm]

Hoisting line (18) diameter (DR) [mm]

Winch drum diameter (DO) [mm]

Actual diameter of winch due to current layer D1 -D4 (DAX) [mm]

Diameter of sheave (DBO) [mm]

Current velocity of sheave (VB) [rpm]

Due to above input, it is possible to calculate current diameter ratio between the two rotating circular objects, in this case the winch drum 22 and sheave 30.

DAX /DBO = current ratio (Kx)

Due to friction from rope 18, forcing the sheave 30 to rotate together with the winch drum 22, the theoretical current rotating velocity of the sheave 30 is calculated.

VB = Kx ^* VA

The above information enables constantly control of current velocity ratio between the drum 22 and the sheave (VB).

VA / VB = Kx

Detection of predetermined differences (Ymax / min) will trig an alarm or/and stop the winch until necessary actions have been taken.

Ymin < Kx < Ymax

Input parameters

The current velocity of the winch is constantly monitored for an example with the aid of an Angle encoder generating a pulse train from the sensor that can be used to calculate the rotational velocity of the winch in the onboard PLC (Programmable Logic Controller).

When winding up the hoisting line, the inner layer on the drum surface is first coiled up in the diameter D1. Then the hoisting line 18 is lifted one step upward to the position layer representing the diameter D2, and in the next turn into the third positioned layer representing the diameter D3. The control system registers these shifts in rotating diameter from D1 , via D2 and D3, and a new value for the equation VA/VB is added as the basis for the computation of a new Kx - value for each layer.

The length L of winch drum 22, the hoisting line 18 diameter Dr and the layered position of the hoisting line is easily determined. Also the sheave 30 diameter is easily measured. Thus the an actual diameter D1 , D2, D3, D4 (figure 5) of the hoisting line 18 on winch 20 drum 22 due to current layer D1 -D4 is constantly monitored for example with the aid of a PLC, together with earlier stated input.

Each time there is a change in actual winding layer, the control system enters the new value for the actual winding diameter, one of D1 - D4 in sequence, for the winch drum 22. When unwinding the hoisting line 18 from the drum, said value KX for each layer, i.e. D4 - D1 , is registered in the opposite sequence.

Monitoring the sheave 30 velocity due to hoisting line 18 frictions is critical and important within this invention and may be obtained with any kind of sensor capable of detecting rotary velocity.

Most common methods for RPM measurement are Encoders, Proximity Sensors, Photoelectric Sensors. Best (most accurate) measurement results will be obtained by utilizing an Angle encoder attached to the shaft of the sheave 30. A less expensive way to obtain the rotary speed of the sheave 30 is to use a magnetic proximity sensor to detect magnets placed on the sheave in such a way that they generate a pulse train from the sensor that can be used to calculate the rotational velocity of the sheave in the onboard PLC for an example. The same method is also valid for photo electric sensors.