WO2012101604A2

WO2012101604A2 - A device for reducing wear on cable in a winch operated wave power plant

Info

Publication number: WO2012101604A2
Application number: PCT/IB2012/050389
Authority: WO
Inventors: Ingvald Straume
Original assignee: Purenco As
Priority date: 2011-01-28
Filing date: 2012-01-27
Publication date: 2012-08-02
Also published as: WO2012101604A3; NO20110155A1

Abstract

The invention is a device to reduce cable wear and tear by allowing the cable to slowly be spooled over onto, or over from an additional winch (2), from or onto the main winch (1). The additional winch is mounted at the opposite end of the cable (3) compared to the main winch. The invention includes means to allow this spooling over to happen by itself, without human supervision or intervention being required. In this way, by allowing the additional winch to position shift the cable in relation to the segments of it rolling most frequently back and forth on the main winch, wear and tear is distributed over a larger portion of the cable, and the cable's life time is extended. In this way the invention becomes a substitute for manual slip and cut operations, which are used as a method for extending life time on cables in derricks. The invention is primarily intended for use with winch activated wave power plants, where long-term reliability, combined with low maintenance costs, is particularly desirable.

Description

A device for reducing wear on cable in a winch operated wave power plant

Background

Some wave energy conversion systems use cable, rope or line or the like— hereinafter referred to as cable only— combined with a winch- or block and tackle system, to absorb and transfer mechanical energy from ocean waves. Amongst these are

5 N0325878 and N03291 10. A challenge associated with these systems is that they often have a tendency that some parts of the cable is exposed to more wear and tear than other parts of the cable. This is valid for winch operated wave power plants, but also in other contexts, where a cable is used for transferring mechanical work, where the cable comes in contact with a winch drum or a pulley sheave or the like, and where the cable moves

10 reciprocatingly a great deal of the operational time, more or less along the same

sections. The cable is typically most worn along those sections at which it most often and with the greatest force spools onto and out of/off a winch drum, around a pulley sheave or the like. Such wear leads to a need for cable replacement after some time, in order to avoid risk of failure or uncontrolled shutdown of the winchVpulley system due

15 to cable break. An alternative to replacing the cable, is performing a so called "slip and cut" operation,— a method used in petroleum industry, as part of maintenance of drilling rigs, i.a. to extend the derrick tackle cable's life time. The method is about unspooling a certain cable length from a winch, releasing the connection point at the end of the cable, making a new end connection point on the cable, shifted appropriately

20 in the direction towards the winch, and then cutting off the excess loose end of the

cable. This operation is performed manually when the winch has moved a certain number of ton-miles. Thus, wear along the cable is distributed, and the cable lasts longer. When it comes to wave energy utilization, an important point is to keep maintenance costs at a low level, in order for wave energy utilization to become

25 commercially interesting. Performing manual maintenance on systems located in the sea, is cost-driving. This is particularly true in periods dominated by bad weather— and that's often when maintenance of the wave energy conversion systems is mostly needed. Shutdown of the plant during maintenance, also means loss of energy and loss of income.

30 The present invention relates to a device which automatically shifts the most high wear parts on the cable of a winch or block and tackle system, achieving the same purpose as manual slip and cut operations. The invention solves the challenge, described earlier, with wear of the cable concentrated in particular areas, without requiring man-hours, and without the need to shut down the system. The purpose of the invention is to extend the life time of the cable and reduce the need for manual maintenance of it. Applications

The invention can be used in situations where a cable is employed in such a way that wear and tear tends to concentrate along certain sections of the cable, for example where the cable the majority of the time and / or with the largest load moves in contact with a pulley, a winch drum or the like. Tackle- and winch systems, e.g. in drilling towers, passenger elevators and cranes, can benefit from the invention. But the area where the invention can be used with the greatest economic prospects, is in contexts where manual maintenance of cable, e.g. in replacing it or in slip and cut-operations, results in considerable costs. Costs include here:

1) direct costs of maintenance work

2) loss of income (e.g. as a result of loss of production) or loss that may be counted in any other way, caused by the need for taking the system out of service during maintenance.

Wave energy has a challenge with potentially large costs relating to both these points. Wave energy conversion systems/wave power systems having cable is the intended primary scope of application for this invention.

Known technology

US6932553 describes a "multipurpose system for a drilling and well intervention" which includes some of the same elements as the present invention:

"Two main hoisting winches 17 and 18 can be used in this invention. If two are used, each end can be wound onto a separate winch. By winding the two ends 26a and 26b each onto a separate winch 17, 18, as shown in FIG. 2, it is possible to achieve the same hoist cable speed at a relatively low speed of revolution on the winches 17, 18. (...) This design also allows hoist cable 25 that has reached its fatigue life to be wound from one winch 18 to the other 17 therefore eliminating the need to slip and cut the fatigued cable from the system thereby reducing

operational non productive time. "

(US6932553, col. 3, line 17 - 31)

However, US6932553 does not describe any activator system with control mechanism providing automatic spooling over, which is a characteristic of the present invention, c.f. claim 1. Neither does US6932553 describe any differentiation in behavior or design of the two winches ( "hoisting Winches 17 and 18 "), contrary to the present invention where the additional winch, c.f. claim 1, operates at a slow pace compared to the laboring/working main winch, and where the activator system— optionally with a blocking mechanism (cf. claim 2)— is connected to the additional winch.

Definitions of terms

In this written account the following terms have the following meanings:

Cable means cable or equivalent, such as rope, wire, etc.

Spooling over means that the cable is spooled out from one winch, i.e. the winch to which one end of the cable is fastened, and onto the other winch, i.e. the winch to which the other end of the cable is fastened, or vice versa.

Activator system means an arrangement of mechanical components— and possibly other components, e.g. electrical, electronic and/or hydraulic components— regulating the spooling over of cable, by determining when and on what conditions rotation of the additional winch is activated, and providing activation of such rotation.

Outward rotation (of winch) is rotation in the rotational direction that causes the cable to be spooled out from the winch drum.

Inward rotation (of winch) is rotation in the rotational direction that causes the cable to be spooled onto the winch drum.

A flow limiter is part of a hydraulic passage that serves to minimize, or on certain conditions prevent— totally or partly— the hydraulic flow through the passage. Figures and reference numbers

1 main winch

2 additional winch

3 winch cable

4 activator system governing the additional winch

5 worm gear wheel

6 worm screw

7 motor controlling unit

8 wave energy absorbing device (float)

9 winch unit

10 anchoring structure

11 umbilical (power cable)

12 water surface

13 pulley sheave (block)

14 gear transmission

14b output shaft from gear transmission

15 overrunning clutch (one-way clutch)

16 hydraulic pump

17 turbine unit with power take-off system

18 reservoir (oil tank)

19 hydraulic motor

20 hydraulic flow limiter

21a,b lock latches - blocking mechanism blocking mechanism

24 funnel

25 bend stiffener

Figure 1 shows the invention in one embodiment with the main components main winch 1, additional winch 2, activator system 4 governing the additional winch, and an exemplified embodiment of the blocking mechanism of the additional winch.

Figure 2 and Figure 5 show one of potentially many possible ways to integrate the invention with a winch activated wave power plant. Figures 3 and 4 show details of the same, with the same exemplified embodiment of the blocking mechanism 5, 6 as shown in Figure 1.

Figure 6 shows yet another example of how the invention may be integrated in a winch activated wave power plant, with main winch 1 and additional winch 2 attached to the same submerged structure and a pulley 13 attached to the float in such a way that the winch system and the pulley together adds up to a block and tackle for the cable 3.

Figure 7 shows an example of a hydraulic implementation of a sensor- and activator system for controlling the additional winch.

Figure 8 and Figure 9 show alternative blocking mechanisms for the additional winch. Description

A main winch 1 has a winch cable 3 spooled onto it, and the other end of the winch cable is spooled onto an additional winch 2 at the opposite end of the cable stretch.

The main winch is the laboring winch in the system, i.e. the one which rolls most frequently in and out. Compared to the wave power system described in

N0325878 this coincides with "vinsj 2" (see page 9, line 27). Compared to

N0329110, it coincides with "trommel 10" (see page 6, line 18).

The function of the additional winch is, at low speed compared to the main winch, to spool over cable, so that the most high wear parts of the cable is shifted as the main winch performs work which causes wear. This spooling over can be performed, either by having extra amount of cable spooled onto the main winch in advance, and spooling it over to the additional winch. Or by having extra amount of cable on the additional winch, and spooling it over to the main winch. The latter is the preferred method, because it requires less energy, as the tension force from the cable (the main winch) acting upon the additional winch, and the cable movement, is in the same direction.

The additional winch is governed by an activator system 4. This activator system controls the spooling over of cable, and determines whether, to what degree and on what conditions the additional winch may rotate. The activator system 4 may include a blocking mechanism which prevents the additional winch from rotating as a result of external tension force in the cable. In the Figures 1 - 7 this blocking mechanism is embodied in the form of a worm gear, with a worm gear wheel 5 mounted at the additional winch's shaft, and a worm screw 6 in contact with the worm gear wheel, arranged with the worm screw's shaft parallel to the tangent of the worm gear wheel disc in the plane of the worm gear wheel. The angle of the worm screw's threads is sufficiently close to 90° in relation to the worm screw's shaft, to produce a friction force greater than the pushing force when a torque acts from the worm gear wheel 5 onto the worm screw 6. Thus, the worm gear becomes self blocking, so that it can only transfer rotation with incoming torque from the worm screw's shaft. This is a standard procedure for constructing a self blocking worm gear, well known by engineers of mechanics. The design of blocking mechanism described here, and shown in the figures, is provided as an example. This is just one of many possible and by engineers known ways that can be employed to block the additional winch, so that torque applied onto the additional winch originating from the activator system 4 only, can cause rotation of the additional winch.

The activator system 4 includes a motor controlling unit 7, which regulates the activity of the activator system. The motor controlling unit includes a motor and means to govern the motor. 'Govern' here means having the ability to determine the motor's rate of work and/or to start and stop it. The term 'motor' is used in a broad sense, and refers to a device which causes rotation of the winch, for example by having one or more mechanical elements which have the ability to perform work to rotate the additional winch and/or suspend the blocking mechanism of the activator system (so that rotation of the additional winch can be done using external force). In principle this can be any device that can be constructed by a person skilled in the art, as long as it results in this ability. In the embodiment referred to by Figure 7, the motor controlling unit's motor is identical with the hydraulic motor 19. But the motor controlling unit's motor is not limited to being a hydraulic motor like shown in Figure 7. Nor are the means for governing the motor limited to being the same as shown in Figure 7.

The motor controlling unit decides when the additional winch is to spool over cable, and how much. In the exemplified embodiment of the activator system with a worm gear, this is done by having the motor controlling unit rotate the worm screw. The rate of spooling over may be chronometrically/time controlled, or determined by other parameters, such as: the frequency of force impulses (jerks) in the winch cable above a certain strength, or the product of force and the traveled distance of the cable (number of ton-miles).

Referring to the embodiment shown in Figure 1, a chronometrically controlled spooling over may be implemented e.g. if the motor of the motor controlling unit is some device with mechanical elements, which an engineer will be familiar with— e.g. a device with a loaded spring— , which over time performs work onto the worm screw's shaft and makes it rotate. In principle, any sort of clockwork mechanism can be used for this. Spooling over determined by the frequency of force impulses in the cable above a certain strength, may for example be achieved by utilizing the force acting axially on the worm screw's shaft when the cable is exposed to said force impulses, and then allowing this force to activate a certain rotation of the worm screw, using mechanics, for which a person skilled in the art who has been presented to the task, without inventive effort, will have no difficulty in providing means to perform the function .

Spooling over as a function of work performed by the winch (number of ton-miles) may for example be implemented by having electronic sensors which register the main winch's work load and traveled distance, and by having these data fed into a processing unit, for example a computer in the motor controlling unit, which calculates, based on the input in data, the amount of cable to be spooled over, and executes this spooling over by activating the motor controlling unit's motor, which may be an electric or hydraulic motor, for instance. Even though, with today's technology, implementing such a sensor- and activator system based on electronics and electrical signals, may be preferable, it is in principle no reason why it could not be implemented purely mechanical or hydraulic. This too, is something that can be expected that a person skilled in the art of the field will be able to perform easily, without inventive effort. One example of such a hydraulic implementation is shown in Figure 7 and explained below. The elements 14 - 18 on the figure show, simplified, a mechanical-hydraulic system for converting and transferring wave energy absorbed by the winch 1. This matches parts of the hydraulic subsystem described in N0329152. In the implementation exemplified in Figure 7 and in the following description, the sensor- and activator system is integrated with this. It is assumed that there is a passage from the hydraulic system connected to the main winch, to the additional winch's motor controlling unit. If the main winch 1 and the additional winch 2 both are attached to the same structure, like in the example shown in Figure 6, it is straightforward to construct such a passage. The main winch transfers its rotary motion to a gear transmission 14 which makes the output shaft 14b from the gear transmission rotate faster than the winch drum. The output shaft is connected to a one-way clutch 15, through which rotation of the winch in the outward direction only is further transferred to a hydraulic pump 16. The pump is connected to a turbine unit with a power take off system 17. The turbine unit and the power take off system is not further described here. It may be assembled as described in N0329152, or have a different design that produces a function of restructuring the energy from the pump 16 into the useful energy. The point here is that every time the winch cable 3 is pulled, a hydraulic fluid will flow from the pump 16 to the turbine unit 17. The hydraulic passage connecting the pump to the turbine unit, has a side course. This side course leads, via a flow limiter 20, to a hydraulic motor 19 in the motor controlling unit 7. The flow limiter may be a throttle valve like shown in Figure 7, a flow control valve, a narrowing of the hydraulic passage or some other hydraulic component which limits the hydraulic flow into the motor 19. When the pump 16 is activated as a result of rotation of the winch in the spooling out direction, a small fraction of the flow from the pump will pass through the flow limiter and activate the hydraulic motor 19, which thus makes the additional winch rotate. Depending on in which direction the motor 19 is mounted according to the rotational direction of the additional winch, the additional winch will rotate outwards and spool out cable, or inwards and spool in cable. Both mounting directions will work, in order to fulfill the function of the invention, though the mounting direction which results in outward direction of the additional winch, will require less energy from the motor 19.

Another possibility is having the activator system 4 governing the additional winch, be manually operated. (Manual operation of the additional winch may be arranged— for instance— by replacing the motor controlling unit 7 with a hand crank.) Or it could be remote controlled.

The worm gear mechanism, shown in the Figures 1 - 7, and assumed in the above description, is one of several possible embodiments of the blocking mechanism of the additional winch. In principle, this can be replaced with any kind of blocking mechanism, no matter what embodiment, whose function is to prevent force from the cable from moving the additional winch, but not vice versa.

An alternative to using a worm gear or similar blocking mechanism (i.e. a blocking mechanism whose function is to prevent force from the cable from moving the additional winch, but not vice versa), is using a one way blocking mechanism. Figure 8 shows the additional winch with such a one way blocking mechanism embodied as a ratchet. Another embodiment is shown in Figure 9, where tilted lock latches 21a, b are brought close to the cable 3 and prevent it from being pulled from the additional winch. The lock latches are positioned close to the cable pointing their loose end in the direction outward from the additional winch along the cable, having a suitable angle, so that the lock latches wedges causes the cable to be stuck in the middle between them, when the cable is attempted pulled from the additional winch, and so that the cable is released from the wedge grips when the additional winch starts spooling in cable, and the lock latches then— as long as the cable moves in the spooling in direction— freely allows the cable to move.

A one way blocking mechanism operates by allowing motion in one direction— here: in the spool-in direction of the additional winch— but blocks motion in the opposite direction. This simply works for the spooling over configuration in which the activator system is put to spooling in cable. A ratchet, or the like, can however operate as blocking mechanism in the spooling over configuration where cable is spooled over onto the main winch. But this requires a more sophisticated functional design of the ratchet and the motor controlling unit 7, by equipping the motor controlling unit with the ability to actively suspend the block by pivoting off the ratchet's blocking pawl 22 so that the ratchet gear 23 is free to rotate outwards one angular segment before the pawl blocks it again. In the spooling over configuration where spooling over is done by having extra cable from the main winch being spooled over onto the additional winch, the additional winch will over time have an increased amount of cable spooled onto it, while the amount of extra cable on the main winch decreases. The additional winch will then have to be dimensioned to have space for the desired amount of extra cable to be spooled over from the main winch. In the spooling over configuration where extra cable from the additional winch is spooled over onto the main winch, the amount of cable on the main winch will over time increase, while decreasing on the additional winch. The main winch will then have to be dimensioned to have space for the desired extra amount of cable from the additional winch. Regardless of configuration: When the amount of extra cable in this way is "consumed", it is time to perform manual maintenance, by removing the old cable and replacing it with new cable, with the extra amount of cable spooled onto the appropriate winch. It is also possible, and probably desirable, to implement a warning system, e.g. in conjunction with the motor controlling unit 7, which notifies the operators of the winch system when it is time to replace the cable.

The essence of the invention, is that the time elapsed between each time manual maintenance of the cable is needed, is prolonged, and that this provides cost savings.

Examples of integrating the invention in a winch activated wave power plant A winch activated wave power plant has a winch, which here coincides with the main winch 1, which is responsible for transferring energy from a wave energy absorbing device, here exemplified as a float 8, as can be seen from Figures 2, 5 and 6. Motion of the main winch 1 is imposed by the waves, and this alternating movement is channeled forward into a power-conversion machinery (not further described, as the design of this will vary for different wave power systems), where the energy is converted into useful energy, such as electric power. Here, like in N0325878 and N0329110, the winch 1 is self-tightening, and thereby automatically spools in when the tension from the cable is sufficiently low.

In Figures 2 and 5 a winch activated wave power plant is shown, where the wave energy absorbing winch 1, i.e. the main winch, is located in a winch unit 9 which is under water, anchored to the seabed or a deeply submerged structure by means of an anchoring element 10 (in the figures visualized in the form of a chain). The figures also show, out from the winch unit in the same direction as the anchoring element: an umbilical 11, which is a wire for transmitting electrical power and, optionally, control signals from the plant to land. The winch unit 9 is connected by cable 3 to the float 8, which floats in the water surface 12. The additional winch is here fixed to the float. Figures 2 and 5 show the cable from the additional winch being conducted through a funnel 24 in the float, exiting through a bend stiffener 25 on the bottom side of the float.

It is also possible to integrate a configuration with the additional winch attached to the float, with a design of a winch activated wave power plant where the winch unit is on land, like in Figure 4 of N0325878. Alternatively, the winch unit 9 with the wave activated winch, and the additional winch, may switch places, meaning that the winch unit will be inside the float, like in N0329110, and the additional winch with the activator system 4 will be under water.

Figure 6 shows another alternative configuration, where both the main winch 1 and additional winch 2 are secured to the winch unit 9, under water. The cable runs from the main winch to the additional winch, through a pulley sheave 13 attached to the float— also known as a block. The cable 3, the pulley sheave and the cable's two end connection points, one on the main winch and one on the additional winch, respectively, on the same structure, namely the winch unit 9, comprise a pulley. This pulley arrangement causes the main winch to be rotated when the waves lift the float, and it will make the cable on the main winch move twice as fast as the float, which in a wave power context can be considered an advantage, because it provides an up-shift of the speed on the main winch. One of the problems with wave energy utilization is that the wave motions initially are very slow. Therefore, shifting up of this motion to a higher speed, is appropriate, because then the transferred power can be handled in the form of lower force and lower torque, and consequently with lower dimensions of the components.

Having a pulley arrangement as shown in Figure 6, the forces from the float on the cable are reduced, to about half, because there are two cable ends holding the float. Thus, the cable 3 and the main winch 1 may be designed with lower dimensions, and still being able to perform equal work, which also may be considered an advantage. Another advantage of this arrangement is that it makes it easier to implement a spooling over function for the additional winch based on input data from sensors that are arranged in connection with the main winch— whether these sensors are electronic, hydraulic or mechanical.

Figure 6 shows a single pulley (shift up factor x 2). But the same placement of the main winch and the additional winch can be used with a double tackle (shift up factor x 4), a threefold purchase (shift up factor x 6) etc., to achieve an even greater shift up of the motion speed, if desired. A luff tackle (shift up factor x 3) or a gyn tackle (shift up factor x 5) etc. is also possible, but then one of the winches, the additional winch or the main winch, will have to be attached to the float.

Claims

1. A winch device with a cable (3), a main winch (1) at one end of the cable, and at the other end of the cable an additional winch (2), c h a r a c t e r i z e d i n t h a t the additional winch (2) rotates slowly compared to the typical rotational speed of the main winch a n d t h a t the additional winch is governed by an activator system (4) comprising a motor controlling unit (7), which controls the spooling over of cable in one direction from one winch to the other, to shift the cable in relation to the main winch's drum and any elements with that the cable is in the tear-inducing contact with, so that wear and tear over time is distributed over larger portions of the cable.

2. A device according to claim 1 where the activator system (4) contains a blocking mechanism which prevents external tension force on the cable (3) from rotating the additional winch (2) if not determined by the activator system (4).

3. A device according to claim 2, where the blocking mechanism is a worm gear, with a worm gear wheel (5) connected to the additional winch, a worm screw (6) connected to the rest of the activator system (4), which blocks transfer of rotating force movement from the additional winch to the activator system, but not vice versa.

4. A device according to claim 2, where the blocking mechanism is a one way blocking of the additional winch, preventing cable from being pulled out from, but freely allows it to be spooled onto the additional winch (2) by means of the blocking mechanism being activated as a result of the cable being attempted pulled out, but being deactivated on motion in the spooling in direction.

5. A device according to claim 4 where the one way blocking is a ratchet, with a ratchet gear (23) connected to the additional winch (2) and a blocking pawl (22) on the ratchet gear, blocking rotation of the ratchet in one direction.

6. A device according to claim 5 where the motor controlling unit (7) can suspend the pawl (22) and allow the ratchet to rotate in the blocked direction.

7. A device according to claim 4 where the one way blocking consists of tilted lock latches (21, b) put close to the cable (3) in appropriate direction and with sufficient angle to wedge when the cable is attempted pulled out from the additional winch (2), but to release from the wedge grips, when the additional winch spools in cable.

8. A device according to claims 1 - 7, where the motor controlling unit includes means for controlling rotation of the additional winch.

9. A device according to one of the claims 1 - 7, where the motor controlling unit includes a processing unit adapted to transmit signals to a motor in the motor controlling unit, for controlled rotation of the additional winch.

10. A method for reducing wear of a cable of a winch device, the winch device

comprising a cable (3), a main winch (1) at one end of the cable, and at the other end of the cable an additional winch (2), c h a r a c t e r i z e d i n

rotating the additional winch (2) slowly compared to the typical rotational speed of the main winch a n d governing the additional winch by an activator system (4) comprising a motor controlling unit (7), to control the spooling over of cable in one direction from one winch to the other, to shift the cable in relation to the main winch's drum and any elements with that the cable is in the tear-inducing contact with, so that wear and tear over time is distributed over larger portions of the cable.

11. A method according to claim 10 where a blocking mechanism prevents external tension force on the cable (3) from rotating the additional winch (2) if not determined by the activator system (4).

12. A method according to claim 11 , where the blocking mechanism is a worm gear, with a worm gear wheel (5) connected to the additional winch, a worm screw (6) connected to the rest of the activator system (4), and blocks transfer of rotating force movement from the additional winch to the activator system, but not vice versa.

13. A method according to claim 11, where the blocking mechanism is a one way blocking of the additional winch, preventing cable from being pulled out from, but freely allows it to be spooled onto the additional winch (2) by means of the blocking mechanism being activated as a result of the cable being attempted pulled out, but being deactivated on motion in the spooling in direction.

14. A method according to claims 10 - 13, where the motor controlling unit controls rotation of the additional winch.

15. A method according to one of the claims 10 - 14, where the motor controlling unit includes a processing unit which transmits signals to a motor in the motor controlling unit, for controlled rotation of the additional winch.