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Title:
LIFTING DEVICE
Document Type and Number:
WIPO Patent Application WO/2011/129705
Kind Code:
A1
Abstract:
Lifting device, such as a winch, crane or similar, especially in connection with maritime applications, which lifting device includes one or more electrical motors (11) for powering a drum (12) with lifting wire, which motor(s) are externally supported independent of the drum (12). The motor(s) (11) is/are permanent magnet motor(s) and is/are arranged for working as both a motor and generator, which motor(s) (11) is/are: - controlled by one or more frequency converters (13), - directly connected to the drum (12) or connected to the drum (12) via suitable transmission means, such as a gear. The lifting device further includes a safety device, which at loss of power (power failure, black-out, phase error, ground fault, etc.) is arranged to: - generate a counter-moment in the motor (11) to brake the fall of a load at loss of power, and/or - braking and possibly locking a load with available moment in the motor (11) at loss of power, or - provide the motor (11) without any moment for releasing/"free fall" of the load.

Inventors:
JOHNSEN, Gunnar (Hofsetraasa 56, Ulsteinvik, N-6065, NO)
SKJELLNES, Tore (Nedre Möllenberg gt. 49, Trondheim, N-7014, NO)
Application Number:
NO2011/000124
Publication Date:
October 20, 2011
Filing Date:
April 13, 2011
Export Citation:
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Assignee:
SMARTMOTOR AS (Jarleveien 8, Trondheim, N-7041, NO)
ROLLS-ROYCE MARINE AS (Sjögata 98, Ulsteinvik, N-6065, NO)
JOHNSEN, Gunnar (Hofsetraasa 56, Ulsteinvik, N-6065, NO)
SKJELLNES, Tore (Nedre Möllenberg gt. 49, Trondheim, N-7014, NO)
International Classes:
B66D5/00; B66C13/26; H02P3/22
Domestic Patent References:
WO2010012455A1
Foreign References:
US2975346A
Attorney, Agent or Firm:
CURO AS (Industriveien 53, Heimdal, N-7080, NO)
Download PDF:
Claims:
Claims

1. Lifting device, such as a winch, crane or similar, especially in connection with maritime applications, which lifting device includes one or more electrical motors (11) for powering a drum (12) with lifting wire, which motor(s) (11) are externally connected to the drum (12) and supported independent of the drum (12), characterized in that the motor(s) (11) is/are permanent magnet motor(s) and is/are arranged for working as both a motor and generator, which motor(s) (11) is/are:

- controlled by one or more frequency converters (13),

- directly connected to the drum (12) or connected to the drum (12) via suitable transmission means, such as a gear.

2. Lifting device according to claim 1, characterized in that

- two or more motors (11) are connected in series at one side of the drum (12),

- two or more motors (11) are connected in series at each their side of the drum (12), or

- two or more motors (11) are connected in parallel at one side of the drum (12).

3. Lifting device according to claim 1, characterized in that the frequency converter (13) is an active front end converter.

4. Lifting device according to claim 1, characterized in that the lifting device includes a safety device, which at loss of power (power failure, black-out, phase error, ground fault, etc.) is arranged to:

- generate a counter-moment in the motor (11) for braking the fall of a load at loss of power, and/or

- braking and possibly locking a load with available moment in the motor (11) at loss of power, or

- provide the motor (11) without any moment for releasing/"free fall" of the load. 5. Lifting device according to claim 4, characterized in that the safety device for braking and possibly locking a load with available moment in the motor (11) at loss of power (power failure, black-out, phase error, ground fault, etc.) includes a first relay switch (20a), which is arranged for directly short-circuiting terminals ( , S, T) of the motor.

6. Lifting device according to claim 4, characterized in that the safety device for braking a load with available moment in the motor (11) at loss of power (power failure, black-out, phase error, ground fault, etc.) includes a relay switch (32), which is arranged for short-circuiting terminals (R, S, T) of the motor over a braking circuit (30) including one or more resistances (21a-c) and one or more coils (31).

7. Lifting device according to claim 4, characterized in that the safety device for generating a counter-moment in the motor (11) for braking the fall of the load at loss of power (power failure, black-out, phase error, ground fault, etc.) includes a second relay switch (20b) and one or more braking and short-circuiting resistances (21a-c), which second relay switch (21) is arranged for short-circuiting terminals (R, S, T) of the motor over the braking and short-circuiting resistances (21a-c).

8. Lifting device according to claim 4, characterized in that the safety device for arranging the motor (11) without any moment for releasing/"free fall" of the load includes an emergency switch.

9. Lifting device according to claim 6, characterized in that the resistances (21a-c) under normal operation of the lifting device is used for relieving reverse power from the frequency converter (13) which is being generated at braking and rotational changes of the lifting device.

10. Lifting device according to claim 3, characterized in that reverse power from the frequency converter (13) which is being generated at braking and rotational changes of the lifting device is supplied back to a supply grid for the lifting device. 11. Lifting device according to claim 7, characterized in that two or more braking and short- circuiting resistances (21a-c) are arranged in series for each motor phase (R, S, T).

12. Lifting device according to claim 7, characterized in that two or more braking and short- circuiting resistances (21a-c) are arranged in parallel for each motor phase (R, S, T).

13. Lifting device according to claim 11, characterized in that between two consecutive braking and short-circuiting resistances (21a-c) arranged in series is arranged a relay switch (22, 23) for activation and deactivation of the number of resistances (21a-c), over which resistances (21a-c) terminals (R, S, T) of the motor (11) are short-circuited by means of the relay switch (20b) for controlling the speed for controlled lowering of the load.

14. Lifting device according to claim 12, characterized in that between braking and short-circuiting resistances (21a-c) arranged in parallel is arranged a relay switch (24) for activation and deactivation of resistances (21a-c), over which resistances (21a-c) terminals ( , S, T) of the motor (11) are short-circuited by means of the relay switch (20b).

15. Lifting device according to any one of the previous claims, characterized in that to each relay switch (20a-b, 22-24) and emergency switch is arranged manual or automatic activation and deactivation means, such as one or more relay coils, capacitors or similar, or an internal or external control unit, such as a PLS, which control unit is provided with a control logic for activation and/or deactivation of the relay switches (20a-b, 22-24) and emergency switch.

16. Lifting device according to any one of the previous claims, characterized in that one or more relay switches (20a-b, 22-24) and emergency switch is/are provided with time-delayed activation and/or deactivation.

17. Lifting device according to any one of the previous claims, characterized in that the safety device includes interlocking between the relay switches (20a-b, 22-24) and emergency switch to prevent that the braking and short-circuiting resistances (21a-c) are used as short-circuiting resistances at normal operation.

18. Lifting device according to any one of the previous claims, characterized in that additional safety is achieved by means of redundancy by arranging additional relay switches to ensure that the desired function is achieved. 19. Lifting device according to any one of the previous claims, characterized in that the electrical motor (11) includes several windings connected in parallel or series, and that the electrical motor (11) is provided with a relay, switch or similar for dividing the windings when needed, e.g. at short- circuit, for thereby to provide at least two "separate motors" in the same electrical motor (11). 20. Lifting device according to claim 19, characterized in that each of the "separate motors" are arranged with a different resistive load, so that the moment of the "separate motors" are completing one another to provide a stable moment having a low peak.

Description:
Lifting device

The invention relates to a lifting device, such as winches, cranes or similar, especially in relation to maritime applications, which lifting device includes one or more electrical motors for powering a drum with lifting wire, which motor(s) is/are externally connected to the drum and supported independent of the drum, according to the preamble of claim 1.

Background

Electrical motor-driven winches or cranes are today utilized to a large extent within many areas in connection with different lifting operations. In connection with lifting operations, reliability and safety in relation to braking systems of the winch are particularly important. It is important that the load does not fall down if one experiences a power failure, phase error or other critical situations which may involve danger for personnel finding themselves in the vicinity of a lifting operation, and avoiding damages of load and vessel.

For a long time it has been known that winches being powered by AC motors generally was provided with two independent brakes, one which is known as a mechanical load brake and one friction brake, known as retaining brake or motor brake. These brakes were designed to stop and retain the load within the capacity of the winch. In this way the winch should not fail if one of these braking devices failed. The mechanical load brake is a device where friction surfaces are brought into engagement with each other by means of rotational moment from the working load for braking and stopping the lowering of the load. The friction surfaces have a tendency to disengage from engagement at moment from the motor in lowering direction. The design is such that, with the retaining brake disengaged and the motor operated downwards, the load brake generates a friction force for holding the speed of the lowering load to some below no speed of the motor. However, if the motor moment then is removed/drops out, for example by a power failure, the brake will stop and retain the load. The load brake is disengaged during hoisting by means of a clutch mechanism.

There are many disadvantages with load brakes, such as that they expensive to build, difficult to maintain, and increase the physical size of the winch. Many designs also have the tendency to increase undesired vibrations. As the load brake needs to absorb and spread the energy from a falling load as heat, it results in that a large amount of heat is created, which limits the workload the winch can carry out.

The electrical retaining brake includes usually an electromagnet which, when activated, disengage the friction surfaces which otherwise are maintained in contact with each other by means of springs. The coil of the electromagnet is usually connected to one phase of the motor power supply, so that when the motor is supplied with power the brake is disengaged and activated again when the motor lose the power.

Recently have several kinds of winches omitted the mechanical brake and relied on regenerative brakes of an asynchronous motor as the second braking means. This is especially intended for loads having a low weight. The phenomenon regenerative braking is a well-known characteristic of asynchronous motors. As the motor is operated over its synchronizing speed it develops a braking moment, which works as a generator returning power to the supply. However, this solution does not provide protection against simultaneously retaining braking and power failure. If the retaining brake during operation of the winch should fail, a free falling load would be the result if the operator tries to stop the winch. A standby operator could however retain the load under control by re-energizing the winch, in either hoisting or lowering direction. If a power failure should arise it would be no way to prevent the load from falling freely. Another disadvantage with eliminating the load brake in prior known winches is that in the absence thereof, the load brake is required to absorb all kinetic energy of the winch and load every time the load is stopped. As it is a friction device it is exposed to overheating and wear, which requires periodical maintenance.

It has for a long time been known that a double braking system, where each brake is effective in case of power failure, has been a desired feature.

On cranes and winches which are powered by a DC power supply it is relatively plain to connect a DC powered motor so that it becomes a self-exciting generator, and in this way provides the second source for braking in the absence of external energy.

On cranes and winches powered by alternating current, this feature can only be obtained by additional equipment. This is usually arranged by that a additional generator is arranged to the same shaft for delivering magnetizing current to the eddy-current brake and thus makes it independent of an external power source.

As dynamical braking in any form is dependent of rotation to generate moment, it will not retain the load stationary, but make a controlled lowering at a speed under normal lowering speed and is thus a relatively safe state, especially compared to a free falling load.

From US 3,971,971 it is known a braking system for apparatus powered by induction motors, such as a winch, where one of the features is that the motor shall be self-magnetizing to set up a braking force at certain conditions. A large disadvantage with the arrangement in US 3,971,971 is that it is used a shared capacitor to achieve the desired function which results in that if an error occurs in this capacitor, it will not be possible to set up the above mentioned brake force.

Even if a winch or crane is provided with a feature as described above, it does not provide opportunities to lock the load in a given position without external braking means. From DE 19911429 it is known a universal motor where it is described that, at an emergency situation, the motor winding can be short-circuited to achieve locking of a load.

In EP 1591409 A2 it is disclosed a solution where the permanent magnet motor is arranged into the winch drum. It is described solutions for short-circuiting over resistances and short-circuiting over the phases of the motor. The disadvantage with this solution is that it is not suitable for heavy lifting operations, as it in connection with heavy hoisting operation is not possible to have the motor "inside" the drum due to the torque requirement is so high that the drum would be too long and have a too large diameter for being user-friendly, for example onboard a boat. In addition its construction would result in that it would not be possible to release the load, so that it drops the load uncontrolled if a need for this should arise.

It exists today no known solutions for heavy lifting operations, especially for application in maritime environments, where it is provided a complete secure braking and stopping (retaining) of a load when a power failure occurs and the motor powering the winch or cranes remain without power supply, without the use of external braking systems, which solution also is able to lower the load down in a controlled manner. It is neither known solutions where the mentioned features are present which in addition have possibilities for releasing the load, known as "winch load release", which is a desired feature in connection with, among others, maritime operations.

Object

The main object of the invention is to provide a lifting device which solves the above mentioned disadvantages with prior art with a view to provide a lifting device adapted for heavy lifting operations, especially in connection with maritime applications. It is further an object to provide a lifting device with a complete safe solution at loss of power (power failure, black-out, phase error, etc.) or other critical situations. An object of the invention is to provide a lifting device which brakes and possibly locks a load at loss of power or a critical situation. It is also an object of the invention that the lifting device is arranged for lowering the load in a controlled manner. It is further an object of the invention that braking and possible stopping of the load in connection with loss of power or other critical situations should be handled only by the motor, even if applications could have external braking means in addition.

It is further an object of the invention that the lifting device has possibilities for releasing the load in connection with loss of power or other critical situations, known as "winch load release", which is a feature demanded in, among others, maritime operations.

It is also an object of the invention that the motor of the lifting device can operate both as a motor and generator, so that power can be supplied back to a supply grid for the lifting device. It is further an object to provide a lifting device which can utilize different kinds of drums or frequency converters, depending of the application.

There is finally an object of the invention that several motors can be arranged to the same drum so that a user may choose desired capacity based on the lifting operation.

The invention

A lifting device according to the invention is described in claim 1.

Details and preferable features of the lifting device are described in the remaining claims. According to the invention it is provided a lifting device, such as a winch or crane, which includes one or more electrical motors, preferably permanent magnet motors, a drum for winch wire, one or more frequency converters, and a safety device for safe braking and possibly stopping, and releasing ("winch load release") of a load hanging in the lifting device at loss of power (power failure, black-out, phase error, etc.) or other critical situations. The lifting device can include several motors arranged in series at one side of the drum, connected on each side of the drum or connected in parallel at one side of the drum. The motor(s) of the lifting device is/are directly connected to the drum or to the drum via transmission means, such as a gear. The motor(s) is/are preferably an AC permanent magnet motor, which motor(s) is/are controlled by one or more frequency converters. At the use of several motors, the motors can be connected to the same frequency converter or they can be connected to own frequency converters.

The development of constantly improved magnets and thereby improved permanent magnet motors, have made these motors very usable and opened for new use of the technology behind these motors.

The safety device of the lifting device is arranged to brake and possibly lock the load at a given position in connection with loss of power (power failure, black-out, phase error, etc.) by short- circuiting terminals of the motor. The safety device is further arranged for braking a load in connection with loss of power (power failure, black-out, phase error, etc.) and/or make a controlled lowering of a load possible by generating a counter-moment in the motor. Braking and possibly locking of the load in a given position is achieved by means of relay switch, which relay switch is directly short-circuiting the motor terminals when loss of power occurs and it is thus generated a counter-moment in the motor by means of the properties of the permanent magnet motor. The motor will then be able to brake and possibly retain the load with the available counter-moment in the motor. As it will not be possible to achieve a full counter-moment in the motor in this way, a load will be braked by the available counter-moment in the motor and is only locked if the weight of the load is less than the available moment in the motor. Braking of a load and/or controlled lowering of the load when loss of power occurs is achieved by a relay switch and braking and short-circuiting resistances. By means of the relay switch the motor terminals are connected over the braking and short-circuiting resistances at loss of power, and it is thus generated a counter-moment in the motor by means of the properties of the permanent magnet motor, i.e. by means of short-circuiting the motor terminals over the braking and short-circuiting resistances.

In normal use of the lifting device/motor the braking and short-circuiting resistances (power resistances) of the safety device may be used to relieve reverse power from the frequency converter, which is generated by braking and rotational changes of the lifting device. As the weight hanging in the lifting device results in that the wire of the drum is pulled out and the drum rotates, the motor will operate as a generator and this reverse power must be handled in an effective way. One way to handle this is by guiding the reverse power to the braking and short-circuiting resistances by means of transistors, so that power is converted into heat. This power can also be supplied back to the grid, e.g. the vessel grid, by means of the frequency converter being an active front end converter. Power which can be used to power other units onboard a vessel.

When a permanent magnet motor loss the power, there is no motor moment to retain the load, i.e. the load drops/falls without control, but by means of the safety device of the lifting device this will be prevented in a safe way, by braking the load and lowering it controlled down, and possibilities to lock the load in a given position if the load has a weight being less than the available counter-moment in the motor.

Besides the two mentioned relay switches the safety device may include means for releasing the load ("winch load release"), a so-called emergency switch. This can be achieved by means of auxiliary contacts in the control circuit of the lifting device which disconnects the above mentioned relay switches and the frequency converter(s) of the lifting device.

It can also be a need for such an emergency switch/functionality if unforeseen and critical situations arise and there is a need for releasing the load quickly. For example, it can be necessary in connection with anchor handling operations or similar at sea, where situations require that one must release the load to secure the vessel. It is then important that a brake or stop of the load, as described above, is not retaining the load.

This means that the lifting device/safety device is provided with relay switches and emergency switch/emergency functionality, which are possible to choose among at loss of power or other critical situations. One provides full short-circuiting over the motor terminals, the second provides short-circuiting over the braking and short-circuiting resistances, while the emergency switch removes a possible moment in the motor. One relay switch will thus provide an available counter- moment so that the fall of the load is braked by means of the available counter-moment in the motor, and possibly stops entirely and the load becomes hanging if the weight of the load is lower than the available counter-moment in the motor. The second relay switch will lower the load down in a controlled manner and the emergency switch removes the moment so that the load can be dropped uncontrolled down.

The implementation of this can be done in several ways and the motor can, for example, brake the load, and possibly lock the load by the available counter-moment in the motor means of the first relay switch at loss of power, whereupon the load may be lowered in a controlled manner by means of the second relay switch. Another possibility is to first brake the fall of the load before the load is stopped entirely by short-circuiting the motor terminals, which only is possible if the load has a weight which makes it possible for the available counter-moment in the motor to retain the load, whereupon the load can be lowered in a controlled manner. The last possibility provides a more careful solution, as less momentary forces will act on the motor and the driving gear of the lifting device, etc.

The safety device is further provided with interlocking between the relay switches to prevent that it is possible to use the braking and short-circuiting resistances at normal operation.

In connection with controlled lowering of a load it will be the properties of the braking and short-circuiting resistances which decide the speed. The number of resistances can be adapted to the actual application and the resistances can be arranged both in parallel or series to provide different properties. At arrangement of resistances in series one achieves the possibility to control the speed at controlled lowering by arranging relay switches which makes it possible to choose which/how many resistances the phases of the motor are short-circuited over. In this way one can choose desired speed at the lowering of a load.

By arranging resistances in parallel for each phase one achieves increased safety by redundancy. In this connection it is preferably arranged a relay switch which changes between the relevant resistances. This solution can also be used to ensure that the resistances are only used in connection with loss of power, phase error or power failure.

All the relay switches and possibly the emergency switch can be arranged for automatic and/or manual activation and deactivation, or the relay switches can be arranged to a control unit which handles a control logic for activation and deactivation of the switches/relays. This is usually handled in the converter cabinet or switchboard of the lifting device.

The relay switches and emergency switch can further be arranged so that they can be manually activated at each time if situations arise that requires this. The emergency switch is preferably a manual switch which can be activated after need, and which switch overrides any state of the motor, i.e. the emergency switch also overrides the other mentioned relay switches. The safety device according to the invention can further include a dedicated braking circuit, formed by one or more resistances and one or more coils, which braking circuit is connected over the motor terminals by means of a relay switch in case of loss of power. A circuit as this will utilize that the momentary moment varies with the frequency. Momentary power is given by P = Τ * ω

p

which gives the following momentary moment T =— , where ω = Inf , which gives the following ω

P e

momentary moment T = . Further will i =— where e∞ ω .

2 z

This means that if a load starts to fall after loss of power will this result in that the moment of the motor that this results in, will be reduced with increasing frequency.

This can be expressed in the following way: | Z |= -^R 2 + {co f , which give the following expression for the current / when the resistance Ri and coil Li of the motor is considered:

I i |= , I 6 I , where R 2 is the resistance of the braking circuit and L 2 is the

■J(R X + R 2 ) 2 + (coL 2 + o)L l ) 2

coil of the braking circuit. This means that the moment a falling load results in is reduced with increasing frequency, which results in that the motor brakes the fall of the load. One can thus by choosing R 2 properly, achieve increasing moment at increasing speed within a given working range.

The above presented equation for / ' is a simplified presentation. While e is proportional with the rotational speed, P will be proportional with i 2 *(Ri+R 2 ). This simplified presentation will irrespective of this provide an acceptable presentation of this.

Also this embodiment can be modified and adapted with several resistances in parallel or series for increased flexibility or safety.

All the above described possibilities for braking and possibly stopping of a load can be combined to form other embodiments.

The implementation of the safety device can be made in many different ways, which will appear from the following example description.

It should be mentioned that the lifting device according to the invention can be utilized for different drums and that the motor can either be an axial or radial motor. Advantages with using several motor is that one easily can choose one or more motors dependent of how high lifting capacity the lifting device should have for the given lifting operation. Another great advantage with the invention is that the same motor can be utilized for different kinds of applications and that the frequency converter can be adapted to desires of the separate user. For example, a frequency converter of 1.4 MW/75rpm would be well suited for offshore operations and provide a lifting device with a capacity of, for example, 140KNm, while a frequency converter with approximately 500KW/24rpm would be well suited for fishing operations and provide the same lifting capacity. This shows that the present lifting device is very suitable and with simple modifications can be modified from a lifting device arranged for heavy operations to one for "light" operations by exchanging the frequency converter. Another advantage with the present invention is the costs, something which results in that the users can get a frequency converter adapted to their use without the need for paying extra for frequency converters of larger capacity than what they require.

Another great advantage with the invention is the need for space and the weight, which often is of essential significance, for example on maritime installations/vessel, where there is a limited space. From prior art it is publication EP 1591409 A2 which is nearest as regards functionality, but if a solution as disclosed in EP 1591409 A2 is to be used for a solution resulting in a lifting capacity of 50 tons, it would be inappropriately large. A solution with a capacity of 25 tons in EP 1591409 would result in approximately 4 meters axial length, with an outer diameter of approximately 2.6 meters and a weight of approximately 25 tons. With the present invention one will have an outer diameter of approximately 2 meters, axial length of approximately 1 meter and total weight of approximately 13 tons. This shows that the solution described in publication EP 1591409, where the motor is arranged into the drum itself will not be suitable to use in connection with heavy operations, especially offshore in connection with vessels. The solution described in EP 1591409 will neither be able to use different kinds of drums, as it includes that the motor is integrated in the drum.

Further details and preferable features of the invention will appear from the following example description.

Example

The invention will in the following be described in detail with references to the attached non- limiting drawings, where:

Figure la-c is principle drawings of a lifting device according to the invention,

Figure 2 is a principle drawing of a safety device according to the invention, where the lifting device/safety device is in a normal state,

Figure 3 shows the principle drawing of Figure 2, where the state of the lifting device/safety device is in error state, i.e. power failure, black-out, phase error or similar, Figure 4 shows a section of the principle drawing of Figures 2 and 3, which shows an alternative embodiment of braking and short-circuiting resistances, where several resistances are arranged in series for each phase, in normal state,

Figure 5 shows a section of the principle drawing of Figures 2 and 3, which shows an alternative embodiment of braking and short-circuiting resistances, where several resistances are arranged in parallel for each phase, in normal state,

Figure 6 is a principle drawing of a braking circuit for a lifting device according to the invention,

Figure 7 shows a moment curve for different loads, and

Figure 8 shows results of an embodiment according to the invention which utilizes that parallel- connected windings are divided into separate electrical motors connected to the same shaft.

Reference is first made to Figures la-c which show different examples of a lifting device 10 according to the invention. Figure la shows an example where a motor 11 is arranged to a drum 12 and where the drum 12 is connected directly to a rotor of the motor 11. The motor 11 is preferably an electrical alternating current permanent magnet motor, which is controlled by a frequency converter 13 arranged in a frequency converter cabinet (not shown). In addition the lifting device includes naturally a switchboard/control panel (not shown).

In Figure lb it is shown a solution where two motors 11 are arranged in series at the same side of the drum 12, while in Figure lc shows two motors 11 arranged at each their side of the drum 12. If desirable the motor(s) 11 can be arranged to the drum 12 via transmission means (not shown), such as a gear. It is also possible to arrange several motors in parallel at the same side, but this requires specially designed connection means between the motors 11 and the drum 12. It can further be utilized one or more frequency converters 13, such that each motor 11 is connected to each their frequency converter 13 or is connected to the same frequency converter 13. The motors 11 are preferably supported independent of the drum 12. By that the motor(s) 11 are supported independent of the drum, different drums 12 can be connected to the motors 11, adapted to the relevant application. Also existing drums can be utilized in the present invention.

The lifting device 10 according to the invention includes a safety device, which is shown in Figures 2 and 3, in the form of principle drawings of an example of a safety device, in normal state in Figure 2 and in error state in Figure 3, respectively. The safety device is formed by relay switches 20a-b, in the shown example two relay switches 20a-b, which relay switches 20a-b have different properties. The first relay switch 20a is a short-circuit relay, which is short-circuiting terminals R, S, T of the motor when loss of power occurs and the motor 11 is losing its power. This results in that the motor 11 will be braking a load hanging in the lifting device 10 with available counter-moment which the motor can provide, and if the weight of the load is not higher than the available counter-moment lock the load in the given position. The relay switch 20a is preferably of known kind and is connected to phases R, S, T of the motor 11, which relay switch 20a is activated or deactivated by, for example, a relay coil. The relay coil is, for example, working in the way that it is supplied with power from one of the phases of the motor under operation and the relay switch is thus deactivated, as shown in Figure 2. If the motor 11 then should lose its power, the relay coil will lose its power and the relay switch will thus be activated, as shown in Figure 3.

The safety device further includes a second relay switch 20b, which relay switch 20b is connected between the phases R, S, T of the motor 11 and an adapted number of braking and short-circuiting resistances 21a, which resistances 21a can either be air or water cooled, and which preferably are arranged in a frequency converter cabinet (not shown), in the switchboard of the lifting device or in a separate cabinet, depending on the application. In the shown example in Figures 2 and 3, one resistance 21a is connected to each their phase R, S, T. The relay switch 20b is preferably of same kind as the relay switch 20a and is also here connected to, for example, a relay coil for activation and deactivation. The relay switch 20b and the braking and short-circuiting resistances 21a result in that a counter-moment is generated in the motor 11, so that a load can be braked or lowered down in a controlled manner. The number of resistances 21a which is used can be arbitrary and will, among others, be dependent of the motor 11 size and capacity, dependent of the properties of the resistances 21a itself, and the total properties of the lifting device 11. The resistances 21a are dimensioned in relation to the size of the lifting device

10/motor 11, i.e. for normal use over the frequency converter 13. It can also be a need for more resistances 21a than what is needed for normal frequency converter use, i.e. that all resistances are first being used at an error state. It can also be one or more resistances per phase, but the resistances 21a preferably have similar properties to provide similar load and simplifying the installation. At the use of several resistances 21a-c, either several resistances 21a-c can be connected in series or several resistances 21a-c can be connected in parallel for each phase. It should be mentioned that the resistances can also be variable resistances (not shown) which can be changed after need. A possible use of variable resistances will require adaption to the frequency converter 13. The different variants of resistances will be elaborated below under the description of the Figures 4 and 5.

Remaining wiring/conductor rail between resistances 21a and relay switch 20b is preferably arranged in the same cabinet as the resistances, but can also be arranged in a separate cabinet, depending on the application.

The safety device further preferably includes means for releasing the load ("winch load release"), which is a so-called emergency switch (not shown), which can be used in situations where the lifting device 10 must drop the load quickly due to critical situations. This can for example be a need during anchor handling in relation to maritime operations or e.g. at a vessel about to tip over in connection with a lifting operation, which results in that the load must be dropped quickly to save the vessel. The emergency switch is for example formed by auxiliary contacts in the control circuit of the lifting device, which disconnects the above mentioned relay switches 20a-b and frequency converter(s) (13) of the lifting device. The emergency switch will then set the motor 11 up with no moment or remove possible moment set up by the relay switches 20a-b, which results in that the load can be released, i.e. dropped quickly.

At normal operation the resistances 21a lies over the DC-link via the frequency converter 13 and in connection with an emergency situation, for example, the power switch of the frequency converter 13 can be deactivated, i.e. that the frequency converter 13 lose the power and load is falling freely, but if relay switch 20a or 20b is activated one must deactivate the relay switch 20a or 20b for the possible moment being set up in the motor 11 over the resistances 21a or through short-circuiting of the motor terminals to be removed so that the load can fall freely.

The safety device can work in different ways when loss of power (power failure, black-out, phase error, etc.) occurs:

1. The first relay switch 20a is short-circuiting the motor terminals R, S, T, so that the motor 11 brakes the load with available moment in the motor, and if the weight of the load is lower than the available moment, the load is locked in a given position, after which the second relay switch 20b can be activated after desire (manually) or automatically for lowering the load down in a controlled manner by means of generating a counter-moment in the motor 11. The relay switch 20a must be deactivated before the load can be lowered down in a controlled manner.

2. The second relay switch 20b hits in first, so that it brakes the moment of the motor 11 by generating a counter-moment, before the motor 11 brakes the load with available moment in the motor by means of the first relay switch 20a and possibly locks the load in a given position if the weight of the load is lower than the available moment, after which the relay switch 20b is activated after desire (manually) or automatically for lowering the load down in a controlled manner by means of generating a counter-moment in the motor 11. The relay switch 20a must be deactivated before the load can be lowered down in a controlled manner.

It can of course be advantages and disadvantages with both these solutions and the time between the second relay switch 20b hits in for braking the speed/moment and the first relay switch 20a can naturally be adapted to the separate application. This can be solved by a time delay between the second relay switch 20b being activated and the first relay switch 20a being activated. In this way a gentler braking/stop of the lifting device 10/motor 11 can be achieved, as available moment in the motor is not applied before the speed/moment is some reduced. This can be achieved by utilizing relay switches 20a-b having time delayed activating or deactivation, or by means of a control unit, for example a PLS, which is arranged to the relay switches and which handles a control logic with in/out time contacts for the relay switches.

By means of the relay switches 20a-b a load can thus be braked and possibly locked in a given position by means of available moment in the motor 11 and be lowered down in a controlled manner by short-circuiting over the braking and short-circuiting resistances 21a. Controlled lowering by short-circuiting over the braking and short-circuiting resistances 21a requires that the relay switch 20a is deactivated, so that the short-circuiting over the motor terminals R, S, T is disconnected. The safety device is preferably arranged in the way that both relay switches 20a-b are activated at full short-circuiting, either momentary or as described above by means of a control logic/time delay. In this way one is ensured that if one goes from braking and possibly locking of a load to controlled lowering of the load, the load will not fall freely before controlled lowering is effectuated or by the use of the emergency switch.

As mentioned above, the number of resistances which are enabled and their properties will determine the speed of the controlled lowering. The load which will become hanging will vary, i.e. that the load which at each time is hanging in the lifting device 10 can have different size, heaviness and weight. In order to be able to choose speed for the lowering, this will mean that one must be able to choose how many resistances which are enabled to be able to lower the load with desired speed.

Reference is now made to Figure 4 which shows an alternative embodiment which includes several resistances 21a-c, connected in series for each phase, to provide the safety device with options for the speed which the load can be lowered down in a controlled manner with. The safety device in this embodiment further includes two relay switches 22 and 23, which are connected between the first resistance 21a for each phase and the motor 11, and between the second resistance 21b for each phase and the motor 11, respectively. By this arrangement, i.e. by means of the relay switches 22, 23 one can choose how many resistances 21a-c which generate a counter-moment in the motor 11, for thereby determining the speed which the load is lowered down with. If the relay switch 23 is activated one will achieve a higher speed than if relay switch 22 is activated, and if none of the mentioned relay switches 22, 23 are activated, the speed will be even lower, as the short-circuit would lie over all the braking and short-circuiting resistances 21a-c. In addition to the number of resistances will of course also the properties of the resistances determine how high counter-moment which is generated. This can be implemented in several ways and the relay switches can be included in a control logic which is controlled by a control unit, such as a PLS. The alternative of the above described will be variable resistances (not shown), so that the generated counter-moment can be varied by means ot changing the properties of the resistances. It will be possible to use variable resistances if the frequency converter 13 is an AFE converter.

In connection with controlled lowering of a load there will only be gravitational forces which pull/drop the load down, while the counter-moment in the motor 11 provided by the resistances 21a-c will then make sure that this happens with controlled speed.

Reference is now mage to Figure 5 for a further alternative embodiment of braking and short- circuiting resistances which provides increased safety in the safety device by redundancy by that several resistances 21a-b are connected in parallel for each phase. In this way one is ensured that even if one braking and short-circuiting resistance 21a-b is defect, the safety device will not lose its function. Preferably there are in connection with the resistances 21a-b arranged a relay switch 24 which can change from a defect resistance to a new resistance if there is a fault of one of the resistances.

In some cases there will also be desirable that the relay switches 20a-b and emergency switch can be activated or deactivated irrespective if there is a loss of power (power failure, black-out, phase error, etc.) or not, and can thus be used as additional safety if the situation call for it, either it is to reduce the speed of a load being lifted/lowered or if the load is to be stopped quickly or released quickly. The above described arrangement can in such situations be used to prevent double use of the resistances, i.e. both as reverse power resistances and as short-circuiting resistances, and to ensure that the safety device has its own dedicated resistances which are used during an error state and that the safety device works as specified. The above mentioned relay switches 24 will then be arranged so that they are activated/deactivated at loss of power, so that one in this way ensures that only one dedicated set of resistances 21a-b are being used in connection with safety states. The resistance 21a can, for example, be used as reverse power resistances, while the resistances 21b are being used in error states as braking and short-circuiting resistances. In this way one will also be sure of that the safety device will work as specified. The implementation of this can be done in several ways and the relay switches can be included in a control logic being controlled by a control unit, such as a PLS, for phasing out possible defect resistances or switch over to dedicated error state resistances.

As mentioned above, safety in connection with such lifting devices is highly important and it is therefore arranged interlocking between all relay switches 20a-b, 22-24 and emergency switch, so that there will not be possible to use the braking and short-circuiting resistances 21a-c at normal operation.

Reference is now made to Figure 6 which shows an alternative embodiment of the present invention. The figure shows a simplified sketch of an arrangement according to the invention for braking of a load by utilizing that the current, i.e. the momentary moment in the motor varies with the frequency. This is according to the present invention utilized by that it is arranged a dedicated braking circuit 30 which includes one or more braking and short-circuiting resistances 21a and one or more coils 31, which braking circuit 30 is connected over the terminals of the motor, and is engaged by means of one or more relay switches 32, of the same kind as described above, at loss of power (power failure, black-out, phase error, etc.) or other critical situations. This means that if load starts to fall after loss of power this will result in that the counter-moment in the motor this results in, will be reduced with increasing frequency, which results in that the motor will be braking the fall of the load. The counter-moment will be provided by the motor resistance 34 and coil 35 together with the braking and short-circuiting resistance 21a and coil 31 of the braking circuit. This embodiment can also be modified with several resistances in parallel or series and with several coils in parallel or series, as described above to increase safety and flexibility.

This shows that the implementation of the safety device can be done in many ways and that this provides opportunities for the arrangement of resistances and braking and short-circuiting resistances, both by that they can be used to relieve reverse power from the frequency converter 13, which is being generated at braking and rotational changes of the lifting device 10, and to provide a counter-moment in connection with error situations.

In addition to the above mentioned advantages, the safety device also has the advantage that if the motor is overloaded the resistances will prevent critical overload.

The safety device will also handle if only one phase is falling out, overvoltage, dissymmetry in the phases, ground fault, etc., and will work as described above in a predictable and safe manner.

All lifting devices have, in addition to the above described safety devices, where it is appropriate, mechanical/external brakes. This especially applies for applications where the lifting device is set to handle heavy lifts.

Reference is now made to Figure 7 which shows a moment curve for different loads. An electrical motor which is connected to a resistive load will have a dependency between moment and speed, given by the parameters of the electrical motor and the resistive load. Such a moment curve for different loads is shown in Figure 7. As the Figure shows, a chosen resistance can provide a high moment at a given speed, but lower moment at higher speeds.

In connection with an embodiment of the present invention the lifting device is arranged for utilizing the fact that the lifting device includes electrical motors with several parallel windings, and that the windings of the electrical motor can be divided, for example, by means of a relay, switch or similar, for in this way to provide several "separate motors" in the same electrical motor when needed. In this lies that the electrical motor at normal operation is one electrical motor, but as short-circuit occurs the electrical motor is divided into two or more "separate motors". Each "separate motor" is then given a different resistive load, so that the moments of the "separate motors" are completing one another, which will provide a more stable moment with a lower peak. The result of such a configuration is shown in Figure 8.

In the simplest example where the electrical motor at short-circuiting is divided into two "separate" motor, each "separate motor" will have a maximal moment corresponding to the half of the original electrical motor.

Modifications

The arrangements described above can be added additional safety by means of redundancy by additional relay switches to ensure that the desired functionality is achieved. If one relay switch then should fail, the functionality will still be achieved through another relay switch.

As mentioned, the safety device can be adapted for both manual and automatic control of relay switches, which is adapted to the relevant application. At automatic control the relay switches can be connected to an external control unit handling the control logic.

Instead of the mentioned relay coils for activation and deactivation of the relay switches, for example, capacitors or other suitable means can be used for control/control logic of the relay switches, such as an external powered control unit, e.g. a PLS. Capacitors can also be used to achieve time control of the relay switches.

If it is not desirable to use an AFE converter, for example, a space distributer and a frequency converter without AFE can be used.

It should also be mentioned that other kinds of switches than the above shown can be used. As described under Figures 7 and 8, an electrical motor can include windings connected in parallel, but it can also include windings connected in series. This will especially be relevant in connection with applications where one have increasing speed within a working range.

Alternatively, the electrical motor can also be provided with windings connected in parallel and series, and that one by means of relays, switches or similar can choose which of the alternatives one desires to use.




 
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