Various embodiments relate to a demounting aid for demounting a hoisting fitting from a workpiece, such as from an aircraft structural component, comprising a first connector and a second connector, a force measurement device for measuring the force applied between the first connector and the second connector, a display for displaying an information corresponding to the respective force applied between the first connector and the second connector and at least one elastic member which allows a relative movement of the first connector to the second connector when an increasing force is applied to the first connector and the second connector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. 371 of International Patent Application Serial No. PCT/EP2017/081013, entitled “Demounting Aid,” filed Nov. 30, 2017, which claims priority from French Patent Application No. FR 1758535, filed Sep. 14, 2017, the disclosure of which is incorporated herein by reference.

FIELD OF THE TECHNOLOGY

The disclosure is directed to a demounting aid for demounting a hoisting fitting from a workpiece, such as from an aircraft structural component, a connection arrangement, and a method for demounting a hoisting fitting from a workpiece.

BACKGROUND

It is well known in the state of the art to mount hoisting fittings to aircraft structural components in order to move them of or onto for example a support frame. These hoisting fittings are usually mounted to the aircraft structural components via dowel bolts. Since the weight of the hoisting fittings is relatively high in order to demount it from an aircraft structural component by loosening the dowel bolts the weight of the hoisting fitting has to be compensated with a lifting equipment. If this is not done, the dowel bolts tend to jam and cannot be pulled out.

Most commonly for the compensation of the weight of the hoisting fittings a crane is used. However, cranes are designed to control the displacement of workpieces, but not to apply a predefined load for compensating the weight of the hoisting fitting.

SUMMARY

Since it is very difficult to set the appropriate load of a crane for the operator, the attempts of the operator to compensate the weight applied to the hoisting fitting with the weight of the hoisting fitting usually ends in a situation where not enough load is applied, thus it is impossible to manually remove the dowel bolts and the operator sets a further displacement of the main crane, which is leading to the second situation, in which too much load is applied and it is difficult or impossible to manually remove the dowel bolts. Additionally, in this situation risk of damaging the aircraft structural component by loosening the dowel bolts is relatively high.

Therefore a spring has been developed, which, when arranged between the hook of a crane and the hoisting fitting, can improve the demounting of the hoisting fitting because it enables the operator of a crane to more accurately set the applied load. The spring enables more flexibility, since a minimum movement of the crane leads to a smaller load increase with the spring than without and, if the spring comprises a visual indicator which shows when the target load value is reached, makes the setting easier.

However, in case of large aircraft structural components it is difficult for the operator to set the target load force with the crane control because the hoisting fitting and/or the spring cannot properly be seen from the position of the operator of the crane.

It is therefore an objective of the disclosure to improve the known demounting aid in such a way, that the target load force can better and more comfortable be adjusted.

The above noted objective is achieved for a demounting aid by the features disclosed herein.

The idea is to provide a demounting aid for demounting a hoisting fitting from a workpiece, such as from an aircraft structural component, which comprises a first connector and a second connector. With the two connectors, the demounting aid can be arranged between the hook of the crane and the hoisting fitting. Thus, a force transmission chain is established between the hook and the hoisting fitting.

The demounting aid further comprises a force measurement device for measuring the force applied to the first connector and the second connector. This enables the operator to more easily set a target load value to the hoisting fitting by operating the crane. The demounting aid further comprises a, in some embodiments remote, display for displaying an information to the respective force applied between the first connector and the second connector. Thereby; the operator can adjust the target load value based on the information displayed in the display and does not need clear view to the demounting aid, what is of particular importance if the workpieces are of large dimensions, as is the case with aircraft structural components.

Since the demounting aid comprises at least one elastic member, such as at least one spring, which allows a relative movement of the first connector to the second connector when an increasing force is applied to the first connector and the second connector, additional flexibility is provided. This makes it easy to adjust the load applied by actuating the crane.

In various embodiments, a force measurement device and the at least one elastic member are connected in series and/or in parallel.

Further embodiments relating to the elastic members are described and embodiments with features of the force measurement device are also described. According to various embodiments a guiding may be provided.

Some embodiments regarding the displaying of the information corresponding to the force applied are described.

Further embodiments of the demounting aid are described.

Additionally, the above noted objective is solved by the connection arrangement described herein.

The same advantages can apply as described in connection with the demounting aid. Reference is made to the features described in conjunction with the demounting aid.

A optional characteristic of the demounting aid in relation to the weight of the hoisting fitting is described.

Additionally, the above noted objective is solved with the method described herein.

Reference is made to the description of the demounting aid as well as the connection arrangement. The same advantages are achieved with the method as described in conjunction with the demounting aid and the connection arrangement.

Various embodiments provide a demounting aid for demounting a hoisting fitting from a workpiece, such as from an aircraft structural component, comprising a first connector and a second connector, a force measurement device for measuring the force applied between the first connector and the second connector, a, optionally remote, display for displaying an information corresponding to the respective force applied between the first connector and the second connector and at least one elastic member which allows a relative movement of the first connector to the second connector when an increasing force is applied to the first connector and the second connector.

In various embodiments, the force measurement device and the at least one elastic member are connected in series and/or in parallel.

In various embodiments, the demounting aid comprises a plurality of, such as at least three or exactly three, elastic members, which are connected in parallel and/or which have essentially equal characteristics, such as equal spring characteristics.

In various embodiments, the elastic members are connected in parallel via a lower plate and a top plate, more so, that the lower plate and/or the top plate comprise an opening which allows the force measurement device to travel at least partly through the lower plate and the top plate, respectively, while an increasing external force is applied to the first connector and the second connector.

In various embodiments, the at least one elastic member is formed by at least one spring, such as at least one helical spring.

In various embodiments, the at least one elastic member is formed by at least one compression spring and/or tension spring.

In various embodiments, the at least one elastic member is compressed when the first connector and the second connector are pulled apart by a force applied to the first connector and the second connector or that the at least one elastic member is extended when the first connector and the second connector are pulled apart by a force applied to the first connector and the second connector.

In various embodiments, the elastic members are arranged such that their longitudinal axes are arranged in fold rotational symmetry, such as in an at least threefold rotational symmetry, more so, in exactly a threefold rotational symmetry, around the force measurement device, such as, that the symmetry axis of the at least threefold rotational symmetry is the axis on which an external force is applied via the first connector and the second connector to the demounting aid.

In various embodiments, the force measurement device is a, in some embodiments electronic, weighting device, such as a crane scale.

In various embodiments, the force measurement device comprises a strain gauge for determining the force applied.

In various embodiments, the demounting aid comprises a guiding for guiding the relative movement of the first connector and the second connector to each other when an increasing force is applied to the connectors, such as, that the guiding comprises at least one guiding-element which is arranged in an elastic member.

In various embodiments, the remote display is wirelessly connected with the force measurement device and that the information corresponding to the force applied between the first connector and second connector is a force value and/or a weight value corresponding to the force applied and/or the difference to a preset force value and/or an information indicating whether the force applied is higher or lower than a preset value.

In various embodiments, the demounting aid comprises at least one stop for limiting the force applied to the elastic members and/or that the demounting aid comprises a recording element for recording overloads applied to the demounting aid.

In various embodiments, the demounting aid comprises at least one, or at least two, handles for handling the demounting aid.

In various embodiments, the at least one elastic member, such as the plurality of elastic members is/are hosted by a housing, such as by a common housing.

Various embodiments provide a connection arrangement comprising a workpiece, such as an aircraft structural component, a hoisting fitting mounted to the workpiece by at least one dowel bolt and a demounting aid according to the disclosure connected to the hoisting fitting.

In various embodiments, the demounting aid is designed such that, when the load applied to the first connector and the second connector is increased by 10% of the weight force of the hoisting fitting, the relative movement of the first connector to the second connector is between 0.1 cm and 3 cm, such as between 0.5 cm and 2 cm, or approximately 1 cm.

Various embodiments provide a method for demounting a hoisting fitting from a workpiece, such as from an aircraft structural component, comprising the steps: connecting a demounting aid according to the disclosure to the hoisting fitting and to a connector of a lifting equipment, such as a crane hook, lifting the connector of the lifting equipment until the force applied to the first connector and the second connector of the demounting aid approximately equals the weight force of the hoisting fitting, loosening the at least one dowel bolt from the workpiece.

DETAILED DESCRIPTION

InFIG. 1a proposed connection arrangement1with a proposed demounting aid2is shown. The demounting aid supports the demounting of a hoisting fitting3from a workpiece4. The hoisting fitting3is mounted to the workpiece4via one or more dowel bolts3a.

The workpiece4may be an aircraft structural component, like for example a hull section and/or a wing section and/or a stringer of an aircraft.

In the aircraft industry such workpieces4are usually moved within the factory building by a lifting equipment such as the factory buildings main crane. This lifting equipment is designed to carry and move, respectively, these large and heavy workpieces4within the factory building from one working station, such as assembly station, or storage station to another. It is also used to take the workpiece4from a frame, on which the workpiece4may has been transported. For carrying the workpiece4with the crane, hoisting fittings3are mounted to the workpiece4and the crane is connected to the workpiece4via the hoisting fittings3during carrying.

Here the hoisting fitting3is mounted to the workpiece4via at least one dowel bolt3aand at least one nut3b. The nut3bis here connected to the workpiece4via a connection member3c, which may comprise a mechanical rotation lock for the nut3brelative to the workpiece4. For example the nut3band the connection member3cmay be designed as a cage nut, where the connection member3cforms the cage for the nut3b.

Hoisting fittings3are usually used to connect the workpiece4with a lifting equipment10, such as a crane, for moving said workpiece4. The hoist fitting3usually comprises a connection surface3dand a mounting member3e. When the hoisting fitting3is mounted to the workpiece4the connection surface lays onto the surface of the workpiece4. The hoisting fitting3and the workpiece4are mounted to each other with one or more dowel bolts3a, which are pushed through corresponding openings of the hoisting fitting3and the workpiece4and a nut3bis applied to the dowel bolt3a, as can be seen in the enlarged view ofFIG. 1.

After the workpiece4has been moved and when the hoisting fitting3is not needed anymore, it has to be demounted. The demounting aid2of the disclosure can be designed to facilitate this demounting.

As shown inFIG. 1the demounting aid2comprises a first connector5and a second connector6. The first connector5and/or the second connector6may be a hook or an eyelet.

The demounting aid2further comprises a force measurement device7for measuring the force applied between the first connector5and the second connector6. As further can be seen inFIG. 1the demounting aid comprises a remote display8for displaying an information corresponding to the respective force applied between the first connector5and the second connector6.

Additionally, the demounting aid2comprises at least one elastic member9, in the embodiment of the figures three elastic members9, which allow a relative movement of the first connector5to the second connector6when an increasing force F is applied to the first connector5and the second connector6. The force F applied is here an external force.

The external force F may be provided by the lifting equipment10, for example the crane. The combination of the force measurement device7and the elastic member9allows an operator to adjust the force F applied to a hoisting fitting3while demounting it from a workpiece4in a comfortable and efficient manner.

While the force measurement device7in combination with the remote display8provides precise information regarding the respective force applied and the at least one elastic members provides flexibility and thus allows a precise adjustment of the load applied to the hoisting by controlling the lifting equipment.

The hoisting fitting3is demounted from the workpiece4with the following steps. The demounting aid2is first connected to the hoisting fitting3and to a connector11of a lifting equipment10, such as the crane hook. The demounting aid2may be connected to the connector11of the lifting equipment10and/or the hoisting fitting3directly or via a lifting belt12or the like.

Then the connector11of the lifting equipment10is lifted until the force F applied to the first connector5and the second connector6of the demounting aid2approximately equals the weight force W of the hoisting fitting3. Then the dowel bolt3aor dowel bolts3aare loosened from the workpiece4. Here the connector11of the lifting equipment10is lifted until the force F, in particular the tension force F, applied to the first connector5and the second connector6of the demounting aid2approximately equals the weight force W of the hoisting fitting3plus the weight force of those parts of the demounting aid2itself, which are carried by the force measurement device7when in use. Then the dowel bolt3aor dowel bolts3aare loosened from the workpiece4. “Approximately equals” here means that the difference between the force F applied and the weight force of the hoisting fitting3is less than 20%, less than 10%, less than 5%, or less than 1% of the weight force of the hoisting fitting3.

Here the difference between the weight force W of the hoisting fitting3plus possibly the weight force of those parts of the demounting aid2itself, which are carried by the force measurement device7, and the force F applied to the first connector5and the second connector6is less than 170 N, less than 100 N, less than 50 N, or less than 10 N. The lower the difference, the easier is the loosening and the pulling out of the dowel bolt3a.

This can be seen from the following calculation with reference toFIG. 1. The hosting fitting3weight results in a weight force W. It is attached to the workpiece4with a number N of dowel bolts3a. As explained before, the hoisting fitting weight force W shall be compensated by a lifting equipment10which therefore applies a vertical lifting load L approximately corresponding to the force F between the first connector5and the second connector6.

Dowel bolts3aare then loosened by the operator with a wrench or a machine: After loosening, there is no more friction between the hoisting fitting3and the workpiece4. Therefore, each dowel bolt3a(i) is submitted to a vertical load V(i), which can be positive or negative (depending on the force F applied via the lifting equipment10), approximated by:
V(i)=(W−L)/N

When only one dowel bolt3aremains, it supports all the vertical load:
V(N)=(W−L)  (1)

This last dowel bolt3a(N) needs to be extracted to unmount the hoisting fitting3:

To manually extract the last dowel bolt, the operator has to apply a pulling force P(N)described as:
p(N)>IV(N)I*fh+fw)  (2)

fh: friction coefficient between the dowel bolt3aand the hoisting fitting3

fw: friction coefficient between the dowel bolt3aand the workpiece4(aircraft structure)

Both friction coefficients have typically values between 0.1 (lubricated contact) and 0.5 (galled contact).

Considering the typical maximum manual pulling load max(P(N)) an operator can apply is approximately 200 N, it can be estimated that the acceptable accuracy of the lifting load, for lubricated bolts (f«0.1) and galled bolts (f*0.6) is:
W+(max(P(N)))I(fh+fw)>L>W−(max{P(N)))I(fh+fw)

The accuracy to set the lifting load L in order to ensure manual extraction shall approximately be at least +/−166 N, which is approximately +/−16 kg.

This is much less than the typical accuracy of a load measurement10aof a crane for handling the workpiece4, since the load measurement accuracy of cranes is usually approximately 2%-3% of the maximum work load, which in case of cranes in factory buildings for the production of aircrafts is very high. Accordingly, the accuracy of the force measurement device7of the demounting aid2can be at least 100 times, at least 1000 times, or at least 10000 times, higher than the accuracy of the load measurement10aof the lifting equipment10, which is used to apply the force F.

In various embodiment, the accuracy of the weight measurement device7is below 10 N, below 1 N, or below 0.1 N, as it is the case in the embodiment shown in the figures.

In the embodiment of the drawings, the force measurement device7and the at least one elastic member9are connected in series. In an alternative embodiment the at least one elastic member9and the force measurement device7may also be connected in parallel. In case a plurality of elastic members9is supplied, some might be connected in series to the force measurement device7, whereas others are connected in parallel.

Here the elastic members9are springs, especially helical springs. Here they are designed as compression springs. Alternatively, in another embodiment, they may be designed as tension springs. In the embodiment of the figures the demounting aid2comprises three elastic members9, as shown inFIG. 2. It may also comprise additional elastic members9.

Here the elastic members9are connected in parallel and have essentially equal characteristics, such as equal spring characteristics.

In various embodiments, the demounting aid2is designed such that, when the load applied to the first connector5and the second connector6is increased by 10% of the weight force of the hoisting fitting3, the relative movement of the first connector5to the second connector6is between 0.1 cm and 3 cm, between 0.5 cm and 2 cm, or approximately 1 cm.

As can be seen fromFIG. 2the elastic members9are connected in parallel via a lower plate13and a top plate14. In the embodiment the top plate14comprises an opening15which allows the force measurement device7to travel at least partly through the top plate14while an increasing external force F is applied to the first connector5and the second connector6. Additionally or alternatively the opening15may be in the lower plate13and then allowing the force measurement device7to travel at least partly through the lower plate13while an increasing external force F is applied.

The elastic member9may be preloaded when no external force F is applied to the demounting aid2. However, in the embodiments no preload is applied to the elastic members9.

As can be seen inFIG. 3the at least one elastic member9is compressed when the first connector5and the second connector6are pulled apart by a force F externally applied to the first connector5and the second connector6. Alternatively, in another embodiment the at least one elastic member9may be extended when the first connector5and the second connector6are pulled apart by a force F applied to the first connector5and the second connector6. In further alternative embodiments, the at least one elastic member is compressed when the first connector5and the second connector6are pushed towards each other by a force applied to the first connector5and the second connector6or the at least one elastic member9is extended when the first connector5and the second connector6are pushed towards each other by a force F applied to the first connector5and second connector6.

As can be seen inFIG. 2the elastic members9are arranged in such a way that their longitudinal axes L are arranged in fold rotational symmetry. The demounting aid2of the embodiment comprises three elastic members9and the longitudinal axes of these three elastic members9are of three-fold rotational symmetry around the force measurement device7. The symmetry axis S is in the embodiment the axis on which the external force F is applied to the demounting aid2via the first connector5and the second connector6. Further, here the symmetry axis S is coaxial with the longitudinal axis of the force measurement device7.

The demounting aid2comprises a guiding16for guiding the relative movement of the first connector5and the second connector6to each other when an increasing force F is applied to the connectors5,6. In various embodiments, the guiding16comprises at least one guiding-element17, which is arranged in an elastic member9.

In the embodiment the guiding-elements17connect the top plate14and the base plate18. The longitudinal axes of the guiding-elements17are coaxial to the longitudinal axes of the elastic members9. Hereby the top plate14, the guiding-elements17and the base plate18form a rigid structure. The lower plate13is moveable relative to the top plate14and the guiding-elements17extend through openings of the lower plate13.

Furthermore, the demounting aid2may comprise at least one stop19for limiting the force applied to the elastic members9. Here the stops19provide a safeguard, since they limit the force applicable to the elastic members9. A failure of elastic members9is efficiently prevented as well as an accidental falling of the hoisting fitting3because of such a failure.

Here three stops19are arranged around the guiding-elements17and form a part of the guiding-elements17.

Additionally or alternatively, recording elements20may be provided which record an overload applied to the demounting aid2.

The recording elements20allow to record the application of an overload provable. Thus, misuse can more easily be proved. As recording elements20for example grub screws may be used.

As shown inFIGS. 2 and 3the force measurement device7can be, pivotable around an axis essentially orthogonal to the direction of the gravitational force, connected to the lower plate13.

The force measurement device7can be an electronic weighting device. It may be a crane scale. For measuring the force F applied to the demounting aid2the force measurement device7may comprise a strain gauge. Additionally or alternatively, the force measurement device7may comprise a capacitive sensor and/or piezoresistive sensor and/or a distance sensor.

Here the force measurement device7further comprises a communication unit16for remotely communicating with the remote display8. Via the communication unit16the remote display8is here wirelessly, such as via a wifi-network, connected with the force measurement device7.

The remote display8may comprise input elements8aand/or a touch screen for configuration auf the force measurement device7. In various embodiments, the force measurement device7is configurable for different types of hoisting fittings3via the remote display8. It displays an information corresponding to the force applied between the first connector5and the second connector6. This enables the operator of the lifting equipment10to adjust the force F applied to the demounting aid2and the hoisting fitting3in order to reach the target force for the hoisting fitting3.

In various embodiments, the target force is approximately the weight force of the hoisting fitting3to be demounted. The information displayed corresponding to the force applied may be a force value and/or a weight value corresponding to the force applied and/or the difference to a preset force value and/or an information indicating whether the force applied is higher or lower than the preset force value. The preset force value here corresponds to the target load value and/or the weight force of the hoisting fitting3.

Here the first connector5is pivotably connected to the force measurement device7. Additionally or alternatively, the first connector5and/or the second connectors6may be connected to the demounting aid2in a rotational manner around a rotation axis which is essentially parallel to the direction of a gravitational force G.

The force transmission chain within the demounting aid2extends here from the first connector5to the force measurement device7. From the force measurement device7the force transmission chain extends via the lower plate13into the elastic members9. From the elastic members9the force transmission chain extends via the top plate14into the guiding-elements17and further into the base plate18. From the base plate18it extends to the second connector6, where it exits the demounting aid2.

In the embodiment the demounting aid2comprises feet21to store the demounting aid2. Their extension in the direction of the gravitational force G is larger than the extension of the second connector6. They are fixed to the base plate20of the demounting aid2, as can be seen inFIGS. 2 and 3.

The demounting aid2may additionally or alternatively comprise one or more handles22. Here the demounting aid2comprises two handles22. In the embodiment they are fixed to the top plate15.

As shown inFIG. 1the demounting aid2comprises a housing23. The housing23houses the elastic members9. Thereby, the housing23prevents operators from putting their fingers into the springs. Thus, injuries can sufficiently be prevented. Here not only the elastic members9, but also the force measurement device7is accommodated at least partly within the housing23. The elastic members9and the force measurement device7may also be at least partly be arranged between the top plate14and the base plate18.

In the embodiment ofFIG. 1 to 3the force measurement device7comprises the on and/or off switch24for the demounting aid2. In order to improve the access to the on and/or off switch24a bar25is detachably mounted to the housing23for switching on and/or off the demounting aid2. Alternatively, the on and/or off switch24may be mounted to the housing23.

The demounting aid2of the embodiment has a maximum workload of approximately 200 kg. The weight is approximately 12 kg. The demounting aid2may also be designed for higher maximum workloads, like approximately 1000 kg. Here the device is CE certified as per 2006/42 requirements.