EP1798188A9

EP1798188A9 - Hydraulic crane

Info

Publication number: EP1798188A9
Application number: EP06125428A
Authority: EP
Inventors: Lars Andersson
Original assignee: Kone Cargotec Patenter HB
Current assignee: Cargotec Patenter AB
Priority date: 2005-12-14
Filing date: 2006-12-05
Publication date: 2007-10-03
Anticipated expiration: 2026-12-05
Also published as: SE0502744L; EP1798188A3; ATE479624T1; SE530761C2; DE602006016540D1; EP1798188A2; EP1798188B1

Abstract

A hydraulic crane (1) comprising a liftable and lowerable crane boom (5), a hydraulic cylinder (8) for lifting and lowering the crane boom (5) and registration means (35) adapted to register lifting up or putting down of a load in dependence on the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8). The registration means (35) is adapted to register that the crane executes a lifting up or putting down of a load when the rate of a detected change in the cylinder force (F_c) exceeds a predetermined value. The invention also relates to the method for registration of lifting up or putting down of a load by a hydraulic crane, and a method for calculating the fatigue stressing of a hydraulic crane based on the registered number of liftings up and/or puttings down of load.

Description

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a hydraulic crane, preferably a lorry crane, according to the preamble of claim 1, a method according to the preamble of claim 5 for registration of lifting up or putting down of a load by such a crane, and a method according to the preamble of claim 8 for calculating the fatigue stressing of such a crane.
A hydraulic crane is, like all other mechanical constructions, subjected to an accumulated fatigue stressing during use. When the fatigue stressing has reached a certain value, large risks of crane breakdowns will ensue, which may result in serious personal injuries and expensive damages to the crane itself or to objects in the vicinity of the crane. In order to make possible a safe and trouble-free operation of a crane, it is therefore a great need of calculating the accumulated fatigue stressing of the crane. Based on such a calculated fatigue stressing, it is possible to estimate the condition of the crane and its need of maintenance.
A method today used for calculating the accumulated fatigue stressing of hydraulic cranes is based on that the operating time of the crane is registered by means of a time counter. In this connection, the time during which the pump included in the hydraulic system is switched in is normally registered. However, this constitutes a rather bad measure of the accumulated fatigue stressing of the crane, since one and the same crane often is used for many different types of working operations having a very varying intensity.
From EP 1 150 019 A1 it is known to provide a hydraulic crane with registration means that registers lifting up and putting down of a load by detecting the rate of the pressure changes in the lifting cylinder of the crane, a lifting up or putting down of a load being registered when the rate of a detected pressure change exceeds a predetermined value. One or several sensors send information to the registration means as to the control and/or movements of the crane, and the registration means determines by means of this information whether or not a lowering movement of the crane is taking place. The registration means is adapted not to register a lifting up of load when a rapid pressure change in the cylinder is detected in connection with a determined lowering movement. In this manner, the registration means is prevented from being "fooled" by the rapid pressure change caused by the induced pressure on the piston side of the cylinder that may ensue during lowering movements due to the fact that a certain pressure is required on the piston stem side in order to open the load holding valve of the hydraulic system. By means of the registered liftings up and puttings down of load the number of lifting cycles performed by the crane is established, which constitutes a measure that is well related to the accumulated fatigue stressing of the crane. It has been shown that the number of performed lifting cycles constitutes a considerable better measure on the fatigue stressing of the crane than the time during which the crane has been in operation. Each lifting cycle is namely contributing in increasing the fatigue stressing of the crane and the duration of a lifting cycle may vary from for instance 30 seconds, when the crane is used for excavation with a hydraulic bucket, up to several hours, when the crane is used in assembly work, for instance in order to lift and position a transformer and to keep this in place until it has been fixed on the intended place. In the first mentioned case, the number of lifting cycles and thereby the total fatigue stressing of the crane will be considerable higher than in the last mentioned case during one and the same time period.

OBJECT OF THE INVENTION

The object of the present invention is to provide an alternative way of registering lifting up and putting down of a load by a hydraulic crane.

SUMMERY OF THE INVENTION

According to the present invention, this object is achieved by means of a hydraulic crane having the features defined in claim 1 and a method having the features defined in claim 5.
According to the present invention, lifting up or putting down of a load is registered in dependence on the rate of the changes in the cylinder force of the hydraulic cylinder of a crane boom, a lifting up or putting down of a load executed by the crane being registered when the rate of a detected change in the cylinder force exceeds a predetermined value. In this way, liftings up and/or puttings down of load executed by the crane can be registered in a very simple manner and with simple and cheap means. By basing the registrations of liftings up or puttings down of load on the changes of the cylinder force instead of on the changes of the hydraulic pressure on the piston side of the hydraulic cylinder, there is no risk of erroneous registrations due to the above-mentioned rapid pressure change caused by the induced pressure on the piston side of the cylinder that may ensue during lowering movements owing to the fact that a certain pressure is required on the piston stem side in order to open the load holding valve of the hydraulic system. In the last mentioned situation, the induced pressure on the piston side of the cylinder is namely balanced by a corresponding pressure on the piston stem side of the cylinder, which implies that the induces pressure will not cause any increase of the cylinder force. With the inventive solution, there is consequently no longer any need of detecting whether or not a lowering movement of the crane is taking place in order to avoid an erroneous registration of load lifting, which is required with the previously known solution according to EP 1 150 019 A1 .
By means of the registered liftings up and/or puttings down of load it will be possible to establish the number of lifting cycles performed by the crane, which constitutes a measure that is well related to the accumulated fatigue stressing of the crane.
According to a preferred embodiment of the invention, a value representing the prevailing cylinder force of the hydraulic cylinder is calculated based on measured hydraulic pressure on the piston side and measured hydraulic pressure on the piston stem side of the hydraulic cylinder, the rate of the changes in the cylinder force of the hydraulic cylinder being established based on the rate of change of this calculated value. Hereby, the registrations of liftings up and puttings down of load can be based on measuring signals from rather simple, cheap and reliable pressure sensors.
Further preferred embodiments of the invention will appear from the independent claims and the subsequent description.
The invention also relates to a method for calculating the fatigue stressing of a hydraulic crane according to claim 8.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be more closely described by means of embodiment examples, with reference to the appended drawings. It is shown in:

Fig 1: a lateral view of a hydraulic crane provided with a bucket,
Fig 2: a lateral view of a hydraulic crane provided with a jib,
Fig 3: a schematic illustration of an embodiment of the invention, and
Fig 4: a schematic perspective view of a control unit with a number of control members for controlling different crane functions.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In this description, the expression force member is used to designate the hydraulic force members which execute the crane movements ordered by the operator of the crane. Consequently, the expression force member embraces the hydraulic cylinders 8, 9, 10, 14, 17 and 19 mentioned hereinafter. The expression control member refers to the members, for instance operating levers or operating buttons, by means of which the operator regulates the valve members included in the control system which control the flow of hydraulic fluid to the respective force member. In the described embodiment, said valve members consist of so-called directional-control-valve sections.
A hydraulic crane 1 attached to a frame 2 is shown in Fig 1, which frame for instance may be connected to a lorry chassis. The frame is provided with adjustable support legs 3 for supporting the crane 1. The crane comprises a column 4, which is rotatable in relation to the frame 2 about an essentially vertical axis. The crane further comprises an inner boom 5 articulately fastened to the column 4, an outer boom 6 articulately fastened to the inner boom 5 and an extension boom 7 displaceably fastened to the outer boom 6. The inner boom 5 is operated by means of a hydraulic lifting cylinder 8, the outer boom 6 by means of a hydraulic outer boom cylinder 9 and the extension boom 7 by means of a hydraulic extension boom cylinder 10. In the shown example, a rotator 11 is articulately fastened to the outer end of the extension boom, which rotator in its turn carries a hydraulic grab tool in the form of a bucket 12. Two bucket parts 13 included in the bucket 12 are moveable in relation to each other by means of a hydraulic grip cylinder 14 for opening and closing the bucket 12. The rotator 11 is rotatable in relation to the extension boom 7 by means of a not shown hydraulic force member.
In the example shown in Fig 1, the crane 1 is equipped for performing excavations. When the crane 1 is to be used for proper lifting operations, the rotator 11 and the bucket 12 can be removed and replaced by a lifting hook. The rotator 11 may possible be retained, in which case the bucket 12 is replaced by a lifting hook. In order to perform lifting operations requiring a great range, the rotator 11 and the bucket 12 are replaced by a jib 15, see Fig 2. The jib 15 comprises a jib boom 16, which is articulately fastened in relation to the extension boom 7 and operated by means of a hydraulic jib boom cylinder 17. The jib may further comprise an extension boom 18 which can be operated by means of a hydraulic extension boom cylinder 19. One and the same crane may consequently be used for a large number of different working operations, the intensity (lifting frequency) of which varies considerably.
In this description and the subsequent claims, the expression liftable and lowerable crane boom refers to a crane boom which by means of a hydraulic cylinder can be turned in a vertical plane in order to perform liftings and lowerings of a load carried by the crane. In the crane illustrated in Figs 1 and 2, the inner boom 5, the outer boom 6 and the jib boom 16 constitute such liftable and lowerable crane booms. The expression "hydraulic cylinder for lifting and lowering the crane boom" refers to the hydraulic cylinder which is assigned to the liftable and lowerable crane boom and which executes turning thereof in a vertical plane. In the cranes illustrated in Figs 1 and 2, the lifting cylinder 8, the outer boom cylinder 9 and the jib boom cylinder 17 constitute such hydraulic cylinders.
In addition to the crane elements shown in Figs 1 and 2, the crane 1 may also be provided with a hydraulically operable winch, which may be used in combination with a lifting hook either with or without a jib 15. The crane 1 may also be provided with outer types of hydraulic grab tools than a bucket, for instance grab tools for handling scrap or pallets with building material such as stone or building plates.
The control system for controlling the different crane functions, i.e. lifting/lowering by means of the lifting cylinder 8, tilting by means of the outer boom cylinder 9, extension/retraction by means of the extension boom cylinder 10 etc, comprises a pump 20 which pumps hydraulic fluid from a reservoir 21 to a directional-control-valve block 22. The directional-control-valve block 22 comprises a directional-control-valve section 23 for each of the hydraulic force members 8, 9, 10, 14, 17, 19, to which hydraulic fluid is supplied in a conventional manner depending on the position of the slide member in the respective directional-control-valve section 23. The position of the slide members in the directional-control-valve sections 23 is controlled either via a number of control members, for instance in the form of operating levers 24, each of which being connected to its own slide member, or by remote control via a control unit 25, see Fig 4, comprising a control member S1-S6 for each slide member. In the case of remote control, the control signals are transmitted via cable or a wireless connection from the control unit 25 to a microprocessor, which in its turn controls the position of the slide members in the valve sections 23 of the directional-control-valve block 22 depending on the magnitude of the respective control signal from the control unit 25.
Each separate directional-control-valve section 23 consequently controls the magnitude and the direction of the flow of hydraulic fluid to a specific force member and thereby controls a specific crane function. For the sake of clarity, only the directional-control-valve section 23 for the lifting cylinder 8 is illustrated in Fig 3.
The directional-control-valve block 22 further comprises a shunt valve 26, which pumps excessive hydraulic fluid back to the reservoir 21, and an electrically controlled dump valve 27, which can be made to return the entire hydraulic flow from the pump 20 directly back to the reservoir 21.
In the shown embodiment example, the directional-control-valve block 22 is of load-sensing and pressure-compensating type, which implies that the magnitude of the hydraulic flow supplied to a force member always is proportional to the position of the slide member in the corresponding directional-control-valve section 23, i.e. proportional to the position of the operating lever 24. The directional-control-valve section 23 comprises a pressure limiter 28, a pressure compensator 29 and a directional-control-valve 30. Directional-control-valve blocks and directional-control-valve sections of this type are well-known and are available on the market. However, also other types of valve devices than the one here described may be used.
A load holding valve 31 is arranged between the respective force member and the associated directional-control-valve section 23, which load holding valve makes sure that the load will remain hanging when the hydraulic system runs out of pressure when the dump valve 27 is made to return the entire hydraulic flow from the pump 22 directly back to the reservoir 21.
The crane 1 further comprises registration means 35, which is adapted to register when the crane lifts up or puts down a load. The registration means 35 registers this by detecting the rate of the changes in the cylinder force F_c of a hydraulic cylinder which is connected to a liftable and lowerable crane boom for lifting and lowering thereof. In the illustrated example, the registration means 35 is adapted to base the registrations of lifting up or putting down of load in dependence on the rate of the changes in the cylinder force F_c of the crane's lifting cylinder 8. The registration means 35 is adapted to register that the crane executes a lifting up or putting down of a load when the rate of a detected change in the cylinder force F_c exceeds a predetermined value. In connection with a lifting up of a load, the cylinder force F_c in the hydraulic cylinder 8 increases very rapidly just at the moment when the load is lifted up from the underlying support surface and becomes free hanging. The same rapid change of force occurs when the load is put down and no longer is carried by the crane. These changes of force are much more rapid than the changes of force caused by the normal natural oscillations which always are present in the steel structure of the crane, and the registration means 35 is hereby able to distinguish between "lifting up/putting down" and "oscillations". A lifting up or a putting down of a load is consequently registered when the rate of the change of force in the hydraulic cylinder 8 exceeds a predetermined value.
By taking into account the direction of the change of force i.e. whether the cylinder force F_c in the hydraulic cylinder 8 increases or decreases, it will be possible to establish whether a lifting up or a putting down of a load takes place. In connection with a lifting up of a load a very rapid increase of the cylinder force will namely arise, whereas a rapid decrease of the cylinder force arises in connection with a putting down of a load.
The cylinder force F_c of the hydraulic cylinder 8 in question can be established by measuring the force on the piston stem 8c or cylinder 8d of the hydraulic cylinder by means of suitable measuring means, such as for instance strain gauges. However, a value representing the cylinder force F_c of the hydraulic cylinder 8 is with advantage calculated based on the following formula: $F_{c} = p_{1} \cdot A_{1} - p_{2} \cdot A_{2}$

where p₁ is the hydraulic pressure on the piston side of the hydraulic cylinder 8, A₁ is the pressure area on the piston side of the piston 8e of the hydraulic cylinder, p₂ is the hydraulic pressure on the piston stem side of the hydraulic cylinder 8, and A₂ is the pressure area on the piston stem side of the piston 8e of the hydraulic cylinder.
When a value representing the cylinder force F_c is calculated based on the hydraulic pressure on the piston side and the hydraulic pressure on the piston stem side of the hydraulic cylinder 8, the crane 1 comprises a first measuring means 34a in the form of a pressure sensor for measuring the hydraulic pressure p₁ on the piston side of the hydraulic cylinder 8 and a second measuring means 34b in the form of a pressure sensor for measuring the hydraulic pressure p₂ on the piston stem side of the hydraulic cylinder 8. The registration means 35 is adapted to receive, from these measuring means 34a, 34b, measuring values related to said hydraulic pressures p₁, p₂. In this case, the registration means 35 is adapted to calculate a value representing the prevailing cylinder force F_c of the hydraulic cylinder 8 based on the measuring values from the measuring means 34a, 34b as to the measured hydraulic pressure p₁ on the piston side and the measured hydraulic pressure p₂ on the piston stem side of the hydraulic cylinder 8. The registration means 35 is further adapted to establish the rate of the changes in the cylinder force F_c of the hydraulic cylinder 8 based on the rate of change of this calculated value.
The registration means 35 is suitable constituted by or included in an electronic processing unit 33 comprising a processor, for instance in the form of a microprocessor.
In the embodiment illustrated in Fig 3, the crane 1 further comprises calculation means 36 for calculating the accumulated fatigue stressing of the crane, this calculation means 36 being adapted to calculate this fatigue stressing based on the number of liftings up and/or puttings down of load registered by the registration means 35. The calculation means 36 is consequently adapted to receive information from the registration means 35 as to registered liftings up and/or puttings down of load. The calculated fatigue stressing is presented to the operator of the crane and/or maintenance personell by means of suitable display means. It is also possible to let a signal or an alarm be emitted when the accumulated fatigue stressing has obtained a certain predetermined value. When it comes to loads which are very small with respect to the crane, (approximately smaller than 10% of the maximum capacity of the crane), it might be problematic to register a lifting up and a putting down of a load in the manner described above. However, these small loads bring about a so small contribution to the accumulated fatigue stressing that they can be neglected in this connection.
Said calculation means 36 is with advantage integrated in one and the same unit 33 as the above-mentioned registration means 35, as illustrated in Fig 3. Alternatively, the calculation means 36 and the registration means 35 could however be arranged in separate and mutually communicating units.
The information from a registration means 35 of the type here described may also be used for other functions of a crane than for calculation of accumulated fatigue stressing. The information may for instance be utilized in a system for regulating the maximum allowed lifting force of a hydraulic crane, such as a system of the type more closely described in EP 1 151 958 A2 or EP 1 607 365 A1 .
The invention is of course not in any way limited to the embodiments described above. On the contrary, many possibilities to modifications thereof should be apparent to a person skilled in the art without thereby deviating from the basic idea of the invention as defined in the appended claims.

Claims

A hydraulic crane comprising a liftable and lowerable crane boom (5), a hydraulic cylinder (8) for lifting and lowering the crane boom (5) and registration means (35) for registration of the lifting up or the putting down of a load, characterized in that the registration means (35) is adapted to register a lifting up or putting down of a load in dependence on the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8), the registration means (35) being adapted to register that the crane executes a lifting up or putting down of a load when the rate of a detected change in the cylinder force (F_c) exceeds a predetermined value.
A hydraulic crane according to claim 1, characterized in:
- that the crane (1) comprises a first measuring means (34a) for measuring the hydraulic pressure (p₁) on the piston side of the hydraulic cylinder (8), and a second measuring means (34b) for measuring the hydraulic pressure (p₂) on the piston stem side of the hydraulic cylinder (8),

- that the registration means (35) is adapted to calculate a value representing the prevailing cylinder force (F_c) of the hydraulic cylinder (8) based on the measured hydraulic pressure (p₁) on the piston side and the measured hydraulic pressure (p₂) on the piston stem side thereof, and

- that the registration means (35) is adapted to establish the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8) based on the rate of change of this calculated value.
A hydraulic crane according to claim 1, characterized in that the crane (1) comprises a measuring means for measuring the cylinder force (F_c) of the hydraulic cylinder (8) by measuring the compressive force (F_c) on the piston stem (8c) or the cylinder (8d) of the hydraulic cylinder, the registration means (35) being adapted to establish the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8) based on the cylinder force (F_c) thus measured.
A hydraulic crane according to any of claims 1-3, characterized in that the crane (1) further comprises calculation means (36) for calculating the fatigue stressing of the crane (1), this calculating means (36) being adapted to calculate the fatigue stressing based on the number of liftings up and puttings down of load registered by the registration means (35).
A method for registration of lifting up and/or putting down of a load by a hydraulic crane (1) comprising a liftable and lowerable crane boom (5) and a hydraulic cylinder (8) for lifting and lowering the crane boom (5), characterized in that a lifting up or putting down of a load is registered by detecting the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8), a lifting up or putting down of a load executed by the crane being registered when the rate of a detected change in the cylinder force (F_c) exceeds a predetermined value.
A method according to claim 5, characterized in:
- that the hydraulic pressure (p₁) on the piston side of the hydraulic cylinder (8) and the hydraulic pressure (p₂) on the piston stem side of the hydraulic cylinder (8) are measured,

- that a value representing the prevailing cylinder force (F_c) of the hydraulic cylinder (8) is calculated based on the measured hydraulic pressure (p₁) on the piston side and the measured hydraulic pressure (p₂) on the piston stem side thereof, and

- that the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8) is established based on the rate of change of this calculated value.
A method according to claim 5, characterized in that the cylinder force (F_c) of the hydraulic cylinder (8) is measured by measuring the compressive force (F_c) on the piston stem (8c) or cylinder (8d) of the hydraulic cylinder, the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8) being established based on the cylinder force (F_c) thus measured.
A method for calculating the fatigue stressing of a hydraulic crane (1) comprising a liftable and lowerable crane boom (5) and a hydraulic cylinder (8) for lifting and lowering the crane boom (5), characterized in that lifting up or putting down of a load is registered by detecting the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8), a lifting up or putting down of a load executed by the crane being registered when the rate of a detected change in the cylinder force (F_c) exceeds a predetermined value, and that the fatigue stressing is calculated based on the number of liftings up and/or puttings down of load thus registered.
A method according to claim 8, characterized in:
- that the hydraulic pressure (p₁) on the piston side of the hydraulic cylinder (8) and the hydraulic pressure (p₂) on the piston stem side of the hydraulic cylinder (8) are measured,

- that a value representing the prevailing cylinder force (F_c) of the hydraulic cylinder (8) is calculated based on the measured hydraulic pressure (p₁) on the piston side and the measured hydraulic pressure (p₂) on the piston stem side of the hydraulic cylinder, and

- that the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8) is established based on the rate of change of this calculated value.
A method according to claim 8, characterized in that the cylinder force (F_c) of the hydraulic cylinder (8) is measured by measuring the compressive force (F_c) on the piston stem (8c) or cylinder (8d) of the hydraulic cylinder, the rate of the changes in the cylinder force (F_c) of the hydraulic cylinder (8) being established based on the cylinder force (F_c) thus measured.