WO2004005180A1

WO2004005180A1 - A system for weighing loads in a lifting and transfer apparatus

Info

Publication number: WO2004005180A1
Application number: PCT/FI2003/000488
Authority: WO
Inventors: Kari PÄRSSINEN; Arto Huhmarkangas; Jouko HYYTIÄINEN; Markku Jaatinen; Pekka Leppänen
Original assignee: Plustech Oy
Priority date: 2002-07-02
Filing date: 2003-06-17
Publication date: 2004-01-15
Also published as: SE527169C2; SE0403140D0; AU2003238103A1; FI20021304A; FI115162B; SE0403140L; FI20021304A0

Abstract

A weighing system for determining the weight of a load that is manipulated by means of a lifting and transfer apparatus that comprises an articulated boom moving on the vertical plane (X-Z) and a tip piece (11) attached thereto, which is intended for the suspension of the load. The system comprises sensor means (23) fastened to said tip piece (11) whose output consists of one or several output signals (23b) proportional to the loading caused by the load, and calculation means (23c, 23d) that are arranged to measure the weight of the load corresponding to said output signals. The system comprises a separate tip piece to be attached to a lifting and transfer apparatus for suspension of loads, said tip piece comprising a first end (11 d) intended for attachment, and a second end (11 c) comprising means for suspension of the load (12, 13). The central part of the tip piece (11) is provided with a location for a measurement device (23) that is intended especially for measurement of deformations and that comprises means (25, 26) for fastening of said measurement device, wherein said deformations are proportional to the loading caused by the weight of the load.

Description

A system for weighing loads in a lifting and transfer apparatus

The invention relates to a weighing system as set forth in the preamble of claim 1 for determining the weight of a load manipulated by means of a lifting and transfer apparatus. The invention relates to a separate tip piece according to the preamble of claim 17 to be attached to a lifting and transfer apparatus for suspension of loads.

For harvesting, working machines, such as harvesters are known which move on a terrain by means of wheels and in which a manipulating apparatus, a so-called harvester head is arranged at the end of a boom assembly for cutting and felling a growing tree stem and sawing it to pieces of desired length. The sawed tree stems are collected with another known working machine that moves on a terrain, wherein the working machine in question is a forwarder equipped with a grapple and the stems are transported in its load space. There are also known combinations of machines in which the functions of a harvester and a forwarder have been combined, wherein the loading grapple is replaced with a harvester head that is also suitable for loading. The tree stems are also manipulated by means of boom assemblies and grapples attached to a vehicle, especially to a timber truck.

The above described working machines comprise a boom assembly for working purposes, wherein the movement of said boom assembly can be a so-called parallel motion and the outer boom part of said boom assembly to which a tool is attached, can function telescopically. The boom assembly comprises at least two, typically three boom parts attached to each other by means of a joint and moving on a vertical plane. The boom assembly is attached to the working machine by means of a rotating joint to swing the boom assembly around the vertical direction. In harvesters the entire boom assembly with its rotating joints can often be tilted at least forward and backward. To the free end of the boom assembly it is possible to attach a suitable tool, such as a harvester head or a loading grapple, typically by means of a rotator. The boom assembly typically operates by means of actuators such as cylinders and control valves under the control of a pressurized medium operated, typically hydraulic control system. There are known load cells, based for example on the principle disclosed in the US patent publication 3911737 for weighing a load to be lifted up by a grapple, such as a single tree stem or a bundle of stems, said load cells being coupled between the end of the boom assembly and the rotator to measure axial and vertical force. The force is directly proportional to the load. The load cell extends the distance between the end of the boom assembly, which increases swinging and complicates the handling of the tool. The location is also susceptible to dam- age and impacts. The damaging of the load cell may impair the load- bearing capacity and cause a safety risk.

There is also a known sensor functioning as a pivot, as disclosed in the patent publication GB 2037444. The device can be utilized for weighing the load of the grapple on the basis of the loading of the pivots. The device requires changes in the joints, and wearing forces and considerable loading are exerted thereon, merely because of the weight of the boom assembly itself. There are also other known systems for monitoring the loading of the structure of the crane, for example the system according to the US patent publication 5557526. The system is intended for monitoring local loads that are strongly dependent on the position of the crane and on the location of the supporting points of the actuators and the joints. There are also known systems according to the US patent publications 4057792 and 5160055 for determining the loading caused by the load. The loading varies as the length of the crane varies, even if the loading remained the same, and thus position sensors must also be utilized to determine the position.

It is an aim of the present invention to introduce a new type of a weighing system for weighing loads, and especially to eliminate the above-mentioned problems. The system is suitable for various lifting and transfer apparatus structures, and it is as independent as possible from the position or range of the crane.

The weighing system according to the invention is presented in claim 1. The tip piece according to the invention is presented in claim 17. One advantage of a preferred embodiment of the invention is the integrated sensoring for the weighing process. The tip piece of the invention is designed in an appropriate manner in view of the measurement, wherein good protection and the possibility to determine the weight of the load on the basis of the loading of the structure are combined in the structure. When the measurement device is a separate unit, it can be changed easily and rapidly. The tip piece is also constructed so that it is suitable in view of the separate unit.

The tip piece can be attached to various lifting and transfer apparatuses and the positioning of the sensoring also makes it possible that the effect of the position of the boom assembly and the supporting points of its supporting structures is as small as possible. Thus, sensors measuring the position can be eliminated and the calculation of the result is facilitated. The system is suitable especially for weighing of tree stems to be manipulated by means of a grapple, wherein the loaded or unloaded total amount can be constantly monitored without interrupting the work. The measurement device can be changed without releasing the boom part, the tool or the rotator.

In the following, the invention will be described in more detail by using as examples some advantageous embodiments with reference to the appended drawings, in which

Fig. 1 shows a side-view of a telescopically functioning boom in which the invention is applied,

Fig. 2 shows in more detail the free tip of the boom according to Fig. 1 , and a positioning point of the weighing device when seen from the side,

Fig. 3 shows the free tip of the boom according to Fig. 1 at the section A - A of Fig. 2,

Fig. 4 shows in more detail the weighing device according to a preferred embodiment of the invention in a top view, and Fig. 5 shows the weighing device according to Fig. 4 and in principle the positioning of strain-gauge sensors at the section B - B of Fig. 4, and

Fig. 6 shows a weighing device and system according to an advantageous embodiment of the invention in a block chart to clarify the operating principle.

The boom assembly 1 according to Fig. 1 comprises a first boom part, a pillar 2. The pillar 2 is typically vertically directed and arranged to rotate around a vertical axis Z1 (vertical direction Z) by means of a rotating device 3 to which the first end 2a of the pillar is attached. The pillar 2 can also be arranged on a base rotating around a vertical axis (vertical direction Z), on which the cabin of the working machine can also be located. The boom 1 comprises a second boom part 4 whose first end 4a is attached to the second end of the pillar 2 by means of a horizontal joint 5a (transverse horizontal direction Y). The second end 4a of the boom part 4 typically moves on the vertical plane (vertical direction Z and the longitudinal horizontal direction X), and rotates around the joint 5a. The rotation is attained by means of an actuator 6a that is connected between the pillar 2 and the boom part 4. The boom assembly 1 also comprises a third boom part 7 whose first end 7a is attached to the end 4b by means of a horizontal joint 5b (horizontal direction Y). The free second end 7b typically moves on the vertical plane (vertical direction Z and horizontal direction X), and rotates around the joint 5b. The rotation is attained by means of an actuator 6b that is connected between the boom parts 4 and 7 by means of a link mechanism. The presented boom 1 functions telescopically to increase the range of the end 7b, wherein the boom part 7 contains a boom part 7c that slides therein and a boom part 7d that slides inside the part 7c, said parts being controlled by means of one actuator 6c and a chain mechanism (not shown). The end 7b of the boom assembly and the tools 8 contained therein can thus be taken further apart from the working machine. Here, the tool 8 is a grapple that is attached to the end 7b by means of a rotator 9, said attachment also corresponding to the attachment of the harvester head. The tool 8 is arranged to rotate around a vertical axis Z2 (vertical direction Z) by means of the rotator 9. Between the rotator 9 and the end 7b there is also a detachable crosspiece 10 that allows free suspension and rotation around the horizontal axes X1 (horizontal direction X) and Y1 (horizontal direction Y) that are substantially perpendicular to each other. The combined weight of the parts 8, 9 and 10 is typically 300 kg, and the weight of the logs to be lifted is typically 300 to 1000 kg. The lifting capacity of the presented boom assembly is typically approximately 3000 kg, depending on the range.

It is easy to apply the invention in various lifting and transfer devices, because the output obtained from the measurement is as independent as possible from other factors than the load. In a simple preferred embodiment of the invention, the system is thus based entirely on calibration, wherein the levels of output signals corresponding to certain weight can be detected by means of experiments, and on the basis of the same it is possible to determine the weights corresponding to other outputs as well for example by means of a table or a mathematical formula. In the calibration loads of known weight are used. In the calculation of the weight, the tool whose weight forms part of the load and also causes loading must be taken into account. The most accurate measurement result is obtained when the load is stationary or moving at constant speed. By means of taring it is possible to remove for example the portion of the grapple from the calculated weight. The table or the mathematical formula can be stored in the calculation means of the measurement device that show the weighing results to the user. Alternatively, the calculation can be implemented in the control system of the working machine to which the output signals of the measurement device are connected by means of cables and wires.

When the load is weighed, the different boom parts and the load can be moving, wherein the accelerations must also be measured and taken into account in the calculation of the weight. The acceleration also indicates the operating state and working stage of the boom assembly, so that a suitable measurement moment could be selected. In the lifting, acceleration occurs in the Z-direction in which gravity is effective as well. By means of a telescopic boom assembly the load is also transferred on the horizontal plane, wherein the acceleration is also effective in the X-direction. When the boom assembly is turned, the acceleration is also effective in the Y direction. Especially the X and Z directions (vertical plane) are essential in view of the measurement. It is possible to measure and estimate maximum acceleration (2 to 8 g) on the basis of the dimensions, mass and actuators of the boom assembly. Disturbance is caused in the measurement especially by rapid stops and accelerations. The velocity of motion typically varies between 5 and 15 m/s.

According to the invention, the forces effective in the boom part (at least in the X and Z direction) are measured with sensor means that measure the tensions effective in the structure. The stress state is proportional to the effective loading, and on the basis of the changes therein it is possible to determine the load or the moment when the load is manipulated. The measurement point is preferably located in the boom part which is projectively attached from its first end, and a load is suspended from its free end. The boom part is a load-bearing structure to which the loading typically has a bending effect on the vertical plane (X and Z directions) as a result of earth's gravity. The movement and the acceleration cause additional forces as well as forces deviating from the vertical direction, which must be taken into account in the calculation and compensated, wherein the measurement mode can be dynamic and it is not necessary to stop the boom assembly for the duration of the measurement. The tensions cause a deformation proportional thereto in the material, said deformation being preferably measured by means of strain-gauge sensors. The same device is also equipped with acceleration sensors, depending on the measurement mode. The changes in the deformations are proportional to the stress state and to the changes therein.

The measurement point is positioned at the end of the outermost boom part, in the embodiment of Fig. 1 at the end 7b of the outer boom part 7 (preferably the boom part 7d or the like, or the boom part 7 without the parts 7c and 7d). The boom 1 can also comprise one telescopic part 7d or only the boom part 7 and its end 7b. Loading is also exerted on the boom part 7 by its own weight that is positioned further outward from the measurement point, as well as by the weight of the crosspiece 10, the rotator 9 and the grapple 8, which must be taken into account in the calculation, for example by means of taring.

At the end, i.e. the tip piece 7b, the measurement point is located in such a point where the moment arm (the distance between the axis Y1 and the measurement point) does not change substantially when the position of the boom assembly changes, and thus it does not substantially affect the loading. For example, between the axis Y1 and the measurement point there is no cylinder attachments or other sup- porting points (for example the attachment between the boom parts 7c and 7d), whose supporting forces would affect the loading of the measurement point. The supporting forces vary for example according to the extension. The measurement point is located as close as possible to the axis Y1 , wherein the part of the boom part 7d that extends out of the boom part 7c can be shortened at the same time. The distance between the axes Z1 and Z2 varies as the extension changes, wherein for example the loadings of the boom parts 2 and 4 would vary even if the load were the same.

In the boom assembly 1 of Fig. 1 the weighing device and the measurement point are located in the tip piece 7b that is attached as a separate piece to the metallic boom part 7d (or directly to the boom part 7) which typically has the cross section of a hollow square beam whose size varies between 100 to 140 mm. The tip piece 7b is for example a continuous metal piece produced by means of casting and having as a special feature a recess in which the weighing device and the sensor means are well protected from all sides. The recesses extend within a distance of approximately 50 to 100 mm in the longitudinal direction of the tip piece. The tip piece 7b is attached to the boom part 7d preferably by means of welding, and its cross section corresponds to an I-beam whose central beam is located on the vertical plane, and in the middle of the tip 7b and on its axis of symmetry or neutral axis. At the same time the central beam forms a vertical wall from which the desired deformation is measured. It is also an advan- tage of the embedding of the tip piece 7 that the rest of the boom structure 1 does not have to be altered. As a welded structure the tip 7b is for example a square beam. The boom part 7d is typically a hollow square beam.

The cross section of the measurement point can also be a square beam or otherwise suitable in its shape. In view of the measurement, it is important to measure the forces effective in the X and Z directions, wherein the measurement point is not necessarily positioned on the neutral axis, but there are two measurement points symmetrically on both sides of the same, for example on both sides of the tip piece 7b. Different measurement point is often a prerequisite for the fact that a ceramic resistor or piezocrystal known as such is used in the measurement. The measurement sensor is attached for example to projections that are produced when H-shaped grooves are formed on the sides of the tip piece 7b, and the projections extend in the longitudinal direction of the tip piece 7b. Corresponding projections can also be formed deeper in the tip piece 7b, for example on the neutral axis of the same.

Fig. 6 shows a weighing system according to a preferred embodiment, in which a weighing device 23 comprises sensor means 23a (for example a strain-gauge sensor 18 - 21 according to Fig. 4), their amplifiers 23b for amplifying measurement signals and calculation means as an integrated entity in the processor 23c that can be attached in a reliable manner. The weighing device 23 also comprises the necessary protective casings and inlets, and if necessary, it can be composed of two or several casing and part entities for separate sensor series (for example 4 strain-gauge sensors in each series). The processor 23c is arranged to calculate the desired data on the basis of measurement signals and by means of the desired calculation algorithm of the weighing result, wherein it utilizes for example the memory 23d to store the data. The calculation means 23c can also be positioned in the control system 24, wherein one or several output signals can be obtained from the device 23, said output signals being used in the desired manner to determine the weighing result. The functions of the calculation means 23c can also be implemented in the system 24 that can also be modified by means of a program. More detailed selection and configuration of the components of the weighing device 23 can vary. Preferably the weighing device 23 can be connected to the boom assembly 1 at a later stage as well, wherein it is connected to another control and computer system 24 of the working machine for example by means of a field bus 23f. The bus 23f, for example a CAN bus (Controller Area Network), is utilized to transmit the desired Input/Output signals. More detailed configuration of the system 24 varies according to the working machine. The output of the weighing machine 23 is especially the total weight of one or several lifted loads when stems are lifted to a load space or away from the same.

Table 1 below shows the inputs and outputs of the weighing machine that are used in a wide weighing system and calculation. The inputs are parameters, constants or other measurement results that are taken into account in the calculation.

INPUT: power supply; calibration constants ¹⁾, taring constant ¹⁾; calibration access right code ¹⁾; acceleration in X, Y and/or Z direction, tension in X and/or Z direction ⁴⁾.

OUTPUT: weight of the load ²⁾, X, Y and/or Z forces ³⁾; X, Y, and/or Z acceleration ³⁾; error or state code.

Description: ¹⁾ stored in the memory of the weighing system or the control system, part of the calibration can also be conducted by means of HW; ²⁾ one weighing result per lifting; ³⁾ constantly or on demand; ⁴⁾ can contain tension only in the X direction.

Table 1

The weighing device 23 determines the weight of the load on the basis of the accelerations and/or changes in the stress state caused by the load that appear as deformations, especially elongations that can be measured by means of strain-gauge sensors and electronic circuits (e.g. Wheatstone bridge) known as such. The result can be determined by means of calculations (SW), digitally in the processor 23c and/or analogically (HW). The result is preferably presented to the user by the user interface means of the control system 24, wherein the device 23 contains suitable connection means (I/O module) 23e for connecting to the field bus 23f. It is obvious that I/O can also comprise the measured force components, wherein the weighing result and other desired results can be calculated in the system 24. In the calibration, feasible output signals are those that are dependent on the load. The parts 23c, 23d can be integrated in the control system 24 that can also control the management, bookkeeping and storing of the results in the desired manner.

Figs 2 and 3 show in more detail a preferred embodiment of a separate tip piece 11 (whose function corresponds to the tip piece 7b of Fig. 1), which is a solid piece manufactured by casting. Its first end 11c contains two next to each other positioned vertical plate-like flanges 12 and 13, between which a crosspiece is suspended on the support of a pivot (Y1 direction). The left side 11a and the right side 11b of the tip piece 11 are equipped with substantially rectangular recesses, embed- dings 14 and 15, at the location of which the tip piece 11 has substantially the cross-section of an I-beam, in which the dimensions of its vertical wall 25 change as a result of the loading. The sensors are arranged to measure the tensions prevailing in the vertical flange 25 to determine at least the forces in the X (tensile stress) and Z direction (shear stress), wherein two series of sensors are attached to the ends of the vertical flange 25 that are located apart from each other in the longitudinal direction of the tip piece 11. The load exerts stress on the entire l-structure, which functions as a load-bearing structure and transmits loading between the suspension means 12, 13 and the boom assembly. There are no other supporting points between the load and the measurement point. The measurement point is located between the ends 11c and 11d aside from the Y1 axis. Attachment to the vertical flange 25 can be easily implemented, and reinforcement can be formed therein for example at the location of a bolt or screw fastening 26. The depth of the opposite embeddings determines the thickness of the I- beam and the prevailing tensions. The tip piece 11 is attached to the boom part 16 that corresponds to the boom part 7 of Fig. 1 (more precisely the part 7d), preferably by welding, wherein the second end 11d of the tip piece 11 can have suitable shapes and fittings for that purpose. The boom part 16 typically has the cross-section of a hollow square beam inside which the electrical conductors of the weighing device can be installed in shield, if desired.

Figs 4 and 5 show a preferred embodiment of the sensor means that comprises a vertically positioned plate-like base 17 to which two series of strain gauges 18a - 21a and 18b - 21b are attached. In practice, there must be at least 4 strain gauges per one force component, so that the disturbances could be compensated. The base 17, in turn, is fastened (bolt or screw fastening 27 at the corners) to the vertical flange 25 of Fig. 3, whose deformation the base 17 now follows. Thus, the changes in the tension of the tip piece can also be determined. The strain gauges are coupled electrically in the desired manner into the form of a Wheatstone bridge. The bridge provides as an output a voltage whose change is proportional to the change in the resistance of the strain gauges, which, in turn, is dependent on the elongation in a known manner. The attachment of the strain gauges, the arrangement of the necessary electronics, shielding and more precise dimensioning of the bridge structure, balancing and selection of the gauges are known as such. By means of strain gauges extending in different di- rections, it is possible to determine the differently extending components of the stress state in the X and Z direction. They can also be utilized to compensate the effect of temperatures on the measurement. The strain gauges are positioned in the middle of the base 17 to measure tensile stress (horizontal and vertical strain gauges) and shear stress (diagonal strain gauges).

In the following, the measurement modes that can be applied are discussed in more detail with reference to Table 2 below. The aim is to determine the force effects F_x and F_z in the X and Z direction, on the basis of which it is possible to calculate the load as a resultant directly by means of their square sum expression, irrespective of the position of the tip piece 11. If the boom assembly is in a tilted position, the force F_γ in the Y direction must also be taken into account, wherein the weight is proportional to the radix taken from the sum of the squares of their F_x, F_z and F_γ terms. In the presented weighing device and sensors the calculation is based on measured values, wherein other dimensions or positions of the boom assembly does not have to be taken into account.

The markings 1), 2), 3) and 4) in the table refer to measurement modes, which will be described shortly. From the table it is possible to select in different combinations desired calculation algorithms, depending on that whether all force and acceleration components are measured as well as on that how the operating stages or sequence of the boom assembly are taken into account. Different combinations are attained in such a manner that one or several sensor types as well as their number are selected to determine the necessary force components and for example to compensate disturbances. The desired measurement result is obtained by means of the selected sensors, and said result is utilized in the determination of the load. The calculation can be synchronized with the other operations of the working machine, wherein the accuracy of the measurement result is improved if the measurement moment is selected accurately and the measurement signals are filtered sufficiently.

Measurement mode: acceleration measurement and/or force measurement.

Sensor types: acceleration sensor ^{2) 3) 4)}; acceleration and gravitation sensors ^{3) 4)}; glued strain gauges ^{1) 2) 3) 4)}; welded strain gauges ^{1) 2) 3) 4)}; separate strain sensors ^{1) 2) 3) 3)}; integrated strain sensors ^{1) 2, 3) 4)}.

Number: 0 to 2 pieces ⁴⁾, 3 pieces ^{3) 4)} (acceleration measurement); 1 to 3 pieces, 4 pieces ^{1) 2) 3) 4)} (force measurement).

Measurement result: magnitude of acceleration ^{2) 4)}; X and Z components of acceleration ⁴⁾; X, Y, and Z components of acceleration ^{3) 4)}; magnitude of force ^{1) 2> 4)}; X and Z components of force ⁴⁾; X, Y, and Z components of force ^{3) 4)}.

Calculation of the weighing result: filtering of the force signal ¹⁾; calculation of an average value for the force ¹⁾; calculation of an average value for the force; triggering on the basis of the acceleration ²⁾; continuous force measurement and calculation (m=F/a) ³⁾; triggering on the basis of the angular difference of the force and acceleration vectors m=F/a ³⁾; selection of the measurement moment by means of an algorithm recognizing the working cycle ⁴⁾; calculation of the result by means of an algorithm remembering the working cycle ⁴⁾; dot product of the force and acceleration vectors ³⁾; calculation by means of an impulse expression.

Table 2

In the first mode of calculation 1) only the force in directions X and Z (force component on the vertical plane) or in directions X, Y and Z is measured. The measurement requires four strain gauges per each force component, and the resultant force is calculated for example by the aforementioned square sum. It is possible to calculate an average value for this resultant as a function of time, said average value indi- eating the corresponding load. Alternatively, to obtain the average value the signal corresponding to the force component is generated analogically and filtered to remove disturbances, wherein an average value is attained. In the second measurement mode 2) the calculation principle is otherwise the same as the one in mode 1), but the calculation is started when the acceleration resultant measured for the acceleration (acceleration components in directions X, Y, and/or Z) are within set limits, wherein inaccurate measurement moment is avoided for example during rapid acceleration or deceleration.

In the third measurement mode 3), in turn, three acceleration components and three force components are measured, on the basis of which the force and acceleration vectors in the desired X, Y, Z coordinate system are attained. The absolute values of the vectors are utilized to calculate the mass M of the load either constantly or at set moments, when the angular difference of the acceleration and force vector is within predetermined limits. The acceleration measurement can also be affected by gravitation. The mass M can be determined on the basis of vector algebra also as a dot product of force and acceleration, wherein only the component parallel to the measured force is taken into account in the acceleration.

The principle of the fourth measurement mode 4) is that the weighing system recognizes from the measurement data what is taking place in the boom assembly, and determines on the basis of the measurement or calculation results at which moment the obtained measurement result is most applicable. The correct measurement moment is immediately identified in the measurement results, or the measurement results obtained from the boom assembly are stored for analysis. The stored measurement results are analysed at the desired moment, for example after detachment from the load, and the correct measurement moment is searched from the measurement data on the basis of predetermined criteria.

The invention is not limited solely to the above-presented embodiment, but it can be implemented within the scope of the appended claims. More accurate processing, applying and integration of the measure- ment results in an optimal manner in another weighing system and control system of a working machine is obvious on the basis of the facts presented hereinabove. More detailed implementation can also vary in accordance with the components and systems available.

Claims

Claims:

1. A weighing system for determining the weight of a load that is manipulated by means of a lifting and transfer apparatus that comprises an articulated boom moving on the vertical plane (X-Z) and a tip piece (11) attached thereto, which is intended for suspension of the load, characterized in that the system comprises

sensor means (23) which are attached to said tip piece (11) and whose output consists of one or several output signals

(23b) proportional to the loading caused by the load, and

calculation means (23c, 23d) that are arranged to determine the weight of the load corresponding to said output signals.

2. The system according to claim 1 , characterized in that the tip piece (11) is provided with a location for the sensor means (23) that is intended especially for measurement of deformation and that comprises means (25, 26) for fastening of the sensor means (23).

3. The system according to claim 1 or 2, characterized in that the calculation means (23c, 23d) can also be attached to the tip piece (11) either separately or together with the sensor means (23).

4. The system according to any of the claims 1 to 3, characterized in that the tip piece (11) comprises means for suspension of the load (12, 13), wherein the sensor means (23) are positioned between these means and the articulated boom.

5. The system according to any of the claims 2 to 4, characterized in that said sensor means are intended for measuring the deformation in the material of the tip piece (11), which is proportional to the loading caused by the weight of the load.

6. The system according to claim 2, characterized in that the sensor means (23) comprise strain gauge means that are arranged to measure loadings occurring on the vertical plane (X-Z).

7. The system according to claim 6, characterized in that the strain gauge means are fastened to a base, which, in turn, can be releasably fastened to the tip piece (11) in such a manner that the base follows the deformation of the tip piece (11 ).

8. The system according to any of the claims 1 to 7, characterized in that it also comprises sensor means for measuring the acceleration of the tip piece (11) on the vertical plane (X-Z) and/or on the horizontal plane (X-Y), wherein the output consists of one or several output signals proportional to the acceleration.

9. The system according to any of the claims 1 to 8, characterized in that it also comprises connection means (23e) that are arranged to connect the signal indicating the weight of the load to the control system (24) of the lifting and transfer apparatus and/or the working machine to which the lifting and transfer apparatus is attached.

10. The system according to any of the claims 1 to 9, characterized in that the calculation means (23c, 23d; 24) are also arranged to sum and store the weights of different manipulated loads.

11. The system according to any of the claims 1 to 10, characterized in that the calculation means (23c, 23d; 24) are also arranged to monitor said one or several output signals constantly and to determine for each load the moment when the output signal fulfils the predetermined criteria, and to select the output signal of said moment to be utilized for determination of weight.

12. The system according to claim 11 , characterized in that the calculation means (23c, 23d; 24) are also arranged to store said one or several output signals and to determine the moment of time on the basis of the stored data.

13. The system according to any of the claims 1 to 12, characterized in that it also comprises user interface means for presenting the weight for the user and to control the operation of the system.

14. The system according to any of the claims 1 to 13, characterized in that the tip piece (11) is integrated to the articulated boom.

15. The system according to any of the claims 1 to 14, characterized in that said articulated boom is an articulated boom of a forwarder.

16. The system according to any of the claims 1 to 15, characterized in that said sensor means can be releasably attached to said tip piece for replacement purposes.

17. A separate tip piece to be attached to a lifting and transfer apparatus for suspension of loads, said tip piece comprising a first end (1 Id) that is intended for attachment, and a second end (11c) that comprises means for suspension of the load (12, 13), characterized in that in the middle of the tip piece (11) there is a location (14, 15) arranged for a measurement device (23) that is intended especially for measurement of deformations and that comprises means (25, 26) for attachment of said measurement device, wherein said deformations are proportional to the loading caused by the weight of the load.

18. The tip piece according to claim 17, characterized in that said location is arranged especially for attachment of the strain gauge means of the measurement device (23), which are arranged to measure loadings occurring on the vertical plane (X-Z) when the tip piece is in the operation position.

19. The tip piece according to claim 17 or 18, characterized in that the tip piece (11) comprises a recess (14, 15) that is intended for attach- ment of the sensor means (23).

20. The tip piece according to any of the claims 17 to 19, characterized in that said tip piece is a tip piece to be attached to an articulated boom in a forwarder.