WO1994009347A1

WO1994009347A1 - Mass measuring system and method for determining the mass of an object

Info

Publication number: WO1994009347A1
Application number: PCT/NL1993/000202
Authority: WO
Inventors: Graham Kenward Gollings
Original assignee: L.M.S. B.V.
Priority date: 1992-10-13
Filing date: 1993-10-13
Publication date: 1994-04-28
Also published as: EP0674762A1; NL9201781A

Abstract

The invention relates to a mass measuring system for determining the mass of a first object (1). For this purpose, the mass measuring system comprises a first measuring unit (3) by which a first quantity is determined which comprises at least information about the mass of the first object (1) to be determined. The mass measuring system furthermore comprises a predetermined reference object (9) whose mass is known and a second measuring unit (4) by which a second quantity is determined comprising at least information about the mass of the reference object (9). A combination unit (15) determines the mass of the first object (1) from the first and second quantities. The mass measuring system operates in static, accelerating, decelerating as well as in periodically moving reference systems.

Description

Title: Mass measuring system and method for determining the - mass of an object.

The invention relates to a mass measuring system for determining the mass of a first object, the mass measuring system comprising a first measuring unit by which a first quantity is determined which comprises at least information about the mass of the first object to be determined.

The invention further relates to a method for determining the mass of a first object, in which a first measurement is carried out on the first object in order to obtain a first quantity at least comprising information about the mass of the first object to be determined.

Such mass measuring systems and methods are common and are used in many different forms in everyday life. Known for instance is a spring balance where the first object is suspended from a spring and the extension of the spring under the influence of the gravitational force acting on the first object is a measure for the weight and hence the mass of the first object.

Quite comparable is the operation of a spring balance where a spring is compressed under the influence of the weight of the first object and in this case the extent of the compression of the spring is a measure for the weight and hence the mass of the object.

Further, electric mass measuring systems are known which also perform a force measurement under the influence of the gravitational field (gravity) so as to determine the weight of an object. For this purpose an iron bar could be used which is reduced in the middle between its lower and upper ends. The bar is for instance suspended by its top while the gravitation to be measured is exerted on the lower end of the bar, so that the bar is loaded with a tensile force. The bar transmits the tensile force to be measured, with the largest tensions building up in the reduced section of the bar. Mounted on the reduced section of the bar is at least one strain gauge, which will contract or expand under the influence of the tensions in the material of the bar and thereby undergo a change in resistance. These changes in resistance can be measured with known means and are a measure for the weight of the first object. Such a mass measuring system is known under the name of "load cell".

The mass measuring systems as mentioned above all have in common that they function in a stable and static reference system. However, as soon as the mass measuring system makes an accelerating movement (positive or negative acceleration) , it is no longer possible to carry out a correct measurement because of the inertia of the first object. If an object suspended from a spring weighing device is accelerated by means of this weighing device, the weighing device will indicate too high a value for the weight of the first object. Conversely, the weighing device will indicate too low a value when the first object is decelerated. When the mass of the first object is determined in a reference system which makes a periodic, for instance harmonic, movement, the mass measuring system will show a periodically changing value for the weight of the object. A comparable effect is evident when a person is weighed by means of scales in an accelerating or decelerating lift.

In certain branches of industry it happens that objects whose weight is to be determined are temporarily situated in a non-static reference system, for instance a crane which has been placed on a ship or on land. If it is desired to determine the weight of an object that is being lifted by a crane, a mass measuring unit is placed between the hook of the crane and the object. The object in this situation is suspended from the measuring unit and the measuring unit is suspended from the hook of the crane. Such measurements are typically carried out to test whether a crane is capable of lifting a certain amount of weight. For such a test, for instance bags filled with water are used. When such first object is lifted, for instance off the quay, the hook of the crane will make a swinging and hence a damped periodic movement. In order to be able to determine the weight of the first object accurately, it will be necessary to wait until the first object has come to rest. This is time-consuming and hence costs a lot of money. If the ship is not at rest by the quay but is rocking at sea, it will not be possible at all to perform an accurate measurement of the weight of the first object.

The mass measuring system according to the invention solves this problem entirely because this system functions completely independently of the reference system in which the measurement is being carried out. The mass measuring system functions in static, accelerating, decelerating as well as in periodically moving reference systems.

The mass measuring system according the invention is characterized in that the mass measuring system additionally comprises a predetermined reference object whose mass is known, a second measuring unit by which a second quantity is determined which comprises at least information about the mass of the reference object and a combination unit which determines the mass of the first object from the first and second quantities.

Because by means of the second measuring unit information is obtained which comprises not only the mass of the reference object but also information about possible disturbances caused by a non-uniformly moving reference system, while the mass of the reference weight is known and by means of the first measuring unit information is obtained which information comprises at least the mass of the first object as well as the possible disturbances caused by the non-uniformly moving reference system, it is possible to eliminate these disturbances and to determine the mass of the first object.

In accordance with a particular embodiment of the invention, the first object and the reference object make at least substantially the same movement, with the first and second measuring units being connected mechanically to each other. In the case of a crane, for instance, this is realized in that the first measuring unit is suspended from a hook of a crane or is rigidly connected thereto or constitutes a part thereof, with the first object hanging from the first measuring unit. The second measuring unit is connected mechanically to the hook of a crane, with the reference object hanging from the second measuring unit. Preferably, the second measuring unit and the reference object are incorporated into the hook of a crane. This construction is characterized in that the first measuring unit exerts a force Fl(t) on the first object which is directly proportional to the mass Ml of the first object and the second measuring unit exerts a force F2(t) on the reference object which is directly proportional to the mass M2 of the reference object. The first quantity represents a measuring value of Fl(t) and the second quantity represents a measuring value of F2(t) . The combination unit can then determine the mass Ml according to the formula Ml = M2 * Fl(t) / F2(t) .

According to an advantageous embodiment of the invention, the first and second measuring units comprise transmitter means for transmitting the measured first and second quantities and the combination unit comprises receiver means for receiving and further processing the transmitted first and second quantities. When used in a crane, it will then be possible to determine the mass in question remotely. It is also possible to provide the combination unit with transmitter means, so that the mass determined by the combination unit can be transmitted and received remotely and further be shown on a display. For this purpose, the measuring system can be further expanded to include a receiver unit and a display coupled thereto.

The mass measuring system according to the invention is not susceptible to disturbances caused by a non-static reference system or to temperature influences. Temperature influences will in principle have an effect on the measured quantities of the first as well as the second measuring unit. Because the first and second quantities are processed together by the combination unit, temperature influences will be eliminated.

It is also possible that the first object is connected mechanically to the first measuring unit, with Fl(t) being the force that the first measuring unit and the first object exert on each other, the reference object comprises the first measuring unit and is connected mechanically to the second measuring unit, with F2(t) being the force that the second measuring unit and reference object exert on each other. In this case the combination unit determines the mass Ml according to the formula Ml = M2 * Fl(t) / ( F2(t) - Fl(t) ).

According to an alternative embodiment of the invention, the mass of the first object can also be determined without the first object and the reference object being in a gravitational field. The orces Fl(t) and F2(t) are generated for this purpose by an accelerating movement of the first and second measuring units. Preferably, for this purpose the first and second measuring units are connected mechanically to each other, the first measuring unit exerting a force Fl(t) on the first object, which is directly proportional to the mass Ml of the first object and the second measuring unit exerting a force F2 (t) on the reference object, which is directly proportional to the mass M2 of the reference object. The mass M2 can then be determined again as described above. A mass measuring system which also uses a second object is a balance. This second object, however, is not a reference object with a predetermined mass. In the case of a balance, the mass of the second object must in principle be adjusted to the mass to be determined of the first object and is therefore indefinite and entirely unsuited to be used, for example, in a crane as described above.

The method according to the invention also solves the above-mentioned problems in that a second measurement is performed on at least a predetermined reference mass whose mass is known, so as to obtain a second quantity at least comprising information about the mass of the reference object, the first and second quantity being processed in combination in order to obtain the mass of the object.

The invention will be further explained with reference to the following drawings, in which: Figure 1 shows a schematic representation of a first embodiment of a mass measuring system and method according to the invention;

Figure 2 shows a schematic representation of a second embodiment of a mass measuring system and method according to the invention;

Figure 3 shows a schematic representation of a third form of construction of a mass measuring system and method according to the invention;

Figure 4 shows a schematic representation of the hook of a crane in which the mass measuring system of Figure 1 is applied; and

Figure 5 shows an alternative schematic representation of the hook of a crane.

In Figure 1 reference numeral 1 inidcates a first object whose mass Ml is to be determined. The first object 1 has been suspended from a first measuring unit 3 by means of connection means 2. The connection means 2 can consist of a cord but the use of rigid connection means such as a metal or synthetic bar is also possible. The mass measuring system further comprises a second measuring unit 4 connected with the first measuring unit 3 by means of a mechanical connection, here schematically represented by connection piece 5. A reference object 6 whose mass M2 has been determined accurately, at least implicitly (for instance by calibrating the system) , has been suspended from the second measuring unit 4 by means of second connection means 7. These connection means 7 can for instance consist of a cord or a rigid bar as shown at the connection means 2. The first and second measuring units 3 and 4 are suspended from a reference system 9 by means of a connection piece 8. Reference system 9 can for instance be the hook of a crane. The first measuring unit 3 is suitable for measuring the force Fl(t) which the first object exerts on the first measuring unit via the connection means 2 and vice versa (action = reaction) . The second measuring unit 4 is suitable for measuring the force which the reference object 6 exerts on the second measuring unit 4. The result of the force measurement of the first measuring unit 3 is converted to a first electrical quantity comprising information about the measured force. Via line 10 this quantity is passed on to a transmitter unit 11. The transmitter unit 11 subsequently transmits a coded electromagnetic signal comprising the force Fl(t).

The second measuring unit 4 is also suitable for measuring a force F2 (t) which the reference object 6 exerts on the second measuring unit 4 via the connection means 7 and vice versa (action = -reaction) . The result of the force measurement of the second measuring unit 4 is converted to a second electrical quantity comprising information about the measured force F2(t) . Via line 12 this quantity is passed on to a transmitter unit 13. The transmitter unit 13 subsequently transmits a coded electromagnetic signal comprising the force F2(t) .

The mass measuring system further comprises a receiver unit 14 which receives, decodes and passes on the signals transmitted by the transmitter units 11 and 13 to a combination unit 15.

Thus the combination unit 15 disposes of a first quantity comprising information about the force Fl(t) and a second quantity comprising information about the force F2(t) . The reference system 9 is a system that makes a non- uniform movement. The reference system 9 will continuously undergo a changing movement which is characterized by the acceleration vector a(t) . For the sake of convenience it is assumed that the connection means 2 and 7 have at least substantially the same direction with regard to each other. Under the influence of the reference system 9, the measuring units 3, 4 will also carry out an acceleration a(t) which is at least substantially equal to the movement of the reference system. The first object in turn will follow the movement of the first measuring unit. The reference object will follow the movement of the second measuring unit 4. The measuring directions of the first and second measuring units 3 and 4 coincide in this case with the longitudinal directions of the first and second connection means 2 and 7, respectively. However, it is also possible that the measuring direction and/or longitudinal directions mentioned differ from each other. The component of the acceleration a(t) in the longitudinal direction of the connection means 2 and 7 is here denoted by a(t) . The component of the gravitation field g in the longitudinal direction of the first and second connection means 2 and 7 is denoted by g. The force Fl(t) which the first object exerts on the first measuring unit in the direction of the first connection means 2 can be formulated as:

Fl(t) = Ml * a(t) + Ml * g = Ml ( a(t) +g ) (l)

The force Fl(t) is measured by the first measuring unit and passed on to the combination unit 15 as described above.

Similarly, the force F2(t) which the reference object exerts on the second measuring unit can be formulated as:

F2(t) = M2 * a(t) + M2 * g = M2 ( a(t) +g ) (2)

The force F2(t) is measured in the longitudinal direction of the second connection means 7 by the second measuring unit and is passed on to the combination unit 15 as described above.

The combination unit 15 can determine the mass Ml from Fl(t), F2(t) and the mass M2, known as such, according to the formula:

Ml = M2 * Fl(t) / F2(t) (3) It is to be noted that the acceleration a(t) no longer occurs in formula (3), so that the mass measuring system functions independently of the reference system 9 to which it is connected and accordingly is independent of the movement a.(t) which is made by the reference system. Formula (3) also shows that not the weight but the mass of the first object is determined. This provides the advantage that this mass measuring system functions independently of the magnitude of the gravitation field (gravitation acceleration g) and accordingly will show the same result at any place on earth. Thus, the system is not only advantageous for use in moving reference systems but also in reference systems where the magnitude of the gravitation field is not accurately known. If the connection means 2 and 7 have a direction differing from the vertical, the component of the gravitation acceleration in the longitudinal direction of the connection means 2 and 7 will have to be substituted for g in formulae 1 and 2. This applies, for instance, in the case of a rocking crane where the connection means change direction constantly. In many cases, this direction will not be known whereas the relative direction of the connection means 2 and 7 will be known, at least within certain limits. In formulae 1 and 2 the component of g in the longitudinal directions of both the connection means 2 and 7 will therefore be equal to each other, so that formula 3 is also valid for systems in which the connection means are not vertically oriented all the time. If the longitudinal directions of the connection means are not equal but deviate only slightly from the vertical, the value of g can be substituted in both formula (1) and formula (2) , so that formula (3) still retains its validity with a certain accuracy.

When used in a crane whose hook makes a swinging movement and goes up and down, the movement of the hook preference system 9) will have no influence on the determination of the mass. If the crane were placed on a rocking boat, the movement of the 'boat would not have any influence on the determination of the mass either. _;

As stated, the first measuring unit 3 will perform an acceleration a(t). When the acceleration a(t) is smaller than, and has the same direction as, the gravitation acceleration of the earth, the first object will follow this movement even when the connection means 2 consist of a cord. Obviously the first object will also follow this movement if a(t) has an opposite direction to that of g. With most weight determinations, such as in the case of the hook of a crane, if so desired, a cord could be used as connection means. If the movement which the reference system imposes on the mass measuring system comprises an acceleration greater than the gravitation acceleration [g] of the gravitation field g, the connection means 2 can be made rigid, so that the first object will follow the movement of the reference system. An entirely analogous consideration to that set out above applies to the reference object. The second connection means 7 are chosen in such a way that the reference object too will follow the movement of the second measuring unit 6.

As stated before, for the measuring units 3 and 4 instruments which are known per se can be used which carry out a force measurement. A measuring unit also referred to as 'load cell' in technical jargon comprises for instance an iron bar which is reduced in the middle between its upper and lower ends. The bar is for instance fixedly suspended by its upper end while the gravitation to be measured is exerted on the lower end of the bar, so that the bar is loaded with a tensile force. The bar transmits the tensile force to be measured, with the largest tensions building up in the reduced part. Mounted on the bar is at least one strain gauge which will contract or expand under the influence of the tensions in the material of the bar and thereby undergo a change in resistance. These changes in resistance can be measured with known means and are a measure for the force which the object exerts on the metal body. The reference object 6 may have a low mass, for instance 100 g, so that the second measuring unit can be of very small design.

Figure 2, where parts corresponding to those of Figure 1 are provided with the same reference numerals, schematically shows a second embodiment of the invention.

The first object 1 is suspended from the first measuring unit 3 by means of the connecting means 2. The first measuring unit 3 also has the function of reference object 6 and in that capacity is supended from the second measuring unit 4 through connection means 7. In this case the first measuring unit also comprises the transmitter unit 11. The second measuring unit 4 is again connected to the reference system 9 through connection piece 8 and also comprises the transmitter unit 13. The force Fl(t) which the first object exerts on the first measuring unit may be written as:

Fl(t) = Ml * a(t) + Ml * g = Ml ( a(t) + g ) (4)

The force Fl(t) is measured by the first measuring unit as described above and passed on to the combination unit 15 as described above.

The force F2(t) which the reference object 3, 6, 10, 11 exerts on the second measuring unit may be written as:

F2(t) = (Ml+M2)*a(t) + (Ml+M2)*g = (M1+M2) (a(t)+g) (5)

Ml is the mass of the first object and M2 is the total mass of the reference object 6, first measuring unit 3, line 10 and transmitter unit 11. The force F2(t) is measured by the second measuring unit and passed on to the combination unit 15 as described above.

Ml = M2 * Fl(t) / ( F2(t) - Fl(t) ) (6) It is to be noted that again the accelerated movement a(t) no longer occurs in formula (6) , so that the mass measuring system functions independently of the movement of the reference system 9 to which it is coupled. Also the acceleration [g] no longer occurs in formula (6) . Formula (6) also shows that not the weight but the mass of the first object is determined. This again provides the advantage that this mass measuring system functions independently of the magnitude of the gravitational field (gravitation acceleration g) and thus will give the same result at any place on earth. Formula (6) , like formula (3) , retains its validity even when only a component of the gravitation acceleration is measured by the measuring units 3 and 4 when the longitudinal direction of the connection means 2 and 7 differ from the vertical.

The system of Figure 1 can also be used to determine the mass of the first object when this is in a condition of weightlessness. Then for instance a harmonic up and down movement is made by the reference system. Such movement can be simply generated, for instance with an electric motor, for example in a spacecraft. In this case the connection means 2 and 7 are made stiff, so that the first object and the reference object will make the same accelerated movement a(t) simultaneously. Of course, this movement can also comprise a centrifugal movement, with the mass measuring system making a circular movement around a center, in that case, the connection means 2 and 7 may again consist of cords which are tightened by the centrifugal force of the first object and the reference object. The force Fl(t) which the first object exerts on the first measuring unit may be written as:

Fl(t) = Ml * a(t) (7)

The force Fl(t) is measured by the first measuring unit and passed on to the combination unit 15 as described above. Similarly, the force F2(t) which is exerted on the second measuring unit by the reference object may be written as:

F2(t) = M2 * a(t) (8)

The force F2(t) is measured by the second measuring unit and passed on to the combination unit 15 as described above.

The combination unit 15 can determine Ml from Fl(t), F2(t) and the mass M2, known as such, according to the formula:

Ml = M2 * Fl(t) / F2(t) (9)

It also holds for the mass measuring system of Figure 2 that it can be used in a similar way in a weightless space. The force Fl(t) which is exerted on the first measuring unit by the first object may be written as:

Fl(t) = Ml * a(t) (10)

The force Fl(t) is measured by the first measuring unit and passed on to the combination unit 15 as described above. The force F2(t) which the reference object 3 and 6 exert on the second measuring unit may be written as:

F2(t) = ( M1+ M2 ) * a(t) (11)

Ml = M2 * Fl(t) / ( F2(t) - Fl(t) ) (12)

It should be noted that the connection between the first, the second and the combination unit can also be made using electrical lines instead of the above- escribed transmitter and receiver units.

Figure 3, where parts corresponding to those of Figure 1 are provided with the same reference numerals, schematically shows a third embodiment of the invention.

The reference object 6 is suspended from the second measuring unit 4 through connection means 7. The second measuring unit 4 also comprises line 12 and transmitter unit 13 and has a mass M3, known as such. The first object 1, together with measuring unit 4, line 12, and transmitter unit 13, is suspended from the first measuring unit 3. Again the first measuring unit 3, line 10, and transmitter unit 11 are shown as being combined into one measuring unit.

The force Fl(t) which the first object, reference object 6 and second measuring unit 4, line 12, and transmitter unit 13 exert on the first measuring unit 3 may be written as:

Fl(t) = { Ml + M2 + M3 ) ( a(t) + g ) (13)

Ml is the mass of the first object and M2 is the mass of the reference object and M3 is the total mass of the second measuring unit 4, which here also includes the line 12 and transmitter unit 13. The force Fl(t) is measured by the first measuring unit as described above and passed on to the combination unit 15 also as described above.

The force F2(t) which the reference object 6 exerts on the second measuring unit 4 may be written as:

F2(t) = M2 ( a(t) + g ) (14)

M2 is the mass of the reference object 6. The force F2(t) is measured by the second measuring unit and passed on to the combination unit 15 as described above. The combination unit 15 can determine the mass Ml from Fl (t) , F2 (t) and the masses M2 and M3, known as such, according to the formula: Ml = M2 * ( ( Fl (t) - F2 (t) ) / F2 (t) ) - M3 (15 )

It is to be noted that again the accelerated movement a(t) no longer occurs in formula (15) , so that the mass measuring system functions independently of the reference system 9 to which it is coupled. The gravitation acceleration too no longer occurs in formula (15) . All this has the same consequences as described above. What also applies to the mass measuring system of Figure 3 is that this system can be used in a similar way in a weightless space. In that case the value of g in formulae (13) and (14) will be zero and formula (15) will keep its validity.

In Figure 4 the system of Figure 1 is shown as being fitted to the hook 16 of a crane 30, with parts corresponding to those of Figure 1 being provided with the same reference numerals.

The hook 16 is suspended by its top from a cable 9 which corresponds to the reference system of Figure 1. The hook 16 comprises a hollow space 17 accommodating the second measuring unit and the reference weight. The second measuring unit is connected mechanically to the body 19 of the crane through connection piece 18. The hook is furthermore provided with a hook part 20 from which the first measuring unit 3 is suspended by means of a suspension part 21, in this case a metal cable or ring. Connection piece 18, body 19, hook part 20 and suspension part 21 together form the connection piece of Figure 1. The transmitter units 11 and 13 are in this case incorporated in the first measuring unit 3 and the second measuring unit 4, respectively. Connection part 18, body 19, hook part 20 and suspension part 21 correspond with connection pieces 5 and 8 of Figure l. The operation of the mass measuring system is entirely analogous to that described with reference to Figure 1.

Finally, in Figure 5 the system of Figure 1 is again at least partly applied to the hook of a crane, with parts corresponding with those of Figure 1 being provided with the same reference numerals.

The hook 16 is suspended by its top from a cable 9 which corresponds with the reference system of Figure 1. The hook 16 comprises a hollow space 17 accommodating the second measuring unit 4 and the reference weight 6. The second measuring unit 4 is connected mechanically to the body 19 of the hook through the connection piece 18. The hook is further provided with a hook part 20 from which the first object 1 is suspended using a suspension part 21, in this case a metal cable or ring.

Connection piece 18 and body 19 together form the connection piece 5 of Figure l. Hook part 20 and suspension part 21 together form connection means 2, it being assumed for convenience that the mass of the connection means 2 is negligible. The first measuring unit 3 is rigidly connected to, and is part of, the body 19 of the hook 16. A particular aspect is that the first and second measuring units are connected directly to the combination unit 15 via lines 10 and 12. The combination unit 15 determines the magnitude of Ml from the values Fl(t) and F2(t) as described above with respect to Figure 1. Transmitter unit 11 is supplied with this value of Ml. The transmitter unit 11 transmits the value of Ml to the receiver unit 14 which subsequently shows this value on a display 22. The advantage over the system of Figure l is that only a transmitter and receiver unit are required. Connection piece 18, body 19, hook part 20 and suspension part 21 correspond with connection pieces 5 and 8 of Figure 1. The operation of the mass measuring system is entirely analogous to that described with reference to Figure 1. If the mass of the connection means 2 in relation to the mass of the first object is not negligible, this can easily be corrected. Because in fact the mass of the first object plus the mass of the first connection means are determined by the system of Figure 4, the mass of the connection means 2, which is known as such, can be subtracted from this in order to obtain the mass of the first object. This calculation can be made by the combination unit. In practice, however, the first measuring unit will often be calibrated in such a way that it measures the value zero if no object is suspended from the hook 16. In that case the first measuring unit will only measure the force Fl(t) as a result of the first object if it is subsequently suspended from the hook 16 and the mass of the connection means 2 is automatically corrected for. It will be clear that the system of Figures 2 and 3 too can advantageously be fitted to the hook of a crane. In that case the whole system consisting of the parts 1, 2, 3, 4, 6, 7, 8, 10, 11, 12 and 13 can simply be suspended from the hook of a crane, with the hook functioning as reference system 9.

In accordance with a particular embodiment of the invention, the measured force F2(t) acting on the reference weight M2 is furthermore used to correct the movements of a crane. In this case signals are derived from the measured force F2(t) by which the engines driving a crane can be controlled, for example through a servo system. If the engine by which the hook of a crane is hoisted is controlled, the hook, despite the movement of the crane, will remain in at least substantially stationary suspension.

In all of the above-described embodiments of the mass measuring system, the reference weight and the object whose mass is to be determined can be interchanged without affecting the principle of the operation of the system. To this end, from formulae (6), (9), (12) and (15), M2 (M2 is now the mass of the object to be determined ) can be derived as a function of Fl(t), F2(t), Ml (Ml is now the reference weight) and, if necessary, M3. For the sake of completeness, it is further noted that for the first and second measuring units all conventional load sensors can be used and that the invention is by no means limited to the use of a 'load cell" as described in the examples of the embodiments.

Claims

CJ JMMS

1. A mass measuring system for determining the mass of a first object, the mass measuring system comprising a first measuring unit by which a first quantity is determined which comprises at least information about the mass of the first object to be determined, characterized in that the mass measuring system further comprises a predetermined reference object whose mass is known, a second measuring unit by which a second quantity is determined which comprises at least information about the mass of the reference object, and a combination unit which determines the mass of the first object from the first and second quantities.

2. A mass measuring system according to claim 1, characterized in that the first and second quantities are determined simultaneously.

3. A mass measuring system according to any one of the preceding claims, characterized in that the first object and the reference object are connected mechanically to each other.

4. A mass measuring system according to claim 3, characterized in that the first object and the reference object make at least substantially the same movement.

5 A mass measuring system according to any one of the preceding claims, characterized in that the first and second measuring units are connected mechanically to each other.

6. A mass measuring system according to claim 5, characterized in that the first measuring unit exerts a force Fl(t) on the first object which is directly proportional to the mass Ml of the first object and the second measuring unit exerts a force F2(t) on the reference object which is at least directly proportional to the mass M2 of the reference object.

7. A mass measuring system according to claim 6, characterized in that the first quantity represents a measured value of Fl(t) and the second quantity represents a measured value of F2(t) .

8. A mass measuring system according to claim 7, characterized in that the first object is connected mechanically to the first measuring unit, with Fl(t) being the force which the first measuring unit and the first object exert on each other, the reference object is connected mechanically to the second measuring unit, with F2(t) being the force which the second measuring unit and the reference object exert on each other.

9. A mass measuring system according to claim 7, characterized in that the first object is connected mechanically to the first measuring unit, with Fl(t) being the force which the first measuring unit and the first object exert on each other, the reference object comprises the first measuring unit and is connected mechanically to the second measuring unit, with F2(t) being the force which the second measuring unit and the reference object exert on each other.

10. A mass measuring system according to claim 7, characterized in that the first object, first measuring unit and second measuring unit are connected mechanically to one another, with Fl(t) being the force which the first measuring unit on the one hand and the first object and second measuring unit on the other hand exert on one another, the reference object is connected mechanically to the second measuring unit, with F2 (t) being the force which the second measuring unit and the reference object exert on one another.

11. A mass measuring system according to claim 8 or 9, characterized in that the combination unit determines the mass M2 from Ml, Fl(t) and F2 (t) .

12. A mass measuring system according to claims 8 and 11, characterized in that the combination unit determines the mass Ml according to the formula Ml = M2 * Fl(t) / F2(t) .

13. A mass measuring system according to claims 9 and 11, characterized in that the combination unit determines the mass Ml according the formula Ml = M2 * Fl(t) / ( F2(t) - Fl(t) ).

14. A mass measuring system according to claim 10, characterized in that the combination unit determines the mass Ml according to the formula Ml = M2 * ( ( Fl(t) - F2(t) ) / Fl(t) ) - M3, wherein M3 represents the predetermined mass of the second measuring unit.

15. A mass measuring system according to any one of the preceding claims, characterized in that the first object is suspended from the first measuring unit through first connection means and the reference object is suspended from the second measuring unit through second connection means.

16 A mass measuring system according to claim 6, characterized in that the forces Fl(t) and F2(t) are generated at least partly by an accelerating movement of the first and second measuring units.

17. A mass measuring system according to claim 6 or 7, characterized in that the forces Fl(t) and F2(t) are generated at least partly by a gravitational field.

18. A mass measuring system according to any one of the preceding claims, characterized in that the first and second measuring units comprise transmitter means for transmitting the measured first and second quantities and the combination unit comprises receiver means for receiving and further processing the transmitted first and second quantities.

19. A mass measuring system according to any one of the preceding claims, characterized in that the combination unit comprises transmitter means for transmitting the value of Ml, the system further comprising receiver means for remotely receiving the transmitted value of Ml.

20. A mass measuring system according to any one of the preceding claims, characterized in that the first and second measuring units are connected mechanically to the hook of a crane.

21. A mass measuring system according to claim 8, characterized in that the first measuring unit is connected mechanically to a hook of a crane, the first object hanging from the first measuring unit.

22. A mass measuring system according to claim 22, wherein the second measuring unit is connected mechanically to the hook of a crane, the reference object hanging from the second measuring unit.

23. A mass measuring system according to claim 22, characterized in that the second measuring unit and the reference object are contained in the hook of a crane.

24. A mass measuring system according to claim 1 or 9, characterized in that the second quantity comprises information about the mass of the first object plus the mass of the reference object.

25. A mass measuring system according to claim 1 or 8, characterized in that the second quantity comprises information about the mass of the reference object.

26. A method for determining the mass of a first object, in which a first measurement is performed on the object in order to obtain a first quantity comprising at least information about the mass of the first object to be determined, characterized in that a second measurement is performed on at least a predetermined reference mass whose mass is known, in order to obtain a second quantity comprising at least information about the mass of the reference object, the first and second quantities being processed in combination in order to obtain the mass of the first object.

27. A method according to claim 26, characterized in that the first and second measurements are made simultaneously.

28. A method according to claim 26 or 27, characterized in that the first object and the reference object are located, respectively, in a first and second interconnected reference systems.

29. A method according to claim 28, characterized in that the first object and the reference object are mechanically coupled to each other.

30. A method according to claim 27, characterized in that the first and second measuring units are connected mechanically to each other.

31. A method according to claim 30, characterized in that the first object is connected mechanically to the first measuring system and the reference object is connected mechanically to the second measuring unit.

32. A method according to claim 31, characterized in that the first quantity comprises a measure for the force Fl(t) which the first object and the first measuring unit exert on each other, the second quantity comprising a measure for the force F2(t) which the reference object and the second measuring unit exert on each other.

33. A method according to claim 32, characterized in that the mass Ml of the first object is determined from the mass M2 of the reference object and the measured forces Fl(t) and F2(t) .

34. A method according to claim 33, characterized in that the first object and the reference object make at least substantially the same movement.