Balance with free-floating weighing pan

Abstract

A balance (1) has a weighing pan (3) that is held in a predetermined free-floating and constant position relative to translatory and rotary displacements in the six degrees of freedom during use. At least six position sensors are used to measure the position of the weighing pan in all three dimensions. A weighing mechanism having at least six electromagnetic mechanisms (5) generate compensation forces (F.sub.c1-F.sub.c6) that act on the weighing pan by sending currents through a force coil (7) associated with an associated permanent magnet. The weight of an object on the weighing pan is determined from the amounts of current flowing in the respective force coils to maintain the weighing pan in position.

Claims

1. A balance, comprising: a weighing pan; at least six position sensors, arranged to measure the position of the weighing pan in all three dimensions; a weighing mechanism with at least six electromagnetic mechanisms, each of which includes at least one permanent magnet and at least one force coil, such that the weighing mechanism generates compensation forces to act, through currents sent to each force coil, in each of the six translatory and rotatory degrees of freedom on the weighing pan, based upon the orientation and position of each force coil relative to the weighing pan; a regulating unit to regulate the individual currents flowing in the force coils, wherein the compensation forces, through the sum of their respective moments, hold the weighing pan in a constant, predefined and free-floating position relative to the six degrees of freedom; and an arithmetic unit provided with software to calculate the weighing result based on the amounts of current flowing in the respective force coils.

2. The balance of claim 1, wherein the at least six electromagnetic mechanisms are arranged relative to each other in a manner that distributes the weight of the weighing pan essentially uniformly over the at least six electromagnetic mechanisms.

3. The balance of claim 2, wherein the weighing pan is arranged above the weighing mechanism.

4. The balance of claim 2, wherein the weighing pan is arranged below the weighing mechanism.

5. The balance of claim 2, wherein the weighing pan is arranged to the side of the weighing mechanism.

6. The balance of claim 1, wherein the electromagnetic mechanisms are arranged essentially in two groups of three that are placed, respectively, along a pair of lines which are in particular parallel and close to each other.

7. The balance of claim 1, wherein at least three of the electromagnetic mechanisms are arranged on a first side of the weighing pan and at least the further three electromagnetic mechanisms are arranged on a second side of the weighing pan, opposite to the first side.

8. The balance of claim 1, wherein the electromagnetic mechanisms are arranged on the weighing mechanism such that the electromagnetic mechanisms act on the weighing pan in the manner of a hexapod.

9. The balance of claim 2, further comprising a coupling element that couples the at least six electromechanical mechanisms with the weighing pan.

10. The balance of claim 9, wherein the coupling element comprises a carrier made of one piece of material and having a plurality of arms, the carrier connecting each of the electromagnetic mechanisms to the weighing pan.

11. The balance of claim 1, wherein the electromagnetic mechanisms are essentially identical and essentially arranged in a plane.

12. A method for operating a balance, wherein the method comprises the steps of: measuring the position of a weighing pan of the balance in all three dimensions by means of the at least six position sensors; generating, during the weighing process, a compensation force in each of at least six electromagnetic mechanisms associated with the weighing pan to act on the weighing pan in the six translatory and rotatory degrees of freedom of the weighing pan, each of the electromagnetic mechanisms including at least one permanent magnet and at least one force coil, wherein the compensation force is generated by a current sent through each force coil, depending on the respective position and orientation of the force coil relative to the weighing pan; simultaneously regulating the respective current flowing in each force coil, so that the compensation forces, through the sum of their respective moments, hold the weighing pan in a predetermined, free-floating and constant position relative to the six degrees of freedom; and calculating a weighing result from the amounts of current flowing in the respective force coils.

13. The method of claim 12, wherein the compensation forces generated act on the weighing pan through a coupling element that is connected to the weighing pan.

14. The method of claim 13, wherein the position of the weighing pan is measured by measuring the positions of the force coils and wherein the position of the weighing pan relative to the position sensors is derived from the measurement and from the known position of the weighing pan relative to the positions of the force coils.

15. The method of claim 13, wherein the position of the weighing pan is measured by measuring the position of the coupling element and wherein the position of the weighing pan relative to the position sensors is derived from the measurement and from the known position of the weighing pan relative to the coupling element.

16. The method of claim 12, wherein the respective amounts of current flowing in the force coils are used to calculate the inclination of the weighing pan.

17. The method of claim 12, wherein the respective amounts of current flowing in the force coils are used to calculate the location of the center of gravity of a weighing object lying on the weighing pan.

18. The method of claim 12, wherein the positions of three predefined points of the weighing pan are measured along the Z-axis, the positions of two predefined points of the weighing pan are measured along the Y-axis, and the position of one predefined point of the weighing pan is measured along the X-axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Different embodiments of the balance with a free-floating weighing pan will be described in more detail in the following and are schematically illustrated in the drawings, wherein

(2) FIG. 1 is shows an electromagnetic mechanism in a schematic representation;

(3) FIG. 2 illustrates a first embodiment of a balance with a free-floating weighing pan located amid the arrangement of electromagnetic mechanisms;

(4) FIG. 3 illustrates a second embodiment of a balance with a free-floating weighing pan located laterally of the arrangement of electromagnetic mechanisms;

(5) FIG. 4 illustrates a third embodiment of a balance with a free-floating weighing pan located laterally of the arrangement of electromagnetic mechanisms;

(6) FIG. 5 illustrates a fourth embodiment of a balance with a balance housing configured in two parts and with a free-floating weighing pan arranged between the two parts;

(7) FIG. 6 represents a configuration for a precision balance; and

(8) FIG. 7 illustrates a narrow-width configuration of the balance with free-floating weighing pan, with the position sensors shown in the drawing.

DETAILED DESCRIPTION

(9) FIG. 1 shows an electromagnetic mechanism 5. The electromagnetic mechanism 5 includes a force coil 7 and a permanent magnet 6. The force coil 7 is mechanically connected to a coupling element 9. The permanent magnet 6 is supported by the balance housing 2. It is connected to a cylindrical barrel 11 and a pole piece 10. The pole piece 10 and the cylindrical barrel 11 serve to conduct the magnetic field. The arrangement of the force coil 7 relative to the permanent magnet 6 is such that the force coil 7 is movable in the direction of the force vector F.sub.c. The electromagnetic mechanism 5 is not oriented vertically. Consequently, the force vector F.sub.c has a vertical and a horizontal component relative to the direction of gravity.

(10) The force coil 7 is connected to a variable power supply. In accordance with the Lorentz force principle, a current flowing through the force coil 7 that is immersed in the magnetic field of the permanent magnet 6 generates a force. The polarity and the amplitude of the current are regulated in such a way that the force coil 7 holds the coupling element 9 free-floating and without physical contact in a predefined constant position above the balance housing 2.

(11) The coupling element 9 can be fastened to the force coil 7 or to the permanent magnet 8. The coupling element 9 is preferably supported by the force coil 7. Thus, fewer fastening means are needed between the force coil 7 and the coupling element 9, whereby the dead load of the weighing pan 3 is reduced.

(12) Alternatively, it would also be possible to connect the permanent magnet 6 to the coupling element 9 and the force coil 7 to the balance housing 2. However, to use the least amount of current, it is of advantage for the electromagnetic mechanism 5, if the lighter of the two elements force coil 7 and permanent magnet 6 is attached to the moving part, i.e. to the coupling element 9.

(13) FIG. 2 shows a balance 1 with six electromagnetic mechanisms 5 and a free-floating weighing pan 3. The electromagnetic mechanisms 5 are attached to a base plate of the balance housing 2. The establish the connection between the coupling element 9 and the balance housing 2 by means of the forces F.sub.c1-F.sub.c6 generated by the electromagnetic mechanisms. The weighing pan 3 is mechanically connected to the coupling element 9. The coupling element 9 has several arms through which the weighing pan 3 is coupled to the electromagnetic mechanisms. The configuration of the coupling element 9 with a plurality of arms has the advantage of being lightweight. The weighing pan 3 is arranged essentially in the middle of the electromagnetic mechanisms 5. This results in an approximately uniform distribution of the weight force of the weighing object on the six electromagnetic mechanisms 5. This increases the weight capacity. The balance 1 can have more than six electromagnetic mechanisms 5.

(14) The six electromagnetic mechanisms 5 are not directed vertically. They are oriented, respectively, to exert forces relative to all six translatory and rotatory degrees of freedom. Each of them is regulated by a current, so that they compensate the weight forces of the weighing pan 3, the coupling element 9 and the weighing object and hold the coupling element 9 in a constant, predetermined and free-floating position. With the theory of the Lorentz force, the force F.sub.c generated by the force coil 7 can be calculated from the current that is required. Based on the positions and orientations of the electromagnetic mechanisms 5 relative to each other, the moments acting on the weighing pan 3 in the three dimensions are calculated. From the sum of all moments, the resultant compensation force can be calculated. The mass of the weighing object can be determined from the vertical component of the resultant compensation force.

(15) The at least six position sensors 8, which are not shown in FIGS. 2 to 7, can be directly or indirectly attached to the balance housing 2. They can measure the position of the weighing pan 3 either directly by way of six predefined points of the weighing pan 3 or by way of six predefined points of the coupling element 9. As an alternative, the positions of the free-floating parts of the electromagnetic mechanisms 5 (force coils or permanent magnets) can be measured. The position sensors 8 are arranged so that they can register the position of the weighing pan 3 in the three dimensions.

(16) FIG. 3 illustrates a balance 1 in a further embodiment with six electromagnetic mechanisms 5 and a free-floating weighing pan 3. The electromagnetic mechanisms 5 are attached to the balance housing 2. They establish a connection between the coupling element 9 and the balance housing 2. The coupling element 9 has several arms. A longer arm is connected to the weighing pan 3, so that weighing pan 3 is not positioned above the weighing mechanism 4 but laterally offset from the latter.

(17) Four of the six electromagnetic mechanisms 5 are arranged closer to the weighing pan 3 than the other two. This configuration allows an essentially uniform distribution of the weight force of the weighing object, the weighing pan 3 and the coupling element 9 over the six electromagnetic mechanisms 5.

(18) The six electromagnetic mechanisms 5 are not oriented vertically. Their respective orientations are such that they exert a force relative to each of the six translatory and rotatory degrees of freedom.

(19) FIGS. 4 to 7 show different configurations of the system of electromagnetic mechanisms 5. Each configuration is particularly suitable for a specific application of the balance.

(20) In a plan view, FIG. 4 schematically illustrates a balance 1 with a free-floating weighing pan 3 that is laterally offset to the side of the balance housing 2. The weighing pan 3 is coupled to the electromagnetic mechanisms 5 by way of a coupling element 9. Four electromagnetic mechanisms 5 are arranged closer to the weighing pan 3 than the two others, i.e. the electromagnetic mechanisms 5 are arranged so that the force is optimally distributed between the six force coils 7.

(21) This configuration has the advantage that the weighing pan 3 is placed very close to the work surface. This facilitates the loading of the weighing object on the weighing pan 3 and the cleaning of the weighing pan 3. In addition, the weighing pan 3 in this configuration is less exposed to air currents.

(22) FIG. 5 shows a balance 1 with six electromagnetic mechanisms 5 and with a first balance housing 17 and a second balance housing 18. Three electromagnetic mechanisms 5 are arranged to one side of the weighing pan 3 on the base plate of the first balance housing 17, while three other electromagnetic mechanisms 5 are arranged to the other side of the weighing pan 3 on the base plate of the second balance housing 18. The coupling element 9 with a plurality of arms connects all six of the electromagnetic mechanisms 5 to each other while contributing only a minimal amount of weight.

(23) This configuration is particularly advantageous if the balance 1 is used in conjunction with a conveyor belt 10. The balance 1 is arranged in such a way that the conveyor belt 10 is not positioned above the balance housings 17, 18. The balance housings 17, 18 can thus be set on a solid base, so as not to be affected by the vibrations of the conveyor belt.

(24) The weight force is uniformly distributed on the six electromagnetic mechanisms 5 around the weighing pan. Consequently their usable capacity is maximized.

(25) FIG. 6 shows a balance 1 with a weighing pan 3 arranged in a free-floating state above the weighing mechanism 4. The electromagnetic mechanisms 5 are arranged in a circle at essentially regular intervals. The weighing pan 3 is centered above the circle of electromagnetic mechanisms 5. The latter are arranged in such a way that they act essentially like a hexapod on the weighing pan 3.

(26) In this embodiment, the force coils 7 or the permanent magnets 6 can be fastened directly to the weighing pan 3. A coupling element 9 is not needed. The accuracy and the weighing capacity of the balance 1 are thereby increased, and the construction of the balance 1 is simplified.

(27) FIG. 7 illustrates an embodiment of the balance with the position sensors shown, wherein the weighing pan 3 is held in a free-floating state in a lateral position relative to the balance housing 2, with a transverse arrangement of the coupling element 9 and the electromagnetic mechanisms located along two lines directly left and right of the coupling element 9, so that the weight is distributed over the six electromagnetic mechanisms 5 as uniformly as possible.

(28) This configuration is distinguished by a narrow width of the balance housing 2. Balances of this kind with a narrow housing are well suited for side-by-side arrangements of many balances, which are used for the calibration of pipettes and in other areas where a plurality of weights are measured simultaneously.

(29) Six position sensors are arranged to measure the position of the coupling element 9 in the three dimensions. The position of the balance pan 3 can be derived from the relationship between the position of the weighing pan 3 and the position of the coupling element 9.

(30) The position sensors 8 are mounted on the base plate of the balance housing 2, each of them measuring the respective distance to the coupling element 9. The position sensors 8a, 8c and 8d are oriented so that each of them measures the respective distance to the coupling element 9 in the Z-direction. The position sensors 8b and 8e are arranged to measure the respective distances to the coupling element 9 in the Y-direction. The position sensor 8f measures the position relative to the coupling element 9 in the X-direction.

(31) Arrangements with more than six position sensors 8 are also possible. However, the minimum number is six, and they should be arranged in such a way relative to the coupling element, or relative to the weighing pan 3, that the position of the coupling element 9, and thus also of the weighing pan 3, can be measured in the three spatial dimensions.

(32) The position sensors preferably include optoelectronic components. However, in principle any kind of position sensor could be used.

(33) The foregoing description and the drawings show examples in which the electromagnetic mechanisms are essentially identical and arranged in a plane, with a coupling element of a predominantly flat configuration. It is considered self-evident that the scope of the invention also includes arrangements wherein the electromagnetic mechanisms are not necessarily identical and/or are arranged in different planes, or wherein the coupling element can have a curved configuration.