GB2111228A

GB2111228A - Weighing machine

Info

Publication number: GB2111228A
Application number: GB08234335A
Authority: GB
Inventors: Walter Sodler; Jurgen Ober
Original assignee: Sartorius AG
Current assignee: Sartorius AG
Priority date: 1981-12-03
Filing date: 1982-12-02
Publication date: 1983-06-29
Also published as: DE8135182U1; JPH0229179B2; FR2517825A1; JPS58108416A; CH660234A5

Abstract

A weighing machine comprises a load receiver (3), which is guided by a parallel-motion linkage (1,2,4,5,6) and connected through a coupling element (9) to a transmission lever (7). The coupling element (9) comprises a round rod which in the region of each of its ends has a portion of reduced diameter (12, 13). This construction provides regions of lower bending stiffness forming hinge points in the coupling element. <IMAGE>

Description

SPECIFICATION Weighing machine The present invention relates to a weighing machine.

In known weighing machines, thin tension bands (DE-GM 80 08 791) or sheet metal strips (DE-PS 26 21 483), which at one or more places have a reduction in cross-section produced by embossing, stamping or etching, are used as coupling elements between a load receiver and a transmission lever. These components, however create problems in handling and assembly. The smallest deviations from the evenness of the coupling element or parallelism of the assembly surfaces lead to the coupling element being stressed during assembly. This can lead to, for example, a variation of the effective force engagement point with the load so that the effective lever arm of the transmission lever varies in dependence on load.Moreover, in the case of a planar coupling band and parallel assembly surfaces, the coupling element can become stressed during the assembly due to the turning moment of the fastening screws and in the extreme case can act like a clickjumping toy frog.

There is therefore a need for a weighing machine with coupling elements of a kind which can be assembled substantially free of problems and in the assembled state provide a consistently reproducible force transmission.

According to the present invention there is provided a weighing machine comprising movable load-receiving means guided by parallel guidance means and coupled to a force transmission lever by a coupling element for transmission of vertically directed force produced by a loading acting on the load-receiving means, the coupling element comprising a substantially circular section rod provided in the region of each end thereof with a circular section portion of reduced diameter.

In a preferred embodiment, the weighing machine has parallel guidance for the load receiver and a coupling element between the load receiver and transmission lever for the transmission of vertical forces. The coupling element comprises a round rod which in the proximity of each of its ends, has a respective, likewise round constriction. Two defined hinge points arise through the two constrictions, whereby slight deviations from parallelism of the assembly surfaces can be compensated for. The problem of the evenness of the coupling element no longer plays a part in view of the continuous round cross-section. Also, the manufacture of a round coupling element is simple, since a pure turned part is concerned.

Expendiently, the diameter of the coupling element in the region of constriction amounts to about one sixth of the diameter in the remaining region. This dimensioning results in a sufficient stiffness of the coupling eiement between the constrictions without significant increase in the mass of the coupling element. The transition from full cross-section of the coupling element to the constricted cross-section expediently takes place gradually in order to avoid notch effects.

The coupling element is preferably clamped at each end in a prismatic groove by a planar plate.

As a result, the coupling element is securely fixed in its position and no stresses are transmitted during assembly to the coupling element through the turning moment of fastening screws that may be used.

The operation of the load receiver and transmission lever is such that normally the constriction of the coupling element closest to the lever is stressed predominantly in bending.

Advantageously, this constriction is therefore thinner and/or longer than the other constriction, so that its bending stiffness is less than that of the other constriction.

A particularly effective protection for the constrictions of the coupling element may be provided if the coupling element in the region of the constriction is surrounded by a protective tube which at one end is fastened to the coupling element in the region of its full diameter and which is slightly widened out at the other end so that it surrounds the coupling element in the region of its full diameter at a small spacing. This protective tube can thus prevent excessive bending of the constriction during manufacture of the weighing machine as well as possible kink stressing of the coupling element in the finished weighing machine.

The round coupling element may have the same bending stiffness in all directions. In cases it should be necessary in a very sensitive weighing machine to further reduce the bending stiffness in the direction stressed in bending during weighing, than expediently in the region of the constriction material is removed, for example by grinding, at mutually opposite sides to create a small region which has a lesser bending stiffness in the direction stressed in bending during weighing.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic vertical sectional elevation of a first electronic weighing machine embodying the invention; Fig. 2 is a side elevation, to an enlarged scale of an upper part of a coupling element in the machine of Fig. 1; Fig. 3 is a sectional elevation of a part of a coupling element in a second machine embodying the invention; Fig. 4 is a side elevation of a part of a coupling element in a third machine embodying the invention; Fig. 5 is a cross-section on the line V-V of Fig.

4; and Fig. 6 is a plan view of the fastening of a coupling element to a transmission lever in a machine embodying the invention.

Referring now to the drawings, there is shown in Fig. 1 an electronic weighing machine which comprises a support 1, which is fastened to a housing and to which a load receiver 2 is connected to be movable in vertical direction through two guide rods 4 and 5 with hinge points 6. The load receiver in its upper part carries a load pan 3 for reception of a load to be weighed and transmits the force corresponding to the mass of the load through a coupling element 9 to the shorter lever arm of a transmission lever 7.

The lever 7 is mounted by a cross spring joint 8 to the support 1. Acting on the longer lever arm of the lever 7 is a compensating force which is provided in this embodiment by a coil 11 and a permanent magnet system 10 for the generation of an electromagnetic compensating force. An associated electronic regulating system is not illustrated, and may be of generally known type.

In place of an electromagnetic compensating force, a compensating force can be generated by, for example, a spring element, the deflection of which is detected by strain gauges and translated into an electrical signal. This method is generally known so that it does not need to be explained in detail.

The coupling element 9 consists of a round rod which in the region of its upper and lower ends has respective round constrictions 12 and 1 3.

These constrictions each produce a region of lower bending stiffness representing the actual hinge points of the coupling elements. In Fig. 2 the upper part of the coupling element 9 is illustrated in side elevation to an enlarged scale.

The round rod coupling element has at its top a region of full diameter provided for clamping of the rod to the lever 7. There follows a transition region 14, within which the rod diameter gradually reduces. Thereafter comes the region of the constriction 12, which has an at least approximately constant, small diameter. In a second transistion region 15, the diameter increases gradually to the full rod diameter. The lower constriction 13, not shown in Fig. 2, is structured correspondingly. The dimensions of the coupling element and of the constrictions depend on the size, maximum load and resolution of the weighing machine. In that case, the coupling element should be as robust as possible so that it is easily handled during assembly and so that ;t can, for example, in the case of shocks, transmit larger than usual forces without damage.On the other hand, the coupling element should be as flexible as possible so that it transmits the smallest possible reaction forces to the weighing system in the case of bending through component tolerances or in the case of deflection of the movable part of the weighing machine out of the intended stable position. As a compromise of these contradictory requirements, it has proved to be expedient to select a diameter for the coupling element in the region of the constriction which is smaller by about a factor of 6 than the diameter of the coupling element in the remaining region.

In the case of a weighing machine having the geometry shown in Fig. 1, i.e. where the coupling element is connected to a very short lever arm of the lever 7, the upper constriction 12 in particularhis stressed in bending on deflection of the movable part of the weighing machine. It is therefore advantageous for this upper constriction 12 to be somewhat longer than the lower constriction 13, as shown in Fig. 1. The same effect can, of course, also be achieved through a smaller diameter of the upper constriction compared with the lower constriction 1 3.

Fig. 6 shows the clamping of the coupling element 9 to the transmission lever 7. The lever 7 has a prismatic or V-shaped groove 17, in which the coupling element 9 is placed during assembly and thereby located laterally. A planar plate 1 6 is then laid on and secured by two screws 1 8 laterally of the coupling element. Through this manner of fastening, no turning moment is transmitted to the coupling element during assembly.

Fig. 3 shows another construction of the coupling element with an additional protective tube 20. A constriction region of the element is illustrated in Fig. 4 in section to an enlarged scale.

The protective tube 20 is fastened at one end 21, for example by gluing or by laser-welding, to the coupling element. From there, it projects beyond the region of the constriction 12 into a region where the coupling element again has its full diameter. At its other end 22, the protective tube is slightly widened out so that an encircling, thin gap is provided between the coupling element and the protective tube. As a result, excessive bending stress of the constricted region of the coupling element is prevented without the freedom of movement being obstructed for the small deflections that arise during normal weighing operation.

Protection of the coupling element against kinking is, of course, also possible in the finished weighing machine without this protective tube.

For this purpose, the load receiver 2 in Fig. 1 can have, for example, horizontal ribs with a vertical bore, through which the coupling element extends.

Figs. 4 and 5 show a further construction of the coupling element 9. In this case, part of the round constriction 12 is ground away at mutually opposite places to provide a small region 19 which is no longer of round cross-section, as Fig.

5 shows. As a result, this constriction 12 has a particularly small bending stiffness in the direction determined by the flats. Although this may make handling of the coupling element somewhat more difficult, this can nevertheless be an effective compromise between the above mentioned contradictory demands imposed on the coupling element when a higher degree of flexibility of the coupling element is required.

Claims

Claims

1. A weighing machine comprising movable load-receiving means guided by parallel guidance means and coupled to a force transmission lever by a coupling element for transmission of vertically directed force produced by a load acting on the load-receiving means, the coupling element comprising a substantially circular section rod provided in the region of each end thereof with a circular section portion of reduced diameter.

2. A weighing machine as claimed in claim 1, wherein the diameter of each reduced diameter portion of the rod is substantially one sixth of the full diameter of the rod.

3. A weighing machine as claimed in either claim 1 or claim 2, wherein the rod has a transition portion at each end of each reduced diameter portion thereof to provide a gradual transition from the full diameter of the rod to the reduced diameter.

4. A weighing machine as claimed in any one of the preceding claims, wherein the rod is clamped at each end portion thereof in a respective substantially V-shaped groove by means of a plate.

5. A weighing machine as claimed in any one of the preceding claims, wherein the diameter of the reduced diameter portion of the rod in the region of an end thereof connected to-the lever is less than that of the other reduced diameter portion.

6. A weighing machine as claimed in any one of the preceding claims, wherein the length of the reduced diameter portion of the rod in the region of an end thereof connected to the lever is greater than that of the other reduced diameter portion.

7. A weighing machine as claimed in any one of the preceding claims, comprising a protective tubular element arranged on the rod to surround one of the reduced diameter portion, the tubular element being connected at one end portion to the rod in a full diameter region thereof and being widened at its other end portion to surround another full diameter region of the rod at a spacing therefrom.

8. A weighing machine as claimed in any one of the preceding claims, wherein at least one of the reduced diameter portions of the rod has a section provided with two diametrically opposite flats thereby to reduce the bending stiffness of said section in a plane parallel to the flats.

9. A weighing machine as claimed in any one of the preceding claims, the machine being an electronic weighing machine.

10. A weighing machine substantially as hereinbefore described with reference to Figs. 1 and 6 of the accompanying drawings.

1 A weighing machine as claimed in claim 10 and substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

1 2. A weighing machine as claimed in claim 10 and substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

13. A weighing machine as claimed in claim and substantially as hereinbefore described with reference to Figs. 4 and 5 of the accompanying drawings.