Load cell .

The present invention relates to a force meter for an elongate mechanical element, e.g. a shaft or a bolt, to be located at a supporting structure for the element, said force meter comprising at least one measuring device, said ring having a central opening for said elongate element, wherein the measuring device of the force meter forms part of the support of the element in the supporting structure and is intersected at least approximately by the plane of the resultant of the force to be transmitted from the element to the supporting structure. The present invention relates to a force meter for an elongate mechanical element, e.g. a shaft, bolt or the like, to be located at a supporting structure for the element, the force meter comprising at least one measuring device.

Such measuring meters are known from DE 2729699, WO 94/07118 and EP 1362115 and are used in rolling mills and paper machines. These force meters all have an outer ring and an inner ring arranged spaced from the outer ring, the rings being interconnected by means of one, two or four radial spokes provided with the measuring device, such as strain gauges or magneto-elastic transducers. The two rings and the interposed spoke or spokes give the force meter a relatively large diameter and complicated structure, and the spokes provide a relatively soft support for the inner ring which may give the ring a natural vibration frequency that can resonate with the rotational speed of the shaft.

The purpose of the invention is to provide a force meter of the introductory type which is compact, robust, reliable and easy to produce. This is obtained according to the invention by the features recited in the charactering clause of claim 1.

The invention also relates to the use of the force meter as recited in claim 12. In gear boxes, the force meter may provide continuous information about the moment load in the transmission. For a winch this may be translated into tension in the rope. Mooring winches holding ships to the dock during a loading or unloading operation will have to be adjusted frequently as regards paying out and hauling in rope in order to maintain the correct tension. Use of the invention may improve and simplify automatic systems for this use.

Advantageous embodiments of the invention are defined in the dependent claims.

For better understanding of the invention, it will be described more closely with reference to the exemplifying embodiments shown in the appended drawings, where

Figure 1 shows in section a part of a gear box where the invention is implemented,

Figure 2 shows a section along the line II - II in figure 1 , the gear box having been deleted,

Figure 3 shows an elevation of a force meter according to the invention,

Figure 4 shows a section along the line IV - IV in figure 3,

Figure 5 shows perspectively a second embodiment of the force meter according to the invention, and

Figure 6 shows perspectively a third embodiment of the force meter according to the invention.

Figure 1 shows a section through a gear box 1, which e.g. may be used for mooring winches, cable drums or anchor winches in a maritime environment. The section shows i.a. a motor 2, a first intermediate shaft 3 and a second intermediate shaft 4 with appurtenant bearings. At one of its bearings 5, the shaft 3 is provided with a force meter 6 according ito the invention. The force meter 6 is received in a supporting structure 7, which is fixedly bolted in an opening in a wall of the housing of the gear box 1. The force meter 6 is fixed in the supporting structure 7 by means of two bolts 8, one of which being shown in figure 1. There will be a small clearance between the underside of the bolt head and a collar in the bolt hole 9 of the force meter 6 (see figure 2), in order for the force meter 6 to have a limited axial freedom of movement so that it may tilt somewhat in order to adapt to bending or misalignment of the shaft 3. Figure 1 also shows electronic components 10 which are used to transmit signals from the measuring sensors of the force meter.

The section in figure 2, which may advantageously be viewed in connection with the elevation in figure 3, shows the shaft 3, the bearing 5, the force meter 6, the supporting structure 7, and the two bolt holes 9. As will appear from figures 3 and 4, the force meter 6 has the form of a circular disk, the thickness of which corresponding approximately to the length of the bearing 5 it is to receive. The thickness of the disk may be held relatively small in order to give the force meter increased measuring sensitivity and self-aligning property.

The force meter 6 has a so-called beam 11, which has a support 12 at either end and which on its concavely curved inner side is subjected to the force which is to be measured, represented in figure 3, solely as an example, of the resultant vector R. When installing the force meter one will attempt to position it such that the resultant will act as closely as possible on the middle of the bean 11. This orientation can easily be obtained by rotating the supporting structure 7, which may be provided with more closely positioned bolt holes than shown in figure 2 in order to improve the adjustment possibilities.

At the supports 12, the beam 11 is delimited by a slot 13 for each support on the force- acting side, and by a common slot 14 on the reaction side. The slot 14 is relatively narrow, the size being a few tenth of a millimetre, and may be wire cut. When compressed, the slot 14 will act as an overload safety for the beam 11, and the magnitude of the permissible overload may be regulated by placing shims or similar spacers in the slot 14. In this manner, the overload safety may easily be adjusted to several different applications with one and the same force meter structure.

The supports 12 comprise recesses 15 performed from both sides of the disk such that a diaphragm 16 remains in the middle, the thickness of which will be adjusted to the force to be measured. The diaphragm is on both sides provided with strain gauges 17, and wires therefrom run through holes 18 in the diaphragm and further out through a bore 19 to the outside of the force meter 6.

If one envisions a section perpendicular to the drawing plane in the middle between the wire holes 18 and delimited of the slots 13, 14, this section will have the form of an H- beam, where the web of the H is constituted by the diaphragm 16. When loading such a

structure, shear strains will occur in the diaphragm 16. These strains can easily be measured by the strain gauges 17, and they will be quite proportional to the subjected load within a large measuring range. This proportionality simplifies and reduces the cost of the connected electronic system for signal processing and controlling, e.g. the motor of the gear box.

In order to ascertain that practically the entire force R is transmitted to the segment of the supporting structure 7 which is delimited by the slots 13, part of the periphery of disk 6 on the opposite side of the slots 13 is provided with relief 20. In order to further ascertain that the force goes through the beam 11 ₅ also the inside of the disk may be provided with relief, specifically in the areas radially inside the supports 12. It will be understood that even if the force resultant R should act somewhat to the side of the middle point of the beam 11, the somewhat different signals from the supports 12 will permit determination of both the magnitude and direction of the load. In other words, the load may be determined quite accurately within an angular area defined by the radii through the supports 12.

Figures 2 and 3 show that the bolt holes 9 do not lie on a common diameter, but are placed somewhat further away from the beam 11 in order to optimise the self-aligning function of the force meter 6. This self-aligning property of the force meter may also be enhanced somewhat by providing a relief in the thickness of the ring 6 below the bolt holes 9.

For the sake of order, it is noted that the section shown in figure 1 is unfolded, the section plane being angled in the centre lines of both shafts 3, 4. In actual fact, the shaft 4 lies at a level above the shaft 3 instead of along the side thereof, which also means that the angle of orientation of the force meter 6 is almost 90° displaced with respect to the position shown in figure 2.

Since the force meter 6 encircles the shaft 3 completely, the force meter may be designed in such a way that it can measure force in any direction. Two examples of such force meters are shown in figures 5 and 6. The circular form shown in figure 5 is the most suitable in the majority of the cases if the supporting structure 7 can be designed or fixed such that the force meter becomes properly centred. The square form

shown in figure 6 can be used if it should be necessary to displace the force meter with respect to the supporting structure in order to centre the force meter properly. It will be understood that the force meter may also have other polygonal forms, e.g. a hexagonal form which will provide the reaction or supporting portions of the beams 11 with the same design.

In figures 5 and 6 the same reference numerals are used for elements having the same function as in figures 2 - 4. In addition, the embodiments in figures 5 and 6 have radially extending slots 21 which separate and delimit the beams 11. It will be understood that also the inner opening 22 of the force meter 6 may have a polygonal cross-sectional form, for instance if the force is to be measured from an immoveable shaft or bolt having a polygonal cross-section. In cases where it is not most appropriate to fix the force meter 6 in the supporting structure by means of bolts, use made be made e.g. by collars or tabs bolted to the supporting structure. The embodiment in figure 5 should also have means, e.g. one or more keys in the periphery, which prevent the force meter 6 from rotating in the supporting structure, if, for instance the friction in the bearing 5 should become too large. Instead of the self-aligning embodiment of the force meter 6, use may be made of a spherical bearing in the support for the shaft 3. In embodiments wherein the shaft is not rotating, the same function may be obtained by the inner opening 22 in the force meter 6 having a double-curved form, e.g. the form of part of a torus, at least in the contact area of the shaft. Furthermore, a sleeve may be used in order to adapt the diameter of the shaft 3 or bearing 5 to the opening 22 in the force meter 6 to permit the latter to be made in standardized sizes.

It will be understood that the measurement principle used in the examples described above may be replaced by a number of other principles. Thus, one envisions measurement of bending stresses by means of strain gauges, measuring of forces by the use of sensors of the fibre-optical type, the use of fibre-optics and Fiber Bragg Grating effect, and silicon based sensors.

Furthermore, it will be understood that the invention is not limited to the exemplifying embodiments described herein, but may be varied and modified by the skilled person within the scope of the appended claims.