EP1583942A1

EP1583942A1 - Force transducer for measuring axial forces

Info

Publication number: EP1583942A1
Application number: EP04702698A
Authority: EP
Inventors: Bernd Futterer; Otto Pfeffer
Original assignee: Ebm Brosa Messgerate & Cokg GmbH; ebm Brosa Messgeraete GmbH and Co KG
Current assignee: Ebm Brosa Messgerate & Cokg GmbH; ebm Brosa Messgeraete GmbH and Co KG
Priority date: 2003-01-16
Filing date: 2004-01-16
Publication date: 2005-10-12
Also published as: DE10302352B4; DE10302352A1; WO2004063691A1

Abstract

Disclosed is a force transducer (10) for measuring axial forces acting upon an axis, especially a measurement axis, in a substantially perpendicular direction. Said force transducer (10) comprises a longitudinally extending axial member (24) that is provided with a force-introducing zone (30) in a central axial area, at least one bearing zone (36, 38) which is located outside the force-introducing zone in an axial direction and is used for mounting the force transducer in a receiving device, and at least one force-measuring zone (52, 54) which is located outside the force-introducing zone (30) in an axial direction and measures the axial forces. At least the area of the at least one bearing zone (36, 38) of the axial member (24) is surrounded by a sleeve (68, 70) outside the force-introducing zone (30). The end (72, 78) of said sleeve (68, 70), which faces the force-introducing zone (30), is free rather than being connected in a fixed manner to the axial member (24).

Description

Force transducers for measuring axial forces

The invention relates to a force transducer for measuring axial forces which act essentially transversely on an axis, in particular a measuring axis, with a longitudinally extending axle body which has a force introduction zone in an axially central region and at least one bearing zone for storing the force transducer axially outside the force introduction zone has at least one force measuring zone for measuring the axial forces in a receptacle and axially outside the force introduction zone.

RFRTÄTIGUNGS0P1E Such a force transducer is generally known.

A force transducer of the type mentioned at the outset is used to measure forces which act essentially transversely on an axis or shaft of rotating parts of machines or systems. Such axial forces can consist in a force acting purely radially on the axis or in a torsional force. For example, such a force transducer is used to measure axial forces on rope pulleys, for example in cable cars. In this application, the measurement of axle forces serves in particular to record overloads on the rope pulleys in order to be able to recognize dangerous conditions in good time.

Conventional force transducers of the type mentioned at the outset have a longitudinally extending axle body which is essentially solid. As an essential part of the force measurement, the axle beam must be designed for the respective application in terms of its dimensions and strength, and it must also have a corresponding fatigue strength.

The axle body has a force introduction zone in an axially central region. The force introduction zone is understood to mean that section of the axle body into which the force to be measured is introduced into the force transducer. In the example of the application of the force transducer for measuring axial forces in a rope pulley, the force introduction zone of the axle body is the axial area on which the rope pulley is mounted directly or indirectly. The axle body also has at least one, usually two force measuring zones, which is or are arranged axially outside the force introduction zone. At least one force measuring system is arranged in each case in the at least one force measuring zone or in the at least two force measuring zones. The force measuring system can detect shear forces, strains and compressions in the axle body and converts them into measurable signals, usually electrical signals, for determining the force. For example, this or the force measuring systems have strain gauges which enable force to be measured via changes in resistance within one or more bridge circuits. However, other force measuring systems based on other physical principles of force detection can also be used.

Force transducers for measuring axial forces are usually placed in a type of receiving fork or receptacle or bearing for their intended use, as is the case, for example, in the application of the force transducer for measuring axial forces in a rope pulley. Correspondingly, the axle body axially outside the force introduction zone has at least one, usually two bearing zones for direct or indirect mounting of the force transducer in one receptacle. When the measuring axis is used, the at least one bearing zone is subjected to forces which are directed in the opposite direction to the forces acting on the force introduction zone. The at least one bearing zone thus acts as an abutment to the force application zone.

In conventional force transducers, which are formed exclusively from the rigid axle body, hysteresis effects are evident in force measurement during practical use. Under these Hysteresis effects are understood to mean that the force measuring system of the force transducer generates different measurement signals at a predetermined applied force, depending on whether the force transducer is loaded on the force to be measured starting from a lower applied force or whether the force transducer is loaded on the force applied by a higher one the force to be measured is relieved. The hysteresis effect is based on the fact that the force transducer bends when a force is applied in the area between the receptacles, ie between the bearing zones, even if it cannot be detected by the eye, ie in the millimeter or sub-illimeter range. This creates very high frictional forces between the force transducer and the receptacles in which the force transducer is mounted, which increase with increasing force application. If the force transducer is loaded with high force starting from the unloaded state and then relieved again, these previously mentioned frictional forces cause the force transducer to remain in a tensioned state when the force decreases due to the high frictional forces, that is, it does not resiliently correspond to a force that is actually applied Relaxed state. The result of this is that the at least one force measuring system detects an apparent higher force than corresponds to the force actually introduced. The force measurement is thus influenced by parasitic or apparent forces, which, however, prevents the most accurate possible force measurement.

Such apparent forces can also occur if the force transducer is installed in bearings that are not exactly aligned with one another. When installing the force transducer, tensioning of the force transducer can occur, which are detected by the force measuring device or the force measuring devices, without this being an axle force that is actually to be measured. It must be taken into account here that force measuring devices based on strain gauges already respond to shear, expansion and compression in the sub-millimeter range and that manufacturing tolerances of the support bearings in which the force transducers are installed are at least of this order of magnitude.

The invention is therefore based on the object of developing a force transducer of the type mentioned at the outset in such a way that the measurement accuracy of the force transducer is improved.

According to the invention, this object is achieved with regard to the force transducer mentioned at the outset in that the axle body is surrounded outside of the force introduction zone at least in the area of the at least one bearing zone by a sleeve, the end of which facing the force introduction zone is not firmly connected to the axle body in the area of the bearing zone, but is free ,

In the force transducer according to the invention, the axle body is therefore partially surrounded by a sleeve which is not firmly connected to the axle body in the region of the bearing zone, but is free. This free end of the at least one sleeve has the effect that parasitic forces or apparent forces, such as due to frictional forces arising in the receptacle (s) due to high abutment forces, can be largely or even completely decoupled from the axle body, so that only the axial forces actually to be measured from the at least one force measuring system are recorded. The free end of the at least one sleeve in the region of the bearing zone can namely move to a certain extent relative to the axle body, such a relative movement in the submillimeter range is already sufficient to significantly reduce measurement errors. Tensioning of the force transducer due to an installation situation that is subject to tolerances or due to high frictional forces in the area of the bearing zone is therefore essentially not transferred to the axle beam and the associated force measuring system and therefore cannot have a negative effect on the accuracy of the force measurement. This advantageously reduces a hysteresis in the force measurement.

In a preferred embodiment, the at least one force measuring zone is arranged axially at approximately the same height as the at least one bearing zone.

This configuration, in which the force measuring zone and the bearing zone in the axle body essentially coincide, has the advantage that, on the one hand, a particularly sensitive force measurement is made possible, since in the area between the bearing zone 0 and the force introduction zone, when the force transducer is loaded, strains, compression and shear forces occur have the greatest impact, and on the other hand, this configuration also achieves optimal decoupling between parasitic or apparent forces and the force measuring zone, since the free end of the at least one sleeve is also located in this region.

In a further preferred embodiment, the axle body is exposed in the area of the force introduction zone and has a larger diameter than the remaining area of the axle body. It is particularly advantageous here that the axle body in the area of the force introduction zone is designed to be particularly solid and stable, as a result of which the force transducer is suitable for measuring particularly high forces with a small overall diameter. The diameter of the axle body in the area of the force introduction zone can essentially correspond to the outside diameter of the at least one sleeve. The force transducer is therefore suitable for measuring forces that are just as high as a conventional force transducer that has only one axle body and no sleeve.

In a further preferred embodiment, the free end of the sleeve is spaced radially on the inside from the axle body.

This measure has the advantage that an even further improved decoupling of the axle body in the area of the bearing zone is brought about by parasitic or apparent forces, because the free end of the sleeve and the axle body in the area of the bearing zone do not touch one another, which results in a kind of articulation in the area of free end of the sleeve is effected.

The radial distance between the free end of the sleeve and the axle body is preferably in the range between approximately 0.1 and approximately 4 mm.

In a further preferred embodiment, the free end of the sleeve which is not fixedly connected to the axle body extends essentially over the axial length of the bearing zone.

This measure also contributes to improving the avoidance of the effects of parasitic or apparent forces on the Force measurement because the "articulation" or elasticity of the free end of the sleeve to the axle body is further increased by a corresponding axial extension.

In a further preferred embodiment, the axle body has a reduced-diameter first section in the region of the free end of the sleeve, to which a second section adjoins on the side axially facing away from the force introduction zone, on which the sleeve is firmly connected to the axle body.

This measure is particularly advantageous if the bearing zone and the force measuring zone coincide axially, because then the diameter-reduced first section reacts most sensitively to loads on the force transducer through expansion, compression or shear, which can then be detected by the force measuring system with high sensitivity, and on the other hand, without Increasing the diameter of the force transducer creates a radial spacing of the bearing zone of the axle body from the free end of the sleeve, which causes the aforementioned decoupling of parasitic or apparent forces from the axle body. In the end region of the axle body, the sleeve then advantageously forms a firm bond with the axle body, which ensures a high fatigue strength of the force transducer, since the sleeve in this area increases the diameter of the axle body and thus reinforces it.

It is further preferred if the first section merges into the force introduction zone and / or into the second section with a concave rounding. This measure has the advantage that notch effects in the area of the transition from the first section into the force introduction zone and / or into the second section are reduced, which could give rise to predetermined breaking points.

It is further preferred if the free end of the sleeve is provided with a convex rounding on the inside.

In this way, the inside of the sleeve in the area of its free end can be kept at a distance from the first section of the axle body in order to bring about the aforementioned desired effect of decoupling between the free end of the sleeve and the axle body.

In a further preferred embodiment, the outer free end of the sleeve is sealed off from the axle body by means of a seal.

The advantage here is that in the event of a spacing of the free end of the sleeve from the axle body in the region of the bearing zone, no dirt can penetrate into the space between the inside of the free end of the sleeve and the axle body, which is detrimental to the decoupling between the free end the sleeve and the axle body could affect.

In a further preferred embodiment, a bearing zone is present on both sides of the force introduction zone, and the axle body is surrounded on both sides of the force introduction zone by a sleeve, the end of which facing the force introduction zone in the region of the bearing zone is not firmly connected to the axle body, but is free. It is advantageous here that, when the force transducer is normally mounted in two receptacles present on both sides of the force application zone, both bearing zones of the force transducer are decoupled from the axle body and thus also from the force measurement zone, which is particularly advantageous if a force measurement zone is present on the axle body on both sides of the force application zone is.

Further advantages and features result from the following description and the attached drawing.

It goes without saying that the features mentioned above and still to be explained below can be used not only in the respectively specified combination but also in other combinations or on their own without departing from the scope of the present invention.

An exemplary embodiment is shown in the drawing and is described in more detail below with reference to this. Show it:

Figure 1 is a side view of a force transducer for measuring axial forces in an exemplary installation situation with a rope pulley, which is partially shown in section.

FIG. 2 shows a partial longitudinal section through the force transducer in FIG. 1; and

3 is an enlarged view of section X in FIG. 2nd 1 and 2 show a force transducer provided with the general reference number 10 for measuring axial forces which act essentially transversely on an axis. The force transducer 10 is also referred to as the measuring axis.

In Fig. 1, the force transducer 10 is shown as an example in an installed position as a measuring axis for a pulley 12. By means of the force transducer 10, the axial forces acting through the rope (not shown) on the measuring axis 10, which forms the axis of the rope pulley 12, essentially transverse to the measuring axis 10, which can also consist of torsional forces, are to be measured.

As shown in FIG. 1, the force transducer 10 is fixed in a receptacle 14 in the manner of a receptacle fork that has two legs 16 and 18 in bores 20 and 22 provided therein.

With further reference to FIG. 2, the force transducer 10 has an axle body 24, which is made in one piece and essentially solid.

The axle body 24 generally has an essentially cylindrical rotational symmetry about a longitudinal axis 26.

In an axially central area, the axle body 24 has a section 28 which forms a force introduction zone 30 of the axle body 24. In Fig. 1, the direction of the force application of the rope pulley 12 to the force transducer 10 is shown by way of example with an arrow 32. The axle body 24 is in the region of the section 28 forming the force introduction zone 30 exposed on the outside, so that the cable pulley 12 is rotatably mounted directly on the section 28. The force transducer 10 itself is held in the receptacle 14 in a rotationally fixed manner by means of an anti-rotation element 34 arranged on the leg 18 of the receptacle 14.

On each side of the force application zone 30 or on both sides of the section 28 of the axle body 24 there is a bearing zone 36 or a bearing zone 38, which are accordingly arranged axially outside the force application zone 30.

The axle body 24 has a further section 40 in the region of the bearing zone 36 and a further section 42 in the region of the bearing zone 38.

As can be seen from FIG. 2, the section 28 forming the force introduction zone 30 of the axle body 24 has a larger diameter than the sections 40 and 42.

On the side of section 40 facing away from the force introduction zone 30 there is another section 44 and on the side of section 42 also facing away from the force introduction zone 30 there is another section 46 of the axle body 24, the sections 44 and 46 being a slightly larger diameter than have sections 40 and 42 in the area of the connection point between sections 40 and 44 or 42 and 46.

When the force is applied according to arrow 32 in FIG. 1, counter forces act on the bearing zones 36 and 38 of the axle body 28, which are directed in the direction of arrows 48 and 50 in FIG. 1 in the sense of an abutment.

Furthermore, the axle body 24 has two force measuring zones 52 and 54 which coincide with the bearing zones 36 and 38 of the force transducer 10, i.e. the force measuring zones 52 and 54 are formed by the sections 40 and 42 of the axle body 24.

For this purpose, a force measuring system 56 is present in section 40 of the axle body 24 in a manner not shown in detail, and a force measuring system 58 is provided in section 42. The force measuring systems 56 and 58 are designed, for example, on the basis of strain gauges (DMS), the DMS being embedded in blind holes in the sections 40 and 42 of the axle body 24 and firmly connected to the axle body 24, the blind holes then being covered with covers on the outside are hermetically sealed so that the strain gauges are protected against environmental influences.

The force measuring systems 56 and 58 are able to react to stresses, strains and shearings of the material of the axle body 24 in the area of the sections 40 and 42 as a result of the axial forces to be measured by a change in resistance and to generate a corresponding electrical signal. For this purpose, there is a connection 60 on the force transducer 10 for connecting an electrical supply and signal transmission cable (not shown), holes 62 to 66 being provided in the axle body 24 for power lines in order to establish the electrical connection with the force measuring system 56 and 58. The axle body 24 is axially partially surrounded by two sleeves 68 and 70.

The sleeve 68 is fastened on the section 44 of the axle body 24, for example shrunk on or by means of screws, and projects beyond the bearing zone 36, i.e. section 40 of the axle beam 24.

An end 72 of the sleeve 68 facing the force introduction zone 30 or the section 28 of the axle body 24 is not fixedly connected to the axle body 24 over the axial length of the bearing zone 36, but is free. The free end 72 extends completely around the sleeve 68, but could also be axially slotted. When a force is applied to the force transducer 10, for example in the direction of arrow 32 in FIG. 1, which leads to a bending of the force transducer 10 in the direction of arrow 32, the free end 72 of the sleeve 68 performs a relative movement relative to the section 40, which avoids a measurement of parasitic or apparent forces by the force measuring system 56.

In the area of the free end 72, the sleeve 68 is spaced from the axle body 24, ie there is an annular gap 74 between the inside of the free end 72 and the outside of the section 40. The annular gap 74 is designed to be completely circumferential and has a radial dimension in the area between 0.1 and approximately 4 mm, in the present exemplary embodiment a radial dimension of approximately 2 mm. The free end 72 is radially spaced from the axle body 24 over the entire axial extent of the bearing zone 36 or the force measuring zone 52. In section 44, on the other hand, the sleeve 68 sits closely on the axle body 24. Section 40 merges into section 28 with a rounding, likewise into section 44, but there with less rounding.

As can be seen from the detailed view in FIG. 3, the free end 72 of the sleeve 68 does not axially abut the section 28 of the axle body 24, but is slightly axially spaced therefrom. A seal 76 in the form of an O-ring seal prevents contaminants from penetrating into the annular gap 74 between the inside of the free end 72 of the sleeve 68 and the outside of the section 40 of the axle body 24.

In adaptation of the free end 72 of the sleeve 68 to the concave curvature of the outside of the section 40 of the axle body 24, the inside of the free end 72 of the sleeve 68 is convexly curved, so that the annular gap 74 has an essentially constant radial seen over its axial extent Has thickness.

Like the sleeve 68, the sleeve 70 has a free end 78 which faces the force introduction zone 30 and which is likewise not fixed to the axle body 24, but is free, as can be seen from FIG. 2. The free end 78 is also radially spaced from the axle body 24, more precisely the section 42 of the axle body 24, in the same way as the free end 72 from the section 40. The configuration of the section 42 and the free end 78 of the sleeve 70 is up to Mirror symmetry identical to the design of the section 40 and the free end 72 of the sleeve 68, so that reference can be made to the description there. A seal 80 in turn seals the free end 78 against the axle body 24.

The sleeve 70 is fixedly connected to the section 46 of the axle body 24, a recess 82 being present in the sleeve 70, into which the anti-rotation element 34 engages when the force transducer 10 is installed, as shown in FIG. 1.

Finally, a lubricant channel 84 extends through the axle body 24, through which a lubricant for lubricating the mounting of the cable pulley 12 on the section 28 can be supplied.

Claims

claims

Force transducer for measuring axial forces which act essentially transversely on an axis, in particular a measuring axis, with a longitudinally extending axle body (24) which has a force introduction zone (30) in an axially central region and at least one bearing zone axially outside the force introduction zone (30) (36, 38) for mounting the force transducer (10) in a receptacle (14) and axially outside the force introduction zone (30) has at least one force measuring zone (52, 54) for measuring the axial forces, characterized in that the axle body (24) outside the force introduction zone (30) is surrounded at least in the area of the at least one bearing zone (36, 38) by a sleeve (68, 70) whose end (72, 78) facing the force introduction zone (30) in the area of the at least one bearing zone (36, 38) is not firmly connected to the axle body (24), but is free.

Force transducer according to claim 1, characterized in that the at least one force measuring zone (52, 54) is arranged axially at approximately the same height as the at least one bearing zone (36, 38).

Force transducer according to claim 1 or 2, characterized in that the axle body (24) is exposed in the area of the force introduction zone (30) and has a larger diameter than the rest of the area of the axle body (24).

4. Force transducer according to one of claims 1 to 3, characterized in that the free end (72, 78) of the sleeve (68, 70) is spaced radially on the inside from the axle body (24).

5. Force transducer according to claim 4, characterized in that the radial distance between the free end (72, 78) of the sleeve (68, 70) and the axle body (24) is in the range between about 0.1 mm and about 4 mm.

6. Force transducer according to one of claims 1 to 5, characterized in that the free end (72, 78) of the sleeve (68, 70), which is not firmly connected to the axle body (24), extends substantially over the axial length of the at least one Storage zone (36, 38) extends.

7. Force transducer according to one of claims 1 to 6, characterized in that the axle body (24) in the region of the free end (72, 78) of the sleeve (68, 70) has a reduced-diameter first section (40, 42) to which a second section (44, 46) adjoins on the side axially facing away from the force introduction zone (30), on which the sleeve (68, 70) is firmly connected to the axle body (24).

8. Force transducer according to claim 7, characterized in that the first section (40, 42) merges into the force transmission zone (30) and / or into the second section (44, 46) with a concave rounding.

9. Force transducer according to claim 8, characterized in that the free end (72, 78) of the sleeve (68, 70) is provided on the inside with a convex rounding.

10. Force transducer according to one of claims 1 to 9, characterized in that the outer free end (72, 78) of the sleeve (68, 70) by means of a seal (76, 80) to the axle body (24) is sealed off.

11. Force transducer according to one of claims 1 to 10, characterized in that a bearing zone (36, 38) is present on both sides of the force introduction zone (30), and that the axle body (24) on both sides of the force introduction zone (30) each has a sleeve (68 , 70), the respective end (72, 78) of the force introduction zone (30) in the region of the bearing zone (36, 38) is not firmly connected to the axle body (24), but is free.