GB2475080A

GB2475080A - Weighing suspended loads having a pivotable load pin attached to a load cell

Info

Publication number: GB2475080A
Application number: GB0919394A
Authority: GB
Inventors: Michael William Ford
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2009-11-05
Filing date: 2009-11-05
Publication date: 2011-05-11
Anticipated expiration: 2029-11-05
Also published as: GB0919394D0; WO2011056865A1; GB2475080B

Abstract

A load cell 30 which weighs suspended loads having two cross members 36, 38 connected at each end by two struts 40, 42 having a fixed angle, at least one strain gauge 44, 46, 48, 50 is connected to one of the cross members to detect flexure in the cross members. A load pin 52 having a longitudinal axis is coupled to the cross members such that the cross members are pivotable about the longitudinal axis of the load pin. Multiple strain gauges may be used on either or both of the cross members to detect compression or tensile forces in the cross members. The load pin may be fixedly coupled between the cross members such that relative rotations between the load pin and cross members is prevented. The longitudinal axis of the load pin may be perpendicular to the longitudinal axis of the cross members. The load pin, struts and cross members may be rigidly connected to each other. The load cell may comprise a tilt sensor and/or a load attachment means. An error correction for pitch and/or roll can be automatically carried out by a software program which operates in electronic equipment electronically attached to the load pin.

Description

IMPROVEMENTS RELATING TO LOAD CELLS

The present invention relates to a load cell for use, in particular but not exclusively, in weighing suspended loads such as a skip, for example.

Conventionally, a Roberval balance mechanism is used as the basis for numerous strain gauge transducers. The function of the Roberval mechanism is to cancel the effect of moments on the output of a weighing scale, so an object to be weighed can be placed on a weighing platform and the indicated weight of the object remains the same regardless of the position of the object on the weighing platform.

Thus, in a Roberval transducer, having top and bottom cross members arranged in a rectangular configuration and being fixed at a lower left end thereof and having a platform attached to the opposite, right upper end, moving a weight on a platform attached to the cross members and located above them causes flexure of the top and bottom cross members in response to different tensile and compressive forces but approximately the same vertical deflection.

If four strain gauges are bonded to the cross members, two to the top cross member and two to the bottom cross member and all four strain gauges are positioned at the corners of the rectangular configuration of the transducer, then the output from a Wheatstone bridge incorporating these gauges will be, to a first approximation, unaffected by the position of the weight on the platform. This principle is widely used in retail scales and small industrial platforms.

The conventional Roberval-based load cell described above gives a satisfactory measurement of relatively small weights which are substantially stationary.

There exist examples involving the weighing of an articulated load. One such example is described in W02008/1 31 574 wherein a dynamic scale for weighing bulk material, in particular for waste collection vehicles, is described. The weighing process is performed during the raising of a filled container and the lowering of the emptied container performed using rigid swivel arms on a refuse truck. Load sensors, in the form of strain gauges, are incorporated into a pipe welded into a hole in each of the two rigid swivel arms of a refuse collection vehicle. The sensors are arranged to detect deformation in the hole in the swivel arm caused by the application of a load, in the form of a refuse skip, applied at an end of the swivel arm(s). The deformation in the hole, as measured by the strain gauges, is then resolved to give the weigh of the container as it is raised and lowered onto and from the vehicle. The scale requires an acceleration sensor to identify the "weighing window" in which the lifting of the container is in a dynamically smooth phase during the lifting and lowering process and also allows for the resolution of the affect of acceleration of the swivel arms on the weight of the container during the lifting and lowering process.

The weighing process described in the prior art suffers from the drawback that the weight of the load remains unresolved for non-vertical forces and is, therefore, unsuitable for a load suspended from the scale. The deformation in the diameter of the hole in the swivel arm only measures the vertical forces and, for accurate load measurement, relies on the load being relatively stationary relative to the swivel arms during the lifting process. This arrangement has drawbacks when the load is suspended in a way which allows articulation of the load itself during lifting and lowering.

In situations wherein a load is suspended from the weighing mechanism, the load is generally free to move about an articulation point, for example in the lifting of a skip using chains. The suspended load will apply eccentric forces to the load attachment point, making resolution of those forces into a substantially vertical force direction more difficult. In addition, the load may not always be lifted vertically. For example, when a load is lifted using chains, the chains themselves may not always be entirely vertical when the lift begins. These factors each make accurate weighing of suspended loads more difficult, therefore necessitating more complex and, therefore, more expensive weighing equipment.

The present invention aims to overcome one or more of the drawbacks

associated with the prior art.

The present invention provides a load cell for weighing suspended loads comprising a first cross member and a second cross member, the cross members being parallel and spaced apart from one another, at least two struts, each strut being attached to an end of the first and the second cross members and each being at a fixed angle to the first and the second cross members, at least one strain gauge located and configured to detect flexure in at least the first cross member, and a load pin coupled to the first and the second cross members and located therebetween, the load pin having a longitudinal axis and the first and the second cross members are pivotable about the longitudinal axis of the load pin.

In embodiments of the invention, the fixed angle is equal to 90 degrees.

More specifically, each strut may be attached to an end of the first and the second cross members and may be substantially perpendicular to both the first and the second cross member.

In embodiments of the invention, the first cross member is located above the second cross member.

In embodiments of the invention, the longitudinal axis of the load pin is perpendicular to the longitudinal axes of the first and the second cross members. In this way, the cross members may rotate about the longitudinal axis of the load pin in a balanced way. In alternative embodiments wherein the load pin is fixedly connected to the cross members, the entire load cell is able to rotate about the longitudinal axis of the load pin in a balanced way.

In preferred embodiments, the load pin is fixedly coupled to the first and the second cross members and located therebetween such that relative rotation between the load pin and the first and the second cross members is prevented.

In preferred embodiments the load pin, struts and cross members are rigidly connected to one another.

More specifically, in various embodiments the load pin, struts and cross members assembly is pivotable about the longitudinal axis of the load pin.

In alternative embodiments, the cross members are rotatably coupled to the load pin. Thus, relative rotation between the load pin and the cross members is permitted. It is preferred that in these embodiments the load pin is fixed and the first and second cross members pivot about the longitudinal axis of the load pin as one unit.

In certain embodiments, the struts and cross members may be integrally formed as a single unit.

In embodiments of the invention, a load pin receiving means is provided between the two cross members and the two struts. More specifically, the load pin receiving means is operable to couple the load pin and the cross members and struts.

In certain embodiments the coupling is a fixable coupling. More specifically, the coupling provides a fixed rigid connection between the load pin and the cross members and struts. Even more specifically the load pin and the cross members and struts, once coupled together, are immoveable relative to one another.

In alternative embodiments, the coupling is a rotatable coupling. More specifically, the coupling between the load pin and the cross members and struts is operable to allow the cross members and struts to rotate relative to the load pin. Such an arrangement is preferred when the load pin is a fixed load pin which itself does not rotate.

In various embodiments, a load pin receiving means is an aperture formed in the single unit between the two cross members and the two struts.

In embodiments of the invention, the load pin is locatable into the aperture for rigid connection therein. More specifically, the load pin and the load pin receiving aperture may be complimentary in shape so as to be releasably coupleable in the initial instance whilst being capable of being rigidly fixed thereafter.

It is much preferred that the complimentary shapes of the load pin and the load pin receiving aperture are such that the load pin is incapable of rotational movement within the aperture. The aperture may, in certain embodiments, be a circular aperture having at least one flattened portion.

The load pin may further comprise a corresponding flattened portion on its circumference.

In preferred embodiments the load pin, struts and cross members assembly (hereinafter "transducer-load pin assembly") is pivotable about the longitudinal axis of the load pin. In this way, the load pin is capable of pivoting about its longitudinal axis and the cross members and struts, due to their being fixed to the load pin, will pivot together with the load pin.

In preferred embodiments, the longitudinal axis of the load pin is perpendicular to the vertical forces of an applied load. The load pin is preferably rotatable about its longitudinal axis to maintain the longitudinal axis perpendicular to the vertical forces of an applied load in use of the load cell.

The load cell comprises at least one strain gauge. More specifically, the strain gauge is located and adhered to the first cross member so as to detect flexure in the cross member. Even more specifically, the strain gauge may be located to detect either tension or compression forces in the first cross member.

In certain embodiments, the load cell comprises at least two strain gauges located and configured to detect flexure in at least the first cross member.

More specifically, a first strain gauge is located and configured to detect compression forces in the first cross member and a second strain gauge is located and configured to detect tensile forces in the first cross member.

In embodiments of the invention, the load cell further comprises at least one strain gauge located and configured to detect flexure in the second cross member.

In certain embodiments, the load cell further comprises at least two strain gauges located and configured to detect flexure in the second cross member.

More specifically, in embodiments comprising at least two strain gauges located and configured to detect flexure in the second cross member, it is preferred that a strain gauge is located and configured to detect compression forces in the second cross member and a further strain gauge is located and configured to detect tensile forces in the second cross member.

In embodiments comprising more than 2 strain gauges, the load cell preferably comprises a multiple of two strain gauges.

In each multiple of two strain gauges it is much preferred that one of the strain gauges is configured and located to detect compression in a cross member and the other of the strain gauges is configured and located to detect tension in the same cross member upon flexure of the cross member to which the two strain gauges are attached.

In embodiments of the invention, two strain gauges are located and configured to detect flexure in the first cross member. The outputs from the two strain gauges form a half Wheatstone bridge arrangement, with one arm of the bridge being formed of the outputs from a strain gauge detecting compression force and another arm of the bridge being formed of the outputs from a strain gauge detecting tensile force. As will be readily understood by the skilled artisan, the other arms of the Wheatstone bridge will comprise dummy resistors. In this arrangement, as load is applied to the load cell, one strain gauge will come under compression and the other under tension as the first cross member flexes in response to the applied load. The output of the Wheatstone bridge may then be measured in a conventional way to indicate the weight of the applied load.

In further embodiments, the load cell may comprise four strain gauges. In this arrangement, the strain gauges may be configured to provide two pairs of strain gauges. More specifically, one pair of strain gauges will detect compression forces and a second pair of strain gauges will detect tensile forces in the load cell. Even more specifically, a first strain gauge in the first pair is attached to the first cross member and will come under compression as a load is applied to the load cell. A second strain gauge in the first pair is attached to the second cross member and will come under compression as a load is applied to the load cell. Likewise, a first strain gauge in the second pair is attached to the first cross member and will come under tension as a load is applied to the load cell. A second strain gauge in the second pair is attached to the second cross member and will come under tension as a load is applied to the load cell.

More specifically, one gauge in each pair of strain gauges is attached to the first cross member and the other gauge in each pair of strain gauges is attached to the second cross member. Both strain gauges in the first pair will come under compression and both strain gauges in the second pair will come under tension as a load is applied to the load cell and flexure in each of the cross members acts on the strain gauges.

The outputs from the strain gauges are resolved, using a conventional Wheatstone bridge arrangement, to indicate the weight of the applied load.

Any number of strain gauges may be used in the present invention.

In embodiments of the invention, two strain gauges are used together in which one of the strain gauges is configured and located to come under compression and the other of the strain gauges is configured and located to come under tension upon flexure of the cross member to which it is attached.

The load cell may comprise a split strain gauge in which two strain gauges on a single adhesive backing are applied, as a pair of strain gauges at either side of the centre line of a cross member. In such embodiments, the pair is located to detect either compression or tension in the cross member to which they are attached. Further, the split gauge will from at least part of a single arm in the Wheatstone bridge incorporating the split gauge.

When a single, i.e. not split, strain gauge is used the strain gauge is preferably located on the centre line of the cross member to which it is attached. In this way, the affect of torsional forces (non-vertical forces) on the strain gauge are reduced or even eliminated as they will affect both sides of the gauge (on either side of the centre line) in equal and opposing ways and are, thus, self-compensating in the Wheatstone bridge.

In embodiments of the invention, the strain gauges are preferably evenly distributed between the first and the second cross members. For example, in embodiments comprising four strain gauges, two strain gauges will be attached to the first cross member and two strain gauges will be attached to the second cross member.

In alternative embodiments of the invention, the second cross member preferably has two more strain gauges than the first cross member. More specifically, in certain embodiments, the second cross member may have a pair of compression strain gauges and a pair of tension strain gauges with a first strain gauge in each pair being located at one side of the centre line of the second cross member and a second strain gauge in each pair being located at the opposite side of the centre line of the second cross member.

In these embodiments, the first cross member preferably has a compression strain gauge and a tension strain gauge both located on the centre line of the first cross member.

In these embodiments, at least one and, preferably both, of the pair of compression gauges and at least one and, preferably both, of the pair of tension gauges on the second cross member have a resistor of known electrical resistance connected in parallel therewith. In this way, the measurement axis of the half of the Wheatstone bridge formed of the strain gauges on the second cross member may be adjusted. This is particularly useful in load cells wherein the mechanical neutral axis, i.e. the axis of the second cross member wherein any torsional force(s) applied to the cross member affect both sides of the cross member in equal and opposing ways, is not co-aligned with the measurement axis. The electrical resistor(s) are then operable to adjust the position of the measurement axis such that it is co-aligned with the mechanical neutral axis.

In embodiments comprising an even number of strain gauges in multiples other than multiples of four, the un-matched pair of strain gauges may be located on either the first or the second cross member. In preferred embodiments, the un-matched pair of strain gauges is located on the second cross member.

The load cell is preferably a Roberval balance load cell. More specifically, the Roberval balance load cell pivots about a pivot point located between the first and the second cross members of the Roberval arrangement.

The Roberval balance load cell is preferably vertically orientated. More specifically, the Roberval balance load cell is configured such that a load may be suspended therefrom.

The load cell may further comprise a load attachment means. Even more specifically, the load cell has a load attachment means below the coupling of the transducer-load pin assembly.

In this way, a load may be suspended to hang below the Roberval load cell and to swing freely until it hangs at its balance point below the load cell.

The load attachment means may be any suitable means for attaching a load to the load cell. In certain embodiments, the load attachment means is a bore through the body of the transducer-load pin assembly proximate a bottom edge thereof. Alternatively, the load attachment means may be a ring, loop, hook, or the like attached to the transducer-load pin assembly.

In preferred embodiments, the load attachment means comprises a pair of holes through the body of the transducer-load pin assembly proximate a bottom edge thereof with each hole being arranged to be coupled to a chain linkage. The chain linkage is preferably the uppermost linkage in a chain having a distal end to which a load may be attached.

The coupling point of the transducer-load pin assembly is located at, or adjacent to, the axis upon which the centre of gravity of the transducer-load pin assembly is located. More specifically, the coupling point is located centrally on, or adjacent to, the longitudinal axis of the transducer-load pin assembly and remote from the edges thereof. The longitudinal axis of the transducer-load pin assembly is perpendicular to the longitudinal axis of the load pin.

By rigidly fixing together the transducer-load pin assembly and allowing the transducer-load pin assembly to pivot as one unit, cabling to and from the strain gauges is simplified. More specifically, the cabling to and from the strain gauges on the load cell may be channelled through the centre of the load pin. In this way, the cabling is protected against wear and damage from collision for example in use of the load cell.

The load cell may further comprise a tilt sensor.

The tilt sensor may be located anywhere where a pitch and/or roll angle is detectable. More specifically, the tilt sensor may be attached to or, alternatively, may be built into the load cell. Alternatively, the tilt sensor may be attached to or, may be built into, the load pin.

Alternatively, or in addition, the load cell may be operably attached to a tilt sensor. More specifically, the tilt sensor may be position on a skip truck dashboard, a skip truck arm or any other suitable position in which it is able to detect the pitch angle of the vehicle/apparatus to which the load cell is attached in use.

The tilt sensor is operable to provide information about the angle of the load cell relative to its datum, which is set with its base being horizontal.

In embodiments of the invention, the load cell will react to only the vertical component of the load.

In exemplary embodiments, when the load cell is attached to a skip truck and the skip truck is tilted, for example by being parked on a slope, the load cell will be tilted through the same angle as an axis passing through the width of the truck. Tilting side to side of the truck is referred to as "roll".

Tilting front to back is referred to as "pitch". The pitch tilt along the length of the truck will be, at least to some extent, self compensating as the load pin and/or the cross members will rotate about the longitudinal axis of the load pin to keep the centre of gravity of the load under the centre of the pivot.

It will be understood that friction in the pivot and none symmetric loads will produce errors in the measurement of the applied load.

For small angles of pitch, the magnitude of the error approximates to: Error = weight multiplied by (1-Cosine pitch angle) This will be combined with errors in the other axis to give a combined error for pitch and roll approximates to: Error= weight ((1-Cosine pitch angle)-'-(l-Cosine roll angle)) In embodiments of the invention, the error correction is automatically carried out by a software programme that operates in electronic equipment operably attached to the load cell.

The direct attachment of the load to the load cell removes the necessity for additional couplings for attaching the load to the load cell. This offers the advantage of a reduction in the height of the load cell. This gives a simplified assembly which maintains high accuracy in weight measurement.

It will be understood that the load cell of the present invention has various applications and uses. An exemplary use is in a skip truck wherein the skip is suspended from two load pins, one at each side of a skip truck, by four chains suspended two at each side of the skip. A pair of chains on each side of the skip may be suspended from a single load pin. The load pin(s) is/are then mounted on the truck arm. A load cell according to the present invention may be provided at one or, alternatively at both, sides of the skip truck.

In an alternative application, a load cell according to the invention may be used in a crane weigher. In such applications, the load cell may itself be suspended in use.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

There now follows a description of a preferred embodiment(s) of the invention, by way of non-limiting example, with reference being made to the accompanying drawings, in which: Figure 1 shows a conventional Roberval balance mechanism according to

the prior art;

Figure 2 shows a conventional skip truck and load pin assembly; Figure 3 shows a load cell according to the invention; Figure 4 shows a perspective view of the load cell of Figure 3; Figure 5 shows a schematic side view of the load cell of Figure 3; Figure 6 shows an isometric schematic view of the load cell of Figure 3 with the first links of a chain attached thereto; and Figures 7a and 7b show a schematic side view of the load cell of Figure 3 looking from the opposing side; While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Further, although the invention will be described in terms of specific embodiments, it will be understood that various elements of the specific embodiments of the invention will be applicable to all embodiments disclosed herein.

In the drawings, similar features are denoted by the same reference signs throughout.

Referring to Figure 1, the invention is based on a Roberval balance mechanism that is used as the basis for numerous strain gauge transducers. The function of the Roberval mechanism is to cancel the effect of moments on the output of a weighing scale, so an object to be weighed can be placed in any position on a platform and still have the same indicated weight.

Figure 1 shows a Roberval transducer 1 fixed at the lower left end 2 with a platform 3 attached to the upper right end 4. Moving the weight on the platform 3 will cause the top and bottom cross members (5, 6) to have different tensile and compressive forces but approximately the same vertical deflection.

When strain gauges (7, 8, 9, 10) are bonded to the top and bottom cross member 5, 6 in the four positions shown in Figure 1, the output from a Wheatstone bridge made from these gauges will be, to a first approximation, unaffected by the position of the weight 11. This principle is widely used in retail scales and small industrial platforms.

Figure 2 depicts part of a conventional skip truck 20. The skip 22 may be lifted by 4 chains 24 suspended two at each side of the skip 22. A pair of chains 24 located on each side of the skip 22 is suspended from a single load pin 26. The load pin 26 is mounted in the truck arm 28. As the truck arm 28 lifts the skip 22 the load pins 26 at each side of the truck are free to rotate (A) to keep the skip 22 level.

In known weighing mechanisms for suspended weights/loads, various methods of determining the weight of the skip are used whereby a sensing element is placed in the force path between the chain 24 and load pin 26.

Figures 3 and 4 depict a load cell 30 according to an embodiment of the invention. The load cell 30 is operable to weigh a suspended load (not shown) by way of chains (not shown) attached to the load cell 30 through apertures 34a and 34b. Load cell 30, has a first cross member 36 and a second cross member 38, the cross members 36, 38 being parallel and spaced apart from one another in an integral, single transducer unit 58 formed of galvanized steel. Two struts 40,42 are attached to ends of each of the first and the second cross members 36, 38 and are perpendicular to the first and the second cross members 36, 38 and integrally formed into the same single transducer unit 58. Four strain gauges 44, 46, 48, 50 are attached to the cross members 36, 38. Strain gauges 44 and 46 are operable to detect flexure in the first cross member 36, and strain gauges 48 and 50 are operable to detect flexure in the second cross member 38. A load pin 52 is fixedly coupled to the single transducer unit 58 between the first and the second cross members 36, 38 and also between struts 40 and 42.

Figure 4 clearly shows the load pin 52 having a longitudinal axis 54 perpendicular to the longitudinal axes of the first and the second cross members 36, 38. The load pin 52 is rigidly coupled to the single transducer unit 58 comprising the cross member 26, 38 and struts 40, 42.

In this way, the entire load cell unit may pivot about the longitudinal axis 54 to the load pin, in use of the cell.

In the embodiment depicted in Figures 3 to 7b, a recess 56 is cut out from the body of the single transducer unit 58. The recess ensures a balanced load cell and is of variable size and shape depending on the specific dimensions of the load cell.

In the embodiment depicted in Figure 5, the load pin 52 passes through the centre of the Roberval mechanism comprising the first and the second cross members 36, 38 and the struts 40, 42. The load pin 52 is rigidly fixed to the single transducer unit 58. The load pin 52 and the single transducer unit 58 in combination are free to rotate about the longitudinal axis of the load pin 52. In this way, the Roberval mechanism is mounted on a rotating load pin 52 located in the centre of the Roberval mechanism which allows the load cell 30 to weigh suspended loads with accuracy.

Thus, the load cell 30 is particularly useful for weighing a skip suspended on chains on a skip truck. The strain gauges 44, 46, 48, 50 are bonded to the single transducer unit 58. The strain gauges 44, 46, 48, 50 are wired up into a Wheatstone bridge in a conventional manner. A skip (not shown) may then be suspended from the apertures 34a and 34b on two chains 60.

The application of weight to the load cell 30 will produce a voltage on the Wheatstone bridge which is proportional to the weight of the skip.

Figure 6 shows an isometric view of the load cell 30 of Figures 3 to 5. The first links of chains 60 are shown depending from apertures 34a and 34b.

The wiring from the strain gauges exits the load cell 30 through a centre hole in the load pin 52 at the point marked 62. In known apparatus requiring relative motion between the load pin and the transducer, the relative motion makes wiring to the strain gauges more difficult. In the present invention, by passing the wires through the centre of the load pin and down the skip arm (not shown), wiring can be protected. This protection of the wires is vital on a skip truck as trees and other objects are often in collision with the vehicle and will damage any exposed wiring.

Figures 7a and 7b show a view of the back of the load cell 30. The recess contains a tilt sensor and analogue to digital converter which are connected, by a cable, down channel 72 to the strain gauges. The cable then passes down a further channel 74 before entering the centre of the load pin (as shown in Figure 6). The load pin 52 and the single transducer unit 58 cannot rotate relative to one another due to the flat on the load pin shaft and matching flat on the load pin receiving aperture 76.

The Roberval mechanism further allows the load cell to be directly connected to the two chains 60 which support the load to be applied.

A load cell according to the invention maintains high accuracy in weight output with simplified installation and fewer parts using a Roberval mechanism which rotates with and on a load pin.

It will be understood that the invention is capable of various modifications and improvements. In embodiments of the invention, for example, the load pin is a circular shaft.

In embodiments of the invention, the Roberval has its signal cable fed through the centre of the supporting shaft.

Embodiments of the invention may utilise a radio transmitter to link the load cell to a load/weight indicating device or printer.

In embodiments of the invention, the two chains from a skip are directly attached to the load cell.

In further embodiments of the invention, there is provided a freely rotating load cell comprising a circular mounting for a circular load pin, wherein the load cell is rotatable relative to the load pin. The load cell may further comprise a wireless link between a battery powered cell and a weight/load indicator.

Claims

CLAIMS1. A load cell for weighing suspended loads comprising a first cross member and a second cross member, the cross members being parallel and spaced apart from one another, at least two struts, each strut being attached to an end of the first and the second cross members and each being at a fixed angle to the first and the second cross members, at least one strain gauge located and configured to detect flexure in at least the first cross member, and a load pin coupled to the first and the second cross members and located therebetween, the load pin having a longitudinal axis and the first and the second cross members being pivotable about the longitudinal axis of the load pin.
2. A load cell according to claim 1, wherein the fixed angle is equal to 90 degrees.
3. A load cell according to claim 1 or claim 2, comprising at least two strain gauges located and configured to detect flexure in at least the first cross member.
4. A load cell according to claim 3, wherein a first strain gauge is located and configured to detect compression forces in the first cross member and a second strain gauge is located and configured to detect tensile forces in the first cross member.
5. A load cell according to any one of the preceding claims, wherein the load pin is fixedly coupled to the first and the second cross members and located therebetween such that relative rotation between the load pin and the first and the second cross members is prevented.
6. A load pin according to any one of the preceding claims, wherein the longitudinal axis of the load pin is perpendicular to the longitudinal axes of the first and the second cross members.
7. A load cell according to any one of the preceding claims, wherein the load pin, struts and cross members are rigidly connected to one another.
8. A load cell according to any one of the preceding claims, wherein the load pin, struts and cross members assembly is pivotable about the longitudinal axis of the load pin.
9. A load cell according to any one of the preceding claims, further comprising at least one strain gauge located and configured to detect flexure in the second cross member.
10. A load cell according to claim 9, comprising at least two strain gauges located and configured to detect flexure in at least the second cross member.
11. A load cell according to claim 10, wherein a strain gauge is located and configured to detect compression forces in the second cross member and a further strain gauge is located and configured to detect tensile forces in the second cross member.
12. A load cell according to any one of the preceding claims, further comprising a load attachment means.
13. A load cell according to any one of the preceding claims, further comprising a tilt sensor.
14. A load cell according to any one of the preceding claims, in which an error correction for pitch and/or roll is automatically carried out by a software programme that operates in electronic equipment operably attached to the load cell.
15. A load cell substantially as hereindescribed with reference to Figures 2 to 7b.