GB2414562A

GB2414562A - Load cell unit

Info

Publication number: GB2414562A
Application number: GB0510680A
Authority: GB
Inventors: Michael James Wing
Original assignee: ADVANCED MEASUREMENT AND WEIGH
Current assignee: ADVANCED MEASUREMENT AND WEIGH
Priority date: 2004-05-26
Filing date: 2005-05-26
Publication date: 2005-11-30
Anticipated expiration: 2025-05-26
Also published as: GB2454993A; GB0411786D0; GB2414562B; GB2454993B; GB0510680D0

Abstract

A load cell 3 is mounted in a unit between body members 1 and 2, the latter having a connection 2a for a load to be lifted and weighed via the load cell unit. To protect the load cell from excessive loads the body 1 has a land 1b engaging with clearance in a groove 2b of body 2, limiting the relative movement between the bodies. The member 2 may be connected to the load cell 3 through a universal bearing to ensure that load is applied evenly (Fig. 2). The output of the load cell may be transmitted wirelessly and it may be used in lifting apparatus, e.g. a crane.

Description

24 1 4562 Load Cell Unit for Weighing Apparatus The present invention

relates to a load cell unit for use in weighing apparatus.

Lois invention finds a main application in load cell arrangements for use in the industrial field where the load cell unit may be located between a lifting apparatus, such as a crane or hoist, and waste container, for example a skip. Whilst the present application proceeds in relation to the use of a weighing apparatus in relation to waste collection, it will be appreciated that the present invention can he used for other applications wherein the weighing of bulk material is required.

lihe collection of waste for disposal or recycling is provided as a service based upon the weight of waste to be collected. l'he weight of material to be collected is generally unknown and so there is a need for mobile installations which can undertake both weighing and removal of material. Particularly with regard to material for recycling, there is an increasing need to accurately weigh the material upon collection in order to be able to. . determine an establishment's contribution towards recycling.

Furthermore there is a need to more accurately measure the amount of material intended for landfill sites. '{hose requremcnts are in addition to those that allow calculation of collection charges based on weight. Additionally knowing the weight carried on a vehicle will help avoid vehicle overloading with benefits of reducing road damage and pollution.

In mobile Installations weighing devices are generally unreliable, And have difficulty in achieving and maintaining the required accuracy for Weights and Measures approval and load cells alone hitherto have not been suitable for installation in the lifting apparatus. One problem concerns overloads which can damage the loadcell and thus compromise the accuracy of the load cell for later use. Another problem is negative loading which can be applied through attempts to compact waste in a skip or by impact with the ground. It will be appreciated that, by the nature of the work involved in waste collection, the lifting equipment is often used in a haphazard manner, which can result in the load cell being dropped or colliding with objects during transit and use, all of which can reduce the accuracy of measurement by the load cell. Furthermore a load cell is required to be vertically oriented to obtain an accurate reading.

Known weighing devices are mounted to a crane or hoist in a manner which allows for rotation about only one axis. Any angular displacement about a different axis can cause the weighing device to be aligned away from the vertical and thus known devices cannot adequately account for lifting taking place On an uneven surface.

A further problem concerns electrical connections required from the lifting apparatus to the loadcell located at the end of the lifting cable or chain system. Cabling is required to allow connection to a storage means such that the weight of material collected can be stored for later retrieval or communication.

lathe use of such cabling is disadvantageous in that it can become loose and/or severed resulting in reduced reliability and increased maintenance costs.

An subject of this invention is to provide a construction which, in a most preferred embodiment, can provide an improved level of accuracy and overcome at least some, and potentially all, of the aforementioned problems.

According to this invention there is provided a load cell unit comprising a load cell, said load cell being located between first and second body members, the first body member with first connection means for a support member and the second body member with second connection means for a load to be lifted, wherein the load cell has one end thereof connected with one body member and the Other end thereof connected with the other body member, said body members being relatively displaceable when subject tail an applied load across the relevant connection means, and the body members including inter- engaging means limiting the relative displacement there<>f.

Preferably the inter-engaging means limits displacement under applied tensile (positive) loads and/or under applied compressive (negative) loads. In one embodiment the application of an applied compressive load beyond a predetermined magnitude causes the load cell and one body member to disengage so as to isolate the load cell from the applied load.

With this arrangement the body members t<> which the load cell is connected may only extend, under tensile load, by a defined amount thus preventing overloading of the load cell. The load cell is therefore protected from the application of excessive loads to be weighed (tensile load), as well as damage due to negative loading (compressive loading) which can occur due to a sh<>ck, such as, for example, when the load cell unit is dropped to the ground.

A preferred construction includes a sliding telescopic connection between the body members with abutment means limiting the travel in both an extension direction under load and a reverse compression direction under negative load.

lthe body members may house the loadcell and in one embodiment, the body members are rectangular in shape. ':[ he one body meml>er may include a peripheral groove engaged by a peripheral land on the other body member. The width of the groove may be greater than the width of the land thus permitting limited axial movement.

In one embodiment, the load cell unit may include a deformable member arranged in the force path between the load cell and either of the first or second body members. Preferably the deformable member is elastically deformable and typically takes the form of a spring.

Preferably, the load cell unit includes one or more mounting means for adjustment of the position and/or orientation of the load cell. 'lihe mounting means may be axially adjustable and locking means may be provided to fix the loadcell in a required position. 'the mounting means can advantageously allow the position of the load cell tc> be set in an unloaded condition, such that the load cell can be calibrated prior to use.

Typically the mounting means includes a threaded bolt Additionally, or else alternatively, the mounting means may include a curved bearing surface so as to allow pivotal movement of the load cell with respect t<> the first ancl/or second body members. l'he load cell may be movably mounted to the other body member and preferably in a manner which allows limited lateral movement. The pivotal mounting may be provided at cane end of the load cell and the laterally movable mounting may be provided at the other end of the load cell such that the orientation of the load cell can be angularly adjusted to a required degree.

degree of pivotal movement between the load cell and body members advantageously allows the load cell to adopt a vertical orientation when a load Is applied. Substantially removing any horizontal component of the load in this manner improves the accuracy of the loading measurement attainable by the load cell.

Additionally, jamming between the load cell and any body member or between body members is avoided.

Additionally, or else alternatively, the mounting means may be disposed in the force path between the load cell unit and the supporting member. l'rcferably the mounting means is a spherical bearing such that the load cell unit can pivot freely about two axes in order to attain a substantially vertical orientation.

It Is preferred to use a self-contained load cell that is a unit with associated circuits to enable wireless transmission of the loading measured by the cell to a remote receiver.

According to a further aspect of the present invention, there is provided a load cell unit comprising a housing, said housing having first connection means for a lifting apparatus and second connection means for a load to be lifted, a load cell located . ' within the housing and arranged to receive a load applied across a the relevant connection means, the housing including signal transmission means for transmitting a loading measurement recorded by said load cell to a remote rccciver.

According to a preferred embodiment, the housing includes a recess for reception of an antenna. '{he antenna may be substantially planar in shape and located within the recess such that a surface of the antenna is substantially flush with an outer surface of the housing. Preferably an antenna is located with respect to one or more sides of the housing.

An embodiment of a loadccll unit in accordance with this invention is described below in further detail by way of example and with reference to the drawings, in which: Figure 1 shows a cross-sectional view through a loadcell unit according to the present invention; Figure 2 shows a front cross-sectional view through a further load cell according to the present invention; Figure 3 shows a side eross-seetional view of the load cell of figure 2; Figure 4 shows a eross-seetional view of a load cell unit bearing; and, Figure 5 shows a load cell unit in use on a mobile installation. .... . . Referring to figure 1, the load cell unit has a first body member 1 and a second body member 2. The body members may be a. ,, rectangular, cylindrical or U-shaped and engage in a telescopic or sliding manner so as to permit limited longitudinal movement. The body member 1 has an eye la for attachment to a lifting apparatus and the body member 2 has an eye 2a for attachment to the load to weighed.

To achieve the object of this invention the body members 1 and 2 are displaceable by a limited distance and this is achieved by a channel or groove 2b in the body member 2 and a cooperating land or projection lb on the body member 1. The channel is wider than the projection permitting limited clisplacement. The channel 1 b may take the form or any recess shaped to accommodate limited movement of the projection lb and may extend entirely or else only part way around the load cell unit.

1\ load cell 3 is located between the two body member 1 and 2 with one connection 3a to the body member 2 and the other connection 3b to the body member 1 being through a mounting in the form of bolt 4 passing through the floor of a recess 5 to engage the Ic>adcell. A spring 6 is interposed between the head of the bolt 4 and the floor of the recess. 'lathe spring 6 preferably comprises one or several conical dished springs also known as a "belleville washers" providing a compact construction.

()n application of tension loading between the body members 1 and 2 progressive loading is applied to the loadcell through the compression of the spring 6 but with the degree of loading limited through abutment between the channel 2b and land lb. the limited movement prevents overloading of the load cell in a positive (tension) loading direction. The application of negative loading on the lcacdcell is limtecl by the abutment c, f land 1 b with the channel 2b in the opposite direction. 2.

In use the crane is attached to the body 1 by a pin through eye I a and the load attached to body 2 by a pin through eye 2a Under normal loads the load cell supports the weight applied and gaps A and B between the sides of channel 2b and sides of land 1 b are open. With excessive applied load the spring 5 compresses and gap closes thus defining the maximum load.

Under compressive loads the load cell moves upward and the load cell mounting is released thus protecting the loadcell from compressive forces.

further embodiment is shown in figure 2, with the eye portions 1 a and 2a removed. 'the embodiment of figure 2 operates substantially as described in relation to figure 1 save for the provision of a modified load cell mounting disposed in the force path between the load cell 3 and each the first 1 and second 2 body members.

The bolt 4 passes through a first 7 and a second 8 spring housing within the recess 5 and engages with the load cell. lihe bolt is threaded such that tightening or loosening of the bolt 4 adjusts the spring pretension. Thus, the application of a load smaller than the spring pretension will cause no displacement of the body members. When the pretension is exceeded by the loading force, gap A will begin to close. Applying additional load will cause gap A to close completely. Thus the bolt 4 allows calibration of the load cell unit such that the spring can be tensioned to the required degree to facilitate correct operation of the load cell unit as described below. Once the bolt 4 has been adjusted as required, locking tab 9 can be located against the bolt head to lock the bolt 4 in position. 'lihe locking tab pivots into engagement with the bolt head by way of a pin 10 which may also be provided with a screw thread to allow tightening of the same. . . .

lthe spring 6 is held in place between the first 7 and second 8 spring housing members, which are separated by a gap C when the load cell unit is in an unloaded condition. The lower spring housing 8 abuts the floor of the recess 5 and passes through an aperture 5a therein such that it contacts the upper surface of the load cell. When the spring housing 8 abuts the recess floor, such as when the load cell unit is unloaded or else positively loaded, the load cell is separated from the first body member 1 by a gap D. The gar)s C and D are larger than the gaps B and A respectively.

When a positive load is applied sufficient to overload the load cell unit, the gap 1Y will reduce to zero and the load will be supported by the body members I and 2. In this condition the gap ( will be non-zero and so the maximum load that can be applied to the load cell is effectively limited. (] ap D will increase separating the load cell 3 from the spring housing 7.

Similarly, under a negative, compressive force the gap B will reduce to zero and the spring housing will lift off the recess 5 floor but gap D will be non-zero, isolating the load cell from negative overloading. Gap C is engineered to be zero when the maximum allowable compressive force is applied to the spring, preventing spring damage due to excessive pretension.

()n application of compressive loading between the body members 1 and 2 loading is not applied to the load cell as the load cell mounting means is lifted clear off the body member, preventing compressive forces acting on the loadcell and avoiding overloading of the load cell in a negative (compression) loading direction. The vertical movement is ultimately limited through abutment between the channel 2b and land lb. . lthe mounting between the load cell 3 and the lower body member 2 is adjustable and takes the form of a bearing 11. lihe. ', . bearing has a curved surface 11a which abuts a correspondingly curved surface 2e provided in a recess in the lower body portion 2. lihe bearing 11 is connected to the load cell by a lower bolt 12 and allows the angular orientation to be ad lusted. This ensures accurate transfer of the applied weight to the load cell.

lihe lower spring housing has a neck portion 8a which is smaller than the aperture 5a through which it passes. Thus the neck portion Ba can move to a limited degree within the aperture 5a. This freedom of lateral movement makes allowance for the angular adjustment at the lower bearing such that the Orientation of the load cell can adjust under application of a load such that it Is arranged vertically in order to achieve the desired level calf accuracy. Such an arrangement also reduces or eliminates inaccuracies occurring due to the machining tolerances of the load cell unit components.

A locking tab may also be provided to lock the lower bearing in a fixed position.

Alternatively it will be understood that the load cell unit could be constructed according to the present invention with the mounting bolt disposed between the loadcell and the body member 2 and the bearing 11 located in the body member 1.

When the bolt 4 and spring housing are fitted beneath the kadcell 3 In this manner, the body member 2 would be lifted clear of the spring housing during negative overloading. Thus it will be appreciated that a load cell unit according to the present invention can effectively operate in an inverted condition without modification.

Figure 3 shows a side view of the load cell unit of figure 2 with : an integral antenna 13. The antenna is substantially flat in profile and is located within a recess of the load cell unit such. ,, . that the surface of the ante nna is substantially flush with the surface of the load cell unit. fin antenna of this sort may be. .., disc shaped and one or more antennas can be located on any or any combination of the front, back or sides of the load cell unit.

1'hc load cell unit may be self-contained and connected to a remote sensing device through a wireless connection. Thus hardware and software interfaces can be provided to allow weight and/or other data captured by the device to be displayed, processed and/-r stored by a remote device, without the need for a cable connection. lihe load cell unit may include data storage means and the remote devices may be portable or mounted in the cab of the mobile installation and may include, laptop pc's, PDA's, mobile phones, printers or the like.

Furthermore, a vehicle reversing display screen within the cab may usefully employed to display the capture or stored clata.

As shown in figure 5, the load cell unit can be fitted to an existing lifting apparatus such as a crane 14 on a vehicle such as a truck 16. The eye la in figure 1 is arranged to receive pin 18 such that the load cell unit is free to rotate about the axis 18c of the pin 18. The engagement between the pin 18 and the eye la is shown in further detail in figure 4. A spherical bearing surface 1 8a is provided on the pin 18 which sits in relation to the correspondingly shaped mounting 19 so' as to form a trunnion mounting. In the event that the truck 16 is not on level grounl in that the rear of the truck is disposed either above or below the level of the front of the truck, the loadcell unit will pivot about the bearing surface 18a upon application of a load, so as to attain a substantially vertical orientation. 'I'he load cell unit can thus rotate about 2 axes in relation to the pin 18 as shown by arrows 1 and F. ..

With an arrangement according to thus invention the stress,, applied to the loadcell is limited both in tension and in '' compression whilst maintaining a short overall length. The. . device can adjust to attain a vertical orientation necessary for, :.

improved accuracy of measurement.

Claims

What is claimed is: 1. A load cell unit comprising a load cell, said load

cell being located between first and second body members, the first body member with first connection means for a support member and the second body member with second connection means for a load to be lifted, wherein the load cell has one end thereo f connected with one body member and the other end thereof connected with the other body member, said body members being relatively displaceable when subject to an applied load across the relevant connection means, and the body members including inter-engaging means limiting the relative displacement thereof. :. .
2. A load cell unit according to claim 1, wherein the inter- . . engaging means are arranged to limit displacement under a tensile load. .
3. load cell unit according to claim 1 or 2, wherein the inter-engaging means are arranged to limit displacement under a compressive load.
4. 1\ load cell unit according to claim 1, wherein the first and second body members are telescopically eonneeted.
5. load cell unit according to claim 1, wherein the inter engaging means includes abutment means limiting displacement in each of an extension direction under positive load and a reverse compression direction under negative load.
6. A load cell unit according to claim 1, wherein either of the first or second body members is provided with a groove and the other of the first or second body members is provided with a land.
7. load cell unit according to claim 1, further including a deformable member arranged in the force path between the load cell and either of the first or second body members.
8. A load cell unit according to claim 7, wherein the deformable member can be provided with an initial tension by way of ad justable mounting means. .
9. load cell unit according to claim 1, wherein the unit:,.

includes one or more mounting means for adjusting the, position and/or orientation of the load cell in relation to the applied load. '
10. A load cell unit according to claim 9, wherein the mounting means is axially adjustable.
A load cell unit according to claim 10, wherein the mounting means includes a threaded bolt.
12. A load cell unit according to claim 9, wherein the mounting means includes locking means for selectively locking the load cell in a required position.
13. A load cell unit according to claim 9, wherein the mounting means allows adjustment of one of said body members in relation to the other body member.
14. 1\ load cell unit according to claim 9, wherein the mounting means includes a curved bearing surface.
15. A load cell unit according to claim 9, wherein the mounting means is disposed in the force path between the load cell unit and the supporting member.
16. load cell unit according to claim 1, wherein the application of an applied tensile load beyond a predetermined magnitude causes the first and second body members to engage so as to limit the load applied to the load cell.
17. A load cell unit according to claim 1, wherein the I ' application of an applied compressive load beyond a: . predetermined magnitude causes the load cell to disengage with either of the first or second body., member so as to isolate the load cell from the applied load. A. 2
18. i\ load cell unit comprising a housing, said housing having first connection means for a lifting apparatus and second connection means for a load to be lifted, a load cell located within the housing and arranged to receive a load applied across the relevant connection means, the housing including signal transmission means for transmitting a loading measurement recorded by said load cell tc' a remote receiving device.
19. A load cell unit according to claim 18, wherein the hocusing includes a recess for reception Off an antenna.
20. A load cell unit according to claim 19, wherein the antenna is substantially planar in shape.
21. A load cell unit according to claim 19, wherein the antenna is located within said recess such that a surface of the antenna is substantially flush with an outer surface of the housing.
22. A load cell unit according to claim 19, wherein the housing has two or more sides and an antenna is located with respect to one or more of said sides. e . e

- Abbe e.