EP2923186A1

EP2923186A1 - A weighing scale

Info

Publication number: EP2923186A1
Application number: EP13801694.4A
Authority: EP
Inventors: Roger HOLLIMAN
Original assignee: Adam Equipment Co Ltd
Current assignee: Adam Equipment Co Ltd
Priority date: 2012-11-12
Filing date: 2013-11-12
Publication date: 2015-09-30
Also published as: GB2507806B; GB2507806A; WO2014072750A1; GB201220339D0

Abstract

A weighing scale having at least a weighing assembly (17) supported by a base (4). The base (4) comprises two layers (8, 9) which are spaced apart to form a space (10) between them. The two layers (8, 9) are joined together at one or more points (11a, 11b, 11c). A weighing scale with a base (4) of this configuration is rigid and strong but also more lightweight than conventional weighing scales.

Description

A Weighing Scale

This invention relates to weighing scales. In particular, this invention relates to lightweight weighing scales.

Weighing scales are used to determine the weight of an object. Some types of conventional weighing scales comprise a weighing assembly and a casing. The casing commonly comprises a separate cover and base components that are bolted together. The weighing assembly comprises a weighing mechanism and a weighing platform (also known as a weighing pan) supported by the weighing mechanism.

The weighing assembly is usually mounted on the base of the casing where it is protected by both the base and the upper cover. Usually the weighing mechanism is entirely contained within the casing, and the weighing platform is provided outside the upper surface of the cover of the casing. This is commonly achieved by mounting the weighing platform on a carrier that is connected to the weighing mechanism, where this carrier can penetrate through the casing without contacting the casing. The weighing platform must be provided outside the casing so that a load can be applied to the platform. However, the cover may be provided with a recess in which the weighing platform can be mounted.

The upper casing of weighing scale or balance is typically made of cast metal such as cast aluminium or injection moulded plastic such as ABS. However the lower base section is typically a solid metal plate or casting to allow for heavier capacities to be loaded onto the weighing platform, this allows for increased stability of the mechanism. This makes the scale heavy, so increasing manufacturing cost and transportation costs. It is therefore an object of the present invention to provide a more lightweight set of weighing scales that are rigid, strong and capable of measuring large loads, but with additional thermal protection capabilities, and reducing potential deflection on the base assembly.

The invention is concerned particularly with weighing scales having an electronic weighing assembly, for example, weighing scales comprising a force motor balance mechanism, but may also apply to other weighing scales, such as those having weighing mechanisms with a load cell or monolithic weighing cell. Typically load cell units are used to weigh heavier capacity's but with lower resolution.

In particular, the present invention relates to weighing equipment that is typically suitable for use on a bench environment.

Suitable weighing equipment includes forced restoration scales that include a monolithic weighing cell. Generally, this forced restoration scales have low capacity, for example, can only measure weights up to a maximum of about 3kg, but high accuracy. For example, such scales can typically resolve from O.OOlg to O.OOOOOOlg.

The present invention may also relate to Strain Gauge scales. These are generally less accurate but carry higher weights. For example, Strain Gauge bench scales often have a capacity up to 20kg but typically only resolve lg up to O.Olg.

According to the present invention there is provided a weighing scale comprising a weighing assembly supported by a base, wherein the base comprises two layers which are spaced apart to form a space between them, wherein the layers are joined together at a plurality of points.

The base of the weighing scale also preferably supports the upper cover of the scales, wherein the upper cover at least partially surrounds the weighing assembly.

Preferably, the two layers of the base and the plurality of points joining the layers are formed as a single piece so that the base has a unitary (i.e. a single unit) construction. This unitary construction may be formed by extruding the base in one piece. Forming the base as a single unit is preferable as it means that there will be no joints that can move about causing instability.

Preferably, the base is formed from metal, preferably aluminium. Preferably, the aluminium base is treated. The layers forming the base are preferably parallel. When the weighing scale is on a horizontal surface, these layers may be configured to be horizontal. The layers may be joined together by one or more longitudinal and/or transverse ribs. The layers may additionally or alternatively be joined by one or more vertical or diagonal ribs (relative to the horizontal position when the scale is positioned on a horizontal surface). Such multiple ribs make the two parallel plates strong and rigid. The base is preferably produced by extrusion methods, to form a continuous frame assembly. Thus both layers and the ribs may be formed as a single extruded body.

The ribs may form hollow sections between the layers. Embodiments of the present invention have the advantage of being lighter than conventional weighing scales, but with increased rigidity. This is because the weighing scales have a base that is formed of two parallel layers with a spaces between the layers. The base is therefore lighter than a solid base that is made from a similar material, with similar overall dimensions. In some embodiments, the base of the weighing scales of the present invention had a weight to overall size ratio that is approximately one third to one quarter of the weight of an equivalent base of the same overall outside dimensions made of solid material.

The base of the weighing scale of the present invention also has the advantage of being very rigid. The base of the present invention has enhanced rigidity over a base made up of a single solid layer. The base of the present invention is therefore more able to withstand bowing or twisting, but with a greatly reduced component mass. The ability of a base to withstand bowing or twisting is key to enabling the scales to function in a reliable manner as bowing or twisting of the base affects the functioning of the weighing mechanism, especially as the mass added to the weighing platform increases or is added to the weighing platform Off Centre, known as Off Centre Loading. The base of the weighing scale of the present invention further has the advantage of being stronger than a base that comprises a single layer. The base of the present invention can therefore be subjected to greater loads without being misshapen.

Preferably, the layers are separated and joined together by multiple ribs extending substantially continuously along a length of the base. The ribs may extend along the base in the longitudinal direction. The ribs may also extend continuously along the base in a vertical and diagonal orientation, the combination of the 2 types of rib contributing significantly to the overall strength of the component.

The plurality of ribs extending along the base result in the formation of boxes between the ribs, where these boxes have a rectangular cross section. The top and bottom of these rectangular boxes are formed by the two layers of the base, and the ribs form the sides of these boxes. The formation of these boxes increases the strength of the base.

The weighing mechanism is preferably fixed to the base.

Preferably, the base is provided with slots on its upper surface, where the weighing mechanism is mounted next to these slots. Other parts of the weighing assembly (such as the battery box (if present) or the main printed circuit board (PCB)) can slot into these slots to fix them to the base. Parts of the weighing assembly may be formed from different modular sections, wherein the different modular sections that form the completed weighing scale can all slot into grooves on the base to allow for a modular build. The formation of the boxes between the layers means that the base is able to withstand compression and not deflect when the weighing mechanism is being fixed to the base. If the upper and lower layers of the base were to be compressed during assembly of the weighing scales, this would deform the structure of the base, causing it to bow and this would affect weighing performance which would clearly be disadvantageous.

The layers are preferably joined together by at least three ribs extending in the longitudinal direction. More preferably, the layers are joined together by at least five longitudinal ribs, and even more preferably, the layers are joined together by at least seven longitudinal ribs.

Preferably, the layers are joined together along all four of the side edges and additionally at multiple points within the structure of the base.

Preferably, the base has also a recessed portion. When the weighing scale is on a horizontal surface, the base is in contact with this horizontal surface and the recessed portion lies above (i.e. vertically higher than) this horizontal surface.

The recessed portion may comprise two vertical up stands, and a portion of the base extending between these two vertical up stands. The vertical up stands may additionally have grooves to locate additional essential sub-assemblies in the weighing balance or weighing scale. These up stands are orientated such that when the base is in its horizontal orientation, the recessed portion formed by the upstands, lies vertically higher than the other regions of the base.

Having this recessed portion in the base has the additional benefit of improving the stability of the weighing scales, by reducing longitudinal and diagonal twist and add additional thermal protection. Preferably, the recessed portion extends along the base by around 60% of the entire length of the base, in the longitudinal direction, and is spaced from the longitudinal edges of the base. The recessed portion may be positioned towards, or in the middle of, the base in the transverse direction. The recessed portion may also be symmetrical about a centre line bisecting the base in the longitudinal direction. There may also be more than one recessed portion in the base.

Preferably the space between the layers contains gaseous material such as air. As metal is such a good conductor of heat, forming a space between the layers of the base that contains such as air (a much worse conductor of heat) also has the advantage of forming a thermal barrier between the two layers of the base. This reduces the rate at which heat is conducted from the atmosphere surrounding the outside of the weighing scales to the internal mechanism and so reduces the thermal drift. It is advantageous to keep the internal mechanism of the scales at a constant temperature as thermal drift can interfere with the functioning of the weighing mechanism, especially if the weighing mechanism is an electronic balance such as a force motor balance, but may also apply to a weighing scale with a load cell, especially when used in higher resolution weigh scale.

Other gases, fluids and/or liquids may be in the space. This may alternatively or additionally be under a partial vacuum or a pressure less than 1 atmosphere.

Preferably, the weighing assembly is secured to the base. The weighing assembly may be secured to the horizontal upper face of the base by means of a three point mounting.

The weighing mechanism is preferably secured to the base at points at which the layers are joined together directly by way of vertical ribs.

In embodiments of the invention where the base comprises plurality of ribs extending substantially continuously along a length of the base to form hollow sections, the weighing assembly is preferably secured to the base by means that pass through the ribs. Preferably, the securing means (for example, bolt) is wider than the ribs. If the securing means is wider than the ribs, then the securing means will be positioned within breaks in the ribs. The base may be pre-formed with such breaks in the ribs.

Having securing means that pass through the ribs is advantageous as this

arrangement helps to prevent the base from bending when the weighing mechanism is secured to the base.

Preferably, at least two vertical walls project from the base; the weighing assembly being fixed equally in between the two walls to firmly secure the weighing assembly to the base. Preferably, the two vertical walls also form part of the separate internal thermal cover. Which completely encases the weighing mechanism. This fixture links the separate thermal cover to the base, allowing a more constant temperature to be maintained within the weighing mechanism area.

There is preferably at least one baffle plate bolted in between the extruded base uprights. This baffle plate helps to prevent heat transfer to the weighing mechanism.

Preferably, the two walls are positioned inwardly of at least two of the outer edges of the base. The walls preferably project upwardly when the base is in a generally horizontal orientation. It is preferable to have two walls positioned inwardly of the outer edges of the base as this allows a weighing assembly comprising a much smaller weighing mechanism to be secured to the base. This arrangement also allows for sub assemblies generating heat or electrical noise to be located outside the inner thermal cover while still being sited inside the main case.

The walls will generally be integral parts of the base, but could be removable.

Preferably they are part of a single unitary construction forming the base. This may be formed by extrusion for example.

In general, the smaller the weighing mechanism, the lighter the weighing assembly will be. In addition, having a smaller weighing mechanism is advantageous as the smaller the weighing mechanism, the quicker the scales stabilise when there has been a large change in the external temperature. The smaller mechanism also allows for a smaller overall case dimension, which aids user operating area and reduces shipping costs, there is also a reduction in raw material used.

Preferably the weighing assembly comprises a chassis, and the chassis is preferably secured to the base at three integral mounting points. The weighing assembly may comprise an internal case surrounding the weighing mechanism. The internal case creates another thermal barrier and so helps protect the weighing mechanism from fluctuations in the ambient temperature. Preferably, the base is manufactured by an extrusion process.

In some embodiments, the scales can measure loads up to 20 kg in weight.

However, the invention is applicable to scales for measuring other values of loads. The base may have at least one adjustable foot. It may have two adjustable feet and a third fixed foot which also forms a spirit level. The weighing scale therefore has the provision to adjust for non-level surfaces, as non-level surfaces have a negative affect on the operation of weighing equipment. The adjustable feet may be located within the base by way of two stepped threaded bushes. These bushes may be located within the base by way of an interference fit with the base. In addition, they may also be fitted with an anti rotation face which locates on a machined edge of the base to prevent the bush from turning when the foot is adjusted. The upper and lower horizontal faces are prevented from collapsing in on them selves by way of the step in the bushing.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows an embodiment of a weighing scale;

Figure la shows an alternative embodiment of a weighing scale;

Figure 2 shows an end view of a base of a weighing scale;

Figure 3 shows a perspective view of the base of Figure 2;

Figure 3 a shows a stepped bushing arrangement;

Figure 4 shows a top view of the base of Figure 2;

Figure 5 shows the base of Figure 2 with a weighing assembly and feet attached; and

Figure 6 shows a cross sectional view of Figure 5; Figure 7 shows the top view of an alternative embodiment of a base of a weighing scale;

Figure 8 shows an enlarged version of a section of the base of Figure 7.

Referring to Figure 1, an embodiment of a weighing scale 1 is shown. The weighing scale 1 has a casing 2 comprising a top cover 3 and a base 4. A digital display window 5 is mounted in an aperture in the top cover 3.

The weighing scale 1 of Figure 1 is also provided with a circular weighing platform (not shown) outside the upper surface of the top cover 3. In Figure 1, the circular weighing platform of the weighing scale 1 is surrounded by a removable protective cylindrical cover 7. The cylindrical cover 7 helps to protect the weighing platform from the effects of atmospheric change, for example from movement in the air, to help improve the accuracy of the reading generated by the weighing scale 1.

In Figure la, the circular weighing platform of the weighing scale 1 is surrounded by a protective rectangular cover 7a. The rectangular cover 7a has a sliding door section. When the door is shut, the rectangular cover 7a helps to protect the weighing platform from the effects of atmospheric change, for example from movement in the air, to help improve the accuracy of the reading generated by the weighing scale 1. However, the door of the cover 7a can be opened to enable a user to reach the weighing platform.

Referring to Figures 2 to 8, two embodiments of the weighing scale base 4 are shown. The base 4 of these embodiments have a recessed portion 6 that is raised relative to the two outer sections of the base 4. The base 4 is also symmetrical about a centre line L bisecting the base in the longitudinal direction.

The base 4 is formed of two layers 8, 9. The two layers 8, 9 are spaced apart so as to form space 10 between them. The layers 8, 9 are joined together by a plurality of ribs 11a, 1 lb, 11c that extend longitudinally along the length of the base. The layers 8, 9 are also joined together at the longitudinal edges 16 of the base 4. Any other spacing means may be utilised. The base 4 shown in Figures 2 to 8 is produced by an extrusion process. Extrusion processes are used to produce objects with a fixed cross-sectional profile and can be used to produce objects with complex cross sectional profiles.

The plurality of ribs 11a, 1 lb, 11c divide the space between the two layers into a number of separate spaces 10a, 10b, 10c, lOd. In some embodiments of the invention, these spaces are filed with air. In other embodiments, the spaces are vacuums.

The ribs 11a, 1 lb, 11c shown in the embodiment illustrated by Figures 2 to 4 extend continuously along the length of the base 4. The ribs 11a, 1 lb, 11c provide structural support to the base 4 and enable the base to withstand high loads, i.e. the ribs prevent the two layers 8, 9 from being compressed together.

Other rib arrangements may be used.

In the embodiment shown in Figures 2 to 6, the base 4 additionally comprises stepped bushings 12a, 12b, 12c. The stepped bushings 12a, 12b, 12c are inserted into the base 4 to provide plain holes that can be used to fix other parts of the weighing scale 1 to the base 4. These stepped bushings can be made of metal, for example brass.

There are 2 types of bushing included, plain stepped bushings are used to fix the weighing mechanism, and internal calibration, and threaded bushings are used to locate the feet assemblies. For example, Figures 5 and 6 show feet 22 attached to the base 4 of the weighing scale 1 through the bushings 12b. These stepped bushings can be made of metal, for example, brass. Adjustable feet may be attached to bushes and one such adjustment foot is shown in Figures 4 and 5, which show a knurled adjustment mechanism 30. An adjustable foot may also be attached to the other one of the threaded foot bushes 12b, but this is not shown for clarity.

Figure 3a shows a stepped bushing such as 12a. This includes a bottom part 40, a wider central part 42 and an even wider upper part 41, all of these parts being generally cylindrical and coaxial. Thus, the bottommost plate (layer) 8 lines in the step between parts 40 and 42, and the uppermost plate (layer) 9 lies directly under the step formed between parts 42 and 41. Figures 5 and 6 show weighing assemblies attached to the base 4 via bushings.

Figure 6 shows the weighing assembly 17 attached to the base 4 by the chassis, where the chassis 21 is screwed into the base 4 via the bushings 12b and 12c.

In further embodiments of the invention, the base 4 can be provided with threaded bushings and parts of the weighing scale 1 can be attached to the base 4 via both the threaded bushings and the points of connection between the two layers 8, 9.

Figures 2 to 6 also show an embodiment of the weighing scales 1 in which the base is provided with a spirit level and foot assembly 15. The spirit level/ foot assembly is inserted into the base 4 and is used to determine how level the mechanism is, as this affects the operation and calibration of the weighing scales 1 are when they are placed on a surface.

As shown in Figures 2 to 4, the base 4 has walls 14 that project from the surface of the upper of the two layers 8, 9 forming the base. The walls 14 can also be used to secure parts of the internal mechanism of the weighing scale 1, for example, parts of the weighing assembly, to the base 4.

Figures 5 and 6 show an embodiment of a weighing assembly 17 that has cover 18 surrounding the parts comprising the weighing mechanism (not shown in the figures). For example, the cover 18 surrounds the chassis 21 and separates the printed electronic circuit board (not shown in the figures) from the weighing mechanism. However, the weighing platform 23 must project outside the cover 18 so that it is accessible to the user. Therefore, in the embodiment shown in Figures 5 and 6, a stem 20 that supports the circular weighing platform 23 projects through an aperture in the cover 18. In alternative embodiments of the invention, the weighing platform can take many different shapes. For example, it can be rectangular or square.

Referring to Figures 5 and 6, the cover 18 of the weighing assembly 17 is attached to the upper horizontal plate 9 of the base 4. As shown in Figure 5, the cover 18 can slot onto of the walls 14 of the base 4. However, in alternative embodiments of the invention, the cover 18 can fit over the walls 14 so that it completely contains the walls 14, or the cover 18 can fit within in the walls 14 so that the walls hold the weighing assembly 17 in place.

Referring to Figures 2 to 4, the base 4 also comprises bolt fixings 13 to allow the top cover 3 to be fitted onto the base 4 to form the casing 2. In some embodiments of the invention the cover 3 and base 4 screwed, glued or otherwise affixed together. In the embodiment shown in Figures 7 and 8, the base 4 does not comprises stepped bushings. Instead, the other parts of the weighing scale are fixed to the base using bolts that are fitted through bolt holes 50, 60 that pass directly through one of the ribs 11a, 1 lb, 11c. These bolt holes 50, 60 have different sizes as the size is dependent on which part of the weighing mechanism is fitted to that part of the base 4.

Claims

1. A weighing scale comprising a weighing mechanism supported by a base, wherein the base comprises two layers which are spaced apart to form a space between them, and wherein the layers are joined together at a plurality of points.

2. A weighing scale as claimed in Claim 1, wherein the layers are parallel.

3. A weighing scale according to Claim 1 or 2, wherein the layers are joined together by a plurality of ribs extending substantially continuously along a length of the base to form hollow sections.

4. A weighing scale according to any Claim 3, wherein the hollow sections are rectangular in cross section.

5. A weighing scale according to any one of Claims 1 to 2, wherein the layers are joined together along at least both edges of the base.

6. A weighing scale according to any preceding claim, wherein the base has a recessed portion.

7. A weighing scale according to any preceding claim, wherein the space between the layers contains gaseous material such as air.

8. A weighing scale according to any preceding claim, wherein the weighing mechanism is secured to the base at three location points.

9. A weighing scale according to any preceding claim, wherein the weighing mechanism is secured to the base at points at which the layers are joined together directly by way of vertical ribs.

10. A weighing scale according to any preceding claim, comprising two vertical walls that project from the base in directions perpendicular to the plane of the layers, the weighing mechanism being fixed to the base equi-spaced between the two walls, securely fixing the weighing mechanism to the base.

11. A weighing scale according to Claim 10, wherein the at least two perpendicular walls are positioned inwardly of at least two of the outer edges of the base.

12. A weighing scale according to any one of Claims 6 to 11, wherein the weighing mechanism comprises a chassis, and wherein said chassis is secured to the base.

13. A weighing scale according to Claim 12, wherein said chassis is secured to the base by way of a three point mounting.

14. A weighing scale according to any preceding claim, wherein the base is composed of metal.

15. A weighing scale according to any preceding claim, wherein the base is composed of aluminium.

16. A weighing scale according to any preceding claim, wherein the base is manufactured by an extrusion process.

17. A weighing scale according to any preceding claim, wherein the two layers of the base and the plurality of points joining the layers are formed as a single piece so that the base has a unitary construction.

18. A weighing scale according to any preceding claim, adapted to measure loads up to 20 kg in weight.

19. A method of manufacturing a weighing scale base, the base comprising two layers spaced apart to form a space between them, and the layers of the base being joined together at a plurality of points, the method comprising extruding the base.

20. A weighing scale substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.

21. A method substantially as hereinbefore described with reference to the

accompanying drawings.