GB2214320A - Weighing apparatus - Google Patents

Abstract

Weighing apparatus 1 has springs S extending from support piece 2, with a rack 3 spring biased in contact with pinion 4a rotatable about axis 5 in pinion housing 4. Housing 4 is mounted to plastics casing 6 by self-tapping screws 5a and the pinion 4a is mounted in nylon bushes 4b having external crushable ribs 4c locating in bores in the housing 4. Each bush 4b has an elongate nose portion 4<1>b and the nose portion 4<1>b of bush 4b which is adjacent to and which locates a bore <b1> in the casing 6 provides along with the screws 5a, a pre-set centred location of housing 4 and pinion 4a relative to the casing b. A nose 4'b on bush 4b adjacent plastics dial 8 locates in a central receiving hole in the dial to avoid float between the dial and pinion 4a. Dial 8 is non-circular, conforming to the shape of casing 6 and is retained in position by a transparent cover 7 snap-fitted to casing 6. An adjusting mechanism 11 has a wide frusto-conical wheel 102 which is direct operating and located in window 103. Wheel 102 operates pivoted support links d to adjust the upwards or downwards spatial location of springs S, and thereby the angular position of pinion 4a (and thus the angular location of a pointer attached thereto) via rack 3. <IMAGE>

Description

WEIGHING APPARATUS This invention relates to weighing apparatus, more particularly of a spring balance type.

In such weighing apparatus involving purely a mechanical action, as opposed to incorporating electronics to give a digital readout of the weight of an object, there have been relatively few dramatic improvements made in recent years; this is because the technology employed is tried and tested and could now be described as being based upon yesterday's technology.

Nevertheless, High-tech products involving electronics can be considerably more expensive to produce and may be disadvantageous in other ways and, therefore, there is still a demand for a purely mechanical weighing apparatus of the spring balance type. Even so it is believed that existing mechanical spring balances tend to be disadvantageous from some points of view, in their overall design, ease of component assembly, accuracy and durability, especially when contrasted against their electronic counterparts.

It is an object of the present invention to provide weighing apparatus which is improved in one or more respects.

According to one aspect of the present invention there is provided weighing apparatus comprising a casing, a dial and a pointer mounted on a spindle projecting from a pinion in a pinion housing, said spindle being rotatable relative to the casing and dial to register a weight measurement on the dial, the arrangement being such that during assembly of the apparatus, the spindle is automatically centrally aligned relative to the casing on assembly of a pinion housing to the casing and/or the dial is automatically centrally located as said dial is introduced onto the spindle, and the angular orientation of the dial in the casing is preferably automatically locked on assembly of a cover onto the casing, said casing, preferably, being a one-piece moulding.

Usually, the pinion housing will be secured to the casing by self-tapping screws introduced into prepared receiving holes in the casing and, preferably a nose on a bush mounting the pinion in the housing is received in a central locating recess in the casing to centralise the housing relative to the casing. The dial may be centralised by a nose on a second bush in the pinion housing and through which second bush the spindle projects, the external dimensions of the nose conforming to the dimensions of a receiving hole in the dial. The dial may conform to the general shape of the casing and rest on a peripheral wall thereof (and possibly be accommodated in a recess in the wall to substantially prevent relative rotation thereof, or such relative rotation may be prevented by the cover itself). The casing is preferably of ABS plastics.The weighing apparatus may have any one of many advantageous features mentioned in the following description such as the zeroadjusting mechanism, rack, adjusting support links, dial and hanger as herein described.

Further according to the present invention there is provided weighing apparatus comprising a rack and pinion assembly, said pinion being mounted in a pinion housing by a bush having a nose portion on which a dial of the apparatus is centred relative to the pinion housing and casing, said dial, preferably, being automatically angularly located on assembly of a cover to the casing, the casing, preferably, being snap-engageable with the cover, said bush, preferably, being of nylon and preferably having crushable ribs which hold the bush in the pinion housing.

Further according to the present invention there is provided a weighing apparatus having one or more of the following features: a) Means for automatically self-centring a dial relative to a casing and pinion housing of the apparatus, as the dial is introduced onto a spindle connected to a pinion in said housing, the spindle being connected to a pointer; b) Means for automatically angularly locating a dial, preferably on assembly of a cover onto a casing of the apparatus; c) Means for automatically correctly aligning component parts of the apparatus comprising casing, pinion housing and dial on assembly of the apparatus; d) Bushes (preferably nylon) for mounting a pinion in a pinion housing said bushes having external, axial, crushable ribs to retain the bushes in the housing, and, preferably, having nose portions; the nose portion of one bush serving to mount and automatically self-centralise a dial, and the nose portion of the other bush serving to centralise the pinion housing relative to a casing of the apparatus; e) A one-piece casing snap-engageable with a transparent cover; f) A pinion housing attached to a casing (preferably of plastics) with the aid of screws and, preferably, the remainder of the assembly of the apparatus not requiring any screws; g) A zero-adjusting mechanism comprising adjusting support links which are precision die-castings, preferably of zinc or mazac, said support links, preferably, being mounted in a symmetric arrangement with a direct acting adjusting wheel mounted on an axis which is radial of a casing and of a dial of the apparatus; h) A zero-adjusting mechanism having a spring-loaded adjusting wheel, preferably spring loaded by a Bellville washer or leaf spring; i) A top hanger of I-shaped cross-section made from glass fibre (preferably long fibre) reinforced material (e.g. nylon) and, preferably, said hanger is located on pins on a casing, said pins preferably being tapered and integral with the casing and heat sealed to hold hanger to the casing, j) A rack and pinion assembly with the rack being made of steel, k) A dial of high impact polystyrene/ABS plastics, preferably, with a moulded guide rail for two parallel springs of the apparatus.

An embodiment of weighing apparatus in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: FIGURE 1 shows a cut-away front elevational view of the weighing apparatus; FIGURE 2 shows a sectional side view taken on the line II-II of FIGURE 1; FIGURE 3 shows a sectional detail view taken on line III III of FIGURE 1; FIGURE 4 shows a sectional detail view taken on line IV IV of FIGURE 1; FIGURE 5 shows a detail view of a bush from a pinion housing of the apparatus; FIGURE 6 shows an adjusting support link from an adjusting mechanism of the apparatus; FIGURE 7 shows a fragmentary cross-sectional view taken through a prior art weighing apparatus of similar type to the apparatus of the present invention; FIGURE 8 shows a zero adjusting mechanism of the prior art apparatus of FIGURE 7;; FIGURES 9 and 10 show views of a leaf spring on an enlarged scale which is employed as an alternative component part, and FIGURES 11 to 13 are views similar to FIGURES 1, 2 and 4 showing a modification, FIGURE 12 is taken on line XII XII of FIGURE 11, and FIGURE 13 is taken on line XIII XIII of FIGURE 11.

It is believed that, the weighing apparatus of a spring balance type 1, as shown in FIGURES 1 to 6 of the drawings, incorporates many new individual features and these features alone or combination may be patent ably inventive.

The content of Registered Design Application No.

1045766 shows the outward appearance of the apparatus 1 and is herein incorporated into this specification by reference.

Overall, the general layout of parallel mounted close-coiled springs arranged extending upwardly from a lower support piece 2, with a rack 3 spring biassed into contact with a pinion 4a rotatable about a fixed axis 5 in a pinion housing 4, is known. The apparatus 1 differs from the prior art apparatus 1' (see FIGURES 7 and 8) in the design of casing 6, cover 7, dial 8, pointer 9 and pointer assembly 10, pinion 4a and pinion bushes 4b, pinion housing retention means 5a, zero adjusting mechanism 11 and in the materials used for various parts.

To aid in contrasting the inventive features of the weighing apparatus 1 with the prior art, FIGURES 7 and 8 show views of some parts of a typical prior art weighing apparatus 1'. FIGURES 7 and 8 are views from a weighing apparatus of the Applicant, which is the "Salter model 235 series", and the content of the data sheets on model Nos. 235-6, and 235-10 are herein incorporated into this specification by reference.

FIGURE 7 shows a fragmentary section of the casing 6', transparent cover 7', and circular dial 8' and FIGURE 8 shows the zero adjusting mechanism 11'. Parts similar to those of the Applicant invention shown in FIGURES 1 to 7 are indicated by the same reference numeral followed by an oblique dash.

One improvement over the prior art arrangement 1'; not evident from the FIGURES, resides in the mounting of the pinion 4a in the diecast pinion housing. Previously, the pinion was made of steel, zinc plated and passivated and mounted in axially spaced, plain, generally cylindrical bearing bushes made of brass. The pinion housing 4 itself has not been changed in shape or material but the bushes are now made of Delrin (nylon) having a good low friction bearing quality.

Additionally, the manner of locating the bushes in place is now much improved. Previously, once the bushes had been assembled into the pinion housing in the prior art arrangement, a peening operation on the housing was necessary to hold the outermost bush (bush nearest the dial) in the housing i.e. to axially locate the bush.

The bores in the housing for receiving the bushes are slightly tapered in a direction towards the central (toothed) part of the pinion both in the prior art and in the Applicant's arrangement. Additionally, and as shown more particularly in FIGURE 2 and FIGURE 5, the nylon bushes 4b have external raised ribs 4c which are slightly tapered. These ribs 4c are crushable to axially and radially locate the bushes 4b (a single bush is shown in enlarged detail in FIGURE 5) in their respective bores in the housing 4 as they are introduced therein, thereby obviating the need for any peening operation or any compressing of the external diameter of the bushes as may take place in the prior art arrangement.

A further improvement resides in mounting the housing to the casing. Previously, the housing 4 itself was mounted on a central indented portion of a metal casing 6' by rivetting. The Applicant's casing 6 is injected moulded from ABS plastics with a spark erode finish to improve appearance. In the prior art, rivets were used to hold the housing 4 to the casing 6' at similar locations to the screws 5a (pinion housing retention means) shown more particularly in FIGURE 1.

Rivetting the housing to the casing tends to cause problems in proper alignment of the housing (and thus of the pinion) centrally of the casing. The diameter of the rivets (not shown) does not usually match exactly the diameter of the rivet receiving holes, which can allow a lateral movement of the housing itself relative to the casing. In contrast, the Applicant provides two self tapping screws 5 which screw into receiving holes moulded into a central raised, integrally moulded base b on the interior of the casing 6. The base b is the same overall shape as the bottom 4d, although it is not solid, and provides a proper seating for the housing 4.

The nylon bushes 4b are identical with one another and, therefore, advantageously, the same moulding can be used for each bush. Most importantly, and in contrast to the prior art, each bush 4b is provided with a central elongate nose portion 4'b of reduced external diameter.

The nose portion 4'b of the bush 4b adjacent to the casing 6 is received in a central, moulded, matching, receiving bore b' in the base b. Therefore, the combination of self-tapping screws 5a and 'this noseportion 4'b provides a reliable positive pre-set, centred location of the housing 4 and pinion relative to the casing 6 in a manner such that any problems in alignment are substantially obviated.

Additionally, and also most importantly, the nose 4'b on the bush 4b adjacent the dial 8 locates in a central receiving hole in the dial 8, which receiving hole is of matching diameter to the external diameter of the nose 4'b. Therefore, there is no float between the dial and the pinion (unlike in the prior art where no such nose is provided) and the dial is fixed independently of the central spindle s extending from the pinion 4a. Therefore, assembly of the pinion housing 4 to the casing 8 and dial location is much simplified since it is automatically self-centralising.

The dial 8 itself is completely different to that of the prior art dial 8'. The dial 8 is moulded from high impact polystyrene/ABS plastics, is self-coloured, print and scratch and damage resistant and cheaper to produce than its prior art aluminium counterpart. The shape of the dial 8 is non-circular, instead of the circular prior art dial, and its dimensions conform to shape of the casing 6 i.e. the edge of the dial 8 rests on the upper edge of the peripheral wall 6a of the casing. The underside of the dial 8 is also provided with two, relatively wide, parallel, slightly raised ribs R (not shown) which extend parallel to, and overlie, the axis of the coiled springs. These ribs R rest on the springs S in the finished assembly, to reduce rattle and act as guide ribs for the springs.The angular location of the dial 8 relative to the casing 6 is fixed when the transparent cover 7, of similar shape to the casing and dial is snap-fitted to the casing by means of four locating lugs L on the casing 6. The lugs L are snapfitted into matching receiving slots on the cover 7 as the cover is introduced on the casing.

Thus, overall assembly of the pinion housing and correct location of the dial in the weighing apparatus is much simpler, automatic, and more accurate than in the prior art arrangement. In the prior art arrangement (see FIGURE 7) the casing 6' comprises a first lower portion X similar in function to the casing 6, but also a second, individually formed steel mounting ring y for the circular dial 8'. The dial 8' then has to be fixed relative to the ring y by two diametrically spaced screws (only one shown at Z). This prior art design necessitates the provision of ten screws (two shown in FIGURE 7) to assemble the two parts of the casing x,y, and the cover 7 onto the casing, instead of the simple two part (rather than 3 part assembly) snap-engageable casing 6 and cover 7 not requiring the use of any screws.

Such an improvement has obvious advantages namely, for example, in the time and manner of assembly of the weighing apparatus. The cover 7 is shaped with a central flat area 7a (see FIGURE 2) to avoid scratching which might take place if the central region were round and the apparatus set down with the cover 7 resting on a support surface.

The pointer 9 is now of plastics and is a simple push-fit onto an externally splined collar 9a. The collar 9a is slipped onto the threaded spindle s and retained axially by a nut 13. The design of pointer and assembly 10 to the spindle is different to the bush and pressed pointer employed in the prior art arrangement (not shown) but may be generally similar to arrangements already known in other technical fields, and therefore, will not be discussed in further detail. The splined collar 9a allows the pointer 9 to be located on the spindle in any one of a multiplicity of angular positions whereas the prior art pointer has a central portion with a square recess receiving a square projection on the spindle so that there is only one sensible relative location of the pointer and spindle (out of four fixed possible relative angular locations).

The rack 3 is of similar shape and material to the rack employed in the prior art mechanism.

The casing 6 is provided with reinforcement ribs or guide rails 6a, which once again extend parallel to the axes of the coiled springs S and help prevent rattle.

The springs S, aluminium support piece 2, and spring biassing arrangement a for the rack are all identical to the prior art arrangement. The upper ends E of the springs S are each located in a hole in one of a pair of identical adjusting spring support links d of the adjusting mechanism 11. An adjusting support link d is shown in more detail in FIGURE 6.

As should be evident from the prior art depicted, the form of adjusting mechanism is completely different to that previously employed. The adjusting spring support links d' used in the prior art arrangement are metal pressings which are formed with rough edges requiring a subsequent machining operation to be performed to remove as much of the roughness as possible.

Nevertheless, it has not been possible, for example, to achieve a smooth radius blend particularly on the holes which receive the spring ends E. Therefore, the machining process is not entirely satisfactory and further finishing is required. These support links d' are of mild steel and need the further operation of zinc plating to protect them from corrosion effects.

The adjusting support links d of the Applicant invention are changed in shape to give additional strength and are precision diecastings of zinc or Mazak.

The precision diecasting process is a relatively cheap process comparable with the prior art pressing process and additionally a chamfered edge ce is easily provided on the receiving hole for the spring ends E (anchor point) and also on the holes h which receive pivot pins 101 which allow pivotal motion of the support links d.

Thus the precision diecasting obviates need for machining and finishing, provides a smooth contact area, substantially prevents "sticking", enables loads to be evenly distributed and overall increases accuracy. The support links d could be precision steel pressings but such a process is expensive.

The adjusting mechanism 11 now has a wide frustoconical wheel 102 of Verton which is direct operating and, advantageously, the arrangement is symmetric about a plane taken on line II-II of FIGURE 1. The wheel is located in the window 103.

The adjusting wheel 102 co-operates with an adjusting screw 102a having a square head 102b seated in the top hanger portion as shown in more detail in FIGURE 4. The thread of the screw engages a hexagon nut n mounted in a hexagon shaped recess in the wheel 102 so that rotation of the wheel 102 about its axis, in the appropriate direction moves the head 102b up and down.

The head 102b operates directly on the ends e of the support links d to pivot the support links about their respective pins 101, and thus adjust the upwards or downwards spatial location of the springs S, and accordingly the angular position of the pinion 4a (and thus the angular location of the pointer attached to the spindle) via the rack 3, in a manner which should be self-evident in order to adjust the zero location of the pointer. A Bellville washer W is positioned as shown in the Figures adjacent nut n (see FIGURE 2) to give some degree of spring loading.

In some instances it has been found that the Bellville washer does not collapse sufficient and advantageously a leaf spring is now used instead. The form of leaf spring found to be most satisfactory is shown in FIGURES 9 and 10. The thickness of the spring material is 0.5mm; dimensions are shown in the FIGURES in millimetres.

As shown in the prior art, there is an adjusting wheel or spindle 102' located at an angle to the vertical axis through the apparatus and this is an indirect operating arrangement with one gear support link backedup by the other.

The top hanger portion 104 which receives the wheel 102 and adjusting support links d has shoulders 105. The casing 6 has integrally moulded, slightly tapered mounting pins 106 (see FIGURE 3). The hanger portion 104 is formed separately from the casing by injection moulding and mounted thereto by introduction into a slot in the casing in a direction generally downwardly at right angles to the paper as shown in FIGURE 1 and parallel to the axes of pins 106, such that the pins extend through matching receiving holes in the shoulders 105. The free ends of the pins are heat sealed to retain the hanger thereto (akin to a rivetting process) and the wheel 102 seats in an open slot in the casing 6 so that it is assessible from the rear of the apparatus 1.

The material of the hanger 104 is critical since it takes the load during weighing. The material and crosssectional shape (generally I-section) have been carefully chosen for added strength and the material selected is a glass fibre reinforced nylon. The fibres are long fibres and generally follow the pattern of the I-section for added strength. The material may be Verton I.C.I. The particular weighing apparatus shown should have a hanger which will take a 100 kg capacity and for overload safety 200 kg. In fact the design allows approximately a load of 500 kg. A lamination technique was tried for the hanger with other plastics materials but the long glassfibre reinforced material was found to be the best coupled with the I-cross section form.

FIGURES 11 to 13 are views similar to FIGURES 1, 2 and 4 in which part 102b has now been replaced by part 102'b having the configuration as shown in FIGURES 11 to 13. The square head 102b has been replaced by cylindrical head 102'b and has a guide notch for the ends e of the suppport links d. It is believed that this arrangement represents an improved, more reliable action over that shown in FIGURES 1, 2 and 4.

It is to be understood that the scope of the present invention is not to be unduly limited by the particular choice of terminology and that a specific term may be replaced by any equivalent or generic term where sensible. Further it is to be understood that individual features, method or functions related to the weighing apparatus or combinations thereof might be individually patentably inventive.

Further, and in summary, the present invention may provide weighing apparatus of a type with suspended springs operating with linear displacement proportional to the load and the reaction via the rack and pinion indicates a weight measurement reading on equi-spaced divisions marked on the dial. The complete assembly may be well protected from all types of contaminants and be corrosion free. The pinion bushes may be made from acetal ensuring minimal friction and providing positive casing and dial locations to ensure concentric movement to dial reading line and fitment may be by tapering crushable ribs. The pointer and bush may be acetal injection moulded and serrated to give positional location.

The zero adjuster may be made from long glass fibre reinforced nylon for strength encapsulating a standard hexagon nut. The dial may be H.I.P.S. injection moulded and the cover may be injection moulded from clear polycarbonate. All parts may interlock and be self snap fixing on assembly. The I-section form of the hanger may maximise its long glass fibre orientation to enhance strength. The support links d provide smooth load contact surfaces and clean positive spring locating and pivot axis; machining and plating to prevent corrosion are thus eliminated.

Claims (10)

1. Weighing apparatus comprising a casing, a dial and a pointer mounted on a spindle projecting from a pinion in a pinion housing, said spindle being rotatable relative to the casing and dial to register a weight measurement on the dial, the arrangement being such that during assembly of the apparatus, the spindle is automatically centrally aligned relative to the casing on assembly of a pinion housing to the casing and/or the dial is automatically centrally located as said dial is introduced onto the spindle, and the angular orientation of the dial in the casing is preferably automatically locked on assembly of a cover onto the casing, said casing, preferably, being a one-piece moulding.

2. Apparatus as claimed in Claim 1 in which the pinion housing is secured to the casing by self-tapping screws introduced into prepared receiving holes in the casing.

3. Apparatus as claimed in Claim 1 or Claim 2, in which a nose on a bush mounting the pinion in the housing is received in a central locating recess in the casing to centralise the housing relative to the casing.

4. Apparatus as claimed in Claim 3 in which the dial is centralised by a nose on a second bush in the pinion housing and through which second bush the spindle projects, the external dimensions of the nose conforming to the dimensions of a receiving hole in the dial.

5. Apparatus as claimed in Claim 4 in which the dial conforms to the general shape of the casing and rests on a peripheral wall thereof.

6. Apparatus as claimed in Claim 5 in which the dial is accommodated in a recess in the wall to substantially prevent relative rotation thereof or, alternatively, is such that relative rotation is prevented by the cover itself.

7. Apparatus as claimed in any one of the preceding claims in which the casing is of ABS plastics.

8. Weighing apparatus comprising a rack and pinion assembly, said pinion being mounted in a pinion housing by a bush having a nose portion on which a dial of the apparatus is centred relative to the pinion housing and casing, said dial, preferably, being automatically angularly located on assembly of a cover to the casing, the casing, preferably, being snap-engageable with the cover, said bush, preferably, being of nylon and preferably having crushable ribs which hold the bush in the pinion housing.

9. Weighing apparatus having one or more of the following features: a) Means for automatically self-centering a dial relative to a casing and pinion housing of the apparatus, as the dial is introduced onto a spindle connected to a pinion in said housing, the spindle being connected to a pointer; b) Means for automatically angularly locating a dial, preferably on assembly of a cover onto a casing of the apparatus; c) Means for automatically correctly aligning component parts of the apparatus comprising casing, pinion housing and dial on assembly of the apparatus; d) Bushes (preferably nylon) for mounting a pinion in a pinion housing said bushes having external, axial, crushable ribs to retain the bushes in the housing, and, preferably, having nose portions; the nose portion of one bush serving to mount and automatically self-centralise a dial, and the nose portion of the other bush serving to centralise the pinion housing relative to a casing of the apparatus; e) A one-piece casing snap-engageable with a transparent cover; f) A pinion housing attached to a casing (preferably of plastics) with the aid of screws and, preferably, the remainder of the assembly of the apparatus not requiring any screws; g) A zero-adjusting mechanism comprising adjusting support links which are precision die-castings, preferably of zinc or mazak, said support links preferably, being mounted in a symmetric arrangement with a direct acting adjusting wheel mounted on an axis which is radial of a casing and of a dial of the apparatus; h) A zero-adjusting mechanism having a spring-loaded adjusting wheel, preferably spring loaded by a Bellville washer or leaf spring; i) A top hanger of I-shaped cross-section made from glass fibre (preferably long fibre) reinforced material (e.g. nylon) and, preferably, said hanger is located on pins on a casing, said pins preferably being tapered and integral with the casing and heat sealed to hold hanger to the casing, j) A rack and pinion assembly with the rack being made of steel; k) A dial of high impact polystyrene/ABS plastics, preferably, with a moulded guide rail for two parallel springs of the apparatus.

10. Weighing apparatus substantially as herein described with reference to FIGURES 1 to 6 of the accompanying drawings or substantially as modified with reference to FIGURES 9 and 10 or FIGURES 11 to 13 of the accompanying drawings.