GB2202055A

GB2202055A - Weighing scale

Info

Publication number: GB2202055A
Application number: GB08705861A
Authority: GB
Inventors: Honkong Woo
Original assignee: Johnson Measures and Weights Ltd
Current assignee: Johnson Measures and Weights Ltd
Priority date: 1987-03-12
Filing date: 1987-03-12
Publication date: 1988-09-14
Anticipated expiration: 2007-03-12
Also published as: GB2202055B; GB8705861D0

Abstract

In a weighing scale, arms 4 of a parallel motion linkage 3 have a leg 10 projecting downwardly therefrom. A lower portion 11 of the leg 10 traces out a path (B) as the load on the scale varies. A pointer 13 is rotatable about a vertical axis (14 Fig. 3) and has a follower (20 Fig. 3) offset therefrom and biased into abutment with the lower portion (11) by a torsion spring (18) to convert the horozontal movement (B) of the leg (10) into rotational movement of the pointer (13) over an arcuate scale (16). The angular position of the arm (13) may be adjusted to indicate zero weight on the scale (16) by sliding a stand member (22 Fig. 3) on which the arm is pivotably mounted about the axis (14 Fig. 3) over a base stand (21), this sliding movement being effected by an eccentric cam and slot arrangement (24, 25, 26, 27, Fig. 3). <IMAGE>

Description

DESCRIPTION WEIGHING SCALE This invention relates to weighing scales of the type with an internal mechanism in which an upwardly biased parallel motion linkage supports a load support carrier above a base part, downwards rotation of the parallel motion linkage upon application of a load to the load support carrier being converted into relative pivotal movement between a pointer and an arcuate scale.

In known constructions, the pointer has a follower which moves vertically with the parallel motion linkage, this vertical motion being converted to pivotal movement of the pointer by the use of mechanisms such as ballcrank levers and/or a rack and pinion. Such an arrangement is complex to manufacture and involves slackness.

According to the present invention, a weighing scale comprises a parallel motion linkage with upper and lower arms, the ends of each of which are pivotally connected one to a load support carrier and the other to a base part whereby the carrier is movable vertically downwards against spring action; an indicator assembly which is pivotable about a vertical axis relatively to the base part and which includes the movable part of a relatively movable pointer and arcuate scale; a leg which is rigid with, and depends downwards from, an arm of the parallel motion linkage; and means for urging the indicator assembly to pivot so that a follower part of the assembly, which is offset from the pivotal axis of the assembly, engages a lower portion of the leg, whereby, when the carrier is forced downwardly upon application of a load, the arms and leg pivot so that the lower portion of the leg moves substantially horizontally causing corresponding moverrent of the follower part, and hence relative movement between the pointer and scale. This construction is simple td assemble and reliable in use as it involves direct engagement between a rigid part of the parallel motion linkage and the rotatable indicator assembly.

Conveniently, the carrier may be biased upwards by compression spring located between the carrier and the base part, and the urging means may comprise a torsion spring acting between the indicator assembly and the base part and located around the vertical axis of the indicator assembly. In this way, the springs may be easily assembled on to and held in position by the other parts of the scale.

Preferably, the base part comprises a base stand and a base member slidably mounted thereon in the direction of horizontal movement of the lower portion of the leg, the indicator assembly being pivotably mounted on the base member and the other ends of the arms of the parallel motion linkage being pivotably connected to the base stand, whereby relative movement between the base stand and base member adjusts the relative positioning, for a given load on the carrier, of the pointer and scale.

Consequently, the pointer and scale may be adjusted accurately to indicate zero weight when there is no load on the carrier or when a first load has been applied to the carrier and it is desired to reset to zero for easy weighing of a second load. To permit easy movement and holding in position of the base member relative to the base stand, there may be provided an adjustment wheel rotatably mounted on the base stand or base member and having a cam surface eccentric to the rotational axis of the wheel and in abutment against a cam follower surface on the base member or base stand respectively, whereby rotation of the wheel causes relative movement between the base stand and base member. Preferably, the adjustment wheel is rotatably mounted on the base stand so that it does not move relative to the stand when rotated, as this would make the wheel difficult to use.

The follower part of the indicator assembly may comprise a surface curved in the plane normal to the vertical pivot axis of the assembly and curved away from the lower portion of the leg. This results in the point of contact between the follower part and the lower portion of the leg moving along the surface as the parallel motion linkage pivots downwards upon application of a heavier and heavier load. In this way, the curvature of the surface and the position of the surface relative to the vertical axis of the indicator assembly and the lower portion of the leg may be selected to permit the use of a linear set of weight graduations on the arcuate scale.

An example of a scale constructed in accordance with the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a front perspective view of the scale from above and one side; Figure 2 is a section through the scale in a vertical plane; and, Figure 3 is a partial sectional view on the line A-A of Figure 2.

The scale comprises a load support carrier 1, in the form of a cover, supported above a base part 2 by a parallel motion linkage 3. As may be seen from Figures 2 and 3, the linkage 3 comprises a pair of parallel upper arms 4 and a pair of parallel lower arms 5, each arm 4,5 being pivotably connected at one end to a support block 6 forming part of the lower side of the load carrier 1 and connected pivotably at the other end to a mounting post 7 forming part of the base part 2.

A compression spring 8 is located between the support block 6 and a pedestal 9 of the base part 2 and this spring serves to bias the load carrier 1 upwards to counteract any load applied thereon. A detachable container 1' is provided on the load carrier 1 for supporting the loads to be weighed.

A depending leg 10 is attached rigidly to a bar (not shown) connecting the two upper arms 4. A lower portion 11 of the leg 10 traces out the generally horizontal path B as the parallel motion linkage 3 rocks in rocks in response to the load on the carrier 1 varying.

An indicator assembly 12 comprises a pointer arm 13 which is pivotably mounted on the base part 2 about a vertical axis 14. A tip 15 of the pointer 13 is movable over a graduated, arcuate scale 16 (see Figure 1) formed on a front surface of the base part 2. A transparent viewing panel 17 formed in the front of the load carrier 1 permits the pointer tip 15 and scale 16 to be viewed for reading off the indicated weight.

A torsion spring 18, which is weak and can be overridden by the compression spring 8, extends generally along the axis 14 of the pointer 13 and has arms at either end which are connected to the pointer 13 and base part 2 so as to bias the pointer 13 to rotate in an anticlockwise direction along a path C.

In this way, a curved surface 19 of a follower 20 forming a part of the arm 13 adjacent to the axis 14 is kept in abutting contact with the lower portion 11 of the leg 10. The follower 20 is offset from the axis 14 and hence, as the lower portion 11 traces out the path B, the pointer 13 rotates and moves along the path C, with the tip 15 of the pointer indicating on the scale 16 the weight of the load which has been applied to the carrier 1 and resulted in the movement of the portion 11 along the path B. The surface 19 is curved in the plane normal to the axis 14 and the curvature of the surface 19, together with the positioning of the surface relative to the rest of the pointer 13, may be varied to permit the use of constantly spaced graduations on the scale 16.As will be appreciated, by using the curved surface 19, the point of contact of the portion 11 on the surface 19 will vary as the portion 11 moves along the path B.

The base part 2 comprises a base stand 21 and a base member 22 slidably mounted thereon. The base stand 21 has a pair of parallel walls 23 which define a channel therebetween in which the base member 22 is slidably located, the base member 22 being slidable along the path D. The indicator assembly 12 is mounted on the base member 22, whilst the parallel motion linkage 3 is mounted via the mounting post 7 on the base stand 21. Consequently, motion of the base member 22 along the path D permits the pointer 13 to be moved along the path C whilst the load on the load carrier 1 is either constant or absent.

Thus, the pointer 13 may be set or reset accurately to have its tip 15 indicating zero weight on the scale 16.

The sliding movement of the base member 22 is effected and controlled by a wheel 24 rotatably mounted about an axis 25 on the base stand 21. The wheel 24 has a circular cam surface 26 which is eccentric to the axis 25 of the wheel. The cam surface 26 is located in a slot 27 formed in the base member 22, the walls of the slot serving as a cam follower surface, and consequently rotation of the wheel 24 produces a sliding, reciprocating movement of the base member 22, to permit the zero-setting of the pointer 13.

Apart from the two springs 8,18 and any fastening devices, the entire scale is constructed in plastics material, relatively movable parts, such as the arms 4 and the mounting post 7, being of a low-friction type of plastics.

Claims

1. A weighing scale comprising a parallel motion linkage with upper and lower arms, the ends of each of which are pivotally connected one to a load support carrier and the other to a base part whereby the carrier is movable vertically downwards against spring action; an indicator assembly which is pivotable about a vertical axis relatively to the base part and which includes the movable part of a relatively movable pointer and arcuate scale; a leg which is rigid with, and depends downwards from, an arm of the parallel motion linkage; and means for urging the indicator assembly to pivot so that a follower part of the assembly, which is offset from the pivotal axis of the assembly, engages a lower portion of the leg, whereby, when the carrier is forced downwardly upon application of a load, the arms and leg pivot so that the lower portion of the leg moves substantially horizontally causing corresponding movement of the follower part, and hence relative movement between the pointer and scale.

2. A scale according to claim 1, in which the carrier is biased upwards by a compression spring located between the carrier and the base part.

3. A scale according to clam 1 or claim 2, in which the urging means comprises a torsion spring acting between the indicator assembly and the base part and located around the vertical axis of the indicator assembly.

4. A scale according to any one of claims 1 to 3, in which the base part comprises a base stand and a base member slidably mounted thereon in the direction of horizontal movement of the lower portion of the leg, the indicator assembly being pivotably mounted on the base member and the other ends of the arms of the parallel motion linkage being pivotably connected to the base stand r whereby relative movement between the base stand and base member adjusts the relative positioning, for a given load on the carrier, of the pointer and scale.

5. A scale according to claim 4, further comprising an adjustment wheel rotatably mounted on r the base stand or base member and having a cam surface eccentric to the rotational axis of the wheel and in abutment against a cam follower surface on the base member or base stand respectively, whereby rotation of the wheel causes relative movement between the base stand and base member.

6. A scale according to any one of the preceding claims, in which the follower part of the indicator assembly comprises a surface curved in the plane normal to the-vertical pivot axis of the assembly and curved away from the lower portion of the leg.

7. A weighing scale substantially as described with reference to the accompanying drawings.