AU646053B2

AU646053B2 - Lightweight fork assembly

Info

Publication number: AU646053B2
Application number: AU80196/91A
Authority: AU
Inventors: Bruce W. Field
Original assignee: University of Melbourne
Current assignee: University of Melbourne
Priority date: 1990-07-06
Filing date: 1991-07-04
Publication date: 1994-02-03
Anticipated expiration: 2011-07-04
Also published as: AU8019691A

Description

P/00/0011 a64 3 0 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: THE UNIVERSITY OF MELBOURNE Actual Inventor(s): BRUCE W. FIELD Address for service in Australia: CARTER SMITH BEADLE, Qantas House, 2 Railway Parade, Camberwell, Victoria, 3124, Australia, Attorney Code SA.

Invention Title: LIGHTWEIGHT FORK ASSEMBLY Details of Associated Provisional Applications: Nos: PK 1084 filed 6th July 1990 The following statement is a full description of this invention, including the best method of performing it known to me/us: -1- 2 LIGHTWEIGHT FORK ASSEMBLY Field of the Invention: This invention relates to fork assemblies for shearing hand pieces.

Background of the Invention: In a shearing handpiece, the fork assembly guides and drives the moving cutting element, called the cutter, across the fixed element, called the comb.

In the design of a fork assembly a significant 10 compromise between two conflicting requirements must be reached: the mechanism for setting and controlling the gee* contact force between the comb and cutter, called the tension, must be as rigid as possible to minimize the tension setting required to sever wool cleanly. Higher rigidity can be achieved by making the fork assembly more massive.

since the fork assembly with its cutter is normally 9..

the only reciprocating part of the shearing 0 20 machine, the machine body must vibrate in contraphase to the reciprocating fork assembly. If the fork assembly is heavy, or if the arc of reciprocation is large, the vibration induced in the handgrip of the machine is uncomfortably high.

Thus it is desirable to minimize the mass of the fork assembly.

In all existing fork assemblies, the tensioning tbspe.056/unimel 91 74 -3 loads are applied to the cutter via a fork in which significant bending stresses are induced by the tensioning device. In the conventional "long fork" machines, the tension pin presses onto the fork at a point roughly midway between the cutter and the center post, inducing bending stresses in the forward part of the fork (Fig. 1).

In the more recent "short fork" machines, where the tension pin is integral with the fork, the equivalent bending stresses are introduced by tensile forces in the tension link (Fig. In each case, the stresses are moderately high, producing unacceptable deflections low rigidity) or the mass must be high, producing unacceptable vibrations.

Summary of Invention and Object: It is the object of this invention to provide a fork assembly in which the tension is applied at a more forward position than previously to tlereby reduce bending stresses and allow the fork assembly to have an unusually low mass.

The invention provides a fork assembly for a shearing handpiece including one or more moving cutting elements which oscillate over a fixed element, said fork assembly being adapted to hold said cutting element(s) in engagement with said fixed element with a predetermined contact force, said fork assembly comprising an oscillating link, tension pin means, having a longitudinal axis, directly or indirectly engaging yoke means at one end and being adapted to accept a biasing force which S 20 causes said contact force, said yoke means having spaced means for in use engaging Sa said cutting element to oscillate it over its fixed element and to transfer said biasing force from said yoke means to said cutting element, said tension pin means and said yoke means being arranged such that an extension of the longitudinal axis of said tension pin means is at least closely adjacent to a line joining said spaced 25 means of said yoke means to thereby minimize bending moments in said oscillating link and said tension pin means.

The invention also provides a fork assembly for a shearing handpiece including one or more moving cutting elements which oscillate over a fixed element, said fork assembly being adapted to hold said cutting element(s) in engagement with said fixed element with a predetermined contact force, said fork assembly TNB:MOT:05740 19 Novcnibr, 1993 -4comprising an oscillating link, a tension pin means directly or indirectly engaging yoke means having spaced means for applying a biasing force to said cutting element(s) at its forward end and being adapted to accept said biasing force which causes said contact force, said yoke means being pivotally supported directly or indirectly by said link such that the application of said biasing force by said tension pin is positioned forwardly of said pivotal support of said yoke means to thereby minimize bending moments in said oscillating link and said tension pin means, said tension pin means and said yoke means being arranged such that an extension of the longitudinal axis of said tension pin means is at least closely adjacent to a line joining said spaced means of said yoke means.

By arranging the link and the yoke means in either of the ways defined above, the necessary biasing force may be directly applied to the moving cutting element without introducing significant bending stresses in the oscillating link, or in the tension pin, whereby the mass of the fork assembly may be significantly reduced.

In one form of the invention, the oscillating link may comprise a sheet metal plate to which a lightweight

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.i y TNB:MOT;:#5740 19 November, 1993 5 upstanding post is rigidly secured, the link having a journal for pivotally supporting the yoke means at its forward end at an inclination corresponding to the axis of the tension pin, said tension pin providing at least lateral support for the upstanding post.

The yoke means may comprise a chicken's foot or a yoke head carrying two or more yokes or chicken's feet in any one of the manners described in Australian Patent AU- B 13160/83. In the latter case, the yoke head is 10 pivotally supported by the link at an angle corresponding to the angle of inclination of the tension pin to ensure that the required cutter biasing force is applied with the introduction of only minimal bending stresses.

In another form of the invention, the yoke means is rotatably mounted at the end of a guide tube rigidly mounted on the upstanding post with the tension pin carried in the guide tube, the yoke means being tensioned or restrained by a cable anchored to the chicken's foot 0* se at either side and passing around said upstanding post, 20 or some other rigid part of the drive assembly. In another form, the link may form part of a typical long fork design of the type discussed above, in which case the drive post is not required but the link still supports the yoke means adjacent the cutter.

As a result of the arrangements described above, the tension pin axis lies in a direction which is nominally on the line between the upper part-spherical cup under tbspe.056/unimel q91 7 4 the tension nut and the centre of pressure between the cutter and the comb. Similarly, the cutter's arc of movement is dictated by tension member(s) connected from near the centre pivot to near the cutter drive points on the fork. It will be appreciated that as the connection point moves nearer the drive points, the bending stresses in the tension pin also become reduced.

Brief Description of the Drawings: In order that the invention may be more readily 10 understood, several preferred embodiments will now be described with reference to the accompanying drawings in which: Figures 1 and 2 are sectional elevations of shearing handpieces showing the regions in which bending stresses are generated; Figure 3 is a schematic perspective view of a fork S. assembly embodying the invention; Figure 3A is a fragmentary perspective view of an alternative yoke means; Figure 4 is an exploded schematic perspective view of a fork assembly embodying the invention for use with a multiple yoke carrying yoke head, and Figures 5 and 6 are schematic perspective views of modified fork assemblies embodying the invention.

The problem which the invention seeks to ameliorate is illustrated schematically in Figures I and 2 of the drawings. In these figures the bending stresses induced tbspe.056/unimel 91 7 74 7 by the application of force by the tension pin to the fork is indicated by the heavy broken outline in each figure.

Referring firstly to Figure 3 of the drawings, the fork assembly embodying the invention comprises a steel strip tension link 1, which operates according to the principles described in Australian Patent AU-S 37980/85, supporting a spherical bearing or ball bearing pivot means 2 at one end, and having an upstanding end portion 10 3 at the other end formed to rotatably support a yoke or *s chicken's foot 4 at the acute angle of inclination shown by means of a bearing pin 5 engaging the forward end of the yoke 4 at a position which is in use adjacent the points of contact between the chicken's foot 4 and the cutter E. Intermediate the bearing 2 and the upstanding portion 3, an upstanding post 6 comprising a hollow steel tube is rivetted or otherwise rigidly secured to the link S1. The post 6 operates as a "drive tube" since it is provided with a vertical slot 7 adapted to receive a 20 conventional drive crank and roller C to cause oscillation of the link in the usual manner. The post 6 is also formed with front and back openings 8 through which a tension pin 9, which is rigid with the yoke or chicken's foot 4 and is adapted to be engaged at the other end by a conventional tension nut and sleeve T, may pass. The tension pin 9 slidably engages an opening in a shaped plug 10 of nylon or other suitable material which tbspe.056/unimel 91 7 4 -8is in turn slidably received within the post 6 in the manner shown in Figure 3, so that the pin 9 supports the post 6 against the driving forces applied by the crank C.

The yoke or chicken's foot 4 is formed in the usual manner with pins P adapted to engage openings in a moving cutting element E, which in Figure 3 of the drawings, is a two-tooth "flexicutter" of the type described in Australian Patent AU- B 86067/82, which is thereby swept over a shearing comb (not shown). If desired, the chicken's foot 4 shown in the drawing may be replaced by a yoke head Y (Fig.

3A) carrying a pair of spaced chicken's feet F in the manner described in greater detail in Australian Patent AU-B 13160/83. The yoke head is rigidly attached to the tension pin 9 and receives the bearing pin 5 in a central opening 0 at its forward end. The chicken's feet F are retained by means of a retaining clip R as shown in Figure 3, or by retaining lugs (not shown) formed on the link 1.

It will be appreciated that since the yoke or chicken's foot 4, or the yoke head Y in the alternative shown in Figure 3A, is pivotally mounted on the link 1 at the forward end of the yoke 4 adjacent the cutter E and at an angle of inclination such that the line of action of the tension pin 9 intersects the region of contact between the cutter E and the comb and is at least adjacent to line joining the pins P, the bending forces applied to both the link 1 and to the pin 9 by the application of forces through the tension pin to the yoke *p 0 0*

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BII:MOT; 5740 19 Noyttmbr, 199 -9- 4 and to the cutting element E will be significantly reduced whereby the overall mass of the fork assembly may be correspondingly reduced. This lower mass not only reduces the cost of the fork assembly but also considerably reduces a source of vibration of the shearing handpiece as the tension link 1 oscillates.

Referring now to Figure 4, the fork assembly of Figure 1 is used with a number of alternative yoke arrangements. In each of the alternative yoke arrangements, bending forces applied to both the link 1 and the tension pin 9 are reduced by the point of application of the 'tension' to the yoke head Y being positioned forwardly of the pivotal mounting of each yoke or chicken's foot F and the line of action of the tension pin 9 intersects or is adjacent a line joining the adjacent pins P of the chickens feet F. The figure also shows a number of alternative drive mechanisms adapted to cooperate with the common parts shown. The arrangement shown ir Figure 4 will be largely self-explanatory to persons skilled in the art but preferably includes an oscillating counterbalance 0 pivoted to the handpiece housing 4 to oscillate in opposition to the link 1 to further reduce vibration.

If desired, the bearing pin 5 may be replaced by allowing a suitably shaped end portion of the tension pin 9 to project through the front face of the yoke 4 to engage the journal in the end portion 3 of the link 1.

20 In the embodiment of Figure 5, the yoke 4 and the tension pin 9 are supported S" within a guide tube 11 rigidly secured to the upstanding post or drive tube 6, while the necessary tension to restrain the yoke and tension pin against sliding movement within the tube 11 is supplied by means of a cable 12 anchored at 13 and 14 to either side of the yoke 4 and passing around the drive____ m..o 1 uun~~ P ill-X---i INBMOiWS740 11 Odober, 1993 10 tube 6 in the manner shown. If desired, the cable 12 may alternatively pass around some other rigid part of the drive assembly, such as its centre post. In this arrangement, the yoke 4 is able to align within the guide tube 11 as the cutter is oscillated across the comb by oscillation of the link 1.

Figure 6 of the drawings shows one of several ways of applying the lightweight fork principle described above to a "long fork" design. In the arrangement shown, 10 the tension link 1 is attached to the long fork structure L, preferably near the fork pivot journal J, and carries the yoke 4 and the tension pin 9 in a manner similar to that described above. The tension pin 9 is in turn received in the usual way within a conventional tension nut and sleeve assembly (not shown). It will of course be go*: appreciated that the single yoke shown may be replaced by a yoke head and two yokes of the type shown in Figures 3 and 4 of the drawings.

*4* o o tbspe.056/unimel 91 7 4

Claims

1. A fork assembly for a shearing handpiece including one or more moving cutting elements which oscillate over a fixed element, said fork assembly being adapted to hold said cutting element(s) in engagement with said fixed element with a predetermined contact force, said fork assembly comprising an oscillating link, tension pin means, having a longitudinal axis, directly or indirectly engaging yoke means at one end and being adapted to accept a biasing force which causes said contact force, said yoke means having spaced means for in use engaging a said cutting element to oscillate it over its fixed element and to transfer said biasing force from said yoke means to said cutting element, said tension pin means and said yoke means being arranged such that an extension of the longitudinal axis of said tension pin means is at least closely adjacent to a line joining said spaced means of said yoke means to thereby minimize bending moments in said oscillating link and said tension pin means.

2. A fork assembly for a shearing handpiece including one or more moving cutting elements which oscillate over a fixed element, said fork assembly being adapted to hold said cutting element(s) in engagement with said fixed element with a predetermined contact force, said fork assembly comprising an oscillating link, a ,tension pin means directly or indirectly engaging yoke means having spaced means 20 for applying a biasing force to said cutting element(s) at its forward end and being adapted to accept said biasing force which causes said contact force, said yoke means being pivotally supported directly or indirectly by said link such that the application of said biasing force by said tension pin is positioned forwardly of said ~pivotal support of said yoke means to thereby minimize bending moments in said S 25 oscillating link and said tension pin means, said tension pin means and said yoke means being arranged such that an extension of the longitudinal axis of said tension S: pin means is at least closely adjacent to a line joining said spaced means of said yoke means.

3. The assembly of claim 1 or 2, wherein said oscillating link comprises an 3% element of low mass and high rigidity, and means for supporting said tension pin T.B:MT:Yr740 19 Ntvcibcr, 1993 -12- means to transfer said biasing force to said yoke means.

4. The assembly of claim 3, wherein said supporting means comprises a low mass post rigidly carried by said oscillating link.

The assembly of any preceding claim, wherein said oscillating link comprises a sheet metal plate to which a lightweight upstanding drive post is rigidly secured, the link having a journal for pivotally supporting said yoke means at its forward end at an inclination corr Mnonding to the axis of the tension pin, said tension pin means providing at least lateral support of the upstanding post.

6. The assembly of any preceding claim, wherein said yoke means comprises a yoke head carrying two or more yokes in any one of the manners claimed in any one of the claims of Australian Patent AU-B 13160/83, said yoke head being pivotally supported by the link at a position adjacent said cutting element and at an angle corresponding to the angle of inclination of the tension pin means.

7. The assembly of any one of claims 1 to 4, wherein said yoke means is rotatably mounted at one end of a guide tube rigidly mounted on the upstanding post with the tension pin carried in the guide tube, the yoke means being tensioned or restrained by a cable means anchored to the yoke at either side and passing around said upstanding post or some other rigid part of the assembly.

8. A fork assembly substantially as hereinbefore described with reference to 20 Figure 3, or as modified by Figure 3A, of the accompanying drawings.

9. A fork assembly substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

A fork assembly substantially as hereinbefore described with reference to i Figure 5 of the accompanying drawings. 25

11. A fork assembly substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

12. A shearing handpiece including a fork assembly as claimed in any preceding S*:cl claim. 'INB:MOT:#S740 19 November, 1993

13 DATED: 19 November, 1993 CARTER SMITH BEADLE Patent Attorneys for the Applicant: THE UNIVERSITY OF MELBOURNE TNBIAMNS740 INB:~rff574019 Navtmb~t 1993

14 ABSTRACT A lightweight fork assembly for a shearing handpiece comprising an oscillating link having a bearing (2) about which the link oscillates, an upstanding portion at the forward end of the link supporting a yoke adapted to engage a cutting element E, the yoke 4 being journalled to the upstanding portion by a bearing pin an upstanding drive tube rigidly attached to the link having a slot adapted to receive a drive crank C to oscillate the link and a tension pin engaging the yoke and passing through a shaped nylon bearing (10) in the tube to laterally support the tube said tension pin having a line of action which intersects the region of action of the cutting element E and the link 1 supporting the yoke (4) at a position adjacent the cutting element E to reduce S-' bending stresses in the link and in the tension pin 4 tbspe.056/unimel 91 7 4