Field of the invention

This invention relates to a link chain guide, typically but not essentially for an endless chain conveyor, and also to a chain conveyor incorporating said guide

Background to the Invention

When a chain of links wraps around the pitch circle of a chainwheel the links effectively form part of a regular polygon with an instantaneous transition to the straight line or catenary formed by the incoming links

Figures la, b and c of the accompanying drawings show a sequence of steps in entry of a link chain onto a chainwheel. Three successive position of the chain in transition are depicted. The incoming chain links are pulled by the roller or pin that last engages a tooth space root of the chainwheel As the chain rotates it causes the chain to lift and then fall during the controlling action of each succeeding tooth.

The velocity of the approaching chain links varies cyclically according to a law typified by the graph of velocity shown in Fig. 2, where the velocity of the in-coming chain, in terms of length/unit time, is plotted against the angle (α) of rotation of the chain in degrees. The magnitude of the alternation depends upon the numbers of teeth in the uptaking or driving chainwheel and ±e angle or approach of the incoming chain The velocity shown in Fig 2 is the horizontal component of the in-coming roller Under the valid assumption that the last chain roller to engage the chainwheel tooth space root is always the controlling one, then there is a resulting step change in the in-coming chain's velocity This is due to an asymmetry in the position of the relinquishing and recipient controlling roller It manifests itself primarily as an impulse in angular velocity of the chain links setting up vibration along the incoming chain

Chain dπve suppliers recommend that not less than 19 teeth should be used to mitigate polygonal effects in high speed requirements However, when the chain links involved are long, such a recommendation results in the necessity for large diameter chaiπwheels

In applications such as in precision conveying where the chainwheels need to be small in diameter then polygonal or chordal effects are very disadvantageous

Prior Art

Known from US Patent No 5306212 is a transition path guide which substantially reduces but does not eliminate the chordal or polygonal effect arising when a link chain passes around a sprocket A transition path is proposed wherein at least at the junction point where the transition path enters into the circular turning path around the sprocket, these two paths have a common tangent. It is also a requirement of the known transition path that the curvature of this path varies so that the difference between its radius of curvature and that of the circular turning path continually decreases from the said junction point One particular transition path which meets these requirements is a clothoid or cornu spiral, defined by the equation K=(LxR) ^{, 2}

In this case, the end points of the transition curve have a curvature (which may be zero) continuous with that of the linear or curved path of the chain beyond the ends of the transition path However, the clothoid only partially eliminates chordal effects Measured in terms of

velocity fluctuation, in an example given for a sprocket wheel having 15 teeth (— effective

teeth), a minimum fluctuation of 2 6% is the best achievable

The invention

According to one aspect of the present invention, there is provided a link chain guide for a link chain passing around at least one sprocket, wherein each chain link carπes a guide means and at the region of entry of the chain into engagement with a sprocket wheel a cam profile is

provided with which the guide means co-operates to cause the cnain iιnκ entering into engagement with the sprocket to follow a transition path, characterised in that, in order to eliminate the chordal effect normally associated with link chains and sprockets, the transition path defined by the cam profile is computed to eliminate the chordal effect from the pitch circle (r) of the sprocket wheel, the parameter angle (α) subtended by the chain link at its instantaneous centres in the initial position of its intended transition path, and the length (L) of the chain link, such that the speed ratio of joints engaging the chainwheel pitch circle and joints lying on the path of the link chain before reaching the intended transition path is constant.

Thus, the computed transition path permits a uniform velocity (zero acceleration) transmission, which enables the possibility of setting a constant pre-tension independent of position along the chain.

It follows, in contrast with the transmission path known from the prior art, that a velocity fluctuation of zero is achieved. Moreover, although the curves must meet, continuity of tangency in respect of curvature at the end points of the transition path is not essential, thereby affording a degree of freedom of design not available with the prior art transition path. However, continuity of tangency is a desirable constraint for practical purposes.

The difference between the prior art transition path is further clarified with reference to Figure 2A, in which the graphs of curvature(C)/travel(T) are shown in full line for the transition path in accordance with the invention (JRJ path) and in dotted line for a clothoid. The non-linear relationship of the curvature travel graph applicable to the present invention is derived from a pair of simultaneous equations of second degree that are subject to a first order, velocity constraint. These are based on intersecting circles having moving centres, and of which the radii are the lengths of the chain links. In general, only one roller is in transition, although the transition path, uniquely for each situation, is computed for the condition where there is a roller at each end of the transition path. This also means that, unlike the prior art transition path, the path in accordance with the invention has a spanning chord equal to the length of one chain link.

In a typical embodiment, an endless chain passes arounα two or more sprocκets, out me invention is also applicable, eg, to long chain hoists.

The invention also relates to a conveyor incorporating the above defined link guide.

Thus, the guide means on each chain link is preferably a guide roller, conveniently fixed to the link, and preferably engaging a cam profile on the inside of the radius of the link chain path In general, therefore, the cam profile will lie on the inside of the chain link path, but it may move from the inside to the outside if at any point there is a change in the sense of curvature of the chain link path.

The invention can enable fewer links to be employed between sprockets than has hitherto been possible while nevertheless giving adequate performance.

The links are preferably interconnected by sealed needle rollers.

According to another aspect of the invention, there is provided an endless link chain conveyor for carrying articles on which a production task is to be performed by tasking means past which the articles are moved when the link chain is driven, characterised in that the link chain is guided on to spaced sprockets by link chain guide means as hitherto defined by the first aspect of the invention, and the chain is pretensioned with a tension which remains constant due to the elimination of chordal effects, whereby motion of the links past the tasking means takes place along a non-varying path.

Various advantages arise, as will be apparent hereinafter.

First, it is to be appreciated that it is because there is a non-varying tension in the link chain due to elimination of chordal effects that the link chain can be pre-loaded with a predetermined tension. If chordal effects are not eliminated, such preloading with tension would not readily be possible, as the system would tend to seize up or the chain would break.

The elimination of chordal effects also means that clearance in tne oeaπngs or tne cnain can oe taken up and, because the chain will run without clearance in its beaπngs, the motion of the chain can be made totally precise and non-varying

In conveying apparatus in which articles are conveyed past tasking means, a stepped advance of the articles, i e an indexed movement, is to be preferred, so that the tasking means acts on the articles while they are stationary However, if, as is obviously preferred for manufacturing efficiency, indexing speed is made as fast as possible, vibrations are excited in the chain which makes it difficult for the tasking means to align accurately with the articles, because they are shaking from the induced vibration. Elimination of clearance in the bearings of the link chain, coupled with the predetermined tension with which the chain is preloaded, enables faster indexing, i e more rapid acceleration and deceleration of the chain movement, and thereby permits increased throughput Acceleration and deceleration for indexing purposes is totally unrelated to the fact that the computed transition path for the chain permits a uniform velocity transmission due to the elimination of chordal effects

Yet again, while a conventional chain drive would normally require at least 18 teeth per sprocket in order to minimise chordal effects, and even then not permit constant tension, as a result of the substantial elimination of chordal effects in the present invention there is no longer a minimum number of teeth required for the sprockets In the present invention, therefore, the number of teeth per sprocket can be reduced to 10 or fewer, and is preferably only 6 The chain, in consequence, has much longer links than is usual for a given pitch circle diameter of the sprockets In effect, in the preferred production apparatus in accordance with the invention, the number of links in the chain, relative to a conventional chain of comparable dimensions, is reduced by a factor of at least three, and the chain pitch, i e length of link, is increased by a factor of at least three The number of chain bearings is thereby proportionately reduced and the space available for the bearings is increased

Frequently, in conveying apparatus in which articles are conveyed past tasking means, materials and substances are involved which are of contaminating or abrasive nature, resulting in damage to and wear on the bearings if the material or substance can penetrate them However, because more space is available for the beaπngs due to the use of longer links, the

s ze of the beaπngs can oe increased, making it possible ror tne oeaπngs to oe seaieu, inus increasing the reliability and life of the chain drive

Description of Embodiment

The invention is further described with reference to the accompanying drawings, in which. -

Figures 1 and 2 are explanatory diagrams described above,

Figure 3 shows some link chain configurations to which the invention is applicable,

Figures 4 to 7 are diagrams to aid understanding of the computations necessary to practise the invention,

Figures 8 to 10 are graphs accompanying the Appendices to the present specification,

Figures 11a, b and c show a link chain conveyor test rig for verification of the invention, respectively in side elevation, plan and end views;

Figure 12 shows one of the test rig sprockets; and

Figures 13a and 13b respectively show the left hand and right hand transistion curves for the test rig of Figure 11, incorporated into a guide plate.

In precision chain conveying several configurations form potential for application of the link chain guide of the invention. These are based upon circular arcs and straight lines Tracks or rails would be used to guide the chain rollers through the straight line or circular arc Some differing possible layouts are shown in Figures 3a to 3d

These figures show only the chainwheel pitch circle and the pitch line or arc constraining the chain-link's rollers In each case a transition profile in accordance with the invention is required at the join of the line or arc to the chainwheel pitch circle

The schematics shown in Figure 3 represent variants of what could be modular transfer arrangements that could osculate with other linear or rotary motions For example, the arc forms in b and c could be used in conjunction with a carousel rotary filler, to off load products

For the purpose of the development of the basic geometry of the transition curves two variants are dealt with separately below. The first form is for the join of a straight line into the pitch circle of chainwheel The second form is for a circular arc into the pitch circle of a chainwheel.

First, therefore, with reference to Figures 4a to 4c, consider two links, AB link 1 and BC link 2, of a chain joined at B. The joint C is running along a straight line parallel to the x axis and offset by e in the y direction. B is initially also on the straight line but about to start along the transition curve. A is in the pitch circle of the chainwheel This condition, position 1, is shown in Figure 4a.

Figure 4b shows the condition where C is still on its straight line path B is on its transition curve (undefined at this stage in the development of the theory) while A has progressed along the pitch circle of the chainwheel This is position 2

The third position of interest is when C has arrived at the original position of B Here both B and A are on the pitch circle of the. chainwheel.

C moves to B through the length L of one chain link. In the same time, r, pin A has moved through an arc of the pitch circle of the chainwheel. This arc subtends an angle

(1) n

where n = number of teeth on the chainwheel.

Alternatively, where r = pitch circle radius of the chainwheel

2 arcsin [ — J (2)

In position 1 the link 2 will have its instantaneous centre at ∞ in the y direction. The link 1 will have its instantaneous centre at In defined by the intersection of the Hne through A and the wheel centre, at the origin of the xy axes, and the line through B normal to the BC (or the straight line path of C). A, B and Iι ₂ form a triangle with one of its sides being the link of length L. Let the other two sides be a and b and the angle contained by these be α.

The ratio a:b is equal to the velocity ratio of A to B relative to ground and perpendicular to a and b respectively. For continuity of tangency this ratio must be

a φ r I τ 1 (3) L i τ

Where r = pitch circle radius of the chainwheel.

From triangle ABI. ₂

b ² - lab cosα - L ² + a ² = 0

Solving for b we have:

If a is regarded as an independent design variable then b can be found and then by substituting back into equation (3), a can be found. In the third position the old I_ ₂ becomes the new

instant centre for link 3, this is In Knowing a then x ₁₃ , y _l3 , the co-ordinates ot the instantaneous centre 113 can be found Then

₁₃ = (a - r) sin

and

_yi3 = -(a - r) cos a

Then the offset of the straight line is

e = b +y ₁₃ (5)

For a given value of a the geometry is determined and the transition path of B can be calculated

Knowing the initial condition from the earlier geometry then the co-ordinates of A and C are known functions of time t, that is xc = -st + (L + n) yσ= e

(6)

X _A = r cos (ωt + a + 90) y _A - r sin (cot + a + 90)

where s is the linear velocity of the chain along the guideway and ω is the angular velocity of the chainwheel

B is on the intersection of two circles, one with its centre at A and the other with its centre at C The intersection is represented by the simultaneous equations

(x - x _A ) ² + (y -^ _A ) ² - I = 0 (7)

(* - *c) ² + O -j _) ² - Z. ² = 0 (8)

On substitution from equation (6) these equations (7) and (8) become

(x - r cos (ωt + a + 90)) ² + (y - r sin (cot + a + 90)) ² = L ² (10)

(x + st - (L + x _l3 )) ² + (y - e) ² =L ²

These are a simple implicit pair of equations in x, y that represents the transition curve from a straight line guideway to the chainwheel pitch circle as a constraint function. An example transition path T is shown in Figure 5, for a 4-toothed sprocket.

Considering now the case where chain rollers are constrained to move around a circular arc and then transfer to a chainwheel, the chainwheel being either inside or outside the circular arc, it is again assumed that the transition is completed over the period that the link CB moves to take the place of BA. The geometry for the transition is depicted in Figures 6a to 6c in analogous manner to Figure 4.

The co-ordinate system xy is fixed in the frame. The chainwheel is pivoted with its centre at the origin of the co-ordinate system xo, _. Arbitrary parameters are

n = number of teeth a = angle subtended by a link at its instantaneous centre when reaching the end of its transition path

R = radius of constraining arc on approach

L = link length

With these pre-specified parameters the calculation of the centre of the constraining arc XR. ,VR, can be made.

The links AB and BC are again numbered as 1 and 2, respectively The start of a transition is with the two adjacent links lying such that joint A is on the chainwheel pitch circle while the

other two joints B and C lie on the circular arc. The instantaneous centre ot AB, Iι ₂ , lies on the intersection of the diameters of the circles containing the chainwheel and the constraining arc passing through A and B respectively A triangle I _.2 , AB is formed, the sides of which are the chain link 1 of length L and sides a and b.

For continuity of tangency, the ratio a:b has to be identically equal to the ratio of the pitch line velocities of the roller in the arc of approach to the velocity of the roller on the chainwheel.

Thus,

where ψ is the angle subtended by a chord equal to a link length L at the centre of a circular arc of radius R. It is given by

ι^=2aresin — \.2

where R = radius of the constraining arc on the incoming side

Then the sides of the triangle I _!2 , AB can be calculated

and from this

nψR

Then the co-ordinates of the instantaneous centre Iι ₂ can be found

_Vi2= - (a-r)cos(a+β

leading to the initial position of point B

XB=XI ₂ - b sin β

and the co-ordination of the centre of the

XR=XB ⁺ Rsinβ

The equations defining the transition curve again include equations (7) and (8) together with a velocity constraint for guideways of arc form. These collectively are

(x-x _c ) ² + (y-.y _c ) -E ² =0 (8)

and (x _A ² +y _A ² ) = (C7) ² (xc ² +^c ² ) (14)

where the dot denotes a derivative with respect to an independent variable and G =1 — j ,

the ratio of the speed of a link pin around the chainwheel pitch circle to that along the guideway.

An example transition path T _. is shown in Figure 7, for entry on to the sprocket from a circular path c,

From the foregoing, it will be understood how the required profile for the cam track employed in the present invention can be determined. It is also to be noted that, in addition to the dynamic benefits resulting from use of the computed transition path in accordance with the invention, the chain drive can be pre-loaded to eliminate backlash effects in the chain

In practice, the required transition path, and thus the required curvature for the cam track, can be computed using two computer programs, one generally known as MATHCAD 5+ (from Mathsoft Inc., USA) and the other referred to herein as CAMLEMKS (from Limacon, UK).

MATHCAD 5+ is used to calculate the initial co-ordinates, x _A , y _A , and x _, yc and the offset e or x _R , y*, referred to in the foregoing. CAI ILINKS is then used to generate the kinematic geometry and profile coordinates of the transition path, either from a straight conveyor path on to the sprocket or from a curved conveyor path on to the sprocket, using the foregoing equations (7), (8) and (14).

The two MATHCAD 5+ procedures are set out in Appendix 1 and Appendix 2, respectively, for the transition from a straight path onto the sprocket and for a curved path on to the sprocket Appendix 1 makes reference to Figure 8 of the accompanying drawings and Appendix 2 makes reference to Figures 9 and 10

The conveyor incorporating the link chain guide of the invention finds application in a wide variety of equipment, and is particularly useful where high speed, high accuracy conveying is required One particular useful application envisaged is in high speed toothpaste filing equipment.

Figures 1 la, b and c show a test rig incorporating an endless link chain conveyor in accordance with the invention. In this test rig, the conveyor is operable by a crank handle 10

In the illustrated test rig, the endless link chain conveyor 12 moves around two similar sprockets 14, 14 A, one of which is shown in detail in Figure 12 The chain links are interconnected by sealed needle rollers 16, which are not required to provide free play for variation in the relative instantaneous velocities of adjacent links

The links, as by means of guide rollers, run on a guide plate 18 which at the left-hand and right-hand ends incorporates transition cam profiles which guide the chain links onto the sprocket along paths which completely eliminate chordal effects. These transition paths 20, 20 A, indicated in Figures 13a and 13b, are computed in the manner hereinbefore described in accordance with the invention.

Means are incorporated for pre-loading the chain under tension. Reference 22 denotes a preload screw block, reference 24 a preload adjuster and reference 26 a preload slider block for the purpose. Due to the provision of the transistion cam profiles, the tension in the chain remains wholly non-varying, and this contributes to a constant path of movement of the chain, even when links are entering into engagement with the sprockets.

It follows that articles (not shown) carried by the chain can be precisely positioned during operation of the conveyor for co-operation with tasking means (not shown) past which the articles are conveyed at tasking stations (not shown).

For completeness, in Figures 1 la to l ie, reference 28 generally indicates the tower structure on which the link chain conveyor is supported, 30 indicates the conveyor drive shaft and 32 the driven shaft.

From Figure 12, it will be seen that each sprocket 14, 14a has only 6 teeth, whereas, in a conventional conveyor, at least 18 teeth would normally be required for chain links of the same length in order even to reduce chordal effects to an acceptable level

In Figures 13a and 13b, references 34 and 34a respectively indicate the regions of the internal guide plate 18 at which the computed transition path constitutes the cam profile 20, 20A leading the link chain on to the sprockets to enable the total elimination of chordal effects in accordance with the invention

In practical apparatus in which the long link chain is motor driven, the chain may be indexed one link at a time past tasking means acting upon articles carried by holders on the chain links,

so that tasks can be performed on the articles while they are stationarily positioned along their precisely defined path of movement achieved by the elimination of chordal effects. An example is a chain conveyor carrying holders for toothpaste tubes to be filled and sealed by suitable taksing means. As toothpaste is abrasive, the fact that the invention facilitates the use of sealed bearings between the chain links is particularly advantageous Moreover, the constant tension in the link chain facilitates high speed indexing with minimal risk of setting up vibrations along the length of the chain, whilst the use of long links running around sprockets with only a few teeth assists in achieving compactness of the machine.

APPENDIX 1

Transition From Straight Line to Chain Wheel Pitch Circle

Here the chain joins the chain wheel from a track that is a straight line The design can start with a set of basic machine dimensions leaving the designer to select from another set of parameters

The machine dimensions may be L - pitch length of chain

The parameters which can be left for the designers arbitration are n = the number of teeth on the chainwheel a = an arbitrary angle for the start m = is the counter of a finite number of values of selected

Given these chosen design parameters the aim is to calculate the offset of the straight line from the centre of the wheel This would then complete the geometrical information from which the transition curve can be calculated using the equations given in the main text or, more easily, directly calculated by CAMLH KS

The following values are used in illustrate the calculations involved in obtaining the offset = 100 ΛΪ = 3 .8 m = 1. 4

Values of α are entered in degrees

αdeg _m =

_ g deg _m _

O m ^π

180

The angle subtended by adjacent tooth (or roller) spaces at the centre of the chainwheel

< , 2π n

The ratio a.b (see main text) is then given by

aoverbn = . .

2__4 h.

The chain pitch circle radius is

r _Λ -

2 sin Φ _n

aoverb _n r„

tfn,m = aoverb„έ-

_{h =} L ^σ n.«ι I 1 [l + (aoverb _n ) ] - 2 aoverb _n cos(αr _BT )

Offset-,,-, = bn, _m +y _ajΛ

The values of these parameters for the m=\ 4 selection a and the n=3 8 teeth are given the respective columns and rows of the submatrices shown below

submatrix(£,3,8,1,4)=

Fll5309 98027 89337 8413 ]

I 122.822 103809 94.366 88741 I

I 125895 106237 96.506 907191

I 127447 107485 97617 91751 I

I 128342 108.214 98268 923581

L 128906 108677 98684 92746_

submatπx (y,3,8,l,4)=

[ ^" -57768 -35737 -25146 -190891

1-46464 -2621 -17052 -120861

1-3501 -1675 -9048 -5168 I

1-23661 -7382 -1112 17 I

1-12385 1942 6796 855 I

L-l 148 11247 14695 15396 J

submatπx (Offset 3,8,1,4)=

The graphs of the instant centre 12 at x, y each for a different a are shown in Figure 8

APPENDIX 2

Transition From Circular Arc to Chain Wheel Pitch Circle

Here the chain joins the chain wheel from a track that is a circular arc. The design can start with a set of basic machine dimensions leaving the designer to select from another set of parameters

The given machine dimensions may be L = pitch length of chain R = radius of circular arc

The parameters which can be left for the designers arbitration are n = the number of teeth on the chainwheel = an arbitrary angle for the start m = is the counter of a finite number of values of α selected β= angle made by radius of B to the y axis

The following values are used in an example of the calculations involved.

L = 100 n = 3. 8 m = 1..4

R = 1000

Values of α are entered in degrees αdeg _m =

25

30

35

40

_ ordeg.

<Zm = ^■ π rads

180

The angle φ subtended by adjacent tooth (or roller) spaces at the centre of the chainwheel

n

The angle ψ subtended by the pitch length if a chain link lying on the constraining arc at the centre of the arc

ψ= 2arcsin I —

The chain pitch circular radius is

L r _n = —

24. ^

The ratio a.b (see main text) is then given by

Φ r aoverb„ ^** ^ ψR

7?

aoverb _n r-

and the values if a and b calculated thus

j[ 1 + (aoverb _n ) ² ] - 2. aoverb _n . co s( a _m )

α ^■ *__y_mn = aoverb 'nπ,--)'.i n

from which the co-ordinates that define the design geometry are.

xUw = (a_-_ - r sin (__-, + β) _yl -._-.-0. -rj cos (a _m + β)\

xB njn nn _j n- -n _j nSin -?) _[ _n.+*n.m,COS(/?)

xR„-. = xB„_ _. + Rsin(?) ^R-^ =-^p, _m - R cos (β)

Tables of values of these parameters are given below for the m value of a (columns) and number of chain wheel teeth (rows)

149835 489.86 48208 4749821 1484194 47517 46692 4594321 [470446 460.83 452.059 44413όJ

submatrix(yR,3,8,l,4)=

submatrix (xB,3,8,l,4)=

T47 019 40 202

1 29 336 21 7

I 13.22 5 183

1 -1.65 -10.14

I -15 806 -24 83

L-29.554 -39 17

submatrix (yB,3,8, 1,4)=

T66358 72038 75631 77742 1 I 89403 91226 91575 90878 I

Graphs of the co-ordinates of the arc centre at R and the design position of the joint B are shown in Figures 9 and 10