WO1992012352A1

WO1992012352A1 - Mechanical adjuster

Info

Publication number: WO1992012352A1
Application number: PCT/GB1992/000019
Authority: WO
Inventors: John Mills
Original assignee: Ransomes Sims & Jefferies Limited
Priority date: 1991-01-07
Filing date: 1992-01-06
Publication date: 1992-07-23
Also published as: GB9100264D0

Abstract

A mechanical adjuster for e.g. the cutting reel of a grass cutting unit comprises a hand wheel (40) on a shaft (44) which is journalled in a trunnion (34). A connecting eye (36) is screw threaded to the hand wheel shaft to provide the desired adjustment. A cam arrangement (58, 62, 68) between the shaft and the trunnion superimposes a reciprocation on this adjusting movement. This serves to impose and then remove the strain energy necessary to overcome resistance to movement, leaving an adjusted mechanism which is unstressed and less likely to loose position if shocks are subsequently encountered.

Description

MECHANICAL ADJUSTER

This invention relates to mechanical adjusters and in an important example to adjusters for use in grass cutting machinery.

In grass cutting machinery of the type having a cylindrical cutting reel and a fixed bottom blade, it is usually necessary to provide means for adjusting the position of the cutting reel relative to the bottom blade, to maintain efficient cutting. Conventionally, the bottom blade is fixed in the frame of the cutting unit and the cutting reel is mounted in bearings which can be shifted relatively to the frame to permit this adjustment. Often, a handwheel adjuster is provided at each end of the cutter reel.

With smaller grass cutting units, it is generally possible to ensure that friction offers sufficient resistance to prevent spurious movement of the cutting reel. This frictional resistance to movement must withstand the shocks and vibrations which are encountered when the unit is moved, for example, at high speeds over rough ground and obstructions. When it is necessary to adjust the position of the cutting reel, this friction is overcome by the force applied to the handwheel.

A special difficulty arises with larger grass cutting units. Because of the greater masses involved, larger forces are required to ensure that there is no spurious movement of the cutting reel. If, as with smaller units, frictional forces are to be relied upon to prevent spurious movement, it will be understood that correspondingly larger forces will need to be applied through the handwheel adjuster. It is then sometimes found that as force is applied to the handwheel adjuster to overcome the frictional resistance to movement, energy is stored in the mechanism. After the cutting reel has been adjusted to the desired position, this energy may remain in the mechanism. If, subsequently, a shock force is applied to the cutting reel through, for example, the cutting machine accelerating, this energy may be released with a spurious movement of the cutting reel. - _. -

In many cases, this problem of movement of the cutting reel in iarger grass cutting machines has led to designers abandoning the use of frictional forces to hold the cutting reel in position. Instead, a separate clamp is provided with adjustment of the cutting reel then becoming a two stage process. First, the clamp is released and, second, the cutting reel is adjusted in position through the handwheels. Movement of the cutter reel in this latter adjustment can be made relatively free so that the difficulties associated with stored energy do not rise. A two-stage adjustment process is cumbersome, however, and the need for a separate clamp or clamps adds to the complexity and cost of the cutting unit.

It is an object of this invention to provide an improved mechanical adjuster which can be used in grass cutting machinery to remove or reduce the problems of stored energy, without requiring separate clamping arrangements.

Accordingly, the present invention consists, in one aspect, in a mechanical adjuster comprising first and second anchorages; a first member rotatably mounted in the first anchorage and a second member secured to the second anchorage, the first and second members being in screw thread engagement such that rotation of the first member relative to the first anchorage varies the distance between the first and second anchorages along a line of action, characterised in that there are provided means acting between the first member and the first anchorage to effect reciprocal movement of the first member relative to the first anchorage along said line of action concomitantly with rotation of the first member.

In this way, the mechanical adjuster effects the desired change in relative position of the two anchorages, with there being superimposed on this adjustment a reciprocal movement. Thus, taking the example of a grass cutting unit with one anchorage secured to the bearings of the cutter reel and the other carried on the frame, the mechanical adjuster will move the cutting reel to a new position representing one adjusting interval determined by the screw thread. The reciprocating movement creates forces sufficient to move the cutting reel and, as the reciprocation is completed, these forces are reduced or removed, the cutting reel remaining in a position corresponding to one adjusting interval. The "over-movement" and "return" of the adjuster serves to release all or part of the additional energy which has been applied through the adjuster in order to overcome frictional resistance. The mechanism thereafter remains in an unstressed state so that the cutting reel is less likely to be dislodged on sudden acceleration of the cutting unit.

Preferably, the reciprocal movement is completed on rotational movement of the first memeber in a single sense.

Advantageously, the means acting to effect reciprocal movement comprises cooperating cam surfaces provided on the first member and the first anchorage respectively. Conveniently, spring biassing means are provided to maintain said cam surfaces in cooperation and to accomodate said reciprocal movement.

Usefully, the cam action can be "felt" by the operator and serves as an index of the adjusting movement.

Suitably, bearing elements are provided between said cooperating cam surfaces.

The present invention will now be described, taking the example of a grass cutting unit, with reference to the accompanying drawings in which:-

Figure 1 is an end view of a grass cutting unit;

Figure 2 is a view of an enlarged scale of the mechanical adjuster shown in Figure 1 ; Figure 3 is a graph illustrating, for the mechanical adjuster of Figure 2, the movement applied through the screw thread and reciprocating elements of the adjuster;

Figure 4 is a graph similar to Figure 3, incorDorating the effects of backlash and strain; and

Figures 5 and 6 are views similar to Figure 2 illustrating respective modifications.

Referring to Figure 1 , a cylindrical cutting reel 10 has a central shaft 1 2 which is rotatably mounted in bearings 14. Each bearing 14 ⁽only one of which is seen in Figure 1 ) is carried on a bearing plate 1 6 which is secured to the unit frame 1 8 through bolts 20 and 22. Bolt 22 is accommodated in an arcuate slot 24 in the frame so that the bearing plate 1 6 can be pivoted about the axis defined by bolt 20. The frame 18 is relieved as shown at 26 to accommodate the corresoonding movement of the bearing 14.

The frame 18 of the grass cutting unit provides a mounting, through biock 28, for a bottom blade 30. It will be seen that clockwise movement of the bearing plate 1 6 about the pivot axis 20 will serve to bring the blades of the cutting reel 10 into closer engagement with the bottom blade 30 to compensate for blade wear. This movement is effected through mechanical adjustor 32. This has a trunnion 34 pivotally connected to the frame 18, a push rod 36 pivotally connected at 38 to the bearing plates 1 6, and a handwheel 40. An identical arrangement is provided at the opposite end of the reel. In a manner which will later be described in more detail, rotation of the handwheel 40 serves to increase the distance between the pivot point of trunnion 34 and pivotal connection 38, so rotating the bearing plates 1 6 clockwise apout the pivot axis 20, without leaving unwanted strain energy in the adjusted mechanism.

it wiii be understood that tnere are no separate clamps which require to be released before the handwheel 38 is rotated. The cutting reel is maintained in position as a result of frictional forces, which are dictated principally through the degree of tightening of bolts 20 and 22. Reference is now αirected to Figure 2 in which the mechanical adjuster 32 is described in more detail.

Fush rod 36 is formed at one end with an eye 42 for pivotal connection with the bearing plate 1 6. At the opposite end of the push rod 36, there is formed a screw threaded portion 44 which cooperates with a screw threaded bore 46 in shaft 48. This shaft 48 is journalled for rotation in the trunnion 34 and carries at its opposite end the handwheel 40. A pair of circlips 50 secure the handwheel 40 against axial movement and the handwheel is fixed for rotation with the shaft 48 by means of key 52.

The trunnion 34 has an internal cavity 54 terminating upwardly in abutment surface 56. A first cam ring 58 is freely rotatable on the shaft 48 and contacts the abutment surface 56. The cam ring 58 is prevented fro rotating relative to the trunnion 34 by means of a dowel 60. A second cam ring 62 abuts a flange 64 provided on the shaft 48. The cam ring 62 is fixed for rotation with the flange 64 (and therefore with the shaft 48) by means of a dowel 66.

Between the opposing faces of cam rings 58 and 62, there are disposed a series of bails or rollers 68 held in a cage ring 70. As shown in the drawings, the opposing faces of cam rings 58 and 62 are formed with valleys and peaks with opposing valleys accomodating the balls or rollers 68 in the illustrated rest position. The two cam rings are held in cooperation by means of a spring biassing arrangement. This arrangement comprises a thrust ring 72 held in the cavity 54 by a circlip 74, a disc spring arrangement 76, a thrust washer 78 and a low friction bearing 80.

The manner in which the described mechanical adjustor can be operated to increase the distance L and thus bring the cutting reel 1 0 into closer engagement with the bottom blade 30, can now be understood. As tne snaft 48 is rotated via the handwheel 40, the distance L is increased tnrough the screw thread engagement between push rod 36 anσ threaded bore 46. At the same time, the lower cam ring 62 is caused to rotate, with the upper cam ring 58 remaining stationary. With this relative rotation of the cam rings, the balls will tend to ride up the illustrated ramps of the respective cam surfaces until the cam rings are opposed peak-to-peak. With the upper cam ring 58 engaging aoutment face 56, the lower cam ring 62 is accordingly driven downwards, followed (through the action of flange 64) by the shaft 48. The depth of this superimposed movement is equal to 2B. B (as shown in the drawing), is the depth of the cam profile which is equal for both cam rings. As the shaft continues to rotate, the bails will run down the illustrated ramp surfaces of the cam rings until they are again positioned in the valleys of those cam rings as shown in Figure 2.

Under the biassing action of spring 76, the reciprocating movement of the shaft 48 is thus completed.

The action of the balls 68 in travelling between the valleys and the peaks of the opposing cam rings 58 and 62 will serve to index the adjusting movement. A "notching" effect will be felt through the handwheel 40, simplifying the equal adjustment of both ends of the cutter reel.

These two superimposed movements, that is to say the linear movement applied through the screw thread engagement of push rod 36 and bore 46, and the movement applied through the cam rings 58,62, are illustrated graphically in Figure 3. The dashed line 100 shows for one indexed adjusting interval or "notch", the movement that would be caused by the action of the cam rings 58,62, in the absence of all other effects. The movement is of course along the line of action of the adjuster and may be regarded as an apparent change in the length L. As will be appreciated, the opposing profiles of the cam rings 58,62 - with the friction reducing balls or rollers 68 - oroduce continuous reci^'Drocation toward and away from the mentioned amplitude 2B. This is seen in the saw-tooth profile of dashed line 100. There is shown in chain dotted line 102 the apparent change in length L that would arise - in the absence of all other effects - from the screw threaded engagement of the threaded portion 44 of push rod 36 and the threaded bore 46 in shaft 48. The scale used in the graph is arbitrary but it will be observed that the adjustment in L arising from the screw threaded engagement, is substantially less than the amplitude 2B of the reciprocation.

The full line 104 in Figure 3 illustrates the combined effect of the reciprocation shown in line 100 and the screw movement shown in line 102. Over the interval of one "notch" - defined of course by the described inαexing action of tne cam rings themselves - there is a net change in L determined by the screw thread parameters.

The apparent movements illustrated in Figure 3 represent the hypothetical situation of a mechanism having no backlash and infinitely rigid components. In a practical situation, the superimposed reciprocating movement ot the shaft 48 serves in succession to remove backlash; to create sufficient energy to move the cutting reel; to release this energy and to permit the taking up of backlash by the described spring biassing arrangement. The energy might include, for example, resilient compression of the push rod 36 together with strain in the pivotal connections of the trunnion 34 and of the push rod and resilient deflection of the other components of the cutting unit.

This effect can be descriDed more easily with reference to the graph of Figure 4. In this graph, full line 204 corresponds to line 104 of Figure 3 and represents the apparent combined movement of the mechanism. On the line 204 are marked points J,K,L,M,N&P which, again to an arbitrary scaie, correspond with identifiable thresholds in the mechanical movement. The chain dotted line 206 represents the actual physical movement or change in the length L. Thus, in the movement JK, backlash in the mechanism is removed and there is no actual movement seen in the line 206. The further movement KL serves to build up sufficient strain energy to overcome all resistances to movement in the mechanism. So actual movement begins only at the point L and continues until point M. The further rotational movement MN acts to release the excess energy buiit up in the system, whilst the movement NP reinstates backlash. Over these two latter movements MN and NP, there is no actual change in length L.

It should be noted that the springs 76, thrust washer 78 and bearing 80 do not form part of the adjustment mechanism itself. They are provided to absorb the effects of backlash, to provide a smooth action of the cams and to absorb looseness in the system.

The length L can if necessary be reduced by rotation of the handwheel 40 in the opposite direction. The axial loads in the push rod 36 are then transmitted to the trunnion 34 through the described spring biassing arrangement including spring 76. If the compressive resistance of spring 76 is arranged to be greater than the pull exerted by the push rod 36, the cam rings will remain in cooperation during this reverse movement, so that a similar "notching" effect will be achieved as that described for the forward movement.

It will be recognised that in the described arrangement, the superimposed reciprocal movement acts to release stored energy only when the adjustment is in the direction to increase the distance L. This is the more typical adjustment, serving to compensate for wear in the blade. If, however, it is desired to have stored energy released irrespective of the direction of adjustment, an additional set of cam rings and balls can be provided.

A further modification is illustrated in Figure 5. This is a view similar to Figure 2 and parts in common with Figure 2 retain the same reference numerals. In this modification, the cam surfaces of rigs 58 and 62 are in direct contact; no intervening bails or rollers are provided. The cam surfaces can, if appropriate to the application, be formed of or coated with low friction material.

The manner of operation of the adjuster shown in Figure 5 will be seen to be analogous to that of Figure 2.

An alternative modification is illustrated in Figure 6 and, again, parts in common with Figure 2 retain the same reference numerals. In this modification, the shaft 48 is provided with an integral collar having a peripheral cam track 300. The radial depth of this cam track is sufficient to accommodate cam follower rollers 302. These rollers are diametrically opposed and are mounted, one each, on bearing pins 304 formed integrally with mounting bolts 306.

It will be seen that as the shaft is rotated, the action of the rollers 302 moving in the cam track 300 will cause reciprocation of the shaft along the line of action of the adjuster. This will serve the same purpose as the reciprocal movement described in relation to Figure 2. It should be understood that this invention has been described by way of examples only and a wide variety of further modifications are possible without departing from the scope of the invention. The described arrangements share the advantage that the reciprocal movement is completed with rotation of the handwheel shaft in one sense. The reciprocation thus occurs automatically requiring only normal adjusting movement from the operator. This is the preferred system. It will in some cases nonetheless be possible to employ an arrangement in which the reciprocating movement comprises a first portion arising on rotation in one sense, and a second portion arising on rotation in the opposite sense. The first rotation would then move the adjuster through the desired length adjustment plus the amplitude of the reciprocation. The second, reverse rotation would retract the adjuster through the amplitude of the reciprocation.

One arrangement of this category would comprise a handwheel connected to a shaft through a pair of one-way clutches, coming into operation on rotation in opposite senses. The shaft is connected through a single screw thread engagement with the second member of the adjuster. The clutch associated with extending movement of the adjuster has close tolerances and rotation of the shaft commences immediately with rotation of the handwheel. The adjuster is thus extended the full screw length interval. The clutch associated with rotation of the handwheel in the opposite sense incorporates a deliberate degree of lost motion. In this way, full counter rotation of the handwheel results in only partial rotation of the shaft and thus only partial retraction of the adjuster. This partial retraction is equivalent to the amplitude of the reciprocation leaving the mechanism adjusted by one interval. The handwheel is conveniently provided with two stops limiting rotational movement in both directions. In certain cases a torsion spring or other arrangement can be provided to effect automatically the desired counter rotation. This will, however, significantly increase the required adjusting force and will not always be acceptable. Whilst the example has been chosen of an on-cut adjuster for a cylinder cutter, the mechanical adjuster according to this invention will find broad application where screw thread adjustments are to be made against a load in a mechanism incorporating a degree of resilience.

Whilst the mechanical adjuster of this invention has been described as overcoming effects of both backlash and stored energy, it will remain useful even in systems having no backlash. The described problem of stored energy leading to unwanted movement on subsequent vibration of the system, may remain even in a system without backlash.

Claims

CLAIMS:

1 . A mechanical adjuster comprising first and second anchorages; a first member rotatably mounted in the first anchorage and a second member secured to the second anchorage, the first and second members being in screw thread engagement such that rotation of the first member relative to tne first anchorage varies the distance between the first and second anchorages along a line of action, characterised in that there are provided means acting between the first member and the first anchorage to effect reciprocal movement of the first member relative to the first anchorage aiong said line of action concomitantly with rotation of the first member.

2. A mechanical adjuster according to Claim 1 , wherein said reciprocal movement is completed on rotational movement of the first member in a single sense.

3. A mechanical adjuster according to Claim 1 or Claim 2, wherein tne means acting to effect reciprocal movement comprise cooperating cam surfaces provided on the first member and the first anchorage respectively.

4. A mechanical adjuster according to Claim 3, wherein spring biassing means are provided to maintain said cam surfaces in cooperation and to accomodate said reciprocal movement.

5. A mechanical adjuster according to Claim 3 or Claim 4, wherein bearing elements are provided between said cooperating cam surfaces.

6. A mechanical adjuster according to any one of Claims 3, 4 and 5, wherein said cooperating cam surfaces are provided on respective cam rings both concentric of said line of action, one cam ring being rotatable with said first member, the other cam ring being fixed against rotation in said first anchorage.

7. A mechanical adjuster according to Claim 1 or Claim 2, wherein said means for effecting reciprocal movement comprises a cam and a cam follower provided respectively on the first member and the first anchorage.

8. A mechanical adjuster according to any one of the preceding claims, wherein said means for effecting reciprocal movement serves further to index rotation of the first member relative to the first anchorage.

9. A mechanical adjuster comprising a hand wheel shaft journalled for rotation in an anchorage; a connecting piece screw threaded to the shaft so as to extend on said rotation; first cam means provided for rotation with said shaft and second cam means fixed against said rotation in the anchorage, the arrangement being such that an in-line reciprocal movement is superimposed on said extension of the connecting piece to impart and to release resilient energy to the system undergoing mechanical adjustment.

10. A grass cutting unit having a frame; a bottom blade fixed in said frame; a cutting reel mounted in the frame for adjustment relative to the bottom blade and at least one mechanical adjuster according to any one of the preceding claims serving to effect said adjustment of the cutting reel.