GB1577126A - Cam mechanisms - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO CAM MECHANISMS (71) We, MOLINS LIMITED, a British Company, of 2, Evelyn Street, Deptford, London, SE8 5DH., do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention concerns improvements in or relating to cam mechanisms; more particularly, but not necessarily exclusively, this invention concerns conjugate cam mechanisms and followers therefor.

A conjugate cam mechanism consists of two cams connected to a common drive, the cams being normally mounted co-axially and each cam having a cam follower. The shape of one cam is complementary to the shape of the other cam, and the respective cam followers are mounted on, or rigidly linked to, a common carrier member in such a manner that they together produce a single output motion with positive drive at all times from one or the other cam. Conjugate cam mechanisms therefore find use in machinery, for example packing machines, where positive and rapid two-way motion is desired.

As against a single cam arrangement, in which a cam follower is biased against the cam, conjugate cams have the advantage of providing a much more positive output motion, even when one of the followers is on a sharply decelerating portion of the respective cam. However, conjugate cams themselves and their follower assemblies require to be machined and assembled to a very high degree of accuracy to ensure that the cam followers are each in contact with their respective cams for the full rotational cycle of the cams. In practice this requirement has been found difficult to achieve economically, and some radial error in the cams has to be accepted.

According to the invention there is provided a conjugate cam mechanism comprising a pair of cams of complementary shapes, and a pair of rotatable cam followers coacting with respective ones of said cams, in which the cam followers are carried at nominally fixed positions relative to one another on a common carrier member, each follower being resiliently mounted at its respective position on the carrier member by a metallic spring bush of substantially tubular section so as to allow a limited degree of radial movement between the follower and the carrier member. This allows radial error in the cams to be accommodated without uncontrolled play in the mechanism.

The spring bush may comprise a central cylindrical portion with spring fingers projecting from each end thereof. The fingers may terminate with lips for engaging opposite ends of the cam follower.

The invention also extends to a cam follower assembly comprising a pin, a rotatable cam follower mounted on the pin, and a metallic spring bush of substantially tubular section interposed between the pin and the cam follower to allow radial movement therebetween. The spring bush may include spring fingers as defined above; and the cam follower may consist of an outer sleeve rotatably carried by roller bearings on an inner race, with the spring bush interposed between the inner race and the pin to allow radial movement therebetween. The radial movement permissible by the spring bush may be about three times the actual radial movement of the outer sleeve corresponding to the expected maximum error in a cam with which the follower is to operate.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic view of a conjugate cam mechanism according to the invention, Figure 2 is a sectional view of a cam fol lower taken on the lines lI-II of Figure 1 but drawn to a larger scale, and Figures 3 and 4 are end and side views respectively of a spring bush shown in section in Figure 2.

Referring first to Figure 1, there is shown a common carrier member in the form of a Y-shaped lever, indicated generally by the reference numeral 10, which lever consists of two conjugate arms 12 and 14 of equal length, and of an output arm 16, only part of which is shown. The lever 10 is pivotally mounted on an axle 18 at the intersection of the three arms. Arm 12 carries at its free end a roller cam follower 20 which rides on a cam 24, while arm 14 likewise carries a roller cam follower 22 which rides on a cam 26. The cams 24 and 26 are secured together and to a common shaft 28. The shape of one cam is complementary to that of the other, in such a manner that during rotation of the two cams the followers 20 and 22 remain in contact with their respective cams at every angular position thereof, and impart to the lever 10 a pivotal movement on axle 18. This movement is transferred by the output arm 16 to produce the desired movement of a mechanism (not shown), for example a mechanism in a cigarette packing machine which forms no part of this invention.

Figure 2 shows a part of the arm 12 to the end of which is secured a pin 30 for mounting the cam follower 20. The pin 30 has a large diameter portion 32 and a reduced diameter portion 34 eccentric to the portion 32 and separated from it by a flange 36.

The cam follower 20 is of a construction similar to a roller bearing, consisting of an outer race 38 which is hardened for rolling on the cam 24, an inner race 40, and needle bearings 42 between said races.

A spring bush 44, shown in greater detail in Figures 3 and 4, is mounted between the reduced portion 34 and the bore of the inner race 40. The bush 44 has a central cylindrical portion 46 from each side of which extend a set of eight outwardly tapering fingers 48.

The ends of the fingers terminate in lips, forming together a castellated flange 50 at each end of the bush.

The bush 44 is made from a spring steel material, such as silver steel. It may be machined from a tubular workpiece and provided with a divergent taper at each end terminating in a flange. Typically the length of the bush is 15 mm and its internal diameter at the central portion 7 mm. The fingers 48 are then formed by making eight axial cuts of about 1 mm width from each flange 50. The bush is finally given the desired springiness by hardening and tempering.

The springiness of the fingers 48 enables the castellated flange 50 to be sprung inwardly sufficiently to allow the bush to be slid axially into the bore of the inner race 40, so that the flanges 50 resiliently engage opposite ends of the bore, as shown in Fig.

2. Preferably the bush 44 is fitted into the inner race before the cam follower 20 is assembled on to the reduced portion 34.

Referring again to Figure 2, the reduced portion 34 terminates at a shoulder 52, from which extends a threaded portion 54 on which a nut 56 and washer 58 are fitted. The length of the reduced portion 34, i.e. the distance between the shoulder 52 and the flange 36, is shorter than the length of the bush 44 such that when the nut 56 is tightened to clamp the washer 58 against the shoulder 52, there is only a slight axial force between the washer 58 and the flange 36. The cam follower 20 is thus able to move radially against the resilience or springiness of the bush 44.

The large portion 32 has a threaded hole (not shown) into which is screwed a bolt 60 bearing against a washer 62. The portion 32 is shorter than the width of the corresponding bore in the arm 12, so that the bolt can be tightened against the washer 62 to pull the flange 36 securely against the arm 12 and hence prevent movement of the pin 30 in the arm.

The construction of the other cam follower 22, and its mounting to the end of the arm 14, are similar to that of the cam follower 20 described above.

The setting up and operation of the conjugate cam mechanism will now be described.

In setting up the cam mechanism, the cams 24 and 26 are slowly rotated, preferably by hand, and the pins 30 are adjusted, by rotation, so that the eccentricity of their reduced portions 34 brings the outer races 38 to such positions (relative to shaft 28) that it is only just possible to rotate the cams fully. In this condition the spring bush 44 on each cam follower will just "bottom" against the respective reduced portions 34, this occurring at the cam position at which the maximum overall error in the cams occurs. The maximum radial error may typically be about 0.1 mm, and the total clearance provided by the bush 44 is preferably about 3 times this error, i.e. 0.3 mm.

Adjustment of each pin 30 may be effected by turning the pin with a tool which engages flat surfaces (not shown) on the flange 36.

When the pin is correctly adjusted, it is locked at its correct position relative to the arm 12 or 14, by screwing down the bolt 60 on to the washer 62, thus gripping the respective arm between the flange 36 and the washer 62.

The resilience of the bush 44 is selected so that when in operation one of the cam followers, say follower 20, is riding up a sharply accelerating portion of the cam 24, the inner race 40 will cause the bush 44 to bottom, due to the outward acceleration imparted to the follower 20. The bush 44 of the other follower 22 will not bottom at the respective position on the cam 26, unless this happens to coincide with the maximum error position.

The cam mechanism described ensures that each of the cam followers is constantly in contact with the respective cam, irrespective of the errors which exist in the cams.

WHAT WE CLAIM IS: 1. A conjugate cam mechanism comprising a pair of cams of complementary shapes, and a pair of rotatable cam followers coacting with respective ones of said cams, in which the cam followers are carried at nominally fixed positions relative to one another on a common carrier member, each follower being resiliently mounted at its respective position on the carrier member by a metallic spring bush of substantially tubular section so as to allow a limited degree of radial movement between the follower and the carrier member.

2. A conjugate cam mechanism as claimed in claim 1 in which said spring fingers projecting from each end thereof.

3. A conjugate cam mechanism as claimed in claim 2 in which said fingers termmate with lips for engaging opposite ends of the cam follower.

4. A cam follower assembly comprising a pin, a rotatable cam follower mounted on the pin, and a metallic spring bush of substantially tubular section interposed between the pin and the cam follower to allow radial movement therebetween.

5. A cam follower assembly as claimed in claim 4 in which said spring bush comprises a central cylindrical portion with spring fingers projecting from each end thereof.

6. A cam follower assembly as claimed in claim 5 in which said fingers terminate with lips for engaging opposite ends of the cam follower.

7. A cam follower assembly as claimed in any of claims 4 to 6 in which the cam follower comprises an outer sleeve rotatably carried by roller bearings on an inner race, with the spring bush interposed between the inner race and the pin to allow radial movement therebetween.

8. A cam follower assembly as claimed in claim 7 in which the radial movement permissible by the spring bush may be about three times the actual radial movement of the outer sleeve, corresponding to the expected maximum error in a cam which the follower is to operate.

9. A conjugate cam mechanism substantially as herein described with reference to, and as illustrated in, the accompanying drawings.

10. A cam follower assembly substantially as herein described with reference to, and as illustrated in, Figures 2 to 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. followers, say follower 20, is riding up a sharply accelerating portion of the cam 24, the inner race 40 will cause the bush 44 to bottom, due to the outward acceleration imparted to the follower 20. The bush 44 of the other follower 22 will not bottom at the respective position on the cam 26, unless this happens to coincide with the maximum error position. The cam mechanism described ensures that each of the cam followers is constantly in contact with the respective cam, irrespective of the errors which exist in the cams. WHAT WE CLAIM IS:

1. A conjugate cam mechanism comprising a pair of cams of complementary shapes, and a pair of rotatable cam followers coacting with respective ones of said cams, in which the cam followers are carried at nominally fixed positions relative to one another on a common carrier member, each follower being resiliently mounted at its respective position on the carrier member by a metallic spring bush of substantially tubular section so as to allow a limited degree of radial movement between the follower and the carrier member.

2. A conjugate cam mechanism as claimed in claim 1 in which said spring fingers projecting from each end thereof.

3. A conjugate cam mechanism as claimed in claim 2 in which said fingers termmate with lips for engaging opposite ends of the cam follower.

4. A cam follower assembly comprising a pin, a rotatable cam follower mounted on the pin, and a metallic spring bush of substantially tubular section interposed between the pin and the cam follower to allow radial movement therebetween.

5. A cam follower assembly as claimed in claim 4 in which said spring bush comprises a central cylindrical portion with spring fingers projecting from each end thereof.

6. A cam follower assembly as claimed in claim 5 in which said fingers terminate with lips for engaging opposite ends of the cam follower.

7. A cam follower assembly as claimed in any of claims 4 to 6 in which the cam follower comprises an outer sleeve rotatably carried by roller bearings on an inner race, with the spring bush interposed between the inner race and the pin to allow radial movement therebetween.

8. A cam follower assembly as claimed in claim 7 in which the radial movement permissible by the spring bush may be about three times the actual radial movement of the outer sleeve, corresponding to the expected maximum error in a cam which the follower is to operate.

9. A conjugate cam mechanism substantially as herein described with reference to, and as illustrated in, the accompanying drawings.

10. A cam follower assembly substantially as herein described with reference to, and as illustrated in, Figures 2 to 4 of the accompanying drawings.