GB2247063A

GB2247063A - A gear mechanism

Info

Publication number: GB2247063A
Application number: GB9110086A
Authority: GB
Inventors: Renzo Francioni
Original assignee: Cavanna SpA
Current assignee: Cavanna SpA
Priority date: 1990-08-17
Filing date: 1991-05-10
Publication date: 1992-02-19
Also published as: IT1240710B; GB9110086D0; IT9067647A1; DE4125294A1; NL9101085A; IT9067647A0; CH682253A5

Abstract

A gear mechanism, particularly for wrapping machines, comprises a driving gear (1), a driven gear (3) and at least two intermediate idle gears (6, 7), connected by arms (8 to 10) which extend in a generally polygonal arrangement and have means (13 to 15) for varying the geometry of the polygon so as selectively to vary the phase of the rotation of the driven gear (3) relative to the driving gear (1). <IMAGE>

Description

op 4 1 1 A GEAR MECHANISM The present invention relates in general to gear

mechanisms and is specifically concerned with a gear mechanism which can be used to vary the angular parameters (the speed and/or phase) of rotation of shafts, for example, in packaging machines and the like.

The present invention constitutes a development of-the prior-art solution to which Figures 1 and 2 relate.

In these drawings, three gears, indicated 1, 2 and 3, form parts of a gear mechanism.

By way of reference, the gear 1 may be considered to act as a drive member since it is keyed to a respective drive shaft which is rotated (by drive means not shown) about a respective axis X 11 The gear 2, which is rotatable about a respective axis X 21 however, acts as a member for transmitting the rotary motion to the gear 3 which constitutes the driven member of the gear mechanism and transmits the -ive output shaft rotatable about an motion to a respect axis X 3 Two rigid arms, indicated 4 and 5, connect the driving gear 1 to the idle gear 2 and the idle gear 2 to the driven gear 3, respectively.

Naturally, thi s representation is deliberately schematic and is intended to show that the arms 4 and 5 operate so as to maintain constant distances between the axis X 1 and the axis X 2' and the axis X 2 and the axis X 3' respectively.

2 According to the conventional principles of mechanics, the ratio between the speeds of rotation of the driven shaft associated with the gear 3 and of the drive shaft associated with the gear 1 is the reciprocal of the ratio between the diameters of the respective gears 3 and 1.

Moreover, it has also been found that the conditions under which the motion is transmitted by the gear mechanism, as regards the relative angular positions (the so-called phase relationship) of the driven shaft and the drive shaft can be varied by changes in the geometry of the gear mechanism. Furthermore, a cyclical phase change can cause a similarly cyclical variation in the speed of rotation of the driven shaft relative to its mean value which is determined by the transmission ratio of the gear mechanism, that is, by the diameters of the gears 1 and 3.

More particularly, this result can be achieved if the the shaft to which the driving gear is keyed is mounted on a rotary device which can cause the shaft, and hence the driving gear 1 as a whole, to move along a circular, orbital path such as that shown by a chain line and indicated T 1 in Figures 1 and 2.

The size of the angle defined by the arms 4 and 5 which are articulated to each other on the axis X2 of the idle gear 2 can thus be varied cyclically. In particular, two values, indicated C>( 1 and Cl' in Figures 1 and 2, substantially coincide with the minimum and maximum values assumed by th-Js angle when the axis of rotation X 1 of the driving gear 1 is in two 1 1 3 positions on its path T 1 which are diametrally opposed along the line of the arm 4.

Naturally, the geometry of the mechanism of Figures 1 and 9.2 could be changed, at least in principle, by the use of various solutions: for example, with the additional and/or alternative variability of the Position of the axis of rotation X3 of the driven gear 3.

In any case, it can readily be seen that such a change in the geometry of the mechanism causes a change in the relative angular positions of the driven gear 3 and the driving gear 1 (their so-called phase relationship).

In this connection, it suffices to compare Figures 1 and 2 to see what happens to the angular position of the driven gear 3 when the gear 1 is moved from the position shown in Figure 1 to the position shown in Figure 2, and vice versa, if the other parameters remain unchanged. In this connection, in order more readily to understand this phenomenon, it suffices to refer to an imaginary operating condition in which it is assumed that the gear 1 is not rotating about its axis and no rotary motion is therefore actually transmitted by the mechanism (except for the angula-orientation of the gear 3 resulting -from the change in the geometry of the mechanism).

It can also readily be seen that, when the mechanism is in operation and the rotary motion is actually transmitted continuously from the gear 1 to the gear 3 by means of the gear 2, its angular orientation results in a kind of advance or retardation of the movement of the gear 3, that is, in practice, an "oscillation" 1 4 of the speed of rotation of the gear 3 about its mean speed of rotation (determined by the gear ratio). This oscillation takes place at a frequency which is determined by the frequency with which the geometry of the gear mechanism is changed. For example, if the axis of rotation X 1 of the gear 1 is made to orbit in the path T 1 at a certain frequency (X revolutions/minute), the speed of rotation of the driven gear 3 will vary more or less sinusoidally about its mean value at the same frequency.

It can also be noted that the amplitude of the oscillation of the speed of rotation of the driven gear 3 (that is, the difference between its maximum speed max and its minimum speed min) can be varied selectively by changes in the degree of eccentricity of the orbital movement of the driving gear 1 (that is, the diameter of its path T 1).

The prior-art solution of Figures 1 and 2 has been used to advantage by the Applicant, for example, to impart the necessary oscillation to the speed of rotation of the rotary closure and welding jaws of packaging machines of the type described in Italian patent No. 1,208,411 and in the corresponding United States patent No. 4,362,673, both in the name of the present Applicant.

in this area of application, the Applicant has found it necessary to take account of some limitations intrinsic in the mechanism of Figures 1 and 2.

In particular, packaging machines of the type mentioned above tend to reach ever higher operating speeds.

With reference to the mechanism in question, this 1 h 1 1 1 1 results in an increase in the speed of rotation of the driven shaft which pilots the movement of the jaws, and hence an increase in the absolute speed of rotation of the whole gear mechanism and, in particular, of the driving gear 1, and a corresponding need to increase frequency of the orbital movement of the driving the - gear 1 in its path T in fact, the speed of rotation of the jaws must complete one full cycle of oscillation for each article which is packaged.

All this results in a considerable increase in the stresses borne by the driving gear 1 which - in operation - is subject both to its normal rotary motion and to the orbital movement along the path T 1 This need to withstand greater stresses could, in principle, be satisfied by the use of larger driving gears. This selection, however, would result in a corresponding need to increase the dimensions of the driven gear 3.

(the transmission ratio of the mechanism is in fact determined by the ratio between the diameters of the gears 1 and 3). As well as making the mechanism as a whole more bulky (making it much less responsive as regards the oscillation of its speed because of its increased inertia) and making the eccentric device on which the gear 1 is mounted even more difficult to manufacture, this solution has an intrinsic 'Limitation, given the physical impossibility of increasing the dimensions of the driven gear 3 beyond the maximum diameter compatible with the dimensions of the machine.

To all this is added the fact that, in the area of application indicated above, it is generally desirable to avoid the need to operate the mechanism and, in particular, the driving gear 1 in an oil bath.

j 6 moreover, in such specific areas of application (such as that to which the present Applicant's patent application of even date relates) it is desirable, in the presence of certain accidental phenomena, such as, for example, a failure to supply an article to the machine for packaging, to superimpose on the oscillation of the jaws a temporary phase difference between the gear 3 and the gear 1 - for a period of time approximately corresponding to the time the article which was not supplied would have taken to pass through the machine - with the immediate, precise reestablishment of normal operating conditions as soon as the transitory phase has passed. - There is thus a need to provide an improved gear mechanism which is based on the prior-art solution of Figures 1 and 2 but overcomes the limitations described above.

According to the present invention, this object is achieved by virtue of a mechanism having the characteristics recited specifically in the claims which follow.

The invention will now be described, purely by way of non-limiting example, with reference to the appended drawings, in which:

Figures 1 and 2, which relate to the prior art, have already been described above, and

Figures 3 and 4 show, in the form of kinematic diagrams and according to principles substantially the same as those adopted above, the characteristics and operating criteria of a mechanism according to the invention.

j, S_ i:1 1 1 I 1 1 1 1 1 1 1 d 1 1 1 1 7 In Figures 3 and 4, parts substantially the same as or equivalent to parts already described with reference to Figures 1 and 2 have been indicated by the same reference numerals.

This applies, in particular, to the driving gear 1, the driven gear 3 and the parts directly associated therewith.

The main characteristic of the mechanism according to Figure 4 is that the motion is transmitted between the driving gear 1 and the driven gear 3 by means of two intermediate idle gears 6 and 7.

In particular, the gear 6 meshes with the gear 1 and the gear 7 whilst the gear 7 meshes with the gear 6 and the gear 3. Three transmission arms, indicated 8, 9 and 10 are articulated to each other and connect respectively:

- the axis of rotation X 1 of the gear 1 to the axis of rotation X 6 of the gear 6 (arm 8), - the axis of rotation X 6 of the gear 6 to the axis of rotation X 7 of the gear 7 (arm 9), and - the axis of rotation X 7 of the gear 7 to the axis of rotation X 3 of the gear 3 (arm 10).

In general, the arms 8, 9 and 10 extend along the sides of a polygon which, as can easily be seen, is not altogether coherent in the sense that, if the axes X 1 and X 3 are kept in fixed positions, the axes X 6 and X 7 nevertheless retain a certain ability to move in the plane of the polygon.

8 This is certainly not the case in the prior-ar-,,-mechanism of Figures 1 and 2, in which, if the axes X 1 and X 3 are kept in fixed positions, the axis X 2 of the idle gear (2) consequently also stays in a fixed position:

in this case, the change in the geometry of the mechanism is achieved by the orbiting of the gear 1, and hence of the axis X,, in the path T 1 The movements of the axes X 6 and X 7 in the solution of Figures 3 and 4 are not, however, completely independent. In fact, if the axes X 1 and X 3 are kept fixed, once the axis x 6 is moved along a certain path (generally in an arcuate, orbital mdvement relative to the axis X 1), the resulting path of movement of the axis X 7 is univocally determined.

The geometry of the mechanism of Figures 3 and 4 and in particular, its variability can be used for at least two different purposes.

A first possibility is to connect the axis X 6 (that is, the shaft or pin about which the idle gear 6 to a mechanism constituted by a connecting rod crank 12. This is rotated about a respective rotates) 11 and a axis X 12 movement so as to impart to the axis X 6 an intermittent to and fro along a generally arcuate path T 2 whose centre lies on the axis X 1 of the gear 1.

Naturally, the mechanism 11, 12 could be connected to the idle gear 7 instead of or as well as to the idle gear 6.

On the basis of the principle described in detail with reference to Figures 1 and 2 in connection with a prior-art mechanism, the to-and-fro movement of the J j 1 m 1 i 1 -1 i 1 3 9 ax:l s X 6 of the gear 3 results, if all else remains the same, in an "oscillation" of the angular position, and hence the angular velocity, of the gear 3 during the operation of the gear mechanism. The amplitude of the oscillation is determined by the length of the path T 2 and hence by the degree of eccentricity of the crank pin 12, which eccentricity may be made selectively variable and adjustable. The frequency of the oscillation is determined univocally by the speed of rotation of the crank 12 about its axis X 12 With the solution of Figure 3, it is thus possible to make the speed of rotation of the- gear 3 oscillate whilst the axis of rotation X 1 of the driving gear 1 is kept fixed.

The oscillation of the speed of the driven gear 3 is achieved by the intervention of parts (the crank 12 and its connecting rod 11) which are not part of the transmission mechanism, in the sense that theypjay no part in the establishment of the transmission factor of the gear mechanism. Moreover, the transmission factor no longer depends on the ratio between the diameters of the driving gear 1 and the driven gear 3, as in the solution of Figures 1 and 2, but also on the diameters of the intermediate gears 6 and 7.

All this means that the problems pointed out in the introductory part of the present description can be prevented.

In particular, the following may be observed.

For a given transmission ratio between the driving gear 1 and the driven gear 3, it is now possible, by the choice of diameters for the intermediate idle gears 6 and 7, to avoid an excessive reduction in the dimensions of the driving gear (1) to alevel such that its wear-resistance properties are crucial. At the same time, it is not necessary to use an excessively large driven aear 3 which would be incomnatible with the 1 typical size limits of the machine in which the mechanism is installed.

i in the second place, it is possible to consider the placing of part of the connecting rod and crank mechanism 11, 12 in an oil bath to improve their operating conditions.

The variant of Figure 4 provides, within the scope of the invention, for the use of an element of the prior-art solution, that is, the ability to impart to the axis of rotation X 1 an orbital rotary movement in the circular path T 1.

In this case, the arm 10, which forms the connection between the axis of rotation X 7 of the intermediate gear 7 and the axis of rotation X 3 of the driven gear 3, takes the form of a true pivoting element which can be oriented selectively by the action of a transmission arm 13. The arm 13 is moved by a triangular element 14 which is pivoted about a respective axis X 14 by a pneumatic or hydraulic jack 15.

in general, the element 10 is movable between a first operating position, shown in continuous outline and indicated A in Figure 4, and a second operating position, indicated B and shown in chain outline in the same drawing.

1 i 1; 1 i 1, 1:

i r P 1 A 1 1 For example, it may be assumed that the element 10 takes up the position A when the jack 15 is in its rest position and reaches the position B when the jack is operated so that its rod moves outwardly.

The movement of the element 10 _from the posi-tion: to the position B, which takes place with a general switching movement, that is, without an appreciable stay in any intermediate positions, results essentially in a change in the geometry of the mechanism and, consequently, a change in the instantaneous phase of the rotation of the driven gear (3) relative to the driving gear 1.

: this character is t- ic, for Advantage may be taken oJ.

example, in wrap-ping machines, and particularly in the wrapping machine disclosed in Italian Patent Application 67648-A/90 by the same Applicant.

in this specific case, it is desirable for the detection (for example, by optical means according to known principles) of the presence of one or more empty positions in the flow of articles supplied to the wrapping machine to cause a phase change in order to hold back the jaws of the machine (which is preferably of the tyme with two closure units in cascade). For example, the jaws have to be slowed down or accelerated according to the position in which they are situated or, in other words, the phase of their rotary closure movement has to be advanced or retarded to take account of the fact that they w-4111 close an empty wrapper, that is, a wrapper which does not contain a product.

in particular, when a space is detected in the supply flow, the control system of the machine (usually a PLC 1 6 9 12 controller) intervenes at a predetermined moment and operates the jack 15. The resultant pivoting of the element 10 from the position A to the position B accelerates or slows the jaws as necessary because of the operation on an empty wrapper. As soon as this transitory event has passed, the controller of the machine returns the jack to its deactivated position, so that the element 10 returns exactly to its previous position (A). All this ensures that once the transitory event has passed the original operating conditions of the jaws are re-established precisely and quickly.

Naturally, the principle of the invention remaining the same.. the details of construction and forms of embodiment may be varied widely with respect to those described and illustrated, without thereby departing from the scope of the present invention.

1 1 1 1 1 i 1 i 4 4 1

Claims

13 CLAIMS

1. A gear mechanism including a driving gear (1), a driven gear (3) and at least one intermediate gear (6, 7) whose axes of rotation (X 1' XO' X7' X3) are connected by arms (8 to 10) which enable the geometry of the mechanism to be varied, characterised in that it has at least two intermediate idle gears (6, 7) and, consequently, at least three arms (8 to 10) extending in a generally polygonal arrangement, and in that it has means (11, 12; 13 to 15) for selectively varying the geometry of the polygon.

2. A mechanism according to Claim 1, characterised in that the means include a connecting rod (11) and a crank (12) which can impart to the axis (X 6) of at least one (6) of the intermediate idle gears a general to-and-fro movement (T 1) so as to cause the angular characteristics of the rotation of the driven gear (3) to oscillate generally relative to the angular characteristics of the rotation of the driving gear (1) -

3. A mechanism according to Claim 1 or Claim 2, characterised in that the means include control members (13 to 15) for orienting at least one (10) of the arms between a first operating position (A) and a second operating position (B) in which the at least one (10) arm assumes different angular orientations.

4. A mechanism according to Claim 3, characterised in that the control member (12 to 15) orients at least one (20) of the arms between the first (A) and second (B) 14 operating positions by a general switching movement substantially without its staying in any intermediate positions.

5. A mechanism according to Claim 3 or Claim 4, characterised in that the control member comprises a fluid jack (16).

6. A mechanism according to any one of the preceding' claims, characterised in that it also includes means for imparting a general orbital movement in a circular path (T 1) to the axis (X,) of at least one of the driving gear -91) and the driven gear (3).

7. A machine, particularly a wrapping machine, including a mechanism according to any one of Claims 1 to 6.

8. A gear mechanism substantially as hereinbefore described with reference to Figure 3 or 4 of the accompanying drawing.

9. A machine including a mechanism substantially as hereinbefore described with reference to Figure 3 or 4 of the accompanying drawings.

Published 1992 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 1 RH Further copies may be obtained front Sales Branch. Unit 6. Nine Mile Point. Cwrnfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques'ltd. Si Marv Cra. Rent.

i; 1 i ' i 1 1