Synchronizer for activating and de-activating a dog clutch, particularly in article-wrapping machines

Abstract: The outputs (17-18) of a pair of intermittence devices (16) operated in phase with the driving shaft (6) for the clutch (4), generate equal movements, however in a 180° out-of-phase relation with each other. With the interposition of respective electromagnetic friction clutches (27-28), these outputs are connected to the driven disc of the clutch. The two clutch discs are normally interconnected by at least one respective dog (9-10). A control logic (22) connected to a generator of clock signals (K1-K2) in phase with the uniform motion and rest times of the outputs from the intermittence devices, commands the clutch to be opened and closed, when the friction clutch at the selected output is closed, and when the said output travels at the same speed as the input into the intermittence devices. The selected clutch is each time closed and opened in phase with the said clock signals, and when the output from the intermittence devices and the driven disc of the clutch are in the same condition of motion, or of rest.

Description: Article-wrapping machines are usually provided with a rotating knife which severs a continuous web transversely so as to form therefrom the wrappers required to enwrap articles. In the majority of the presently-used wrapping machines, in case of absence of an article to be wrapped, the knife and web-feeding unit are stopped to discontinue the production of wrappers. This discontinuance requires the installation, in the kinematic chain which actuates the knife and web-feeding unit, of a dog clutch capable of timely re-activating said means and the knife connected thereto (see US-A- 4075816). Due to the high operating speed of the modern wrapping machines, the dogs of said clutch are submitted to mechanical stresses of considerable value in the re-activation step, with the disadvantages resulting from this condition. The object of the invention is to overcome said disadvantages by means of the following solution. First of all, the two discs of the clutch are provided each with only one dog. The driven part of the clutch is connected, via a rigid drive with interposed respective electromagnetic friction clutches, to a pair of intermittence devices of equal characteristics, 180° out of phase from each other and connected at the inputs thereof to the same shaft which actuates the driving part of the clutch. Each intermittence device produces at the output thereof a variable motion which changes as follows at 60° intervals: it proceeds at the same speed as the input shaft; it decelerates down to a stoppage; it keeps still; it accelerates up to the same speed as the input shaft. The driving shaft of the clutch has mounted thereon a generator which produces clock signals on each revolution of said shaft, which are 180° out of phase from each other. One of these signals is concurrent with the coincidence of the recess in the clutch-driving cam with the respective disengagement roller. During the normal operative condition of the wrapping machine, the dog clutch is engaged and the friction clutches of the intermittence devices are de-energized. In case of absence of an article, the action of the clutch-disengagement roller is commanded and when said roller enters the recess in the respective cam the energization is commanded of the electromagnet of the stoppage intermittence device which at that moment produces through 60° at the output thereof a motion which is equal to the input motion. During this step, the friction clutch becomes engaged with no fretting. Before the end of said equal motion condition, the dog clutch is disengaged. Thereafter, the driven disc of the dog clutch, which is controlled by the stoppage intermittence device, slows down and then stops and during the stoppage period the friction clutch of said intermittence device is de-energized. The dog of the driven disc of the dog clutch, therefore, is out of phase with respect to the dog of the driving disc, of such an extent whereby every time said dog clutch re-engages due to the action of the low contour of the disengagement cam, the two dogs never interfere with each other. In the presence of an article, upon reception of a clock signal for engagement of the dog clutch, the retraction is controlled of the roller for the disengagement cam. At this same moment and through sixty degrees, the output of the starting intermittence device is at a standstill. The energization of the friction clutch is then commanded. Thereafter, the driven disc of the dog clutch is accelerated and the respective dog is reached by the dog of the driving disc, whereafter both discs will rotate at the same speed. In the sixty degree interval wherein the starting intermittence device maintains the driven disc at the same speed as the driving disc, when the other clock signal is reached, the friction clutch of said intermittence device is de-energized and the driven disc is controlled solely by the driving disc. In the apparatus of the invention, therefore, the rotating knife which forms the wrappers can be timely stopped and re-activated, avoiding the harmful mechanical stresses which presently affect the dogs of the clutch upon each re-activation. Further characteristics of the invention, and the advantages resulting therefrom, will become apparent from the following description of a preferred but not sole embodiment thereof, shown merely as a non-limiting example in the accompanying drawings, wherein: Figure 1 is a diagrammatic plan view and partly sectional view of the synchronizer according to the invention, the clutch being disengaged; Figure 2 is a front elevational view of the double intermittence device used in the apparatus according to the invention; Figure 3 shows a diagram of the motions of the input and output shafts of the double intermittence device; Figures 4 and 5 show by means of an angular diagram, the various mutual positions of the dogs of the clutch during the stoppage step and starting step of the driven disc of said clutch. In figure 1, the numeral 1 indicates the wrapper-forming knife which rotates about its axis 2 and which, via a rigid drive 3, for example of the chain and sprocket type, is connected to the driven disc 104 of a dog clutch 4 which in the illustrated example is rotatably supported, with the intermediary of bearings 5, on the driving shaft 6 which is connected to the prime mover M of the machine and which is supposed to be rotating continuously. The driving disc 204 of the dog clutch is keyed on the shaft 6 as shown at 7 and is movable axially on said shaft against the action of a spring 8 which urges it to abut against the disc 104. The discs 104 and 204 are provided each with a dog, shown at 9 and 10, respectively. The hub of the driving disc 204 is formed integrally with a cam 11 for disengaging the dog clutch, said cam being formed with a low contour as shown at 111 having an angular amplitude of about 60°. Said recess 111 of the cam can receive under command a roller 12 carried by a mechanism which can move perpendicularly to the shaft 6, as indicated by the arrow 13. According to the invention, the shaft 6 or any other suitable member of the kinematic chain of the machine is connected, via a positive drive 14, to the input of a double intermittence device 16 having parallel axes, for example, of the type shown in figure 2 and known under the name "Parablock". The numerals 17 and 18 indicate the two parallel outputs of the intermittence device. The two intermittence devices incorporated in the unit 16 are equal to each other, are 180° out of phase to each other and are characterized in that they provide at the outputs 17-18 a variable motion that, at suitable intervals (for example, 60°) changes as follows: a- it proceeds at the same speed as the input shaft; b- it slows down to a stoppage; c- it keeps still; d- it accelerates up to the same speed as the input shaft. Figure 3 shows, by a broken line and a dot-and-dash line, the motion variations of the outputs 17-18, and by a solid line is shown the motion of the input 15 and the shaft 6. From this diagram it appears that when the output 17 is at a standstill the output 18 is moving, and when any one of said outputs accelerates, the other one decelerates. In the same diagram of Figure 3, 11 indicates the development of the contour of the disengagement cam of the dog clutch 4, the recess 111 being timed with the movements a- and c- of the outputs 17-18 of the double intermittence device. K1 and K2 indicate clock signals which are 180° out of phase from each other, the former beginning substantially at the beginning of the steps a- and c- mentioned above. These signals can be generated, for example, by a cam 19 which is keyed on the shaft 6 and is scanned by two stationary sensors 20-21 which are spaced apart 180° angularly. The signals from the two sensors flow into a control logic 22 having connected thereto a terminal 23 from a sensor which detects the presence of an article at or towards the wrapping station. The numeral 24 indicates a power input, and the numerals 25,26 indicate the corresponding terminals which are connected to the electromagnetic friction clutches 27,28 arranged between the outputs 17,18 and a positive composite drive 29, e.g. of the chain-and-sprocket type, connected to the drive 3 connecting the dog clutch 4 to the knife 1. Finally, the numeral 30 indicates the terminal controlling the displacement 13 of the roller 12. The apparatus conceived as above operates as follows: In the presence of an article, the friction clutches 27,28 are disengaged and the dog clutch is engaged. The roller 12 is in its rest position, away from the cam 11. If a signal of absence of an article comes from the terminal 23, the unit 22 causes, via the terminal 30, the approach of the roller 12 to the cam 11. When the roller 12 enters the recess 111 of the cam, the group 19,21,22 generates the clock signal K1 which activates the friction clutch 27. It can be appreciated from figure 3 that, at this moment, the output 17 of the intermittence device 16 moves at the same speed as the input 15 and kinematic chain 29, whereby no relative motion exists between the discs of the engaged friction clutch. Through these first 60°, the dogs move from the position shown at A to that shown at B in figure 4. Through the following 120° rotation, while the clutch 4 is disengaged by the co-operation of the roller 12 with the upper portion of the contour 111 of the cam 11, the output 17 of the intermittence device 16 decelerates and lags through 60°, whereby when the dog 9 is in the position shown at D, the dog 10 is in the position C. At C the dog 10 is at a standstill, while the dog 9 from D continues moving at constant speed. From figure 3, it appears that when the dog 10 arrives at C, the output 17 of the intermittence device is at a standstill and so remains through 60°. In this time interval, timely with the clock signal K2, the friction clutch 27 is de-energized automatically, whereby the dog 10 remains at a standstill irrespective of the successive variations of motion of the output 17. Each time the dog 9 moves through the space A-B, the roller 12 co-operates with the recess 111 of the cam 11 and the disc 204 approaches the disc 104. From B to A the disc 204 moves away and remains away from the disc 104, so that when the dog 9 goes through C, it does not interfere with the dog 10 which is at a standstill. To prevent that mechanical and/or electromagnetic inertia from modifying the position of the dog 10 at C upon disengagement of the friction clutch 27, the disc 104 may be advantageously provided integrally with a peripheral projection 31 (figure 1) which, when the roller 12 is inserted in the cam, abuts against a projection 32 secured to the support of said roller 12. Upon reception of a signal of presence of an article from the terminal 23 (figure 1), the logic 22 waits for the clock signal K1 from the group 19,20 which indicates the presence of the roller 12 in the recess 111 of the cam 11, and timely with said signal said logic 22 causes the energization of the friction clutch 28 and the retraction of the roller 12, whereby the projection 32 moves away from the projection 31. It can be noted in figure 3 that the output 18 of the intermittence device, starting from said signal K1, remains at a standstill through 60°, whereby while the dog 9 of the dog clutch 4 moves from A to B (figure 5), the dog 10 keeps still at C. Thereafter, while the dog 9 moves from B to D and travels through 120° (remember that the dog clutch 4 is now engaged), the dog 10 moves from C to D with such an acceleration (figure 3) as to reach the same rotational speed as the dog 10, so that when both dogs will contact with each other at D they move at the same speed and are not subjected to those harmful stresses that occur in the known art. At D the clock signal K2 is received. From that moment, while the dogs 9 and 10 move from D to E, the output 18 of the intermittence device moves at the same speed as the input. During this time interval, timely with the clock signal K2, the friction clutch 28 de-energizes automatically. The dog 10 of the dog clutch is thus disconnected from the output 18 and is under the control of the dog 9 which drags it into rotation as required, timely with the other components of the machine. It is to be understood that a single intermittence device may be used, having a control logic 22 capable of operating during the intervals a- and c- of the movement of the output of said intermittence device. This modified embodiment, with respect to the embodiment illustrated herein, has the disadvantage of a less timely action. A further modification may be made in the control for the engagement and disengagement of the dog clutch 4, which may not be provided of the cam and may be provided with a conventional axial-shift fork which is moved by an actuator connected to the terminal 30.

Claims: A synchronizer for activating and de-activating a dog clutch (4), particularly adapted for timely controlling the rotating knife (1) and the group forming and feeding the wrappers in an article-wrapping machine, the driving disc (204) being axially movable away from the driven disc (104) of the dog clutch by any suitable means, characterized in that the two discs of the clutch are normally coupled with each other by means of at least one respective dog (9,10) and that via a positive drive (29) the driven disc (104) is connected, with the intermediary of at least one electromagnetic friction clutch (27), to the output of at least one intermittence device (16) whose input (16) is connected, via a positive drive (14), to the driving shaft (6) of the dog clutch, said output of the intermittence device being subjected to the following variations of motion succeeding at suitable intervals : a- it proceeds at the same speed as the input shaft; b- it decelerates down to a stoppage; c- it keeps still; d- it accelerates up to the same speed as the input shaft; means (19,20,21) being provided to generate clock signals (K1,K2) at said steps a- and c- at the output of the intermittence device, said signals being transmitted to a control logic (22) having connected thereto the terminal (23) of a sensor which detects the presence or the absence of an article and having terminals (25,30) stemming therefrom to control said electromagnetic friction clutch (27) and the control means (13) for engaging-disengaging the dog clutch, the arrangement being such that either the disengagement or the engagement of the dog clutch in case of either absence or presence of an article, respectively, occur timely with said clock signals, when the electromagnetic friction clutch has been engaged and the output of the intermittence device moves at the same speed as the input to avoid undesired interferences between the dogs of said clutch, while the friction clutch is engaged and disengaged, timely with said clock signals (K1,K2), during the time intervals wherein the output of the intermittence device and the driven disc of the dog clutch are in the same condition of movement or of rest. A synchronizer according to claim 1, characterized in that the driven disc (104) of the dog clutch is connected to a positive drive (29) and via respective electromagnetic clutches (27,28), to the outputs (17,18) of a double intermittence device (16), wherein said outputs are characterized by the variations of motion mentioned above (a-b-c-d-), equal but out-of-phase 180° from each other, whereby while one of them is at a standstill, the other is moving and while one of them accelerates, the other decelerates, all being devised to carry out the controls for engaging and disengaging the dog clutch (4) quickly and timely. A synchronizer according to claim 1, characterized in that the dog clutch (4) is controlled by means of a cam (11) whose contour comprises a lower portion (111) having an amplitude of 60° and timed with one of the clock signals (K1) generated by said suitable means, the device for moving the roller (12) acting, under command, on the contour of said cam, being provided with a projection (32) which, when said roller is operated for the disengagement of the dog clutch, interferes with a projection (31) provided on the periphery of the driven disc (104) of said clutch when the latter disc has been stopped, all being devised to avoid any undesired displacement of said disc caused by mechanical and/or electromagnetic inertia of the mechanical and electromagnetic devices connected thereto.

Inventors: SALICINI SANDRO, SALICINI, SANDRO
Applicants: CARLE & MONTANARI SPA, CARLE & MONTANARI S.P.A.
Application year: 1991
Main classification: F16H3
IPC codes: F16H3, B65B57, F16D11