EP1032536B1 - Method for controlling a screwing spindle - Google Patents

Abstract

The invention concerns a method for controlling a screwing spindle comprising a motor supplied with fluid and having a motor element (18) coupled with the spindle shaft (5) to drive it in rotation, the method comprising the step of supplying the screwing spindle in nominal pressure conditions and flow rate generating the required tightening torque, and a prior step during which the screwing spindle is supplied in conditions less than the nominal conditions in sufficient proportion for the screwing spindle to rotate at a speed generating kinetic energy producing a tightening torque less than the required tightening torque.

Description

The present invention relates to a method of control of a screw spindle such as those used for fitting screw caps on packaging with threaded necks. Such a process is described in document CH 637 600 A.

We know screwing pins such as described in document FR-A-2,754,750, published on 24.04.1998, which include a linear cylinder having a piston connected to a spindle shaft to drive it in rotation. A commonly used process used for the control of such pins consists of subject the piston to a differential pressure of tightening generating the required tightening torque of the plug on the neck of the packaging. There is a problem that at the beginning of the screwing of the cap, there is little friction between the cap and the neck, so that a low torque resistant opposes rotation of the spindle. The tree of spindle then acquires a high rotational speed and, from the makes inertia the spindle tree stores energy important kinetics. The kinetic energy thus stored causes a rapid screwing of the cap until the moment when it comes to a stop, which causes the sudden stop of the spindle shaft. During this stop, the kinetic energy stored is returned by application to the cap under the form of a dynamic couple, greater than the couple of tightening required. This dynamic couple risks causing deterioration of the packaging cap or neck, or to oblige a user of the packaging to use a tool to loosen the cap.

An object of the invention is to propose a method control of the screw spindle allowing obtaining precise the required tightening torque.

With a view to achieving this goal, provision is made, according to the invention, a method of controlling a spindle screwing, including a step of feeding the spindle screwing in fluid under nominal pressure conditions and flow generating a required tightening torque and a previous step during which the screw spindle is powered under conditions below the conditions nominal in sufficient proportion that the spindle shaft has a rotational speed generating kinetic energy producing less torque than tightening torque required.

In particular, in the case of a linear cylinder comprising a piston, the piston is subjected during the step prior to an average differential pressure less than a differential clamping pressure.

So the average differential pressure ensures the rotation of the spindle shaft at a speed weak resulting in weak energy accumulation kinetic. When the clamping pressure is applied to the piston, the resistant torque opposing the screwing is then sufficient to prevent the rotational speed of the spindle increases so that the plug stops as soon as the resisting torque is equal to the motor torque corresponding to clamping pressure. There is therefore no refund brutal kinetic energy so the couple of effective tightening applied to the plug is equal to the torque of tightening required.

According to a first mode of implementation of the invention, during the prior step, one face of the piston is subjected in a screwing direction to a constant pressure lower than the differential clamping pressure.

Two different pressures are used. So, once the tightening operation is completed, the pressure constant below the clamping pressure can be used for the return of the cylinder so that an economy significant fluid is achieved.

According to a second embodiment, the piston is subjected to constant pressure in one direction screwing, and at a back pressure.

The average differential pressure is then equal to the difference between the constant pressure applied to the face of the piston and back pressure. Preferably, the constant pressure is equal to the clamping pressure. A single pressure level, corresponding to the torque of tightening required, is then necessary. The regulation of cylinder fluid pressure is simplified.

According to a third embodiment, the piston is subjected intermittently to a pressure of constant value.

Thus, the rotation of the spindle is initiated by the pressurization and the kinetic energy is restored during the pressure cut-off times so that it is possible to control the spindle speed in acting on the pressurization times and the pressure cut.

Advantageously in this variant, the pressure differential has a constant value equal to the pressure Clamping.

As in the previous case, only one level of pressure, corresponding to the required tightening torque, is then employed so that the pressure regulation of the feed fluid is simplified.

Other characteristics and advantages of the invention will emerge on reading the description which follows particular non-limiting variants of the invention.

• la figure 1 est une vue partielle en perspective d'une broche de vissage,
• les figures 2, 3 et 4 sont des représentations schématiques de l'organe de commande de la broche correspondant à trois modes de mise en oeuvre du procédé selon l'invention.

Reference will be made to the accompanying drawings, in which:

• FIG. 1 is a partial perspective view of a screw spindle,
• Figures 2, 3 and 4 are schematic representations of the spindle control member corresponding to three embodiments of the method according to the invention.

With reference to the figures, the screw pin controlled according to the method of the invention has a structure and a functioning known per se and some of its elements have not been represented. In the mode of illustrated embodiment, it includes a guide tube vertical 1 fixed to a spindle support 2 and sliding vertically in a sleeve 3 secured to a platform rotary 4. The tube 1 rotatably receives a spindle shaft 5, the lower end of which protrudes from the tube 1 and carries a jaw gripper 6. The end upper part of spindle shaft 5 carries a bevel gear 7 cooperating with an engine assembly generally designated as 11.

Spindle holder 2 is mounted to slide on a column 9 fixed to the rotary platform 4 and carries a roller 8 intended to cooperate with a cam of a frame fixed to position the support 2 and the parts in height associated with it.

A support plate 10 is fixed on the side of the spindle support 2 and carries the motor assembly 11.

The motor assembly 11 comprises an intermediate shaft 12 rotatably mounted in a bearing 13 carried by the support plate 10. The shaft 12 has one end bearing, by via a free wheel 45, a return pinion conical 14 whose teeth are in contact with those of the pinion 7, and an opposite end carrying a pinion input 15 whose teeth are in contact with those of a rack 16. rack 16 is fixed by its lower end to the rod of a jack 17 whose body is fixed to the support plate 10.

The jack 17 conventionally comprises a piston 18 mounted to slide in the cylinder body and define two chambers 19, 20 inside of it. The jack 17 is connected to a control unit generally designated by 21. It will be understood that in this type of installation the couple applied to the spindle when it is blocked depends directly from the differential pressure at which the piston 18 is subjected.

Referring more particularly to FIG. 2, and according to the first mode of implementation of the method, the control member 21 comprises a monostable distributor 22 controlled by a control input 24 between a screwing position in which the chamber 19 is set the exhaust while the chamber 20 is connected to a power input 23 and a return position in which the chamber 19 of the jack 17 is placed in communication with the feed inlet 23 of the distributor 22 while the chamber 20 is exhausted. The entrance 24 is connected to a first sensor (not shown) of the position of the screw spindle with respect to to the fixed frame.

A monostable distributor 25 is disposed between power inlet 23 and two air sources under pressure, an air source at the clamping pressure PS corresponding to a required tightening torque and a source of air at a pressure P lower than the pressure PS. The valve 25 is controlled by a control input 26 between a low pressure supply position in which the pressure source P is connected to the input supply 23 while the pressure source PS is closed, and a supply position at the pressure of tightening in which the pressure source P is closed while the pressure source PS is connected to the inlet supply 23. The control input 26 is connected to a second screw spindle position sensor by compared to the fixed frame.

In operation, the platform 4 is driven in rotation relative to the fixed frame by a motor. of the packaging with threaded necks are brought successively and are kept in line with the gripping device at jaws 6 previously provided with a plug.

When passing a first position of the spindle relative to the frame, the distributor 22 is brought by the control input 24 in the screwing position while the distributor 25 remains in the feeding position low pressure. Air at pressure P is then brought into the chamber 20 of the jack 17 and is exerted on the corresponding face of the piston. The rod of the jack 17 pushes the rack 16 upwards. The rack 16 drives in rotation the input pinion 15 which transmits its movement to the gripping device 6 via shaft 12, pinions 14 and 7, and spindle shaft 5 pivoting in the guide tube 1. Note that the pressure P is less than the clamping pressure PS in a sufficient proportion for the spindle shaft 5 to have a speed of rotation generating kinetic energy producing a torque lower than the required tightening torque.

During screwing the spindle continues to move relative to the frame by rotation of the platform 4. When passing from a second position of the spindle by report to the frame corresponding for example to an end of screwing on the cap, i.e. the bottom of the cap is in abutment on the neck of the bottle, the distributor 25 is brought by the control input 26 to the position supply at the clamping pressure. Air to the clamping pressure PS is then introduced into the chamber 20. Note that the second position determining the start of feeding of chamber 20 by the air at the clamping pressure PS, is defined so that the resistant torque then opposing the screwing of the cap on the threaded neck is sufficient to prevent that under the action of the clamping pressure, the speed of rotation of the spindle shaft 5 increases until it generates a sufficient kinetic energy to produce a torque greater than the required tightening torque.

When the tightening of the cap on the neck causes a resistant torque having a value equal to that of the motor torque, the spindle shaft 5 stops rotating and the rack 16 stops.

For a third position of the corresponding spindle at the end of the tightening cycle, the distributor 25 is returned to the low pressure supply position, and the distributor 22 is returned to the return position. Of air at pressure P is then introduced into the chamber 19 of the jack 17 so that the jack is retracted. Wheel free 45 associated with the pinion 14 allows retraction of the cylinder without unscrewing the cap. Once the cylinder is retracted, the jaws of the gripping device 6 can be open without damage to the plug and the spindle screwing is then ready for a new cycle.

Elements identical or analogous to those previously described will relate in the following description the same reference number.

Referring to Figure 3, in the second mode of implementation, the control member 21 comprises a bistable distributor 30 disposed between an air source at the clamping pressure PS and the supply inlet 23 a distributor 22 identical to that of the first mode of Implementation. Distributor 30 is controlled by two control inputs 31 and 32, respectively between a supply position in which the air source at the clamping pressure PS is connected to the supply inlet 23, and a power cut position in which the air source at the clamping pressure PS is blocked. The control input 31 of the distributor 30 is connected to a timer element 33 and control input 32 is connected to a timing element 34, both connected to the pressure source PS.

Before the start of a tightening cycle, the organ 21 is in the position illustrated in the figure 3, that is to say that the distributor 22 at rest provides a connection between the supply inlet 23 and the return 19 while the distributor 30 provides a connection between the source at pressure PS and the supply inlet 23. When passing from a first position of the spindle by relation to the frame a cam simultaneously triggers an action on the control input 24 of the distributor 22 and a setting timers 33 and 34 in operation. distributor 22 causes a supply of the chamber 20 in fluid at the clamping pressure PS, which causes a rotation of the screw spindle.

At the end of a time T1, the timer element 34 acts on the control input 32 of the distributor 30 to bring it to the power cut-off position. The supply of the chamber 20 is then interrupted and the displacement of the piston 18 continues at a decreasing speed by the relaxation of the air contained in the chamber 20.

After a time T2, greater than T1, which determines the end of the previous step, the element of timer 33 acts on control input 31 of the distributor 30 to return it to the position Power. Air at clamping pressure PS is then again introduced into chamber 20 so that the required tightening torque is applied to the plug.

Due to the power interruption of the cylinder during the time difference between T1 and T2, the mean differential pressure on the piston during the previous step is less than the clamping pressure. T1 and T2 are determined so that a sufficient amount of air is introduced into chamber 20 so that the screw cap is almost total at expiration of time T2 and that the spindle then has a sufficient speed low so that the corresponding kinetic energy generates a torque when the stopper is brought into abutment dynamics lower than the torque generated by the pressure of Tightening. The re-pressure of chamber 20 at the clamping pressure PS then causes clamping at speed slow so that when the rotation stops spindle the required tightening torque is reached but not exceeded.

When the spindle reaches an end position of cycle, the distributor 22 is put to rest and the pressure tightening PS is sent to chamber 19 of the cylinder to cause it to retract. The jaws of gripper 6 are open and the spindle is ready for a new cycle.

Referring to Figure 4, and according to the third mode of implementation, the power input 23 of the distributor 22 is directly connected to a source of air at the clamping pressure PS. An exhaust pipe 40 extends between a monostable distributor 41 and a outlet 43 of distributor 22 corresponding to the exhaust of chamber 19 when the distributor 22 is in the screwing position.

The distributor 41 is controlled by an input 44 between a rest position in which the pipe 40 is connected to an exhaust regulator 42, itself pressure controlled PS, and an exhaust position regulated in which line 40 is brought to free exhaust. Distributor control input 44 41 is connected a position sensor 50 of the rack 16. The position sensor 50 is arranged for correspond to the end of screwing the cap before tightening of it.

When passing a first position of the spindle relative to the frame, the distributor 22 is brought in screwing position so that air at the pressure of PS clamping is introduced into chamber 20 while the exhaust from chamber 19 is subjected to the exhaust regulation 42. The face of the piston 18 opposite of chamber 20 is therefore subjected to the clamping pressure PS while the opposite face of the piston 18 is subjected to back pressure resulting from exhaust restriction exercised by the regulatory body 42. The difference between pressure and back pressure is set using of the regulating member 42 to avoid runaway the screw spindle.

When the rack 16 reaches the sensor 50, this actuates the control input of the distributor 41 in the unregulated exhaust position thus releasing the exhaust from chamber 19. The piston 18 is then subjected to the tightening pressure PS and the tightening torque required is applied to the cap.

Of course, the invention is not limited to embodiment described and we can add variant embodiments without departing from the scope of the invention as defined by the claims.

In particular, although the command entries distributors have been described in relation to particular means of actuation, we can use any means of actuation appropriate to the installation in question in order to delimit a preliminary stage during which the piston 18 is subjected to a differential pressure reduced mean and a final stage where it is subject to the differential clamping pressure.

Although in the second mode of implementation described, the clamping pressure PS is only applied only once during time T2, the clamping pressure, or a pressure of different constant value, could be applied repeatedly during time T2 according to pulses of a duration appropriate to the type of packaging or the type of plug used.

Although the invention has been described in relation with a spindle rotated by a linear cylinder, which provides a tightening torque which is directly proportional to the supply pressure, we can also implement the method according to the invention in connection with a motor supplied with fluid having a motor unit linked to the spindle shaft via a torque limiting device, for example a motor rotary equipped with a friction clutch. In this case, the process according to the invention makes it possible to avoid exceeding tightening torque due to the triggering inertia of the torque limiting device in relation to energy kinetics stored by the engine.

Claims (8)

1. A method of controlling a screwing spindle including a fluid-fed motor and having a drive member (18) connected to a spindle shaft (5) to cause it to rotate, the method comprising the step of feeding the screwing spindle under nominal conditions of pressure and flow rate for generating a required tightening torque, the method being characterized in that it comprises a prior step during which the screwing spindle is fed under conditions that are lower than the nominal conditions by a ratio that is sufficient so that the spindle shaft has a speed of rotation generating a kinetic energy producing a torque lower than the required tightening torque.
2. A method according to claim 1, characterized in that the motor is a linear actuator and the drive member is a piston, and in that in the prior step, the piston is subjected to a mean differential pressure that is less than a tightening differential pressure.
3. A method according to claim 2, characterized in that, in the prior step, one face of the piston is subjected to a constant pressure in the screwing direction.
4. A method according to claim 3, characterized in that the constant pressure is lower than the tightening differential pressure.
5. A method according to claim 3, characterized in that the piston is subjected to a counter-pressure.
6. A method according to claim 5, characterized in that the constant pressure is equal to the tightening differential pressure.
7. A method according to claim 2, characterized in that in the prior step, the piston is subjected to pressure intermittently.
8. A method according to claim 7, characterized in that the pressure is a differential pressure of constant value equal to the tightening differential pressure.

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