Patent Publication Number: US-2010125991-A1

Title: Pneumo-Hydraulic Rivet Gun

Description:
TECHNICAL FIELD 
     This invention concerns the technical sector of rivet guns, with particular reference to power-activated rivet guns which are used for cylindrically-shaped rivets having a partially threaded axial hole, a strike collar in proximity of a head, and a suitably weakened portion where the plastic deformation is localized. 
     The rivets are destined to join two walls stably, for example instead of using spot welding, or to constitute an adequately sturdy threaded anchoring bush for structures made with materials which are too soft or too thin to afford sufficiently resistant threading. 
     The rivets can be of considerable dimensions, and the equipment necessary to put them in place must be capable of exerting a high compression force upon them. 
     BACKGROUND ART 
     A rivet gun known from European Patent EP 0.999.906, which belongs to this Applicant, comprises a body and a grip which house the following: 
     a pneumatic motor, which makes a threaded tie-rod rotate rightwards or leftwards, respectively to engage the threaded tie-rod with, or disengage the threaded tie-rod from, the threaded axial hole of a corresponding rivet; 
     an oleodynamic system, which imposes axial translation on the motor-tie-rod group, so as to determine the plastic deformation of the predetermined portion of the rivet, with a force which is pre-set by a maximum pressure valve; 
     a pneumatic thrust booster driving a plunger which compresses the fluid of the oleodynamic system; 
     a pneumatic system, in which the following are provided: an auxiliary valve which is opened by the tie-rod; a main valve, which is activated to open by a relative trigger; a discharge valve, which is opened at the end of a predetermined travel of the motor-tie-rod group; a flow regulation valve, which is opened at the end of the rivet fastening stage; a timing device, which activates the motor to rotate leftwards and can automatically stop the motor after a predetermined time. 
     The gun functions as follows: 
     the rivet is arranged in the hole which has been prepared for this purpose in the structure, with the relative strike collar strikingly against the structure, or alternatively, the rivet is manually positioned in front of the tie-rod of the gun; 
     the tie-rod is inserted into the axial hole of the rivet, up to the beginning of the threading of the rivet, in this way determining an axial thrust on the tie-rod towards the body of the gun, thus causing the auxiliary valve to open and allowing compressed air to be sent to the motor, thereby making the motor rotate rightwards and screwing the tie-rod into the rivet; when the strike collar of the rivet is strikingly against the forward head of the body, the auxiliary valve automatically closes and thus the motor stops; 
     depressing the trigger and releasing it immediately initiates the automatic operating cycle of the gun; pressure on the trigger opens the main valve, which allows the compressed air to be sent to the thrust booster, consequently increasing the pressure of the oleodynamic fluid and initiating the axial translation of the motor-tie-rod group; 
     the translation continues, causing progressive compression of the rivet, the weakened portion of which therefore deforms towards the outside, thereby defining an annular edge, which adheres to the surface of the structure which is opposite that on which the collar rests, thus securing the rivet in place; 
     depending on whether the maximum travel operating modality or the maximum pressure operating modality respectively has been selected, the discharge valve or the maximum pressure valve intervene, closing the main valve and stopping the flow of air towards the thrust booster; 
     part of the compressed air stored in the thrust booster is discharged externally through the flow regulation valve, while the remaining compressed air is sent to the timing device, which makes the motor rotate leftwards, thus unscrewing the tie-rod from the rivet; when the compressed air contained in the thrust booster is exhausted, the motor stops automatically; 
     by acting on the flow regulation valve the time of functioning of the motor can be adjusted in relation to the length of the rivet. 
     The rivet gun above described functions extremely well, but its automatic operating cycle has shown a limitation regarding fulfilling the requirements of intensive or excessive use, where it is important to reduce downtimes between applying one rivet and the next to a minimum. 
     The motor, being activated to rotate leftwards to disengage the threaded tie-rod from the rivet just applied, continues to function automatically for the time which is predetermined by the timing device, therefore this time needs to be sufficiently long to allow the threaded tie-rod to be completely unscrewed. 
     Under normal conditions, therefore, when the tie-rod disengages from the rivet which has just been applied, the motor continues to function residually for a short time, thus preventing a new rivet from being engaged immediately, since this would damage the thread of the new rivet. 
     If, for any reason, faulty conditions of resistance arise while unscrewing the tie-rod, air “consumption” by the motor increases, with the motor probably stopping precociously, leaving the tie-rod still partially engaged; in this case it is necessary to activate an emergency command with which the gun is provided, and which further supplies the motor to extend its functioning. 
     It is easy to understand how, given a complex structure with a large number of pre-positioned rivets, even a few seconds of unnecessary pause, when passing from one rivet to the next, determine an overall onerous increase in operating times, which is further compounded by the operator&#39;s “loss of working rhythm”. 
     The presence of the timing device, posteriorly associated to the pneumatic motor, entails a considerable increase in the weight and bulk of the rivet gun, which over prolonged use augments the exertions required of the operator and limits the gun&#39;s maneuverability in close spaces. 
     The choice which the above-described known rivet gun offers between the maximum pressure and the maximum travel operating modalities has proved to be of little practical use, the maximum travel option often being ignored, since compared with the maximum pressure option the maximum travel parameter is less important for obtaining an optimal fastening of the rivet to the structure. 
     To increase ease of handling for an operator, the need has arisen to eliminate the timing device and modify the automatic functioning of the gun, leaving the operator to decide when to interrupt the leftwards rotation of the motor for unscrewing, thereby adapting the rotation to the requirements of the moment and synchronizing the rotation with disengagement of the tie-rod from the rivet. 
     Thus the aim of the invention is to provide a gun for applying rivets, designed in such a way that after having engaged the tie-rod in the rivet, the operator has to depress the trigger to start the automatic operating cycle, and keep the trigger depressed until the tie-rod disengages from the applied rivet, with the motor rotating leftwards, the stopping of the motor being subordinated to the release of the trigger. 
     Another aim of the invention consists in providing a gun which is much more compact and lighter than those in the prior art. 
     A further aim of the invention concerns simplifying production of the gun, by eliminating components such as the timing device and the discharge valve, which are dependent on the maximum travel option. 
     DISCLOSURE OF INVENTION 
     A pneumo-hydraulic rivet gun, comprising: a pneumatic motor, which sets a threaded tie-rod in rightwards or leftwards rotation to engage the tie-rod or disengage the tie-rod from the threaded hole of a rivet; an oleodynamic system for determining a plastic deformation of a portion of the rivet, such as to secure the rivet to a wall; a pneumatic booster which activates a plunger that compresses the fluid of the oleodynamic system; a pneumatic system provided with an auxiliary valve, which is opened by the tie-rod and allows the supply of the rightwards rotating motor, and with a main valve, which is opened by a trigger subsequent to the reclosing of the auxiliary valve in order to allow the connection of an air supply conduit to a source of compressed air: a hydro-pneumatic exchange valve, connected to the air supply conduit, oleodynamic system, pneumatic booster, the exchange valve allowing, in the following order and subsequent to intervention by the operator on the trigger, activation of the pneumatic booster, the pressurization of the oleodynamic system with consequent plastic deformation of the rivet, the activation of the pneumatic motor with leftward rotation of the tie-rod which uncouples from the rivet and, following the release of the trigger, a halt of the pneumatic motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The characteristics of the invention will emerge from the following description of a preferred embodiment thereof, in accordance with the claims and with the aid of the appended figures of the drawings, in which: 
         FIGS. 1 to 8  show schematic views of the rivet gun of the invention, during the most salient operating stages; 
         FIG. 9A  shows, on an enlarged scale, an axial section of a component of the gun, in a first embodiment thereof; 
         FIG. 9B  shows the same component of  FIG. 9A , in a second embodiment thereof. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In the figures, the gun for applying rivets of the invention is indicated with  100 . 
     The gun  100  comprises a body  101  and a grip  102  within which the following are housed in a known way: 
     a pneumatic motor  1 , which rotates a threaded tie-rod  2  leftwards or rightwards, respectively for engaging the threaded tie-rod  2  with, or disengaging the threaded tie-rod  2  from, the threaded axial hole  3 A of a corresponding rivet  3 ; 
     an oleodynamic system  4 , which imposes an axial translation on the motor-tie-rod group, thus causing plastic deformation of a predetermined portion of the rivet  3 , in such a way as to secure the rivet  3  to a corresponding wall P; 
     a pneumatic thrust booster  5  activating a plunger  50  which compresses the fluid F of the oleodynamic system  4 ; 
     a pneumatic system  6 , which is provided with an auxiliary valve  60 , which is opened by the tie-rod  2 , allowing supply to the rightwards-rotating motor  1 , and a main valve  61 , which is opened by a relative trigger  62 , subsequent to re-closing of the auxiliary valve  60 , allowing the supply to the pneumatic thrust booster  5  and the leftwards-rotating motor  1 . 
     The gun further comprises an emergency command  63  of a substantially known type, which is associated to the pneumatic system  6  and sets the motor  1  in leftwards rotation, in conditions which will be illustrated below. 
     The gun  100  according to the invention is provided with a hydropneumatic exchange valve  10 , which is connected to the oleodynamic system  4  and the pneumatic system  6 , and which comprises: 
     first mobile organs  11 , constituted by an assembly  110 , which slides axially inside a jacket  20  of the exchange valve  10  with which it is solid at one end thereof, a stem  111 , which slides in an axial hole afforded in a head  20 A of the jacket  20  from which it exits, extending inside a blind conduit  41 , which blind conduit  41  is connected to the oleodynamic system  4  and occupied by the fluid F thereof; the assembly  110  is subjected to the action of first elastic organs  112 , which are provided on the side opposite the stem  111  and maintain the stem  112  strikingly against the head  20 A when the pressure in the lower conduit is below a predetermined value; 
     an opening  21  in the jacket  20  for injecting compressed air coming from the main valve  61  into the jacket  20 , through an air supply conduit  65  provided in the pneumatic system  6 ; 
     second mobile organs  12 , which switch the compressed air supply coming from the main valve  61  from the pneumatic thrust booster  5  to the pneumatic motor  1 , constituted for example by a sleeve  120 , slidingly and sealingly constrained on the assembly  110 , inside the jacket  20 , and subjected to the action of respective second elastic organs  121 , which generate a force directed towards the head; the sliding of the sleeve  120  is limited by its striking against a stop  113  afforded by the assembly  110 , thus defining an initial position R for the sleeve  120 . 
     The sleeve  120  gives rise at its ends to a forward collar  122  and a collar  123  in which ring seals  124 ,  125  are inserted, which slidingly meet the internal wall of the jacket  20 ; 
     an annular passage  22 , defined between the jacket  20  and the portion of sleeve  120  included between the respective collars  122 ,  123 , which communicates with the opening  21  and with a chamber  23 , in a phase relation with the initial position R of the sleeve  120 ; the chamber  23  is connected to a first delivery conduit  66  directed towards the thrust booster  5 ; 
     an annular chamber  24 , defined between the jacket  20 , the head  20 A of the jacket  20 , and the forward collar  122  of the sleeve  120 , which communicates with the opening  21  and with a transfer port  25 , in a phase relation with the moving of the sleeve  120  to an operating position K which is determined by the translation of the assembly  110  as a consequence of the oleodynamic fluid F reaching a predetermined maximum pressure; the transfer port  25  is connected to a second delivery conduit  67  directed towards the pneumatic motor  1 , to make the motor  1  rotate leftwards. 
     In a first embodiment (shown in  FIGS. 1 to 9A ), the hydropneumatic exchange valve  10  is provided with a cartridge  30 , containing the first elastic organs  112 , acting on the assembly  110  with a predetermined elastic reaction, which is calibrated on the basis of the maximum pressure of the oleodynamic fluid F to be reached. 
     The cartridge  30  is interchangeable with others, the elastic organs  112  of which have different settings, in order to modify the maximum pressure reachable by the fluid F. 
     In a second embodiment, shown in  FIG. 9B , the cartridge  40  comprises a pawl  41 , which is adjustable from the outside, and is able to modify the preload of the first elastic organs  112 , in order to vary the elastic reaction of the first elastic organs  112  within a range between minimum to maximum, corresponding to predetermined maximum pressure values of the fluid F. 
     Holes  31  afforded in the cartridge  30 ,  40  place the rear part  20 B of the jacket  20  in communication with the outside, the inner diameter thereof being greater than the remaining part, the function of which will be described below. 
     There follows a description of how the gun  100  functions when applying a rivet  3  to a wall P. 
     In  FIG. 1 , the gun  100  is not operating, with: 
     the pneumatic motor  1  inactive; 
     the pressure of the oleodynamic system  4  at the minimum, with the motor-tie-rod group which is advanced towards the forward head  101 A of the body  101 , through the action of a relative contrast spring  103 ; 
     the pneumatic system  6 , supplied with compressed air coming from an external source (not shown), creates pressure only in the infeed conduit  64 , which branches towards the auxiliary valve  60 , the main valve  61  and the emergency command  63 , all of which are in the respective closed or rest positions; 
     the exchange valve  10  at ambient pressure, with the assembly  110  strikingly against the head  20 A of the jacket  20  (advanced position HI) and the sleeve  120  in the relative initial position R, in which the ring seal  125  of the rear collar  123  is situated anteriorly to the rear part  20 B, closing the passage between the rear part  20 B and the remaining part of the jacket  20 . 
     The rivet  3  is arranged in the hole provided in the wall P for this purpose, with the relative collar  3 B which is strikingly against the wall P, or alternatively, the rivet  3  is positioned manually in front of the tie-rod  2  of the gun  100  (see  FIG. 1 ). 
     As with the known rivet gun mentioned in the preamble, the tie-rod  2  is inserted in the axial hole  3 A of the rivet  3 , as far as the start of the thread thereof, thus determining an axial thrust on the tie-rod  2 , with translation of the tie-rod  2  towards the body  101  of the gun  100 ; this causes the auxiliary valve  60  to open, thus allowing compressed air to be sent to the motor  1 , setting the motor  1  in rightwards rotation in order to screw the tie-rod into the rivet  3  ( FIG. 2 ). 
     When the collar  3 B of the rivet  3  is strikingly against the forward head  101 A of the body  100 , the auxiliary valve  60  is automatically closed and therefore the motor  1  stops ( FIG. 3 ). 
     Depressing the trigger  62  makes the main valve  61  open and initiates the automatic operating cycle of the gun  100 . 
     When the main valve  61  opens, compressed air flows into the air supply conduit  65 , entering the hydropneumatic exchange valve  10  through the opening  21  of the jacket  20 . 
     With the sleeve  120  in the initial position R, the compressed air coming from the opening  21  is diverted towards the annular passage  22 , and from here to the chamber  23 , thereafter being channelled into the first delivery conduit  66  and reaching the cylinder  51  of the thrust booster  5  (see  FIG. 3 ). 
     Keeping the trigger  62  depressed results in air continuing to be sent to the thrust booster  5 ; the increase in the air pressure inside the cylinder  51  makes the piston  52  rise, contrasting a relative spring  53 , and the contemporaneous rise of the plunger  50  acting on the fluid F, consequently raising the pressure of the fluid F, and starting the axial translation of the motor-tie-rod group ( FIG. 4 ). 
     Translation continues, causing progressive compression of the rivet  3 , the weakened portion of which therefore deforms towards the outside, thus defining an annular edge  3 C, which adheres to the surface of the wall P opposite the surface on which the collar  3 B rests, thereby securing the rivet  3  (see  FIG. 4  again). 
     The increased pressure in the oleodynamic system  4  also affects the fluid F present in the blind conduit  41 , determining an axial thrust on the stem  111 , and on the assembly  110 , which can overcome the resistance of the elastic organs  112 ; therefore the assembly  110  is translated backwards, drawing with it the sleeve  120 , also overcoming, by means of the stop  113 , the resistance of the relative elastic organs  121 . 
     When the maximum pressure of the oleodynamic fluid F is reached, the assembly  110  is pushed to the extreme retracted position H 2 , bringing the sleeve  120  to the relative operating position K, in which the ring seal  124  of the relative forward collar  122  is situated on the opposite site of the opening  21  ( FIG. 5 ). 
     Consequently the supply of air towards the annular passage  22  is closed, thus interrupting delivery to the thrust booster  5 ; contemporaneously the rear collar  123  is in proximity of the widened rear part  20 B of the jacket  20 , in which the relative seal ring  125  does not adhere to the jacket  20  and allows the air which is contained in the thrust booster  5  to travel back along the trajectory through the first delivery conduit  66 , the chamber  23 , the annular passage  22  and then to exit from the exchange valve  10  through the holes  31  in the cartridge  30 . 
     Discharge of the air from the thrust booster  5  is favoured by the elastic reaction of the spring  53 , which by extending, brings the piston  52  and the plunger  50  back down ( FIG. 6 ). 
     The aforementioned causes a sharp drop in the pressure of the oleodynamic fluid F, thereby terminating retraction of the motor-tie-rod group and thus also the pressure on the rivet  3  ( FIG. 6 ). 
     The switch in the position of the sleeve  120 , sets the opening  21  in communication with the annular chamber  24 , so that the compressed air entering the annular chamber  24  is directed towards the transfer port  25 , thereafter reaching the motor  1  through the second delivery conduit  67 , thus making the motor  1  rotate leftwards to start unscrewing the tie-rod  2  from the rivet  3  now fastened to the wall P ( FIG. 6 ). 
     The rapid drop in the pressure in the oleodynamic system  4  allows the first elastic organs  112  to bring the assembly  110  back to its advanced position, striking against the head  20 A ( FIG. 6 ). 
     The air pressure which is established inside the annular chamber  24 , despite air being delivered to the motor  1 , is sufficient to overcome the weak resistance of the second elastic organs  121 , so that the sleeve  120  is maintained in the operating position K, despite the thrust for the shift from the initial position R, which was originally provided by the assembly  110 , dying out (see  FIG. 6  once more). 
     The above-described condition lasts for as long as the trigger  62  is kept depressed, thus the leftwards rotation of the motor  1 , which is required for unscrewing the tie-rod  2  from the rivet  3  just applied, continues for as long as the operator wishes. 
     When the trigger  62  is released, with the closing of the main valve  61 , the supply of air to the air supply conduit  65 , and thus also to the exchange valve,  10  is interrupted; since there is no longer any pressure inside the annular chamber  24 , the second elastic organs  121  can push the sleeve  120  back to the initial position R, thus closing the passage towards the second delivery conduit  67  ( FIG. 7 ). 
     Thus leftwards rotation of the motor is stopped, while the residual compressed air which is contained in the exchange valve  10  flows back through the air supply conduit  65  and is discharged externally through suitable holes  610  provided in the main valve  61  (see  FIG. 7 ). 
     At this point the gun  100  is once again in the condition described in  FIG. 1 . 
     Thus an operator can optimally synchronize the completion of disengagement of the tie-rod  2  by stopping the motor  1 , thus immediately readying the gun  100  for another rivet  3  which was priorly positioned in the wall P. 
     If the trigger  62  is released by mistake or for any other reason before disengagement of the tie-rod  2  is completed, the unscrewing operation can be completed by depressing the emergency command  63 ; in this way, the compressed air present in the infeed conduit  64  is injected into the second delivery conduit  67 , to supply the motor  1  and make it rotate leftwards ( FIG. 8 ). 
     Note that the gun  100  as described is not minimally affected by any operating error if, after anticipated release of the trigger  62 , renewed pressure is exerted on the trigger  62 , instead of activating the emergency control  63 . 
     In this case, in fact, the gun repeats the automatic operating cycle on the tie-rod  2  without applying unwanted pressure on the secured rivet  3 , since when the prior maximum pressure of the fluid F is reached again, the exchange valve  10  interrupts the action and starts unscrewing, so that the only resulting drawback is a slight loss of time. 
     The particular characteristics of the gun of the invention emerge extremely clearly from the foregoing, in particular the fact that it provides an automatic cycle which ensures a precise halt to the pressure on the rivet when the predetermined maximum pressure is reached, and prompt activation of the motor to disengage the tie-rod, while leaving the operator to decide when to interrupt the disengagement operation, thus avoiding difficult calibration operations on the timing device and reducing to a minimum the downtimes and drawbacks which accompany intensive use of the gun. 
     The elimination of the timing device, and of the components necessary for the maximum travel modality of operation, makes this gun, in comparison with guns in the prior art, as illustrated in the preamble, much more compact and lighter, which is definitely advantageous for ease of handling in restricted spaces and for reducing operator fatigue when it is used for extended periods of time. 
     The foregoing in any case is a non-limiting example, thus any modifications to details which should become necessary, for constructional and/or functional reasons, must be considered as falling within the ambit of protection defined by the following claims.