Abstract:
A process for loading a lathe in which a new bar to be machined is introduced laterally into a guide-bar device in form of a tube during the machining of a last piece at the end of a preceding bar. The new bar causes the ejection of the remnant of the preceding bar by pushing against the rear of the preceding bar. A device for loading a lathe with bars to be machined comprises a guide-bar device in form of a tube having two parts which can be opened for laterally introducing a new bar to be machined into the tube. The bar in the tube is fed by a hydraulically controlled push-piston. Pressure pistons press the two parts of the tube against each other in order to ensure a fluid tight seal. Return pistons are utilized radially move the upper part of the tube at the time of loading.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for loading a lathe with bars to be machined, and more specifically to a process where the bars are held in a gripping unit of the lathe, each bar being guided in a guiding tube formed of two parts and in which a bar is pushed toward a head-stock of the lathe by a push-piston. A new bar to be machined is introduced laterally in the guide-bar device after the two guiding tube parts have been opened. The invention further relates to a loading device for loading a lathe with bars to be machined and more specifically to a loading device in which the guide-bar device is in the form of a tube for rotatingly supporting the bar to be machined in machine-oil which provides hydrodynamic support for the bar. Feeding of the bar in the tube is provided by a push-piston which supports the rear part of the bar and which is hydraulically controlled. The guiding tube is formed of two parts capable of being separated for laterally inserting a new bar to be machined in the guiding tube. 
     2. Background 
     Hydraulic guide-bar devices are known which are manually loaded and which permit great speeds of rotation of the bars to be attained. The remnant of a bar which has been machined is generally removed by a feed collet on the head-stock of the lathe. However, such non-automatic machines have long idle periods to accomodate stepping of the spindle and manual insertion of the next bar, all of which considerably increases the loading time and reduces the output of the machine. 
     Such a bar loading device for a machine-tool is described in U.S. Pat. No. 2,577,203 in which a guide-bar device is disclosed which comprises a segment pivoted to the end of a rocker arm. During normal working of the device the bar which is in the lowest portion of a bar magazine rests on a surface of the segment and a slide for holding the bars in the magazine is disengaged. At the time of loading, the segment is pivoted which opens the guide-bar tube and the lowest bar of the magazine falls laterally into the tube while the slide is advanced by a spring in order to hold the other bars in the magazine. A push-piston, controlled pneumatically, feeds the bar in the tube. At the time of loading the push-piston is retracted by vacuum. However, the guide bar tube described in the above-noted patent is not subjected to the pressure of machine oil for hydrodynamically supporting the bar to be machined, thus limiting the speed of rotation of the bar within guide-bar device. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to shorten the loading time and to increase the speed of rotation of the bar to be machined. 
     To achieve the above as well as other objects, the process according to the present invention is characterized in that during the machining of the last piece of a bar, a signal indicating termination of the bar and a signal indicating shutting of a gripping unit, cause the push-piston to retreat toward the rear part of the guide-bar device. The arrival of the push-piston at the rear part of the guide-bar device causes opening of the guiding tube, introduction of a new bar to be machined into the tube and closing of the tube. A signal indicating the closing of the tube and an &#34;order of loading&#34; signal delivered at the end of the machining of said last piece, causes the feeding of a new bar in the tube. Due to the fact that the new bar to be machined is introduced in the guide-bar device during the operation of machining of the last piece of the preceding bar, loading time is shortened. 
     The loading device according to the present invention is characterized in that in the closed state, the two parts of the guiding tube bear against each other on a common bearing surface under the influence of a pressure pistons or the like, acting on at least one of the two parts to make said tube fluid-tight and capable of supporting the oil pressure required for hydrodynamic support without leakage and to ensure retreat of the push-piston by vacuum. The speed of rotation of the bar to be machined can be increased because it is hydrodynamically supported by the oil pressure in its guiding tube. The feed collet of the lathe may be eliminated because the feed of the bar is entirely controlled by the push-piston in the guide-bar device, the remnant of the preceding bar being ejected by the new bar loaded in the device. The elimination of the feed collet contributes to an increase in the reliability of machining operations and to decreasing machining costs. 
     The invention will be described further by way of example and with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1-3 schematically illustrate the respective sequences of the machining operations of a long bar in an automatic working cycle, of the machining of the last piece in the automatic working cycle and of the subroutine for loading of a new bar; 
     FIG. 4 is a schematic lateral view of a loading device according to the invention; 
     FIG. 5 is a cross section of the tube of the loading device of FIG. 4; 
     FIG. 6 shows the pistons for closing and opening the loading device; 
     FIG. 7 is a front view of the loading device of FIG. 4; 
     FIG. 8 is a cross sectional view of the loading cam; 
     FIG. 9 illustrates the loading cam according to the present invention; and 
     FIG. 10 is a simplified hydraulic diagram of a loading device according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 depicts the sequence of machining operations during an automatic working cycle of a long bar on a lathe which incorporates a loading device according to the invention. The lathe is preferably, but not necessarily, of the numerically controlled type. The series of steps are as follows: 
     (a) Terminating machining; 
     (b) Positioning a stop 3 of a turret 2 of the lathe opposite the bar to be machined 1; 
     (c) Opening the gripping unit for the bar; 
     (d) Retreating of the turret 2 and simultaneously feeding the bar toward the head-stock of the lathe while in contact with the stop 3 of the turret 2; 
     (e) Closing the gripping unit 1; 
     (f) Machining a new piece; 
     (g) Terminating machining. 
     As long as the bar to be machined is long enough, the above sequence of operations is repeated automatically, each complete cycle corresponding to the production of one piece. During this automatic cycle of operations, a push-piston in the guide-bar device continuously contacts the rear part of the bar to be machined. 
     FIG. 2 shows the sequence of operations at the time of machining the last piece at the end of a bar; 
     (h) Positioning the stop 3 of the turret 2 opposite the bar to be machined 1. The push-piston 4 remains in contact with the rear of the bar 1; 
     (i) Opening the gripping unit; 
     (j) Retreating of the turret 2 and simultaneously feeding the bar toward the head-stock of the lathe by means of the push-piston 4 pushing against the stop 3 of the turret 2. The rear part of the push-piston 4, when passing in front of a detector, generates &#34;bar termination&#34; signal; 
     (k) Closing the gripping unit. Reception of the bar termination signal and of a signal indicating the closing of the gripping unit causes withdrawal of the push-piston which moves away from the head-stock of the lathe; 
     (l) Machining the last piece. The arrival of the push-piston at the rear of the guide-bar device causes the radial opening of the two parts of the tube, the lateral insertion of a new bar between the two parts and the subsequent closing of the tube; 
     (m) Termination of the machining. The reception of a &#34;termination of machining&#34; or &#34;loading&#34; signal and of a &#34;tube closed&#34; signal causes the newly inserted bar to be fed toward the head-stock of the lathe and progression of the operation to a subroutine for loading. 
     As illustrated in FIG. 3, the sequence of operations during the subroutine for loading is as follows: 
     (n) Positioning the turret 2 in front of the head-stock at a distance equal to the maximal length of the remnant of the preceding bar 1 plus a reserve, and feeding the new bar 1&#39; into the guiding tube toward the head-stock until the &#34;bar termination&#34; signal ends; 
     (o) Feeding the new bar 1&#39; against the rear part of the remnant 1 and delivering a &#34;pressure checking&#34; signal indicating the end of the &#34;bar termination&#34; signal; 
     (p) Opening of the gripping unit, pushing the new bar 1&#39; against the rear part of the remnant 1 and ejecting the latter; 
     (q) positioning the new bar against the stop 3 of the turret 2; 
     (r) Moving the turret toward the head-stock to position the new bar 1&#39; in a working position; 
     (s) Closing the gripping unit on the new bar 1&#39;; 
     (t) Machining the front face of the new bar 1&#39;; and 
     (u) Terminating the loading operation and proceeding to the &#34;automatic cycle&#34; corresponding to point (a) (FIG. 1) of the operation for machining a long bar in automatic cycle. 
     The process for loading according to the present invention shortens of the idle periods during the loading operation due to the fact that the new bar is inserted into the guiding tube during the machining of the last piece of the preceding bar. Because ejection of the remnant occurs at the time of opening of the gripping unit when the new bar pushes against the rear part of the remnant to eject it, the present invention also eliminates the need for feed collets normally installed on lathes for removing the remnants of the preceding bar. From the preceding description it should be appreciated that the process for loading in accordance with the present invention is preferably carried out on a numerically controlled machine because of the great flexibility of controlling such a machine. 
     FIG. 4 is a schematic, lateral view of a loading device for a bar machining lathe according to the present invention. The loading device works in accordance with the above described process and comprises a guiding tube 5 comprising two parts, 5a and 5b (FIG. 7). The tube is mounted on supports 6. The upper part 5a of the tube is fastened to return pistons 7 which function to lift up the tube part 5a and separate it from the lower tube part 5b. Cams 9 operate at the time of loading to laterally and progressively introduce a new bar to be machined between the separated parts 5a and 5b. The tube 5 is part of a guide-bar device in which a push-piston 4 (FIG. 6), preferably hydraulically controlled, operates to feed the bar to be machined toward the machining station. The push-piston 4 also functions to support and center the rear part of the bar. Radial pipes 22 (FIG. 10) feed oil under pressure between the bar and the tube in order to create hydrodynamic support for the rotating bar in the tube. In order to ensure the tube 5 is fluid tight in its closed state the pressure exerted by the pistons 8 on the common bearing surface 5c of the parts 5a and 5b (FIG. 5) of the tube must be greater than the hydraulic pressure acting within the tube. The distribution of the pressure exerted on the tube 5 is determined by the arrangement of the pressure pistons 8 in a manner to ensure that the pressure is regularly distributed. 
     In order to open the tube 5 for the introduction of a new bar to be machined 1, the push-piston 4 is retracted, preferably by vacuum toward the rear end of the loading device. Therefore the tube 5 must also be air-tight. The required tightness is preferably provided by providing flat bearing surfaces 5c and by exerting sufficient pressure on them. Sealing joints may be used but are not obligatory. The loading device is axially aligned with and in immediate proximity with the head-stock 10. A hydrualic distributor 11 controls the pressure pistons 8, the return pistons 7, the push-piston 4 and the supply of oil in the closed tube. 
     FIG. 5 shows a cross section of the tube 5 with a pressure piston 8 acting against the tube part 5a. The bar 1 is supported within the tube 5. 
     FIG. 6 shows a cross section of the pistons 7 and 8 and of the tube 5. The return piston 7 is coupled to the upper part 5a of the tube 5 by means of a U-shaped yoke 13 extending along the upper part and on the two lateral sides of the part 5a. The yoke 13 is coupled to the part 5a by a punched opening in which a pin 12, fastened to the part 5a, is engaged. This arrangement facilitates changing the part 5a of the tube 5 as necessary to accomodate different diameter bars to be machined. During the loading operation, the pistons 7 are withdrawn by hydraulic pressure. These pistons then lift up the upper part 5a of the tube 5 in order to open the latter. FIG. 6 further shows proximity switches 21 which deliver a signal indicative of when the tube 5 is closed. 
     FIG. 7 is a front view of the loading device according to the invention. As alluded to above, the tube 5 comprises the fixed part 5b mounted on a frame 14 of the loading device and the mobile part 5a on which the pressure pistons 8 act and which, at the time of loading, is lifted up by the return pistons 7 for permitting the lateral introduction of a new bar into the fixed part 5b. The bars 1 to be loaded are arranged side by side on an inclined table 15. The axis of the bars is generally parallel to that of the tube 5. The lowest bar rests in a waiting position against a bearing surface of one or more cams 9 which rotate under the influence of a motor 16, each cam making a revolution at the time of loading. A stop 22, adjustable in accordance with the diameter of the bars to be machined, is provided on the table 15 in the vicinity of the cam 9. Centering pins 17 may be provided between the yokes 13 and the centering studs 18 of the tube to ensure perfect alignment between the parts 5a and 5b of the tube 5 in its closed state. 
     FIG. 8 shows a cam 9 mounted on a shaft 19 and set into rotation by a conical gear 20 driven by the motor 16. FIG. 9 shows a preferred configuration of a cam 9. As viewed in FIG. 8, the lowest bar 1p is in a waiting position against the bearing surface A of the cam 9 which is perpendicular to the axis of the cam. 
     At the time of loading, the cam is set into rotation and its helicoidal surface H ensures a progressive descent of the bundle of bars 1, 1p toward the tube 5. During this first phase of rotation, the lowest bar 1p is progressively brought against the adjustable stop 22. As the cam 9 rotates further, the second bar contacts the bearing surface A of the cam 9 and the rise B of the cam progressively lifts the bar 1p until it reaches a level from which it rolls above the stop 22 and the part of the frame 14 adjacent the stop 22 and gently into the fixed part 5b of the tube. 
     FIG. 10 shows a simplified hydraulic diagram of the loading device. The system comprises a first pump M1 and a hydraulic valve V1 for controlling fluid flow to the rear part of the push-piston 4 for feeding the piston 4 in the tube 5 and for distributing oil between the tube 5 and the bar to be machined. A second pump M2 and hydraulic valve V2 controls fluid flow to either the pressure pistons 8 or the return pistons 7 when the mobile part 5a of the tube is to be retracted. A proximity switch D4 delivers a signal when the push-piston 4 reaches a stop position at the rear part of the tube 5. A pressure detector P3 delivers a &#34;bar termination signal&#34; when the rear part of the push-piston 4 is in the tube at the right hand side of the detector P3. A detector P1 monitors the pressure on the push-piston 4 and a detector P2 monitors the closing pressure of the tube. The working of the loading device will now be explained in the form of a summary of the loading sequences: 
     
         ______________________________________Starting PositionLOADING DEVICE       LATHE______________________________________Position &#34;automatic&#34; &#34;Automatic cycle&#34;,                long barstube 5 closed, push-piston                continuous machining4 bears against the barM2 switched onV2 switched outM1 forward motionV1 switched onAt the time of reception of both signals:&#34;bar termination&#34; signals from                &#34;gripping unit closed&#34;detector by P3       signal by lathe controlM1 backward motion(vacuum)V1 switched onpush-piston moves backward                the lathe machines theand actuates D4      last pieceM2 switched onV2 switched onThe tube opens, the pistons8 are without pressure, thepistons 7 are hydraulicallycontrolledmotor 16 is switched on, cam9 rotatesthe tube closes, the pistons8 are under pressure, thepistons 7 are without pressureAt the time of reception of both signals&#34;Tube closed&#34; by the detector 21                &#34;loading&#34; byM1 forward motion    lathe controlV1 switched onthe push-piston moves                the lathe jumps to theforward              subroutine of loading                indexing and positioning                of the stop                waitAt the time of reception of the signal&#34;pressure checking&#34; by P1when the new bar bearsagainst the remnantthe loading cycle is opening of the grippingterminated           unitthe bar moves forward                ejection of the remnantthe bar moves backward                the stop moves forward                shutting of the gripping                unit                termination of the                &#34;loading&#34; operation                commence &#34;automatic                cycle&#34; operation______________________________________