Abstract:
Devices are provided for detecting a mutual reference position of tool parts of a pressing tool, e.g., a punch and die. The device include (a) first and second reference elements that are moveable, by the pressing device, into a relative position that corresponds to a predetermined relative position of the first tool part and the second tool part as mounted in the mountings; (b) a control pressure generator that generates a control pressure when the first and second reference elements are moved into the relative position; (c) a switch that is activated by the control pressure; and (d) a detection unit that is activated by activation of the switch to detect the relative position of the first and second reference elements.

Description:
CLAIM OF PRIORITY 
   This application claims priority under 35 U.S.C. § 119 to European Patent Application Serial No. 04 018 859.1, filed on Aug. 9, 2004, the entire contents of which is hereby incorporated by reference. 
   TECHNICAL FIELD 
   The disclosure relates to a press for machining workpieces, in particular to a press with a device for detecting a mutual reference position of tool parts of a pressing tool. 
   BACKGROUND 
   On previously known presses (e.g., as disclosed in European Patent Application, EP 1 123 169 B1), a punch and a die of a pressing tool are moved against each other in a stroke direction until the punch meets the die or a plate arranged between the punch and the die. The resulting relative position of the die and punch forms a reference position from which the length of the die is determined. To this end, with the punch sitting on the die or on the plate supported by the die, the position of the punch end remote from the die must be detected. 
   This can be achieved by means of a detection unit that is activated as soon as the punch comes into contact with the die or the plate. The detection process is triggered by the rise in power consumption of the press drive connected with the action of the punch upon the die or plate. Accordingly, the control of a switching device for the detection unit is integrated in the press drive. The punch and die serve simultaneously as reference elements to detect their mutual reference position. If the position of the punch end that remote from the die is determined, then the punch length is calculated from this position and from the known position of the die surface impacted by the punch and, where applicable, from the known thickness of the plate between the die and the punch. 
   It would be advantageous to constructionally decouple the control of a detection unit to detect a mutual reference position of the tool parts from the functional machine components necessary for the regular machine operation. 
   SUMMARY 
   As disclosed herein the function control of the tool parts of a press can be decoupled at least with substantial parts from the machine drive for regular machine operation of the press. This results in particular in the possibility of supplementing the functionality of existing presses with the function “reference position detection” at relatively low cost. 
   In a first general aspect, a press adapted for machining a workpiece, in particular for embossing and/or punching metal plates, includes a pressing tool that includes a first tool part mounted in a first tool mounting and a second tool part mounted in a second tool mounting. The first part and the second part are located so as to be on opposing sides of the workpiece during machining of the workpiece. The press further includes a pressing drive adapted to move the first part and the second part toward and away from each other in a stroke direction during machining of the workpiece and first and second reference elements, where the reference elements are moveable into a relative position that corresponds to a predetermined relative position of the first tool part and the second tool part as mounted in the mountings. The press further includes a control pulse emitter that generates a control pulse when the first and second reference elements are moved into the relative position, where at least part of the control pulse emitter is mounted on one of the reference elements or on one of the mountings, such that the control pulse emitter generates the control pulse automatically when the first and second mountings move into the relative position. The press further includes a switch that is activated by the control pulse and a detection unit that is activated by activation of the switch to detect the relative position of the first and second reference elements. 
   Implementations can include one or more of the following features. For example, the switch can be activated by pressure, and the control pulse emitter can provide a control pressure that is tapped to activate the switch. The control pressure emitter can include a pressure volume, and a pressure of the pressure volume can be tapped as the control pressure to activate the switch, and the pressure of the pressure volume can be set to the control pressure to activate the switch when the first and second reference elements are moved into the relative position. The control pressure emitter can include a pressure volume of a flowable pressure medium that is connected to a source of flowable pressure medium, and under movement of the reference elements into the relative position, an outlet opening of the pressure volume can closed or reduced in area such that the pressure of the pressure volume is increased from an initial pressure to the control pressure or opened or increased in area such that the pressure of the pressure volume is reduced from an initial pressure to the control pressure. 
   At least one of the reference elements can include two element parts that are movable relative to each other, and, under movement of the reference elements into the relative position, the two element parts can be moved relative to each other to generate the control pulse. The control pressure emitter can include a pressure volume of a flowable pressure medium that is connected to a source of flowable pressure medium, and at least one of the reference elements can include two element parts which, under movement of the reference elements into the relative position, can be moved relative to each other to generate the control pulse, and that cause an outlet opening of the pressure volume to be altered. 
   The reference element parts together can form a pilot valve, and the pilot value can be a piston valve. At least one of the reference elements can be mounted on at least one of the tool mountings. At least one reference element can include a tool mounting having a connection to a source of flowable pressure medium. The connection to a source of flowable pressure medium can form part of a tool detection device within the tool mounting. The control pulse emitter can be provided at least partly on a reference element, and the outlet opening of the pressure volume can be provided on a reference element. The pilot valve can be provided on a reference element. 
   The detection unit can form a part of a device that controls a stroke position of the first and second tool parts. The detection unit can form a part of a device that determines a thickness of the workpiece. 
   In another general aspect, a reference element for detecting a mutual reference position of tool parts of a pressing tool of a press for machining workpieces includes at least a part of a pulse emitter on which a control pulse can be tapped to activate a switch device by means of which a detection unit can be activated to detect a relative position of the reference element and a further reference element, where the reference position is defined in relation a relative position of the tool parts. 
   The control pulse emitter can be arranged in an area of the press such that it is easily accessible, for example, for maintenance and service or repair. 
   The control pulse emitter provided in the case of the invention can be of various types. 
   The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIGS. 1 and 2  the structure and function in principle of a press with a first design of the device to detect a mutual reference position of the tool parts of a pressing tool, 
       FIGS. 3 and 4  detailed views of a reference element of the device shown highly diagrammatically in  FIGS. 1 and 2  for reference position detection, and 
       FIG. 5  the structure and function in principle of a press with a second design of a device to detect a mutual reference position of the tool parts of a pressing tool. 
   

   Like reference symbols in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
   As shown in  FIGS. 1 and 2 , a press  1  for emboss machining of workpieces includes a punch holder  2  as a tool mounting for a machining punch and a die holder  3  as a tool mounting for a machining die. Corresponding conditions exist on presses for other applications, for example, on presses for punch machining, forming, and/or surface treatment of workpieces. 
   The die holder  3  can be integrated stationarily in a machine table (not shown). The punch holder  2  can be provided on a ram (also not shown) that is mobile by means of a motorized press drive  4  in a stroke direction  5  that is illustrated by the double arrow in  FIG. 1 . The press drive  4  of the press  1  is controlled by means of a numerical machine control  6  through which the stroke end positions of the ram of the press  1  are adjustable in the stroke direction  5 . 
   During regular operation, i.e., during workpiece machining, a machining punch of normal design is inserted in the punch holder  2 , and a conventional machining die is inserted in the die holder  3 . A compressed air supply  7  of the press  1  can be opened to a compressed air line  8  in the wall of the die holder  3 . 
   Before use of the press drive  4 , the compressed air line  8  exsposed to compressed air by corresponding control of compressed air valve  9  by means of the machine control  6 . When a machining die is inserted in the die holder  3 , this closes the opening of the compressed air line  8  at the wall of the die holder  3 , such that positive pressure then builds up in the compressed air line. However, this pressure build up does not occur if a machining die is not inserted in the die holder  3 . In each case the pressure in the compressed air line  8  is tapped by a manometer  10 . Only when a positive pressure is established in the compressed air line  8  does the manometer  10  generate a signal for the machine control  6 , which sets the press drive  4  in motion. Consequently, the compressed air line  8  forms part of a device for tool detection used in workpiece machining. 
   The press  1  can be used to machine workpieces in the form of plates  11 . By means of the press drive  4  of the press  1 , the machining punch mounted in the punch holder  2  of the ram is moved to and fro in the stroke direction  5  between an upper and a lower stroke end position. The upper and, particularly also, the lower stroke end position of the machining punch are set such that the machining punch penetrates sufficiently deep into the plate  11  and gives a good machining result. 
   For various reasons during continuous operation of the press  1  an undesirable shift of the stroke end position of the machining punch can occur. A possible cause for such stroke position shift is the operational heating of the normally hydraulic press drive  4 . External temperature influences are also possible reasons for a stroke position shift. 
   An undesirable shift of the lower stroke end position can cause the machining punch to either not penetrate far enough into the plate  11  to be machined or to penetrate too far into the plate  11 , an incorrect immersion depth of the machining punch can lead to a reduction in quality of the machining result. Fluctuations in the thickness of the plate  11  to be machined can have a similar effect. For example, if the thickness of a plate  11  is unpredictably less than assumed, this can lead to the machining punch, at a given stroke end position setting, not being pressed with sufficient penetration depth into the plate  11  in the lower stroke end position. 
   To avoid an impairment in the machining result, on the press  1  particularly the lower stroke end position of the machining die is checked from time to time and if necessary reset. To achieve this, first a mutual reference position of the machining punch and the machining die in the stroke direction  5  is detected. To this end, at the punch holder  2 , the machining punch is exchanged for an upper reference element  12  and at the die holder  3 , the machining die is exchanged for a lower reference element  13 . This exchange is performed automatically like a conventional tool change. After the exchange, the punch holder  2  and the die holder  3  then form reference element mountings. For provisional fixing in the punch holder  2  and in the die holder  3 , the reference elements  12  and  13  have mounting devices that correspond to those of the machining punch and the machining die. 
   Then the plate  11  to be machined is moved by means of a conventional co-ordinate guide into the space between the upper reference element  12  and the lower reference element  13  where it comes to lie on a workpiece support  14  of the lower reference element  13 . This gives the conditions shown in  FIG. 1 . 
   In the stroke direction  5 , the workpiece support  14  is spaced relatively far from a base part  15  of the lower reference element  13 . In the stroke direction  5 , the workpiece support  14  is guided mobile on the base part  15 . A pilot valve  16  with an air passage  17  is attached to the workpiece support  14  and protrudes into a chamber  18  on the base part  15 . Thus, the pilot valve  16  closes a compressed air line  19  of the base part  15  on the side of the chamber  18 . Opposite the chamber  18 , the compressed air line  19  of the base part  15  opens into the compressed air line  8  on the die holder  3 . 
   Starting from this operating state, the compressed air valve  9  is opened by a corresponding command via the machine control  6 . Consequently, the compressed air line  8  at the die holder  3  and the compressed air line  19  at the base part  15  of the lower reference element  13  are supplied with compressed air from the compressed air supply  7  of the press  1 . After the compressed air line  19  is closed by the pilot valve  16  at its end lying towards the chamber  18  of the base part  15  a positive pressure builds up, in the inside of the compressed air lines  8  and  19 , which finally reaches the value of the positive pressure in the compressed air line  8  at the machining die  3  present in the die holder  3 . The pressure volume contained in the compressed air lines  8  and  19  forms a pressure emitter for the manometer  10  by which the internal pressure in the compressed air lines  8  and  19  is tapped. If the pressure inside the compressed air lines  8  and  19  corresponds to the pressure in the compressed air line  8  when the press  1  is ready for function, the manometer  10  generates a signal for the numerical machine control  6  via which the press drive  4  of the press  1  is consequently set in motion. By means of the press drive  4 , the die holder  2  with the upper reference element  12  is lowered in the stroke direction  5 . The upper reference element  12  runs onto the plate  11  and presses this together with the workpiece support  14  of the lower reference element  13  in the direction of the base part  15  of the lower reference element  13 . This is associated with a corresponding displacement of the pilot valve  16  on the workpiece support  14 . The pilot valve  16  with the air passage  17  reaches the opening of the compressed air line  19  lying towards the chamber  18  of the lower reference element  13  which gives the conditions shown in  FIG. 2 . Compressed air in the compressed air lines  8  and  19  can now escape via the air passage  17  of the pilot valve  16  into the chamber  18  of the lower reference element  13 , and from there through a gap remaining between the workpiece support  14  and the base part  15  of the lower reference element  13 , and, as a result, the internal pressure in the compressed air lines  8  and  19  falls. The reduced pressure is also detected by means of the manometer  10 . 
   The workpiece support  14  together with the pilot valve  16  is lowered in the stroke direction  5  until the workpiece support  14  sits on the base part  15  of the lower reference element  13 . In this position of the workpiece support  14  in the stroke direction  5 , the air passage  17  of the pilot valve  16  lies as before at the height of the opening of the compressed air line  19 . Up to this operating state, the lowering movement of the ram of the press  1  to shift the workpiece support  14  of the lower reference element  13  down in the stroke direction  5  was performed with relatively large speed. As a result of the action upon the base part  15  the lower reference element  13  is pressed as a whole against the base of the die holder  3 . This eliminates any incorrect positioning of the lower reference element  13 . 
   The reaching of the lowering end position of the ram on contact of the workpiece support  14  on the base part  15  of the lower reference element  13  is detected by the machine control  6  from the increasing power consumption of the stroke drive  4 . The machine control  6  then initiates a slow return stoke of the ram of the press  1  in the upward stroke direction  5 . This return stroke movement of the ram is accompanied by a relief of the workpiece support  14  from the pressure exerted by the upper reference element  12 . Under the effect of a return spring, pretensioned on the previous downward movement, between the base part  15  and the workpiece support  14 , the workpiece support  14  with the plate  11  now performs a return stroke movement in the upward stroke direction  5 . The workpiece support  14  is supported over the plate  11  on the upper reference element  12 . Connected with the return stroke movement of the workpiece support  14  is a corresponding movement of the pilot valve  16 . The pilot valve  16  leaves with the air passage  17  the area of the opening of the compressed air line  19  and again reaches its position according to  FIG. 1  in which it closes the compressed air line  19  at the side facing towards the chamber  18 . Connected with closure of the compressed air line  19  is a pressure rise in the compressed air lines  8  and  19 . 
   As soon as the pressure rise begins and is tapped by the manometer  10  at the compressed air lines  8  and  19 , the manometer  10  generates a signal for the machine control  6  which firstly shuts down the pressure drive  4  and secondly causes the position of the upper reference element  12  in the stroke direction  5  to be detected. To this end, the signal generated by the manometer  10  under pressure control causes the activation of a switch device integrated in the machine control  6  for a distance measurement system of the machine control  6  serving as a detection unit. The detection unit or distance measurement system is thus activated and detects the position of the upper reference element  12 . In the detection position shown in  FIG. 1 , the upper reference element  12 , with the workpiece support  14  lying thereon via the plate  11  of the lower reference element  13 , was moved from the previous maximum lowered position with relatively low speed. Consequently, a prompt and precise detection is ensured of the start of the pressure rise upon the transition of the pilot valve  16  from a position allowing the emergence of compressed air from the compressed air line  19  into a position blocking the emergence of compressed air. 
   At the same time, i.e., at the start of the pressure rise in the compressed air lines  8  and  19 , the lower reference element  13  lies with the top of the workpiece support  14  in the stroke direction  5  at a level that represents the level of the top of the machining die in workpiece machining. In the example shown in  FIG. 1 , the level of the top of the workpiece support  14  at the lower reference element  13  corresponds to the level of the top of the machining die. 
   Once this position is known, it is stored in the numerical machine control  6 , and from the known position of the lower reference element  13  or the workpiece support  14  and from the result of the detection initiated by the manometer  10  of the position of the upper reference element  12 , the numerical machine control  6  can calculate the thickness of the plate  11 . 
   The position assumed by the upper reference element  12  on direct pressurization of the workpiece support  14  of the lower reference element  13 , being in the position according to  FIG. 1 , stands in a defined connection with the lower stroke target end position into which the machining punch on workpiece machining should be moved in the stroke direction  5  in order to achieve a high quality machining result. The upper reference element  12  according to  FIG. 1  is separated from this position by the previously determined thickness of the plate  11 . Using this determined plate thickness, the position of the upper reference element  12  can be determined, which can then be allocated to the lower stroke target end position of the machining punch. From the position of the upper reference element  12  determined in this way, finally the lower stroke target end position of the machining punch can be derived. The stroke target end position arising from the detected position of the upper reference element  12  for the machining punch is compared in the machine control  6  with the stroke end position actually set that is stored there. On deviation of the target from the actual position, the machine control  6  corrects the stroke end position setting to eliminate the positional deviation. 
   A corresponding stroke end position control or correction can be performed by means of the reference elements  12  and  13  even without inclusion of the plate  11 . In this case the upper reference element  12  sits directly on the workpiece support  14  of the lower reference element  13 . Here too the time of position detection is marked by the start of the pressure rise in the compressed air lines  8  and  19  on slow return of the tool support  14  from the maximum lowered position. 
   Finally, the upper reference element  12  and the lower reference element  13  are replaced by the respective machining punch and machining die. The plate  11  is then machined with the previously optimized stroke end position setting of the machining die. 
     FIGS. 3 and 4  show in detail the lower reference element  13  previously described. The base part  15  of the lower reference element  13  is shown pot-like and with an inwardly protruding pot edge  20  that extends over the pilot valve  16 . The pilot valve  16  forms a piston valve that is bolted to the tool support  14  of the lower reference element  13 . The diameter of the piston valve or pilot valve  16  is less than the diameter of the undercut holding it and limited by the pot edge  20  on the base part  15  of the lower reference element  13 . Consequently, between the pilot valve  16  and the base part  15  is formed an annular chamber  21 , which, together with a line section  22  passing through the base part  15 , forms the compressed air line  19  previously described. 
   As shown in  FIGS. 3 and 4 , the lower reference element  13  is in the functional state according to  FIG. 1 . The piston valve or pilot valve  16 , under the effect of a return spring supported at one side on the base part  15  and on the other side on the workpiece support  14  of the lower reference element  13 , is pressed on the underside of the inwardly protruding pot edge  20 . Due to the tight seal between the pot edge  20  and the pilot valve  16 , compressed air is prevented from flowing out from the compressed air line  19 . 
   If the workpiece support  14  of the lower reference element  13  is lowered starting from this operating state under pressurization by the upper reference element  12 , between the top of the pilot valve  16  and the underside of the inwardly protruding pot edge  20  is formed a space through which compressed air can escape from the inside of the compressed air line  19 . The compressed air takes a path via the resulting free space between the pot edge  20  and the closing valve  16 , an annular chamber  23  between the pot edge  20  and the workpiece support  14 , and a space  24  between the top of the pot edge  20  and the underside of the edge of the workpiece support  14 . In comparison with the conditions shown in  FIG. 4 , the space  24  is reduced in height when the workpiece support  14  is lowered. Together with the annular chamber  23  and the free space between the underside of the pot edge  20  and the top of the pilot valve  16  when the workpiece support  14  is lowered, the space  24  between the top of the pot edge  20  and the underside of the edge of the workpiece support  14  forms the air passage  17  according to  FIGS. 1 and 2 . 
   As is evident from  FIG. 5  in comparison with the conditions in  FIGS. 1 and 2 , a lower reference element  33  is inserted in the die holder  3  on the press  1 . This is formed as one piece and fitted with a chamber  38  and a compressed air line  39 . The compressed air line  39  is connected to the compressed air line  8  of the die holder  3 . An upper reference element  32  allocated to the lower reference element  33  corresponds in structure to the upper reference element  12  according to  FIGS. 1 and 2 . 
   In the case of the arrangement according to  FIG. 5 , detection of the relative position of the upper reference element  32  and lower reference element  33  in the stroke direction  5  is triggered as soon as the upper reference element  32  meets the lower reference element  33 . This closes the chamber  38  in the inside of the lower reference element  33  and under the effect of the compressed air from the compressed air supply  7  a positive pressure builds up inside the chamber  38  and in the compressed air lines  8  and  39 . The pressure volume inside the chamber  38  and the compressed air lines  8  and  39  forms a control pressure emitter for the manometer  10 . This taps the positive pressure and, according to the function principle described above in  FIGS. 1 and 2 , causes detection of the relative position of the upper reference element  32  and the lower reference element  33 , and via this relative position detection, causes detection of a mutual reference position of the machining punch and machining die in the press  1  in the stroke direction  5 . The lower stroke target end position of the machining punch determined by detection of the mutual reference position is compared with the stroke end position set and the position setting corrected where necessary. 
   A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other embodiments are within the scope of the following claims.