Abstract:
A method for positioning a tool ( 24 ) on a tool chuck ( 20 ) employs a tool holding device ( 22, 50, 58 ), which includes a tool-accommodating area ( 32, 52, 66 ) for at least partly receiving the tool ( 24 ), a connecting area ( 26, 54 62 ) to be arranged on the tool chuck ( 20 ), and a positioning opening ( 48 ) through which a positioner ( 18 ) can be placed against the tool ( 24 ), which is located at least in part in the tool-accommodating area ( 32, 52, 66 ). The tool ( 24 ) is optically scanned to obtain a measurement. Subsequently, the tool holding device ( 22, 50, 58 ) is removed from the chuck ( 20 ), and the chuck is heated. Then, the tool ( 24 ), which is separated from the tool holding device ( 22, 50, 58 ), is shrink fitted in the chuck ( 20 ) at a position that is based on the measurement.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application is a divisional of U.S. patent application Ser. No. 10/536,957, filed on May 31, 2005 and entitled TOOL HOLDING DEVICE AND METHOD FOR POSITIONING A TOOL, now U.S. Pat. No. 7,371,036, which in turn is a PCT National Stage of PCT Application No. PCT/EP2003/011592, filed on Oct. 20, 2003, and which claims priority from German Application No. 102 58 055.3, filed on Dec. 11, 2003, the contents of each being incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   The invention relates to a tool-holding device and a method of positioning a tool. 
   For the exact machining of a workpiece, in particular with a multispindle machine tool, it is advisable to clamp the cutting tools in each case in an exact position in the tool chucks of the spindles. For the exact positioning of a tool in a tool chuck, EP 1 155 765 A1 has disclosed a method and a tool chuck in which the tool is held in a small supporting opening and calibrating and measuring operations can be carried out on the tool before the tool is fastened in the tool chuck. In this case, however, exact alignment of the tool with the locating opening of the tool chuck can only be maintained to a moderate degree, so that there is the risk of an imprecise tool measurement, in particular in the case of long tools and/or tools tapering to a point. 
   The object of the invention is therefore to specify a tool-holding device and a method of positioning a tool in a tool chuck, with which method the tool can be positioned in a tool chuck with a high degree of accuracy. 
   SUMMARY OF THE INVENTION 
   With regard to the tool-holding device, a tool-holding device for holding a tool on a tool chuck is proposed, the tool-holding device comprising a tool-locating region for at least partly locating the tool, a connecting region for arranging on the tool chuck, and a positioning opening, through which a positioning means can be placed against the tool arranged at least partly in the tool-locating region. A supporting opening in the tool chuck can be dispensed with, as a result of which the tool chuck can be kept compact. In addition, the tool-holding device can be separated from the tool chuck and therefore, without having to interfere with the configuration and the dimensioning of the tool chuck, can be adapted for the exact holding of the tool relative to the tool chuck. If the tool is not positioned in the tool chuck in such a way that it is exactly in alignment with the tool chuck, this leads to incorrect determination of the axial length of the tool when measuring the tool at angular cutting edges of the tool. This applies in particular in the case of very long tools. Even slight angularity of the cutting edge, an error caused by manual focusing of an optical measuring unit, or the wobbling of the tool directly affect the measuring accuracy of the axial length. A tool-holding device can be arranged in alignment on the tool chuck with very high accuracy. In addition, it can be adapted to the shank of the tool in such a way that the tool is likewise held in the tool-holding device in alignment with the axis of the tool chuck. Measuring errors resulting from radial positioning inaccuracies are therefore largely avoided when measuring, for example, very long tools or angular characteristic elements of the tool, such as a cutting edge for example. 
   Due to the ease with which the positioning means can be placed against the tool, the position of the tool can be additionally detected with a high degree of accuracy. The position, thus determined, of the tool can be used for positioning the positioning means in such a way that the tool, when bearing against the positioning means, is arranged in the tool chuck in the desired position. In addition, the ease with which the positioning means can be placed directly against the tool ensures that, during the measurement for the pre-positioning and when the tool is placed on the positioning means before a fastening operation, e.g. by shrink fitting, the identical stop location and the identical stop are used. This is especially advantageous in the case of tools having internal cooling, which have an inner passage in the tool interior and therefore can only be positioned by a stop with difficulty. 
   The expression “tool chuck” refers to any device which is provided for retaining the tool during an operation of the tool on a workpiece. In particular, this refers to a shrink-fit chuck for the thermal shrink fitting of the tool. The tool-locating region preferably serves to locate the shank of the tool. The tool-holding device is arranged with the connecting region on the tool chuck. Such an arrangement refers to the fact that said tool-holding device and said tool chuck are brought together in contact with one another, for example placed one on top of the other, or are connected in a positive-locking or frictional manner. The connecting region may also be at least partly arranged in the tool chuck. The positioning opening is expediently arranged in the connecting region. 
   The tool-locating region, when the tool chuck is arranged in the connecting region, is intended for holding the tool in alignment with a locating opening of the tool chuck. In this way, the tool can be kept oriented outside the tool chuck in the way it is held in the tool chuck in the fastened state. Measurement of the tool can be carried out in a simple manner in this way. 
   A simple arrangement of the connecting region in the tool chuck can be achieved by the connecting region having a shank for arranging in a locating opening of the tool chuck. The shank can be inserted into the tool chuck and can expediently be positioned exactly in the locating opening. 
   Very exact orientation and an arrangement of the tool in the tool-locating region expediently free of play can be achieved by a holding element provided for the elastic deformation being arranged in the tool-locating region. In an especially simple manner, such a holding element may comprise an O-ring, other elastic means which are provided for bearing against the tool and for holding the same also being conceivable. In a similarly advantageous manner, a holding element provided for the elastic deformation is arranged in the connecting region, as a result of which the connecting region, which is designed as a shank for example, can be arranged in a precise position and expediently free of play on the tool chuck, this also referring to an at least partial arrangement in the tool chuck. 
   A further advantage can be achieved if a movably mounted holding element is arranged in the tool-locating region. Due to the movable mounting of the holding element, a tool can be inserted in an especially simple manner into the tool-locating region, designed as a tool-locating opening for example, and sliding friction during the insertion of the tool can be at least largely avoided. In a similarly advantageous manner, the movably mounted holding element is arranged in the connecting region, a factor which is advantageous with regard to the mounting of the connecting region on the tool chuck. The movably mounted holding element may be a rolling element, in particular a ball or a rolling-element cage, in particular a ball cage. 
   The holding element is advantageously a rolling-element cage, for example a ball cage or a rolling cage, other forms of rolling elements also being conceivable. In this way, an especially simple arrangement of the holding element in the connecting region or in the tool-locating region can be achieved. 
   An especially advantageous arrangement of the connecting region on the tool chuck can be achieved if the connecting region has an inner wall for arranging around an outer wall of the tool chuck. The tool-holding device can be put onto the tool chuck with the connecting region, in which case, in an expedient tapered design of the outer wall of the tool chuck, canting of the connecting region on the outer wall can be avoided. In this way, the tool-holding device can be arranged free of play and thus in an exact position on the tool chuck. This advantage is achieved in an especially effective manner if the inner wall is of tapered design. 
   With regard to the method, a method of positioning a tool in a tool chuck is proposed in which a tool-holding device is arranged on the tool chuck and the tool is held by the tool-holding device, and a characteristic element of the tool is scanned for positioning a positioning means, a force being applied to the tool by the positioning means through a positioning opening in the tool-holding device. As described above, the tool can be held very accurately by the tool-holding device in a desired orientation on the tool chuck and the tool can be thus measured. By the force being applied to the tool, for example by the positioning means being placed directly or indirectly against the tool, the positioning means, without calibration, can then be brought into a position in which the tool placed against the positioning means is located very precisely in a desired position. 
   The tool-holding device is arranged on the tool chuck, in which case it can also be arranged, for example inserted, partly in the tool chuck. The characteristic element may be a tip of the tool or an edge, cutting edge, flank, side, contour, envelope curve or another element of the tool that is important during the machining of a workpiece. The scanning of the characteristic element of the tool may be effected mechanically, for example by applying a measuring element, or in a non-contact manner, for example optically by recording an image of the element. 
   The force on the tool is advantageously maintained during the measuring of the characteristic element. In this way, a position reference between the characteristic element and the positioning means can be retained during the measurement, as a result of which exact positioning of the tool in the tool chuck can be achieved. 
   A further advantage of the invention is achieved by the positioning means being placed against the tool before the measuring of the characteristic element, and by the tool being scanned when said positioning means is placed against it. By the positioning means being placed against the tool, and by the force flow which takes place as a result, the tool can be moved by a short distance. This movement can be detected by the scanning and can serve as a trigger for starting the measurement of the characteristic element. The scanning may be effected mechanically, or optically in a non-contact manner, electrical scanning, for example by a capacitive measurement, also being conceivable. The characteristic element is preferably scanned. 
   The placing of the positioning means against the tool expediently causes the tool to move, and the movement is expediently used as a trigger for stopping the movement of the positioning means. As a result, the positioning means can be moved from its unknown position in a simple manner until the movement of the tool is recorded by the force flow which takes place. Even without knowledge of the position of the positioning means, a measuring operation can be started and exact positioning of the tool in the tool chuck can be achieved. 
   A reliably exact measurement of the characteristic element can be achieved by the tool being lifted in the tool-holding device by the positioning means before the measuring of the characteristic element and by it remaining lifted during the measuring. 
   An automated and thus cost-effective sequence of the measuring of the characteristic element can be achieved by an optical measuring system being focused on a predetermined point, by the optical measuring system, if the tool is absent or visible in the field of view of the optical measuring system, being brought closer to or respectively moved away from the tool chuck in the axial direction of a tool-locating region of the tool-holding device, and, after the characteristic element appears in the field of view, by its actual position being determined and by the force then being applied to the tool. Due to such an automatic search run of the optical measuring system, for example a camera, in combination with a lighting element, manual setting of the optical measuring system to the characteristic element can be dispensed with. The predetermined point preferably lies in the axial direction of the characteristic element of the tool. For example, the point may be arranged at a visible edge of the shank of the tool, and the optical measuring system may be moved in such a way that the field of view travels along the visible edge of the tool up to the characteristic element. 
   After the application of the force, the actual position is expediently measured again for determining the desired position of the positioning means. Due to the initial determination of the actual position of the characteristic element, a movement of the tool by the positioning means being placed against the tool can be recorded, namely by the characteristic element being moved out of the initial actual position. To determine the desired position of the positioning means, the actual position of the characteristic element is measured again in order to achieve exact positioning of the tool in the tool chuck. 
   The tool and the tool-holding device are advantageously separated from one another after the measuring and the tool is advantageously inserted into the tool chuck. Due to this separation of the tool-holding device and the tool chuck fastened in the tool, the tool chuck can be of especially simple design, for example in the form of a commercially available standard tool chuck. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages follow from the description of the drawing below. An exemplary embodiment of the invention is shown in the drawing. The drawing, the description and the claims contain numerous features in combination. The person skilled in the art will also expediently consider the features individually and form appropriate further combinations therefrom. 
       FIG. 1  shows a schematic illustration of a tool setting and measuring apparatus, 
       FIG. 2  shows a section through a tool chuck with a positioning means and a tool-holding device, 
       FIG. 3  shows the tool chuck from  FIG. 2  with positioned tool, 
       FIG. 4  shows an alternative tool-holding device with inserted tool, 
       FIG. 5  shows a further tool chuck with a mounted tool-holding device in a sectioned illustration, 
       FIG. 6  shows the tool-holding device from  FIG. 5  with a holding element, during the process for inserting the tool, 
       FIG. 7  shows the tool inserted into the holding element, and 
       FIG. 8  shows a detail of the holding element from  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The setting and measuring apparatus  2  shown in  FIG. 1  comprises an optical-system carrier  4 , a camera system with an optical measuring system  6  in the form of a camera, a control unit  8 , an induction slide  10 , an induction coil  12  and a tool-mounting spindle  14 . In addition, the setting and measuring apparatus  2  has an evaluating unit  16  and an automatic length-setting and stop system with a positioning means  18 , or positioning member. Fastened in the tool-mounting spindle  14  is a tool chuck  20 , into which a tool-holding device  22  is inserted. A tool  24  designed as a shank-type tool is inserted into the tool-holding device  22 . The elements mentioned can be moved in accordance with the arrows shown. 
   A method of fastening the tool  24  in the tool chuck  20  is described below with reference to  FIGS. 1 to 4 . The tool chuck  20  is inserted into the mounting spindle  14  and preferably clamped in place there. After that, the tool-holding device  22  is inserted with a connecting region  26 , shaped as a shank, into a locating opening  28  of the tool chuck  20 . The connecting region  26  serves to arrange the tool-holding device  22  on the tool chuck  20  and is ground in the shank in such a way that it can be inserted into the locating opening  28  in a sliding manner and virtually free of play without heating a locating region  30  of the tool chuck  20 . Above the connecting region  26 , the tool-holding device  22  has a tool-locating region  32 , or tool-accommodating region, with a tool-locating opening  34 , which is designed in such a way that the tool  24  can be inserted virtually free of play. In the process, the tool  24  can be pressed into the tool-locating opening  34  until it bears with its shank end against the bottom of the tool-locating opening  34 . The tool-locating region  32 , with tool chuck  20  arranged in the connecting region  26 , is intended for holding the tool  24  in alignment with the locating opening  28  of the tool chuck  20 . 
   After the tool  24  has been inserted into the tool-holding device  22 , a data record assigned to the tool  24  is loaded into the evaluating unit  16 . At this instant, the type of tool  24  involved and the desired position Z desired  at which it is to be located in the tool chuck  20  and then shrunk in place is known to the evaluating unit  16 . A measuring sequence by means of the control unit  8  is now started by an operator, as a result of which the optical measuring system  6 , with its field of view  36 , is focused on a predetermined point. The point lies, for example, at a predetermined height above a reference point of the tool chuck  20  and on a visible edge of a cylindrical shank  38  of the tool  24 . The tool  24  is visible in the field of view  36  of the optical measuring system  6 . This visibility is recorded by the evaluating unit  16  and the optical measuring system  6  is moved in such a way that the field of view  36  is moved away from the tool chuck  20  in the axial direction  40 —that is to say it is moved upward. Finally, a characteristic element  42  of the tool  24 , for example a cutting edge, appears in the field of view  36 , as a result of which the characteristic element  42  is optically scanned. The characteristic element  42  is detected by the evaluating unit  16 , the movement of the optical measuring system  6  is stopped, and the actual position Z actual  of the characteristic element  42  is determined. In this case, the actual position Z actual  relates to the position of the characteristic element  42  relative to a fixed reference point on the tool chuck  20 . It is likewise readily possible to direct a field of view  36   a  of the optical measuring system  6  toward a predetermined point which lies above the tool  24 , so that the tool  24  is absent in the field of view  36   a . In this case, a downward movement of the optical measuring system  6  in the axial direction  40  is started by the evaluating unit  16 , and the optical measuring system  6  is brought closer to the tool chuck  20  until the characteristic element  42  appears in the field of view  36   a  of the optical measuring system  6 . 
   After completion of the determination of the actual position Z actual  of the characteristic element  42 , the positioning means  18  in the form of a rod-like plunger is moved upward from a rest position by a drive (not shown). In the process, the positioning means  18  is guided with a top stop  46  through a positioning opening  48  in the connecting region  26  of the tool-holding device  22 , to be precise until the stop  46  abuts against the shank of the tool  24 . By this placing of the positioning means  18  against the tool  24 , the tool  24  is lifted slightly, for example by a few hundredths of a millimeter up to a few millimeters. 
   During the raising of the positioning means  18 , the characteristic element  42  is scanned by the optical measuring system  6 , and the image of the characteristic element  42  appearing in the field of view  36 ,  36   a  is regularly checked for a movement by the evaluating unit  16 . The movement of the characteristic element  42 , for example by a few tenths of a millimeter, caused by the abutting of the stop  46  against the tool shank, is detected by the evaluating unit  16  by means of the optical measuring system  6  and is used as a trigger for stopping the movement of the positioning means  18 . The tool  24 , held by the tool-locating region  32 , then rests on the positioning means  18 . 
   The characteristic element  42  is now again measured for its actual position Z actual  and, in combination with the stored desired position Z desired  of the characteristic element  42 , a desired position of the positioning means  18  or a displacement distance Z Δ , into this desired position is determined. The positioning means  18  is now moved downward by this displacement distance Z Δ , and is held there in awaiting position. 
   After that, the tool  24  can be removed from the tool-holding device  22  and the tool-holding device  22  can be removed from the tool chuck  20 , and the heating of the locating region  30  of the tool chuck  20  and thus the operation for shrink fitting the tool  24  can be started by moving the induction coil  12  into position manually or automatically. After sufficient heating of the locating region  30 , the tool  24  is inserted into the locating opening  28  of the tool chuck  20  by an operator or automatically by a robot, in the course of which it is offered to the already pre-positioned positioning means  18  ( FIG. 3 ). The characteristic element  42  is now located in the desired position Z desired . The complete tool shrunk in place, consisting of tool chuck  20  and tool  24 , is then cooled with air, cooling adapters or water-flushed cooling bells. The shrink-fitting operation is ended, and the tool  24  can be measured again in the cooled state. The positioning means  18  can be retracted into an initial state. 
   On multiple-edged tools, first of all the largest of all the cutting edges can preferably be traced and this cutting edge can then be used for the measuring and setting. A further advantage is that the tool-holding device  22  may be designed with such a length that both the shank length of the tool  24  itself and the insertion depth into the tool chuck  20  can be optimally dimensioned. Thus a wobbling error during the measurement is largely avoided. On account of the simple and inexpensive design, individual tool-holding devices  22  may in principle also be provided for one and the same tool type (shank diameter) for special tools or for different shank tolerances. 
   For the at least partial correction of any wobbling of the tool  24  in the tool-holding device  22 , it is additionally possible to determine the outer contour of the tool  24  at four points P 1 , P 2 , P 3  and P 4 , for example by means of the optical measuring system  6 , and to determine the theoretical center axis of the tool  24  therefrom. This center axis is the straight connecting line from a first calculated center point which lies between the points P 1  and P 2  to a second calculated center point which lies between the points P 3  and P 4 . This theoretical center axis can be included in the determination of the position of the characteristic element  42 . Such a determination of the theoretical center axis is especially appropriate in straight-fluted tools and in tools in which an outer contour of the shank can be measured as described above. 
   An alternative tool-holding device  50  is shown in  FIG. 4 . A holding element  56  in the form of O-rings is arranged in both the tool-locating region  52 , or tool-accommodating region, and the connecting region  54 , these O-rings ensuring that the tool  24  is retained free of play in the tool-locating region  52  and respectively that the connecting region  54  is retained free of play in the locating opening  28  of the tool chuck  20 . The O-rings are each inserted into annular grooves of the tool-holding device  50  and are held in position by said grooves. The holding element  56  is produced from an elastic material and can be compressed, for example, by the inserted tool  24  in such a way that the tool  24  can be inserted with its shank into the tool-locating region  52  and held elastically by the O-rings. In a similar manner, the holding element  56  in the connecting region  54  retains the tool-holding device  50  free of play and elastically in the locating opening  28 . 
   A further tool-holding device  58  is shown in  FIG. 5 . This tool-holding device  58  is not inserted into the locating opening  28  of the tool chuck  20  but is put onto a tapered outer wall  60  of the tool chuck  20 . To this end, the tool-holding device  58 , in its connecting region  62 , has a tapered inner wall  64  which is intended for arranging around the outer wall  60  of the tool chuck  20 . 
   The outer wall  60  and the inner wall  64  are each ground and are designed to fit one another exactly, so that the tool-holding device  58  sits on the tool chuck  20  free of play and with only a slight risk of tilting. In this case, a tool-locating region  66 , or tool-accommodating region, of the tool-holding device  58  is designed in such a way that the tool  24  held in it is oriented in alignment with the locating opening  28 . 
   A holding element  68  in the form of a ball cage, which is shown in detail in  FIG. 7 , is arranged in the tool-locating region  66  of the tool-holding device  58 . The holding element  68  has rows of rolling elements  70  in the form of balls arranged in a circle around the tool  24 , rolling elements  70  which are adjacent in the tangential direction in each case being arranged offset in the axial direction  40  by slightly more than a ball radius. The rolling elements  70  are produced from steel and have slight but sufficient elasticity in order to hold the tool  24  elastically and free of play in the tool-locating region  66 . When the tool  24  is inserted in the tool-locating region  66 , the rolling elements  70  are elastically compressed by between 2 μm and 3 μm. 
   To insert the tool  24  into the tool-locating region  66  of the tool-holding device  58 , first of all the holding element  68  is pressed into a tool-locating opening  76  of the tool-locating region  66  up to a stop  74  ( FIG. 6 ), that is to say about halfway into said tool-locating opening  76 . The tool  24  is then inserted with its shank into the holding element  68 , the rolling elements  70  which project from the tool-locating opening  76  being pressed outward slightly in an elastic connecting means  72  holding the rolling elements  70  together. 
   When the tool shank is pressed further into the holding element  68 , the topmost rolling elements  70  in the tool-locating opening  76  are pressed by the shank against the inner wall of the tool-locating opening  76  and, with further downward movement of the shank, are forced to roll on the inner wall. As a result, the connecting means  72  is drawn downward and into the tool-locating opening  76 , the annular stop  74  being pressed radially inward. To permit this pressing-in of the stop  74 , the connecting means  72  is produced from an elastic plastic ( FIG. 8 ). 
   The tool  24  can now be pressed down to the tool chuck  20 , the holding element  68  being inserted into the tool-locating opening  76  at half the speed of movement of the tool  24 . Due to the central arrangement of the stop  74  in the axial direction  40 , the holding element  68 , when the tool shank is inserted completely into the tool-locating opening  76 , is likewise arranged completely inside the tool-locating opening  76  and holds the tool  24  in a movable manner in the axial direction  40  and in the tangential direction and in a fixed manner in the radial direction; tilting is thus prevented.