Abstract:
To center a tool restrained within a collet coupled to a driven portion (9) which, in turn, is coupled to a driving portion (2), and to compensate for possible axial offsets of the respective portions, a coupling element connects the driving and driven portions and two first spring elements (23, 24) are located on the driving portion, two further spring elements (31, 32) are located on the driving portions offset with respect to the first spring elements of 90 degrees. Each one of the spring elements can be adjusted with respect to a centrally located counter support portion (29, 31) by adjustment screws passing through the spring elements and bearing against the counter support, to thereby position the axis of the driven portion (9) carrying the collet, in congruence with the axis of the driving portion (2) even if there are manufacturing tolerances or other offset conditions, such as tolerances in the tool clamped in the collet.

Description:
The present invention relates to a centering system to center a removable machine tool element, such as a boring tool, drill, reamer, milling tool or the like with respect to a driven spindle and to compensate for axial misalignments of the tool and the driving element. 
     BACKGROUND 
     Removable tools are often carried in collets or chucks coupled to rotary machine tools, or driving spindles thereof by floating holders which permit compensation for misalignments between the machine spindle, to which, for example, the tool is secured and a hole into which it is to enter. Such floating holders customarily have two slider guides, respectively offset by 90 degrees, to permit compensation between the axis of the drive spindle and the axis of a bore, into which the tool is to enter. Such floating holders are not provided to set an axial offset with respect to a fixed amount, or to compensate for actual offsets and reduce them to a value of 0. 
     THE INVENTION 
     It is an object to provide an adjustment system, and specifically a centering system for rotary machine tools which permits compensation for a predetermined axial offset between the axis of coupled elements and to retain the axial offset compensation for a long period of time. 
     Briefly, a coupling element is provided connecting a driving part, such a driving disc, or the like, to a driven part which is adapted to be coupled to a tool element. Two spring elements are located on one of the parts, for example the driving part and coupled to the other, typically the driven part. Counter support means are then coupled to one of the parts, for example to the driven part, or forming, for example, part of the driven part. Two first adjustable spring position adjustment elements are coupled to the two respective ones of the first spring elements and engaging the counter support means to set the spring position of the respective first spring elements. 
     In accordance with a feature of the invention, another and similar set of two second spring elements, a second counter support means and two second spring adjustment means are provided, arranged at 90 degrees with respect to the first spring elements, counter support means and position adjustment means, so that compensation for axial offset can be effected based on two mutually perpendicular directions or vectors. The spring elements preferably are flexible in a first plane parallel to the axis of rotation, stiff in a plane perpendicular to the first plane. 
     The system has the advantage that two, or four, respectively, spring elements are provided in order to couple the driving and the driven components of the system. Complex guide systems, therefore, are not necessary in order to permit the necessary movability of the elements with respect to each other. It is only necessary to provide for deflection of the spring elements and then to set the deflected positions by the adjustable spring position means in order to determine the desired position of the elements with respect to each other. As an additional advantage, the connection of the respective driving and driven elements is free from play. Manufacturing, therefore, is simplified. 
    
    
     DRAWINGS 
     FIG. 1 is an axial side view, partly in section, of the adjustment system; and 
     FIG. 2 is a transverse cross sectional view along line 2-II of FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     The invention will be described with reference to a collar-tightening or collet holder for a rotary tool such as a boring tool, a reamer, rotary rasp or the like. FIG. 1 shows the overall system 1, which is adapted for attachment to a machine tool spindle, not shown. The collet holder 1 has an attachment flange 2 at one end thereof, formed with respectively parallel facing sides 3 and 4. The side 4 is ground to a plan configuration and is coaxial with the longitudinal axis of the attachment flange 2, and formed with a cylindrical centering bore 5 therein, to permit attachment of the flange 2 with minimum tolerance on a suitable machine tool head. The flange 2 is further formed with an indexing bore 6 and threaded attachment bores 7, to place the flange 2 in a predetermined position on a machine head and to secure it on the machine head by attachment screws passing into the threaded holes 7. 
     A unitary, prismatic, or cylindrical shaft 8 is connected to the flange 2. Preferably the shaft 8 is unitary with the flange 2, for example being formed therein. The longitudinal axis of shaft 8 is essentially congruent with the longitudinal axis of the attachment flange 5, and hence with the axis of rotation of a drive spindle to which the flange 2 can be coupled. At the end 9 remote from the flange 2, the shaft 8 is formed with an inwardly constricting tapering bore 12 for a longitudinally slit jaw holder, or collet 13. The jaw, or collet 13 is formed as a compression holder of customary shape. The shaft 8 has a cylindrical outer thread 14 adjacent its remote end to receive a tightening coupling nut 15 which engages the clamping sleeve 13 forming the collet, or jaws, and for tightening the clamping sleeve into the conical opening 12. A tool inserted into the clamping sleeve 13 then will be held as in a collet. 
     End 9 and the attachment flange 2 form two elements which have axes that can be offset with respect to each other. 
     In accordance with a feature of the invention, and to permit such adjustment, the cylindrical shaft 8 is formed with two generally U-shaped slits 16 and 17. With respect to the longitudinal axis of the cylindrical shaft 8, they are located at right angles to each other. These two U-formed slits 16 and 17, located in crossing axial planes, have essentially the same shape. They are offset longitudinally with respect to each other, leaving a disc-shaped intermediate element 18 there-between free from the slits 16 and 17. 
     The U-shaped slit 16 passes through the cylindrical shaft 8 completely from one side to a diametrically positioned opposite side and defines two respectively parallel legs 19 and 21. Legs 19 and 21 extend parallel to the longitudinal axis of the shaft 8. The transversely extending base portion 22 is located in a plane which intersects the longitudinal axis of the shaft 8 at a right angle. The widths of the slits, in the region of the legs 19 and 21, as well as of the base portion 22, can be uniform throughout and is between 1 mm and a maximum of about 2 mm, that is the width of the slits is small with respect to the diameter of the cylindrical shaft 8--see FIG. 1. 
     The spacing of the two straight legs 19 and 21 is, preferably, about the same as their length, measured in a direction parallel to the longitudinal axis of the shaft 8. It may be, as shown in FIG. 1, roughly about the dimension of the radius of the shaft 8 although the dimension is not critical and will depend largely on the material used for shaft 8 and the use to which the system is to be put. 
     As best seen in FIG. 2, the two legs 19 and 21 of the slit 16 extend clear through the shaft 8 from one side to the other such that the intermediate portion 18 is coupled to the flange 2 or to, in cross section segmentally shaped parts 23, 24, unitary with the flange 2. Due to the material used for the clamping sleeve or collet, the elements 23, 24 can be elastically deflected. Due to their non-rotation symmetrical cross sectional area, they have some slight resiliency in the direction perpendicular to the legs 19 and 21, while exhibiting high rigidity strength in the direction parallel thereto. These portions 23, 24 can deflect somewhat resiliently having the general characteristics of leaf springs. The intermediate element 18, thus, is coupled to the attachment flange 2 via two parallel extending spring elements. The disc-shaped intermediate element 18 and the attachment flange 2 can be moved in a plane parallel to the plane of the drawing of FIG. 1 by comparatively low force; in a direction perpendicular thereto, they are essentially undeflectable, or stiff. Due to the parallel course of the two spring elements 23, 24, an offset parallel to their respective axes of the flange 2 and the shaft 8 is possible. 
     To permit a predetermined position between the disc-shaped element 18 and the attachment flange to be obtained also in a direction parallel to the plane of the figure, the spring elements can be fixed in predetermined position with respect to the element 8. The spring elements 23, 24 have aligned threaded bores 25, 26 therein (FIG. 1) which extend to the slit 16. Two set screws 27, 28 are located in the respective bores 25, 26, engageable with a counter element 29, forming a counter bearing and positioned inwardly of the slit 16. The counter bearing element 29 is an essentially block-like body which remains when the slits 16 are formed, unitary with flange 2. It is essentially stiff and strong in all directions, so that it can form a counter bearing or a counter abutment for the adjustment screws 27 and 28. 
     The slit 17 has the same dimensions as the slit 16, and, in all respects, is essentially similar thereto. It is positioned between the disc-shaped intermediate portion 18 and the end 9 which has the conical bore 12 formed therein. It is located at 90 degrees with respect to the slit 16, with respect to the longitudinal axis of the cylindrical shaft 8. Thus, it is cross-positioned as is clearly seen in FIG. 1. Two additional spring elements 31, 32 will there be formed, located at right angles with respect to the spring elements 23, 24. The spring element 32 is not visible in FIG. 1, since it is located at the side opposite the element 31. A counter element 33, as before, extends between the spring elements 31, 32 against which two aligned screws 34 can bear; only one of these screws is visible in the figure. The screws 34, just as the spring 26, 27, are located close to the base portion of the respective slit, that is, close to the base part 22, or 35 respectively. In all respects, the slits 16 and 17 can be identical, except for their position with respect to the circumference of the shaft 8, and longitudinally thereon. 
     The system is sturdy, and easy to make. The flange 2, with the shaft 8 and the holding collar at end 9 thereon is first made in accordance with standard manufacturing technology; the slits 16 and 17 can be formed in the shaft by an electro erosive machining process, for example using copper electrodes. 
     USE AND OPERATION 
     The respective tool to be used is introduced into the collar 12, 13. A depth adjustment screw 36, in the base of the opening 12, can determine the insertion depth of the tool in the clamping system 1. The coupling nut 15 is then tightened, thus clamping the tool in the collar or jaw arrangement. Due to tolerances between the position of the conical bore 12 and the cylindrical centering bore 5, there may be an offset between the axis of the tool clamp in the collar 13 and the axis of the center bore 5. To compensate for this offset, that is to set the axis of the tool clamp in the collar 13 to zero with respect to the axis of the centering bore 5, the system, with the tool therein, is mounted on the machine spindle or a centering jig fitting into the opening 5. The four adjustment screws 27, 28, 34 (and another screw 34 not visible in FIG. 1) are then loosened. By selectively tightening the respective screws adjacent the U-shaped slits 16 and 17, it is then readily possible to set the shaft of the tool clamped in the collar 13 to an offset of 0 with respect to the axis of the shaft entering into the centering hole 5. The respective adjustment screws 27, 28, 34 will engage the counter bearing element 29 and 33, respectively, in order to press the disc-shaped intermediate element 18, or the cylindrical end 9 of the shaft 8 to the opposite side of the longitudinal axis of the tool, in alignment with the respective adjustment screw 27, 28, 34 which is then tightened. After the respective screws have been turned to compensate for any offset of the tool in collar 13 with respect to the center of the axis of rotation of the recess 5, so that the axis of rotation of the flange 2 and that of the tool is set to zero deviation, the respectively opposite adjustment screw 27, 28, 34 of the respective set of screws is tightened against the counter bearing 29. Thus, the respective spring elements are tightened with respect to each other against the counter element, providing for adjustment of the tool in collar 13 in all rotary directions. Laterally occurring forces cannot laterally offset the tool except, of course, for inherent elasticity of the materials of the centering or adjustment system, and the tool respectively. 
     A suitable material for the flange-shaft combination 8 to which the collar 13 can be secured is any material suitable in the machine tool field, for example steel. 
     It is not necessary to provide both slits 16, 17. In dependence on the spring elements, positioned parallel to each other and spaced transversely, with respect to the axis of rotation, and with respect to each other, it is possible to provide for adjustment in one plane. If the spring elements are so made that they are deflectable elastically only in a single plane, which includes the longitudinal axis of the one of the elements, whereas the system is effectively stiff with respect to a plane at right angles to that single plane, a parallelogram guidance is obtained, in which the two spring elements can be relatively changed in one plane. Since positioning tolerances can occur in any random direction, it is preferred to use the further set of similar spring elements 32, 33, that is, spring elements similar to elements 23, 24, and positioned 90 degrees rotated with respect to each other, to provide for universal adjustability. 
     The spring elements of any pair 23, 24 and 32, 33 respectively, are similar to and act like leaf springs; this, necessarily, results in precise parallel offsets of the elements with respect to each other. The counter or abutment element 29, 34 respectively, located between the spring elements, results in a particularly compact overall system. 
     The permanent adjustment elements, in the simplest form, are the set screws 27, 28, 34, simply screwed into suitable tapped openings in the spring elements themselves. 
     The structure forming the system can be made easily and simply as a unitary element which couples the flange 2 to the collar portion 9, in which, as desired, one or two slits 16 and 17 are worked, preferably, with respect to the longitudinal axis, passing through diametrically opposite side portions of the intermediate part, to define two legs extending parallel to the longitudinal axis and a base located in a plane transverse to the longitudinal axis. Thus, the slit legs 19, 20 and the base 22 can be easily made. They can readily be manufactured by a suitably formed electrode, by an electro erosive process, eroding the intermediate element. The manufacturing tolerance of the erosion process can be comparatively large. The shaft 8, secured to the flange 2 and terminating in end 9, may have any suitable shape, for example polygonal, square, or round; a round shaft is easiest to make and does not require additional machining to provide the cylindrical contour for the thread 14 (FIG. 1). 
     Various changes and modifications may be made, within the scope of the inventive concept.