Abstract:
A device aids the setter of a cutter head for cutting, e.g., milling or hobbing, of spiral bevel gears to align all rod-shaped blades with their tip cutting edges to an axial height which is as uniform as possible and to move them with their profile cutting edges to a correct radial position in the cutter head so that uniform chip removal can take place. The device has a stable arm which can be moved numerically controlled axially and radially to the cutter head, with positions which are continuously measured and with which each individual blade can be automatically pushed into its chamber in the cutter head. A probe which is connected to the arm measures the axial height of the tip cutting edge of each blade before, during and shortly after each blade is pushed in. An evaluation computer determines from the measurements of the probe and the simultaneously measured positions of the arm the value of the height of the tip cutting edge relative to the end face of the cutter head which is considered as a reference.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to a device for adjusting stick-type blades in a cutter head, e.g., of the type used for milling or hobbing of spiral bevel gears.  
           [0002]    These devices help the setter of a cutter head in aligning all blades with their tip cutting edges to an axial height which is as uniform as possible and at the same time in moving them with their profile cutting edges to a correct radial position in the cutter head. On the one hand, this should result in that the tip cutting edges in plunge cutting of tooth gaps remove chips of the same thickness and do not wear the individual projecting blades to an excess degree. On the other hand, in the generating process, all profile cutting edges will execute uniform profiling cuts so that a correct tooth profile is produced.  
           [0003]    This adjustment process is necessary not only when the cutter head is first equipped with new blades, but also after each resharpening of the blades. Specifically, all blades must be dismounted from their chambers in the cutter head for sharpening, resharpened, and then re-installed exactly. Nevertheless, this tool system is economically advantageous since the stick blades can be resharpened many times only when the adjustment process is prompt, reliable and accurate. Therefore adjustment devices are used for support.  
           [0004]    A device of this type is described for example in WO 97/07930. Accordingly, it was prior art that the blades were inserted by hand into the chambers of the cutter head, pushed with their tip cutting edges in the axial direction against a stop, and preferably clamped with pressing screws in their chambers. On this basis, the invention of WO 97/07930 relates essentially to the process for acquiring the radial position of each blade, the probe which is provided being located in a measurement plane which is offset from the axial plane of the cutter head. Sensing takes place therefore almost vertically on the lateral relieved surface of each blade. If it is ascertained that the radial position of the individual blade is outside the stipulated tolerance, these blades must be briefly released in the conventional manner in the cutter head, their tip cutting edges pressed by hand against the now correspondingly corrected stop, and screwed tight again.  
           [0005]    The described manual displacement of the blades against the fixed stop consisting mostly of hard metal has the major defect that damage can easily occur on the tip cutting edges: On the one hand, when the cutter encounters the stop at an overly high speed, on the other, when the cutter is moved somewhat radially by screwing tight and/or is pressed axially with the tip cutting edge against the fixed stop. Damage can occur especially when the cutters themselves also consist of hard metal and their tip cutting edges are accordingly more sensitive.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention can reliably prevent damage to the tip cutting edges when the blade is adjusted and in doing so nevertheless within a short time to achieve the required tolerance for the location of the blades in the cutter head. The cutter head may be one which is used for cutting, e.g., hobbing or milling of spiral bevel gears, each cutter or blade, e.g., stick-type blade, having a shaft, a tip cutting edge and at least one profile cutting edge. The cutter head includes a disk-shaped base or tool body with an axis of rotation, two parallel end faces, and a plurality of chambers which are located around the periphery and into which the respectively assigned blade with its shaft is pushed and releasably fixed. The device for adjusting such blades includes a frame, a numerically controlled turntable provided on the frame for coaxially supporting the cutter head, and a stable arm attached to the frame, the stable arm being movable at least axially and radially to the cutter head supported on the turntable and being numerically controlled and having, on its front end, a push head with which each blade can be pushed automatically into its chamber down to a stipulated height. At least one measuring device is provided for measuring positions of the push head relative to the frame. A probe is connected to the stable arm, the probe having at least one deflectable feeler which can be deflected perpendicular to one end face of the cutter head, the deflectable feeler having a sensing surface located in an immediate vicinity of the push head. The probe measures before, during and shortly after a blade is pushed in, positions of the tip cutting edge relative to the push head. An evaluation means is provided for evaluating the measured values of the measuring device and the probe to determine the attained height of the tip cutting edge of each blade relative to an end face of the disk-shaped tool body.  
           [0007]    One main advantage of the device of the present invention is that it can automatically push the inserted cutters or blades into the stipulated axial position in the cutter head and in doing so works much more uniformly and accurately than is possible in manual setting. In particular, damage to the tip cutting edges is precluded by the push head with its pressure surface made as claimed in the invention coming down on the blade behind the tip cutting edge with a stipulated noncritical speed, while the sensitive tip cutting edge is touched only by the sensing surface of the probe which exerts a low measurement force of roughly 0.2 N. With the received measurement values not only is the insertion of the blades controlled, but also their final position in the cutter head is measured.  
           [0008]    If, in one embodiment of the device, the turntable has a vertical axis of rotation, in the supported cutter head its chambers are also roughly vertical. This leads to the blades which have be inserted for adjustment being able to slip too far down. In this case it is provided that all blades are exposed to a friction force which is preferably applied by narrow leaf springs. They are all located in turn preferably on a thin disk which is matched to the size of the cutter head and which is seated on the cutter head before assembly so that one leaf spring projects into each chamber. If at this point the blades are inserted into the chambers, they are held by the leaf springs and nevertheless can be pushed down by the arm as claimed in the invention against a roughly constant friction.  
           [0009]    A similar advantageous action is attained when instead of the narrow leaf springs in each chamber there is a coiled compression spring which is attached coaxially to that side of the existing pressing screw which presses against the blade and holds it. This embodiment of the invention has the additional advantage that each blade can also be exposed to the correct force when it is to take an altered radial location in the cutter head using a spacer plate in its chamber.  
           [0010]    If in another embodiment of the invention a multicoordinate probe is used, a feeler combination with two feelers can be applied. While one is used as claimed in the invention to sense the tip cutting edges in the axial direction, after attaching the clamping blades in the cutter head, the other feeler can measure the location of the profile cutting edges in the radial direction. If this measurement shows that individual blades exceed the tolerance for the radial cutting edge position, the device as claimed in the invention offers potential for simple correction of the cutting edge position which will be detailed later.  
           [0011]    In another embodiment of the invention the device is integrated in a conventional, numerically controlled multicoordinate measurement device which either already has a turntable or is retrofitted with one. In addition, on such a measurement device there is a carriage which carries the probe and which can be moved axially and radially to the turntable. When this carriage also acquires an arm with a push head, as claimed in the invention, all structural prerequisites for an adjustment device as claimed in the invention are met. Then the CNC control of the measurement device is provided with a software expansion and on the probe a corresponding feeler for axial measurement of the tip cutting edges is inserted in order to obtain a serviceable device as claimed in the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Embodiments of the invention are detailed below with reference to the drawings.  
         [0013]    [0013]FIG. 1 shows a perspective view of a cutter head with rod-shaped cutters or blades;  
         [0014]    [0014]FIG. 2 shows an overall schematic view of the device as claimed in the invention;  
         [0015]    [0015]FIG. 3 shows a perspective view of an arm as claimed in the invention in conjunction with a probe;  
         [0016]    [0016]FIG. 4 shows four coherent detailed representations of a push head before, during and shortly after the blade is pushed in;  
         [0017]    [0017]FIG. 5 shows a section through a cutter head with leaf springs as claimed in the invention; and  
         [0018]    [0018]FIG. 6 shows a section through a cutter head with compression springs as claimed in the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    The cutter head  1  is shown in FIG. 1 coaxially supported on the turntable  22  of an adjustment device. The cutter head  1  includes a disk-shaped base or tool body  2  with one axis  4  of rotation and two parallel end faces  5  and  6 . On the periphery of the cutter head  1  is a plurality of chambers  7  which must be very exactly manufactured in their dimensions. Rod-shaped cutters or blades  10 , e.g., stick-type blades, are inserted into these chambers  7  and are clamped tight with pressing screws  8  and  9 . Each of these blades  10  consists of a shaft  11 , a tip cutting edge  12 , a profile cutting edge  13  and a secondary cutting edge  14  which is not intended for cutting when this cutter head is used on a gear cutting machine.  
         [0020]    So that the cutter head can cut, e.g., hob or mill precise bevel gears, all profile cutting edges  13  of the inserted blades  10  must have the correct radial distance from the axis  4  of rotation. For two reasons this cannot be achieved without an adjustment process for each blade  10 .  
         [0021]    On the one hand, it is an advantageous property of this tool system that the blades in their axial height are freely adjustable in order to be able to equalize different resharpening states of the blades. On the other hand, the individual production tolerances of each chamber, of the shaft used and of the blade edges relative to the respective shaft add up to a value which is often outside of the allowable radial position tolerance. Therefore, these production tolerances must be equalized when the blades are being adjusted. To do this the radial position of the profile cutting edge can be influenced via the axial height of the blades, it being less a matter of the absolute radial dimension in the cutter head than of the location of the profile cutting edges among one another differing by only a few microns.  
         [0022]    This accuracy can be achieved with a device  20  as shown in FIG. 2. On the frame  21  is a turntable  22  which using a numerical control  25  can be turned into definable angular positions around the axis  24 . The turntable  22  is provided with a cone  23  with which for example the cutter head  1  is held coaxially in the same way as on the tool spindle of a bevel gear cutting machine.  
         [0023]    On the frame  21  there is furthermore mounted an equipment base which is not detailed with a compound slide with which the arm  26  can be moved in a conventional manner by computer numerical control (CNC) in the Y and Z direction; this corresponds to the radial direction  27  and the axial direction  28  relative to the turntable  22 . The arm  26  is provided with a probe  30  which thus executes the same movements as the arm  26 . The fragile probe  30  is protected by a tubular sleeve  31  which at the same time imparts the necessary bending stiffness to the arm  26  (this is shown more clearly in FIG. 3). A conventional numerically controlled, multicoordinate measurement device can be provided for measuring the position of the probe  30  and arm  26 .  
         [0024]    Furthermore, FIG. 2 shows the evaluation means  40  with a display monitor  41 . The panel  42  of the device  20  as claimed in the invention is located above the control  25 .  
         [0025]    [0025]FIG. 3 shows the arm  26  in conjunction with the probe  30 . On the front end of the arm is a push head  32  which in this case consists of two parallel cylindrical pins  33  and  34 . The feeler  35 , which is designed for axial measurement of the tip cutting edges  12 , ends between these two pins. The required flat sensing surface  36  on the bottom end of the feeler  35  is aligned with three screws of a calibration device  37  with which the feeler  35  is attached to the probe  30 . Since the probe  30  can be deflected in two directions, specifically Y and Z, which are given in FIG. 3 by two arrows, on the probe  30  there is a combination of the feeler  35  and another feeler  38  which is designed with its sensing ball  39  for radial measurement of the profile cutting edges  13 .  
         [0026]    [0026]FIG. 4 shows in a coherent diagram four positions A to D of a blade  10  which is being pushed into the chamber of a cutter head which is not completely shown; but, as a common reference only, its upper face surface  5  is indicated as a broken line. Before pushing them in, all the blades of the cutter head  1  have been inserted manually into their chambers  7  and moved to roughly the same height. In another preparation step, using the panel  42  the arm  26  with its push head  32  is positioned over the first blade, this initial position as position A for all other cutters is sent to the storage of the numerical control  25  and then the automatic adjustment process is started.  
         [0027]    In position A, the push head  32 , represented schematically by the two cylindrical pins  33  and  34 , together with the feeler  35 , is located above the blade  10 , the probe  30  recording the value MZ=0 as the deflection of its feeler  35 . The measurement means for the Z position of the arm  26  is calibrated such that the read Z value corresponds to the distance of the flat sensing surface  36  from the end face  5 . The lower end face  6  of the cutter head which coincides with the mounting surface of the cutter head in the cutting machine may also be chosen as a reference. This would have the advantage that in series production no differences in the heights of the cutter heads in use have to be considered by the machine control. The height Z′ of the lower part of the pins  33  and  34  is irrelevant as long as it is in the vicinity of the flat sensing surface  36 . It must in any case be aligned exactly parallel to the end face  5 .  
         [0028]    In position B, the arm  26  with the push head  32  has been lowered slowly to the unknown position of the blade  10 , first the sensing surface  36  touching the tip cutting edge  12  and starting to deflect the feeler  35 . At this instant the control  25  determines the instantaneous axial height of the tip cutting edge  12  from the read Z value of the measurement means plus the simultaneously recorded deflection MZ of the probe  30 . At the same time, the arm  26  continues to move down slowly until one of the two pins  33  or  34  rests on the blade  10 , in this case the pin  33 . For another cutter head with the opposite direction of cutting the pin  34  would be used. The contact of the pin is recognized by the control  25  from the fact that the deflection MZ of the probe  30  no longer increases. At this instant the arm  26  remains stationary for a short time, the deflection MZ 1  is stored and the numerical control  25  computes the defining points for the further path over which the blade  10  must now be pushed until the stipulated height of the tip cutting edge is reached. If, as in this case, the chambers  7  do not run parallel to the axis  4  of rotation, but are tilted in the peripheral direction, the push head  32  must move exactly in the direction of the chambers  7  in order not to offset relative to the blade  10  during insertion. It then follows from the computed points that the arm  26  must move not only in the Z direction, but also in the Y direction, and at the same time the turntable  22  must turn the cutter head  1  simultaneously, as corresponds to the tilt angle of the chambers  7 .  
         [0029]    In position C, the tip cutting edge  12  of the blade  10  should have reached the stipulated height. There the arm  26  has pushed the blade  10  first with a continuous speed and then the last segment which corresponds to the stored MZ 1  value at a slow speed. In doing so the control  25  has recorded the last deflection MZ 2  of the feeler. Since the insertion of the blade  10  is not possible without small deformations in a device  20  as claimed in the invention, the position C also shows the location of the pins  33  and  34  by broken lines when the device is not loaded in a somewhat exaggerated representation. It follows that the blade  10  has not yet entirely reached its stipulated height.  
         [0030]    Position D therefore shows the push head  32  shortly after lifting from the blade  10 , when the control  25  recognizes that the deflection MZ of the feeler  35  has been reduced relative to MZ 2  and stops the unloaded arm  26 . Now the attained axial height of the tip cutting edge  12  can be determined accurately, as in position B. The control  25  computes therefrom the still lacking amount of the difference relative to the stipulated height, slowly lowers the arm  26  again until the deflection MZ 2  of the feeler  35  which was recorded last is reached and then pushes the blade  10  again by the measured amount of difference.  
         [0031]    When the push head  32  is lifted, the finally attained height of the tip cutting edge  12  is now recorded and then the arm  26  is moved into the stored initial position A, while the turntable  22  turns the next blade  10  to under the push head  32  and the adjustment process can be automatically repeated. If all blades of the cutter head  1  are moved to the same axial height, they are tightened with the pressing screws  8  and  9 . Then, with the device  20  as claimed in the invention the radial position of the profile cutting edges  13  can be automatically measured using the feeler  38 . If in doing so it is ascertained by the evaluation device  40  that the individual single blades exceed the tolerance, they are indicated to the tool setter on the monitor  41 . For small deviations one can create equalization by specifically changing the tightening moment of the pertinent screws  8  and  9 . Using the feeler  38 , the radially altered cutting edge position is directly monitored. If this measure should not be sufficient, after the screws  8  and  9  are loosened once more, automatic pushing of the pertinent blades  10  again can be started. To do this, the control  25  computes an axial correction value from the amount by which the tolerance is radially and by exceeded and by using the corresponding angle of the profile cutting edge  13  and then, with consideration of the respectively stored value MZ 2 , resets this blade in the same way as was done for equalization of the load-induced deformations.  
         [0032]    This section of the cutter head shown in FIG. 5 is placed through the tool body  2  such that two roughly opposite chambers are visibly open. Inside there is the respective blade  10  which is held by a narrow leaf spring  45  until all blades are aligned by the arm  26  in order to clamp each individual blade  10  past the narrow leaf springs  45  with the screws  8  and  9 . Then, the disk  46  to which preferably all leaf springs  45  are attached and from which they project into the chambers  7  can be removed.  
         [0033]    [0033]FIG. 6 shows a section of the cutter head  1  similar to FIG. 5. In this case each individual blade  10  is movably held in its chamber  7  not by a narrow leaf spring, but by a coiled compression spring  47 . For this purpose the extension  48  of the pressing screw  8  which presses against the blade  10  when clamping has been somewhat lengthened. Thus the compression spring  47  can be pushed coaxially over the extension  48  and attached there. The other end of the compression spring  47  projects at first somewhat beyond the extension  48  so that when the pressing screw  8  is screwed in, then the spring  47  is compressed and produces the desired retaining force on the blade  10  (shown in FIG. 6, left). In this case, it is irrelevant what radial position the blade  10  is to take in the cutter head  1 , whether with or without a spacer plate  49 . Only when the blade  10  is aligned with the device  20 , the pressing screw  8  is tightened further until its extension  48  clamps the blade in its chamber  7  (shown in FIG. 6, right).