Abstract
The invention relates to a method for shaping a periodic structure, in particular a toothing on a workpiece, wherein a lifting mechanism lifts the shaping tool, within the working stroke, off of the workpiece for the return stroke after a machining operation, characterized by a rotational angular region of the lifting cam functionally assigned to a circumferential cam profile region of a lifting cam, the same driven to rotate by a motor, of the lifting mechanism, which circumferential cam profile region determines the engagement distance between the shaping tool and the workpiece in a working stroke portion of a stroke cycle, wherein the rotational angular region of the lifting cam is passed through a further timealbeit in the opposite direction of rotationduring the same stroke cycle.
Claims
1. A method for shaping a periodic structure in which a lifting mechanism (10, 20, 99) lifts the shaping tool (40), within the working stroke (Mxc1), off of the workpiece for the return stroke (Mxv1) after a machining operation, characterized by a rotational angular region ([?2B;?2C]) of the lifting cam functionally assigned to a circumferential cam profile region (DcF; 2) of a lifting cam (10), the same driven to rotate by a motor, of the lifting mechanism, determining the engagement distance between the shaping tool and the workpiece in a working stroke portion of a stroke cycle, wherein the rotational angular region of the lifting cam is passed through a further timealbeit in the opposite direction of rotationduring the same stroke cycle.
2. The method according to claim 1, wherein the rotational angular region in the working stroke portion is used at least in regions as an azimuthal acceleration path.
3. The method according to claim 1 or 2, comprising a movement reversal point (D) in the return stroke and/or a movement reversal point (B) in the working stroke.
4. The method according to claim 1 wherein the azimuthal position of a movement reversal point on the rear stroke side on the lifting cam can be variably adjusted, and in a later stroke cycle of the machining of a workpiece, is adjusted to a position causing a lower degree of lifting.
5. The method according to claim 1 wherein the azimuthal position of the movement reversal point on the return stroke side is phase-shifted relative to the axial center of the return stroke by at least ?/18 in the direction of the return stroke end.
6. The method according to claim 1 wherein a circumferential cam profile region of the lifting cam assigned to the return stroke and determining the lifting movement, together with the cam profile region assigned to the working stroke, has an azimuthal overall extension of less than 360? and as such, does not cover a third azimuthal region.
7. The method according to claim 6, wherein the third azimuthal region is also profiled in some regions for a lifting process, but with a different profiling and for a lifting process of another workpiece type, another workpiece, or an earlier or later stroke cycle of the same workpiece, and/or for a working stroke with a flank modification of the shaped periodic structure that is modified at least in part via this profiling.
8. The method according to claim 1 wherein the angular region of the lifting cam passed through in a stroke cycle is a periodic function that, as a function of time, correlates with the frequency of the stroke cycle.
9. The method according to claim 8, wherein the time derivative of the periodic function is sinusoidal or is a modulated sinusoidal wave.
10. The method according to claim 1 wherein the quotient of the maximum amplitude of the angular velocity and the cycle time, measuring in rpm/s, is less than 24.
11. The method according to claim 1 wherein the stroke rate, in strokes/min, is greater than 50.
12. The method according to claim 1 wherein the periodic function of the angle of the lifting cam as a function of time includes four changes in the direction of curvature in a period.
13. The method according to claim 1 wherein a shaping head is mounted pivotably about an axis, and the lifting movement is effected by pivoting the shaping head.
14. The method according to claim 13 wherein the lifting mechanism has a preloaded pressure roller arranged between the lifting cam and the shaping head.
15. A control program comprising control instructions that, when executed in a control device (99) of a shaping machine, causes the machine to carry out a method according to claim 1.
16. A rotary lifting cam (10) of a lifting mechanism of a shaping machine, having a first circumferential cam profile region (1, 2) for adjusting the relative distance between the shaper cutter and the shaped workpiece in a first operating mode, and a second circumferential cam profile region (2, 3; 1, 6) for adjusting such a relative position in a second operating mode with a different path of the relative movement compared to the first operating mode.
17. The rotary lifting cam according to claim 16, comprising at least one cam profile region (5) which is modified for generating a flank profile line modification and has a non-constant radius.
18. A shaping machine comprising a controller which has a control program according to claim 15.
19. The method of claim 1 wherein said periodic structure comprises a toothing on a workpiece.
20. The method of claim 9 wherein the periodic function is sinusoidal or is a modulated sinusoidal wave.
Description
[0029] FIG. 1 is an explanatory illustration of cam movement curves,
[0030] FIG. 2 is an explanatory illustration of the cam angle as a function of time,
[0031] FIG. 3 is an explanatory illustration of two lifting movements,
[0032] FIG. 4 is a schematic illustration of a shaping head with cams,
[0033] FIG. 5 is a schematic illustration of a cam with different cam segments,
[0034] FIG. 6 is an explanatory illustration of a lifting movement for the cam region VI of FIG. 5,
[0035] FIG. 7 is an explanatory illustration of a lifting movement for the region VII of FIG. 5,
[0036] FIG. 8 is an explanatory illustration of a lifting movement for the region VIII of FIG. 5, and
[0037] FIG. 9 is an explanatory illustration of a lifting movement for the region IX of FIG. 5.
[0038] FIG. 4 schematically shows a shaping head 100 which carries a shaper cutter 40 in order to carry out a toothing shaping machining process for generating a toothing 55 on a workpiece 50. For this purpose, the shaping head executes a stroke movement along the stroke axis shown by the double arrow provided with the reference numeral Z. This is achieved in a known manner by means of a crank drive (not shown), which has a shaping spindle axis (A axis) which is a continuously rotating rotational axis. An illustration of the stroke movement is shown by way of example in FIG. 12 as an a-Z diagram.
[0039] Also not shown in FIG. 4 is a suspension of the shaping head, which enables a lifting movementillustrated by the double arrow with the reference sign xnto prevent return stroke collisions. The degree of lift is based on the diameter (and/or radius) of the profiled cam 10, which in FIG. 4 is in contact with a preloaded pressure roller 20 in the 3 o'clock angular positionwherein only one region of the cam is shown in FIG. 4. The structure of the shaping head could thus be designed as in FIG. 3 of DE 10 2019 004 429, which is incorporated here by reference with regard to this basic design.
[0040] In FIG. 4, the direction of rotation of the continuous rotation of the cam used in the prior art reference here, which controls the lifting movement synchronously with the stroke movement, is drawn as a dotted arrow 11. The cam rotation, as well as the other machine axes, are controlled with numerical control; a controller for this is indicated in FIG. 4 with the reference sign 99.
[0041] In contrast, the cam rotary movement used in the method according to the invention is represented by a rotation double arrow 12. The cam rotation thus does not take place continuously with the same direction of rotation, but rather the direction of rotation during a (double) stroke is changed, and an angular region in a (double) stroke is passed through more than oncein the present exemplary embodiment, exactly twicespecifically with different directions of rotation of the rotary cam for each passage.
[0042] In a representation over time, such as that of FIG. 2, which extends over somewhat more than three full double strokes, this is readily apparent from the example with the bold solid curve Mt1, compared to the thin dashed curve Mt0 of the prior art. The sawtooth-like depiction of the curve Mt0 from the prior art is due to the fact that, after a full rotation of the cam 10, the angle is specified again starting at the zero crossing corresponding to the 360? position. For the curve Mt1 of a first operation, in contrast, only one angular region of approximately 100? is passed over, for the example shownas a periodic function of time with a period duration corresponding to the period of the double stroke, and in this exemplary embodiment in the form of a sinusoidal curve.
[0043] FIG. 1 shows the movement corresponding to curve Mt1 from FIG. 2 in an illustration in which the cam radius is plotted as a function of the cam angle ?2. The dotted curve D?2 represents the profile of the cam in the rotational angular region in question. It has a region of constant radius Dc, and a region Dv in which the radius decreases as a function of the cam angle ?2. For illustration purposes and identification of the different directions of rotation, the curve M?21 is depicted in FIG. 2 above the cam curve D?2, corresponding to the movement Mt1 for the one direction of rotation below, and the other direction of rotation above. In reality, of course, the curve M?21 lies on the cam curve D?2. The effects of the paths Mt1 and M?21 from FIGS. 2 and 1 on the lifting movement can best be seen in the illustration of FIG. 3, and specifically the momentary situations A, B, C and D also shown in FIGS. 1 and 2.
[0044] Momentary situation A describes the beginning of the movement as a working strokewithout a lifting movementwhich ends at C. During the working stroke, the radial distance of the shaper cutter 40 from the workpiece 50 should be constant during the working operation (assuming that a width crowning, or conical or other flank profile line modification is not desired). Accordingly, the curve M?21 from FIG. 2 is passed through in the region Dc of the constant cam radius, specifically from the transition of the varying radius region Dv to the constant radius region Dc via momentary situation B, in which the rotational speed of the cam is reduced to zero after deceleration, and then rises again in the reverse direction of rotation. In the working stroke (without modifications), the position at a given point on the curve M?21 plays a subordinate role. The specification of the angular velocity ?2 (=d?2/dt) is therefore entirely variable, and the reversal point B, where ?2=0, in the region Dc does not have to lie in the center of the stroke as shown in FIG. 3. Rather, it can, in accordance with a phase shift with respect to FIG. 2, lie at a different position than the central position in the axial stroke direction Z.
[0045] The angular region [?2B; ?2C] in FIG. 1 between the momentary situations B and C can be used as an acceleration path, such that the beginning lifting movement starting from momentary situation C takes place when the angular velocity of the cam can already have a comparatively high value, in particular close to its maximum value. However, it should also be understood here that, by means of the numerical control of the axis ?2, the maximum speed of the cam can also be shifted with respect to the lifting movement in FIG. 3. For example, the angular velocity ?2 would not need to begin to decrease starting at the moment of the beginning of the lifting movement. Rather, it could also rise briefly, in order to then decrease, and to rise again starting at momentary situation D, the other reversal point with respect to the direction of rotation of the angular velocity. In FIG. 3, the reversal point D, which according to FIG. 1 corresponds to the maximum lifting movement for the selected cam profile D?2, is also drawn in the center of the axial movement z; however, this could equally well be displaced in the direction of, for example, the end of the return stroke movement Mxv1. With the cam rotation from the reversal point D to the transition of the region Dv into Dc, in momentary situation A in FIG. 1, the lifting movement ends, and the starting point for the example is again reached.
[0046] In FIG. 3, a further lifting movement Mx2 is also shown, which in the working stroke (Mxc2) coincides with the movement Mxc1 of the lifting movement Mx1 (with return stroke Mxv1) just discussed; however, in the return stroke, as can be seen by the dashed movement path, is lifted with a comparatively greater degree of lift. This is achieved by rotating the cam (cam angle ?2) beyond the region of the reversal point D of the previously described movement M?21 in FIG. 1, by means of the numerical controller 99, and thus passing through a greater angular region in the region Dv, with variable cam radius in the one direction and then in the other direction of rotation, between momentary situations C and A (via D). Accordingly, as can be seen from FIG. 2, setting a greater amplitude for the curve Mt2 with respect to curve Mt1 allows for a greater lifting movement. In the M?22 path in FIG. 1, a greater angular region is also passed through in the region Dc of the constant cam radius. However, it should again be understood here that the positioning of the reversal point B along the region Dc has no influence on the radial distance between the shaper cutter 40 and the workpiece 50, and can thus also be changed in principle (corresponding to a displacement along with stretching/compression of the curves from FIG. 2 in the direction of the vertical axis).
[0047] Accordingly, different lift paths can be realized with the same cam, i.e., without cam changes, and the lifting movement can also be realized after passing through an angular acceleration section.
[0048] The full peripheral region of the lifting cam is also not required to carry out the lifting movement; the angular region shown in FIGS. 1 and 2 for explanatory purposes, of approximately 100? for the curves/paths Mt1/M?21 and approximately 200? for Mt2/M?22, can certainly be reduced further. In a further aspect of the invention, lifting cams can thus also be realized which have different profiling regions for carrying out different lifting movements and/or modulations of the working stroke (beyond the above-explained amplitude adjustment).
[0049] This is explained below with reference to FIG. 5, which shows the profiling of a cam in different segments 1 to 6 in a very greatly exaggerated representation. In an illustration which uses times on a clock as angular positions, the drawing shows a first segment 1 between the 0 o'clock position and 2 o'clock position, a second segment 2 between the 2 o'clock position and 4 o'clock position, a third segment 3 between the 4 o'clock position and 6 o'clock position, a fourth segment 4 between the 6 o'clock position and 8 o'clock position, a fifth segment 5 between the 8 o'clock position and 10 o'clock position and a sixth segment 6 between the 10 o'clock position and 12 (0) o'clock position.
[0050] The segment 2 has a constant radius and corresponds to the region Dc of FIG. 1. Segment 1 has a radius decreasing in the counterclockwise direction, and corresponds to the region Dv from FIG. 1. The two segments 1 and 2, combined in FIG. 5 as region VI, can be used for shaping external toothings as shown in FIG. 6. A lifting movement of the type of lifting movement Mx1 or Mx2 according to FIG. 3 results, wherein, in turn, by means of numerical control (e.g., amplitude adjustment according to FIG. 2), different degrees of lifting can be set. As explained above with reference to FIG. 3, these can additionally be set continuously via the positioning of the reversal point D.
[0051] However, the segment 2 can also be used for shaping internal toothings with which the lifting movement in the radial direction must occur in the opposite direction with respect to the direction in which an external toothing is shaped. For this purpose, segment 3 is provided, which connects to segment 2 on the other side from segment 1, and has a region of a cam radius that rises in the clockwise direction. The region of segment 2 and segment 3, denoted by VII in FIG. 5, can thus be used for shaping internal toothings. the corresponding lifting movement is shown in FIG. 7. Here as well, the variations of the lifting movement explained with reference to FIGS. 1 to 3 can be adjusted in particular with regard to the degree of lift, since, in addition to the angular region of the cam traversed twice (with different directions of rotations), determined by means of a numerical-control adjustment of the angular velocity, there are further degrees of freedom for the speed at which these paths are traversed (variation in the shape of the curve Mt1 in FIG. 2).
[0052] The remaining angular region of the cam with the segments 4, 5 and 6 can be used for this purpose, as shown in FIG. 5, to realize topological modifications of the toothing geometry of the workpiece 50. This is initially explained using the example of a flank profile line crowning or width crowning. Segment 6 produces a cam profile that is mirror-symmetric to segment 1i.e., a region with a cam radius increasing in the counterclockwise direction. This adjoins segment 5, which, however, does not have a constant radius. It is designed in such a way that initially the radius, coming from segment 6, is initially reduced during further rotation, and then increases again approximately starting at the halfway point of the angular region assigned to segment 5. Here as well, the representation of the deviation of constant diameter (symbolized by the double dashed line) is shown highly exaggerated for explanatory purposes. Segments 5 and 6, indicated together by IX in FIG. 5, are used together for the shaping of an external toothing with a toothing modification with width crowning. The lifting movement associated with this is shown in FIG. 9. In comparison to FIG. 6, the comparatively small convex lifting movement can also be seen in the working stroke.
[0053] Finally, segment 4, which is designed to be mirror-inverted to segment 3, can be used together with segment 5, as shown in FIG. 5 by VIII, for rolling an internal toothing with width crowning. The associated lifting movement is shown in FIG. 8.
[0054] For this exemplary embodiment of a crowning, the degree of lift of the lifting movement in the return stroke can continue to be set via the angular region passed through in the segments 4 (FIG. 8), 6 (FIG. 9), 3 (FIG. 7) and 1 (FIG. 6).
[0055] The different lifting movements with different degrees of lift shown by means of FIGS. 1 to 3 can be used not only for shaping toothings of different workpieces, but also for a shaping toothings of one and the same workpiece, by using, for example, the lifting path in the return stroke Mxv2 from FIG. 3 for the return strokes for rough-machining strokes, wherein a smaller lifting movement can be set in the return stroke after the one or more finish-machining passes for one or more finish-machining strokes, by shifting the reversal point and/or the momentary situation D in the direction of the region Dc of constant cam radius. It is understood that, alternatively or in addition to a crowning, other flank profile line modifications, not explicitly illustrated, such as conicities or end taperings, can be realized by modifying a circumferential region of the rotary cam.
[0056] As can be seen from the above detailed description of the invention, flexibility in the shaping process is further increased, and downtime, which would otherwise be incurred by removing and installing another cam, can also be reduced.
[0057] Moreover, the invention is not limited to the details illustrated in the preceding description. Rather, the individual features of the above description, and in the following claims, may be essential, individually and in combination, for implementing the invention in its different embodiments.
