Page 17 - StanochnyPark

METALWORKING EQUIPMENT METALWORKING EQUIPMENT
AND TOOLS AND TOOLS
Heidenhain sensors installed on the machine: the ERA4282 sensor with an error of ≈1"on the
mill, the RCN729 sensor with an error of ≈1" on the table. angle angle angle
Figure 3 shows a typical graph of the kinematic error of the machine at z = 24 and n = miller revolution
50 min-1, on which it is possible to distinguish the accumulated error of the relative rotation
(mismatch angle) of the tool spindles and the workpiece φк.н., as well as high-frequency peaks
of errors - cyclic errors φк.ц, the frequency of which is equal to the number of teeth.
Figures 4, a and b show the dependence of the accumulated and cyclic errors on the
number of teeth for machines of different classes.

Figure 5 shows graphs of cyclic errors miller revolution miller revolution
depending on the number of teeth, which are
angle
obtained with the settings of the drives of the
24 peaks cutter and the work piece, providing good
dynamic characteristics. Their analysis showed
the following: b) c)
● when the frequency and direction of rotation Fig. 5. Change in cyclic errors from the angle φ of table rotation at z = 6 (a), 24 (b), 96 (c).
of the spindles are changed, the kinematic error
practically does not change. The accumulated
error does not depend on the number of teeth The table shows the results of measurements of the indicators of the kinematic error.
and does not exceed 20"; INFLUENCE OF DRIVE DYNAMIC CHARACTERISTICS ON ACCURACY
● cyclic error is caused by oscillations with The peculiarity of the occurrence of the kinematic error in the machine tools of new
several frequencies: the minimum oscillation generation lies in the influence of the dynamic characteristics of drives, which depend on the
frequency in all three cases is equal to the parameters of the electromechanical (mechatronic) system, i.e. on the inertial and elastic
revolution of work pieces number of teeth of the wheel (cog frequency); dissipative properties of the mechanical part of the drive, as well as on the adjustment coefficients

Fig. 3. Graph of the kinematic error of the machine for one high-frequency components φк.ц are of the speed and position contours [5, 6].
revolution of work pieces at Z = 24, n = 50 min-1 superimposed on the cog errors in the same The tool rotation is driven by a motor spindle [2] and is not amenable to optimization.
The table rotation drive, in addition to the rotation spindle, includes work pieces and accessories
for its installation (pedestals), therefore, a special approach is required when designing it - one
class
class should take into account the parameters of the table spindle, rigidity of the tooling and inertial
characteristics of the tooling and work piece. The choice of the parameters of the mechanical
class class system should provide the highest, for a given design, drive bandwidth and be carried out, for
angle angle example, similar to feed drives [5, 6].
class class In experiments on a prototype machine tool, only the drive settings were changed, without
optimization of the parameters of the mechanical part of the drive.
experiment experiment
Figure 6 shows the logarithmic amplitude-phase frequency characteristics (LAFC) of the cutter
and the table when the gains of the speed loop are changed by about 10 times. Here graph 1
corresponds to a "good" setting of the cutter and table drives, and graphs 2 and 3 - to a "bad"
b) setting of the table and cutter, respectively.
Figure 7 shows the graphs of the kinematic error of the corresponding LAFC shown in Fig.
Fig. 4. Graphs of accumulated φк.н. (a) and cyclic φк.ц. (b) errors depending on the number Z of teeth for machines of
classes P, B and A (- - -) and an experimental graph (──). 6, when set to Z = 60. Analysis of settings 1 and 3 (see Fig. 7, a, b) showed that the dynamic
characteristics of the cutter drive have
way as the periodic cyclic error φк.ц superimposed on the accumulated φк.н. (see Fig. 1) The little effect on the kinematic accuracy Hz
magnitude of the cyclic error decreases with an increase in the number of teeth and at 15 ≤ Z of the machine: the accumulated Hz
≤ 100 does not exceed 5". The largest amplitude of the cyclic error has the tooth frequency, errors amounted to 18.7" and 18,
which is especially high with a small number of teeth (φк.ц. = 20" at z = 6). respectively, 1", and the cyclic error is
Thus, a machine made with an accuracy of class P, in terms of kinematic accuracy, 3.5". Analysis of options 1 and 2 in Fig. Amplitude dB
corresponds to a machine of accuracy class A. 7, c, corresponding to the LAFC in Fig.
Table 1. 6, b, showed that the main influence on
Errors of the machine with a different number Z of the teeth of the machined gear. the cyclic error is exerted by the table
drive setting: the accumulated errors Hz
indicator Z amounted to 18.7" and 18.5", and Hz

6 24 96 periodic errors - 3.5" and 350"! That is,
the periodic error increased by about
φк.н., angle 19,1 18,7 19,7 100 times. Amplitude dB
φк.ц., angle 25 4,2 3,3
The number of oscillations per work piece revolution at n = 50 min 6 24 96
-1 (double amplitude of oscillations, angle) (20) (5) (2,5) b
Fig. 6. LAFC of the cutter (a) and table (b) drives.

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