SOFTWARE MODULE, PRECISION MACHINE, METHOD AND COMPONENT

Abstract

In a method for calculating reference variables for interpolating moving single axes of a precision machine based on a given 3D tool path firstly for all points of the tool path offline assuming a freely selected path velocity or single-axis velocity, the velocity, acceleration and jerk profiles of all the interpolating axes are calculated cohesively and without specifying limiting values and then velocity, acceleration or jerk profiles are varied on regions on the 3D tool path.

Claims

1. A method for calculating reference variables for interpolating moving single axes of a precision machine based on a given 3D tool path characterized in that wherein firstly for all points of the tool path offline assuming a freely selected path velocity or single-axis velocity, the velocity, acceleration and jerk profiles of all the interpolating axes are calculated cohesively and without specifying limiting values and then velocity, acceleration or jerk profiles are varied on regions on the 3D tool path.

2. The method according to claim 1, wherein the velocity of the projection of the tool on one plane is used as path velocity.

3. The method according to claim 1, wherein the calculation is carried out for a segment of a 3D tool path and is composed of segment calculations.

4. The method according to claim 1, wherein as interface output of the calculation rule for the control of the precision machine, position target values are output as a reference variable for each interpolating moving single axis of the precision machine with equitemporal distances in a continuous individual file or a plurality of individual files.

5. The method according to claim 1, wherein by an analytical and/or numerical calculation, a number of the position target values per single axis greater than 3,000 points/s, preferably greater than 5,000 points/s or even greater than 10,000 points/s, are output in polynomial-based calculation.

6. The method according to claim 1, wherein the motion profiles are stored in files as a buffer before the control of the individual axes, which are streamed with data rates greater than 3,000 points/s, advantageously greater than 5,000 points/s or even greater 10,000 points/s, directly to a servo to drive a single axis with decentralized integrated position control.

7. The method according to claim 1, wherein the motion profiles are stored in files as a buffer before the control of the individual axes, which are streamed with data rates greater than 3,000 points/s, advantageously greater than 5,000 points/s or even greater 10,000 points/s, directly to a position controller which runs centrally on a computer of precision machine.

8. The method according to claim 6, wherein during the streaming of the pre-calculated values, the path velocity of the tool is influenced by a limiting actuator (override).

9. The method according to claim 6, wherein the files are called from a conventional CNC program of the precision machine as a subroutine, started and terminated.

10. The method according to claim 1, wherein as interface output, in addition to the position target values of the individual axes, velocity, acceleration or jerk values with equitemporal intervals are output as additional reference variables for the single-axis control.

11. The method according to claim 1, wherein the calculation of the reference variables for the interpolating individual axes is carried out such that the velocity of a main spindle in the axis group is continuously increased to a defined maximum value to ensure a constant longest possible cutting velocity in the turning process.

12. The method according to claim 1, wherein a starting velocity for all individual axes along a complete 3D path or a subsystem of the individual axes in a partial projection of the 3D path is specified and before driving the individual axes, the other reference variables of the individual axes are fully calculated with temporal reference such as speed, acceleration and/or jerk.

13. The method according to claim 12, wherein after the calculation of the reference variables based on the starting velocity, the reference variables velocity, acceleration and jerk are maximized taking into account predetermined dynamic limit values locally along the entire 3D path.

14. The method according to claim 13, wherein after local maximization of the reference variables velocity, acceleration and jerk, the respective reference variable profiles, in particular acceleration and jerk, are smoothed over individual sub-segments of the path in order to achieve an increase in precision on these sub-segments in particular with respect to dimensional stability or surface roughness.

15. The method according to claim 1, wherein before controlling the individual axes, a complete reference variable data set is calculated and optimized analytically precisely for the entire 3D space curve or subsections of the curve.

16. The method according to claim 5, wherein for the creation of the reference variable data set, iterative, numerical calculations or analytically precise calculations for the interpolation are performed in parallel on several kernels and then assembled in a synchronized manner in order to achieve an acceleration of the production compared to single-kernel calculations.

17. An ultraprecision or precision machine with a control or drive servo-side interface, in order according to claim 1 to read in advance for machining calculated files with equitemporal reference variables for interpolating single axes of the precision machine and to stream to the position and/or velocity controller of the respective individual axes.

18. A component manufactured by a precision machine or the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

[0036] In the drawings,

[0037] FIG. 1 schematically shows a surface which can be described by point clouds or can be approximated as closed surfaces by geometric elements.

[0038] FIG. 2 shows a milling tool guided over a material blank with a respective infeed between the individual grid steps via a meandering grid in order to generate a surface on the component.

[0039] FIG. 3 shows the distance between interpolation points for describing the path.

[0040] FIG. 4 shows a linear interpolation.

[0041] FIG. 5 shows a polynomial interpolation.

[0042] FIG. 6 shows a movement profile using the example of x, y, and z axes.

[0043] FIG. 7 shows determination of spatially and temporally synchronized movements of the individual axes taking into account the real performance of the machine tool.

[0044] FIG. 8 shows the programmed set path for eight blocks.

[0045] FIG. 9 shows a velocity profile for the geometric path of FIG. 8 with a look-ahead function.

[0046] FIG. 10 shows a velocity profile for the geometric path of FIG. 8 without a look-ahead function.

[0047] FIG. 11 shows the reference variables for a simple movement of an axis between two points calculated via the polynomial-based offline approach according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0048] In the prior art DE10343809A1 describes the online readout of a table for determining set position values for n subsequent axes as a function of a reference value of a control axis. Alternatively to the set position values of the subsequent axes, functions can be called up. However, it is not described how the creation of the set position values comes about. This therefore obviously does not involve an offline calculation rule for the analytic and/or numeric synchronization of axes taking into account velocity, acceleration, and jerk profiles in order to fabricate particularly good surfaces under economic conditions, as described in the present application. The new method is explicitly aimed at avoiding such so-called look-up tables.

[0049] The descriptions from DE10343809A1 are known, inter alia, for the prior art for fast tool systems in diamond turning and can be found in the paper published in 1985 Design and testing of a fast tool servo for diamond turning by S. R. Patterson and E. B. Magrad. Here, in addition to the readout of a set value table as a function of a control value, interpolation routines are also described which must be performed for such velocity-related non-synchronized values. The person skilled in the art talks in this case of a master-slave control architecture. Further extensive descriptions have been published under Manfred. Weck, RWTH Aachen as part of the Forschungsgesellschaft Ul-traprzisionstechnik.

[0050] The aim of DE10 2008 018 962 B2 is the improved synchronization of several robots in cooperation with additional equipment. In addition to pure movement sequences, further robot-relevant functions can be synchronized by means of the described approach. FIG. 2 illustrates that the interpolation, that is the generation or calculation of reference variables with velocity, acceleration and jerk reference are calculated online in the course of the conventional robot control.

[0051] This previously known patent describes a modification of this control architecture insofar as via a so-called movement driver, the interpolation routines can be predefined by externally pure set position values which have a higher geometrical quality and which have been created in advance for the movement sequences of here a press and a second robot. The values are Cartesian/axis-specific positions in a fixed cycle. As a result of the inadequate basic accuracy of CAD data or the inadequate accuracy in the interpretation and processing of CAD data by conventional robot software, the approach is appropriate for applications to robots.

[0052] The main idea of the method now claimed is the offline interpolation to increase the viable support point densities and optimize velocity, acceleration and jerk profiles for an improved surface quality in metal cutting machines.

[0053] The textbook WECK, Manfred, BRECHER, Christian Machine toolsFabrication system Vol. 4 describes in detail the prior art with conventional axis interpolation inside the CNC. The introductory description of the velocity profiles provides a complete stop with renewed acceleration at setpoints. For the continuous movement along a path with the most uniform possible velocity guidance, forward-looking path guidance (look-ahead) is described which acts in the interpolation cycle and during the machining online. Using the look-ahead, taking into account static specifications of respectively maximum position (startup movement) and maximum negative (braking process) axial velocities, axial accelerations and axial jerks, the reference variable profiles of the individual axes are calculated iteratively in an optimizing manner. A typical look-ahead comprises the simultaneous optimization over about 200 points. In addition to path panning, the textbook describes the importance of look-ahead for safety-relevant aspects in the sense of a possible emergency braking when limiting situations arise.

[0054] The procedure described in the filed patent for analytic and/or numeric calculation of reference variables without static specification in advance for the actual machining (offline) is in no way mentioned.

[0055] The procedure now described is not an optimization step during the CAD/CAM routine, but rather the actual functionality of the CNC. The calculated data are preferably no longer pushed through another CNC kernel, but flow directly to the position controller of the single axis.

[0056] Using the look-ahead in a conventional CNC control, a velocity planning for the guidance of the tool is carried out in such a way a following of the path is realized as quickly as possible, taking into account the specified target speed, without violating the contour (geometry).

[0057] Acceleration and jerk are calculated as a result of the velocity planning. If there are overshoots of predefined limit values during acceleration or jerk, the velocity is reduced at the respective points until the permissible limit values are fallen below.

[0058] As a result, the limit values of velocity, acceleration or jerk are never exceeded across the entire path. However, it may be that the course of the acceleration and the jerk is very uneven or noisy. This leads to dynamic unwanted excitations in the machine, which lead to a deterioration of the surface quality.

[0059] FIGS. 7 and 11 show the reference variables for a simple movement of an axis between two points. FIG. 7 was conventionally calculated via a CNC linear block and FIG. 11 via the polynomial-based offline approach according to the invention. In particular, the differences in acceleration and jerk are noticeable in this case.

[0060] This makes it possible, if necessary (there may be many reasons for a higher frequency excitation, e.g., surface structure, limit movement cases of the axes, chipping of special materials) for velocity, acceleration and jerk to optionally introduce new smoothing functions that not only locally control and reduce a limit value (and thereby lead to high-frequency excitation), but achieve a continuous smoothing and thus a calming of the tool guide over a sub-segment of the path. Such a smoothing function results in influencing or reducing the velocity in the respective area.

[0061] In practice, the method can be described in three steps:

[0062] 1. Calculating all reference variables with temporal reference (velocity, acceleration, jerk) for the individual axes on the basis of a starting velocity.

[0063] 2. Adjusting these calculated reference variables locally along the entire 3D path such that predefined maximum values for velocity, acceleration, jerk are not exceeded. 3. Smoothing the adjusted reference variable profiles for velocity, acceleration, and jerk along parts according to a given requirement, such as short machining time (smooth, maximized velocity), or good surface roughness (smoothing the acceleration profile of the axes for smooth behavior). In this case, the smoothing of any desired reference variable profile (e.g., acceleration) always has an influence on all other profiles (e.g., jerk, velocity).

[0064] This makes it possible to increase the machining velocity significantly and to increase the quality of the machining by an increased number of interpolation points per second. This is needed for precision machines and especially for high-precision machine tools to be able to produce, for example, structures for head-up displays significantly faster.

[0065] A novel feature with respect to the prior art is the possibility of making a continuous adjustment of the spindle velocity up to a maximum value with the method without there being any influence on surface quality.