Data processing: generic control systems or specific application – Generic control system – apparatus or process – Optimization or adaptive control
Reexamination Certificate
1998-07-23
2001-07-24
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Optimization or adaptive control
C700S170000, C700S193000
Reexamination Certificate
active
06266570
ABSTRACT:
SUMMARY OF THE INVENTION
The present invention relates to the use of conventional elements of a machine tool, a robot or the like for determining and optimizing their operating accuracy.
BACKGROUND INFORMATION
In developing and starting up machine tools or robots, the development or installation engineer often encounters the problem, independently of the control task at hand, of having to properly adjust tightened controller configuration or pilot controls, and of being able to simply recognize their effects. For this, auxiliary measuring systems are usually needed, which, due to the level of accuracy required, entail substantial additional outlay for development and start-up operation. For example, to determine the operating accuracy of a machine tool, a plurality of expensive measuring instruments are used, often costing more than DM 150,000. In addition, such measuring instruments require specially trained personnel.
To perform a synchronous measurement, for example, one needs expensive acceleration sensors, a charge amplifier and spectral analyzers. Thus, for example, inductive displacement probes can be used, but only those having a ruler (i.e., straight-edge rule) of the highest possible surface quality, which entails correspondingly high costs. Besides the costs, when such auxiliary devices are used to determine synchronism, problems arise with respect to axial overlapping. In addition, spindle influences are not easily ascertained.
To determine positioning trueness (i.e. accuracy), inductive displacement probes are usually used. These are very slow, however. When working with optical encoders (i.e. indicators), the problem arises that the location where the position is measured—usually a glass scale—is not easily accessible.
To measure the contour trueness or other contour features, such as corners, using conventional methods, a very time-consuming workpiece measurement is required. For this, in turn, expensive measuring instruments are needed.
To perform a test of circularity, conventional methods require a circular calibration standard having a two-dimensional probe head, which entails costly adjustment with respect to the circle center. In addition to this, a separate circular calibration standard is required for each circle radius. The costs this entails are substantial and, depending on the (i.e. required) accuracy, amount to over DM 100,000.
Similarly, by enlarging a segment (i.e. detail) of the setpoint path and the actual path, the trueness of contour can be determined, it no longer being possible in this case to examine the entire path curve, since enlargement factors within the range of 100 to 1000 are needed.
European Patent Application No. 165 436 describes a method for programming robot movements in a manner the economizes on memory space. To determine and optimize the synchronism, the causes of inaccuracies are determined by performing a spectral analysis on the path deviation values, in particular by performing a Fourier analysis. In this manner, besides a programming that economizes on memory space, the dynamic performance of the robot being used is able to be described by a transfer function, rendering possible a speed-independent compensation of the robot's dynamic performance in the spectral region.
A method for testing the operating accuracy of an NC machine is described in International Patent Application No. 94/07187. The operating accuracy of the NC machine is checked by comparing a circular setpoint path to an actual circular path that describes the machine's actual motion in accordance with a position control signal that describes the setpoint path of motion. However, this is only possible for an at least two-axis NC machine. Also, the method is limited to a circular setpoint path.
A method for determining the operating accuracy of a numerically controlled machine is described in European Patent Application No. 510 204. Positions which occur in response to the corresponding actuating signals for the machine axes in question are periodically detected in the X and Y direction. The setpoint path is contrasted to the active actual path, and it is checked whether deviations lie within the scope of a permitted range or exceed the range.
SUMMARY OF THE INVENTION
An object of the present invention is to provide methods for determining and, moreover, optimizing the operating accuracy of machine tools, robots or other numerically controlled machines, which will not require any additional cost outlay for expensive measuring systems, and which will enable a statement of accuracy to be made to the ultimate consumer, without having to measure the workpieces and, moreover, also render possible an early detection and localization of errors.
The object is achieved according to the present invention by using existing position measuring systems of a machine tool, a robot or the like for determining and optimizing their operating accuracy. Path information on any desired number of axes is sampled (i.e. scanned) over a predefinable measuring interval and stored in a numerical control (i.e. operation) using a position measurement. The thus acquired data is converted and prepared in a way that enables conclusions to be drawn about the actual operating accuracy and about causes of inaccuracies, and compensation parameters that have an effect on the causes are calculated so as to counteract the causes of the inaccuracies, in that the data representing the path information is converted and prepared according to the following additional method steps:
from the data representing the path information, an actively described actual path of the designated axes is determined in accordance with the underlying contour, and compared to the profile of a corresponding setpoint path;
a geometric relation is established between the actual path and the setpoint path, in that a setpoint-value vector is determined, which has the same angle as the active actual-value vector;
a contour deviation at a desired path point is determined as the distance (i.e. spacing) between the actual-value vector and the setpoint-value vector at the path point named;
deviations in contour from the setpoint path are minimized through a corresponding adjustment of compensation parameters, such as static friction compensation, momentum precontrol and/or speed precontrol.
Thus, any desired setpoint path can be advantageously optimized. A contour deviation can be determined, which can be retrieved as a direct measure of the machine's operating accuracy at each desired contour. This enables the path accuracy to be determined, for example, of those types of machine tools for which the so-called test for circularity is not very useful (for example, looping-type lathing, camshaft grinding or in form design), since, in these cases, in terms of the axis, no path resembling a circle is driven, i.e., attention is directed to much more complicated geometric forms. Thus, the operating accuracy of numerically controlled machine tools is able to be checked at every desired contour.
In a first advantageous exemplary embodiment according to the present invention, an active actual path is determined quite effectively from the data representing the path information, in that the data representing the path information are measured as following-error values, and the actively described actual path of the designated axes is determined using these following-error values and the setpoint-path values.
In another advantageous exemplary embodiment according to the present invention, the advantages described above are also achieved when working with such machine tools, robots or the like which have linear axes and at least one rotary axis. The setpoint path values and the actual path values pertaining to the rotary axis and existing as polar coordinates are converted into the Cartesian coordinate system, in that radius information is obtained from the linear axis values, and angular information from the rotary axis values.
In another advantageous exemplary embodiment according to the present invention, a contour deviation i
Höcherl Günther
Moser Roland
Trondle Hans-Peter
Wiegärtner Georg
Grant William
Hartman Jr. Ronald D
Siemens AG
Staas & Halsey , LLP
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