Machine Tool Axis Compensation for Repetitive Contour Errors
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Solution Overview
Problem
Machining methods for machine tools often result in deviations between the desired and actual contours of workpieces, which can be disturbing despite small control errors, especially when these errors are periodic or repetitive.
Innovation Solution
A method involving a control device with a position controller and a model that simulates the mechanical dynamic behavior of a position-controlled axis, using compensation values and actuating signals to adjust the tool's position or orientation, and incorporating a frequency filter and data buffers to manage and filter control errors, allowing for improved error compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a model simulating mechanical dynamic behavior is used to determine compensation values, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The control device pre-determines compensation values by simulating mechanical dynamic behavior before actual machining operations. The model predicts control errors based on stored control data from previous operations, allowing compensation to be prepared in advance rather than reacting to errors in real-time, thus improving precision without proportionally increasing complexity
Solution Approach 2:
The system creates a virtual copy or model of the mechanical dynamic behavior of the machine tool axis. This software-based model replicates the physical system's characteristics, allowing the control device to simulate and predict errors without requiring additional physical sensors or actuators, thereby improving precision while limiting complexity growth
2Manufacturing precision
If control errors are stored and processed sequentially from a storage device, then manufacturing precision is improved, but loss of time increases
Solution Approach 1:
Control errors and their corresponding compensation values are determined and stored in advance during idle periods or between machining operations. The model processes historical control data to build a library of compensation values that can be quickly retrieved during actual machining, trading off initial processing time for faster real-time operation
Solution Approach 2:
The system replaces real-time complex dynamic calculations with pre-computed compensation values stored in memory. Instead of performing time-consuming simulations during each machining operation, the control device simply retrieves and applies stored compensation data, significantly reducing processing time while maintaining precision
3Manufacturing precision
If a frequency filter and data buffers are used to manage control errors, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
A frequency filter is introduced as an intermediary component between the storage device and the model. This filter selectively processes control error signals to remove periodic disturbances at specific frequencies, allowing the model to work with cleaner data and improve compensation accuracy for periodic errors without requiring fundamental changes to the core system architecture
Solution Approach 2:
Data buffers create temporary copies of control error data at different stages of processing. These buffer copies allow the frequency filter to analyze and process historical error patterns without disrupting the real-time control flow, enabling sophisticated error management while maintaining a relatively simple overall system structure
Data Source
AI summary
A control device of a machine tool includes a position controller and a model of a position-controlled axis. The position controller receives a position setpoint value, a corresponding actual position value and a compensation value; determines therefrom a resulting value; determines based on the resulting value an actuating signal; and outputs the actuating signal to the position-controlled axis. The position and/or the orientation of the tool relative to the workpiece are adjusted based on the actuating signal. A sequence of successive control errors is stored, in a storage device and read out sequentially in accordance with a sequence of the position setpoint values and supplied to the model. The model determines from the read-out control error a respective compensation value which is then supplied to the position controller, while simulating the mechanically dynamic behavior of the position-controlled axis.