Servo Motor Control System for Helical Machining Precision
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Solution Overview
Problem
Existing servo motor control systems face challenges in maintaining precision during helical machining operations, especially when dealing with holes of varying diameters or complex shapes like free closed curves, due to issues with angle synchronization and backlash, leading to decreased productivity and precision.
Innovation Solution
A control system that uses a host control device to generate position command values, position detectors to compute position errors, and a reference angle generating part to calculate a monotonously increasing or decreasing reference angle, enabling angle synchronization type learning control by defining any point inside a closed figure as the center, allowing for precise control even when processing shapes like closed curves or polygons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If helical machining operation is used to bore holes of different diameters with a single end mill, then productivity is improved, but machining precision deteriorates due to delayed response and lost motion of servo motors
Solution Approach 1:
The learning control mechanism performs preliminary learning during the first pass of helical machining to predict and compensate for position errors in subsequent passes. The system accumulates position error information during initial machining and uses this learned data to pre-correct servo motor commands, eliminating delayed response and lost motion effects before they impact precision.
Solution Approach 2:
The system implements feedback by continuously monitoring the actual position of servo motors during helical machining and comparing it with the commanded position. The position error information is fed back to the learning control mechanism, which updates the compensation data for future operations, creating a closed-loop system that progressively improves precision while maintaining high speed.
2Manufacturing precision
If angle synchronization type learning control is applied to improve machining precision, then a reference angle signal is required, but no suitable reference angle signal exists for arc motion of two-axis coordinated drive
Solution Approach 1:
The system introduces an intermediary reference angle signal generated through angle synchronization between the two servo motors. Instead of requiring an external reference angle signal that doesn't exist for two-axis arc motion, the patent creates a synthetic reference angle by synchronizing the angular positions of both servo motors, which then serves as the basis for learning control without adding external complexity.
Solution Approach 2:
The patent transforms the two-dimensional coordinated motion problem into an equivalent one-dimensional angular synchronization problem. By projecting the two-axis arc motion onto a synchronized angular reference frame, the system enables learning control to function as if it were controlling a single rotating axis, simplifying the control architecture while maintaining precision.
3Adaptability or versatility
If conventional learning control is used with cumulative addition of command values, then simple circular motion can be controlled, but the system cannot handle cases where the diameter of the arc slowly changes or complex closed curves
Solution Approach 1:
The system dynamically adapts the learning control parameters based on the instantaneous geometry of the machining path. Instead of using fixed cumulative addition suitable only for constant-diameter circles, the patent continuously updates the reference angle calculation to account for changing arc diameters and complex curve geometries, maintaining learning control accuracy across varying conditions.
Solution Approach 2:
The patent changes the fundamental parameter used for learning control from simple cumulative command value addition to a dynamically calculated reference angle that accounts for instantaneous path geometry. This parameter transformation enables the learning control mechanism to accurately track and compensate for position errors regardless of whether the path is a constant-diameter circle, varying-diameter spiral, or complex closed curve.
Data Source
AI summary
A control system of servo motors in a machine tool, comprising a host control device which generates position command values for processing a workpiece, servo control devices which drive servo motors to operate a tool for processing using the position command values, and position detectors which detect positions of the servo motors or a tool position and further a position error computing part computes position error between the position command values and detected positions of the servo motors, a reference angle generating part calculates a reference point on a closed figure and a reference angle which varies monotonously from a current processing point under the condition that any position inside of the closed figure which the position command value forms as the center, and learning control parts use the reference angle and the position error as the basis to perform angle synchronization type learning control to control the servo motors.