Linear Motor Positioning Control Using Magnetic Sensors
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Solution Overview
Problem
The existing techniques for positioning control in linear motors require the use of linear scales across the entire range of motion, leading to increased manufacturing costs and reduced accuracy due to attachment errors and errors in magnetism detection by MR sensors.
Innovation Solution
A control apparatus for a linear motor that includes a magnet unit with alternately arranged N-poles and S-poles, an armature with coils, and a position detection unit using a magnetic sensor to calculate the mover's position and speed, allowing for improved positioning accuracy without the need for a linear scale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a linear scale is mounted in all range of motion to ensure positioning control, then positioning accuracy is improved, but manufacturing cost increases
Solution Approach 1:
The patent divides the motion range into multiple sections, each with its own magnetic sensor and drive magnet assembly. By segmenting the linear motor into modular units, the system achieves full-range positioning control without requiring a single long linear scale, thereby reducing manufacturing cost while maintaining positioning accuracy across the entire range of motion
Solution Approach 2:
The patent replaces the traditional mechanical linear scale system with a magnetic field-based detection system using MR sensors and drive magnets. This substitution eliminates the need for physical linear scales while maintaining positioning accuracy through magnetic field measurements, thereby reducing manufacturing complexity and cost
2Ease of operation
If MR sensor is used to detect magnetism of drive magnet for position calculation, then positioning control is achieved, but attachment errors reduce accuracy
Solution Approach 1:
The patent performs preliminary calibration to determine the relationship between MR sensor output and actual position before operation. By pre-establishing this relationship and compensating for attachment errors in advance, the system eliminates the impact of attachment errors on position calculation accuracy during actual positioning operations
Solution Approach 2:
The patent implements a feedback mechanism where the MR sensor continuously detects magnetic field strength, the control unit calculates position based on this detection, and the system adjusts to compensate for attachment errors. This closed-loop feedback ensures high position calculation accuracy despite initial attachment variations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the positioning accuracy of linear motors by reducing errors in position detection and speed calculation, thereby improving control accuracy without the use of linear scales.
Implementation Method 1
a magnetic sensor which the armature has and which outputs a signal according to a direction of a magnetic field generated by the drive magnets
Implementation Method 2
a magnetic field generated by allowing a current to flow to the plurality of coils of the armature
Implementation Method 3
a magnetic field generated by the plurality of drive magnets of the magnet unit
Data Source
AI summary
A control apparatus (10) includes a position detection unit (108) which detects a position of a mover of a linear motor (20) based on a change in an output signal from a magnetic sensor (27), a position control unit (102) which calculates a speed command value based on the position of the mover detected by the position detection unit (108) and a position command value of an external input, an estimation unit (150) which estimates a moving speed of the mover from a current value of a current flowing to a plurality of coils of the linear motor (20), a speed control unit (104) which calculates a current command value based on the speed command value and the estimated moving speed, and a power converter (106) which supplies power to the plurality of coils according to the current command value.