Miniaturized Linear Motor Position Control via Magnetic Sensing
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Solution Overview
Problem
Existing linear drives for optical systems in endoscopes face challenges in achieving precise positioning of the armature independent of external loads and limited miniaturization, leading to inaccuracies in focal length and focus point adjustment.
Innovation Solution
A miniaturized linear drive with a rotationally symmetrical design featuring a stator and armature, utilizing one or two coils and permanent magnets, along with soft magnetic materials and magnetic field sensors for precise position determination, allowing for independent control of the armature's position and enabling adjustment of the focal length and focus point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed current magnitudes are used to control the armature position, then the control system is simple, but the positioning accuracy deteriorates due to external forces like friction and gravity
Solution Approach 1:
The patent implements a feedback control system where the actual armature position is measured and compared with the desired position. The controller adjusts the coil currents based on the position error signal, compensating for external disturbances like friction and gravity. This closed-loop approach maintains positioning accuracy without requiring overly complex open-loop control schemes.
Solution Approach 2:
The patent replaces mechanical position sensing mechanisms with electromagnetic field-based measurement. By measuring the magnetic field strength generated by the permanent magnets at different armature positions, the system achieves precise position detection without mechanical contacts or complex mechanical linkages, thereby maintaining simplicity while improving accuracy.
2Volume of moving object
If the linear drive is miniaturized for endoscope insertion, then the device size is reduced, but the positioning accuracy and control precision deteriorate
Solution Approach 1:
The patent replaces mechanical position measurement systems with magnetic field sensing. The permanent magnets in the armature generate a position-dependent magnetic field that is measured by sensors in the stator. This electromagnetic approach allows for compact miniaturization while maintaining high measurement precision, as magnetic field sensors can be made very small and provide high-resolution position data.
Solution Approach 2:
The patent utilizes the change in magnetic field strength as a function of armature position as the measurement parameter. By measuring the magnetic field strength at different positions and correlating it with armature location, the system achieves precise position determination in a miniaturized configuration. The strong magnetic fields from permanent magnets provide sufficient signal strength even in small-scale implementations.
3Ease of manufacture
If calibration is performed after setup to achieve predetermined current-position relationships, then the initial setup is simplified, but the system requires additional time and complexity for calibration procedures
Solution Approach 1:
The feedback control system automatically performs calibration by measuring the actual armature position at various current levels and storing the relationship in a lookup table or calibration curve. This calibration process is integrated into the normal operation, requiring minimal additional time and can be performed in-situ without disassembling or resetting the system.
Solution Approach 2:
The system performs self-calibration by using its own measurement capabilities to characterize its behavior. The controller commands the armature to various positions, measures the actual positions using magnetic field sensing, and automatically establishes the current-position relationship. This eliminates the need for external calibration equipment or complex manual calibration procedures.
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
The solution provides high measurement accuracy and independence from external influences, enabling precise control of lens positions within endoscopes, suitable for miniaturized applications like video endoscopes and surgical instruments.
Implementation Method 1
One or more coils generate Lorentz-forces in the stator
Implementation Method 2
rings of soft magnetic iron are disposed at the permanent magnets (pole shoes)... allowing a defined flow of the magnetic fields of the permanent magnets through the coil towards the magnetic member
Implementation Method 3
the magnetic field strength, which depends on the position of the armature, is measured by means of a magnetic field sensor
Data Source
AI summary
A linear drive for a miniaturized optical system, as used for example in an endoscope, includes a stator and an armature. The stator has a coil with two stator pole shoes arranged in axial direction, and two magnetic field sensors arranged at the outer side of the stator pole shoes. The armature has permanent magnets which are polarized in opposite directions, and a center armature pole shoe between the two permanent magnets, and an armature pole shoe at each side of the permanent magnet, opposite to the center armature pole shoe in axial direction. The magnetic field of the outer armature pole shoe goes completely or only in part, dependent from the armature position, through the magnetic field sensor and thus generates a position-dependent signal. This signal can be used for measuring and/or controlling the position of the armature.