Linear Motor Initial Positioning via Inductance and Sensor Fusion
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Solution Overview
Problem
Existing linear motor systems face challenges in determining the initial position of a moving body during start-up operations when the position sensor's measurement range is shorter than the magnet array, leading to ambiguous positioning.
Innovation Solution
The system employs a combination of stationary elements with coils and position sensors, where the inductance change between the coils and the magnet array is used to determine a rough position, followed by fine positioning using the position sensor, allowing for unambiguous absolute positioning even with a shorter measurement range. Direct and alternating currents are applied to the coils to facilitate this process, with Hall elements providing auxiliary information for accurate determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a position sensor with measurement range shorter than the magnet array is used, then the cost is reduced, but the initial position determination becomes ambiguous during start-up operations
Solution Approach 1:
The positioning process is divided into two stages: rough positioning using inductance detection with stationary elements, and fine positioning using the position sensor. This segmentation allows the use of a lower-cost position sensor with limited measurement range while still achieving accurate absolute position determination through the combination of both methods.
Solution Approach 2:
Stationary elements with coils are introduced as intermediary components between the magnet array and the position sensor. These stationary elements detect inductance changes to provide rough position information, which serves as a mediator to resolve the ambiguity that would otherwise occur with a limited-range position sensor during start-up operations.
2Measurement precision
If a position sensor with measurement range longer than the magnet array is used, then the initial position can be determined unambiguously, but the cost increases
Solution Approach 1:
The positioning function is segmented between the stationary elements (handling rough positioning via inductance) and the position sensor (handling fine positioning). This eliminates the need for a single high-cost sensor with extended measurement range, as the stationary elements compensate for the limited range of the position sensor.
Solution Approach 2:
The stationary elements create a coarse copy of the position information through inductance detection, which is then refined by the position sensor. This copying approach allows the system to achieve absolute position determination without requiring the position sensor to cover the entire magnet array range.
3Device complexity
If discrete position sensors are used to determine position by counting magnets, then the system complexity is reduced, but the measurement range must be longer than the magnet array to avoid ambiguity
Solution Approach 1:
Stationary elements with coils are inserted as intermediaries between the magnet array and the position sensor. These intermediaries detect inductance changes to provide rough position information, enabling the use of discrete position sensors with limited measurement ranges without requiring them to span the entire magnet array length.
Solution Approach 2:
The mechanical counting method is supplemented with electromagnetic inductance detection. Instead of relying solely on mechanical magnet counting which requires full-range sensors, the system uses electromagnetic field interaction (inductance changes) to provide position information that works with limited-range sensors.
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 method enables reliable and unambiguous determination of the moving body's initial position, reducing costs associated with longer position sensors and ensuring accurate positioning during start-up operations.
Implementation Method 1
determination of a rough position of the movable element based on a change of inductance of a coil of any of the stationary elements resulting from interaction with the magnet array
Implementation Method 2
detecting a position of the moving body using linear sensors
Data Source
AI summary
In a moving body system, a movable element of a linear motor is provided on a moving body, and stationary elements of the linear motor and position sensors are provided on the ground. The stationary elements are arranged between the position sensors to enable determination of a rough position of the movable element based on a change of inductance resulting from interaction with a magnet array. An initial position of the moving body when a power supply for the moving body system is turned on is determined based on the rough position of the movable element relative to the stationary element and a signal from the position sensor.