Linear Actuator Position Detection via Coil Impedance Modulation
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Solution Overview
Problem
Existing methods for determining the position of a movable element in a linear actuator for motor vehicles are complex and require additional sensors or adjustments for factors like temperature-dependent viscosity, making them unreliable and costly.
Innovation Solution
A method that modulates the coil current with an alternating variable of a constant frequency to measure impedance changes, allowing for position determination without additional sensors, using conventional hardware and low computing effort, and is applicable to various influences such as temperature and viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional sensors are used to determine position independent of coil current, then position determination reliability is improved, but device complexity and cost increase
Solution Approach 1:
The coil serves dual functions: both actuating the movable element and sensing its position. The same coil that generates the magnetic field for movement also provides the inductivity signal for position detection, eliminating the need for separate sensors and achieving self-service functionality.
Solution Approach 2:
The coil is designed to perform multiple functions simultaneously: it acts as both the actuator coil for generating magnetic force and the sensor coil for detecting position through inductivity changes. This multi-functionality resolves the contradiction by eliminating additional components while maintaining reliability.
2Measurement precision
If coil current is adjusted to compensate for temperature-dependent viscosity, then position determination accuracy is improved, but control complexity increases
Solution Approach 1:
The patent replaces complex mechanical compensation methods with an electrical measurement approach. Instead of adjusting coil current to compensate for viscosity changes, the system directly measures position through inductivity changes, which automatically accounts for all environmental influences without requiring complex control algorithms.
Solution Approach 2:
The system uses the inductivity signal as feedback to directly determine position. The control unit processes the inductivity measurement to obtain position information, creating a simple feedback loop that naturally compensates for temperature and viscosity effects without requiring complex predictive control.
3Measurement precision
If impedance measurement methods are used to detect anchor position, then position determination is achieved, but the methods require complex signal processing at specific frequencies
Solution Approach 1:
The coil's own inductivity serves as the measurement signal source. By monitoring changes in the coil's inductivity caused by the movable element's position, the system achieves position detection using the actuator's inherent electrical properties, eliminating the need for complex external measurement circuits.
Solution Approach 2:
The inductivity of the coil acts as an intermediary parameter that links the mechanical position of the movable element to an electrical measurement signal. The control unit uses this intermediary inductivity signal to infer position without requiring direct mechanical sensing or complex signal processing.
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 simplifies position determination of a movable element in a linear actuator, ensuring reliability and cost-effectiveness by using existing hardware and not requiring special geometry or materials, while being robust against influences like temperature and viscosity changes.
Implementation Method 1
the movable element is movable by means of a magnetic field of a coil of a linear actuator
Implementation Method 2
The position of the movable element relative to the coil is determined based on a change of an impedance or inductivity or an admittance of the coil
Implementation Method 3
The position of the movable element relative to the coil is determined based on a change of an impedance or inductivity or an admittance of the coil
Data Source
AI summary
A method for determining a position of a movable element of a linear actuator of a motor vehicle includes supplying a current to a coil of the linear actuator so as to move and/or hold the movable element by a magnetic field of the coil generated by the supplied current; modulating the current supplied to the coil with an electrical alternating variable having a predetermined frequency; determining an impedance or an admittance of the coil at the predetermined frequency by measuring a further variable at the predetermined frequency; and determining the position of the movable element as a function of the determined impedance or admittance.