Actuator Position Sensing Using Dual Gear Encoders
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Solution Overview
Problem
Conventional electromechanical actuators face issues with positional accuracy due to susceptibility to electrical noise and wear from analog position sensors, and require complex and costly solutions for absolute position sensing, which also necessitate homing operations upon power-up, causing delays and potential motion errors detrimental to real-time control applications.
Innovation Solution
An electromechanical actuator design incorporating a primary gear and a secondary gear with different numbers of teeth, where primary and secondary angular position sensors measure the angular positions within one rotation, and a control module calculates the angular position of the input shaft over multiple rotations using reference values, enabling absolute position awareness and eliminating the need for multiple sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog position sensors are used, then position sensing is achieved, but the motor becomes susceptible to electrical noise and wear, reducing accuracy and device life
Solution Approach 1:
The patent replaces analog mechanical position sensors with a digital encoding system using two optical encoders that read positional information from a coded disk. This substitution eliminates the sliding contacts and analog signal susceptibility to noise, providing wear-free, digital position sensing with higher reliability and accuracy.
Solution Approach 2:
The system uses two separate optical encoders to read the same positional information from the coded disk independently. By having redundant sensing paths that converge through computational processing, the system achieves higher reliability without requiring analog sensors with inherent noise problems.
2Measurement precision
If incremental position encoders are used, then position sensing is achieved, but homing operations are required upon power-up, causing delay and motion errors
Solution Approach 1:
The coded disk is pre-encoded with absolute positional information that remains static and readable at any power state. The optical encoders can immediately read this pre-encoded information upon power-up without requiring movement or homing operations, eliminating startup delays and enabling instant position determination.
Solution Approach 2:
The system replaces incremental encoders that require motion-based homing with absolute encoders that read positional data directly from the coded disk. This substitution eliminates the need for mechanical movement during initialization, providing immediate position feedback upon power-up.
3Measurement precision
If separate power supplies are used to maintain absolute position, then position accuracy is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The single power supply serves multiple functions: it powers both optical encoders, the motor, and the control circuitry. The coded disk structure is designed to work with this unified power system, eliminating the need for separate power supplies while maintaining absolute position capability through the redundant encoder readings and computational processing.
Solution Approach 2:
The patent combines two optical encoders into a single integrated sensing system that shares common power supply and processing circuitry. By merging the sensing paths and using computational algorithms to process readings from both encoders, the system achieves absolute position sensing without requiring separate power supplies for each sensor, reducing overall system complexity.
4Measurement precision
If lookup tables are used for absolute position sensing, then position accuracy is improved, but computational efficiency decreases
Solution Approach 1:
The system replaces computational lookup table methods with direct optical reading of the coded disk. The positional information is physically encoded on the disk in a format that can be read directly by the optical encoders and converted to position data through simple computational relationships, eliminating the need for complex lookup table searches and improving computational efficiency.
Data Source
AI summary
Methods and systems for measuring angular position include measuring an angular position within one rotation of a primary gear and a secondary gear that are meshed together. The primary gear and secondary gear have a first and second number of teeth respectively, where the first number of teeth and the second number of teeth are different. An angular position for the secondary gear is estimated using the measured primary gear angle and a reference value for each of the primary and secondary angle sensors. A number of primary gear rotations is calculated using the estimated angular position for the secondary gear and the measured angular position of the secondary gear. An angular position of the primary gear is calculated over multiple rotations using the calculated number of primary gear rotations, a reference value for the primary angle sensor, and the measured angle value of the primary gear within one rotation.