Motor Resolver Distance Tracking for Autonomous Vehicles
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Solution Overview
Problem
Current methods for determining the distance traveled by autonomous vehicles, especially during small movements like creeping forward, lack accuracy and rely on expensive or unreliable components, making it difficult to track the vehicle's position relative to known reference points effectively.
Innovation Solution
The use of an electric motor with a motor resolver and a controller to determine the distance traveled by measuring the change in the electric motor's position, which is connected to a drive wheel through a drive train, allowing for precise calculation of distance based on the motor's rotations and the set ratio between motor position changes and wheel rotations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If LIDAR or radar is used to determine vehicle position relative to reference points, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex optical/radar systems with a mechanical sensing approach using an encoder disk coupled to the motor shaft. The encoder disk with radial openings provides mechanical position encoding that is simpler and more cost-effective while achieving sufficient measurement precision for dead reckoning applications.
Solution Approach 2:
The invention creates a simplified copy of the position determination function by using motor shaft position as a proxy for vehicle position. Instead of directly measuring vehicle position with complex sensors, the system copies the positional information from the motor shaft through the encoder, which is then used to calculate vehicle displacement through integration.
2Device complexity
If GPS is used to determine vehicle position, then device complexity is reduced, but measurement precision deteriorates for small movements
Solution Approach 1:
The patent segments the position determination into two components: coarse position from GPS and fine position changes from motor encoder integration. This segmentation allows GPS to provide overall location while the encoder captures small displacements that GPS would miss, combining the advantages of both approaches.
Solution Approach 2:
The system performs preliminary position determination using GPS to establish a baseline location, then uses motor encoder data to track subsequent small movements. This preliminary action with GPS sets the stage for more precise incremental measurements, allowing the system to leverage both measurement types effectively.
3Measurement precision
If dead reckoning is used to track vehicle position changes, then measurement precision for small movements is improved, but reliability deteriorates due to accumulation of errors
Solution Approach 1:
The patent implements feedback by periodically using external reference points (stop signs, traffic lights) to correct accumulated dead reckoning errors. When the vehicle passes these known reference points, the system compares the dead reckoning position with the actual known position and applies corrections to reset accumulation errors, maintaining long-term reliability.
Solution Approach 2:
The system prepares for error accumulation by designing the dead reckoning system with built-in correction mechanisms at predetermined intervals. Reference points are strategically used as correction opportunities before errors become significant, cushioning against the natural drift of integration-based position tracking.
4Measurement precision
If expensive and unreliable components are used for distance determination, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent employs inexpensive encoder disks and standard motor position sensors instead of expensive dedicated distance measurement sensors. These simple mechanical components are cost-effective and easily manufactured, providing sufficient precision for the application without the high cost of specialized sensors like LIDAR or radar.
Solution Approach 2:
The motor position sensing system serves multiple functions: it provides both motor control feedback and distance travelled measurement. This multi-functionality eliminates the need for separate expensive distance sensors, reducing overall system cost while maintaining measurement precision through the dual-use of motor position data.
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 provides an accurate and cost-effective method for determining distance traveled, compensating for variables like gear lash, drive train twist, and signal delay, ensuring reliable navigation in autonomous driving systems.
Implementation Method 1
A motor resolver is positioned adjacent to the motor rotor shaft, where the motor resolver is configured to determine a motor position of the electric motor based on revolutions of the motor rotor shaft
Data Source
AI summary
Vehicles, systems, and methods for determining a distance travelled are provided. In an exemplary embodiment, a vehicle includes an electric motor with a motor rotor shaft. A motor resolver is positioned adjacent to the motor rotor shaft, where the motor resolver is configured to determine a motor position of the electric motor based on revolutions of the motor rotor shaft. A controller is in communication with the motor resolver, where the controller is configured to determine a distance travelled from a change in the electric motor position.