Spatial Domain Steering Control for Low Speed Vehicle Stability
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Solution Overview
Problem
Existing vehicle control systems perform poorly at very low speeds due to limited sensor data, noisy GPS and IMU signals, and integrator windup, leading to instability and reduced tracking accuracy.
Innovation Solution
A low-speed steering control algorithm is developed, transforming state equations from the time domain to the spatial domain, allowing the vehicle to operate in an asynchronous mode with position-based control, using asynchronous variable rate controllers and position/velocity filters to improve accuracy and stability at low speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional time-domain control algorithms are used, then the control system is simple and easy to implement, but performance deteriorates at very low speeds due to noisy sensor data and integrator windup
Solution Approach 1:
The patent transforms the control algorithm from the time domain to the spatial domain by changing the independent variable from time (t) to position (s). This dimensional transformation allows the control system to maintain stable performance at very low speeds by eliminating time-based integrator windup and noisy sensor data issues that plague traditional time-domain controllers. The state equations are rewritten using spatial derivatives instead of temporal derivatives, fundamentally changing how the controller processes sensor data and generates commands.
Solution Approach 2:
The patent changes the fundamental parameter used for control execution from time-based sampling to position-based sampling. By using position (s) instead of time (t) as the independent variable, the controller adapts its behavior based on the vehicle's spatial state rather than temporal elapsed time. This parameter change eliminates the need for time-based integrators that cause windup at low speeds and allows the system to maintain effective control regardless of vehicle velocity.
2Measurement precision
If synchronous control mode is used at high speeds, then tracking accuracy is good, but the system becomes unstable at very low speeds due to large time constants and integrator windup
Solution Approach 1:
The patent implements a dynamic control system that automatically adapts its behavior based on the vehicle's operating conditions. The controller switches between asynchronous low-speed mode and synchronous high-speed mode depending on the vehicle's velocity threshold. This dynamic adaptation allows the system to maintain stability at very low speeds while preserving tracking accuracy at high speeds, effectively resolving the contradiction between stability and precision across different operating regimes.
Solution Approach 2:
The control system is segmented into two distinct operational modes: asynchronous low-speed mode for very low speed operation (0.0-1.0 mph) and synchronous high-speed mode for normal operation (>1.0 mph). This segmentation allows each mode to be optimized for its specific speed range, with the asynchronous mode using position-based control to eliminate integrator windup and the synchronous mode using traditional time-based control for optimal tracking performance at higher speeds.
3Reliability
If position-based spatial domain control is implemented, then closed loop performance is maintained at low speeds, but the controller complexity and computational requirements increase
Solution Approach 1:
The patent replaces the traditional time-based mechanical control system with a position-based spatial control system. By substituting time-domain mathematics with spatial-domain mathematics, the controller eliminates the need for complex integrator windup compensation and noisy sensor data filtering that are required in time-based systems. The spatial domain approach uses position derivatives and spatial state equations that are computationally simpler and more robust at very low speeds.
Data Source
AI summary
A method of operating a vehicle at a substantially low speed based on change in the vehicle position. The method comprises the following steps: (A) transforming a steering control algorithm into a substantially low speed (SLS) steering control algorithm, wherein the (SLS) steering control algorithm is configured to operate the vehicle in an asynchronous low speed mode; and (B) implementing the SLS steering control algorithm as a controller configured to operate the vehicle in the asynchronous low speed mode.