Coordinated Differential Traction Steering for Wheel Sink Obstacles
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Solution Overview
Problem
Traditional robotic mowers face issues with steering faults and getting stuck due to the traction wheels sinking into obstructions, leading to steering motor over-current and loss of steering control, especially when encountering obstacles like irrigation pod holes or sprinkler heads.
Innovation Solution
A differential traction drive system with steering axis coordination that uses independent traction motors to coordinate left and right wheel speeds based on target forward speed, steering rotational speed, and wheel distances, allowing for robust and continuous steering operations without additional mechanical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single motor and transaxle with fixed differential lock mechanism is used, then differential lock function is provided, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical differential lock mechanism with an electronic control system that independently adjusts the speed of left and right traction wheels through separate motors. This substitution eliminates complex mechanical components while achieving the same functional effect of preventing wheel slippage and improving steering reliability during obstacle negotiation.
Solution Approach 2:
The patent divides the single motor system into two independent motors, one for each traction wheel. This segmentation allows independent control of each wheel's speed and torque, enabling differential speed control without requiring a mechanical differential lock, thus simplifying the overall mechanical structure while maintaining steering reliability.
2Force
If steering motor outputs high torque to steer over obstructions, then steering capability is improved, but motor over-current and steering stall occur
Solution Approach 1:
The system performs preliminary action by detecting potential obstructions before the steering motor encounters them. When an obstruction is detected, the control system proactively adjusts the speed differential between left and right wheels to create a turning moment, allowing the mower to steer over the obstruction using traction force rather than relying solely on high steering torque, thereby preventing motor over-current and stalls.
Solution Approach 2:
The control system acts as an intermediary between the steering command and the motors. Instead of directly commanding high torque to the steering motor, it mediates by adjusting the speed differential of the traction wheels, which indirectly achieves the steering effect while avoiding excessive current draw and potential motor stalls.
3Device complexity
If traction wheels are used for both traction and steering, then device simplicity is improved, but steering control reliability deteriorates when wheels sink into obstructions
Solution Approach 1:
The patent applies dynamics by continuously and dynamically adjusting the speed of each traction wheel based on real-time steering requirements and terrain conditions. This dynamic speed control allows the system to adapt to varying conditions such as wheels sinking into obstructions, maintaining steering control reliability while using a simple structure where traction wheels perform both traction and steering functions.
Solution Approach 2:
The system implements feedback by continuously monitoring the actual position and speed of the traction wheels, as well as terrain conditions, and using this information to adjust the motor speeds in real-time. This feedback mechanism ensures that even when wheels sink into obstructions, the control system can compensate by adjusting speeds to maintain steering control, thereby improving reliability without adding mechanical complexity.
Data Source
AI summary
A system and method for differential traction drive and steering axis coordination for an autonomous mower or other turf device includes initiating a steering motion based on determining a target forward speed and a steering rotational speed, calculating a left wheel speed and a right wheel speed, and applying the left and right wheel speeds, wherein the steering rotational speed is driven by a steering motor and the traction wheels associated with the autonomous mower, and the left and right wheel speeds are based on the target forward speed, a distance from a steering axle to the center of the respective wheel, and the steering rotational speed.