Dual Ultrasonic Mower Sensing for Angled Obstacle Detection
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Solution Overview
Problem
Existing mower obstacle avoidance systems using ultrasonic sensors struggle to detect objects or obstacles positioned at angles relative to the mower, as the sound energy may be deflected away from the sensors, and also receive false signals from non-blocking objects.
Innovation Solution
A mower obstacle avoidance system employing a pair of ultrasonic sensors, one on the left and one on the right of the mower, transmitting signals at different frequencies. The system compares the reflected signals to determine the proximity and orientation of obstacles, commanding the mower to slow down or stop if an object is in the path, and to turn accordingly to avoid the obstacle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single ultrasonic sensor is used on the mower, then the device complexity is reduced, but the detection precision for angled obstacles deteriorates because sound energy is deflected away from the sensor
Solution Approach 1:
The single sensor is divided into multiple sensors (left and right ultrasonic sensors) positioned at different locations on the mower. Each sensor covers a different angular sector, allowing the system to detect obstacles at various angles relative to the mower's path, thereby resolving the detection precision issue while maintaining manageable system complexity through modular segmentation.
Solution Approach 2:
The system transitions from a single-point detection approach to a distributed spatial arrangement of sensors across the mower width. By adding the lateral dimension to sensor placement, the system can detect obstacles approaching from different angles, converting a one-dimensional detection problem into a two-dimensional detection coverage area.
2Speed
If ultrasonic sensors transmit high energy signals to detect distant obstacles, then the detection range is improved, but false signals from non-blocking objects increase due to signal reflection
Solution Approach 1:
The system uses multiple sensors transmitting at different frequencies rather than a single high-power sensor. This distributes the detection effort across multiple lower-energy sources, achieving adequate detection range through cooperative sensing while reducing the intensity of individual signals that could cause false reflections from non-blocking objects.
Solution Approach 2:
The system varies the frequency parameter of ultrasonic signals between left and right sensors. By using different frequencies (first frequency and second frequency), the system can distinguish between genuine obstacle reflections and spurious signals, improving reliability while maintaining detection range through frequency-based signal differentiation.
3Productivity
If the mower operates at high speed to maintain productivity, then the productivity is improved, but the safety margin for obstacle avoidance is reduced
Solution Approach 1:
The dual-sensor system provides earlier obstacle detection by monitoring a wider angular sector ahead of the mower path. The left and right sensors can detect obstacles at greater distances and wider angles, giving the control system more advance notice to initiate avoidance maneuvers, thereby maintaining safety margins even at higher operating speeds.
Solution Approach 2:
The system continuously monitors reflected ultrasonic signals from both sensors and provides real-time feedback to the control system. This ongoing feedback loop enables dynamic speed adjustment and steering corrections based on current obstacle proximity and position, allowing the mower to maintain high productivity when clear while ensuring safety when obstacles are detected.
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
The system effectively detects and avoids objects or obstacles positioned at angles relative to the mower, ensuring safe operation by accurately determining the presence and location of obstacles within the mower's path.
Implementation Method 1
Ultrasonic sensors may detect obstacles without coming into contact with an object or obstacle, by transmitting energy in the form of ultrasonic sound waves and then receiving waves that reflect from the object or obstacle back to the sensor
Data Source
AI summary
A mower obstacle avoidance system includes a pair of sensors mounted on a robotic mower, each sensor emitting ultrasonic signals in a trajectory in front of the robotic mower, and receiving reflected signals from the other sensor. A controller commands a traction drive system to stop and turn the mower if either of the pair of sensors receives a reflected ultrasonic signal from an object at a stop distance in front of the robotic mower, if the object also is within a window of passage based on a height of cut, a width and a height of the robotic mower.