Autonomous Mower Bumper Sensing for Plant vs Obstacle Detection
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Solution Overview
Problem
Autonomous self-propelled mowing vehicles face issues with impact detectors being triggered by plants to be mowed, leading to unnecessary stalls, and adjusting settings to prevent this is restricted by safety concerns.
Innovation Solution
The implementation of a dual impact detection system, comprising a rigid first impact detector and a deformable second impact detector, allows the vehicle to differentiate between plant contact and hard obstacles, enabling safer operation by reducing unnecessary stops and ensuring effective collision protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the impact detector is positioned low to detect hard obstacles, then collision detection capability is improved, but the detector is pushed in by plants during mowing causing unnecessary stops
Solution Approach 1:
The impact detection system is segmented into two independent detectors: a first impact detector for detecting hard obstacles and a second impact detector for detecting plant contact. Each detector is positioned and configured to detect specific types of obstacles, allowing the system to distinguish between plants and hard obstacles and avoid unnecessary stops while maintaining safety.
Solution Approach 2:
The first impact detector is positioned at a height and orientation optimized for detecting hard obstacles, while the second impact detector is positioned to detect plant contact forces. Each detector has localized sensing capabilities tailored to its specific detection purpose, enabling differentiated response to different obstacle types.
2Productivity
If the impact detector settings are adjusted to prevent plant-triggered stops, then mowing efficiency is improved, but safety is compromised as the detector may not activate in case of collision with child or pet
Solution Approach 1:
The safety system is segmented into two independent detection channels with different sensitivity thresholds and response characteristics. The first detector maintains high sensitivity for safety-critical hard obstacle detection, while the second detector is optimized for plant contact detection with higher tolerance, allowing both safety and efficiency requirements to be met simultaneously.
Solution Approach 2:
The control unit acts as an intermediary that receives signals from both impact detectors and intelligently determines the appropriate response. It distinguishes between plant contact (second detector only) and hard obstacle collisions (first detector or both detectors), enabling differentiated control actions that maintain both safety and productivity.
3Reliability
If the first impact detector is made rigid to detect obstacles across its width, then detection coverage is improved, but plant forces across the entire width push it beyond the switching point causing stops
Solution Approach 1:
The detection function is segmented between two detectors with different structural characteristics. The first impact detector maintains rigid structure for comprehensive obstacle detection coverage, while the second impact detector provides localized pressure-sensitive detection. This segmentation allows the rigid first detector to maintain detection coverage without being overly sensitive to distributed plant forces.
Solution Approach 2:
The system changes the detection parameters by using two detectors with different sensitivity thresholds and mechanical properties. The first detector uses a higher force threshold suitable for rigid obstacle detection, while the second detector uses a lower pressure threshold for plant contact detection, allowing the system to differentiate between the two obstacle types based on force magnitude and distribution.
Data Source
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Figure 3
AI summary
An autonomous self-propelled mowing vehicle comprises a frame fitted with a drive mechanism, a mowing device for mowing plants, a bumper device, and a control unit. The bumper device comprises a first and a second impact detector. The first impact detector is depressible up to a stop and is provided with a first switch which emits a first signal to the control unit at a first switching point, if the first impact detector is depressed beyond the switching point. The second impact detector is deformable and locally depressible, and is provided with a second switch which emits a second signal to the control unit if the second impact detector is depressed at least beyond a predetermined depression threshold. The control unit is configured to stop the drive mechanism upon receiving the second signal, and to regulate the drive mechanism in such a way that the speed of the mowing vehicle is reduced to a lower mowing speed upon receiving the first signal without receiving the second signal. This prevents plants to be mowed from pushing the bumper away across the bumper width beyond the switching point of the first impact detector, without losing its long depressibility, because the second impact detector, which itself has a much smaller depressibility, detects obstacles at the lower (mowing) speed by being depressed itself.