Stone Detection Circuit for Agricultural Harvesters
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Solution Overview
Problem
Existing stone detection systems in agricultural harvesters fail to reliably detect large stones due to their size and low-frequency impact signatures, often causing damage to machinery, and lack adjustable sensitivity settings to differentiate between background noise and stone vibrations.
Innovation Solution
Modifying the stone protection module to center the upper filter at 1 kHz for detecting large stones, adding a high pass filter to prevent overload, and implementing a sliding sensitivity scale for improved detection in varying crop conditions, with a microprocessor-controlled detection circuit to adjust amplification and threshold settings for precise stone identification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the bandpass filter centre frequency is set to 5 kHz for stone detection, then small stones can be detected, but very large stones with low-frequency impact signatures (below 2 kHz) are not detected
Solution Approach 1:
The detection system is divided into two separate detection circuits: a first detection circuit with a first bandpass filter centered at 5 kHz for detecting smaller stones, and a second detection circuit with a second bandpass filter centered at 1 kHz for detecting very large stones. This segmentation allows each circuit to be optimized for specific stone size ranges, resolving the contradiction between detecting small stones and detecting large stones with low-frequency signatures.
2Productivity
If the peak signal detector uses a fixed threshold amplitude, then processing is simple, but it cannot adapt to varying background noise levels causing false positives or missed detections
Solution Approach 1:
The fixed threshold amplitude is replaced with variable threshold values that can be adjusted based on detected background noise levels. The system dynamically adapts the threshold to current operating conditions, improving reliability by reducing false positives during high-noise periods while maintaining detection sensitivity during quiet periods, all while preserving real-time processing capability.
3Reliability
If the trap door opens frequently to remove detected objects, then stone removal is aggressive, but valuable crop material is spilled on the ground
Solution Approach 1:
The system incorporates feedback mechanisms where detected objects are logged and their characteristics are analyzed. The trap door activation is controlled by multiple criteria including object size, impact strength, and contextual information from the feedback loop, allowing the system to distinguish between true stones and crop material more accurately, thereby reducing unnecessary crop spillage while maintaining effective stone removal.
4Adaptability or versatility
If the detection circuit sensitivity is increased to detect all possible stones, then detection coverage improves, but background noise from engine vibrations and rock impacts is also detected
Solution Approach 1:
Different detection circuits are assigned different frequency response characteristics tailored to specific detection needs. The first detection circuit uses a 5 kHz bandpass filter optimized for smaller stones, while the second uses a 1 kHz bandpass filter for very large stones. This local optimization of frequency response at different levels allows the system to maintain high sensitivity for stones of various sizes while filtering out irrelevant background noise through frequency-selective detection.
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
Enhances detection performance for both large and small stones, minimizing crop loss and machinery damage, with improved user interface and internal adaptation to external influences.
Implementation Method 1
The sensor is a piezoelectric sensor that generates an electrical signal in response to mechanical vibrations
Implementation Method 2
the bandpass filter removes low frequency signals from the sensing signal before sending the filtered signal to the peak signal detector
Implementation Method 3
an amplifier, which sends an activating signal to a solenoid, which operates to open the trap door so that the hard foreign object will fall out of the header
Data Source
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AI summary
A hard object or stone detection method and apparatus for detecting and removing discrete hard foreign objects from mobile agricultural equipment, particularly an agricultural harvester (1) including apparatus (12) for providing a flow of cut crop material to an elevator (21) for delivery to a threshing system (3). The apparatus includes a foreign object detecting mechanism (35), including a foreign object detecting circuit (42) for detecting foreign objects and an object exclusion or rejection mechanism (44) operationally connected to be activated by the detecting circuit. The detecting circuit includes at least one vibration sensor (40) operable for outputting a signal (I1), and a combination of a high pass filters (140) and frequency bandpass filters (52, 152) and variable threshold comparators (54, 154) for processing the signal along first and second signal paths, and at least one microprocessor (60) or microcontroller including a pulse rejection network. The microprocessor can be electronically connected to control the threshold comparators and programmable amplifiers, and activates the object exclusion or rejection mechanism when the pulse rejection network generates an internal signal indicating presence of a hard object.