Stone detection method and apparatus for a harvester

A method for detecting hard objects in a flow of cut crop material softer than the hard objects flowing along a flow path between harvesting apparatus of an agricultural harvester and threshing apparatus thereof, comprising steps of:

• providing a detector element along the flow path so as to be vibrated by the flow of crop material therealong, and such that at least some of any hard objects in the flows of crop material generate vibrations of the detector element at least generally within a first frequency band and a second frequency band, and wherein at least some of the vibrations within the first and second frequency bands generated by the hard objects have amplitudes greater than amplitudes of vibrations generated by the crop material alone;
• sensing the vibrations of the detector plate and responsively outputting signals representative thereof over a first signal path and a second signal path, respectively;
• filtering the signal outputted over the first signal path to suppress frequencies thereof below a first frequency within or below a lower portion of the first frequency band to create a first frequency filtered signal, filtering the first frequency filtered signal so as to pass frequencies thereof generally within the first frequency band as a first bandwidth filtered signal, and selectively outputting the first bandwidth filtered signal when the first bandwidth filtered signal is representative of vibrations having the amplitudes greater than the amplitudes of vibrations generated by the crop material alone;
• and
• filtering the signal outputted over the second signal path so as to pass frequencies thereof within the second frequency band, and selectively outputting the second bandwidth filtered signal when representative of vibrations having the amplitudes greater than the amplitudes of vibrations generated by the crop material alone.

A hard foreign object detecting circuit for detecting hard foreign objects in a flow of cut crop material toward a threshing system of an agricultural harvester, comprising:

• at least one vibration sensor operable for generating a first input signal in response to vibrations generated by a hard foreign object;
• a frequency high pass filter that receives the first input signal and removes frequencies below a first frequency therefrom to produce a first high pass filtered input signal;
• a first programmable amplifier that receives the first high pass filtered input signal and generates an amplified first output signal;
• a frequency bandpass filter that receives and filters a bandwidth of the amplified first output signal to generate a first frequency filtered signal;
• a first variable threshold comparator that receives the first frequency filtered signal and generates a first pulse output signal when the first frequency filtered signal exceeds a minimum threshold amplitude;
• a microprocessor including a first pulse rejection network that receives the first pulse output signal and generates an internal signal when a frequency calculated from a pulse train of the first pulse output signal corresponds to a predetermined frequency bandwidth, the microprocessor being electronically connected to the first variable threshold comparator and to the first programmable amplifier, and the microprocessor being operable to control the value of the minimum threshold amplitude of the first threshold comparator and to control a magnitude of signal amplification performed by the first programmable amplifier, and the microprocessor being operable to activate a hard object removal mechanism responsive to the generation of the internal signal;
• a second programmable amplifier which receives the first input signal and produces a second amplified input signal;
• a low frequency band pass filter which receives the second amplified input signal and produces a second frequency filtered signal;
• a second variable threshold comparator that receives the second frequency filtered signal and generates a second pulse output signal when the second frequency filtered signal exceeds a minimum threshold amplitude;
• a microprocessor including a second pulse rejection network that receives the second pulse output signal and generates an internal signal when a frequency calculated from a pulse train of the second pulse output signal corresponds to a specified frequency bandwidth, the microprocessor including the second pulse rejection network being electronically connected to the second threshold comparator and to the second programmable amplifier, the microprocessor including the second pulse rejection network being operable to control the value of the minimum threshold amplitude of the second threshold comparator and to control a magnitude of signal amplification performed by the second programmable amplifier, and the microprocessor including the second pulse rejection network being operable to activate the hard object removal mechanism responsive to the internal signal generated when the frequency calculated from the pulse train of the second pulse output signal corresponds to the specified frequency bandwidth.