Method and equipment for measuring firmness of fruits and vegetables

Equipment for measuring and testing the firmness of a fruit or a vegetable in order to determine its ripeness stage in the form of a firmness tester or firmness sensor, comprising a vibrator assembly, a fruit-holding assembly, frame assembly, processing means, signal generation means, control means, electric power means and weighing means;

• wherein said vibrator assembly includes a vibration actuator provided with a first vibrating gripper body adapted to hold and vibrationally excite said fruit or vegetable at a first point, said gripper body containing a first acceleration transducer adapted to emit an input acceleration signal in response to the vibrational excitation of the fruit or vegetable at said first point;
• wherein said fruit-holding assembly includes a movable gripper body adapted to hold said fruit or vegetable at a second point approximately diametrically opposed to said first point and containing a second acceleration transducer adapted to emit an output acceleration signal in response to the vibration of the fruit or vegetable at said second point;
• electrically or manually operated, mechanical means for urging said movable gripper body onto said fruit or vegetable;
• spring means positioned between said movable gripper body and said electrically or manually operated urging means permitting said fruit or vegetable to be vibrated;
• pressure sensing means adapted to automatically control and display the pressure or force applied to said fruit or vegetable by said electrically or manually operated urging means;
• wherein said frame assembly is in the form of a flat base or self contained frame incorporating said vibrator assembly and said fruit holding assembly;
• wherein said processing means includes conditioning circuity for operating said acceleration transducers and pressure sensor means:
• a difference amplifier to effect deduction of said output acceleration signal from said input acceleration signal to obtain a relative acceleration signaling in real time;
• analog or digital computer means for processing the signals obtained by said acceleration transducers for obtaining said firmness index value by dividing the root mean square of the output acceleration signal by the root means square of the relative acceleration signal;
• wherein said signal generation and control means includes an analog function generator or digital computer means adapted for generating narrow band random signals or composite waveform signals with predetermined frequency content, composed of a sum of sinusoids with frequencies, amplitudes and phase shifts specialized for the kind of fruit or vegetable to be tested and a power amplifier adapted to amplify said signals for driving said vibration actuator while using said input acceleration signal in a feedback loop for controlling and maintaining a preset vibration level applied to said fruit or vegetable by said vibration actuator;
• wherein said electric power means includes a power supply and regulating means for operating said firmness tester or sensor and said vibration actuator, processing means, signal generation and control means and computer means;
• wherein said weighing means includes electronic scales adapted to transmit a voltage signal to said computer means proportional to the weight of said tested fruit or vegetable.