Optical Food Sorter

Overview

An optical food sorter removes defective and foreign material from a flowing stream of product. It looks at every piece, decides whether it is good product, a defect, or something that should not be there, and physically removes the bad pieces with a burst of air. The product can be almost anything that flows in bulk: potatoes, nuts, frozen vegetables, coffee beans, rice, diced fruit, leafy greens. The defects it catches range from discoloured, rotten or misshapen product to foreign material like stones, glass, plastic, sticks and insects. Sorting at this speed by eye is impossible, so the machine does it with cameras, spectral sensors and a bank of fast air valves, processing tonnes per hour while a person only empties the reject bin and checks the result.

The machine has a few cooperating subsystems. The Feed System spreads and launches the product. The Inspection Chamber lights it. The Camera & Sensor Head images it. The Image Processing & Detection decides what each piece is. The Ejection System removes the rejects, fed by the Compressed Air System, and the Product Separation catches the two streams.

Presenting the product

A sorter is only as good as how the product is presented to the cameras. Bulk product arrives uneven and clumped, so the Vibratory Feeder vibrates it forward and fans it out across the full width into a single layer where pieces do not overlap. From there the Accelerating Belt runs faster than the feeder, pulling the pieces apart and launching each one off its end on a fixed parabolic path. Because every piece leaves at the same speed from the same point, the system knows where any given piece will be at any later instant, which is what lets it aim an air pulse at it. The Bed Depth Sensor trims the feed so the layer stays thin even as the incoming rate changes.

How the inspection works

As the product crosses the inspection point, it is lit from both sides by LED Light Bar units against a calibrated Reference Background, viewed through sealed Viewing Window glass. Light interacts with each piece differently: a good potato reflects one way, a green or rotten patch another, a stone or a clod another again. The RGB Line-Scan Camera records the colour of every point across the lane thousands of times per second, building a continuous image. Colour alone is not enough when a defect or foreign object matches the product colour, so the NIR Sensor reads near-infrared absorption, which tracks water and chemical makeup and tells, say, a clod of dirt from a potato that looks the same to the eye. Where foreign material like glass or plant stalks must be caught, the Laser Structure Sensor adds a structural and chlorophyll reading. The Camera Lens sets how fine a feature each camera resolves, and a White-Balance Tile is imaged at startup to fix white balance.

Deciding and ejecting

The signals go to the Image Processing & Detection electronics. A FPGA Processing Board classifies every pixel at full line rate, and a GPU Classification Board runs the colour and spectral models that label whole objects as product, defect or foreign. Once a piece is marked for rejection, the system already knows its trajectory, so it computes which nozzles will be above it when it reaches the air knife and at what instant. The Valve Driver Board then fires those nozzles. The Ejection System is a dense bank of High-Speed Solenoid Valve units on a 4-8 mm pitch, fed from a shared Air Manifold through a Nozzle Strip. Each valve opens for a fraction of a millisecond and a short jet of air knocks the bad piece off its natural path. Good pieces continue undisturbed. The Product Separation then splits the two: good product falls into the accept chute, the blown-off rejects into the reject chute. Steady air matters here, so the Accumulator Tank holds a reserve and the Pressure Regulator keeps every burst at the same pressure.

Materials and hygiene

The machine handles food, so wetted parts are 304 stainless steel and food-grade polymers, and the whole frame washes down. The Frame Weldment holds the optics and ejector in fixed alignment so calibration survives vibration. During a run, juice and fines build up on the glass and would read as false defects, so the Window Cleaning system runs Air Wiper blasts and Cleaning Brush sweeps on a schedule. The Operator Panel is sealed for washdown so it runs with wet gloves.

Variants and use

Two layouts dominate. Belt sorters carry the product on the Accelerating Belt and inspect it on or just off the belt, which suits sticky, wet or delicate product. Chute or freefall sorters drop the product down an inclined chute and inspect it in the air, which gives a clean all-around view and higher throughput for free-flowing product like nuts and grain. Sensing also scales: a basic line runs RGB only, while a high-end line adds NIR and hyperspectral sensing through the Camera & Sensor Head to catch foreign material and subtle quality defects. Operators set sensitivity and recipes per product on the Control & HMI, trading yield against purity: tighten the sort and fewer defects pass but more good product is rejected, loosen it and the reverse. The Microcontroller in the controller keeps the timing between camera and valve fixed so the aim stays true across the run.