Vision system measures burger buns in three dimensions

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A hamburger bun factory is using Sick's IVC3D camera-based inspection system to inspect products to ensure that their height and diameter are within tolerance and that the sesame seeds are evenly distributed.

Sick's IVC3D camera-based inspection system is claimed to have brought a new level of detail and accuracy to the inspection and robot picking of buns. The hamburger buns are inspected as a final step in an automated production line; faulty buns are rejected and those that pass are automatically packaged into boxes by a robot.

Quality control consists of measuring height, volume and diameter to verify that each bun is within tolerance, plus there is a check to ensure that the sesame seeds are evenly distributed on the top surface. Based on these measurements and observations, a good/bad bun decision is made. The co-ordinates of the good buns are then reported to a robot that picks the buns from the conveyor and places them into boxes. If a bun has a defect of any kind, the picking is skipped and the bun falls into a reject basket at the end of the conveyor.

Sick's IVC3D camera combines the flexibility of a smart camera with high-speed 3D image capture and processing - in one robust, industrial standalone system that has all the required functionality built-in (no external PC is required during normal operation). This powerful combination addresses the fact that many vision inspection applications often miss vital information because the majority of cameras currently in use only operate in two dimensions.

Food-grade hardware

With food applications in mind, shatter-proof glass is standard on the IVC3D, and the system is available in 'food-grade' plastic. The robust IP65-rated enclosure contains the optics, laser, 3D sensor, processor, I/O, and serial and Ethernet communication architecture.

In operation, the IVC3D is capable of capturing and processing 5000 height profiles per second with a resolution of 0.04mm, with each profile incorporating 1024 individual height points. A PC or laptop running IVC Studio software is needed during the development of the system; this can then be disconnected when the system is put in operation.

The images are grabbed in free running mode, which means there is no photo-switch to trigger the acquisition. To ensure that each bun is fully analysed, the subsequent images are grabbed with an overlap corresponding to 150 per cent of the nominal bun diameter. The overlap causes each bun to be presented in its entirety in at least one image.

The laser is set to flash mode to ensure a constant exposure independent of the conveyor speed. When an image has been grabbed, the size and centroid (centre of gravity) of each bun is found by blob analysis. The main loop of the camera program is where the height, volume and number of sesame seeds are measured. The looping over all buns is made by a FOR loop. The height and volume are relative measurements, which means that they need to be related to a reference point or surface, ie the conveyor belt. Thus the true height of the bun is given by the measured height in the camera's co-ordinate system, minus the measured height of the conveyor.

Since the conveyor is not visible under the bun itself, it can be estimated by measuring points close to the bun perimeter. Assuming that the conveyor belt is flat, the Fit Surface tool in the camera is used to mathematically fit a plane to approximate the conveyor under the bun.

With quality being so high on the agenda with both manufacturers and consumers alike, equipment such as the IVC3D is starting to gain greater acceptance as part of overall quality programmes in many industries.

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