A ring sensor system using a modified polar coordinate system to describe the shape of irregular objects

Abstract

For agricultural produce such as potatoes, size and shape determination is very important in grading lines. If electronic sensor systems are installed, weighing cells and optical sensors such as cameras or simple shadow solutions are predominantly used. These systems are limited with regard to the numbers of 'views' of the object, which determines the accuracy for the determination of geometrical parameters. A ring sensor system is described consisting of a large number of optical transmitters and receivers which are arranged alternately. The emitters strobe infrared light in sequence round the ring, creating a large number of 'viewpoints'. Optical connections to each receiver are made. As an object passes through the ring, a shadow zone of each transmitter beam is created. As a result, the tangential chords can be found. A modified polar coordinate system, an algorithm and trigonometrical functions are described which allows the contour of the convex hull of three-dimensional objects to be formed. One advantage of this system is that the data from the ring is in the form of components of vectors and can be used to describe the whole object. As a result an enveloping spiral of the object is created.

Non-destructive technologies for fruit and vegetable size determination – A review

“…Some of the measurement systems referred to in this paper could be assigned to more than one of the above-listed groups; for example, the optical ring sensor system (Gall, 1997), described in the next subsection, which could be assigned to the first and third groups.…”

“…One of these systems is the optical ring sensor system developed by Gall (1997). This light-blocking-based system consists of a circular frame on which a large number of infrared transmitters and receivers are alternately arranged (Fig.…”

“…The optical ring sensor system (Gall, 1997) has a good performance on elongated produce. It does not require correctly oriented fruits for volume determination but it does for axes determination.…”

Effect of orientation on the fruit on-line size determination performed by an optical ring sensor

“…Size was determined by blocking of light as fruits passed between two lateral vertical arrays of optical transducers, one of them equipped with LED's and the other with phototransistors. Gall (1997) devised an optical ring sensor for measuring the size and shape of potato tubers. The optical ring sensor is an electro-optical device based on the blocking of light, which measures the size of objects that pass through it.…”

“…On the other hand, the advantage of the optical ring sensor over simpler light blocking electro-optical systems is that in the ring sensor the objects are scanned from a large number of viewpoints, resulting in higher measurement accuracy. Moreda, Ortiz-Cañavate, García-Ramos, Homer, and Ruiz-Altisent (2005) determined optimal levels of speed and passage zone for an on-line size determination system comprised of the optical ring sensor devised by Gall (1997) and a singulator made of two angled belts which fed two types of models -truncated spheres and elongated cylinders -to the optical ring sensor.…”