On-line machine vision system for fast fruit colour sorting using low-cost architecture

The work presented in this paper is part of a system developed for fruit sorting. The machine vision unit is part of a distributed control system in which several machine vision modules can be integrated with a control module and a user interface unit. The control module takes care of the distributed control of the conveyor belt, weight units and fruit output units. The user interface is a front end to the user who can watch and control any part of the distributed system. The machine vision units are connected through a LAN to the user interface and through a CAN bus to the control unit in order to send and receive real time information during the on-line sorting process. Information that does not need real time communications are sent trough the LAN under an ethernet protocol. The machine vision unit is a self-contained module based on a Pentium-II processor with an image acquisition card, with no user interface. All the image processing is done under the Pentium-II processor. Each machine vision module can process two lines at the time. The system allows fruit size and colour sorting at 20 fruits/second using the aforementioned hardware. The segmentation process is performed using the information the user specifies through the user interface which allows to define complex colour classes and colour classification rules interactively. Real time performance at rates specified before are achieved using a colour camera in asynchronous reset mode and programming techniques avoiding hard computational processes. Size calculation accuracy depends on the camera set-up. Typical camera set-ups in the fruit sorting system developed can provide 1 mm error approximately using one camera per two lines.