Firmness sensor and system for date sorting

A device which sorts dates on the basis of firmness was developed and tested in a commercial packing house. This development was based on previous work in which firmness of dry dates (var. 'Daglat Nur') in the Arava region of Israel was found to be well correlated with grade standard, moisture content, water absorbability during the hydration process, and consumer appeal. Firmness measurement is based on pressing the date between two parallel plates-one fixed and the other moving toward the first. The position of the moving surface relative to the fixed surface is measured by a linear encoder. Personal computer-based software was developed to calculate firmness from size (position of the moving surface for applied force of 5 N, 1.12 Ibf), applied forces, elasticity of the support spring, and deflection of the date (position at 8 N, 1.8 Ibf). The personal computer identifies each date according to its cell and controls a sorting mechanism for four groups. The prototype system operated at a rate of one date per second using a single channel. Results suggest that by sorting to four firmness groups, the proper hydration duration to achieve high quality and high uniformity of each batch can be selected. A faster system was developed and applied for patent, but it is yet to be implemented in the date industry. Hand sorting is still the common method.