Optical granular material-sorting apparatus utilizing piezoelectric valve

An optical granular material-sorting apparatus comprising:

• a transfer means for transferring objects-to-be-sorted;
• an optical detection means for detecting, at a detection position, objects-to-be-sorted while they are dropping from an end of the transfer means;
• and
• a blasting means provided below the optical detection means and designed to blow away objects-to-be-sorted through blasting of air based on the result of detection by the optical detection means;
• said optical granular material-sorting apparatus characterized in that the blasting means has a piezoelectric valve which is driven to blast air based on the result of detection by the optical detection means, and the piezoelectric valve comprises:
• a valve main body formed in which are a gas pressure chamber that takes in compressed gas supplied from the outside as well as a gas release channel through which the compressed gas is released from the gas pressure chamber;
• a valve body placed in the gas pressure chamber to open and close the gas release channel;
• a piezoelectric element that generates, in the form of displacement, a driving force needed to operate the valve body;
• at least one displacement amplification mechanism that amplifies a displacement of the piezoelectric element and causes it to act upon the valve body;
• and
• a driving means for applying voltage to the piezoelectric element in order to drive the valve body to open the valve and thereby open the gas release channel;
• said piezoelectric valve characterized in that the driving means applies voltage to the piezoelectric element in multiple stages so as to suppress fluctuation in the amount of gas ejected from the gas release channel when the valve opens.