Optoelectronic detector with high, uniform sensitivity and large field

Abstract

The device ascertains existence of a small inkdrop to be ejected from a thermal-inkjet pen. It includes a light source (preferably a nonpoint source with extended threadlike form perpendicular to the light path), detector, and optical element--preferably a cylindrical lens--for passing light from source to detector through an inkdrop probe volume, and for causing that light to be concentrated near the detector. Along a segment of the light path near the detector, the light is concentrated into a cross-section which is much smaller than that of the probe volume and is, within that segment, approximately independent of position along the path. The detector intersects the light within that segment; both the light beam within that segment and the detector have elongated, narrow shapes transverse to the light path, with regions in which brightness and sensitivity are approximately independent of position along the elongated shapes, and which are mutually crossed within these regions--so that positioning of the detector need not be precise in any direction. The apparatus has provision for firing an inkdrop through the probe volume, from a thermal-inkjet pen. Preferably the device is made for use with two or several different thermal-inkjet pens, each having a respective array of nozzles for ejecting such inkdrops; the several pens include some that have different nozzle-array footprints; and the probe volume accommodates drops ejected through all the different footprints. Analysis of the system detection sensitivity reveals a controllable variation with respect to drop position within the probe volume--including at least one constant-sensitivity contour. Preferably the inkdrops pass along at least one of the constant-sensitivity contours.