1. Field of the Invention
This invention relates to an ink droplet catcher assembly for an ink jet printer.
2. History of the Prior Art
During ink jet printing, ink droplets are selectively deflected to a printing surface to form desired characters. This deflection is controlled by using an energized charging electrode to apply varying electrical charges to the ink droplets. The droplets which are not deflected to the printing surface are captured by an ink droplet catcher assembly.
The patent to Michael Brown, et al entitled "Droplet Microphone," U.S. Pat. No. 4,128,841, issued Dec. 5, 1978, discloses an ink droplet catcher assembly having a housing with an opening through which undeflected ink droplets enter the housing from an ink jet printer. However, unlike ink droplet catchers disclosed in the July, 1972 Technical Disclosure Bulletin of IBM, Volume 15, No. 2; the David E. Lundquist, et al patents entitled "Air Turbulence Control of Inflight Ink Droplets in Non-Impact Recorders," U.S. Pat. No. 3,972,051, issued July 27, 1976, and "Liquid Jet Droplet Generator," U.S. Pat. No. 4,005,435, issued Jan. 25, 1977; and the Richard G. Sweet patent entitled "Fluid Droplet Recorder," U.S. Pat. No. 3,596,275, issued July 27, 1971, which merely collect ink droplets not impacting the printing surface, the "Droplet Microphone" by Brown uses the captured droplets to better deflect subsequent droplets for printing. In the Brown device, nondeflected ink droplets strike an exposed side of a diaphram which has a bimorph sensor affixed to the unexposed side. The bimorph transmits electrical signals to a controller which varies the electrical charges applied to ink droplets by an energized charging electrode. These electrical signals from the bimorph vary according to the position of ink droplet impact on the diaphram. Consequently, the diaphram conducts the impact of the ink droplet to the bimorph and protects the sensor from ink impact and wear. Nevertheless, improvement in the sensor outputs was desired to better control ink droplet deflection.
The applicant's invention improves upon the signal generating ability of the Brown device by eliminating the diaphram and directly exposing the bimorph to the impacts of incoming ink droplets. The bimorph is coated with an electrically nonconductive material so that when the sensor is wetted by impacted droplets, the generated signals are not short circuited. In addition, the exposed bimorph is protected by angular plates of rigid material secured to the lid of the catcher housing. These plates are positioned between the bimorph and the housing droplet opening and spaced apart a certain distance to intercept objects larger than a predetermined size. As a result, the bimorph is protected while the housing droplet opening remains large to capture ink droplets of varying trajectories and to limit ink spillage.