Ink jet sensor method and apparatus

• US 4,410,895 A
• Filed: 10/26/1981
• Issued: 10/18/1983
• Est. Priority Date: 10/26/1981
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Houston, Robert D., Liptak, Frank J.
• Primary Examiner(s): GRIFFIN, DONALD
• Application Number:
  US06/314,634
• Time in Patent Office: 722 Days
• Field of Search: 346/1.1, 346/75, 346/140
• US Class Current: 347/81
• CPC Class Codes: B41J 2/125 Sensors, e.g. deflection sensors nozzle clogging detection for cleaning reasons B41J2/16579; detection for compensation for failed nozzles B41J2/2139

Abstract

In an ink jet printer, improved ink droplet sensing method and apparatus. The disclosed full width ink jet printer includes a number of ink jet nozzles which direct ink droplets to specific regions of a print plane. The present sensing technique insures ink drops from the multiple nozzles "stitch" together properly across the printing plane. Multiple sensing sites (two for each nozzle) are comprised of a light input optical fiber and two output fibers coupled to circuitry to monitor light intensity at the sensing site. The sensitivity of the site is enhanced by electroformed input and output masks which reduce the effective send and receive area of the optical fibers.

Claims

1. In an ink printer having one or more nozzles for directing one or more ink streams toward a recording medium, apparatus for sensing the presence of individual droplets from said one or more ink streams toward a recording medium, apparatus for sensing the presence of individual droplets from said one or more ink streams in their trajectory toward said medium comprising:

at least one input optical fiber for each nozzle having a first end coupled to a light source, said input optical fiber directing light from said source to an associated planar sensing site from a second end, so that droplets following certain trajectories over the planar sensing site intercept said light;

two output optical fibers being provided for each input optical fiber, the output fibers having receiving ends for receiving light from their associated input optical fiber, the receiving ends of each of the two output fibers being adjacent each other and located in the planar sensing site of their associated input fiber, the receiving ends of the output fibers being positioned in spaced relation to said input fiber second ends, each of said two output fibers having ends opposite the receiving ends which terminate at a separate photodetector, so that changes in light intensity caused by passage of said droplets past said planar sensing sites may be detected; and

a mask being interposed between said output fiber receiving ends and the region of ink droplet travel above the planar sensing site to mask light received from the input fiber and define two circular optical receiving sites for each sensing site, one receiving site for each receiving end of the two output fibers and each receiving site having an area less than the receiving ends of the output fibers, the receiving ends of the output fibers abutting said mask, so that only a portion of the output fiber receiving ends is exposed to light directed to that particular sensing site by the input fiber.

2. The apparatus of claim 1, wherein the photodetectors have outputs coupled to a difference amplifier and wherein the two circular optical receiving sites in said mask are positioned for zero dimensional separation of the receiving site boundaries in the drop deflection direction, so that any droplet traversing this boundary provides a maximum gradient of differential signal from the difference amplifier, thus enabling more precise droplet stitching control.

3. In an ink jet printer having multiple nozzles for directing a plurality of ink streams toward a recording medium, apparatus for sensing the presence of individual droplets from said streams as they move toward said medium comprising:

a plurality of light sources mounted across the printer width such that each nozzle has two light sources for sensing droplets as they are deflected away from their initial trajectory,

two optical sensing fibers mounted near each of said light sources to collect light from said sources and having input surfaces located so that the droplets may pass between an associated source and said fiber input surfaces,

masking means positioned between said input surfaces and said droplets to define a plurality of sensing sites, each site having two transmitting regions spaced from each other along the direction of droplet travel to allow light from a light source to impinge upon one of the two sensing fibers for that sensing site, and

means for sensing movement of ink droplets past said sensing sites by detecting changes in the intensity of light transmitting through said sensing fibers.

4. The apparatus of claim 3 which further comprises a mask mounted in close proximity to said light sources including light transmitting regions at each sensing site which limit the area of said light sources and wherein said sources comprise optical fibers coupled to a light emitting diode.

5. The apparatus of claim 3 or 4 which further comprises means for supporting said output optic fibers having an opening through which said fibers extend to a sensing site and including means for limiting moving away from said site while allowing bending and flexing of said fibers.

6. In ink jet printers having multiple nozzles for directing a plurality of ink streams toward a recording medium, a method for sensing the presence of individual droplets from said streams as they move toward said medium comprising the steps of:

mounting two light sources for each nozzle across the printer width for sensing droplets as they are deflected away from their initial trajectory;

directing the light from each of the light sources to a sensing site;

collecting the light from the light sources at the sensing site by two optical sensing fibers at each sensing site, the optical sensing fibers having input surfaces locates so that the droplets may pass between an associated light source and said fiber input surfaces;

positioning a masking means having two circular passages therethrough for each light source between said input surfaces and said droplets to define two transmitting regions spaced from each other along the direction of droplet travel to allow light from one of the light sources to pass through said circular passages in the masking means and impinge upon the two sensing fibers for that sensing site, each of the two input surfaces of said sensing fibers abutting a respective one of the circular passages in the masking means, and each circular passage having a smaller area than its associated sensing fiber input surface; and

sensing the movement of the ink droplets which pass said sensing sites by detecting changes in the intensity of light transmitted through said circular passage and said sensing fibers.