IBM 3800 Laser Printer


 IBM 3800 Laser Printer Development
Technical Exchange presented February 1970

In the late '60s, IBM San Jose began development of an electrophotographic printer to replace the mechanical chain printers.  The project code name was Jubilee, later became Argonaut, and the product was announced in 1975 as the IBM 3800.  Using continuous forms rather than sheet feed paper, it printed at a speed was 32"/sec or about 180 pages per minute.  The fastest IBM printer at that time was 1,100 lines per minute or about 17 pages per minute.

Prototypes used a 5,000 page/month IBM copier which had to be completely redesigned to meet the typical customer demands for over 1,000,000 pages/month.   Inventions were required in all areas: paper handing, electrophotography, optics, materials, fusing, electronics, etc.  This was one of the first products to use a microprocessor rather than a hard-wired controller.

The technology and innovations of the 3800 paved the way for the inexpensive but slower desktop laser printer available today.

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IBM held an annual Technical Exchange to update technical personnel about various programs throughout the lab.  Two sessions were required in the Century 21 movie theater to accommodate San Jose lab's huge attendance.  This presentation lasted 20 minutes.
On the left is a concept drawing of the printer.  It's about 5 feet high and perhaps 12 feet wide along the front.  The control unit is on left back with the printer along the front.  Most of the volume in the control unit was for the 4 kilobytes of TROS memory.  There was one gate of electronics.
Here's the printer with the paper path shown in green.  Continuous form (fanfold) paper is feed from a box on the left.  The control unit sends formatted data to the CRT which in turn exposes the photoconductor on the rotating 30" diameter drum.  The resultant electrostatic image on the photoconductor is developed with toner.  Next the toner image is transferred to the paper.  The paper pass through the fuser that melts the toner into the paper then continues to be refolded on the right.
IBM contracted to have this 14" fiber optic faced CRT developed for exposing the photoconductor.  It was later replaced with an LED array.  Neither transducer was suitable because they were too easily damaged by the electrophotographic process.  This lead to the development of a state-of-the art gas laser and 17,000 rpm precision faceted rotating mirror.
The light from the CRT/LED/laser exposes the photoconductor forming an electrostatic image on the photoconductor.  The image is then developed with toner and transferred to the paper as print.  Unfortunately, there are distortion in the process requiring corrections to the exposure shape.  On the left is the predicted character and on the right is the actual character.
This details the step of transferring the developed image from the drum to the paper.  The drum is continuously turning with a surface speed of  32"/second.  When data is ready for transfer to the paper, the paper must be lowered to the drum and accelerated to match the drum speed and image position.  Also, once each drum revolution the paper must stop and separate from the drum  to let the photoconductor seal pass.  The upper image is a profile of the paper and drum.  Below is a graph of the paper's position versus time.  The challenge is like merging a car into traffic.  In this case, we had only 0.022 second to merge into position within 0.002 inch.  Too fast or too slow would smear the image.  Misregistration could occur too.
Here an engineer checks the temperature of the fuser.  This is an early robot that used roll paper to simplify paper handling.  Static sparks from the fast moving paper caused electrical interference with many of the tests.
This is another test robot but the real reason for the photo was the beards.  There were about 100 people in our program and we enjoyed each other's company.  Those were the fun days!

Copyright Protege Marketing 1998 - Revised 05 Aug 2005