Original HP OfficeJet 5740 Printer (photo credit HP Inc.)
The main concerns with converting the printer to function without gravity were:
Very early on, it was determined that the actual printing from ink cartridges to paper would not pose a problem in zero-gravity. This is because HP thermal inkjet technology uses thermal excitation to expel tiny droplets of ink about 3 picolitres in volume (1 tablespoon equates to about 15 billion picolitres). Therefore, gravity has insignificant effects on print quality due solely to the cartridge print head. To verify, Simplexity and HP separately ran negative gravity print tests, by printing upside down. The results proved the ink cartridges themselves are not an impediment to zero-gravity printing.
Printer mounted upside down to confirm that print cartridges and paper handling would function correctly in zero-gravity
Computer Aided Design (CAD)
of sheet metal output tray
Prototype of sheet metal
Dis-assembled MJF 3D printed
output tray (photo credit HP Inc.)
PAPER HANDLING: CONTAINMENT OF PRINTER OUTPUT
The standard output paper tray on the HP OfficeJet 5740 is open, which could allow the paper to float away after printing in zero-gravity. Thus, a new paper tray needed to be designed that would capture the output. Initially, a sheet-metal tray with a cover was designed to hold the paper.
Then, HP converted the design entirely to MJF. The advantage of switching to MJF 3D printed parts was a significant reduction in unique part count, including the elimination of 18 mechanical fasteners, impossible with conventional sheet metal. Simplexity performed post conversion refinements to help enable the final MJF design.
Though HP had previously developed a hinged bail concept for a multifunction product, Simplexity leveraged this concept and designed a hinged bail with a curved lip to capture media during ejections, especially in fast print modes, through extensive print testing to determine the proper shape and orientation. The bail design was later converted to MJF.
Simplexity helped solve the challenges posed by dedicating one of the most printer-experienced teams, with cumulative combined printer-experience exceeding 50 years. In Simplexity engineers, who had prior involvement with the design and development of the original HP OfficeJet 5740 printer, HP found the experienced team to minimize risk and design cycles.
A prototype finger used to bias media on to the output tray
Closeup of the biasing "fingers" in the output tray
HP print cartridges mounted inside the carriage that travels side-to-side (photo credit HP Inc.)
PAPER HANDLING: PAPER FEEDING AND PRINTED PAGE OUTPUT
A challenge in paper feeding was to redirect printed media to mitigate the risk of paper jams due to potential collisions within the enclosed output tray. We took HP’s design concept of flexible “fingers” and engineered them to gently bias the paper to the bottom of the output tray during paper feed and eject. Working with HP engineers, the fingers were designed and tested for the optimal size, location, and material properties to provide the appropriate bias, while minimizing paper path risks. Video capture of finger angles during paper feed testing was utilized for verification. Additional print tests were performed to show fingers did not mar ink on prints. All the changes were later validated during a zero-gravity flight test. The final output tray was manufactured using HP Multi Jet Fusion (MJF) technology.
HANDLING THE WASTE INK
When a printer prints, periodically ink is expelled from the ink cartridge into a spittoon for pen maintenance. The process of spitting ink creates puddles that are gradually captured by a sponge-like absorber. However, in zero-gravity ink puddles may not be absorbed, but may migrate. Therefore, in partnership with HP engineers ink absorbent materials were allocated throughout the printer internals since ink could travel elsewhere. Verification of absorber attachment was tested in environmental and drop testing. Paper feed tests proved non-interference.
MOUNTING OF THE PRINTER TO THE ISS
Since the printer cannot be simply placed on a table in the ISS, a method for attachment was needed. Simplexity designed a rigid sheet metal bottom plate, which allows the printer to be attached to various points on the ISS using hook-and-loop fastening. Simplexity performed mechanical load testing to verify the plate’s structural integrity.
Print quality is affected by many different factors. One factor that affects print quality is the distance of the print cartridge from the paper. In the original HP Officejet 5740 printer, the print cartridge is mounted on a carriage that moves side to side during printing.
The distance between the bottom of the print cartridge and the paper is set by the carriage being biased down by gravity. For the absence of gravity, working with HP Engineers, we helped design spacers to maintain the proper pen to paper spacing during print operations. These spacers also withstood excessive wear due to the printer carriage cycling back and forth.
Simplexity modified the base Officejet 5740 firmware extensively to enable the space ready printer. Firmware code modifications focused on removing scanner, automatic document feeder, and related functionalities. Simplexity extensively tested the firmware revisions in collaboration with HP prior to release.
The highest risk area was the inability to verify the engineering design in zero-gravity conditions during product development. While we ran print tests in various printer orientations, including upside down, any paper feed error or paper jam could behave differently in an actual zero-gravity environment. The Simplexity and HP team had one chance at passing product validation through a pre-planned zero-gravity flight test at the end of the development phase, where an airplane flies parabolically at high altitude, representing about 20-seconds of zero-gravity conditions during fast descents.
HP Envy ISS Printer (photo credit HP Inc.)
The test was successful! Through months of careful planning, anticipation, testing and working with the HP team, all the design changes were validated successfully during the first zero-gravity flight test. Simplexity was also chosen by HP to assemble and deliver all 50 flight-ready printers to NASA. While only 2 printers are on the ISS for printing, the others are built at the same time to have replacements for years to come.
The final printer is called the HP Envy ISS. Simplexity is honored to be selected as HP’s engineering partner to help deliver HP’s first ever space-ready printer.
Simplexity Technical Team reviewing the output tray assembly.
Simplexity Technician assembling ink absorbers into the HP ENVY ISS Printer. The added absorbers are designed to capture ink in the zero-gravity environment.
Simplexity CEO, Dorota Shortell (center) with the HP Specialty Printing Systems (SPS) team at the worldwide announcement of the HP Envy ISS printer at HP Headquarters. The jackets are custom-made by NASA for this mission, including the project patch.
NASA project patch that is sewn onto the jackets to commemorate the HP Envy ISS mission (photo credit HP Inc.)