HP 1055CMHP - Manual (Page 294)

Functional Overview
10-8
HP DesignJets 1050C and 1055CM Printers Service Manual
remaining ink. These two coils are part of a flex PCB that also
includes the connection pads and the ink leak detection pads.
The ISS board includes the electronics required to measure the level
of ink using this variable transformer. The circuit generates the
excitation signal applied to the primary coil and reads both the
current flowing through the primary coil and the voltage induced at
the secondary coil. The secondary voltage vs. primary current ratio
gives a measure of the coupling coefficient.
The measured ratio increases with decrease in ink remaining, but the
relationship is not linear. Due to the complexity of the bag collapse
process an empirical relationship has been developed using
characterization data obtained in an experimental way. The ratio vs.
remaining ink curves are different for each one of the available
supply sizes (175 cc and 350 cc).
The ISS board also includes the circuitry needed to monitor the
status of the reservoirs. It is possible to check the electrical
continuity of both the primary and the secondary coils and also to
detect if the bag has an ink leak. This last function is performed by
measuring the current flow between the two ink leak detection pads
located in the flex PCB.
Leak Detect System (LDS)
The purpose of the Leak Detect System (LDS) is to detect the
breakage of any of the tubes that deliver ink from the Ink Cartridges
to the Printheads.
With the tube routing, the tubes are continuously stressed in
flexture. When the Carriage moves back and forth, the section of the
tube that is stressed also moves causing fatigue cycling.
When a tube breaks, a small crack appears. As the system is
pressurized, the ink flows through the crack and gets between the
tube and the tube carrier, filling it.
The Carriage end of the tube carrier is sealed with an O-ring that has
been overmolded to the tube carrier. This joint prevents the ink from
going to the carriage. As one end of the tube carriage is plugged, the
ink is forced to go to the other end, which is fixed to the Printer. At
that point, below the end of the tube carrier there is an ink collector
that retains the ink that drops from the tube carrier by gravity.