Functional Overview

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.

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HP DesignJets 1050C and 1055CM Printers Service Manual