HP Design Jet 750C
M3 has owned this printer for about the entire life of the company. It is a full-color, ink jet paper plotter. It was well-used for many years. Of late, it has not been regarded very highly. Rather than retire to the pasture, its carcass has been donated to science and to the mercy of the Mechatronics Team…
We expected to find a lot of interesting goodies inside, and were well-rewarded in that regard. This teardown has helped with the design of a film feed system for another client.
Before we got started, we gave the printer one last chance to prove its worthiness to live. We powered up the printer – the lights flashed, things jolted, and then died. We didn’t try again.
The printhead carriage is shown below. While there are a number of moving mechanisms, there are only two major axes. The other “carriages” including the maintenance stage and cutter are engaged and driven by the printhead carriage. This eliminates redundant drive hardware, but also forces the head to leave the maintenance area to perform routine operations like cutting.
Unlike Epson printers, this product uses a thermal ink jet system – like Canon’s bubble jet. The cartridge and print heads are all one, disposable unit. In contrast, an Epson head stays with the printer – only the ink cartridge is replaced. Color scheme is CYMK.
Our ME team dismantling the HP.
Carriage drive hardware. This used a DC servo motor with a linear encoder tape supported in free space as the feedback device. A toothed belt was the actuator.
Cutter mechanism is cool — the printhead carriage picks the cutter up via a two-way catch. If the carriage moves past the first catch the cutter connects to it. Once the pair have returned the cutter to a home position the carriage moves past the second catch, releasing the cutter.
Power entry and distribution board:
Head drive electronics shown at bottome of carriage. The cable track was simple – the ribbon cable was clamped in a semi-circle profile at top and bottom to impart enough flexural rigidity for it to be self-supporting.
The paper feed/release mechanism communicated (via mechanical linkage) to this sensor and flag.
Head capping and maintenance station.
Vacuum pump drive. This mechanism used multiple cams to pinch shut solvent tubes to each ink cartridge during cleaning. An eccentric shaft provided the reciprocating mechanism for a diaphragm pump using a one-way spring clutch.
