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Media Path for a Small, Low-Cost,
Color Thermal Inkjet Printer
The DeskJet 1200C media path is heated for media independence,
requiring development of a new grit drive roller and pinch wheel
combination. A new stepper motor was developed to attain the target
speed and accuracy. Media flatteners and precise gearing with an
antibacklash device contribute to accuracy.
by Damon W. Broder, David C. Burney, Shelley I. Moore, and Stephen B. Witte
The media path is the part of a printer that moves media
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Right Shim • Move media very quickly through the print area while main- taining high placement accuracy for good graphics print Center Shim quality. • Keep the price low. The parts of the media path (Fig. 1) that drive and meter the media include the stepper motor, the drive pinions, the drive gears, the antibacklash device, the shaft bushings, the ad- justable plate, the drive rollers, and the pinch rollers. While driving the media these components work together to en- Grill sure fast, accurate
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Writing Zone A traction surface designed to tolerate thermal shock with a Preheater low thermal expansion needed to be developed. The low- cost, high-quality advance mechanism goals also required a reliable manufacturing process that would produce 100% in-specification parts. The traction surface characteristics were initially defined from a customer satisfaction viewpoint: • The combination of nip pressure and drive roller roughness Main Heater could not mar transparencies or leave tracks in pl
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Stepper Motor Simulation Model The model used to simulate a permanent magnet stepper motor for the simulations simulated velocity clearly does not reach the desired 1400 steps per second. This described in the accompanying article originated from a classic control systems motor fails and stalls in the real system. In Fig. 3,* the simulated velocity of a point of view. The model includes simple position and velocity feedback control 2-ohm motor is shown. In this successful run, it appears that th
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1600 0.8 1400 0.6 1200 0.4 1000 0.2 800 0 600 –0.2 400 –0.4 200 –0.6 0 –200 –0.8 0 0.005 0.01 0.015 0.02 0.025 0 5 10 15 20 25 30 Time (seconds) Time (ms) Fig. 2. Simulated velocity profile of a failing motor (8-ohm). Fig. 4. Simulated currents in a failing motor. 1.5 1600 1 1400 1200 0.5 1000 0 800 600 –0.5 400 –1 200 0 –1.5 0 5 10 15 20 25 30 –200 0 0.005 0.01 0.015 0.02 0.025 Time (ms) Time (seconds) Fig. 5. Simulated currents in a stable, running stepper motor. Fig. 3. Simulated velocity pro
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Reducing Stepper Noise. Once we had the speed that we move at slow speeds by using two function generators con- needed, we had several more hurdles to pass. It was neces- strained in a phase-locked loop to be 90 degrees out of phase, sary to control the motor and make it start and stop pre- then connecting their amplified outputs to the phases of the cisely without the noises that normally come from stepper motor. Effectively, this became a sine-wave drive for the motors. When the first DeskJet
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stepper at slow speeds. For the first time we could measure Mean + 3 0.1080 Measured pinion quality after the gears had been mounted on the motor 0.1075 shaft. With this measurement ability, we were able to work 0.1070 with the vendor and resolve tricky problems such as damag- ing the pinions and bending the motor shafts while mounting 0.1065 the gears on the shafts. The resultant print quality of the HP 0.1060 DeskJet 1200C printer is good enough that few swath ad- 0.1055 vance accuracy proble
