Canon BJC 6000 Service Manual - Page 115

BJC-6000 Part 4: Technical Reference 5.1.4 Ink sensor Consists of an LED and photosensor to optically check for ink in the ink chamber part of the ink tank. At the ink chamber bottom is a protrusion that acts as a prism. If ink is present in the chamber, the refraction rates of ink and the prism resin are nearly equal, producing less reflection. If there little ink left, the difference in refraction rate between the ink and the resin increases so that more incident light to the sensor will be reflected, thus increasing the intensity of reflected light. The printer decides whether there is any ink in the ink chamber or not based on the difference in the amount of reflection. The MPU, then, detects the voltage varying with reflection, and the the A/D converter converts this analog voltage to a digital value. When the printer decides that there is no ink left in the ink chamber, it generates a message on the status monitor telling that ink is running low in the relevant ink chamber. After the printer has decided that no ink is left, it starts counting the number of dots equivalent to the amount of ink absorbed in the sponge (20% of the ink) to detect "ink-out." This detection takes place when the power is on, the front cover is closed, after pumping operations are completed, or after a specified number of dots have been printed. Do not open the front cover while measurement is going on, as external light can make accurate measurement impossible. Note that ink tank presence cannot be detected. If no ink tank is installed, the printer will determine that ink is present. Ink Refracted Light Ink Chamber Air Incident Light Photo-transistor Ink Sensor Ink Present Reflected Light Incident Light Photo-transistor Reflected Light Ink Sensor (Full Reflection) No Ink Figure 4-36 Ink Sensor Prism 5.1.5 Cover sensor Detects whether the front cover is open or closed. If the printer detects the cover is open, the carriage is moved to the replacement position. 5.1.6 Pump sensor Switch-type sensor that detects the rotational position of the tube type pump. The printer controls the pumping operation based on the detected rotational position of the pump. 5.1.7 Printer temperature sensor (TH201) Located on the control board, this sensor detects the temperature inside the printer to control the print head drive. The thermistor resistance varying with the temperature inside the printer is detected by the MPU as a varying voltage, so the incoming analog values are converted into digital values by the built-in A/D converter. 4-43