A new method of ink drop velocity measurement has been developed. A plane electrode facing to an ink jet head charges an ink drop and then detects the current induced by this flying ink drop. The drop velocity is calculated from ink drop flight time. This method achieves accurate and quick measurement of a multinozzle ink jet head with a simple construction.

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Specific features of the magnetography by optical writing are elucidated in the study of the recording and developing characteristics. Firstly, the londitudinal and perpendicular modes of magnetic recording are compared in relation to magnetography by a simulation study using a magnified scale model. Secondly, experimental studies of the optical writing and the developing characteristics for CrO₂ specimens are carried out. The results are shown on the longitudinal recording mode and the optimum method for optical writing is discussed.

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In thermal transfer printing, the analysis of thermal diffusion is a serious problem with respect to printing quality. The problem of thermal diffusion is solved, using the finite difference method in a two dimensional substrate/ink/paper domain. Experimental data of a temperature profile of a thermal head are applied for boundary conditions.
These expererimental data converted into the temperature data of the loaded thermal head by computation, and used as boundary conditions. Because the computing domain does not include the thermal head, the computing time and the required memory area of the computer are decreased. The heat of fusion and the heat of solidification of the thermal transfer ink, and the movement of a serial head are considered in this calculation.
Some examples are calculated by this method. The following are obtained in conclusion.
1. Applied energy varies very much with the characteristic value of ink.
2. The effect of an ink ribbon with a substrate of good thermal conductivity is not much expected.
3. Good quality of printing on rough paper may not be achieved in view of thermal diffusion.
4. At the continuous printing, transfered ink may be melted again by thermal diffusion of the subsquent heat of resistors.

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Image of non impact color printer using dry toner is formed with toner particle of 10 µm or so, while offset print image is formed with ink film of only 1 µm or less thickness. To minimize the difference of Color reproduction of both image, &ldqup;microstructure&rdqup; of image in dry toner system has been discussed in this paper.
Image structure factors concerning color gamut are extrected, and the quantitative relationship among these factors identifies an optimum image structure. This paper indicates the possibility to achive the image quality of dry toner system eguivalent to offset printing.

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Paper handling technologies have been developed actively. It is important to obtain a better paper registration accuracy with a small registration system using paper curl. In this system, the paper hits the gate and makes a curl. Then the gate moves down and the paper is released. The motion of paper in this case has been analyzed. The theory about bending vibration of elastic beam can apply to the motion when the deformed curl paper is flattened. And it has been confirmed that the theory fits in with the experiments.

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In October, 1984, Canon announced the two-sided copying machine NP-7550 equipped with the recirculating document feeder. In this copier, the shape of the holding guide plate was devised to put the first-side copied paper in the duplexing tray so that there is no movable parts in the paper storing area. Therefore, the durability was dramatically improved and the cost was effecitvely reduced. After the various inventions, high reliability was confirmed in any conditions.
Partial inter-meshing upper separation roller and lower separation roller were introduced for the paper feeding in the second pass. From the experiments, the amount of overlap and the readjustment method of the overlap after wear were decided. Re-adjustment of the worn (partially worn) partial inter-meshing rollers was achieved by controlling the driving torque (friction torque) of the feeding roller, fixing a sheet of paper between them.
It was considered from the endurance test that the reliability is maintained actually through overwhole intervals under one re-adjustment stated above after the installation of the copier.

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