To meet the demands for increased speeds in color printing, 4-drum tandem engines are becoming the standard in color copiers and color laser printers.
4-drum tandem engine
Whereas the conventional method for color printing involved transferring an image via a 4-step process that divided an image into four colors and printed each color individually, the 4-drum tandem engine arranges independent imagining units for black, yellow, magenta and cyan into a single line. The timing is aligned with the paper feed, and all four colors are processed consecutively.
This makes it possible to print a color A4 page at high speeds similar to those in monochrome printing - 25ppm (small machine) to 60ppm (large machine).
High-quality printing needs
For network printers with large paper feeders, large color photocopiers, and mid-sized high-end devices supporting high-quality, high resolution printing, it is necessary to measure the electric potential on the surface of the photosensitive drums and optimize the electrification status, as performed to the conventional single drum machines, in order to reduce development quality gaps caused by environmental humidity changes and overuse/continuous use.
Need for 4CH-specific surface potential sensors
It goes without saying that machines equipped with 4-drum tandem engines are easily able to achieve a high level of image quality control by incorporating the brilliant sensing capabilities of the EFS series.
However, creating a control circuit specifically designed for the 4-drum tandem engine would enable rationalization, such as using just one high voltage circuit for the feedback of detecting voltage. When you consider this, it quickly becomes clear that in terms of board space and cost, there are limits to the current method of using a probe and a control circuit for each of the four photosensitive drums.
To solve this issue and to support the needs of downsizing and low pricing which high-speed color output systems are facing, TDK sought high-efficient and small-sized designs and produced 4-probe control circuit boards optimized for 4-drum tandem engines. Below are the overview and basic specifications of the board.
Significant size and cost reductions realized through unique design rationalization
The detecting voltage control circuits all share the feedback high-voltage generator circuit (high voltage amplified). At the same time, we have developed a unique rationalized circuit that can control 4CH detecting potential simultaneously without the need for sequence. The area of the resulting board, on which all 4CH detecting voltage control circuits are mounted, is approximately 67% of the area required by the conventional method of joining together four individual probe control boards. Also, this allows for significant cost reduction, an extremely difficult task in the conventional method of applying a probe and circuit combination to each of the four individual photosensitive drums.
Single offset adjustment method using a sub-board that removes the one-to-one relationship between board and probe
Up to now, the configuration involved a cable connected to each control circuit board, each of which had its own corresponding probe. This meant that the probe offset adjustment construction was also mounted on the control circuit board, and the entire device was delivered as an optimized set. As a result, the probes and control circuit boards always had to be treated on a one-to-one basis during the process of loading them into the printer. When replacing a probe as a service part, it was necessary for the customer to perform an on-site probe offset adjustment for the probe after installation.
In developing the 4CH/1 control circuit method, consideration was given to making device installation and maintenance work simple and rational. An intermediary sub-board was fitted onto the end of each probe cable and the probe offset mechanism and connector was installed there.
Using this setup, the independent adjustment of the probe unit is made possible. This means that during device installation, as well as for stock management, control circuit boards and probe units can be treated as separate and universal. On-site probe replacement services can also be done without any need for adjustments.
In addition, it is possible to stock probe units as necessary, significantly speeding up the maintenance process.