There is growing demand for small and inexpensive laser printers that can offer the speed, image quality, and reliability suitable for the business environment. In a tandem color laser printer, the exposure and developer units of Y, M, C, and K are placed in line, and an intermediate transfer belt rotates below them. A full-color image is formed by transferring a toner image onto the intermediate transfer belt one color after another. Thus, belt walk of the intermediate transfer belt must be suppressed to prevent toner image displacement among different colors, and thus achieve a high-quality color image.
Existing high-speed printers adopt a method of detecting the amount of belt walk with a sensor and adjusting the tilt of a steering roll that controls the direction of belt walk. In contrast, a protruding part called the rib is attached to the inner peripheral surface of the belt in low-speed printers. Engaging the rib with the depression of the steering roll reduces belt walk to a minimum level. This time, we have developed a new auto belt walk suppressing technology (called Leverage Self Belt Aligner or LSBA) for small color laser printers. (Fig. 1)
This technology forms an intermediate transfer belt unit with a drive roll and a steering roll. One end of the steering roll is fixed, while the other end has a pulley, an arm, and a coil spring attached, as shown in Fig. 1. Belt walk can be suppressed to a minimum by maintaining the steering roll at a right tilt angle.
The belt walk suppressing mechanism is explained below.
The belt moves to the pulley side under the default setting. Force (1) is generated along the edge of the steering roll when the belt contacts the pulley. Then force (1) is transformed into force (2) that makes the arm (fixed at one end) push down the shaft based on the "principle of leverage." Along with the shaft, the spring is also compressed.
The tilt angle of the steering roll is thus adjusted automatically to balance out force (1) and the spring's repulsive force. In this way, belt rotation is stabilized and belt walk can be suppressed to a minimum.
In principle, this technology is not affected by the belt rotation speed. Thus, belt walk can be suppressed with high precision even when the belt rotates at high speed. With this advantage, increasing the rotation speed of the intermediate transfer belt allows small color laser printers to achieve high productivity.
Fig.1: Image of auto belt walk suppressing mechanism