Figure 1: Developer powder flow in a channel observed with visible ray
Figure 1 shows developer powder flow in a channel observed using visible ray. The shape of the rotating screw is scarcely visible and the detailed flow cannot be observed.
Injecting a tracer, which has a high X-ray-absorption rate, enables visualization of the internal flow structure with X-ray. Because X-ray penetrates the developer powder and the container, the tracer movement inside the flow can be observed. We have confirmed that the tracer shows a good tracking ability for the developer powder flow. Thus, observation of the tracer reveals the characteristics of the powder flow.
Figure 2: Structures of flows of developer powder transported by screws of various types visualized with X-ray
Figure 2 shows flows of developer powder transported by screws of various types. The flows are visualized by path lines in color. The color indicates the length of time. The flow characteristics are easily grasped from the images. Computer image processing analysis of tracer behavior can quantitatively measure flow velocity and the magnitude of mixing.
Since the fluid dynamics equation (the Navier-Stokes equation) cannot precisely represent the powder flow because of its complexity, the definite element method (DEM) is used to predict the flow. The method calculates the movements of all the particles composing the powder. Although the method can exhibit the flow precisely, the calculation time is long because the powder is composed of a huge number of particles.
Figure 3: Area-divided calculation using cluster computing
To solve this problem, we have developed a cluster computing system in which all the computers are interconnected by a high-speed LAN. For the system, we have developed a program involving division of the powder flow into areas, assignment of each area to a computer, and distribution of the computation load (Figure 3). The method dramatically reduces calculation time.
Figure 4: 3D simulation of magnetic brush calculated by DEM
Figure 4 shows three-dimensional behavior of the developer powder, namely, the magnetic brush phenomenon, calculated by DEM with the system.
In a development process, an elastic blade is pressed hard against the developer powder in a narrow channel to electrically charge the toner. Figure 5 shows computer simulation results of the process. The color of the powder indicates the initial particle location. Transportation and mixing of the powder around the blade are presented clearly.
Figure 5: Computer simulation results of developer powder passing around the blade in a narrow channel
The simulation method is useful in designing the development process. Beyond that, the visualization technique is needed not only for observation but also for validation to improve accuracy of the simulation. It is necessary to enhance these technologies simultaneously.