Ricoh has developed X-ray visualization and computer simulation techniques for analyzing
developer powder flow in copiers and printers.
New Observation Technology for Designing Development Process for Copiers and Printers
Electrophotographic devices such as copiers and printers use developer powder to form
images. The powder consists of resin toner with a diameter of 5 to 6 microns and ferrite carrier with a diameter
of 30 to 50 microns. Whereas the toner forms images directly on paper, the carrier transports the toner in the
machine. Developer powder is continuously circulated and mixed by rotating screws or paddles. In the development
process, toner is consumed to form images. Control of the powder flow is important for stabilizing image quality.
Instability of the powder flow causes problems such as image bleeding and toner scattering.
When designing a new development process, the developer powder flow must be predicted precisely. However, since
the powder flow exhibits complicated behavior, it is difficult to predict the flow using conventional computer
simulation. Moreover, experimental evaluation is also difficult because observation inside the developer powder
flow is impossible with visible ray.
In view of this background, Ricoh developed a new observation technology called X-ray visualization, and a new
numerical simulation method called powder flow simulation employing parallel computing.
X-ray Visualization of Developer Powder Flow
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.
Powder Flow Simulation with Parallel Computing
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.
Ricoh's Technology
X-ray visualization
The X-ray visualization we have developed provides precise information on what happens
inside the developer powder flow. Using the technique, we have made new discoveries concerning the powder flow.
Information on the great variation in powder flow structure depending on the screw configuration is particularly
useful. A research paper on the discoveries received an annual congress award of the Visualization Society of
Japan in 2008.
Powder flow simulation with parallel computing
Practical application of DEM for calculation of powder flow was not previously available.
Ricoh realized practical application of DEM by employing a cluster computing system and optimized parallel programming.
A two-dimensional simulation tool is now available for designing the development process.
Enhanced Product Value by Applying Visualization Technology in the Production Process
In accordance with its "Create without Making" policy, Ricoh has been promoting rapid
large-scale reform of the product development process and other processes. The visualization technology described
here shows how Ricoh's emphasis on computer simulation is a source of decisive advantages.
? The visualization technology plays a vital role in clarifying the physical mechanism in an important process.
By employing this technology, we are enhancing product value.
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