Chapter 2 Literature Reviews
2.1 Printing Technologies
2.1.2 Laser Print
The process of forming images in laser printer can be divided into six steps.
Step 1: Drum preparation - In preparation for printing, the drum must be cleaned to remove any traces of previous pages. First, a rubber blade wipes the excess toner from the drum, and then erase lamps (in older models) or a charged drum (in newer models) electrostatically clean it by neutralizing residual electrical charges on it.
Step 2: Drum writing - The data in the printer’s memory is written to the drum using a laser. Rather than writing it with ink or toner, however, it writes by shining a very precise laser on the photosensitive drum in certain spots, changing the electrical charge in those spots.
As the drum cylinder rotates past the laser, it sweeps across the surface, turning on and off to neutralize certain areas to about -100V. These neutralized areas will be the spots where toner adheres to the drum later in the process and then transfers to the paper.
Step 3: Paper feed - Feed rollers draw the paper into the printer from the paper tray.
The toner cartridge contains a rotating, magnetic, metal-developing cylinder, a toner reservoir, and a height control mechanism that limits the amount of toner the cylinder can pick up at a time. Toner consists of plastic resin particles (the particles that melt to produce the image on paper) and iron oxide (the particles that are affected by magnetic attraction and electrical charges). The toner’s metal particles adhere to the magnetic cylinder, and the cylinder presents the toner to the drum as it passes by.
Step 5: Toner transfer to paper - At this point, the image exists on the drum, complete with toner. As the paper feeds into the printer, the transfer corona applies a positive charge to the paper. When the paper passes by the drum, the -100V charged toner on the drum jumps off onto the positively charged paper. Then, the paper runs past a static charge eliminator, which is a row of teeth with a negative charge that reduces the paper’s highly positive charge.
Step 6: Fusing the toner to the paper - The image is on the paper, but it’s not secure there; it’s just loose toner held in place by gravity and a weak electrostatic charge. For permanent application, it must be fused. Fusing is basically melting the toner’s particles so that they stick, or fuse, to the fibers in the paper.
Fig.2.3 and Fig.2.4 show the components of laser printer and the paper path while printing [6].
As shown in Fig.2.5, while printing, paper rollers and ink ribbon rollers rotate, and the line velocity of the paper is the same with ink ribbon. At the same time, the thermal print head is pressed against the platen roller. The ribbon with yellow, magenta, cyan dyes and an overcoating will sublimate to vapor because of the heat generated from the thermal print head, and then be absorbed by the coating on the special paper step by step. Since each heating element on thermal print head can generate 256 gradients of heat and there are three different colors of dye, D2T2 can print a colorful image with 16 million colors. Besides, compared with other print technologies, there is an overcoating on the photo printed by D2T2.
Therefore, the photo preservation is easier and there is a better resistance to ultraviolet, water, or dirt. There are three steps during the printing process [7].
Step 1: Ribbon Searching – Before printing, the ribbon must be located at the initial position for the whole printing. As shown in Fig.2.6, the paper is at the opposite side of the printer at this time. The ribbon rollers rotate to search the initial position of the ribbon.
During this step, the tension of the ribbon is in a loose state.
Step 2: Paper Feeding – As shown in Fig.2.7, the paper is drawn into printer by capstan roller and passes through the platen roller to the other side. At this time, the ribbon rollers are fixed.
Step 3: Printing – As shown in Fig.2.8, when the ribbon is ready for printing, thermal
paper will be rewound to the state before printing for the next color printing until all the dyes of yellow, magenta, cyan and the coating are printed on the paper.
2.1.4 Thermal Wax Transfer
Thermal wax transfer is also called thermal transfer. It typically consists of a donor, a receiver and a thermal print head. In the case the thermal print head has a fixed energy level and results in an approximately fixed dot size and constant density. This system is shown in Fig.2.9.
Thermal wax transfer printers operate with the same steps as dye diffusion thermal transfer printers to form images on papers and the configuration is almost the same.
Thermal wax transfer printers use cyan, magenta, and yellow wax type of pigments instead of dye to produce images. Thermal wax transfer has a binary process. It means that for a given location on a page, either a lot of pigments are deposited or not. And various dithering techniques are used in order to create half tone level [8].
2.1.5 Variable Dot Thermal Wax Transfer
The working principle of variable dot thermal wax transfer is almost the same with thermal wax transfer. The difference is that in variable dot thermal wax transfer, the thermal print head is able to modulate energy. This results in a dot with a roughly fixed density but
2.1.6 Continuous Tone and Half Tone
As shown in Fig.2.11 and Fig.2.12, for example, while generating a gradation from black to white, the printer with continuous tone can form the continuous color gradation because each dot has its own fullness of color. But in the printer with half tone, each dot has only one kind of color fullness, and it must use the dithering technique which is that there are lots of dots close to each other in a small area, and changing the density of dots to simulate the gradation. Therefore, the image quality of half tone can not reach the quality of continuous tone, especially when enlarging the photos.
For this reason, more dots per inch are needed in the printer using half tone to form clear images. But using continuous tone, 300 dots per inch is enough to form clear images. In above printing technologies, only dye diffusion thermal transfer is continuous tone. Variable dot thermal wax transfer is close to continuous tone, and the others are half tone [7].
2.1.7 Comparison with These Printing Technologies
Compared with inkjet, laser, dye diffusion thermal transfer, thermal wax transfer and variable dot thermal wax transfer, laser and inkjet are not fit for the requirements of mobile printer because the configuration of the laser printer is more complicated and inkjet needs larger space for the print head movement. Therefore, dye diffusion thermal transfer, thermal
performance, dye diffusion thermal transfer is the best because the way to form color gradation is continuous tone, and the performance of thermal wax transfer is inferior in the same dpi. As shown in Fig.2.13, the figures from left to right are printed individually on thermal wax transfer, variable dot thermal wax transfer and dye diffusion thermal transfer.
In continuous printing, thermal wax transfer and variable dot thermal wax transfer are better than dye diffusion thermal transfer because less energy is required to melt wax than to diffuse dye. Therefore, the thermal print head in dye diffusion thermal transfer may overheat while continuous printing. For the same reason, in power consumption, dye diffusion thermal transfer is higher than the others. Consequently, with the same power, thermal wax transfer and variable dot thermal wax transfer can print more pieces than dye diffusion thermal transfer.
Finally, in the cost, because the pigment (wax) and the receiver (paper) of thermal wax transfer or variable dot thermal wax transfer are less expensive than the corresponding things of dye diffusion thermal transfer, the cost of dye diffusion thermal transfer is higher.
According to the reasons above, variable dot thermal wax transfer and dye diffusion thermal transfer are the better printing technologies and both of them can be used in the future print module design because of the same configuration.
2.2 Marketing Research
2.2.1 CANON
Table 2.2 lists the four mobile printers of CANON on market. The specifications of four products are almost the same. The most differences between them are the print paper size and whether it can use the battery or not.
2.2.2 ALPS
There are three products of ALPS, PTMTL28, PTMTL27 and PTMTL14. (In Table 2.3) They are just the print modules. It seems that ALPS only produce the print module, not the whole printer.
2.2.3 Other Companies
As shown in Table 2.4, there are also other mobile printers made by other companies, such as SONY, PANASONIC, KODAK and FUJIFILM, etc. Both of SONY and PANASONIC have one product. And there are several mobile printers of KODAK, here list only one product because other products just support for different kinds of digital cameras.
Besides, the mobile printer of FUJIFILM can print the photos taken by the camera on mobile phones. Users can use IrDA to send the photos from cell phone to the printer directly.
image input such as cameras.
2.3 The Configuration of Thermal Transfer Printer
As shown in Fig.2.14, a thermal transfer printer can separate into five subsystems, print module, paper feed, power supply, frame, control unit and user interface. Besides the control unit and paper feed, the main subsystem for the printing is the print module. It includes paper feed, thermal print head and ink ribbon modules.
2.3.1 Print Head Module
Print head module consists of thermal print head, platen roller, transmission means, motor, spring, platen roller and cooling means. The thermal print head is separated from the platen roller normally. While printing, the motor will rotate and the thermal print head will be pressed with the platen roller by transmission means. The spring will make the pressure uniform.
2.3.2 Ink Ribbon Module
Ink ribbon module consists of ink ribbon, ink ribbon cassette, tension limit means, motor and roller. While printing, the rollers will wind ink ribbon and tension limit means will keep the tension of ink ribbon and remain the line velocity of ink ribbon in a constant without
2.3.3 Paper Feeding Module
Here the paper feed also need at least one motor for driving the paper rollers to draw the paper into printer.
As mention before, there are three times repeating from step 2 to step 3 to form the colorful image. In general thermal transfer printer, it may need three or four motors to drive the paper feed, thermal print head movement and wind ink ribbon. And using more motors will cause more power consumption and larger space. Therefore, how to drive all these three parts with fewer motors is important.
2.4 Remarks
1. Dye diffusion thermal transfer and variable dot thermal wax transfer are better choices for using on mobile printer.
2. Most of the mobile printers on the market use dye diffusion thermal transfer printing technology now.
3. Thermal print head module, ink ribbon module and paper feeding module are the main parts for the design of print module.
4. General thermal transfer printers use three motors to complete the whole printing process.
Fig.2.1 Inkjet - Thermal bubble [5]
Fig.2.3 Basic laser printer components [6]
Fig.2.5 Dye diffusion thermal transfer [7]
Fig.2.6 Step1 – Ribbon search in dye diffusion thermal transfer
Fig.2.7 Step2 – Paper feed in dye diffusion thermal transfer Paper
Fig.2.9 Thermal wax transfer [8]
Fig.2.11 Dithering technique
Fig.2.12 Fig. 2.12 Continuous tone and half tone [7]
Black Gray Light gray White
Table 2.1 Comparison of thermal printing technologies
Preservation Good Good Good
Configuration Simple Simple Simple
Color performance Best Good Better
Continuous printing Bad Good Good
Power consumption Higher Lower Lower
Cost Higher Lower Lower
Fig.2.13 Portion of 300 dpi image printed on thermal printing technologies [8]
Table 2.2 Canon’s products
Table 2.3 Products of ALPS
Company ALPS
Model PTMTL28 PTMTL27 PTMTL14
Photo
Printing Method Variable Dot Thermal Wax Transfer
96.6x17.4x61.1 (mm) 88.6x17.4x61.1 (mm) 71.6x17.4x61.1 (mm)
Weight(g) 159 148 120
Table 2.4 Products of other companies
Company Kodak Fuji Film OLYMPUS PANASONIC
Model Printer Dock Plus NP-1 P-200 SV-P20
MIN: 51x34 86x54 80x125.6 85.725x54
Fig.2.14 Subsystem of thermal printer
Chapter 3 Design Method and Requirements
3.1 TRIZ
3.1.1 Introduction of TRIZ
TRIZ, as a Russian abbreviation, is equal to “Theory of Innovative Problem Solving”
(TIPS). And it was born in the second half of the twentieth century and developed by Genrich Altshuller and his colleagues. Now it is being developed and practiced throughout the world [9].
Before TRIZ, authorized thought about creative and human innovations was based on a paradigm that believed the creation as an unknown phenomena. But Altshuller believed that:
1. Creation is not an unknown and unreachable function.
2. Creation followed a special and achievable principles.
3. It is possible to do the inventions with non-inventor persons, if they learn the innovating principles and algorithms.
analyzed to look for principles of innovation. The three primary findings of this research are as follows:
z Problems and solutions were repeated across industries and sciences.
z Patterns of technical evolution were repeated across industries and sciences.
z Innovations used scientific effects outside the field where they were developed.
In the application of TRIZ all three of these findings are applied to create and to improve products, services, and systems.
3.1.2 The Foundation of TRIZ
This section provides a short introduction to some basic TRIZ tools. There are five ideas in TRIZ, technical systems, levels of innovation, law of ideality, contradictions and evolution of technical systems [10].
Technical Systems
Everything that performs a function is a technical system. Any technical system can consist of one or more subsystems. Each of the subsystems is also a technical system unto itself and each performs its own function. The hierarchy of technical systems spans from the least complex, with only two elements, to the most complex with many interacting elements.
Levels of Innovation
Analysis of a large number of patents reveals that not every invention is equal in its inventive value. Altshuller proposed five levels of innovation.
z Level 1: A simple improvement of a technical system.
z Level 2: An invention that includes the resolution of a technical contradiction.
z Level 3: An invention containing a resolution of a physical contradiction.
z Level 4: A new technology is developed containing a breakthrough solution that requires knowledge from different of science.
z Level 5: Discovery of new phenomena
Altshuller concluded from his research that a large number of patents belong only to Level 1 and Level 2. Using TRIZ can help designers elevate the innovative solutions to Level 3 and Level 4.
Law of Ideality
The goal of any technical system is to provide some function. And the Law of Ideality means that the technical system can have the same functions without introducing any new mechanism or device into the system, and the system tends to become more effective, reliable
3. Transfer some functions of the system to a supersystem or to the outside environment.
4. Utilize internal and external resources that already exist and are available.
Contradictions
Contradiction analysis is a powerful tool. As mentioned before, the most effective solutions are achieved when solving a technical problem which contains a contradiction.
Contradictions can be divided into technical contradiction and physical contradiction. A technical contradiction occurs when designers try to improve one characteristic or parameter of the technical system and it causes another characteristic or parameter to worsen. Physical contradiction appears when two opposite properties are required from the same element of a technical system or from the technical system itself.
(A) Solving technical contradiction
After Altshuller analyzed more than 40,000 patents, he generalized 40 inventive principles [11]. Altshuller developed contradiction matrix in 1970s, the column and row of matrix include 39 features, as shown in Table 3.1. First process of this method is to find the parameter that designers want to improve in the column. Then find the relational harmful parameter in the row. The intersection of two parameters includes some useful principles. All 40 principles are common concepts, as shown in Table 3.2;
and designers must use creativity to let these principles apply questions.
(xi, yi, zi) . The method is let A > 0 at time t = tj , position X = (xj, yj, zj) ; A < 0 at time t
= tk , position X = (xk, yk, zk). This way can solve contradiction A > 0 and A < 0 simultaneously.
Evolution of Technical Systems
Altshuller established eight Patterns, or Lines, of technical systems evolution:
1. Life cycle 2. Dynamization
3. Multiplication cycle (Transition to Bi- or Poly- system) 4. Transition from macro to micro level
5. Synchronization 6. Scaling up or down
7. Uneven development of parts
8. Replacement of human (Automation)
Designers can follow the eight patterns to realize the trend of evolution and get some innovative ideas from the index of system evolution.
3.2 Requirements
section.
3.2.1 Size
Size of Component
Compared with general printer, the components for mobile printer, such as gears, motor, thermal print head, must be smaller to satisfy the mobile requirement. During the design process, the size of these components has to be concerned.
In order to satisfy the requirement, the size of print head used here is about 64mm*22.45mm*5mm, and the module number of gear used in power transmission is 0.3.
Allocation
In mobile printer, most of the space is used for the paper in and ink ribbon cassette.
Therefore, the space for drive mechanism is less oppositely. When considering the small size for mobile, the allocation for all the components is important.
Furthermore, motor is one of the components with large size and much weight. Because all the three main parts, print head module, ink ribbon module and paper feed, need the driving means, at least three or four motors are required in general. It results in the larger
3.2.2 Printing time
Another important requirement of mobile printer is the printing time. If finishing one colorful printing costs too much time, users may complain the product and reduce the interest to buy the product. Here are two factors which will effect the total printing time.
Motor
Both the ribbon and paper are drawn by rollers which are driven by motors. Therefore, the rotational speed of motor is the main factor to effect the printing time. But the rotational speed of motor will be limited by the accuracy, the heating elements on print head, etc.
Mechanism
Most of printers use about three motors to drive the whole print module. Therefore, each module, for example, the print head module or capstan roller, is driven by independent motor and it will not spend too much time while changing steps. But when designing a small print module, it may use some mechanism to reduce the number of motors. Therefore, it may take some time for change steps.
From the requirements above, using some mechanism design to reduce motors may be
3.3 Objectives
After the marketing research, the objectives for the print module on mobile printer have been decided.
1. Size: According to the present mobile printers, the average size is about 138mm*104.5mm*44mm, but the design of ALPS is smaller than other products.
Therefore, the design of print module on mobile printer should be near or smaller to the size of ALPS products.
2. Printing time: Here ALPS PTMTL28 is the objective product. The printing time, 90s for one color photo print, is the objective value.
3. Motors: In order to increase the number of pieces which can be printed with charging the battery one time, the number of motors used in the print module must equal or less than
3. Motors: In order to increase the number of pieces which can be printed with charging the battery one time, the number of motors used in the print module must equal or less than