Chapter 5 Embodiment Design and Prototype
5.2 Prototype
5.2.2 Manufacture
In the prototype, there are some components which should be manufactured, including cam gear for step changing, support plate, ribbon clutch arm, power switch plate and arm.
The material used here is acrylic plastic. The thickness of acrylic plastic plate for support frame is about 1cm and the thickness of plate for the arm or power switch plate is 3mm.
Since the gear size of prototype is twice of the gear size in embodiment design, size of these components is also doubled. Fig. 5.22 to Fig. 5.25 are the drawings of these components of embodiment design whose size is half of the prototype. Follow these drawings, these components have been manufactured, as shown in Fig. 5.26 to Fig. 5.28.
bushings to clip the gears. Combine all the sections, Fig. 5.32 (a) and (b) are photos of the whole prototype of print module. The size of the prototype is about 160mm*62mm*60mm whose lengths are almost twice as long as the lengths of embodiment design.
5.3 Remarks
1. The size of the embodiment design is 107.4mm*81.6mm*32.1mm.
2. Two spring sets are used in the print head assembly for releasing the print head and supply enough pressure to melt the ink on the ribbon into paper.
3. The capstan roller and passive paper roller are near and under the ink ribbon cassette for space saving.
4. Ribbon gear connects to main power transmitting gear and the rotating arm is not downward vertically while the step of printing, so that it can reduce the gears used to connect ribbon roller or capstan roller.
5. The prototype proves the feasibility of concept 5. The main part, mechanism for step changing and power transmitting can work successfully.
Table 5.1 Gears used in prototype
Module No. of Teeth Pitch diameter(mm) No. of Gears
16 8 16
24 12 7
40 20 6
48 24 9
0.5
64 32 1
Fig. 5.1 The printer design
Gear train
Print head module
Ribbon cassette Motor
(a)
(b)
Fig. 5.3 (a) Front view (b) Top view of the whole print module
Fig. 5.4 Printer frame Paper guider
Fig. 5.6 Design of print head module
A B
B 1
2
3 4
5
Platen roller Cam
Print head assembly
Light interception plate
Fig. 5.8 State of print head released
B Cam
Cam
B
Fig. 5.10 State 2 of print head pressed Cam
A
Axis
Hollow area
Feeding roller Winding roller
Fig. 5.12 Side view of ink ribbon cassette
Fig. 5.13 Gear train of printer design Passive paper roller
Capstan roller Platen roller
Fig. 5.14 Section 1 of gear train
Fig. 5.15 Section 2 of gear train
Main power-transmitting gear
Step-change cam gear
Surface 1
Surface 2 Planet gear
Motor
Axis 1
Fig. 5.17 Gear train 3A to ribbon roller Ribbon gear
Ribbon clutch gear arm
Gear line 1
Gear line 2
Fig. 5.19 Step 1 – Ribbon Searching
Fig. 5.20 Step 2 – Paper Feeding
Engage
Disengage
Engage Engage
Fig. 5.25 Drawing 4 (Power switch plates)
Fig. 5.26 Photo of the components
Ribbon clutch arm Cam gear for step changing
Power switch plate
Fig. 5.28 Photo of two acrylic plastic plates One side of printer frame
Support plate for gear train
Fig. 5.29 Section 1 of gear train
Fig. 5.30 Section 2 of gear train
(a) 160mm
62mm
60mm
Chapter 6 Analysis
6.1 Weight
After the embodiment design, the size of print module has been confirmed. Besides of the space and power consumption, weight is also a key factor for mobile. In the embodiment design the material of frame is SECC and thickness is 0.8mm. The material of gear is DURACON® M90-44 and the material of axis is steel.
Density of SECC: 8225kg/m3
Density of DURACON® M90-44: 1410kg/m3
Density of Steel: 7860kg/m3
Here are some assumptions about the components which are assembled by different things, for example, the print head, motor and photo-interrupter. Table 6.1 shows the components weight and total weight which is calculated by the software, CATIA. The total weight of print module is about 308g.
6.2 Displacement of Paper and Ribbon
while printing, the paper can be located by sensors precisely.
The number of teeth on the motor gear is 12 and there are three deceleration gears in section 1. The teeth ratio of two deceleration gears is 16:48, and the other is 24:48. As shown in Table 6.3, the speed ratio from motor to ribbon roller is 1:60, and 1:160 from motor to capstan roller because of there is another deceleration gear, and teeth ratio of which is 24:64. According to present design, the radius of capstan roller is 3mm. Therefore, the displacement of paper per step is,
Paper displacement per step = 0.00589
160 R: Radius of capstan roller Dr: Deceleration ratio
6.3 Motor
Here the motor used in the print module is a stepping motor. While choosing the motor, the maximum and minimum torque and the rotating speed should be confirmed. If the standard of motor after calculation can not be manufactured by the present motor companies, it is not feasible. On the contrary, it is workable if the standard can be found.
printer. Use these data as the reference to calculate the rotating speed.
Drawing sheet into printer
The linear speed for drawing paper into printer = = s mm 7
85 12.14 (mm/s)
Pulse rate of stepping motor= = mm
The linear speed for printing = = s mm 15
85 5.67 (mm/s)
Pulse rate of stepping motor= = mm
According to Table 6.2, the pressure for printing is about 12.7 N. Here assume that, first, the friction coefficient of rubber on the capstan roller and platen roller is 0.35. Second, the tangent force to draw paper into printer is 0.2 kg. Third, the efficiency of gear transmitting is 95%. Therefore, the torque the motor needs can be calculated by the following equation.
The torque of motor= t n
T: Torque resistance
Tangent force to draw paper while printing = × × = 8
When pressing thermal print head, print head cam will rotate and press pressure plate to supply required pressure. As shown in Fig. 6.1, the length from heater line to supporting axis is about 22.38 mm. The original angle between pressure plate and the thermal print head is 10 degrees. Therefore, the spring coefficient k of spring set A which supplies the force for print head is,
6.2. The rotating speed of cam is 150 degrees per second which means the pulse rat of stepping motor is 500 PPS. The print head cam will rotate counterclockwise to press the pressure plate. Fig. 6.3 shows the simulation result, the real line is the result of present design. Point A is the maximum of torque resistance the cam must overcome. The value is 481.434 N-mm, equaling to 4912.59 gf-cm. After the speed ratio, 1:60, and the gear efficiency of gear transmitting, 95%,
The torque of motor = =
It is too large for a small stepping motor. Therefore, the design of cam is not feasible.
If the cam can rotate clockwise, the torque that the print head cam can supply will be larger because the contact point is farer from the rotating axis of torsion spring than the contact point when the print head cam rotates counterclockwise. The dotted line in Fig. 6.3 is the result while print head cam rotates clockwise. Point B is the maximum value which is 145.4 N-mm, equaling to 1483.67 gf-cm. After the speed ratio and gear efficiency of gear transmitting,
maximum torque is 39.23 gf-cm while the pulse rate is 500 PPS. The minimum torque is 0.769 gf-cm while the pulse rate is 2061 PPS.
6.4 Action Analysis
The key part in present design is section 2 of gear train, the mechanism for power switch and step change. Generally gear is used for transmitting power. But here the function of power switch is applied by the engagement or disengagement of planet gear. In this mechanism, because both the rotating arm and planet gear can rotate freely, it is hard to ensure which component will rotate so that here discuss the cases.
There are one force and two resistances that will effect the movement of these components,
1. F: rotating force
2. Rp: resistance of planet gear rotating 3. Ra: resistance of rotating arm rotating
Case 1: If Rp < Ra
As shown in Fig. 6.4 (a), while F is larger than Rp, the planet gear starts rotating but the rotating arm does not.
planet gear does not.
In the present design, it only needs case 2 because Ra will become larger than Rp after the planet gear engages the step-change cam gear or power transmitting gear. Therefore, here the way to ensure that the mechanism always working in case 2 is to increase the resistance of planet gear rotating.
There are two ways to increase the resistance. First one is to increase the friction between the gear bore for axis and the axis. Second is to increase the friction between the planet gear and the rotating arm. But first way is more difficult than second one so that here uses second way. As shown in Fig. 6.5, a spring is added between rotating arm plate and gear axis to supply a lateral force to planet gear so that the friction between gear and rotating arm will increase.
6.5 Remarks
1. The weight of present design is about 308g.
2. The maximum torque is 39.23 gf-cm while the pulse rate is 500 PPS and the minimum is 0.769 gf-cm while the pulse rate is 2061 PPS. One more gear must be added into the gear train to change the rotating direction of print head cam.
3. In order to ensure the movement of section 2, increasing the resistance on the planet gear
Table 6.1 The weights of print module
Component Weight
Printer frame 89g
upper cover 70g
motor support plate 5g
Frame
Axis support plate 16g
Ribbon cassette 19g
Thermal print head module(with spring,
frame and cam) 35g
Motor 15g
Platen roller 25g
Capstan roller 8g
Passive paper roller 7g
Gear train(including axis) 14.94g
Others 4.06g
Total 308g
Table 6.2 Specification of thermal print head
Model No. KPC-54-8PAO1-LO
Effective print width 54 ± 0.2mm Number of heater elements 432 dots/HEAD
Dot density 8.0 dot/mm
Subsequent scanning density 8.0 line/mm
Dot pitch 0.125mm
Table 6.3 Simulation result of rotation angle after deceleration
Fig. 6.1 The position of print head module
Print head cam
Pressure plate
Print head
Fig. 6.3 Simulation result of print head module A
B
(a) (b)
Fig. 6.4 The two cases of planet gear
Spring
Gear axis
Planet gear
Chapter 7 Conclusions
7.1 Conclusions
1. TRIZ provides principles to designers, and these principles are related to design parameters. Therefore, these principles are usually suitable to solve the problem. It is different from designer’s checklist method that developed by themselves. Therefore, using checklist method needs more creativity.
2. Compare these concepts in this study, concept 5 uses only one motor and need not any other electrical device to support the action. For the requirement of power saving, design of concept 5 can print more pages than other concepts with the same power.
3. The size of the present print module design is 107.4mm* 81.6mm* 26.8mm and its weight is about 308g. For the mobile requirement, it is lighter and smaller than general printers and near to ALPS products.
4. Compared with the design of ALPS, as shown in Table 7.1, there are two advantages, first, the design of ALPS needs to detect paper first, and then draw the paper back for printing.
Therefore, it needs 4 steps to complete the whole printing process. Second, while step
Therefore, the present design will save more time than ALPS products while printing.
7.2 Future Works
1. Search more related information. Patent is one of the important sources for the product design. Read more patents to make the database more complete. Other production related to printer can also be searched, such as the borderless printing, to increase the functions of printer.
2. Reduce the size of the present design. Here the study uses TRIZ to generate concepts about motor reduction. TRIZ or other optimum methods may be used to improve the size or weight of the present design.
3. Propose more new concepts. Use TRIZ or other innovative tools to find other better concept which can also use only one motor and the size is smaller.
4. Real size prototype. In the study, the size of prototype is twice to the embodiment design. Fabricate the whole mobile print module with real size to see if there is any other problem in the design.
Table 7.1 Comparison
ALPS Present design
Size 96.6 x 17.4 x 61.1 mm3 107.4 x 26.8 x 81.6 mm3
Motor 1 1
Steps 4 3
Gear 17 26
Rotating angle > 270° 120° & 240°
Rotation 1 Paper change & change Power output
Rotation 2 Paper out Change
References
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http://www.howstuffworks.com/inkjet-printer.htm, last visited on May, 30, 2005.
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http://computer.howstuffworks.com/laser-printer.htm, last visited on May, 30, 2005.
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[8] Moroney, N. M. and Viggiano, J. A., “Color Imaging Using Variable Dot Thermal Wax Transfer”, RIT Research Corporation, Rochester, New York, 1994.
[9] Mohammad, H. S. and Nezafati, N., “A New Method for Creating the Non-Technologic Principles of TRIZ.” TRIZ-Journal, Oct. 2003.
[10] Altshuller, G., “40 Principles: TRIZ Keys to Technical Innovation”, 1997.
[11] Terninko, J., Zusman, A., and Zlotin, B., “STEP-by STEP TRIZ: Creating Innovative Solution Concepts”, St. Lucie Press, 1996.
[12] Unite States Patent Number: 6,392,682, May 21, 2002.