Chapter 4 Conceptual Design
4.2 Conceptual Designs
4.2.5 Concept 5
the other is used to change the steps.
Concept 5 can be divided into three sections. Section 1 in Fig. 4.44 is the device to control the power output transmitting to drive ribbon roller and capstan roller or to change the steps. There is a gear E rotatably jointed at one end of plate B and a component with gear teeth F fixed at the other end of plate B. There is a gear G rotatably jointed at the end of rotating arm C. The distance between component F and axis D is the same as the distance between gear G and axis D. And the axis of gear G and component F are coaxial. Plate B and rotating arm are fixed on axis D. Component A which includes two gears A1 and A2 can rotate about axis D and engage gears E and G.
Fig. 4.45 shows that section 2 consists of a cam, gear H, rotating arm J planet gear K and sun gear I. Gear H and cam are fixed on the axis. Planet gear K is jointed rotatably at the end of rotating arm J, and rotating arm J is fixed on one side of gear H. Sun gear I engages gear K.
Section 3 includes four gears, as shown in Fig. 4.46. Gear L and gear N can transmit power to ribbon roller and the other two gears M and O can transmit power to capstan roller.
Gear N and gear O are fixed together. However, the paper will be drawn into printer when power is output from gear M and be drawn out when power is output from gear O because there is one more gear in the gear train connecting with gear M or the gear train connecting with gear O.
down right of Fig. 4.47 is to output the power of motor to ribbon roller and capstan roller.
While changing one step to another step, gear A rotates clockwise and plate B rotates in the same direction. Then gear E will engage gear H and rotating arm will rotate clockwise to change step. After the rotating arm reaches the right position, the sun gear A will rotate counterclockwise and bring drive plate B rotating in the same direction. Then gear E will disengage and gear G will engage gear I. At the same time, component F will engage gear H and fix it. Therefore, the power will be only transmitted to ribbon roller and capstan roller.
Step 1: Ribbon Searching – In this step, after motor transmits power to rotate gear H making the planet gear K engaging gear L, motor will rotate in the opposite direction transmitting power to ribbon roller. (Fig. 4.48)
Step 2: Paper Feeding – After motor drives rotating arm and make gear K engaging gear M, power can be transmitted to capstan roller and draw paper into printer. (Fig. 4.49)
Step 3: Printing – When ribbon and paper is ready, motor drive rotating arm again make gear K engaging gear N. At the same time, print head is also pressed by cam. Then power transmits from gear K to gear N and O to drive ribbon roller and capstan roller for printing.
(Fig. 4.50)
As the concepts mentioned above, the design will repeat the step 2 and step 3 until three
used in concepts 4 and 5. Next, more steps in the printing process will take more time to form a colorful image. Concept 3 is worse than other concepts because it needs more steps for one color printing. Third, since there are some special components which need to be manufactured in concept 3 and concept 4, for example, the gears in concept 3 and component B in concept 4, the cost of manufacture are higher than other concepts. Fourth, besides the sensor to locate the length of paper, the position of ribbon or the position of mechanism, concept 4 needs an extra electrical device, the electromagnetic switch. Therefore, it will have higher power consumption.
Compare the five concepts about the power consumption, concept 1 to concept 3 need two motors to complete the printing process and concept 4 needs a electrical device. Only concept 5 uses one motor without other electrical device. For the reasons above, concept 5 is the better than the other four concepts. Therefore, concept 5 is chosen to be the design of print module.
4.3 Remarks
1. General printers use more than one motor to complete the printing process, but only one motor is used in the printer design of ALPS.
2. Concept 1 uses one motor to control pressing or releasing print head, another motor use to drive ribbon roller and capstan roller.
3. Concept 2 uses one motor to supply the power and the other motor to change steps and
one motor is used in the design.
6. Concept 5 uses one rotating direction of motor to drive the capstan roller and ribbon roller, the other direction to change steps and control print head.
7. Concept 5 is better than other concepts because of the lower power consumption.
Table 4.1 Part of contradiction matrix
Characteristics that is getting worse Characteristics
Table 4.2 Conceptual design comparison
Concept Concept 1 Concept 2 Concept 3 Concept 4 Concept 5
Number of motors 2 2 2 1 1
Steps 3 3 3 3 3
Manufacture Easy Easy Hard Hard Easy
Other electrical Device No No No Yes No
Fig. 4.1 Product of Olympus
Fig. 4.3 Products of ALPS
Motor
Fig. 4.5 Cam gear in ALPS design
B3
To ribbon roller
B1
B2 Ribbon lever
A2 A1 A4
Cam for Ribbon gear A3
Area without Teeth
A Cam for platen roller Area without Teeth
Fig. 4.7 Step 1- Ribbon Searching of ALPS
Fig. 4.8 Step 1 to Step 2 of ALPS B2
B3 B1
Ribbon gear To ribbon roller
B4
A
Fig. 4.10 Step 3- Feeding Paper Backward of ALPS
Fig. 4.11 Step 4- Printing of ALPS
Fig. 4.12 3D view of concept 1
Fig. 4.13 Section 1 of concept 1
B
C D Motor A
Motor
E
Fig. 4.15 Step 1 – Ribbon Searching of concept 1
Fig. 4.16 Step 2 – Paper Feeding of concept 1
Fig. 4.18 3D view of concept 2
Fig. 4.19 Section 1 of concept 2
Fig. 4.20 Section 2 of concept 2
A
B
C D
E
Fig. 4.22 Step 1 – Ribbon Searching of concept 2
Fig. 4.23 Step 2 – Paper Feeding of concept 2
Fig. 4.25 3D view of concept 3
Fig. 4.26 Section 1 of concept 3
Fig. 4.27 Section 2 of concept 3
Motor 1
A
Motor 2 B
C
D F
Fig. 4.29 Step 1 – Ribbon Searching of concept 3
Fig. 4.31 Step 3 - Print Head Compressing of concept 3
Fig. 4.32 Step 4 – Printing of concept 3
Fig. 4.33 3D view of concept 4
Fig. 4.34 Section 1 of concept 4 A
B
Frame
F
Motor D
E
H G To print head
C B1 B2
Spring
I
Fig. 4.36 State 1 of section 1 of concept 4 Frame
B2
A
B2
Fig. 4.38 State 3 of section 1 of concept 4 A
B1
Frame
I B
Fig. 4.40 Step 1 – Ribbon Searching of concept 4
Fig. 4.41 Step 2 – Paper Feeding of concept 4
Fig. 4.43 3D view of concept 5
Fig. 4.44 Section 1 of concept 5
Fig. 4.45 Section 2 of concept 5 A
B
C
D E
G F
H
I
J K
Cam
L
Fig. 4.47 Way of step-changing and power output of concept 5 E
H
F, G
H, I
L K
Fig. 4.49 Step 2 – Paper Feeding of concept 5
Fig. 4.50 Step 3 – Printing of concept 5 K M
K N
Chapter 5 Embodiment Design and Prototype
Because of the lower power consumption and only one motor used, concept 5 is chosen to be the design of print module. As mentioned before, the print module consists of print head, ink ribbon and paper feeding module. In this chapter, the whole design of print module is presented.
5.1 Embodiment
Because of the requirement of space, the allocation of concept 5 should be redesigned.
Fig. 5.1 is the present design of print module. It includes printer frame, a motor, gear train, print head module and ink ribbon cassette, as shown in Fig. 5.2. The motor and gear train are at the left side and the ink ribbon cassette can be inserted from the right side. Paper can be drawn in and printed out from the front. The size of the embodiment design is 107.4mm*81.6mm*32.1mm, as shown in Fig. 5.3 (a) and Fig. 5.3 (b).
5.1.1 Printer Frame
The printer frame consists of the base and an upper cover. As shown in Fig. 5.4, there is a paper guide plate at the paper entrance so that paper can be directed to capstan roller straight. There is a hollow whose shape is like the ribbon cassette on the left side.
fully inserted into the print module.
5.1.2 Thermal Print Head Module
As mentioned before, general printer use cam to press or release thermal print head, but the printer of ALPS use cam to press or release platen roller. Here the design also uses cam to press thermal print head. Fig. 5.6 is the figure of present design. Use cam to press print head assembly against platen roller or release it from the platen roller.
Fig. 5.7 shows the detail of print head assembly. Print head 3 is fixed on the print head frame 2 by two screws 4. The print head assembly can rotate around the axis 5. Number 4 is a pressure plate. There are two spring set A and B in the assembly. One end of spring set A is fixed on the pressure plate 4, and the other is fixed on print head frame 2. One end of spring set B is fixed on the print head frame 2 and the other is fixed on the printer frame.
The spring constant of spring A is larger than spring B. Spring set A is used to supply the pressure needed while printing and spring set B is used to release print head.
When print head is released in the steps of ribbon searching or paper feeding, the surface with smaller radius of cam attaches to the pressure plate because of the spring force of spring set B, as shown in Fig. 5.8. While printing, the cam will rotate and press the pressure plate.
The spring set A will be compressed first and the print head assembly will attach to the platen
5.1.3 Ink Ribbon Cassette
Fig. 5.11 shows the 3D view of ink ribbon cassette. The roller for feeing ribbon is lower than the winding roller. There is an axis in the front of the feeding slot to make sure that the ribbon will follow the surface of ribbon cassette to the winding slot. And one hollow area is at the middle of the ribbon cassette for the print head to pass through.
Because of the requirement of space, the capstan roller, passive paper roller and platen roller are under the ribbon cassette, as shown in Fig. 5.12.
5.1.4 Power Transmitting Mechanism
Fig. 5.13 is the side view of gear train in the printer design. It can be divided into three sections. Section 1 is the side of power source and consists of one motor, three compound gear and one power-transmitting gear as shown in Fig. 5.14. Section 2 in Fig. 5.15 is similar to concept 5, but the gear which connects to the gear train of ribbon roller (in Fig. 5.17) always engages the main power transmitting gear. And the cam is fixed on the axis 1 with a power-transmitting gear and a light interception plate. Use the light interception plate to determine the position of cam. Fig. 5.16 is the step-change cam gear. There are two surfaces on the cam, surface 1 is flat and surface 2 is circular with same radius. One planet gear which engages with main power transmitting gear is at the end of the rotating arm.
Section 3 consists of gear train 3A for ribbon roller and gear train 3B for capstan roller,
5.1.5 Three Printing Steps
Step 1 in Fig. 5.19 shows that planet gear in section 2 doesn’t engage any gear and the ribbon clutch gear engages with the gear train 3A because surface 2 of cam gear in section 2 contacts with the clutch gear arm of gear train 3A. Therefore, ribbon can be searched without drawing paper.
Fig. 5.20 is the step to draw paper into printer. At this time planet gear of section 2 has rotated about 120 degrees and engaged with gear line 1 in gear train 3B. Surface 1 of cam gear in section 2 contacts with clutch gear arm in gear train 3A causing the clutch gear disengaging with gear train 3A so that ribbon will not be drawn while feeding paper.
While printing, as shown in Fig. 5.21, planet gear of section 2 rotates about 120 degrees again and engages with gear line 2 in gear train 3B. Surface 2 of cam gear in section 2 contact with the arm again so that the clutch gear will engage with gear train 3A. At the same time print head is pressed. Then printer can drive paper and ribbon simultaneously to complete one printing process.
After one color printed, the cam gear will rotate clockwise about 240 degrees to step 2 again for next printing.
5.2.1 Gear
The module of gears used in the embodiment print module design is 0.3. This kind of gear is hardly found on market. Therefore, the prototype use gears whose module is 0.5 and the pitch diameter is doubled. Because the gear thickness is only 3mm, some gears stick together instead of special thicker gears. Table 5.1 shows the total gears used in the prototype. Here use iron axes as the gear axes and its diameters depend on the bores of the gears. If the diameter of bore is larger than 4, a bushing is used so that the gear can use axis with the diameter about 3mm.
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
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