The 14th IFToMM World Congress, Taipei, Taiwan, October 25-30, 2015 DOI Number: 10.6567/IFToMM.14TH.WC.OS10.004

Polymer-made Robot Mechanisms and their Applications

Mikio Horie1

Tokyo Institute of Technology

Yokohama, Japan

Abstract: This paper is described about the polymer robot

mechanisms, for examples, a 2DOF(degrees-of-freedom)

pantograph mechanism and a 3DOF planar parallel

mechanism for new surface mount system in one room

factory. First, the displacement characteristics, the

relationship between frequency and positioning accuracy,

etc. are discussed about a polymer-made 2DOF pantograph

mechanism, and its application is shown. Second, the

dynamic displacement of output link, the result of the impact

test, etc. are discussed in experiments about a polymer-

made 3DOF planar parallel mechanism, and its application

is shown, where in this study, 2DOF XY direction motion is

discussed. In the results, the displacement characteristics

of polymer-made robot mechanisms proposed in this

research became clear. Keywords: Polymer-made 2DOF pantograph mechanisms, Polymer-

made 3DOF planar parallel mechanisms, Large-deflective hinges

I. Introduction

Recently, the use of cellular phones has become

prevalent worldwide. It is expected that the number of

cellular phone subscribers will reach 4 billion more and the

number of cellular phones shipped will reach more than 1

billion more by 2010 or later. Surface mount technology

related to the production of mobile products, such as the

electronic parts mounted on a cellular phone, are numbered

from several hundred to approximately a thousand. There is

a great number of a various parts mounted on the surface of

a printed circuit board. In order to effectively encourage

downsizing as well as increase the production rate of

installation machinery, a new miniature placement system

has been proposed by Horie [1] ~ [3]. Moreover, many

researches are done about optimization of a mounting

procedure, and there is also an example which applies to an

actual mounting line and is achieving success[4],[5].

The above system proposed by Horie is divided into two

groups. One group is the miniature manipulator that picks

up electronic devices, and then mounts them on a printed-

circuit- board. The other group is the positioning

mechanism that carries printed-circuit-board between

assembling-process stations, and its mechanism has a

positioning function at a station. The pantograph

mechanism and the positioning mechanism made of

polypropylene are used in the miniature manipulator and the

positioning table, respectively. The purpose of this study is

to experimentally produce a miniature surface-mount-

system that can be used for both downsizing the labor

necessary as well as speeding up the installation systems

followed by evaluation.

1mahorie@pi.titech.ac.jp

II. Proposal for a Miniature Surface Mount System

using an Injection Molding Pantograph Mechanism

A. Pantograph mechanisms and their application

The strategy of the 2DOF pantograph mechanism used in

this system is that the input displacement (SY, SZ) is

magnified minus 4-times in Y direction and plus 5-times in

Z direction, and the link and hinge pieces are combined and

molded by an injection molding. The injection-molding

pantograph mechanism is lightweight and is characterized

by an ease of mass-production as well as a rapid assembly

time.

As shown in Fig. 1, this study proposes a system

consisting of a group of miniature manipulators using an

injection-molding pantograph mechanism and a 2DOF XY

table. The printed circuit boards to be carried are presumed

to be a maximum of 100mm x 50mm. The width of a station,

which is an operating unit, is presumed to be 100mm. The

manipulators, which perform pick-and-place operation, go

and return on a path(50mm*20 mm) between a point on a

printed circuit board and a feeder. The manipulators can

handle anything from microchip parts to odd-shaped parts,

and in principle, one manipulator handles one kind of part.

This study presents a surface mount system with multiple

XY tables which move independently along the same rail.

The XY tables have 2DOF in the X and Y directions, and

one XY table carries one substrate.

This study will also decide the mounting procedures to

evaluate the mounting efficiency. Unique mounting

procedures are necessary because it is conditional that the

mounting parts should be timed nicely between the front

and rear substrates on the rail, and that fixed manipulators

perform pick-and-place operation independently in this

system.

First, an equation is formulated to evaluate the mounting

system. When one manipulator mounts only one part on one

substrate at one time, the number of stations (NS) becomes

N1NM, and the length of the mounting line (L) can be

derived by the equation L=NS(WS+WD), where, WS and WD

means the length of a station and the distance between

manipulators in a station, respectively.

When time, which is required for the operation at a

station and moving to the next station (TS), is the same as

between all of the stations, individual substrate moves

without delay. Therefore, cycle time (CT) expressed by

CT=NSTS and throughput of the system can be improved by

reducing TS. At this time, the number of parts mounted on

the whole system per unit time can be expressed by

EC=N/TS, where, N means the number of parts mounted on a

substrate.

TS becomes the smallest if the conditions are met, such

as (1) XY tables do not wait for the operation of

manipulators, (2) The movement of XY tables in the X

direction does not wait for the movement in the Y direction,

and (3) The movement of XY table in the X direction is

only in the positive direction. Therefore, it is necessary to

establish a mounting system to meet the conditions. The

equation necessary to express these conditions are

determined by the Equations. And, finally, TS, that is, time

required for the operation at a station and moving to the

next station, is expressed by the equation:

Next, the method for the mounting procedures is decided.

Afterward, the following method will be used as the unified

method to evaluate the mounting efficiency.

The system is divided into ten in the X-direction, and

mounting is started from the lower left toward the X-

direction. When mounting reaches the right end, it loops

back to the minus X-direction. When it reaches the left end,

it loops back again toward the X direction, proceeding on

toward the upper end.

Finally, the mounting efficiency was simulated when

conditions of the system and the number of the parts were

assumed.

The mounting efficiency determined by the following

methods is listed in Table 1.

1. The target positions of parts given by random number

are sorted by the method mentioned above.

2. Conditions are substituted into the TS equation to

determine TS.

3. When the results do not match the conditions, max

latency will be added to TS.

4. Mounting efficiency is determined by TS and

conditions.

5. The mean value of mounting efficiency is determined

after repeating the simulation ten times.

From the results of Table 1, the values of mounting takt

time were over several hundred thousand CPH (chip per

hour), which is just as good or better efficiency as the actual

use of a mounting machine.

Table 1. Computational results of efficiency [ UNIT: cph(chip per hour) ]

10 30 50 10 30 50 10 30 503 41087 44565 44565 66007 84309 85919 95339 140296 154242 32405 46790 46790 46790 79893 90045 90045 111180 162749 169014 18807 34007 34649 34649 54828 64935 64935 78261 108434 115311 14003 112254 132548 133185 171429 233312 248447 230769 365854 412371 64405 101152 101666 101666 163043 189873 189873 221402 320856 335508 38807 90407 96904 96904 138143 168776 168776 186239 254237 254237 28133 652884 769889 769889 965665 1366743 1446945 1269394 2068966 2365309 332405 641483 740436 740436 1025641 1298701 1388889 1408451 2080925 2275601 198807 539245 645161 680015 797519 1054482 1127113 1047730 1640839 1704545 14226

NM

VX mm/s

L mm

100 200 400Vy mm/s Vy mm/s Vy mm/s

50

100

500

N

Fig. 1. An example of placement machines line using

pantograph mechanisms

Fig. 3. A pantograph mechanism moved by DC solenoids Fig. 2. A fabricated pantograph mechanism with large-deflective hinge

B. Experimental Production of Miniature Surface mount

System

The manipulators for the miniature surface mount system

proposed in this study consist of injection-molding

pantograph mechanisms shown in Fig. 2, DC solenoids

driving manipulators shown in Fig. 3, and vacuum tweezers,

to absorb and detach minute parts. The DC solenoid is

moderate in price and rapid in operation.

Moreover, because the manipulators are used only at the

both ends of a certain stroke, the use of DC solenoid is

considered to be appropriate for driving miniature

manipulators.

With the stroke of the DC solenoid being magnified by

the pantograph, the tip of pantograph can move within an

intended work area, 50mm x 20mm. The tip of the

pantograph advances or climbs upward using a magnetic

force when the solenoid is energized, and then steps retreats

or is lowered with a return spring. The solenoid is controlled

by on-off signals from a PC. In order to know the response

time of solenoid, the current waveform of when the

injection-molding pantograph mechanism was mounted and

activated was measured, and as a result, it was found that

the time length from switch-on to the completion of iron

core movement in Y direction was 0.05s. It was also found

that the time was 0.06s in Z direction as shown in Fig. 4,

from which it is known that the pulse voltage applied to

solenoid is 10 Hz at the highest.

Figure 5 shows the graphs which illustrate the repeated

positioning accuracy for placement by performing pick and

place operation while changing frequency. From the graphs,

it is revealed that errors are becoming greater near where the

frequency exceeds 1.5 Hz. Approximately 100% of

placement operations and pick-up operations were

performed successfully during 50 µs for the chips with the

size from 0603（0.6[mm]×0.3[mm]）to 3216 （3.2[mm]

×1.6[mm] ).

Fig. 6. Picture of 2 DOF XY table

Fig. 7. Relationship between a moving displacement

and maximum error

Displacement L mm E

rro

r Δ

L

m

T a r g e t

: X direction

: Y direction

50

40

30

20

10

0 50 100 150 200

Fig. 5. Relationship between frequency

and positioning accuracy

Maxim

um

erro

r m

m

Y direction error

of end-effector

Frequency Hz

0 0.5 1 1.5 2 2.5 3

0.6

0.5

0.3

0.2

0.2

0.1

Maxim

um

erro

r m

m

X direction error

of end-effector

0.6

0.5

0.3

0.2

0.2

0.1

0 0.5 1 1.5 2 2.5 3

Frequency Hz

Fig. 4. Vibration of output point of manipulator

1.5

-0.6

-0.4

-0.2

0

0.4

0.6

-0.5 0.5 1

0.2

Time s

Y

1.5

-0.6

-0.4

-0.2

0

0.4

0.6

-0.5 0.5 1

0.2

Time s

Y

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

-0.5 0.5 1 1.5

Time s

X

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

-0.5 0.5 1 1.5

Time s

X

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

-0.5 0.5 1 1.5

Time s

Z

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

-0.5 0.5 1 1.5

Time s

Z

C. Experimental Production of 2DOF XY Table

Rack pinion mechanisms have been applied because

numerous XY tables carrying print circuit boards are placed

on the same rail in X direction. Ball screw mechanisms are

applied on the X-direction actuators in Y direction for the

purpose of accuracy. Each actuator uses a DC coreless

motor.

Analog positioning control, which is superior in fast

response, is applied for the control of 2DOF XY tables, for

which a positioning instruction value is input through a PC.

The signal output from an encoder equipped in the motor is

fed back, compared with the positioning instruction value

through the PC. The PI control performed by an

integrating circuit and a derivative circuit. The PWM circuit

is used for the amplification of input voltage to motors. The

manufactured 2DOF XY table is shown in Fig. 6

Responses to the step input for an approximately

60mm moving distance in X direction and an approximately

4.5 mm moving distance in Y direction of the 2DOF XY

tables experimentally produced were measured by an

encoder. As a result, because the power supply voltage was

12V at the maximum, a linear rise is shown, from which the

maximum velocity to each direction of the 2DOF XY table

can be known. The maximum velocity in X direction is

approximately 190 mm/s and in Y direction approximately

30 mm/s.

Then, the accuracy of positioning was measured by an

experiment. For the measurement of arrival positions, a

displacement sensor was set near the target value and

measured the distance between the displacement sensor and the target. Figure 7 is a graph demonstrating the relationship between moving distances and errors for the measurement of positioning accuracy. From this graph it can be seen that the positioning accuracy is approximately 50 µm in X direction and approximately 10 µm in Y direction. As a result of repeated measuring of the positioning accuracy by changing moving velocity, it can be seen that it was approximately ± 15 µm in the X direction and approximately ± 5 µm in the Y direction with a velocity range between 0~10 mm/s as shown in Fig. 8.

D. Experiment and Evaluation of the Operation of

Miniature Surface mount System Figure 9 shows experimentally produced experimental equipment consisting of a station with three surface mount systems and a 2DOF XY table. The control system of the entire equipment is shown in Fig. 10. All control is performed in accordance with the sequence control using input signals sent through a PC. The performance of the surface mount system proposed in this study is evaluated by the experimental results obtained so far. The placement efficiency calculated using parameters obtained thus far for the purpose of evaluation of the miniature surface mount system included the experimentally produced experimental equipment shows that the placement tact time is 63989 cph when the number of products is 50, 166821 cph when it is 100, and 941423 cph when it is 500.

Fig. 8. Relationship between velocity of actuator and max. positioning accuracy repeatability

[(a) X direction, (b) Y direction]

(b)

Po

siti

on

acc

ura

cy

rep

eata

bil

ity

m

Velocity of actuator mm/s

8

6

4

2

0 5 10 15

(a)

Po

siti

on

acc

ura

cy

rep

eata

bil

ity

m

Velocity of actuator mm/s

0 50 100 150 200

30

25

20

15

10

5

Fig. 10. Control systems of surface mount system

Fig. 9. Picture of surface mount system

E. A New Pantograph Mechanism with Constant

Orientation of Output Link The new pantograph mechanism is shown in Fig. 11. The static output link orientation is measured by use of the new pantograph mechanism. In the results, its direction was found to be substantially vertical direction in the area of the working space of the mechanism.

III. Polymer-made 3DOF parallel manipulatorIn order to realize the downsizing and speeding up of a

surface mounting device for assembling fine electronic components, our laboratory is proposing a surface mounting system consisting of a set of pantograph mechanisms and a planar parallel manipulator with an injection-molding 3PRR link chain as shown in Fig. 12[6]. A table was used for fixing the position and orientation [7] ~ [11]. As this mechanism consisting of a 3PRR link chain has three degrees-of-freedom of X and Y directional movements and revolving movement around the Z-rotation axis, it plays the role of fixing the position and orientation. As its input section is a direct driven type, it plays the role of carrier machine for big movements between workplaces. Being that all components of this device are made of plastic formed by injection molding, the realization of being more compact, weight saving and speeding up of devices can be expected compared to conventional ones. However, on the other hand, there is a fear that the vibration caused by the decrease in their rigidity may affect the devices.

Therefore, in this section, we actually produced a

3DOF planar parallel manipulator and clarified its vibration

property through experiments.

.

A. Molding 3DOF Planar Positioning-and-Orientation

Table and its Hinge

This is the three-degree-of-freedom planar parallel

manipulator actually produced. In Figs. 12-14, rack-and-

pinions were used in the three direct input parts. Next,

please look at the moving image of the device actually being

operated. As can be seen from this image, because this

manipulator was given three inputs, the table that was an

output section was able to perform the movements in the X

and Y directions and Z-axis rotation movement.

This time, in consideration of the size of the base of

mobile phones and a was 25 mm; the work area in the y

direction, W, was 30 mm; the distance between rails, R, was

66 mm and the range of orientation angles was from -10° to

+10°. As the link lengths without singularity problem in the

parallel mechanism under these conditions have been

parallel mechanism under these conditions have been

decided according to the conventional research, we

produced this device applying these values, as shown in Fig.

3.

The manipulator with a planar parallel mechanism

produced consisted of three links and one table, each of

which was fixed with adhesive. The thickness and width

of the links are 5 and 8 mm respectively and they were unified

with hinges using polypropylene by injection molding. The hinge

dimension is 0.2 mm in length and 0.2 mm in width, as shown in

Fig. 12. In Fig. 12, the thickness of the central circle, that is, the

output link is 3 mm.

B. Dynamic displacement of the output link of the 3DOF manipulator We observed the vibration phenomena that occurred at the output section when the operation of the manipulator was actually stopped. The activation was made by moving the X coordinate at point P in parallel with the X axis from 0 to 73 mm, while maintaining a constant position and orientation, and we measured the displacement of the center position P of the table that occurred when the operation was stopped, by placing displacement sensors in the neighborhood of the target point in the direction of the X axis and Y axis. The measurements were made at the four positions of the output section between Yp=24 mm~58 mm and at the three orientation angles of Φp= -10°, 0°, +10°. This time, the absolute value of the maximum amplitude of vibration and the natural vibration frequency calculated

Input links

Pantographmechanism

Laser displacement sensors

Outputlink

100 mm

Fig. 12. Miniature surface mount systems

Station i

Inputs

Output

Pantograph mechanisms

3-DOF parallel mechanisms

Station i+1

Station i

Inputs

Output

Pantograph mechanisms

3-DOF parallel mechanisms

Station i+1

p P(X, Y)

Proposed 3-DOF positioning- and-orientation mechanisms

Parallel arrangement pantograph mechanisms

Fig. 11. Measurement of orientation angular error of output link in the pantograph mechanism

Fig. 13. Dimension of molding 3DOF planar positioning and

orientation table with large-deflective polymer (PP) hinges and

links

l 2=60 mm X

Y

O

P(Xp,Yp

)

ΦP＝ -10°~ 10°

W=30 mm

a=25 mm

R=66

mm

Input Input

l 1=93

mm

l 3=60 mm

Input

)

from the measured data were used as the evaluation values

of the vibration. The results are as follows. The horizontal

axis of all graphs is Yp of the Y axis at the center point P of

the table. The vertical axis shows the maximum amplitude

of vibration in the X axis direction in Fig. 15 (a), the

maximum amplitude of vibration in the Y axis direction in

Fig. 15 (b), and the natural vibration frequency, respectively.

First, Fig. 15 (a) and (b) show that the more the

measuring point separates from the point of 33 mm(= R/2),

the center of rail, the larger the maximum amplitude of the

vibration becomes. From Fig. 15 (c), the natural vibration

frequency exists approximately between 30 Hz and 60 Hz.

C. Impact test

In order to observe the vibration phenomena of this

mechanism in detail, a percussion test was conducted. For

the method, a vibration was given parallel to the x axis

direction presuming that the vibration would shift to the x

axis direction. And, placing displacement sensors parallel to

the X axis and Y axis, we measured the displacements of the

target placed at the center point P of the table when the

orientation angles are -10°, 0°, +10°. The maximum

amplitude of vibration and natural vibration frequency thus

obtained are shown in Fig. 16. In the Fig. 17(a) and (b), the

maximum amplitude of vibration at each position and each

orientation on the table in the X axis direction and Y axis

Fig. 14. Experimental equipment

Yp mm

(c) Amplitude |AY|

Fig. 15. Amplitude and natural frequency

Fig.16. Impact test

0 0.02 0.04 0.06 0.08

-0.04

-0.02

0

0.02

0.04

0.06

Dis

pla

cem

en

t

in X

ax

is d

irec

tio

n

mm

Time s

AX

P（Xp, Y

p）

Acceleration

sensor

Fixed end

X

Gap sensor

Fixed end

(a) Yp=0~62mm, Φp=-10o, 0, +10

o

φP

(b) Displacement in X axis direction

Hammer

direction are shown, and in the Fig. 18 (a) and (b), first and

second natural vibrat ion frequencies are shown.

The more the measuring point separates from the point of

33 mm, the center of rail, the larger the maximum amplitude

of the vibration becomes, and the primary natural vibration

frequency exists approximately between 30 Hz and 60 Hz,

which is the same result as that at the time of operation. In

the range surrounded by the gray color, that is, rectangular

area, in particular, the amplitude of vibration tends to

rapidly become large, and the natural vibration frequency

Fig. 19. Amplitude |AY|

Fig. 17. X and Y direction amplitude

Fig. 18. First and second frequencies

Yp mm

X

Fig. 20. The mechanism shape

tends to become small. The phenomena that occurred in the

range surrounded by the gray color is discussed as follows.

For support conditions, a magnet zipper was used as a

fixed end support. The measurements were conducted at 16

points between Y=0~60 mm at each orientation angle of

-10o, 0

o, +10

o.

Figure 19 shows the maximum amplitude of vibration in

the Y axis direction at each position and orientation of the

table, measured at the impact test. The orientations of the

table at the positions more than Yp=58 mm shown in Fig.

20(A) are shown in the upper figure. As the links 2 and 3

are parallel to the Y axis direction, the rigidity to the X axis

directions considered to become weak. The orientations of

the table at the positions less than Yp=24 mm shown in Fig.

20 (C) are shown in the lower figure. The links 1 and 3 are

parallel to the X axis and the restriction to Y axis direction

becomes weak shown in Fig.20(C), so that the rigidity to Y

axis direction is considered to become weak.

IX. Conclusions1) A polymer-made(PP) manipulator consisting of an

injection-molding pantograph mechanism and vacuum tweezers for a miniature surface mount system was designed and experimentally produced. A control circuit for manipulators was produced and operated, and the numeric values to be used for the miniature surface mount system were clarified.

2) The 2DOF XY table for the miniature surface mountsystem was designed and experimentally produced, and its dynamic characteristics, positioning accuracy and repeated positioning accuracy were clarified.

3) A polymer-made(PP) 3DOF parallel manipulator inthe miniature surface mount system was experimentally produced and the miniature surface mount system included in the equipment experimentally produced was subsequently evaluated.

4) Because the results of the percussion test agreed with

that of the driving test, it was revealed that the vibration

occurred in the mechanical section.

5) The rigidity was low in the positions of Yp<24 mm and

>58 mm, and the effect of vibration was remarkable.

6)There are no differences in the natural vibration

frequency caused by a orientation angle at and more than 35

Hz.

Acknowledgments This study is partially supported by the Scientific Research Grant-in-Aid No.13555040 from the Japan Society for the Promotion of Science.

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