- Email: [email protected]
feeding in PC board assembly
A Design for Parts Storage/Feeding in PC Board Assembly J.A. Khwaja, E.I. Dupont DeNemours & Co., Newark, Delaware T. Radhakrishnan, Villanova University, Villanova, Pennsylvania
small tolerances for the holes and component pins, fragility of the component pins, various shapes and sizes for the components, and high production rates. These factors contribute to make PC board assembly a formidable challenge for flexible assembly automation, with a general purpose PC board assembler capable of handling many different parts. The assembly system is required to successfully interface with the component storage and presentation subsystem, as well as with subsequent joining operations. Existing dedicated assembler systems can handle a few components at high speeds. ~3 However, they do not handle the odd-form components, which make up a significant portion of all assembled components. Flexibility is therefore important for an efficient assembler system to handle a variety of components for assembling various types of PC boards. Existing robotic assembly systems 4s involve limited flexibility and slower speeds of assembly. High speeds are desirable along with flexibility, to keep up with increasing demands on productivity. To enable such high-speed, flexible assembly, an important requirement is the storage and feeding (delivery) of a large variety of components at high speeds. 9 The problem has become all the more critical today, with an increasing number of pins and decreasing pitch distances for the component.t° A need therefore exists to develop alternate component delivery systems that enable components to arrive accurately positioned at the pick up
Abstract The flexible, automated, high speed assembly of printed circuit (PC) boards offers productivity gains over hard automation. While significant progress has been made to automate the component insertion on PC boards, there still remains a class of components, commonly referred to as 'oddform' components, whose handling has posed significant constraints on the flexibility of automation designs. This paper presents conceptual designs for the storage and feeding of such odd-form components to facilitate their automated assembly. Moreover, the problem is made more difficult because the component storage and feeding system technology has lagged behind the development of flexible assembly systems that it supports. In this paper, different design alternatives for the component storage/feeding system and its integration into an overall flexible assembly workstation are presented and quantitatively analysed. With appropriate software control and sensing techniques, these designs will enable a large variety of components to be assembled on a number of different types of PC boards, facilitating flexible, automated assembly at high speeds.
Keywords:Automated Assembly, PC Boards, Component Feeding, Component Storage.
Introduction The printed circuit (PC) board assembly involves high accuracy in component placement,
129
Journal of Manufacturing Systems Volume 9/No. 2
point. Like a truly flexible delivery system, it should have the capacity to deliver a variety of physically different components, instead of just a few. 5,u The development of such systems, however, poses a number of basic and applied research issues, including the following: 1. A large variety of different component geometries are encountered in each assembly task. 2. Often 100 or more components are utilized in a given assembly. With certain PC boards, this number increases to about 600 components per board. 3. Many of the components are mechanically compliant due to the leads used for electrical connections. 4. Components have 2 to 10 leads for discrete parts and 24 or more leads for dual-in-line packages (DIPS). 5. Electronic assembly of components requires acquisition, orientation, and insertion of components. The acquisition will require the capability to visualize the component position and orientation. This paper discusses general concepts by which odd-form components can be stored and delivered along with standard components, to enable automation, flexibility and high speeds in the PC board assembly process. The concept can also be extended to the storage and feeding of surfacemount devices which are increasingly being used today. 1o,12
IIIIDII!I il magazines
(carousels) with component tubes component tubes
~ ..--~ It--'-dm
im .....
:
bm - ~
"1
.........
7-i
. o tl.
[
I
IHRpresentation sites
component reels
wa
1
assembler
trays for odd-form components
88~
table
/ Ia
4
*[
Figure 1
Storage System Layout Design 1
storage and feeding subsystem, and that many types of components can be packaged in rigid tubes (which have proved to be effective storage containers). These tubes are arranged vertically on carousel-type magazines. Through an appropriate control program, these magazines can be moved to index and present the right component (tube) at the right time. The arrangement of tubes in the magazines and the number of magazines required will depend upon the type of components involved, the assembly sequence, and their rate of usage. In this design configuration, a number of individual magazines are located within a given rectangular area space behind one side of the workstation. One or more high-speed shuttles can be provided, depending upon the insertion speeds involved, for fetching the required components from the component-feeding ends (bottom ends) of the tubes. The shuttle picks up a component from the feeder, using suction. One or more types of suction/grippers may have to be used (with a gripper quick-change mechanism), to handle a variety of components. The shuttle(s) presents the components to the high-speed x-y assembler head (inserter unit) at one or more presentation sites. These sites may involve a registration plate to register the component before pick up by the assembler head.
Design of Storage Subsystem Layout The PC board assembly system concepts presented here are specifically designed to incorporate great flexibility so that various types and quantities of boards can be produced with minimum changeover time. The flexible assembly workstation is also configured in a manner that allows a wide variety of components to be stationed at the workstation at any one time. Many components can be stored in tubes which are prearranged into supply magazines that are moved by electronic drives and locked into position. Layout Design 1. The design (Figure 1) is based on the assumption that only one side (back of the workstation) is available for the component
130
Journal of Manufacturing Systems Volume 9/No. 2
The assembler head may also involve a variety of suction grippers for component pick up and handling. The magazines are individually controlled by the assembly system software to bring (index) the right tube (component) to the shuttle at the right time. Depending on the number and type of components, all storage tubes would be arranged in one or more interchangable modules. To facilitate presentation, certain odd-form components such as pin grid arrays, end connectors, and stiffeners may be alternatively arranged in tray-type containers. These trays can be placed on one side of the assembler table, as shown in F i g u r e 1. These odd-form components will be in proper orientation for assembly so that they can be directly picked up by the assembler head and inserted. Also, any axial lead components that the assembler head may be capable of handling can be stored in tape reels and arranged over one or more comers of the assembler table as shown. In order to quantitatively evaluate Design l, let: l m , w m -- total length and width of module enclosing all the magazines la, w ~ = length and width of the assembler table b,,, -- width of each magazine dm= distance between adjacent magazines w t = average (width of tube + distance between adjacent tubes) n s -- number of shuttles.
of having to successively fetch two components, has an average of ty seconds to fetch a component and present it to the assembler. The maximum distance which the shuttle will have to travel within this time is lm/n s (from the presentation site to the farthest magazine in that segment and back). Additionally, in an extreme case when a shuttle has to fetch two successive components located at the farthest ends on the same magazine, the time required for the magazine to index itself will also be ty. The maximum distance involved for indexing will be w,,, and this would occur when the two components are at opposite ends of the same magazine. Under these conditions, the maximum shuttle speed required will be: ss(max)
= (l,,/ns) / tf =
l m / (nstf)
and the maximum magazine indexing speed required will be: si (max)
= w m / tf.
Also, the approximate component storage area for this design is A s = l,, w m
and the approximate total area for the assembler system is A = As + l,,w,,. It should be noted, however, that a compromise exists between the possible shuttle or magazine-indexing speed and the size of the storage module. The indexing speed of the magazines and shuttle speed are critical if the desired component insertion rate is to be achieved. Also, the number of component storage and feeding tubes required for each component will depend on the estimated rate of use for that component, its dimensions and the tube length. If any checks are performed before a component is picked up by the inserter unit, the time involved for this should also be included in these calculations. Such checks may include:
Now, the total number of magazines that can be accommodated in the module is: n m --- l , n / ( b m + d m)
while the total length available (on all magazines) to accommodate tubes is -- n,,, x 2 w m -- 2 n m w m . Hence, the average number of tubes that can be accommodated in all the magazines is: nt = 2 n m W m / Wt = 2lmWm / {(bin + d m ) w t } .
The underlying assumptions here are: 1. Each shuttle covers an equal segment (length) of the module. 2. Each shuttle has its own presentation site, located at the mid-point of its working range. Hence, for an average component-fetching time of t f seconds, each shuttle, in the extreme case
• Check for the appropriate tube, using bar-code sensing. This check will establish whether the indexed tube is the one that was desired. • Check for the component stock level in the tube--this can be made using an optical or proximity sensor. This check will signal when-
131
Journal of Manufacturing Systems Volume 9/No. 2
ever the component quantity falls below a predetermined level. • Check for component pin straightness. This can also be achieved using optical sensors. L a y o u t D e s i g n 2. Design 2 (Figure 2) assumes that up to three sides of the assembly workstation are available for arranging the component storage tubes. Therefore, only the front side of the assembler table will be available for such tasks as loading/ unloading of the PC boards. In Design 2, component fetching-and-presenting shuttles move rapidly to get the right component at the right time. One shuttle is p r o v i d e d for each of the threetube-carrying magazines. Here, each magazine has its front half (the side near the assembler table) feeding the shuttle until that side runs empty. The magazine will remain stationary during this component feeding cycle. Once this component feeding side is empty or partially empty, the other half (back) of the magazine, with an identical arrangement of components, indexes to provide the components with practically no loss of time for component replenishment. The first side of the magazine can now be replenished while the second side is feeding components. To perform the quantitative analysis for this design, let:
magazines (carousels)
lead components
I/tes
presentation
3
bm ---~
I"
1a
,I
Figure 2
Storage System Layout Design 2
and the approximate total area for the assembler system is: A = A s + l,w,.
In a variation of Design 2, the magazines move each time, instead of the shuttles, to index the proper component tube at the presentation site. The assembler head will pick up the components from the presentation site and insert them into the PC board. No shuttle mechanism will be needed in this case. However, the indexing speeds will be very limited here due to the physical size of the magazines. Also, in both cases of Design 2, only a limited number of components can be stored at a given time. This limitation is imposed due to constraints on the magazine length (due to limits on the workstation size). L a y o u t D e s i g n 3. Design 3 (Figure 3) is based on the assumption that three sides of the assembly workstation table are available for component storage and feeding modules, with the fourth side (front side) kept open for PC board loading/unloading and operator intervention. Instead of indexable magazines, the storage/feeding modules in Design 3 consists of component tubes arranged in two layers (or more, if necessary) at an angle. F i g u r e 3 shows both layers of the tubes inclined at the same angle (front and back layers parallel); however, if required, it is possible to arrange the back layer at a relatively larger angle than the front layer. A larger tilt angle will help provide access to the back layer
W t
and the maximum shuttle speed (which is required when a shuttle has to fetch a component from the end of the longest magazine), is: Ss(max) =
1
dI
assembler Table
Hence, the average number of tubes that can be accommodated on all the three magazines is: (21a + 4 w , ) /
~a
shuttl track
the magazine at the back of the assembler w a = width of the assembler table; length of each of the two magazines at the sides of the assembler b m = average width of a magazine w t = average (tube width + distance between adjacent tubes).
=
E
inserter ooit
la = length of the assembler table; length of
12t
~
max {laJtf, WaJtf}.
The approximate storage area for this design is: A s = bm(l a + 2 W a)
132
Journal of Manufacturing Systems Volume 9/No. 2
(with a presentation site at the mid-point of each side of the workstation), the maximum shuttle speed required will be:
front layer of component tubes
t
Ss(max)
back layer o f component tubes
;
= m a x {1,]tf, w , / t f } .
The approximate component storage area for this design is: A s = lab + 2 w a b
and the approximate total area for the assembler system is: A
~b - -
An essential assumption for all design layouts is that the inserter unit has rotational capability. This rotational capability on the inserter unit will make possible the insertion of components in different angular orientations on the plane of the assembler table. This also increases the reliability of the system, since only the inserter unit will have the rotational capability instead of designing a number of component presentation pallets capable of rotation.
trays f o r o d d - form
components
Figure 3
Storage System Layout Design 3
of tubes for the assembler head to pick up the components presented. The entire module will be replaced when the components reach a certain minimum level. One important advantage of this layout design is the increased reliability of the system. This increased reliability is achieved since no moving mechanisms are used in the component storage and feeding system designs. However, this design may be modified to include a shuttle for each of the three component tube modules, as in the case of Design 2. To quantitatively evaluate Design 3, let:
Quantitative Analysis To obtain a comparative evaluation of the different layout designs, the following values may be used in the formulas derived under each design. Let: la = w a = 6.0 ft. (for all designs) w t = 1.5" -- 0.125 ft. (for all designs) lm = w m 6.0 ft. b m = 1.0 ft. d m = 0.5 ft. b = 1.0 ft. =
Ia, w a = length and width of assembler table Ia + 2 w a -- total length of the storage tubes (on all three sides) b = width of the module w t = average (tube width + distance between tubes).
Hs=3 ~- = 2.0 seconds. With this data, the calculated values of the various parameters or performance measures such as n t (total number of tubes), and n t / A s (number of tubes per unit area of storage space) are shown in T a b l e 1. It can be seen, for example, that Design 1 can hold a larger number of tubes (and can be expanded to hold more), compared to the other two designs. However, the space utilization ( n t / A , ) is lower (better) for Design 1.
Then, for a two-layered module, the average number of tubes that can be accommodated on the entire module is: nt
=
(21 a +
-- A S + l a w a.
4w a) / w t.
Also, if shuttles are used to fetch the components
133
Journal of Manufacturing Systems Volume 9/No. 2
Table 1 Comparison of the Three Layout Designs
the net average assembly time per board is: t b = Nctf + I N c / (nctnt)] tm~, or
Aspect
Desifln 1
Desifln 2
4
3
384
288
Ss(max) , i n / s e c .
12
36
si (max) , i n / s e c .
36
.
nm nt
Desifln 3
t b ---- N e [tf +
3*
where ~ is the average pick up and assembly time per component. Hence, the net yield is = 1/t b. Table 1 also indicates the yield factor, which compares the relative yields (assembled boards/unit time) for the three designs. The following values were used to obtain this factor:
288 36** .
.
.
As, sq.ft.
36
18
18
A, sq. ft.
72
54
54
nt/As, tubes/sq, ft.
10.66
16
16
nt/A , tubes/sq, ft
5.33
5.33
5.33
yietd factor
1.00
1.05
1.08
*
number of 2-tayered storage racks ( i n s t e a d of magazines)
**
i f s h u t t t e s are used in t h i s design
N~ = 500 components/board net = 30 components/tube tf = two seconds
tree = 60 minutes for Design 1, 30 minutes for Design 2, 20 minutes for Design 3. (n t values used are indicated in Table 1).
It is also of interest to determine the net average yield (assembled boards per unit time), given by the net average assembly time per board, with these designs. This time includes assembly (insertion) time, time to replace the entire set of magazines (or modules) and the time required for any maintenance or adjustments. The last quantity can be expected to be larger for designs with a larger number of moving elements. Hence, Design 1 may take the longest time for component replacement and adjustments, due to the size of the storage/ feeding module and the number of moving parts (magazines and shuttles). Design 2 assumes no magazine replacement, but only the replacement of individual tubes during the assembly process. Any interruptions for this design will be only for periodic adjustments or maintenance, which may be assumed to be done after each set of/7 t tubes are replaced. Design 3 will require minimal maintenance or adjustments, since there are no moving parts in the component delivery system. For a quantitative evaluation, let:
It can be seen that under these conditions, Design 3 has the highest yield factor (most productive) and Design 1 has the lowest. Such an analysis can be performed with various combinations of the parameter values, to decide on the optimum design for a given situation. Furthermore, the net cost of the component delivery system per board can be determined if the actual costs are known for the various aspects of the designs. These aspects include space, magazines (or modules) including any shuttle and feeding units, and component replacement and maintenance/adjustment processes (times).
Component Containers and Feeding For automatic component insertion on PC boards, it is necessary that the components be fed to the assembler head in correct orientation and at the right place at the right time. The design concepts presented in the following pages emphasize simple storage, feeding, and component placement. The component storage and feeding mechanisms thus involve a combination of conventional and nonconventional material handling techniques. C o m p o n e n t C o n t a i n e r s . The basic function of a component container is to hold a particular component in a specified orientation and to facilitate feeding it at the presentation site. The following
N c = average number of components
required per board average number of components per tube (which will depend on the tube length) t,, c -- average time required for the component module replacement and/or any maintenance/adjustments. nct
tmc / (nctnt) ]
=
Neglecting the board loading/unloading times,
134
Journal of Manufacturing Systems Volume 9/No. 2
guidelines are formulated for this purpose: 1. Components should be conveniently held and fed/presented. 2. The possibility of storing a wrong component or storing the component in an incorrect orientation should be minimized or eliminated. 3. Components should rest stably and slide smoothly in the storage containers. 4. The possibility of any pins on a component getting entangled or damaged due to adjacent components should be eliminated. 5. Replenishment of empty containers should not be complicated. 6. Provision should be made for any checking required to be done on the component before it is picked up by the assembler head. 7. These requirements should be achieved by as simple mechanisms as possible. Either a tube-type container or a tray-type container can be used to store the components, including odd-form components like pin grid arrays, pinned board assemblies and end connectors. Figure 4 and 5 shows appropriate tube designs for these odd-form components. Figure 6 shows an example of suitable tray designs for pin grid arrays and end connectors. The proposed tube or tray designs closely conform to the component outline, to reduce the chances of loading a component in a wrong orientation. The tube (or tray) size would be slightly larger than that of the component, thereby enabling the components to move freely. In all these designs, the component storage tubes are assumed to be held vertically in the storage magazine, with an inclined or curved section (chute) at the bottom (Figure 7) to facilitate feeding the component in the proper orientation. Alternatively, the tubes may be arranged at an angle, as shown in Figure 3. For feeding a component to the assembler head, a component transfer mechanism is provided at the bottom of a tube to hold and locate the components as they are released from the tube, and then to move the component to the presentation site for pick up. Trays are especially useful when components cannot be fed through tubes due to their fragile nature or because of their odd shape. Such trays provide a queue of properly placed and accurately secured compofients, accessible to the assembler head. As shown in Figure 1, components placed in
pin grid array with heat sink
pinned board assembly
protrusions to guide/orient the heat sink slot to gulde/orient ~ /
/
edge of base i
tube ..... iner
~!
sensor to check
ii
component leve~
II
/
" '
bar-code (a)
~
# ;b)
Figure 4 Tube Designs for a) Pin Grid Array and b) Pinned Board Assembly
trays along an edge of the assembler table can be directly picked up by the assembler head at specified locations (at the end of each tray). In this manner, tubes or trays for other types of odd-form components can be designed. The choice between a tube or a tray for storage and feeding of components depends upon factors such as difficulties in feeding a component by a particular design, cost of one design against the other, and space constraints. It will be very efficient if the vendors could deliver components in appropriate containers (tubes or trays), which can be directly placed in the workstation. Component Feeding. To obtain a component from the tubes (on the magazines) shuttles may be used to fetch the component from a particular magazine and present it in a proper orientation, to the assembler head, at specified presentation sites (Figure 1). To make the system less complex, shuttles may not be used at all and it is better to have the assembler head directly pick up the component from each magazine. Assuming that the assembler head directly
135
Journal of Manufacturing Systems Volume 9/No. 2
end connector
pins ~ ~
~~
tray
end c o n n e c t o r
sensortocheck component level
~...~l,m
and c o n n e c t o r platform tray
_ ~
component containertube. Figure 6 Tray Designs for End Connectors and Pin Grid Arrays
sensorto check componentlevel bar-code_~~ slotsto guide/ orientpins
lit .J
Figure 5 Tube Design for End Connector
picks up the components from a magazine, there will be one presentation site for each magazine (Figure 1 with no shuttles, or, Figure 2). A component transfer mechanism is used to bring (feed) the component from the bottom of the tube to the presentation site for pick up. At the bottom of each tube will be a component holder (or platform) to properly hold and locate the component with the right side up (i.e., with the pins facing down). This may be achieved by designing inclined or curved chutes to carry a component from the bottom part of the tube to the component holder. The component holders or the bottom portions of the tubes may be provided with suitable sensors to detect bent or missing pins on the component. Figure 7 shows a conceptual example of how the component transfer mechanism can be designed. A component holder is specifically designed for a particular component and attached to the appropriate tube at the bottom, along with the chute. The
co.taine~"~[~
pl. iocator hole~
chute
to presentation "re
. . . . .
comp....t ~id~" ~ ";:~:rdised componentholder
base
Figure 7 Component Feeding Arrangement for Pin Grid Array
chute and the component holder move with the tube as the magazine indexes, in the case of Design 1. However, they remain stationary in Design 3. For feeding, a component holder with a component is placed on a standard pallet and carried to the presentation site. All component holders have a standard base to fit the standard pallet. The compo-
136
Journal of Manufacturing Systems Volume 9/No. 2
replenishment at the appropriate time). 4. Other information such as the type of the gripper to be selected (if various grippers are used) by the inserter unit, safe holding forces, angular component orientation (to control rotation of part presentation pallet or inserter unit) and exceptional or error condition handling routines.
nent holders are temporarily disengaged from the tube container unit during the component feeding, and retract after the component is picked up. The pallet translates on a slide and can also be rotated (in a horizontal plane) to change the orientation of the component if required, in the case of Design 1. Instead of this arrangement, it is less complex and more efficient to have the assembler head capable of rotation to change the component orientation for insertion. Providing rotational capability to the assembler head instead of every pallet is a better approach, since it will reduce the number of moving mechanisms.
Concluding Remarks This study presents the concepts and quantitative analytical methods to efficiently design the component storage and feeding system for a highspeed, flexible, automated PC board assembler. Odd-form components can be stored in suitable tubes or trays, as outlined in this paper, to be incorporated in such a flexible component delivery system. Depending on the actual situation, a suitable component storage and feeding system can therefore be built for assembling a large number of different components on a variety of PC boards.
Additional Considerations Two other important areas which should be considered for an efficient assembly process are sensors and the control program. They are briefly mentioned here since they are complementary to this study; further details are beyond the scope of this paper. Sensors. Various sensing devices may be used to sense proper component feeding and assembly. Some of the key sensing situations are: 1. Monitoring the level of components in the tubes (or trays); optical or proximity sensors can be used. 2. Checking if the tube (or tray) feeding a component is the correct one; a bar-code reader can be used. 3. Checking if any pins on a component are bent or missing; optical (photo) sensors may be used. The need for such sensing will depend on the quality of the components and can be avoided at the assembly workstation if the component quality can be assured by prior checking. 4. Information regarding the components being ready to be picked up. Control Program. The program controlling the entire sequence of assembly operations should have a database that includes the following, pertinent to component presentation and pick up: 1. Component insertion sequence and locations. 2. Component storage locations. 3. Component inventory information (to keep track of each component's usage and to call for
Acknowledgement This project was sponsored by the Unisys C o r p o r a t i o n and the C o m m o n w e a l t h of Pennsylvania and was a subcontract from the Mechanical Engineering Department, University of Pennsylvania.
References 1. W.T. Cusik. "Design Parameters for Automatic Printed Circuit Board Assembly", NEPCON-West Conference Proceedings, February 1986, pp. 326-335. 2. H.R. Stillwell. " A n Automated Printed Circuit Board Assembly Factory", NEPCON-East Conference Proceedings, June 1985, pp. 357-360. 3. M. Matsunaga, T. Ooi. " F A System for Automatic Component Insertion on Printed Circuit Boards", Hitachi Review, Vol. 35, No. 1, 1986, pp. 21-24. 4. R.R. Schreiber. "Robots and Electronics Manufacturing", Manufacturing Engineering, December 1985, pp. 43-46. 5. M. DeLaCruz. "The Development of a High Performance Robotic Assembly Center for Printed Wiring Board Non-Standard Electronic Component Assembly",. SME/Robots-8 Conference Proceedings, June 1984, pp. 8.11-8.44. 6. J.A. Henderson, R.N. Hosier. "New Robotic Systems Change the Electronics Assembly Factory", SME/Robots-8 Conference Proceedings, June 1984, pp. 8.57-8.75. 7. C.H. Mangin. "Component Insertion and Placement", Assembly
137
Journal of Manufacturing Systems Volume 9/No. 2
Engineering, May 1987, pp. 20-23. 8. J. Garin, T. Stiles. "Robotic Assembly for Printed Circuit Boards", SME/Robots-ll Conference Proceedings, April 1987, pp. 4.33-4.47. 9. D. Ford. "Favorite Feeder", Circuits" Manufacturing, April 1989, pp. 41-44. 10. M.L. Martel. "Going Off-Line: Component Changes Drive Assembly", Circuits Manufacturing, July 1989, pp. 30-32. 11. R.D. McCleary. "Printed Circuit Board Assembly and Test is Automation Adaptable", SME/Robots-8 Conference Proceedings, June 1984, pp. 8.76-8.91. 12. R. Cook. "Surface Mount is Taking Hold", Managing Automation, November 1988, pp. 50-54. 13. C. Dupont-Gatelmand. " A Survey of Flexible Manufacturing Systems", Journal of Manufacturing Systems, Vol. 1, No. 1, 1984, pp. 1-16.
14. P.F. Ranky. "FMS in CIM", Robotica Journal, Vol. 3, 1985, pp. 205-213. 15. R. Harrison, R.H. Weston, P.R. Moore, T.W. Thatcher. " A Study of Application Areas for Modular Robots", Robotica Journal, Vol. 5, 1987, pp. 217-221. 16. A.E. Christy, K.B. Maynard. "Multi-function ComputerControlled Component Inserter", IBM Technical Disclosure Bulletin, July 1980, pp. 455-457. 17. F. Aldana, E. Olinas. E.J. Salvador. "Julius: A Printed Circuit Board Program for PC-IBM", IEEE/IECON '86 Proceedings, 1986, pp. 431-436. 18. J.A. Khwaja. "Design of a Parts Storage and Feeding System for Robotic Assembly of PC Boards", Master's Thesis, Mechanical Engineering Department, Villanova University, Villanova, Pennsylvania, 1986.
Author(s) Biography Jamil A. Khwaja is currently employed at E.I. Dupont DeNemours & Co., Mechanized Systems Group in Newark, Delaware. He obtained his B.S.M.E. from the University of Engineering and Technology in Lahore, Pakistan, and his Master's degree from Villanova University in Villanova, Pennsylvania. He has prior work experience at the Research Institute in Dhahran, Saudi Arabia. His current areas of interest include flexible assembly automation and expert systems for manufacturing. T. Radhakrishnan is an Assistant Professor of Mechanical Engineering at Villanova University in Villanova, Pennsylvania. He was previously a faculty member at the University of Rhode Island in the Industrial Engineering Department. He received his B.Tech. (ME) from the Indian Institute of Technology, Madras, India, and his Ph.D. (ME) from the University of Wisconsin, Madison. Professor Radhakrishnan has been actively involved in developing a CAD/CAM program at Villanova. His research interests include manufacturing processes and automated manufacturing systems.
138
small tolerances for the holes and component pins, fragility of the component pins, various shapes and sizes for the components, and high production rates. These factors contribute to make PC board assembly a formidable challenge for flexible assembly automation, with a general purpose PC board assembler capable of handling many different parts. The assembly system is required to successfully interface with the component storage and presentation subsystem, as well as with subsequent joining operations. Existing dedicated assembler systems can handle a few components at high speeds. ~3 However, they do not handle the odd-form components, which make up a significant portion of all assembled components. Flexibility is therefore important for an efficient assembler system to handle a variety of components for assembling various types of PC boards. Existing robotic assembly systems 4s involve limited flexibility and slower speeds of assembly. High speeds are desirable along with flexibility, to keep up with increasing demands on productivity. To enable such high-speed, flexible assembly, an important requirement is the storage and feeding (delivery) of a large variety of components at high speeds. 9 The problem has become all the more critical today, with an increasing number of pins and decreasing pitch distances for the component.t° A need therefore exists to develop alternate component delivery systems that enable components to arrive accurately positioned at the pick up
Abstract The flexible, automated, high speed assembly of printed circuit (PC) boards offers productivity gains over hard automation. While significant progress has been made to automate the component insertion on PC boards, there still remains a class of components, commonly referred to as 'oddform' components, whose handling has posed significant constraints on the flexibility of automation designs. This paper presents conceptual designs for the storage and feeding of such odd-form components to facilitate their automated assembly. Moreover, the problem is made more difficult because the component storage and feeding system technology has lagged behind the development of flexible assembly systems that it supports. In this paper, different design alternatives for the component storage/feeding system and its integration into an overall flexible assembly workstation are presented and quantitatively analysed. With appropriate software control and sensing techniques, these designs will enable a large variety of components to be assembled on a number of different types of PC boards, facilitating flexible, automated assembly at high speeds.
Keywords:Automated Assembly, PC Boards, Component Feeding, Component Storage.
Introduction The printed circuit (PC) board assembly involves high accuracy in component placement,
129
Journal of Manufacturing Systems Volume 9/No. 2
point. Like a truly flexible delivery system, it should have the capacity to deliver a variety of physically different components, instead of just a few. 5,u The development of such systems, however, poses a number of basic and applied research issues, including the following: 1. A large variety of different component geometries are encountered in each assembly task. 2. Often 100 or more components are utilized in a given assembly. With certain PC boards, this number increases to about 600 components per board. 3. Many of the components are mechanically compliant due to the leads used for electrical connections. 4. Components have 2 to 10 leads for discrete parts and 24 or more leads for dual-in-line packages (DIPS). 5. Electronic assembly of components requires acquisition, orientation, and insertion of components. The acquisition will require the capability to visualize the component position and orientation. This paper discusses general concepts by which odd-form components can be stored and delivered along with standard components, to enable automation, flexibility and high speeds in the PC board assembly process. The concept can also be extended to the storage and feeding of surfacemount devices which are increasingly being used today. 1o,12
IIIIDII!I il magazines
(carousels) with component tubes component tubes
~ ..--~ It--'-dm
im .....
:
bm - ~
"1
.........
7-i
. o tl.
[
I
IHRpresentation sites
component reels
wa
1
assembler
trays for odd-form components
88~
table
/ Ia
4
*[
Figure 1
Storage System Layout Design 1
storage and feeding subsystem, and that many types of components can be packaged in rigid tubes (which have proved to be effective storage containers). These tubes are arranged vertically on carousel-type magazines. Through an appropriate control program, these magazines can be moved to index and present the right component (tube) at the right time. The arrangement of tubes in the magazines and the number of magazines required will depend upon the type of components involved, the assembly sequence, and their rate of usage. In this design configuration, a number of individual magazines are located within a given rectangular area space behind one side of the workstation. One or more high-speed shuttles can be provided, depending upon the insertion speeds involved, for fetching the required components from the component-feeding ends (bottom ends) of the tubes. The shuttle picks up a component from the feeder, using suction. One or more types of suction/grippers may have to be used (with a gripper quick-change mechanism), to handle a variety of components. The shuttle(s) presents the components to the high-speed x-y assembler head (inserter unit) at one or more presentation sites. These sites may involve a registration plate to register the component before pick up by the assembler head.
Design of Storage Subsystem Layout The PC board assembly system concepts presented here are specifically designed to incorporate great flexibility so that various types and quantities of boards can be produced with minimum changeover time. The flexible assembly workstation is also configured in a manner that allows a wide variety of components to be stationed at the workstation at any one time. Many components can be stored in tubes which are prearranged into supply magazines that are moved by electronic drives and locked into position. Layout Design 1. The design (Figure 1) is based on the assumption that only one side (back of the workstation) is available for the component
130
Journal of Manufacturing Systems Volume 9/No. 2
The assembler head may also involve a variety of suction grippers for component pick up and handling. The magazines are individually controlled by the assembly system software to bring (index) the right tube (component) to the shuttle at the right time. Depending on the number and type of components, all storage tubes would be arranged in one or more interchangable modules. To facilitate presentation, certain odd-form components such as pin grid arrays, end connectors, and stiffeners may be alternatively arranged in tray-type containers. These trays can be placed on one side of the assembler table, as shown in F i g u r e 1. These odd-form components will be in proper orientation for assembly so that they can be directly picked up by the assembler head and inserted. Also, any axial lead components that the assembler head may be capable of handling can be stored in tape reels and arranged over one or more comers of the assembler table as shown. In order to quantitatively evaluate Design l, let: l m , w m -- total length and width of module enclosing all the magazines la, w ~ = length and width of the assembler table b,,, -- width of each magazine dm= distance between adjacent magazines w t = average (width of tube + distance between adjacent tubes) n s -- number of shuttles.
of having to successively fetch two components, has an average of ty seconds to fetch a component and present it to the assembler. The maximum distance which the shuttle will have to travel within this time is lm/n s (from the presentation site to the farthest magazine in that segment and back). Additionally, in an extreme case when a shuttle has to fetch two successive components located at the farthest ends on the same magazine, the time required for the magazine to index itself will also be ty. The maximum distance involved for indexing will be w,,, and this would occur when the two components are at opposite ends of the same magazine. Under these conditions, the maximum shuttle speed required will be: ss(max)
= (l,,/ns) / tf =
l m / (nstf)
and the maximum magazine indexing speed required will be: si (max)
= w m / tf.
Also, the approximate component storage area for this design is A s = l,, w m
and the approximate total area for the assembler system is A = As + l,,w,,. It should be noted, however, that a compromise exists between the possible shuttle or magazine-indexing speed and the size of the storage module. The indexing speed of the magazines and shuttle speed are critical if the desired component insertion rate is to be achieved. Also, the number of component storage and feeding tubes required for each component will depend on the estimated rate of use for that component, its dimensions and the tube length. If any checks are performed before a component is picked up by the inserter unit, the time involved for this should also be included in these calculations. Such checks may include:
Now, the total number of magazines that can be accommodated in the module is: n m --- l , n / ( b m + d m)
while the total length available (on all magazines) to accommodate tubes is -- n,,, x 2 w m -- 2 n m w m . Hence, the average number of tubes that can be accommodated in all the magazines is: nt = 2 n m W m / Wt = 2lmWm / {(bin + d m ) w t } .
The underlying assumptions here are: 1. Each shuttle covers an equal segment (length) of the module. 2. Each shuttle has its own presentation site, located at the mid-point of its working range. Hence, for an average component-fetching time of t f seconds, each shuttle, in the extreme case
• Check for the appropriate tube, using bar-code sensing. This check will establish whether the indexed tube is the one that was desired. • Check for the component stock level in the tube--this can be made using an optical or proximity sensor. This check will signal when-
131
Journal of Manufacturing Systems Volume 9/No. 2
ever the component quantity falls below a predetermined level. • Check for component pin straightness. This can also be achieved using optical sensors. L a y o u t D e s i g n 2. Design 2 (Figure 2) assumes that up to three sides of the assembly workstation are available for arranging the component storage tubes. Therefore, only the front side of the assembler table will be available for such tasks as loading/ unloading of the PC boards. In Design 2, component fetching-and-presenting shuttles move rapidly to get the right component at the right time. One shuttle is p r o v i d e d for each of the threetube-carrying magazines. Here, each magazine has its front half (the side near the assembler table) feeding the shuttle until that side runs empty. The magazine will remain stationary during this component feeding cycle. Once this component feeding side is empty or partially empty, the other half (back) of the magazine, with an identical arrangement of components, indexes to provide the components with practically no loss of time for component replenishment. The first side of the magazine can now be replenished while the second side is feeding components. To perform the quantitative analysis for this design, let:
magazines (carousels)
lead components
I/tes
presentation
3
bm ---~
I"
1a
,I
Figure 2
Storage System Layout Design 2
and the approximate total area for the assembler system is: A = A s + l,w,.
In a variation of Design 2, the magazines move each time, instead of the shuttles, to index the proper component tube at the presentation site. The assembler head will pick up the components from the presentation site and insert them into the PC board. No shuttle mechanism will be needed in this case. However, the indexing speeds will be very limited here due to the physical size of the magazines. Also, in both cases of Design 2, only a limited number of components can be stored at a given time. This limitation is imposed due to constraints on the magazine length (due to limits on the workstation size). L a y o u t D e s i g n 3. Design 3 (Figure 3) is based on the assumption that three sides of the assembly workstation table are available for component storage and feeding modules, with the fourth side (front side) kept open for PC board loading/unloading and operator intervention. Instead of indexable magazines, the storage/feeding modules in Design 3 consists of component tubes arranged in two layers (or more, if necessary) at an angle. F i g u r e 3 shows both layers of the tubes inclined at the same angle (front and back layers parallel); however, if required, it is possible to arrange the back layer at a relatively larger angle than the front layer. A larger tilt angle will help provide access to the back layer
W t
and the maximum shuttle speed (which is required when a shuttle has to fetch a component from the end of the longest magazine), is: Ss(max) =
1
dI
assembler Table
Hence, the average number of tubes that can be accommodated on all the three magazines is: (21a + 4 w , ) /
~a
shuttl track
the magazine at the back of the assembler w a = width of the assembler table; length of each of the two magazines at the sides of the assembler b m = average width of a magazine w t = average (tube width + distance between adjacent tubes).
=
E
inserter ooit
la = length of the assembler table; length of
12t
~
max {laJtf, WaJtf}.
The approximate storage area for this design is: A s = bm(l a + 2 W a)
132
Journal of Manufacturing Systems Volume 9/No. 2
(with a presentation site at the mid-point of each side of the workstation), the maximum shuttle speed required will be:
front layer of component tubes
t
Ss(max)
back layer o f component tubes
;
= m a x {1,]tf, w , / t f } .
The approximate component storage area for this design is: A s = lab + 2 w a b
and the approximate total area for the assembler system is: A
~b - -
An essential assumption for all design layouts is that the inserter unit has rotational capability. This rotational capability on the inserter unit will make possible the insertion of components in different angular orientations on the plane of the assembler table. This also increases the reliability of the system, since only the inserter unit will have the rotational capability instead of designing a number of component presentation pallets capable of rotation.
trays f o r o d d - form
components
Figure 3
Storage System Layout Design 3
of tubes for the assembler head to pick up the components presented. The entire module will be replaced when the components reach a certain minimum level. One important advantage of this layout design is the increased reliability of the system. This increased reliability is achieved since no moving mechanisms are used in the component storage and feeding system designs. However, this design may be modified to include a shuttle for each of the three component tube modules, as in the case of Design 2. To quantitatively evaluate Design 3, let:
Quantitative Analysis To obtain a comparative evaluation of the different layout designs, the following values may be used in the formulas derived under each design. Let: la = w a = 6.0 ft. (for all designs) w t = 1.5" -- 0.125 ft. (for all designs) lm = w m 6.0 ft. b m = 1.0 ft. d m = 0.5 ft. b = 1.0 ft. =
Ia, w a = length and width of assembler table Ia + 2 w a -- total length of the storage tubes (on all three sides) b = width of the module w t = average (tube width + distance between tubes).
Hs=3 ~- = 2.0 seconds. With this data, the calculated values of the various parameters or performance measures such as n t (total number of tubes), and n t / A s (number of tubes per unit area of storage space) are shown in T a b l e 1. It can be seen, for example, that Design 1 can hold a larger number of tubes (and can be expanded to hold more), compared to the other two designs. However, the space utilization ( n t / A , ) is lower (better) for Design 1.
Then, for a two-layered module, the average number of tubes that can be accommodated on the entire module is: nt
=
(21 a +
-- A S + l a w a.
4w a) / w t.
Also, if shuttles are used to fetch the components
133
Journal of Manufacturing Systems Volume 9/No. 2
Table 1 Comparison of the Three Layout Designs
the net average assembly time per board is: t b = Nctf + I N c / (nctnt)] tm~, or
Aspect
Desifln 1
Desifln 2
4
3
384
288
Ss(max) , i n / s e c .
12
36
si (max) , i n / s e c .
36
.
nm nt
Desifln 3
t b ---- N e [tf +
3*
where ~ is the average pick up and assembly time per component. Hence, the net yield is = 1/t b. Table 1 also indicates the yield factor, which compares the relative yields (assembled boards/unit time) for the three designs. The following values were used to obtain this factor:
288 36** .
.
.
As, sq.ft.
36
18
18
A, sq. ft.
72
54
54
nt/As, tubes/sq, ft.
10.66
16
16
nt/A , tubes/sq, ft
5.33
5.33
5.33
yietd factor
1.00
1.05
1.08
*
number of 2-tayered storage racks ( i n s t e a d of magazines)
**
i f s h u t t t e s are used in t h i s design
N~ = 500 components/board net = 30 components/tube tf = two seconds
tree = 60 minutes for Design 1, 30 minutes for Design 2, 20 minutes for Design 3. (n t values used are indicated in Table 1).
It is also of interest to determine the net average yield (assembled boards per unit time), given by the net average assembly time per board, with these designs. This time includes assembly (insertion) time, time to replace the entire set of magazines (or modules) and the time required for any maintenance or adjustments. The last quantity can be expected to be larger for designs with a larger number of moving elements. Hence, Design 1 may take the longest time for component replacement and adjustments, due to the size of the storage/ feeding module and the number of moving parts (magazines and shuttles). Design 2 assumes no magazine replacement, but only the replacement of individual tubes during the assembly process. Any interruptions for this design will be only for periodic adjustments or maintenance, which may be assumed to be done after each set of/7 t tubes are replaced. Design 3 will require minimal maintenance or adjustments, since there are no moving parts in the component delivery system. For a quantitative evaluation, let:
It can be seen that under these conditions, Design 3 has the highest yield factor (most productive) and Design 1 has the lowest. Such an analysis can be performed with various combinations of the parameter values, to decide on the optimum design for a given situation. Furthermore, the net cost of the component delivery system per board can be determined if the actual costs are known for the various aspects of the designs. These aspects include space, magazines (or modules) including any shuttle and feeding units, and component replacement and maintenance/adjustment processes (times).
Component Containers and Feeding For automatic component insertion on PC boards, it is necessary that the components be fed to the assembler head in correct orientation and at the right place at the right time. The design concepts presented in the following pages emphasize simple storage, feeding, and component placement. The component storage and feeding mechanisms thus involve a combination of conventional and nonconventional material handling techniques. C o m p o n e n t C o n t a i n e r s . The basic function of a component container is to hold a particular component in a specified orientation and to facilitate feeding it at the presentation site. The following
N c = average number of components
required per board average number of components per tube (which will depend on the tube length) t,, c -- average time required for the component module replacement and/or any maintenance/adjustments. nct
tmc / (nctnt) ]
=
Neglecting the board loading/unloading times,
134
Journal of Manufacturing Systems Volume 9/No. 2
guidelines are formulated for this purpose: 1. Components should be conveniently held and fed/presented. 2. The possibility of storing a wrong component or storing the component in an incorrect orientation should be minimized or eliminated. 3. Components should rest stably and slide smoothly in the storage containers. 4. The possibility of any pins on a component getting entangled or damaged due to adjacent components should be eliminated. 5. Replenishment of empty containers should not be complicated. 6. Provision should be made for any checking required to be done on the component before it is picked up by the assembler head. 7. These requirements should be achieved by as simple mechanisms as possible. Either a tube-type container or a tray-type container can be used to store the components, including odd-form components like pin grid arrays, pinned board assemblies and end connectors. Figure 4 and 5 shows appropriate tube designs for these odd-form components. Figure 6 shows an example of suitable tray designs for pin grid arrays and end connectors. The proposed tube or tray designs closely conform to the component outline, to reduce the chances of loading a component in a wrong orientation. The tube (or tray) size would be slightly larger than that of the component, thereby enabling the components to move freely. In all these designs, the component storage tubes are assumed to be held vertically in the storage magazine, with an inclined or curved section (chute) at the bottom (Figure 7) to facilitate feeding the component in the proper orientation. Alternatively, the tubes may be arranged at an angle, as shown in Figure 3. For feeding a component to the assembler head, a component transfer mechanism is provided at the bottom of a tube to hold and locate the components as they are released from the tube, and then to move the component to the presentation site for pick up. Trays are especially useful when components cannot be fed through tubes due to their fragile nature or because of their odd shape. Such trays provide a queue of properly placed and accurately secured compofients, accessible to the assembler head. As shown in Figure 1, components placed in
pin grid array with heat sink
pinned board assembly
protrusions to guide/orient the heat sink slot to gulde/orient ~ /
/
edge of base i
tube ..... iner
~!
sensor to check
ii
component leve~
II
/
" '
bar-code (a)
~
# ;b)
Figure 4 Tube Designs for a) Pin Grid Array and b) Pinned Board Assembly
trays along an edge of the assembler table can be directly picked up by the assembler head at specified locations (at the end of each tray). In this manner, tubes or trays for other types of odd-form components can be designed. The choice between a tube or a tray for storage and feeding of components depends upon factors such as difficulties in feeding a component by a particular design, cost of one design against the other, and space constraints. It will be very efficient if the vendors could deliver components in appropriate containers (tubes or trays), which can be directly placed in the workstation. Component Feeding. To obtain a component from the tubes (on the magazines) shuttles may be used to fetch the component from a particular magazine and present it in a proper orientation, to the assembler head, at specified presentation sites (Figure 1). To make the system less complex, shuttles may not be used at all and it is better to have the assembler head directly pick up the component from each magazine. Assuming that the assembler head directly
135
Journal of Manufacturing Systems Volume 9/No. 2
end connector
pins ~ ~
~~
tray
end c o n n e c t o r
sensortocheck component level
~...~l,m
and c o n n e c t o r platform tray
_ ~
component containertube. Figure 6 Tray Designs for End Connectors and Pin Grid Arrays
sensorto check componentlevel bar-code_~~ slotsto guide/ orientpins
lit .J
Figure 5 Tube Design for End Connector
picks up the components from a magazine, there will be one presentation site for each magazine (Figure 1 with no shuttles, or, Figure 2). A component transfer mechanism is used to bring (feed) the component from the bottom of the tube to the presentation site for pick up. At the bottom of each tube will be a component holder (or platform) to properly hold and locate the component with the right side up (i.e., with the pins facing down). This may be achieved by designing inclined or curved chutes to carry a component from the bottom part of the tube to the component holder. The component holders or the bottom portions of the tubes may be provided with suitable sensors to detect bent or missing pins on the component. Figure 7 shows a conceptual example of how the component transfer mechanism can be designed. A component holder is specifically designed for a particular component and attached to the appropriate tube at the bottom, along with the chute. The
co.taine~"~[~
pl. iocator hole~
chute
to presentation "re
. . . . .
comp....t ~id~" ~ ";:~:rdised componentholder
base
Figure 7 Component Feeding Arrangement for Pin Grid Array
chute and the component holder move with the tube as the magazine indexes, in the case of Design 1. However, they remain stationary in Design 3. For feeding, a component holder with a component is placed on a standard pallet and carried to the presentation site. All component holders have a standard base to fit the standard pallet. The compo-
136
Journal of Manufacturing Systems Volume 9/No. 2
replenishment at the appropriate time). 4. Other information such as the type of the gripper to be selected (if various grippers are used) by the inserter unit, safe holding forces, angular component orientation (to control rotation of part presentation pallet or inserter unit) and exceptional or error condition handling routines.
nent holders are temporarily disengaged from the tube container unit during the component feeding, and retract after the component is picked up. The pallet translates on a slide and can also be rotated (in a horizontal plane) to change the orientation of the component if required, in the case of Design 1. Instead of this arrangement, it is less complex and more efficient to have the assembler head capable of rotation to change the component orientation for insertion. Providing rotational capability to the assembler head instead of every pallet is a better approach, since it will reduce the number of moving mechanisms.
Concluding Remarks This study presents the concepts and quantitative analytical methods to efficiently design the component storage and feeding system for a highspeed, flexible, automated PC board assembler. Odd-form components can be stored in suitable tubes or trays, as outlined in this paper, to be incorporated in such a flexible component delivery system. Depending on the actual situation, a suitable component storage and feeding system can therefore be built for assembling a large number of different components on a variety of PC boards.
Additional Considerations Two other important areas which should be considered for an efficient assembly process are sensors and the control program. They are briefly mentioned here since they are complementary to this study; further details are beyond the scope of this paper. Sensors. Various sensing devices may be used to sense proper component feeding and assembly. Some of the key sensing situations are: 1. Monitoring the level of components in the tubes (or trays); optical or proximity sensors can be used. 2. Checking if the tube (or tray) feeding a component is the correct one; a bar-code reader can be used. 3. Checking if any pins on a component are bent or missing; optical (photo) sensors may be used. The need for such sensing will depend on the quality of the components and can be avoided at the assembly workstation if the component quality can be assured by prior checking. 4. Information regarding the components being ready to be picked up. Control Program. The program controlling the entire sequence of assembly operations should have a database that includes the following, pertinent to component presentation and pick up: 1. Component insertion sequence and locations. 2. Component storage locations. 3. Component inventory information (to keep track of each component's usage and to call for
Acknowledgement This project was sponsored by the Unisys C o r p o r a t i o n and the C o m m o n w e a l t h of Pennsylvania and was a subcontract from the Mechanical Engineering Department, University of Pennsylvania.
References 1. W.T. Cusik. "Design Parameters for Automatic Printed Circuit Board Assembly", NEPCON-West Conference Proceedings, February 1986, pp. 326-335. 2. H.R. Stillwell. " A n Automated Printed Circuit Board Assembly Factory", NEPCON-East Conference Proceedings, June 1985, pp. 357-360. 3. M. Matsunaga, T. Ooi. " F A System for Automatic Component Insertion on Printed Circuit Boards", Hitachi Review, Vol. 35, No. 1, 1986, pp. 21-24. 4. R.R. Schreiber. "Robots and Electronics Manufacturing", Manufacturing Engineering, December 1985, pp. 43-46. 5. M. DeLaCruz. "The Development of a High Performance Robotic Assembly Center for Printed Wiring Board Non-Standard Electronic Component Assembly",. SME/Robots-8 Conference Proceedings, June 1984, pp. 8.11-8.44. 6. J.A. Henderson, R.N. Hosier. "New Robotic Systems Change the Electronics Assembly Factory", SME/Robots-8 Conference Proceedings, June 1984, pp. 8.57-8.75. 7. C.H. Mangin. "Component Insertion and Placement", Assembly
137
Journal of Manufacturing Systems Volume 9/No. 2
Engineering, May 1987, pp. 20-23. 8. J. Garin, T. Stiles. "Robotic Assembly for Printed Circuit Boards", SME/Robots-ll Conference Proceedings, April 1987, pp. 4.33-4.47. 9. D. Ford. "Favorite Feeder", Circuits" Manufacturing, April 1989, pp. 41-44. 10. M.L. Martel. "Going Off-Line: Component Changes Drive Assembly", Circuits Manufacturing, July 1989, pp. 30-32. 11. R.D. McCleary. "Printed Circuit Board Assembly and Test is Automation Adaptable", SME/Robots-8 Conference Proceedings, June 1984, pp. 8.76-8.91. 12. R. Cook. "Surface Mount is Taking Hold", Managing Automation, November 1988, pp. 50-54. 13. C. Dupont-Gatelmand. " A Survey of Flexible Manufacturing Systems", Journal of Manufacturing Systems, Vol. 1, No. 1, 1984, pp. 1-16.
14. P.F. Ranky. "FMS in CIM", Robotica Journal, Vol. 3, 1985, pp. 205-213. 15. R. Harrison, R.H. Weston, P.R. Moore, T.W. Thatcher. " A Study of Application Areas for Modular Robots", Robotica Journal, Vol. 5, 1987, pp. 217-221. 16. A.E. Christy, K.B. Maynard. "Multi-function ComputerControlled Component Inserter", IBM Technical Disclosure Bulletin, July 1980, pp. 455-457. 17. F. Aldana, E. Olinas. E.J. Salvador. "Julius: A Printed Circuit Board Program for PC-IBM", IEEE/IECON '86 Proceedings, 1986, pp. 431-436. 18. J.A. Khwaja. "Design of a Parts Storage and Feeding System for Robotic Assembly of PC Boards", Master's Thesis, Mechanical Engineering Department, Villanova University, Villanova, Pennsylvania, 1986.
Author(s) Biography Jamil A. Khwaja is currently employed at E.I. Dupont DeNemours & Co., Mechanized Systems Group in Newark, Delaware. He obtained his B.S.M.E. from the University of Engineering and Technology in Lahore, Pakistan, and his Master's degree from Villanova University in Villanova, Pennsylvania. He has prior work experience at the Research Institute in Dhahran, Saudi Arabia. His current areas of interest include flexible assembly automation and expert systems for manufacturing. T. Radhakrishnan is an Assistant Professor of Mechanical Engineering at Villanova University in Villanova, Pennsylvania. He was previously a faculty member at the University of Rhode Island in the Industrial Engineering Department. He received his B.Tech. (ME) from the Indian Institute of Technology, Madras, India, and his Ph.D. (ME) from the University of Wisconsin, Madison. Professor Radhakrishnan has been actively involved in developing a CAD/CAM program at Villanova. His research interests include manufacturing processes and automated manufacturing systems.
138