Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
1999-03-26
2001-07-10
Smith, Matthew (Department: 2825)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
C716S030000, C706S013000
Reexamination Certificate
active
06260178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of automated assembly, and in particular to the field of printed circuit board component placement and assembly.
2. Description of Related Art
Printed circuit boards are typically assembled via the use of component placement machines, typically called “pick and place” machines. Electronic components are automatically placed on the printed circuit board by a placement machine and subsequently electrically attached to the board, using, for example, wave soldering techniques. Typically, the component placement machine comprises multiple component placement modules, so that multiple components can by placed on the printed circuit board at the same time. For mechanical efficiency, component placement machines or modules have a limited range of travel for placing the components, and therefore, the printed circuit board is typically processed in steps, each step placing a different portion of the printed circuit board within the range of the placement machine or module.
FIG. 1
illustrates a top view of an example assembly line of printed circuit boards
100
(
100
A,
100
B,
100
C,
100
D, and
100
E) and a component placement machine that includes eight component placement modules
150
(
150
A-
150
H). Each placement module
150
includes a feeder bar
160
that supplies components (not shown) to a movable head
170
. The feeder bar
160
includes feeder slots
162
through which each component is supplied. The movable head
170
subsequently places the component at its appropriate location (x, y) on the printed circuit board
100
that is within its range. The movable head
170
travels in a latitudinal (y) direction on a movable bar
175
that moves in a longitudinal (x) direction to reach the appropriate location (x, y), and then moves in a vertical (z) direction (perpendicular to the view of
FIG. 1
) to place the component on the printed circuit board
100
. The movable head
170
also rotates within the x-y plane, so that components may be placed in different orientations on the printed circuit board
100
. After each of the placement modules
150
place their allocated components, the printed circuit boards
100
move a predetermined distance, traveling for example on a conveyor system
120
. After moving the predetermined distance, the placement modules
150
place the next set of allocated components, the allocation being determined based upon the area of the printed circuit board
100
that is within the reach of each placement module
150
.
As is commonly known in the art, the speed with which the component placement machine can populate each board
100
is a function of the particular components allocated to each particular placement module
150
, and the order in which each placement module
150
obtains these selected components. Ideally, for example, one would want all of the placement modules to complete their placements of allocated components at exactly the same time at each step, thereby avoiding periods of inefficiency when only a few of the heads are being utilized. Other constraints also limit the speed of operation, or throughput, of the component placement machine. For example, the number and type of feeder slots
162
provided to each feeder
160
may limit the choice of components that may be allocated to a particular placement module.
The allocation of components to placement modules is a combinatorially complex problem having no known closed-form solution. Conventionally, the allocation is performed manually, or via the use of conventional programs based upon, for example, heuristics algorithms. U.S. Pat. No. 5,390,283, “Method for Optimizing the Configuration of a Pick and Place Machine”, by Larry J. Eshelman and James D. Schaffer, issued Feb. 14, 1995, presents a method for determining a near-optimal allocation of components to placement modules through the use of an evolutionary algorithm, and is incorporated herein by reference. In that patent, as in the conventional method of component allocation, the step size is predetermined for a given placement machine, based upon the pitch of the printed circuit boards on the conveyor system. The pitch is defined as the distance from the start of one printed circuit board to the start of the next printed circuit board; it is the width of the printed circuit board plus the space between boards on the conveyor system. A stepping scheme for a printed circuit board with a pitch of 360 mm, for example, is presented in the referenced patent as a sequence of a 40 mm step followed by four 80 mm steps.
As discussed above, each step movement of the conveyor system determines the area of each printed circuit board that is within the reach of each placement module. As such, the choice of step movements will have a direct effect on the allocation options provided for each module, and therefore a direct effect on the speed of the component placement process. The choice of step movements, however, has a combinatorial effect on the allocation process, which is already a combinatorially complex problem. As such, the determination of a step movement that provides for optimal or near optimal throughput from the component placement machine does not currently have a closed form solution. For example, the aforementioned pitch of 360 mm could be processed as six steps of 60 mm each, rather than the steps of 40 mm followed by four 80 mm presented above. There will be, for example, a delay time associated with the starting, moving, and halting of the conveyor system for the additional sixth step, against which any gains of speed by different allocations must be weighed. In like manner, the pitch of 360 mm could be processed as nine 40 mm steps, three 120 mm steps, and so on. Even if the number of steps is the same, the choice of step size can affect the allocation; for example, a step of 80 mm followed by four steps of 70 mm might allow for a faster process than the aforementioned 40 mm followed by four 80 mm steps. Each choice of step sizes produces a substantially different set of options to the allocation process, dependent upon the relationships of the components being placed in the different areas within range of each movable head at each step.
BRIEF SUMMARY OF THE INVENTION
It is an object of this invention to provide a device or method for determining a preferred step movement sequence for a component placement machine. It is a further object of this invention to provide a preferred step movement sequence that optimizes the throughput of a component placement machine. It is a further object of this invention to provide a device or method for determining the preferred step size that does not require an exhaustive assessment of all possible step sizes.
These objects and others are achieved by representing the step size parameters as genes in a component placement chromosome, and applying evolutionary algorithm techniques to evolve offspring that have step size parameters that provide an improved component placement speed. The offspring that have these preferential step size parameters are used to generate additional offspring that provide further improvement in the component placement speed. After a number of generations, the step size parameters of the offspring that provides the best component placement speed are used to program the component placement machine to achieve an improved throughput.
REFERENCES:
patent: 5390283 (1995-02-01), Eshelman et al.
patent: 5909674 (1999-06-01), Schaffer et al.
patent: 0 763 796 A2 (1996-10-01), None
patent: 07022784A (1993-07-01), None
patent: 07141438A (1993-11-01), None
patent: 10209682A (1997-01-01), None
patent: 09216135A (1997-08-01), None
Philips Electronics North America Corporation
Smith Matthew
Speight Jibreel
Waxler Aaron
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