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Line Controller Software: A Crucial Element in PCB Assembly Lines.

In a typical mid- to high-volume surface-mount production line, two or more pick-and-place machines are used per line. At least one machine is dedicated to the smaller passive components such as chip capacitors and resistors, and the other machine is used for the larger quad flat packs (QFPs), connectors, odd-shaped components or components that must be very accurately placed.

Most pick-and-place machines have their own internal controller, which allows the machine to operate independently from the other machines in the same line or be used as a stand-alone island of automation. This machine modularity is an important consideration in the printed circuit board (PCB) assembly industry, where manufacturers continually strive for smaller line footprints, faster line throughputs and better automated assembly production. To fully utilize the modular aspect of today's pick-and-place machines, equipment manufacturers have developed and evolved line controller software packages.

Line Controller Software

Pick-and-place equipment companies developed line controller software in the early to mid-1980s. This requirement was driven by the surface-mount industry's need to install multiple pick-and-place machines in an in-line fashion.

Line controller software is usually installed and run from a separate off-the-shelf personal computer system and is typically connected, in one form or another, to the pick-and-place machines (Figure 1). Software used in some of the earlier line controller systems was very limited. Most systems could do file editing and pick-and-place program storage, and they had limited uploading/downloading ability and some form of simplistic line monitoring. Some packages were required or needed to control machine-to-machine board flow (pre-SMEMA).

Today, most systems offer features to assist manufacturing or production engineers with the day-to-day challenges of operating surface-mount pick-and-place assembly lines.

Line Controller Features

Line controller software features and capabilities should be an important part of the machine selection process, whether the purchase is for one machine or multiple machine assembly lines. A line controller software package should offer the following basic features to enhance modularity:

- true factory networking capabilities

- line configuration editor

- pick-and-place programming editor

-preprogrammed component database li-brary with editor

- automatic pick-and-place program and production line optimization program

-pick-and-place program production time estimator module

- centralized line and production monitoring ability

- production results reports

- the ability to use all of the above editors and modules, while running the assembly line using the same MSWindows(r)-based workstation.

Networking capabilities

The ability to network the line controller station with the pick-and-place machines quickly and easily is very important when modularity is a factor. Line controller software and hardware should be compatible with existing networks that are installed in electronics manufacturing facilities. The most widely used standard is the Ethernet-based 10/100 Mbps type systems.

With this in mind, line controller software should allow the end user to set up the line controller workstation and placement machines anywhere in the manufacturing facility. The distance between the line controller workstation and the pick-and-place machines should only be limited by the production facility's network infrastructure.

The networking of production equipment in today's manufacturing facilities could mean as many as three different network scenarios:

- Utilize the existing installed network infrastructure in a manufacturing facility. Connect the line controller workstation and the pick-and-place machines to the network hub (Figure 2). Establish a fixed Internet protocol (IP) address for the pick-and-place equipment. Then configure the line controller software with the IP address of the pick-and-place machines. The line controller workstation will then have access to the machines and also the ability to archive files and pull computer-aided design (CAD) data and bills of materials (BOM) data from the network hard drives.

- Create a stand-alone network on the production floor. Some manufacturing facilities do not want the manufacturing equipment on the corporate network or may not have an established factory network. The line controller software should allow the user to create a stand-alone network (Figure 1). This network enables production engineers to quickly connect a line for communication with the controller. By having the line controller and pick-and-place machine software based on an MSWindows(r)a operating system, this task is easy. The hub and cabling can be found at most local PC dealers and will cost under $500 in most cases.

- Utilize floppy disk transfer. The user can save data at the line controller workstation to a diskette and hand-carry it to the pick-and-place machine. Conversely, the user may save changes made at the machine level and upload them from the diskette to the line controller workstation.

Line configuration editor

To be cost effective in today's economy, production engineers must be able to quickly reconfigure their surface-mount assembly production lines to handle frequently fluctuating manufacturing de-mands. If production engineers could treat the pick-and-place machines in a production facility as modular capacity blocks, the production facility could reconfigure the lines based on the number of capacity blocks needed to produce a particular PCB assembly or a grouping of assemblies.

Being able to physically move pick-and-place equipment or capacity blocks quickly in and out of a production line is very important. But just as important, the line controlling software must be able to look at this new line configuration, and with a minimum amount of data entry, "learn" from the pick-and-place machines installed in the line the type of accessories and options that are on each piece of equipment.

The line configuration portion of this software should allow the new line configuration to be virtually established at the workstation before any equipment is physically repositioned (Figure 3). Then, based on this new virtual line configuration, the program generation module of the line controller software could be used to create new programs that will allow for line optimization and throughput simulation of the proposed model before any equipment is moved.

If the required throughput is estimated to be too high or too low based on the needed capacity, the line could be reconfigured and reoptimized to obtain the required throughput. When the physical line must be reconfigured, the hardware is moved, the new virtual line configuration is moved to the active configuration, and the line is ready to run.

Pick-and-place programming editor

All line controller packages should include a program editor module. This module would allow program data to be brought in and organized into pick-and-place programs and allow editing of existing programs. Key features should include:

- a standard preprogrammed surface-mount component library with the ability to add and customize components

- the ability to split-up and optimize programs for single stand-alone machines set up as islands of automation, as well as across a multi-machine line, depending on the current line configuration

- the ability to optimize a program for fastest possible throughput only, fastest changeover time only or a combination of both

- the ability to bring in board size information, board x and y placement data and BOM component information for program generation (Figure 4)

- the ability to develop or edit new and existing programs while using the same workstation for line monitoring or to allow parts of the program editor to be used on separate workstations.

Production time estimator

This module is an essential part of a line controller software package. This estimator module should use the actual pick-and-place program file, generated by the program editor module, to create a numerical and graphical report of the actual time that will be needed to build the required amount of circuit boards (Figure 5). With this module, a production engineer can very precisely estimate the cost per placement to accurately bid on new production jobs.

How does a pick-and-place machine production time estimator work? Once the program has been generated and optimized for the best throughput, an estimator program can look at the placement sequence, number and type of nozzle changes required, where the component feeders should be positioned, and the conveyor transfer time. After this data has been analyzed, all the individual movements should be broken down to their length of travel. The following movements would then occur once the board has entered the machine:

- move placement head from the park position to the first fiducial (x and y move)

- move placement head from first fiducial to second fiducial (x and y move)

- move placement head from second fiducial to feeder pick location (x and y move)

- move nozzle down to pick component (z and theta move)

- move nozzle up after pick (z and theta move)

- move placement head to placement location (x and y move)

- move nozzle down to place component (z and theta move)

- move nozzle up, after placement (z and theta move).

The eight multi-axis movements would be required to place one component on one circuit board, with a pick-and-place machine that has one placement nozzle. To place additional components, the fiducial steps would not need to be duplicated, but the six other steps would be repeated for each standard surface-mount component placed. So, a pick-and-place program for 200 standard surface-mount components populated onto a circuit board that has two fiducials for offset correction would require 1,202 separate movements of various lengths or distances from point-to-point.

A good estimator program should look at each of these movements in terms of distance from point-to-point, and calculate the required distance to ramp-up to maximum velocity, distance traveled at maximum velocity, and the distance needed to ramp-down to stop including any movement settling time. Other factors that should be considered are time needed to change nozzles or pick up tools and the conveyor overhead time.

The accuracy of this program is very important in the job-estimating process and should not be overlooked in the evaluation process when searching for new equipment.

Centralized line and production monitoring

In a multi-machine line, the ability to send programs to the line and monitor all the pick-and-place machines from a centralized workstation makes it easier for a single operator to manage the assembly line (Figure 6).

This module of the line controller software should have the following features:

- Single-point monitoring capability for multiple pick-and-place machines in an assembly line. While the line is being monitored from the workstation, access to the other modules of the software package is needed. This feature is important for true off-line programming capabilities. A MSWindows(r)- based workstation would be the best platform for this type of software package. This workstation would provide the easiest and most widely accepted method of multitasking by allowing different modules of the line controller software package to be running in multiple windows.

- Upload and download pick-and-place programs to the line, including the ability to upload any changes made locally at the machine.

- The ability to view real-time, upload and save the production management data from the line after the job has been completed. The final report should include data for the entire line as well as individually by machine.

Production results reports

After the production management data has been uploaded, the data should be presented in a format that is easy to view and that allows the production engineer to customize the output format. The format most widely available in software packages is text-based with very little organization and description of each data field, subsequently complicating evaluation. Instead, output formats should be easily tailored for the desired audience, allowing the data to be presented as formatted text, bar charts, time lines and pie charts.

Conclusion

When purchasing a pick-and-place assembly line, many factors must be considered. The three main attributes considered by many production engineers when evaluating new equipment are:

- throughput capability, measured in components per hour (CPH)

- equipment flexibility, which is the ability to adapt the basic machine platform to meet changing market requirements

- modularity, which is how easily the line can be reconfigured to allow for better equipment utilization.

Line controller software is often overlooked or only given a cursory inspection during pick-and-place machinery purchases. A multi-machine surface-mount assembly line represents an expensive, long-term investment. If the line is down for program generation or product changeover, or if an excessive amount of time is needed to reconfigure changes in production capacity, the payback on the equipment will be slow in coming and the cost-per-placement will be too high to compete in the current economic conditions. An exceptional line controller package should eliminate the bottlenecks involved with program generation, changeover and assembly line reconfiguration, and it should aid in securing new business for a surface-mount production facility.

---

Chris Lawing is director of technical services with JUKI Automation Systems Inc., Morrisville, NC; e-mail: clawing@jas-smt.com.

http://www.circuitsassembly.com

Copyright [copyright] 2001 CMP Media LLC
COPYRIGHT 2001 UP Media Group, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2001, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Author:Lawing, Chris
Publication:Circuits Assembly
Date:Sep 1, 2001
Words:2068
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