Improving Aerospace Manufacturing Productivity

The aerospace manufacturing industry is unique in the challenges it faces, in the quality demanded of it, and in its foundation in technology and innovation. Manufacturing operations are highly complex and spread over vast facilities, with the most stringent safety-critical quality requirements. In a competitive industry where efficiency must prevail in the face of such unique challenges, a precise real-time location system (RTLS), such as ones that use ultra wideband (UWB) technology, can make a significant impact on a company's profits.

Manufacturing operations are the subject of deep study, with every aspect of facility design and workflow optimized for efficiency. However, things don't always go according to plan: parts show up late, tools get lost, people are delayed, items have to be reworked; there's no end to the number of ways that a simple process can take longer than expected, with an effect that ripples back through the operation like a stack of dominos falling.

There are several crucial questions that must be answered if a plant is to maintain optimum efficiency in the face of the unexpected:

1. How do you measure performance to identify trouble spots?
2. How do you troubleshoot the trouble spots to find the root cause?
3. What system do you put in place to fix the problem?
4. How do you measure the effectiveness of the solution?

One way to address these issues is to install a precise RTLS to monitor and manage workflow. Analogous to an indoor GPS, a precise RTLS allows you to locate all of your tooling, work-in-process and personnel at all times and in relation to each other. The rest of this article describes how a RTLS achieves this, discusses technology options and challenges and makes a recommendation for the optimal RTLS technology.

Identifying Problems

Manufacturing efficiency is all about having the right people, tools and parts in the right work cell at the right time. Efficiency drops when those elements are delayed, or when a particular process takes longer than expected. A precise RTLS, with tags on tools, work in process (WIP) and personnel, can quickly identify deviations from expectation at every stage of the process. The graphic above shows an example of a wearable UWB badge tag. Reports looking back over hours, days, weeks or longer can show how elements move through the process and where delays are occurring.

Troubleshooting Problems

Having identified an issue, it is necessary to drill down to find the root cause. Here again a precise RTLS adds significant value by showing a history of activity down to the most detailed level. For example, a report shows that the WIP was idle in Work Cell 2 for four hours before work started, and a closer look reveals that all elements were in place except for one special tool. The location system shows that the tool was not returned to the tool store after it was last used, and that the bulk of the delay was caused by a prolonged search.

Many other problems can be identified in this way including personnel delayed in other work cells and partially assembled parts taking longer to traverse from one cell to another.

Fixing Problems

A precise RTLS can also be used to look for solutions to problems. Because manufacturing efficiency is about having the right elements, in the right place, at the right time, what better tool to enable the process than a real time location system?

On one level, a precise RTLS can solve problems like missing tools and jigs by showing their location on a map of the facility. Search times are dramatically reduced when the exact location of items is known with confidence.

On another level, a RTLS can trigger changes in workflow when problems occur. WIP delayed in Work Cell 9? Then the team waiting in Work Cell 10 might be better employed elsewhere, rather than waiting for the delayed assembly.

If everything works according to the workflow simulation used to design the plant and processes, then efficiency is at its peak at all times. The second something starts to go wrong, a precise RTLS can alert supervisors to the issue and provide the necessary data to recover or re-optimize the process.

Once a problem is fixed, the final question is whether the fix works, and to what extent. Using the same long-term reporting function that alerted supervisors to the initial problem, a precise RTLS provides ongoing efficiency metrics to quantify the effectiveness of the solution.

Technologies and Challenges

Throughout this article, the term "precise RTLS" has been used - but why "precise?" What does that mean?

There are several different technologies that enable real-time location systems and each achieves a particular level of location accuracy. For any particular technology, the location accuracy is also affected by the environment in which it is operating. The cavernous buildings and highly-metallic structures associated with aerospace manufacturing are the worst of all places to achieve any location accuracy.

How precise does a RTLS really need to be when tracking things as big as aircraft? Does the system have to tell me where a wing is to within a meter for me to find it? The answer, of course, is not at all. But what about a tool or a small jig? Some things are harder to find than others and the closer the RTLS can point you, the less time you waste searching.

But cutting down on search times is only part of the value of a RTLS. A key value is the ability to automate trouble shooting and recovery. For this to be reliable and effective, the RTLS must give some indication of what is happening in addition to where things are.

For example, the knowledge that the assembly worker and tool cart are in Work Cell 5 but that the WIP has not yet arrived is a certain indication that the Work Cell 5 process has not yet begun. This might be an alarm state that requires intervention and re-planning. The question therefore becomes not one of how accurate the RTLS has to be in order to find an object, but how accurate it has to be to reliably report which cell a tagged person or item is in. The RTLS must have better accuracy than the size of the work cell. For example, a system that can only tell you the location of an item to ±30ft has no chance of telling you whether that item is inside or outside a 10ft x 10ft cell.

However, that's only part of the story. Some location systems will promise "room level accuracy" - many relying on the physical walls of the room in order to achieve that. But in aerospace, work cells don't have walls, or often any other demarcation apart from the yellow line painted on the floor. So how far is one cell from another? It's often just the thickness of a painted line. The result is that in these situations the RTLS must provide location accuracy much better than the size of the cell, approaching that of the thickness of the line. Clearly, the more accurate the location, the higher the reliability of deciding which cell a tagged object is in.

Traditionally, manufacturing facilities have used a variety of techniques from proximity sensors and limit switches to barcodes and passive RFID to manage WIP in a linear, deterministic process. If the workflow is constrained to determined paths following lines and conveyors, then these techniques work well. However, aerospace manufacturing processes are much more mobile, and involve large items moved throughout immense facilities. In this environment a system somewhat like a GPS is required, with a network of infrastructure devices communicating to tags over a radio link to determine the location of the tags.

Several technologies operate in this manner, and they fall into one of two camps: those that measure the location of a tag using signal strength (the louder the signal, the closer the tag) such as Wi-Fi, UHF, etc., and those that measure location using the time of arrival of the signal (the sooner the receiver hears the tag, the closer it is), such as UWB and 2.4GHz systems.

Signal strength systems can be immediately ruled out for use in aerospace manufacturing due to the wide open nature of the facilities. The trouble with signal strength is that it is indeed affected by how far the receiver is from the transmitter, but also by a host of other issues including tag orientation, blockages, etc. You have only to watch the bars on a cell phone constantly change while the cell phone is stationary to realize that signal strength is not just affected by location. To a signal strength RTLS, the cell phone is moving. In the wide open spaces of aerospace manufacturing, the signal strength does not change terribly with location (since the signal is just going through air), and those small changes which might indicate the location of the tag are swamped by those other effects.

The time-of-arrival (TOA) class of technologies is therefore the one that is being widely adopted in manufacturing. However, these technologies still face a number of challenges with one particular technology having an edge over all others.

Technology Recommendation

Even TOA systems vary in their ability to achieve location accuracy, particularly in a highly metallic manufacturing environment. These systems rely on an ability to accurately time the arrival of pulses in order to calculate the location of tags. Most systems have rather long pulses, however, causing reduced timing and therefore location accuracy. By way of analogy, think of timing the arrival of a thunder clap to measure how far away a storm is: long rumbles are hard to time accurately because it's hard to recognize when they start. A sharp clap of thunder is better defined and easier to time accurately.

The RTLS equivalent of a sharp clap of thunder is a UWB-based system. UWB is a radio technology that employs very short pulses with excellent timing and therefore location accuracy. Where a traditional TOA RTLS might achieve 5ft to 10ft accuracy in the best conditions, UWB can achieve 6" to 1ft accuracy.

In a manufacturing environment, the reflections of the pulses off metallic structures and objects cause even TOA systems to falter. A traditional system will struggle to achieve 20ft to 30ft of accuracy, whereas UWB still functions with better than 3ft precision.

In summary, a precise RTLS can add value in many ways, alerting supervisors to workflow inefficiencies, pinpointing the root cause of a problem, providing the solution to the problem and monitoring progress to calculate return on investment (ROI). At a personal level, a RTLS can improve the work environment by removing frustrations and wasted time, and also improve safety around dangerous machinery or processes.

The value of a RTLS is measured in the reliability of the data produced, which is based on the accuracy of location measurements. In the challenging aerospace manufacturing environment, only UWB-based systems offer the required performance to drive real improvements in efficiency by preventing interruptions and costly errors in workflow.

In the complex, competitive world of aerospace, when every last drop of efficiency must be wrung from manufacturing facilities, an ultra wideband real-time location system offers the precise real-time operational visibility to streamline business processes and increase profits.