Brian Lewis
ITI Manta

It happens every day. Product developers are stuck playing Russian roulette with high warranty returns and customer dissatisfaction as the deadly results. Too often, engineers spend countless hours developing the perfect analytical model without really understanding the environment in which the final product must survive. Assumptions about input loads, number of occurrences, and usage hours must be made early in the development process to establish design criteria. At best, uninformed decisions result in over-designed, costly components. At worst, incorrect assumptions can really hit the bottom line in the form of increased warranty exposure, poor performance and unhappy customers.

Customer Usage Profiling (CUP) is a data acquisition and analysis methodology used to define the performance of products while in the hands of the customer. Profiling activities involving direct measurements and statistical analysis can take the guesswork out of product development. While this type of process has been used in the automotive community for some time, other industries are now beginning to take advantage of information garnished from a well thought out program. In fact, the very chair that you are sitting on right now could have benefited from an extensive CUP program.

Benefits of Customer Usage Profiling

Figure 1 - While this may seem like a very extreme case, it emphasizes the importance for manufacturers to define how their products are being used. Unintended or extreme uses are just two of the reasons why understanding customer usage is so important.

CUP captures unbiased, real-world data while the product is in service. This process provides a true picture of product performance outside the confines of a traditional laboratory environment. Gathered data enable companies to design and manufacture reliability, durability, and quality into their products. Collecting and understanding this information decreases the likelihood of under or over-designing in the early development stages. This translates directly into reduced warranty and manufacturing costs and improved market share through superior quality.

Collecting and Analyzing Field Data

Computer and electronic advances in the last 40 years have brought about the proliferation of digital data acquisition systems. Equipment that once required all of the free space within a vehicle can now be packaged into the size of a deck of cards. Smaller, custom acquisition systems can be designed and manufactured for those projects particularly tight on space.

Before the first measurement is made, a suitable strategy for gathering the required data must be developed. At this stage, engineers need to exercise caution to avoid the trap of over complicating the project by trying to measure every nuance of the product's operating environment. Maintaining more channels of data than necessary adds cost and complexity to the overall project. Conversely, care must also be taken to capture all information pertinent to the product's performance. Past history and warranty records can provide valuable insight into which measurements are important.

In addition to determining which data should be collected, the allowable level of customer interaction must also be defined before instrumented products are released into the field. Based on the project requirements, one of three levels of interaction is usually adequate:

• User actively participates in the acquisition --- An example of this type of project might be data collection in a factory environment. In a recent project completed by ITI Manta temperature information was collected on a large piece of food service equipment as the machine operated. During the acquisition, the machine's operator actively monitored the tests. ITI Manta is an engineering testing and analysis firm located in Milford, OH. ITI Manta is a member of the International TechneGroup Incorporated (ITI) family.
• User is aware of the acquisition but does not actively participate --- A project completed by ITI Manta for Herman Miller, Inc. involving office chairs is an example of this. This program is described in more detail later.
• User has no knowledge of the data gathering activity --- This type of acquisition can be used on virtually any product where customer knowledge could unacceptably bias the data. Keeping the data collection process completely autonomous and hidden is the most difficult to do from a practical standpoint. A recent ITI Manta project illustrating this procedure involved profiling a fleet of recreational vehicles. Standard production vehicles were instrumented with channels that measured acceleration, displacement, temperature and event occurrences. All of the data acquisition equipment and sensors were hidden from view. In addition, the tests ran completely autonomously. No interaction whatsoever was required for several weeks at a time while the systems recorded performance data.

Most CUP programs are broken down into at least three phases: product instrumentation, field data collection and data analysis. During the product instrumentation phase, all of the data acquisition equipment is installed and its operation verified. Very often, standard transducers and signal conditioning required are not readily available. In this case, special sensors and electronic equipment may need to be designed specifically for the project.

Once a product is instrumented, it can be given to customers to collect data. Depending on the level of interaction required, this may simply entail handing the product over to a group of users. Typical data acquisition systems can log several megabytes of information. Based on the number of channels and type of data recorded, this capacity may be enough storage for weeks of uninterrupted operation. Typically, data are uploaded periodically as different users are exposed to the product. This allows the performance to be recorded as a function of different types of users. In addition, correct operation of the system can be verified by studying the field data.

Data from a CUP program, coupled with the appropriate analysis, can be used to answer many questions regarding a product's performance. Depending on the goal of the program, customer usage data can be used to do everything from determining maximum load levels to helping quantify why a specific product is viewed by the customer as "more comfortable". CUP can help answer questions like the following:

• How many times will this (door be opened, latch be pushed, switch be activated) in the normal service life of the product?
• What is the 95th percentile (or the 90th, or the 50th, or the maximum) load that my customers are putting on my product's armrest (or faucet handle, or trigger switch) ?
• How does my product's performance compare against a competitor?
• How do my customers in (Ohio or Florida or Arizona) use the product compared with customers in (Taiwan or Germany or Mexico) ?
• What kind of laboratory test represents (1 day or 1 month or 25 years) of normal service?
• What is the fatigue life of this (chair post, bicycle frame, mixer blade) based on a 99th percentile user?
• What demographic of users are statistically the most damaging to my product?

Figure 2 - This figure depicts a fully instrumented chair used during the data acquisition portion of the program. The main power circuit contained an accelerometer that was used to "wake up" the system when the chair was disturbed. The entire system was self-contained, allowing chairs to easily be dispersed at several locations without any daily interaction.

Office Seating CUP Project

Recently, ITI Manta completed a CUP project with furniture manufacturer, Herman Miller, Inc. In order to maintain the high level of quality Herman Miller is known for, ITI Manta helped institute a program incorporating customer profiling of their standard office seating line. Data collected were used to generate laboratory tests simulating the most damaging users and to develop a more complete understanding of an office chair's daily environment. Based on a preliminary study involving several seating lines, the Ambi model chair was eventually chosen for the customer usage field test. Because of its clean construction and well-defined geometry, the Ambi proved to be the perfect candidate for extrapolating results into other chair lines.

A total of twelve Ambi model chairs were instrumented (Figure 2) and given to customers at six different locations over a four-month time period. Over 100 users were eventually studied during the program. Data were harvested and reviewed at one-week intervals by Herman Miller and ITI Manta personnel.

Six measurements of load and position were made on each of the instrumented chairs. Three of the channels were dedicated to measuring loads and moments at the seat post (Figure 3). To achieve repeatable measurements, ITI Manta designed a special seat-post load cell and calibrated it with known forces (Figure 4). In addition to the seat post location, moments were also measured at the seat back and armrest. In order to evaluate the chair's configuration during various loading conditions, the position of the seat back was also measured.

Commercially available computer systems collected the field data. An onboard, 12-volt gel cell battery provided power for each of the systems by way of a custom designed power circuit. The power circuit used an accelerometer to "wake up" the data acquisition equipment when the chair was moved or jostled in any way. If the chair was not disturbed for a period of time exceeding two hours, the power circuit shut down all of the equipment in order to conserve resources.

Figure 3 - Several modifications to the chair structure were required in order to incorporate the custom load cell. The picture above shows the modified framework of the chair along with the installed seat post load cell.

Once the data collection phase of the program was complete, ITI Manta engineers analyzed the results to define the severity of each user based on a fatigue-life model. The end product of this analysis was a spreadsheet that contained the user's physical information (sex, height, weight, occupation, etc.) and a number for each of the load channels indicating the amount fatigue sustained by the chair in one week. This allowed Herman Miller to quantify the durability requirements for office-seating products based on customers' use.

The second portion of the data reduction phase included developing an accelerated laboratory bench test. The final bench test simulates use by applying varying loads to different areas of the chair. Dynamic loads are applied automatically and repeated until the desired damage has been accumulated (Figure 5). The magnitude, direction, number of repetitions and order of the loading events all correlate to data from the CUP program. Using this procedure, Herman Miller engineers can simulate many years of use in only a matter of a few weeks. This capability allows verification of new designs, design modifications, and manufacturing processes such that every Herman Miller chair lives up to strict durability standards.

Figure 4 - This is the seat post load cell being calibrated using a hydraulic actuator. The actuator applies a known load to the cell as a computer measures the output of the transducer. All of the load cells were calibrated using this method.

Usage profiling can benefit manufacturers of everything from enormous mining equipment to miniature cell phones. A complete understanding of a product's environment is essential for any development team. Well-designed programs pay for themselves many times over in the form of reduced warranty claims, improved performance and superior reliability.

Figure 5 - The red arrows depict two of the locations where loads are applied to the chair during the bench test. The test is designed to reproduce the damage for one week of use. Multiple repeats of the test allow for longer time periods to be studied.

Corporations spend millions of dollars each year to attract customers and maintain brand loyalty. It stands to reason that those in charge of development should at least know how consumers will likely use their products. A complete CUP program provides the required information so manufacturer's can design durability and quality into every product.