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Build vs Buy HMI Interface

2010-03-04 15:23:00views: 864David Pascoe (QSI Corporation)

Build vs Buy HMI Interface

Many of the machines and vehicles in daily use in commercial and industrial settings worldwide feature displays and touch pads for operator input and control. These devices are known as Human-Machine Interfaces or HMIs, but are also commonly called Operator Interface Terminals and Mobile Data Terminals. As the main means of communication between machines and their human operators, HMIs must be functional, durable and reliable. In many cases, they must be ruggedised to operate in extreme conditions, impervious to heat, cold, dust, liquids, shaking, jarring or other environmental hazards. Any manufacturer of complex machines or vehicles that include HMIs must face a crucial decision: should you build your own human machine interfaces or should you buy these vital components ready-made or customised from an outside source?

To help solve the build versus buy dilemma, let us take a closer look at what is involved in designing, building, testing and maintaining a human machine interface system by outlining a typical product development cycle.

  • Planning
    Begin by making an honest assessment of your engineering capabilities. Given your company’s core competencies and priorities as well as the opportunity costs involved, is the design of a human-machine interface terminal the best use of precious engineering resources?
  • Design Phase
    The first consideration in the engineering design phase is whether your engineers have the experience to design and build for environmental ruggedness.
    Next, consider that many aspects of electrical and mechanical design are highly specific, if not unique, to the requirements and constraints of environmental ruggedness.
    In particular, the ability to specify components that will operate at extreme temperatures, to mount components so they can withstand vibration and shock, and to seal displays and keypads from liquids, dust and other environmental hazards is highly specialised knowledge that most engineering design teams struggle to master. Developing those skills from scratch is a costly and time-consuming effort.
    Finally, do not discount the complexity of software development for even a simple human-machine interface. Today, most displays provide graphical feedback to the human operator. The demands of programming in a graphical environment are many times more complex than programming for character-only displays.
    Unless you build your terminals to use a general purpose software platform such as Microsoft Windows or Windows CE, you must plan for a significant software development task in addition to the hardware development of your human-machine interface.
    In addition, using an OS such as Windows involves a very challenging and costly ‘port’ to the specific hardware platform. Decisions such as these can greatly affect time-to-market for your final product.
  • Prototyping
    It is important to prototype early and often in the design phase of a new product. Assess your company’s ability to develop mechanical prototypes quickly and cost effectively.
    Do your engineers have access to a 3D printer, for example, or will they have to send CAD files to an outside service? Have they identified prototype sources for custom components of your human machine interface such as keypads, touch screens and housings? Prototyping is costly and time-consuming if you do not have the necessary tools in-house or strategic partner relationships in place.
  • Testing
    How will your engineering team address the issues of testing both the hardware and software components? Does your team have the capability to design and build test fixtures and write the testing software?
    Also, fixtures and software must be created prior to the final assembly of product. It is important to note that manufacturers of rugged human machine interface terminals typically ‘burn-in’ production terminals in an environmental chamber for 24 hours at temperatures ranging from -20 °C to +70 °C to ensure the units’ production quality. Does your company have the equipment to perform environmental tests such as these?
  • Iteration
    How many iterations of a design will your product development schedule allow? There are many potential failure points in the design and manufacture of an human-machine interface that must function in harsh conditions.
    Multiple re-designs and prototypes can use up critical weeks of development time. Yet most complex engineering projects require from three to six prototype stages to fully optimise the final product.
  • Final Testing & Certification
    The final testing and certification of rugged HMIs is a demanding discipline. Depending on the environment in which the machine will be used, HMIs may have to be tested for operation over extreme temperature ranges, as well as for thermal shock as devices are taken instantaneously from one temperature extreme to another.
    They may have to meet humidity requirements or be tested for sealing against immersion or high volume liquid spray. They may need to meet vibration and shock tests, and they must withstand electrostatic discharge and electromagnetic interference. In addition, they will have to pass regulatory certifications such as FCC Part 15, UL , CSA , or CE.
  • Release To Manufacturing
    The final release to manufacturing involves the generation of many types of documentation, including manufacturing documents, assembly drawings and flow diagrams. Repair manuals are required for service technicians and operator manuals for end users. The documentation task alone for an HMI involves many man hours of coordinated work, as well as a documentation tracking and updating system.
    Manufacturing also requires its own specially designed testing software and fixtures.
  • Sustaining Engineering
    Once a human machine interface is incorporated into your product, the issues of maintenance, repair or replacement are major cost factors that must be planned for up front. If you source a terminal from a third party, product maintenance and repair will be covered by warranty, so no internal engineering effort is required on your part.
    In addition, when an HMI that you design requires an upgrade or becomes obsolete, your engineers will be responsible for the redesign. A strategic partnership with an experienced third-party manufacturer, however, will provide an upgrade path or replacement products in a timely, efficient and cost effective manner.
  • Product Management
    A key issue for the product manager to weigh in determining whether to build or buy an HMI is time to market. While your engineering team may have the skills and resources to design, build, test, certify and manufacture the human-machine interface you need, does the product manager have the time to wait for a non-core competency piece of technology to be developed and deployed for the first time?
    The alternative is to turn to a specialist in HMIs for a customised product. Another issue for the product manager to consider is cost. There are many hidden costs to developing a rugged human machine interface that your engineering team may not consider or may not be able to estimate accurately.
    Risk factors must be honestly assessed by the product managers.
    These run the gamut from the risk of losing key members of an in-house design team to the need to change a crucial specification, such as screen size, in the middle of product development.
    A final consideration for the product manager is the product upgrade path for an in-house human-machine interface terminal.
    The Bottom Line
    The build versus buy question in any manufacturing industry finally comes down to a handful of key questions. Three questions are crucial to consider: time to market, risk assessment and cost analysis. All three are subject to the overriding question of core competency and opportunity costs.
    If designing and building reliable terminals for your company’s line of products is not a core competency of your business, then the fastest, safest and most cost-effective course is to partner with a reputable manufacturer of rugged human machine interfaces.


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