Context – The Heavy-Duty HMI as an Integrated System

The development of human-machine interfaces (HMIs) for heavy-duty applications—in construction machinery, agricultural vehicles, maritime applications, or industrial control systems—has undergone a fundamental transformation in recent years. In the past, the focus was on selecting individual components: a robust display, a durable touch sensor, a sturdy housing. Today, this approach is still valid, but it is no longer sufficient.

Interior of a construction vehicle with modern HMI and controls

A modern heavy-duty HMI is not a modular system made up of individual parts, but a highly integrated system in which the interaction of the components determines overall performance, readability, and service life. The interfaces between the components have become the most critical elements of the design.

Exploded view of a VIA optronics display stack

{
  "markers": [
    {
      "id": "m1",
      "num": 1,
      "type": "dot",
      "dot": {
        "x": 600,
        "y": 100
      },
      "title": "Cover Lens – Flat or Curved",
      "text": "Different glass and plastic materials as well as different types of coatings, etchings and finishing"
    },
    {
      "id": "m2",
      "num": 2,
      "type": "dot",
      "dot": {
        "x": 600,
        "y": 320
      },
      "title": "Touch Sensor/Module – Flat or Curved",
      "text": "Projective Capacitive (PCAP)"
    },
    {
      "id": "m3",
      "num": 3,
      "type": "dot",
      "dot": {
        "x": 600,
        "y": 610
      },
      "title": "LCD Matrix – open Cell",
      "text": "LCD or OLED"
    },
    {
      "id": "m4",
      "num": 4,
      "type": "dot",
      "dot": {
        "x": 600,
        "y": 795
      },
      "title": "Backlight",
      "text": "LED rails, light guide or film stacks"
    },
    {
      "id": "m5",
      "num": 5,
      "type": "range",
      "arrow": {
        "x": 1775,
        "y1": 110,
        "y2": 1050,
        "labelY": 575
      },
      "tooltipPosition": "left",
      "title": "DHA/Hinge Up",
      "text": "LCD with touch or cover lens, with housing or frame and including controller boards for LCD and touch"
    }
  ]
}

The traditional method of mounting a display and a touch sensor behind a cover glass or behind cover glasses leaves an air gap, that is, a space between the individual components. This space is the source of most problems that occur in the field: it leads to optical losses due to reflections, allows moisture to penetrate during temperature fluctuations, and represents a mechanical weak point.

Optical bonding—that is, bonding the individual components together over the entire surface using a highly transparent optical adhesive—eliminates this air gap and transforms the HMI stack from a collection of individual parts into a solid, monolithic unit. The optical bonding process turns individual components into a solidly bonded complete system with significantly higher robustness and durability.

Note on the technical information in this chapter

The technical values, test profiles, and performance data stated in this chapter are provided for technical classification purposes. Actual results depend on the specific display configuration, material system, bonding process, application profile, and scope of qualification. Product-specific values are validated on a project basis using data sheets, measurements, test reports, and customer specifications.