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Human-machine interface

Perhaps more than any other machine component, the human-machine interface (HMI) brings full meaning to the concept of usability engineering. It's the plane where man and machine must interact, ultimately determining a machine's ease of use and, by extension, its productivity. In this forum, Motion System Design editors speak with industry experts about HMI trends.

Marc B&R: The machine designer must be very intimate with the actual operation of the machine from an end-user's perspective. At the end of the day, it's an operator who runs the machine day-in, day-out not the engineer who designed it. The designer needs to have insight into the mind of the end-user in order to develop a machine and an interface that truly meets the demand for highest value. All too often the end-user is forced to try to recreate the thought process of the designer.

Roy GE Fanuc: HMI systems can take many forms, from dedicated panel devices to higher-level PCs running Windows and HMI software. On PC/Windows platforms, basic HMI functionality may be augmented with high-level analytics and data acquisition, features more often thought of as SCADA (supervisory control and data acquisition). In the more general case, where the HMI functions as the machine controller and operator interface, the emphasis is more focused on running machines more effectively, measuring performance, and managing downtime more efficiently.

The greater the role of the HMI, the more important it is to select one with a high degree of scalability one that provides operator controls and connectivity to supervisory systems. In motion applications, HMIs must also be able to respond quickly to commands as well as unanticipated situations requiring complex maneuvers.

To maximize productivity, HMIs should display information in the context of the machine state. It's not the job of an operator to navigate to the correct screen at the correct time; it's the job of the HMI to react to machine conditions (the machine context) and deliver displays appropriate for the current state.

Today's HMIs must also deliver a wealth of information, from operation manuals to troubleshooting guides. They should not only run, but also help maintain a machine. They should track downtime history and capture reason codes, and take responsibility for the lifecycle of the equipment.

Eyal Unitronics: From the operator's point of view, the HMI is the communication focal point, the "ear and mouth" of the machine, accepting commands and directions while displaying processes, values, results, errors, and other status messages. This calls for an intelligent interface with built-in diagnostic qualities and immediate access to real-time information required to troubleshoot common machine problems. From a PLC hardware perspective, this means having access to internal registers and program variables.

The right HMI implementation provides not only built-in diagnostics eliminating the need for external testing equipment during troubleshooting but also increases the operator's overall productivity:

  • It may replace most printed documents, providing online help, operation "wizards," and even tutorials
  • It allows international implementation of a system by using more graphics and less text, being less language dependent
  • It facilitates operation using color-coded icons, values, and gauges, guiding the operator within the normal operation envelope
  • In a well-designed system, it consolidates all relevant information to one screen, popping up only the values and statuses that need immediate attention
  • Using a combined HMI and PLC can save development time, wiring, and component cost as well

Marc B&R: The main challenges involve complexity and usage needs. Allowing operators to control a complex machine in a way that hides the complexity is the first test. The HMI needs to be intuitive and simple, yet should not limit the operator's interaction with the machine. Second, different operators and assorted machine operations require different levels of user interface. What works for one might not be the optimum for the other.

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© 2014 Penton Media Inc.

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