Safe, reliable & ergonomic HMI design

Jan. 9, 2017

Consider operators and other personnel during equipment design and selection to prevent accidents

Human machine interfaces (HMI) include all the elements a person uses to interact with a machine. The task of an HMI expert is to build innovative, intuitive and reliable interfaces. HMIs play a vital role in machinery design and industrial automation, enabling the efficient operation and monitoring of essential processes. This article provides a viewpoint of those important tactile, electromechanical controls that remain essential for safe, reliable, ergonomic HMI design.

Progress in the industrial machinery sector is synonymous with increasing automation. Precision, speed, performance, miniaturization and networking are the key ingredients to success. However, industrial machinery of every kind is becoming more complex, and this leads to greater safety demands in its operation.

The European Agency for Safety and Health at Work makes this clear in its report on the machinery sector: The high proportion of employees working with machines or computers means that proper design of the HMI is essential. Poor design of an HMI can give rise to occupational maladies, such as stress or musculoskeletal disorders, and lead to occupational accidents. The potential cost to an employer, because of reduced productivity, damaged reputation or users’ dissatisfaction, is clear. The report goes on to say that, because a poorly designed HMI can have serious consequences, ensuring its proper equipment design and use in the workplace is of utmost importance.

To meet increasing demands, developing specially engineered HMI components and HMI systems that will ensure safe operation even under the most adverse conditions has become an EAO philosophy. When keeping people safe, there can be no compromises. For many manufacturers, such as EAO, developing and manufacturing HMI components and systems for basic and complex industrial machinery helps promote safe and error-free operation.

Precise, efficient & safe

HMIs are important in machinery design and industrial automation, enabling the efficient operation and monitoring of essential processes. While traditionally slower to experiment with new HMI technologies, innovations within supervisory control and data acquisition (SCADA) systems are pushing industrial companies to generally improve the quality of the interfaces to reflect modern styles. Screen-based master controllers have enhanced capabilities to visualize and display production processes, typically in combination with a tactile control panel for primary system startup, safety and security functions. Despite this migration of features to screens and visualization software, illuminated switches – such as pushbuttons, indicators, selectors and toggle switches – remain essential for important, primary functions.

Food & beverage manufacturing

Machine and process controls in the food and beverage industry must work efficiently and safely around the clock and are frequently subjected to moisture, dust and cleaning fluids. Considering the variety of operating requirements, making the interaction between the operator and the machine safe, intuitive, reliable and repeatable is critical.

Taking into account the long service life required, reliable, high-quality operating concepts must be developed for machines in accordance with Ingress Protection or International Protection (IP), National Electrical Manufacturers Association, International Electrotechnical Commission, Americans with Disabilities Act, American National Standards Institute (ANSI) and Occupational Safety and Health Administration requirements.

Semiconductor & electronics production

Applications in semiconductor and electronics production require many operator control terminals. These often consist of industrial PCs with touchscreen displays interfaced with production machines and a number of discrete electromechanical components. Emergency stops, for example, are considered to be a discrete function in this market. The system design needs to be made in accordance with the SEMI S2 guidelines.

When developing and designing HMI systems for semiconductor production, intuitive operation, interactivity and full functionality are vital. The design must be to industry specific requirements, such as clean-room regulations and precision control with flexible, high-quality components.

Packaging equipment

Packaging systems, especially those in the food and beverage industries, operate in a clean production environment geared toward high work volumes. HMI systems must comprehensively guard against the ingress of fluids or solids often found in packaging facilities while making it easy and safe for users to perform their tasks. Control systems must allow operators to quickly and easily set up and adjust new production processes.

The goal is an easier, faster and more accurate process. To be successful, an HMI manufacturer needs:

  • Expertise in machine integration and functioning logic
  • Project management capabilities
  • Appropriate documentation for line qualification
  • Testing of centralized advisory services such as SCADA

CNC milling & machine tools

The ability to quickly visualize and control every aspect of the production environment is critical within simple and complex machine tool operations – such as computer numerical control (CNC) milling, lathing, forging, stamping and boring equipment. Operator controls must be designed and arranged for maximum user-friendliness to ensure error-free switching between production steps.

Advanced HMI components

HMI component technology has undergone major changes over the years to serve the increasingly specialized needs of machinery. Designers face an astonishing range of choices in electromechanical components that encompass:

  • The type of device
  • Electrical specifications
  • Environmental sealing
  • Mounting and termination styles
  • Ergonomic considerations such as appearance, configuration, size, illumination and tactile feel

Advanced HMI components are precisely crafted devices, made to exacting design specifications and very close tolerances from high-grade plastics, metals and carefully calibrated springs. To achieve reliable, long service lives, they are engineered like fine watches with the performance, feel and look required of modern HMI systems.

Ergonomics play a key role in modern switch design, assuring the right switch for each application, whether a flush-mount design to avoid inadvertent actuation or an emergency-stop switch with an oversized actuator for fast, palm-slap shutdown and safe twist or key release to enable the repowering of a circuit.

Switch specification

Switches come in a wide variety of shapes, sizes, ratings and functions. They are built for long life to minimize the need for replacement. High-quality switches are expected to have mechanical lives of 1 million to 10 million operations.

Many switches are modular, comprised of quickly assembled components that include actuators, switching elements, illumination blocks, lenses, marking plates and mounting systems. This flexible, configurable approach allows for many switch variations within a single product series to be used within one application for various required functions.

Industrial water- and oil-tight switches are designed for front- and back-of-panel environmental protection against the intrusion of dust, dirt, water, solvents and other foreign materials and are certified to meet different levels of ingress protection as specified by NEMA and IP Codes.

Designers can simplify their search for the perfect switch by carefully analyzing application requirements first, then, based on their needs, determining the following:

  • Electrical ratings – determine the right specifications for the job
  • Actuation preferences – choose the most appropriate switch type
  • Physical configuration and mounting needs – decide on overall size, style and placement
  • Special requirements – select the type of illumination, marking and environmental sealing options

Standard, diversity & individuality

Classic HMI components include pushbuttons, illuminated pushbuttons, indicators, emergency-stop switches, keylock switches, buzzers, joysticks and rotary lever switches. Numerous additional HMI components can complete a comprehensive range.

Illuminated pushbuttons

Some pushbuttons are illuminated. Universal switch actuators and indicators are found everywhere in applications that depend on reliable and positive feedback. Typical areas of use are machinery, public and private transport, heavy-duty and special vehicles, the automotive industry, and building installations.

Illuminated pushbuttons benefit machinery applications in many ways:

  • Excellent haptic feedback
  • Large selection of switch sizes
  • Wide range of colors for lenses and illumination
  • Wide variety of symbols and markings with customer-specific design
  • Very long service life for mechanical and electrical components
  • Large range of switching capacities

Mushroom-head pushbuttons

Mushroom-head pushbuttons are used in harsh environments throughout the world as on/off switches. Their large, distinctive operating elements also enable them to be operated with gloves.

Mushroom-head pushbuttons benefit machinery applications through:

  • Excellent haptic feedback
  • Operating elements with different diameters
  • Large selection of colors and materials
  • Illuminated versions

Emergency-stop & stop switches

Emergency-stop switches with forced-opening contacts (compliant with DIN EN ISO 13850 and EN 60204-1) are primarily used to enhance personal safety. Emergency-stop switches are always foolproof and can be easily identified by their red lens with a yellow actuator.

Stop switches do not have to be foolproof. With their snap-action switching element, they are used predominantly around the world as on/off switches in mobile control units, equipment construction and machinery.

Illuminated selector switches

Illuminated selector switches offer ergonomic design as well as reliable visual feedback and status display. Selector switches can be equipped with up to three switching positions and up to six electrical contacts. Non-illuminated versions can be equipped with up to 12 switch positions and up to 16 contacts.

Selector switches benefit machinery applications because of the following:

  • Easily visible switch positions
  • Variety of combinations of momentary and latching switch positions
  • Illuminated selector switch
  • Full range of base colors for illumination
  • Long service life of mechanical and electrical components
  • Support all commonly used connection systems


Indicators are universally popular for applications that depend on clear messages and status indication. Some indicator machinery application benefits are:

  • Wide range of colors for lenses and illumination
  • Wide variety of symbols and markings with customer-specific designs
  • Bright, uniform, full-face illumination
  • Multicolored illumination compatible
  • Different lighting effects, including flashing and dimming
  • Hidden-until-lit capabilities for quick visual recognition


Buzzers are audible warning devices. They generate tones of a predefined volume and frequency. Their compact dimensions ensure units are optimized for worldwide use in machinery, medical equipment, lifting and transport equipment, cockpits, driver cabins, and building installations.

Some buzzers benefit machinery applications with:

  • Large selection of designs
  • High sound pressure
  • Very long service life of electrical and audio components
  • Models with wide voltage ranges
  • IP65 front protection

Keylock switches

Keylock switches are used to prevent erroneous or unauthorized operation. They also enable access control systems to be implemented for user groups. Today’s keylock switches are beneficial because of:

  • A large selection of lock systems
  • Two or three possible switch positions
  • Different combinations of momentary latching switch positions
  • Supporting commonly used connection systems


Some manufacturers offer modular assembly that allows the components to be easily configurable to meet most of the demanding requirements of many applications. However, when those requirements cannot be addressed, existing equipment may be enhanced to meet customer needs, both quickly and cost effectively.

Some modifications to standard components may include:

  • Altering the shape and size of buttons and bezels
  • Adding tactile surface textures and coatings
  • Laser engraving and printing of text or symbols on lenses, text plates and film inserts
  • Lighting colors and animated effects – such as flashing, pulsing and chasing countdowns
  • Changing voltage ranges and adding protective circuits
  • Fitting specialized cabling, wiring harnesses and connectors

HMI system design process

At the onset of a project, defining the requirements is the most critical step for developing an HMI system. The basic concept is to be mindful that the HMI is the user’s link to all system functions. Failure to consider this can affect the acceptance and usability of the entire machine.

Industrial design & ergonomics

Industrial design refers to the shape, configuration, pattern and ergonomic features for a device that is designed for the machinery sector. A definition for much of the design will come from the operational requirements of the application. It can include the user environment, operating temperature range, presence of moisture and ambient light requirements.

A design should strive for an intuitive presentation of user tasks, for example, one that is immediately understandable. An intuitive layout with the use of dimensional shapes and well-thought-out groups of operations provides a predictable, consistent and efficient HMI system.

Component selection: The mixed- technology approach

Expert HMI system design and manufacturing focus on providing the necessary components effectively packaged to meet the customer’s application requirements. After finalizing a complete review of the application and functional requirements and needs of the operator, selecting the appropriate control technology puts the knowledge gained in this learning process into practical use.

Using mixed technologies can differentiate function, increase usability and control production costs. Typically, this method incorporates a base set of electromechanical components or a more complex integration of keyboard, display, touch screen and industrial PC components, depending on the required functional sophistication and level of visualization. This flexible approach to using technology offers customers a competitive edge.

Typical interfaces should include:

  • Main operator panel using discrete switches for system startup and shutdown including emergency-stop functions
  • Handheld control units and tethered pendants with displays and short-travel keypads for data entry
  • Touch screens and industrial PCs with serial bus interfaces for linking to the core system

Software & interface design

Modern HMI solutions feature fieldbus connections for communicating with complex systems. Software adaptations make the configuration and control of HMI subsystems possible. Many conventional and new communication protocols are available including:

  • ProfiBus, InterBus and DeviceNet
  • CANbus, CANopen and CAN-J1939
  • USB, Ethernet and variations
  • GUI touch-screen integration

Some CANbus modules can connect buttons, indicators and other components as part of an integrated HMI solution and can be preconfigured for plug-and-play connectivity.


Standards are of the highest level of concern within design considerations. The criteria specified within these general and industry-specific requirements dictate features, functional attributes and design elements.

Facilities are usually required to abide by these conditions to be approved for participation within the identified market segment. Although the standards benefit end users by promoting an increase in accuracy, performance and safety, they sometimes can become a web of details for design engineers involved with the creative process. Without sufficient knowledge of industry standards, design, production and delivery timelines can be affected drastically.

Standards for Human Factors design within the machinery market include:

  • Ergonomics, design and materials standards
  • Market and application specifications: SEMI S2-93/12.4c
  • IEC 60947-5-1/5 and ISO 13850
  • ANSI or American Society for Testing and Materials
  • Safety agencies: Underwriters Laboratories (UL), cUL (UL in the Canadian market), European Commission and VDE

John J. Pannone is the vice president of HMI Systems at EAO Corporation. With a degree in industrial technology and more than 20 years of direct involvement with all phases of HMI, Pannone is recognized as an expert within the industry for product selection, ergonomic design factors and system integration. He is currently an active member and contributor to several global industry associations including Human Factors and Industrial Design. EAO AG, a Swiss, family-owned company founded in 1947, is a manufacturer of switches, keyboards, control elements, HMI control units and HMI systems. For more information contact [email protected] or 41-62-286-91-11.


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