The human machine interface (HMI) is the point at which a machine and its user meet. It is the user interface (UI) for all types of interaction with a mechanical machine’s functions, successful actions and any error states.
There is a critical importance in the design of a machine's HMI, as it will determine the usability of the machine. Even the most state-of-the-art, futuristic machine is rendered useless if it lacks an intuitive, quality interface from which humans can access it.
For designers of HMI’s, the crucial element is to bridge the gap between the engineers of the physical machine and the machine’s end users. However, it is important to understand that not all end users will have the same goals, and that there are specific design rules which will apply to HMI design, even when the principle's primary application seems an unrelated world away from a particular industrial machine.
Considerations for HMI Design
As machines have evolved in complexity and application, the world of HMI design has reached the stage where there is little room for error in the application of key principles from elsewhere in the discipline of UX (user experience) and UI design.
Machine and software technology are still consistently evolving too, meaning the HMI must be designed with future upgrades to both hardware and software in mind.
Successful HMI design incorporates the following set of considerations:
- Varied skill levels for each user. Users don’t want to have to call an expert out for every single error log.
- User identity. How has the individual using the machine come to be using it and why?
- Environmental effects on the machine. Where and how is the machine being used in the context of the physical world around it?
- The primary and secondary functions of the user. What are the main end goals of the user, both primary and secondary, and how can they be accomplished with minimal disruption to UX flow.
A good HMI must be both easy to learn AND easy to use. These two qualities can be gauged in terms of how intuitive the HMI is and its consistency.
Consistency is a key element in design across all fields and a prime metric in determining successful UX. Ease of use is an important factor in determining the usability of a product and both consistency and how intuitive a design is will be decisive in the outcome.
The Role of Designers in HMI
The role of the designer in HMI, as we touched upon earlier, is to bridge the gap between the engineers designing the physical components and workings of the machine and the end users.
In engineering, outcomes are extremely tangible and performance metrics are often binary, with a machine either successfully completing a task or failing to do so.
For end users, there is a need for an intuitive interface which gives them a tangible sense of instruction for the physical operation of the machine.
With this in mind, the role of the HMI can be understood as the component which looks to bridge the gap between the physical capability of the machine and the desired outcome for a variety of end users.
The End User
For the end users of a machine, the HMI’s goal should be to minimise the onboarding process, reducing training time and capacity for error. An HMI should therefore be simple to understand and easy to use, the first time a user interacts with it.
To assist with the successful application of these principles, it should be remembered that the HMI design team probably has a greater knowledge of the workings of the machine than the end user will do (for a time at least). Therefore, the design team is not a good sample to test the HMI on.
Instead, we should be thinking about the specific user groups which will interact with the end product. Here, we don’t want to imagine how an average person will use an HMI, rather, we want to think about the small sets of specific user groups which will be interacting with a machine, and how we can design an interface to suit their needs.
We need to understand the various problems each of these groups might face and ask how the HMI we are designing can solve them.
4 Keys to Great HMI Design
1. Know your user
Is your end user simply operating the machine, or are they part of the maintenance personnel? This will define what they want from the system. To assist with keeping each user on track with their specific goals, consider separate screens for different use-cases.
A core component in modern design is to keep the design simple. Complex designs have been shown to be distracting and reduce usership of products, therefore we want to keep our HMIs as simple as possible. As is standard in the field of UX, don’t clutter the design. Doing this will keep training and onboarding time to a minimum.
Users should be able to chart their end goal and any options they have from the start of their interaction with an HMI. Here, we again borrow principles from the wider field of design in terms of animations to draw attention and colour coding in line with established practices. Combine this with intuitive navigation and links to key areas in the HMI like error states and recovery modes.
Mentioned earlier, consistency is a massive factor in the usability of a product. This applies to all screens and all users. Typography and colour palettes should be standardised, along with established menu locations (eg. if it’s at the top, keep it at the top for all users and all screens).
The field of HMI design is broad and each machine can vary wildly along with a significant variation in possible use-cases. This can make it hard to write a detailed, specific guide. Instead, here we have focussed on some underlying principles which we at WQA adhere to in our application of design knowledge to the discipline of HMI design.
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To see if WQA can help simplify your interface design, reduce your onboarding time and the number of error states, whilst keeping users at the heart of the experience, you can chat to us or email us for a conversation and assessment of your unique digital context.