How do you balance functionality and aesthetics of MES user interface design?

Absolutely agree with this, Must keep in mind its 1 solution which caters all the level of operators, some with basic literacy to the elite management. The UI and UX must be done keeping in mind who is the real owner of the screen.

In manufacturing environment user may not have a holistic view about the entire manufacturing eco-systems. To enhance the user experience (UX) integration and automation should always keep in mind to meet the goal of the screen. There may be opportunities of less entry as data are available somewhere and more reliable for integration rather a new human entry. It should be a system aided UI.

For operational users you need to consider the form factor. These people are responsible for operating their equipment, so s much should be automated as possible reducing the need to interact with the system. MES screens on the shopfloor should be highly visible so users can see what is happening from a distance (clear colour coding and large fonts). Most MES implementations now opt for touchscreen devices on the shopfloor, rather than keyboard and mouse. So it's important to design for this - including considerations for things like the operator wearing gloves. Increasingly operational users are interacting with MES through mobile and scanner devices, so it's important for user screens to adapt to the correct device types.

MES is the execution system for the super users and management, but for the operational users it is the enabler. Shop floor UI should be very informative rather than interactive. I know many will disagree but operators should not feel it as an overhead and feel it as they are forced. High level of automation can meet the need. In simple words colors, font and user interaction count should be part of the design and off-course multiple device compatibility.

Performance is the most important facet of MES UI design, in my opinion. You simply cannot afford to have shopfloor operators waiting on a lagging or high latency user interface. Every second counts in production and an MES UI should enable the user to enter data or perform a transaction very quickly. Don't be afraid to make MES screens incredibly simple and minimalist. If a user only needs one field to scan a barcode and a button to click to record the transaction, then that is all that needs to be on the screen! Reduction of complication increases the performance. Security also impacts performance. Users entering a 16 character password for every transaction slows production. Consider using SSO, cards and biometrics to authenticate.

Avoid angry fruit salad color schemes and consider the possibility of color blindness among certain users complicating their use of the application.