Experimental Physics and
Industrial Control System

> The conventional input devices, like mouse or keyboard, are not suitable
> to fine-tuning operation.
> The operators has requested a set of control knobs to this task,

"Sliders" are the preferred ways to fine tune a parameter with a standard widget kit.
In a traditional desktop, you can easily represent 1-d and 2-d sliders.
For example, in my accelerator, we use 2-d sliders to control our corrector magnets.

In our case, it turns out setting our corrector magnets correctly is a very delicate/sensitive operation.
Indeed the mouse cannot be used, but thankfully the keyboard (i.e. arrow keys) can.
So this particular widget has mouse events disabled.
My point is that for that particular operation, the mouse and keyboard cannot both be used, but at least one of them can.

Now if keyboard AND mouse do not work, you can explore different input devices.
Here you can proceed with elimination, by first looking at the commercially available input devices.
For a robotic project (not work related!), I explored input devices including: 3d mouse, leap motion, xtion/kinect (openni), joysticks, touch (Qt mobile on ipad+bluetooth). Those input devices by themselves will not solve your "fine-tuning" issue.
Worse, keyboard and mouse are often used as fallback input device (i..e with phone, if voice recognition fails, the key pad is the fallback input device).

About custom hardware knob, one could argue that this is also a User Interface that could in theory be replicated on a screen.
There are a few reasons hardware interfaces are preferred over software ones: (1) limited and controlled access (2) haptic feedback (a big difficult-to-move on/off switch to switch off your power plant). But as far as your fine tuning issue, hardware knobs are no better than software ones.

To me, the problem you describe is in large part due to wrong UI design.

> This would be installed on a new control system, therefore I'm looking
> to an updated solution with a minimum effort to maintenance in the
> future, but strongly reliable to be in production on an operator console.

If the stock widgets do not work for you, at the minimum you will have to create a custom widget (with either mouse or keyboard, or both enabled)!
Of course, a custom widget is as good as its fitness to the task the user/operator want to perform.
In our field, most UI are designed by engineers who overly use the bottom-up approach, i.e. I know what is easy and possible with the software, so I offer this interface. For UI design, it is often better to take the top-down approach, i.e. imagine everything is possible and ask yourself the question "how do I want to interact with the 'system'?"

The answer you will find there is likely to be specific to your case at hand.
Therefore for a more detailed answer, you probably will need to share more of the details of what you are trying.
What do you want to set through those knobs? How many knobs do your need? Where is the user? etc.

> Thank you very much to your collaboration in advance,
> -Mauro