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  • Writer's pictureDavid Peterson

Humans and Machines Interacting

Using machines to accomplish tasks with more than mere human effort alone has been the goal of humanity for ages.

Before motors and combustion engines, horses and oxen were used to move massive loads, unthinkable with our relatively puny muscles.

Rewinding way back in history (although exactly how far can be argued), simple machines gave added benefits of inclined planes, levelers, and pulleys to make work easier.

In modern times, automated manufacturing has changed the face of machinery integration.

When I say 'face', I literally mean face.

This picture is Sawyer, a robot developed by ReThink Robotics. It's a collaborative robot designed to work alongside people with its friendly appearance.

But this article isn't exactly about faces on robots, nor is it meant to be a psychological discussion about humans and machines working alongside each other.

This is a bit more hardware-based.

But I like hardware.

One of the big questions that is raised by the machines and people working together is simply this: "How do you get a machine and person to interface and communicate with each other simply and reliably?"

The answer is through the continual evolution of a group of devices called the "Human-Machine Interface" or HMI.

There's actually no specific limitation on what can be considered an HMI, as long as there is some information transmitted between the people and the equipment.

Even a red or green LED on the machine to show a status could really be a primitive HMI.

But the normal type of control device which is referred to by the formal acronym is usually one of two types.

  1. The touch screen monitor as shown above. They have a variety of sizes, resolutions, touch abilities, physical buttons, communication ports... You get the idea. Lots of variety.

  2. The other kind is a set of buttons and control knobs with a small screen nearby to show key operating parameters. This is commonly seen as the user input for a motor drive unit, as shown below.

The second type, used for motor control units, is simple but effective. A few input buttons to turn on and off, reverse directions, and set parameters along with a knob for speed control.

But that touch-screen type is a little fancier...

It can be a bit more difficult to program, but the information sent to the system or displayed for the user can be far more comprehensive.

What kind of information you may ask?

Here's a short list of some example types of data that can be sent into the controller (inputs):

- Momentary Buttons

- Latching Switches

- Radio Buttons of which only one can be active at a time

- Virtual 'knobs' and variable numbers

- Number Entry (10-key pad)

- Numeric Increment/Decrement

- Text Entry (keyboard)

- Passwords

Along with inputs, the HMI can also display information through another impressive set of controls:

- Indicator Lights

- Illumination right inside the input Buttons

- Number value display box

- Graphs of data over time

- Visual meters to show variable data

- Static images and pictures

- Moving (dynamic) images

- Different screens (like desktops) to show extra information

How easy is it to program these screens?

Surprisingly easy... But they don't work alone.

HMI machines like these require a PLC that is compatible in order to transfer information.

If you press a button, that information needs to go to a controller. Likewise, if you want to see the status of a button or the temperature at a thermocouple, that information must be coming from some controller.

The whole key is in the effective use of tag sharing. A 'tag' is a piece of information in a PLC corresponding to an on/off value, or a variable number, or text.

Those tags must be replicated in the HMI, then used to show and edit that information as necessary. When you 'turn on' a virtual button in the HMI, it goes over the communication wire and 'turns on' the bit inside the PLC.

The great thing is that the HMI doesn't need to be anywhere near the PLC, it can be hundreds of feet away!

Need to add another button, or show another indicator light?

Edit the program, hit download, and watch the screen update in a couple of seconds.

No more adding hardware... No more drilling 22mm holes in a cabinet to add controls... No more re-wiring or tightening screw terminals when a button needs replacing...

Lots of benefits.

If you know PLCs, the very next step is to learn HMI programming.

It might surprise you just how easy it can be to program an HMI.

Your project can be up and running in no time at all!

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