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The ins and outs of a motion control system

Dec. 18, 2023
A Control Intelligence podcast with Matthew Tellier, sales manager, Advanced Micro Controls (AMCI)

Founded in 1985, Advanced Micro Controls is a U.S.-based manufacturer with a global presence. AMCI industrial control products are designed for PLC-based automation systems with specialized position sensing and motion control technology.

Matthew Tellier, sales manager at AMCI, has been with the company for nearly 30 years, starting off as an applications engineer. He earned his bachelor’s degree in engineering from University of Connecticut.

In this episode of Control Intelligence, editor-in-chief Mike Bacidore and Tellier talk about motion control and position sensing.

Transcript

Mike Bacidore: Can you explain the roles of motors, feedback sensors, drives and controllers in a motion control system?

Mattew Tellier: Whenever I'm in front of a group and I'm doing an introduction of what motion control is all about.

I really break it down into the three components, the controller, the drive and the motor and just kind of explain how each one of those components comprises of the complete system. You know the controller is going to be providing a signal to the drive.

That signal can be something as simple as an analog signal, say zero to 10 volts for speak control, or it could be something like a step and direction signal that we would have in a more common system like a stepper system for example, where we're going to give it a pulse train which is going to be relative to speed, and the number of steps that it moves and then I direction signal which is going just tell it which way I'm going clockwise or counter clockwise.

That signal would then go to the drive, the drive, then just basically creates an current well, an HT current like we would have in a servo or or or DC current for a stepper that would energize the motor and then that as we energize the motor we're going to create a magnetic field within the motor windings, and that magnetic field is going to cause motion. That motion can be translated into a Rotary application. Something as simple as like say a Rotary table.

Or it could be linear motion where we take that motor and attach it to something like a leadscrew ballscrew, or even a conveyor to take that Rotary motion from the motor and translate that into linear mechanical motion.

And then when we're feedback comes into play in the system, you know, oftentimes we think about encoders.

When we think about motors and that's going to give us position data, it can give us the lacity data, but we also have other sensors that we don't always typically think of as motion feedback sensors that could be a home switch, it could be end limit switches, things of that nature which tell us you know when we get to a certain position, we've gone too far.

You know, when I'm at home again still feedback to the system.

And then when it comes to a closed loop system that that encoder feedback is integral in the the motion control of the whole system, because we're working on, you know, position feedback versus commanded position and how that motion control then turns into our actual position where we want to be and when we get there.

Mike Bacidore: Great explanation. Building on that then, What motion control applications can benefit from position or angle sensors?

Mattew Tellier: I always think about things in a practical way and go. Hey, you know what? If you could, if you can have one, use one. You know, when it comes to position sensing, but obviously not everything needs one. You know, a lot of stepper applications run open loop, you know simple DC brush motors will run open loop.

But I tell people, even if it's a system that can run open loop, if you need something like a little bit more precision in your motion, whether it's relative to positioning or speed, you you might wanna add feedback there just so you can verify when you commanded it to go to a specific place that it actually get there.

Is it going the correct speed that I'm commanding it those types of things is where you would want to have a position feedback.

I think of an application that I talked about many, many years ago with someone and they had a gate and it was opening and closing and the only feedback they had to the system we're end limits and every so often the end limits would they would the the door would swing past the end, limit the end limit wouldn't toggle so the door would just keep going until it slammed into a wall.

You know you think about something like that by adding by adding an encoder.

They now knew exactly where they were throughout that entire motion.

And then they could also say, OK, I know exactly where I am, if I'm if I'm getting no signal, I know I have a problem with my feedback, so let's fix the problem that we have and get our system up and running correctly.

Mike Bacidore: Great example. So switching gears a little bit here, how does pulse-width modulation affect motor speed?

Mattew Tellier: So when we're, when we're talking about pulse with modulation in, in this discussion, I'm thinking about it being you used with say a DC motor, a DC motor.

We think of it as being full on full off. It's either running a 0 speed or full speed. Say it's a 12 Volt DC. What we can do with pulse width modulation is basically just vary the duty cycle of that voltage we're using to power the motor.

So instead of being full 12 volts or 0 volts, 100% of the time, or 0% of the time, we can say OK, turn the voltage on 12 volts for say 50% of the time off, or 50% of the time, and we're gonna get, say, half the speed.

Or we could say turn it off, turn it on 20% of the time off 80% of the time and go even slower.

So basically what we're doing is we're creating almost like an averaging of that voltage by switching that current on and off at a relatively high frequency, say two kilohertz or something.

That nature and now we can vary the speed by varying that duty cycle through pulse width modulation.

Mike Bacidore: Great explanation. What features differentiate servo, stepper, brushed and brushless motors?

Mattew Tellier: So let's start with a the more basic one and and start with a brushed motor with a brush motor, or basically just sending a voltage through the commutation winding of that motor and with a brush motor.

The magnets are on the on the stator of the of the motor and and the the windings that are energized are the rotor and you know as we energize those windings we create a magnetic field.

It's going to alternate the, you know, it's gonna cause motion of that rotor as the magnets in the stator and the windings of the rotor align.

And then as we start to rotate the commutation voltage changes from 1 winding to the next and we just get continuous motion that way with with a brushless motor.

We've now eliminated those brushes, but now we have to come up with a way to control the current that's going through the windings.

And with a brushless motor instead of the windings being energized of the rotor, we now have the magnets within the rotor and then the stator is what gets energized and then by varying the the current, whether it's an AC signal in a servo you know we have three different phases in there.

We energize them a little bit out of phase. We each other and by varying the frequency of that signal or the voltage level that signal we can increase the torque and change the speed of the motor. So that's a basic concepts between behind a brushless and brushed motor.

When it comes to steppers and servos, there's a little bit more going on there as far as how they're constructed relative to the number of Poles that are in the windings of the motor, but with a stepper.

Basically, we're running that using a DC current to generate our magnetic field, and then toggling off and on between two different wings called the A phase and B phase to generate that magnetic field to generate motion. With a servo we have three different phases of voltage.

That AC voltage that we're sending through those windings to generate motion because it's an AC signal and we have to kind of make sure that we have alignment between the phases and those voltages that we're putting through the windings of the servo.

We have to have some sort of feedback and it's most basic sense we would have, say 3 hall effect sensors in there.

So that way we can make sure that the voltages stay within phase of each other. More sophisticated systems have encoder feedback to get us a little bit more precision, but basically that kind of is that feedback is really what makes it become a closed loop system.

Mike Bacidore: Great explanations on all of them, so sticking with servo motors, how do dual-port networking, safe torque off and built-in move verification make servo motors more amenable to integration?

Mattew Tellier: A lot of times we weren't doing motion, especially more sophisticated motion. Precision as far as positioning is concerned. Torque torque control is concerned. Speed. All of that stuff because of that closed loop nature of a servo system that really makes it an ideal choice for those more sophisticated motion profiles.

Then when we start adding functions like say safe torque off, really what we're doing is we're just adding an additional feature to make the servo a little bit more part of the system.

So for example, with safe torque off, I can disable a motor so I can do things like say maybe do some sort of setup operation so motion cannot occur in in that part of the system and and it's that integration into the overall machine control that takes that feature like safe torque off.

And then when we talked about the networking networkingf just gonna make make it easier for me to get into my control system and because I'm using a network instead of, say, a dedicated controller that's within say A PLC, it gives a little bit more flexibility because now I can take that same control solution using networking and I can use it with various different control brands.

You know I'm not stuck with one controller type. I can take it to say Siemens PLC or a Rockwell PLC or Siemens, the LCI depending upon the network protocol that I'm talking with. So it makes it a little bit more flexible as well in that manner.

Mike Bacidore: Building on that, what are the advantages of connecting a servo motor to a PLC vs. a dedicated servo controller?

Mattew Tellier: Most control systems now, especially on the factory floor, have some sort of centralized control on the machine.

If I have a dedicated control solution, say a standalone servo Dr handling some motion, I have to have a separate HMI or users interface to make modifications to the motion if that's necessary or I have to bring out my PC when I need to make changes external to the the overall centralized machine control by making it where it can integrate directly into the PLC that same PLC's controlling everything can now control the motion profile.

So the the operator if they have to make a change to the overall system that overall system change can also affect the motion as required for say a setup change. So that's really where having that integration comes into play. It just kind of helps eliminate separate interfaces and helps kind of simplify the overall control scheme.

Mike Bacidore: One final question for you then: what are the advantages of decentralized vs. centralized motion control?

Mattew Tellier: We here at AMCI like to centralize everything through the PLC through a network interface and the benefits are just as explained that hey, hey, operator can go over there, push a button and effects everything on the machine but that's not always necessary and sometimes it's not always practical or possible.

Sometimes I just don't have enough cabinet space to have everything in one enclosure, so I have to maybe put something out separate on the machine, somewhere else.

Or maybe I have a piece of equipment that comes in different stages, so to speak it, you know, stage a stage beast stage C and you know, maybe function B is only needed 40% of the time.

So I actually remove that stage from the system and push A and C together. If everything centralized removing that B portion can sometimes be a little bit more difficult.

So decentralization you can help reduce cabinet space, reduce overall system wiring because now instead of running all of this control signals back to a central cabinet, I keep everything dedicated to a decentralized location, you know on the machine. But then I can always have part of that decentralization.

I could always have some sort of network protocol like an IO link or an Ethernet type network that still allows me some basic communication back to the PLC for some sort of information sharing things with that nature.

Mike Bacidore: Obviously the cabinet space is at such a premium, are you seeing any customers who are looking for components that are IP67 or IP69 that that can come out of the cabinet to reduce that footprint and then be placed on the machine? Is that a trend that you're seeing?

Mattew Tellier: It's really a big part of what we do here at AMC every day.

We we started probably 15 years ago taking as I talked about earlier, the classic motion system drive motor and control and putting everything in one and putting everything in one package.

And by doing that, we now take the drive and the control out of the cabinet and put it in the motor, which now mounts out on the machine.

And by doing that, we could especially for multi access applications, we can help reduce cabinet space, we can reduce cabinet heating by taking the drive out of the cabinet.

So now, now you know air handling can be different within the cabinet and and it helps reduce wiring because now instead of running, you know, encoder cables, motor cables, 304050 feet along the length of the motor.

I now run one power cord could be say 24 Volt DC or 48 Volt DC and a network cable and that's all I have to do and with the dual port networking that we offer, I only run one network cable and can Daisy chain several motion axes together or even.

Mike Bacidore: Do you know some of the the network integrity systems like DLR for example, with the dual port networking?

Mattew Tellier: But yeah, we see a lot of that. Everything's gone that way. A lot of our encoder position feedback. Traditionally we were a resolver manufacturer with plug-in modules that would take that resolver and plug in to the PLC. Now all of that can be done within the encoder using an Ethernet IP connection, so again reduce cabinet space, reduce the number of slots required in a PLC module. Condensing that cost reduction that everyone's looking for can can be done really well as using a network technologies.