Episode #49: What is Feedback in Motion Control?

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The Motion Control Show

What is feedback?  I defined it a bit back in Episode 20 when I was talking about linear mechanics, but I want to talk a little bit more philosophically about what feedback is in a broader view, because no matter what type of system you have, you need to have feedback.  You may not think of it as feedback, but it really is.  So let's talk a little bit more about that philosophically.  I'm Corey Foster at Valin Corporation.  Let's see what we can learn.

What is feedback?  Something is going to have an action on a target that's going to give a response.  And then you want to know what happened since there's a purpose for it.  So, what happened?  Well, however you find out what happened is your feedback.  Now, in the case of the example here, with a golf club striking a golf ball, it may be the sound...maybe the sound of the club striking the ball or the ball landing out in the weeds or the fairway, as it may be.  A little bit better than that is seeing what happened to the ball, right?  It's more accurate.  You have a better response as to knowing what happened.  Another option is to have somebody standing either next to you or even out there in the fairway, or out in the weeds, seeing where the ball landed and then even measuring how close it is to your target and where you want to go.  Another way is maybe a GPS tracker, either on a smart phone or perhaps embedded in the ball itself using high technology.  So those are all different types of feedback in order to see what happened.  Some are faster.  Some are better.  Some are more accurate.  Some are more expensive than others.

Let's take a look at another application, perhaps a tractor.  A tractor has an action placed on it like your pushing a button starting it to go.  Let's say it's a fully automated tractor and then the response is the tractor going out there on the fields.  Maybe it has multiple responses because it keeps going back and forth, back and forth, and it is all GPS directed.  Then something happens.  Well, at what point do you want to know whether you had a problem or not?  Do you want to wait until the problem here?  Or do you want to know here, here or here along the way that you have a problem?  Or perhaps you want to know here, here or here on the tractor itself at the wheels or the engine that there may be a problem.  So where do you put your feedback?  Well, there are different types, right?  So perhaps you put the sensors on the wheels, or on the engine itself, so you are close to the problem and get really quick information back from those sensors.  Or perhaps you put it a little bit further out where it's a little bit slower to respond.  Now that sensor is going to see the result of multiple actions because actually your system has a lot of little action/reaction devices in it: the wheels, the engine, the muffler, the exhaust pipe, the controls, and the GPS.  All of those are little pieces of the system that you could put sensors on.  Or you could put one sensor further out that is going to indicate a problem.  If you put the sensor out there, that is only going to tell you that you had a problem.  It is not necessarily going to tell you where that problem occurred on the tractor itself.

Here is one type of sensor that could be on/off, an alarm or no alarm, and it's only going to tell you at that point whether or not the tractor got there or not.  Perhaps you put a speedometer on there, an analog output that tells you how fast it's going, or how much it's traveling, so it's more of an analog feedback.  Or maybe you have a different type of feedback on there that announces its location as it goes along, so periodically you get an update. 

If we look at a motion control system, this is the five or six building blocks that I talked about back in Episode 2 where if we put a sensor on the end of it, maybe just on/off, but it could also be analog, but let's say this sensor is just on/off, it will tell us whether or not the motion control system got to where it was supposed to be.  We can look at the speed or the various positions by the feedback on the back of the motor.  We can have the controller announcing the positions and the updates along the way to the HMI.  Of course, there are a lot of different variations on the feedback here, but those are the things we need to look and think about when we are talking about feedback.  How fast do you get an update?  What kind of information do you get from it?  Is it specific enough?  Is it cost effective?  Do we want to put sensors all over the system or do we just need to know whether it worked at a certain point or not?  It really comes down to how much your critical your cost is, how critical your product is, and how sensitive that information is. 

I hope this helps.  Reach out to us at www.TheMotionControlShow.com or email us at this email address here.  I'm Corey Foster at Valin Corporation.  I hope this helps.

If you have any questions or are just looking for some help, we're happy to discuss your application with you.  Reach out to us at (855) 737-4716 or fill out our online form.