Virtual axes in motion control

[Plc_User]

In what kind of applications in motion control do you use a virtual axis, and in that case for what reason do you use a virtual axis and not some kind of other techniqe?

 

[Peter Nachtwey]

What other technique are you going to use?

Gearing to virtual is much more flexible than moving as a function of time. Time can't be ramped up or down but a virtual axis can.

Virtual axes have perfect target generators. Physical devices are not perfect.

I can ramp up sine and cosine functions and other functions that start with derivatives not equal to 0.

BTW, the Salt Lake City Airport WIFI is very slow.
I had to wait about 5 minutes to get this page to show.

 

[SMOKE]

Damn you were here.... Wish you would stop by.
Lov Delta Don... but he is not you.

 

[Peter Nachtwey]

Off topic

Damn you were here.... Wish you would stop by.
Lov Delta Don... but he is not you.

I was out on an emergency call. I got a call on Monday from a new customer that I had never been in contact with before. They wanted to try our controller to replace another that hadn't been working for over a year. I got the red eye flight out Monday night and flew to Orlando then drove out into the sticks of Florida. I didn't even stop to see Mickey, dolphins or anything else on the way back. I was tired from being up too much. The first day I did get one hour of sleep by sleeping in the car at the saw mill. My trip was successful. The personal touch makes a big difference. I was too tired to stop anywhere on the way back. I only brought my mill clothes and steel toed shoes. Steel toed shoes are not that comfortable.

There was no need for virtual axes in this application.

I like being in my office with my Lazy Boy recliner but when duty calls.......

 

[jdbrandt]

Virtual axis, or, more correctly, virtual master axis, is useful when you have multiple axis systems, spread over many controllers... I have done 77 and 84 axis systems, with four motion controllers, and the virtual master is the most practical implementation for all axis to follow 'one'

 

[chavak]

Interesting topic, although very new to me.
Can somebody explain with an example application please.

Thank you
_________

 

[Peter Nachtwey]

The Nascar test system

The physical axes are pushing on the tires as function of the recorded track information. The virtual master represents the speed of the car and controls how fast we index through the table of track elevations.

Imagine having track data recorded. One would need about 10000 points for each wheel if the track is about 2 miles long. Essentially this is a big cam table. A Nascar racer may go about 0 to 200 ft per second or one foot every 5 milliseconds. The motion controller can be given a command to a 5th virtual master to move at 200 ft per second. Every scan the virtual masters position is used to index into the cam tables to determine the positions, velocities and accelerations for each wheel a that point. The virtual master can be slowed down and speed up. Sometimes they find an interesting spot and back up the virtual master to the point of interest and play through the data slowly my moving the virtual master slowly.

By changing the speed of the virtual master they can see how the car will react to the bumps on the track at different speeds and the different speeds are simulated by controlling the speed of the virtual master.

I have a video
http://www.deltamotion.com/peter/Videos/Nascar Perf ADI 020607 Commercials Out.mpg

This video was provided to me by ADI where the first machine is. You can't see what is happening when indexing through the data at 200 ft/sec so the speed is slowed down. Notice how the car geometry changes as the wheel goes up and down.

 

[TConnolly]

Darn Peter. Too bad you didn't have time. You know you are welcome to drop in if you are in the area again.

 

[mordred]

considering he was flying dropping in may not be the safest expression lol

 

[chavak]

Thankyou Peter :site:

 

[rpoet]

Peter,
I just saw this in Entertainment Engineering:

http://www.entertainmentengineering.com/v6.issue05/index.html?page.12-13.html

I see one of your motion controllers was used to run this thing, and that you used a virtual axis to control everything.

A very unique application for a hydraulic motion controller. Well done!


-rpoet

 

[Peter Nachtwey]

Do a search for "prototype this water slide" for videos. One of the other engineers at Delta actually set that system up.