Messages

51

General Mach Discussion / Re: Height Control for Router Table

« on: August 13, 2011, 05:22:47 PM »

Sorry I didn't have time earlier to respond to everything.

I wanted to use something existing just to reduce the time required for the project. I'm not quite sure what you mean by a floating Z... Does it have a depth guide that contacts the material?

The ultrasonic sensor has a response time of 2.5ms.... should be plenty fast for a table with max speed of 130ipm. That translates to a response roughly every 0.0055" at max speed. The swarf should be cleared with compressed air, but may randomly be picked up by the sensor if they happen to move past it at the wrong time, but should be rare. That is one reason for wanting PID.

What do you mean by a linear scale? Please elaborate, I'm not sure what you're referring to.

Thanks for all the help/ideas/insight. It's much appreciated.

I thought surely someone would have done this by now... but maybe not...

Chris

52

General Mach Discussion / Re: Height Control for Router Table

« on: August 13, 2011, 01:26:15 PM »

I said the material is not flat, not that I have a problem holding the material. I do indeed use a vacuum system strong enough to pull down 3/4" HDPE. That definitely isn't the problem. The material itself can have variations, and some materials are either too thick or too ridgid to hold with vacuum. That's why I want height control.

Thanks in advance for any help you can offer!

Chris

53

General Mach Discussion / Re: Height Control for Router Table

« on: August 13, 2011, 11:10:52 AM »

Any of the affordable THC's out there (hobby level) do not have built in PID loops.  They simply monitor tip voltage and send THC UP/DOWN commands to Mach.  The lack of a PID loop is exactly why you get excessive oscillation if the THC feed rate is set too high.

That sucks!

An stand alone industrial THC with PID capability can cost a few grand.  Thermal Dynamics gets just over $10k for theirs.

That is absolutely ridiculous! PID is bordering on ancient technology! We're still in 2011, right? Good. When you said that I thought maybe I had gone back 50 years.... PID has been around almost as long as electronics... Wow... Thanks for the insight. If I need it I'll be happy to develop it myself at those prices. Then sell it for a few hundred and steal the market.... hmmm..... lol

Are you looking to just measure the material height and apply a Z offset to compensate for variations in material height?

That is exactly what I need, but if it does see a chip I don't want it pulling Z up.... I suppose using a slow feedrate for compensation may work alright... Any suggestions?

54

General Mach Discussion / Height Control for Router Table

« on: August 13, 2011, 09:14:12 AM »

I want to use an ultrasonic sensor for height control as my sheets are not always perfectly flat. Blowing compressed air will clear the chip so I get accurate readings from the sensor. The ultrasonic sensor is ideal for this application as it can be used on transparent material and doesn't contact/damage the material.

The sensor output is 0-10V. I can use an op-amp and adjust the gain to condition the signal for THC or similar device. Or I could use it to compare to a set-point to generate THC UP or THC DOWN, but that doesn't solve the problem of no PID loop. I need PID to smooth out the signal so it's not constantly moving up and down. Any recommendations that don't involve electronic design, or at least very simple with minimal development time?

Has anyone developed a PID that works well for this application? If not, can anyone recommend a THC for this application?

Any thoughts?

Someone must have done something like this already!

Thanks,
Chris

55

Mach Screens / Re: VB code for jogging...

« on: August 13, 2011, 07:19:54 AM »

Check the OEM Button codes. Use DoOEMButton() in your new button's script to call whatever button you want to press. Get the list of OEM buttons from the Mach wiki here http://www.machsupport.com/MachCustomizeWiki/index.php?title=OEM_Buttons.

You will find everything you need there.

56

General Mach Discussion / Re: MACH as a CMM machine

« on: August 13, 2011, 07:11:02 AM »

Sorry for hijacking the topic  

Moderators, can we move these messages to a new thread?

57

General Mach Discussion / Re: MACH as a CMM machine

« on: August 13, 2011, 07:09:23 AM »

You won't need to buy a THC.  You'll have to build your own using the ultrasonic sensor.  All the THC does is compare tip voltage to a set voltage.  If the tip voltage is lower than the set voltage, the THC sends a THC UP command.  If it's higher, it sends a THC DOWN command.  You'll need to build some electronics to read the ultrasonic sensor, compare it's output to a set constant and output to a second PP on the Mach3 PC.

You will also have to create a PID loop to stabilise the function OR you will be chasing it all day. Most THC have the built in pid loop to filter the results and tune out the oscillations.

For the most part it cannot be done without using the THC functions in mach. Only the THC functions can interact with the already  buffered moves for Z.

Depends on the output of the sensor   Do you have the specs?

(;-) TP

The sensors are capable of providing a current or voltage signal, and I believe the voltage range is 0-5V, but will confirm when I go in today. It is trivial to condition the signal IF it doesn't match the THC voltage range. An extremely simple Op-Amp circuit would suit the purpose. Set the gain and you're done. Designing a PID controller on the other hand is not quite so trivial. Not extremely hard or anything, but it would take time that I don't have. Even if I design and/or build a PID, I will have to tune it to get it to work as desired. PID in THC controllers are already tuned for the application. I would much rather just use an existing, proven design then reinvent the wheel. I'll check the specs on those sensors.

A THC seems to fit the bill, unless anyone knows of a simpler, proven solution?

That being said, what THC would people recommend?

58

VB and the development of wizards / Re: Using G-code files in Button Scripts

« on: August 13, 2011, 06:43:57 AM »

32 bit is the standard.

(;-) TP

Thanks for stating the obvious.

59

VB and the development of wizards / Re: Using G-code files in Button Scripts

« on: August 12, 2011, 09:19:42 PM »

OK, I'll check on another machine. I only said I was surprised that they weren't working on my machine. This is a quad-core on Win7 64bit so that may be my problem. If that's it then it's the first script problem I've noticed on this configuration.

Thanks for confirming.

Chris

60

VB and the development of wizards / Re: Using G-code files in Button Scripts

« on: August 12, 2011, 08:18:05 PM »

Nice to know the exact extension limitations. Thanks.

Chris