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Author Topic: Need Guru input on an idea: Using Mach as dynamic balancer  (Read 14837 times)

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Offline simpson36

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I am looking at acquiring the capability to do some simple dynamic balancing, and I need some help from the electron guys who are also familiar with Mach scripting.

A very simple form of dynamic balance is simply a sensor (accelerometer) that triggers a strobe light. The light is pointed at the spinning object and similar to a timing light, the strobe freezes the part at a specific point. You throw on some weight and go thru "worst/better" iterations until the balance is close enough. Not efficient, but it does work if you have the time and patience.

A new USB based balancer that runs on a laptop is over $6,000 and has capabilities far in excess of what I need, so I am looking at DIY (read cheap) alternatives. Basically, all that is needed is to fire a strobe based on movement (vibration) of the part.

First, are there any oscilloscopes or other off-the-shelf devices that can do this?
Second, how difficult would it be to design a circuit to do this?

Third, it occurs to me that Mach can take an input (tachometer) and of course can generate outputs. I think I can figure out how to fire a strobe from a 5v output pin. How would one go about connecting a digital or analogue accelerometer to Mach as if it were an index? And can the index input signal be detected by script?
Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #1 on: May 14, 2010, 09:23:54 AM »
What are you going to try and balance?

Crankshafts? What size motors?
Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #2 on: May 14, 2010, 09:25:58 AM »
Not sure how an accelerometer would help you.  I believe the way tire balancers typically work is to have strain gauges on the spindle support, which will give you a cyclic strain reading that can be correlated with the angular position of the wheel, to determine the location of the heaviest point, while the magnitude of the strain gives an indication of the amount of imbalance. 

For lower precision, I'd try using a proximity sensor.  If the spindle is mounted on compliant mounts, you should be able to get enough motion through compression of the mounts to get a good reading from the proxiimity sensor.  Since you'll inherently know angular position courtesy of Mach3, and a simple calibration with a few known weights will tell you how to scale the proximity sensor reading, the math to calculate the weight required, and the correct position, should be pretty trivial.  A quadrature setup should give high sensitivity.

Regards,
Ray L.
Regards,
Ray L.

Offline simpson36

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Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #3 on: May 14, 2010, 01:56:46 PM »
Thanks for the replies. I am interested in balancing R8 and 5C machine spindles running in the 8,000 RPM range.

'Spin' balancers for tires (fairly crude actually) and similar devices for industrial dynamic balancing are designed to balance a 'disembodied' rotating part. There are balancing services that do this, the most obvious would be a tire store, but there are balancing shops where I could send the spindles out to be balanced . . .  but where's the fun in that? It seems to me that it would be very useful for the Mach community to have an inexpensive but effective way to smooth out the operation of their CNC machines.

Strain gages are used for low RPM unrestrained shafts. A tire 'spin' balancer actually has one end of the shaft completely unsupported, but that application is under 1,000 RPM. I am not an expert in this field, but to my knowledge, higher speeds are done with constrained shafts and rely on vibration analysis.

In-place or 'field balancing' (pumps, motors, fans, etc) relies on vibration analysis. This is done with accelerometers which detect minute movements . . probably several orders of magnitude more sensitive than a proximity sensor, I would imagine. There are basically two methods (that I know of). Both methods use accelerometers attached to the machine. The more sophisticated method uses two accelerometers 90 degrees apart and also a photo (or proximity) sensor to count revolutions (and create a ref azimuth). These devices then tell exactly where and how much weight to add, and can do each end of the shaft separately, but simultaneously.

I am not expecting to mimic this type of balancer. The simpler form has one accelerometer and a strobe. It simply fires a strobe in responce to the vibration, thereby identifying the imbalance spot, but without quantification. In the hands of a very experienced person, only a few 'better/worse' iteration usually get the machine dialed in pretty close.
 
Accelerometers can be digital or analogue. A simple analogue 3 axis accelerometer is contained in a single IC and is about 20 bucks. These can be hooked up to a scope and the magnitude of the imbalance read directly. What is needed then is a trigger for a strobe. I have been talking to a company than makes an inexpensive USB oscilloscope and that looks promising, but I think it can be done for 'free' with Mach if there is someone out there with the combination of electronics and Mach3 knowledge to do it. I would be willing to work it out and share the process, but while I can contribute to the project, I do not have all of the knowledge needed, hence this thread.



« Last Edit: May 14, 2010, 02:06:01 PM by simpson36 »
Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #4 on: May 14, 2010, 03:55:07 PM »
I balance crankshafts.

Ended up buying a vibration analyzer on Ebay, Balmac model. 2 plane with strobe. Then just built my own holding fixture.

An oscilliscope will give you way to much noise from what I was told, I looked into that a bit.

Try and get ahold of a manual for one of the commercial vibration analyzers... very informative.

Offline simpson36

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Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #5 on: May 14, 2010, 04:31:19 PM »
http://www.datastick.com/products/bal2000.html?gclid=CKjJ_LO3zaECFR5rswodFXUafA

If one has USD$6,000 burning a hole in their pocket, the solution is easy. Actually I just watched an old analyzer/balancer sell on eBay complete with sensor, strobe and 'lots of cables' . . . but the fellow did not know if it worked or not and I don't have the resources to fix something like that if it didn't, so I passed on it. It sold for $135

Most likely I will end up with the USB scope which has outputs and a scripting language that allows it to be read and programmed from a PC. Add an accelerometer (or two) and a strobe and it's Miller time. Plus then I have the scope for other uses.

I though it would be interesting and useful to use Mach3 since it seems capable of the task and everyone already has it, but so far it seems there are no Gurus up to the task.  :'(

Offline Fastest1

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Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #6 on: May 14, 2010, 08:48:48 PM »
Simpson, you are the guru up to the task! And we are waiting for the results and following videos. ;D
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

Offline RICH

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Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #7 on: May 15, 2010, 07:53:55 AM »
Simpson,
Just a thought, but look into what the RC helecopter guys do. Balance is lost once you put something into the spindle.
Make note that the active system must be looked at, not just a single item, so even tool chatter can create a condition for resonance.

FWIW....RICH

Offline poppabear

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Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #8 on: May 15, 2010, 09:13:47 AM »
I think it could be done as you originally discribe, given some "adjustment" capability of your sensor (accelerometer).

Machs current loop time is 10hrz, so in theory your max Trigger time (RPM) would be 6000 rpm, I would probably
limit your spindle to no more than 5000 rpm, since real world loop is approx 1.0x to 1.1x dependig on the speed of your comp. That is important since to act on the information with scripts, you have to capture that data, and act on it, within
the loop time.

On your accelorometer, I would pick one that you could adjust its trigger, since each thing you try to balance may have different out of balance amounts. I would put the Unknown object in the spindle, then turn it on, then I would "increase" the trigger force until the strob quits lighting all together, then come back in, till the stobe lights again, at the very edge of max detection. that would show the "Top of the bell curve" of your deflection.

At any rate: I would use the PP, and bring in the Index trigger, and use the  Index OEM LED as my trigger object.
I wold then send out an Output that would power your strobe.

Here is a Brian, that would do what you want, if you can get your Accelarometer to adjust properly (a digital one).

here is the logic in Brian words(using Output 4 in this example that represents the signal to trigger your strobe light, brain is attached).

IndexSpindle(LED) ->NoOp ->Output4

Here is a MacroPump that would do the same thing in VB.

'MacroPump.m1s

If GetOEMLED(826) Then
ActivateSignal(OUTPUT4)
else
DeActivateSignal(OUTPUT4)
End If

'scott
Commercial Mach3 & Mach 4, Design/Build/Retrofit CNC and Industrial machines.
http://www.ss-systems-llc.com/

Offline simpson36

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Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #9 on: May 15, 2010, 03:19:13 PM »
Simpson,
Just a thought, but look into what the RC helicopter guys do. Balance is lost once you put something into the spindle.
Make note that the active system must be looked at, not just a single item, so even tool chatter can create a condition for resonance.


There is nothing attached to the rotating part. The sensor goes on the housing (magnetic usually) and measures the movement. The balancing is done with the spindle running free, so there is no cutting chatter or other influences. 

As it happens, I used to be an RC helicopter guy. I flew a gasser. Goal was a camera ship. but I started tinkering and next thing I was into aerobatics. Still have it on a shelf in the garage.