P.C. Router quit while cutting

[ralph@moreheadkreations.com]

recently I was carving a large sign,where I had an area cut that took about 4 hours. I stepped out of the shop,(which I usually don;t )for about 20 min.When I came back The machine was still going but the router had quit.I figured that it had been off for about 10 min.
First question, will all that slipping on the stepper motors damage them? I finished cutting the sign and they seemed to worked ok.
Has anyone else have this happen with a p.c.
I took it apart and found that a wire had vibrated off the little circut board.
After this expirence I got the idea that what is needed is a saffty switch that could since when the router is off and trigger the shutoff switch on the bot.It could work on the line voltage, when there is a change in the current it would trip a relay that would trip the shutoff switch.A "pump saver" for well pumps works in this manner I beleive.
Has anyone thought of doing this or know of such a thing?

[RTM (Unregistered Guest)]

I ask again if anyone has had this happen?
has anyone herd of a safty switch as discribbed above?

[watswood]

RTM, I am not familiar with the pump saver switch you are speaking of, but I've thought of this for some time, especially in my first year when crashes were frequent. Send me a link of one of these witches and I'll check it out.
I googled a current sensor switch and found this: http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR4395
This looks like it would work fine, though I have no idea of cost. This device could also be used to measure over current. For example, if you crashed your router while away and it started cutting into things it shouldn't, the device would sense too much current draw and shutdown the shopbot and the router. What would be nice about a device like this unlike a fuse or breaker, is that it can shutdown the shopbot along with the router. Two of these devices would cover both cases, one set for over current and one set for under current. You can get fancy with the shopbot conrol box by using a spare input and writing your own code such as:

ON INPUT (2,1) GOTO SHUTDOWN
'input 2 is your sensor

SHUTDOWN:
JZ,1 'pull up router
SO,1,0 'turn off router
SO,3,0 'turn off dust collector
SO,2,1 'turn on siren and wake up operator
END

Let me know if this helps.
Eugene

[gerald_d]

RTM, we know too little of stepping motors to say whether slipping them will damage them permanently. But, a lot of us have had small disasters in this department, and I can't recall any SB'er ever mentioning that they had damaged an Oriental Motor in this way.

The PumpSaver comes from this company (http://www.symcominc.com/). Before I consider adding such a device, I would want to know what this device is supposed to be able to detect. If my router draws 8 Amps with new brushes and no cutting, 6 Amps with bedded brushes and no cutting, 7 Amps with bedded brushes and light cutting, 10 Amps if I push a 1/4" cutter to the limits, 9 amps if the surfacing cutter is working very lightly, when should the device trip?

We might have to have different current settings for each type of job, and the starting point will be to actually measure how much current each job uses.

[watswood]

Gerald, the device you located appears to do what RTM wants though I too could not find what the threshold would be in terms of load current draw. Here is what I found in the faq's:

Q: I heard there’s a high sensitivity mode for PumpSavers. How do I utilize this feature?

A: PumpSavers trip on an under load (dry-well) condition when the current drops below 80% of the calibrated value. Sensitivity may be increased to 87% of the calibrated value.
Call factory for field adjustment instructions. 1-800-843-8848

So what is the calibrated value? I guess we have to call. If all RTM wants to do is detect no or very little current, then maybe the threshold is not so important.

What you and I seem to be leaning toward is a device that can sense over current with a user variable threshold point. Ultimately wouldn't it be nice to have a device set just above your measured max current draw (application specific) so that just the slightest out of wack condition (hit a clamp, programming error, etc.) could shut things down instantly (like a limit switch), and safely, before even the possibility of throwing the z or x out of alignment. Am I dreaming? Maybe, but I think it is possible. I also know that a breaker set for worst case won’t be fast enough or smart enough to shut down the shopbot with it. I’m not saying this device would replace a worst-case breaker, just supplement it.

By the way, for those of us who own spindles, we already have a current sensing device, the VFD. All we need is a cable between the vfd and control box and a little vfd and shopbot programming. I have only figured out a scenario for the low current situation as in RTM’s case (an open wire in the spindle). Check out parameters 06-12 through 06-15.
I can’t find anything in the vfd manual that would give a variable threshold, though there is an analog output that will give a voltage range of 0-10v that can be programmed to represent output current (parameter 03-05). I believe there may have to be an additional circuit to actually cause a threshold trigger; I’ll work on it.

[RTM (Unregistered Guest)]

Thank you Eugene and Gerald for your responces. I will be checking these links out to see if it would br practicle to get one. I had'nt thought of the over powering contoll such as running into things
The main thing this type of devise would give is peice of mine. I don't ususally leave the machine unattended but even while working in the shop with the bot running I can't totally be babysiting it .
I would be interested if anyone else has tried such a device.

[gerald_d]

Lest someone gets the wrong impression, I am not promoting the use of such a device. I think that folk are going to get a lot of "nuisance tripping" and then set the device to be less sensitive......so that it doesn't trip on the day it is really needed. With waterpumps, the current draw is constant and totally predictable - with a router the normal current is all over the show. What might be a healthy current for one job is a "wrong" current for another.

We need to look at the sensing of other parameters as well.....
- Maybe a microswitch above a motor. If a carriage wants to jump the rails, the motor has to swing down.
- Maybe a tiny proxy switch looking at the rack teeth, If the motor is stepping, then the rack teeth should be moving.
- Maybe something more sensitive in the stepper driver electronics to detect motor overload.
- Maybe a true speed sensor on the router to sense excessive speed drop.
- Maybe an infra-red thermometer looking at the bit
- etc.

[richards]

How about a double shaft stepper motor with an encoder? (The Oriental Motor steppers cost about $5.00 more for the double shaft model. Encoders cost about $60.00 - $75.00 to fit motors with 1/2-inch shafts.) The encoder could be connected to a $2.00 TI-555 timer used as a missing pulse detector. A SBP file could contain some very simple INPUT code that would trigger a shutdown. Which axis triggered the shutdown and the time delay necessary for a shutdown could easily be modified to fit the file being run.

[watswood]

I came up with the idea for sensing over-current based on my observations of the ouput current on my vfd’s display. I was amazed at how predictable and consistant it was for ‘my’ applications. I will still pursue this device for my own use, but, as Gerald pointed out, it may be tricky and unreliable for most applications. I apologize for not looking at the bigger picture as Gerald has done.

I will however, still endorse the use of ‘a’ current sensing switch for low/no-current conditions as in the case of RTM (an open circuit in the router). Here all we would want to do is detect the lack of current to shutdown the shopbot, and not fiddle with detecting the proper over-current condition. You would basically set it (well below the router’s no-load current) and forget it. I’m not sure the pump saver device would work as I can’t find enough info about it. The crmagnetics device in my first post has a set range of 10ma-60amps and I still believe this device will work for detecting a low/no current condition, but I would still recommend a phone call to the techies.
Another benefit of having a lo/no-current detecting device is in the scenario where the router pops the breaker due to a short circuit or a major crash; the sensor will then detect the lack of current draw (with the breaker popped, there is no current) and shutdown the shopbot. Even if the crmagnetics device is not the right part for the job, there has to be a way to accomplish this.

[mikejohn]

Old fashioned 'ball' type mouses worked with optical encoding disk, which simply counted the pulses from an LED passing through a slotted disc. Could this be adapted to connect to the rotary motion of the router somehow?
Router stops, the pulses stop. The light becomes either continuous or is switched off.
...........Mike

[gerald_d]

I think the PC routers have a metal fan. Can one of these (http://www.cherrycorp.com/english/sensors/index.htm) be pushed in there to look at the fan blades? Might even help to find the true speed of these animals.

[zeykr]

Could one of the sensors Gerald links to be used to watch the teeth on both x and y tracks and used to stop the machine if carriage movement is not seen in X amount of time?

[dirk]

If you could put a sensor on the blade, you could also monitor actual rpm

[watswood]

Check out the infrared sensor:
http://www.reliabilitydirect.com/tachometerproducts/tachsensorproducts.htm