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  #1  
Old Sat 20 January 2007, 05:46
fabrica
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Jerky movement of the gantries - Limit Overides activated in Mach

Gerald, I have another problem which needs to be solved with your advice.

When the gantry is moving at some points the motors on the x axis is moving very erratically. This is the reason for the Gantry to climb onto the x rail. When you look at the motors from the other end of the shaft you see it not moving at all but making a noise. It happens to both the X axis motors at the same time.

We changed the current limiting Resistors from 2 amp to 5 amp and finally to 1 amp, but the problem did not get solved. What should be the correct resistor.

We connected the second grub screw to all motor shafts and screwed them in very tightly but the same problem continued. It happens all of a sudden.
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  #2  
Old Sat 20 January 2007, 06:01
fabrica
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Below given is photo of the final control we had. In our haste to get the thing going we had got the main wire which provdes a/c cpower to transformer bundled togethr with the screened running to motors bundled together and running out of the control box together through the same bottom hole.

Do you think that this is causing the erractic behaviour of the motors due to A/C riples being piched by the motor wires. The erratic behavou happens on most times when both the X and Y axis are moving together. This means more power running through the A/C power cord.

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  #3  
Old Sat 20 January 2007, 06:29
Gerald_D
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I can't see a problem with cut quality in that photo. Are you happy with it?

Does the erratic behaviour start at a certain speed? The current resistors depend on the motors and how you have wired them

Looking very quickly, I am a bit concerned about how close your big power supply is to the PMDX. That is not a toroid transformer and your power supply is maybe "noisy". The cable from the PC to the PMDX also looks thin - is it shielded? What are your motor wire shields connected to?
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  #4  
Old Sat 20 January 2007, 06:59
fabrica
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Regarding cutting quality, I am very happy with it.

I have so far noticed any relationship with the erretic behaviour and speeds.

Gerald do you think that this errectic behaviour is noise related.

The transformer which we use were with us we did not bother to do up a toroid. But if everthing fails we could think of it.

The parallele cable is shielded. The motor wire shields are not connected to anything.

Do you think that we should the table as well.
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  #5  
Old Sat 20 January 2007, 10:07
Gerald_D
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Fabrica, glad to hear the cut quality is okay for you.

It is very difficult to diagnose this "erratic behaviour" because I can't see/hear it and it is not something that is common......

The ShopBots were fond of getting the shakes when the speed went too high and two axes had to move together. But you say your problem does not depend on speed. (The ShopBot issue was related to resonance of the gantry structure). Does it look like your V-rollers are bouncing up and down because of mechanical flexibility in the structure? I doubt it. (If this was the case, it would happen only at high speeds and dynamic movements).

Therefore, if it is not mechanical, then we must look for something electrical...and interference is the first thing that we worry about. Everything must be properly grounded. The table, the gantry, the y-car, the z-slide, and the shields of the cables. Only ground the cable shields at one end, the end nearest the control box. Also, the negative of the power supply must be attached to the same ground point as the shields, table, cars etc. If you do all this and the problem remains, we can look somewhere else. But it will not be a waste of time to do proper grounding - especially if you plan to use a dust sucker later.
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  #6  
Old Sat 20 January 2007, 10:54
fabrica
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The v rollers are properly seated on the Rails while travelling from one end to the other (X and Y both).

I too feel that this is a problem created by electrical noise. OK, I will start work the comming Monday and start with concentrating totally on the elctrical side of issues.

I have a few questions to ask from you about this microstepping issue which I will ask you later.
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  #7  
Old Sat 20 January 2007, 12:33
Gerald_D
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Did you adjust the trimpots on the gecko's for the lowest mid-band resonance?
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  #8  
Old Sat 20 January 2007, 20:32
fabrica
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No.
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  #9  
Old Sat 20 January 2007, 21:08
Gerald_D
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It must be done. See the gecko instructions.
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  #10  
Old Sat 20 January 2007, 22:41
fabrica
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To adjust the midband resonance you have set motor speed to 1/4 rev per second and adjust the pot until you hear a distinct null in the motors vibration. Am I correct?
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  #11  
Old Sun 21 January 2007, 00:13
fabrica
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Gerald, Do you have to provide a good earth to the table as well. At the moment it is not earthed and its sitting on a concrete floor.
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  #12  
Old Sun 21 January 2007, 00:58
Gerald_D
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Yes, that is how to adjust the driver/motor resonance. Remember you have gearbox on the stepper - the 1/4 rev/sec is for the motor only.

The ground/earth issue is illustrated here. Use the earth point in the control box
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  #13  
Old Sun 21 January 2007, 09:01
fabrica
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Gerald, As you assumed I too feel that this so called erratic behavior of the motors is due to electrical noise.

One final question the earth point (what you have reffered to in your earleir posting) in the control box is the alu plate onto which the Gecko drivers are mounted. And also the negative wire of the power supply (connected to the transformer) should also be connected to the same alu plate. The earthing leads comming from the table (x,y,z) should be connected to the same alu plate.

Please correct me if I am wrong.
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  #14  
Old Mon 22 January 2007, 09:11
fabrica
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Manjeet Happy to hear that you are making some progress.

Gerald, After doing everything that I promised to to do today I still have this erratic behavoir on the motors.

I gounded all wires running from the Gecko's to the motors to alu plates. Connected the negative of the power supply to the same alu board. X,Y and Z were grounder in serise to the same alu board. Tuned the pot on the Gecko's to the minimum humm levels(to overcome midband resonance).

The symptoms on the final run I made in the evening were as follows.

While jogging (with only one axis working) the steppers were running without any problem on all three axis. When you run the machine on a programme where all three axis start to work together we get some motors to miss their steps and direction specially at the accelataration stage of moving.

We took the router wiring completly out of the control box. Even the on/off switch was disabled and was done manually at the router point. Still nothing changed. We closed shop at 7.00 pm today. Tomorrow out first job would be to take the transformer out of the box and see weather this component is the culprit of undue noise generation. At this point we are almost sure that what we are encountering are noise related problems.

Even after taking the transformer out if the problem still persists I would replace the PMDX card to see weather this unit is diffective.
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  #15  
Old Mon 22 January 2007, 10:12
Gerald_D
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My project completed! - Fabrica (Sri Lanka) - Serial No. 1

If the the acceleration factor in Mach3 (motor tuning) is set too high, then it is completely normal for a motor to get overloaded and lose steps during the accel. stage of the movement. But then it will do it also when runnning only one axis....

Does your power supply perhaps lose voltage when it has to push 4 motors? Is there a regulator in your power supply that starts to clip/oscillate? The transformer is maybe too small? (should be around 300VA - looks much smaller in the photo). You say it is a standard power supply in your company - can you give each axis its own supply as a test?
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  #16  
Old Mon 22 January 2007, 12:30
DocTanner
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Fabrica,
Is your computer fast enough? An underpowered computer would cause these same symptoms.

DocTanner
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  #17  
Old Mon 22 January 2007, 12:45
Gerald_D
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Very true Doc. Thanks. (How is your animal behaving itself?)

At this point I don't think it is an interference issue.

Extremely unlikely that the PMDX has anything to do with it....it is actually a pretty dumb device. MUCH more likely the PC driving the PMDX.
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  #18  
Old Mon 22 January 2007, 16:26
fabrica
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My settings for acceleration for x and Y axis is 500 mm/sec and for Z it is given as 1500 mm/sec.

The transformer which we are using was just lying around in our factory. It has a wattage of around 1500 Watts. This is putting out 48 V AC into the PMDX 135-8020 power preparation module. The powder comes out of the prower prep module after getting multiplied by a factor of 1.66.

If everything fails I will provide each axis a individual power supply.

The computer is a Dual core running at 2.8 Ghz with 1 GB RAM.

Could any software on the PC be interfearing with the signals.
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  #19  
Old Mon 22 January 2007, 16:44
DocTanner
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Fabrica,
Your computer is more than adequate. There are a lot of things that interfere with Mach3. It wants fulls control There is a file on Mach's website http://www.machsupport.com/optimisation%20XP.txt Backup your system first!!!
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  #20  
Old Mon 22 January 2007, 17:09
fabrica
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Doc, Up from 4.00 am trying to figure out this problem.

Since you pointed me towards the problems that I may have on the computer side. Below given are my observations while setting up mach 3.

The mach version I use is Version R2.0.015. Does this have a special driver for PMDX cards. I could not find the PMDX option in the drop down list while configuring the mach 3. On the device manager list I found the PMDX card listed as a pulse generator.
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  #21  
Old Mon 22 January 2007, 17:20
fabrica
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Does the PMDX card have a driver for it. It is definitly not plug and play.
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  #22  
Old Mon 22 January 2007, 20:36
Gerald_D
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It is very early here...have to got to work. The PMDX card has zero intelligience, zero memory - it cannot even talk to a PC to tell that is plug&play. A PC could never detect its ID. It cannot use a driver (too stupid), so there is no driver for it. You could connect the printer cable direct to the geckos (some people do this) but the PMDX makes the wiring easier - that is why it is called a "parallel breakout card".

The 0.5 degrees is after considering the gear ratio.
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  #23  
Old Mon 22 January 2007, 22:10
fabrica
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Gerald, In the morning cleaned up the computer as per the intructions given in the link provided by doc.

We feel that their is slight improvement in the smoothness of the motors.

Now when engaging the router on a samlla cutting programme (without tool) the motors are moving smoothly when cutting straight lines. When cutting arcs all three motors on x and Y axis stagger and move.

Gerald, on the motor tuning and setup screen you get two inputs called step puls (1-5) and dir pulse. What is the normal velocity you use for all axis.
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  #24  
Old Mon 22 January 2007, 23:53
Gerald_D
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Cutting speeds are mostly in the range 1800 to 3600 mm/min. Sign letters in MDF typically 2400 mm/min. Just cutting a lot of straight shallow grooves at 7200 mm/min.
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  #25  
Old Tue 23 January 2007, 00:11
fabrica
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Gerald now the only problem (for the moment) that I am facing is that while only one axis is moving (cutting on a straight line) the movement is ok and smooth. When two or more axis are moving (cutting arcs and circles)the whole gantry is jerking.

Gerald, on the motor tuning and setup screen you get two inputs called step puls (1-5) and dir pulse. Whet do these two inputs mean.
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  #26  
Old Tue 23 January 2007, 00:12
fabrica
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I have just started to move the bulky transformer and place it outside the control box.
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  #27  
Old Tue 23 January 2007, 00:29
Gerald_D
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On Saturday afternoon I asked if the problem was speed related and you said it was not....

It is known on ShopBots, and also on the MechMate, that the gantries and cars start to resonate at higher speeds when cutting arcs and circles. This problem is definitely speed related.

From the mechanical side it is critical that the V-rollers sit very correctly and firmly on the rails. The Y-car must have the spring roller (M130100) on the side away from the motor.

But, the above problem does not cause the motors to lose/gain steps. You are telling me that you are gaining/losing steps?? We have to be very clear about this.

If you cut around a full circle, and you have the erratic problem, does the cutter finish at the starting point, or is there an error?

error = electrical problem
no error = mechanical problem
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  #28  
Old Tue 23 January 2007, 00:40
Gerald_D
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"on the motor tuning and setup screen you get two inputs called step puls (1-5) and dir pulse. Whet do these two inputs mean." I think it is a way of lengthening the pulses coming from the PC - have never used them so I don't know.
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  #29  
Old Tue 23 January 2007, 07:48
fabrica
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On saturday afternoon Gerald we were working on the jogging mode. We ran the machine fast and slow but the problems that we encountered happened while running fast as well as slow. That is why I informed you that speeds are not linked to the problems encountered.

We checked the V rollers and also the bearing fitted to the opposite side of motor mount on Y car. They were ok.

To get a conformation on weather this was mechanical or electrical related problem we disengaged the Pinions from the racks and ran a circle cutting programme. All three motors are jerking while turning. We are now very sure that this is a electically related problem.

We also cut a full circle with motors engaged to racks although the movenet of the gantry is Jerky the circle was ok it ended up at the same place.

We are still working.
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  #30  
Old Tue 23 January 2007, 08:38
DocTanner
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Trouble Shooting:
Disengage motors by removing the springs
Gantry should go from one end to the other with a firm push
Y-car should do the same
Z-axis should remain stationary with motor spring removed.
All v-wheels should remain in full contact during all of this. Movement should be very smooth.
With springs replaced, Move the gantry. It should take a firm push to move.
Reverse movement of the gantry. There should be no "slack" when going from one direction to the other.
Slack indicated a loose pinion gear
Do the same for each axis.
Use pin connector for every connection to breakout board and Gecko
If you don't have a quality crimping tool for pin connectors, then it's best to solder then cover with heat shrink tubes.
Motor wiring: From Gecko to motor:
Pin 1 Ground
Pin 2 Power <---possible culprit "I'm using 70 volts from toroidal transformer"
Pin 3 Coil A = PK296A1A black
Pin 4 Coil A~ = PK296A1A green yellow Do Not Connect- Insulate from any contact
Pin 5 Coil B = PK296A1A red white Do Not Connect- Insulate from any contact
Pin 6 Coil B~ = PK296A1A blue
Pin 7 Not Connected
The PMDW-122 board is recommended, but a simple breakout board will work for trouble shooting
Pin 8 Direction - From Breakout board
Pin 9 Step Pulse - From Breakout board
Pin 10 "Common" 5 volts <---- from computer or breakout board (correctly jumpered PMDX-122)
Pin 11 resistor 8.2K 1/4 watt resistor
PIN 12 other end of resistor

If everything checks out, then go to www.machsupport.com/videos.htm They have some great tutorials.

Hope it helps.
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