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Message |
    
Mike John
Registered
Username: Mikejohn
Post Number: 5
Registered: 12-2005
| | Posted on Wednesday, June 07, 2006 - 06:51 am: | 
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In the Shopbot Forum Mike posted a message about "G100 pulse generator " which you are not allowed to respond to.
To me, trying to understand, this pulse generator is something new.
Is it possible for someone to create a diagram going backwards from the motors to the PC computer, showing where all the bits link together, and what they do?
I don't mean a circuit diagram, just schematic (I think thats what I mean).
Thanks
............Mike
(Link to ShopBot forum message - Admin)
Mike, your requested schematic is in a thread of its own. The rest of this thread has lead to a revision of the title. |
Mike Richards
Registered
Username: Richards
Post Number: 10
Registered: 05-2006
| | Posted on Wednesday, June 07, 2006 - 04:15 pm: |
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There are four main electrical components in a CNC machine's drive path:
1. Higher level software that the operator uses to command the machine to do something. In the case of the Shopbot, this would be the SB3 program.
2. Controller. In an ideal machine this module would receive commands from #1 above and convert those commands into a series of pulses for the appropriate motor - in essence, an intelligent pulse generator. The G100 performs this function. It also handles all I/O for the machine.
3. Stepper/Servo drivers. These modules amplify and convert step pulses into a form that fits the motors being driven. The G202/212/320/340 perform this funtion. One module is required for each motor in the system. The type of module, G202/212 or G324/340, is determined by the type of motor being used, stepper or brushed servo.
4. Motors and encoders. These modules, of course, perform the actual work to move each axis exactly as commanded by the software in #1. If encoders are used and properly integrated, the whole system becomes closed loop, meaning that automatic compensation is performed, allowing all axes to stay synchronized regardless of the cutting conditions.
The G100, contrary to popular belief, can be used with any software, not just MachIV. It is my opinion that if a company is not actively integrating the G100 into their software right now, that company is going to become an emeritus player in the CNC game. |
Evan Curtis
Registered
Username: Evan
Post Number: 5
Registered: 12-2005
| | Posted on Wednesday, June 07, 2006 - 06:29 pm: |
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Once again way out of my element, but... are you saying you could swap out the SB control (#2 above)
with the G100 and have a true closed loop system?
Would you have to completely rework the SB3 software and encoders?
Mike R have you offered your consulting services to SB? |
Mike John
Registered
Username: Mikejohn
Post Number: 6
Registered: 12-2005
| | Posted on Wednesday, June 07, 2006 - 06:53 pm: |
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Mike
Does this mean that when Gerald gets to RV2 with his boards, if he includes the G100 he will get improvements?
Do I have encoders in my PRT96 motors?
I am sorry to be a pain, but for some reason electronics have always been a mystery to me.
Even electrics. It was only last year I felt comfortable leaving the plugs out of sockets in case electricity leaked out 
............Mike |
Mike Richards
Registered
Username: Richards
Post Number: 11
Registered: 05-2006
| | Posted on Wednesday, June 07, 2006 - 07:51 pm: |
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Evan,
The SB3 code would have to be completely changed (and I believe significantly simplified) if the G100 were used. The G100 has its own internal computer, meaning that it expects to receive certain commands from the SB3 software. It would send the SB3 software status reports as the original commands were processed. The alpha stepper motors have built in encoders. With proper wiring, the G100 could use the pulse train from the alpha's encoder. (I have not studied the pulse train output from the alpha stepper motors, nor have I studied the required input into the G100 to see if one encoder pulse equals one stepper pulse. If the two pulse trains do not match, additional manipulation would be necessary.)
Mike,
The G100 is a completely different device than the PMDX-122 breakout board that I believe Gerald now uses. The G100 offers tremendous improvements over the breakout box approach, but it requires that the software be totally rewritten, whether the software is Mach or SB3 or something else.
I don't think that Shopbot attached encoders to any stepper motors pre-alpha. The Oriental Motor's Alpha stepper motor has an encoder built into the motor. Usually, you would add an encoder to the shaft sticking out the back of a stepper motor. Lacking a double ended shaft, you would need to attach an encoder somewhere in the drive assembly. |
Evan Curtis
Registered
Username: Evan
Post Number: 6
Registered: 12-2005
| | Posted on Wednesday, June 07, 2006 - 09:06 pm: |
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Thank you. I'm still out of my element but I find this very interesting, and I'm sloooowly learning thanks to all of you that share your knowledge. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 118
Registered: 11-2005
| | Posted on Wednesday, June 07, 2006 - 09:44 pm: |
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Just a quick post because I am between hotels....
The G100 could replace the PMDX-122 that I have in my box, but it is not user-friendly enough yet. Give it a few months....
Instead of plugging the printer parallel cable into it, this one takes a USB. The G100 can have encoder feedback from the motors, but it can also operate without, albeit to a lower level.
Mike, did you spot that MachIV is being dropped and that there will be a plugin for Mach3 instead? |
Dirk Hazeleger
Registered
Username: Dirk
Post Number: 12
Registered: 12-2005
| | Posted on Thursday, June 08, 2006 - 01:43 am: |
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Mike
This little speed demo of the Grex has me wondering. I understand that encoders will feedback and keep position, and if the unstallable materializes they will slow all steppers to compensate. So what are we really looking at in the video. What is the roll of Grex for the speed? I would think the motor has more to do with it than the Grex. Is it just an increased step rate, or are the step signals better, cleaner to allow the motor to turn faster? |
Mike Richards
Registered
Username: Richards
Post Number: 12
Registered: 05-2006
| | Posted on Thursday, June 08, 2006 - 06:11 am: |
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Gerald,
I haven't visited the Mach website/yahoo group for about a week. I must have missed the announcement.
Dirk,
Other than being entertaining, the video showed some important features of the G100. Encoder feedback is being used so that ramping is maximized. (The ramp is set faster than the motor can respond, but the feedback compensates so that no steps are missed, which is shown when the 'dollman' stops exactly where he should.) The G100 generates the pulse train. Mariss didn't give the gear ratio of the ball screw. Perhaps it's 1:1, but it looks to be a 'standard' 5:1 screw, meaning that the G100 is sending out pulses 5X faster than the 'dollman' is moving! The speed difference between the G100 and Mach software, sans the G100, is incredible. The G100 can pulse at a rate of up to 4mhz (4 million) pulses per second. The Mach software running through a traditional breakout box has a maximum pulse rate of 45khz (45 thousand) pulses per second - and even that 45khz requires a robust computer.
You're certainly right that the motor has to be able to respond to that kind of pulse rate. It was not an accident that a size 23 motor was used in the video instead of the larger size 34 motors that we use on our machines. The PK268-02 motors that I've tested are 'snappier' than the PK299 motors. However, I have been able to drive the PK299-02 and the PK299-F4.5 motors much faster with the G101 that I have than I can with the PMDX-122 running off Mach software. Granted, ramping plays a bit part of the increased speed. If you were using short moves, much of the power of the G100 would be wasted.
To me, the most amazing part of the G100 is that, for $400, you can do things that are just not possible with either SB3 or Mach software running via other controllers. I don't know what the Shopbot controller costs to make, but, if I were designing any new controller, I would first test the G100 to see if it could be used. Mariss knows what he is doing. He knows how to wring out the last drop of performance from a system. Between the G100 and the G2xx stepper drivers, he has developed hardware that puts everyone else to shame. He has also done much of the software. The CNC software (SB3, etc.) only has to send simple commands to the G100. The G100 does everything else and responds with a result code. I used that method clear back when I was designing with Z80 computers. It separated the 'user friendly' code from the 'machine' code. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 119
Registered: 11-2005
| | Posted on Thursday, June 08, 2006 - 07:26 am: |
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Mike_J, who started this thread, I'll put together the diagram you asked for at the beginning, but I have a foreign colleague visiting at the moment and his entertainment comes first.
The G100 (also known as the GRex) is going to change the face of CNC routing at the price levels of the ShopBots/ShopSabres etc. Within months, the parallel cable and serial cable driven hardware will be "old-fashioned". But, there is going to be about a year before the GRex settles down and becomes known as the state of the art. As an end-user, I wouldn't be bothered with the G100 now. As a developer/producer of CNC machines, I would certainly look very seriously at "GRex", but I wouldn't tell anyone that I am looking at it. Mike_R, want to take a bet that SB is looking if they can run their proprietary software front-end on Grex?...... (Re-reading the thread, Mike already said that!)
If you have wondered why the PMDX looks so lonely in the big space in the MechMate box, picture a GRex in that space. And that is as far as I am getting involved with that project now. All the rest is still a very moving target. |
Mike Richards
Registered
Username: Richards
Post Number: 13
Registered: 05-2006
| | Posted on Thursday, June 08, 2006 - 03:55 pm: |
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Here's a little more information about Mariss's video. The linear stage has a 1-tpi ball-screw (one turn per inch), not the 5-tpi that I speculated about in another post. The step rate to run at 3900 ipm or 65-ips is 130,000 pulses per second!
Although I can't imagine anyone trying to run a CNC router at speeds like that, I can imagine having that kind of pulse rate pulsing a motor that has a 10:1 belted reduction unit. Think of the torque that would be available! There would never be any missed steps. In fact, with a step rate like that, there would never be the need to even use stepper motors. Brushed servo motors would match the G100's speed perfectly. Can anyone say smooth and quiet?
Unless anyone thinks that I'm beating this drum too long and too loud, I'm just trying to make sure that companies that should be aware of the paradigm shift that's taking place, are fully awake and alert to what's going on all around.
Incorporating a G100 into system software is not practical for the enduser. It is something that a company would have to do. (I've toyed with the idea of writing an SBP file reader interface that would read an SBP file and then feed the commands to the G100, because the translation between SBP code and G100 code is extremely easy, but doing that would only enable the programmers among us to become higher level geeks.) Art F. at Mach software is doing an excellent job merging his software with the G100. Although his software is excellent, it would be a sad day for us 'botters if only Mach software took advantage of the G100. |
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70. Control Systems