Following error monitoring on stepper machines
25 Jan 2017 18:25 #86648
by 109jb
I have been reading about this and found in the documentation the way to test for it. Once I get that far I will check it out more but I'm thinking just another PP and BOB will be what is needed down the road anyway. I've been thinking what I want to implement and it seems like I would need the following in the future:
Outputs:
9 for 4 axes worth of steppers + enable
1 for spindle direction
1 for spindle PWM
Inputs:
6 for encoders (Only XYZ axes with following error detection)
2 for spindle encoder and 1 for spindle index (So I can swing the mill head 90 deg and use it as a lathe for threading)
at least 1 for combined home/limits
1 for probe input
1 for tool setter
I understand that LinuxCNC can do a pretty good job lathe threading using only an index pulse, so it seems I would need a minimum of 11 outputs and 10 inputs which could be achieved with cheap BOB's if I only use a spindle index pulse, but I do like the idea of more inputs and will look into the X-mode more thoroughly If I had 5 inputs on the first PP, and 9 on the second, I would have 14 which means I could do everything I want to. Thanks for the tip.
Replied by 109jb on topic Following error monitoring on stepper machines
There is also mode X for parallel ports, but some do not support that.
All the ports i have do support it. That will do 8 out/9 in pins on it.
I have been reading about this and found in the documentation the way to test for it. Once I get that far I will check it out more but I'm thinking just another PP and BOB will be what is needed down the road anyway. I've been thinking what I want to implement and it seems like I would need the following in the future:
Outputs:
9 for 4 axes worth of steppers + enable
1 for spindle direction
1 for spindle PWM
Inputs:
6 for encoders (Only XYZ axes with following error detection)
2 for spindle encoder and 1 for spindle index (So I can swing the mill head 90 deg and use it as a lathe for threading)
at least 1 for combined home/limits
1 for probe input
1 for tool setter
I understand that LinuxCNC can do a pretty good job lathe threading using only an index pulse, so it seems I would need a minimum of 11 outputs and 10 inputs which could be achieved with cheap BOB's if I only use a spindle index pulse, but I do like the idea of more inputs and will look into the X-mode more thoroughly If I had 5 inputs on the first PP, and 9 on the second, I would have 14 which means I could do everything I want to. Thanks for the tip.
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25 Jan 2017 22:55 #86655
by andypugh
That is the correct way to think about it.
You need to consider how fast your motors turn at full speed, and that the system needs to see no more than one edge-event per base-thread cycle. From that you can work out what the maximum encoder count is that the system could handle, but there is no point going any higher than you are talking about.
Replied by andypugh on topic Following error monitoring on stepper machines
Based on this, I think a 200 PPR encoder that would have 800 counts per rev should be more than enough for this, and would be less taxing on the system than a higher PPR encoder in terms of reading the encoder pulses. Is this a correct way to think about this or is there a reason to go to higher counts per rev?
That is the correct way to think about it.
You need to consider how fast your motors turn at full speed, and that the system needs to see no more than one edge-event per base-thread cycle. From that you can work out what the maximum encoder count is that the system could handle, but there is no point going any higher than you are talking about.
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25 Jan 2017 23:14 #86660
by 109jb
Replied by 109jb on topic Following error monitoring on stepper machines
Thanks. I just ordered a 100 PPR encoder, so with 400 counts per rev I should still be good for the 0.002" following error detection. I only ordered one right now to test on the x axis of my machine. I went with the 100 PPR because the 200 PPR was 5X the price and I didn't want to go up to a 400 PPR encoder as totally unnecessary. We'll see how it goes. It's coming from China, so will be a while before I can update. Thanks for the help and support.
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