[Help] New Project - Rebuild an Old CNC Machine

Great support from this community!

I have a really low budget, thats why I cant use that kind of solution andy

PCW wrote:

a 1024 PPR encoder will have 4096 counts per turn using quadrature so ~600 RPM is about as fast as it can be tracked with the software encoder. Probably the simplest solution if you need to track higher speeds would be to swap the 1024 PPR encoder for a encoder with lower PPR, say 50 or 100 PPR. You can add hardware that will count the 1024 PPR encoder but this is probably overkill.

I do have CPLD code for a encoder divider that can divide the count by 2 to 64 (and stretch the index pulse appropriately) that could be used to lower the effective PPR of your existing encoder, if you are comfortable with CPLDs (a $2.00 part will do)

Instead of buying a new encoder, the CPLD seems like a great solution.
Nevertheless, before all of this I need to explain that I have an VSD-E driver (from Granite Devices), this driver controls the motor, he have an PID and everything. The question is, what is better:
Use this driver to control the motor (instead of the linuxcnc), or using the linuxcnc to control the motor (disabling the PID from the driver)?

Another thing, I've left the PWM control, because my driver needs an 3...5 kHz input frequency, and in order to have a great resolution (in the duty-cycle) I needed very high sampling frequency (min 500 kHz = max 2us for every sample), and the software cant handle this kind of speed
The solution I've seen is using ADC (HAL component) and using DAC (hardware component). A question, I havent seen anywhere, does ADC existis on HAL? (if so, can anyone explain or show an example?)

Great feedback people, after I conclude this I'll pay the next round!

Are you saying that the spindle is controlled by the VSD-E?
In that case, its probably easiest to just use the encoder for
feedback to the VSD-E and drive the VSD-E with step/dir

EngEC wrote:

Nevertheless, before all of this I need to explain that I have an VSD-E driver (from Granite Devices), this driver controls the motor, he have an PID and everything. The question is, what is better:
Use this driver to control the motor (instead of the linuxcnc), or using the linuxcnc to control the motor (disabling the PID from the driver)?

What motor are you trying to control with the VSD-E? Not the spindle motor I presume, so there is some confusion here.
Please clarify.

PCW wrote:

Are you saying that the spindle is controlled by the VSD-E?
In that case, its probably easiest to just use the encoder for
feedback to the VSD-E and drive the VSD-E with step/dir

Yes it is. My question was made because I dont know how important is to use feedback on the linuxcnc, like using linuxcnc to make a screw.
I know that in theory I should close the loop on the main controller, but is it really important or can I use a loop of "trust" for the linuxcnc? (trust that VSD-E is working just fine)

emcPT wrote:

What motor are you trying to control with the VSD-E? Not the spindle motor I presume, so there is some confusion here.
Please clarify.

Yes I am using VSD-E controller for the spindle motor I've post earlier:

EngEC wrote:

I have progressed with the machine, the hardware aint a problem now, but now I am asking some help with this awesome software.
I need to use PWM to control spindle, but I have a problematic situation, I achieve 3500 RPM with the motor, and have a differential encoder that turns 2 times that value, making the 7 kRPM. The problem is that the encoder is a differential encoder with index 1024ppr. Do I have a solution for the high-frequency? (I've read that the max frequency of the HAL encoder component is 10~50 kHz)
These PWM must be 50~95% (for CW) and 5~50% (for CCW), is there a component that I can use? [note: the 50% means that the motor is stopped]

but instead of using PWM for the listed reasons, I've been working a solutions with you (experienced guys )

andypugh wrote:

EngEC wrote:

Yes it is. My question was made because I dont know how important is to use feedback on the linuxcnc, like using linuxcnc to make a screw.
I know that in theory I should close the loop on the main controller, but is it really important or can I use a loop of "trust" for the linuxcnc? (trust that VSD-E is working just fine)

To perform a spindle-synchronised move LinuxCNC needs to know where the spindle is. This means that for threading there needs to be feedback from the spindle encoder to LinuxCNC.

I can think of ways round this, you could run the VSD-E in step-dir mode, and trust it to track exactly, then use the position command as the input to the LinuxCNC motion controller. But you would need to find a way to emulate the index behaviour of an encoder. I think this would be called an "interesting project" rather than a "recommended solution"

So, for threading I need the feedback?
I haven't yet worked with a rotary encoder, that's the real problem for me, because I don't know what is the output timing diagram. If the index just shows once per revolution I can calculate the spindle speed just by the index pin.

andypugh wrote:

From a scan of the VSD-E manual it looks like it only offers a pass-through of the encoder signals. Some drives have a programmable divider built-in, so that the feedback to the controller can be at a lower pulse-rate. I think you will need to connect the encoder to the VSD-E whatever else you do.

Any of these signals can lower their pulse-rate just by adding counters (hardware) to their pins. The only inconvenience is that the resolution will be lowered, but that aint a problem for my system.
[note: the encoder is external]

andypugh wrote:

What type of motor drives your spindle?

The motor is a 1.1 kW BLDC (135VDC) 1.5 HP (3500 RPM) with 2 inputs. The difference between the inputs demands the direction and speed of the motor.
[haven't yet measured the difference between the gears of the encoder and the motor, but if it is not 1:1 it'll be not bigger than 1:2]

If you only want to make the spindle rotate "more or less" you do not need the feedback up to linuxcnc.
You can use only the feedback until the drive and you can use a large encoder resolution, because the drive will be able to use it.
Linuxcnc will then be "blind" and trust that the drive will do what he is asking. Normally this is ok for normal lathe work, except threading and other work where the axis move accordingly to the chuck position.
1.1Kw is probably too much for your drive and too low for a spindle lathe (only if it is really small).

I have 500cpr encoders, used, if you like.