Originally Posted by
N4NV
The only thing I have to get straight on the DigiSpeed is the CW and CCW relays. When making adjustments to Mach, I found that by varying the "steps per" motor tuning section, I could adjust the linearity of the speed over the full range. I started with 1000 and found that a setting of 785 gave me a speed within 1% of what was commanded.
Vince
Hi Vince,
Good to see things are working out. In producing an analog voltage out of the DC-06 DigiSpeed-SD the step/inch in the spindle motor setup tab work like this.
The DC-06 passes the step pulse through a monostable. This converts the narrow step pulse into one of a fixed and known width. The advantage of this is that when you change the step pulse width in Mach, the analogue voltage is not affected.
The step pulse generated from the monostable then feeds a RC charge pump. Think of the step pulse as a small charge of energy. The more pulses you generate the more energy goes into the charge pump and the higher the output voltage that is generated.
In the end you can only produce a voltage that is slightly less that the supply being fed to the DC-06 from the VFD (say 10V). If you set the steps/inch too high then the output voltage hits the 10V ceiling too early. As a higher step pulse stream is supplied, the output voltage is clamped to the 10V thus creating the non-linearity.
What you want is for the maximum steps/inch setting to supply just enough energy to the charge pump to reach the 10 volts. If it is too much the spindle will run faster that the set speed. If there are not enough pulses, the spindle will not reach the set speed.
What you need to do is what you have done. Play around with the steps/inch setting until the maximum actual spindle speed is reached at the same time the maximum set spindle speed is reached.
I hope this helps explain what is going on.
Cheers,
Peter.
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