tony ennis
New Member
Disclaimer - I'm a beginner at electronics.
I'm working on a project that requires either a rather large number of pulses from an encoder wheel, or I need to generate a lesser number of pulses and use a PLL to produce the desired number.
This is for a machine tool where the rotation of the first spindle must remain synchronized with the timing of a 2nd. In short, I've got a lathe and I want it to cut screw threads using a stepper motor.
My problems are solved if I can determine that a PLL can reliably generate a pulse train even when the input signal varies. Every distortion in the signal generated by the PLL will result in a positioning error on the stepper.
I don't know how to describe the load variation, but it's something like this:
Assume the spindle is turning at 60 RPM (1 RPS.) From this, I could be generating 128 PPR the thus generate a 128 Hz signal. My PLL would have to receive this and generate a signal 50x as great - 6.4 KHz. So we're guiding one piece of steel into another... when they meet, the spindle's RPMs will drop, at least for in instant, as the load increases. The drop is nearly instantaneous in a physical sense. It might be glacially slow in the electronic sense. I don't know. So the signal would drop from 128Hz to perhaps 100Hz in a fraction of a second. The PLL would have to respond without transmitting too many extra, or too few, pulses. Further, the frequency of the spindle pulses would be varying by a lesser degree all the time. Nothing is perfect. The PLL would have to respond in kind.
There are two cases. Since the PLL can't respond instantly, it can either 'sneak up' on the right frequency, or oscillate and settle on the right frequency. The first case is to be avoided - say the PLL's output frequency is too low - it generates too few pulses, adjusts, generates too few, etc. The end result is that we've dropped pulses to the stepper, and there's no mechanism to recover them. The stepper is 'behind' and will stay that way. The second case is better because if we generate too few pulses on one iteration, we'll generate too many on the next. On average, the stepper will be 'out' fewer pulses.
Also, I realize the 50x freq increase may be difficult to achieve in an acceptable way. I can reduce it with some effort (or expense) by producing more spindle pulses.
That's a lot of typing for not a lot of information. Can anyone here explain to me the capabilities of a PLL to keep this signal synced?
I'm working on a project that requires either a rather large number of pulses from an encoder wheel, or I need to generate a lesser number of pulses and use a PLL to produce the desired number.
This is for a machine tool where the rotation of the first spindle must remain synchronized with the timing of a 2nd. In short, I've got a lathe and I want it to cut screw threads using a stepper motor.
My problems are solved if I can determine that a PLL can reliably generate a pulse train even when the input signal varies. Every distortion in the signal generated by the PLL will result in a positioning error on the stepper.
I don't know how to describe the load variation, but it's something like this:
Assume the spindle is turning at 60 RPM (1 RPS.) From this, I could be generating 128 PPR the thus generate a 128 Hz signal. My PLL would have to receive this and generate a signal 50x as great - 6.4 KHz. So we're guiding one piece of steel into another... when they meet, the spindle's RPMs will drop, at least for in instant, as the load increases. The drop is nearly instantaneous in a physical sense. It might be glacially slow in the electronic sense. I don't know. So the signal would drop from 128Hz to perhaps 100Hz in a fraction of a second. The PLL would have to respond without transmitting too many extra, or too few, pulses. Further, the frequency of the spindle pulses would be varying by a lesser degree all the time. Nothing is perfect. The PLL would have to respond in kind.
There are two cases. Since the PLL can't respond instantly, it can either 'sneak up' on the right frequency, or oscillate and settle on the right frequency. The first case is to be avoided - say the PLL's output frequency is too low - it generates too few pulses, adjusts, generates too few, etc. The end result is that we've dropped pulses to the stepper, and there's no mechanism to recover them. The stepper is 'behind' and will stay that way. The second case is better because if we generate too few pulses on one iteration, we'll generate too many on the next. On average, the stepper will be 'out' fewer pulses.
Also, I realize the 50x freq increase may be difficult to achieve in an acceptable way. I can reduce it with some effort (or expense) by producing more spindle pulses.
That's a lot of typing for not a lot of information. Can anyone here explain to me the capabilities of a PLL to keep this signal synced?