Steps per Rev / Pulse Frequency Relationship? Panasonic Servos.

[Chaz]

On the Denford Triac I am converting, this uses ballscrews with a pitch of 5mm per turn.

The Panasonic Minas A6 system uses 10000 pulses per revolution as the default setting however this can be changed.

Currently the Acorn setup is set at 100K Step Rate.

The gearing I am using on the X Y and Z drives is all 1 for 1, so no ratio changes.

If for example, I then set the machine to 10000 steps / Revolution, should I see 5mm of movement in one full rotation of the motor?

In all 3 axis, I dont. Its not far off but its not 5mm. It tends to be a bit over. I've managed to 'correct' this by playing around with the drive's own ratio settings however I'd like to understand this before making these changes to correct (and its still not perfect).

The Panasonic system can also run at higher rates, it looks like this is advised, if the Step Rate increases, does this impact all the steps per rev calcs?

Thanks

[Chaz]

Looking at the Panasonic manual, it states 500K Pulse / Sec for the photocoupler / line driver and up to 8M Pulse per Sec on the Line Receiver. I'm 99% sure that I have gone into the Photcoupler / Line Driver input.

[Chaz]

The options in terms of ratios on the pulses per rev etc.

[Chaz]

Sorry, this shouldnt be under Plasma, I was looking up other threads that were similar and landed up 'here'. Thanks.

[suntravel]

Related reading:

viewtopic.php?f=63&t=1801

Uwe

[Chaz]

Related reading:

viewtopic.php?f=63&t=1801

Uwe

Thanks. I had seen that some time back when I did an early retrofit, let me review again.

[Chaz]

A lot of the info is very pertinent to steppers and I understand the logic. With higher end servo systems (and I put Panasonic in this bucket), there are other variables to consider.

It just feels 'wrong' to modify the overall turns ratio when I know mechanically it *should* move 5mm per revolution. I'm currently using Open Collector for Pulse / Direction. Ill change this to see if i can get something better (either closer to the 5mm I should have) or if that's not a factor.

The Panasonics (A6 Series) can do 8 M Pulses per second in the right mode / interface .... however I can run at max speed on 100K. Is there any benefit in increasing this number then?

[suntravel]

The info is for drives with Pulse / Dir control, no matter if it is a servo or a stepper.

Max. pulse frequency is not affecting the pulse / turn ratio, but it determines how fast the drive can turn.

Uwe

[ShawnM]

A lot of the info is very pertinent to steppers and I understand the logic. With higher end servo systems (and I put Panasonic in this bucket), there are other variables to consider.

It just feels 'wrong' to modify the overall turns ratio when I know mechanically it *should* move 5mm per revolution. I'm currently using Open Collector for Pulse / Direction. Ill change this to see if i can get something better (either closer to the 5mm I should have) or if that's not a factor.

The Panasonics (A6 Series) can do 8 M Pulses per second in the right mode / interface .... however I can run at max speed on 100K. Is there any benefit in increasing this number then?

Here's my 2¢ worth.....

Pulse rate - If you can reach the rapid speeds you want with 100,000 as your step rate then I see no real benefit in increasing it in my opinion. It will only increase your chances of missing steps. More so on stepper drives than servo drives but why risk it if you can achieve the rapid rates you want. Then there's the whole speed versus torque thing and the faster you go you need more voltage to keep the same torque and yada, yada, yada. Why open that can of worms if you are happy with the rapid speeds?

Turns ratio - This is exactly how you adjust the mechanical travel distance, by adjusting the overall turns ratio. There are many factors in the mechanical drive train that will cause you to have to slightly tweak this number to dial it in if you want precision and accuracy. No drive train is perfect and no two axis will ever be the same. You may have a 5mm screw but that's only ONE part of the drive train. Remember, your 5mm ball screw is coupled to several other mechanical parts to make the machine move. Combine all those together and now some minor tweaking will be required to your turns ratio to get that precise movement back.

As stated by Centroid, modifying the step/rev to some odd number to adjust the mechanical movement is simply wrong. Set Acorn and your drive to the same whole number, in your case 10,000 steps/rev if that the number you want.

If you use a dial indicator that measures down to .0005" (or a metric one) you'll NEVER see a whole number (or even two decimal places) for your overall turn ratio. I see so many reports where people have 2.54 or 5.08 for their turns ratio and while it may be "close enough" for some router users cutting wood, it's not as accurate as it could be. I even see reports where users have the same for both X and Y which also isn't even possible. If you want precision and accuracy then you'll need to adjust your turns ratio ever so slightly to get there. This means you may need to carry it out to maybe 5 decimal places or more for all axis and again no two will be the same, ever. This will take a little more time but it's worth the effort.

[tblough]

Stepper motors have an integral number of poles. This means it is a whole number, no fractions or decimal places. You can have micro-steps, but these are, again, integral numbers. You can't have 16.5 or 32.7 microsteps. Therefore steps per rev will always be a whole number - some multiple of two of the number of poles, which is usually 200.

Ballscrews have manufacturing tolerances, and therefore are not exact. You can get C7 or C9 ground screws that have very precise tolerances, but there will still be errors. That is why you adjust the turns per inch number.