Hi there

what is exactly the meaning of electronic gear ratio in Delta asda b2 Servo Driver?

and how to calculate it?

regards
jhonansaro

Hi,
if your servo encoder is 10,000 count per rev then Mach would have to produce 10,000 pulses in one second to cause the servo to turn one revolution.
If you want the servo to run at 3000 rpm it will have to run at 50 revolutions per second and Mach would have to produce 500,000 pulses per second to
do it. A parallel port installation can't even get close to 500,000 pulses per second, 25,000 per second is the norm.

Thus because of the limited pulse speed of Mach you can't use the full potential of the servo. One way around that is to use electronic gearing.
If the denominator is set to 20 then for each pulse received by the drive from Mach the servo will turn 20 counts of its encoder. If Mach produces its
max 25,000 pulses per second the servo will turn 20 *25,000=500,000 counts per second ie 3000 rpm.

You don't get it for nothing. Without electronic gearing the servo resolution is 1/10,000 rev=0.036 degrees or 2.16 min of arc. With an electronic gear ratio of 1/20
the resolution is 20/10,000 rev=0.72 degree or 43.2 min of arc. Using electronic gearing trades resolution for speed.

Most external motion controllers have pulse speeds much higher than Machs parallel port, 100kHz is a minimum, my ESS can manage 4MHz. Most servo drives
can't even with differential signaling accept more than 500kHz so 4MHz is somewhat academic.  It is still useful if reading an encoder however. Many Delta servos
for instance have 17 bit encoders for 131,072 counts per rev or 6.5MHz at 3000 rpm!

Give me some details about what your trying to achieve and I'll try to help with the two numbers you require (numerator and denominator). You'll need to know the maximum
useful signaling rate of your controller and the maximum speed that you wish to run the servo. Note that single ended signaling is good to about 75kHz (the manual
might say more, but 75Khz is safely conservative) and beyond that you'll need differential signaling. If your BoB can't do it you'll have to make a circuit with a line
driver IC on it.

Craig

Hi,
just realized that I don't know what servo you are using, or in particular what is the encoder count per rev?

Craig

Hi joeaverage

Many thanks for the reply, i have a 750 w delta servo motor, and delta adas b2 driver. as you said my driver has a 17 bit encoders for 160,000 counts per rev.
And my BOB is a Mach3 Motion Card (ESS- Ethernet Smooth Stepper----HM-LAN-4Axis)

The physical Top Speed that I require is a bout 12,000 mm/min or 3200 Rev/min.

I have done some math, Which off course I am not so sure of, and they are as Follow:

(No. tooth)=25  -----   (Pitch Dist. mm)   =7     linear Travel  175 mm

Encoder   160000
   
P1-44   5000 (Neominator)
   
P1-45   10     (denominator)

From the above If I have a 10:1 Gear Box Then with 3200 rev/min I will get a actual 320 rev/min and every revolution at 175 mm I will end up with 56,000 mm/mi

Therefore if I increase the value of p1-44 I can Lower the speed. by the way with above assumption the value for Steps per Unit in mach3 should be

about 4.57

Could you verify all that

regards
jhonansaro
 

Hi,
still trying to digest the details but that encoder count doesn't sound right.
A 17 bit encoder I think has a count of 131,072 per rev. Double and triple check the manual
about that count number.

Craig

Hi,
if I understand your numbers the axis moves 175mm per revolution of the gear.
If you want 12000mm/min travel then:
12000/175=68.7514 rev per min of the gear, or 685.714 revs per min of the input shaft of your 10:1 reducer,
ie 658.714 rpm of your servo.
At 131072 pulse per rev:
658.714 *131072 /60=1,497,965 pulse per second. Thats too fast to signal your servo, I would recommend reducing
the pulse rate required using electronic gearing by a factor of ten:
1,497,965 / 10=149,796 pulse per second. Thats about 150kHz. You could, at a stretch, do that with single
ended signalling.

This would require a denomintator of 10 and a numerator of 1. Easy!

Hi,
with the numbers I've proposed the 'step per mm':

1mm / 175mm  gear revs=0.00571428 gear revolutions/mm

0.00571428 * 10=0.0571428 reducer input shaft revs/mm =0.0571428 servo revs/mm

0.0571428 *131,072=7489.82 encoder counts per mm

7489.82 / 10 (electronic gearing denom.)=748.98 Mach pulses/mm

Rounding 'steps per mm'=749 or a resolution of 1.33um, pretty damn fine!

Craig

Hi,
have been reading the manual and it turns out you can program the encoder count. Page 7-40.

P1-46▲ GR3 Encoder Output Pulse Number Address: 015CH
015DH
Operation
Interface: Keypad/Software Communication Related Section: N/A
Default: 2500
Control
Mode: ALL
Unit: pulse
Range: 4 ~ 40000
Data Size: 32-bit
Display
Format: Decimal
Settings:
This parameter is used to set the pulse numbers of encoder outputs per motor
revolution.
Please note: When the following conditions occur, the output frequency for pulse
output may exceed the specification and cause that the servo drive fault AL018
(Encoder Output Error) is activated

Note the default is 2500 ppr which corresponds to an encoder count of 10,000 counts per rev.

My suggestion is stick with that.

The calculations change:

12000/175=68.571428
68.571428 *10=685.7142
685.7142 *10,000/60=114285.7142 pulse per second. or 114.2855kHz

ie You don't need electronic gear reduction at all.

The 'steps per mm':
1 /175=0.005714285
0.005714285 *10=0.05714285
0.05714285 *10000=571.428 pulse per mm

This is easier again. Program the servo to produce 10000 count (2500 ppr), which is its default programming. As you only require 685 rpm to reach
your target speed with a 10:1 reducer you don't need electronic gearing. The maximum pulse rate required is 114 kHz and within the drives singled ended
signaling capacity, easy.

Craig

Hi Craig

Excellent job, your detailed explanation is awesome. thanks again.

Ok from your calculation is clear that if I want to have a speed of 12000 mm/min then the motor must have  around 685 rev/min, but do not you agree

That I will get better performance and more torque at speed around 3000 rev/min, therefore I should have a 4:1 electronic gear ration in order to force the motor

to run at higher speed of 4*685=2740 ?

also again I am quoting from your calculations that with   (685.7142 *10,000/60=114285.7142 pulse per second. or 114.2855kHz) ,

Then how about the mach3 kernel speed which is around 45 kHz, isn't this some what over mach3's  kernel speed?


regards
jhonansaro
KHz

Hi,
if your machine can handle speeds approaching 1m per second and handle the G forces involved then
you have a  pro machine and should not be pissing around with Mach.

Who cares abouts Machs kernel? You are running an ESS, its 'kernel' if thats what you want to call it is 4Mhz.

Without electronic gearing you could still make the axis go four times faster just by increasing the pulses per second
from 114k to 456k. Differential signalling required but no change in electronic gearing required.

The torque from an AC servo is indepenednt of speed, it has no more torque at high speed than at low speed. So I don't
agree you'll get any more performance by going faster. In fact unless you plan the decceleration phase properly
and have the servo fault on decel then you risk a crash.