Dynomotion

Group: DynoMotion Message: 543 From: Azd M Date: 8/4/2010
Subject: PWM and DAC resolution is quite low.
Hi
Is there any plan to increase the PWM resolution of the SnapAmp1000 and the DAC resolution of the Kanalog. I belief both are quite low 155 bits and 12 bits.

Regards
Azed
Group: DynoMotion Message: 544 From: Tom Kerekes Date: 8/5/2010
Subject: Re: PWM and DAC resolution is quite low.
Hi Azed,
 
No we don't.  I think you will find the resolutions are usually more than adequate.  This is because a servo output is integrated over time.  The classic example is that you can control the temperature of a room quite accurately with a 1-bit output.
 
For example doing the math for a system with a max commanded speed of 600ipm (15000mm/min) the error purely due to 12-bit resolution would be:
 
600 / (60 x 2048 x 2) = +/- 0.0024 ips (62 um/sec).
 
This velocity error for a servo sample period of 90us will result in a position error of:
 
0.0024 x 90e-6 = +/- 0.22ui (5.6nm)  !!
 
Regards
TK
Group: DynoMotion Message: 545 From: Azd Md Date: 8/6/2010
Subject: Re: PWM and DAC resolution is quite low.
I am trying to use the system for dynamic parameter identification where the estimated parameters of the plant  depend significantly on the accuracy of the actuation signal and the axis current. 8 bit resolution for the actuation signal is quite low to obtain an accurate parameters.
Thanks

--- On Thu, 5/8/10, Tom Kerekes <tk@...> wrote:

From: Tom Kerekes <tk@...>
Subject: Re: [DynoMotion] PWM and DAC resolution is quite low.
To: DynoMotion@yahoogroups.com
Date: Thursday, 5 August, 2010, 11:35 PM

 

Hi Azed,
 
No we don't.  I think you will find the resolutions are usually more than adequate.  This is because a servo output is integrated over time.  The classic example is that you can control the temperature of a room quite accurately with a 1-bit output.
 
For example doing the math for a system with a max commanded speed of 600ipm (15000mm/min) the error purely due to 12-bit resolution would be:
 
600 / (60 x 2048 x 2) = +/- 0.0024 ips (62 um/sec).
 
This velocity error for a servo sample period of 90us will result in a position error of:
 
0.0024 x 90e-6 = +/- 0.22ui (5.6nm)  !!
 
Regards
TK
Group: DynoMotion Message: 546 From: Tom Kerekes Date: 8/6/2010
Subject: Re: PWM and DAC resolution is quite low.
Oh I see.  Actually the current measurement resolution on SnapAmp is 14 bits.  But since it is over a fairly large range of +/- 35Amps the resolution comes out to be ~4ma.