Re: [CAD_CAM_EDM_DRO] Servo Dynamics 1525 tuning?

Thanks John!!! I appreciate the info. I have a Fluke 123 hand held 20mhz
scope that I will use with the procedure you described. If I have any
further questions I will let you know.
Thanks again

----- Original Message -----
From: "Jon Elson" <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, October 20, 2003 10:16 AM
Subject: Re: [CAD_CAM_EDM_DRO] Servo Dynamics 1525 tuning?


>
>
> shawncd@... wrote:
>
> >Does anyone have experience tuning the Servo Dynamics
> >SD1525 series servo drives? I'm having problems. This
> >is the first time I have tried to tune analog servo
> >drives. Any info or direction on where to go from here
> >would be great.
> >
> >
> Not specifically that model, but the SD amps are totally classic
> analog servo amps. I have some amps that are made after the same
> model. What problems are you having? Do you have a digital
> storage oscilloscope? If not, are you using EMC (it essentially
> has this built in)?
>
> I've included the servo tuning info for my servo amp. Much of
> it should apply.
>
> Jon
>
> ----------
>
> Setup and tuning procedure for Pico Systems PWM Servo Amplifier
>
> Connect +12 Volts to card edge pins U and 17, -12 Volts to
> pins S and 15, and ground to pins 21, 22, Y and Z. Check
> current draw for any shorts, reversed chips, etc.
>
> Step 1 is to set the frequency of the PWM oscillator. Use an
> oscilloscope at pin 1 of U22(A) or the junction of R28 and R29.
> You should see a trinagle wave with about a 4 V P-P amplitude.
> Set it to 100 KHz. Note that the signal should be symmetric
> about the 6V level, so it should go from about 4V to 8V. if it
> is not symmetrically balanced around the 6V level, make sure the
> +12V DC power is correct, and then check the 6V reference,
> at U11B, pin 1. It should read exactly 1/2 of the 12V power
> source.
>
> Once this checks out, turn Tach and Command gain pots (R61 and
> R92) to minimum (full counterclockwise until they click).
> Turn Current Limit (R68) to minimum also. Set Current gain
> (R39) to half way, by turning CCW until it clicks, then CW
> 10 full turns. Since no power is available to the full
> bridge switch, there can be no current in the output sense
> resistor R22. So, use this opportunity to zero the current
> error amp. Note that in this condition, the current error
> amp (U10A) is almost open loop, since its output is barely
> fed back to the input. So, it won't null easily, just get
> it close. Use a scope or DVM to read voltage at U10, pin 1,
> while turning R105 (Current Offset). When the DVM swings from
> rail to rail (-12 to +12) you just crossed the null.
>
> Now, null the velocity error amp (U11A) by reading voltage
> at pin 1 and set R69 until it crosses the null, same as
> above.
>
> Now, you have to hook it up to close the loops! So, you
> need the DC tachometer connected to pins 18 and V. Connect
> the DC motor to pins H, J, 7 and 8 for one side of the
> armature, and D, E, 4 and 5 for the other. A variable
> DC power supply for the power switch is a big plus at this
> stage. It is best to not hook up the computer, and get the
> current loop and velocity loop stable before adding the
> positioning loop. So, enable the amp by driving pin 20 to
> +12 Volts, and then start turning up the variable power
> supply, with the + connected to pins A, B, 1 and 2. (Ground
> the - output to 21, 22, Y and Z, the common ground point.)
> Observe the current feedback signal at U8, pin 6. After
> turning the power supply up to about 3-6 Volts, observe
> if any current is indicated by a non-zero voltage from
> U8, pin 6. If so, adjust the current offset, R105, and
> see if the current indication changes. the motor may
> also begin to turn. Set it for zero current.
> If oscillations develop, turn R42 clockwise, to increase
> loop compensation. Then, turn the current limit, R68,
> about 2-3 turns CW from the zero where it was. If
> current develops, readjust velocity offset, R69, to
> null it out as best as you can. Then, start turning
> the tach gain up with R61. At some point, you should
> notice that the motor either resists efforts to turn it,
> or starts to spin wildly. If it spins wildly, reverse
> the tach leads (or motor leads). If the motor resists
> turning by hand, then the tach is correctly phased, and
> your attempt to turn the motor is sensed by the tach, and
> a compensating current was delivered by the amp to
> prevent it from turning. If oscillation develops, turn
> R46, velocity compensation, CW. Once you get here,
> you can start turning the variable power supply up and
> look for instability. (Increasing the DC power supply's
> voltage acts to increase system gain, because the same
> pulse width delivers more voltage and current to the motor.)
> When you get it stable at, say, 24 Volts, you can try
> connecting the computer, and turning up the command gain
> control (R92) to get desired servo performance.
>
> Note: Don't try to run a motor using one +12 Volt
> power supply both for the logic and the motor power.
> It WON'T work! I already know that! The motor load
> will affect the power supply's output, and the amp
> will go haywire!
>
> Finally, you have to accomplish servo tuning and
> loop compensation including the CNC control, which
> sets up a whole new ball of worms. I have found,
> through many hours of frustration, that it is best
> to tune the servo amp without the computer, and then
> DON'T change any setting on the servo amp (with the
> possible exception of command gain) while getting
> the positioning loop to run right. Hopefully, your
> CNC control gives enough control over its software
> servo loop that you can damp out any vibrations
> or instabilities. If you will be using the NIST
> EMC software, I know how to tune this. If not,
> you pretty much need a Digital Storage Oscilloscope.
> This stuff just happens too slowly, and is non-
> repetitive, for an analog scope. but, once you get
> it moving the machine, you can do a good deal of
> tuning with your ear. Any resonances or instability
> are easily heard.
>
> [Non-text portions of this message have been removed]
>
>
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