Servo Systems with SERCOS

[walter]

I`m wondering if these servo drives can be used in "dumb" mode, without controller card. They all seem to take step and dir inputs... Has anyone here ever tried this with Sanyo Denki PV or PY series drives?

Thanks

[NC Cams]

If the system has "step" and "direction" input, it is more than likely a stepper, not a servo.

Servo's are merely motors that have an encoder to provide position feedback. In an oversimplifed fashion, If you apply the appropriate power to the terminals, it will run until power is removed. YOu'd have to switch the terminals on a DC motor to change direction - not familair enought with AC to splain how to do direction reversal on one of these.

A stepper is sort of like a "electronic ratchet". Each time to energize a coil, the motor cogs over so many degrees (ala the ratchet concept) as established by the internal design. IF you energize the coils fast enough and in the proper sequence, actual commutation occurs and the armature turns like a motor. Otherwise it will merely tick over a step at a time.

Technically, a simple pushbutton swith can provide the step signals to a stepper control board (needed to provide commutation). A knife or toggle switch could provide the direction input. This would be about as "dumb" as you could get.

YOur photo shows controller cards (not servos) that appear to be PC driven. Unless you're electronically adept, it is not very likely one could make them function in a dumb fashion.

[turmite]

Servo drives are the "cards" of a servo system and many of them do take step and direction signals. I know nothing of dumb mode though.

Mike

[walter]

Originally Posted by NC Cams If the system has "step" and "direction" input, it is more than likely a stepper, not a servo.

Most servo drives seem to work in Torque, Velocity and Position modes. I though that Position mode is simply takind step and dir signal? If true then device should work just by taking step/dir signal even from printer port and Mach3 controller?

[trubleshtr]

I've used these cards with indramat drives, they slipped directly into the axis drives. I believe you will need more than the cards to make them work though. You will need the rest of the sercos system to make the ring work, and then fiber optic cable to communicate. We stuffed the package into an indramat BTV unit and drove it off a 133 computer runing windows NT. We had numerous "blue screen of Death" problems as well as master/slave heart beat problems trying to communicate.
We tossed ours in the trash....literly....

[walter]

I guess that`s why these drives sell on Ebay for $100-$200

Thanks trubleshtr

[NC Cams]

Walter:

Servo's are motors that have an enconder that provides position feedback. IE: controller tells it to move at a certain speed in a certain directio all the while the encoder on the motor "tells" the controller card how far it went and in what direction it went. When it gets to where one wants it to go, the controller stops driving the motor.

A stepper merely goes in the direction that the driver tells it to go and does so by the number of steps that were sent out by the controller card. IF the motor misses a step, oh well. THe controller card has NO way of knowing if the motor or what it controlled went to where it was actually told to go.

torque mode means torque (IE current) is monitored by controler for control purposes

Velocity means that motor velocity is fedback from the motor for regulation purposes.

Position is ulitmately the thing you need to monitor. Position feedback is usually COMBINED with velocity or torque to control the motor. Position tells you "did the motor get me where I want to go". The monitoring of torque or velocity merely enables one to control the current or voltage (respectively) while the motor is traveling to keep it from running away while it's making its journey.

Simply put, steppers do what they are told and give no position feed back,

Servos do that too only they report where they went and if they got there.... as long as the encoders work properly.

[walter]

Yes, but in real world like here on CNCZone there are no controller cards. Software is the controller card. Like Mach 3. And the feedback does`t go that far. Only the drive, the black box, like Gecko, has feedback loop. Controller does`t know if the motor got there, it`s just an assumption. So the controller, I mean software, sends the step and dir signal and that`s the end. No feedback. Encoders are wired to drives and only drives "care".

That`s why I wanted to (and I`m sure it`s doable) control servo drive with software, bypassing all the crap, including specialized cards

[NC Cams]

I think somebody already did it - Mach 3. They drive the STEPPER cards via step and direction with the parallel port and do so with intense sophistication. They indicated to me in P/M that they could NOT interface with servo's however.

Even "servosoft" (interesting name as you'd think it would imply what they can/are doing) is using special cards to interface between the PC and the motors.

It is my understanding that this interfacing was a bit easier with ISA slots but now that PCI has taken over, you need to have something inbetween the processor/mother board to get the needed command signals.

Unless I"m totally missing your point (quite possible) you need somthing inbetween the PC and the motors to translate machine code into commands that the motor driver card (either stepper or servo) can understand/interpret.

BTW, my servos only need a +/- 10vdc signal from the computer to run at any speed in any direction. Sadly, no standard PC has such a D-A converter onboard. THis DAC is found on the interface card that links the PC to the servo amps. Might be doable from parallel but 8 bit resolution (typical of lpt) will surely give poor linearity of motor speed over that range.

Dealing with some "crap" seems to be inevitable in life 8-))

[HillBilly]

The difference between step and direction servos and analog commanded servos is where you are closing the loop. Even if you have +/-10v servos in front of your D to A converter you are digitally comparing commanded position to actual position ( which are usually in the form of step and direction.)to produce an error signal. The same theory is used for step and direction servos. Yes these drives can be used in either manner or Sercos mode.

Darek

[Al_The_Man]

Originally Posted by NC Cams torque mode means torque (IE current) is monitored by controler for control purposes

It depends what you mean by 'controller' if you mean the NC control, it has no idea of what current the motor has, in the torque or current mode the controller feed a voltage to a transconductance amplifier, this is an amplifier who's output current is directly proportional to the voltage in.
The controller only knows the present move status of the motor via the encoder, and provides a voltage accordingly, the motor amplifier does the rest.
Al.

[walter]

Thanks guys, your input was very much appreciated..
HillBilly was right, look what I just dug up:

"...Are you an existing user of stepper systems and are you experiencing any application limitations? Yes, then we have some great news for you! You can keep your existing indexer with the easy and intuitive command interface and just substitute the PV and/or PE ac servo system for the stepper system. This is possible because the PV and PE ac servo systems have a "step & direction" command interface and programmable gearing to match the speed range of the existing stepper system. The following figure illustrates the substitution concept..."