interpolation

[rimcanyon]

Hi, I'm still a beginner, same as last week, but I've moved on from trying to figure out what the SloSyn single axis controllers were capable of to a more general question: how do current controllers handle interpolation?

e.g. how does a command like this:

G02 X1.8206 Y.5364 R18.7759

get executed in the case of dual controllers, one per axis? If there are as many answers as there are controllers capable of interpolated motion, then the next question would be, what works best and why?

-Dave

[ger21]

Most people here use systems with a software controller capable of handling multiple simultaneous axis moves. For example, use Mach2 ( http://www.artofcnc.ca ) , load in your g-code file, and Mach2 will output step and direction signals for up to 6 axis of movement. Each motor has a driver, one example of which would be the Gecko ( http://www.geckodrive.com ) which takes these step and direction signals and supplies current to the motors. To use your single axis controller, you'd need software to interpret the g-code, do the interpolation, and send that info to each controller. I doubt if this software exists.

The easiest thing to do would be to use either Mach2 or TurboCNC, and get some drivers that take step and direction signals to run your motors. Any other way is much more complicated, and you'd be pretty much on your own, in my opinion.

[rimcanyon]

Ger21, thanks for the explanation. What are the step and direction signals like that go to the motor driver? Are they also G codes, or are they standardized in some other way, so that Mach2 is capable of talking to any brand of driver that follows the standard?

-Dave

[abasir]

Dave,
The step/dir signal are electrical signals from your controller (PC+software in most cases) to your driver (which control your motor). For every transition of the step signal (eg. 0 to 5V), the driver will move the motor one step. The direction, either clockwise or anti-clockwise, will depend on the DIR signal. For every axis, there will be one pair of STEP/DIR signal.

[rimcanyon]

OK, thanks everyone. I guess that the capability for CAD/CAM to talk to multiple controllers and keep them synchronized is not common if it exists at all.

I'll look more closely at the parallel port capabilities of the SloSyn controller; perhaps it can be used as a simple driver only.

How do half-steps or fractional steps get signalled to the driver?

-Dave

[abasir]

CAM ability to synchronise multiple axis is VERY common. TurboCNC can sync upto 8 axis!

For half/fractional steps, the CAM software will still send a single STEP/DIR signal to the driver. The driver will move the motor half/fractional step as required. In setting up the CAM, you would configure it to say that the driver is half/fractional driver and the CAM will send the needed number of steps, i.e., if the driver is set to half step, set the CAM to half-step as well, then the CAM will send two step/dir signal to make a full step. Make sense?

[rimcanyon]

i.e. CAD/CAM synchronizes multiple axis systems from a single point of control.

I work on distributed systems that synchronize state and have multiple points of control, so I was looking at those SloSyn controllers with daisy-chained rs-232, and thinking, this is a distributed system. And it could be. What is missing is a way to extract the CAD/CAM commands that require interpolation and re-interpret them for each controller, then synchronize the motion in small increments...

Dave

[ger21]

CAM ability to synchronise multiple axis is VERY common. TurboCNC can sync upto 8 axis!

Abasir, he doesn't have step and direction drivers. He has single axis "controllers" that each need their own "directions how to move". Not a simple task.

Dave, to elaborate a litlle on what abasir said. Controller software (or g-code interpreters) basically are set up to output a certain number of step pulses per inch of movement. For example, a 200 step motor with a 10 tpi leadscrew would need 2000 steps per inch. if, for example, you're driver is set to 1/8 step mode, you need 8 times as many steps, or 1600 steps per inch.

And this really is not related to CAM. CAM software generates the g-code. Controller software interprets that g-code and converts it into the step and direction pulses that the motor drivers need.
You might want to download the Mach2 manual from the link I listed above. It's an excellent source of information

[abasir]

Just pop over to slosyn website just now. The slosyn controller will OUTPUT, not input, STEP/DIR signals. Thanks to gerry for correcting me.

I guest, if Dave need multiple axis, then Slosyn multi-axis motion controller fits the bill. As alternative, use a PC & Mach2 instead and no more problem with G-code interpolation, etc.

[rimcanyon]

Abasir, thanks for checking on the SloSyn controller. It won't handle STEP/DIR input, so it looks like it is not compatible with Mach 2. I learned a lot from this exercise, even if it didn't yield the results I was hoping for.

Gerry, the Mach2 manual is a *great* resource. Thanks for suggesting it.

There is still one remaining possibility - the 3180 PI uses Step/Direction between the PI board and the 3180 driver internally. SloSyn has a base unit called the 3180-PT (I just visited the website and looked at the manuals), that takes external step/direction signals. I may be able to convert the PI to the PT just be disconnecting the PI board internally (the 3180 PI already has the "translator" port that the PT uses for step/direction input, but it is not described in the PI manual).

Dave