Finding hardware limits without limit switch.

[serkanb]

Hello,

I have a mechanical system which is actuated by a brushless dc servo motor.

It's very small and close system so it's not possible to place micro swithces in it. But I have to find its forward and reverse limits.

How can I find its limits.

Could you help me please?

Thanks....

[Highland_Controls]

There is no real good way to do this without a switch, but the next best thing is to find the hard limit.  Run the axis slowly in one direction, and either watch following error or drive signal, and stop the axis when these start to rise sharply.  You can do the same thing in the other direction, or if you know the travel of the system, set software limit.  What controller are you using?

[serkanb]

Hello,

Thank you for your reply.

I'm using NI-7358 pci board.

I've tried to track following error to find limits. When the following error occures, the axis is killed. When the axis is killed, system loses its position and move backward due to stifness of system. It's not a desired movement because during this backward movement it passes index point but I want to find the index point. Is there a way to find limits without killing the signal.

[Highland_Controls · Accepted solution]

Don't look at the following error bit, but to look at the following error counts.  Stop the motion(don't kill it) when the following error rises, but before it reaches your limit.  You can even raise your limit for the homing move and set it lower when you are done.  If your index is within the hysteresis of the hard stop, then there is a good chance you won't have reliable homing.  You might be off by one revolution from one homing move to the next.