How should I handle a single forward/reverse limit signal?

[Howard]

I have one optical sensor that is active in the home position and another that is active at either the forward or reverse limits. I know this far from ideal but I cannot change this.

I must write some software to control an open-loop stepper using a MID-7604/7602 controller. From what I have read so far, I will not be able to utilize the built-in homing function using the same signal for both limit inputs because if the reverse limit becomes active while motion is in the forward direction (or vice versa), motion is stopped.

Is there some way to override this functionality so that when traveling in one direction only that limit signal is used?

Can the controller automatically produce a direction signal
from the controller so that I can externally disable the appropriate limit input?

Since I must write my own homing algorithm for the rare case when the system wakes up out of bounds, I might just abandon the notion of using the built-in homing function and write an algorithm that handles both in- and out-of-bounds starting conditions.
However, the idea using proven code to handle all but the rarest of situations appeals to me.

Any suggestions on how to handle this situation?

[asdf]

Hello Howard,

Why do you have only 1 limit switch?
- And why is it both the forward and reverse?

"Can the controller automatically produce a direction signal from the controller so that I can externally disable the appropriate limit input?"
- The most common configuration for stepper motor amplifiers is a step and direction signal.
- There is a direction signal from the motion controller that you can use to select the appropiate limit switch. It will require you to use an external logic circuit to switch sources depending of the state of the direction line.
- Since you are using the 7604, the direction pulse is routed internally, and it will be difficult to narrow it down inside the amplifier.

One other option that you have is to wire the limit to only 1 of t
he 2 limit inputs to the 7604.
- If your travel is in 1 direction more than the other, then this might be an acceptable solution.

[Howard]

Hi, asdf. Thanks for answering my question.

"Why do you have only 1 limit switch?
- And why is it both the forward and reverse?"
The limit switch is a C-shaped IR sensor. The beam is blocked by a C-shaped gate when either end is reached. I could add another IR sensor, but I was hoping the controller could be easily configured to accept the current arrangement.

"One other option that you have is to wire the limit to only 1 of the 2 limit inputs to the 7604."
Great suggestion! That is much simpler than what I was trying to do.

If I cutoff one end of the gate so that the IR beam is blocked at just one limit, and I always start homing in that direction, it should work.

Thanks for you help!