Help on pulse monitoring please

[DaytonPLC]

I need to watch a prox sw that will read the cogs on a gear. When that pulse stops I know when the movement has completed. The pulse may stop on a high or a low signal.

I've been trying to use a compare with a counter on the prox signal. Not working out so good. Using an AB 5000 not that matters.

It shouldn't be this hard lol...

Thanks for any insight.

 

[James Mcquade]

DaytonPLC,

welcome to the forum.

several questions for you.

1. how many teeth on the cog.
2. are you reading the sideof the teeth or the tip of the
teeth and is the area of detection uniform on all teeth.
3. speed of the cog.
4. is the cog covered in grease? by that i mean is there
grease on some teeth and not on others?
5. sensor type.
6 type of input?

regards,
james

 

[robertmee]

I need to watch a prox sw that will read the cogs on a gear. When that pulse stops I know when the movement has completed. The pulse may stop on a high or a low signal.

I've been trying to use a compare with a counter on the prox signal. Not working out so good. Using an AB 5000 not that matters.

It shouldn't be this hard lol...

Thanks for any insight.

It's pretty easy...Have a free running timer with a preset that is longer than the distance in time between cogs.

Use an XIC of the prox + a one-shot to reset the timer using a RES instruction. The one-shot takes care of the motion stopping on or off the prox.

If the timer times out, you know you haven't seen any cogs for that amount of time and you can use the DN bit of the timer to say motion has stopped.

 

[DaytonPLC]

DaytonPLC,

welcome to the forum.

several questions for you.

1. how many teeth on the cog.
2. are you reading the sideof the teeth or the tip of the
teeth and is the area of detection uniform on all teeth.
3. speed of the cog.
4. is the cog covered in grease? by that i mean is there
grease on some teeth and not on others?
5. sensor type.
6 type of input?

The gear is just for the prox to monitor the movement. Pretty simple setup. I get pulses as the gear is turning. I may turn 180 degree or 270 degree or some other range, doesn't matter. depending on the position of the part we are building.

We are using a cylinder to push and rotate a part. When that part gets in the proper index position, the part stops spinning. The part sits in a nest that also spins with the part. that is what the gear is attached to and what we are monitoring.

I just need to know when that part stops spinning to go on to the next step in the process. As I said before, the signal to the plc may be high or low depending where the gear stops spinning. In other words, it may stop where the prox sees the tooth or it may stop where it does not sees the tooth...
regards,

 

[dmargineau]

As @Robertmee suggested, configure a TON (with a preset longer than the longest interval between two consequent "pulses"-right before the monitored shaft completely stops).
Connect your sensor to a system input and use the NC "contact" of your sensor to control the TON; every state change will reset the timer's Accumulator until the sensor stops changing states.
When the TON Accumulator equals the Preset declare "System Stopped" and then Reset the Acumulator.

 

[robertmee]

Also to add to my earlier suggestion, you'll need a second timer if this cog has any type of ramp up/ramp down and you only want to monitor at speed. Otherwise, you can just use a longer preset on the one timer if your process is not mission critical to know EXACTLY when the cog stops.

In otherwords, let's say the interval between cogs is 100 ms. But it takes 2 seconds to ramp up/down during which time the interval is longer than 100 ms.

Either make your one timer 2.5 seconds, or have a second timer with a 2 second preset that ignores an interval timer of 125 ms during ramp up.

The one timer at 2.5 seconds, means you'll detect no motion after 2.5 seconds of no motion. The second method means you'd detect no motion after 25 ms of no motion when at speed.

EDIT: After reading your description, it sounds like you are most interested as to no motion after a possible decel. In that case use the one timer and just make the preset long enough that you can tolerate for your process, allowing for ramp down time of the gear and also covering ramp up time. If your interval is 100 ms but it takes 1 second to ramp up, just make the one timer 1 second long. You'll start to see pulses as it ramps up and the 1 second timer won't time out. On ramp down, the intervals will get longer to the point that the part has stopped and the 1 second timer times out. If you have really fast up/down times (servo), then set your timer closer to actual interval time. If you have really long up/down, then the timer is longer and the overall effect is you may be sitting a second after no motion before you declare no motion.

 

[DaytonPLC]

Thats perfect! I knew it couldn't be that hard, I just had a brain ****...

Thanks a million.,