Linear Actuator moves past limit switches

[Luid101]

Hey guys!
We have a setup where there is a linear actuator with two limit switches above and below. The limit switches are wired directly into our jaguar to stop the actuator from going too high or too low and destroying itself. However sometimes it just goes past the limit switches. We thought the limit switches where malfunctioning but when we took them off and clicked them by hand the actuator didn't move. Then we thought the actuator wasn't clicking the limit switches so we bent the switches and tried again, but still no luck. Now we think the actuator might be moving to fast come to a complete stop once it hits the switch.
Long story short, now I need to create a code with labview that slows down the actuator before it hits the limit switches. I am thinking of starting a timer once the driver clicks the go up or down button, then once the timer has reached a particular time (a.k.a the time it takes for the actuator to reach a limit switch) I set the motor to a slower speed. Now here is the problem, I need to create a toggle switch to start the timer only once after the up or down button has been pushed (because the buttons are held to go up and down). And I need the timer to be updated only once but i don't know how to do that since my drive program is in a loop. Honestly I am stumped on how to program this with labview without creating code that will be extremely slow and buggy.
if you guys have a better idea on why the actuator is not working or have a better way to slow down actuators or have any idea about anything that you think would be helpful we would greatly appreciate it. At this point we already have two broken limit switches and one frustrated electrical team.

[Ether]

Originally Posted by Luid101

We have a setup where there is a linear actuator with two limit switches above and below.

Please post a (focused) close-up picture showing how you have each of the limit switches mounted.

[Ether]

Originally Posted by Luid101

We thought the limit switches where malfunctioning but when we took them off and clicked them by hand the actuator didn't move.

Did you mean to say the actuator didn't stop?

[Luid101]

Originally Posted by Ether

Did you mean to say the actuator didn't stop?

No the actuator stopped like it was supposed too when we clicked the limit switches by hand. Eliminating the possibility that there was a problem with the wiring or the device.

[Ether]

Originally Posted by Luid101

Now we think the actuator might be moving to fast come to a complete stop once it hits the switch.

Are your motor controller(s) set to "brake" or "coast" mode?

[otherguy]

This is a bit of a bandaid, but have you considered extending the length of the arm coming off the minor switch so that the actuator stays in contact with the limit switch for a longer period of time?

[adciv]

The reason it's probably not working is you have momentum in the system. Once the limit switch is triggered, you are telling the motor controller to stop applying power, but the momentum in the system will keep it moving for a while longer. At some point, the limit switch releases and the system no longer thinks it needs to stop.

You can also use a different method for sensing the actuator limits or ensure the limit switch is triggered even once the actuator is past the stop position.

[Alan Anderson]

To see how to do something only once when a joystick button is first pressed, search using the phrase "toggle button". There's an example code snippet attached to this post from 2013.

[GeeTwo]

Definitely sounds like your inertia is taking you out the other side of your switch's range.

Limit switches really are meant to define limits, to keep motors from burning up. They really aren't so good at providing a "set point" unless the device moves slowly enough that you can stop it quickly. If you actually want to drive quickly to a set point, and then settle out on that point, use some sort of potentiometer and a PID or other feedback control loop. AndyMark has a string potentiometer good for 30", and you can make longer ones by using the same style potentiometer and larger reels. Short of that, you may want to put a second switch past the first one (maybe with overlap) so that even when neither switch is triggered, you have some information as to where the load is.

[Luid101]

Originally Posted by otherguy

This is a bit of a bandaid, but have you considered extending the length of the arm coming off the minor switch so that the actuator stays in contact with the limit switch for a longer period of time?

We might just use that if we have no other choice.

[Luid101]

Originally Posted by Ether

Are your motor controller(s) set to "brake" or "coast" mode?

Honestly we've never heard of coast or break mode until now but I think our jaguar is in coast mode now.

[Ether]

Originally Posted by Luid101

Honestly we've never heard of coast or break mode until now but I think our jaguar is in coast mode now.

You will get a lot less overshoot in brake mode. Move the brake/coast jumper on the Jag from "coast" to "brake" and try that. It's very simple to do, so worth trying.

[Luid101]

Originally Posted by Ether

You will get a lot less overshoot in brake mode. Move the brake/coast jumper on the Jag from "coast" to "brake" and try that. It's very simple to do, so worth trying.

Thanks! we did that and the problem hasn't come up since.