About Limit Switch

[leq_82]

Hi,All

I use NI  PCI-7344,UMI-7764 and servo motor in my project.Now I meet a problem about limit switch----That's PCI 7344 can't detect the limit

switch's status if I set the motor's velocity a little faster(for example,1500RPM).It's very dangerous,my compents are allways hit.If I set the

motor's velocity at 500RPM or 1000RPM,this situation won't happen.

After I diable the Limit Filter in MAX,this situation still happened.My limit switch is producted by OMRON,their type is EE-SX671,they are photomicrosensor.their parameter as follow:Sensing distance(slot width):5mm.Response frequency*2:1KHZ min.(3KHZ average).After I

change the photomicrosensor to mechanical switch,the problem still occur.

I am very vexatious,Where is the problem?The Response frequency is not enough?How can I resolve the problem?Pls help me!

Thanks you in advance!

B&R

EnquanLi

[AnalogKid2DigitalMan]

I have seen similar situations with motion controls other than NI. What could be happening is that at higher speeds of travel, the limit switch is indeed still seen. However, due to the greater inertia of the load it carries the stage past the limit switch and ends up hitting the hard mechanical stop at the end of the stage travel.

[leq_82]

Hi,

Thank you for your kindly reply!

Could you give me some suggestions to resolve this problem?How I to resolve it?

Is my deceleration is not enough big?or my deceleration time is too long?

Thank you in advance!

EnquanLi

[AnalogKid2DigitalMan]

You can try increading the rate of deceleration.

What is the motor connected to, can you give some description of what is moving?

[Jochen]

Hm, I don't think that increasing the rate of deceleration will help here as in default mode the 7344 executes a HALT when a limit switch is hit (this ignores the deceleration settings). This means that the controller tries to stop the motor as fast as possible. But there are two things you could try:

1. Improve the PID tuning. Maybe your system is tuned too conservatively and there is some room for optimizing the stiffness of your axis. Please have a look at this link if you need help for tuning your system.
   
   
2. The limits of the improvements that you can achieve with PID tuning are defined by the system stability and the motor torque which is proportional to the current provided by the drive. If your drive runs into a current limit, this will also limit the torque and the deceleration capabilities of your motor. Please check if there is a way to increase the current limit of your drive (make sure that you don't exceed your motor's specs!).
   Please note: Increasing the current limits may require some adjustments of the PID parameters.
   

I hope this helps,

Jochen