Hi,
Thisd discussion is moving hot and I thought I should give my views on this as I have implemented an emergency stop successfully in my application. First of all,I feel that the emergency stop button should be application independent. It means that even if I close my labview application and then the emergency stop is pressed, then the motors should stop. Also, while the application is running, if I press the emergency stop button, then the axis should be disabled physically, and should also execute the stop motion VI in the software.
Now, how to implement this is the question. All drives have a motor enable \ disable bit, which in most cases may require 24V DC to be enabled. The Normally closed emergency stop button should be wired such that on end goes to a 24V supply and the other to the drive enable \ disable bit. Now parallely acquire this 24V enable signal into the motion card through the digital inputs. Now, you have the status of the emergency stop button in your application, in the form of a boolean variable. You can now continously scan this status in a while loop. As soon as you receive a logic 0 in the boolean variable, you can execute a stop motion VI using a case structure. In this way, a complete foolproof solution can be acheived for this problem. Also as our friends suggest, you can use the 24V DC to switch a relay and hence activate the brakes simultanously in case of a vertical axis. These steps can be duplicated to have 4 seperate emergency stop buttons.
Feel free to correct any mistakes.
Regards,
Giridhar Rajan
Automation Engineer, Design
Cruiser Controls
Mumbai, India
