Two-Handed Control

Hello all,

I am new here and I'm currently using the RSLogix to solve a problem. For safety purposes, I am looking to implement a two-hand control generally used on presses. I have the process coded out in the PLC program, and I am wondering what timer I would need to implement to break the Automatic process down into individual steps. (Basically the machine won't run if both buttons are not pressed.)

Also, if there is a more effective alternative besides the timer, I am open to suggestions.

Thanks

I wouldn't do it in the PLC. Even if your program is perfect, that doesn't mean that someone else a year from now wouldn't screw it up.

I'd use something like this: Two Hand Control

This is NOT SAFE in the real world, presses require special safety considerations depending on the press. See Pilz and Siemens Safety for guidance or consult a safety expert, plc control for two handed is not suitable.

For saftey purposes don't use the plc as a saftey device I would use what s7guy posted. They work good we have alot of machince's where pinch point can't be gaurded that we use them on.

I do not recommend a software implemented two hand control as your primary safety. However, if you do have a qualifying primary safety that is hardwired around the PLC, such as a light curtain or safety monitored safety shield, and press operation is guarded such that a two-hand control would not nomrally be required but you still want to use a two handed start, then the basic logic is:

IF Left_Hand OR Right_Hand AND NOT START_BIT then start .3 second ANTI_TIE_DOWN_TIMER.

IF Left_Hand AND Right_Hand AND NOT ANTI_TIE_DOWN_TIMER.DONE then OUT START_BIT

We have discussed this before, see this thread: http://www.plctalk.net/qanda/showthread.php?t=17879 The thread has some links to regulations on the matter.

See an anti-tie down example at http://forums.mrplc.com/index.php?dlcategory=2