UMI 7764 and Emergency Stop

[tir38]

I have a UMI-7764 running two P70530 drives. I am enclosing all of this in a rack mount chassis. I want to put an emergency stop button on the front of the box.  From the UMI7764 Users manual: (http://www.ni.com/pdf/manuals/370943a.pdf)

• Inhibit All—The Inhibit All signal acts as a global inhibit, and, when driven low, activates the
Inhibit Outputs. The Inhibit All signal includes a 3.3 kΩ pull-up resistor on its input. You can leave
the Inhibit All signal unconnected if it is not used.


• Shutdown—The Shutdown signal is passed through to the motion controller and, when enabled in
software, disables the controller by asserting the controller inhibits, setting the analog outputs to
0 V, and stopping any stepper pulse generation.

So it looks like the "Inhibit All" is a hardware E-stop and "Shutdown" is a software E-stop.  On the next page the voltage range of the Inhibit All is listed as 0-12 VDC. So if i have a switch that, when pressed, closes the loop between Inhibit All and Digital Ground, then that will shut off all motors. Is this correct?

[JtotheB · Accepted solution]

Correct.

[Buechsenschuetz]

You should consider that the INH and the SH_DN signal will cause different things in your motor drives. 

An INH signal usually causes the driver to shut off the current to both motor coils. The motor will have no holding torque in this state.

A SH_DN will stop sending step pulses to the driver. This means that the motor will remain in its position and will have still holding torque. (On some driver units it is possible to configure them for reduced output current after missing step pulses, the holding torque will be reduced.)

It depends on the mechanical design what finally will happen. If you are not using self-latching (i.e. worm) gears for lifting equipment, for example, the load will drop when the driver receives an INH signal.

Also, when implementing an emergency stop, you have to keep to national regulations concerning safety of machinery and mechanical equipment. Over here in Europe governments are very concerned about safety now and require a detailed survey and analysis of possibly harmful scenarios.  

[tir38]

Yes, I'd like the holding current to be zero. Its a two axis Cartesian system (horizontal and vertical motion). I want the horizontal axis to be "limp" in an emergency so that the operator can drag it out of the way. I am fine if the vertical axis falls in the process. Thanks for your input.