Control bus- can a loop be used?

[TheRocketScientist]

Suppose one wishes to control a series of electric motors via a control bus such as serial, ethernet, RS232, whatever... can these devices be arranged in a loop?

Think of an electric fence around a field... with the control signal being sent out both directions down the fence... each post representing a controlled motor.

Can this be done, or would the signal from each side confuse some of the controlled items? A possible advantage of this scheme is that if the control cable were severed once, the controlled units would still have control feed from the other portion of the loop. In the event that a loss of control would be, shall we say, extremely painful to bear, it'd be nice to add some measure of backup like this.

Of course each motor should also have a fail-safe mode to revert to in the event that loss of control signal is detected, minimizing the pain that must be borne.

 

[jraef]

That totally depends upon your network topology. Some networks support rings, some do not, and some that do not have the ability to seek alternate paths in a ring-like fashion should a cable be cut. It's a network issue, not necessarily a motor control issue.




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[ozmosis]

What do you mean by "control a series of electric motors"?
Do you mean VFD's or other devices controlling the motors?
and what is your definition of control?

 

[TheRocketScientist]

OK, good, some configurations do support rings.

As for the type of control, let's say similar to VFD- or specifying a position or other operating parameter via a 1-10V signal [subject to noise], or 4-20mA type signal... or the digital equivalent.

Basically, provide half the control signal and expect each motor to do half of whatever it is it does. Open something, go to a specified RPM, etc.

 

[djs]

As jraef said some networks support loops. It is really dependent on what hardware is used to support the network. For example Ethernet uses switches. Most managed switches implement spanning tree protocol, which can mange loops. However unmanaged switches do not implement spanning tree and can not support loops. The same can be said for just about any of the more common networks: Profibus, DeviceNet etc.