Don't have any solution yet, just making sure I understand the problem properly- I guess you are NOT looking for ideas on possible mechanical coupling for this.

From a control point of view, we've to see that the backup motor-control should keep track of the position information; also it should not offer any significant load to the active motor (prime motor - PM). Once the prime motor fails, the backup should take over from where the PM has left.

One doubt- can we assume that once the PM has failed, and the backup is up, the PM will not become a signifcant load for the backup motor?

>you are NOT looking for ideas on possible
> mechanical coupling for this

True - The purpose of the backup motor is to provide control if the primary drive shaft fails.

>it should not offer any significant load
>to the active motor

True - some "drag" is inevitable and a loss of efficiency is acceptable.

>can we assume that once the PM has failed,
>and the backup is up, the PM will not become
>a signifcant load for the backup motor?

Yes - either motor needs to be sized to carry the load of a "dead" partner.

Thanks for your questions - I look forward to your replies...

1- How much time delay between motor to motor switch over ?
2- Do you need vari-speed or would 1,2,or 3 pre set's work?
3- Does the backup motor need to switch on at the same speed, the (PM) failed or can it ramp up ?
4- Can you give us some type $ amount to work up a control ckt ?

>1- time delay?

I do not know - the travel speed of the carriage is between creep (say, 3 inch per minute) and 600 inch per minute. The speed of the motors can be reduced appropriately. As for "switch over" there would be none - the two motors drive as if each is the "driver" and the other is the "slave." They would be "electrically geared" to each other and any inefficiencies resulting from this coupling would be minimized.

>2-Varispeed?

Variable speed is desired. Three presets can be used however.

>3-Switch on or ramp up?

The two motors would both be active during moves. The trick is to have them both make simultainious moves (some error is expected) that allow each to independantly drive the carriage.

>4-$$

Such a system is applicable to a wide variety of motion control applications. I am currently working on a tool that inspects composite aerospace parts - the tool has a budget of $3.6M for inspection of parts worth an average of $500k each. It is expected to inspect 200 parts per year...

I expect thisto be applicable to tools worth much less - on the order of $20,000 each. I would expect to pay as little as $3,000 for such a drive / carriage device with control system.

If your looking for accuracy on the larger system , I might
try two VSR drives with an encoder hooked to each.This would
give you flexiblity,speed,position,monitering.They could be slaved together to match speed and direction.If your hooking
to a PLC you would be able control and moniter from the VSR
drives.

On a less expensive smaller system, I think I would look at
DC motors . Smaller size and more torque simplier control.
For a DC power supply try a fullwave bridge rectifier
"cube type" inexpensive & durable use mechanical contactors
to start,stop,reverse the motors.If you current limit and
ground fault protect the motors indepently after the control circuit.You would only need one variable speed drive control,maybe just a reastat,limit switches could be used to change directions.
This is just a couple of ways to do this,their is many more.

Electricken,

Thanks for your reply - now tell me, of the two options listed I prefer the last because of its simplicity and minimal expense. My carriage weighs approximately 100 lbs and is currently driven using an AC drive motor. Could this drive motor be replaced with a DC? The carriage can be seen at http://www.bugo.com, reference the model DC IV Tractor. Does this model really use a DC motor? (I can't tell from the literature). If so, could a control system be added that would allow me to use two of these carriages in tandem?

Mike Van Voorhis
MJVanVoorhis@Compuserve.com

I wasn't able to formulate a positive conclusion at the bugo page. The carriages I"ve seen of this style are normally hooked to another control system "CNC-CAD or PLC" incorporating them into the welder, cutter or machine. I would call the bugo people, with the opportunity of sale they would be helpful. I'm sure two of these carriages could be electrically coupled, maybe a micro Plc. There are some 8 function for less then $300 on the market.As far as AC or DC motors take a look at the page below FAQ's it might help you, follow the links. http://www.west.net/~rondoc/motworld.html
I'm not quite sure if your building a stand alone system or an add on system, Plc control would let you sell it either way.

Electricken,

Again, thanks for your reply - I will make another contact with the Bug-O people - they are a bit slow to respond to my queries - I'm not a "typical" customer because I'm using their device in a unique way. As a result, they tend to have a, "show me the money" attitude. In any event, A micro PLC like the Toshiba T1-16 is what you had in mind - yes? I'm making a stand-alone system so most options are available to me.

Mike Van Voorhis
MJVanVoorhis@Compuserve.com