how to achieve constant velocity at base origin

simonhickey · May 10, 2017 at 4:41 PM

Robot: KR210 R3100 ultra
Controller: KRC4

I am trying to program a mandrel of a complex shape through the base origin and maintain a constant velocity at the base origin, which is proving difficult. The mandrel has the same diameter along it, but has a series of bends.

I am over braiding carbon fiber on to the mandrel with an axial braid machine. The base origin is at the center of the braid machine and as the mandrel passes through the base origin, a constant velocity is required at this point.

If the mandrel was perfectly straight, this would be achievable with a linear movement. But as the robot moves to the sides to accommodate circular movements, the mandrel velocity at the origin changes.

Is there a way of setting a velocity at the base origin, where the robot will speed up and slow down while twisting to maintain velocity at the point?

**panic mode** · May 10, 2017 at 5:19 PM

picture or sketch would be appreciated... is this base moving (rotating?) is mandrel rotating? do you know the radius of mandrel at any time?

simonhickey · May 10, 2017 at 5:32 PM

The base origin is at the center of the overbraid ring, see image 1. the base is not moving.

the mandrel is held by the robot flange/chuck on one end, and is passed through the base origin (center of the overbraid ring).

We know the radius of the mandrel yes, but for this issue, i am just assuming a constant radius.

so yes, the mandrel is being rotated through the base origin (braid point)

See mandrel in image 2.

Spl · May 10, 2017 at 6:19 PM

Have you tried using spline motion?

**panic mode** · May 10, 2017 at 9:41 PM

ok so diameter is more or less constant but you have part that is irregular and you need to thread it though the braiding point.
not sure how many revolutions part needs to make from begin to end of the braiding but it looks like A6 may need to be endless.

wes_mcgee · May 11, 2017 at 1:04 AM

what $IPOMODE are you using? If #BASE, then this would be very hard, as of course the tcp is not always at the center of braid ring. In #TOOL, this sounds pretty easy to do.

simonhickey · May 11, 2017 at 10:03 AM

Yes I have tried using spline motion. This does not change the situation.

Yes, diameter is more or less constant but I have a part that is irregular and I need to thread it though the braiding point. The mandrel does not need to revolve at all. The braid machine revolves independently of the mandrel. So A6 does not need to be endless. In fact, we do not want the mandrel to revolve at all, just simply to stay in the same orientation in axis 6, and to be moved through the braid point.

I have been moving in #BASE, as I found this easier to visualize my mandrel movements when teaching motions. Perhaps moving in #TOOL is worth a try. Why would this be much easier in #TOOL?

I am still wondering though is there a way of setting a constant velocity at the braid point?

MetsaToll · May 11, 2017 at 10:38 AM

That for is external TCP. As robot trying maintaining velocity of TCP, then you basically need to give fixed tool TCP function. Have not self used.

simonhickey · May 11, 2017 at 10:56 AM

Thanks MestaToll. Has anyone used external tool TCP function?

**panic mode** · May 11, 2017 at 3:06 PM

external TCP just swaps tool and base so part carried by robot becomes workpiece and external TCP is a base.
TCP allows for convenient rotation about point. i dont see how this would change things as you still need to move workpiece relative to it.
how about keeping things as they are (stationaty base and tcp is on product) but keep recalculating TCP using model data for product?

since the part is not straight rod you need to know the shape in one way or another (cad, polynomial expression, learned, manually taught or whatever). since all parts seem to be same (at least in one batch) and they in one plane, learning could be a good way to get the shape profile fairly quickly (much faster than any other method) - only need a sensor and few lines of code.

MetsaToll · May 12, 2017 at 12:22 PM

So if robot move 1mm towards the base, TCP would move same? And this would make TCP being always in center off the base?

**panic mode** · May 12, 2017 at 3:06 PM

if TCP of robot guided tool is closer to robot flange, and robot is commanded to go to same fixed point, robot will move closer to that point to compensate for shorter tool (programmed point will bring any TCP to same point). by feeding new TCP data and sending robot to same point, robot will do all the work of "threading the needle".

wes_mcgee · May 13, 2017 at 4:40 PM

Quote from panic mode

external TCP just swaps tool and base so part carried by robot becomes workpiece and external TCP is a base.
TCP allows for convenient rotation about point. i dont see how this would change things as you still need to move workpiece relative to it.

Wouldn't the difference be that the speed (in #TOOL mode) will be calculated at that (fixed) tcp point in the center of the braider? My understanding was that was the whole problem/goal. Otherwise in Base mode, reorientations will cause the actual mandrel speed going through the braider to get larger as the actual TCP gets farther from the center of the braider (not to mention the complexity of programming that motion). When you jog in #TOOL mode everything looks similar but the reorientations always pivot around the external tcp (which seems like it would make this easy).

I suppose it would also be worth asking whether this is being programmed offline or teach based.

how about keeping things as they are (stationaty base and tcp is on product) but keep recalculating TCP using model data for product?

I agree this would work but changing the TCP will cause advance run stop correct? I assume the braider is constant speed (not synchronous to the robot)...

since the part is not straight rod you need to know the shape in one way or another (cad, polynomial expression, learned, manually taught or whatever). since all parts seem to be same (at least in one batch) and they in one plane, learning could be a good way to get the shape profile fairly quickly (much faster than any other method) - only need a sensor and few lines of code.

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how to achieve constant velocity at base origin

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