2 6-DOF sensors attached to the same plate
2 6-DOF sensors attached to the same plate
(OP)
For a project I'm using 2 6 DOF-sensors attached to the same plate. I'm using 2 sensors because the sensors can be loaded to a maximum torque of 20 Nm and my test need sensors that withstand 50 Nm.
I've attached a sketch of the setup. (the circles are the sensors, the plate will be loaded by a force and a moment)
My problem is that 1 sensor will fully determine the plate, adding the second sensor will make it statically indeterminate. First problem I need to determine how far the sensors should be placed apart to withstand the loading situation. Second problem how can I attach the two sensors (statically indeterminate, so temperature changes will cause large forces..)
I've attached a sketch of the setup. (the circles are the sensors, the plate will be loaded by a force and a moment)
My problem is that 1 sensor will fully determine the plate, adding the second sensor will make it statically indeterminate. First problem I need to determine how far the sensors should be placed apart to withstand the loading situation. Second problem how can I attach the two sensors (statically indeterminate, so temperature changes will cause large forces..)





RE: 2 6-DOF sensors attached to the same plate
If you need something to withstand 50 using two of something good for 20 doesn't get you there.
And not because 20+20=40 < 50
RE: 2 6-DOF sensors attached to the same plate
RE: 2 6-DOF sensors attached to the same plate
Now that I have looked at the attachment...
RE: 2 6-DOF sensors attached to the same plate
TTFN
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RE: 2 6-DOF sensors attached to the same plate
don't sensors respond to displacement (linear and rotational) ? a torque applied to the plate will rotate the plate as a whole ?
RE: 2 6-DOF sensors attached to the same plate
RE: 2 6-DOF sensors attached to the same plate
The sensors are Force-Torque sensors.
RE: 2 6-DOF sensors attached to the same plate
the applied torque will try to rotate the plate.
if the springs were Rigid, then the plate won't rotate, the two points are fixed, and the torque will be reacted by a couple.
if the springs are very flexible, then the plate will rotate a lot (unlikely, i think); say 50% of the applied torque will be reacted at each point.
if the springs are reasonably stiff, then the plate will rotate a little; maybe 10% of the applied torque will be reacted as moment at the constraints (5% per) and 90% will be reacted as a couple between the points.
RE: 2 6-DOF sensors attached to the same plate
I would go with the assumption that the you could frame the problem by assuming a linear and torsional motion of the sensors each with their "spring constants" in the sensors assuming plate infinitely stiff.
You then can write the 3 equations either static or dynamic,using the CM as the reference coordinate for dynamic case.
BUT, the problem is you have 9 variables with 3 equations .
Statically indeterminate, and BTW, the single sensor problem is equally indeterminate.
I'll pass on this one.
You need a canned program.
RE: 2 6-DOF sensors attached to the same plate
Statically indeterminate, and BTW, the single sensor problem is equally indeterminate."
Correction
should be
6 variables,3 equations, single sensor determinate
RE: 2 6-DOF sensors attached to the same plate
You translate and rotate the plate at the origin, x,y,@.
This motion by the transformation matrix results in new positions at the sensors at the plate to be
x1,y1, and x2,y2 each a linear function of x,y,@.
Now you can write the 3 force equations
Fx=k(x1-x10)+k(x2-y20)
Fy similar
T= kt@1+kt@2+L1k(x1-x10)+L2k(x2-y20)+L3k(y1-y10)+L4k(y2-y20)
where
L's are arms to origin
kt torsion spring constant
k=linear spring constant
Now there are 5 variables,namely
x,y,@,@1,@2
and we so far have 3 equations
You next write the strain energy equation ( I'll leave that to you)
To get the final 2 equations, invoke the minimum energy theorem by minimizing with respect to @1 and @2.
RE: 2 6-DOF sensors attached to the same plate
x10,y10,x20,y20 are original ground positions of sensor
RE: 2 6-DOF sensors attached to the same plate
more than six unknowns (so statically indeterminate)
what happened to Fz ? Mx, My (assuming T = Mz) ?
RE: 2 6-DOF sensors attached to the same plate
I believe the OP shows motion only in x-y plane
RE: 2 6-DOF sensors attached to the same plate
RE: 2 6-DOF sensors attached to the same plate
I'm not convinced there is a big issue with the outputs
Simply, if we mount one on the x axis of the other at distance d and make their axes parallel and z vertical
FX=fx1+fx2
similar FY and FZ
RX=rx1+rx2
RY=ry1+ry2+d(fz1-fz2)
RZ=rz1+rz2+d(fy1-fy2)
or something like that
Cheers
Greg Locock
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