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This simulation is based on the next prototype design we expect to build, test and evaluate. It has been developed based on a combination of finite element modelling - static & normal modes modes, augmented with in-house matlab simulations. The non-linear influences have been modelled and evaluated in matlab, against test results of earlier prototypes.

This 2nd generation simulation includes temperature influence, though still not the algorithm to translate between frequency and load. We knew from earlier testing that the configuration has minor thermal distortions. We modelled the thermal effects, upgrading the analysis after making a minor design change to improve thermal conditions. From a modelling perspective, the thermal errors are non-existent for 4 of the 6 degrees freedom. The simulation includes the projected errors on the remaining 2 degrees of freedom (the shear directions).

Design ParameterMaximumMinimum
Measureable force90 lb0.4 lb
Measureable moment 250 ft-lb0.6 in-lb Nm
Allowable Drift (10% of measurement)8 hoursn/a
Rotational Stiffness25.4e4 lb-in/rad27.e3 lb-in/rad
Surviveable Force150 lbn/a
Surviveable Moment370 ft-lbn/a
mass, excluding electronics3.5 lb n/a
dimensionsdiameter: 9 1/8"height: 2 1/4"
1st resonancen/a617 Hz

If you're interested trying out the sim, as part of your control program, you can download the matlab and sample files fms simulation , the matlab code. Of course, its still just a design and analysis.

The mass properties are taken as linear, without cabling. The table was taken from Nastran output file. Mass units are lb f- sec 2/inch. RIGID BODY MASS MATRIX AT ORIGIN
9.130E-03 0.000E+00 0.000E+00 0.000E+00 7.840E-03 7.522E-19
0.000E+00 9.130E-03 0.000E+00 -7.840E-03 0.000E+00 1.613E-18
0.000E+00 0.000E+00 9.130E-03 -7.522E-19-1.613E-18 0.000E+00
0.000E+00 -7.840E-03 -7.522E-19 6.190E-02 -3.226E-18 5.557E-18
7.840E-03 0.000E+00 -1.613E-18 -3.226E-18 6.190E-02 -1.152E-18
7.522E-19 1.613E-18 0.000E+00 5.448E-18 -5.014E-19 9.877E-02

US Patent No 5,033,314: expired

Provisional Patent filed: Jan 20, 2014

Input and Output

Initially the required input is:

But the h/w FMS will use accelerometers, and these will be used to extract shape information. Eventually low frequency acceleration of the robot will be required.

The coordinate system for the fms is Z along the longitudinal direction of the end effector. The origin is taken as the end effector to wrist roll joint interface (roll assumed as joint adjacent to end effector)

Axes system: right hand coordinate system. The unloaded fms X and Y flexibilities are same; the unloaded sensor is axi-symmetric.

The units of force: pound, inch, seconds. For angle: degree, for solar flux: Watt, Meter. The output flexibility units are: in/lb, & rad/in-lb. Sorry.

sample input file: ldinput.txt . Time series, 6 dof load input, solar flux, angle of sun

sample output load file loadout.txt . Time series, 6 dof load output

sample output flexibility file flexout.txt Time series, triangular portion of 6x6