41 lines
1.6 KiB
Matlab
41 lines
1.6 KiB
Matlab
%*** CHAPTER 8: DYNAMICS OF OPEN CHAINS ***
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function grav = GravityForces(thetalist,g,Mlist,Glist,Slist)
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% Takes thetalist: A list of joint variables,
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% g: 3-vector for gravitational acceleration,
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% Mlist: List of link frames i relative to i-1 at the home position,
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% Glist: Spatial inertia matrices Gi of the links,
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% Slist: Screw axes Si of the joints in a space frame.
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% Returns grav: The joint forces/torques required to overcome gravity at
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% thetalist
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% This function calls InverseDynamics with Ftip = 0, dthetalist = 0, and
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% ddthetalist = 0.
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% Example Input (3 Link Robot):
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%{
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clear;clc;
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thetalist = [0.1; 0.1; 0.1];
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g = [0; 0; -9.8];
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M01 = [[1, 0, 0, 0]; [0, 1, 0, 0]; [0, 0, 1, 0.089159]; [0, 0, 0, 1]];
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M12 = [[0, 0, 1, 0.28]; [0, 1, 0, 0.13585]; [-1, 0 ,0, 0]; [0, 0, 0, 1]];
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M23 = [[1, 0, 0, 0]; [0, 1, 0, -0.1197]; [0, 0, 1, 0.395]; [0, 0, 0, 1]];
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M34 = [[1, 0, 0, 0]; [0, 1, 0, 0]; [0, 0, 1, 0.14225]; [0, 0, 0, 1]];
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G1 = diag([0.010267, 0.010267, 0.00666, 3.7, 3.7, 3.7]);
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G2 = diag([0.22689, 0.22689, 0.0151074, 8.393, 8.393, 8.393]);
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G3 = diag([0.0494433, 0.0494433, 0.004095, 2.275, 2.275, 2.275]);
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Glist = cat(3,G1,G2,G3);
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Mlist = cat(4,M01,M12,M23,M34);
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Slist = [[1; 0; 1; 0; 1; 0], ...
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[0; 1; 0; -0.089; 0; 0], ...
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[0; 1; 0; -0.089; 0; 0.425]];
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grav = GravityForces(thetalist,g,Mlist,Glist,Slist)
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%}
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% Output:
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% grav =
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% 28.4033
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% -37.6409
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% -5.4416
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n = size(thetalist,1);
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grav = InverseDynamics(thetalist,zeros(n,1),zeros(n,1),g, ...
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[0; 0; 0; 0; 0; 0],Mlist,Glist,Slist);
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end |