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two_link_object_impedance.m
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close all
clear
%% robot modeling
lx = 1; lr = 0.1; g = [0 -9.81 0]; fvis = 0; fcou = 0;
rod = Cuboid([lx,lr,lr]);
Irod = rod.inertia;
dpm = {'a', lx, 'm', rod.mass, 'r', [-lx/2,0,0], 'qlim', [-pi/2, pi/2],'I', Irod,...
'B', fvis, 'Tc', [fcou -fcou]};
rob(1) = SerialLink([Revolute(dpm{:}),Revolute(dpm{:})],'name','r1','gravity',...
-g,'base',SE3([-1,0,0]/2));
rob(2) = SerialLink([Revolute(dpm{:}),Revolute(dpm{:})],'name','r2','gravity',...
-g,'base',SE3([1,0,0]/2));
%% object modeling
obj = Cuboid([lx,lx,lr]);
%% joint positions (x,y)
x0 = [-1,1.5,0;
0,1.5,0];
for i=1:2
q(i,:) = rob(i).ikine(SE3(x0(i,:)),'mask',[1,1,0,0,0,0]);
end
q(1,:) = [sum(q(1,:)),-q(1,2)];
dq = zeros(size(q));
qd = q;
%% object position (x,y,th)
Xo = [sum(x0)/size(x0,1),0,0,0];
dXo = zeros(1,6);
ddXo = dXo;
ro = x0-Xo(1:3);
r = @(Xo,i) (SO3.rpy(Xo(4:6))*ro(i,:)')';
%% visualize systems
ws = [-4 4 -4 4 -4 4];
plotopt = {'workspace', ws, 'nobase', 'notiles', 'noshading', 'noshadow', 'nowrist'};
for i=1:2
hr(i) = rob(i).plot(q(i,:),plotopt{:}); hold on
end
ho = obj.plot(Xo);
view(2);
%% object trajectory
dXd = [0.2,0,0,0,0,0];
Xd = Xo+rand(size(Xo)).*[1,1,0,0,0,1]/10;
md = 3; kv = 5; kp = 5;
Fimp = @(Xo,dXo,Xd) -kv*(dXo-dXd)-kp*(Xo-Xd);
%% object impedance
Mo = blkdiag(obj.mass*eye(3),obj.inertia);
Co = @(dXo) [-obj.mass*g';skew(dXo(4:6))*obj.inertia*dXo(4:6)'];
G = @(Xo) [eye(3),eye(3);
skew(r(Xo,1)),skew(r(Xo,2))];
%% virtual linkage
e12 = @(Xo) (r(Xo,2)-r(Xo,1))/norm(r(Xo,1)-r(Xo,2));
E = @(Xo) [-e12(Xo),e12(Xo)]';
Kpe = 1;
f12 = @(x) -Kpe*(norm(x(2,:)-x(1,:))-norm(ro(2,:)-ro(1,:)));
Fint = @(x,Xo) -(E(Xo)*f12(x))';
%% null-space
Fint = @(Xo) ((eye(6)-pinv(G(Xo))*G(Xo))*[0.1,0,0,0,0,0]')';
%% command force
Fcmd = @(Xo,dXo,Xd) (pinv(G(Xo))*(Co(dXo)+Mo*md^-1*Fimp(Xo,dXo,Xd)')+Fint(Xo)')';
%% simulation
dt = 0.05;
T = 5;
k = 0;
for t=0:dt:T
k = k+1;
% update robot
F = Fcmd(Xo,dXo,Xd);
for i=1:2
% J = rob(i).jacob0(q(i,:),dq(i,:)); J(3:6,:)=[];
% dXr = (skew(dXo(4:6))*(SO3.rpy(Xo(4:6))*ro(i,:)'))';
% dqd(i,:) = pinv(J)*(dXo(1:2)'+dXr(1:2)');
% qd(i,:) = qd(i,:)+dt*dqd(i,:);
% ddqd(i,:) = -kv*(dq(i,:)-dqd(i,:))-kp*(q(i,:)-qd(i,:));
% tau(i,:) = rob(i).inertia(q(i,:))*5*ddqd(i,:)'+J'*F(3*i-2:3*i-1)'+...
% rob(i).coriolis(q(i,:),dq(i,:))*dq(i,:)'+rob(i).gravload(q(i,:))';
% end-effector trajectory
J = rob(i).jacob0(q(i,:),dq(i,:)); J(3:6,:)=[];
Jdq = rob(i).jacob_dot(q(i,:),dq(i,:)); Jdq(3:6,:)=[];
x(i,:) = rob(i).fkine(q(i,:)).t;
dx(i,:) = J*dq(i,:)';
% desired trajectory
xd(i,:) = Xo(1:3)+(SO3.rpy(Xo(4:6))*ro(i,:)')';
dxd = reshape((G(Xo)'*dXo')',[3,2])';
% joint torque
Mq = rob(i).inertia(q(i,:));
Cq = rob(i).coriolis(q(i,:),dq(i,:));
Gq = rob(i).gravload(q(i,:))';
Jinv = Mq^-1*J'*(J*Mq^-1*J')^-1;
Mx = Jinv'*Mq*Jinv;
Cx1 = Jinv'*Cq*Jinv;
Cx2 = Jinv'*Mq*Jinv*Jdq;
Gx = Jinv'*Gq;
kvq = 15; kpq = 25;
tau(i,:) = J'*(-Mx*(kvq*(dx(i,1:2)-dxd(i,1:2))+kpq*(x(i,1:2)-xd(i,1:2)))'+...
Cx1*dx(i,1:2)'+Cx2+Gx+F(3*i-2:3*i-1)');
ddq(i,:) = rob(i).accel(q(i,:),dq(i,:),tau(i,:)-F(3*i-2:3*i-1)*J);
end
dq = dq+dt*ddq;
q = q+dt*dq;
for i=1:2
rob(i).animate(q(i,:));
end
% update object
ddXo(1,:) = Mo^-1*(G(Xo)*F'-Co(dXo));
dXo = dXo+dt*ddXo;
Xo = Xo+dt*dXo;
obj.animate(Xo);
% update trajectory
Xd = Xd+dt*dXd;
drawnow
% save data
t_data(k) = t;
Fcmd_data(k,:) = F;
tau1_data(k,:) = tau(1,:);
tau2_data(k,:) = tau(2,:);
Xo_err(k,:) = Xo-Xd;
x1_err(k,:) = rob(1).fkine(q(1,:)).t'-(SO3.rpy(Xo(4:6))*ro(1,:)')'-Xo(1:3);
x2_err(k,:) = rob(2).fkine(q(2,:)).t'-(SO3.rpy(Xo(4:6))*ro(2,:)')'-Xo(1:3);
end
figure
subplot(2,4,1)
plot(t_data,Fcmd_data(:,1),t_data,Fcmd_data(:,2),t_data,Fcmd_data(:,3));
axis([0 5 -.5 .5])
legend('$F_x$','$F_y$','$F_z$','Interpreter','latex')
title('robot 1 command force')
subplot(2,4,2)
plot(t_data,Fcmd_data(:,4),t_data,Fcmd_data(:,5),t_data,Fcmd_data(:,6));
axis([0 5 -.5 .5])
legend('$F_x$','$F_y$','$F_z$','Interpreter','latex')
title('robot 2 command force')
subplot(2,4,3)
plot(t_data,tau1_data(:,1),t_data,tau1_data(:,2));
axis([0 5 -.5 .5])
legend('$\tau_1$','$\tau_2$','Interpreter','latex')
title('robot 1 torque')
subplot(2,4,4)
plot(t_data,tau2_data(:,1),t_data,tau2_data(:,2));
axis([0 5 -.5 .5])
legend('$\tau_1$','$\tau_2$','Interpreter','latex')
title('robot 2 torque')
subplot(2,4,5)
plot(t_data,Xo_err(:,1),t_data,Xo_err(:,2),t_data,Xo_err(:,6));
axis([0 5 -.5 .5])
legend('$x$','$y$','$\theta$','Interpreter','latex')
title('object position error')
subplot(2,4,6)
plot(t_data,x1_err(:,1),t_data,x1_err(:,2));
axis([0 5 -.5 .5])
legend('$x$','$y$','Interpreter','latex')
title('robot 1 end-effector error')
subplot(2,4,7)
plot(t_data,x2_err(:,1),t_data,x2_err(:,2));
axis([0 5 -.5 .5])
legend('$x$','$y$','Interpreter','latex')
title('robot 2 end-effector error')