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Old 04-28-2018, 09:45 PM
amin_ucf2002 amin_ucf2002 is offline
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Join Date: Jan 2015
Posts: 26
Default SpineFixationWithForceDependentKinematics Model

Hello AnyBody,

I am trying to understand how FDK feature is added in SpineFixationWithForceDependentKinematics Model(AMMR1.6.3). I read the following example in tutoral:

AnyRevoluteJoint KneeJoint = {
AnyRefFrame &Shank = .Shank.KneeCenter;
AnyRefFrame &Thigh = .Thigh.KneeCenter;
// Prepare the joint for FDK: Define the reaction types in x and y
// directions to be FDK-dependent. These reaction forces must then
// be switched off and provided by some elastic element that we
// define explicitly below.
Constraints = {
CType = {ForceDep, ForceDep, Hard, Hard, Hard};
// Define springs in the knee, simulating the effect of cartilage
// and ligaments.
AnyForce KneeStiffness = {
AnyKinLinear &lin = Main.MyModel.KneeJoint.Linear;
F = {-1000*lin.Pos[0], -5000*lin.Pos[1], 0};

However, I am trying to find the translational stiffness defined in SpineFixation model. I cannot find them. What I can find is the following codes:
// define joints, which have force-dependent behaviour
AnySphericalJoint &jntt12l1 = .refJoints.T12L1Jnt;
AnySphericalJoint &jnt12 = .refJoints.L1L2Jnt;
AnySphericalJoint &jnt23 = .refJoints.L2L3Jnt;
AnySphericalJoint &jnt34 = .refJoints.L3L4Jnt;
AnySphericalJoint &jnt45 = .refJoints.L4L5Jnt;
//AnySphericalJoint &jnt5sacrum = .refJoints.L5SacrumJnt; // this joint is commented to avoid over-constrained situation

// constraints type has to be set ForceDep for the force-dependent
// degrees of freedom of the joint
CType = {
ForceDep, ForceDep,ForceDep,
ForceDep, ForceDep,ForceDep,
ForceDep, ForceDep,ForceDep,
ForceDep, ForceDep,ForceDep,
ForceDep, ForceDep,ForceDep
//ForceDep, ForceDep,ForceDep // commented joint

Reaction.Type = {
//Off,Off,Off // commented joint

So I have one questions. 1. the FDK feature defined in SpineFixation model is for 3 ration dofs or 3 translational dofs ? 2. If it is translational FDK feature, where I can check stiffness?


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Old 04-30-2018, 10:12 AM
pgalibarov's Avatar
pgalibarov pgalibarov is offline
Senior Member
Join Date: Oct 2010
Posts: 948

Hi Amin,

In this example it is a rotational dof. The idea was to find the curvature of the spine. But yes, you could also subject translational dof to the FDK analysis.

I believe some of the customers have tried to do this - maybe start looking at this publication.

Kind regards,
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