Problems with Standing Model

Hello,

I have a problem regarding the posture of the Standing Model. I have
been investigating the effects of multiplanar deformities of the femur
on knee joints. In order to do this, I modified the Thigh segment of
the Seg.any file so that it represents a deformed femur. I calculated
the necessary posture angles (e.g. PelvisRotY, HipExternalRotation,
HipAbduction) and wrote them in the Mannequen.any file. I based my
posture angle calculations on the assumption that when a person stands
up, his/her hip joint centers and ankle joint centers are aligned on
axes that are vertical to the ground on both sides.

When I load the model, I see on the “Model View” that the body posture
is as I want it to be: the hip joints and the ankle joints are aligned
on both limbs. I also confirm this by comparing the positions of jip
and ankle joint reference points in the global frame. However, when I
run an Inverse Dynamic Analysis, I see that the upper body rotates
along with the pelvis while the feet positions stay stable, and the
hip and ankle joints are not aligned anymore. When I look at the
MannequinValuesFromModel.any file, I see that the body posture angles
that I set have been modified (especially PelvisRotX-Y-Z values).

To trace the source of the problem, I ran some posture trials with the
standard Standing Model (with a non-deformed Seg.any file), and found
out that the upper body and pelvis rotation occurs only when there are
nonzero HipExternalRotation and HipAbduction values in the Mannequin
file for the same side.

I was wondered if any of you fellow researchers experienced the same
problem. It is very important for my work that the body posture is
retained after inverse dynamic analysis. Thank you in advance for any
help you can provide.

Ceren

Hi Ceren

I will start by exaplaining how the standing model is driven, it is
all going on in the JointsAndDriver.any file, then i will describe
the concept of initial positions.

The feet are driven to stay vertical on the ground and the are driven
in the forward/backward direction so that the ankle joint stay at x=0;

Then the entire body center of mass is driven in the global x and z
direction so that it stays centered above origo.

The spine is driven by setting the rotation between pelvis and the
thorax, this is the also named PostureDriver.

All dof in the arms are driven by joint drivers on each of the dof’s.

The legs are also entirely driven by joint drivers except the ankle
flexion, since this dof is basically driven by the contact between
the foot and the ground.

In commen for the joint drivers are that they get the values from the
Mannequin.any file.

When you load the model the segments will have initial positions
which are defined by the properties in the Mannequin.any. This is an
easy way to set the model in any kind of initial position. So when
you load the model it will make use of all the parameters in the
mannequin file for setting the intitial position of the model. These
positions serves ONLY as the initial guess on a solution for the
kinematic solver. When solving the kinematics of this problem the
solver will try to fullfill the constraints imposed to the model by
the JointAndDrivers, using the initial positions as a good guess,
nothing else. So it is the joint and drivers that really determines
the kinematics of the model.

If you look at the model FreePosture you will find a model which are
driven entirely like described in the mannequin file. Meaning that
you set the position of the pelvis and it’s rotation wrt. the world
and then drive each joint in the body as an open kinematic chain.

This is also how the initial positions are set in the StandingModel,
but once the kinematics are solved the joint and drivers between the
feet and the floor etc. are imposed on the model instead.

I think it is this fact that has cause you the problem.

You decribe that the upper body rotates with the pelvis, this is
correct, it is because the PostureDriver that drives the rotation
between the pelvis and thorax. You also write that the feets stay
stable on the floor, again this is because of the drivers and joints.

I am uncertain what kind motion you are searching for?

I think you should try to review the JointsAndDriver.any file for the
StandingModel and make a small sketch on how this model is driven.
Then try change some of the settings in the mannequin.any file and
see the effect it has once the kinematics has been solved.

I hope this helps you move on, otherwise please write again.

Best regards
Søren, AnyBody Support

— In anyscript@yahoogroups.com, “cerensaglamer”
<ceren.saglamer@…> wrote:
>
> Hello,
>
> I have a problem regarding the posture of the Standing Model. I have
> been investigating the effects of multiplanar deformities of the
femur
> on knee joints. In order to do this, I modified the Thigh segment of
> the Seg.any file so that it represents a deformed femur. I
calculated
> the necessary posture angles (e.g. PelvisRotY, HipExternalRotation,
> HipAbduction) and wrote them in the Mannequen.any file. I based my
> posture angle calculations on the assumption that when a person
stands
> up, his/her hip joint centers and ankle joint centers are aligned on
> axes that are vertical to the ground on both sides.
>
> When I load the model, I see on the “Model View” that the body
posture
> is as I want it to be: the hip joints and the ankle joints are
aligned
> on both limbs. I also confirm this by comparing the positions of jip
> and ankle joint reference points in the global frame. However, when
I
> run an Inverse Dynamic Analysis, I see that the upper body rotates
> along with the pelvis while the feet positions stay stable, and the
> hip and ankle joints are not aligned anymore. When I look at the
> MannequinValuesFromModel.any file, I see that the body posture
angles
> that I set have been modified (especially PelvisRotX-Y-Z values).
>
> To trace the source of the problem, I ran some posture trials with
the
> standard Standing Model (with a non-deformed Seg.any file), and
found
> out that the upper body and pelvis rotation occurs only when there
are
> nonzero HipExternalRotation and HipAbduction values in the Mannequin
> file for the same side.
>
> I was wondered if any of you fellow researchers experienced the same
> problem. It is very important for my work that the body posture is
> retained after inverse dynamic analysis. Thank you in advance for
any
> help you can provide.
>
> Ceren
>

Hello Søren,

Thank you for your response. Basically, what I am trying to do is to
put the body in a specific posture, and then investigate the changes
in joint reaction forces and muscle lengths on a static model. You
pointed out correctly that the fact that the inverse dynamic analysis
is imposing different posture angles on the model is causing the
problem. Is there anyway I can build a model on which I can impose
predefined posture angles and investigate the outcome?

Best wishes,
Ceren

— In anyscript@yahoogroups.com, “AnyBody Support” <support@…> wrote:
>
> Hi Ceren
>
> I will start by exaplaining how the standing model is driven, it is
> all going on in the JointsAndDriver.any file, then i will describe
> the concept of initial positions.
>
> The feet are driven to stay vertical on the ground and the are driven
> in the forward/backward direction so that the ankle joint stay at x=0;
>
> Then the entire body center of mass is driven in the global x and z
> direction so that it stays centered above origo.
>
> The spine is driven by setting the rotation between pelvis and the
> thorax, this is the also named PostureDriver.
>
> All dof in the arms are driven by joint drivers on each of the dof’s.
>
> The legs are also entirely driven by joint drivers except the ankle
> flexion, since this dof is basically driven by the contact between
> the foot and the ground.
>
> In commen for the joint drivers are that they get the values from the
> Mannequin.any file.
>
>
> When you load the model the segments will have initial positions
> which are defined by the properties in the Mannequin.any. This is an
> easy way to set the model in any kind of initial position. So when
> you load the model it will make use of all the parameters in the
> mannequin file for setting the intitial position of the model. These
> positions serves ONLY as the initial guess on a solution for the
> kinematic solver. When solving the kinematics of this problem the
> solver will try to fullfill the constraints imposed to the model by
> the JointAndDrivers, using the initial positions as a good guess,
> nothing else. So it is the joint and drivers that really determines
> the kinematics of the model.
>
> If you look at the model FreePosture you will find a model which are
> driven entirely like described in the mannequin file. Meaning that
> you set the position of the pelvis and it’s rotation wrt. the world
> and then drive each joint in the body as an open kinematic chain.
>
> This is also how the initial positions are set in the StandingModel,
> but once the kinematics are solved the joint and drivers between the
> feet and the floor etc. are imposed on the model instead.
>
> I think it is this fact that has cause you the problem.
>
> You decribe that the upper body rotates with the pelvis, this is
> correct, it is because the PostureDriver that drives the rotation
> between the pelvis and thorax. You also write that the feets stay
> stable on the floor, again this is because of the drivers and joints.
>
> I am uncertain what kind motion you are searching for?
>
> I think you should try to review the JointsAndDriver.any file for the
> StandingModel and make a small sketch on how this model is driven.
> Then try change some of the settings in the mannequin.any file and
> see the effect it has once the kinematics has been solved.
>
>
> I hope this helps you move on, otherwise please write again.
>
> Best regards
> Søren, AnyBody Support
>
> — In anyscript@yahoogroups.com, “cerensaglamer”
> <ceren.saglamer@> wrote:
> >
> > Hello,
> >
> > I have a problem regarding the posture of the Standing Model. I have
> > been investigating the effects of multiplanar deformities of the
> femur
> > on knee joints. In order to do this, I modified the Thigh segment of
> > the Seg.any file so that it represents a deformed femur. I
> calculated
> > the necessary posture angles (e.g. PelvisRotY, HipExternalRotation,
> > HipAbduction) and wrote them in the Mannequen.any file. I based my
> > posture angle calculations on the assumption that when a person
> stands
> > up, his/her hip joint centers and ankle joint centers are aligned on
> > axes that are vertical to the ground on both sides.
> >
> > When I load the model, I see on the “Model View” that the body
> posture
> > is as I want it to be: the hip joints and the ankle joints are
> aligned
> > on both limbs. I also confirm this by comparing the positions of jip
> > and ankle joint reference points in the global frame. However, when
> I
> > run an Inverse Dynamic Analysis, I see that the upper body rotates
> > along with the pelvis while the feet positions stay stable, and the
> > hip and ankle joints are not aligned anymore. When I look at the
> > MannequinValuesFromModel.any file, I see that the body posture
> angles
> > that I set have been modified (especially PelvisRotX-Y-Z values).
> >
> > To trace the source of the problem, I ran some posture trials with
> the
> > standard Standing Model (with a non-deformed Seg.any file), and
> found
> > out that the upper body and pelvis rotation occurs only when there
> are
> > nonzero HipExternalRotation and HipAbduction values in the Mannequin
> > file for the same side.
> >
> > I was wondered if any of you fellow researchers experienced the same
> > problem. It is very important for my work that the body posture is
> > retained after inverse dynamic analysis. Thank you in advance for
> any
> > help you can provide.
> >
> > Ceren
> >
>

Hi Ceren

I assume that you want the model to be standing and have reactions on
the feet, then the standing model is still good choice.

You can adjust the posture of the standing model by changing the
valeus of the mannequin file which are being used by its drivers, the
most important for you are these:

Ankle flexion
Knee flexion
Hip all three dof

PelvisThorax rotation

If you want your model to be entirely controlled by the mannequin
file then you should use the freeposture model, but the drawback is
that it will not put the feets on the floor all limbs will be free in
the air.

In order to have proper reactions you will need to switch off
reaction between pelvis and the globalref and impose new reactions
between the feet and the floor, by using an AnyReacForce.

This is a posibility but this model has no balance control build into
its drivers like the standing model which automatically enforce the
center of mass to stay above origo. So i would still try to change
the settings of the standing model to obtain the wanted posture.

So to answer your question: the standing model can be set into
predefined postures, it is just not entirely as flexible as the
freeposture model because it is enforced to have its feet on the
ground etc.

Please write again if you have further questions.

Best regards
Søren, AnyBody Support

— In anyscript@yahoogroups.com, “cerensaglamer”
<ceren.saglamer@…> wrote:
>
> Hello Søren,
>
> Thank you for your response. Basically, what I am trying to do is to
> put the body in a specific posture, and then investigate the changes
> in joint reaction forces and muscle lengths on a static model. You
> pointed out correctly that the fact that the inverse dynamic
analysis
> is imposing different posture angles on the model is causing the
> problem. Is there anyway I can build a model on which I can impose
> predefined posture angles and investigate the outcome?
>
> Best wishes,
> Ceren
>
>
> — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
wrote:
> >
> > Hi Ceren
> >
> > I will start by exaplaining how the standing model is driven, it
is
> > all going on in the JointsAndDriver.any file, then i will
describe
> > the concept of initial positions.
> >
> > The feet are driven to stay vertical on the ground and the are
driven
> > in the forward/backward direction so that the ankle joint stay at
x=0;
> >
> > Then the entire body center of mass is driven in the global x and
z
> > direction so that it stays centered above origo.
> >
> > The spine is driven by setting the rotation between pelvis and
the
> > thorax, this is the also named PostureDriver.
> >
> > All dof in the arms are driven by joint drivers on each of the
dof’s.
> >
> > The legs are also entirely driven by joint drivers except the
ankle
> > flexion, since this dof is basically driven by the contact
between
> > the foot and the ground.
> >
> > In commen for the joint drivers are that they get the values from
the
> > Mannequin.any file.
> >
> >
> > When you load the model the segments will have initial positions
> > which are defined by the properties in the Mannequin.any. This is
an
> > easy way to set the model in any kind of initial position. So
when
> > you load the model it will make use of all the parameters in the
> > mannequin file for setting the intitial position of the model.
These
> > positions serves ONLY as the initial guess on a solution for the
> > kinematic solver. When solving the kinematics of this problem the
> > solver will try to fullfill the constraints imposed to the model
by
> > the JointAndDrivers, using the initial positions as a good guess,
> > nothing else. So it is the joint and drivers that really
determines
> > the kinematics of the model.
> >
> > If you look at the model FreePosture you will find a model which
are
> > driven entirely like described in the mannequin file. Meaning
that
> > you set the position of the pelvis and it’s rotation wrt. the
world
> > and then drive each joint in the body as an open kinematic chain.
> >
> > This is also how the initial positions are set in the
StandingModel,
> > but once the kinematics are solved the joint and drivers between
the
> > feet and the floor etc. are imposed on the model instead.
> >
> > I think it is this fact that has cause you the problem.
> >
> > You decribe that the upper body rotates with the pelvis, this is
> > correct, it is because the PostureDriver that drives the rotation
> > between the pelvis and thorax. You also write that the feets stay
> > stable on the floor, again this is because of the drivers and
joints.
> >
> > I am uncertain what kind motion you are searching for?
> >
> > I think you should try to review the JointsAndDriver.any file for
the
> > StandingModel and make a small sketch on how this model is
driven.
> > Then try change some of the settings in the mannequin.any file
and
> > see the effect it has once the kinematics has been solved.
> >
> >
> > I hope this helps you move on, otherwise please write again.
> >
> > Best regards
> > Søren, AnyBody Support
> >
> > — In anyscript@yahoogroups.com, “cerensaglamer”
> > <ceren.saglamer@> wrote:
> > >
> > > Hello,
> > >
> > > I have a problem regarding the posture of the Standing Model. I
have
> > > been investigating the effects of multiplanar deformities of
the
> > femur
> > > on knee joints. In order to do this, I modified the Thigh
segment of
> > > the Seg.any file so that it represents a deformed femur. I
> > calculated
> > > the necessary posture angles (e.g. PelvisRotY,
HipExternalRotation,
> > > HipAbduction) and wrote them in the Mannequen.any file. I
based my
> > > posture angle calculations on the assumption that when a person
> > stands
> > > up, his/her hip joint centers and ankle joint centers are
aligned on
> > > axes that are vertical to the ground on both sides.
> > >
> > > When I load the model, I see on the “Model View” that the body
> > posture
> > > is as I want it to be: the hip joints and the ankle joints are
> > aligned
> > > on both limbs. I also confirm this by comparing the positions
of jip
> > > and ankle joint reference points in the global frame. However,
when
> > I
> > > run an Inverse Dynamic Analysis, I see that the upper body
rotates
> > > along with the pelvis while the feet positions stay stable, and
the
> > > hip and ankle joints are not aligned anymore. When I look at the
> > > MannequinValuesFromModel.any file, I see that the body posture
> > angles
> > > that I set have been modified (especially PelvisRotX-Y-Z
values).
> > >
> > > To trace the source of the problem, I ran some posture trials
with
> > the
> > > standard Standing Model (with a non-deformed Seg.any file), and
> > found
> > > out that the upper body and pelvis rotation occurs only when
there
> > are
> > > nonzero HipExternalRotation and HipAbduction values in the
Mannequin
> > > file for the same side.
> > >
> > > I was wondered if any of you fellow researchers experienced the
same
> > > problem. It is very important for my work that the body posture
is
> > > retained after inverse dynamic analysis. Thank you in advance
for
> > any
> > > help you can provide.
> > >
> > > Ceren
> > >
> >
>