Segments

The usual method of building a human model is to create a complete set of body segments and then to reduce the number or redefine the fidelity of the individual segments.

The segments are created from one of five anthropometric databases generating segment dimensions, mass and inertia tensor.

The graphic representations include skeletal, skin/clothed, crash dummy, ellipsoid and stick figure. Each graphical representation is scaled based on the data from the anthropometric database.

LifeMOD/BodySIM generates 19 segments by default, however each segment may be further reduced to individual bones.

Sections:

• Base Level Segment Set
• Creating the Base Segment Set
• Creating a Segment Set from the GeBOD Anthropometric Database
• Creating a Segment Set from the PeopleSize Anthropometric Database
• Creating a Segment Set from the US Army - Natick Anthropometric Database
• Changing an Individual Segment
• Updating the Contents of a Segment
• Deleting Segments

Base Level Segment Set

The first step in the human model creation process is to create the base level segment set. The general properties and dimensions of the 19 segments are created using data from the anthropometric databases. The base level segment is created set includes:

• Head
• Neck
• Upper_Torso
• Central_Torso
• Lower_Torso
• Right_Scapular
• Right_Upper_Arm
• Right_Lower_Arm
• Right_Hand
• Left_Scapular
• Left_Upper_Arm
• Left_Lower_Arm
• Left_Hand
• Right_Upper_Leg
• Right_Lower_Leg
• Right_Foot
• Left_Upper_Leg
• Left_Lower_Leg
• Left_foot

Every bone in the human body is included and segments may be broken down into individual bones for greater model fidelity. While the graphics are scaled to the proper dimensions as dictated by the anthropometric databases, the alignment may need to be modified. (See Cervical Spine and Total Knee Replacement examples) This can be done using the Adams/View Move tools.

Figure 1 displays an exploded -- or separated -- view of the segments of the human model and a close-up of the foot segment. Contact ellipsoids are automatically created on the foot segment. These ellipsoids may be later used to create contact forces with the environment (floor). The dimensions of the ellipsoids may be scaled in the parameters panel any time during the modeling and simulation process.

Figure 1: Body segments (exploded view) and detail of the foot model

Creating the Base Segment Set

Segments -> Create BASE Set

Figure 2: Segments creation panel

Figure 3: BodySIM Display Toolbox displaying the function of the active body when multiple bodies are created.

Select SEGMENTS on the main-menu and CREATE BASE SET on the sub-menu. The process begins by specifying the world for the human model(s). In ADAMS/view this becomes the model name. The next step is to specify the name of the human body. Since LifeMOD/BodySIM allows for the creation of multiple human models in one environment, each one must be created individually. The active body selection option field in the BodySIM Display toolbox (see Figure 3) specifies which human model to be modified and displayed when multiple human models exist in an environment. The user could specify the units system and specify the color of the ellipsoids for each model. After the model is created, the user has the choice of displaying the model in a variety of internal and external graphics representations using the BodySIM Display Toolbox.

The user may specify a full body model or just a lower body model. The lower body consists of the lower_torso, upper and lower leg segments and feet. This type of model is most typically used for gait simulation.

The starting condition of the hands may be specified to save the user some time. Hands may be specified as open or closed.

The user has a choice of two methods to create a human body. The first method allows for the creation of the body using minimal parameters to extract a representation from one of the three internal anthropometric databases. The second method involves importing a SLF file from either the model library or an externally generated SLF file. (see _Xchange chapter)

Figure 4: Details of the segment creation panel

Creating a Segment Set from the GeBOD Anthropometric Database

Segments -> Create BASE Set -> Create From Anthropometric Database-> GeBOD
The GeBOD database creates a human model based on simple descriptions such as gender, age (for child), height and weight. From this description the body parameters are created and may be edited if necessary. Before the human model is created the body measurement tables are created. This is done by selecting CREATE BODY MEASUREMENT TABLE. When this button is selected a pull down menu is displayed allowing the user to edit either the body measurement table (Figure 6) or the joint center location table (Figure 7).

Figure 5: Creating the body measurement table from the GeBOD anthropometric database.

Figure 6: Body Segment Measurement Table created from the GeBOD anthropometric library.

Figure 7: Joint Center Location Table created from the GeBOD anthropometric library.

Creating a Segment Set from the PeopleSize Anthropometric Database

Segments -> Create BASE Set -> Create From Anthropometric Database -> PeopleSize
The PeopleSize database can be used to create the segment dimensions and mass properties. The database contains data for USA, UK, Japan and China nationalities, average, 5th percentile, 95th percentile, male and female body types. From this description the body parameters are created and may be edited if necessary. Before the human model is created the body measurement tables are created. This is done by selecting CREATE BODY MEASUREMENT TABLE. When this button is selected, a pull down menu is displayed allowing the user to edit either the body measurement table (Figure 6 above) or the joint center location table (Figure 7).

Figure 8: Creating segments from the PeopleSize database.

Creating a Segment Set from the US Army - Natick Anthropometric Database

Segments -> Create BASE Set -> Create From Anthropometric Database -> US Army - Natick
The US Army - Natick database can also be used to create the segment dimensions and mass properties. The database contains data for US Army personnel for both male and female and 1st through 99th percentiles. From this description the body parameters are created and may be edited if necessary. Before the human model is created the body measurement tables are created. This is done by selecting CREATE BODY MEASUREMENT TABLE. When this button is selected a pull down menu is displayed allowing the user to edit either the body measurement table (Figure 6) or the joint center location table (Figure 7).

Figure 9: Creating segments from the US Army-Natick database.

Creating an Individual Segment

Segments -> Create Individual Segment
For greater fidelity or narrower focus, single segments may be created for the model. This method creates non-human segments or more finite models that require individual or additional segments. (see the Cervical Spine Tutorial, Total Knee Replacement Tutorial and Total Hip Replacement Tutorial for usage of this feature). The segment is first given a name, CM location and orientation. Next, mass properties are specified/estimated either using ellipsoids or based on material properties of the geometry.

Geometry for the segment may exist already, such as one or several bones created in the original model. Geometry may also be imported by using a shell file format (see Appendix), or a parasolids solid geometry format.

This panel is used to create higher fidelity segments for the individual base segment. For example, the individual vertebra may be created as a single part or multiple geometric entities may be selected for the single part (see Cervical Spine example). The geometric entities can ONLY exist in a shell file format (see Appendix) and may already exist in the database or may be imported.

Figure 10: Single segment creation panel

Figure 11: Single segment creation panel

Segments -> Create Single -> Calculate Mass Properties Based on Material
Select Calculate Mass Properties Based on Material from the pull-down menu and specify desired values for CM location (designates the center of mass) and enter an orientation for the alignment of the inertia tensor to its reference axis system. Next, specify a material type from the material library and select whether the item is either existing or imported.

This method may also be used for non-human segments such as prosthetic joints (see Total Knee Replacement Tutorial).

Figure 12: Creating a single segment by calculating mass properties for a binding geometry

Segments -> Create Single -> Calculate Mass Properties with Ellipsoids
Select Calculate Mass Properties with Ellipsoids from the pull-down menu and specify desired values for CM location (designates the center of mass) and enter an orientation for the alignment of the inertia tensor to its reference axis system. After entering the CM location and orientation, enter the dimensions of the corresponding ellipsoid and the density into the appropriate windows. Additional geometry may be imported or selected from the existing set on the model, however, these will NOT affect the mass property calculation.

For an example of this method see the Cervical Spine Tutorial .

Figure 13: Creating a single segment by calculating mass properties for a bounding ellipsoid

Segments -> Create Single -> Specify Mass Properties
Select Calculate Mass Properties with Ellipsoids from the pull-down menu and specify desired values for CM location (designates the center of mass) and enter an orientation for the alignment of the inertia tensor to its reference axis system. Next, the mass and the inertia values are entered. Additional geometry may be imported or selected from the existing set on the model, however, these will NOT affect the mass property calculation.

For an example of this method see the Total Hip Replacement Tutorial.

Figure 14: Creating a single segment by specifying mass properties

Updating the Contents of a Segment

Segments -> Update Segment Contents
This panel is used to update the contents of each human segment. This is used when additional elements are added to a segment, such as markers or geometry. It is used to build the parametric associations within each part. If this process is not done after markers or other geometry are added to the human segment, they will not move with the segment when updating the posture of the model.

Figure 15: Update segment contents panel

Deleting Segments

Segments-> Delete
Since LifeMOD/BodySIM has the capability to create multiple models in one environment, this panel can be used to delete the individual body or the entire environment (World model). Individual segments may be deleted by checking the appropriate boxes on the form.

Figure 16: Body delete panel