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--- visual3d:documentation:kinematics_and_kinetics:external_forces:force_structures [2024/06/19 13:57] – created sgranger
+++ visual3d:documentation:kinematics_and_kinetics:external_forces:force_structures [2025/09/12 19:04] (current) – [Structure consisting of 2 force platforms and 1 surface] wikisysop
@@ Line 1: / Line 1: @@
+====== Force Structures ======
 Force Structures were conceived as a mechanism for combining force platform data (e.g. treating several contiguous platforms as a single platform), and for accommodating structures that are attached to the force platform as a super-structure such as the stairs manufactured by AMTI.
 Our original implementation treated these "entities" as different FORCE_PLATFORM types, but this decision caused problems with other manufacturers that didn't recognize the new types. After consideration we determined that the introduction of a new C3D parameter group for FORCE_STRUCTURES was a more general solution because it didn't affect the force platform parameters.
-===== Theory =====
+==== Theory ====
 External forces require the specification of 9 components
-Force= (Fx, Fy, Fz)
+Force= (Fx, Fy, Fz)\\
-Center of Pressure= (COPx, COPy, COPz)
+Center of Pressure= (COPx, COPy, COPz)\\
-Free Moment= (Tx, Ty, Tz)
+Free Moment= (Tx, Ty, Tz)\\
 Only 6 pieces of information, however, are available from a force platform, so it is necessary to specify (or assume) 3 components.
 For a typical platform:
-Tx and Ty are assumed to be zero. This means that we assume that the subject is **not** pulling up on the platform.
+Tx and Ty are assumed to be zero. This means that we assume that the subject is **not** pulling up on the platform.\\
-COPz is assumed to be on the top surface of the platform.
+COPz is assumed to be on the top surface of the platform.\\
 For a surface (e.g. a step) placed on top of the force platform, the COP is translated along the Force Vector to the new surface. (e.g. the intersection of the force with the new surface).
-{{Force_Structure.jpg}}
+{{:Force_Structure.jpg?500x}}
 This figure shows a picture of an oblique force applied to a step. This figure shows one type of force platform, but the concept applies equally to all platforms.
@@ Line 34: / Line 36: @@
 A consequence of this is that it is important to filter the ANALOG signals rather than filtering the FORCE, COP, and FREEMOMENT signals. Remember to select the Settings Option to use Processed Analog signals for computing the force vectors.
-===== Pipeline Command =====
+==== Pipeline Command ====
 The edit dialog invoked either by selected Modify Force Structures under the Force Menu or by the Pipeline command [[Visual3D:Documentation:Pipeline:Force_Commands:Modify_Force_Structure_Parameters|Modify_Force_Structure_Parameters]] as follows.
-{{AMTI_steps2.jpg}}
+{{:AMTI_steps2.jpg}}
 Each structure is defined as a plane (or polygon) defined by four corners.
@@ Line 44: / Line 46: @@
 If the force structure is not a single plane, but multiple planes, each surface should be defined in the Force Structure Surfaces list box
-==== Modify_Force_Structure_Parameters ====
+=== Modify_Force_Structure_Parameters ===
-**Modify_Force_Structure_Parameters**
+<code>
+Modify_Force_Structure_Parameters
 /USED= Number of Force Structures Used
 ! /TYPE= Not currently used
@@ Line 61: / Line 64: @@
 /USE_FORCES_FOR_KINETICS= are forces kinematics only?
 /COMBINE_INPUT_FORCES= combine all forces for each structure into a single force
-! /[[Visual3D:Documentation:Pipeline:File_Commands:Update_C3D_File|Update_C3D_File]]=FALSE
+! /Update_C3D_File=FALSE
-**;**
+;
-For example, the following force structure has one surface attached to two force platforms.
+</code>
-{{ForceStructureDlg1x2.jpg}}
+For example, the following force structure has one surface attached to two force platforms.
-\\
+{{:ForceStructureDlg1x2.jpg}}
-**Modify_Force_Structure_Parameters**
+<code>
+Modify_Force_Structure_Parameters
 /USED=2
 /TYPE=0+0
@@ Line 86: / Line 90: @@
 /COMBINE_INPUT_FORCES=TRUE+FALSE
 ! /UPDATE_C3D_FILE=FALSE
-**;**
+;
+</code>
 See also [[Visual3D:Documentation:Pipeline:Force_Commands:Modify_Force_Structure_Parameters|Modify_Force_Structure_Parameters]]
-===== Structure consisting of 1 force platform and 2 surfaces =====
+==== Structure consisting of 1 force platform and 2 surfaces ====
 The following dialog creates a force structure that is comprised of 2 surfaces attached to the same platform.
-{{AMTI_steps3.jpg}}
+{{:AMTI_steps3.jpg}}
 Visual3D creates two surfaces, so it creates two force signals.
@@ Line 109: / Line 114: @@
 **COP_1**, **FORCE_1** and **FREEMOMENT_1**
-{{ForceStructureDataTree.jpg}}
+{{:ForceStructureDataTree.jpg}}
 In the following figure the right foot makes contact with 2 steps
-{{ForceStructureGraph.jpg}}
+{{:ForceStructureGraph.jpg}}
-===== Structure consisting of 2 force platforms and 1 surface =====
+==== Structure consisting of 2 force platforms and 1 surface ====
 The following dialog creates a force structure that is comprised of 1 surface spanning 2 force platforms.
-{{ForceStructureDig1x2.jpg}}
+{{:ForceStructureDlg1x2.jpg}}
 The user has the option to treat each force independently, which means that each force FP1 and FP2 could be assigned to the same segment.
@@ Line 132: / Line 138: @@
   * solve the following 6 equations for the resultant force and moment
-{{ForceStructureEqn1.jpg}} solve for the 3 components of the force
+{{:ForceStructureEqn1.jpg}} solve for the 3 components of the force
-{{ForceStructureEqn2.jpg}} assume the resultant center of pressure lies on the output surface, and that the Free Moment is computed only about the normal to the surface
+{{:ForceStructureEqn2.jpg}} assume the resultant center of pressure lies on the output surface, and that the Free Moment is computed only about the normal to the surface
   * solve for the x and y component of the COP on the surface
@@ Line 140: / Line 146: @@
   * Transform these values back into the laboratory coordinate system
-If there are two force platforms, the resulting signal will appear in the data tree as
+If there are two force platforms, the resulting signal will appear in the data tree as:
 **FS1_1** and **FS1_2**
 This is interpreted as Force Structure 1 contribution from Force platform 1, and Force Structure 1contribution from force platform 2.
-\\
+If, for example, instead of FP1 and FP2, there was FP1 and FP3, the signals would be:
-If, for example, instead of FP1 and FP2, there was FP1 and FP3, the signals would be
 **FS1_1** and **FS1_3**
-\\
-if the option to combine all input forces is selected, there will be one resulting signal
+If the option to combine all input forces is selected, there will be one resulting signal:
 **FS1_1**
-===== Curved Surfaces =====
+==== Curved Surfaces ====
 If the force structure is actually a continuous curved surface, it must be approximated by a series of contiguous surfaces.