Solid element with properties derived from external file
Simscape / Multibody / Body Elements
The File Solid block models a solid element with geometry, inertia, color, and reference frame derived from an external file. The file must be of a part model, which is to say that it contains at least solid geometry data. Some formats may provide color and inertia data, though such properties can be specified manually if need be.
Among the supported formats are those native to CATIA (V4, V5, and V6), Creo, Inventor, Unigraphics NX, Solid Edge, SolidWorks, and Parasolid (all CAD applications common in industry and academia). These include CATPART, PRT, IPT, SLDPRT, and X_T (and its binary version, X_B). Other valid formats, not associated with a specific application but common in 3-D modeling, include SAT (often referred to as ACIS), JT, STL, and STEP.
(CAD drawing and assembly files, which do not contain the necessary data for a solid element, cannot be imported to the block.)
For part model files with density data, the block gives the option to
(automatically) set the mass, center of mass, and inertia tensor of the solid from
calculation. This behavior is enabled by default (through the
Type and Based On parameters under the
Inertia node, which, in their original states, will read
Calculate from Geometry and
If the imported file does not contain density data, you must specify it (or,
equivalently, mass) for the calculations to be made. Set the Based
On parameter to
Custom Density or
Custom Mass to enter the missing data.
Alternatively, if you have the complete mass properties of the imported part—often
provided, for CAD models, by the CAD application itself—you can enter them directly
as block parameters. Set the inertia Type parameter to
Custom in order to do this.
Note that the frame in which the moments and products of inertia are defined will vary among CAD applications. In this block, the origin of that frame is assumed to be at the center of mass (and its axes parallel to those of the reference frame). This frame is referred to here as the inertia resolution frame. (The center of mass, on the other hand, is defined in the reference frame.) For more information, see Specifying Custom Inertias.
If the mass properties are computed from geometry, you can view their values
in the block dialog box. To do so, expand the Derived
Values node under Inertia and click
Update. (This feature, as it is specified to computed
properties, requires that the inertia Type setting be
Calculated from Geometry.) If a geometry or
inertia block parameter changes, click the Update button
once again to display the new mass properties. All values are in SI units of
m) and mass (
The block dialog box contains a collapsible visualization pane. This pane provides instant visual feedback on the solid you are modeling. Use it to find and fix any issues with the shape and color of the solid. You can examine the solid from different perspectives by selecting a standard view or by rotating, panning, and zooming the solid.
Select the Update Visualization button to view the latest changes to the solid geometry in the visualization pane. Select Apply or OK to commit your changes to the solid. Closing the block dialog box without first selecting Apply or OK causes the block to discard those changes.
Solid Visualization Pane
Right-click the visualization pane to access the visualization context-sensitive menu. This menu provides additional options so that you can change the background color, split the visualization pane into multiple tiles, and modify the view convention from the default +Z up (XY Top) setting.
Like most components, the solid connects through frames, of which it has at least one. The default frame, which serves as its reference and is associated with port R, gets its origin and axes from the data in the imported file. (The origin is generally the zero coordinate of the CAD model or, if such technology is used, the 3-D scan, contained in the file.)
For those cases in which the reference frame is ill-placed for connection, or in which multiple connection frames are needed, the block comes with a frame creation tool. Treat this tool as an interactive alternative to the Rigid Transform block (the latter a numerical means to add and translate as well as rotate frames, though one that keeps the frames separate from the solid).
You can create (and edit) frames using geometry features as constraints—placing the frame origin on, and orienting the frame axes along, selected vertices, edges, and faces. You can also use the reference frame origin and its axes, as well as the center of mass and the principal inertia axes, to define the new frames. Each frame adds to the block a new frame port (its label derived from the name given in the frame creation pane).
To create or edit a frame, first expand the Frames node in the block dialog box. Click the button to create a frame or the button to edit a frame (if one, other than the reference frame, already exists). The frame definitions depend on a mix of geometry and inertia data, so you must have previously imported a part geometry file. If a block parameter changes, you must refresh the visualization pane (by clicking the button) in order to create or edit a frame.
A custom frame is fully defined when its origin and axes are too. Of these, the axes require the most care. You must specify two axes, one primary and one secondary. The primary axis defines the plane (that normal to it) on which the other axes must lie. The secondary axis is merely the projection of a selected direction—axis or geometry feature—on that plane.
The remaining (and unspecified) axis is set by requiring that all three be perpendicular and ordered according to the right-hand rule. Naturally, the secondary axis must have a vector component perpendicular to the primary axis. If the two are parallel, the frame is invalid. If the frame is then saved, its orientation is set to that of the reference frame.
To use a geometry feature for the frame origin or axis definitions:
In the frame creation pane, select the Based on Geometric Feature radio button.
In the solid visualization pane, click a vertex, edge, or face. Zoom in, if necessary, to more precisely select a feature.
Again in the frame creation pane, click the Use Selected Feature button.
It is common in a model to parameterize blocks in terms of MATLAB variables. Instead of a scalar, vector, or string, for example, a block parameter will have in its field the name of a variable. The variable is defined elsewhere, often in a subsystem mask or in the model workspace, sometimes by reference to an external M file.
This approach suits complex models in which multiple blocks must share the same parameter value—a common density, say, or color, if defined as an RGB vector. When the MATLAB variable definition then changes, so do all block parameters that depend on it. Consider using MATLAB variables here if a parameter is likely to be shared by several blocks in a large model.
(For a simple example with solid blocks parameterized in terms of workspace
variables, open the
Exporting Geometry Properties
The File Solid block can generate a convex hull geometry representation of an imported CAD file in the Simscape Multibody environment. This geometric data can be used to model spatial contact forces.
As shown in the figure, the convex hull geometry is an approximation of the true geometry. Note that the block calculates the physical properties, such as mass and inertia, based on its true geometry.
R — Reference frame
Frame by which to connect the solid in a model. The frame node to which this port connects—generally another frame port or a frame junction—determines the position and orientation of the solid relative to other components. Add a Rigid Transform block between the port and the node if the frames they represent must be offset from one another.
File Name — Name of the part model file to import
custom character vector
Name and extension of the part model file to import. If the file is
not on the MATLAB path, the file location must be specified. The file
location can be specified as an absolute path, starting from the root
directory of the file system—e.g.,
'C:/Users/JDoe/Documents/myShape.STEP'. It can
also be specified as a relative path, starting from a folder on the
Unit Type — Source for solid geometry units
From File (default) |
Source of the solid geometry units. Select
File to use the units specified in the imported file.
Custom to specify your own
Unit — Length units in which geometry coordinates are specified in the imported file
m (default) |
Length units in which to interpret the geometry defined in a geometry file. Changing the units changes the scale of the imported geometry.
Convex Hull — Generate a convex hull representation of the true geometry
off (default) |
Select Convex Hull to generate a convex hull representation of the true geometry. This convex hull can be used for contacts by connecting the Spatial Contact Force block.
To enable this option, select Convex Hull under the Export.
Type — Inertia parameterization to use
Geometry (default) |
Point Mass |
Inertia parameterization to use. Select
Mass to model a concentrated mass with negligible
rotational inertia. Select
Custom to model a
distributed mass with the specified moments and products of inertia. The
Calculate from Geometry,
enables the block to automatically calculate the rotational inertia
properties from the solid geometry and either density or mass.
Based on — Parameter to base inertia calculation on
Density from File (default) |
Custom Density |
Parameter to use in inertia calculation. The block calculates the inertia tensor from the solid geometry and the parameter selected.
Use the default setting of
File to base the calculations on the density obtained
from the imported file. (Note that only some formats can carry density
data. Of those that do, only some will actually carry it. Often this
data is specified in a CAD application before saving or exporting the
part model file.)
Custom Density to specify a density
other than that obtained from the imported file. Use
Mass to instead specify the total mass of the
Density — Mass per unit volume of material
1000 kg/m^3 (default)
Mass per unit volume of material. The mass density can take on a positive or negative value. Specify a negative mass density to model the effects of a void or cavity in a solid body.
Derived Values — Display of calculated values of mass properties
Display of the calculated values of the solid mass properties—mass, center of mass, moments of inertia, and products of inertia. Click the Update button to calculate and display the mass properties of the solid. Click this button following any changes to the block parameters to ensure that the displayed values are still current.
The center of mass is resolved in the local reference frame of the solid. The moments and products of inertia are each resolved in the inertia frame of resolution—a frame whose axes are parallel to those of the reference frame but whose origin coincides with the solid center of mass.
The option to calculate and display the mass properties is active
when the Inertia > Type block parameter is set to
Type — Graphic to use in the visualization of the solid
From Geometry (default) |
Choice of graphic to use in the visualization of the solid. The
graphic is by default the geometry specified for the solid. Select
Marker to show instead a simple graphic
marker, such as a sphere or cube. Change this parameter to
None to eliminate this solid altogether
from the model visualization.
Marker: Shape — Shape of the marker to assign to the solid
Sphere (default) |
Shape of the marker by means of which to visualize the solid. The motion of the marker reflects the motion of the solid itself.
Marker: Size — Width of the marker in pixels
10 (default) | scalar with units of pixels
Width of the marker in pixels. This width does not scale with zoom level. Note that the apparent size of the marker depends partly on screen resolution, with higher resolutions packing more pixels per unit length, and therefore producing smaller icons.
Visual Properties — Parameterizations for color and opacity
Simple (default) |
Parameterization for specifying visual properties. Select
Simple to specify color and opacity.
Advanced to add specular highlights,
ambient shadows, and self-illumination effects. Select
File if the imported file has color data and you want
to use it in the model.
(Only some file formats allow color data. In those that do, that data is often optional. If your file does not specify color, the solid will take on a gray hue (the default solid color). Select another parameterization to customize color in such cases.)
Show Port R — Show reference frame port for connection to other blocks
on (default) | off
Select to expose the R port.
New Frame — Create custom frame for connection to other blocks
Click the Create button to open a pane for creating a new body-attached frame. In this pane, you can specify the name, origin, and orientation for the frame.
To name the custom frame, click the text field of the Frame Name parameter. The name identifies the corresponding port on the solid block and in the tree view pane of the Mechanics Explorer.
To select the Frame Origin of the custom frame, use one of the following methods:
At Reference Frame Origin: Make the new frame origin coincident with the origin of the reference frame of the solid.
At Center of Mass: Make the new frame origin coincident with the center of mass of the solid.
Based on Geometric Feature: Make the new frame origin coincident with the center of the selected feature. Valid features include surfaces, lines, and points. Select a feature from the visualization pane, then click Use Selected Feature to confirm the location of the origin. The name of the origin location appears in the field below this option.
To define the orientation of the custom frame, under the Frame Axes section, select the Primary Axis and Secondary Axis of the custom frame and then specify their directions.
Use the following methods to select a vector for specifying the directions of the primary and secondary axes. The primary axis is parallel to the selected vector and constrains the remaining two axes to its normal plane. The secondary axis is parallel to the projection of the selected vector onto the normal plane.
Along Reference Frame Axis: Selects an axis of the reference frame of the solid.
Along Principal Inertia Axis: Selects an axis of the principal inertia axis of the solid.
Based on Geometric Feature: Selects the vector associated with the chosen geometry feature of the solid. Valid features include surfaces and lines. The corresponding vector is indicated by a white arrow in the visualization pane. You can select a feature from the visualization pane and then click Use Selected Feature to confirm the selection. The name of the selected feature appears in the field below this option.
FrameN — Edit or delete existing custom frame
Frames that you have created.
N is a unique identifying number for each
Click the text field to edit the name of an existing custom frame.
Click the Edit button to edit other aspects of the custom frame, such as origin and axes.
Click the Delete button to delete the custom frame.
To enable this parameter, create a frame by clicking New Frame.
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