Mechanism Design and Mechanism Dynamics > Mechanism Dynamics > Mass Properties > About the Mass Properties Dialog Box
About the Mass Properties Dialog Box
Click Mass Properties to open the Mass Properties dialog box and define or change mass properties for your mechanism. Select the type of mechanism and the method used to specify the mass properties.
Reference type—Select one of the following entities from the list:
Part or Top-Level Layout—You can select any part in the assembly, including component parts of subassemblies, to specify or review its mass properties.
Assembly—You can select a component subassembly or a top-level assembly from the graphics window or from the Model Tree. You can assign mass properties or edit existing ones.
Body—Mass properties of the selected body can be reviewed but not edited.
Define properties by—Select a method to define mass properties. Your options differ depending on the reference type selected.
Default—This option, for all three reference types, causes all input fields to remain inactive. The dialog box displays mass property values based on the density or mass properties file defined in Creo Parametric. If neither have been assigned to the model, default values are displayed.
Density—If you have selected a part or an assembly as the reference type, you can define mass properties by density. Because density is the ratio of the mechanism's mass to its volume, you can only select a part or an assembly with a volume greater than zero. When you select this option, all input fields except Density remain inactive.
Mass properties—If you have selected a part as the reference type, you can define mass, center of gravity, and moment of inertia.
Coordinate system—Use to select a coordinate system for the part or body. This option is not available if you select an assembly as the reference type.
The dialog box changes depending on your previous selections. If you have selected a body as the reference type, the following items remain inactive and you can only review them. If your selection is an assembly, you can only see the Density field on the dialog box. When you change the entries in any of the following text boxes, dependent values are automatically updated.
Density—Enter a density value for the selected part or assembly when you define mass by the density.
Volume—The volume of the selected mechanism cannot be edited.
Mass—Enter a mass value for the selected part when defining its mass by the mass properties.
Center of gravity—Define the location of the center of gravity with respect to a specified coordinate system. Center of gravity is an imaginary point in the mechanism where, for convenience in certain calculations, the total mass of the mechanism is considered concentrated.
Inertia—Use this area to calculate the moment of inertia. Moment of inertia is a quantitative measure of the rotational inertia of the mechanism–in other words, the tendency of a body rotating about a fixed axis to resist a change in this rotating motion. You can select one of the following locations for the axis about which the selected mechanism rotates:
At coordinate system origin—Measures the moment of inertia relative to the current coordinate system.
At center of gravity—Measures the moment of inertia relative to the principal inertial axis of the mechanism.