CAE-04.ppt

1、Motion Simulation,CAE Application: Motion Simulation,Joint,Joints are what join the mechanisms links so they can move in a cohesive manner. In addition to permitting movement, joints can also restrict or constrain movement between links.,Revolute,Slider,Universal,Cylindrical,Planar,Screw,Fixed,Spher

2、ical,Before joints are created, the links within a mechanism “float” unconstrained in space with six degrees of freedom (DOF): 3 degrees of translation (the X, Y, and Z directions) and 3 degrees of rotation (about the X, Y, and Z axes). When a joint is created, freedom of movement is restricted or c

3、onstrained in one or several of these directions/rotations. The concepts of joint constraints and degrees of freedom within a mechanism lead to what is known as a mechanisms Gruebler count. For now, it is important to remember that joints serve a dual purpose: to allow desired motion and/or to restr

4、ict undesired motion.,Select the link(s) the joint is to constrain. Locate the Origin(s) of the joint on the link(s). Specify the Orientation(s) of the joint on the link(s).,Steps of creating joints,Limits Allow you to limit a joints range of motion. Friction Allow you to model energy loss due to he

5、ating when two parts move while in contact with each other. Including friction in your analysis is useful for situations when this energy loss is enough to change the behavior of the mechanism. Joint friction will be covered in detail in a later lesson. Driver Type Allow you to define the motion dri

6、ver to be applied to the joint. Motion drivers will be covered in detail later in this lesson. Display Scale Control the relative size of the Joint icon displayed on the graphics window. Name Allow you to specify a name for the joint.,Parameters of joint,A mechanisms Gruebler count is an approximati

7、on of the total degrees of freedom (DOF) that exist within a mechanism. This value is displayed in the status line on the graphics screen after a joint has been created. This value will decrease (approach 0) after each joint is created with a link or links. Gruebler count = (number of links * 6) - (

8、sum of DOFs removed by joints or other constraints) - (number of motion drivers),Gruebler count,Greater than zero indicate freedom of movement Within the mechanism. An under-constrained mechanism will have freedom of movement that lends itself to a true Dynamic solution. Equal to zero indicate a mechanism that is fully constrained. Modeling a mechanism to zero DOF (Gruebler Count = 0) was a principal goal when motion analysis was limited to kinematic solutions. Less than zero indicate a mechanism that is over c