CATIA Kinematics: Rigid Joints vs. Dressups

Both Rigid Joint and Dressup tools can be used to attach an object to a moving part in a CATIA mechanism, so that the object moves along with the part it is attached to.

Consider the example of the Vise assembly shown below. The kinematic mechanism consists of three parts: the Base, the Screw, and the Jaw. The Screw joint between the Base and the Screw is angle-driven, so that the Screw translates along its axis when rotated. The Prismatic joint defines the sliding motion of the Jaw along the Base, and the Point-Surface joint makes the Screw either push or pull the Jaw.

At this point, the Handle, the Plate, and the M4 Screws are not included in the mechanism. Therefore, when the mechanism is simulated, those parts don’t move, making the Handle separate from the Screw and the Plate separate from the Jaw.

The first method for attaching the parts to the mechanism involves using Rigid joints.

Select  (Rigid Joint) icon, select the Handle and the Screw parts, then click OK. This joint will make the Handle move along with the Screw.

Create three more Rigid joints, per the table below.

Simulate the mechanism and note that now the Handle, the Plate, and both M4 Screws move along with the parts they are attached to.

The second method involves using the Dressup feature.

Delete all four Rigid joints. Select  (Mechanism Dressup) icon to open the Mechanism Dressup dialog box.

Click the New Dressup button, select your mechanism, and click OK to return to the Mechanism Dressup dialog box.

Select the Screw part in the pull-down list at the top of the dialog box, the Handle part in the list of Available products, then click the arrow to move the Handle into the Products attached to link area. This will effectively attach the Handle to the Screw, similarly to the Rigid Joint.

The dialog box displays as shown below.

Select the Jaw part in the pull-down list at the top of the dialog box and add the Plate and both M4 Screws to the Products attached to link area, which will attach the Plate and the screws to the Jaw part. Note that to achieve the same result with the Rigid Joints, we had to create three separate Rigid Joints.

Simulate the mechanism and note that all parts move as intended.

As you have seen, both methods work well, but – which method should you choose? The answer is – it depends on how many parts you need to attach to your mechanism.

Because a Rigid joint can only involve two parts, a separate Rigid joint must be created for each pair of the connected parts. Therefore, when you need to attach multiple parts, the setup process could be quite tedious and time consuming, and the preferred method would be to use the Dressup feature.

Should you wish to learn more about Kinematics in CATIA, the workbench is covered in detail in the ENOVIA: DMU Kinematics training class.

About the Author

Senior Technical Training Engineer<br><br>As a senior member of the Rand 3D team with a doctorate degree in Finite Element Analysis (FEA) and over 35 years of experience, Iouri provides design, consulting, and training services to those in the aerospace, automotive, electronics, and consumer goods industries. Iouri is a seasoned pro in 3D parametric design and prototyping using knowledge-based engineering methods, and has worked on a wide range of projects including BOM automation, CMM points generation, automated 3D annotation creation, and die tooling automation design. He is also a sought-after instructor and holds the designations of both CATIA Certified Professional (Expert level) and CATIA Certified Instructor.

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