# Catia Kinematics problem - Mechanism Simulation

#### MechEngFta

##### New member
Hello,
I am new to this forum and beginner in Catia. I have a problem and I need your valuable help! I designed a gripping mechanism, and I am in the process of creating the joints in order to simulate its motion, but for some reason it doesn't work the way I want it to. I am attaching a pic with the design so far
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I hope it does get uploaded...So, I have made rigid joints between parts 5, 6, 7, 8, 9, 10 and the screw. (I am only describing one side, the other side is mirrored obviously...)And I have added a cylindrical joint between the screw and part 1(I want it to move only linearly though). Part 1 and rod 11 have a rigid joint as well, and so do part 2 and rod 12. Then I created a revolute joint between 11 and 2, and between 12 and 3. So far so good. It moves perfectly. Then, I wanted to make a revolute joint between 3 and 9 but it wont let me go on with the simulation any more. It says "The created command has no effect on the degree of freedom of the mechanism". The motion I want it to perform is this. As part 1 goes linearly up and down, part 15 closes and opens. rod 9 is fixed and part 3 revolves around it. Do you have any idea how I can fix that?

#### MrCATIA

##### Super Moderator
Sorry for the delay. I don't have access to the Kinematics workbench to verify this for you. I hope you have this working by now. But if not, my comments below are based on the picture you attached.

a. To simplify the mechanism, I suggest ignoring (hide) all the pins (8, 9, 11, 12, 13 & 14). Just add a revolute joint between the holes in each set of linked parts. Once you get this working, you can add the pins later as rigid to their mating part.

b. I agree with you that parts 5, 6, 7, 8, 9 & 10 are all rigid to each other. Are these parts also fixed (do not move)?

c. The screw is not rigid to parts 5, 6, 7, 8, 9 & 10. The screw has to rotate about parts 6 & 7 and 1.

d. The screw must be engaged with a threaded hole, but I'm not sure if the threaded hole is in part 1 or parts 6 & 7. Could you please clarify this. Whichever part does not contain the threaded hole must have a clearance hole.

e. I'm surprised you were able to validate the screw portion of the mechanism (you said "it moves perfectly"). How were you able to get part 1 to move up and down without having a screw joint? Which part is fixed and which part/joint is the input command?

f. The picture shows several joints on the left-side. I would delete those until you get the right-side working.

g. After you added the revolute joint to part 3, I would suggest adding the other revolute joints to parts 3 & 15, 15 & 4 and 4 & 5 to "close the loop" and then try the simulation.

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