# Force calculation - Gripper (Torsion Spring)

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1. Nov 24, 2014

### psugumaran

Hi,

Currently I am working on a project to find out the force required to open/close the gripper for holding a circular tube. I have used torsion spring between the two gripper and it will work like a clip. The circular tube is SS316 and the gripper is made out of Aluminium 6061.

Stainless tube 316 OD = 30mm and ID=20mm (Attached figure for reference) length of the tube = 100mm

#### Attached Files:

• ###### Torsion spring_Calculation.JPG
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Last edited: Nov 24, 2014
2. Nov 24, 2014

### OldEngr63

If I correctly understand your figure, the force on the spring depends on the way you preload the spring which is a function of the unloaded versus loaded spring geometry. Your figure shows the loaded geometry, but not the unloaded geometry, so there is not enough information to evaluate the spring force.

3. Nov 24, 2014

### psugumaran

Thanks for your reply. You are right, spring is preloaded when the gripper is in closed position. The gripper has to be opened by manual pressing (finger) force then the circular tube is pressed into the gripper to hold it in position (Attached Figure for reference)
I thought of using double torsion spring in the gripper, It will work like opening and closing of hair clip. Hope this will give you a clear idea.

#### Attached Files:

• ###### Gripper opening_Torsion.JPG
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4. Nov 25, 2014

### OldEngr63

There is still not enough information to calculate the spring load.

It all depends on how the spring is made.

For example, the spring could be made such that, with the gripper closed, there is no force in the spring and consequently no contact force between the gripper and the tube (even though the gripper is "closed.")

For a second example, with a spring made differently, with nothing in the gripper (no tube), the ends of the gripper could be pressed together with some very high force, and when the tube is inserted, an even higher contact force will develop.

It all depends upon how the spring is made (as I think I said previously).