While making an animation which animating one or double hand linked to another object we use IK targets. Linking an IK target saves us from animating objects seperately such as holding sword, rotating a car wheel etc. For sword example, mostly the position and rotation of the sword matters, not the hands. So when animating a sword, we expect that hands follow the sword handle by keeping their position on the sword.
I will explain it with a basic human CAT object. For ones who dont know how to create a CAT object, it can be found below Create Panel> Helpers> CAT Object
If you successfully create the human figure click Motion Panel. You will find the Layer Manager as you can see in left picture. Press and hold the button which I marked with red and release the button on Abs (Absolute Layer). Then press Setup/Animation Mode Toggle button so it will transform from red stop image to green play image.
Select any hand bone. If hand bone selected in the figure, you will see the Limb Animation rollup in Motion Panel. The button which I marked with red, creates the Target Point we need. You should press this button for each hands for this tutorial. If you did it right a cross must show up just front of the hands.
If you move this crosses, hands wont follow it. We will solve it very soon. Now its time to positioning the hands. I created a very basic sword for demonstration as you can see below.
I moved the hands until it looks like the figure is holding the sword with two hands but targets are still keeping their position.
Below the Limb Animation rollup, inside the IK System tab click the button which says Move IKTarget to Palm. This button will relocate the targets to the place where they have to be. Below this tab there are three scrolls as you can see in left picture. The scroll which says IK/FK must be “0,0”. Now the hands will follow the targets. So link the targets to the sword. Now the hands will moved by sword. Try to rotate or move the sword. If you didn’t miss anything, your animation must work well. I showed a picture below when my figure holds the sword.
Tip: After creating the sword, move the pivot point to the middle of the hands. When you rotate the sword the hands will animate very realistic.
For another example the figure below move its hands as the wheel rotates.
I hope it was helpful. If you have any questions leave a comment.