How to make the arm grip the ball?

Hey Everyone i am trying to learn and apply reinforcement learning in robots using simulation but i just cant figure out how to make the arm pick up the ball?

I have made the rewards to reach till the ball (force lock the claw to open position before it) and then allowing it to close its claw when it reaches it approx destination
if the ball is lifted for like 5 cm i reward it. but the arm just doesnt lift the ball and reward stays constant and arm just cant lift the ball