Someone with a significant background in robotics once told my daughter that robotics is always harder than it looks. She is now studying to be a mechanical engineer and will likely be stealing my copy of this book as soon as I let go of it. The quote is very applicable to something that sounds as simple as a robot grip.
A robotic gripper is likely found at the end of a robotic arm. The arm is its own problem but the grip can be equally complex. This book tries to tackle a wide range of grip designs. While it covers very articulate designs, they are concentrated on grips that would be useful in production environments rather than a more complex replication of a human hand.
It starts with a definition of the kinds of gripping methods including impactive, ingressive, contigutive and astrictive. The book then goes into great detail about forces, uses, and operation of various implementations complete with an extensive set of mechanical and electrical schematics that are easy to understand for anyone that understands basic physics.
The books seems exhaustive in it coverage of grippers, delving into materials and mating details that more novice designers might overlook. It addresses more advanced topics such sensors and multiple grip systems.
If you are working with any aspect of robotics that will deal with a gripper in some fashion then this book will definitely help. I have yet to see one that is better.