Abstract: A gripper assembly is provided for use in an autonomous mobile robot for grabbing and holding an object to be transported by the robot. The gripper assembly includes two rotatable shafts and two counter-rotating flippers, each fixedly connected to a different one of the rotatable shafts for engaging the object on opposite sides thereof. The gripper assembly also includes two drive elements, each engaging a different one of the rotatable shafts. Two drive arms engage the two drive elements to transfer torque and rotation from each drive arm to a respective drive element and rotatable shaft to open or close a respective flipper around the object. Each drive element can be disengaged from a respective drive arm and then rotated in order to adjust a radial position of a respective rotatable shaft and flipper relative to the drive arm so that objects of different sizes can be accommodated.