  Safe yet stable grasping requires a robotic hand to apply sufficient force on
the object to immobilize it while keeping it from getting damaged. Soft robotic
hands have been proposed for safe grasping due to their passive compliance, but
even such a hand can crush objects if the applied force is too high. Thus for
safe grasping, regulating the grasping force is of uttermost importance even
with soft hands. In this work, we present a force controlled soft hand and use
it to achieve safe grasping. To this end, resistive force and bend sensors are
integrated in a soft hand, and a data-driven calibration method is proposed to
estimate contact interaction forces. Given the force readings, the pneumatic
pressures are regulated using a proportional-integral controller to achieve
desired force. The controller is experimentally evaluated and benchmarked by
grasping easily deformable objects such as plastic and paper cups without
neither dropping nor deforming them. Together, the results demonstrate that our
force controlled soft hand can grasp deformable objects in a safe yet stable
manner.
