# Recent Improvements in the Development of Soft Grippers
## 3 Dexterous Manipulation
### Achieving Dexterity for Soft Grippers
#### 3.2.1 Stable Grasping  
To stably manipulate an object, the gripper must be able to grasp it stably. Various strategies have been implemented in order to ensure a stable grip. This part of the article presents some techniques reported in the literature.  
Optimization is often a means to achieve dexterity for soft grippers. In [60], the design and performance are optimized by performing a characterization test on casted fingers and comparing the joint displacements with an equivalent simulation set up in the SOFA framework [43] for setup validation. Topology optimization is applied in [61; 62] to design new soft fingers capable of grasping various objects. The grasping force and the loading capacity are other characteristics that can be optimized by investigating the effects of the design parameters as explained in [63].  
The number of bending segments and, hence, the level of actuation play an important role in the type of grasps achieved. Achieving pinch grasps requires at least two independent bending segments, and actuating the proximal segment lets the fingers achieve precision grasps while uniform actuation, i.e., actuating both proximal and distal segments, allows for power grasps [64]. The fingers of the gripper in [65] contain two independently actuated sections that are aligned on the same axis, making them capable of complex deformations. Adaptive grasping is made possible for the gripper in [66], which also contains two-segment soft fingers. The self-adaptive fingers presented in [67] can adaptively grasp objects and achieve precise angle positioning. They are actuated by tendons which can move two joints independently by controlling two motors.  
Soft grippers often integrate active palms that provide firm support and stabilize the grip, as discussed in [66]. The hand proposed in [68] has three actuators in its palm, which confers it with large range motions and force capability. The palm of the bionic soft hand in [69] is capable of mimicking the elongation of the muscles on the back of the human hand, thereby modifying its curvature.  
Structure hybridization was previously presented as a way to improve grippers' performances in Section 2.4. The grippers in [62; 63; 70] combine soft and rigid structures to achieve stable grasping. The gripper in [70] integrates rigid fingernails. The authors proved their hypothesis that rigid fingernails improve precision grasping. The harder outer layers of the pneumatic actuators in [62] impose constraints on the grasped objects, allowing the gripper to perform various grasping tasks. The palm of the soft hand in [69] combines pneumatic actuation with particle jamming, making it capable of stiffness variation, hence improving grasp stability.  
Fiber-reinforced air chambers whose cross-section has an ellipse shape reducing the material stress at their edges [65], making the gripper capable of reliably grasping objects of varied shapes and sizes while overcoming external disturbances. The flexion movement of the three palm actuators in [68] was enhanced and constrained with a proposed novel elastic fiber reinforcement.  
A motion planning algorithm could also improve grasping stability. In [71], an autonomous motion planning algorithm which encapsulates the object shape and position allows the gripper to autonomously grasp and place a variety of objects at random positions in the system's workspace.