## 3 Soft Robot Design Overcoming Challenges in Sensor Integration  
### Considerations for the Design of Soft Surgical Robots Integrated with Sensory Capabilities  
Flexible and soft manipulators have promising applications in minimally invasive surgery as they allow surgical tools to reach targets that are inaccessible with conventional rigid surgical instruments. However, a principal challenge in the implementation of such devices is controlling their pose and it is with this in mind that we discuss our approach to creating a soft robotic device for use in minimally invasive surgery (MIS). Our designs aim to address the requirements outlined in Section 2, a key feature being the robot's capacity to have sensors embedded within it without impacting on the robot's \"softness\". Our soft robot manipulator is based on designs developed during the EU project STIFF-FLOP. It is made of silicone rubber and equipped with pneumatic actuation chambers to enable bending in any direction away from the longitudinal robot arm axis. What makes a soft robot'soft' is the selection of materials used in the production of its main body (Rigid-bodied robots are sometimes called \"soft\" when in fact they would be better described as \"compliant\". Compliance can be achieved through various compensatory mechanisms using smart sensors and compensatory algorithms. For the purposes of this paper, however, \"soft\" means physically soft). Traditional robots are made of rigid materials, their stiff parts interacting with each other in a well-defined way, and within well-defined constraints, by way of mechanisms composed of rigid links and stiff joints. Most roboticists are well versed in determining the dynamics and kinematics of rigid robotic systems and are able to create rigid robots that are both precise and reliable. These are not however infallible, and accidents still happen, and the stiffness of these devices' components is often a factor [20]. Soft robots offer certain advantages, in particular in relation to safety and physical adaptability or deformability--a characteristic that clearly reduces its impact, during any collision, upon an external object [21]. This natural compliance also helps to compensate for any minor control inadequacies on the part of the robot [22; 23], see Figure 2.  
With a soft robotic device, motion can be distributed across its entire body. Because of the compliant properties of the material, an entirely new level of dexterity becomes achievable. Of course, this is not without its challenges. The lack of stiffness, for example, makes the kinematics and dynamics of the soft robot significantly more complex than that of its rigid counterpart, especially during the interaction with the environment [24]. Similarly, precise control of a soft robot's movement and its positional tracking are also rendered more difficult. The reason for this is that while the rigid robot has a strictly limited  
Figure 2: A soft robotic hand with a simple binary controller is naturally able to adapt, when handling delicate objects [22]. number of degrees of freedom, its soft equivalent, thanks to its distributed deformation properties, has a virtually infinite number. The inverse kinematics required for calculation of input control parameters therefore become considerably more complex, and numerical solutions can be slow and difficult to compute. One possible solution to these problems is to use simplified kinematic models, such as constant curvature or beam-based models [25] and to carefully track the state of the soft robot, collecting a constant stream of data with which to create a feedback loop. This, however, is dependent on integrating greater sensing capabilities into the robot. An immediate problem arises, as current sensors that have been created for use in rigid structures, cannot be transposed into soft structures. They are themselves rigid devices that are usually attached to the body of a rigid robot, collecting data on joint and associated link movements.