**2. Hyper-redundant mechanisms**

Modern surgical robots have been designed and implemented to help surgeons in operations requiring high dexterity and minimal invasiveness. Although great versatility and control have been realized using large, rigid, and serial-link robots such as Da Vinci, catheter-type robotic platforms having smaller dimensions can present an alternative and less expensive solution especially for minimally invasive surgery [3].

In conventional medical use, catheters are manually controlled devices for diagnosis, drug delivery, and basic operations which do not require intricate motion patterns or application of a well-controlled force on the surgical site. Catheters often have a tendon-driven guidewire and a sheath to cover the guiding mechanism which may or may not feature a surgical head/clipper or a micro-mechanism to operate on sensitive tissues. Although originally being passive medical devices, the catheters can be re-designed to gain features such as

**3**

*Safe Human-Robot Interaction Using Variable Stiffness, Hyper-Redundancy, and Smart Robotic…*

multiple degrees of freedom, mobility, controllability, and perception. With these improvements in their structure, the catheters can become autonomous or semiautonomous surgical platforms which can travel in difficult passages in the human body without harming the inner tissues and help the operation itself to be more

Most of the hyper-redundant or piecewise continuum structures still use rigid or semirigid backbones or general frames. Recently proposed hyper-redundant modular structures can be found in [4–6]. In [4], high dexterity and stiffness requirements are met, whereas the design has poor flexibility, limited compliance, and intricate mechanical structure which can be difficult to miniaturize for medical applications. Other prototypes can feature stiffness control [5] but may fall short in module-based controllability. It is even possible to see applications with better control [6] featuring continuum elastic backbone while segmenting the structure into modules using coupling plates; however, the size and compactness criteria are not fulfilled. The cable-driven structures are lightweight and compact, but there is an inherent limitation of such mechanisms due to cable friction and interdependency between the sections of the modules. As the limitations and drawbacks of such mechanisms are given, in the next section the advantages are highlighted to

The main idea of a hyper-redundant robotic platform with a modular building block is to increase the controllability and maneuverability of the robot. Increasing the number of DOF seems to be the main advantage; however, it is surpassed by the fully continuous robot (i.e., tubular/telescopic pre-curved continuum robots) that can be manipulated in 3D space without the need of complicated inverse kinematic calculations due to their inherent compliancy. Although fully continuum robotic platforms have this advantage, for most of the cases, the segment-based local control is not possible to obtain, and in most of the continuum prototypes despite their inherent compliancy, the stiffness control is not possible. Therefore, in this section, we would like to highlight the modular hyper-redundant robotic designs that can offer segment-based position control as well as adjustable stiffness. When the robotic catheter has both the position and the stiffness control, the navigation of the robotic catheter inside the torturous channels becomes an optimal control problem where the position and force are controlled with varying priorities according to the path planning and the operation task. This greatly increases the inherent safety of the robotic catheter. In the following section, designed mechanism modules are

A recent hyper-redundant manipulator can be found in [7] which has electromagnetically actuated manipulator. Early examples of hyper-redundant manipulators with full solution on kinematics and dynamics are given in [8–10]. However, control algorithms suggested for such mechanisms are still in progress. For exam-

In this section, the design of hyper-redundant and modular robotic structures is detailed by emphasizing the functional properties such as independent module/ segment controllability and variable-adjustable stiffness. The proposed designs [12] are aimed at improving both position and force control of such structures employing whole-body shape control and local stiffness control in the robotic catheter.

*DOI: http://dx.doi.org/10.5772/intechopen.92693*

successful with superior position and force control.

draw attention to their potential in medical robotics.

**2.1 Advantages: modularity and controllability aspects**

introduced and compared using workspace and stiffness analysis.

**2.2 Example applications of hyper-redundant mechanisms**

ple, a modular control scheme is proposed in [11].

*Safe Human-Robot Interaction Using Variable Stiffness, Hyper-Redundancy, and Smart Robotic… DOI: http://dx.doi.org/10.5772/intechopen.92693*

multiple degrees of freedom, mobility, controllability, and perception. With these improvements in their structure, the catheters can become autonomous or semiautonomous surgical platforms which can travel in difficult passages in the human body without harming the inner tissues and help the operation itself to be more successful with superior position and force control.

Most of the hyper-redundant or piecewise continuum structures still use rigid or semirigid backbones or general frames. Recently proposed hyper-redundant modular structures can be found in [4–6]. In [4], high dexterity and stiffness requirements are met, whereas the design has poor flexibility, limited compliance, and intricate mechanical structure which can be difficult to miniaturize for medical applications. Other prototypes can feature stiffness control [5] but may fall short in module-based controllability. It is even possible to see applications with better control [6] featuring continuum elastic backbone while segmenting the structure into modules using coupling plates; however, the size and compactness criteria are not fulfilled. The cable-driven structures are lightweight and compact, but there is an inherent limitation of such mechanisms due to cable friction and interdependency between the sections of the modules. As the limitations and drawbacks of such mechanisms are given, in the next section the advantages are highlighted to draw attention to their potential in medical robotics.

#### **2.1 Advantages: modularity and controllability aspects**

The main idea of a hyper-redundant robotic platform with a modular building block is to increase the controllability and maneuverability of the robot. Increasing the number of DOF seems to be the main advantage; however, it is surpassed by the fully continuous robot (i.e., tubular/telescopic pre-curved continuum robots) that can be manipulated in 3D space without the need of complicated inverse kinematic calculations due to their inherent compliancy. Although fully continuum robotic platforms have this advantage, for most of the cases, the segment-based local control is not possible to obtain, and in most of the continuum prototypes despite their inherent compliancy, the stiffness control is not possible. Therefore, in this section, we would like to highlight the modular hyper-redundant robotic designs that can offer segment-based position control as well as adjustable stiffness. When the robotic catheter has both the position and the stiffness control, the navigation of the robotic catheter inside the torturous channels becomes an optimal control problem where the position and force are controlled with varying priorities according to the path planning and the operation task. This greatly increases the inherent safety of the robotic catheter. In the following section, designed mechanism modules are introduced and compared using workspace and stiffness analysis.

#### **2.2 Example applications of hyper-redundant mechanisms**

A recent hyper-redundant manipulator can be found in [7] which has electromagnetically actuated manipulator. Early examples of hyper-redundant manipulators with full solution on kinematics and dynamics are given in [8–10]. However, control algorithms suggested for such mechanisms are still in progress. For example, a modular control scheme is proposed in [11].

In this section, the design of hyper-redundant and modular robotic structures is detailed by emphasizing the functional properties such as independent module/ segment controllability and variable-adjustable stiffness. The proposed designs [12] are aimed at improving both position and force control of such structures employing whole-body shape control and local stiffness control in the robotic catheter.

**Figure 2.**

*Modules for hyper-redundant backbone construction, from left to right: Hybrid module, radially reconfigurable 3x SPS parallel kinematic mechanism, and seahorse tail section, featured in [12].*

Three different module designs for hyper-redundant mechanisms are depicted in **Figure 2**. The first mechanism is called "hybrid" and essentially a universal joint placed in between two parallel plates and supported by a concentric shaft. This mechanism has three DOF per module, having pan and tilt for adjusting the heading angle while using the translational movement to shrink or elongate while adjusting its stiffness.

The second mechanism is 3x SPS having spherical-prismatic-spherical joints in each strut and is essentially a reconfigurable parallel mechanism. This mechanism provides stiffness adjustments by relocating the connection points of the struts on the lower plate. The struts can also elongate and contract along their axis so that the hyper-redundant platform can be adjusted when passing along difficult cavities.

Finally, the last module is named after the seahorse tail since it is inspired by the cross section of the biological counterpart. This mechanism can radially contract and widen to mimic the function of oblique muscles in seahorse tail structure. The modules are connected by a spherical joint in the middle. Since the radial struts are spring-loaded, the radial stiffness can be adjusted.

The main advantage of hyper-redundant mechanisms is that each segment can be controlled separately, and the multi-degree-of-freedom makes it possible to control the whole-body shape of the manipulator to reduce the risk of harming the tissues during the navigation task. If the modules also have variable stiffness or re-configurability as it is shown here, the versatility and the safety of the hyperredundant platforms increase. Since robotic platforms should accomplish tasks such as navigation, diagnosis, and operation, they may have to support different levels of stiffness when required. This type of adjustability can be achieved via special actuators as well. The next section expands on this view by supporting these mechanisms with variable stiffness actuators.
