**3. Functional complex by a differential mechanism**

An overview of the screw-drive-type in-pipe robot that we first introduced [12] is illustrated in **Figure 2**. This in-pipe robot consists of a front rotator that generates thrust and a rear stator that supports the reaction of the rotator. The rotator has several tilted passive wheels arranged on its circumference and can move forward and backward while tracing a spiral curve.

By arranging a motor and a gear reduction along the pipe axis, the output drive axis can be connected directly to the rotator without changing the direction of rotation through a transmission mechanism, such as a miter. This implies that the screw-drive type can be miniaturized easily, although it would face difficulty passing through T-branches with only a drive mechanism. To solve this challenge, an

**Figure 2.** *Screw-drive in-pipe mobile robot for 5-in pipelines [12].*

active steering joint with a simple miter-geared differential mechanism is installed between the rotator and the stator. The rotator can be swung by only a single actuator in both the longitudinal and lateral directions depending on the in-pipe constraint condition.

Accordingly, the robot can be steered by only a single actuator in both the longitudinal and lateral directions depending on the constraint condition in pipes. Owing to friction, the passive wheels of the middle unit maintain their position during rotation of the steering motor, and the front unit can be swung. Nonetheless, the robot can change its direction of navigation in pipes where steering movement is constrained by the inner wall, e.g., in straight sections. Driven by the orbiting miter gear, the entire middle unit rotates around the central axis; simultaneously, the wheels of the middle unit rotate in the circumferential direction as casters (**Figures 3** and **4**).

Meanwhile, we also developed an in-pipe robot called multi-module parallel arrangement type [13], which has a structure in which multiple belt-driven crawler mechanisms are arranged parallel to the pipe axis and on the circumference. Although it tends to increase in size, a large traction force can be generated by coupling each propulsion force, and the orientation can be changed omnidirectionally by adjusting the speed balance among each module. In this study, we propose a new mechanism called an underactuated parallelogram crawler. We confirm its ability to cope with changes in internal pipe diameter without necessarily an increase in the number of motors (**Figure 5**).

**Figure 3.** *Schematic of the screw-drive in-pipe mobile robot.*

**5**

**Figure 5.**

**Figure 6.**

*(b) Parallelogram mode (arm-lifting).*

*Robotic Search and Rescue through In-Pipe Movement DOI: http://dx.doi.org/10.5772/intechopen.88414*

*Three-module parallel arrangement type in-pipe mobile robot for 8-in pipelines [13].*

To achieve differential motion, a pair of spur gears is mounted on the front flipper of each parallelogram crawler module. With the motion of the front flipper constrained by gravity and the pantograph-spring combining expansion mechanism in a normal driving mode, the motor torque is transmitted to the front driving pulley (**Figure 6a**). The front flipper is lifted up once the motion of the robot is stopped (**Figure 6b**). An additional timing belt in these modes enables the simultaneous rotation of the front and rear flippers. To avoid an endless rotation of the

*Driving mode and parallelogram mode using a spur-geared differential mechanism. (a) Driving mode and,* 

**4. Functional complex by arranging multiple DoFs on a common axis**

On one hand, the screw-drive type can be easily downsized but with an associated limit of travel to pipelines without any junction. On the other hand, the multimodule parallel arrangement type can generate large propulsion by coupling each force but tends to increase in diameter. We thought that the differential mechanism could be one solution for downsizing; however, it leads to the complexity of the whole robot mechanism and eventually causes an increase in size and weight.

flippers, stopper pins are attached to stop at 30°.

**Figure 4.** *Steering mode and rolling mode using a miter-geared differential mechanism.*

*Robotic Search and Rescue through In-Pipe Movement DOI: http://dx.doi.org/10.5772/intechopen.88414*

#### **Figure 5.**

*Unmanned Robotic Systems and Applications*

constraint condition.

number of motors (**Figure 5**).

*Schematic of the screw-drive in-pipe mobile robot.*

active steering joint with a simple miter-geared differential mechanism is installed between the rotator and the stator. The rotator can be swung by only a single actuator in both the longitudinal and lateral directions depending on the in-pipe

Accordingly, the robot can be steered by only a single actuator in both the longitudinal and lateral directions depending on the constraint condition in pipes. Owing to friction, the passive wheels of the middle unit maintain their position during rotation of the steering motor, and the front unit can be swung. Nonetheless, the robot can change its direction of navigation in pipes where steering movement is constrained by the inner wall, e.g., in straight sections. Driven by the orbiting miter gear, the entire middle unit rotates around the central axis; simultaneously, the wheels of the middle unit rotate in the circumferential direction as casters (**Figures 3** and **4**). Meanwhile, we also developed an in-pipe robot called multi-module parallel arrangement type [13], which has a structure in which multiple belt-driven crawler mechanisms are arranged parallel to the pipe axis and on the circumference. Although it tends to increase in size, a large traction force can be generated by coupling each propulsion force, and the orientation can be changed omnidirectionally by adjusting the speed balance among each module. In this study, we propose a new mechanism called an underactuated parallelogram crawler. We confirm its ability to cope with changes in internal pipe diameter without necessarily an increase in the

**4**

**Figure 4.**

**Figure 3.**

*Steering mode and rolling mode using a miter-geared differential mechanism.*

*Three-module parallel arrangement type in-pipe mobile robot for 8-in pipelines [13].*

#### **Figure 6.**

*Driving mode and parallelogram mode using a spur-geared differential mechanism. (a) Driving mode and, (b) Parallelogram mode (arm-lifting).*

To achieve differential motion, a pair of spur gears is mounted on the front flipper of each parallelogram crawler module. With the motion of the front flipper constrained by gravity and the pantograph-spring combining expansion mechanism in a normal driving mode, the motor torque is transmitted to the front driving pulley (**Figure 6a**). The front flipper is lifted up once the motion of the robot is stopped (**Figure 6b**). An additional timing belt in these modes enables the simultaneous rotation of the front and rear flippers. To avoid an endless rotation of the flippers, stopper pins are attached to stop at 30°.

## **4. Functional complex by arranging multiple DoFs on a common axis**

On one hand, the screw-drive type can be easily downsized but with an associated limit of travel to pipelines without any junction. On the other hand, the multimodule parallel arrangement type can generate large propulsion by coupling each force but tends to increase in diameter. We thought that the differential mechanism could be one solution for downsizing; however, it leads to the complexity of the whole robot mechanism and eventually causes an increase in size and weight.

As introduced in the earlier sections, the key point for downsizing is combining the three components (propulsive, steering, and extending) in a common component. To achieve this compact design, we have been working on a multi-linkarticulated wheeled-type in-pipe robot whose wheel shaft (as propulsive) and joint (as steering and extending) are all arranged on the same axis. This configuration leads to a drastic miniaturization to 3–4 in. in the inner diameter of pipes and is even adaptable to winding pipelines and T-branch [14–19].

An overview of the multi-link-articulated wheeled-type in-pipe robot [20] is shown in **Figure 7**. This robot consists of four links and joints connecting them and moves back and forth using actively rotatable omni wheels installed on each joint axis. A torsional coil spring mounted in each joint allows the robot to form a zigzag shape, making the robot move up in vertical pipes by pressing the omni wheels to the inner wall of pipes. When the robot enters into a bent pipe, the joints can be opened and closed passively according to the shape of the curved section, thus making the robot easily pass through winding pipelines.

Another major feature of this robot is that the rotational axes of all joints are parallel to each other (**Figure 8**). As the positions of all joints move only on the same single plane, the robot cannot pass through bent pipes if the bending direction of the joints does not match the pathway direction of the pipes. However, this is not a disadvantage to the robot. For example, in a situation where the inner wall of pipelines has obstacles, such as holes and dents, the robot can avoid them by displacing the trajectory of the wheels and the obstacle.

To align the bending direction of the robot joints and the pathway direction of the pipe, we proposed a method of changing the robot's orientation around the pipe axis by rolling spherical wheels [21–23] installed at its head and tail ends (**Figure 9**). The spherical wheel rotates freely in the direction of the robot movement; thus, it

**Figure 7.** *A multi-link-articulated wheeled-type in-pipe robot named AIRo-2.2 [20].*

**7**

**Figure 10.**

*Active and passive degrees of freedom of the AIRo-2.2 [20].*

*Robotic Search and Rescue through In-Pipe Movement DOI: http://dx.doi.org/10.5772/intechopen.88414*

does not disturb the movement of the omni wheels. Similarly, the omni wheel has several small free rollers arranged on its circumference; thus, they do not interfere

We confirmed the robot's ability to pass through a 15-m-length and 4-in-diameter vinyl chloride pipeline, including vertical sections with 12 bent and 1 T-branch pipes, as shown in **Figure 10**. Here, the operator operates the robot using a gamepad while only watching the camera images. It took approximately 6 min for the robot to

We have been in pursuit of a year-by-year improvement of the robot. The multi-link articulated wheeled-type in-pipe robots that we have been developing so far and their extended versions with some modifications (called AIRo-series) are

with an active joint with both angle and torque control systems (**Figure 11**).

AIRo-2.2 mini is specially designed for cleaning inside flexible ducts. As it does not have to generate a large traction force, the robot is only composed of two links. By rotating the head brush, the inner surface of the duct can be cleaned. AIRo-3.0 [24, 25] has the same multi-link structure as the AIRo-2.0 series. However, each joint has a differential mechanism to generate two movements: moving back and forth and twisting the body. AIRo-2.4 is a downsized version; from a 4-in diameter, its size was shrunk to 3 in. AIRo-2.3s is the latest version of the in-pipe robot and is equipped

with the rolling motion of the robot by the spherical wheels.

reach the end of the pipeline and back to the entrance.

*Experiment in a 15-m pipeline with 12 bent and 1 T-branch pipes.*

displayed in **Figure 11**.

**Figure 9.**

**Figure 8.** *Two robot orientations depending on the passability to the bent pipe.*

*Robotic Search and Rescue through In-Pipe Movement DOI: http://dx.doi.org/10.5772/intechopen.88414*

*Unmanned Robotic Systems and Applications*

even adaptable to winding pipelines and T-branch [14–19].

making the robot easily pass through winding pipelines.

displacing the trajectory of the wheels and the obstacle.

*A multi-link-articulated wheeled-type in-pipe robot named AIRo-2.2 [20].*

*Two robot orientations depending on the passability to the bent pipe.*

As introduced in the earlier sections, the key point for downsizing is combining the three components (propulsive, steering, and extending) in a common component. To achieve this compact design, we have been working on a multi-linkarticulated wheeled-type in-pipe robot whose wheel shaft (as propulsive) and joint (as steering and extending) are all arranged on the same axis. This configuration leads to a drastic miniaturization to 3–4 in. in the inner diameter of pipes and is

An overview of the multi-link-articulated wheeled-type in-pipe robot [20] is shown in **Figure 7**. This robot consists of four links and joints connecting them and moves back and forth using actively rotatable omni wheels installed on each joint axis. A torsional coil spring mounted in each joint allows the robot to form a zigzag shape, making the robot move up in vertical pipes by pressing the omni wheels to the inner wall of pipes. When the robot enters into a bent pipe, the joints can be opened and closed passively according to the shape of the curved section, thus

Another major feature of this robot is that the rotational axes of all joints are parallel to each other (**Figure 8**). As the positions of all joints move only on the same single plane, the robot cannot pass through bent pipes if the bending direction of the joints does not match the pathway direction of the pipes. However, this is not a disadvantage to the robot. For example, in a situation where the inner wall of pipelines has obstacles, such as holes and dents, the robot can avoid them by

To align the bending direction of the robot joints and the pathway direction of the pipe, we proposed a method of changing the robot's orientation around the pipe axis by rolling spherical wheels [21–23] installed at its head and tail ends (**Figure 9**). The spherical wheel rotates freely in the direction of the robot movement; thus, it

**6**

**Figure 8.**

**Figure 7.**

**Figure 9.** *Experiment in a 15-m pipeline with 12 bent and 1 T-branch pipes.*

does not disturb the movement of the omni wheels. Similarly, the omni wheel has several small free rollers arranged on its circumference; thus, they do not interfere with the rolling motion of the robot by the spherical wheels.

We confirmed the robot's ability to pass through a 15-m-length and 4-in-diameter vinyl chloride pipeline, including vertical sections with 12 bent and 1 T-branch pipes, as shown in **Figure 10**. Here, the operator operates the robot using a gamepad while only watching the camera images. It took approximately 6 min for the robot to reach the end of the pipeline and back to the entrance.

We have been in pursuit of a year-by-year improvement of the robot. The multi-link articulated wheeled-type in-pipe robots that we have been developing so far and their extended versions with some modifications (called AIRo-series) are displayed in **Figure 11**.

AIRo-2.2 mini is specially designed for cleaning inside flexible ducts. As it does not have to generate a large traction force, the robot is only composed of two links. By rotating the head brush, the inner surface of the duct can be cleaned. AIRo-3.0 [24, 25] has the same multi-link structure as the AIRo-2.0 series. However, each joint has a differential mechanism to generate two movements: moving back and forth and twisting the body. AIRo-2.4 is a downsized version; from a 4-in diameter, its size was shrunk to 3 in. AIRo-2.3s is the latest version of the in-pipe robot and is equipped with an active joint with both angle and torque control systems (**Figure 11**).

**Figure 10.** *Active and passive degrees of freedom of the AIRo-2.2 [20].*

**Figure 11.** *Multi-link-articulated wheeled-type in-pipe robots in the AIRo-series developed by the authors.*
