Development of a Small-Sized Urban Cable Conduit Inspection Robot

Abstract

Cable conduits are crucial for urban power transmission and distribution systems. However, current conduit robots are often large and susceptible to tilting issues, which hampers the effective and intelligent inspection of these conduits. Therefore, there is an urgent need to develop a smaller-sized conduit inspection robot to address these challenges. Based on an in-depth analysis of the characteristics of the cable conduit working environment and the associated functional requirements, this study successfully developed a small-scale urban cable conduit inspection robot prototype. This development was grounded in relevant design theories, simulation analyses, and experimental tests. The test results demonstrate that the robot’s bracing module effectively prevents tilting within the conduit. Additionally, the detection module enables comprehensive 360-degree conduit inspections, and the vacuuming module meets the negative pressure requirements for efficient absorption of dust and foreign matter. The robot has met the expected design goals, effectively enhanced the automation of the cable conduit construction process, and improved the quality control of cable laying.

1. Introduction

With the rapid development of cities, the importance of infrastructure, such as electricity, has significantly increased. Cables play a crucial role in this context, and their safe and stable operation is essential for ensuring the smooth functioning of urban areas. Typically, cables are laid in underground ducts, but due to construction activities, these ducts are prone to misalignment and the accumulation of debris, such as sand and dust. This not only affects cable operation but also poses potential risks to the power grid’s operation. Given the narrow, inconvenient, and complex environment of cable ducts, developing a small-sized intelligent inspection robot capable of reliably detecting duct defects and taking corrective actions is highly necessary [1,2,3].

Researchers have developed a variety of conduit robots, which provide foundational cases for the research presented in this paper. Traditional conduit robots, utilizing wheels or tracks for movement, offer high stability and practical utility. Elankavi R S et al. comprehensively summarized traditional conduit robots equipped with different types of wheels, including magnetic wheels, standard wheels, and mechanical wheels [4]. Thung-Od, K et al. introduced a train-type conduit inspection robot equipped with two sets of vertical omnidirectional wheels capable of longitudinal and lateral movements to ensure the robot navigates the conduit path effectively [5]. M. Cardona et al. invented a single-degree-of-freedom wheeled conduit inspection robot featuring adjustable detection height, strong driving force, and significant engineering practicality [6]. To enhance obstacle avoidance, Tang, S. et al. developed a tracked conduit inspection robot with two independently driven side track motion mechanisms and posture adjustment systems, capable of performing well on various terrains and overcoming obstacles [7]. However, traditional wheeled and tracked robots generally lack support mechanisms, making them susceptible to tilting or even overturning within the conduit.

To address the issue of tilting within conduits, bionic conduit inspection robots have been developed. Wang, J. et al. proposed a small six-legged conduit robot equipped with a support mechanism, providing a structural foundation for subsequent obstacle avoidance robot designs [8]. Additionally, Manhong Li et al. developed a soft crawling robot for conduit detection [9], and Jingwei Liu et al. designed a snake-like conduit robot [10]. These robots mimic the characteristics of mollusks, allowing them to better adapt to conduits through creeping excavation, thus enabling stable movement and preventing tilting. Fang et al. highlighted that the design inspiration for bio-inspired robots is drawn from the wall-climbing abilities of insects and animals, offering considerable advantages in specific operational environments. This has advanced the development of bio-inspired climbing robots, making them suitable for applications on conduit walls as well [11]. However, the current application of bionic robots remains limited to ideal laboratory conditions, and their capabilities for practical engineering applications require further development.

To achieve both engineering practicality and anti-tilt capability in conduit robots, we can refer to external conduit inspection robots. For instance, Wang Z. et al. developed an external cable pipe wall-walking inspection robot that employs a non-enclosed four-bar clamping mechanism, ensuring stable operation [12]. Li J. et al. invented a flexible obstacle-crossing conduit robot, which significantly enhanced stability and obstacle-crossing capability through a rotating joint mechanism and an elastic shock-absorbing suspension system [13]. Additionally, Z. Tang et al. drew inspiration from the conduit outer diameter inspection robot developed by Z. Zheng et al. [14] and designed an adaptive diameter conduit inspection robot. This robot utilizes a support structure and a lifting structure arranged at 120°, with the outer diameter of the grinding wheel system adjusted through a screw adjustment module to accommodate different pipe diameters and prevent tilting issues [15]. Furthermore, to prevent the robot from tipping over within the conduit, Yan H. introduced a spiral conduit robot that reduces slippage by increasing the spiral angle, thereby providing an effective driving force for the adaptive conduit robot [16]. Concurrently, Zhang L. et al. conducted an in-depth study on the stability of conduit robots, providing a theoretical foundation for maintaining the stability of the robot’s posture [17]. Subsequently, Y. Zhang et al. simulated and optimized the support and drive mechanisms of the adaptive diameter conduit robot, further advancing research into anti-roll solutions for conduit robots [18].

In addition to the detection function, the robot must be equipped with specialized devices to address various conduit defects. For instance, Y. Chen et al. designed an adaptive conduit robot drilling device capable of removing stones and debris from the conduit [19]. Moreover, Fanghua Liu et al. enhanced the conduit inspection robot by incorporating a rotating device to grind internal conduit defects coupled with a brush for cleaning purposes [20]. The robot developed in this paper is designed to detect internal defects of the conduit and clean the inside of the conduit at the same time, especially to transport sand and soil inside the conduit after construction.

In this context, this paper presents the development of a small-scale cable conduit inspection robot. This wheeled, single-degree-of-freedom inspection robot features a uniform four-wheel drive to prevent slipping, a bracing mechanism to avoid tilting, and a 360° all-round inspection device for accurate feedback on conduit defects. Additionally, it is equipped with a vacuuming device to collect dust and sand, thereby preventing any adverse impact on the cable insulation layer. By integrating these functionalities, the robot can complete inspection tasks more efficiently, providing a model for the development of future wheeled inspection robots.

2. Functional Requirements and Technical Indicators

The small-volume urban cable conduit inspection robot focuses on detecting and addressing internal defects in urban cable conduits. As shown in Figure 1, such defects include foreign matter such as dust, sand, and stones left in the conduit due to construction activities, as well as interface misalignment defects formed during the conduit connection process. All the defects significantly impact the laying and discharge of cables.

Therefore, the following points are particularly important for small-sized urban cable conduit inspection robots to effectively complete their tasks in the complex environment of cable conduits:

• Small Size: To ensure that the robot can fit into the confined space of the cable duct, it must be designed to be compact and small.
• Reasonable Drive: When the robot is moving in a circular cross-section cable duct, it is necessary to ensure that each driving force has sufficient power to avoid slipping.
• Comprehensive Inspection: Given the differences in conduit diameters, the inspection device needs to be appropriately adjustable to ensure effective defect detection.
• Stable Operation: When a wheeled robot maneuvers within a circular cross-section cable conduit, the center of gravity often shifts away from the conduit’s center, leading to tilting. In severe instances, this can result in the robot rolling over. Hence, strict control of the tilt angle is crucial to prevent it from becoming excessive.

In addition to these requirements, the robot should also have the capability to clean foreign objects (vacuum) to meet the practical needs of engineering and production.

According to project indicators and functional analysis, the main quantitative indicators of the small-scale urban cable conduit inspection robot are presented in

Table 1. Quantitative indicators of robot.

Robot Mass m/kg	Conduit Diameter Range D/mm	Number of Driving Wheels	Detection Angle α0/(°)	Inclination Angle θ/(°)	Vacuuming Negative Pressure p/kPa
≤12	225–275	4	360	≤8	≥3

.

3. Robot Working Principle and Structural Design

3.1. Robot Overall Structure Design

The structural design of the small-volume urban cable conduit inspection robot (hereinafter referred to as the robot) includes a main module, a bracing module, a detection module, and a vacuuming module. The overall structure is illustrated in Figure 2.

The camera detection module is positioned at the front end of the robot’s main module, equipped with components such as an industrial camera, fill light, servo, and rotary motor drive. A bracing module is located in the middle section of the robot, comprising a push-rod motor and bearing rollers. The push-rod motor is adjustable for different conduit diameters with a specific stroke. At the rear end, there is a vacuuming module designed for collecting dust and foreign matter.

3.2. Robot Body and Bracing Module Design

As illustrated in Figure 3, power transmission within the robot’s main body module occurs through a plane cross-axis gear to an odd-parallel-axis gear set, which subsequently transfers power to the front and rear output shafts. This transmission method ensures even distribution of power to the four sets of non-slip rubber drive wheels, thereby ensuring uniform power output.

The selection of the drive motor significantly influences the operational performance of the robot. Parameters such as the robot’s mass, drive wheel radius, driving speed, and friction coefficient directly affect the motor’s torque and power requirements. To simplify calculations, it is assumed that all four sets of drive wheels maintain non-slipping contact with the conduit wall.

T₁ is the torque required to overcome the rotational inertia:

$$\left\{\begin{array}{l}{T}_1=J\alpha \\ \alpha ={\displaystyle \frac{\omega }{t}}\end{array}\right.$$

(1)

In the equation, J represents the equivalent rotational inertia of the drive motor itself, the transmission system, and the four sets of drive wheels. The variable α denotes the angular acceleration of the drive motor, ω represents the angular velocity of the motor, and t is the motor startup time.

The torque T₂ required by the wheel to overcome friction:

$$T_2=\mu mgR$$

(2)

where μ represents the maximum static friction coefficient between the driving wheel and the conduit, m is the weight of the robot, and g denotes the acceleration due to gravity.

Thus, the power P₁ required by the motor to overcome the load and the power P₂ required to overcome friction can be determined.

$$\left\{\begin{array}{l}{P}_1={\displaystyle \frac{T_{1}n}{9550}}\\ P_2={\displaystyle \frac{T_{2}n}{9550}}\end{array}\right.$$

(3)

where n represents the motor speed.

From the above, the required safety torque T and safety power P for the motor can be determined:

$$\left\{\begin{array}{l}T=(T_1+T_2)N\\ P=(P_1+P_2)N\end{array}\right.$$

(4)

where N represents the safety factor.

Dynamic analysis reveals the necessary driving torque and power:

$$\begin{array}{l}T=\left({\displaystyle \frac{J\omega }{t}}+\mu m\mathrm{g}\right)N\\ P=\left({\displaystyle \frac{J\omega n}{9550t}}+{\displaystyle \frac{\mu m\mathrm{g}n}{19100}}\right)N\end{array}$$

(5)

Based on the calculated torque and power requirements, the selected motor dimensions, as shown in Figure 4, fulfill both the design specifications and spatial constraints. This motor is produced by DJI Technology Co., Ltd., Shenzhen, China.

To ensure stable operation and prevent tilting or tipping due to poor conduit conditions, a high center of gravity, or excessive speed, it is crucial to carefully analyze tilt phenomena and implement corresponding measures. Figure 5a illustrates the analysis of the robot without anti-tilt measures.

In Figure 5a, G and G₁ denote the positions of the center of gravity before and after tilting, respectively; θ represents the tilt angle; H is the distance between the center of gravity and the bottom of the robot; 2W denotes the length of the bottom of the robot; F represents the weight of the robot; F_x is the component of gravity parallel to the wheel axis; F_y is the component of gravity perpendicular to the wheel axis. Given the robot’s relatively slow forward speed, only static tipping is considered in tipping scenarios. Under tilting conditions, gravity generates a tipping moment, M₁, and a tipping-preventing moment, M₂, expressed as follows:

$$\begin{array}{l}{M}_1=F_x\times H\\ M_2=F_y\times W\end{array}$$

(6)

The component expressions of gravity are:

$$\begin{array}{l}{F}_x=F\times \sin \theta \\ F_y=F\times \cos \theta \end{array}$$

(7)

If the tipping moment exceeds the anti-tipping moment, the robot will tilt over. To prevent tilting, the tilt angle must be maintained below a certain critical value, denoted as:

$$\theta \le \arctan \left({\displaystyle \frac{W}{H}}\right)$$

(8)

In actual conduit inspection processes, without implementing anti-tilt measures, it becomes impractical to maintain the tilt angle within a controllable range, thereby making it difficult to prevent tipping from occurring reliably.

Therefore, it is essential to implement anti-tilt measures. As illustrated in Figure 6, bracing bearing rollers and push-rod motors are utilized to stabilize the robot and prevent tilting and rotation. The push-rod motor provides a specific amount of force and stroke to act as rigid bracing, adapting to the actual conditions within the conduit. The thrust on the duct wall is maintained by a passive system. First, the 3D model of the robot is placed within a 225–275 mm cable conduit, and the stroke of the push-rod motor is determined based on its position in the 3D space. The cable conduit is produced by Hebei Zhongming Environmental Protection Engineering Co., Ltd. in Cangzhou City, Hebei Province, China. The appropriate voltage and thrust (self-locking force) are then selected according to the power supply requirements. The selected push-rod motor operates at 12 V, with a 50 mm stroke and a thrust of 150 N.

An MX471 current sensor module is added to the main control board, which extends the push-rod motor through the main control board. The MX471 current sensor module is produced by Shenzhen Nuojing Technology Co., Ltd., China. When an increase in current is detected, it indicates that the roller has contacted the cable conduit wall, prompting the motor to stop extending. At this point, the push-rod motor generates a self-locking force to hold against the duct wall, preventing the robot from tilting.

Additionally, the use of bracing bearing rollers reduces friction, transforming sliding friction between the bracing and the conduit wall into rolling friction, thereby minimizing the robot’s travel resistance. During conduit inspections with this bracing mechanism, depicted in Figure 5b, if a clockwise tilt tendency occurs, the left bracing bearing roller generates a vertical downward force F₁, while the right side produces a vertical upward force F₂. These forces collectively create a torque that prevents the robot from tilting, ensuring smooth operation during conduit inspections.

3.3. Robot Detection and Vacuuming Module Design

Currently, most wide-angle camera modules used for inspections feature structures with adjustable relative heights, necessitating adjustments based on conduit diameter. As depicted in Figure 7a, when the camera axis deviates from the conduit centerline, the quadrilateral wide-angle area ABCD formed becomes asymmetric relative to the axis. This asymmetry results in variations between upper and lower observation areas, which can affect the assessment of conduit defects. Rotating the camera to view the asymmetric area can lead to image distortion if the rotation angle is excessive, significantly impacting the detection of conduit misalignment defects.

Therefore, the height of the adjustable detection device should be adjusted to align the two axes as closely as possible. In Figure 7b, where W is half of the robot width, D is the wheel diameter, R is the conduit radius, l is the vertical distance from the center of the conduit to the bottom of the wheel, and h_max is the maximum adjustable height of the camera relative to the bottom of the vehicle. Using these parameters, the approximate adjustable height h can be calculated as:

$$h=h_{\max }-\sqrt{R^2-W^2}-D/2$$

(9)

Therefore, the range of the conduit diameter should determine the corresponding adjustable height range, ensuring that h_max exceeds this adjustable height range. It is important to note that in Equation (9), the values of R and W should account for the thickness of the wheel.

Figure 8 illustrates the adjustable height range calculation, which incorporates a single-axis servo and rotary motor to compensate for the camera height in the detection module of the robot.

When the detection module identifies a defect in the cable duct, targeted treatment of the defect is necessary. The small-volume urban cable duct detection and vacuuming robot utilizes a vacuuming module to absorb and collect dust and foreign matter. This prevents degradation of cable insulation performance, obstruction of heat dissipation, and corrosion damage caused by dust.

The dust collection module structure consists of a cyclone motor, a dust collection box, an air conduit joint, and a dust collection head, as illustrated in Figure 9. The cyclone motor serves as the core component, generating airflow and negative pressure to suction dust and dirt. The air conduit joint connects to the external dust collection head, directing airflow and dust entry. During operation, the cyclone motor creates negative pressure, efficiently drawing in dust and dirt from the conduit bottom. The dust collection head acts as the inlet, while the air conduit joint guides airflow and particulate matter into the dust collection box. To safeguard the motor from large particles, a filter is installed between them, and the dust collection box is sealed to securely store and collect dust and dirt.

4. Robot Simulation Analysis

4.1. Simulation Analysis of Robot Body and Bracing Module

Based on the above analysis, it is evident that without anti-tilt measures, the robot moving in the conduit may tilt or even overturn. However, after incorporating the bracing module, the robot’s tilt issue is mitigated. To further investigate the influence of the robot’s speed within the conduit on tilting, dynamic analysis was conducted using the Motion plug-in of SolidWorks2021 software. This analysis considered different speeds and the presence or absence of bracing devices for the robot. The abbreviations for different simulation conditions are detailed in

Table 2. Abbreviation for simulation of center of mass position under different conditions.

Abbreviation	Direction of Center of Mass	Bracing Mechanism Presence	Operating Speed v/(m/s)
Case 1	X	Without bracing	0.1
Case 2	X	With bracing
Case 3	Y	Without bracing
Case 4	Y	With bracing
Case 5	X	Without bracing	0.2
Case 6	X	With bracing
Case 7	Y	Without bracing
Case 8	Y	With bracing
Case 9	X	Without bracing	0.3
Case 10	X	With bracing
Case 11	Y	Without bracing
Case 12	Y	With bracing

below.

For robots equipped with bracing mechanisms, a detailed analysis of the contact forces and friction forces generated during their interaction with cable conduit walls is required. Additionally, the forces exerted by the bracing mechanisms on the duct walls at different speeds should be compared. Abbreviations for the various simulation conditions are presented in

Table 3. Abbreviation for simulation of dynamic analysis under different conditions.

Abbreviation	Types of Forces	Operating Speed v/(m/s)
Case 13	Contact force	0.1
Case 14	Rolling friction force
Case 15	Contact force	0.2
Case 16	Rolling friction force
Case 17	Contact force	0.3
Case 18	Rolling friction force

.

The selected parameters were validated by observing the relative position changes between the robot’s center of mass and the origin, as shown in Figure 10. When the robot moves along the axial direction of the cable conduit, only the changes in the center of mass in the X and Y directions relative to the origin need to be measured to reflect the robot’s inclination during motion, while changes in the Z direction can be disregarded.

In Figure 10, the observed parameters are the distances between the robot’s center of mass and the origin along the X and Y directions. Using the Motion plug-in, gravity, contact, material, and other parameters are set, providing the robot with a specific rotational speed (given speed), and the calculation time is set to 8 s. Subsequently, using the drawing plug-in integrated with SolidWorks, the vertical distance between these points is selected for data export and further processing.

Firstly, for the robot without a bracing device, vertical gravity and contact between the robot and the conduit are configured. The tire material is set to rubber, and the cable conduit material is set to glass-reinforced steel. The wheel speeds are set at 0.1 m/s, 0.2 m/s, and 0.3 m/s, respectively, allowing it to travel in a theoretically infinite cable conduit for 8 s.

Next, the same boundary conditions are applied to the robot with a bracing device, with the addition of contact settings between the auxiliary roller and the conduit. The tire material remains rubber, and the cable conduit material is glass-reinforced steel. Wheel speeds are set at 0.1 m/s, 0.2 m/s, and 0.3 m/s, allowing travel in a theoretically infinite cable conduit for 8 s.

After completing the simulations, a comparative analysis of the changes in the robot’s center of mass in the X and Y directions under different conditions was conducted, as shown in Figure 11. Figure 11a illustrates the position changes of the center of mass in the X direction relative to the origin for robots with and without bracing mechanisms at a speed of 0.1 m/s. Figure 11b shows the corresponding changes at a speed of 0.2 m/s, and Figure 11c at 0.3 m/s. Similarly, Figure 11d–f display the changes in the Y direction relative to the origin at speeds of 0.1 m/s, 0.2 m/s, and 0.3 m/s, respectively, for both bracing and without bracing robots.

A comparison of the six plots in Figure 11 reveals that robots without bracing mechanisms exhibit significant fluctuations in the center of mass in both the X and Y directions, indicating displacement in these directions and resulting in an overall inclination of the robot. In contrast, robots equipped with bracing mechanisms show minimal fluctuations in the center of mass in both directions, demonstrating the effectiveness of the bracing mechanism in mitigating the robot’s inclination.

After completing the robot motion analysis, further investigation into its dynamics is required, focusing specifically on robots with bracing mechanisms. The analysis will primarily examine the relationship between the contact force and rolling friction force between the bracing mechanism and the inner wall of the cable conduit. As shown in Figure 12, Figure 12a,d present the contact force and rolling friction force at a speed of 0.1 m/s, respectively. Figure 12b,e display these forces at 0.2 m/s, while Figure 12c,f show the corresponding forces at 0.3 m/s.

Figure 12a–c show that the maximum contact forces at different speeds are approximately 7.5 N at 0.1 m/s, 12 N at 0.2 m/s, and 20 N at 0.3 m/s, respectively. This indicates that the magnitude of the contact force between the bracing mechanism and the cable conduit wall increases with the robot’s speed. The fluctuations in contact force suggest that the bracing mechanism operates in a state of dynamic equilibrium, passively adjusting to mitigate inclination. Observing Figure 12d–f, it is noted that the maximum rolling friction forces are approximately 0.75 N at 0.1 m/s, 1 N at 0.2 m/s, and 1.5 N at 0.3 m/s. This demonstrates that, like the contact force, the rolling friction force also increases with the robot’s speed. However, since the rolling friction force remains relatively small, its impact on the robot’s forward motion is minimal.

4.2. Simulation Analysis of Robot Detection and Dust Collection Module

In the ADAMS2019 motion simulation software, connections were added to the visual inspection module. A fixed pair was applied to the motor rack located at the right end of the module. Additionally, rotation pair 1 was established between the right-end motor shaft and the middle servo rack, while rotation pair 2 was set between the middle servo and the left-end camera rack. The configured visual inspection module setup is illustrated in Figure 13.

The revolute pair drive is configured to simulate actual motor operation in the ADAMS motion simulation software. Initially, during setup, the visual inspection module remains static. Subsequently, revolute pair 2 rotates, orienting the camera’s horizontal symmetry plane at a 30° angle relative to the horizontal plane, simulating the camera’s adjustment to observe or capture road and conduit conditions ahead, crucial for transmitting conduit conditions for image recognition. Following this, revolute pair 1 initiates rotation, causing the camera and servo to rotate, mimicking a 360° observation (adjustable as per actual requirements) of the conduit’s current position. Finally, revolute pair 2 rotates again to conclude the camera’s capture session, returning it to its initial position. This sequence is illustrated in Figure 14.

To limit the angle of the servo motor and prevent collisions or interference between the camera and the conduit wall, a comprehensive kinematic simulation of the servo’s position within the cable conduit was conducted at its maximum operating angle, as shown in Figure 14. The results indicate that the camera does not collide or interfere with the cable conduit wall at any of the four orientations tested, confirming that the servo’s maximum operating angle of 30° is a reasonable design choice.

After detecting defects such as dust and foreign matter, the detection module activates the suction module in collaboration with the main module to perform suction operations. To ensure sufficient negative pressure for effective dust and foreign matter removal, an internal fluid simulation of the suction pressure is conducted.

Using the Flow Simulation plug-in in SolidWorks, the dust collection motor was selected, and the volume flow rate at the outlet of the collection box was calculated to be 0.005 m³/s based on its parameters. The inlet ambient pressure was set to the standard external ambient pressure, boundary conditions were established, and grids were divided prior to solving. As depicted in Figure 15, the minimum static pressure recorded was 97.24844 kPa, resulting in a negative pressure of 4.07656 kPa relative to the ambient pressure. Typically, dust collection requires a negative pressure range of 1 kPa to 3 kPa, and the maximum negative pressure generated by the dust collection motor at the collection port is 4.07656 kPa, meeting operational requirements.

5. Robot Experiment Verification

The designed small-volume urban cable conduit inspection robot was processed and manufactured, and the robot and its host computer terminal interface were obtained, as shown in Figure 16. Its key parameters are shown in

Table 4. The key parameter table of the robot prototype.

Key Parameter	Numerical Value
Robot mass m/kg	10
The traveling speed of the robot v/(km/h)	0.5–15
Driving motor power P/W	14
Adaptable conduit diameter D/mm	225–275
Battery endurance of the robot T/h	4

.

The robot can be directly connected to the power supply through the line. To enable emergency work, the robot is also equipped with an internal battery that can provide about 4 h of working time.

The robot’s drive motor, suction motor, camera rotation motor, and servos communicate with the main controller via CAN communication, facilitated by the TJA1050 CAN transceiver chip (Zhidashunfa Electronics Co., Ltd., Shenzhen City, China) embedded in the main control board. The image transmission module communicates with the main controller through an Ethernet connection, as shown in Figure 17.

5.1. Experimental Verification of Robot Body and Bracing Module

Through the theoretical analysis and simulation verification above, it is evident that during actual conduit inspections, a robot without anti-tilt measures tilts after a period of operation. Conversely, integrating an anti-tilt device effectively mitigates this tilt.

The following is an experimental verification conducted by the robot prototype. As shown in Figure 18, in order to restore the real cable conduit scene more realistically, the prototype robot entered a conduit consisting of two sections of 225 mm diameter cable conduits with the same length and a misaligned interface in the middle at a speed of 0.2 m/s in both the bracing and unbracing states.

During the same distance of travel, observations of the robot equipped with and without a bracing device from the entrance of the conduit are depicted in Figure 18. Figure 19a reveals that the robot equipped with a bracing device exhibits less tilt. The close proximity of the bracing wheel to the inner wall is evident through reflection, demonstrating its effective role in mitigating tilt and keeping the robot within acceptable tilt angles. Conversely, Figure 19b shows a noticeable tilt of the robot without a bracing device relative to the center of the cable conduit. This experimental validation aligns with theoretical predictions and simulations, confirming the beneficial anti-tilt effect of the bracing device during the robot’s traversal in the cable conduit.

5.2. Experimental Verification of Robot Detection and Vacuuming Module

The robot, under coordinated action of the main module and bracing module, enters the 225 mm cable conduit. Utilizing commands from the host computer terminal, the robot’s detection module proceeds to survey the conduit in all directions. As depicted in Figure 20, the experiment validates the detection device’s capability to reach four positions: upper, lower, left, and right. Adjustment of the detection device enables a comprehensive 360° detection coverage of the cable conduit.

The simulation of the dust collection module demonstrates that the negative pressure generated by the dust collection motor, operating through the dust collection box and related components, achieves 4.07656 kPa, surpassing the required negative pressure for effective dust collection. As depicted in Figure 21, dust and other foreign particles are strategically placed within the conduit to simulate real-world conditions. Upon activation of the dust collection device, a noticeable reduction in dust content is observed before and after collection. These results affirm the device’s efficacy in effectively suctioning and collecting dust and foreign matter within the conduit, thereby mitigating their potential impact on cable insulation and ensuring cable protection.

6. Conclusions

Addressing the requirements for cable conduit inspection robots across various tasks, this study successfully developed a wheeled, small-volume urban cable conduit inspection robot prototype. This development was achieved through theoretical analysis, simulations, and experimental verification. The main conclusions are as follows:

To ensure smooth movement within the conduit, a four-wheel drive system and an anti-tilt and rollover bracing device based on gear transmission were designed for the robot. The feasibility of this device was validated through theoretical modeling and simulation analysis. Experimental observations at equivalent speeds and conduit distances demonstrate that the deflection angle of the robot equipped with the bracing device is smaller compared with the one without it. The results indicate that the support device effectively resolves the issues of tilting and tipping of the robot within the cable duct.

To meet the requirements of conduit inspection and cleaning, an inspection and vacuuming module for the robot was designed, followed by simulation and experimental verification. The results demonstrate that the detection device can rotate to four positions within the cable conduit without interference, thereby fulfilling the requirements for 360-degree conduit inspection. Furthermore, the dust collection module achieves a maximum negative pressure of 4.07656 kPa, effectively cleaning dust and other foreign matter from the conduit.

The research findings present an example for advancing the study of cable and conduit robots, contributing to the secure and stable operation of urban power grids.