In-Pipe Inspection Micro Robot Adaptable to Changes in Pipe Diameter
1. Background of this research
In recent years, many accidents owing to the shortage of inspection of piping have occurred. In this research, it has aimed to find abnormality by running and checking in piping, and to prevent the accident beforehand.The purpose of this research is to realize a small robot which can negotiate inside pipes, 1 to 5 inches in diameter.
2. Driving Principle
In this research, we proposed new driving principle "Snaking Drive". Manufacture of 1st and 2nd robot was performed until now, and it has checked about the efficacy of a "Snaking Drive".The robot consists of 13 links and 12 rotational joints driven by sine wave signals with small phase differences between adjoining joints, and the robot moves in direction of the delayed phase link (Fig.1). The greatest advantage of this driving principle is that this robot can negotiate piping of different diameter.
Fig.1 Driving principle Fig.2 One joint
3．Manufacture of 3rd robot
3-1．Control system
Because the motor controller had been arranged outside in the second machine that had produced it so far, a lot of wiring was necessary between the robot and the motor controller (Fig.3). Then, the solution of this problem is attempted by producing a small servo amplifier with the function similar to the motor driver in the third machine, and installing it in each link. First of all, the target value is sent from PC to the small servo amplifier through the master. Next, the small servo amplifier feeds back the output value of the encoder, and the instruction value sent to the motor is decided. At this time, deciding the instruction value of the motor by feeding back the output value of the encoder by installing the small servo amplifier in each link in this small servo amplifier becomes possible. In addition, it becomes only two lines (SCL and SDA) by using the I2C communication to communicate with the master between links regardless of the number of links. As a result, greatly reducing the number of cables becomes possible.
Fig.3 Appearance of drive of the 2nd machine Fig.4 Control system applied to this robot
3-2．Manufacture of small servo amplifier
The small servo amplifier consists of a motor driver circuit and a PIC microcomputer (Fig.5). Small servo amplifier carries out mutual communication with a master, and an actuator is made to drive so that a target value may be made to follow (Fig.6). I2C communication is used for the mutual communication with this master.
Fig.5 Composition of Small servo amplifier Fig.6 Concept diagram of Small servo amplifier
3-3. Rubber cover
This robot is made of aluminum, so it slipped in pipes. To enlarge the grip power, the cover made of the silicone was produced. This design is determined based on the friction and the weight of the robot.Two kinds of covers were produced. One is a link’s cover and other is a joint’s cover. As a result the robot can smoothly propel various shaped pipes and negotiate vertical pipes.
Link’s cover Joint’s cover
Fig.7 Rubber covers
4．Driving experiment
To obtain the image of pipe inside, a camera is mounted on the front link. The front link is necessary to keep its orientation parallel to pipe walls for the stabilization of camera image. Experiments of the camera image stabilization wereconducted. Fig.8 shows the measured angle between the front link to pipe wall in pipe axial direction. In case of applying the camera image stabilization, the value of integration of the angle during one cycle decreased at 63%.
Fig.8 Angle between front link and pipe
We experiment in piping. In this experiment, it carried out using the pipe with a diameter of 80mm and 55mm as shown in Fig.9. As a result of the experiments, the traveling velocity in horizontal pipe was 19.3 mm/sec and 6.2 mm/sec in pipes of 80 mm and 55 mm in diameter, respectively. The robot can negotiate pipes whose diameter is changed, T-pipes and vertical pipes. Each experiment was shown in Fig.10, 11, 12. Because of attachment of rubber cover, the robot can smoothly propel various shaped pipes and negotiate vertical pipes bearing weight of itself.
Fig.9 Driving experiment Fig.10 Driving experiment in pipe where diameter changes
Fig.11 Driving experiment in T-shape pipe Fig.12 Diving experiment in vertical pipe