Small Pipe Characterization System (SPCS)

Small Pipe Characterization System

Project Summary

Conducting characterization and inspection activities within piping systems is critical to comprehensive decontamination and dismantlement activities throughout the Department of Energy (DOE) facilities. Current technologies for characterizing large piping exist. However, the ability to accurately characterize small-diameter piping is not currently available. Because contaminated facilities have a wide range of pipe in systems that require characterization, a system that has the capability to enter and inspect small pipe systems would promote inclusive characterization efforts.

The research objective of the Small Pipe Characterization System (SPCS) is to develop a robotic system to characterize the internal surfaces of horizontal and vertical piping with a diameter of 2-3 inches without removal from the pipe for reconfiguration. A further objective is to achieve advances in miniature system components such as cameras, actuators, gears, and power supplies.

The SPCS was developed at the Idaho National Engineering Laboratory under funding by the Department of Energy's Office of Technology Development. This technology is currently available for license.

The SPCS development team includes:

Our development partner for 1995 was Foster Miller, Inc. who supplied the fiber optic communications and vehicle power supply.

The SPCS is designed to traverse small piping systems between 1 and 3 inches in diameter. The current prototype is capable of travel within 2 to 3 inch pipes. It is able to pass through elbows, expansion fittings, and ball valves.
Traversing an expansion fitting: Travel in both directions through the fitting has been demonstrated.
It will also drive through vertical pipes.
Transition from horizontal to vertical through an 90 deg elbow
The vehicle currently carries a radiation detector and a video camera.
Video camera and lights on the front of the SPCS.

Tractor details

Each of the three wheeled units are refered to as half-tractors. The three wheels are held against the interior of the pipe by a parallel linkage with springs at its corners.
Half-tractor A, with camera pod and camera
The wheeled parts of the half tractor are called drive units. Each half tractor has one Top Drive Unit and two Base Drive Units (similar to the top and base of a triangle). The main torsion springs which provide the holding force in the pipe are located at the joints nearest to the top drive unit.
Detail of the joint nearest the top drive unit.
When the three drive motors are turned on, the half tractor drives down the pipe. If the motors were to fail while the vehicle was in the pipe, it is easy to pull the crawler back out. This is because the gearboxes which drive the motors use a 125:1 spur gear train, not a worm gear. This allows the gearmotors to be easily backdriven. A single gearmotor is strong enough to drive the half tractor through the pipe with two of the three drive units not working.

Going through a corner, the half tractor folds up on itself to get around the bend. The drive units disconnect from the parallel linkage and the parallel linkage folds in the middle. This allows the vehicle to hold itself in larger pipes while still turning corners in small pipe.
The parallel linkage bends in the middle
When the vehicle approaches a corner, it must enter the corner at near the correct orientation for the vehicle to bend around the corner. Some misalignment is allowable, because the vehicle tends to self align itself if it is not off much. If it is 180 degrees from curve of the elbow, it will just drive into the back of the elbow wall. Therefore it is necessary for the operator to align the vehicle with the elbow. This is accomplished by rotating the drive units, driving the wheels until the desired orientation is reached, and straightening the wheels back out.

The mechanism that allows the wheels to turn is actuated by a second gearbox on the top drive unit of each half tractor. The drive gearboxes have output shafts that come out the side of the gearbox. The steering gearboxes output shafts come out the bottom. A spur gear on the output shaft meshes with another mounted on the vehicle frame. When the steering motor runs, the top drive unit rotates with respect to the vehicle frame.
The top drive unit, showing the steering gears.
A face gear mounted on the top of the steering drive unit transmits the rotation to a spur gear. From this spur gear, the motion is transmitted through another set of spur gears, through the flexable shaft and into the base drive unit. The base drive unit has a similar spur/face gear set and is steered along with the top drive unit. In this way all three drive units are steered with a single actuator.
The base drive unit, showing the spur/face gears.
One of the base drive units has a set of contacts on it which acts as a limit switch. The control system gives a voltage command to the steering motor, and it runs at that voltage until it reaches the limit. This limit switch is visible in the picture above. Normally, the exposed gears, wires, and limit switches are protected by a smooth cover. This cover is shown clearly in the picture of the camera and foremost base drive unit.

The mechanism for transmitting the steering motion through the flexable shaft decouples when the vehicle goes around a corner. This is accomplished by having each end of the shaft connected to sockets like hex socket head cap screws. The drive units on each end have hex balls which fit into the sockets. These balls are like those on a ball end allen wrench. This joint on the top drive unit is in an earlier picture. On the base drive unit, it is shown below.
The base drive unit ball and socket joint.
When the base drive units are decoupled from the flexable shaft, they will turn freely unless they are restrained. Inside the cover that holds in the gears connected to the hex ball is a pair of spring loaded wedges. These wedges have teeth on the upper side and are pressed into the hex ball spur gear, locking it in place. When the drive unit couples with the parallel linkage, two fingers enter angled holes in the wedges through a slot in the cover. These fingers hold the wedges away from the spur gear and allow it to be turned by the flexable shaft. When the base unit is coupled, it is free. When it decouples to enter a corner, it locks.

System Details

The half tractor mechanics described above are connected to a single payload pod which contains the drive electronics for that half tractor. There are standardized connectors on each end. This allows half tractors to be strung together in any configuration.

A single half tractor is able to drive horizontally and vertically in straight pipe. It will also go around a gradual curved elbow. Two half tractors make a full tractor. A tractor can go around elbow fittings. It takes two half tractors because when the half tractors decouple, they loose purchase on the interior of the pipe and need help from the other half. The prototype we have built has two tractors, so as to allow for extra payload pods to be carried between them.

The physical and electrical interface between parts of the system is modular. A power and data bus runs throughout the vehicle. This allows any sensor to be added in a payload pod. The sensor must have its own power conditioning and be able to recieve commands and send data over serial data lines. It would also be possible to add battery pods and eliminate the power lines from the tether.

The front and rear half tractors in the vehicle are somewhat special. The front half tractor has an extra pod that does the processing for the video camera. The rear half tractor has two extras, one for vehicle power, and one for fiber optic data communications. The middle two half tractors are of the standard modular design, consisting of the mechanical drive system and one control pod.

Vehicle Control

Two control interfaces have been written for the SPCS. The first was written during the development of the hardware. It is written in Labview for windows and uses the mouse and keyboard for user input. During testing of the vehicle, it was decided that a joystick would greatly increase the functionality of the vehicle. A second interface was written, using Visual Basic. This GUI incorporates all the functionality of the development interface, but can be run from an executable with no need for a Labview license. The main control window is shown below. There is also a status window which reports the current status of all controllable vehicle functions and sensors. A video window shows the video from the camera so an additional monitor is not needed to operate the robot.
The joystick control window.

The prefirred hardware configuration is a PC running windows. Installed in the computer are a joystick game port card, a video capture card, and a custom card which communicates with the vehicle. In addition to the computer, there is a vehicle power supply. The video from the robot can be sent directly to the computer, can be sent to a VCR for recording, and/or can be sent to an external monitor for an inspector to view the inside of the pipe.

Pictures

Half tractor A in a clear pipe.
Half tractor D.
The joint between the camera pod and half tractor A.
The front of the vehicle.
The crawler drives by.