CHAPTER 5 ARTIFICIAL INTELLIGENCE
5.1 Localization Methods
Mapping the environment is not feasible for a USAR robot, as the environment can continuously change during a disaster. The environment consists of explosions, the ignition of fire and the collapsing of building materials. Different localization sensing methods have been investigated. These include, Global Positioning System (GPS), Differential GPS (DGPS), Indoor GPS, wireless Cell Of Origin (COO) networks, triangulation, imaging methods and Simultaneous Localization And Mapping (SLAM). Most of these localization methods have their problems.
GPS will not work as the satellite signals do not penetrate through building materials. Indoor GPS will not be reliable as buildings will not necessarily have these units built in them, and the transmitters location could vary as the building collapses. Wireless COO networks could be an alternative, but there are not necessarily cellular networks at suitable positions to assist with the robot location.
Imaging methods are also not reliable as the imaging system could malfunction during the collapsing of the building. SLAM is not reliable as the environment changes rendering the mapping data ineffective.
Triangulation is an option to identify a 3 dimensional location within the building, but will not possibly always correlate with the floor plans of the building. The reason being that there are not always floor plans available and the mapping of the collapsing building will not necessary correctly correlate with these. The only reason that the triangulation would be useful is to derive an estimation of the robot position to notify the rescuers as to the position of possible victims.
To be able to use a triangulation method, at least three transmitters would be needed to be located at strategic points around the building, each with its own ID.
The intersection of the signals will indicate a virtual position of the robot, which could be transmitted to the control station. This system works on the same principle as
GPS and is referred to lateration. [52]
Two transmitters could be used for the localization of the robot, but then the known location transmitting stations must be completely stationary, be perpendicular to the horizon as a reference, and have 180° directional antennas that are able to move in the vertical position. This method which is also known as angulation [52], measures angle or bearing relative to the two transmitters of known separation. This would allow for the robot location in the x and y co-ordinates, while the angle of the antennas indicate the z co-ordinate, which identifies the altitude of the robot.
The localization with two or three transmitters could be viable methods should the rescue attempts endure for numerous hours. This is not usually the case, as rescuers have limited time to locate victims in a disaster scenario. These methods could be investigated in future research for rescue attempts that happen over a lengthier time period.
5.1.1 CAESAR Localization Method for Semi-Autonomy
AI similar to RatSLAM was considered for the CAESAR robot. RatSLAM is the localization method that rats use. Rats know their local surroundings and react on this information. An example of this will be a rat running down a corridor until it approaches a wall. It will identify the wall and turn as required. The rat could also identify a hole in the wall and thus continue running to enter the hole.
The CAESAR robot is remotely controlled and should relieve the controller from deciding whether the obstacles in front of it are large enough for transformation to be required. The sonar sensors are used for this.
With the CAESAR robot in automatic mode these transformations occur automatically. There could possibly be times that the user would desire to override the autonomous transformation and thus would prefer to transform at their own discretion.
The CAESAR robot detects objects via the ultrasonic distance sensor up to a distance of about 400 mm. The reference of the flipper arm angles are calculated from the point where the flipper arms are contracted within the body on a longitudinal plane, as shown in figure 5-1. The reference to the front of the CAESAR robot refers to the side that is traveling forward, while the rear side is considered to be the opposite side.
Figure 5-1: Diagram indicating the reference plane of the flipper arms
There are different scenarios to be considered. Should the CAESAR robot be traveling in a horizontal position, the default position for the front and rear flipper arms will be at 150°. This allows for stabilization as it maneuvers over a rough terrain. Should there be a small undetected object in front of the robot, or a small ditch that it has to cross, the angle of the flipper arms will assist it to continue with movement as the traction of the tracks are increased.
In the event that the CAESAR robot is traveling in a horizontal position and approaches an obstacle, the front flipper arms will move to 135°, while the rear flipper arms will move to 150°. This allows the CAESAR robot to move over the obstacle, while supporting the rear side as it climbs the incline.
While the CAESAR robot is climbing an incline and no object is detected, the front flipper arms will be at 150°, while the rear flipper arms will be at 135°. Should an object be detected while on the incline, the front flipper arms will move to 135°.
Should the CAESAR robot be on a decline and no object is detected, the front flipper arms will move to 135° and the rear flipper arms will move to 150°. This will support the front of the CAESAR robot should it approach or slide to an object. It would appear as if an object is being detected when the CAESAR robot approaches a horizontal terrain. With the front flipper arms at 135°, it will assist it to stabilize on the horizontal terrain.
A summary of the flipper arm orientation for the CAESAR robot in the normal orientation or upside down orientation is shown in table 5-1.
Table 5-1: Flipper orientation with the corresponding robot orientation
Angle Object
Detection
Action
- 10° to 10° Front and rear flipper arms @ 150°
-170° to 180° or 170° to 180° Front and rear flipper arms @ 240°
-10° to 10° √ Front flipper arms @ 135°, rear flipper arms @ 135°
-170° to -180° or 170° to 180° √ Front flipper arms @ 225°, rear flipper arms @ 225°
10° to 90° Front flipper arms @ 150°, rear flipper arms @
135°
-90° to -170° Front flipper arms @ 240°, rear flipper arms @ 225°
10° to 90° √ Front flipper arms @ 135°, rear flipper arms @ 135°
-90° to -170° √ Front flipper arms @ 225°, rear flipper arms @ 225°
-10° to -90° Front flipper arms @ 135°, rear flipper arms @ 150°
90° to 170° Front flipper arms @ 225°, rear flipper arms @ 240°