Pioneer 2 / PeopleBot manual Sonar Arrays with Gain Adjustment

Figure 12. ActivMedia robot sonar array

ActivMedia Robotics

All models come with an access port near the center of the Deck through which to run cables to the internal components.

Sonar Arrays with Gain Adjustment

Natively, ActivMedia robots support both front and rear sonar arrays, each with eight transducers that provide object detection and range information for features recognition, as well as navigation around obstacles. With sonar expansion electronics, you may add up to 16 more sonar in two additional arrays of eight sonar each. PeopleBots, for instance, have an additional array at the front of the upper Deck.

The sonar positions in all arrays are fixed: one on each side, and six facing outward at 20- degree intervals. Together, fore and aft sonar arrays provide 360 degrees of nearly seamless sensing for the platform.

Each sonar array comes with its own driver electronics for independent control. Each arrays’ sonar are multiplexed; the sonar acquisition rate is 25 Hz (40 milliseconds per sonar per array. Sensitivity ranges from ten centimeters (six inches) to nearly five meters (16 feet). You may control the sonar’s firing pattern through software; the default is left-to-right in sequence 0 to 7 for each array.

The driver electronics for each array is calibrated at the factory. However, you may adjust the array’s sensitivity and range to accommodate differing operating environments. The sonar gain control is on the underside of the sonar driver board,

which is attached to the floor of each sonar module.

Sonar sensitivity adjustment controls are accessible directly, although you may need to remove the Gripper to access the front sonar, if you have that accessory attached.7 For the front sonar, for instance, locate a hole near the front underside of the array through which you can see the cap of the sonar-gain adjustment potentiometer. Using a small flat-blade screwdriver, turn the gain control counterclockwise to make the sonar less sensitive to external noise and false echoes.

Low sonar-gain settings reduce the robot’s ability to see small objects. Under some circumstances, that is desirable. For instance, attenuate the sonar if you are operating in a noisy environment or on uneven or highly reflective floora heavy shag carpet, for example. If the sonar are too sensitive, they will “see” the carpet immediately ahead of the robot as an obstacle.

Increase the sensitivity of the sonar by turning the gain-adjustment screw clockwise, making them more likely to see small objects or objects at a greater distance. For instance, increase the gain if you are operating in a relatively quiet and open environment with a smooth floor surface.

7It’s easier to remove the DXE’s Nose with Gripper attached.

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