Help in choosing the correct sensor for small object detection close near ground

I am making a white board cleaning robot using suction ( sliding suction cups to be particular). The edges of the white board are barely 1 cm high. But the robot needs to stop before hitting it and turn and go on cleaning. Can I use ultrasonic sensors for it? Will it detect the edge at all? I'm worried it won't, even if i place the sensor very close to the board. I do not want to use limit sensors, but if i don't have a choice then I must use it anyways.. Any help would be appreciated. :slight_smile: Thanks.

  • magnetic strips and a hall sensor?
  • barcodes on the board near the edges with a permanent marker?

Also, I want the robot to work on any whiteboard without any pre-preparations. So using the techniques you mentioned wouldn't work I think. I think using limit switches would be the best. Do you agree?

seen this - -

You could use the suction as a sensor. If the airflow increases you are on the edge. use a pattern of suction holes so it wont fail if one or two passes the edge. (check biomimicry - octopus)

The IRobot Roomba uses IR reflective sensors to detect edges. They have a IR LED that shines downward and a photo transistor, along side, that picks up the reflected IR. If there is an edge the IR is no longer reflected the robot stops. If there is a raised edge around the white board you could use the same technique but have the sensors point out parallel to the board and will sense the reflected IR from the "wall" and turn the cleaner.