Shop OBEX P1 Docs P2 Docs Learn Events
Ping Ultrasonic distance sensor efficiency depending on angle detection ? — Parallax Forums

Ping Ultrasonic distance sensor efficiency depending on angle detection ?

alex93alex93 Posts: 11
edited 2017-10-16 20:27 in Robotics
Hi all,

I have a little problem with my activity bot which has an ultrasonic distance sensor to avoid obstacles.
In fact , everything is working well when the wall is exactly in front of the sensor.

But when the robot is arriving at an angle like in the picture below , the detection is not working and the robot hits the wall most of the time :

Wall2.jpg

I tried with a high value of detection distance but it's the same problem..

Do you have an idea about this issue ?
Is it possible to improve the accuracy of this sensor?

Thanks in advance,

Alex.

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    That's just the nature of sound waves. When they hit a hard, flat surface like a wall, they will reflect at the same angle as the incoming wave. Think of the ultrasonic pulse as a billiard ball, and you'll get the idea. So in your diagram, the pulse will bounce off to the left, instead of reflecting back to the Ping))). That's why the Ping))) can't "see" the wall.

    -Phil
  • ercoerco Posts: 20,250
    Yep, that's exactly why there's a Ping bracket to rotate it with a servo to look in many directions. PING-dar remains one of my favorite demos (top video) and its ingenious onscreen display inspired my laser sensor scanner in the bottom video.



  • WhitWhit Posts: 4,191
    See...http://learn.parallax.com/tutorials/robot/activitybot/activitybot/navigate-ultrasound/build-and-test-ping-sensor-circuit

    Look at the the Ping))) Tests section... It says

    "The PING))) sensor's echo-location works on objects that can effectively reflect sound back at the sensor, from up to 3.3 meters away. Small objects don't reflect back enough sound. Hard-surfaced cylinders, ball-shaped obstacles, and walls if faced directly, work well. Walls that are approached at glancing angle will simply reflect the sound further away instead of back at the PING))) sensor. Soft items such as curtains and stuffed animals tend to muffle the sound and not bounce the echo.

    ping-wrong-situation.png

    For obstacles that do reflect sound back, the PING))) sensor and ping library provide centimeter distance measurements in the 3 cm to 3 m range. Air temperature can affect the accuracy of these distance measurements."
    ping-wrong-situation.png
    571 x 303 - 36K
  • Heater.Heater. Posts: 21,230
    That's it. I was just reading how bats have the same problem.

    https://www.aaas.org/news/bats-have-vertical-blind-spot-when-using-echolocation

  • alex93alex93 Posts: 11

    I understand , it's a physic limit of this sensor.

    Thank you very much all for your answers.
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2017-10-17 20:18
    Parallax sells a nice servo-operated turret to handle this exact issue. The turret scans about 45-50 degrees (or so) to either side. This allows the sensor to (at times) point straight at a wall or other obstacle. You can think of it as a kind of sweeping radar, where the robot can see more than just in the direct line of travel.

    It makes for a terrific challenge to integrate the sweep with real-time detection and forward motion, but this is what robotics is all about.
  • ercoerco Posts: 20,250
    GordonMcComb wrote: »
    It makes for a terrific challenge to integrate the sweep with real-time detection and forward motion, but this is what robotics is all about.

    Spoken like the Robo-Guru you are Gordon!

    @alex93: "Sensor Fusion" is a terrific buzzword, meaning relying on a combination of sensors. Parallax sells a bracket to mount both a PING sensor and a Sharp IR sensor in close proximity. They measure distance by different means, occasionally one will catch something the other misses. AFAIK these are used in stationary positions (often with MANY unit$ around the periphery of a circular robot), but with some grit, verve and moxy, one could scan both sensors together using one servo.

    https://www.parallax.com/sites/default/files/downloads/725-28915-Alum-Stand-Sharp-IR-Sensor-and-Ping-v1.0.pdf



  • varnonvarnon Posts: 184
    The bat article is very interesting. It is somewhat of an "of course!" moment, but I had never considered that. I wonder if there are bats, or other echolocating animals that live near very flat objects that might have a solution to this. I'm thinking about bats or echolocating birds living near very flat cliffs perhaps.
  • Heater.Heater. Posts: 21,230
    I don't think you will find many cliffs that are that flat.

    If you do I suspect there might be a reason bats don't live there :)
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    A tall, glass-sided building is a pretty flat cliff.

    -Phil
  • varnonvarnon Posts: 184
    Yeah, but bats aren't adapted to that... yet.

    Or are they? Another question might be obstacle avoidance behaviors in rural vs urban echolocators.
    Fun stuff. Somebody go do it.
  • Heater.Heater. Posts: 21,230
    And there perhaps is a problem. If you are a bat.

    But a building is not a cliff.

    I used to be upset as kid by the birds breaking their bones as they smashed into a large window on one side of our living room, expecting to be able to fly through and out the large window on the other side.

  • GordonMcCombGordonMcComb Posts: 3,366
    Heater. wrote: »
    I used to be upset as kid by the birds breaking their bones as they smashed into a large window

    Though not directly related, one time an adult barn owl smashed into our living room window -- on his way to try to snatch up our very large and fully-grown house cat. The poor owl saw something juicy, and decided to order for take-out. (Owls often concuss larger prey, then come back later to pick them apart.)

    The next morning, we found the wounded owl huddled near the house and took it into a local vet who has a contract with the city for mending such things. Apparently the owl wasn't too damaged.

  • PublisonPublison Posts: 12,366
    Heater. wrote: »
    And there perhaps is a problem. If you are a bat.

    But a building is not a cliff.

    I used to be upset as kid by the birds breaking their bones as they smashed into a large window on one side of our living room, expecting to be able to fly through and out the large window on the other side.

    Happens about twice a year on our large bay window also.

  • msrobotsmsrobots Posts: 3,704
    how about curtains?

    Mike
  • WhitWhit Posts: 4,191
    My Dad recently installed one of these on his storm door. http://www.birdscreen.com/Index.htm

    This is interesting too - https://newatlas.com/bird-protection-glass/16107/

    I wonder how a Ping))) would interact with a screen material? Might be fun to test. Would there be enough "surface" to make a reflection or would it be "invisible" to reflections?

    Lastly, would this be Ping))) resistant?

    F-117_Nighthawk_flight.jpg

    See - https://en.wikipedia.org/wiki/Stealth_technology
    F-117_Nighthawk_flight.jpg
    442 x 650 - 33K
Sign In or Register to comment.