Ping Ultrasonic distance sensor efficiency depending on angle detection ?

alex93alex93 Posts: 11
edited October 16 in Robotics Vote Up0Vote Down
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.
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Comments

  • 16 Comments sorted by Date Added Votes
  • 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
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • 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.



    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • 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."
    571 x 303 - 36K
    Whit+

    "We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
  • 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


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

    Thank you very much all for your answers.
  • GordonMcCombGordonMcComb Posts: 3,142
    edited October 17 Vote Up0Vote Down
    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.
  • 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



    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • 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.
  • 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 :)
  • A tall, glass-sided building is a pretty flat cliff.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • 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.
  • 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.

  • 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.

  • 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.

    Infernal Machine
  • how about curtains?

    Mike
    I am just another Code Monkey.

    A determined coder can write COBOL programs in any language. -- Author unknown.

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this post are to be interpreted as described in RFC 2119.
  • 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
    442 x 650 - 33K
    Whit+

    "We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
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