Ultrasonic and infrared range finder

rmnietormnieto Posts: 4
edited 2005-02-15 - 12:40:41 in Robotics
·Hello all,

·· I'm looking for a very small ultrasonic or infrared distance sensor with a hight accuracy (0,1 inches/3mm) in short distances, less than 11 inches/30 cm.
·Thanks for your help.

······················· Rodolfo



  • Robert SchwartzRobert Schwartz Posts: 141
    edited 2005-02-12 - 03:30:28
    Acroname has a huge amount of devantech ultrasonic sensors such as the SRF10 and the smaller srf235. These are rather expensive though. About what size are looking at. You could theoreticly make your own IR detector with SMT parts and make it really, really small.
  • rmnietormnieto Posts: 4
    edited 2005-02-13 - 11:50:28
    ·What I want is to mount two distance sensors (ultrasonic or infrared) in a 5cm/1,95 inches surface.
    ·The goal is two take both distances and to calculate where is the detected object respect the surface.

    ·Again, thanks for your help.

  • inakiinaki Posts: 262
    edited 2005-02-13 - 14:40:05
    The problem I see in your case is not sensor size (you can place most sensor on a 5cm surface)·but sensor precission.

    You say you need 3mm precission in a range up to 30cm.
    At least the IR and US sensors I have tried do not give that kind of precission.

    High precission US sensors have a resolution of 0.03 inches, that is about 7mm.

    Also, ultrasound·sensors must be callibrated every time you use·them because temperature and humidity affect the measures. This problem does not happen with IR.

    On the other hand, for short·distances you must take into acccount that both·ultrasound and infrared have a gap between the sensor and the minimum distance they can measure. This minimum distance varies with the kind of sensor and model·but falls between 3cm and 10cm.

  • rmnietormnieto Posts: 4
    edited 2005-02-14 - 10:38:27
    ·Thanks, but which is the IR·sensor precission?

    ·Do you think it would be possible to have a unique·IR emitter and two IR receiver·measuring the distance (look the picture for details)?


    ·········· rodolfo

    600 x 559 - 22K
  • inakiinaki Posts: 262
    edited 2005-02-15 - 12:40:41
    Using two simple·emitters and one IR receiver is used·to detect the presence of an obstacle, not specially to measure distances.

    Using two receivers and one emitter, your scheme,·does not serve per se to measure distances. The triangle would be flatter as the object gets nearer but you need a way to measure how flat is it, that is to measure the angle of the incoming beam.

    To get measure distance two techniques are used:·using an emitter and a receiver calculate the time·it takes for the light to travel. As the light travels so fast is necessary to add a switcher in front of·the receiver. The speed of the switcher combined with the incoming light·is used to calculate distance. Unless a fast switcher is used it gives poor performance. This was the method used to measure the speed of light many years ago. The most common method is using 'angle of incidence'. In this case a lens is placed on top of receiver and a sensor behind the lens detects the place where the incoming ligh falls. If the object is far the incident light falls in a place different that when the object is near. The sensor in the receiver is a ccd strip or an array of ir receivers. This method is used for example by Sharp detectors.··However these detector have a pretty large gap in front of the detector of about 10cms where no measure can be obtained.

    Look·at the following Acroname page so read an explanation of the subject: http://www.acroname.com/robotics/info/articles/sharp/sharp.html
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