Hi,With Sonar and IR being the Two popular environment detection methods, I'd be interested to hear how people have got on with both, in their Serializer Projects?In addition, what have you found to be the primary advantages and disadvantages of using each? ie: Put straight any myths about glass doors or Black walls! Laters,Dan.
Hello Dan,
The Sharp IR sensors are remarkably accurate even with black surfaces. To compensate for differences in the IR reflectivity of a surface the angle of incidence of the light is actually measured instead of the light intensity. This is a very clever use of some basic trigonmetry. With the length between the emitter and detector being known and the angle to the object being calculated, they can derive the distance to the object. Some information on this topic is available here.
In general, IR sensors are better at short range sensing, and the ultrasonic sensors are better at long range. This is why many robots will have a mix of both. Also the time to acquire a measurement is generally longer with an ultrasonic sensor, though some models of the Sharp sensor have a surprisingly slow sample rate and require many milliseconds between measurements. IR sensors are also unusable outdoors because the IR light is washed out by ambient sunlight. This is why most rear bumpers on vehicles use ultrasonic sensors for collision detection.
One thing to be careful about with ultrasonics, which is never an issue with IR sensors because of the confined beam of IR light, is the need to sequence each sensor when used in combination with other ultrasonics. If one ultrasonic emits a ping, you must be sure the others are not in receiving mode or they may mistake the ping of one sensor for their own and produce a false distance measurement.
I don't have much experience using ultrasonics around glass since most of my robots are only a few inches from the ground where walls and shoes live. :-)
The ultimate ranging sensor, IMHO, are laser range finders. Many of the vehicles in the DARPA challenge were bristling with laser range finders of various types. They are the least noisy, and can precisely locate the heading to the object, at a specific point is space. The cost factor is what keeps the hobbyist community from adopting them, and perhaps their use indoors could present a hazard to human optics, but I am not sure of this.
James Y. Wilson http://www.learningce.com Fortudine Vincimus!
Hi James,Thankyou for your comprehensive reply, discussing both IR and Ultrasonic sensors also. Have been looking for similar write-ups on the internet, discussing one VS the other.However have to say that your Post above covers the subject very nicely!Do either of these sensor types make any audible sound as they are pinging off their light/sonar? I take it the IR sensors would be quieter? My robot project will (also) be primarily used indoors - therefore, the IR sensor sounds the better option in this case?Totally agree, re the ultimate sensor being laser finders! There are some amazing videos on YouTube that demonstrate these, that display the laser 'map' of the terrain as the vehicle (I take it) navigates a fairly un-even road / dirt track. Wonder how long it will be before prices of these units drop to an extent where their purchase becomes a cost effective option for the home/school robotics project !