What kind of sensors are normally used to find the distance to an object?

Hi all, I was wondering what are the common types of sensors that are used industrially to measure a distance to an object (e.g. another robot)
to avoid collision for instance?
Thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sonar and IR.
Best, - Joe
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks Joe, are they any particular advantages of using either one over the other?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's a good question; I'm sure there must be a compare & contrast article somewhere, but I don't know of one of the top of my head. So I'll wing it based on what I know, and hopefully others will chime in.
IR is nice and simple (I recommend the Sharp GP2Y0A21YK, available from Junun.org among elsewhere); it simply gives you an analog signal that corresponds to the distance of something in front of the sensor. It's a continuous reading, and you can have as many of these on your bot as you like, mounted in pretty much any fashion, and they will not interfere. (Or at least, I've never heard of such a problem.) They are quite reliable and not much affected by ambient light levels, color of the objects, etc., though when the robot they're on is in motion, they tend to work better mounted vertically than mounted horizontally.
Ultrasonic distance sensors (i.e. sonar) are generally for longer-distance sensing. I haven't actually used these yet, but I think they tend to work up to 5 meters or so. These have to be "pinged", and they can interfere, so if you have multiple such sensors on your bot you ping them one at a time in succession. That's no big deal; a bigger problem is if you're in a room (or arena) with other bots also using sonar, then the bots may pick up each other's pings and get rather confused. FIRST LEGO League discourages the use of the ultrasonic range sensor for this reason. (Why in the world LEGO doesn't include an IR distance sensor in the standard kit, I can't imagine.)
Hope this gets you started -- use your google-fu to find out more; there is a lot of information on these sensors out there.
Best, - Joe
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks for the reply Joe, very helpful information and definitely will google about it more.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sorry to bother you again, but I just thought of some other issue. To measure the distance to an object in 3 D, would using 1 sensor be sufficient? Also, do we have to place a sensor at each link to ensure that the robot will sense any obstacle?
Thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

To measure the distance to it, yes. To measure its 3D position, no.

I'm not sure what you mean by a "link." But it's true that to sense ANY obstacle will require quite a few sensors.
Best, - Joe
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

By the link I just meant the link between two joints Thanks for the info Joe appreicated
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I was wondering how many sensors would we need to know the location of an object in 3D space, so we would know when to avoid colliding with it for instance. Is there an optimal location of sensors on the manipulator?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
They are quite

Joe - I'm afraid you're not entirely correct about this. I've found that the classic sharp IR sensors are *quite* dependent on color and type of object. I did an experiment where I graphed the output voltage of an IR sensor looking at a white piece of paper, and at a black piece of paper, at varying lengths, and the two plots were substantially different from each other. Both had a fairly smooth curve though. I found similar results by changing the texture of the object being looked at.
-Mike
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

So does the sensor response time changes as the ambient light level changes? Is there a big difference in finding the distance to an object?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's interesting. I wonder if the sensor you tested is different from the newer ones. AIUI, older sensors worked based on the (IR) brightness of a reflected spot, whereas new ones work based on the *position* of the reflected spot, just like a laser range finder (but of course these inexpensive sensors are not using a laser). The position isn't much affected by the reflectance or texture of the object -- except in an extreme case, of course, where the spot is so absorbed that it can't be reliably detected at all.
But, this is an understanding gleaned in typical human fashion from many different sources, whose details are now lost, and may be all wet.
Best, - Joe
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I used a new GP2Y0A02YK.
I thought it was an interesting result as well, since the sensor uses a PSD, and PSDs are supposed to not be sensitive to the brightness of the reflected spot. However, the results were verified by other people with other parts. My suspicion was that some materials reflected the light better than others, with the scattered light messing up readings.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mike wrote:

All PSD devices are suspectible to misreadings with high ambient light, which can definitely occur when comparing an all-white object to an all-black one. These sensors tend to be used in applications where the reflective medium is known -- if it's a high-speed paper printer, for example, it will be calibrated for white reflectivity. If it's for automatic toilet flushing, it may be calibrated to an 18% gray (or some other standard), approximating average clothing color tones. An automatic sink faucet may be calibrated somewhat differently. These are not meant as universal proximity/ranging sensors, though we in amateur robotics often try to use them as such.
This is one why sensor fusion is so important. If you have 2-3 different ranging technologies, and compare/constrast the outputs, you are more likely to be able to determine a valid value. Some things, like thick black velvet, will continue to be a difficult object to measure using any non-contact sensor. Nothing -- even high-end vision systems, which can also be fooled -- will ever be perfect.
-- Gordon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
crazygrey wrote:

Actually it's a good idea to use both (as well as other means, such as mechanical limit switches). So-called sensor fusion helps to overcome the peculiarities and limitations in each technology. It's rarely a good idea to settle on just one type of sensor.
-- Gordon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Isn't there any problem arise of using both types? From Joe's post it seems like IR is mostly used for short-distance sensing and pretty accurate. What kind of limitation are they beside the interference of other sensors? If using both of them, do we have to configure them in such a way that they are communicating with each other? How do the switches help to over the limitations?
Thanks Gordon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
crazygrey wrote:

There are no absolutes because different sensors have different behaviors. You have to look at the specific sensors. They are pretty well documented, and test cases exist on their use. Use Google or Yahoo to dig these up.
Apart from space and possible power considerations, there is no "interference" between different types of sensors -- infrared light doesn't affect ultrasonic sound, and vice versa.
Finally, the use of limit switches should be pretty obvious: it's the same as the sense of touch.
-- Gordon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Thanks Gordon, very helpful info. I will certainly dig it up further
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Go to Omega online and go through their fantastic catalog to explore virtually every conceivable sensor in use today and the price, availability and specifications.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.