SRF04 Specular Angle failure.
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Posts: 46,084
Bruce: Thank you for your assistance. My problem with the srf04 and I think
with any sonar unit is not the working of the device or the accuracy, it is
a function of sound bouncing around corners, or in my case following a wall.
At 3 am last night I dug out an answer on the internet, I will quote the
following. I am sure it will be of help to others.
"Another significant error is specuIar reflection, which occurs when the
angle of incidence of the beam falls below a certain critical angle. Below
the critical angle the reflected energy does not return to strike the
transducer (Figure 4). This occurs because most targets are mirror smooth at
the 0.25 inch wavelength of ultrasonic energy. In specular reflection, the
angle of reflection equals the angle of incidence; in diffuse reflection,
energy is scattered in various directions by surface irregularities. The
critical angle is thus a function of the operating frequency chosen and the
smoothness target. For the sensors used on RSSCy this angle is approximately
65 degrees for a flat target surface of unfinished plywood such as would be
encountered for maze walls or for dividers in the wall following contests.
In Figure 4a the ranging system would not see the target and would indicate
instead maximum range, whereas in Figure 4b the range reported would reflect
the total round trip through points A,B, and C as opposed to just A and B.
The website I read this at is
http://www.seattlerobotics.org/encoder/may97/sonar2.html
There is a nice photo of my problem as well. FIgure 4a and 4B
In my case the reflection does return to the srf04, however it is the
measurment of the total length of the hall. In my case, an erroneus reading
If what I really want to detect is the distance from robot to the nearest
point on the wall.
I am pretty stumped now as to what to do for collision avoidance [noparse]:([/noparse]
-Kerry
At 10:24 AM 2/9/04 -0500, you wrote:
>SRF-04 Users:
>
>For those who may be interested in more information on the Devantech SRF-04
>as regards its idiosyncrasies, and some of the experimenting done by other
Stamp Users, take a look at the thread entitled "SRF04 Ultrasonic Range
Finder" which
>appeared about 10/15/2003 here on the Yahoo Groups Stamp List.
>
>Included in these postings, by numerous contributors, is a full description
of the Devantech software program which drives the SFR04 Range Finder, as
well as numerous comments about erroneous reading, and how to deal with
them. All of the posts are quite thorough and address many areas of concern.
>
>Regards,
>
>Bruce Bates
>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>Yahoo! Groups Links
>
>
>
>
>
>
Very respectfully, your obedient servant.
Brig. Gen. Johnston Pettigrew
Admin@M...
WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
Kerry Barlow
p.o. box 21
kirkwood ny
13795
607-775-1575
with any sonar unit is not the working of the device or the accuracy, it is
a function of sound bouncing around corners, or in my case following a wall.
At 3 am last night I dug out an answer on the internet, I will quote the
following. I am sure it will be of help to others.
"Another significant error is specuIar reflection, which occurs when the
angle of incidence of the beam falls below a certain critical angle. Below
the critical angle the reflected energy does not return to strike the
transducer (Figure 4). This occurs because most targets are mirror smooth at
the 0.25 inch wavelength of ultrasonic energy. In specular reflection, the
angle of reflection equals the angle of incidence; in diffuse reflection,
energy is scattered in various directions by surface irregularities. The
critical angle is thus a function of the operating frequency chosen and the
smoothness target. For the sensors used on RSSCy this angle is approximately
65 degrees for a flat target surface of unfinished plywood such as would be
encountered for maze walls or for dividers in the wall following contests.
In Figure 4a the ranging system would not see the target and would indicate
instead maximum range, whereas in Figure 4b the range reported would reflect
the total round trip through points A,B, and C as opposed to just A and B.
The website I read this at is
http://www.seattlerobotics.org/encoder/may97/sonar2.html
There is a nice photo of my problem as well. FIgure 4a and 4B
In my case the reflection does return to the srf04, however it is the
measurment of the total length of the hall. In my case, an erroneus reading
If what I really want to detect is the distance from robot to the nearest
point on the wall.
I am pretty stumped now as to what to do for collision avoidance [noparse]:([/noparse]
-Kerry
At 10:24 AM 2/9/04 -0500, you wrote:
>SRF-04 Users:
>
>For those who may be interested in more information on the Devantech SRF-04
>as regards its idiosyncrasies, and some of the experimenting done by other
Stamp Users, take a look at the thread entitled "SRF04 Ultrasonic Range
Finder" which
>appeared about 10/15/2003 here on the Yahoo Groups Stamp List.
>
>Included in these postings, by numerous contributors, is a full description
of the Devantech software program which drives the SFR04 Range Finder, as
well as numerous comments about erroneous reading, and how to deal with
them. All of the posts are quite thorough and address many areas of concern.
>
>Regards,
>
>Bruce Bates
>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>Yahoo! Groups Links
>
>
>
>
>
>
Very respectfully, your obedient servant.
Brig. Gen. Johnston Pettigrew
Admin@M...
WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
Kerry Barlow
p.o. box 21
kirkwood ny
13795
607-775-1575
Comments
can be easily used to detect something which
is 'close' (3 to 6 inches), to corroborate the
ultrasonic distance measurement.
Just a suggestion. It would give you a
non-contact 'whisker' for wall-following.
--- In basicstamps@yahoogroups.com, Kerry Barlow <admin@m...> wrote:
> Bruce: Thank you for your assistance. My problem with the srf04 and
I think
> with any sonar unit is not the working of the device or the
accuracy, it is
> a function of sound bouncing around corners, or in my case
following a wall.
> At 3 am last night I dug out an answer on the internet, I will
quote the
> following. I am sure it will be of help to others.
>
> "Another significant error is specuIar reflection, which occurs
when the
> angle of incidence of the beam falls below a certain critical
angle. Below
> the critical angle the reflected energy does not return to strike
the
> transducer (Figure 4). This occurs because most targets are mirror
smooth at
> the 0.25 inch wavelength of ultrasonic energy. In specular
reflection, the
> angle of reflection equals the angle of incidence; in diffuse
reflection,
> energy is scattered in various directions by surface
irregularities. The
> critical angle is thus a function of the operating frequency chosen
and the
> smoothness target. For the sensors used on RSSCy this angle is
approximately
> 65 degrees for a flat target surface of unfinished plywood such as
would be
> encountered for maze walls or for dividers in the wall following
contests.
> In Figure 4a the ranging system would not see the target and would
indicate
> instead maximum range, whereas in Figure 4b the range reported
would reflect
> the total round trip through points A,B, and C as opposed to just A
and B.
>
> The website I read this at is
> http://www.seattlerobotics.org/encoder/may97/sonar2.html
> There is a nice photo of my problem as well. FIgure 4a and 4B
>
> In my case the reflection does return to the srf04, however it is
the
> measurment of the total length of the hall. In my case, an erroneus
reading
> If what I really want to detect is the distance from robot to the
nearest
> point on the wall.
> I am pretty stumped now as to what to do for collision avoidance [noparse]:([/noparse]
> -Kerry
>
>
>
>
>
> At 10:24 AM 2/9/04 -0500, you wrote:
> >SRF-04 Users:
> >
> >For those who may be interested in more information on the
Devantech SRF-04
> >as regards its idiosyncrasies, and some of the experimenting done
by other
> Stamp Users, take a look at the thread entitled "SRF04 Ultrasonic
Range
> Finder" which
> >appeared about 10/15/2003 here on the Yahoo Groups Stamp List.
> >
> >Included in these postings, by numerous contributors, is a full
description
> of the Devantech software program which drives the SFR04 Range
Finder, as
> well as numerous comments about erroneous reading, and how to deal
with
> them. All of the posts are quite thorough and address many areas of
concern.
> >
> >Regards,
> >
> >Bruce Bates
> >
> >
> >
> >To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> >from the same email address that you subscribed. Text in the
Subject and
> Body of the message will be ignored.
> >
> >Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> Very respectfully, your obedient servant.
> Brig. Gen. Johnston Pettigrew
>
> Admin@M...
> WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
> Kerry Barlow
> p.o. box 21
> kirkwood ny
> 13795
> 607-775-1575
problem with IR is it will not read certain white smooth surfaces. The other
day it would not read an orange wall. So IR is not dependable either.
I can go back to bumper sensors, but then I may as well buy a $2 kids toy
and do the same thing without any electronics.
_kerry
At 08:21 PM 2/9/04 -0000, you wrote:
>A very simple IR_LED and IR_Detector pair
>can be easily used to detect something which
>is 'close' (3 to 6 inches), to corroborate the
>ultrasonic distance measurement.
>
>Just a suggestion. It would give you a
>non-contact 'whisker' for wall-following.
>
>--- In basicstamps@yahoogroups.com, Kerry Barlow <admin@m...> wrote:
>> Bruce: Thank you for your assistance. My problem with the srf04 and
>I think
>> with any sonar unit is not the working of the device or the
>accuracy, it is
>> a function of sound bouncing around corners, or in my case
>following a wall.
>> At 3 am last night I dug out an answer on the internet, I will
>quote the
>> following. I am sure it will be of help to others.
>>
>> "Another significant error is specuIar reflection, which occurs
>when the
>> angle of incidence of the beam falls below a certain critical
>angle. Below
>> the critical angle the reflected energy does not return to strike
>the
>> transducer (Figure 4). This occurs because most targets are mirror
>smooth at
>> the 0.25 inch wavelength of ultrasonic energy. In specular
>reflection, the
>> angle of reflection equals the angle of incidence; in diffuse
>reflection,
>> energy is scattered in various directions by surface
>irregularities. The
>> critical angle is thus a function of the operating frequency chosen
>and the
>> smoothness target. For the sensors used on RSSCy this angle is
>approximately
>> 65 degrees for a flat target surface of unfinished plywood such as
>would be
>> encountered for maze walls or for dividers in the wall following
>contests.
>> In Figure 4a the ranging system would not see the target and would
>indicate
>> instead maximum range, whereas in Figure 4b the range reported
>would reflect
>> the total round trip through points A,B, and C as opposed to just A
>and B.
>>
>> The website I read this at is
>> http://www.seattlerobotics.org/encoder/may97/sonar2.html
>> There is a nice photo of my problem as well. FIgure 4a and 4B
>>
>> In my case the reflection does return to the srf04, however it is
>the
>> measurment of the total length of the hall. In my case, an erroneus
>reading
>> If what I really want to detect is the distance from robot to the
>nearest
>> point on the wall.
>> I am pretty stumped now as to what to do for collision avoidance [noparse]:([/noparse]
>> -Kerry
>>
>>
>>
>>
>>
>> At 10:24 AM 2/9/04 -0500, you wrote:
>> >SRF-04 Users:
>> >
>> >For those who may be interested in more information on the
>Devantech SRF-04
>> >as regards its idiosyncrasies, and some of the experimenting done
>by other
>> Stamp Users, take a look at the thread entitled "SRF04 Ultrasonic
>Range
>> Finder" which
>> >appeared about 10/15/2003 here on the Yahoo Groups Stamp List.
>> >
>> >Included in these postings, by numerous contributors, is a full
>description
>> of the Devantech software program which drives the SFR04 Range
>Finder, as
>> well as numerous comments about erroneous reading, and how to deal
>with
>> them. All of the posts are quite thorough and address many areas of
>concern.
>> >
>> >Regards,
>> >
>> >Bruce Bates
>> >
>> >
>> >
>> >To UNSUBSCRIBE, just send mail to:
>> > basicstamps-unsubscribe@yahoogroups.com
>> >from the same email address that you subscribed. Text in the
>Subject and
>> Body of the message will be ignored.
>> >
>> >Yahoo! Groups Links
>> >
>> >
>> >
>> >
>> >
>> >
>> Very respectfully, your obedient servant.
>> Brig. Gen. Johnston Pettigrew
>>
>> Admin@M...
>> WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
>> Kerry Barlow
>> p.o. box 21
>> kirkwood ny
>> 13795
>> 607-775-1575
>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>Yahoo! Groups Links
>
>
>
>
>
>
Very respectfully, your obedient servant.
Brig. Gen. Johnston Pettigrew
Admin@M...
WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
Kerry Barlow
p.o. box 21
kirkwood ny
13795
607-775-1575