Why a Laser sensor ?

markuster

Hi,

Just to understand why Parallax has a laser sensor to detect distance since
Parallax has the ultrasonic PING module?

Even I read that the laser sensor has less measure distance.

I don't understand , sorry perhaps the Laser sensor has other
functions better than the ultrasonic sensor module. But I can not find them.

Could you help me to understand the product ?
Thanks

Jen J.

As I understand it, the laser has a longer range and can be more accurate. Plus, it's cool.

Ken Gracey

markuster,

There are times when an ultrasonic sensor won't effectively measure distance. One time is when the angle of transmission is sharp, so that the reflected sound wave doesn't come back to the sensor. It seems to work most effectively when the detected object is dead in front. Another time when ultrasonic doesn't work is when there's a fabric or soft surface that absorbs the sound waves. In these cases the laser rangefinder would be a better choice.

Sometimes neither sensor is good, too. Long distances, very short distances, or in wet environments are a couple of examples.

Ken Gracey

mindrobots

What kind of distance sensor are you going to put inside the plexiglass bubble of your robot submarine?
What if you stumble into some place with spurious 40khz frequencies?
What if somebody covers everything in sound deadening foam?
What if you want laser targeting for your Nerf cannon because all the cool kids have it?
What if your pet bat gets REALLY upset by your Ping)))?
Better resolution?

Other than that, I'm sure some very good applications will show up once the smart guys get hold of them!

Ken Gracey

mindrobots wrote: »

What if your pet bat gets REALLY upset by your Ping)))?

Rick, how about dogs - anybody know if dogs are upset by a Ping)))? I imagine they aren't bothered by low frequencies and I didn't research the answer to the question.

Ken Gracey

mindrobots

Ken,

From the Trivial Research division of Parallax.

FYI....to protect your animals:

Species Approximate Range (Hz)
human 64-23,000
dog 67-45,000
cat 45-64,000
cow 23-35,000
horse 55-33,500
sheep 100-30,000
rabbit 360-42,000
rat 200-76,000
mouse 1,000-91,000
gerbil 100-60,000
guinea pig 54-50,000
hedgehog 250-45,000
raccoon 100-40,000
ferret 16-44,000
opossum 500-64,000
chinchilla 90-22,800
bat 2,000-110,000
beluga whale 1,000-123,000
elephant 16-12,000
porpoise 75-150,000
goldfish 20-3,000
catfish 50-4,000
tuna 50-1,100
bullfrog 100-3,000
tree frog 50-4,000
canary 250-8,000
parakeet 200-8,500
cockatiel 250-8,000
owl 200-12,000
chicken 125-2,000

Compilation of various experimental methods, so YMMV!

It's rather apparent why chickens don't use echo location.

Ken Gracey

Okay, I'll quit using my Madeusa robot with ten Ping sensors around the family opossum. Thanks for the research!

Ken Gracey

Laser Developer

Laser range finders are my favorite subject. I became interested in them many years ago when I worked on a "black-ops" project that I can't talk about. Our first laser rangefinder worked on the time-of-flight principle and within a few months of starting the project it was already measuring over a mile with a resolution of about an inch. I was just blown away by the astonishing performance of the laser - it seemed able to measure the distance to anything that it was pointed at, trees, buildings, grass, rocks, muddy water, traffic signs...

More recently, I worked for a company that manufactures both laser and ultrasonic distance measuring sensors. We were able to do performance comparisons to find the limits/pros/cons of each technology.

The ultrasonic sensors that we tested used the time-of-flight of a sound pulse to measure distance (like the Ping). The laser sensors that we tested came in two types: triangulation (like the new Parallax laser) and time-of-flight (like the laser being developed on the Sensors forum at http://forums.parallax.com/showthread.php?133632-Time-of-Flight-Laser-Project).

Whilst the actual performance of a particular sensor has limitations by design (to keep the cost down), there are some consistent performance differences between ultrasonic and laser sensors that relate to the laws of physics underpinning the two types of technology. Below is an incomplete comparison list:

Ultrasonic TOF
Pros:

• Easy technology to make work.
• Low cost.

Cons:

• Wide beam angle (not able to isolate specific targets or "see" through gaps).
• Loses signal on smooth, angled surfaces (reflections).
• Gets multiple return signals from flat surfaces (echoes).
• Susceptible to background noise and wind.
• Signal is absorbed by soft or rough surfaces.
• Can't see through glass.
• Accuracy changes with temperature and atmospheric pressure.

Laser Triangulation
Pros:

• High accuracy possible (<1 mm).
• High speed measurements possible.
• Narrow beam for accurate aiming.
• Can measure to target surfaces at any angle with any surface texture.
• Can be used to create high resolution, 3D images by scanning.
• Fairly easy technology to make work.

Cons:

• Limited maximum and minimum ranges (the Parallax version is typical).
• Sensitive to bright background light patterns (can be improved with an optical filter)
• Requires very good mechanical stability of the optical components (it's an opto-mechanical system).

Laser TOF
Pros:

• Very wide dynamic range possible (from 0m to >100m)
• Accurate aiming to targets and through gaps (very small beam divergence).
• Can measure to target surfaces at any angle.
• Can be set to measure through glass or to the surface of glass.
• Immune to background light, noise, wind, surface texture, surface color etc.
• Very easy to use in practice - WYSIWYG - "if you can see the target then the laser will probably be able to measure it."
• Can be used to create large scale, 3D images by scanning.

Cons:

• Few companies have the technology.
• Can be more expensive (depending upon maximum range).
• Range is limited by dust, fog and rain.

SRLM

I don't think the new laser sensor is better than a ping for many applications. The range is comparable, and the sampling frequency is disappointing (1Hz to at ~10Hz plus with the ping). It seems that the laser ranger is better for measuring a specific point or measuring through a transparent surface. Still, it will do things the Ping can't.

erco

Jen J. wrote: »

Plus, it's cool.

If a lady brandishing a chainsaw says something's cool, this court will not dispute it!

SRLM

The laser sensor also has the advantage of a red laser dot that indicates the point being measured...

prof_braino

SRLM wrote: »

The laser sensor also has the advantage of a red laser dot that indicates the point being measured...

The laser read the distance to dot, this is handy when there are many items at difefernt distances in the sensor range. Consider a ball under a table with many chairs.

The ultra sonic would return several readings or garabage.

The right tool for the right job, as always.