accelerometer or gyroscope ?

[banh]

accelerometer tilt gravity gyro

in headlamp levelling system, i wonder if gyroscope or accelerometer should be used?

according to this link:
https://www.analog.com/UploadedFile...01503599017955374255071695672126HEADlevel.pdf
an accelerometer has been used..

but for tilt sensing, i think a gyroscope should be more suitable?

 

[IanP]

difference between gyroscopes and accelerometers

To measure/control tilt you need an inclinometer rather than a gyro which is used to measure/control heading ..
Here is an example of using ADXL202 accelerometer as tilt sensor:
**broken link removed**

Using a gyroscope by itself seems reasonable, but the gyro develops a slow creeping tilt error that continues to increase. An example of this is when you tilt the gyro you'll see a change in the output voltage, but it quickly returns to it's resting level, if the tilt doesn't change. Thus if your robot was to tilt forward a few degrees and stay at that angle, the gyro will report that the robot is standing straight up after a second. So eventually the errors add up and the robot falls over. Using an accelerometer helps to solve this problem. The accelerometer outputs a steady duty cycle when the robot is standing straight up, and if the robot tilts one way or the other the duty cycle changes, and stays changed, until you have the robot's computer correct for the tilt.

Regards,
IanP

 

[nilesh_etc]

using a gyroscope to measure tilt

hi whats ur querry ?The purpose of using accelerometer and gyroes are ingenerally same . But according to my opinion u should use accelerometer because for finding tilt in navigation system many people use accelerometers. there are many accelerometers available on analog devices website for 3 axis,2 axis and single axis.

 

[banh]

To measure/control tilt you need an inclinometer rather than a gyro which is used to measure/control heading ..
Here is an example of using ADXL202 accelerometer as tilt sensor:
h**p://www.dprg.org/projects/2003-01a/

Using a gyroscope by itself seems reasonable, but the gyro develops a slow creeping tilt error that continues to increase. An example of this is when you tilt the gyro you'll see a change in the output voltage, but it quickly returns to it's resting level, if the tilt doesn't change. Thus if your robot was to tilt forward a few degrees and stay at that angle, the gyro will report that the robot is standing straight up after a second. So eventually the errors add up and the robot falls over. Using an accelerometer helps to solve this problem. The accelerometer outputs a steady duty cycle when the robot is standing straight up, and if the robot tilts one way or the other the duty cycle changes, and stays changed, until you have the robot's computer correct for the tilt.

Regards,



IanP

wow, this contradicts my understanding of gyroscope and accelerometer..
originally i thought for tilt sensing gyroscope should be used, and for acceleration (like in airbag system) accelerometer should be used.

why here for tilt sensing, i can use accelerometer here? for e.g. if the car is tilted on a slope, and is not moving, what should the output of the accelerometer be?

Added after 2 minutes:

btw, anyone know any project for this headlamp levelling system ? i'm not sure how the mechanical part has been designed..
(i.e. how many motors & how they are positioned..)

 

[IanP]

Some accelerometers are better suited towards measuring vibration and shock such as the piezo-film and piezoelectric. Others are used for tilt measurements such as liquid tilt and micromachined types. The type of sensor selected then dictates the signal conditioning circuitry requirements.
Some accelerometers have AC response, some DC. Some sensors have analog outputs, others digital. In other words, one accelerometer does not fit into all applications.

Quoted from:
"Measure Tilt Using PIC16F84A & ADXL202"
https://ww1.microchip.com/downloads/en/appnotes/00715a.pdf

Regards,
IanP

 

[banh]

thanks IanP, i willl digest the above AN.

so which application is a gyroscope more suitable?

 

[IanP]

Gyroscopes are well known as sensors to detect the revolution movements or angular velocities of objects as they are not affected by distance between its installation position and the centre of revolution.

Conventional gyroscopes - spinning mass gyroscopes, originally the gyroscopes of choice for space applications, determine changes in angular direction, traditionally by virtue of a rapidly spinning, heavy mass.

Gyroscopes using piezoelectric vibrators are called piezoelectric vibrating gyroscopes.
They are extensively used for car navigation systems and video movies as angular velocity sensors that were excellent in precision, and significantly lower in cost compared with conventional ones.

Other applications include automotive safety, image stabilization, inertial measurement units, and platform stabilization et cetera, et cetera ..

Regards,
IanP

 

[banh]

Gyroscopes are well known as sensors to detect the revolution movements or angular velocities of objects as they are not affected by distance between its installation position and the centre of revolution.

ok got it,thanks IanP.

because gyroscope is for angular velocity. the output waveform only changes when the object moves. after it rests at a tilted position, the output waveform will return to its original as at this time angular velocity is 0.

 

[Kral]

banh,

What was the question?

Regards,
Kral

 

[banh]

i saw the link (in my first post) which uses accelerometer fo tilt sensing, and i think it should be gyroscope...

just my confusing of accelerometer and gyroscope and their usage.

 

[Kral]

banh,
The problem with using a gyroscope in this application, is that the gyroscope, along with its associated sensor, would measure the angle with respect to the center of the Earth. For this discussion I'm ignoring the problem associated with drift. However, what we want to measure is the angle of the headlight axis wrt the surface of the road. We obviously don't want to change the headlight tilt as we start to climb a hill, which is what a gyroscope would do! By integrating the ouput of an accelerometer within a specified frequency range, we can measure slow changes in tilt while ignoring changes in angle with respect to the center of the Earth. The high pass portion of the bandpass filter takes care of this. It removes the constant 1 g associated with gravity.
~
Incidentally, the only difference between a tilt sensor and an accelerometer is the way they are calibrated. The output of an accelerometer = (Vertical Acceleration) X Sin(Tilt angle), assuming that there is no linear acceleration along the sensitive axis of the accelerometer. This equation assumes that the sensitive axis of the accelerometer is horizontal. Otherwise you would use Cosine instead of Sine.
Regards,
Kral

 

[puviarasu]

Then there is no need of a gyro or accelerate meter as you can measure the lamp angle with respect to the ground (ie the body of the car) by using a inexpensive potentiometer of capacitive sensor. As it is not affected by earths gravity or acceleration of the car.

 

[banh]

Then there is no need of a gyro or accelerate meter as you can measure the lamp angle with respect to the ground (ie the body of the car) by using a inexpensive potentiometer of capacitive sensor. As it is not affected by earths gravity or acceleration of the car.

yes good idea!

i actually think about potentiometer.

what is capacitive sensor that can be used in this case?

 

[kadetsenior]

I'm not sure about this potentiometer of capacitive sensor, but if you only need the tilt (estatically) you can use an accelerometer. I use the MMA7260Q 3 axis. But if you need the tilt in motion(dinamically) you should use gyroscope because the coriolis efect.