Types of Encoders

Google or Find in WIKI both have these in details.

Cam? Why? Homework?

sounds like you might be after a rotary encoder - http://en.wikipedia.org/wiki/Rotary_encoder - its often used to measure the angular velocity of a rotating shaft. Regarding your 'cam' question - its a bit vague, you'll need to provide more information. You could certainly use the data recorded by the encoder to switch another device at a certain angular position of the shaft, like a cam is often used to do.

Hope that helps

TinTin

Hi rakheshrh

On a CNC machine a stepper motor can be instructed to advance a number of steps and any position on the workpiece can be instructed to step accuracy. A servo motor is fast but not that precise and some or other mechanism have to be used to correct any errors.

A circular encoder is mostly used. A basic encoder can be made of a transparent disk with spaced lines. a "light" and a sensor is placed on both sides enabling counting the number of lines passing the eye. Enabling accurate positioning.

Advanced encoders must also detect direction.

The next step in encoders can be a linear encoder where the lines are on a transparent bar (like a ruler)

Ther are of course others.

It is used in Computer Aided Manufacturing and not as.

ftp.cnchungary.com/.../Encoders/Eltra.../Elte_incremental_encoders_DataSheet.pdf

Go thru this link,u will find useful information about encoders....

Regards

R.Arun

Hello rakheshrh,

Can you please say whether you want computer info' or, engineering answer?

Ok, many thanks for the info'. It did seem that your first request could be either Mechanical or IT driven.

At least we know what you want, thanks once again.

Hello Guest,

Yes an encoder and PLC can be used instead of mechanical cams to carry out certain activities. However this does not mean that you can throw out all the cams and just put in an encoder - if you wished to throw out all ofthe cams then this would require a substantial rebuild of your existing machines. In addition to this the controller (PLC or PC) that you are using would need to be able to handle all the drives and the normal I/O that exists on a typical machine.

If you were to purchase a modern high speed packaging machine you will probably find that most have very few (if any) mechanical cams installed, see PacDrive at www.elau.de/Rahmen.asp?Knoten=170 for further details.

Kind Regards

Mr. W.A Snow

It can be achieved, but you'll have to modify or retrofit your control, you need room on your PLC and the capability to use Hi-Speed Counter modules or Axis Position Modules, some PLCs can do this like GE Fanuc or Allen-Bradley. These modules relieve much of the math operations to the CPU, thus having a fast program scan cycle.

Besides these module have some outputs that you can configure and use if you need immediate response to your position related conditions.

Yahlasit

Hai,

I have the PLC with high speed input please tell me

which type of encoder I can use absolute or incremental?

Presently I am using Fateks FBs 40MAT Model PLC.

Oh you have to do better than that to really make a knowledgeable answer.

1. First questions are how fast is high speed, both for your PLC and for the shaft connected to the encoder? (You did list a model for the PLC but I'm not going to do your leg work.)
2. Next you have to identify what resolution you need in this encoder?
3. Next do you require position knowledge at startup or can you hunt for "home"? (This question will determine absolute or incremental encoder.)
4. Identify mechanical mounting type required for encoder.
5. Lastly, but most important, what is the task this PLC is doing with this encoder?

Once you identify the answer to these questions you should be able to select which encoder on your own and likely succeed in your engineering design. If you cannot answer all of these questions, then a likely guess will permit choosing a suitable at the higher risk of guessing wrong.

Hello Guest,

Why do you want to change your encoder?

And what do you need to do with the replacement?

I need more info' to allow me to find the encoder which suites your computer.

Saying "I have a high speed computer" is not enough as almost all computers are 'hi speed'!

encoders are all the rage because they are simple. an optical pair (an LED and a phototransistor facing each other) are situated on either side of a precision etched disk and the encoder counts how many steps go past the optical pair. they are actually a little more complex than that. there are actually a set of two photodetectors and the disk is encoded with two sets of lines out of phase with each other such that the encoder knows whether it is counting up or down, and therefore knows what direction it is counting. There is a third optical pair to detect the zero or home position.

But the problem with encoders is that the stepper/servo has to turn, usually a full revolution, at startup before it knows where it is. resolvers do not. encoders also have a minimum step size resolution and if the commanded location falls between the two, the system will constantly seek between the two.

resolvers are a four pole transformer with a rotating core. they have infinite resolution and know where they are on startup, but they are larger and more expensive.

http://www.optoresolver.com/help/tutorials/resolver_v_encoder.htm

http://www.ormec.com/LinkClick.aspx?fileticket=I0Fu66PzelM%3D&tabid=91&mid=866

There are also absolute optical encoders that immediately know their position. They immediately display their position in a host of different techniques; parallel, serial, binary, grey code progression. BEI makes a nice collection encoders. The basic thing of all encoders is that they only determine the position of a rotated shaft. Some to ludicrously high precision while others can barely tell the hour of a clock's hour hand.

Encoders do not actually move something the way a cam does. But if your cam is moving the mechanism of a switch then a simple "encoder" of just a shuttered opto switch will do for you, probably to higher precision than you've had before. If your cam opens a manifold valve of a 5.0 liter engine, then you'll need some serious mechanical and electrical design work to use an encoder to time the opening of that valve.

I don't know how complex your control project is or what your budget is like but you can find information relating to electrical cams and machine control at Electro Cam Corp.

I have used their devices in the past with great success. They are an easily programmed interface between a resolver and a PLC or they can stand alone in machine control.

Just another avenue to search. Good luck!

encoder is nothing but the improved version of electronic cam.
earlier people using coged wheel for position feed backwhich is cam