encoder robotics

[josef_slg]

Hello,

my question: I have got a industriel robot with standard encoders (3 Phase, A, B and Z) at each joint (6). Now I want to use a DAQ System to read these values while we re moving this device manuelly. (no motors, just a measuring device).
Now I want to know, which Hardware you can recommend and what the easiest and fastest way is to implement the Software to get a running DAQ.
Data Aqusition is new for me, so please help me.

Thank you in advace.
Peter

[Brian_Beal]

I would recommend an encoder input card from Measurement Computing.  You will need 2 of them.  They have Labview drivers.  The other option is to use a 6-axis NI motion card, and only wire up the encoder inputs.

[josef_slg]

and what about implementing the software ? Which one works easier and can I just take example code ? Do they provide example code for 6x  quadrature encoders ?

[Brian_Beal]

I guess I should ask what software you are using.  Examples are provided, but they would be portions of your application, not the exact thing.

[Kevin_Price]

I'm not familiar with Measurement Computing's hardware, so I would have recommended NI's 6602 counter/timer board.  One board can handle up to 8 quad encoders, provided that you only need software-timed or slow-ish (kHz realm or less) interrupt-based sampling.

One advantage of an NI board is the ability to use MAX for debugging and troubleshooting.

It's not clear to me how you're going to accomplish "homing" with your incremental encoders though.  When you first start your DAQ program, the driver will (by default) call your present position "0" for all the joints' encoders.  Some other day if you start the program fresh, you're liable to get a different "0".  The available Z-index pulses may help you, but depending on robot type & kinematic constraints, they may not be enough.

-Kevin P.

[josef_slg]

I will use LabView or will have to use LabView. SO there is no piece of Software what I can use as am example, means no 6 quadrature encoder example ?
We realise "homing" with a calibration rig, that means having a "zero" position, moving with our device and reading out the end effector position with this DAQ device I should create. Than we got another measurement system, a cmm (doordinate measurement machine), which we use to compare the measurement results. We will gav eher the same "homing" and can compare so both systems.
What about filtering noise (lowpass) and so on, is it included in this DAQ or do I have to implement a low pass filter ?

My only concern is the Software for the DAQ, because I haven´t done it before, you know implementing, testing a filter, implementing the DAQ Software, testing, calculating the endeffector position and so on. We will use LabView, so if there is existing example Code, it will help me a lot.

And the hardware, we are going to spent a bit money on it, for sure with a NI-card.
So maybe you can help me going on ?

[Brian_Beal]

Is there some controller running this robot already? 

You need to check what kind of encoders you have before you buy a card.  The NI 6602 is a counter card, the Measurement Computing card is an encoder card.  You may be able to use the 6602, but you need to look into that.

[josef_slg]

I will let you know on Monday which encoders we use and what the control system is like.

[Kevin_Price]

The 6602 is indeed a general purpose counter board but one of its capabilities is true 4x quadrature decode and support for reset on z-index, if desired.  In particular, the 6602 would need TTL/CMOS compatible encoder signals. 

However, many encoders put out differential pairs, which would require you to put a differential line receiver circuit between the encoder signals and the 6602. 

Maybe the Measurement Computing board can accept either differential or TTL signals?  Still following the thread, Brian? 

-Kevin P.

[Brian_Beal]

Yes, it can inherently handle single-ended or differential encoders.