7344 encoder input and index signal

[Buechsenschuetz]

We are using encoders which use a logic circuit to produce the index signal. It appears only when both phase A and phase B are on high level. From the 7344 hardware manual p. 5-8 I understand that the 7344 controller detects a valid index signal only when both phase A and phase B are low. This is no problem for us - we have differential encoder outputs and can simply swap the wires so the output of the signal receiver has correct polarity.

All this works on an axis which has a positive direction. On a different axis where both the motor and the encoder run in negative direction the index signal is not detected by the 7344 controller.

Is there a certain phase relationship required between phase A, phase B and the index signal, or i
s it just as shown on the above mentioned diagram (phase A and phase B both have to be low to make the index signal valid). Or, in other words, do the output signals phase A and phase B have to follow a certain sequence so that the 7344 controller can detect a valid index signal?

[Brent_R]

This is not expected behavior. The 7344 should detect the index signal in either direction regardless of the phasing of the lines, as long as the polarity requirements are met. I would try this encoder on multiple axes to see if the behavior is the same or if the problem is related to just one axis. If it is feasible, try a different model of encoder to troubleshoot this issue.

Also make sure you have the latest version of the Motion Driver, which is currently 5.2. Several rare encoder problems were fixed between version 5.1.1 and 5.2, which you can read about in the release notes.

Regards,

Brent R.
Applications Engineer
National Instruments

[Buechsenschuetz]

I understand that an index signal should always be detected as long as its polarity (i.e. active low) is correct, and there is no relationship to the state or phase of the PHA/PHB inputs?

We will check with the V5.2 software. Using other encoders will be difficult since we are designing an upgrade to fit to 20+ year old devices of which quite a few are in the field.

[Brent_R]

The only requirement is that both PHA and PHB are low when the index pulse is encountered. So yes, there is a state requirement, but the relative phase of PHA and PHB is irrelavent. The 7344 should find the index pulse in either direction. You can take the encoder out of the picture by just applying voltages directly to the pins to see if you get a response. Please keep me updated on the progress.

Regards,

Brent R.

[Buechsenschuetz]

In the meantime we found the same state requirements for PHA and PHB. Unfortunately this is not pointed out very clearly in the 7344 hardware manual - the diagram about pulse sequences gives just an idea but there is no clear statement. Obviously the dotted vertical lines show the sampling period for the index pulse but this is not mentioned in the description.

The UMI (Universal Motion Interface) manual mentions the state requirement of PHA and PHB on p.23. But - on the following page this manual shows a required polarity of the index pulse different from the 7344 manual.

I have to admit that this problem was partially our fault, since we reversed PHA on one axis to get a correct direction information. On our encoders the index
pulse is linked with PHA, so in our previous arangement the index occured with PHA = high. When reversing BOTH PHA and PHB again, of course PHA was low when the index occured, and since PHA and PHB have 90 deg. overlap in our encoders there will always a moment where PHA and PHB are both low together with the index - this was the situation described in my question.

Now we have connected PHA properly and inverted PHB only to receive correct direction information, it works this way.

May I suggest to describe the state requirements of PHA, PHB and index more detailed in the 7344 hardware manual.

Strange enough, even with our first setup everything worked on both axes with the UMI box. It seems as it rather responds to both slopes of the index signals, while the 7344 controller rather responds to proper levels.

[Jochen]

Hello,

this comment is not related to the question you have posted here.
As you are very active in the Motion Control forum I have come across several of your comments and answers and all of them suggest that you have very good expertise in the area (NI) motion control.
I am the leader of a group of application engineers at NI Germany that amongst others is responsible for the support of NI's motion control products.

I am always interested to learn about customer applications and I am also looking for companies who offer motion control solutions based on NI components to end users. So if you would like to contact me because of these or other reasons please feel free to send me an email: jochen.klier@ni.com
Telling from you
r nick name I think you could contact me in German.

Best regards,

Jochen Klier
National Instruments Germany