Description

SSI Posital absolute encoders can be used through a software package which is added to the project. Posital encoders are not supported under the Setup Tab however the software package provides similar features. A software controlled driver chip is enabled by the software turning some of the encoder signals into outputs to provide the required clock and preset signals.

Wiring

MMC-T controller wiring is as follows:

Encoder A+ --- Clock+ --- Gereen
Encoder A- --- Clock- --- Yellow
Encoder B+ --- Data+ ---- Gray
Encoder B- --- Data- ---- Pink
Encoder I+ --- Preset --- Blue
GND ---------- GND ------ White
+24V --------- +Vs ------ Brown

(Red DIR wire is not used. Coordinate inversion is handled in software) 

Using the SSI Postal Software Package

The Posital Software Package can be understood by using it in the test scaffolding program MMC-T SSI Posital.DSM project. Select "File | Open Resources" from the main menu, open the "Software Packages" directory, and choose "MMC-T Posital.dsm". This project provides a position display and some controls to manipulate and test the package:

Select the Posital package and click on the Blocks tab to see required settings.

The Bits In Packet parameter has to do with the total number of bits required to transmit the motor position and pulses-within-one-rotation information. Typical numbers are 24 if there are 12 bits for the motor anc 12 bits of resolution in one rotation. Encoders with 12 bits for motor rotations and 16 bits for resolution in one rotation use the parameter 28. The counts per user unit block sets the User Units to provide a meaningful position number in relationship to the machine structure. Set Coordinate Inversion changes the sign of the reported position so that positive encoder readings correspond to the positive direction of motion of the machine.

After making the needed changes to these values run the project and see this console:

Spin the encoder and manipulate the parameters to appreciate how the software package works and to confirm proper wiring.

Adding the Package

Open the current work-in-progress project, or select File | New Project. Select the Add Software Package Tool:

Choose the MMC-T Posital project and the Posital Software Package will be place into the currently open project. Select the Posital Package, click on the Blocks Tab, and make the necessary adjustments for the particular encoder being used. The package named can be changed from Posital to something more specific to the application for clarity

Using the Package

Click on the Blocks tab, click on the More Blocks Category, and choose the Posital package, or whatever name it now has after naming. The block list will show these blocks:

The Preset block zeros the actual position of the encoder. The Actual_Position expression returns the encoder position in user units established with Set Counts Per User Unit.