MachPro M31 Enable Absolute Encoder

Explanation

The MachPro M31 motion controller can use an absolute encoder to keep an axis position after the machine is powered off. An absolute encoder is a feedback device that reports a fixed position value, not only a change in position. In motion-control systems, the controller can save an absolute encoder offset in non-volatile memory so the position is not lost after power is cycled.

The M31 absolute encoder feature can use either a servo motor or a stepper motor if the motor system has these features:

• An encoder, which is a feedback device that reports axis position.
• A method to retain the encoder count when power is off.
• EtherCAT communication with the M31. EtherCAT is an Industrial Ethernet fieldbus for machine control and drive communication.

An encoder count is the numeric position value from the encoder. The Absolute Enc Offset (Counts) field stores the count offset that aligns the encoder position with the machine zero position.

Homing is the procedure that sets the machine zero/home coordinate reference position. A home switch is a sensor used to find a repeatable home position. A machine can be homed with switches, encoder index signals, absolute encoders, or visual alignment marks, but operation without home switches reduces the repeatable and accuracy provided by home switches.

Reference

Use absolute encoder mode only when all required hardware is installed and configured. Complete Axis Setup and Inputs and Homing Setup 

Required hardware and communication:

1. Servo motor or stepper motor with encoder feedback.
2. Encoder count retention when the system is powered down. Often this is a battery pack on the encoder cable.
3. EtherCAT drive or device connected to the M31.
4. Complete Axis Setup and Inputs and Homing Setup (yes, I repeated this intentionally)

M31 plugin configuration field descriptions:

• Control Output: Match each motor to the EtherCAT Drive. SubID will be set to 0.
• Feedback Source: This field will be EtherCAT Feedback. Index will be set to 0.
• Homing Method: Select the correct homing method for the machine.
• ECAT Absolute Encoder: This checkbox enables absolute encoder mode.
• Absolute Enc Offset (Counts): This field stores the encoder-count offset for the axis.

How-to configure an axis for an absolute encoder

1. Home the desired axis to it's machine zero location and disable the software
2. Open the M31 Config Plugin. Pull down Configure -> Plugins -> M31
3. Select the motor tab to configure.
4. Verify that Control Output, Feedback Source, and Homing Method are set according to the M31 Setup Manual - Axis Setup and Inputs and Homing Setup 
5. Select ECAT Absolute Encoder.
6. Click the Reset Offset button and the current encoder offset will be entered into the Absolute Enc Offset (Counts) field

7. That encoder count will now be the machine zero location on that axis, and it will be retained after power cycles.

8. Click OK to save the changes and close the M31 Config Plugin.
9. Repeat for each axis that has an absolute encoder

When all absolute encoder axes have their settings enabled, and all other axes have their homing correctly set, use the test process in the M31 manual to verify homing. 

Recalibrate the absolute encoder offset

After encoder replacement, motor replacement, mechanical repair, coupling movement, belt slip, lost encoder memory, or any other work that changes the mechanical relationship between the motor, encoder, and axis. After the mechanical repairs or issues have been completed, repeat the process for configuring the absolute encoder as listed above.

MachLabs Terms and Conditions

The MachLabs Team
14518 County Road 7240, Newburg, MO 65550
support@mach-labs.com