Calibration Procedure

Prerequisite

Performing the procedure

Attention

If two encoders are used, please calibrate encoder 2 (typically the motor shaft) first and then repeat the procedure for encoder 1 (typically the output shaft).

  • Download and install a special calibration version of the firmware

  • In order to reliably execute the calibration procedure, the velocity should be tuned softly. Go to the velocity tuning section and set the Bandwidth slider up to 20 Hz (the changed parameters will not be saved to the Drive memory). Make sure the velocity control mode is functional by running some slow motion profile.

  • Use the CHECK ENCODER SYSTEM button to verify the current state of the encoder system.

  • The calibration requires mechanical rotation of the motor with an attached encoder.

  • The encoder will perform several revolutions in the positive direction and then will return to the original position. This will be repeated several times.

    Motion during calibration:

Encoder

Revolutions, speed

Circluo 7, Encoder 1 (Inner ring)

2 revolutions, 20 RPM

Circluo 7, Encoder 2 (Outer ring)

18 revolutions, 180 RPM

Circluo 9, Encoder 1 (Inner ring)

2 revolutions, 20 RPM

Circluo 9, Encoder 2 (Outer ring)

9 revolutions, 90 RPM

  • Each iteration requires approximately 10 seconds.

  • After the analog calibration procedure is successfully finished, check the estimated phase error plot. Note the resulting phase error margin. Smaller margin results in more robust behavior of the encoder system: small mechanical changes, vibration and temperature expansion are less likely to cause an error.

../../../../../_images/good_error_margin1.png
  • Additionally, if the magnetic target was damaged mechanically or magnetically, this will be visible from the data as a single spike or an irregular error pattern.

After the optimal calibration parameters have been found:

  • Install the latest version of the firmware

  • Run Offset Detection again to find your optimized offset

  • Perform Velocity Tuning or Position Tuning (depending on the application)

Attention

The analog calibration procedure must be repeated when the mechanical position of the magnetic ring has changed. This can also occur when mechanical wear has impaired the system performance.

An error will be triggered during startup in the Error Report Object 0x203F when the calibration is required again: BisErBit

Troubleshooting

If the Encoder Calibration Procedure has failed during recording, please check the error description and contact our support. If the calibration is finished, but the resulting phase error exceeds the permissible value, this is usually related to a mechanical issue or magnetic ring damage. It’s possible to identify the cause based on the resulting Estimated phase error graph. There are 3 common outcomes:

The magnetic ring is too close to the encoder chip

Note the Nominal air gap for each encoder ring. If the ring is significantly closer, the following pattern will appear in the calibration results: regular high frequency oscillations with a high amplitude.

../../../../../_images/airgap_too_small.PNG

In this case, adjust the encoder ring mounting to ensure the nominal air gap.

The magnetic ring is too far from the encoder chip

Note the Nominal air gap for each encoder ring. If the ring is further away than specified, the following pattern will appear in the calibration results: irregular high oscillations and isolated points (outliers) due to high noise.

../../../../../_images/airgap_too_big.PNG

The magnetic ring is damaged

The two main reasons for damaged magnetic rings are mechanical scratches and demagnetization. Scratches are typically visible and minor ones could be tolerated. Their effect on encoder performance can be observed on the phase error curve. The resulting phase reserve should be more than 25%. On the other hand, demagnetization can’t be observed visually or with a gaussmeter. Only the calibration procedure can be used for diagnostics. Note that even a magnetic tip of the screwdriver can disrupt the magnetization pattern.

Attention

Please observe the general handling guidelines for magnetic rings to prevent demagnetization.

../../../../../_images/metal_ring_damaged.PNG

In case of a ring damage, the phase error curve would have a unique error peak.

Encoder system diagnostic

This set of features allows to:

  • Check the distance between the chip and the magnetic ring

  • Detect axial runout of the encoder ring

  • Read error states directly from the encoder chip

Magnetic ring distance checker

This feature can assist during the prototyping phase of the design. It computes the air gap based on the ring’s magnetic field strength and recommends next action.

Note

Earlier batches of the encoder rings had a weaker field and thus the computed distances might be overestimated. Please use this feature carefully with older encoder rings. It shouldn’t be a primary information source during the ring mounting process, mechanical design should take a priority.

Note

The releases of the OBLAC Drives at version v21.1.0-beta.4 and before display the estimated air gap based on nominal air gap of 0.5 mm. Please update the OBLAC Drives.

Check encoder system

Performs a diagnostic test of the encoder system. One rotation of the currently selected encoder will be done in the open-loop field control mode. The obtained data will be used to compute a distance map over a full revolution. This is helpful to detect distance variations and hence axial runout of the encoder ring or eccentric motion.

../../../../../_images/distance_checker.png

This visualisation helps you detect possible problems with the mounting of the encoder ring:

  • Case 1: Some axial runout detected, the ring is too close. This can lead to a collision with the read head.

  • Case 2: Axial runout present, check the quality of the encoder ring assembly.

  • Case 3: No Axial runout detected, this should be the goal.

Check encoder errors

This command establishes a direct communication with the encoder chip and the Multiturn counter (if configured). Error registers are read and displayed:

Name

Description/remedy

Startup error

Encoder initialization error. Power cycle the drive, connect the multiturn battery (if multiturn is used).

Signal error: clipping (nonius track)

A magnetic ring is too close to the encoder chip. Check the mechanical assembly.

Signal error: poor level (nonius track)

A magnetic ring is too far from the encoder chip. Check the mechanical assembly.

Signal error: clipping (master track)

A magnetic ring is too close to the encoder chip. Check the mechanical assembly.

Signal error: poor level (master track)

A magnetic ring is too far from the encoder chip. Check the mechanical assembly.

Excessive signal frequency for internal 12 Bit converter

Encoder maximum speed is exceeded.

Excessive signal frequency for ABZ-converter

Encoder maximum speed is exceeded.

Period counter consistency error: counted period ↔ calculated Nonius position

Phase error is too high. The absolute position can’t be computed reliably. Can be caused by changed mechanics, thermal expansion or magnetic target damage. Run diagnostics and repeat calibration.

Multiturn data consistency error: counted multiturn ↔ external MT data

Multiturn counter doesn’t work properly. Check if the MT battery is connected and power cycle the drive.

Multiturn communication error

The multiturn counter chip is in error state. Check the battery voltage and replace it if needed.

I2C communication error: No EEPROM or I2C communication error

Communication with the EEPROM memory of the chip is distorted. Power Cycle the drive. If this can’t be reset, there is a hardware problem.