Question/Problem
 
How do I troubleshoot motion fault alarms in BOSS 3 for a servo drive? How do I used the Drive Tune screen in BOSS?

 
Environment

High speed merge servo drives or gap optimizer servo drives displaying 'motion fault' alarms in BOSS.
 

Answer/Solution

A motion fault alarm for a servo drive is thrown under one condition: BOSS is not receiving sufficient encoder input pulses while commanding a forward speed to a servo drive.

BOSS sends the desired speed signal to the servo drives through the DAC card in the RTC by outputting an analog voltage. At the same time, the encoder for the conveyor belt counts how fast the belt is moving. While calibrating, BOSS determines a linear graph of what output voltages result in what conveyor speed - this way it is able to know what voltage to send to the servo drive to return a desired speed.

The BOSS Drive Tune screen provides the ability to test how well a servo-driven belt is performing in several circumstances, including acceleration, deceleration, constant speed and stopped.

The example above shows a drive tune test for a servo drive running properly (Belt 230F). To perform a Drive Tune Test for an individual drive, left click the drive in question and click the leftmost button in the screenshot below. To begin the test for all drives on the screen click the second from the left button below. The test will take about a minute - it will force a series of signals from the DAC card to the drive and measure the results from the encoder. To stop the drive tune test, click the buttons on the right.

There are 6 tests conducted per drive - Noise, Offset, Scale, Tune, Track, and Stress. The three have are related to motion faults are Offset, Scale, and Track.

Offset - Forces the DAC card to output 0 V and measures ticks on the encoder. With no input to the servo drive the belt should not move. If the encoder registers any ticks it immediately fails the offset test. If this test fails, adjust parameters like zero offset until the motor does not move at a forced speed of 0 fpm. This test needs to pass before addressing any other test failures, as it will have an impact on many of them.

Scale - Forces the DAC card to output the calibrated voltage for 100 fpm (and 500 fpm) over 20 seconds and measures the number of encoder ticks. Usually one encoder tick is 1/16th of an inch of conveyor belt, so running the belt at 100 fpm and 500 fpm should result in 1,600 and 8,000 ticks respectively. If it deviates from either of the expected number of ticks by more than 16 ticks (1 inch), the test fails. If this test fails adjust the scale parameter on the drive until the measured speeds match the expected speeds. If the measured encoder ticks are extremely off from the expected ticks, inspect the encoder. If the deviation between 100 fpm and 500 fpm are extremely different and inconsistent (off by more than a factor of 10), inspect the health of the servo drive.

Track - Tests the ability to track product on the belt. If offset or scale fails, this is likely to fail too.

Below is an example of a failed Drive Tune Test and how to modify calibration values:

The Scale test failed from a deviation of 177 ticks (11 inches) while running at 500 fpm. This tells us the calibration values may be off. To modify them, we will be using the results of the 500 FPM test because it is closer to the speed the conveyor will be running.

Select the Notepad icon in the upper left corner:

Change Zero FPM Calibration to 0. Calculate the new 1,000 FPM Calibration by multiplying the existing value by the expected number of encoder ticks divided by the actual number of encoder ticks: New Value = Existing Value x (Expected Ticks / Actual Ticks). In this example, the formula would be: New Value =  4357 x (8000 / 8177) = 4263. Input the new value and select OK. Rerun the test for new values. Repeat the process and make adjustments until the Scale test passes.

The 1,000 FPM Calibration has a range of values it will accept. If the calculated value is outside of this scale, the parameters in the servo drive will have to be modified. Most drives contain a parameter called V_Scale - this parameter creates a linear scale between the outputted speed of the drive and the inputted analog voltage. We highly recommend engaging Intelligrated Technical Support for this to record the change in parameters. Technical Support may also explore additional causes of the need to change of this parameter, as it should not be a common occurrence.

After all tests pass, run production and ensure the conveyor is behaving properly (i.e. not causing collisions / gapping cartons correctly). After monitoring for at least 10 minutes, save the configuration by clicking the floppy-disk icon in the upper left-hand corner.

Related items

KB-10899 - How to Troubleshoot Shaft mounted encoder

KB-10123 - How Does a Gap Optimizer Work?

 
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