Introduction
• What is Inertia?
– Inertia is the resistance of an object to rotational acceleration
– Anything that is rigidly coupled with the motor shaft
– Example: The drum of a washing machine
• What is NOT Inertia?
– Anything that does not immediately change directions with the motor
– Example: Clothes/Water in a washing machine
Example of What is Inertia
Rotating Mass
Rotation
Motor
Load
Non-Rotating Mass
Simple Motion System
Rotating Mass
Rotation
Motor
Non-Rotating Mass
Identifying Inertia
Disconnected
Importance of Inertia
• Why is Inertia Important?
– Represents the amount of mass the motor is rotating
– Informs speed controller how strongly to respond to disturbances
– Allows for the most responsive speed control
– Direct Input to SpinTAC Speed Controller
SpinTAC Velocity Identify
• Identifies the system inertia
• Simple, one-button operation
• Accurate and repeatable inertia result
• Compensates for the influence of friction
• Only run during development
– Needs to be run on the final application
• Implemented in InstaSPIN-MOTION GUI & InstaSPIN-MOTION Lab 5c
Accuracy of Estimated Inertia
The inertia result is highly repeatable, the maximum and minimum values for these 100 tests are within 0.5% of the mean
Tolerance of Inertia Error
SpinTAC Speed Controller can tolerate up to 4x of inertia mismatch
TI Confidential - Maximum Restrictions
Estimation Process Torque
This continuous torque profile is sent to the motor, it is important to note that the
torque needs to be drive negative for this test
Estimation Process Speed
Even though we applied negative torque to the system it resulted in little to no
negative speed on the motor.
Troubleshooting Common Errors
• 2003
Bad Estimation Value
– High friction/cogging force
– Automotive Pumps
Solution:
– Increase RampTime
• 2004
Process Timeout
– Motor Spins • Washing Machines
Solution: • Decrease GoalSpeed
– Motor starts slowly
• Compressors
Solution: • Increase OutputTorque
Get Error Code:
uint16_t STVELID_getErrorID(ST_VELID_Handle)
Difficult Applications for Inertia ID
• Features of Difficult Applications
– Large Cogging Force
– Large Friction
– Low Rated Speed
– Large Start-up Current
• Difficult Applications
– Automotive Pumps -> Large Friction
– Washing Machines -> Low Rated Speed
– Compressors -> Large Start-up Current
• User’s Guide goes into specifics for these applications
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