Inertia Identification

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

InstaSPIN-MOTION Lab 05c

• Implements SpinTAC Velocity Identify

– Identifies the system inertia

– Provides the system inertia to use with the SpinTAC Velocity Controller