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CIP Motion Tuning Explained

Keith Schultz - April 2017

Do we need to Tune?

How does a Servo System work?

Position Controller

Feedback

Servo Drive

MotorLoad

Simplified Control Loops

d^2/dt

d/dt

Acc FF Gain

(Kaff)

Vel FF Gain

(Kvff)

Pos P Gain

(Kp)

Pos I Gain

(Ki)

Vel P Gain

(P)

Vel I Gain

(I)

Motor

Position

Command

d/dt Kd

d/dt Kd

Low Pass

FilterTest for Ki

Zone

Unlimited

Current

Command

Motor

Encoder

Feedback

Feedback

Position

Feedback

Velocity

Error

Accumulator

Current

Limiting

Current

Command

Error

Accumulator

Position Loop

Velocity Loop

Torque Loop

Weight and Inertia as it is to the Load

What is Backlash?

Sources of Compliance

Servo Loop Bandwidth

Bandwidth is the usable range of frequencies in [Hz] where the gain through the

system is above -3dB

• Bandwidth indicates servo drive performance and directly equates to

transient response, i.e. how fast the servo physically responds to the

load

• Higher bandwidth → higher performance

• Factors affecting bandwidth are:

• Feedback resolution (higher is better)

• Load inertia ratio (lower is better)

• Drive update rate (faster is better)

• Load compliance (rigid is better)

• Drive Model Time Constant (lower is better)

8

Drive Model Time Constant (DMTC)

DMTC is the sum of all the delays around the torque loop

• Its value in [sec] is based on the drive/motor/feedback combination

selected

• It is used to calculate the Torque Loop Bandwidth, which is then used to

calculate servo gains during an auto-tune and out-of-box

9

DMTC Comparison Chart

• The drive, motor, and feedback device have a significant

impact on the bandwidth that can be achieved on an axis

through tuning10

Why is Motion System Tuning Necessary?

What is the Autotune Test?

When is the Autotune Test Effective?

What does Load Observer or Adaptive Tuning do?

CIP Motion Tuning Explained

Improve system response

Overcome compliance & backlash

Respond to Inertia and torque disturbances

All machines are different and behave uniquely, with various levels of:

Why is Motion System Tuning Necessary?

Compliance

Backlash

Load

Variance

When Autotune provides unsatisfactory results…manual tuning is required

Requires expertise and time

Must connect to each axis to run the motor in step moves and tune

Autotune Overview

Calculates

combined motor

& drive

characteristic

values –

then sets control

loop gains

Performs

physical bump

test to measure

the load –

then sets axis

dynamics & limits

Acceptable for

systems with

rigid load ratios

of 10:1 or less

Autotune Functionality

Kpp = Position Loop Bandwidth [Hz]

Kpi = Position Integral Bandwidth [Hz]

Kvff = Velocity Feedforward [%]

Kvp = Velocity Loop Bandwidth [Hz]

Kvi = Velocity Integral Bandwidth [Hz]

Kaff = Acceleration Feedforward [%]

• Series Form - Proportional term (top) in series with the integral term (bottom)

• All gains have a 2π factor applied this makes all gains in [Hz]

• All terms are proportional to each other and represent physical Bandwidth

CIP Drive PI Controllers

Damping Factor

• Commonly referred to as zeta (z)

• It affects the rise time for a given bandwidth

• Lower Damping → higher response

• Higher Damping → lower response

• Sercos: default z = 0.8

• CIP: default z = 1.0 (Medium)

Under-damped

High: z = 0.8

Over-damped

Low: z = 1.5Critically damped

Medium: z = 1.0

Highest possible rise

time, but has overshoot

Fastest possible rise

time without overshoot

Lowest possible rise time ,

similar to decreasing BW

15

When is the Autotune Test Effective?

Autotune10%

Additional Tuning Required

90%

Simple Loads• Rigid mechanics, non-changing loads• High dynamic systems with rigid load ratios ≤10:1

Remaining Applications• Compliant loads• Variable loads• Optimal performance• >10:1 load ratios

Autotune Effectiveness

Load Observer Functionality

Operates in real

time as the

machine runs

Dynamically

estimates the

load torque &

provides a

feedback signal

to cancel its

effect

Causes the

motor to behave

as though it is

unloaded

What is Load Observer?

Additional Tuning

Required5%

When is Load Observer Effective?

Systems Requiring Optimal Performance

Rigid/Compliant/ Changing Loads

• No 10:1 limitation on

load ratio

Load Observer Effectiveness

Systems with Mechanical

Resonance

19

What is Load Observer

Load Observer Settings

Adaptive Tuning Feature

The adaptive tuning feature is only in Kinetix 5500 and Kinetix 5700

drives as of today.

Automatically adjust torque loop notch and low pass filter parameters

to suppress resonances.

Automatically de-tune control loop gains to avoid instability when it is

detected.

Adaptive Tuning Overview

Adaptive Tuning Benefits

Enables machine

awareness

Eliminates the

need to manually

tune

Provides

information that

can be used to

schedule

machine

maintenance

Adaptive tuning how does it work

Adaptive tuning is always running in the background to detect

motor side resonances. Every few seconds, it analyzes frequency

response of torque loop signals to identify, track, and measure

resonances.

It also analyzes frequency response of command signals to make

sure dominant command frequencies are not mistaken for

resonances.

Kinetix® 5500/5700 Tuning Technology

Load Observer: Improved performance and time savings• Tune servo loops similar to a motion control expert.

• Automatically compensates for unknown mechanics, and compliance – such as in

belts, flexible couplings, and shafts

• Applications where inertia varies during operation.

• Save time by eliminating the need for tuning each axis.

Adaptive Notch: Time savings and ease of use• Higher performance tuning possible as tracking notch can eliminate harmful

resonance and vibration in systems.

• Automatically adapts to changing frequency over time.

• Use tracking notch as an indicator to proactively monitor machine performance.

Tuningless Documentation

• Motion System Tuning Manual

MOTION-AT005-EN-P

- Covers tuning Kinetix 6000, 7000, 6200, 6500, 5x00, 300,

- Load Observer (section 1.5)

- Adaptive Tuning (section 1.6)

- Recommended settings (section 2.2)

• Tuningless Quick Start Guide - Kinetix 5000 Family MOTION-QS001-EN-P

- 8 page Document

- Steps through configuring tuning for Kinetix 5000 Drives

Key Takeaways

▪ Enable BOTH Load Observer & Tracking Notch Filter

▪ Do NOT run the Autotune test when using Load

Observer

▪ Disable the Low Pass Filter

▪ Use “Load Observer with Velocity Estimate”

configuration

▪ Leave Load Observer Bandwidth at default value

▪ Use “Notch Filter Tuning” (Tracking Notch)

configuration

▪ Leave Adaptive Tuning limits at default values

Load Observer

Adaptive Tuning

Tuningless Configuration Recommendations