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CNC Robot Accuracy

Traditional Machine Tool Process ChainWhere do robots fit?


• 840D sl Post processor

incl. Cycles

• Adaptable to individual application with

Post Configurator

CADCAM

Programming

CAM

Simulation

CAM

Post processorProduction

NX SINUMERIK

• Integrated Solution for product development • Complex drilling and multi-axis operations • Simulation of the operation on the basis of

the real kinematics

Path Accuracy ?

Absolut Accuracy?• Highest path Accuracy

Test Setup


All following Test results were conducted with SINUMERIK/

SNAMICS/ SIMOTICS

Test were conducted with different robot types and vendors

Error Classifications


Static Error

Dynamic Error

Geometric Error

(e.g. link length, tools, objects in workspace)

Elasticities (base, run-out, gears)

Temperature (quasi static)

Following error

Gear Cyclic Errors

Axis Dynamic Limits

Static Accuracy Approach


1) Statement on the absolute accuracy of a robot

2) Statement stating under which conditions this applies

3) Consideration of the specific system features

4) Ensuring accuracy along the whole life cycle of the

system

Automated creation of the customer-

specific calibration travel on the basis

of the CAD data

Fast measurement of several hundreds

of points using an in-line measuring

system

Calculation of the 56 model parameters

and creation of the offset data record

Compensation

Important Constraints: At the TCP, for arbitrary manual orientations, for approaching positions from

arbitrary directions, in the whole machining area

End Customer

Requirements

Calibration

ProcessCompensation

Compensation data set

Compensation data set

Reference Calibrations


Siemens AG Technology Center, Chemnitz

Robot type: KUKA KR300 R2500 Quantec with milling spindle

Max. arm length: 2.75 m,

Distance TCP – flange: 283 mm

Application: Robot-based milling

Independent tracker check measurement :

Average fault (AF): 0.91 0.10 mm

Standard deviation (SD): 0.49 0.07 mm

Maximum error (MaxErr): 2.41 0.32 mm

Robot on the linear axis

Arm length: 3.4 m

Distance TCP - flange: 190 mm

Application: Fiber Placement

Independent tracker check measurement




Robot on the linear axis

Max. arm length: 2.6 m

Distance TCP - flange: 470 mm

Application: NDT

Independent tracker check measurement




Customer A Customer B

Error Classifications


Static Error

Dynamic Error

Geometric Error

(e.g. link length, tools, objects in workspace)

Elasticities (base, run-out, gears)

Temperature (quasi static)

Following error

Gear Cyclic Errors

Axis Dynamic Limits

Idea: Universal 3D Multibody Model


• Real Robot 840D SL – SINAMICS/SIMOTICS

Compile cycle ROCO

X

Z

Y

3D-multibody-simulation Contains entire drive train of all axes

Simulation in Matlab-environment

Any kind of machine/ robot can be modelled

Source: MABI Robotics

Input data for each axis:

Joint specific data:

Inertia Tensor, Mass, Center of gravity, Stiffness

(Trans/Rot)

Axis specific drive train:

stiffness and inertia of motor and gears

Maximum allowable torque

Functionality:

Adaptive torque feed forward

Compensation of cyclic errors at joints

Adaptive Dynamic Limits

More .. .

Conformity of Model to Robot


X‐direction

Y‐direction

Z‐direction

External device for measurement

3 N/µm

0.3 N/µm

0.6 N/µm

0.04 N/µm

1.1 N/µm

0.08 N/µm

X

Z

Y

Adaptive Torque Feed Forward


Functionality:

Feedforward the adapted torque depending on

the current pose /inertia of the robot axis

Effect:

Elimination of pose dependent path deviations

by reducing the following error to a minimum

Higher path accuracy independently of the

programmed feed rate

Pose 1

Adaptive T.-FFW

Fixed T.-FFW: Jax = 0,01 kgm2



Pose 2

Adaptive T.-FFW




Pose 3

Adaptive T.-FFW




0 1 2 3 4 5 6-0.02

-0.01

0

0.01

0.02

Posi

tion

RA

11-A

xis

[°]

Time [s]

5° 3° 1°

RRR11.ST1RU11.ST1RM11.ST1RR11.ST1

0 1 2 3 4 5 6-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

Posi

tion

RA

11-A

xis

[°]

Time [s]

5° 3° 1°

RRR14.ST1RU14.ST1RM14.ST1RR14.ST1

0 1 2 3 4 5 6-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

Posi

tion

RA

11-A

xis

[°]

Time [s]

5° 3° 1°

RRR1A.ST1RU1A.ST1RM1A.ST1RR1A.ST1

Measure Joint Cyclic


- Exemplary for axis 2

Functionality:

Measure path deviation (in multiple directions)

for each axis

Determine periodic error function

Compensate for load dependent cogging effects

of the gears based on the 3D multibody model

Effect:

Higher path accuracy

-0.1

-0.05

0

0.05

0.1

Dev

iatio

n[m

m]

Per

pend

icul

ar to

circ

ular

pla

ne

-140-120-100-80-60-40-20-0.1

-0.05

0

0.05

0.1

Dev

iatio

n[m

m]

in c

ircul

ar p

lane

Angle [°]

Setpoint path

Measured path

Characterize Compensation Model


- Exemplary for axis 2

Functionality:

Measure path deviation (in multiple directions)

for each axis

Determine normed periodic error function

Compensate for load dependent cogging effects

of the gears based on the 3D multibody model

Effect:

Higher path accuracy

i

i

n

iiAx

2

122 2sin

-20 -40 -60 -80 -100 -120 -140-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

Angle [°]

Posi

tion

[mm

]-140-120-100-80-60-40-20

-3000

-2000

-1000

0

1000

2000

3000

Angle [°]

Torq

ue [N

m]

-0.1

-0.05

0

0.05

0.1

Dev

iatio

n [m

m]

Per

pend

icul

ar to

circ

ular

plan

e

-140-120-100-80-60-40-20-0.1

-0.05

0

0.05

0.1

Dev

iatio

n[m

m]

In c

ircul

ar p

lane

Angle [°]

-20 -40 -60 -80 -100 -120 -140-0.1

-0.05

0

0.05

0.1

Angle [°]

Posi

tion

[mm

]

20 10 9 8 7 6 5 4 3 2 1,5 10

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

Wave length [°]

|Pos

ition

[mm

]|


Functionality:

Adapt the acceleration of an axis depending on

the pose of the robot (up to factor 5 between

worst and best pose)

Adapt the jerk depending on the 1st Eigen

frequency (up to factor 4 between worst and best

pose)

Effect:

Optimized dynamics for each robot pose

Higher productivity while keeping the same high

path accuracy

Faster positioning with PTP

- Exemplary for Axis 1

- The jerk limitation is proportional to the first Eigen frequency of the robot axis

- It has been verified that the overshoot remains under 0,005°during positioning

012345678910

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.01 0.02 0.03 0.04 0.05 0.06 0.07

Jerk limit [m

/s3 ]

Acceleratio

n [rev/s

2 ]

Inertia [kgm2]

Max. accel Computed max. jerk Max. jerk for tol. 0,005°

Dynamic Acceleration and Jerk

Dynamics Example


Functionality:

Adapt the acceleration of an axis depending on

the pose of the robot (up to factor 5 between

worst and best pose)

Adapt the jerk depending on the 1st Eigen

frequency (up to factor 4 between worst and best

pose)

Effect:

Optimized dynamics for each robot pose

Higher productivity while keeping the same high

path accuracy

Faster positioning with PTP

- Exemplary for Axis 1

- Positioning time (45°, F5000) when adapting acceleration and jerk

0

0.5

1

1.5

2

0.01 0.02 0.03 0.04 0.05 0.06 0.07

Pos. Tim

e [s]

Inertia [kgm2]

Pos. Time with adaption Pos. Time without adaption

New Applications for Robots



Roger HartSiemens Digital FactoryMotion Control R&[email protected]

CNC Robot Accuracyadditivemanufacturingseries.com/wp-content/uploads/2017/09/Hart-Roger.pdf ·...

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