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SmartManufacturingSeries.com
CNC Robot Accuracy
Traditional Machine Tool Process ChainWhere do robots fit?
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• 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
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All following Test results were conducted with SINUMERIK/
SNAMICS/ SIMOTICS
Test were conducted with different robot types and vendors
Error Classifications
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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
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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
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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
Average fault (AF): 1.61 0.22 mm
Standard deviation (SD): 0.74 0.10 mm
Maximum error (MaxErr): 4.19 0.52 mm
Robot on the linear axis
Max. arm length: 2.6 m
Distance TCP - flange: 470 mm
Application: NDT
Independent tracker check measurement
Average fault (AF): 4.91 0.22 mm
Standard deviation (SD): 2.22 0.09 mm
Maximum error (MaxErr): 10.79 0.54 mm
Customer A Customer B
Error Classifications
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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
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• 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
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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
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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
Fixed T.-FFW: Jax = 0,018 kgm2
Fixed T.-FFW: Jax = 0,025 kgm2
Pose 2
Adaptive T.-FFW
Fixed T.-FFW: Jax = 0,01 kgm2
Fixed T.-FFW: Jax = 0,018 kgm2
Fixed T.-FFW: Jax = 0,025 kgm2
Pose 3
Adaptive T.-FFW
Fixed T.-FFW: Jax = 0,01 kgm2
Fixed T.-FFW: Jax = 0,018 kgm2
Fixed T.-FFW: Jax = 0,025 kgm2
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
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- 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
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- 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
]|
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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
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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
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Roger HartSiemens Digital FactoryMotion Control R&DRoger.Hart@siemens.com
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