CNC Robot Accuracy. SmartManufacturingSeries.com

Transcription

1 CNC Robot Accuracy

2 Traditional Machine Tool Process Chain Where do robots fit? CAD CAM Programming CAM Simulation Integrated Solution for product development Complex drilling and multi-axis operations Simulation of the operation on the basis of the real kinematics NX CAM Post processor 84D sl Post processor incl. Cycles Adaptable to individual application with Post Configurator SINUMERIK Production Path Accuracy? Highest path Absolut Accuracy Accuracy?

3 Test Setup All following Test results were conducted with SINUMERIK/ SNAMICS/ SIMOTICS Test were conducted with different robot types and vendors

4 Error Classifications Static Error Geometric Error (e.g. link length, tools, objects in workspace) Elasticities (base, run-out, gears) Temperature (quasi static) Dynamic Error Following error Gear Cyclic Errors Axis Dynamic Limits

5 Static Accuracy Approach End Customer Requirements Calibration Process Compensation 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 customerspecific 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 data set Compensation Compensation data set Important Constraints: At the TCP, for arbitrary manual orientations, for approaching positions from arbitrary directions, in the whole machining area

6 Reference Calibrations Siemens AG Technology Center, Chemnitz Customer A Customer B Robot type: KUKA KR3 R25 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):.91.1 mm Standard deviation (SD):.49.7 mm Maximum error (MaxErr): mm Robot on the linear axis Arm length: 3.4 m Distance TCP - flange: 19 mm Application: Fiber Placement Independent tracker check measurement Average fault (AF): mm Standard deviation (SD):.74.1 mm Maximum error (MaxErr): mm Robot on the linear axis Max. arm length: 2.6 m Distance TCP - flange: 47 mm Application: NDT Independent tracker check measurement Average fault (AF): mm Standard deviation (SD): mm Maximum error (MaxErr): mm

7 Error Classifications Static Error Geometric Error (e.g. link length, tools, objects in workspace) Elasticities (base, run-out, gears) Temperature (quasi static) Dynamic Error Following error Gear Cyclic Errors Axis Dynamic Limits

8 Idea: Universal 3D Multibody Model Real Robot 84D SL SINAMICS/SIMOTICS Compile cycle ROCO Source: MABI Robotics 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 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...

9 Conformity of Model to Robot.3 N/µm X direction 3 N/µm.6 N/µm.4 N/µm Y direction X Z Y.8 N/µm Z direction 1.1 N/µm External device for measurement

10 Pose 1 Adaptive Torque Feed Forward Adaptive T.-FFW Fixed T.-FFW: J ax =,1kgm 2 Fixed T.-FFW: J ax =,18kgm 2 Fixed T.-FFW: J ax =,25kgm 2 Pose 2 Adaptive T.-FFW Fixed T.-FFW: J ax =,1kgm 2 Fixed T.-FFW: J ax =,18kgm 2 Fixed T.-FFW: Jax =,25 kgm2 Pose 3 Position RA11-Axis [ ] Position RA11-Axis [ ] RRR11.ST1 -.1 RU11.ST1 RM11.ST1 RR11.ST Time [s] RRR14.ST1 -.1 RU14.ST1 RM14.ST RR14.ST Time [s].2 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 Adaptive T.-FFW Fixed T.-FFW: J ax =,1kgm 2 Fixed T.-FFW: J ax =,18kgm 2 Fixed T.-FFW: Jax =,25 kgm2 Position RA11-Axis [ ] RRR1A.ST1 -.1 RU1A.ST1 RM1A.ST RR1A.ST Time [s]

11 Measure Joint Cyclic - Exemplary for axis 2 Functionality: Setpoint path Measured path Deviation [mm] Perpendicular to circular plane 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 Deviation[mm] in circular plane.5 Effect: Higher path accuracy Angle [ ]

12 Characterize Compensation Model Deviation [mm] Perpendicular to circular plane Deviation [mm] In circular plane Angle [ ] Position [mm] Torque [Nm] Angle [ ] Angle [ ] 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 Position [mm].5 Position [mm] Angle [ ] x n 2 2 A i 2 sin 2 i i 1 i ,5 1 Wave length [ ]

13 Dynamic Acceleration and Jerk Acceleration [rev/s 2 ] Max. accel Computed max. jerk Max. jerk for tol., Inertia [kgm 2 ] Jerk limit [m/s 3 ] - 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,5 during positioning 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 1 st 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

14 Dynamics Example Pos. Time [s] Pos. Time with adaption Pos. Time without adaption Inertia [kgm 2 ] - Exemplary for Axis 1 - Positioning time (45, F5) when adapting acceleration and jerk 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 1 st 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

15 New Applications for Robots

16 Roger Hart Siemens Digital Factory Motion Control R&D