A new approach to measuring inertia properties

Transcription

1 A new approach to measuring inertia properties Robert Klöpper, PhD Technical Director Resonic GmbH

2 Importance of inertia properties

3 3 (Rigid body) inertia properties Mechanical structure Measurement Inertia Properties: - Mass - Center of gravity m (ζ, ζ, ζ ) x y z T - Inertia tensor I xx I xy I xz I yy I yz sym. I zz Prediction of dynamic behavior

4 4 Common automotive applications Models related to: - Engine vibrations - Dynamics of full vehicles - Rollover propensity - Handling - Comfort

5 5 Outline 1) About the company 2) Conventional measurement processes 3) measurement process 4) implementations

6 1) About

7 7 Company outline - Young startup company - Origin: research at Okuma Laboratory, Tokyo Institute of Technology - Currently supported by the Technology Venture Initiative at TU Berlin

8 8 Resonic team

9 9 Resonic approach Test object Measurement process Signals Computation Result Current methods Complicated Simple Simple Advanced => Complexity shifted from hardware to software

10 2) Current measurement processes

11 11 Current measurement principles Force/motion Pendulum

12 12 Force/motion methods Test object Advantages: - Single setup - Horizontal position - Automation Motion sensor Actuator Force sensor Disadvantages: - Strong actuators - High-quality sensors - Friction bias

13 13 Pendulum methods Natural frequency - Single MOI per setup - 6 different setups necessary Well-defined axis Restoring force Time-consuming Dangerous - Key advantage: use of natural - frequencies

14 Accuracy of natural frequency measurements Perfect signal Spectrum Time Contaminated signal - Calibration errors - Inaccurate excitation - Moderate damping - Noise - Drift - Offset Frequency Time Frequency Natural frequency (unaffected!) => Outstanding accuracy with conventional sensors Resonic Inertia Measurements ATE Europe, May 19,

15 15 Current methods vs. Resonic Pendulum methods Natural frequencies 6 x repositioning Only MOIs 1 position Complete inertia properties Force/motion methods Automation Horizontal position Strong, accurate actuators Accurate force and motion sensors e.g. manual excitation or gear motors e.g. simple strain gages No influence on accuracy

16 3) process

17 17 Resonic Resonance: measurement process (1) Positioning Measurements N =1 Force sensor (2) Suspension in (1) soft springs Test object Platform Alternative: (3) Random excitation (2) (e.g. impact) 4.65 Time domain 10 4 Frequency domain (4) Signal of free (3) vibration (5) Identification of (4) natural frequencies N 3 (5) Modification of (5) boundary condition No N = Time [s] Frequency [Hz] N =3 N = N+1 Identification Algorithm - N sets of natural frequencies - Position of test object Constant properties of the measurement device Inertia properties

18 18 Parameters of measurement device 1) Suspension coordinates Space-fixed e ~ 1 O ~ e ~ 2 e 2 O Bodyfixed e 1 2) Gravity orientation (space-fixed) 3) Stiffness 4) Natural length 5) Platform inertia Constant properties of the measurement device

19 19 Modification of boundary condition Dummy masses Spring modification Displacement 1 2 3

20 20 Identification algorithm (basic principle) Measured natural frequencies Mathematical model of natural frequencies Inertia properties Inertia properties (Platform and test object) Stiffness model of support Nonlinear optimization

21 4) implementations

22 22 Range of implementations Temporary Semi-manual Automatic Low manufacturing effort Low experimental effort

23 4.1) Temporary setups

24 24 Modification of boundary condition: dummy masses Additional masses in 3 positions 1 2 3

25 Experimental procedure (using dummy masses) Excitation 2 3 Test object 4 1 Dummy mass Single accelerometer Errors: Mass: 0.3% COG: 4 mm MOI: < 0.8% Resonic Inertia Measurements ATE Europe, May 19,

26 26 Modification of boundary condition: wire rigidification

27 Experimental procedure (using rigidification) Rigidification Errors: Mass: 0.25% COG: 3 mm MOI: < 0.5% Resonic Inertia Measurements ATE Europe, May 19,

28 4.2) Semi-manual systems

29 29 Resonic 100: capacity 0.8 m Support frame Platform <100 kg

30 30 Resonic 100: modification of boundary condition Steel cylinder (dummy mass)

31 31 Resonic 100: sensors and excitation Force sensor Excitation

32 4.3) Automatic systems

33 33 Resonic robot: capacity 0.45 m <3 kg

34 34 Resonic robot: suspension mechanism Strain gage Spring Motor Kevlar wire Thread rod

35 35 Resonic robot: excitation and boundary condition

36 36 Resonic robot: Typical errors Mass: < 0.1% COG: < 2.1 mm MOI: < 2.1%

37 Unique capabilities

38 38 Very large and heavy objects (temporary setups) (anything that can be suspended in tension springs)

39 39 Customization Low mechanical complexity => Economical customization of devices regarding size, weight and interface requirements

40 40 Mobile measurement devices Maximum size of test object Weight and size of measurement device similar to weight and size of test object

41 5) Conclusion

42 42 Resonic process: conclusion - Single horizontal setup - Simple, robust hardware - High accuracy - Small accelerations (no fixtures necessary) - Scalable

43 Thank you very much! Booth 1151