Enhancing Signal Quality of Capacitive Displacement Measurements in Machine Tool Environments †
Abstract
:1. Introduction
1.1. Spindle Error Motion
1.2. Capacitive Sensing in Spindle Metrology
1.3. Electromagnetic Interference in Machine Tool Environments
- A disturbance source acting as disturbance sender is located at effective distance to the susceptible device.
- To allow disturbances to travel from the sender to the receiver, links between both need to be established. Physical mechanisms such as electrical conduction and electromagnetic radiation potentially provide the mentioned coupling. Radiation as coupling mechanism may be further divided into mechanisms based on inductive and capacitive effects, which occur in the near field, whereas in the far field electromagnetic waves are significant [10].
- The device has to be accessible for disturbances with respect to frequency range and disturbance power [11].
Disturbed Spindle Measurements in Machine Tool Environments
1.4. Potential Handling Strategies for Electromagnetically Disturbed Measurements
1.4.1. Temporary Elimination of Disturbance Sources
1.4.2. Signal Filtering
1.4.3. Disturbance Attenuation
1.5. Objective of this Work
2. Materials and Methods
2.1. Measurement Device under Test
2.2. Machine Tool Environments
- Machine tool FEHLMANN Picomax® Versa 825 equipped with a HEIDENHAIN iTNC 530 control and a main computer MC 422C.
- Machine tool Präzoplan®, which is equipped with a SIEMENS SINUMERIK 840D SL CNC. Linear drives and the spindle are controlled by SINAMICS S120 modules.
2.3. Determination of Sensor Behavior under Disturbance Influence
2.4. Assessment of Signal Quality
2.5. EMI Testing Device
2.6. EMI Testing Procedure
- The measurement device behavior under shop floor conditions is tested on a currentless machine tool. This status is defined as MT OFF.
- The status NC OFF is defined by the circumstance that the machine tool is powered, but position control is not active.
- The activation of the position control of axes and drives to force the axes to maintain their current position is defined by NC ON. Depending on the type of control, either individual axes or the entire axis system is set in mode NC ON.
- The geometric testing of spindles is carried out under operational speeds and the position control of the linear axis is set active. These operating modes are described by the term SPEED.
3. Results
3.1. Sensor Characterization
3.2. Electromagnetic Disturbance Impact Analysis
- The machine tool was turned ON, but position control was switched OFF (Operating Mode NC OFF).
- The position control for spindle unit and linear axes were switched ON (Operating Mode NC ON).
- The disturbance influence at different spindle speeds, in the range of –, was tested (Operating Mode SPEED).
- After the spindle had run down and stopped completely, the position control remained active (Operating Mode NC ON).
- Finally, the position control was turned off (Operating Mode NC OFF). Thus, nominally, the same status as at the beginning of the test sequence was reached.
3.3. Performance Testing of Attenuation Approach
3.3.1. Performance Evaluation in Different Machine Tool Environments
3.3.2. Repeatability of Attenuation Approach
4. Discussion
5. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Abbreviations
CDF | Cumulative Density Function |
EMC | Electromagnetic Compatibility |
EMI | Electromagnetic Interference |
ENOB | Effective Number of Bits |
ETH | Swiss Federal Institute of Technology |
IWF | Institute of Machine Tools and Manufacturing |
MT | Machine Tool |
NC | Numerical Control |
Probability Density Function | |
PP | Peak-to-Peak |
PWM | Pulse Width Modulation |
RMS | Root-Mean-Square |
SCR | Silicon Controlled Rectifier |
SGR | Shaft Grounding Ring |
SINAD | Signal-to-Interference ratio including Noise And Distortion |
SNR | Signal-to-Noise Ratio |
UPR | Undulations Per Revolution |
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Spindle Type | Tolerance for Radial Error Motion | ||||
---|---|---|---|---|---|
air bearing spindle | 1 nm | < | ≤ | 100 nm | |
precision ball bearing | 0.1 m | < | ≤ | 1 m | |
standard machine tool spindle | 1 m | < |
Parameter | Unit | Channel | |||||
---|---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | |||
peak-to-peak value (pp) | [nm] | 58.9 | 49.7 | 52.9 | 75.3 | 40.3 | |
root-mean-square value () | [nm] | 6.6 | 5.2 | 5.5 | 6.1 | 5.0 | |
Specifications: | output voltage | ±10 V | sensitivity | 80 mV/m | |||
measuring range | 250 m | near gap | 125 m | ||||
bandwidth | 15 kHz |
No | Test Case | Switchboard Configuration | Description | |||||
---|---|---|---|---|---|---|---|---|
T | G | K | M | |||||
i | ii | iii | ||||||
1 | V1 | 0 | 1 | 0 | 1 | 0 | 0 | target coupled to machine tool table |
2 | D1 | 0 | 1 | 0 | 0 | 0 | 0 | fully decoupled cap test |
3 | D2 | 1 | 0 | 0 | 0 | 1 | 1 | target coupled to spindle |
4 | D3 | 1 | 0 | 0 | 0 | 1 | 0 | decoupled spindle measurement setup |
5 | D4 | 0 | 1 | 0 | 1 | 0 | 0 | target coupled to machine tool table |
Material | Stainless | Silicon | Aluminium | |
---|---|---|---|---|
Steel | Nitride | Oxide | ||
Type | X105CrMo17 | |||
1.4125/440C [26] | CS45 [27] | CS20 [27] | ||
Density | [g/cm] | |||
Yield Strength | [MPa] | 450 | - | - |
Flexural Strength at 20 C | [MPa] | - | 900 | 350 |
Weibull module m | [-] | - | 25 | 12 |
Young’s module E | [GPa] | 220 | 320 | 380 |
Poisson’s ratio | [-] | |||
Thermal conductivity at 20 C | [W/(m K)] | 15 | 25 | 30 |
Thermal expansion coefficient for 20–100 C | [/K] | 10.4 | 2 | 6.5 |
Electrical resistivity at 20 C | [cm] | ≈ | ≈ | ≈ |
Permittivity at 1 MHz | [-] | - | 7 | 10 |
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Böhl, S.; Weikert, S.; Wegener, K. Enhancing Signal Quality of Capacitive Displacement Measurements in Machine Tool Environments. J. Manuf. Mater. Process. 2019, 3, 76. https://doi.org/10.3390/jmmp3030076
Böhl S, Weikert S, Wegener K. Enhancing Signal Quality of Capacitive Displacement Measurements in Machine Tool Environments. Journal of Manufacturing and Materials Processing. 2019; 3(3):76. https://doi.org/10.3390/jmmp3030076
Chicago/Turabian StyleBöhl, Sebastian, Sascha Weikert, and Konrad Wegener. 2019. "Enhancing Signal Quality of Capacitive Displacement Measurements in Machine Tool Environments" Journal of Manufacturing and Materials Processing 3, no. 3: 76. https://doi.org/10.3390/jmmp3030076