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DMU
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LMU
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Measuring procedure |
Distance measurement between an
electrode and a dielectric (tire surface). The measured capacity is a
measure for the distance. The dielectricity of the measuring object must
remain equal on the entire measuring track. |
Distance measurement at the
triangulation procedure. The light spot of the laser is reflected on the
measuring surface (tire surface) with an optical system on an
photo-sensitive recipient. The angle with which it will receive, is a
measure for the distance. |
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Suitability for measurements of tires |
Very good suitability. Particularly
co-ordinated measuring surfaces on measurement of tires. Very high
dynamics, suitably for numbers of tire rotations up to 2400 1/min at the
measurement. |
Very good suitability. Unequally
reflecting areas in the measuring track are compensated during the
measurement. CCD technique and special adjustments permit clear distance
information’s also outside of the measuring range. High dynamics,
suitably for numbers of rotations up to 650 1/min at the measurement. |
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Measuring track |
According to the active measuring
surface of the sensor a surface is scanned on the measuring object also.
The distance value is an integrated value according to the size of the
surface. The measuring track width at the DMU amounts 23mm at the side
wall. |
The laser sensor scans spot by spot.
The measuring track is a line. Since visible light is used the measuring
track can be detected. |
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Breakdown sensitivity |
Advantage:
Before each measurement variable disturbances are compensated
automatically such as temperature, air humidity and contamination. This
meant independence from environmental influences in case of rough
operations. Mechanically very durable sensor.
Disadvantage:
Sensitivity on changing dielectricity during the measurement. Bad GND
connection of machine and sensor technology can falsify the measuring
signal. |
Advantage:
During the measurement different reflection ability are compensated to
surface. Because of this regulation and also the use of the CCD
technique the system is independent of the optical characteristics of
the measuring object, of shining metal surface up to matt black rubber
surface. The electrical characteristics of tires doesn‘t matter.
Disadvantage:
Sensitivity against contamination of the optics. Highly exact aligned
optical items within the sensor make laser sensor sensitive to
mechanical impacts. |
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Runout |
Advantage:
A width measuring track with integrating effect is a prefiltration of the
signal. Fine surface structures such as letterings and pin vents are
suppressed at the signal originally already. A simple digital rework of
the signal leads to good results of measurement.
Disadvantage:
Fine surface structures are not entered. |
Advantage:
Fine surface structures are entered. For example the height of the
letterings or the depth of profile is detected.
Disadvantage:
The signal originally has many breakdown information’s of fine surface
structures and must be reworked with complex digital filters again. Each
type of tire must be non-standard adapted. |
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Bulges and depressions at tire sidewalls |
Advantage:
The flat elevations (bulge) can be differentiated by the flat measurement
principle clearly by other elevations at the tire side wall of the sensor.
The selection of the measuring surface of the sensor is optimized on a
typical bulge. Good results during the standard bulge measurement. It
reaches excellent results combined with the measurement of the bulge
dynamics.
Disadvantage:
Possibly large letterings and pin vents in the measuring signal cannot be
suppressed sufficiently. |
Advantage:
- / -
Disadvantage: Already
in the rough signal bulges, letterings and pin vents are not to
differentiate from each other in cases unfavorable. That means also a
rework of the signals cannot lead to a distinction safely. Bulges can be
entered only in a " free " measuring track (without letterings,
deflation holes...). |
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Range of measurement |
3 – 14 mm
Advantage:
By close positioning of the sensors at the tire a small range requirement
exists for the measuring instrument.
Disadvantage:
Collisions at the sensors can occur through badly centered tires. |
40 – 60 mm
Advantage:
Because of the large measuring distance collisions with tires are not
expected.
Disadvantage:
Because of the distant positioning of the sensors at the tire a larger
range requirement exists for the measuring instrument. A suitable
preventive measure for the laser class 3A is necessary.
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Accuracy |
Output of the measured value: 1/100mm
Typical standard deviation during repeat
measurements of tires: 0,03mm |
Output of the measured value: 1/100mm
Typical standard deviation during repeat
measurements of tires: 0,03mm |
Result:
Both measuring procedures have it’s special advantages, which should be adapted to the measuring task. Both measuring procedures are applicable at RFP-5 systems and also exchangeable
later.
Note:
Capacitive sensors prove it worth in the industry through measuring accuracy and robustness very much. Tires with high SILICA proportion in the bearing surface mixture were developed shortly. The low dielectricity of these rubber mixtures can be measured also with capacitive sensors. However, we know a tire manufacturer who produces tires having a higher dielectricity at the joint of the bearing surface strip than in the rest of area (perhaps using adhesives with higher dielectricity?). These tires are less suitable for the measurement of the tread with capacitive sensors. Therefore we particularly recommend companies which have to check tires of different manufacturers to use laser sensors for runout measurements. Tire manufacturers should check whether the problem described above also could be relevant at their company.
