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Measurement of form and waviness
D
D
Waviness Angle D
D D D
y
x
Slope measurement and integration of the angles
D1 D2 D3 D4
D
dx
y i
x
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Statistical profile analysis
The scattering value So is a statistical
roughness parameter which is closely related
to the DIN EN ISO profile parameter Rdq
Rdq represents the distribution of the profile
angles; δ and S0 describe the distribution of
the scattering angles φ. (φ = 2 · δ)
I.e. So correlates best with Rdq.
If the machining process does not change,
So or Rdq correlates also with the
vertical parameters Rz or Ra
φ
δ
Probability
P
Scatt. angle φ
Probability
P
Profile angle δ
Rdq
So
φ = 2 ∙ δ
So ~ Σ (φ – φ)
2
· P(φ)
R2
dq ~ Σ (δ – δ)
2
· P(φ)
φ
δ
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Comparison with stylus parameters
Profilometer
Light
scattering
Stylus
profilometer
Part Rz
(µm)
1 1,2
2 1,5
3 1,8
4 1,4
5 3,5
6 2,9
7 1,0
8 1,7
9 2,5
Part So
1 10,5
2 11.8
3 14,0
4 12,0
5 25,3
6 15,7
7 10,8
8 12,9
9 19,8
Correlation measurements to
calculate the curve fitting
parameters a,b
So
Rz
Rz = a·So+b
1 2 3
20
15
10
Samples from production
Rdq
(%)
1,5
1,9
2,1
1,7
7,3
5,1
0,9
2,5
4,7
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Application: 100% in-line measurement
Schleif 5
ALARM
456
1500
So: 24,6
I : 450
M: 0,4
Go part
No go part
Go/No go Trigger
Alarm signal
Teile Nr.
Rz
Teile Nr.
Sigma
Rz
Teile Nr.
Intensität
So: 17,6
I: 456
M: 0,5
I.O. Alarm n.I.O.
So-values
Computer based roughness measurement
1. Sensor trigger detects the part and sends a Start/Stop signal for measurement reading
2. Sensor measures 1000 values/s and transfers So +/- σ value to the PC
3. PC calculates ISO-value (Rdq, Rz, ..) and checks the I/M value (sensor alignment)
4. Exceeding the limit starts the „no go – trigger“ or sends an alarm to realign the sensor
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Application: Profile pattern inspection
Wrong dressing can cause different
surface profile patterns although the
vertical roughness value Rz remains
constant (see picture bottom)
The profile angle parameter Rdq
differentiates this change (see picture
middle)
Also the optical light scattering value
So is able to detect this change within
the same order of magnitude (see
picture top)
In a grinding process the pattern of a
surface profile should not change,
because the functional behaviour of the
surface will be influenced (e.g. wear).
With light scattering measurement this
can be detected easily.
So=9 So=17
Rdq=1,2 Rdq=2,2
Rz=0,5 Rz=0,5
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Benefits
1. Measurement speed Up to 1000 roughness measurements per s
2. Sensor alignment Due to the specially designed OS 500 optics the So value
is hardly influenced by small misalignments of the sensor
(tolerance: working distance: ~ 1 mm, Tilt: ~ 2°)
3. Workpiece speed The workpiece speed does not affect the So value
4. Working distance The measurement distance (sensor – workpiece surface) is
3mm. (with a special light protection adapter, 50 mm is
possible)
5. Vibration Small vibrations do not disturb the measurement (see 3:)
6. Environment Even the harsh environment of the shop floor is acceptable
