00193407-02 HWWS SIPLACE Machine Accuracy EN.pdf - 第6页
© Siemens AG . . Änderungen vorbehalten SIPLACE Placement Systems Capability Indices Indices are used to assess the qua lity of machines, steps in a process an d complete pro cesses. A single index does not provide suffi…
© Siemens AG . . Änderungen vorbehalten
SIPLACE
Placement Systems
Machine Capability
© Siemens AG . . Änderungen vorbehalten
SIPLACE
Placement Systems
Capability Indices
Indices are used to assess the quality of machines, steps in a process and complete processes.
A single index does not provide sufficient information for the complete characterization of a
process. A comprehensive overview of the qualification status of the process under examination
can only be achieved by studying a combination of several indices.
Placement accuracy takes the deviation from the actual position and the target position of the
components into account.
This contains positioning errors for the linear axis, rotational errors at the placement head,
twisting of the gantry system, errors at the vision modules, .....
More and more fine pitch components are being placed and an increasing number of very small
passive components, size 0402, 0201 and more smaller. Consequently, higher and higher
placement accuracy is a demand of placement machines.
Many natural and technical processes which occur randomly (stochastically) can be described by
a normal distribution.
The deviation of the placement position from the target value consists of a reproducible
component and a random component. The reproducible component can be kept relatively low
through calibration measures. The random component is close to normal distribution (this has
been experimentally confirmed). The normal distribution provides an exact mathematical model
for describing placement accuracy.
Machine Capability
© Siemens AG . . Änderungen vorbehalten
SIPLACE
Placement Systems
how do we define the capability indices?
¾ is it an approximate or exact estimation of the number of defects???
¾ is it a comparison of specifications??
¾ is it a question of interpretation?
example pick & place head Siplace 80F
sigma Cm; Cmk accuracy defect rate
±
1
68,27% 0,33
±
12,5
μ
317300
±
2
95,45% 0,66
±
25
μ
45500
±
3
99,73% 1
±
37,5
μ
2700
±
4
99,994% 1,33
±
50
μ
60
±
5
99,99994% 1,66
±
62,5
μ
0,6
±
6
99,9999998% 2,00
±
75
μ
0,002
which one is better??
50 µm / 4 sigma ⇔ 60µm / 5 sigma
it‘s not visible at the first view !!
Machine Capability