KE-750_MAINTE.pdf - 第94页
Figures 2 and 3 show the vacuum blow timing when mounting on KE-730/740. For chip parts, the vacuum is set off 70 ms before the nozzle (Z axis) moves down, and the part is mounted being held by the remaining pressure (ne…
3.8 Vacuum and Blow timing When Mounting Parts
3.8.1 Timing on KE-730/740
When blow operation is performed during part mount on KE-730/740, the nozzle
pressure becomes positive or negative at the same timing of mounting.
Therefore, the following may occur when there is an offset in the mount timing.
The part is picked at the negative pressure.
The part immediately after mount is rotated at positive pressure.
The parts those placed around are blown away at positive pressure.
For this reason, mounting is performed not using vacuum destruction by blow
but giving the time for the pressure to naturally recover to normal room
atmosphere. When recover the pressure not using blow but turning the
vacuum off only, the pressure inside the nozzle becomes normal room
atmosphere in 70 ms (for KE-730/740) as shown in Figure 1.
Negative pressure
Atmosphere
Positive pressure
Vacuum off
Figure 1
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Figures 2 and 3 show the vacuum blow timing when mounting on KE-730/740.
For chip parts, the vacuum is set off 70 ms before the nozzle (Z axis) moves
down, and the part is mounted being held by the remaining pressure (negative
pressure) in the pipe. For heavy parts, the vacuum is set off 40 ms (or 20 ms)
before the downward movement is complete, and the nozzle is held for 30 ms
(or 50 ms) above the board. Then, the nozzle is moved up after vacuum
pressure is released.
Square chip parts
Z axis
Vacuum
Blow
Figure 2
For Melf, aluminum electrolytic capacitor, network resistor, trimmer, SOT, SOJ, SOP, and
PLCC
Z axis
Vacuum
Blow
For QFP, TSOP, BGA, connector, and socket
Figure 3
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For large parts, as shown in Figure 3, the pressure in side the nozzle is
negative when the part is mounted on the board, and the part is firmly held.
However, for chip parts, the nozzle cannot be held above the board (otherwise
mount accuracy becomes worse), and the part is held by rather low remaining
pressure when it is immediately before mounting.
3.8.2 Improving point of KE-750/760
For KE-750/760, as described before, the part is held at low negative pressure.
In fact, the part is better to be firmly held immediately before mounting.
However, to set the pressure in the nozzle to normal room atmosphere within a
short time, blow is necessary. When a blow operation is performed on
KE-730/740, the pressure in the nozzle occasionally becomes negative and
positive. There are two reasons as follows:
① Location of air pressure related parts, and air pipe
② Blow operation timing
3.8.2.1 Location of air pressure related parts, and air pipe
Figure 4 shows the location of air pressure related parts, and air pipe on
KE-730/740. The problem is with the relation among the ejector, the blow SV,
and the nozzle. The length of the air tube between the blow SV and the
ejector is 1180 mm but it is 130 mm between the blow SV and the nozzle.
Therefore, when the blow SV is turned on and vacuum destruction is started,
the pressure at the nozzle immediately becomes from negative to normal room
atmosphere but the pressure at the ejector part does not. At this moment, if
the blow SV is turned off, the pressure at the tip of the nozzle is pulled negative
by the remaining negative pressure at the ejector. If blow is continued without
turning off the blow SV, the pressure at the nozzle becomes positive. The
direction of union Y used at the connection part of the ejector, the blow SV, and
the nozzle is also set for the blow air to easily move to the nozzle.