Clean bench

Clean bench having an outlet wind velocity measuring apparatus for the filter. The measuring apparatus comprises an air duct on a downstream of the filter, a rectifier means at the passage of the air duct, and a wind velocity sensor for detecting the velocity of the outlet wind rectified by the rectifier means.

BACKGROUND OF THE INVENTION 
The present invention relates to an outlet wind velocity measuring 
apparatus for a filter that is used in a clean bench. 
Conventionally, it has been desirable for measurement of the wind velocity 
in a work space of the clean bench to carry out at the wind outlet side of 
filter. 
However, if the filter has a complicated structure such as, for instance, a 
high capability one in which each filter element is offset to form a 
corrugated shape from air intake side to air outlet side, thereby 
providing a greater filtering area, there has been a problem that such a 
corrugated structure can cause the outlet wind velocity to vary at the air 
outlet side in the direction along the filter (that is, in the direction 
transversely crossing the air flow) and thus it is not possible to measure 
the wind velocity correctly. 
Therefore, it has been suggested for measuring the wind velocity of the 
filter having the complicated structure as mentioned above to employ a 
method of detecting a volume of wind at the filter inlet side and of 
converting this value into the wind velocity, or in the case of measuring 
the wind velocity at the air outlet side, its measurement has been made at 
a position relatively remote from the filter's underside. The former 
method has a problem that greater fluctuations in the measurement values 
impair results of measurement, while the latter method is also problematic 
in that necessity of installing a measuring apparatus within the working 
space inevitably sacrifices the space available for the working operation. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a clean bench which has an 
outlet wind velocity measuring apparatus adapted to uniform the outlet 
wind velocity that is otherwise made variable by the structure of filter, 
thereby making it possible to correctly measure the outlet wind velocity 
at the filter's outlet side. 
Another object of the present invention is to provide a clean bench which 
has an outlet wind velocity measuring apparatus adapted to secure an ample 
space available for the working operation at the filter's air outlet side. 
These and other objects and advantages of the present invention are 
accomplished by a provision of an outlet wind velocity measuring apparatus 
for a filter, wherein an air duct having a passage of suitable 
cross-sectional area adequate for the outlet wind flowing from the filter 
to pass is vertically secured to the filter's outlet side, the outlet side 
being formed in a corrugated shape by offsetting filter elements from air 
intake side to air outlet side, the passage of the air duct is provided 
with a flow rectifier or airflow straightener adapted to rectify the flow 
of outlet wind passing through the passage, and the rectifier is provided 
at its air outlet side thereof with a wind velocity sensor adapted to 
detect the outlet wind velocity rectified by the rectifier.

DETAILED DESCRIPTION OF THE INVENTION 
With reference to FIG. 1, the clean bench is constructed such that it can 
feed a clean air vertically to the working space 11. That is, the clean 
bench is constructed in such way that it can draw an air via a prefilter 
15 from an air inlet port 13 defined at the lower side thereof, and after 
a thorough removal of dirt, vertically feed the clean and asceptic air to 
the working space with a subsequent discharge thereof out of the front. 
For its corrugated structure of offsetting filter elements from air inlet 
side to air outlet side, the filter 1 ensures greater filtering area. 
The filter 1 is provided at the air inlet side thereof with an outlet wind 
measuring apparatus adapted to measure the velocity of outlet wind flown 
from the filter 1. A defined air space 2 is located on the output side of 
the filter. As shown in FIGS. 2, 3 and 4, the outlet wind velocity 
measuring apparatus 19 has the air duct 5 including the passage of 
suitable cross-sectional area (squarely shaped in the embodiment shown) 
vertically secured to the outlet side of the filter 1 in a close 
relationship with the filter 1, and being supported by a machine frame 23 
via a support frame 21. 
Tensionably horizontally mounted with the passage of the air duct 5 is a 
rectifier 7 or airflow straightener adapted to rectify the flow of air 
passing through the passage. The rectifier 7 is made of, as for example, a 
stainless steel wire gauze having outside diameter of 0.5 mm and pitch 
size of 1.8 mm. 
The rectifier 7 is provided at the lower portion thereof a wind velocity 
sensor 9 such as a hot-wire anemometer and the like capable of detecting 
the outlet wind velocity rectified by the rectifier 7. The wind velocity 
sensor 9 is supported by a support bracket 25 provided at the side wall 5' 
of the air duct 5 and is interposed into the passage. 
Though not shown in Figures, a controlling means is provided to connect the 
wind velocity measuring apparatus to the air blower. The controlling means 
function to compare the wind velocity detected by the wind velocity sensor 
9 with the predetermined wind velocity, and if there is any discrepancy 
between the two values, it further controls the air blower automatically 
for increasing or slowing down its r.p.m. Furthermore, the controlling 
means is adapted to produce an alarm upon a minimum wind velocity being 
detected. 
There are further arranged a shutter 27, a fluorescent lamp 29 respectively 
provided at the front and upper portions of the working space 11, and a 
light diffuser 31. 
Several functions attainable by the present invention will be described 
hereinbelow. 
The air drawn via the prefilter 15 from the air inlet port 13 provided at 
the lower portion of the clean air bench is blown by the air blower 17 to 
pass through the filter 1 to the air outlet side. Despite a tendency for 
the outlet wind velocity to vary and fluctuate under the influence of 
filter's structure, use of the air duct 5 can serve to uniform the 
fluctuating wind velocity by the rectifier 7 which functions to rectify 
the air flow while passing through the passage in the air duct. The wind 
velocity sensor 9 detects the velocity of outlet wind thus uniformed, 
thereby making it possible to correctly measure the outlet wind velocity 
at the air outlet side of filter 1. 
Measurement results of the outlet wind velocity taken at a fixed point of 
the secondary side of the HEPA filter, used as a filter 1 are given below, 
comparing the results of the case where the wind velocity sensor 9 is 
installed directly with those of the case where the wind velocity sensor 9 
is installed via the outlet wind velocity measuring apparatus constructed 
in accordance with the present invention. 
______________________________________ 
Installing Condition of 
Variance at 
Laternal Longitudinal 
Wind Velocity sensor 
Fixed Point 
Fluctuation 
Fluctuation 
______________________________________ 
Without wind .+-.0.01 0.07 (m/s) 
0.10 (m/s) 
velocity measuring 
0.57 (m/s) 
apparatus 
With wind velocity 
.+-.0.005 0.02 (m/s) 
0.01 (m/s) 
measuring apparatus 
0.36 (m/s) 
installed (as embodyed) 
______________________________________ 
As apparent from the above table, variance in the outlet wind velocity by 
positions can be uniformed to 1/3.5 to 1/10 times less in the case where 
the wind velocity sensor 9 is installed via the outlet wind velocity 
measuring apparatus 19, compared to the case where the wind velocity 
sensor is installed directly. 
In addition, the clean bench with the wind velocity measuring apparatus 
secured to the understream of the filter, and is equipped with the 
controlling means adapted to control the r.p.m. of the air blower in 
response to the wind velocity detected by the wind velocity sensor 3, can 
afford the effects as undermentioned. 
a. By providing the wind velocity sensor upwardly of the working space at 
the understream of the filter, the wind velocity at the working space can 
be directly detected, making it possible to correctly detect the air 
current condition. 
b. A provision of a controlling means adapted to control the r.p.m. of the 
air blower by comparing the wind velocity detected with the predetermined 
value can permit the wind velocity at the working space to be kept at 
constant as predetermined, thereby realizing a stable air current 
condition. 
c. In the case that the operation is carried out with the shutter slightly 
opened, the filter can extend its working life by predeterming the wind 
velocity lower than usual beforehand. 
Meanwhile, the present invention is not limited its application merely to 
the embodiment mentioned as above, but the air duct, as for example, may 
be constructed with its cross-sectional area as circular. 
As apparent from the foregoing description, the construction in accordance 
with the present invention can serve to uniform the outlet wind velocity 
that may otherwise be functuated at the air outlet side of the filter 
wherein filter elements are offset to form a corrugated shape from air 
intake side to air outlet side. Therefore, it becomes possible for the 
wind velocity sensor to be mounted closely to the filter, and to obtain a 
correct wind velocity simultaneously. As a result, the working space to be 
formed at the air outlet side of the filter can be made ample.