Railway switches and signals – Miscellaneous – Signals and indicators
Reexamination Certificate
2000-12-20
2002-09-03
Le, Mark T. (Department: 3617)
Railway switches and signals
Miscellaneous
Signals and indicators
C246S00100C, C340S435000
Reexamination Certificate
active
06443400
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic transport system for transporting articles by an automatic transport vehicle at an assembly location in a plant and the like without human attendance, and particularly to an automatic transport system which detects by a sensor an obstruction located ahead of the automatic transport vehicle in its moving direction to control the operation of the automatic transport vehicle.
2. Description of Related Art
Automatic transport vehicles (hereinafter referred to as vehicles) are advantageously used in transporting parts in an assembly process in a plant and the like. Particularly, in a manufacturing semiconductor process, vehicles are used in transferring and assembling semiconductor wafers in the clean room without human intervention for preventing the contamination-with dust and the like. For example, an Overhead Hoist Transport vehicle (hereinafter referred-to as “OHT vehicle”), which travels along a ceiling rail in the clean room is used in the assembly process of semiconductor wafers and the liquid crystal devices.
Moreover, an optical beam reflection sensor. (hereinafter referred to as “optical sensor”) such as an infrared type sensor, serving as a non-contact obstruction detecting apparatus of vehicles. The optical sensor detects an obstruction ahead in the moving direction by emitting an optical beam which is conical-shaped. If a long range detection sensor is provided at the front of the vehicle as a front detection sensor, the vehicle is stopped when the long range detection sensor is triggered while it is traveling. If a vehicle has two front detection sensor as a front detection sensor, detection may be carried out in two steps by two front detection sensors.
FIG. 9
is an operation conceptual view of an OHT system used in the semiconductor wafer manufacturing process or the like. The right portion of
FIG. 9
is a side view of an OHT vehicle and the left portion of
FIG. 9
is a view showing a projection of the OHT vehicle ahead in the moving direction at a predetermined position in the. moving direction.
In
FIG. 9
, a rail
21
is laid down on a ceiling of a clean room (not shown) along the process line, and a part of the rail
21
is shown therein. An OHT vehicle
22
movably hangs on a lower portion of the rail
21
. For example, the OHT vehicle
22
is constituted such that it has a box-like frame and can hold a wafer cassette
23
in this frame and runs along the rail
21
.
Moreover, a front detection sensor
24
is attached to the front portion of the OHP vehicle
22
in the moving direction. As the front detection sensor
24
, an optical sensor of such as an infrared sensor is generally used such that an obstruction in the moving direction of the OHT vehicle
22
can be detected in a non-contact state. In other words, an obstruction ahead is detected by optical beams emitted in a conical shape from the front detection sensor
24
. Then, when the front detection sensor
24
detects the obstruction ahead, the OHT vehicle
22
is designed to automatically stop.
Additionally, in
FIG. 9
, although the front detection sensor
24
at the left side surface of the OHT vehicle
22
is provided for movement to the left side of the figure, the OHT vehicle
22
normally moves in two directions. In such a case, the front detection sensor
24
is also provided at the right side surface of the OHT vehicle
22
.
However, in some cases, an associated manufacturing apparatus may be present very close to the periphery of the rail
21
, the door of the manufacturing apparatus may be opened, or parts being processed are located close to the periphery of the rail
21
. Further, in other cases, in locations outside of the passage of the OHT vehicle
22
, there may be a stepladder, a workbench or the like for maintenance, or a person. For this reason, in order to prevent the OHT vehicle
22
from colliding with them, the front detection sensor
24
on the OHT vehicle
22
detect obstructions ahead. However, as shown in
FIG. 9
, if the detection area of light emitted from the front detection sensor
24
is widened as shown in a detection area A in order to detect obstructions located in the passage area of the OHT vehicle
22
, there is a possibility that objects which are at the periphery of the running path will unnecessarily be detected and that the OHT vehicle
22
will not run.
In other words, the left side of the drawing indicates the passage area C of the OHT vehicle
22
, as seen from the front of the OHT vehicle
22
in the moving direction, by a solid line. Also, a wide detection area A where the entire passage area C of the OHT vehicle
22
can be detected is indicated by a broken line. This large detection area A is the bottom surface of the cone of the-light beam emitted by the front detection sensor
24
at a predetermined position.
Unlike the wide circular detection area A that is the bottom of a conical surface, if the front shape of the OHT vehicle
22
that is the passage area C of the OHT vehicle
22
is rectangular, for example, as illustrated in the figure, excess detection area D, in which the wide detection area A lies outside of the passage area C to be detected will occur. If an object is located in this excess detection area D, the OHT vehicle
22
will stopped even though the object is not actually obstructing the passage of the OHT vehicle
22
.
On the other hand, if the detection area is narrowed as in the narrow detection area B indicated by a broken line, the corner portions of the passage area C of the OHT vehicle
22
cannot be detected, and form a non-detection area E. In such a case, there is the concern that the OHT vehicle
22
will collide with an object in the non-detection area E which is in the corner portion of the vehicle, when the vehicle passes the object.
FIG. 10
is an explanatory view showing the front detection sensor of the OHT vehicle
22
and an example of an obstruction. As illustrated in this figure, a stepladder
25
is placed in front, in the moving direction, of the OHT vehicle
22
. In this case, if the detection area at the front detection sensor
24
is wide, as in the wide detection area A, the stepladder
25
is detected as an obstruction and the OHT vehicle
22
is stopped even though the OHT vehicle
22
will not collide with the stepladder
25
. Furthermore, if the detection area is narrowed as in the narrow detection area B, the stepladder
25
is not detected. However, if workpieses or the like are placed at a location very close to the OHT vehicle
22
, there is the concern that the OHT vehicle
22
will collide with them and break them since they cannot be detected.
FIG. 11
is a conceptual view showing an OHT vehicle used in a semiconductor manufacturing apparatus. As illustrated in this figure, for example, in the apparatus for manufacturing a 300 mm wafer, a distance P between the end surface of the OHT vehicle
22
that transports the wafer and the front surface of the semiconductor manufacturing apparatus
26
is set to about 30 mm on the basis of a standard distance. It is assumed that working is carried out in such small distances. If the detection area is too wide, the front detection sensor
24
will detect the door of the semiconductor manufacturing apparatus
26
, so that the OHT vehicle
22
will not operates well and workcannot be carried out. Moreover, if the detection area is narrowed, there is the concern that the corner of the OHT vehicle
22
will contact semiconductor wafers (not shown) mounted on the semiconductor manufacturing apparatus
26
and these semiconductor wafers will be broken.
FIG. 12
is a conceptual view showing a vehicle using two front detection sensors for long range and medium range detection. The vehicle
111
is provided with a medium range detection sensor (not shown) which can detect over a medium detection range
113
and a long range detection sensor (not shown) which can detect over a long detection range
112
. The vehicle
111
detect an obstruction which is loaded ahead in
Kyutoku Senzo
Murata Masanao
Onishi Hisashi
Le Mark T.
Scully Scott Murphy & Presser
Shinko Electric Co. Ltd.
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