Conveying device

Details Conveying device Conveying device

2003-01-30

2004-06-29

Joyce, William C. (Department: 3682)

Machine element or mechanism

Gearing

Backlash take-up

C414S744200, C310S112000, C901S023000

Reexamination Certificate

active

06755092

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a conveying device for conveying a work piece such as a silicon wafer, for example.
2. Description of the Related Art
For etching of a wafer, CVD (chemical vapor deposition) and the like, for example, it is necessary to convey the wafer in a multi-chamber in a clean and ultra-high vacuum environment. In such an environment, the conveying device operates. A conveying device which does not require the use of a magnetic fluid seal, that is, a conveying device provided with a separating wall between a rotor and a stator in a motor has been devised in order to prevent the environment in the chamber from being deteriorated. The conveying devices described in Japanese Patent No. 2,761,438 and U.S. Pat. No. 5,720,590 are examples of such conveying devices.
FIG. 9
is a longitudinal sectional view showing a conveying device
101
having the same basic structure as the conveying devices described in the above-mentioned publications. The conveying device
101
comprises a coaxial shaft mechanism including a first shaft
121
and a second shaft
122
which are independently rotatable, and a conveying arm assembly
130
fixed to the upper ends of the shafts
121
and
122
. The first shaft
121
extends downward from the lower end of the second shaft
122
and penetrates the second shaft
122
. A rotor R′ is attached to the outer peripheral sides of the first shaft
121
and the second shaft
122
, and a stator S′ is attached to a housing
190
accommodating the first shaft
121
and the second shaft
122
. A motor M′ is constituted by the rotor R′ and the stator S′. By controlling the rotation of the motor M′, the expansion, contraction and turn of the conveying arm assembly
130
can be controlled. The reference numeral
145
denotes an optical encoder for detecting the rotation of the first and second shafts
121
and
122
.
In the conveying device
101
having such a structure, it is required that the conveying arm assembly
130
should be quickly set in a conveying position and be rapidly stabilized in the conveying position. For this purpose, adequate characteristics are required for the shafts
121
and
122
.
FIG. 10
is a chart showing a process of controlling the rotation of the shaft, wherein an axis of ordinate indicates angular velocity of the shaft and an axis of abscissa indicates time. In general, the rotation of the shaft is controlled to reach a stopping step “e” from a stopping step “a” through an accelerating step “b”, a constant-velocity rotating step “c” and a decelerating step “d” as shown in FIG.
10
. In the conveying device
101
, it is necessary to rapidly accelerate or decelerate the shafts
121
and
122
, that is, to increase an angular acceleration at the accelerating step “b” and an angular deceleration the decelerating step “d” shown in
FIG. 10
in order to quickly set the conveying arm assembly
130
in the conveying position. Moreover, the oscillation of the angular velocity is observed in the early stage of the constant-velocity rotating step “c” and that of the stopping stage “e” in FIG.
10
. In order to quickly stabilize the conveying arm assembly
130
in the conveying position, however, it is necessary to reduce times t
1
and t
2
taken to cause the oscillated angular velocity to converge on a constant value, that is, stabilizing times. With an increase in the size of the work piece, furthermore, the conveying device should have the characteristics that a conveying distance is long and the conveying device is resistant to a great load. In order to satisfy these requirements, the torsional rigidity of each of the shafts
121
and
122
should be increased. If it is desired to increase the torsional rigidity of each of the shafts
121
and
122
, it is necessary to shorten the shafts
121
and
122
or to increase a modulus of section of each of the shafts
121
and
122
.
Moreover, when the conveying arm assembly
130
connected to the two shafts
121
and
122
is to be driven, the synchronous driving of the two shafts
121
and
122
is required. For this purpose, it is necessary to reduce a difference in the torsional rigidity between the two shafts
121
and
122
. In order to reduce the difference in the torsional rigidity between the two shafts
121
and
122
, it is necessary to reduce a difference in a length between the two shafts
121
and
122
and a difference in a modulus of section between the shafts
121
and
122
.
In the conveying device
101
, however, the first shaft
121
extends downward from the lower end of the second shaft
122
to penetrate the second shaft
122
. For this reason, particularly, it is hard to reduce the length of the inside shaft
121
and to increase an outside diameter thereof. If the outside diameter is increased, the inside and outside diameters of the second shaft
122
should also be increased. Consequently, the outside dimensions and weights of both the shafts
121
and
122
are increased. Therefore, a large-sized motor is required for controlling the expansion, contraction and turn of the conveying arm assembly
130
. Moreover, it is impossible to avoid an increase in the outside diameter of the housing
190
.
With the structure of the conveying device
101
, furthermore, the shaft
121
has a greater length and a smaller modulus of section than the shaft
122
. Therefore, the difference in the torsional rigidity between both the shafts
121
and
122
is great. Accordingly, both the shafts
121
and
122
cannot be synchronously driven by rapid acceleration and deceleration.
In order to perform positioning with high precision, run-out of the shaft should be small. In the conveying device
101
, the run-out is generated on the shaft
122
due to the precision of a bearing
100
B during the rotation thereof. Similarly, when the shaft
121
is relatively rotated with respect to the shaft
122
, relative run-out is generated on the shaft
121
with respect to the shaft
122
due to the precision of a bearing
100
B′. In the conveying device
101
, therefore, when the shaft
121
and the shaft
122
are rotated at the same time, accumulative run-out is generated on the shaft
121
due to the precision of each of the bearings
100
B and
100
B′. Consequently, it is impossible to perform the positioning with high precision.
The conveying device
110
has such a structure that the operation of one conveying arm assembly
130
is controlled by a set of shafts
121
and
122
. If the operations of a plurality of conveying arm assemblies are to be controlled by plural sets of shafts, the above-mentioned problems become more remarkable. For example, if two conveying arm assemblies are to be controlled by two sets of shafts, four shafts are coaxially provided to control the operation of one of the conveying arm assemblies by means of two inner shafts and that of the other conveying arm assembly by means of two outer shafts. With such a structure, it is harder to reduce the length of the inner shaft and to increase the modulus of section thereof. Furthermore, the torsional rigidity of the inner shaft cannot be increased. Moreover, the lengths and moduli of section of innermost and outermost shafts have very great differences. Therefore, a difference in the torsional rigidity becomes very great. In particular, the innermost shaft is attached to the housing through much more bearings. Therefore, the accumulation of the run-out due to the precision of the bearing is increased so that the run-out becomes very great, resulting in poor positioning precision.
In solving the above-described problems, it is desirable to make the vacuum chamber and a device (semiconductor fabricating device herein) using the vacuum chamber as compact as possible. Further, the conveying device requires sufficient strength.
By way of example, the related arts associated with the problems are disclosed in Japanese Patent Application Publication No. Hei., 11-220863 and Japanese Patent Application Publicatio

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