Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
2002-02-20
2004-10-19
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
C310S012060, C310S015000
Reexamination Certificate
active
06806594
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coil unit for a linear motor, more specifically relates to a technology for cooling the coil with the refrigerant.
2. Description of the Related Art
Conventionally, in exposing devices for manufacturing semiconductor devices and high precision machining devices, it has been required to position an object (for example, a wafer to be exposed or a workpiece) fast and precisely. As a device for precisely positioning used for that purpose, devices for converting a rotation of a rotary motion type motor into a linear motion through a ball screw, and linear motion type motors (so-called linear motors) are widely used.
Among them, the linear motor has a simple structure, includes a small number of parts, has merits that its linear motion is directly used, and positions an object fast. It also includes characteristics that its small friction resistance during driving increases the motion precision. Because of the reasons describes above, the linear motor has been becoming a mainstream as a linear drive device in all fields where a precise positioning is required, and is widely used in a manufacturing process for a liquid crystal display device, for example.
This linear motor generally comprises a magnetic pole unit provided with magnets, and a coil unit provided with a coil. Either one of the magnetic pole unit and the coil unit is connected with a certain base, and functions as a stator, and the other of them is connected with a moving table, for example, and functions as a movable element. The magnetic unit and the coil unit are separated by a certain gap to avoid a contact, and relatively move linearly while the gap is maintained.
A coil provided for the coil unit generates heat when an electric current is supplied. This generated heat transfers to the entire coil unit, and further to the base and the moving table, for example, connected with the coil unit. As a result, problems described below occur.
(1) The heat from the coil causes thermal expansions of the coil unit itself and an associated machine connected with the coil unit, and causes an error in a positioning precision. Specifically, when the associated machine connected with the coil unit is a low thermal expansion material (thermal expansion coefficient is 1×10
−6
) of 100 mm in length, for example, a thermal deformation of 100 nm is generated when the temperature increases by 1° C. If a positioning precision of the order of one nanometer is required, this thermal expansion prevents satisfying the requirement sufficiently.
(2) A laser interferometer or the like is installed in the vicinity of the linear motor to measure a motion of the linear motor. When the coil unit heats an atmosphere around to generate a “fluctuation”, a light path of laser light is influenced, and a measurement error occurs.
It is known as a technique for solving the problem in (1) that a refrigerant is flowed between a mounting surface to an associated machine, and the coil in the coil unit to prevent the heat transfer from the coil. However, this technique cannot restrain temperature of an atmosphere around the coil unit from increasing, and the problem in (2) still remains unsolved.
A coil unit shown in FIG.
13
and
FIG. 14
is proposed to solve both of the problems in (1) and (2). The coil unit
10
is used for a linear motor
1
, and is placed so as to oppose to magnets
3
in a magnet unit
2
.
Specifically, this coil unit
10
is provided with a plate-shape coil
12
placed opposing to the magnets
3
while extended in a traveling direction X, and a shell
14
for storing the coil
12
inside, and passing a refrigerant through gaps
13
between itself and the coil
12
to cool the coil
12
. On the other hand, the magnet unit
2
is provided with a base
4
whose cross section is in a U shape, and the magnets
3
installed on inner walls
4
A opposing to each other in the base
4
.
A mounting surface
16
agaist to an associated machine is formed outside of one edge in a widthwise direction Y of the shell
14
, a supplying hole
18
is formed on one end in a lengthwise direction X of the mounting surface
16
for supplying the gaps
13
of the shell
14
with the refrigerant, and a draining hole
20
is formed on the other end for draining the refrigerant. When the coil unit
10
is connected with an associated machine on a “fixed side” through this mounting surface
16
, the coil unit
10
serves as a stator, and the magnet unit
2
serves as a movable element. Inversely, when the coil unit
10
is connected with an associated machine on a “traveling side”, the coil unit
10
serves as a movable element, and the magnet unit
2
serves as a stator.
The refrigerant supplied from the supplying hole
18
diffuses in the gaps
13
between the coil
12
and the shell
14
, and exchanges heat with the coil
12
. Thus, the coil
12
which generates heat due to a current is cooled, and the refrigerant is heated. Because the heated refrigerant is drained from the draining hole
20
, the heat does not accumulate inside the coil unit
10
, a radiation to the atmosphere around is reduced, and a transfer of the heat from the coil
12
to the mounting surface
16
is restrained, thereby reducing a thermal expansion of the associated machine. As a result, this linear motor
1
has a reduced influence on the outside caused by the heat generation from the coil
12
, and provides a more precise positioning.
However, this coil unit
10
does not always provide a sufficient cooling effect.
FIG. 15
specifically shows a schematic diffusion status of the refrigerant inside the shell
14
. The refrigerant gradually spreads as A, B, C, . . . , becomes a parallel flow, converges as F. G. and H, and is finally drained from the draining hole
20
. Because the refrigerant is heated as it moves toward the downstream side, the temperature increases roughly in this order of A, B, C, . . . E, G, and H.
As a result, especially, the temperature of the refrigerant close to the downstream side (E, G, and H) is much higher than that on the upstream side, the cooling efficiency decreases, and simultaneously the heat transfers to the shell
14
through the refrigerant in this high temperature state, and is radiated outside. Further, the heat transfers to the mounting surface
16
through the refrigerant in this high temperature state on the downstream side, and becomes a cause for inducing a thermal expansion of the associated machine.
This property unavoidably presents even if the pressure of the refrigerant (a supplying pressure) and the width of the gaps are designed relatively favorably. If the design is not favorable, it is highly probable that a part where the refrigerant hardly flows actually occurs, and the defect sometimes becomes more remarkable.
Because it is required to increase the flow rate of the refrigerant to increase the cooling efficiency for avoiding this problem, problems such as increasing the capacity of a recirculating pump for the refrigerant occur.
The present invention is devised in view of the problems describe above relating to the cooling.
SUMMARY OF THE INVENTION
A coil unit for a linear motor relating to the present invention comprises a shell for using a refrigerant to cool a coil of a linear motor, a main flow passage formed inside the shell while extending in a lengthwise direction of the coil for leading the refrigerant supplied from the outside into itself, and a plurality of branch flow passages, formed on the main flow passage at a predetermined interval in the lengthwise direction, for draining the refrigerant led into the main flow passage in a widthwise direction of the coil, where the refrigerant drained from the branch flow passages after flowing through the main flow passage, flows through a gap between the shell and the coil to cool the coil.
This coil unit leads and stores the refrigerant in the lengthwise direction of the coil, and simultaneously branches the stored refrigerant toward the widthwise direction. Specifically, the coil
Kato Tatsuro
Koyanagawa Yasushi
Mori Hidehiko
Shinohira Daisuke
Sugimine Masanobu
Le Dang
Mohandesi Iraj A.
Sumitomo Heavy Industrie's, Ltd.
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