Three-dimensional structure forming apparatus provided with a liquid-level control system for a main resin tank

A three-dimensional structure forming apparatus for forming an optical three-dimensional structure by sequentially laminating hard resin layers by repeating a hard resin layer forming cycle by irradiating the surface of a liquid photosetting resin with a light beam including a main resin tank which contains liquid photosetting resin and has a liquid level control so as to maintain the liquid level of the photosetting resin constant. A replenishing tank and a resin supply, supply resin to the main resin tank at a predetermined rate so that the resin continuously overflows the main resin tank.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a three-dimensional structure forming 
apparatus for forming a three-dimensional structure on the basis of an 
optional stereographic image by irradiating a liquid photosetting resin 
with a light beam and, more particularly, to a liquid level controller for 
controlling the liquid level of the liquid photosetting resin contained in 
a main resin tank. 
2. Description of the Prior Art 
A method of forming a structure having a desired morphology by irradiating 
a liquid photosetting resin with a light beam is proposed, for example, in 
Japanese Patent Application No. Sho 63-267945. FIG. 5 shows an essential 
portion of a three-dimensional structure forming apparatus 51 for carrying 
out the method. 
The three-dimensional structure forming apparatus 51 has a main resin tank 
52 for containing a liquid photo-setting resin A which sets when exposed 
to ultraviolet rays, a horizontal stage 53 having the shape of a plate and 
placed in the main resin tank 52, an elevating mechanism 54 for vertically 
moving the stage 53, a scanning unit 55 for irradiating the surface of the 
liquid photosetting resin A with a light beam, and a molding controller 56 
for controlling the exposure and scanning operation of the scanning unit 
55 and the operation of the elevating mechanism 54 for moving the stage 
53. 
In forming a three-dimensional structure of a desired morphology by the 
three-dimensional structure forming apparatus 51, the elevating mechanism 
54 locates the stage 53 an initial position indicated by continuous lines 
where the liquid photosetting resin A spreads in a predetermined thickness 
over the stage 53, and then the surface of the liquid photosetting resin A 
is scanned with a light beam B for raster scanning in a pattern 
corresponding to the pattern of one of a plurality of parallel planes 
obtained by slicing an optical stereographic image, which will be referred 
to as "parallel decomposed planes". 
Portions of the liquid photosetting resin A irradiated with the light beam 
B set in a hard resin layer of a shape corresponding to the pattern of the 
decomposed plane. Every time one hard resin layer is formed, the elevating 
mechanism 54 lowers the stage 53 by a predetermined distance corresponding 
to the pitch of the decomposed planes of the stereographic image to spread 
the liquid photosetting resin A over the hard resin layer in a thickness 
corresponding to the pitch of the decomposed planes. Then, the liquid 
photosetting resin A spreading over the hard resin layer is scanned with 
the light beam B in a pattern corresponding to the pattern of the next 
decomposed plane to form a hard resin layer of a shape corresponding to 
the pattern of the corresponding decomposed plane on the previously formed 
hard resin layer. These successive hard resin layers join together. 
Thus, hard resin layers of shapes respectively corresponding to the 
patterns of the decomposed planes are formed successively in adjoining 
layers to form a desired three-dimensional structure. 
Thus, a three-dimensional structure can be formed on the basis of an 
optical image by this method of forming a three-dimensional structure. 
In irradiating the surface of the liquid photosetting resin A contained in 
the main resin tank 52 with the light beam B by the three-dimensional 
structure forming apparatus to harden portions of the liquid photosetting 
resin A in a pattern, the diameter of the spot of the light beam B is 
dependent on the distance between the objective lens of the 
three-dimensional structure forming apparatus and the surface of the 
liquid photosetting resin A. Accordingly, if the liquid level of the 
liquid photosetting resin A contained in the main resin tank 52 is 
variable, the diameter of the spot of the light beam B is variable and 
hence it is impossible to form a three-dimensional structure in accurate 
dimensions. 
The liquid level of the liquid photosetting resin A in the main resin tank 
52 is liable to vary with the variation of the temperature of the liquid 
photosetting resin A or with the reduction of the amount of the liquid 
photosetting resin A contained in the main resin tank 52. 
When a very large main resin tank is used or when the light beam is focused 
in a very small spot to reduce the terminal depth, in particular, the 
liquid level of the liquid photosetting resin must precisely be 
controlled. However, no effective liquid level control system for such a 
purpose has been developed so far. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a 
three-dimensional structure forming apparatus provided with a liquid level 
control system capable of precisely controlling the liquid level of a 
resin contained in a main resin tank by a simple control method so that a 
three-dimensional structure can be formed in accurate dimensions. 
In one aspect of the present invention, a three-dimensional structure 
forming apparatus, which laminates hard resin layers sequentially to form 
an optional three-dimensional structure by repeating a hard resin layer 
forming cycle comprising irradiating the surface of a liquid photosetting 
resin with a light beam in a pattern corresponding to the pattern of one 
of a plurality of parallel decomposed planes obtained by slicing an 
optical stereographic image to form a hard resin layer of the pattern of 
the corresponding decomposed plane and spreading the liquid photosetting 
resin over the hard resin layer, comprises: a main resin tank, a 
replenishing tank installed near the main tank; and a resin supply means 
for supplying the liquid photosetting resin from the replenishing tank to 
the main resin tank. The three-dimensional structure forming apparatus is 
characterized in that the main resin tank is provided with a liquid level 
control system for returning the liquid photosetting resin that overflows 
the main resin tank through a suction opening or an overflow weir formed 
in one side surface of the main resin tank. 
According to the present invention, the liquid photosetting resin contained 
in the replenishing tank is supplied continuously to the main resin tank, 
and the liquid photosetting resin that overflows the main resin tank is 
returned through the suction opening or the overflow weir to the 
replenishing tank. Consequently, the quantity of the liquid photosetting 
resin contained in the main resin tank is maintained constant so that the 
liquid level of the liquid photosetting resin contained in the main resin 
tank can be maintained constant. Accordingly, a light beam can precisely 
be focused in a spot of a constant diameter to form a three-dimensional 
structure in accurate dimensions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a main resin tank 2 and associated equipment included in a 
three-dimensional structure forming apparatus 1 in a first embodiment 
according to the present invention. The main resin tank 2 containing a 
liquid photosetting resin A which sets when exposed to ultraviolet rays is 
mounted on a base 3 provided with a leveling mechanism 3a. A heater 4 is 
wound around the main resin tank 2 to heat the liquid photosetting resin 
contained in the main resin tank 2 at a predetermined temperature. The 
heater 4 is controlled by a temperature controller 6 on the basis of the 
temperature of the liquid photosetting resin A detected by a temperature 
detector 5 so as to maintain the temperature of the liquid photosetting 
resin A contained in the main resin tank 2 at the predetermined 
temperature. 
A stage, not shown, is placed in a horizontal position in the main resin 
tank 2 and is moved vertically by an elevating mechanism, not shown. A 
scanning unit, not shown, is disposed above the main resin tank 2 to 
irradiate the surface of the liquid photosetting resin A for scanning with 
a light beam. A molding controller, not shown, controls the scanning unit 
for exposure and scanning operation and controls the elevating mechanism 
for vertically moving the stage. The liquid photosetting resin A is 
irradiated with a light beam to form a hard resin layer of a shape 
corresponding to the pattern of a decomposed plate. 
The main resin tank 2 is provided with at least one overflow weir 7 in one 
side wall thereof. The surplus liquid photosetting resin A overflows the 
overflow weir 7 and is returned to a replenishing tank 8, so that the 
liquid level of the liquid photosetting resin A is maintained constant. 
The overflow weir 7 consists of an edge member 9 having a sharp edge 9a 
and disposed slightly below the upper end 2a of the main resin tank 2, and 
a resin receiver 10 provided on the outer surface of the side wall of the 
main resin tank 2 to receive the liquid photosetting resin overflown the 
overflow weir 7. The position of the sharp edge 9a of the edge member 9 
corresponds to a predetermined liquid level of the liquid photosetting 
resin A in the main resin tank 2. 
Although the liquid photosetting resin A is heated by the heater 4 to 
reduce its viscosity, the liquid photosetting resin A has a very high 
viscosity and a high surface tension. Accordingly, the liquid photosetting 
resin A forms a meniscus and the liquid level of the liquid photosetting 
resin A varies as shown in FIG. 2B before the liquid photosetting resin A 
overflows the main resin tank 2. This variation of the liquid level of the 
liquid photosetting resin A is a significant problem in precisely 
controlling the liquid level of the liquid photosetting resin A. 
To solve such a problem, the edge member 9 is used to make the liquid 
photosetting resin A overflow the sharp edge 9a of the edge member 9 
continuously so that the liquid level of the liquid photosetting resin A 
is constant. 
The liquid photosetting resin A which overflows the overflow weir 7 into 
the resin receiver 10 is returned through a return pipe 17 to the 
replenishing tank 8 where the surplus liquid photosetting resin A is 
stored. 
The liquid photosetting resin A is supplied continuously at a predetermined 
rate through a supply pipe 13 to the main resin tank 2 by a supply pump 12 
to replenish the main resin tank 2 with the liquid photosetting resin A so 
that the surplus liquid photosetting resin A overflows the overflow weir 7 
continuously and the liquid level of the liquid photosetting resin A in 
the main resin tank 2 remains constant. 
As shown in FIG. 3, a filter 14 may be inserted in the supply pipe 13 to 
remove set photosetting resin particles, dust and impurities from the 
liquid photosetting resin A before supplying the same to the main resin 
tank 2. 
The main resin tank 2 may be provided with a laser liquid level detector 15 
to detect the liquid level of the liquid photosetting resin A in the main 
resin tank 2 for monitoring and controlling the liquid level. The laser 
liquid level detector 15 comprises a laser 16 and a line sensor 17. The 
liquid level of the liquid photosetting resin A is detected from the 
position of incidence on the line sensor 17 of a laser beam projected by 
the laser 16 and reflected by the surface of the liquid photosetting resin 
A. A liquid level control bar 18 partly immersed in the liquid 
photosetting resin A is raised or lowered according to a liquid level 
detection signal provided by the laser liquid level detector 15 to 
regulate the liquid level of the liquid photosetting resin A precisely by 
varying the volume of the immersed portion of the liquid level control bar 
18. 
Referring to FIG. 4, a three-dimensional structure forming apparatus in a 
second embodiment according to the present invention employs a main resin 
tank 2 provided with one or a plurality of suction openings 21 instead of 
the overflow weir 7. The suction opening 21 is formed in the side wall of 
the main resin tank 2 at a position corresponding to a predetermined 
liquid level, and a return pipe 11 is connected to the suction opening 21. 
The surplus liquid photosetting resin A overflowing the suction opening or 
suction openings 21 is sucked directly by a suction pump 20. The liquid 
photosetting resin A sucked through the suction opening or suction 
openings 21 is returned to a replenishing tank 8. 
The main resin tank 2 may be provided with a laser liquid level detector 
15, and the liquid level may be controlled positively by controlling the 
suction pump 20 and a supply pump 12 according to a liquid level detection 
signal provided by the laser liquid level detector 15 so that the liquid 
level of the liquid photosetting resin A is maintained constant. 
Although the invention has been described in its preferred forms with a 
certain degree of particularity, obviously many changes and variations are 
possible therein. It is therefore to be understood that the present 
invention may be practiced otherwise than as specifically described herein 
without departing from the scope and spirit thereof.