WO2015140604A1

WO2015140604A1 - Single mirror scanning mechanism

Info

Publication number: WO2015140604A1
Application number: PCT/IB2014/064071
Authority: WO
Inventors: Mohammad Reza NIKOOMANESH; Shahriyar TAVOUSI TAFRESHI
Original assignee: Nikoomanesh Mohammad Reza
Priority date: 2014-08-26
Filing date: 2014-08-26
Publication date: 2015-09-24

Abstract

The purpose of the present invention is to review and improve the components of apparatus which has been applied in rapid prototyping technology, especially SLA apparatus. In software section, new algorithms have been developed in order to accelerate STL three dimensional model layering, compensate for the radius of the laser beam, correct contours of each layer based on radius of laser beam, calculate various layer thicknesses based on model surface curvature and diagnose specific contours. Using innovative mechanism (one mirror instead of two mirrors) leads to a decline in machine volume as well as increase in accuracy and speed of segment fabrication. In this design, we try to reach our goals by reviewing and improving components of applied apparatus in rapid prototyping technology especially SLA apparatus.

Description

SINGLE MIRROR SCANNING MECHANISM

DESCRIPTION

Field of the Invention

The technical field of this invention is related to surface scanning and prototyping apparatus in which electronic, laser and mechanical knowledge has been utilized.

Problems found in previous methods

The usual methods of segment production have always had so many limitations regarding segment geometry that the designer has to consider product ability in segment designing. Moreover, fabricating the segments requires mold construction or using numerical control machines that are highly costly and time consuming. Regarding the available software, information processing methods leads to a decline in speed and accuracy.

On the other hand, in all floating platform prototyping machines in resin which are applied for fabricating each layer, the segment moves as much as the thickness of bottom layer and some liquid which is utilized for fabricating the next layer is placed on the previous solid layer as thick as the resin liquid. However, due to the fact that resin is slimy and the considered thickness is low, there is a high possibility for the liquid resin not to be spread all over the solid surface. Consequently, some equipment is considered in these apparatuses in order to spread the liquid resin on the previous tough surface equally which results in the extension of required equipment and the increase of the general volume of apparatus and segment production process.

Background of the invention

Primarily, rapid prototyping apparatus used plastic powder and paste in order to fabricate segment layers but gradually metallic powders and laser were utilized for solid modeling and material boiling.

In SLA prototyping apparatus, the UV ray available in laser beam is used to solidify light sensitive resin. Considering the figure, each layer of laser hits some parts of the resin surface and solidifies them. As a result, the parts that are not hit by the laser remain liquid. Then, as the floating platform in resin descends as thick as the next layer, another layer of photo resin comes to the platform and laser keeps solidifying resin surface. Continuing this process, the next three dimensional segment is made layer by layer and the next layer is placed on the previous layer and is connected.

In these machines, some mirrors are utilized to fabricate segment which increases the cost of machine production and information processing time.

Brief description of figure

Figure 1 : flowchart algorithm of three dimensional layering of SLT

Figure 2: calculating layer thickness for cutting three dimensional models regarding surface perpendicular vector angel relative to horizon

Figure 3-a: schematic figure of surface scanning mechanism by a mirror

Figure 3-b: surface scanning mechanism by a mirror

Figure 4: descriptive equations of control angles movement

Figure 5: the special mechanism of floating platform

Figure 6: electronic circuit plan of interface circuit

Detailed description of the invention

The purpose of the present invention is to review and improve the components of apparatus which has been applied in rapid prototyping technology, especially SLA apparatus. In software section, new algorithms have been developed in order to accelerate STL three dimensional model layering, compensate for the radius of the laser beam, correct contours of each layer based on radius of laser beam, calculate various layer thicknesses based on model surface curvature and diagnose specific contours. Visual Basic .Net programming language has been used for software coding and creating user friendly graphic environment. In hardware section, the surface scanning mechanism has been reviewed and a new, innovative mechanism has been designed which increases the accuracy and decreases the volume of the machine. In contrast to conventional mechanisms which use two mirrors, this mechanism has used just one. Electronic and micro- control circuits have created a linkage between hardware and software sectors. Using innovative mechanism (one mirror instead of two mirrors) leads to a decline in machine volume as well as increase in accuracy and speed of segment fabrication. In this design, we try to reach our goals by reviewing and improving components of applied apparatus in rapid prototyping technology especially SLA apparatus.

Software section

In software section, new algorithms have been developed in order to accelerate STL three dimensional model layering, compensate for the radius of the laser beam, correct contours of each layer based on radius of laser beam, calculate various layer thicknesses based on model surface curvature and diagnose specific contours. Visual Basic .Net programming language has been used for software coding and creating user friendly graphic environment. In hardware section, the surface scanning mechanism has been reviewed and a new, innovative mechanism has been designed which increases the accuracy and decreases the volume of the machine. In contrast to conventional mechanisms which use two mirrors, this mechanism has used just one. Electronic and micro-control circuits have created a linkage between hardware and software sectors.

A new algorithm has been used for STL model layering which you can see in figure 1 .In this algorithm information processing speed has increased due to elimination of extra triangles in layering to accelerate the process.

Primarily, the algorithm seeks for a triangle among STL model triangles which intersect with the plane that is placed in a specific height. Once a triangle is found which has an intersection with that plane, two points will be obtained. One point is considered as the beginning of contour to which it must finally end. The other point is used to find a triangle adjacent to the previous one. In other words, in STL file we seek for a triangle which this point is located on one of its sides. Having found this triangle, the first triangle is intersected with the triangle of the mentioned plane. The result is two points which the first one is related to the previous adjacent triangle and the second belongs to unknown adjacent triangle. The previous triangle is removed from the STL file and the algorithm looks for a triangle that the second point is placed on one of its sides.

This process continues and finally one of the points resulting from the intersection of triangle and horizontal plane of the beginning point of contour coincide. Here, a closed contour related to that section has been completed. The set of STL file triangles in which the fundamental triangles of previous contour have been eliminated are again intersected with the mentioned plane and follow the same processes to find the next contours. If another triangle has not intersected with horizontal plane in the set of triangles in reformed STL file, it means no contour is left in that section. Now, an algorithm as high as horizontal plane and as thick as the next layer is added and above-mentioned cutting applying primary STL file is repeated for that height.

Calculating various layering thickness based on surface curvature

Typical Rapid prototyping software consider layering thickness to be the same in all segment height which results in a decline of layering accuracy in highly curved parts of the segment and consequently segment surface is extremely stepped, surface smoothness decreases, the accuracy of created surface falls, and the supplementary processes of model fabrication by RP apparatus increases. If we consider the layering thickness to be low, the speed of segment fabrication will be lowered. Therefore, in this new invention, various thicknesses regarding surface curvature will be utilized for segment layering. As it can be seen in figure 2 in some parts of the segment which perpendicular vector angle relative to horizon is nearly 90 degree, the layering is done with the least possible thickness and in some sections that accuracy is highly important, segment fabrication continues with less thickness. The above explanation is applicable for pivotal symmetric models and in order to extend it to asymmetric models, we can use the perpendicular vector sides average of composing triangles of segment surface contours relative to horizon.

Hardware section:

Single mirror scanning mechanism

This single mirror 1 mechanism does surface sweeping and directs laser 2 beam to desired (x, y) coordinates in x y plane 3. As it is clear in figure 3 -a, the point in the middle of mirror is hold stable in space during surface sweeping. Controlling rotational speed as well as Θ and β angle values, it is possible to control the speed and direction of laser beam movement on x y surface.

In order to activate this mechanism, an apparatus has been designed which can be seen in figure 3-b. This apparatus is composed of a U-shaped 4 chassis which is linked to upper edges by a shaft 5. In the middle of the shaft, a half of its diameter has been deleted and its surface is polished by abrasive particle dough which is used as a mirror 6. This shaft is responsible for angular rotation of β angle and two bearings in two sides of U-shaped chassis help it move. In the lower surface of U-shaped chassis, another shaft 7 is applied which is responsible for rotational movement of Θ angle by the help of installed bearing. The intersection part of these two shafts is the same stable point which has already been pointed out.

In order for the shafts to move, two stepper motors 8 have been installed. Two gear chains 9 have been utilized in order to transform stepper motor drive. An interface circuit is responsible to send play and stop signals to the motor. The descriptive equations of control angles movement which can be seen in figure 4.

The special mechanism of resin-floating platform

In this invention, platform movement has been predicted from an upper level to optimize the performance of floating platform (in the typical systems, the movement is from a lower level). Therefore, the floor of resin tank is clear 10 and laser 11 ray is directed from bottom. When the floating platform is distanced from tank floor within the thickness of first layer, the first layer is produced, as the platform ascends, the next layers 12 are produced. In this mechanism, the sudden increase of section surface is less sensitive and in some special cases we can use the supports that are produced along with the segment. Moreover, the pressure resulting from resin liquid in tank floor causes the resin to be spread equally all over the surface between toughened layer of tank floor which is the component part of the next layer and no other equipment is required. (Figure 5)

Electric interface circuit

After transforming the information of each section surface into some steps and stepper motor stops, this data is imported into interface micro-control circuit through computer serial port 13 and sends the signals into stepper motors which revolve Θ and β axis within a regular stop. Data are transformed in serial format through organized serial logic in a specific voltage. So, first the data must be changed into TLL logic which is easily understood by micro contour. Therefore, MAX232 chip 14 has been utilized to transform the data. (Figure 6)

Two AVR ATMEGA32 micro contours 15 have been utilized to send signal to two stepper motors 8 in order to coincide and increase the accuracy of motor rotation by a large degree. One of the motors acts as a master and the other as a slave. Therefore, first the data transformed into TTL logic enter MASTER micro contour. Some of these data are related to stepper motor rotating Θ axis and some are related to stepper motor rotating β axis. Thus, MASTER micro contour preserves some data related to this axis and transfers the information related to the rotation of β axis to SLAVE micro contour. Then, creating a signal from micro SLAVE which signifies the end of information transferring from MASTER micro contour to the SLAVE and through a hardware suspension, two micro contours start to send signals to stepper motors. The external buffer of pins of ATMEGA32 micro contour ports can sink 20mA maximally which is very low to run stepper motors. So, two ULN2003A initiators 16 which their maximum external flow for each base is 500 mA are utilized to strengthen external signal from micro contour bases.

Application of the invention

1. Industries

2. Medicine

3. Archeology

4. Biology

The explicit and accurate expression of the invention advantages

1. Less volume of scanner apparatus

2. Less expensive compared to similar samples

3. Higher accuracy during segment fabrication regarding software calculation Higher accuracy during segment fabrication regarding resin-floating platform performance

Higher speed in scanning and segment production

Claims

FABRICATING AND DESIGNING SURFACE SCANNING MECHANISM BY SINGLE MIRROR IN SLA APPARATUS Claims

1. Fabricating and designing surface scanning mechanism by single mirror, wherein:

Composed of a U-shaped chassis which is linked to upper edges by a shaft.

2. The method of claim 1 , wherein:

an apparatus is composed of a U-shaped chassis which is linked to upper edges by a shaft. In the middle of the shaft, a half of its diameter has been deleted and its surface is polished by abrasive particle dough which is used as a mirror.

3. The method of claim 2, wherein:

The shaft is responsible for angular rotation of β angle and two bearings in two sides of U-shaped chassis help it move.

4. The method of claim 2, wherein:

In the lower surface of U-shaped chassis, another shaft is applied which is responsible for rotational movement of Θ angle by the help of installed bearing.

5. The method of claim 2, wherein:

In order for the shafts to move, two stepper motors have been installed. Two gear chains have been utilized in order to transform stepper motor drive.

6. The method of claim 5, wherein:

An interface circuit is responsible to send play and stop signals to the motor.

7. The method of claim 1, the special mechanism of resin-floating platform, wherein:

The floor of resin tank is clear and laser ray is directed from bottom.

8. The method of claim 7, wherein:

After the first layer is produced, as the platform ascends, the next layers are produced.

9. The method of claim 1 , electric interface circuit, wherein: MAX232 chip has been utilized to transform the data.

10. The method of claim 9, wherein:

AVR ATMEGA32 micro contours have been utilized to send signal to two stepper motors in order to coincide and increase the accuracy of motor rotation by a large degree.

11. The method of claim 9, wherein:

Two ULN2003A initiators which their maximum external flow for each base is 500 mA are utilized to strengthen external signal from micro contour bases.

12. The method of claim 1, software section wherein:

The algorithm seeks for a triangle among STL model triangles which intersect with the plane that is placed in a specific height.

13. The method of claim 12, wherein:

Once a triangle is found which has an intersection with that plane, two points will be obtained. One point is considered as the beginning of contour to which it must finally end. The other point is used to find a triangle adjacent to the previous one. In other words, in STL file we seek for a triangle which this point is located on one of its sides. Having found this triangle, the first triangle is intersected with the triangle of the mentioned plane. The result is two points which the first one is related to the previous adjacent triangle and the second belongs to unknown adjacent triangle. The previous triangle is removed from the STL file and the algorithm looks for a triangle that the second point is placed on one of its sides.