CN113370528A

CN113370528A - Liquid level continuous molding system based on photocuring

Info

Publication number: CN113370528A
Application number: CN202110590741.XA
Authority: CN
Inventors: 王宜怀; 施连敏; 陈琳; 叶柯阳; 何双辰; 朱轩
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2021-05-28
Filing date: 2021-05-28
Publication date: 2021-09-10
Also published as: WO2022247084A1

Abstract

The invention provides a liquid level continuous forming system based on photocuring, which comprises: a sliding guide rail; a roller screw rod; forming a table top; a stepping motor; a PCB control board; a liquid bath; a UV lampshade; a raspberry pie and control screen; a motor driver; a wiring terminal; an LCD screen; a UV ultraviolet parallel light source; the forming table is fixed on the liquid tank, and the sliding guide rail, the roller screw rod, the stepping motor, the liquid tank and the UV lampshade are fixed on the main body plate; the motor driver is respectively connected with the stepping motor and the PCB control panel and is connected with the raspberry group and the control panel through a wiring terminal; the LCD screen is located the cistern bottom, and UV ultraviolet ray parallel light source is located the UV lamp shade. The invention has high positioning precision and high uniformity of UV light projected by the LCD.

Description

Liquid level continuous molding system based on photocuring

Technical Field

The invention relates to the technical field of intelligent rapid molding, in particular to a liquid level continuous molding system based on photocuring.

Background

A rapid prototyping technology based on photocuring projects ultraviolet light into a liquid photosensitive resin, thereby continuously curing the resin layer by layer. The problems of limited molding size, high equipment price, lens distortion and the like of a Digital Light Processing (DLP) molding technology restrict the development of the technology, so that a Liquid Crystal Display (LCD) is adopted as an area selection type light transmission equipment, and the DLP molding technology can be used for manufacturing parts with larger size and higher precision. However, the difficulty in coordinating the molding efficiency and the molding quality is a major factor limiting the development of LCD molding technology, and therefore, a blending strategy for the two is needed to be found.

Disclosure of Invention

The purpose of the invention is realized by the following technical scheme.

The invention provides a liquid level continuous forming system based on photocuring, which comprises:

a sliding guide rail; a roller screw rod; forming a table top; a stepping motor; a PCB control board; a liquid bath; a UV lampshade; a raspberry pie and control screen; a motor driver; a wiring terminal; an LCD screen; a UV ultraviolet parallel light source;

the forming table is fixed on the liquid tank, and the sliding guide rail, the roller screw rod, the stepping motor, the liquid tank and the UV lampshade are fixed on the main body plate; the motor driver is respectively connected with the stepping motor and the PCB control panel and is connected with the raspberry group and the control panel through a wiring terminal;

the LCD screen is located the cistern bottom, and UV ultraviolet ray parallel light source is located the UV lamp shade.

Preferably, the lamp further comprises a heat dissipation aluminum sheet, wherein the heat dissipation aluminum sheet is positioned on the back of the UV lamp shade.

Preferably, a fan is further included, the fan being mounted on the motor drive.

Preferably, the roller screw rod can drive the forming table top to lift and descend.

Preferably, the liquid tank further comprises a release film which is arranged at the bottom of the liquid tank and is in a tight state.

Preferably, the PCB control board includes a main controller, a DC power supply, a motor control module, a sensor, and a UV lamp switching module, the main controller controls the motor driver using PWM, and the motor driver controls the motor to rotate; and the main controller controls the sensor and the LED switch module through the GPIO.

Preferably, the main controller comprises a main control chip, a function board and a sensor board; the main control chip is used for receiving an upper computer instruction and analyzing and sending the upper computer instruction to the function board and the sensor board, the function board is used for controlling the movement of the motor and the UV lamp, the sensor board is used for controlling the limit switch of the forming table board, and the sensor is installed on the sensor board.

Preferably, the molding table further comprises a limit switch, wherein the limit switch comprises an upper limit switch and a lower limit switch, and the limit switch is used for limiting the movement range of the molding table.

Preferably, further comprising an isolation circuit comprising a motor control isolation circuit and a sensor signal input isolation circuit; the motor control isolation circuit is arranged between the main control chip and the stepping motor, and the sensor signal input isolation circuit is arranged between the sensor and the main control chip.

Preferably, the LED switch module is used for controlling the bright and dark state of the UV backlight plate, the signal end is connected with a pin of a GPIO (general purpose input/output) of the main control chip and is used for controlling the conduction state, the input end is connected with power supply voltage, and the output end is connected with the UV lamp.

The invention has the advantages that: the liquid level continuous forming system based on photocuring is high in positioning accuracy and high in uniformity of UV light projected by an LCD.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

fig. 1 is a schematic structural diagram of a liquid level continuous molding system based on photocuring according to an embodiment of the invention.

Fig. 2 shows a schematic view of a forming mesa structure according to an embodiment of the present invention.

Fig. 3 shows a schematic view of a UV lampshade according to an embodiment of the invention.

Figure 4 shows a schematic view of a fluid bath structure according to an embodiment of the invention.

FIG. 5 shows a hardware control system schematic according to an embodiment of the invention.

Fig. 6 shows a motor control isolation circuit diagram according to an embodiment of the invention.

FIG. 7 shows a sensor signal input isolation circuit diagram according to an embodiment of the invention.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

The invention introduces the overall design of machinery and a hardware platform in detail, and firstly gives the design principle of key parts of the machinery. The UV lampshade comprises an easily calibrated forming table board, the airtightness and the heat dissipation of the UV lampshade and the design key points of a liquid tank. Then, a design method of the hardware control system and related hardware model selection are set forth, wherein the design method mainly comprises resource division of a main control chip and design of an isolation circuit, and technical indexes of the hardware model selection are introduced in detail.

1 mechanical part structural design

Key parts of the mechanical structure require stable quality and high precision, so the key parts are manufactured by adopting a CNC (computerized numerical control) process. The whole machine is processed by adopting an aluminum piece, and only the light shield adopts an acrylic material for preventing UV ultraviolet light from overflowing. As shown in fig. 1, the LCD screen is not visible at the bottom of the bath, and the UV parallel light source is not visible within the UV lamp housing. Other parts are marked.

1-a sliding guide rail; 2-roller screw rod; 3-forming a table top; 4-a stepper motor; 5-radiating aluminum sheets; 6-PCB control panel; 7-a liquid bath; 8-UV lamp shade; 9-raspberry pie and control screen; 10-a fan; 11-a motor driver; 12-terminal.

The forming table is fixed on the liquid tank, the sliding guide rail, the roller screw rod, the stepping motor, the liquid tank and the UV lampshade are fixed on the main body plate, and the radiating aluminum sheet is positioned on the back of the UV lampshade; the motor driver is respectively connected with the stepping motor and the PCB control panel and is connected with the raspberry group and the control panel through a wiring terminal; the fan is mounted on the motor driver.

1.1 design principles of mechanical Key Components

The various parts of the machine need to be designed according to the light curing characteristics of the LCD. The main components of concern are the shaped table top, the UV lamp shade, the fluid bath. The design points and the effects of the parts are analyzed by the section aiming at the parts.

1. Forming table top

The calibration of the molding table is a troublesome problem in photocuring rapid molding, and is difficult for a novice to use a professional tool for leveling during printing. Therefore, the forming table top designed by the invention adopts a hydraulic balance self-calibration technology, can simply and conveniently finish calibration, and is very friendly to novice users.

The lead screw rotates to drive the forming table top to lift up and descend, the forming table top is required to be parallel to the release film, and the distance of the forming table top is consistent with the thickness of the slice. In the molding process, if the release film is not parallel to the molding table, the problems of uneven curing thickness of the photosensitive resin, failure in demolding, incapability of adhering to the molding table and the like can be caused. Therefore, whether the forming table surface is parallel to the release film directly influences whether the forming can be successful.

In addition, the molding table top needs to be frequently disassembled, so that frequent leveling is needed, and the design of a leveling mode needs to meet the characteristics of simple operation and high precision. As shown in figure 2, the molding table comprises a disassembly and assembly handle, a hydraulic locking piston, a hydraulic cavity, a pressing piston and a universal ball head. And loosening the screws before leveling, and screwing the screws when the table top to be molded descends to the lower limit switch.

UV lampshade

The UV lamp box module is used as an LCD imaging light source, and as shown in fig. 3, the module includes three parts, which are a lamp box, a UV lamp, and a heat dissipation aluminum sheet. The LCD screen is arranged above the module to form a sealed space to prevent the ultraviolet light from leaking. The inside mirror surface stainless steel that adopts of lamp box is favorable to ultraviolet reflection. Since the UV lamp produces a large amount of heat when it is operated for a long time, a heat-radiating aluminum sheet is installed at the bottom for heat radiation.

3. Liquid bath design

The design principle of the liquid tank is firstly to consider the size problem, and the optimal size for saving the photosensitive resin is slightly larger than the forming table top. As shown in figure 4, the release film is arranged at the bottom of the liquid tank, the metal clamping piece is used for clamping the release film to prevent liquid leakage, and then the release film is arranged on the liquid tank to be in a tight state. The release film is made of Fluorinated Ethylene Propylene copolymer (FPE), the material has good light guiding property, the UV light passing rate reaches 95%, and the curing time can be shortened; and secondly, the material has good wear resistance and low friction coefficient, and is not easy to deform after repeated demoulding.

2 hardware control System design

The PCB control panel comprises a main controller MCU, a DC power supply, a motor control module, a sensor control module, a UV lamp switch module and the like, as shown in figure 5. The raspberry pi replaces a PC to be used as an upper computer to control and interact with the MCU, is connected with a slice display LCD screen through MicHDMI, and is connected with a control screen through DSI to realize off-line forming.

The hardware control system adopts two kinds of voltage power supplies, and the difference is that the UV lamp directly uses DC29.4V power, and other modules all use the 5V power of DC power step-down. The MCU uses PWM to control the motor drive, and the motor drive controls the motor to rotate. And controlling the sensor and the LED switch module through the GPIO. In order to achieve accurate control, an optical coupling isolation circuit is designed to isolate an interference source from an easily interfered part, so that the aim of isolating field interference is achieved.

2.1 Main controller hardware System design

The hardware main control system adopts the separated design of each module, and then uses the flat cable to connect each module. This design of the solution enables easy replacement or repair of the device during the experiment. The hardware main control system comprises a main control chip, a function board and a sensor board. The main control chip is used for receiving the instructions of the upper computer, analyzing and sending the instructions to the function board and the sensor board, the function board is used for controlling the movement of the motor and the UV lamp, and the sensor board is used for controlling the limit switch.

Due to the variety and complexity of microcontrollers, different companies have different chips, and even chips of the same company may be of different types and families. Therefore, selecting the core processing chip for the entire control system is a significant task. The main control chip is required to be easy to debug and has good expansibility. By way of model selection, the invention uses a KEAZ128 type micro-control chip from Enzhipu corporation, which is based on

The M0+ kernel has the kernel frequency of 48MHz, is widely used in the field of automobile electronics, and has stable chip performance. And the LQFP package is adopted, so that the welding is convenient. The specific properties of the chip are shown in Table 3-1.

TABLE 3-1 Master control chip Performance

1. Master control chip pin assignment

The control system uses external resources such as general purpose input/output (GPIO), an elastic timer (FTM), a Universal Asynchronous Receiver Transmitter (UART), keyboard interrupt (KBI) and the like provided by the KEA chip to realize the acquisition of sensor signals, information transmission and control of each execution component. The allocation of the pin resources of the master chip is designed according to the needs of each execution unit, as shown in table 3-2.

TABLE 3-2 Master control chip Pin resource Allocation

2. Isolation circuit design

The isolation circuit comprises a motor control isolation circuit and a sensor signal input isolation circuit. The motor can generate inverse current at the moment of braking and stopping to influence the signal output of the main control chip, so that a motor control isolation circuit is designed between the main control chip and the motor. A sensor signal input isolation circuit is also designed between the sensor and the main control chip to prevent signal interference.

In the present invention, a 6N137 optocoupler is selected, with a slew rate of up to 10Mbits/s, open collector output. The PWM frequency input by the main control chip is 8KHz, so that the optical coupler of the model is enough to be used. As shown in fig. 6, the motor control isolation circuit includes a PTC5 as an output PWM signal pin and a PTD2 as an output motor rotation direction signal pin, both of which are connected to an input pin 3 of the 6N137 and output from an input pin 6.

The upper limit pin and the lower limit pin are set to be GPIO and are set to be input. As shown in fig. 7, the connection mode adopts a normally open connection, the power supply at the rear end of the optical coupler is connected with the power supply of the limit switch, the signal pin is connected with the normally open pin, the limit switch is not triggered, the normally open pin is at a high level, and light is blocked and converted into a low level.

2.3 hardware Module selection

The appropriate hardware module is selected as required by the task of the machine implement component. The section is further explained aiming at main hardware modules, wherein the hardware modules comprise an LCD screen, a stepping motor, a limit switch, a voltage reduction and stabilization module, an LED switch module and an ultraviolet parallel backlight source.

LCD screen

The LCD screen is selected from Japanese brand JDI model TFTMD089030, the LCD screen leaves a factory without a backlight plate, is convenient to use in a photocuring molding system, and if the LCD screen with the backlight plate is purchased, the backlight plate needs to be detached.

The size of the liquid crystal screen determines the molding area, but the larger the screen is, the better the screen is, and when the larger size liquid crystal screen is used, the demolding difficulty and the heat dissipation difficulty are increased correspondingly. The 8.9-inch screen can basically meet the requirements of most practical applications. Another consideration is the working temperature range, the currently used UV lamp panel is 120W, and the temperature reaches 60-70 ℃ under long-term working conditions. The temperature exceeds the normal working temperature range of the liquid crystal screen, which results in short service life of the liquid crystal screen, and therefore, heat dissipation measures need to be added to improve the service life of the liquid crystal screen.

In order to protect the surface of the liquid crystal screen from being damaged easily, toughened protective glass needs to be attached to the surface of the screen, and the toughened protective glass needs to meet the requirements of high light transmittance, high strength, difficulty in light transmittance of a silk-screen area and the like. In addition, an adaptive LCD screen driving board needs to be selected, and a driving IC with the model R69429 is already bound to the LCD screen with the model TFTMD 089030.

2. Stepping motor selection

The motor selected by the present invention is a 42 step motor and its motor driver. The stepping angle of the stepping motor is 1.8 degrees, namely, the motor driver can drive the stepping motor to rotate 1.8 degrees after receiving a pulse. The driving subdivision of the stepping motor driver can be selected as 2ⁿ(n is more than or equal to 1 and less than or equal to 5), the drive selected in the item is subdivided into 8, which can be described as that the motor driver receives a pulse to drive the motor to rotate by an angle of 1.8 degrees, but at the moment, the 1.8-degree subdivision is further subdivided into 8 equal parts, namely 0.225 degrees. The lead of the screw rod is 4mm, namely the distance of the motor driving the screw rod to rotate for a circle of movement of the forming table top is 4 mm. From these necessary parameters, the pulse equivalent, i.e. how many pulses are required for each 1mm movement of the forming table, can be calculated according to equation (3.1).

Where δ denotes the pulse equivalent, α denotes the step angle of the stepping motor, η denotes the drive subdivision set by the motor driver, and ρ denotes the lead of the lead screw. The pulse equivalent for use with the present invention can be calculated to be 400 pulses/mm.

3. Limit switch

The limit switch comprises an upper limit switch and a lower limit switch and is used for limiting the movement range of the forming table board. The limit switch is selected to be an ohm dragon lead-out type photoelectric switch EE-SX 671-WR. The limit switch adopts a normally open mode, when the blocking piece reaches the optical groove, the limit switch monitors a signal and sends the signal to the main control chip, and the main control chip stops the motor. The installation limit switch need notice down limit switch's mounted position, when guaranteeing that the separation blade touches limit switch, becomes the form face this moment and keeps a definite value from the distance between the type membrane, and this definite value is section one deck thickness usually.

4. Voltage reducing and stabilizing module

The supply voltage is DC29.4V, so it is necessary to drop the voltage to DC5V for use by other components. The module adopts a chip LM2596S, the conversion efficiency reaches 92%, and the working frequency is 65 KHz. The input end of the module is connected with the anode and the cathode of a power supply DC29.4V, and the output voltage is DC5V which is connected with the connecting terminal for other modules to use.

LED switch module

The LED switch module is used for controlling the bright and dark state of the UV backlight plate, and the signal end is connected with the GPIO pin of the main control chip and used for controlling the conduction state. The input end is connected with power voltage, the output end is connected with a UV lamp, and the controllable power reaches 400W. The power of the UV backlight plate designed by the invention is 120W, so that the module is sufficient for use.

6. Ultraviolet parallel backlight source

The ultraviolet parallel backlight module comprises a bottom plate and an ultraviolet LED lamp bead. The LED lamp beads adopt a seoul 3535 quartz lens lamp bead, the wavelength is 405nm, and the light-emitting angle of the lens is 30 degrees. In order to ensure good forming effect, it is noted that the ultraviolet light projected on the LCD screen requires uniform light intensity distribution.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. A system for continuous molding of a liquid level based on photocuring, comprising:

2. A stereolithography-based level continuous molding system as claimed in claim 1,

the lamp further comprises a heat dissipation aluminum sheet, wherein the heat dissipation aluminum sheet is positioned on the back of the UV lampshade.

3. A stereolithography-based level continuous molding system as claimed in claim 1,

further comprising a fan mounted on the motor drive.

4. A stereolithography-based level continuous molding system as claimed in claim 1,

the roller screw rod can drive the forming table top to lift up and down.

5. A stereolithography-based level continuous molding system as claimed in claim 1,

further comprises a release film which is arranged at the bottom of the liquid tank and is in a tight state.

6. A stereolithography-based level continuous molding system as claimed in claim 1,

the PCB control panel comprises a main controller, a DC power supply, a motor control module, a sensor and a UV lamp switch module, wherein the main controller controls the motor driver by using PWM, and the motor driver controls the motor to rotate; and the main controller controls the sensor and the LED switch module through the GPIO.

7. A stereolithography-based level continuous molding system as claimed in claim 6,

the main controller comprises a main control chip, a function board and a sensor board; the main control chip is used for receiving an upper computer instruction and analyzing and sending the upper computer instruction to the function board and the sensor board, the function board is used for controlling the movement of the motor and the UV lamp, the sensor board is used for controlling the limit switch of the forming table board, and the sensor is installed on the sensor board.

8. A stereolithography-based level continuous molding system as claimed in claim 1,

the forming table further comprises a limit switch, wherein the limit switch comprises an upper limit switch and a lower limit switch and is used for limiting the movement range of the forming table.

9. A stereolithography-based level continuous molding system as claimed in claim 7,

the isolation circuit comprises a motor control isolation circuit and a sensor signal input isolation circuit; the motor control isolation circuit is arranged between the main control chip and the stepping motor, and the sensor signal input isolation circuit is arranged between the sensor and the main control chip.

10. A stereolithography-based level continuous molding system as claimed in claim 6,

the LED switch module is used for controlling the bright and dark state of the UV backlight plate, the signal end is connected with a GPIO pin of the main control chip and used for controlling the conduction state, the input end is connected with power supply voltage, and the output end is connected with the UV lamp.