Application of LabVIEW in Fully Automatic Glue Dispensing Machine

Application areas: industrial automation, industrial vision, motion control
Challenge: Use the combination of LabVIEW+Vision+Motion to quickly develop a commercial-oriented fully automatic dispensing machine.
Application solution: Use NI's motion control card and vision development module to quickly develop a fully automatic dispensing machine system.
Products used: NI-7344, NI-6601, LabVIEW 8.6.1, Vision Module

Introduction:
First, the diode cup image information is obtained by taking a photo with a 1394 camera, and then the XY pixel coordinates of the dispensing diode cup are quickly found through some visual judgment modules in the NI Vision Module. After conversion, the XY actual motion coordinates are obtained, and the motion control card NI-7344 and NI-6601 pulse card are used to control the motion of the dispensing valve and dispensing. The motion execution system uses the Panasonic servo system to ensure the accuracy of the movement. The dispensing speed is controlled by the NI-6601 pulse card to ensure the consistency of dispensing. Due to the use of NI motion control and related products, the development time is greatly shortened. It saves a lot of time and cost for customers to put products on the market.

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1. System background
LED (Light Emitting Diode), a solid-state semiconductor device, can directly convert electricity into light. The heart of LED is a semiconductor chip. One end of the chip is attached to a bracket, one end is the negative pole, and the other end is connected to the positive pole of the power supply, so that the entire chip is encapsulated by epoxy resin. The semiconductor chip consists of two parts, one is a P-type semiconductor, in which holes dominate, and the other end is an N-type semiconductor, which is mainly electrons. But when these two semiconductors are connected, a "PN junction" is formed between them. When the current acts on the chip through the wire, the electrons will be pushed to the P area, where the electrons and holes recombine, and then they will emit energy in the form of photons. This is the principle of LED light emission. The wavelength of light, that is, the color of light, is determined by the material that forms the PN junction.
There are more than 20 steps in the production process of LED and the production steps of packaging technology, among which the more important one is LED glue dispensing. Apply silver glue or insulating glue to the corresponding position of the LED bracket. (For GaAs and SiC conductive substrates, red, yellow, and yellow-green chips with back electrodes, silver glue is used. For blue and green LED chips on sapphire insulating substrates, insulating glue is used to fix the chips.) The difficulty of the process lies in the control of the amount of glue dispensed, and there are detailed process requirements for the height of the colloid and the location of the glue dispensed. Since silver glue and insulating glue have strict requirements for storage and use, the waking up, stirring, and use time of the silver glue are all matters that must be paid attention to in the process.
According to the survey, in 2007, China's total electricity consumption was about 2421 billion kWh. According to the calculation that lighting electricity accounts for 12% of the total electricity consumption, China's lighting electricity consumption in 2007 was about 290.5 billion kWh. If 50% of China's lighting devices use LED lamps (calculated based on the use of low-end products that save 50% of electricity), at least 72.6 billion kWh of electricity can be saved each year, which is equivalent to building two new Three Gorges power stations or 8 to 9 million-kilowatt supercritical coal-fired generators, saving nearly 100 billion yuan in power plant construction funds and nearly 12.52 million tons of original electric coal each year. If calculated based on the emission of 0.638 kg of carbon dioxide per kilowatt-hour of coal-fired power generation, 46.32 million tons of carbon dioxide emissions can be reduced each year.
At the same time, the demand for LED production is large, and corresponding production equipment is needed to support it. Machines with low speed, poor glue spraying accuracy, and uneven glue amount can no longer meet the production needs. Therefore, the market needs a fully automatic glue dispensing machine with high-speed dispensing, uniform glue amount and easy control.

2. System composition and workflow

The system mainly consists of the following parts:
1) 3-axis motion screw and corresponding mechanism
2) motion controller and servo
3) dispensing valve
4) dispensing valve control equipment
5) visual recognition equipment
NI PCI-7344 stepper/servo motion controller is one of the mid-range motion products of National Instruments. This controller is simple and easy to use and is recommended for simple stepper or DC motor control and complex multi-axis motion control. NI PCI-7344 includes dual processors and a real-time onboard operating system, and has multi-axis interpolation capabilities. [page]

Combined with the rich example programs in LabVIEW software and its example finder, a servo motion control system was built in a very short time through simple cable connection. A large number of IO ports are required in the dispensing machine. The NI-7344 board also provides up to 32 digital IO channels for some digital controls such as whether the fixture is in place, the opening and closing of the air valve, the dispensing signal indication, and the alarm light control.
In addition, the actual height of the light source and the dispensing valve is controlled by the 8 analog input ports built into the NI-7344. Through these ports, the position height information of the light source and the dispensing valve can be obtained in real time.
Since the dispensing amount needs to be controlled in real time to improve the quality of dispensing and meet the requirements of uniform glue control. The NI-7344 board comes with an onboard programming function, which directly inputs the position information required for dispensing into the board memory for real-time operation, avoiding the problem of dispensing uniformity being affected by software control of dispensing. Combined with the NI-6601 digital pulse output card, the dispensing accuracy can be controlled at the microsecond level. Combined with the Festo high-speed pneumatic solenoid valve to achieve high-speed dispensing.
Finished product appearance and on-site pictures

On-site pictures
Program main interface

Program back panel

Workflow

3. System Functions
This system mainly completes the automatic loading of LED brackets, automatically identifies the precise XY position of LED cups, and automatically controls the amount of glue dispensed.
1) Automatic loading of brackets
The LED bracket is pushed to the specified position by the cylinder, and the LED bracket is fixed to the position that the camera can identify through the adsorption of magnets and the rolling clamping device. [page]

2) LED cup accurate XY position recognition

The following is the original picture taken by the 1394 camera

By using the NI Vision pattern matching function, the corresponding template is made, and the position information of all cups in the picture is obtained by multi-point matching. After the corresponding physical displacement conversion, the actual movement coordinates of the cup are obtained.

See the figure below to obtain the cup coordinate information in Vision-Assistant.

3) Automatically control the amount of glue dispensed
After obtaining the motion coordinates of the cup identified in Vision, the motion coordinates are input into the motion control card (NI-7344 four-axis stepper servo motion control card). The motion control card moves to the specified position in sequence and outputs the Breakpoint signal. Through a 74HC08 AND gate logic circuit, the Breakpoint signals of the three axes XYZ are collected into a TTL output signal to NI-6601 (pulse signal generation board). Through the pulse number and pulse interval set in NI-6601, a series of uniform and stable pulse signals are generated to the dispensing valve, and a stable and uniform dispensing amount has been obtained.

4. System advantages
Due to the use of NI motion control cards and corresponding boards, combined with the powerful graphics processing function of NI Vision, this project went very smoothly from the beginning, and the system construction was completed in just 2 months. The glue output is stable, and the user can adjust the glue output at will. While completing the LED fully automatic dispensing work, it also provides good upgrade space in some future product design and development.

Conclusion
Combining the powerful graphical programming function of LabVIEW, using a series of ready-made toolkits, graphical analysis functions, and NI hardware that is perfectly integrated with the LabVIEW platform, we have developed a commercial product with a reliable system, stable glue spraying volume, fast motion dispensing speed, and obvious competitive advantages in the market in a very short time. Shortening the development cycle, enabling products to be put on the market faster, and providing a more perfect dispensing product for the majority of LED manufacturers.