Johnathan Titone, product line specialist: automation, Nordson EFD
There are many factors that manufacturers need to consider when deciding which equipment to invest in for fluid dispensing operations. Critical is the need to deposit very small and precise amounts of fluid, such as adhesives and silicones, to assemblies such as microelectronics and other minuscule parts. These tiny amounts of fluid must be dispensed accurately on the substrate in terms of both dosage and placement, since this is vital to those parts’ assembly, function, quality, appearance and viability. In addition to maintaining precision standards, the fluid dispensing method must meet requirements for throughput volume, worker safety and cost efficiency.
Robotic fluid dispensing
Many fluid dispensing applications use robots to achieve the aforementioned objectives. Robots provide flexible process-critical automation, which also maintains consistent fluid deposition with extreme accuracy, time after time. This precision repeatability optimises fluid usage, whilst reducing waste and production costs.
The robots’ software adjusts the positioning of dispensed material automatically to accommodate curves or complex contours as well as slight errors in workpiece positioning in the nest or fixture, which would otherwise prove difficult to achieve with non-robotic methods. Controlling fluid deposition via vision-capable substrate and pattern recognition ensures that the deposit is in the correct location up to positional tolerances of +/-4 μm. Furthermore, it enables the different materials being dispensed—for example, adhesives, greases, epoxies, silicones and sealants—to be precisely managed.
The software also permits the importing of AutoCAD drawing exchange format (DXF) files, so that the manufacturer can program fluid dispensing patterns in their preferred CAD software, then import the DXF file from that software seamlessly into the fluid dispensing automation platform.
A Nordson EFD G4V automated fluid dispensing robot being used to dispense grease on an aerospace pinion gear.
Vision guidance systems
Robotic fluid dispensing is essential for applications that require extremely accurate and repeatable fluid deposit placement, complex dispensing patterns and/or high-volume throughput. Vision guidance systems are central to robots’ performance, providing the flexibility they require to achieve precise deposit placement.
Vision guidance systems have been used in fluid dispensing applications for over twenty years and are becoming more prominent as the robots and their software become smarter. They enable robots to deliver faster production cycles—by removing the guesswork from the dispensing process and minimising programming times—as well as reduce overall operational costs.
Point-to-point teach method
The most fundamental form of fluid dispensing automation programming is carried out using the point-to-point teach method, in effect eyeballing the location of the dispensing tip on the substrate being dispensed onto.
Essentially, the point-to-point teach method is executed manually. The operator moves the tip of a point-to-point teaching pendant device over the substrate location where dispensing is to be targeted. Once the substrate location and coordinates of the X, Y, Z axes have been determined, they are saved in the software. This process is repeated for all substrate locations where deposition is targeted. The robot will move to these precise locations every time and dispense fluid as dictated by the fluid dispensing software.
A high volume of dispense patterns can be programmed using the point-to-point teaching pendent. However, the quantity of patterns being dispensed can be a limiting criterion, simply because of the amount of time they take to program. Furthermore, the more complicated the dispensing process, the increased need for an offsetting capability. This means being able to look at a location on the substrate before dispensing is carried out and offset the program if there are any changes to the substrate. This is where vision guidance systems are better suited for the application than non-vision guidance systems.
Simple versus sophisticated vision
Vision systems for robotic fluid dispensing vary from simple pencil cameras to sophisticated CCD cameras. The defining differences are in the camera’s sensor resolution and shutter speed ability. A pencil camera is adequate for most robotic fluid dispensing applications. However, a CCD camera is required for high-resolution photos of substrate parts.
Both cameras function by taking a picture of a part on the substrate, then applying any necessary offsets by adjusting the dispensing program to match the location and shape of the path against the location and shape of the part. More specifically, the camera verifies the location of a part by identifying a distinguishing edge of the part that can be referenced. This reference point allows the dispensing software to offset fluid dispensing in the event that said point changes location (for example, if the substrate registration is slightly displaced as it is positioned in the robot).
Both pencil and CCD cameras convert analogue camera image pixels into digital values for extremely precise image management. Some relatively inexpensive pencil cameras, assisted by intuitive fluid dispensing software, allow first-time users to program complex dispense patterns and arrays at high repeatability, for example, the pencil camera on Nordson EFD’s EV Series of three-axis automated fluid dispensing robots allows for repeatabilities of up to +/-8 µm (0.008 mm).
Comparatively, CCD cameras capture higher definition images, for example, the CCD camera on Nordson EFD’s PRO Series of three-axis automated fluid dispensing robots obtains detailed component part images, namely shadow enhancement allows vision identification and processing of faint marks, and ensures there are minimal interruptions to the dispensing cycle. CCD cameras’ global shutters enable them to rapidly capture high-contrast part images, eliminating blurriness and small distortions in the case of rolling shutters. The CCD camera on the PRO Series, complemented by intuitive dispensing software as well as a closed-loop motion control system, allows for repeatabilities of up to +/-4 µm (0.004 mm).
Some automated fluid dispensing robots, for example, Nordson EFD’s PRO3L and PROPlus3L, incorporate a laser height sensor. This allows the camera to map the topography of the substrate and pass those measurements back to the robot so that it can automatically offset the Z-axis values and maintain the correct dispense gap over the substrate. The process occurs in real time for every part that runs, ensuring high-quality dispense outcomes, even on warped or twisted substrates.
Automated fluid dispensing robots can also incorporate a needle tip detection device. This is used to position the tip of the dispensing needle at an exact Z-axis location relative to the substrate.
Automated fluid dispensing robots afford three types of feedback if a CCD camera, needle tip detection device and laser height sensor are installed, namely optical, contact and non-contact, respectively. These allow for easy programming of dots, lines, circles, arcs, compound arcs and complex patterns. The tip-detection device changes the offsets to the program if a tip changes on the syringe or valve.
Vision-guided software
Key to enabling high-speed, ultra-precise simple vision and sophisticated vision in the latest-generation robotic fluid dispensing systems is vision-guided software programs such as Nordson EFD’s DispenseMotion.
A significant benefit of DispenseMotion is its precision in the control and management of the critical offsetting capability, whereby it compares the current workpiece location to a reference location that it has stored as an image file. If the robot detects a difference in the X and Y positions and/or the angle of rotation of the workpiece, the software automatically adjusts the dispensing path to correct the difference. The offsetting function constantly receives process data to ensure that the fluid dispensing process is precisely controlled.
Summary
Automated fluid dispensing robots bring precision and repeatability to assembly operations. Many are suitable for dots, lines, potting, damming, filling, underfilling, encapsulation, sealing, coating and jetting in a number of syringe- and valve-based inline and batch applications.
Their integration of advanced fluid dispensing software and vision guidance systems offers manufacturers considerable benefits, including: greater part production capacity; reduced manufacturing time; consistent accuracy over rough and uneven surfaces; improved product quality; and the ability to take on more complex projects that require very precise dispensing and fluid placement.
Nordson EFD
www.nordsonefd.com