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Whether a manufacturer is considering the purchase of a new robotic dispensing system or simply considering converting or upgrading an existing line, there are a number of factors that will determine the project’s ultimate success. Selecting the wrong dispensing equipment, robots or even materials can lead to problems down the road. These problems can include long delays, cost overruns and even misapplied equipment that can cause the project to fall short of the desired return on investment, thereby necessitating additional follow-up or even a complete overhaul.
The key to avoiding these situations is to assemble a trained and experienced team that includes the manufacturer, the system integrator, the dispensing equipment manufacturer, the robot supplier, the material supplier, the fixture builder and the parts supplier.
Equally important, every member of the team should be provided with a complete process specification. This should include details of the part, or parts, that need to be processed (including drawings), and the requirements of the dispensed material, including placement, profile and volume of to be dispensed. The specifications should also detail the processes times for things like loading, unloading, dispensing and indexing of parts from station to station.
Ideally, all team members will have experience with systems similar to the application in question. There is nothing wrong with performing minor modifications to customize a product for a given process. However, it is important that a supplier not substitute an inferior component due to the lack of product offering. With this in mind, manufacturers need to be sure and look at the details when comparing multiple proposals. They should also be sure question and understand any differences between them.
Finally, each team member should be familiar with the products supplied by the various team members to ensure compatibility.
Dividing Up the Work
Throughout the team building and component-selection process, the manufacturer should be sure and stay involved to ensure the final product meets its required results.
In terms of particular responsibilities, the material supplier will generally select or custom-formulate a one- or two-part material formulation based on the specific needs of the application. Dispensing system engineers will then select the appropriate supply, meter and dispensing components. Some dispensing engineers will also be capable of engineering end-of-arm tooling, material headers, robot dress-out, control software and bead path programming.
Material handling engineers, on the other hand, will be responsible for creating part fixturing and tooling. In doing so, they will also often work with the robot supplier to select the correct robot. To perform these tasks, both the material handling engineers and robot supplier will need to know the exact size and number of parts involved in the process, parts per hour that will be processes, and the speed with which material will be dispensed on the parts.
Again, the specification is the key document, like an architect’s drawings when building a house. If the process specification changes at any time during the build cycle, all team members should be notified.
With regard to systems integration, the manufacturer should select a turnkey provider with experience in its particular field. Typically, the robot or the dispensing system suppliers will be able to provide references. Make sure that, the integrator has the engineering experience and installation know-how to support both startup and any future needs you might have, not just a stable of programmers writing systems code.
Prior to potting, aluminum pallets, containing four 80-pin power
train connector assemblies each consisting of two 40-pin
chambers, are loaded onto the conveyor. Preheated in an oven
(consisting of medium-wave quartz emitters and aluminized walls
for maximum conductivity), they arrive at S.E.E.’s potting
station at approximately 185°F. This preheated stage allows for
elimination of any ambient moisture, improves the flow of the
potting material and enhances the polyurethane-to-part bond.
Dispensing System Options
When it comes to dispensing, a number of different equipment suppliers are available. Some suppliers have equipment that is specifically designed for use with robots, while others have equipment that has been adapted for these kinds of applications. Some dispensing system suppliers incorporate one or two principles of metering in their machines, while others offer as many as eight types of metering. The option of more metering principles ensures a manufacturer will be able to employ the most effective type of dispensing. The wrong technology may cause poor dispensing, longer downtimes, more frequent maintenance and higher spare parts cost. Keep in mind that higher initial capital equipment cost may result in more efficient product assembly, better product quality, more uptime and lower lifecycle cost in the long run.
In selecting a specific dispensing system, the dispensing equipment supplier will look at both the material formulator’s selection and the manufacturer’s process specs to ensure it selects the correct type of products.
Among other components, the dispensing system components, the supplier will size and spec supply equipment such as pressure tanks for pourable materials or pumps for non-flowable materials. With respect to the daily volume of material dispensed, it man be necessary to employ a dual supply unit with automatic crossover for nonstop dispensing. Other requirements may include material level monitoring or de-gassing, as well as dehumidifying for bubble-free and moisture sensitive materials.
At the heart of every dispensing system is its metering equipment. Selecting the right metering approach is therefore critical to ensuring the robot will dispense the material consistently every time ensuring quality. Technologies commonly used in robotic applications include positive rod displacement, piston displacement, reciprocating piston, or precision gear, metering. These types of metering principals have been used with robotic applications since the 1970’s. Positive displacement metering principle has proven itself as the preferred method of metering. With the integration completed between the robot and the metering system, dispense rates, location, purge warning, purging, as well as part recovery can be achieved.
Double-acting piston, progressive-cavity, piston cup, and time and pressure technologies are typically not used in a robotic setting. These types of metering principles are OK for many applications today, but because they lack the positive displacement principle, part quality may suffer do to the lack of integration or system feed back. To ensure part quality, the metering system should use a servomotor for precise metering movements to accurately control displacement of material by volume, not by pressure.
Popular robotic dispense methods, or patterns, include a bead extruded according to a specific cross-section and length; a predesigned profile drop, also known as “kiss”; coating; multiple short beads in what is called a stitch pattern; and potting or filling by volume. Pattern choice combined with the properties of the material being dispensed has a direct bearing on the valve, nozzle tip and, if necessary, mixer that will be used.
 Choosing a Robot
Not surprisingly, selecting a robot supplier is as important as choosing the dispensing system supplier. The robot model, software and hardware should be designed specifically for fluid dispensing and bead path programming, so that they will work well with the dispensing system. A specific robot model is selected primarily according to reach requirements, payload, application speed and bead path, as well as start-stop accuracy. In practice, the robot can hold and position the dispense valve, or it can present and manipulate the part as it is presented to a fixed dispense valve mounted on a pedestal. In some cases the dispense valve will be mounted to a Z-axis slide for adding clearance.
Dispensing robots are available in many different styles and sizes. Cartesian robots generally have three linear axis of control. Each axis is at right angles to the other and moves in a straight line. These robots are also referred to as gantry, or XYZ robots. Cartesian robots tend to be lower cost, but are limited in terms of motion and their work envelopes.
Scara style robots are also available. Scara robots are design for handling and assembling work pieces on a parallel level to each other, only one axis is used to lift a part or object straight up and away from the work surface. Scara style of robots are known for there speed and accuracy.
The most common robot type in use in dispensing application is the six-axis articulating robot. Six-axis robots can accommodate higher payloads, multi-plane bead paths and part sizes. Cartesian and six-axis robots can be mounted on the floor, on a pedestal or on a gantry to facilitate access to the part being dispensed, assembly automation and cycle time.
 When integrating a dispenser with a robot, meter location is critical for ensuring a precision bead profile and precise volume control, especially when working with a two-component material. In most cases, it’s best to mount the meter as near as possible to the point of dispense. This means mounting the meter assembly next to the robot, on the robot shoulder or even on the robot wrist. In some cases, the meter can be mounted on an overhead catwalk or mezzanine. Correct hose selection is also important for precision dispensing and ratio control.
Part Presentation
Effective fixturing and tooling are essential to precise robot dispensing of adhesives, sealants or lubricants. The fixture may be a simple one, in which an operator: manually loads the part, initiates the robot dispense cycle and then manually unload the part after dispensing. Then again, the fixture may be semi- or fully automated, using rotary or linear indexing to position the part into the dispense station.
In either case, the fixture requires precision tooling for accurate positioning. The fixture needs to include safety devices to ensure hand and fingers are out of the way of any moving machinery. It should also include part-in-place sensors to ensure material is dispensing only when the part is present.
To reduce tooling costs, fixtures and other tooling can be designed to accept multiple part configurations and even different sized parts. Of course, the robot will need to have a separate program for each uniquely tooled part. In some applications, a battery of sensor will be used to identify each unique part to define which dispensing program to use. In addition, common part designs with different dispensing requirements may used the same tooling but require different dispense routines.
Finally, fixtures should be designed to accommodate expected future design changes or production demands. Anticipating future needs can substantially extend the life of the robot dispensing system.
Communication Options
There are many choices when it comes to robotic dispensing communication. In fact, the robot will typically have many more inputs and outputs (I/O) than then dispensing system will actually require.
In a basic system the robot starts its cycle, moves to the point of dispense, signals the dispenser to “start dispense,” moves to the final dispense position, removes the signal to stop dispense, then moves to a home position. Additional signals are transmitted through the I/O to ensure proper part, dispensing, faults, quality control and safety.
The human machine interface is the user interface screen located on each control panel or pendant. These screens can be a simple keypad display, a small color touch-screen or a larger graphical user interface. Advanced robot and dispensing system controls improve user interface capabilities, machine uptime and supervisor convenience. Controls may be a PLC or PC based. Basic controls may use digital or discrete I/O communication, while advanced controls may use DeviceNet, Profibus or Ethernet IP communication.
One advantage to high-end communication is that is also enable remote access to the machine controls in the production manager's office. Advanced controls collect job data, display faults and warnings and inform where and how to fix system issues.
Precision is Critical
Always remember that product selection choices made in the beginning of the project can directly affect the end product quality. Selecting the right robot, metering-dispensing system, controllers and communication interface provides the largest impact on the fluid application process for product quality. In addition, accessories are available to further improve dispensing and robot positioning accuracy.
An example of one of these accessories is the use of temperature control of the material to ensure consistent material dispensing profiles irrespective of ambient temperatures. This can be done through the use of heating and cool water, a heat-only electric system, or a heating and cooling Peltier electric system.
Another means of ensuring consistency and precision is through the used of vision bead control. With this technology, cameras view the fluid exiting the dispense nozzle and compare the profile to preset parameters to ensure proper bead placement and size. This allows the system to automatically correct the dispensing application or mark it for physical inspection.
Another use for vision is when the part is not consistently in position for dispensing. Cameras are used to locate the part position, and this information is then used to change the robot path program to new coordinates. |
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