Assembly Planbook - April 2008 - (Page 40) Dispensing valve, nozzle tip and, if necessary, mixer that will be used. 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. 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 configured specifically for fluid dispensing and bead path programming, so that they will work well with the dispensing system. Robot selection is generally based on the application’s reach requirements, payload, application speed, Part Presentation Choices made early in the design process are critical to the success of a robotic bead path and accuracy. In dispensing system. In this workstation, a small six-axis robot is dispensing an Effective fixturing operation, the robot can adhesive on a manually fixtured part. and tooling are essential, hold and position the diswhether the system is dispense valve, or it can present and manip- multiplane bead paths and part sizes. pensing adhesives, sealants or lubriulate the part, while the valve remains in They can be mounted on the floor, on cants. The fixture may be a simple one, a fixed position. In some cases the dis- a pedestal or on a gantry to facilitate in which an operator manually loads the pense valve will be mounted on a Z-axis access to the part being processed, as part, initiates the robot dispense cycle slide for additional flexibility. well as minimize the system footprint. and then manually unloads the part after Dispensing robots are available in When integrating a dispenser with dispensing. Or, the fixture can be semimany different styles and sizes. Car- a robot, meter location is critical for or fully automated, using rotary or lintesian robots generally have three lin- ensuring a precision bead profile and ear indexing to position the part into the ear axes of control, with each dispense station. axis positioned at a right angle In either case, the fixture to the other and moving in a requires precision tooling for straight line. These robots are accurate positioning, as well as also referred to as gantry, or enough safety devices to ensure X-Y-Z robots. Cartesian robots that all hands and fingers are tend to cost less, but are limited out of the way of any moving in terms of motion and their machinery. The fixture should work envelopes. also include part-in-place sensors SCARA robots are also to ensure material is dispensing available, and function best only when the part is present. when processing workpieces To reduce tooling costs, fixthat are oriented in the same tures and other tooling can be plane, like flat parts presented configured to accept multiple on a conveyor. Only one axis part configurations or even is used to lift the part, or parts, parts of different sizes. Of straight up and away from the course, each different part type work surface. SCARA robots will require its own unique are known for their speed and dispensing program. In some accuracy. applications, sensors are used Another common technolto identify the specific type of ogy used in dispensing applicapart being processed, so that Small, tabletop X-Y-Z gantry robots are well suited to applications tions is the six-axis articulat- involving small parts and moderate production rates. In this the system controller can autoing robot. Six-axis robots can application, a single fixture accommodates three separate matically select the correct disaccommodate higher payloads, assemblies. pensing path. 40 ASSEMBLY / April 2008 www.assemblymag.com http://www.assemblymag.com
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