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VOLUME -22 NUMBER 9
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September 2007 Issue
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Automating Tight Dispensing Needs
TR300 dispensing robot.
By Cliff R. Bockard, Vice President, Global Automation Inc., Old Saybrook, CT
Over the last few years, the manufacture of medical equipment has grown to the point where a number of operations have become fully automated. One of these applications is the automation of the dispensing processes. Dispensing of fluids, liquid or viscous, such as epoxies, silicones, polyurethanes, greases, oils, lacquers, and one- or two-component materials becomes more and more significant in the medical industry. As the trend towards smaller end products continues, the dispensed volume decreases and applications get progressively more complex. This means in-depth knowledge is required to control and apply the dispensed liquid, and in many cases customized solutions are necessary.
Specifically, in cases where two-component products are dispensed manually, the preparation of the homogeneous mix in the proper ratio requires a skilled operator. In manually handling this operation, there is a very high risk of improper handling; at the same time, the operator is exposed to the adhesives, or other dispensed liquids during the preparation and application. Such personal contact with resins can create drastic and unpleasant symptoms.
Manually weighing, mixing and pouring polymers into syringes is wasteful and time-consuming. The product is mixed in larger quantities, yet only a smaller amount of the previously mixed product is useful, since its physical properties change after preparation. In addition, the product reaches is pot life (double viscosity) much sooner than if mixed in smaller quantities. It is important, therefore, to fully automate the mixing and dispensing of the product to be dispensed — eliminating operator exposure to and handling of resin and hardener. By dispensing volumetrically (positive displacement), the same amount of product is mixed and dispensed within the same machine, ensuring repeatability and consistent physical properties. This underscores the need for precise mixing and metering dispensing, made possible by systems currently provided by Global Automation.
A patented design allows for ease of use and highly accurate volumes dispensing. Two cartridges are filled with the associated product to be dispensed and the prepackaged cartridges are placed on two numerical-volumetric dispensing heads. The resin and hardener are dispensed into a patented mixing chamber using a programmable mixing ratio and thoroughly mixed just before being applied to the product. This mixer/dispenser allows for dynamic mixing of small volumes for two-component products. The quality of the mix can be achieved by altering mixing time, mixer speed and the selection of three different mixing chamber sizes. For some products, it is important to mix with a low speed to prevent cavitation and degassing. The ratio of the product can be freely programmed and does not depend on the sizes of the dispensing units. One of the main advantages is that the mixed product is very small (max. 2300mm
) and that the materials are mixed just before dispensing. Furthermore, the repeatability of the dispensed volume does not depend on the viscosity of the material and is always constant. The advantages of the system are: volumetric piston pump dispensing; piston and liner in Al2O3; no moving seals; liner is driven by a stepper drive and all wetted parts are reduced to PTFE/PVDF/PP/V2A and Al2O3 materials.
Because the chamber is of such low volume — as low as 60mm
, only the volume that is going to be dispensed is actually mixed. The mixing chamber is completely flushed and the product within the chamber is constantly renewed. Since it is designed as a consumable, there is no need to use any hazardous and expensive cleaning agents after it has been used. In addition, the mixing chamber is chemically inert, with a design based on PTFE/PVDF, PP and Stainless Steel. Therefore, there is no contact between the operator and the adhesive at any time, nor does the operator have any direct physical access to the metering and mixing process, thus eliminating all possible errors to improper handling.
Tiny Volume Needs
In the field, there are certainly many examples of required precision in dispensing. One such project included dispensing fluid product to manufacture contact lenses. The target was to have highly accurate dispensed product with low deviation from nominal volume (less than 1 percent). The nominal volume was less than 40mm
. Currently, these dispensers run in a clean room class 10000 in three shifts. To date, this company has produced over 40 billion lenses with Global's equipment.
Filling up a medical pump with a two-component epoxy (Delo Duopox 1895) was another recent project requiring precision and accuracy. For this application a two-component dispenser was used. The main objective was to dispense the product into a small hole to fill up a cavity and to avoid any air bubbles, citing the mixture and ratio of the two-component product to be perfect. In addition, the acceptable tolerance of quantity to dispense was very small. The process described here resolved these issues with ease.
Specific to the vascular field, we were challenged with the solution of dispensing a mono-component RTV-silicone NuSil Med 1011 onto a pacemaker and subsequently assemble another element with this dispensed module. For this application we used our RC500 robot with a clean-room conveyor and tip-cleaning unit. After re-centering the tip on a special device, the job was to dispense the product on a predefined trace, interpolated accordingly. This part was picked up with a pneumatic slide, returned and placed on the other part. Our experience in automation technology allowed us to design and produce the whole robot with mta automation standard components.
Generally, the automation of dispensing can be done in 3 ways: semi-automatic in-line, semi-automatic manual and fully automatic. For dispensing operations which cannot be integrated into fully automatic production lines, the TR300 offers a table top, 4-axis solution for maximum flexibility. When volumes increases and throughput demand is high, the RC500 is customizable for virtually any production line job, with automated handlers ranging from z-movement to full-scale robotics with rotary tables, conveyors and choice of dispensing heads.
Whatever the solution, the automation of dispensing products is moving forward at a rapid pace and continues to show dramatic repeatability and throughput superiority over manual operations.
For more information, contact: Global Automation, Inc., 8 Custom Dr., Old Saybrook, CT 06417
860-399-1141 fax: 860-399-1159 E-mail: email@example.com Web:
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