Automated dispensing equipment

More and more pharmacies are using automated dispensing equipment. 

This chapter introduces the reader to the automated dispensing equipment commonly used in electronics packaging, printed circuit board assembly, and other electronics manufacturing. Automated dispensers excel in the areas of manufacturing that can be most helpful in the construction of fuel stacks. 

They are very often found in MEMS devices when the use of automated dispensing equipment makes it easier to place precise amounts of materials in areas where it would be difficult or impossible to apply them by other methods. By applying them in liquid form with automated dispensing equipment, the amount and placement of the material can easily be adjusted to suit the needs of the task at hand. 

A wide variety and numerous suppliers of automated dispensing equipment are available as listed in Table 4.22. An important consideration in selecting an automated, contact-type dispensing system is the pump used in the system, of which there are three types time-pressure, auger, and linear piston or positive displacement. " ... 

Ease of use (automated dispensing equipment or hand-held glue guns). 

Highly reactive adhesives are more difficult to mix and apply because of their short working life, resulting in inaccuracies and material waste. Automated metering, mixing, and dispensing equipment may be required. 

Before developing an automated process for dispensing fluids, it is critical to know and understand the desired results and this begins by understanding the fluid characteristics. Often it is best to collaborate early with both the fluid supplier and the supplier of the dispensing equipment. 

When developing an automated dispensing process, the equipment suppliers need to know the desired end result. This may seem like a trivial... 

Most of the equipment used in automated dispensing in the electronics industry is designed to place fluid on flat or nearly flat surfaces. This significantly simplifies the process since the motion of the robot during the dispensing operation can be limited to two axes. Robots that can dispense... 

There are a variety of drive mechanisms commonly used automated dispensing including cable drive, lead screw, and linear motors. Most modern equipment uses closed loop servo mechanisms, although open loop stepper motors can be found in some less expensive equipment. The drive mechanism is not as important as the overall speed and accuracy of the equipment. Other factors, such as the alignment process and dispensing technology often overshadow the characteristics of the drive mechanism. 

The number of dots that can be dispensed per unit of time also depends on viscosity. The use of low-viscosity adhesives increases the number of dots that can be dispensed. However, there is a tradeoff between the speed at which the adhesive can be dispensed and the speed of device placement. Most automated component-placement equipment operate faster than adhesive-dispensing equipment. A comparison of the effect of viscosity on dispensing and placement times is shown in Table 4.19 for an 86-lead plastic-encapsulated leadless chip carrier (PLCC). ... 

Jet-dispensing equipment uses a closed-loop, positive shut-off piston to dispense the adhesive. The adhesive is pressurized at the syringe to assure constant flow. Using a spring-driven ball and seat mechanism, the adhesive fills the void left when the ball retracts from the seat. When the ball returns, the force due to acceleration breaks the stream of adhesive, which is then jetted through the nozzle in precisely controlled amounts onto the printed-circuit board (Figure 4.14). Unlike contact automated... 

Because many acrylic adhesives cure very rapidly with a significant exotherm, manufacturers generally recommend that quantities greater than a pint (ca. 0.47 L) should not be mixed at one time. As a consequence of the rapid exothermic cure of many acrylic adhesives, the use of dual component cartridges is often ideal. Most products can be purchased in ready-to-use cartridges. For large continuous operations, various automated types of meter-mix-and-dispense equipment are marketed by a number of engineering companies. 

During any filling run at least 1% to 2% of the containers filled are selected at intervals for check weighing, as a measure of the variability of the material dispensed over the period of the fill. This is a limitation imposed by the practicalities of check weighing on our automated filling equipment. Table 3 shows the CV of fill weights for some of the materials established by ECBS in the year 2000. 

With the increased use of adhesives in the construction of structural assemblies, the need for dispensing equipment should expand. Indeed, control of the machines will become more complex as they find their way into the world of robotics and automation. 

Selection of the robot and the dispensing equipment are of primary importance when automating sealant and adhesive application processes. Those installations that have taken into account all aspects of the application requirements have been successful. 

The cycle time has an important bearing on the investment required to automate the system and the number of operators or workstations that may be necessary. Whether manual, semi-automatic or automatic, the dispensing equipment system specified will depend on the type of application and workplace conditions, such as dispense rate, parts per hour, operator availability and materials handling. Adhesive dispense systems are available for most production lines varying from bench-top applicators to fully automated robotic units with dispense times of <50 ms. 

The introduction of robots to these applications has not been matched by any development by the dispensing equipment suppliers, the equipment being essentially automated versions of the manual system. 

A second strategy relies on parallel experimentation. In this case, the same experimental step is performed over n samples in n separated vessels at the same time. Robotic equipment such as automated liquid-handlers, multi-well reactors and auto-samplers for the analysis are used to perform the repetitive tasks in parallel. This automated equipment often works in a serial fashion as, for example, a liquid handler with a single dispensing syringe filling the wells of a microtiter plate, one after another. However, the chemical formation of the catalyst or the catalytic reaction are run at the same time, assuming that their rate is slow compared to the time needed to add all the components. The whole process appears parallel for the human user whose intervention is reduced. 

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