The miniaturization trend extends across all industries; however, the ever-decreasing product sizes are a challenge to the automation technology, e.g. when it comes to accurately applying the correct amount of soldering paste, adhesive, lubricant, potting material or sealant. Dosing according to volume has been proven to be the simplest and most flexible method in practice, since the substance that needs to be delivered “only” needs to be moved back to the dosing tip by pumps delivering uniform quantities. Precision dispensers such as these should also be as compact as possible so that they can be easily integrated into the production systems. They are therefore reliant upon small, powerful drives that provide the best possible dynamics and can be precisely controlled.
ViscoTec Pumpen- u. Dosiertechnik GmbH manufactures dosing systems and components for semi-automatic and fully-automatic production systems as well as assembly processes. Using the preeflow® micro-volume dosing units, the company already set the standards in the precision dispensers area almost 10 years ago.
Typical applications range from semiconductor and electronics manufacturing, optics and photonics and all the way to biochemistry and medical technology. Many different liquids can be dosed. The range extends from “A” for anaerobic adhesives to “Z” for zinc chloride solutions.
The basic functionality of the precision dosing unit is easy to understand: The heart of the dispenser unit is a rotating, completely pressure-sealed displacement system. It consists of a self-sealing inner rotor and the outer stator. The medium that is delivered is transported by means of displacement by a controlled rotating movement of the rotor. Changing the direction of rotation also allows the system to transport backwards. This ensures that the material separates in a neat and controlled way without dripping. The medium itself is transported in a protective way without changing the structure. The system is designed to be self-sealing with water up to a feed pressure of 2 bar. As the viscosity increases, so does the self-sealing effect. Dosing pressures of 16 to 20 bars are therefore easily possible. In turn, this high feed pressure makes it possible to use smaller needle and nozzle cross-sections for delicate application surfaces. The heart of the dispenser unit is a rotating, completely pressure-sealed displacement system.
A high feed pressure in the dispenser module requires a high-torque drive. “With the limited unit sizes, only a micro motor with an ancillary gearhead came into question”, recalls Diringer. “We have therefore been collaborating closely with FAULHABER for almost ten years now. Together with the drive specialists from Schönaich, we quickly found a suitable powerhouse. Small dimensions and high power density are important, so that the preeflow® eco-PENs can also be built with small dimensions and fitted directly to the robot in the automated dosing process without problems.”
The best price/performance ratio turned out to be a DC-micromotor with encoder and planetary ancillary gearhead. The brush commutation makes simple pulse-width regulation and direction of rotation changes possible. The encoders and planetary gearheads in the motor diameter make it possible to have a slim design. The compact drive block measures just 22 mm in diameter with an overall motor length of 32 mm, depending on the dispenser design. There is also the gearhead, which provides ratios of 9:1 to 23014:1 with a length of between 27 and 48 mm. The smaller motors supply a continuous torque of 10 mNm and the bigger motors achieve 28 mNm. This torque is increased by the respective gearhead to the 20 bar of feed pressure that is needed for the dispenser unit.The push-on encoder only increases the overall length by 1.4 mm, and supplies 64 to 512 pulses per revolution depending on the model. This enables precise quantity allocation, provides drip-free medium separation due to the precise feedback of the rotor position of the drive. The gearheads and the motor bearings have lifetime lubrication and are maintenance-free. “We have found a reliable, robust and dynamic drive solution for our micro dispensers”, concludes Diringer.
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