Motors deliver accuracy in precision dispensers
Dosing according to volume has proven to be the simplest and most flexible solution for delivering the correct amount of soldering paste, adhesive, lubricant, potting material or sealant. But ever-decreasing dispenser sizes are presenting a challenge to the automation technology.
Precision dispensers for many applications have to 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 manufactures dosing systems and components for semi-automatic and fully-automatic production systems as well as assembly processes, and its Preeflow micro-volume dosing units set the standards in precision dispensing.
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 – indeed the dispensers cover the A to Z of fluid dispensing, covering everything from anaerobic adhesives to zinc chloride solutions.
At 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 bar 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.
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 could meet the requirements,” recalls Viscotec business unit manager Thomas Diringer. To address the drive needs for the Preeflow, Viscotec worked closely with miniature motor specialist Faulhaber, whose products are available in the UK via EMS. “”Small dimensions and high power density were 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,” comments Diringer.
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 22mm in diameter with an overall motor length of 32mm, 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 48mm. The smaller motors supply a continuous torque of 10mNm and the bigger motors achieve 28mNm. 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. 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 completely maintenance-free.
“We have found a reliable, robust and dynamic drive solution for our micro dispensers,” concludes Diringer.
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