Motoring On to Increased Lab Production
Wed, 12/02/2009 - 4:29am
With ever increasing needs for medical laboratories to produce new flu vaccines and additional quantities of pharmaceuticals for our aging population, technology has to meet the challenge with higher throughput equipment. This article focuses on the motor specifications needed while increasing the capacities when automating a pipette system for a lab automation company.
Paul McGrath is the regional sales engineer at maxon precision motors. He can be reached at 508-677-0520 or firstname.lastname@example.org.
Design challenges for the pipette system included the need for a mechanism that would withstand substantial axial loads during the pressing-on of the pipette tips. It was found that the system also needed to have adequate motor thrustenough to overcome a pierceable foil that required 0.5 pounds of thrustand pierceable caps that required 1.6 pounds of thrust. Finally, the system acceleration and deceleration speeds had to be slow enough to prevent liquid from splattering.
It was found that brushed motors could drive the system as needed. By using Maxon RE13DC moving coil motors with Neodymium magnets, the system also gained long life, low electrical noise, and high efficiency with this design. Since great accuracy was vital, the solution was to drive the helical racks carrying pipette tips with motors using planetary gear reduction, encoder feedback for smooth servo controlled displacement motion, and recirculating linear bearings for precision and repeatability.
Smoothness of operation and freedom from cogging was critical for the application. Cogging could impede the motion of the pipette probe and lead to pipetting errors. The planetary gear reduction and encoders integral to the system allowed the motors to facilitate excellent servo control and minimal backlash, resulting in high positioning accuracy and long life. The ironless rotor design of the motor allowed for zero cogging, a significant aid in the motor's simple and accurate control.
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