X-Y positioning is necessary in a variety of lab automation equipment including analyzers, pipetting machines, array analyzers, etc. Often the method used for positioning feedback for the servo motors is problematic. Typically indirect rotary encoders on ball screws, synchronous belts or rack and pinion mechanisms provide inaccurate position information due to backlash in the linear drive system. Glass scales can help with backlash, but are difficult to maintain and easily damaged. Balluff’s Magnetic Linear Encoder (BML) (or rotary for vertical positioning) offers a physically small, low cost, non-contact and easy-to-use option compared to traditional forms of positioning/measurement systems on automated lab instruments.

■ For high speed/accuracy applications up to 48 m of travel at 20 m/s with resolution down to 1 μm
■ Non-contact technology equates to long, wear-free life with no signal degradation over time
■ Immune to catastrophic position errors caused by drive belt slippage/breakage
■ Two components to the BML system; a small sensor head and an encoded magnetic strip

In this application, a tabletop multi-function automated lab instrument uses a BML sensing system to precisely position sample trays, microplates, and vial clusters which are mounted on the instrument platen apparatus carrying the samples. It is critical to the function of the machine that they are aligned perfectly under pipette arrays for processing to occur without errors. The BML’s non-contact technology allows the linear motion to be monitored directly, eliminating the need for rotary encoders and associated mechanical couplings, which could potentially cause position inaccuracies.

Sensor Head Series*	Output signal type	Resolution	System Accuracy	Distance to tape
BML S1A	Digital or analog (sin/cos)	1...10 μm	±10 μm/ ±20 μm	0.1...0.35 mm
BML S1E/B	Digital square wave	5...50 μm	±50 μm/ ±60 μm/ ±100 μm	0.1...2 mm
BML S1C	Digital square wave	100...2000 μm	±100 μm	0.1...2 mm
BML S2E	Quadrature	4600...46000 CPR (5...50 μm)	0.16 degrees	0.1...2 mm