4260914 Differential Linear Velocity Transducer Mar79

This patent describes a differential linear velocity transducer designed to convert linear mechanical motion into an electrical signal, particularly for use in magnetic disk recording systems to control head positioners.

The transducer features a stationary permanent magnet housed within a closed-path iron pole piece assembly. Key to its operation are two separate, movable coils. These coils are wound around parallel segments of the pole piece assembly, on opposite sides of the magnet, and are mechanically linked to move in tandem.

Crucially, the two coils are connected in series and are wound in opposite directions relative to the magnetic flux generated by the stationary magnet. This configuration provides significant advantages:

1. Noise Cancellation: External electromagnetic noise induces common mode signals of equal magnitude but opposite polarity in the coils, causing them to subtract and substantially cancel.
2. Signal Addition: Signals generated by the desired linear motion induce differential mode signals that add together, increasing the transducer's sensitivity.

As a result, the invention achieves a significantly improved signal-to-noise ratio and higher sensitivity compared to prior art designs, making it more robust against external interference while accurately detecting velocity. Experimental results showed a doubling of sensitivity and a substantial reduction in noise pick-up (up to 100x improvement in signal-to-noise ratio in some tests).