A company of Schneider Electric

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ScrewCoder™ Provides True Straight-Line Positioning

Combining a lead screw assembly with a linear encoder, Newall’s ScrewCoder™ is certainly an industry first. True straight-line positioning is now possible as the nut and screw are integral parts of the measuring components.

As opposed to the traditional separate lead screw and rotary encoder assembly, the accuracy of the ScrewCoder™ is not influenced by screw pitch or reversal errors. This is due to the fact that the nut is the actual reader head and the lead screw is the actual scale. This provides for true straight-line linear measurement of the axis that is generated from a rotary movement. Linear positional readings will register only when linear movement of the nut occurs. In addition, the system does not require period recalibrating due to screw wear and it will not misread due to geometric errors such as pitch, roll and yaw of the machine.

The ScrewCoder™ is based on Newall’s Spherosyn™ technology which operates on the principle of induction. A drive coil contained within the nut generates an electromagnetic field. This field interacts with high precision nickel-chrome ball bearings that are contained in the screw. A set of pickup coils detect the variations of the induced field, which are then combined and processed to generate signals that vary in sine and cosine form caused by axial (not rotary) movement along the scale. The degree of phase shift between 0 and 360 degrees is related to the position of the nut over a ball bearing.

A high-speed Digital-Signal-Processor (DSP) samples the signals and converts them from their natural analogue state to an industry standard differential quadrature at TTL levels. The DSP also synchronizes the periodic reference marker pulse to the A and B High output levels. 

The ScrewCoder™ offers accuracy to +/-10 micron, includes the performance benefits of an IP67 environmental rating (fully submersible), and is highly shock and vibration resistant.