Inductive Encoder Technology
A POSICoder inductive encoder is in fact a differential transformer integrated on a silicon chip. Below you find a short explanation how such a differential transformer works and how it is implemented in a POSICoder encoder chip.
Working principle of a Differential Transformer
The primary coil generates a high-frequency magnetic field. This field is coupled into the two secondary coils that are arranged in a differential configuration. If everything is perfectly symmetrical, the two coils generate opposite signals, so the differential output is zero.
Interaction with a Ferromagnetic Object
A ferromagnetic object modulates the coupling between the primary and secondary coils. In fact, the object attracts the magnetic field lines, leading to an output signal, the amplitude and sign of which depend on the position of the object. Thanks to this interaction, an inductive encoder chip can be operated with a steel gear.
Interaction with an Electrically Conducting Object
The Eddy-current effect makes that the differential transformer is also sensitive to electrically conducting objects. The interaction is the same as for ferromagnetic objects, but with opposite sign. Thanks to this interaction, an inductive encoder chip can be operated with a linear scale or a disc made of FR4 and copper strips.
Dual-channel sensing
When an object is moved in front of the sensor coils, a sinusoidal signal is generated. By placing two pairs of secondary coils at the right distance from each other, sine and cosine signals are generated.
Sine and Cosine Signals
POSICoder scales and discs consist of a printed circuit board with copper patterns. When the copper pattern is matched to the geometry of the coils, sine and cosine signals are generated when the scale is moved along the encoder chip.
Interpolation
The analog sine and cosine signals can be converted into digital A quad B signals by means of interpolation. To the left you see the A and B signals for interpolation x1, x2 and x4. The interpolation in POSICoder's inductive encoder chips goes up to x16384.
Electronics
The primary and secondary sensor coils, the analog sensor electronics, the digital signal processor as well as different interfaces are integrated together on a silicon chip measuring only a few square millimeters!
The Encoder Chip
The silicon chip is packaged into a small package measuring 5 x 6 x 0.8 mm, leading to the smallest inductive encoder in the world!
The Targets
A variety of electrically conducting or ferromagnetic objects can be used as targets for the inductive encoder chips. Particularly suited are scales and discs made of FR-4 printed circuit boards with copper strips, steel gears with module 0.5 or aluminum gears with module 0.8.
