Mosolver = Motor + Resolver

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The Mosolver - a combined Motor and Resolver - senses position by adding a patented passive sensing circuit to the interior of the existing motor magnetic structure. The ripple current from the existing motor PWM drive provides the flux variation that allows this sensor to continue operation even when the motor is stationary.

The sensor consists of a novel sense coil pattern on a polyamide flex circuit, and provides position feedback at 32,000 counts per revolution. The polyamide flex circuit material covers a wide range of temperatures, and is available in low out-gassing as well as radiation resistant formulations. The sensor is embedded within the structure of the motor stator, reducing the size and weight of the package while providing good protection for the sensor.

By use of this rugged and inexpensive sensor, the Mosolver environmental ratings are essentially limited only by the motor for wide temperature, wet, and vacuum applications as well as for operation in radiation environments. Further, the system does not require alignment nor phasing for effective servo operation.

The fragile encoder discs and expensive resolver and R/D elements are eliminated from the servo system.

How it Works:
The sensor coil is configured to intercept a portion of the flux that passes between the stator teeth and rotor teeth of a high pole count permanent magnet synchronous motor, typically used for Hybrid Servos. As the rotor position with respect to the stator changes, the tooth alignment between the various rotor and stator teeth also changes. The degree of overlap of these teeth determines the paths the flux takes through the motor.

The flux through the motor structure is continuously varying, even when the motor is stationary, due to the presence of ripple current from the PWM drive. This flux variation is converted to a voltage by the sense coil, with its sign and magnitude modulated by the rotor position. This produces approximate sine and cosine signals when sampled. These signals are decoded into motor position, while also providing sinusoidal commutation information without any need to move at power-on. As the position information is not dependent upon motor movement, it is useful for both position and velocity servo control.

The Mosolver requires only the use of a couple of A/D channels on the DSP that controls the PWM drive, and a couple of buffer amplifiers. This technology enables a robust, low cost, high performance servo system in a compact and rugged package. The technology is also applicable to other motor types including 2 axis Sawyer motors.

The Mosolver is available now in a NEMA 23 frame format with other sizes in development.

Detailed specifications, videos, and detailed internal operational descriptions are available at


  • Awards

  • 2014 Machinery/Automation/Robotics Honorable Mention
  • 2014 Top 100 Entries


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  • Name:
    Donald Labriola
  • Type of entry:
  • Profession:
  • Donald is inspired by:
    Elegant designs that simplify sophisticated systems for the average user.
  • Software used for this entry:
    Matlab, Altium, Geomagic
  • Patent status: