Radiation hardened stepper motors for closed or open loop operation

For certain scenarios in the fields nuclear power or scientific research, we are confronted with irriadated environments (environments subjected to high levels of radiation, especially gamma rays). This type of environment means it's impossible to use industrial-grade motors and rotor angle measurement systems, as they will disintegrate sooner or later, due to the effects of radiation on the non-metallic parts.  For situations like this, MACCON has designed and built a radiation-hardended motor, based on stepper motor technology. The motor is available with or without a rotor angle measurement system (resolver feedback) and can therefore be operated in closed loop or open loop mode.

In the image on the right-hand side, the version with resolver feedback can clearly be seen (additional connector for feedback cable).

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Technical features

The key features of the closed-loop version (with resolver) are as follows:

  • Hybrid stepping motor with resolver
  • 2-phase bipolar serial winding
  • Motor size: NEMA34
  • 200 steps per revolution
  • Operating voltage 120Vdc
  • Holding torque 3.5Nm
  • Pull-out torque 2.4Nm
  • Qualified for high radiation resistance (> 30MGy) and already proven in the field
  • Life-time > 1.65 x  1013 revolutions
  • Weight: 2.8kg (resolver version)

The key features of the open-loop version (without resolver) are as follows:

  • Same as above, except no resolver included. See image on the right-hand side: the feedback connector is not present.

The key features of the resolver

  • Excitation voltage 7V
  • Input current 54mA
  • 1 pole pair
  • Excitation frequency 7kHz
  • Qualified for high radiation resistance (> 30MGy) and already proven in the field
  • Life-time > 1.65 x  1013 revolutions

Torque-Speed characteristics of the radiation-hardened stepper motor

The following diagram shows the torque-speed curve of the radiation hardened motor. Certain combinations of speed and torque determine will determine which continuous output mechanical power is possible e.g.

    2.7Nm  @ 100 rpm results in approx. 27W
    2.9Nm  @ 150 rpm results in approx. 43W
    1.75Nm @ 400 rpm results in approx. 70W
     

Thus, for linear motion applications (e.g. when the motor is used to drive a screw), the speed-torque combination can be selected to match the screw pitch and the desired force and linear speed by setting the corresponding values in the stepper drive electronics.

Dimensional drawing of radiation hardened motor with resolver

Dimensional drawing of radiation hardened motor without resolver