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Extreme Motor Performance
Gear motors designed to withstand radiation doses generated by neutron scattering
Al Presher, Contributing Editor -- Design News, July 20, 2009
Vacuum and radiation-hardened gear motors and resolvers are utilized by the Australian Nuclear Science and Technology Organization (ANSTO) on research instruments at the organization's Bragg Institute research facility. To perform reliably in the extreme conditions, all the organic materials used in the standard motor design needed to be evaluated against specific radiation dose requirements.
Everything from the magnets and bearings to the glue and lubricants was analyzed. Radiation-resistant materials were substituted, if required, to withstand the radiation generated to test materials and equipment. Teflon motor lead wires, for example, don't perform well under radiation and were replaced with a specialized material called peek to maintain high system reliability.
In the final design, specialty motors and resolvers from Empire Magnetics are being used in ANSTO's TAIPAN and SIKA 3-axis spectrometers, its PELICAN cold-neutron time-of-flight spectrometer and the QUOKKA small angle scattering instrument. These instruments perform neutron scattering, and are essentially scientific research tools for physicists, engineers and chemists. The instruments allow the atomic, electronic, and magnetic structure of materials to be analyzed on a resolution and depth not possible with any other instruments.
The TAIPAN instrument is a triple axis instrument used for measuring phonons or "solid state waves" which can give scientists insight into processes such as high temperature superconductivity. This instrument is closest to the core of the nuclear reactor and has a moment of inertia of 15,000 kgm2. High torque, high inertia motors are needed to function in a radion environment with a high degree of reliability and quality.
In a nuclear research facility, all electrical control components are subjected to extreme environmental conditions, including gamma and neutron radiation. Components are embedded inside radiation shielding that is keyed together in large monolithic slabs. If a motor fails, the instrument is shut down and engineers wait up to a week for the radiation to die down. The radiation shielding is then removed; the motor is replaced; and the shielding is keyed back together, a process that can take up to two weeks.
Empire Magnetics' radiation-hardened motors are available with continuous output torque ranging from 15 to 400 inch-lb (1.7 to 46 Nm) or momentary peak torque from 30 to 1000 inch-lb (3.4 to 113 Nm). Motors are rated for a total standard accumulated dose of 2x108 rads (radiation absorbed dose), with ratings to 1x109 rads available on a custom basis.
An anti-backlash, radiation-hardened resolver with gearing provides precision encoding in a radiation environment. Using a precision spring to eliminate backlash in the encoding system allows accurate values to be sent to the motion control system.
