Morrison's QUBIK Inertial Measurement Unit Magnetically Levitated Cube

Melvin Mark Morrison

Abstract:	The QUBIKtm Inertial Measurement Unit (IMU) is a magnetically levitated cube that has been developing for the past twenty years. The one gram 0.420 inch cubic proof mass has bias sensitivities of 0.01 degrees per hour and less than 1 micro g with an arrangement of linear parallel orthogonal arrays of permanent magnets embedded into it. Likewise there is an arrangement of electromagnets that push and pull on the permanent magnets to keep the proof mass centered within its housing cavity. The entire surface of the proof mass makes up one side of 36 variable capacitance plates within the housing wrapped around the proof mass. The proof mass is levitated by three orthogonal linear and three orthogonal angular accelerometer closed servo loops. Angular rate is detected by injecting a reference AC drive signal into one of the angular accelerometer channels to establish an alternating momentum or “dithering” of the proof mass. When the entire system, is rotated about a second axis, there is an AC precession about the third axis. The phase of the precession signal is either in phase or 180 degrees out of phase with the reference depending on the direction of rotation and the amplitude is proportional to the angular rate. Many technical problems have been resolved with the latest development effort during a Small Business Innovative Research (SBIR) PHASE I contract with the Missile Defense Agency (MDA). Using new non-ferrous leaded diodes (not available before) packaged close to the variable capacitance detectors eliminated the magnetic contamination to the fields around the proof mass. The absolute bias stability of the QUBIKtm IMU is three orders of magnitude better than current MEMS technology. Replacing the aluminum outer housing of the QUBIKtm IMU with Printed Circuit Board’s (PCB) has resulted in a 25 gram one inch cube IMU including all servo loop electronics. The PCB design also permits packaging the electromagnetic coils inside grounded vias which eliminated the problem of transformer cross talk between the electromagnetic coils. This was a very important discovery since transformer coupling in previous designs made it a difficult challenge to develop the electronics to measure angular rate. The PCB version of the QUBIKtm IMU can be transferred to MEMS technology to further reduce the size and weight to 10 grams. The military applications require angular rate whereas the commercial automotive "black box" accident recorder does not. Therefore the commercial and military designs may use some of the same parts with a different set of electronics.
Published in:	Proceedings of the 2005 National Technical Meeting of The Institute of Navigation January 24 - 26, 2005 The Catamaran Resort Hotel San Diego, CA
Pages:	928 - 938
Cite this article:	Morrison, Melvin Mark, "Morrison's QUBIK Inertial Measurement Unit Magnetically Levitated Cube," Proceedings of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2005, pp. 928-938.
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