TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes, Sensors

OBJECTIVE: To explore the use of and demonstrate the effectiveness of novel torque sensing devices for condition based maintenance of Navy rotating machinery (motors, generators, pumps, gear systems, etc.). Rate-of-change torque sensors, for example, have demonstrated both a sensitivity and time resolution high enough to not only recognize failing machinery, but to specifically identify the failing part. This topic is open to rate-of-change torque sensors and alternative torque sensing approaches having potential for benefitting the Navy from a cost, maintenance, reliability, or performance standpoint.

DESCRIPTION: Rate-of-change torque sensors1-3 differ from normal torque sensors in that the torque rate-of-change is not calculated, but measured directly. The sensors consist of a circumferentially-magnetized shaft and a pick-up coil1. In many cases, the original shaft material can be utilized either by permanently magnetizing the shaft or by using a sensor arrangement including a small magnet. In either case, no contact between the shaft and sensor is required. As compared to simply differentiating the output of a normal torque sensor, the direct measurement results in higher sensitivity, higher time resolution, and lower noise. The lower noise results from the avoidance of differentiation which inherently accentuates the high frequencies.

An example of rate-of-change sensor performance is given in Reference 2. In one test, two, four and six flute one inch diameter end mills were used to mill an aluminum block. The magnetic properties of the high speed steel used in the end mill were such that an external magnet was not needed. Instead the tool was magnetized by a 550 A, 2 ms axial current pulse. The pickup was a 1000 turn coil on a bobbin slipped over the shank of the tool. At 600 rpm, the moment that each flute contacted the aluminum block was clearly delineated. A second experiment progressively dulled one of the flutes on the two flute end mill. The signature of the damaged flute was visible and noticeably different from the good flute.

The rate-of-change torque sensor technology shows great promise for use in condition based maintenance applications. It is sensitive, has enough time resolution to pinpoint the point in the rotation that is failing, is temperature tolerant, and, if the existing shaft has suitable properties, can be retrofitted onto existing machinery without dissembling the machinery. Further S&T is needed however to gain an understanding of which shaft alloys and / or treatments are best suited to the task, the method of magnetizing shafts, the transfer functions necessary for interpreting the data, suitability for a Navy environment, and the scaling potential for the technology with respect to torque levels, shaft speed, applications, etc.

PHASE I: Phase I consists of laboratory scale experiments into the limits of sensitivity, time resolution and noise floor accompanied by a modest modeling effort to predict scalability and performance in specific applications. Investigate materials and magnetization methodology for various classes of applications. Model transfer functions necessary for sensing and data analysis. Develop an understanding of operating environment on performance of the proposed torque sensing approach.

PHASE II: Phase II consists of studies on actual machinery with simulated failures to validate the Phase I results under realistic conditions. For example, a motor-pump system where a motor bearing is replaced by bearings with various states of wear.

PHASE III: Installation of proof-of-principle torque sensors on in-service Navy machinery. Multiple platforms/applications shall be chosen for demonstration to validate performance and Naval value of the sensor technology.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Improved condition based maintenance (CBM) is an important goal in many areas of the private sector, especially in the manufacturing sector. Without CBM, either the equipment must be allowed to fail and the results of the failure dealt with or, if the consequences of failure are unacceptable, preemptive replacements of equipment or parts must be accomplished, even if the parts would have had substantial service life remaining. Obvious examples are pumps in municipal water systems, machine tools, vehicles, and construction equipment such as cranes.

REFERENCES:
1. Ivan J. Garshelis, Ryan J. Kari, and Stijn P. L. Tollens, "A Rate of Change Torque Sensor," IEEE Transactions on Magnetics 43, 2388 (2007).

2. Ivan J. Garshelis, Ryan J. Kari, Stijn P. L. Tollens, and James Cuseo, "Monitoring Cutting Tool Operation and Condition with a Magnetoelastic Rate of Change Torque Sensor," Journal of Applied Physics 103, 07E908 (2008).

3. MagCanica website, 18 September 2009: http://www.magcanica.com/rateofchange.html.

4. US Patent 7,330,602, "Production method for a magnetostrictive torque sensor"

5. I. J. Garshelis and C. A. Jones, "A torque transducer based on local bands of naturally stabilized remanent circumferential magnetization", Journal of Applied Physics 85, 5468 (1999).

KEYWORDS: condition based maintenance, torque sensors, failure sensing

Questions may also be submitted through DoD SBIR/STTR SITIS website.