Harmonic drive gear error: Characterization and compensation for precision pointing and tracking

Imperfections and geometry effects in harmonic drive gear reducers cause a cyclic gear error, which at a systems level, results in high frequency torque fluctuations. To address this problem, gear error testing was performed on a wide variety of sizes and types of harmonic drives. It was found that although all harmonic drives exhibit a significant first harmonic, higher harmonics varied greatly with each unit. From life tests, small changes were found in harmonic content, phase shift, and error magnitude (on the order of .008 deg peak-to-peak maximum) occurred for drives with many millions of degrees of output travel. Temperature variations also influenced gear error. Over a spread of approximately 56 C (100 F), the error varied in magnitude approximately 20 percent but changes in a repeatable and predictable manner. Concentricity and parallelness tests of harmonic drive parts resulted in showing alignment influence gear error amplitude. Tests on dedoidaled harmonic drives showed little effect on gear error; surprisingly, in one case for a small drive, gear error actually improved. Electronic compensation of gear error in harmonic drives was shown to be substantially effective for units that are first harmonic dominant

BEYOND BUDGET RATIONALITIES: THE SOCIAL STRUCTURE OF PERFORMANCE BUDGETING AND ITS INDIRECT EFFECTS ON ORGANIZATIONAL PERFORMANCE WITHIN PUBLIC ORGANIZATIONS

Performance based budgeting reform in its latest stage continues to evolve after resurgence in popularity resulting from the Clinton Administration's National Performance Review and the international new public management (NPM) movement. Performance based budgeting is sometimes viewed with skepticism for various reasons including the capacity to determine and collect performance information, the veracity of performance information, and efficacy in terms of performance budgeting's ability to improve performance. The majority of performance based budgeting studies focus on the prevalence of performance budgeting in government jurisdictions, and whether or not performance based budgeting influences resource decision making. Few, if any studies focus on whether performance based budgeting actually influences organizational effectiveness or performance, for which performance based budgeting was intended. This study intends to observe whether certain organizational characteristics associated with performance budgeting indirectly affect organizational performance. While organizational performance can also be observed through performance measures and bench marks, individual and organizational perceptions are equally important for gauging organizational performance. In doing so, this study applies an alternative approach to observe the indirect effects associated with performance based budgeting. The paradigm for public budgeting theory is the budget rationalities theory that describes budgeting's bargaining, negotiating, and control processes. However, a large portion of budgeting behavior linked to organizational performance may occur outside of the budget rationalities construct. This study proposes there is a second layer of budgeting; a management layer of budgeting focused on different priorities than those within the budget rationalities construct, and applies economic sociology theory to explain budgeting behavior in this management layer of budgeting. Data Collected from the NASP - IV, National Administrative Studies Project is used to test one research question and three hypotheses. Results confirm the existence of performance budgeting's indirect effects on organizational performance, where information sharing and certain characteristics of trust moderate performance budgeting's influence on organizational performance. The results suggest that average and high performing organizations benefit the most from implementing performance budgeting. The study concludes with recommendations for potential approaches for further research

On the Design Optimisation of Direct Energy Deposited Support Structures to Repair Aero-Engine Turbine Segments

A novel approach for down-selection of a repaired support structure design produced using Laser Blown Powder – Direct Energy Deposition (LBP-DED) and filled with interstitial Ni-Al powder (∼0.75 area fraction) in a turbine segment was investigated. Simulation of flattening and un-flattening of the segment with implications to degradation of the support structure was quantified using a four-point bend test to identify the role of axial Young’s modulus in out-of-plane flexure. Two markedly different LBP additive structures; Diamond Lattice (DL) - nodal and Continuous Path (CP) – non-nodal, were produced and compared with the un-repaired condition. At room temperature, the forward and rear walls and internal nodes of the original equipment (OE) and DL support structures were found to contribute significantly to the Young’s modulus, with significantly reduced stiffness observed in the CP structures. Oxidation plays a key role in the development of internal compressive stresses within the abradable, with a two-fold increase in elastic modulus in the CP structure, but a smaller increase occurred in OE and DL support structures. A decrease in elastic modulus and concomitant increase in radius of curvature (flattening) occurred with an increasing number of flexural cycles. Cracking is most prominent in the nodal design within the front and rear walls and cracks propagate either to the surface or towards the base of the abradable lattice. No such degradation was observed for equivalent flexural cycles in the original and CP support structures, even up to a significant number of cycles. A criterion for catastrophic failure of the abradable was deduced from a steep decrease in flexural elastic modulus accompanied with a marked change in curvature. A non-nodal design support structure is optimum to counter in- service flattening/un-flattening

Computational and experimental investigation of the strain rate sensitivity of small punch testing of the high-entropy alloy CoCrFeMnNi

The suitability of determining the strain rate sensitivity (SRS) of the CoCrFeMnNi high-entropy alloy (HEA) by small punch (SP) testing has been assessed at displacement rates ranging from 0.2 to 2 mm∙min-1. The stress was found to increase as the displacement rate was raised from 0.2 to 2 mm∙min-1, whereas the plastic strain distributions were similar in all cases. However, for a higher displacement rate of 10 mm∙min-1, the sample was found to exhibit a drop in strength and ductility attributed to casting defects. The strain-rate sensitivity exponent (m) was found to be 0.1387 whilst the Finite Element Analysis (FEA) simulations predicted a slightly smaller value of 0.1313. This latter value is closer to m = 0.091 obtained from nanoindentation strain rate jump tests since the results are insensitive to the presence of small casting defects. The relationship between the experimental and the empirically derived predicted properties from the SP tests revealed a high level of agreement for maximum stress properties. The properties predicted at 2 mm∙min-1 (R2 = 0.96) offered a stronger fit than at 0.5 mm∙min-1 (R2 = 0.92)

Ariel - Volume 3 Number 8

Editors Richard J. Bonanno Robin A. Edwards Associate Editors Steven Ager Tom Williams Lay-out Editor Eugenia Miller Contributing Editors Paul Bialas Robert Breckenridge David Jacoby Mike LeWitt Terry Burt Michael Leo Editors Emeritus Delvyn C. Case, Jr. Paul M. Fernhof