Uncertainty evaluation of a 10N·m dead weight torque standard machine and comparison with a 1kN·m dead weight torque standard machine

A 10N·m dead weight torque standard machine (10-N·m-DWTSM) has been developed and evaluated since 2006 at the National Metrology Institute of Japan (NMIJ), a part of the National Institute of Advanced Industrial Science and Technology (AIST). Previously, the lengths of a moment arm, made of a low-thermal-expansion alloy (Super Invar), and the sensitivity limit of the fulcrum were evaluated. However, it is known that mechanical parts made of Super Invar vary in size with time. Therefore, the sensitivity limit of the fulcrum should be investigated under real calibration conditions. In this study, the moment arm lengths and the sensitivity limit of the fulcrum were re-evaluated. The moment arm lengths were found to have increased by an average of 6.3 μm in five years. The relative combined standard uncertainty of the moment arm length, w_arm, was re-evaluated in consideration of the uncertainty of the secular length change and was found to be 1.8 × 10⁻⁵. The sensitivity limit of the fulcrum was investigated by using a highly accurate, small-rated-capacity torque measuring device. The relative combined standard uncertainty due to the sensitivity limit of the fulcrum was 2.5 × 10⁻⁵ in the 0.1–10N·m torque range. The uncertainty budget table of the 10-N·m-DWTSM was completed. The relative expanded uncertainty of torque realized by the 10-N·m-DWTSM, W_tsm, was evaluated in the 0.1–10N·m torque range and was found to be 6.6 × 10⁻⁵, with a coverage factor, k, being equal to 2. In addition, the 10-N·m-DWTSM was compared with the existing 1-kN·m-DWTSM at NMIJ by using small-rated-capacity torque measuring devices at 5N·m and 10N·m torque steps. Two loading conditions were adopted in this comparison. The comparison results showed good agreement within the uncertainties in all cases. Thus, the torque realized by the 10-N·m-DWTSM was shown to be equivalent to that achieved by the 1-kN·m-DWTSM.     

Uncertainty evaluation of the 20 kN m deadweight torque standard machine

A deadweight-type torque standard machine of 20 kN m rated capacity (20 kN m-DWTSM) has been designed and developed by the National Metrology Institute of Japan (NMIJ) at the National Institute of Advanced Industrial Science and Technology (AIST). Each uncertainty contribution comes mainly from the performance of each mechanical part of the 20 kN m-DWTSM. Authors evaluated the uncertainty of the mass of the linkage weights, local acceleration of gravity, influence of air buoyancy on deadweight loading, initial moment-arm length (including CMM measurement and temperature compensation), and sensitivity of the fulcrum. This report deals especially with evaluation of the remaining contributions, namely the influence of arm flexure and reference line variation at the end of the moment-arm on best measurement capability (BMC). Estimation of BMC in the 20 kN m-DWTSM gave a relative expanded uncertainty of less than 7.0 · 10⁻⁵ (k = 2) for the calibration range from 200 N m to 20 kN m.     

Range expansion of the reference torque wrench calibration service to 5 kN m at NMIJ

The reference torque wrench (RTW) calibration service within the range from 5 N m to 1 kN m has been provided to industry by the National Metrology Institute of Japan (NMIJ) in the National Institute of Advanced Industrial Science and Technology (AIST). Reflecting the strong demand from Japanese industry, the calibration range was extended to 5 kN m. First, a high-precision torque transducer in the form of a torque wrench with a rated capacity of 5 kN m was developed in order to establish a calibration method for such a large RTW. Second, the calibration method was investigated using a deadweight type torque standard machine with a rated capacity of 20 kN m as a reference standard. Aimed expanded calibration range is from 200 N m to 5 kN m. As a result of calibration experiment using three transducers having different rated capacities, a relative expanded uncertainty of less than 7.0 × 10⁻⁵ could be obtained at a certain calibration point in the best case.     

NMC–NMIJ bilateral comparison of millimeter-wave attenuation in WR-15 waveguide band at 50 GHz and 54 GHz

This paper reports on a bilateral comparison of millimeter-wave attenuation in WR-15 waveguide band between the National Metrology Institute of Japan (NMIJ) and the National Metrology Centre, A1STAR (NMC). Different types of attenuation measurement systems were independently developed at both laboratories. The systems are based on a stabilized single-channel intermediate frequency (IF) substitution method at NMIJ, and a dual-channel audio frequency substitution method at NMC. A comparison was carried out at 50 GHz and 54 GHz using a programmable step attenuator fitted with precision coaxial to waveguide adaptors as a traveling standard. Good agreement of the measurement results between both laboratories was verified in the attenuation range up to 60 dB.     

A motorized 5 m tape comparator for traceable measurements of tapes and rules

A motorized 5 m tape comparator was constructed in TUBITAK UME for calibration of tapes and rules up to 5 m length in one set-up and further lengths in multiple set-ups. The system is a practical development and provides a cost effective solution for calibration of tapes in which the highest grade’s accuracy requirement in OIML R35-1 e.g. is 600 μm for 5 m length and 1100 μm for 10 m length. It is mainly composed of 6 m rail system, mechanical parts, optical units and an integrated 6 m incremental linear encoder as a reference measurement axis for traceable measurements. The rails are kinematically located on a heavy marble construction and a motorized carriage, which employs a camera for probing of the scales on the tapes, is moved along the rails during the measurement. The image of the scale taken by the camera is viewed on the monitor screen together with the running software. The operator can perform the probing process by simply moving the carriage over the measured scales (tapes or rules) using a joystick. The carriage movement is measured by the incremental linear encoder previously calibrated by a laser interferometer and the software automatically takes the measurement results from the incremental linear encoder, applies correction values previously defined and determines the length of the tapes and rules as well as deviations from nominal lengths. The estimated expanded uncertainty of the steel tape measurement is U = 54 μm in one set-up (for 5 m length) and U = 77 μm in two set-ups (for 10 m length) at the confidence level of approximately 95%. Uncertainty budget for calibration of the device itself and for calibration of the test tapes are explained in detail. The results of extensive experimental work and analysis are provided by demonstrating application of science and technology of measurement and instrumentation. Investigations for long term stability of the system are given with the reported test results for the years of 2003-2011 and participated intercomparison results to validate the device scientifically are illustrated.     

Evaluation of actual sensitivity limit in a 10 N·m dead weight torque standard machine and stability of a new 1 N·m torque transducer

A 10 N·m dead weight torque standard machine (10-N·m-DWTSM) has been under development at NMIJ/AIST since 2006 to expand the range of the torque standard. Estimation of the sensitivity limit of the fulcrum is one of the most important issues to realize a precise reference torque of small capacity by using a dead weight torque standard machine. In this study, a torque transducer was installed on the 10-N·m-DWTSM in order to keep the moment-arm on the horizontal line (balancing). The sensitivity limit of the fulcrum under real calibration conditions was estimated by reading the change in the output from the torque measuring device (TMD: the torque transducer with a cable and an indicating device) when small weights were loaded or unloaded. The small weights used in the experiment were 0.5 mg, 1 mg, 10 mg, and 100 mg. Equivalent radial loads from 0.1 N·m to 10 N·m were imposed on the fulcrum during the sensitivity measurement.     

1 Ω and 10 kΩ high precision transportable setup to calibrate multifunction electrical instruments

A temperature controlled 1 Ω and 10 kΩ transportable setup was developed at National Institute of Metrological Research (INRIM) for the calibration and adjustment of multifunction electrical instruments as digital multimeters (DMMs) and multifunction calibrators (MFCs). The two standards are made of two 10 Ω and 100 kΩ resistor nets connected in parallel and inserted in a temperature controlled aluminum structure. Novelties of the realization are the oil insertion of the 1 Ω net with the internal side of the connectors lowering the thermo-electromotive forces (EMFs) effects, and the possibility to know instantly the temperatures of the environment, of the internal of the structure and the last calibration values of the 1 Ω and10 kΩ standards. Short- and mid-term stabilities of the setup standards resulted on the order and in some cases better than other metrology-grade 1 Ω and 10 kΩ commercial items. The transport of the setup even turning off its temperature control did not cause appreciable measurement variations on the two standards. The standards uncertainties meet those requested by DMMs and MFCs manufacturers to calibrate and adjust these instruments. A test to adjust a MFC gave satisfactory results.     

Evaluation of moment arm length and fulcrum sensitivity limit in a 10 N·m dead weight torque standard machine

Many torque tools, such as torque wrenches and torque screwdrivers, as well as torque measuring devices (TMDs) with a rated capacity of less than 5 N·m are being widely used in industry. Thus, a small-rated-capacity torque standard has to be established as soon as possible. A 10 N·m dead weight torque standard machine (10 N·m DWTSM) has been under development since 2006 at the National Metrology Institute of Japan (NMIJ), part of the National Institute of Advanced Industrial Science and Technology (AIST). Characteristically, the main parts of the moment arm are made of low thermal-expansion alloy (Super INVAR), and an aerostatic bearing is employed as the fulcrum supporting the moment arm to minimize rotational friction. The moment arm was evaluated with regard to the coefficient of thermal expansion (CTE), the lengths measured by a 3D coordinate measurement machine (CMM), and temperature correction realized by measuring the moment arm temperature. The sensitivity limit of the fulcrum in the 10 N·m DWTSM was also estimated. As a result, the apparent overall CTE of the moment arm was 1.06 × 10⁻⁶ K⁻¹, and the expanded uncertainty was 2.24 × 10⁻⁹ K⁻¹ (k = 2). The results of the CMM measurement were a right-hand side length of 510.2773 mm and a left-hand side length of 510.2657 mm, with a relative expanded uncertainty of 4.0 × 10⁻⁵ (k = 2). The moment arm temperature increased by approximately 0.6 K during the ordinary calibration process. The corresponding change in the lengths of the moment arm was estimated to be approximately 0.3 μm, which is considered to be sufficiently small compared with the expanded uncertainty of the lengths of the moment arm. The fulcrum of the 10 N·m DWTSM was found to have sufficient sensitivity under three conditions: without the weight loading components, with the weight loading components, and with loaded weights. In particular, the fulcrum had sufficient sensitivity of at least 0.5 mg when weights of 100 g were loaded on both 5th stages in the weight loading components to generate a radial load equivalent to 1 N·m.     

International comparison of volume measurement for a 1 kg silicon sphere between KRISS and NMIJ

1 kg single-crystal silicon spheres are presently used as primary density standards in many countries. The absolute density of the spheres is determined from the measurements of their mass and volume in conformity with the definitions of the SI base units. Since the mass of the spheres is almost 1 kg, a mass comparison with the prototype of the kilogram can be performed with very low uncertainty. Absolute volume measurements for the spheres therefore have a crucial role in realizing a reliable density traceability system. To confirm the reliability of the volume measurement, the volume of a silicon sphere was measured independently using optical interferometers at the Korea Research Institute of Standards and Science (KRISS, Korea) and the National Metrology Institute of Japan (NMIJ, Japan). An optical interferometer with an etalon scanning system was used at KRISS. On the other hand, an optical interferometer with an optical frequency scanning system was used at NMIJ. The volume was measured at 20 °C and 0 Pa, and the results are in agreement with each other within their uncertainties. Details of the two interferometers and the comparison results are described.     

Tribological properties of polymer-sheet-adhered metal hybrid gear

A preliminary study was made on the tribology of nylon 66/poly(phenylene ether) polymer sheets adhered to steel gear teeth against a counter steel gear with reference to friction, surface morphology, noise reduction and torque in comparison with a pair of steel gears lubricated with molybdenum grease. Tribological experiments were performed in a gear-testing machine at a rotating speed of 1000 rpm under high torques of the driving and driven gears, recording torque of each gear and noise-frequency profiles. It was found that periodical torque changes in a range of 17–5 N m at 1000 and 3000 cycles (revolutions) turned to 13–8 N m at 5000 cycles, indicating a change to stable cycle and torque conduction, probably due to a plastic surface deformation of the adhered polymer sheet for a smooth contact of pairing teeth. A harsh noise emission in the frequency range of 3–5 kHz was reduced circa 5 dBA as compared with a pair of steel/steel gear. It was found, however, that noise abruptly increased when only one of the adhered polymer sheets was spontaneously removed from the gear surface, probably because of its low adhesive strength against a shear during gear cycle.     

High-precision and high-speed positioning of 100 G linear synchronous motor

The present paper describes a moving permanent magnet linear synchronous motor (MPM LSM) that can move with an acceleration above 100 G (=980 m/s²), and is also capable of high-precision and high-speed positioning. The MPM LSM consists of a mover including permanent magnets and a double-sided electromagnet stator. It can produce a thrust of 4.56 × 10³ N and has a working range wider than 1 m. The MPM LSM mover is improved for light weight and is driven using a suitable phase lead for flux weakening. The combination of the improved mover and the suitable phase lead provides motion at an acceleration above 100 G and a velocity above 12 m/s. The positioning characteristics of the improved MPM LSM are examined using a controller with two suitable phase lead functions. The control system shows a positioning accuracy and a positioning resolution of 500 nm, which is similar to the vibration amplitude of the sensor output in open loop. In 300-mm step positioning, the improved MPM LSM shows an acceleration above 660 m/s² and a velocity above 8.3 m/s. It takes less than 101 ms to reduce the positioning error to less than 5 μm. The temperature rise during positioning is also examined experimentally. Continuous positioning for longer than 30 minutes increases the temperature of the MPM LSM, but by less than 6 °C.     

On reliable measurement of micro drilling forces and identification of different phases

Mechanical micro-drilling process is often used in the manufacture of miniature components and molds. Frequent breakage of micro-drill is a major problem necessitating a thorough investigation into the process. One of the important responses measured during micro-drilling process is variation of thrust force and torque. Since the values of thrust force and torque are very low in micro-drilling, reliable measurements have to be carried out using high-resolution dynamometer. In the present work, micro-drilling is carried out using 0.5 mm diameter drill on Al 6061-T6 sheet of 3 mm thickness. The measurement results obtained from multi-component dynamometer are discussed first. Subsequently, a torque sensor mounted on the multi-component dynamometer is used to measure the torque, while the thrust force is acquired from latter. Since it is practically impossible to start acquiring the signals at a given time instant, the signals have to be synchronized in time domain using a novel signal processing technique. Different phases in micro-drilling, namely entry, full penetration and dwell are identified uniquely.     

Design and experimental evaluation of a precise and compact tubular ultrasonic motor driven by a single-phase source

A precise and compact tubular ultrasonic motor driven by a single-phase source is proposed and tested in this study. The motor is designed by modeling a motor stator in FEM software. The motor fabricated according to the design is tested experimentally and its working characteristics including speed and torque are measured and presented. The maximum speed and torque of the motor are 59 rpm and 0.28 mN m at 80 V_pp of applied voltage. The proposed motor possesses advantages such as a simple and compact structure with application in the fields of robotics, space, medical devices and high-resolution stages, among others. The proposed motor is a good candidate for applications where accurate control and high resolution at low speed is required.     

Atomic force microscope probe calibration by use of a commercial precision balance

In this paper, we investigate the characteristics of a piezoresistive AFM cantilever in the range of 0–1.6 μN by using nano force calibrator (NFC), which consists of a high precision balance with resolution of 1 nN and 1-D fine positioning stage. Brief modeling of the cantilever is presented and then, the calibration results are shown. Tests revealed a linear relationship between the probing force and sensor output (resistance change), but the force vs. deflection is not as linear as the force vs. sensor output curve. The force constant of the cantilever was measured to 0.26 N/m with a standard deviation of 0.01 N/m. It shows that there is big difference between measured and nominal spring constant of 1 N/m provided by the manufacturer’s specifications.     

Study of TiAlSiN coatings post-treated with N and C + N ion implantations. Part 2: The tribological analysis

Ion implantation has found to be an effective approach to modify surface properties of materials. The present research investigates the effect of (1) nitrogen (N), and (2) carbon subsequently with nitrogen (C + N) implantations on the mechanical and tribological properties of the titanium–aluminium–silicon–nitride (Ti–Al–Si–N) coatings. Superhard TiAlSiN coatings produced by magnetron sputtering, of approximately 2.5 μm thickness, were post-treated by implantations of N or C + N at an energy level of 50 keV. The dose range was between 5 × 10¹⁶ and 1 × 10¹⁸ ions cm^?2. After implantation, the tribological performance of the coatings was investigated by a ball-on-disk tribometer against WC–6 wt.%Co ball under dry condition in ambient air. The wear performance of the samples was examined by a variety of characterization techniques, such as secondary electron microscopy (SEM), 3D profilometry, atomic force microscopy (AFM), and micro-Raman. The results showed that the wear performance of the samples depended strongly on the implanted elements and doses. There was slight improvement on the samples implanted with N whereas significant improvement was found on the C + N implantations. Particularly, the friction coefficient of the sample with 5 × 10¹⁷ C⁺ cm^?2 and 5 × 10¹⁷ N⁺ cm^?2 could reach 0.1. In addition, the specific wear rate of the sample was extremely low (0.85 × 10^?7 mm³/Nm), which was nearly two orders of magnitude below that of the un-implanted coating. The speculation of the mechanical and tribological analyses of the samples indicates that the improvement of the N implanted and C + N implanted TiAlSiN samples could be due to a combined effect of improved hardness, plus enhanced adhesive and cohesive strength. In addition, the improved performance of the C + N implanted samples could be explained by the formation of lubricating implanted-layer, which existed mostly in sp² C–C and C–N forms. The formation of such implanted layer could lead to a change of wear mode from strong abrasive wear to mostly adhesive wear, and result in a drop of friction coefficient and wear rate.     

Tribological properties of Ni3Al produced by pressure-assisted volume combustion synthesis

The production of Ni₃Al was performed under an uniaxial pressure of 150 MPa at 1050 °C for 1 h. The formation temperature of Ni₃Al was determined to be 655 °C. The presence of Ni₃Al was confirmed by XRD analysis. SEM analysis revealed that the Ni₃Al phase has very low porosity. The relative density and microhardness of test materials were 97.8% and about 359±31 HV_1.0, respectively. The specific wear rate of Ni₃Al was 0.029 mm³/N m for 2 N, 0.017 mm³/N m for 5 N and 0.011 mm³/N m for 10 N, respectively. The distribution of alloying elements was determined by energy-dispersive spectroscopy (EDS).     

Effects of carbon fiber length on the tribological properties of paper-based friction materials

Four kinds of paper-based friction materials reinforced with carbon fibers of 100, 400, 600 and 800 μm were prepared by paper-making processes. Experimental results showed that the friction materials became porous with fiber length increasing. The friction torque curves were flat except the sample with 100 μm fibers. The wear rate of the sample with 100 μm fibers was only 1.40×10⁻⁵ mm³/J. Tiny debris and fine scratches formed in the worn surface were the reason for excellent wear resistance of friction pairs with 100 μm fibers. The friction pairs with 400, 600 and 800 μm fibers showed typically abrasive wear and fatigue wear.     

Machining with AlCr-oxinitride PVD coated cutting tools

AlCrO_xN_1−x coatings were arc deposited onto HSS drills and WC–Co end mills at N₂/O₂ ratios of 0.9–0.75 using DC or 10 kHz pulse bias. Lower O₂ content coatings had a hardness of 32.5 GPa. whereas 0.25 O₂ ratio coatings were 24–25 GPa. AlCrO_xN_1−x coated 6.35 mm Dia. HSS jobber drills were tested by drilling 2.5D holes in AISI D2. 10 kHz 0.9 N₂ 0.1 O₂ coatings drilled a mean of 17.6 holes/µm, similar to commercial AlCrN coated drills at 17.8 holes/µm, whereas DC 0.75 N₂ 0.25 O₂ coatings drilled 9 holes/µm. AlCrO_xN_1−x coated WC–Co end mills had low steady state wear in milling AISI 316L (70 m/min, MQL) and cut >24 m whereas uncoated tools cut 6 m. In contrast to drilling DC 0.75 N₂ 0.25 O₂ tools had the least corner wear and low adhesion on the rake face.     

Uncertainty analysis of slot die coater gap width measurement by using a shear mode micro-probing system

A shear mode micro-probing system was constructed for gap measurement of a precision slot die coater with a nominal gap width of 90 μm and a length of 200 mm. A glass micro-stylus with a nominal tip ball diameter of 52.6 μm was oscillated by a tuning fork quartz crystal resonator with its oscillation direction parallel to the measurement surfaces. An on-line qualification setup was established to compensate for the influences of the uncertainty sources, including the water layers on the measurement surfaces. The measurement uncertainty of the measured gap width was estimated to be less than 100 nm.