Fiber deflection probe for small hole metrology

This paper presents the development of a new probing method for coordinate measuring machines (CMM) to inspect the diameter and form of small holes. The technique, referred to as fiber deflection probing (FDP), can be used for holes of approximately 100 μm nominal diameter. The expanded uncertainty obtained using this method is 0.07 μm (k = 2) on diameter. The probing system consists of a transversely illuminated fiber (with a ball mounted on the end) whose shadows are imaged using a camera. We can infer the deflection of the probe from the motion of the image seen by the camera, and we infer the position of the measured surface by adding the fiber deflection along x- and y-directions to the machine scale readings. The advantage of this technique is the large aspect ratio attainable (5 mm deep for a 100 μm diameter hole). Also, by utilizing the fiber as a cylindrical lens, we obtain sharp crisp images of the fiber position, thus enabling high resolution for measured probe deflection. Another potential advantage of the probe is that it exerts an exceptionally low force (ranging from a few micronewtons down to hundreds of nanonewtons). Furthermore, the probe is relatively robust, capable of surviving more than 1 mm over-travel, and the probe should be inexpensive to replace if it is broken. In this paper, we describe the measurement principle and provide an analysis of the imaging process. Subsequently, we discuss data obtained from characterization and validation experiments. Finally, we demonstrate the utility of this technique for small hole metrology by measuring the internal geometry of a 129 μm diameter fiber ferrule and conclude with an uncertainty budget.     

A dual-purpose positioner-fixture for precision six-axis positioning and precision fixturing: Part II. Characterization and calibration

The kinematics, stiffness, and repeatability of a moving groove, dual-purpose positioner-fixture were determined experimentally. A dual-purpose positioner-fixture is an alignment device that may be operated in a fixture mode or a six-axis nanopositioning mode. When operated in fixture mode, experiments show standard deviation in repeatability of 11, 11, and 38 nm in x, y, and z; and 0.7, 0.3, and 0.3 μrad in θ_x, θ_y, and θ_z. The stiffness characteristics were shown to match predictions within 5%. When operated in nanopositioner mode, the device demonstrated 4 nm resolution and a range, of 40 μm × 40 μm × 80 μm in translation and 800 μrad × 800 μrad × 400 μrad in rotation. The fixture possesses a load capacity of 450 N and a natural frequency of 200 Hz when the fixture is preloaded to 225 N.     

Defect characterization of roller bearing surfaces with laser Doppler vibrometry

Laser Doppler vibrometry is presented as an effective method of surface profile measurement and surface crack detection in rolling bearing balls. For both inspections, a surface velocity profile is used in addition to surface displacement profile. An experimental setup and a signal-processing algorithm are used to obtain digitized surface profiles and power spectral density measurements of ball surfaces. Profile measurements are presented that match lobed ball frequency results with a resolution of 0.025 μm. Velocity measurement provides a much higher bandwidth for defect detection. Cracks down to 22 μm in width can be detected with a 150 μm by 500 μm wide laser spot size. Cracks smaller than 22 μm can be detected by decreasing the laser spot size. The method is well suited for a manufacturing environment because of its durability, simplicity, and high speed.     

Surface profile measurement of a sinusoidal grid using an atomic force microscope on a diamond turning machine

This paper describes the surface profile measurement of a XY-grid workpiece with sinusoidal microstructures using an atomic force microscope (AFM) on a diamond turning machine. The sinusoidal micro-structures, which are fabricated on an aluminum plate by fast tool servo-assisted diamond turning, are a superposition of periodic sine-waves along the X- and Y-directions (wavelength (XY): 150 μm, amplitude (Z): 0.25 μm). A linear encoder with a resolution of 0.5 nm is integrated into the AFM-head for accurate measurement of the Z-directional profile height in the presence of noise associated with the diamond turning machine. The spindle and the X-slide of the machine are employed to spirally scan the AFM-head over the sinusoidal grid workpiece. Experiments fabricating and measuring the sinusoidal grid workpiece are carried out after accurate alignment of the AFM cantilever tip with the spindle centerline.     

Design of a six-axis micro-scale nanopositioner—μHexFlex

This paper presents the design of a small-scale nanopositioner, the μHexFlex, which is comprised of a six-axis compliant mechanism and three pairs of two-axis thermo-mechanical micro-actuators. In this paper, we cover the modeling, design and fabrication of the μHexFlex. Specific attention is given to: (1) the use of constraint-based design in generating the compliant mechanism design, (2) the modeling of the actuators, and (3) the system model which links the actuator input and mechanism response. The measured, quasi-static performance of a 3 mm diameter prototype shows a maximum range of 8.4 μm × 12.8 μm × 8.8 μm and 19.2 mrad × 17.5 mrad × 33.2 mrad (1.1° × 1.0° × 1.9°). Experimental results indicate that a constant mechanical/electrical material property system model may be used to predict the position and orientation over a range of 3.0 μm × 4.4 μm × 3.0 μm and 6.3 mrad × 6.3 mrad × 8.7 mrad (0.36° × 0.36° × 0.5°). The dynamic characteristics of the device were investigated experimentally. Experimental results show a lowest natural frequency of 4 kHz. The resolution characteristics of the device have been measured at 1 Å/mV. The device was created using deep reactive ion etching (DRIE). Bulk fabrication costs are estimated at less than $ 2 per device.     

Precision surface finish of the mold steel PDS5 using an innovative ball burnishing tool embedded with a load cell

A load-cell-embedded burnishing tool has been newly developed and integrated with a machining center, to improve the surface roughness of the PDS5 plastic injection mold steel. Either the rolling-contact type or the sliding-contact type was possible for the developed ball burnishing tool. The characteristic curves of burnishing force vs. surface roughness for the PDS5 plastic injection mold steel using the developed burnishing tool for both the rolling-contact type and the sliding-contact type, have been investigated and constructed, based on the test results. The optimal plane surface burnishing force for the PDS5 plastic injection mold steel was about 420 N for the rolling-contact type and about 470 N for the sliding-contact type, based on the results of experiments. A force compensation strategy that results in the constant optimal normal force for burnishing an inclined surface or a curved surface, has also been proposed to improve the surface roughness of the test objects in this study. The surface roughness of a fine milled inclined surface of 60 degrees can be improved from R_a 3.0 μm on average to R_a 0.08 μm (R_max 0.79 μm) on average using force compensation, whereas the surface roughness was R_a 0.35 μm (R_max 4.56 μm) on average with no force compensation.     

Design and construction of a two-degree-of-freedom linear encoder for nanometric measurement of stage position and straightness

This paper presents a two-degree-of-freedom (two-DOF) linear encoder which can measure the position along the moving axis (X-axis) and the straightness along the axis vertical to the moving axis (Z-axis) of a precision linear stage simultaneously. The two-DOF linear encoder is composed of a reflective-type scale grating and an optical sensor head. A reference grating, which is identical to the scale grating except the scale length, is employed in the optical sensor head. Positive and negative first-order diffracted beams from the two gratings are superposed with each other in the optical sensor head to generate interference signals. The optical configuration is arranged in such a way that the direction of displacement in each axis can also be detected. A prototype two-DOF linear encoder is designed and constructed. The size of the optical sensor head is about 50 mm (X) × 50 mm (Y) × 30 mm (Z) and the pitch of the grating is 1.6 μm. It has been confirmed that the prototype two-DOF linear encoder has sub-nanometer resolutions in both the X- and Z-axes.     

Ball array calibration on a coordinate measuring machine using a gage block

The distances between the balls of a ball array used in machine geometry calibration have to be very accurate. These distances can be calibrated using a laser measurement system, which requires specially designed optical devices and measuring probes. In this paper, a new and economical alternative method for calibrating the ball array is described. A single gage block is used for measuring the standard distance at the starting position. Then, the exact distances between the balls can be obtained by using the coordinate measuring machine (CMM) probe motion. This method does not depend on the accuracy of the CMM. Also, this method does not require expensive instruments or devices, but a CMM and a gage block. A simple “parallel-plane” bracket, mounted on to the measuring end of a CMM probe, is used to determine the centers of the balls automatically and accurately.     

Micro-structuring of glass with features less than 100 μm by electrochemical discharge machining

Micro-electrochemical discharge machining (ECDM) was studied in order to improve the machining of 3D micro-structures of glass. To minimize structures and obtain good surface microstructures, the effects of the electrolyte, the pulse on/off-time ratio, the voltage, the feedrate, the rotational speed, and the electrolyte concentration in the drilling and milling processes were studied.In ECDM, voltage is applied to generate a gas film and sparks on a tool electrode; however, high voltage produces poor machining resolution. To obtain a stable gas film over the whole surface of the tool at a low voltage, a new mechanical contact detector, based on a loadcell, was used; the immersion depth of the tool electrode in the electrolyte was reduced as much as possible. In this study, various micro-structures less than 100 μm in size, such as Ø 60 μm micro-holes, a 10 μm-thin wall, and a 3D micro-structure were fabricated to demonstrate the potential for micro-machining of glass by ECDM.     

Comparison between precision roughness master specimens and their electroformed replicas

Two random profile precision roughness calibration specimens with R_a = 0.028 and 0.043 μm are compared with their electroformed replicas. Measurements of surface texture and roughness parameter values show very good agreement. Fluctuations in the R_a values across the replicas track those across the masters to within 1.8 nm. However, the form errors of the replicas, approximately 0.6 μm over a 3.2 × 2.6 mm² area, are much bigger than those of the masters, and their hardness (HV = 243) is not as good as the master specimens' (HV = 852).     

Shape measurement of long microbores applying photon counting method

New technology, especially in the field of microelectronics and mechatronics, created the need for making, positioning and inspection techniques of long microbore-holes and gaps (defined by length/width to diameter ratio l/d > 10 for d < 200 μm). The technological aspect is, in principle, subdued but the metrological one is still unsolved.In Zosel et al. [Zosel J, Guth U, Thies A, Reents B. Flow measurements in micro holes with electrochemical and optical methods. Electrochim Acta 2003;48:3299–305] the properties (power loss and phase distortion) of focused laser microbeam penetrating extremely long through microbores is described; it was proved that the measurement information is distorted depending on the microbore geometry. The samples were prepared of glass–resin laminate with microbore diameter ranging from 35 to 200 μm.In present research an adjustable 100 μm microbore is used as a master. It is formed of mutually accurately adjusted 20 metal plates 100 μm thick set of coaxially in pile. Precise positioning of each plate enables creating free-shaped microbore.The photon batching device emitting 2.5 million photons per second is used as a generator of incident photon beam. The measured transmission efficiency is understood as a relation between outgoing and incoming light energy. The outgoing energy, for particular microbore, was determined by scanning linearly and angularly the bore with photon beam and integrating the results. Experiments were performed in dark room with background 2/5 photons per second (including dark current of photomultiplier).These changes describe the relationship between the shape of the microbore and the transmission energy and can be considered as a measure of microbore cylindricity deviation.     

Diagonal in space of coordinate measuring machine verification using an optical-comb pulsed interferometer with a ball-lens target

This paper presents a new optical method of coordinate measuring machine (CMM) verification. The proposed system based on a single-mode fiber optical-comb pulsed interferometer with a ball lens of refractive index 2 employed as the target. The target can be used for absolute-length measurements in all directions. The laser source is an optical frequency comb, whose repetition rate is stabilized by a rubidium frequency standard. The measurement range is confirmed to be up to 10 m. The diagonals of a CMM are easier to verify by the proposed method than by the conventional artifact test method. The measurement uncertainty of the proposed method is also smaller than that of the conventional method because the proposed measurement system is less affected by air temperature; it achieves an uncertainty of approximately 7 μm for measuring lengths of 10 m. The experimental results show that the measurement accuracy depends on noise in the interference fringe, which arises from airflow fluctuations and mechanical vibrations.     

Suspension of molybdenum–sulphur complexes in paraffin oil as extreme pressure lubricants

Molybdenyl aryl thiobiurets were evaluated as extreme pressure lubrication additives in a four ball test using steel balls of 12.7 mm diameter. A comparative account of performance of the tested compounds is presented on the basis of various tribological parameters such as initial seizure load, 2.5 s seizure delay load, weld load, mean Hertz load, flash temperature parameter, pressure wear index, friction coefficient (μ) and wear scar diameter (d), etc. All the tested complexes have been found to possess significant Extreme Pressure (EP) efficiency under the experimental conditions of four ball test. The best performance was shown by p-methoxyphenyl and p-chlorophenyl thiobiurets. The surface topography and tribochemistry of wear scar surface of balls in the presence of p-methoxyphenyl derivative at different loads have been studied by scanning electron microscopy and Auger Electron Spectroscopy (AES). The presence of molybdenum, sulphur, oxygen, nitrogen, etc. on the ball surface, detected by AES, suggests that these compounds act as precursors of tribologically active chemical layers formed under extreme pressure conditions.     

Measurement of lathe Z-slide straightness and parallelism using a flat land

A method is described to measure the straightness of travel of the carriage of a single-point diamond turning machine. The method also measures the slide parallelism to the workhead spindle. A cylindrical artifact was produced on the lathe and used as a straightedge. A flat land was cut in the artifact that was parallel to the workhead axis of rotation. The flat land was measured with a LVDT indicator. The method was demonstrated on a Moore Special Tool Co. M18 Aspheric Generator. The quality of measurements achieved were better than 0.1 μm.     

Precision nano-fabrication and evaluation of a large area sinusoidal grid surface for a surface encoder

This paper describes the fabrication of a large area sinusoidal grid surface, which is used as the measurement reference of a surface encoder for multi-axis position measurement. The profile of the grid surface is a superposition of sinusoidal waves in the X-direction and the Y-direction with spatial wavelengths of 100 μm and amplitudes of 100 nm. Diamond turning with a fast tool servo (FTS) was chosen as the fabrication method. The constructed FTS, which employs a piezoelectric tube actuator (PZT) to actuate the diamond tool and a capacitance probe as the feedback sensor, was confirmed to have a bandwidth of approximately 2.5 kHz and a tool displacement accuracy of several nanometers in the closed-loop mode. Experiments of fabricating the sinusoidal grid surface were performed on a commercially available precision diamond turning machine. An aluminum alloy workpiece was vacuum chucked on the spindle and the FTS was mounted on the X-slide. Efforts were made to position the tool tip to the center of the spindle (center-alignment) since it was verified that the center-alignment is important for the fabrication accuracy of the sinusoidal grid surface. An evaluation technique based on the two-dimensional (2D) discrete Fourier transform (DFT) of interference microscope images was also developed to evaluate the fabricated grid surface effectively. The fabrication result of a grid surface over an area of 150 mm has indicated the effectiveness of the fabrication system.     

Measurement and compensation of error motions of a diamond turning machine

This paper describes the measurement and compensation of error motions of a diamond turning machine for nanofabrication of large sinusoidal metrology grids. The diamond turning machine has a T-base design, which consists of a spindle with its rotation axis along the Z-direction and a cross-slide with its movement direction along the X-direction. A fast-tool-servo (FTS) unit is mounted on the X-slide to generate sinusoidal microstructures on a flat workpiece surface mounted on the spindle. The error motions of the X-slide and the spindle, which introduce Z-directional profile errors (out-of-flatness) on the grid surface, are measured and compensated. The out-of-straightness of the X-slide is measured to be approximately 60 nm over a travel of 80 mm by using the reversal method. It is also confirmed that the out-of-straightness of the X-slide has a 10-nm periodic component with a period of 11 mm corresponding to the diameter of the needles used in the roller bearing of the X-slide. The angular motion of the spindle is measured to be approximately 0.3″ by using an autocollimator, which can cause a 73-nm out-of-flatness over a workpiece 100 mm in diameter. The axial motion of the spindle is measured to be approximately 5 nm, which is the smallest error motion. The out-of-flatness of the workpiece is reduced from 0.27 to 0.12 μm through compensating for the error motions by utilizing the FTS unit based on the measurement results of error motions.     

Design of high-precision ball screw based on small-ball concept

This paper addresses a design method of ball screws for high-precision feed drives of machine tools. The torque fluctuation of a ball screw influences position deviation, which deteriorates the contorting accuracy. The torque fluctuation comes from the load change of the contacting balls between the nut and the screw shaft during ball circulation. In order to decrease the load change, a ball screw that employs smaller balls was designed and evaluated in the measurement tests. The experimental results showed that the designed ball screw could decrease both the torque fluctuation and position deviation.     

Fabrication of various tip-size AFM probes for evaluating single-molecular retraction force between actin and anti-actin

The authors fabricated a probe tip with various sizes and examined the size dependency of the probe tip on the distribution of retraction forces between actin and anti-actin. Probe tips of various sizes were fabricated by two-photon polymerization methods on a micro cantilever of an atomic force microscope (AFM). The authors succeeded in fabricating a spherical tip having a smooth surface and the tip size varied between φ 0.8 and 5.5 μm. Anti-actin was immobilized on the fabricated probe tips and force curves were measured against an actin-immobilized mica substrate by AFM to analyze the retraction forces. The histograms of retraction forces showed that the single-molecular retraction force between actin and anti-actin was ca. 350–400 pN. It was observed that the average retraction forces for each tip size correlated with the square of the tip radius.     

A low cost, high accuracy roundness measuring system

This work presents a new architecture of a roundness measuring system in which the roundness measuring accuracy is not dependent on motion accuracy of the rotary element. In this architecture, the influence of motion errors on roundness measurement is minimized by applying a new error separation technique developed by Horikawa et. al. [1 and 2], the improved Reversal Method — IRM. A prototype that uses: a rotary table supported by ball bearings, non-contact gap sensors and a computer system that collects and process sensor readings has been developed. Experimental results have shown that even using a rotary table supported by ball bearings, that has non-repetitive motion errors larger than 2μm, the final measurement repeatability is better than 0.3μm of peak-to-peak value. In order to ensure the same levels of accuracy of the proposed system, a traditional roundness measuring system design must use a more precise and therefore more expensive type of bearing with a motion error no larger than 0.1μm.     

Development of a microgripping system for handling of microcomponents

This paper reports the development of a semi-automatic microgripping system that consists of a microgripper and an x, y, z positioning system. The microgripper has two 1DOF fingers fabricated by an amorphous, soft magnetic material and is actuated electromagnetically. The microgripper is embedded in the 3DOF positioning system with the help of a stainless steel holder under an angle, which is manually adjusted, in respect to the working field. The position of the microgripper is observed optically and by three digital indicators¹ from Mitutoyo, which offer easy reading and continuous position tracking. All axes are actuated by step motors which allow precise positioning of the microparticles under manipulation. The microgripping system was tested in pick and place cases, under an optical microscope in atmospheric conditions. Optical fibres (125 μm in diameter) and bonding wires (50 μm in diameter) were handled. The temperature on the actuator, on the microgripper fingers and on the microgripper tips during manipulation was measured using K type (Ni/CrNi) thermocouples. The gripping force was evaluated as well.