Confocal probes, which consists of a point light source and a point detector, have been widely used in the manufacturing industry for a surface profile measurement of a measurement target object. In recent years, a mode-locked laser, which has advantages; high-stable optical frequency and wide-range optical frequency, and high-stable intensity, has been employed as a light source of the confocal probes, enabling to non-scanning and precise height measurement. However, a non-smoothness of the optical spectrum of the mode-locked laser affects a confocal response curve, which is utilized for the target position measurement, and leads to loss of the measurement accuracy. Therefore, a dual-detection chromatic confocal probe has been proposed and researched to reduce the effects of the non-smoothness optical spectra. In this paper, a review about the dual-detection chromatic confocal probe is summarized.
Methods of using optical frequency comb for angle measurement are discussed. Autocollimation is the most commonly used method for angular displacement measurement. Here, a diffraction grating is attached to the measurement target instead of a mirror, which is used in the conventional autocollimation method. Each mode of the optical frequency comb with a wide wavelength bandwidth is angularly dispersed by the grating. The angular displacement of the target is determined from the most strongly detected optical frequency modes.
This paper presents a fabrication method of two-dimensional micro patterns for adaptive optics with a micrometric or sub-micrometric period to be used for fabrication of micro lens array or two-dimensional diffraction gratings. A multibeam two-axis Lloyd’s mirror interferometer is employed to carry out laser interference lithography for the fabrication of two-dimensional grating structures. In the proposed instrument, the optical setup consists of a light source providing a laser beam, a multi-beam generator, two plane mirrors to generate a two-dimensional XY interference pattern and a substrate on which the XY interference pattern is to be exposed. In this paper, pattern exposure tests are carried out by the developed optical configuration optimized by computer simulations. Some experimental results of the XY pattern fabrication will be reported.
A multiprobe surface encoder for optical metrology of six-degree-of-freedom (six-DOF) planar motions is presented. The surface encoder is composed of an XY planar scale grating with identical microstructures in X- and Y-axes and an optical sensor head. In the optical sensor head, three paralleled laser beams were used as laser probes. After being divided by a beam splitter, the three laser probes were projected onto the scale grating and a reference grating with identical microstructures, respectively. For each probe, the first-order positive and negative diffraction beams along the X- and Y-directions from the scale grating and from the reference grating superimposed with each other and four pieces of interference signals were generated. Three-DOF translational motions of the scale grating Δx, Δy, and Δz can be obtained simultaneously from the interference signals of each probe. Three-DOF angular error motions θX, θY, and θZ can also be calculated simultaneously from differences of displacement output variations and the geometric relationship among the three probes. A prototype optical sensor head was designed, constructed, and evaluated. Experimental results verified that this surface encoder could provide measurement resolutions of subnanometer and better than 0.1 arc sec for three-DOF translational motions and three-DOF angular error motions, respectively.
A nanopipette ball probe has been introduced for the dimensional measurement of the micrometer-scale structures. A hollow glass nanopipette, which is fabricated by thermal pulling process, is used as the shaft of the probe for the detection of the contact. Since the stiffness of the glass nanopipette is lower than that of metal shaft which is similar size of the glass nanopipette, the contact force between the probe and the sample will be able to reduce in comparison with the probe of the metal shaft. The edge of the nanopipette is filled with the thermosetting resin, and a micro glass sphere with 9 mm diameter is fixed on the edge of the nanopipette probe by the thermosetting resin. By attaching the micro sphere at the edge of the nanopipette, the edge of the probe will be possible to maintain a uniform shape in all directions. With regard to the detection of the contact, the method of the shear-force detection has been employed because of its high-sensitivity and nanometer-scale resolution. The resolution and the sensitivity of the nanopipette probe are evaluated, and then surface profile measurement of the microstructure is demonstrated.
For measuring the surface profile of many micro-optical components which are made of non-conductive material, such as diffractive grating and Fresnel lens, with complicated shapes on their surfaces, the electrostatic force microscopy (EFM) was recommended in noncontact condition. When a bias voltage is applied between the conducting probe tip and a back electrode where a non-conducting sample was put on, an electrostatic force will be generated between the probe tip and the sample surface. The electrostatic force will change with the distance between the probe tip and the sample surface. Firstly, the relationship between the electrostatic force and the tip-sample distance was analyzed based on the dielectric polarization theory. The theoretical result shows that the electrostatic force is proportional to 1/d2, where d is the distance between the probe tip and sample surface. Then, a numerical method (finite element method -FEM) was employed to calculate the electrostatic force and the result shows accordance with the theoretical method. Finally, the prototype of a scanning electrostatic force microscopy was built which is composed of a conducting probe unit with a Z scanner driven by piezoelectric actuators, a XY scanner unit for mounting the sample and back electrode and a circuit unit for detecting the frequency shift. The force curve, which shows the relationship between the electrostatic force and the tip-sample distance, was achieved by using the EFM prototype. All results demonstrated that it is feasible for using the EFM system to measure the surface profile of non-conductor.
This keynote starts from an overview of micro-optics from fundamental functions, fabrication methods and applications
in precision engineering and nanotechnology. State-of-the-art measuring systems for surface form metrology of microoptics
with micro-structured surfaces, including diffractive micro-optics such as diffraction gratings and refractive
micro-optics such as micro lenses and micro-lens arrays, are then be presented. The measuring systems introduced in the
presentation are classified into scanning probe microscope-based systems, mechanical stylus profiling systems and
optical evaluation systems. Related research activities carried out in the authors' group are also highlighted.
To fabricate a scale grating for a surface encoder in a cost-effective way, a blue laser diode with a wavelength of 405 nm is employed in a Lloyd’s mirror interferometer to carry out interference lithography (IL) of the grating. The beams from the laser diode are collimated by an aspherical collimating lens to form beams with a diameter of 50 mm. These beams are then projected towards the Lloyd’s mirror and the grating substrate, which are aligned perpendicularly with each other and are mounted on a rotary stage. One half of the beam directly goes to the grating substrate, and the other half reaches to the grating substrate after being reflected by the mirror. The direct beam and the reflected beam interference with each other to generate and expose the interference fringes, which correspond to the scale grating structures, on the substrate coated with a photoresist layer. The pitch and area of the grating structures are set to be 570 nm and around 300 mm2, respectively. The fabricated grating structures are evaluated with an AFM to investigate the influence of the spectrum width of the laser beam.
This paper presents the analysis of a prototype scanning electrostatic force microscope (SEFM) system developed for noncontact surface profile measurement. In the SEFM system, with a dual height method, the distance between the probe tip and the sample surface can be accurately obtained through removing the influence of the electric field distribution on the sample surface. Since the electrostatic force is greatly influenced by the capacitance between the probe tip and the sample surface, a new approach for modeling and analysis of the distribution of capacitance between the probe tip with an arbitrary shape and the sample surface with a random topography by using the finite difference method (FDM) is proposed. The electrostatic forces calculated by the FDM method and the conventional sphere-plane model are compared to verify the validity of the FDM method. The frequency shift values measured by experiment are also compared with the simulation results computed by the FDM method. It has been demonstrated that the electrostatic force between arbitrary shapes of the probe tip and the sample surface can be well calculated by the finite difference method.
This paper presents a micro-stylus probe, which is composed of a precision glass micro-ball and a shaft made by a glass
tube. The diameter of the micro-ball was 50 μm. The tip angle of the glass-tube shaft was approximately 10 degrees.
Strength test shows that the tolerance of glass tube micro-stylus against external forces is 90 mN. To reduce the stick-slip
phenomena, a micro-tapping probe employing the glass tube micro-stylus and a PZT actuator was demonstrated. The
micro-stylus probe was mounted to an air-bearing displacement sensor for scanning surface form metrology.
Experimental results showed that the micro-tapping probe was effective for reducing the influence of the stick-slip
phenomena.
This paper presents a linear-rotary micro-stage that can generate motions along and about the Z-axis using piezoelectric
elements (PZTs). The small stroke of a PZT is extended by repeating the PZT motions based on a mechanism of impact
friction drive. The friction drive mechanism has a simple driving unit, which only consists of a PZT element and a
friction element. The moving element of the stage, which is a steel cylinder, is supported and actuated by a driving unit,
which consists of two PZTs and a friction component made by permanent magnet. The magnetic force is employed for
holding the moving element and stabilizing the driving condition. The dimension of the stage is 7.0 mm × 8.8 mm × 7.5
mm. The moving ranges of the stage are about 5.0 mm in the Z-direction and 360 degrees in the θz-direction,
respectively. The maximum moving speeds are approximately 30 mm/s and 84 rpm in the two directions, respectively.
Scroll compressors are widely used in air conditioner compressor, vacuum pump and so on. Profile measurement of a
scroll compressor is important for improving compression efficiency. This paper describes the involute profile
measurement of a scroll compressor by using r-&Tgr; measurement system for the manufacturing line. Involute profile
measurement system consists of X-Z-&Tgr; stage and contact type scanning probe. Scanning probe draws Archimedean spiral
locus by X-&Tgr; stage. Output of scanning probe includes profile error and difference of Archimedean spiral and involute.
To confirm that influence of coordinate system error, simulation was carried out. It was confirmed that profile
measurement error was a one tenth or less compared with the rotation setting error of work piece. From the simulation
result of Y-directional offset between rotation center of &Tgr; stage and center of probe sphere, to achieve the required
accuracy of profile measurement, it is necessary to reduce or measure the probe alignment error to under the required
accuracy order. Fixed scroll outside-involute profile error is measured by developed measurement system. The difference
from CMM result is seen in the center part. It is caused by residual Y directional alignment error of scanning probe.
Excluding the center part, measurement result is corresponding to CMM result.
Single crystal diamond tools are used for fabrication of precision parts [1-5]. Although there are many types of tools that
are supplied, the tools with round nose are popular for machining very smooth surfaces. Tools with small nose radii,
small wedge angles and included angles are also being utilized for fabrication of micro structured surfaces such as microlens
arrays [6], diffractive optical elements and so on. In ultra precision machining, tools are very important as a part of
the machining equipment. The roughness or profile of machined surface may become out of desired tolerance. It is thus
necessary to know the state of the tool edge accurately. To meet these requirements, an atomic force microscope (AFM)
for measuring the 3D edge profiles of tools having nanometer-scale cutting edge radii with high resolution has been
developed [7-8]. Although the AFM probe unit is combined with an optical sensor for aligning the measurement probe
with the tools edge top to be measured in short time in this system, this time only the AFM probe unit was used. During
the measurement time, that was attached onto the ultra precision turning machine to confirm the possibility of profile
measurement system.
An atomic force microscope (AFM) system is used for large-area measurement with a spiral scanning strategy, which is
composed of an air slide, an air spindle and a probe unit. The motion error which is brought from the air slide and the air
spindle will increase with the increasing of the measurement area. Then the measurement accuracy will decrease. In
order to achieve a high speed and high accuracy measurement, the probe scans along X-direction with constant height
mode driven by the air slide, and at the same time, based on the change way of the motion error, it moves along Zdirection
conducted by piezoactuator. According to the above method of error compensation, the profile measurement
experiment of a micro-structured surface has been carried out. The experimental result shows that this method is
effective for eliminating motion error, and it can achieve high speed and precision measurement of micro-structured
surface.
KEYWORDS: Sensors, Distortion, Modulation transfer functions, Spatial frequencies, Imaging systems, Optical transfer functions, Point spread functions, Optical engineering, Signal to noise ratio, Prototyping
A novel sensor for use in displacement metrology is proposed. It is based on grating imaging, which conventionally uses two amplitude gratings to generate a sinusoidal image. In the conventional method, the poor signal-to-noise ratio of the displacement output is one of the barriers to precise measurement, because 75% of the illumination light is trapped by the two amplitude gratings. In the proposed sensor a cylindrical lens array and a sine phase grating are used as the first and the second grating, respectively. Therefore, the illumination light is intercepted by neither, so that four times higher displacement signal amplitude than that of the conventional sensor can be expected. Consequently, four times higher signal-to-noise ratio can be obtained. Furthermore, the proposed sensor generates a sinusoidal output with little distortion by using the sine phase grating with optimized conditions, so that accurate measurement can be expected. In our prototype, a cylindrical lens array with a 200-µm period and a reflective sine phase grating with a 100-µm period were used.
This paper describes the replication of a precision sinusoidal grid surface, which is used as the measurement reference of a surface encoder for measurement of planar motions. The profile of the grid surface is a superposition of sinusoidal waves in the X-direction and the Y-direction with spatial wavelengths of a hundred micrometers and amplitudes of a hundred nanometers. The master surface is fabricated on a diamond turning machine equipped with a fast tool servo. Two kinds of replication methods, the hot embossing and UV casting are employed for replicating the grid surface on polymer materials. The replication on a glass plate is also carried out by UV-casting. The replication systems and some experimental results are presented.
This paper presents a prototype rotary/linear dual-axis positioning system consisting of a θ-Z actuator and a rotary-linear angle sensor. In the system, an aluminum rotor (moving element) can be moved along and rotated about the axis (Z) of a ceramic cylinder (driving rod). The θ-Z actuator is composed of a Z-piezoelectric actuator (maximum stroke: 12 μm) for linear motion, two θ-piezoelectric actuators (maximum strokes: 9.1 μm) with an added weight for rotation, a driving rod and a rotor. The two θ-piezoelectric actuators with the added weight are attached to the driving rod via a clamping device made with steel. The inner face of the rotor is made contact to the driving rod with a certain friction force. The linear-axis positioning employs the smooth impact drive mechanism to achieve a large stroke by applying a periodic saw-toothed motion from the Z-piezoelectric actuator to the rotor via the driving rod. Sinusoidal motions are applied to the θ-piezoelectric actuators for rotary positioning, which is with a different mechanism form the smooth impact drive mechanism. The stroke of the prototype system along the Z-axis, which is limited by the length of the cylinder, is designed to be 10mm and there is no limitation in the rotary motion. The positioning resolution and maximum speed along the Z-direction are approximately a few nanometers and 2.4mm/sec, respectively. The maximum revolution speed is approximately 50 rpm. An optical surface encoder is also designed for precision positioning of the rotor.
This paper describes high-speed positioning of a surface motor-driven planar motion stage with a XYθz surface encoder. The surface motor consists of two pairs of linear motors. The magnetic array is mounted on the platen and the stator winding of the linear motor on the stage base. The platen can be moved in the X- and Y-directions by the X-linear motors and the Y-linear motors, respectively. It can also be rotated about the Z-axis by a moment about the Z-axis by the X- or Y-linear motors. The surface encoder consists of two two-dimensional angle sensors and an angle grid with two-dimensional sinusoidal waves on its surface. The angle grid is mounted on the platen. The sensors are placed inside the stage for a compact design of the stage system. The surface encoder is improved for high speed positioning. Measurement errors of the surface encoder using two kinds of detectors, the quadrant PD and two-dimensional PSD, are estimated by simulation. A modification of the motors for increasing the speed of the stage is also carried out. Verification experiments of the improved system are also performed.
This paper describes a micro-angle sensor based on laser autocollimation. The sensor consists of a light source, an objective lens and a positioning-sensing device. The position-sensing photodetector, which is a quadrant photodiode, is placed at the focal position of the objective lens. Differing from a conventional autocollimator, the angle sensor employs a laser diode as the light source. The laser beam is collimated to a thin parallel beam with a diameter of 1 mm so that the angle sensor can be used to detect the surface local slope of a specimen. The thin laser beam also makes it possible to use a small target mirror for measurement of stage angular error motions. Because the sensitivity of angle detection does not depend on the focal length of the objective lens by using a laser source, an objective lens with a short focal length is employed for realizing a compact sensor size. The prototype micro-angle sensor has a dimension of 26mm x 22mm x 12 mm. The resolution is better than 0.1 arc-seconds. Optical design and experimental results of confirming the performance of the sensor are presented.
This paper describes the optical design of a new type surface encoder, which consists of a 2D angle grid and a 2D slope sensor for 2D position detection. The sensitivity of the new type surface encoder is two times higher than that of a conventional surface encoder through employing a double pass. A wave optical model of the surface encoder is established for the optical design. Simulations based on the wave optical model are carried out to analyze the behavior of the diffraction pattern on the photo-detector of the slope sensor. Basic experiments are also carried out to confirm the
feasibility of the double pass surface encoder.
KEYWORDS: Sensors, Optical transfer functions, Distortion, Modulation transfer functions, Metrology, Point spread functions, Spatial frequencies, Staring arrays, Signal to noise ratio, Reflectivity
A novel sensor for use in displacement metrology is proposed. The proposed displacement sensor is based on the grating
imaging, which conventionally uses two amplitude gratings with rectangular apertures of fifty percent width of the
period. In the conventional way, signal to noise ratio of displacement output is one of issues to be overcome for precise
measurement because about seventy five percent of the illumination light is trapped by two amplitude gratings. On the
other hand, in the proposed sensor a cylindrical lens array and a phase grating are applied as the first and the second
grating, respectively. Therefore, the illumination light is trapped neither by the first grating nor the second grating except
absorption.
In our experiments, the cylindrical lens array with 200 μm period and the reflective sine phase grating with 100 μm
period are used. Experimental results demonstrate that higher position resolution and higher accuracy of the
displacement measurement is feasible by our proposal.
In angle grid based 2D-position measurement system, building up an accurate correspondence between the angle and the coordinates for the angle grid is very important to ensure the final accuracy of the measurement system. This paper introduces a calibration method for the angle function so as to realize the software datum. After introduce the iteration calibration algorithm, the convergence of the algorithm is discussed in detail and is proved analytically. Digital simulation has confirmed the calibration algorithm.
To measure roundness errors of cylindrical workpieces and spindle errors of machine tools in on-machine conditions, it is important to separate the roundness error and spindle error from each other. Basically there are two kinds of error separation methods. One is known as the multi-orientation method, and the other is the multi-probe method. Multi-orientations including the step method and the reversal method can separate the spindle error and the roundness error effectively, if the spindle error has good repeatability. Compared with multi-orientation methods, multi-probe methods are more suitable for on-machine measurements, because the repeatability of the spindle error is not necessary. In this paper, we present a new error-separation method using multiple angle probes. In the angular three-probe method, three angle probes are fixed around the workpiece to detect roundness profile and two-dimensional spindle error components simultaneously. The effect of the spindle is canceled in the differential output of the probes and the correct roundness profile can be evaluated from the differential data. In this paper, the principle of the angular three-probe method is described. Experimental results of comparing with the conventional displacement three-probe method are also presented.
The authors have being working on a new position detection method, which can detect two-dimensional position of an xY stage with a single sensor [1]. Conventionally, position detection is carried out by utilizing either a linear scale or a laser interferometer [2]. Displacement probes like capacitance-type probes or laser displacement probes are also used for position detection in short ranges. Basically, such measuring instruments are for one-dimensional measurement. It is necessary to increase the number of sensors for detecting multi-degree-of-freedom positions. This makes the measuring system complicated and expensive. The uncertainty of measurement could also be increased with the increase of number of sensors. In the new position detection method proposed by the authors, a two-dimensional angle grid and a two-dimensional angle senor are utilized [11. The angle grid has a two-dimensional angular pattern on the surface. The two-dimensional position between the angle grid and the angle sensor in the XY plane can be detected simultaneously from the output of the angle sensor. Since only a single probe is used, the problems in the conventional methods could be overcome. In order to realize this new position measuring system, it is necessary to develop a machining method of the specially designed angle grid. The angle grid has two-dimensional sinusoidal micro-patterns on its surface with a wavelength on the order of several hundreds of microns and an amplitude on the order of several hundreds of nanometers. The micro-pattern should be generated over a large area to ensure the measurement range. A machining system based on diamond turning with the fast tool servo technique [3 has been constructed for generating the micro-patterns. To accurately generate the micro-pattern, it is desired to monitor the machining force in the machining process. In this paper, an instrument was designed and fabricated to monitor the machining forces during diamond turning of such micro-patterns. Instrument design and measurement results are presented.
An optical probe for profile inspections of mirror surfaces is developed. This probe can detect the displacement and angle at one point on the measured surface simultaneously. Both the displacement meter and the angle meter of the probe use position sensing detectors (PSD) to detect the position of the optical spot. The principle of the displacement meter is the image formation system, and that of the angle meter is the autocollimation. The displacement meter and the angle meter have two important characteristics. One is the good linearity, the other is that they can detect the displacement and angle independently without interfering with each other. An optical fiber output is used as the light source so that the probe is made compact and to have good characteristics. To eliminate influences of disturbance lights, the light intensity of the laser diode is modulated by a sine wave of 20 kHz, only the position signal is taken out from signals obtained from the PSD in the demodulation circuit. According to the geometrical relation and the active size of the PSD, the displacement meter can measure more than 1000 micrometers and 120 minutes (arc) with good linearity, respectively. Estimating from the signal to noise ratio of the system, the displacement resolution and the angle resolution are 10 nm and 0.1 arcsec, respectively. Some experimental results to confirm the performance of the proposed probe are shown in this paper.
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