A multilevel calibration technique for an industrial robot with parallelogram mechanism

This paper presents a multilevel calibration technique for improving the absolute accuracy of an industrial robot with a parallelogram mechanism (ABB IRB2400). The parallelogram structural error is firstly modeled based on the partial differential of the position function of a general four-bar linkage and the linearization of the position constraints of the parallelogram mechanism, the model coefficients are fitted from experimental data. Secondly, an absolute kinematic calibration model is established and resolved as a linear function of all the kinematic parameters, as well as the base frame parameters and tool parameters. Finally, contrary to most other similar works, the robot joint space (rather than Cartesian space) is divided into a sequence of fan-shaped cells in order to compensate the non-geometric errors, the positioning errors on the grid points are measured and stored for the error compensation on the target points. After the multilevel calibration, the maximum/mean point positioning errors on 284 tested configurations (evenly distributed in the robot common workspace) are reduced from 1.583/0.420 mm to 0.172/0.066 mm respectively, which is almost the same level as the robot bidirectional repeatability.     

Development and evaluation of a two-axial shearing force sensor consisting of an optical sensor chip and elastic gum frame

We developed a promising shearing force sensor that is small in size and can measure shearing force along two axes independently. This sensor consists of an elastic gum frame and an optical sensor chip (6 mm × 6 mm × 8 mm). From the experimental results, the resolutions of the sensor along the x- and y-axes are found to be 0.070 N and 0.063 N. We also experimentally demonstrated that the sensor can separately measure shearing force along two axes. Finally, we demonstrated that the scale factor which correspond to resolution and linear portion which correspond to measuring range of the signals can be changed easily by using three types of elastic gum frame. This sensor can be embedded in the finger of a robot hand and use it to not only measure shearing force but also detect the slip phenomenon.     

Dynamic error compensation for industrial robot based on thermal effect model

This paper analyses the kinematic parameters and the positioning accuracy of robot end effectors influenced by temperature factors. Temperature factors include robot self-heating and environmental temperature changes. This paper also builds the thermal distribution model and deformation model using finite element theory. A thermal compensation strategy is presented to validate the significant correlation between the robot kinematics parameters and previous thermal models mentioned above. It is convenient and suitable for industrial field. Thermal compensation is experimentally proved to adjust the position error of the end effectors by less than 0.1 mm.     

Large range nanopositioning stage design: A three-layer and two-stage platform

In this article, a novel two-dimensional nanopositioning platform (NanoPla) design is described. Its requirements are not only sub-micrometer accuracy for nanotechnology applications, but also long working range (XY-motion 50 mm × 50 mm). These features increase the common range operation of devices for nanotechnology issues (e.g. an atomic force microscope), and the number of potential metrological applications: positioning for manufacturing, manipulation or sample characterization. This novel design is characterized by a three-layer architecture and a two-stage motion strategy, which minimizes the measurement error. The manufactured prototype is here justified considering precision engineering principles and a wide state-of-art study of the literature, regarding long range nanopositioning stages. The simulations, the experimental results and the error budget also allowed, first, the optimization and, secondly, the validation of the design at nanometer scale.     

Feasibility of tracking laparoscopic instruments in a box trainer using a Leap Motion Controller

Motion analysis is employed to assess minimally invasive surgical psychomotor skills in box trainers. Tracking of laparoscopic instruments requires sensor-based systems that can be expensive, limit movements and modify their ergonomic properties. We evaluate the feasibility of using Leap Motion as a cheap, unobtrusive alternative. Four experiments were performed to determine its precision while tracking a laparoscopic instrument inside and outside a box trainer. Static long and short term precision of the Leap Motion was <2.5 mm. Precision between 12 different positions within the box trainer was <0.7 mm for all measured distances between neighbors. Dynamic precision when moving the instrument for 200 mm ranged between 2 and 15 mm. Leap Motion presents acceptable precision values inside a box trainer. Improvements are still required (e.g.: multiple instruments’ tracking). Once solved, a validation study should verify the usefulness of Leap Motion to objectively measure skills of novices and residents during training.     

Development and calibration of an integrated 3D scanning system for high-accuracy large-scale metrology

Quality control in advanced manufacturing requires automated and high-accuracy large-scale 3D measurement. This paper proposes a high-accuracy, low-cost 3D scanning system by integrating industrial robot with precise linear rail and laser sensor. The measuring principle and system construction of the integrated system are introduced in detail. A mathematical model is established for mapping the change of the laser sensor frame while it scans along the linear rail and a sphere-based algorithm for rail orientation calibration is introduced. Subsequently, taking the robot positioning error into consideration, an enhanced hand–eye calibration method is proposed to determine the relationship between robot end-effector and rail scanning frame. Validation experiments were performed, a maximum distance error of 0.071 mm was detected within the rail range and a mean/maximum distance error of 0.309/0.604 mm was detected in the robot volume. A large-scale scanning instance also shows that integrated robotic scanning system features high-efficiency and high-accuracy.     

Calibration of a 3D-ball plate

The presented 3D-ball plate is used for testing machine tools with a workspace of 500 mm × 500 mm × 320 mm. The artefact consists of a 2D-ball plate which is either located by a kinematic correct coupling on a base plate or on a spacer. The spacers are placed between the base plate and the ball plate and are also kinematic coupled to the other elements of the artefact. The kinematic couplings provide a high repeatability of the measurement setup. Because of the specific application the known calibration procedures for 2D-ball plates are not applicable.A calibration method for the pseudo-3D-artefact on a coordinate measuring machine (CMM) is presented, with the aim to minimise the influence of geometric CMM errors. Therefore a computer simulation is used to analyse the effects of these disturbing errors on the calibration of the ball plate and the spacers. Using a reversal method, the plate is measured at four different horizontal positions after rotating the ball plate around its vertical axis. A couple of the CMM errors, e.g., a squareness error C0Y between the X- and Y-axis of the CMM, can be eliminated by that method—others have to be determined with additional measurements, e.g., the positioning errors EXX or EYY of the X- and Y-axis, respectively. The paper also contains a measurement uncertainty estimation for the calibration by use of experiments, tolerances and Monte Carlo-simulations. The achieved uncertainty for ball positions in the working volume is less than 2.1 μm (coverage factor k = 2).     

Videogrammetric technique for three-dimensional structural progressive collapse measurement

In order to solve the shortcomings of the traditional transducers for monitoring the structural progressive collapse, this paper proposes to adopt the high-speed videogrammetric measurement technique to monitor the structural progressive collapse. First, the videogrammetric hardware components are presented. Second, three key issues about the stereo videogrammetric technique are studied in the paper, including camera calibration and placement, movable network control and tracking targets layout and image sequences processing. At last, three different kinds structural progressive collapse of five-story reinforced concrete frame-wall are performed, and the absolute accuracy of 0.43 mm, 0.87 mm and 0.65 mm and the relative accuracy of 0.61 mm, 0.29 mm and 0.62 mm are achieved in the X, Y and Z direction. The results show that the non-contacted videogrammetry is an alternative technique to monitor the structural progressive collapse.     

Synthesis of multiple degrees-of-freedom spatial-motion compliant parallel mechanisms with desired stiffness and dynamics characteristics

This paper presents a new design method to synthesize multiple degrees-of-freedom (DOF) spatial-motion compliant parallel mechanisms (CPMs). Termed as the beam-based structural optimization approach, a novel curved-and-twisted (C-T) beam configuration is used as the basic design module to optimize the design parameters of the CPMs so as to achieve the targeted stiffness and dynamic characteristics. To derive well-defined fitness (objective) functions for the optimization algorithm, a new analytical approach is introduced to normalize the differences in the units, e.g., N/m or N m/rad, etc., for every component within the stiffness matrix. To evaluate the effectiveness of this design method, it was used to synthesize a 3-DOF spatial-motion (θ_x − θ_y − Z) CPM that delivers an optimized stiffness characteristics with a desired natural frequency of 100 Hz. A working prototype was developed and the experimental investigations show that the synthesized 3-DOF CPM can achieved a large workspace of 8°×8°×5.5 mm, high stiffness ratios, i.e., >200 for non-actuating over actuating stiffness, and a measured natural frequency of 84.4 Hz.     

A force-matching method for quantitative hardness measurements by atomic force microscopy with diamond-tipped sapphire cantilevers

We present a new method to improve the accuracy of force application and hardness measurements in hard surfaces by using low-force (<50 μN) nanoindentation technique with a cube-corner diamond tip mounted on an atomic force microscopy (AFM) sapphire cantilever. A force calibration procedure based on the force-matching method, which explicitly includes the tip geometry and the tip-substrate deformation during calibration, is proposed. A computer algorithm to automate this calibration procedure is also made available. The proposed methodology is verified experimentally by conducting AFM nanoindentations on fused quartz, Si(1 0 0) and a 100-nm-thick film of gold deposited on Si(1 0 0). Comparison of experimental results with finite element simulations and literature data yields excellent agreement. In particular, hardness measurements using AFM nanoindentation in fused quartz show a systematic error less than 2% when applying the force-matching method, as opposed to 37% with the standard protocol. Furthermore, the residual impressions left in the different substrates are examined in detail using non-contact AFM imaging with the same diamond probe. The uncertainty of method to measure the projected area of contact at maximum force due to elastic recovery effects is also discussed.     

Reaffirmation of measurement uncertainty in pressure sensitivity determination of LS2P microphones by reciprocity method

The paper presents the accuracy and precision associated with realization of primary standard of sound using the reciprocity method. An experimental determination of the front cavity volume on Universal Measuring Machine has lead to reaffirmation of measurement uncertainty in pressure sensitivity determination to 0.04–0.15 dB in frequency range 31.5 Hz to 25 kHz. The reduced measurement uncertainty has also been validated from the results of the recent APMP Key comparison and also by comparison to the manufacturer’s value for LS2P microphones. The use of optical method for measuring the front cavity volume has refined the measurement methodology followed with adaptation of a self reliant, traceable and systematic measurement procedure in comparison to the earlier use of nominal values for sensitivity fitting exercise conducted on MP.EXE program. Consequently, the measurement uncertainty associated with the calibration of working standard microphones, multifunction acoustic calibrator and A-weighted sound pressure level measurements is also reduced.     

Performance tests of a new non-invasive sensor unit and ultrasound electronics

Industrial applications involving pulsed ultrasound instrumentation require complete non-invasive setups due to high temperatures, pressures and possible abrasive fluids. Recently, new pulser-receiver electronics and a new sensor unit were developed by Flow-Viz. The complete sensor unit setup enables non-invasive Doppler measurements through high grade stainless steel. In this work a non-invasive sensor unit developed for one inch pipes (22.5 mm ID) and two inch pipes (48.4 mm ID) were evaluated. Performance tests were conducted using a Doppler string phantom setup and the Doppler velocity results were compared to the moving string target velocities. Eight different positions along the pipe internal diameter (22.5 mm) were investigated and at each position six speeds (0.1–0.6 m/s) were tested. Error differences ranged from 0.18 to 7.8% for the tested velocity range. The average accuracy of Doppler measurements for the 22.5 mm sensor unit decreased slightly from 1.3 to 2.3% across the ultrasound beam axis. Eleven positions were tested along the diameter of the 48.4 mm pipe (eight positions covered the pipe radius) and five speeds were tested (0.2–0.6 m/s). The average accuracy of Doppler measurements for the 48.4 mm sensor unit was between 2.4 and 5.9%, with the lowest accuracy at the point furthest away from the sensor unit. Error differences varied between 0.07 and 11.85% for the tested velocity range, where mostly overestimated velocities were recorded. This systematic error explains the higher average error difference percentage when comparing the 48.4 mm (2.4–5.9%) and 22.5 mm (1.3–2.3%) sensor unit performance. The overall performance of the combined Flow-Viz system (electronics, software, sensor) was excellent as similar or higher errors were typically reported in the medical field. This study has for the first time validated non-invasive Doppler measurements through high grade stainless steel pipes by using an advanced string phantom setup.     

Designing and producing large-volume liquid gamma-ray standard sources for low radioactive pollution measurements of seawater samples by comparison between experimental and simulation results

In order to in-situ measurement of large volume water samples, using of a portable HPGe detector was considered. Because of necessity of efficiency calibration of the detector for the geometry (100 L), the large volume standard sources were prepared. Before making large volume standard sources (100 L), the Monte Carlo method has been applied in order to optimizing the calibration procedures and in agreement with experiment results, has been caused reducing the amount of produced radioactive wastes. First, the efficiency of the portable coaxial P-type HPGe detector for 1 L liquid standard sources in Marinelli beaker geometry was simulated. Then, the experimental efficiency calibration was carried out using the detector for those 1 L liquid standard sources in Marinelli beaker geometry. The detector dead layer was determined by comparison of the simulation and experimental efficiency curve results. Then, a relation between simulation and experimental measurements, that is, between pulse-height per emitted particle, F8 tally, and estimated amount of spiked radioactive solution into the 1 L distilled water in Marinelli beaker was found. Then, the efficiency calibration of the large volume liquid standard sources was simulated. The estimated amount of spiking radioactive solution into the large volume distilled water (100 L) has been taken into account dividing experimental efficiencies (in Marinelli beaker) by the simulated efficiencies (in 100 L). Finally, by spiking the large volume distilled water with the radioactive solution, efficiency calibration of the potable HPGe detector for 100 L geometry was done.     

Parameters optimization on surface roughness improvement of Zerodur optical glass using an innovative rotary abrasive fluid multi-jet polishing process

With the advance of contemporary technology, high precision surface finishing techniques for optical glasses are of great concern and developing to meet the requirements of the effective industrialized processes. Not only the used tools but also process parameters have great influence on the surface roughness improvements. In this paper, surface roughness improvement of Zerodur optical glass using an innovative rotary abrasive fluid multi-jet polishing process has been presented. For the same purpose, a tool for executing ultra precision polishing was designed and manufactured. Taguchi's experimental approach, an L₁₈ orthogonal array was employed to obtain the optimal process parameters. ANOVA analysis has also been carried out to determine the significant factors. It was observed that about a 98.33% improvement on surface roughness from (R_a) 0.360 μm to (R_a) 0.006 μm has been achieved. The experimental results show that a surface finished achieved can satisfy the requirements for optical-quality surface (R_a < 12 nm). In addition, the influence of significant factors on surface roughness improvement has been discussed in this study.     

Leap motion controller three dimensional verification and polynomial correction

We propose a leap motion controller (LMC) dimensional verification based on ISO 10360-2:2009 with a coordinated measuring machine (CMM) as the reference framework. A pointer device comprising a thin aluminum cylinder was used to simulate a human finger. This was mounted on the spindle of the CMM to mark known positions over the LMC workspace. Polynomial tendency line corrections were applied to reduce the error in the LMC and CMM framework alignment. One dimension verification results were less than 0.1 mm in the X and Z axes, whereas the Y axis produced unsuitable results. The mean error was 9.6 mm in three-dimensional (3D) verification. Our findings demonstrate the difference between manufacturer quoted accuracy (0.01 mm) to that practically obtainable when the pointer was placed in a known position. LMC needs to add tracking models and position error compensation in applications requiring high accuracy, such as industrial processes or surgical procedure simulations.     

Quasi-constant rotational stiffness characteristic for cross-spring pivots in high precision measurement of unbalance moment

This paper proposes a design method for cross-spring pivots with quasi-constant rotational stiffness in the field of unbalanced moment measurement. To achieve high precision measurement of unbalance moment, the relationship between instrument sensitivity and the rotational stiffness of the cross-spring pivot is revealed. In order to eliminate the impacts of payload changes on instrument sensitivity, the relationship between geometric parameters and the rotational stiffness of the pivot is studied. Further, cross-spring pivots with quasi-constant rotational stiffness are designed as the rotation unit of a static balancing instrument, while the center shift of pivot takes the minimum value. Certain amount of unbalance moments is measured by the instrument. Experimental studies of the instrument show that the maximum measurement errors of unbalance moments 0.162 g mm, 0.319 g mm and 1.300 g mm are 0.068 g mm, 0.086 g mm and 0.053 g mm, respectively, when the payload ranges from 0 g to 7000 g. The instrument can achieve a relatively high precision measurement and the instrument sensitivity is almost not affected by the changes of payloads. The effectiveness of the method and the stiffness property of the pivot are verified by the experiments. So this kind of pivot has good prospects in unbalance moment measurement.     

Structural optimization for flexure-based parallel mechanisms – Towards achieving optimal dynamic and stiffness properties

Flexure-based parallel mechanisms (FPMs) are a type of compliant mechanisms that consist of a rigid end-effector that is articulated by several parallel, flexible limbs (a.k.a. sub-chains). Existing design methods can enhance the FPMs’ dynamic and stiffness properties by conducting a size optimization on their sub-chains. A similar optimization process, however, was not performed for their sub-chains’ topology, and this may severely limit the benefits of a size optimization. Thus, this paper proposes to use a structural optimization approach to synthesize and optimize the topology, shape and size of the FPMs’ sub-chains. The benefits of this approach are demonstrated via the design and development of a planar X − Y − θ_z FPM. A prototype of this FPM was evaluated experimentally to have a large workspace of 1.2 mm × 1.2 mm × 6°, a fundamental natural frequency of 102 Hz, and stiffness ratios that are greater than 120. The achieved properties show significant improvement over existing 3-degrees-of-freedom compliant mechanisms that can deflect more than 0.5 mm and 0.5°. These compliant mechanisms typically have stiffness ratios that are less than 60 and a fundamental natural frequency that is less than 45 Hz.     

Design,calibration and tests of versatile low frequency impedance analyser based on ARM microcontroller

Numerous simple impedance analysers based on the microcontroller (μC) and dedicated impedance converter integrated circuits (IC) were reported recently. In many applications sophisticated analogue circuitry has to be appended to enhance the measurement possibilities or to circumvent the limitations. In this paper the impedance analyser IMP-STM32 based solely on the μC and general purpose operational and instrumentation amplifiers is presented. It uses the internal DAC and ADCs in the μC to generate the excitation and to measure the response of the measured object. It also uses the external analogue circuits to condition the excitation signal and measure voltage and current. The magnitudes and phase shifts of voltage and current are evaluated using the three parameter sine fitting algorithm allowing for fast low-frequency impedance measurements. The calibration procedure of completed device is presented as well as the tests of its accuracy. The device allowed for measurements at frequency range between 1 mHz and 100 kHz in 1 Ω to 1 GΩ impedance range with 1% accuracy. IMP-STM32 was also compared to the Agilent 4294A precision impedance analyser. In the middle of the impedance ranges (1 Ω to 300 kΩ) the discrepancies between the two were less than 0.2%.     

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.     

A piezoelectric motor for precision positioning applications

This study presents a novel precise piezoelectric motor capable of operating in either an AC drive mode or DC drive mode. In the AC drive mode, the motor acts as an ultrasonic motor which is driven by two orthogonal mechanical vibration modes to generate elliptical motion at the stator to push the slider into motion. In the DC drive mode, stick-slip friction between the stator and slider is used to drive the motor step-by-step. The experimental results show that the AC drive mode can drive the motor at a high moving speed, while the DC drive mode can simply drive the motor with a nanoscale resolution. In our experiments, a prototype motor is fabricated and its actions are measured. The results demonstrate that in the AC drive mode, the piezoelectric motor can achieve a 106 mm/s speed without a mechanical load and a 34 mm/s speed with 340 g of mechanical load when applying two sine waves with a drive of 11.3 V at 38.5 kHz. Meanwhile, in a DC driving mode, the motor is capable of performing precision positioning with a displacement resolution of 6 nm when driving at 100 Hz.