Abstract: A novel two-DOF pointing mechanism using a bending–bending hybrid piezoelectric actuator was proposed. The pointing mechanism realized rotary motions around two orthogonal axes by single actuator based on the inertial driving principle. The pointing mechanism was designed and its operating principles were described in detail. The theoretical analyses were performed to design the piezoelectric actuator. The piezoelectric actuator was fabricated and a prototype of the pointing mechanism was assembled. The measured results indicated that the maximum rotary velocities of the rotor were 0.153 rad/s around X -axis and 0.154 rad/s around Y -axis under the voltage of 400 V p - p and frequency of 460 Hz, respectively. Moreover, the angular displacement resolutions achieved 2.49 μrad around X -axis and 2.52 μrad around Y -axis under a voltage increment of 3 V. The two-DOF pointing mechanism could be applied to precision pointing and attitude adjustment systems as its merits of high speed, high resolution, and large motion space.

Abstract: This paper selects delta high-speed parallel robot with three degrees of freedom as the research object. The trajectory planning strategies of Cartesian space and angular displacement, angular velo...

Abstract: In dimensional metrology it is necessary to carry out multi-axis angle and displacement measurement for high-precision positioning. Although the state-of-the-art linear displacement sensors have sub-nanometric measurement resolution, it is not easy to suppress the increase of measurement uncertainty when being applied for multi-axis angle and displacement measurement due to the Abbe errors and the influences of sensor misalignment. In this review article, the state-of-the-art multi-axis optical sensors, such as the three-axis autocollimator, the three-axis planar encoder, and the six-degree-of-freedom planar encoder based on a planar scale grating are introduced. With the employment of grating reflectors, measurement of multi-axis translational and angular displacement can be carried out while employing a single laser beam. Fabrication methods of a large-area planar scale grating based on a single-point diamond cutting with the fast tool servo technique and the interference lithography are also presented, followed by the description of the evaluation method of the large-area planar scale grating based on the Fizeau interferometer.

Abstract: This paper proposes a new optical angle measurement method based on second harmonic generation with a mode-locked femtosecond laser source by taking use of the unique characteristic of high peak power and high-intensity electric field of the femtosecond laser pulses. The angle is measured from the second harmonic wave intensity, which is a function of the angle between the laser beam axis and the optic axis of a nonlinear crystal attached to the target of interest. It is found that the beta barium borate (BBO) crystal is suitable as the nonlinear crystal for this purpose through theoretical simulation. As the first step of research, an experimental demonstration is also carried out in such a way that a change of the second harmonic wave intensity due to the angular displacement of BBO crystal is measured to verify the feasibility of the proposed principle of the angle measurement method.

Abstract: This paper presents the design and development of a non-contact capacitive sensor suitable to measure both angular and linear displacements. The sensor is composed of two parts: a rotating shaft and three fixed pairs of electrodes. The shaft has a semi-cylindrical rectangular slot at its middle. Two pairs of electrodes are designed for the measurement of angular displacement and the remaining pair, for linear measurement. A suitable signal conditioning circuit is developed to obtain the change in capacitance between the electrodes and the shaft-slot combination. A function is defined to calculate the absolute angular and linear positions of the shaft. A prototype of the sensor, capable to measure 360° for angular measurement and ±45 mm for linear measurement, was built and tested in the laboratory. The measurement results show that the resolution of the prototype is 0.15° for angular displacement and $41~\mu \text{m}$ for the linear displacement. The linearity error in measurement was found to be less than 0.9% for both angular and linear displacements.

Abstract: This paper presents a high-precision absolute capacitive angular position sensor based on time grating. The sensor includes two single ring incremental type sensors arranged as outer and inner rings of capacitive arrays forming $N$ and $N-1$ measurement periods, respectively. The outer ring incremental sensor is employed as a fine measurement component to provide high-precision angular displacement values. The phase difference between the two incremental sensors is employed as a coarse measurement component to achieve absolute angular positioning according to a measurement principle similar to that of a vernier caliper. The proposed design is validated and optimized via tests conducted for a prototype sensor with $N\,\,=180$ and a diameter of 154 mm fabricated using standard printed circuit board manufacturing technology. Based on these results, a differential induction electrode structure is proposed to greatly reduce the magnitude of crosstalk interference signals captured by the induction electrodes of one array produced by the lead wires of the excitation electrodes of the other array. The optimized sensor achieves absolute angular position measurements with an original measurement accuracy of ±2” over a full 360° measurement range. The proposed sensor has advantages of low cost, high measurement precision, simple positioning method, and ease of manufacture.

Abstract: As an application of noncontact transportation utilizing the near-field acoustic levitation phenomenon, a rotary-type noncontact-synchronous ultrasonic motor (NCSyn-USM) using acoustic viscous force was examined. The NCSyn-USM consisted of six fan-shaped stators arranged in a circle and a flat fan-shaped rotor installed above stators via small an air gap. The possibility of the NCSyn-USM was investigated by both of numerical simulation and measurement. From the acoustic-structure and fluid-structure interaction analyzes by finite element method, the correlation between the sound pressure in the air gap and the rotational force was obtained, and it was found that the rotational force was increased by utilizing the acoustic resonance of the air gap. In the experiment, the change of rotational torque with respect to the rotor angular position approximately corresponded with analysis results. The rotation of the rotor by switching driving stators was actually obtained, so that a rotary-type NCSyn-USM would be realized.

Abstract: To achieve the quick and accurate calibration of the geometric errors of NC machine tool, a new method with laser tracker on the basis of space vector’s direction measurement principle is proposed in the paper. A series of measuring points are mounted on the moving part of the machine tool, and then adjacent measuring points are connected to form a space vector respectively. Due to the motion error of the machine tool, the direction of the vectors composed will be changed. Meanwhile, the deviation of vector’s direction only relates to angular displacement error rather than linear displacement error. Based on the characteristic, the change of vectors’ direction is measured by laser tracker based on the multi-station and time-sharing measurement during the motion of machine tool, and then the angular displacement errors and linear displacement errors of each axis can be accurately identified successively, which reduces the complexity of error identification. By establishing the mathematical model of geometric error measurement of machine tool based on the principle of space vector’s direction measurement, the base station calibration algorithm by measuring the motion of the designed precise turntable, the measuring point determination algorithm and geometric error separation algorithm are derived respectively, and the accuracy of these algorithms are verified by simulations. In addition, the results of the experiments show the feasibility of the proposed method.

Abstract: This paper describes the design, fabrication, and testing of a lightweight and compact torque sensor system based on a gradient grating period guided-mode resonance (GGP-GMR) filter and a flexure–elastic-force-sensing element. The GMR filter exhibits a characteristic resonant reflection, when illuminated with a broadband light source at normal incidence. Instead of a fixed grating period, the GGP-GMR filter consists of grating periods varying from 250 to 550 nm with an increment of 2 nm. Given the flexibility of the plastic-based GGP-GMR filter, it can be bent conform to the cylindrical surface of the flexure. The applied torque induced deformation of the flexure and angular displacement of the attached GGP-GMR. For a stationary light source, the angular displacement of the GGP-GMR filter results in illumination at different locations (grating periods), leading to a shift of the resonant reflection wavelength. The magnitude of shift in the reflection wavelength can be correlated to the magnitude of deformation and the applied torque. In addition, commercial software based on the finite element method was used to simulate the proposed design, which indicates that the flexure made of medium-carbon steel can withstand the torque of 35 Nm without yielding. Furthermore, the simulation results (torque-induced deformation) were consistent with those obtained using the proposed torque sensor system. Torque measurements from 0 to 25 Nm showed good linearity. The limit of detection achieved was 0.77 Nm.

Abstract: This paper presents a new self-calibration method for angular displacement sensor, named coaxial sensors relative rotation (CSRR) method, which is suitable for sensors working in harsh environments. With a few slight modifications to the machine, CSRR method can also self-calibrate sensors on their application axes. This method works with two sensors. One sensor provides a benchmark and the other provides relative rotation against the benchmark, then each sensor can be self-calibrated by measuring the synchronized angular displacements of sensors and calculating the relative rotation angles. Experimental results indicate that this method is insensitive to relative rotation error of the two coaxial sensors, and it is also insensitive to sampling uniformity in particular situation. In that particular situation, the calibration accuracy can be better than ±2” when the system error of sensor is about ±650”. Compared with equal division averaged method, CSRR method mostly requires fewer sensors to get the same calibration accuracy; and compared with time-measurement dynamic reversal method, CSRR method performs better on the axis supported by rolling bearing. What is more, we propose an evaluation indicator $\vert Y_{\boldsymbol {\Omega }}\vert $ to evaluate the effective range of the CSRR method, and the $\vert Y_{\boldsymbol {\Omega }}\vert $ makes it easier for others to determine whether this method is suitable for their applications.

Abstract: Microgrippers are MEMS technology-based devices, able to handle objects of dimensions similar to those of cells (i.e. between 10 and 100 μm); these particular devices, are able to move and grasp object positioned between their grippers when a voltage is applied. In recent years, the demand for low-invasive, reliable, low-energy, small-sized devices with high performance repeatability is growing, and microgrippers seem to satisfy these expectations and are very promising in biomedical applications. However, the contributions relating to the characterization of such devices are still lacking, both from the metrological and performance point of view. In this study a methodology to characterize a microgripper prototype for biomedical applications is proposed, that includes the analysis of images through an in-house software developed ad hoc, acquired through a light trinocular microscope and an embedded camera. In particular, the Comb-Drive angular displacement, gripper rotation and the gripper displacement due to applied voltage have been measured. The results gave an estimate of the total uncertainty of 0.021°, 0.09° and 4 µm for Comb-Drive angular displacement, gripper rotation and gripper displacement respectively, referred to the whole range of the applied voltage.

Abstract: Advances in fine photoelectric displacement measurement technology have made image angular displacement measurement technology via imaging method a popular research topic; it is now easier than ever to realize small-scale high-resolution angular displacement measurement. This paper proposes a small-sized high-resolution image angular displacement measurement technique based on near-field image acquisition. A measuring mechanism based on the lensless near-field image acquisition is first established. Next, based on the error code problem, a space-value-based code value correction algorithm is proposed. Finally, the proposed device is validated on an experimental system. The proposed technology can achieve 21-bit resolution and 20.14” angle measurement accuracy. The results presented here may provide a workable foundation for further research on image-type fine photoelectric displacement measurement technology.

Abstract: Based on the linear displacement motion similarity and angular displacement motion similarity, the similarity law for free flight test of light store separation from aircraft is deduced. The proble...

Abstract: This paper presents the experimentation to define the final angular position of the Maxon RE 25 brushed DC Motor shaft, when using an implementation in closed-loop position control configuration is proposed of the Digital Precision Motion Controller LM629. Reporting the final angular position through a GUI implemented in LabVIEW. The Digital Controller LM629 generates a trapezoidal velocity trajectory profile, which by integration defines the reference angular position as a ramp for the final angular position of the Maxon RE 25 DC motor shaft. The experimentation and experimental results are described, showing high performance, high precision, and effective positioning time.

Abstract: This study proposes a novel model-based automatic search algorithm to realize the self-calibration of nonlinear signal model for angular position sensors. In some high-precision angular position sensors, nonlinearity of the signal model is the main source of errors and cannot be handled effectively. By constructing a signal flow network framework and by embedding a modeling search network, the parameters of the nonlinear signal model can be searched, and the calibration signal can be obtained. The convergence of the network search process was analyzed. The relationship between the optimization threshold and the convergence accuracy was also studied in simulations. Compared with the maximum angular error reduction to 47.42% after the calibration with simplified model that ignores signal nonlinearities, the proposed scheme was able to reduce this error to 0.0025% in simulations. By implementing the technique in a capacitive angular position sensor, the experimental results showed that the maximum angular error was reduced to 1.63% compared to a reduction of 86.02% achieved with the simplified model calibration. The effects of the search network order and layer number on the calibration accuracy were also analyzed, and the optimal parameters under experimental conditions were obtained. Correspondingly, the proposed scheme is able to handle calibration of nonlinear signal model and further improve sensor accuracy.

Abstract: This paper deals with the problem of uniaxial stabilization of the angular position of a rigid body exposed to a nonstationary perturbing torque. The perturbing torque is represented as a linear combination of homogeneous functions with variable coefficients. It is assumed that the order of homogeneity of perturbations does not exceed the order of homogeneity of the restoring torque, and the variable coefficients in the components of the disturbing torque have zero mean values. A theorem on sufficient conditions for the asymptotic stability of a programmed motion of the body is proven using the Lyapunov direct method. The determined conditions guaranteeing the solution to the problem of body uniaxial stabilization do not impose any restrictions on the amplitudes of oscillations of the disturbance torque coefficients. Results of numerical modeling are presented that confirm the conclusions obtained analytically.

Abstract: Most of the engineering problems can be easily solved by using biomimetic designs . Biomimetic is the process of imitating live animals to create new designs. For example, by mimicking the movements of a fish or snake, it is possible to transfer the desired swimming or crawling movements to a robot. This research is based on an amphibious robot where the propulsion system is imitated by a cuttlefish. In this study, to obtain the required sine wave motion for the cuttlefish's fin, crank-rocker mechanisms are used. Additionally, a circular slot mechanism was used to move these crank-rocker mechanism up and down as in the cuttlefish fins. Since the cuttlefish has two symmetrical wings, these crank-rocker and circular slot mechanisms are repeated symmetrically on both sides. Two separate servo motors (one on the right and one on the left) were used to control the angular position of the crankshafts in circular slots. These servo motors allow the fins to move up and down while the robot is in the water. They also serve to hold the wings at a fixed angle in terrestrial mode. In similar applied robotic researches, dozens of servo motors are used to obtain the required sine motion. This study proposes a propulsion system that can be operate with simple crank-rocker and circular slot mechanisms, instead of using too many servo motors that are expensive and constitutes control complexity. In this study, a design methodology is proposed for this new propulsion system. Various conditions have been considered in the design procedure. In the design criteria section, the required force and velocity, the capacity to overcome obstacles and the motion requirements has been considered for an amphibious robot. Furthermore, the requirements of a continuous movement for oscillating motion have been also considered. As a result of this study, minimum crank number and crank angles were obtained for the undulating motion. It has been also considered the necessary continuous balance condition, in order to make motion on land without tumbling. The calculation of the part lengths that meets the design criteria is described in the mechanism synthesis section.

Abstract: An adaptive method of control of a system with single degree of freedom along a given trajectory of displacement under the conditions of unpredictable variation of a surmountable external load is set forth. Simulation of the load with the use of a special force vector that reflects the nature of its variation is proposed. The components of the force vector (averaged values of partial derivatives of the load with respect to time and spatial coordinate) are calculated from the working information which the control system receives at previous moments of displacement of the control object. The order of the model is the maximumorder of the derivatives included in the model. The general structure and derivation of formulas for models of zero, first and second order are given. The practical case of measurement of the angular displacement of a shaft using incremental encoders is given separately. Initially, direct load models are considered in which time is the independent variable. Then, for a drive with incremental encoders, inverse models are presented separately in which the angle of rotation of the output shaft is the independent coordinate. Conditions under which the adequacy of the parameters of the power vector and the redundancy and insufficiency of the order of the control model is estimated are considered separately. Based on these conditions, a general algorithm for the functioning of the control system by means of which both the parameters and the structure of the control system may be dynamically changed is given.

Abstract: The problems of optimal control of kinetic moment of a rigid body (for example, a spacecraft) during the reorientation maneuver from an arbitrary initial to a given final angular position, taking into account the requirements for the energy of rotation, are investigated. An analytical solution for the problem of optimal control of solid body reorientation is obtained. Formalized equations are presented and calculation expressions for the construction of an optimal control program are given. The task of controlling the turn is solved taking into account the restrictions on control moments. An analytical relationship is found between the turning time and the maximum rotational energy. The moment of the start of deceleration is determined by the actual parameters of movement (the mismatch quaternion and the kinetic moment), based on the principles of terminal control (using information about the angular position and measuring the angular velocity). Control algorithms created make it possible to make turns in a given time with a minimum rotational energy. For a dynamically symmetric solid body, the control problem is solved to the end — dependencies are obtained, as explicit functions of time, for control variables and relations for calculating the key parameters of the kinetic moment control law. A numerical example and the results of mathematical modeling of the motion of a spacecraft with optimal control, which demonstrate the practical feasibility of the developed orientation control algorithms, are presented.

Abstract: A system for determining angular position includes a dipole magnet having an axis of rotation, wherein the dipole magnet produces a magnetic field. A first magnetic field sensor produces a first output signal and a second magnetic field sensor produces a second output signal in response to the magnetic field. The magnetic field sensors are operated in a saturation mode in which the magnetic field sensors are largely insensitive to the field strength of the magnetic field. Thus, the first output signal is indicative of a first direction of the magnetic field and the second output signal is indicative of a second direction of the magnetic field. Methodology performed by a processing circuit entails combining the first and second output signals to obtain a rotation angle value of the magnet in which angular error from a stray magnetic field is substantially cancelled.

Abstract: The dynamic problem of the rotation of a rigid body (for example, a spacecraft) from an arbitrary initial to the required final angular position in the presence of control restrictions is considered and solved. The end time of the maneuver is known. To optimize the rotation control program, a quadratic quality criterion is used, the minimized functional characterizes energy costs. The construction of optimal turn control is based on quaternion variables and the L. S. Pontryagin maximum principle. The features of optimal motion are studied in detail. Key properties of the optimal solution are formulated in an analytical form. It is shown that in the case of limited control, the moment of forces in the process of optimal rotation is parallel to a straight line that is stationary in inertial space, and during rotation of a rigid body (spacecraft) the direction of the kinetic moment is constant relative to the inertial coordinate system. Optimal control is presented in the form of synthesis—the synthesizing function is found and the dependence of the control variables on the phase coordinates is given. Formalized equations and calculation expressions are obtained to determine the optimal rotation program. The constructive scheme for solving the boundary value problem of the maximum principle for arbitrary rotation conditions (initial and final positions and moments of inertia of a solid body) is also described. An example and results of mathematical modeling of the motion of a spacecraft as a solid with optimal control are presented, demonstrating the practical feasibility of the developed method for controlling the spatial orientation of the spacecraft. For a dynamically symmetric solid, a complete solution of the reorientation problem in closed form is given, control variables and the optimal trajectory of motion as functions of time are presented in an analytical form.

Abstract: The invention relates to the technical field of robots, in particular to a robot collision detection method and device, a storage medium and a robot. The method comprises the steps of acquiring the first motor torque, the first angular displacement, the first angular velocity and the first angular acceleration of a robot joint; updating kinetic parameters of the robot in a preset updating mode andcalculating the theoretical torque of the joint according to the updated kinetic parameters, the first angular displacement, the first angular velocity and the first angular acceleration; obtaining the first external torque of the joint according to the first motor torque and the theoretical torque; inputting the first motor torque, the first angular displacement, the first angular velocity and the first angular acceleration into a preset observer model to obtain the second external torque of the joint; judging whether the first external torque is greater than a first preset threshold value or not and judging whether the second external torque is greater than a second preset threshold value or not; and determining that collision occurs to the robot if the first external torque is greaterthan the first preset threshold value and the second external torque is greater than the second preset threshold value.

Abstract: A new design approach of microwave rotation sensor using separated ring of double split ring resonator (DSRR) is presented in this work. The proposed sensor provides the contactless determination of angular displacement by investigating the shift in resonant frequency. The novel design configuration helps to obtain the wide dynamic range, resolution, linearity and sensitivity. In this work two rings of DSRR has been separated vertically to attach them one at stator and other one at rotor to perform the contact less wide range rotation measurement using the asymmetry of rectangular SRR ring. Rotation of inner ring attached on the rotor results into change in its coupling with the outer ring present at the stator. This actually changes the overall capacitance of the sensing region thereby changing the resonant frequency of the sensor. The designed sensor dimensions are optimized in order to get the improved sensitivity and linearity in the wide dynamic range of 0 to 120°. Maximum achievable frequency shift using the proposed sensor is found to be nearly 19 MHz/°. Moreover, the designed sensor can cover the maximum angular displacement range of nearly 5 mm with 2 GHz bandwidth using only the single sensor arrangement, unlikely the multi cell SRR arrangement where the maximum displacement coverage is ~ 1 mm with 0.5 GHz bandwidth.