Paired double parallelogram flexure mechanism clamped by corrugated beam for underconstraint elimination.

This Note presents a kind of paired double parallelogram (DP) flexure mechanism clamped by a sinusoidal corrugated beam to solve the problem of underconstraint of its secondary stages. The results show that the proposed mechanism effectively constrains the undesired motions of the secondary stages without changing the stiffness and the first-order natural frequency in the working direction. The second- and third-order natural frequencies of the mechanism are increased by 9.2% and 30.8%, respectively, which can effectively improve the dynamic characteristics of the DP mechanism.

Development of a novel line structured light measurement instrument for complex manufactured parts.

This paper studies a novel structured light measurement instrument for complex manufactured parts. In this research, a quick and accurate light plane calibration method and a novel light strip center extraction method were used to establish the measurement instrument. First, the intrinsic and external parameters of the camera are calibrated by Zhang's method. Second, a novel light plane calibration technique is proposed by using the original parameters and images in the process of camera calibration, which can be used to improve the accuracy of the measurement system because both the camera calibration and light plane calibration are based on the same target. Third, a subpixel extraction method is presented to extract the light strip center on the basis of the geometric center method. Finally, the constructed instrument is used to detect the geometric information of the complex manufactured parts. The experimental results show that the maximum measurement error is 0.1 mm under a measurement range of 50 mm and the accuracy is 0.2%, which indicates that the measurement instrument is fast, robust, and accurate enough to be applied to many kinds of measurements, such as railroad track deformation, the inner wall of a pipe, and so on.

Design and analysis of a displacement amplifier with high load capacity by combining bridge-type and Scott-Russell mechanisms.

To improve the load capacity of flexure-based amplification mechanisms, a flexure-based displacement amplification mechanism is developed in this study by combining the bridge-type and the Scott-Russell mechanisms. The four arms of the traditional bridge mechanism are replaced by four Scott-Russell mechanisms that provide the advantages of good symmetry, compact structure, and higher load capacity. An analytical model is formulated using a stiffness matrix to analyze the natural frequency, input and output stiffnesses, displacement amplification ratio, and load capacity of the proposed mechanism. The design model was subjected to both experimental methods and finite element analysis for verification, and the two sets of results were in good agreement. This proves the effectiveness and applicability of the analytical model and the proposed amplification mechanism. The output stiffnesses of the modified bridge-type amplifier and the traditional bridge-type amplifier are 0.158 N/µm and 0.041 N/µm, respectively, indicating excellent load performance of the modified bridge-type amplifier.

Development of an electrochemical micromachining instrument for the confined etching techniques.

This study proposes an electrochemical micromachining instrument for two confined etching techniques, namely, confined etchant layer technique (CELT) and electrochemical wet stamping (E-WETS). The proposed instrument consists of a granite bridge base, a Z-axis coarse/fine dual stage, and a force sensor. The Z-axis coarse/fine dual stage controls the vertical movement of the substrate with nanometer accuracy. The force sensor measures the contact force between the mold and the substrate. A contact detection method based on a digital lock-in amplifier is developed to make the mold-substrate contact within a five-nanometer range in CELT, and a force feedback controller is implemented to keep the contact force in E-WETS at a constant value with a noise of less than 0.2 mN. With the use of the confined etching techniques, a microlens array and a curvilinear ridge microstructure are successfully fabricated with high accuracy, thus demonstrating the promising performance of the proposed micromachining instrument.

Development of an automatic approaching system for electrochemical nanofabrication using visual and force-displacement sensing.

In this paper, a fast automatic precision approaching system is developed for electrochemical nanofabrication using visual and force-displacement sensing. Before the substrate is fabricated, the template should approach the substrate accurately to establish the initial gap between the template and substrate. During the approaching process, the template is first quickly moved towards the substrate by the stepping motor until a specified gap is detected by the visual feedback. Then, the successive approach using the switch of macro-micro motion with a force-displacement sensing module is triggered to make the template contact with the substrate to nanometre accuracy. The contact force is measured by the force-displacement sensing module which employs the high-resolution capacitive displacement sensor and flexure compliant mechanism. The high sensitivity of this capacitive displacement sensor ensures high accuracy of the template-substrate contact. The experimental results show that the template can reach the substrate accurately and smoothly, which verifies the effectiveness of the proposed approaching system with the visual and the force-displacement sensing modules.

Design and control of a decoupled two degree of freedom translational parallel micro-positioning stage.

This paper presents a novel decoupled two degrees of freedom (2-DOF) translational parallel micro-positioning stage. The stage consists of a monolithic compliant mechanism driven by two piezoelectric actuators. The end-effector of the stage is connected to the base by four independent kinematic limbs. Two types of compound flexure module are serially connected to provide 2-DOF for each limb. The compound flexure modules and mirror symmetric distribution of the four limbs significantly reduce the input and output cross couplings and the parasitic motions. Based on the stiffness matrix method, static and dynamic models are constructed and optimal design is performed under certain constraints. The finite element analysis results are then given to validate the design model and a prototype of the XY stage is fabricated for performance tests. Open-loop tests show that maximum static and dynamic cross couplings between the two linear motions are below 0.5% and -45 dB, which are low enough to utilize the single-input-single-out control strategies. Finally, according to the identified dynamic model, an inversion-based feedforward controller in conjunction with a proportional-integral-derivative controller is applied to compensate for the nonlinearities and uncertainties. The experimental results show that good positioning and tracking performances are achieved, which verifies the effectiveness of the proposed mechanism and controller design. The resonant frequencies of the loaded stage at 2 kg and 5 kg are 105 Hz and 68 Hz, respectively. Therefore, the performance of the stage is reasonably good in term of a 200 N load capacity.