The requirements of large thrust in bidirectional motion, high specific power (power/weight ratio), reliable self-locking at power off state, and compact size envelope for various applications of existing piezoelectric actuators are still urgent. To address these challenges, this study makes full use of the piezoelectric material’s excellent dynamic performance, robust force output, and high energy density to propose a novel inchworm piezoelectric actuator, which relies on the alternate clamping of two nuts independently rotated by two ultrasonic motors on a feed-screw in accordance with a piezoelectric stack (piezo-stack) excitation to accumulate the piezo-stack’s electric field-induced strain periodically and realize power output. The operation principle and design process of the presented actuator were elaborated, and a prototype was fabricated and experimented. Results indicate that the actuator has achieved an expected bidirectional motion for powering the tensile load and compressive load, attained a micrometer-sized step resolution, produced a 3.08 mm/s free speed, a 700 N stall load, and a 1.34 W/kg specific power, and shown a favorable prospect for further development.

This paper presents a hybrid linear actuator using screw clamp operation principle. The actuator mainly consists of a hollow electromagnetic torque motor located between two clamping nuts, two hollow cylindrical shaped piezoelectric stacks symmetrically configured at two ends of the actuator and a feed-screw (also considered as the mover of the actuator) assembled throughout all the parts. The torque motor is symmetrically connected to two clamping nuts via two torsion coupling springs located at either end of the motor spindle. Two piezoelectric stacks can work independently to propel the opposing loads, which effectively take advantage of the anti-compression and non-tensile characteristics of piezoelectric element. The special feature of the actuator is the screw clamp mechanism, the operation of which involves intermittent rotation of two nuts (driven by the torque motor) on a feed-screw to achieve the bi-direction piezoelectric motion accumulation. Furthermore, the application of feed-screw could decrease the actuator’s sensitivity to wear, in order to realize a rigid self-locking and thus ensure the actuator’s holding capacity. A prototype was fabricated and the experimental results show that the no-load speed, maximum thrust, and peak power of the actuator were 20 mm/s, 280 N, and 1.54 W, respectively.

A new piezoelectric inchworm actuator with screw clamping mechanisms has been developed recently for the wing folding mechanism of a small unmanned aircraft where the actuator power density is a great concern. Considering that the prototype actuator was designed just with engineering intuition and the performance optimization through experimental developments would take a vast amount of cost and time, a mathematical model was developed to investigate the actuator’s critical design parameters and optimize its presently undesirable performance. Based on the lumped parameter method reported previously, and taking full account of the detailed modeling of the complex actuator housing and the actual nonlinear behaviors from the high-force contact and friction occurring at the screw-nut interface, as well as the output performance of the main drive elements including the piezoelectric stack and hollow ultrasonic motors (HUSMs), this model was built and then was experimentally verified for its accuracy and availability. Finally, nine design parameters were studied for their individual effect on the actuator’s output using the proposed model. The simulation results indicate that the performance can be considerably improved by performing a slight modification to the prototype, and the dynamic modeling and parameter optimization methods used in this study can also serve as a useful reference for the design of similar piezoelectric inchworm actuators with intermittent clamping behaviors.

The precise location of the needle tip is critical in robot-assisted needle-based percutaneous interventions. An automatic needle tip measuring system based on binocular vision technology with the advantages of noncontact, excellent accuracy and high stability is designed and evaluated. First the measurement requirements of the prostate intervention robot are introduced. A laser interferometer is used as the reference for measuring the position of the needle tip whose relative position variation is described as the needle tip distance in the time domain. The parameters of the binocular cameras are obtained by Zhang's calibration method. Then a robust needle tip extraction algorithm is specially designed to detect the pixel coordinates of the needle tip without installing the marked points. Once the binocular cameras have completed the stereo matching, the 3D coordinates of the needle tip are estimated. The measurement capability analysis (MCA) is used to evaluate the performance of the proposed system. The accuracy of the system can be controlled within 0.3621 mm. The agreement analysis is conducted by the Bland-Altman analysis, and the Pearson correlation coefficient is 0.999847. The P/T ratio value is 16.42% in the repeatability analysis. The results indicate that the accuracy and stability of the binocular vision needle tip measuring system are adequate to meet the requirement for the needle tip measurement in percutaneous interventions.

Ti-Al intermetallic compounds (Ti-Al IMCs) are emerging as lightweight, high-temperature structural materials with considerable application potential. Owing to their low density and high-temperature capability, these materials can improve the thrust-to-weight ratio of aeroengines, enhance the high-temperature service performance of aircraft, increase fuel efficiency, and improve adaptability to harsh environments. However, their intrinsic room-temperature brittleness leads to high cutting forces, elevated cutting temperatures, and severe tool wear during machining, making it difficult to ensure machining quality and limiting their large-scale applications in the aerospace industry. Ultrasonic vibration-assisted machining (UVAM) introduces a high-frequency, low-amplitude intermittent cutting mechanism that actively regulates material removal and offers a feasible route for overcoming the machining bottleneck of Ti-Al IMCs. This review summarizes the recent progress in UVAM for machining Ti-Al IMCs. First, the typical applications and machining characteristics of Ti-Al IMCs are discussed. Existing studies are then reviewed in terms of cutting performance, including cutting force, cutting temperature, chip morphology, tool wear, and post-machining surface integrity, including surface roughness, surface defects, residual stress, and work hardening. The reviewed evidence indicates that UVAM can reduce cutting forces and temperatures, improve chip morphology, and extend the tool life. It can also improve machined surface integrity by decreasing surface roughness, suppressing surface defects, inducing beneficial residual compressive stress layers, and regulating work-hardening behavior. This review provides systematic theoretical guidance and technical references for improving the machinability of Ti-Al IMCs via UVAM, thereby enabling the controllable, high-performance, and high-reliability fabrication of these difficult-to-machine materials in aerospace precision manufacturing.