This paper presents a novel impact rotary motor based on a piezoelectric tube actuator with helical interdigitated electrodes which has a compact structure and high resolution. The assembled prototype motor has a maximum diameter of 15 mm and a length of 65 mm and works under a saw-shaped driving voltage. The LuGre friction model is adopted to analyze the rotary motion process of the motor in the dynamic simulations. From the experimental tests, the first torsional resonant frequency of the piezoelectric tube is 59.289 kHz with a free boundary condition. A series of experiments about the stepping characteristics of different driving voltages, duty cycles, and working frequencies are carried out by a laser Doppler vibrometer based on a fabricated prototype motor. The experimental results show that the prototype rotary motor can produce a maximum torsional angle of about 0.03° using a driving voltage of 480 V_p-p (peak-to-peak driving voltage) with a duty ratio of 0% under a small friction force of about 0.1 N. The motor can produce a maximum average angle of about 2.55 rad/s and a stall torque of 0.4 mN∙m at 8 kHz using a driving voltage of 640 V_p-p with a duty ratio of 0% under a large friction force of about 3.6 N. The prototype can be driven in forward and backward motion and is working in stick-slip mode at low frequencies and slip-slip mode at high frequencies.

A compact linear-rotary impact motor based on a single piezoelectric tube actuator is proposed. The motor can realize independent linear and rotary motions. With two independent electrodes, the piezoelectric actuator has an outer diameter of 6 mm, a thickness of 0.5 mm, and a length of 25 mm. The actuator produces a maximum axial displacement of 2.17 µm with a driving voltage of 720 V_p-p (peak-to-peak driving voltage), and it produces a maximum torsional angle of 599.98 µrad with a driving voltage of 720 V_p-p. The prototype motor can achieve the independent linear velocities of 6263.45 µm/s and −6331.58 µm/s in the positive and negative directions of motions under the saw-shaped driving voltage of 560 V_p-p at 8 kHz. The motor can realize the independent rotary velocities of 1.22 × 10⁶ µrad/s and −1.21 × 10⁶ µrad/s in the two motions under the saw-shaped driving voltage of 560 V_p-p at 9 kHz. The maximum output force of the motor is 0.45 N, and the maximum output torque is 0.80 mN m for linear and rotary motions, respectively.

A novel impact two-degree-of-freedom (2-DOF) motor based on the decomposed screw-type motion of a piezoelectric actuator (PA) has been proposed. The fabricated prototype motor has a maximum diameter of 15 mm and a length of 100 mm which can produce a maximum torsional angle of about 1000 μrad and a maximum longitudinal displacement of about 1.03 μm under a saw-shaped driving voltage with 720 V_p-p (peak-to-peak driving voltage). When the axial prepressure generated by the spring is about 1N and the radial prepressure generated by the snap ring is about 14 N, the fabricated motor realizes rotary motion with the driving frequency from 200 Hz to 4 kHz. When the axial prepressure generated by the spring is about 11.7 N and the radial prepressure generated by the snap ring is about 21.1 N, the fabricated motor realizes linear motion with the driving frequency from 2 kHz to 11 kHz. In the experiments, the prototype motor can achieve 9.9 × 10⁵ μrad/s rotary velocity at 2 kHz and it can achieve 2.4 mm/s linear velocity at 11 kHz under the driving voltage of 720 V_p-p.

A two-degrees-of-freedom (2-DOF) linear piezoelectric impact drive mechanism (PIDM) is actuated by two independent piezoelectric actuators (PAs). The coupled motion interactions of a two orthogonal DOF linear PIDM with a single friction interface are introduced and analyzed. A complete dynamic model of the 2-DOF PIDM is established with the Karnopp friction model considering the distribution of friction in the x-axis and y-axis. The output displacements of the 2-DOF PIDM and two corresponding independent 1-DOF PIDMs are investigated numerically. When the two input exciting signals of a 2-DOF PIDM have the same driving voltage of 100 V with a duty ratio of 98% at 10 Hz and two 1-DOF PIDMs are driving under the same conditions, the step displacements in the two axes of 2-DOF PIDM are improved compared to the corresponding 1-DOF PIDM. When the two input exciting signals of a 2-DOF PIDM have the same driving voltages of 100 V with a duty ratio of 98% but the driving frequency is 10 Hz in the x-axis and 20 Hz in the y-axis, the results show that the displacement of high frequency achieves a slight decrease and displacement of low frequency shows a large increase compared to the two corresponding 1-DOF PIDMs.

A compact impact two-degree-of-freedom linear-rotary piezoelectric motor is proposed using a single actuator. The proposed piezoelectric actuator has a pair of deformation counteracting helical interdigitated electrodes on its outside surface, which can be divided into two parts. When the two parts of the piezoelectric actuator are driving under the same driving voltage signals, the motor can realize independent linear motion. When the two parts of the piezoelectric actuator are driving under the driving voltage signals with opposite duty cycles, the motor can realize independent rotary motion. The fabricated piezoelectric motor can produce a maximum average linear velocity of 1.9 and −2.3 mm/s with a saw-shaped driving signal of 400 Vp-p (peak-to-peak driving voltage) at 9 kHz. Experiments also show that the fabricated piezoelectric motor can realize a maximum average rotary velocity of 2440 and −2235 mrad/s with a driving signal of 400 Vp-p at 9 kHz. The maximum load force and torque of the prototype are about 0.4 N and 1.5 mN m, respectively. The proposed motor provides a wide driving frequency and realizes high velocity in both linear and rotary motions.

T ² control chart, a prevalent statistical process control technique, has extensively employed in the realm of bearing early failure monitoring within the setting of prognostics and health management. However, insufficient historical data as well as the nonidentical distributions between training and testing date, caused by stochastic noise and fluctuating operational conditions, inevitably increase the risk of false alarms and hinder the robustness of bearing early failure monitoring. To address the challenges, a covariance transfer enabled T ² control chart (CTET2CC) is proposed for bearing early failure monitoring under varying operational conditions. Firstly, feature extraction is conducted via the multi-time scale phase space warping (MPSW) method. Thereafter, a Gaussian process is employed to derive functional relationships in the source and target domains, respectively, in order to construct the T² profile control chart. Then, the domain-invariant statistics can be efficiently learned from a large number of source domain profile samples through singular value decomposition (SVD), which excels in capturing the essential features of profile samples, and providing a robust representation of the underlying structure. Furthermore, a covariance transfer through SVD strategy is designed by reweighting the target statistics. Finally, the corresponding T² control chart is reconstructed to boost the stability of the controlled phase for target task. Experimental results verify that the proposed method is expected to be an effective technique for bearing early failure monitoring.