Piezoelectric actuators are widely used in precision positioning, micro/nano fabrication, and microrobotics due to their high precision, fast response, and compactness, yet their inherently limited stroke (typically ~1/1000 of their length) constrains broader applications. To extend travel, stepping actuation approaches—such as inchworm, ultrasonic, and stick-slip mechanisms—have been explored, with stick-slip attractive for its relatively simple structure and control. However, many stick-slip designs still struggle with bidirectional motion consistency and motion smoothness/linearity: particularly, parasitic-motion-based actuators often exhibit structural asymmetry, making forward and reverse driving processes unequal and degrading precision, repeatability, and bidirectional control. Even symmetric solutions may require multiple piezo elements and manual pre-adjustment, increasing complexity and reducing practicality. This motivates the search for a simpler, more robust driving concept that can deliver consistent bidirectional motion with improved smoothness. “This work presents a novel rolling driving principle (RDP) for stick-slip actuators to achieve high motion consistency, inspired by the rack-and-pinion mechanism.” said the author Dunfa Long, a researcher at Tianjin University, “This RDP utilizes a symmetrical driving structure and tangential contact to realize the pure rolling motion between the stator and the slider, requiring just a single lead zirconate titanate (PZT). This configuration ensures a consistent bidirectional driving process with a constant contact force, which improves both motion consistency and linearity. ”
The structure of the proposed Rolling Driving Principle (RDP) actuator is based on an isosceles trapezoidal flexible mechanism (ITFM), incorporating a four-bar linkage and a piezo stack driving unit. The core of the RDP-type actuator is the ITFM, which contacts the slider with a curved driving surface to achieve pure rolling motion during operation. This structure ensures constant contact force during driving, reducing contact force fluctuations and enhancing motion linearity. The piezo stack drives the four-bar linkage, generating rotational motion. By expanding and contracting periodically, the piezo stack moves the ITFM to produce linear displacement of the slider. The design of ITFM is symmetric, ensuring bidirectional motion consistency in both forward and reverse directions. This symmetry eliminates the need for manual pre-adjustment and allows the system to adapt to assembly errors, simplifying the overall system complexity. Finite element method (FEM) optimization was employed to minimize axial drift, improving the actuator's precision and consistency. This actuator design reduces complexity and manual adjustments, improving bidirectional consistency and linearity, making it suitable for high-precision motion control applications.
The testing results show that the RDP-type actuator demonstrates outstanding performance across both low and high-frequency ranges. In terms of bidirectional consistency, at 10 Hz, the velocity difference ratio between forward and reverse motion is 1.96%, and at 560 Hz, it is 7.54%, indicating excellent bidirectional consistency. Regarding motion linearity, the forward and reverse motion linear correlation coefficients are 0.99969 and 0.99962 at 10 Hz, and both reach 0.99999 at 560 Hz, demonstrating extremely high linearity and smooth motion. Additionally, the speed fluctuation coefficients at 560 Hz are 0.0494 for forward and 0.0842 for reverse motion, significantly lower than other designs, highlighting its smooth motion characteristics. In terms of load capacity, the actuator maintains stable bidirectional output speed under a vertical load of up to 1200g in low-frequency tests, showing strong load-bearing capacity. At high frequencies, the actuator achieves output speeds of 37.73 mm/s (forward) and 34.99 mm/s (reverse) at 560 Hz, with minimal speed fluctuation, demonstrating excellent high-frequency performance. These results demonstrate the superior performance of the RDP-type actuator under various conditions, making it highly suitable for applications requiring high precision and linearity.
The RDP-type actuator significantly enhances bidirectional consistency and motion linearity due to its symmetric driving structure and constant contact force. Through practical application tests, the paper demonstrates that this actuator can maintain excellent performance at both low and high frequencies, while generating sufficient output speed and load capacity without the need for pre-adjustment. Based on this actuator, an MRI-compatible microsurgical instrument was developed, successfully achieving opening and closing motions, and its potential for real surgical applications was validated through cutting experiments. “In future, we will focus on dynamic modeling of the actuator, fiber Bragg grating (FBG) force sensing technology, and closed-loop control to further expand its applications.” said Dunfa Long.
Authors of the paper include Dunfa Long, Fujun Wang, Chengzhi Hu, and Chaoyang Shi.
This work is supported in part by the National Key Technologies R&D Program of China (grant 2023YFC2415900), the National Natural Science Foundation of China (grants 62373182, 92148201, and 52475029), and the International Institute for Innovative Design and Intelligent Manufacturing of Tianjin University in Zhejiang, Shaoxing, China.
The paper, “A Novel Rolling Driving Principle-Enabled Linear Actuator for Bidirectional Smooth Motion” was published in the journal Cyborg and Bionic Systems on Jan 9, 2026, at DOI: 10.34133/cbsystems.0424.
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