Stick-slip Actuators Research Articles

Improving Velocity of Stick-Slip Piezoelectric Actuators With Optimized Flexure Hinges Based on SIMP Method

Flexure hinges have been widely applied in driving mechanisms to achieve the high velocity of stick-slip piezoelectric actuators. However, the majority of driving mechanisms are designed with existing flexure hinge forms, and it is difficult for the actuators to realize the optimal velocity performance. Therefore, a systematic method based on the topology optimization to design flexure hinges of driving mechanisms is proposed in this paper for improving the velocity of the actuators. According to the working principle, the velocity can be increased by maximizing displacement of a driving foot along the positive direction of $x$ -axis. The optimization problem of flexure hinges is described utilizing the Solid Isotropic Material with Penalization (SIMP) method. To illustrate the proposed method in detail, a four-bar mechanism with optimized flexure hinges is designed. Among them, three optimization schemes are implemented based on positions of flexure hinge design domains, and then deformations and equivalent stresses of the four-bar mechanism are investigated by simulation to find optimal flexure hinge forms. To prove the feasibility of the proposed method, the characteristic experiments of prototype are conducted. When the driving voltage and driving frequency of prototype are 100 Vp-p and 470 Hz, the maximum velocity is 17.50 mm/s, the maximum load is 220 g. And it is interesting to find that the prototype has no backward motion. Compared with the previously reported actuators with four-bar mechanisms, the velocity of prototype is significantly improved.

A Linear Piezoelectric Stick-Slip Actuator via Triangular Displacement Amplification Mechanism

In the field of piezoelectric actuators, high speed piezoelectric stick-slip actuators have received considerable attention. A linear stick-slip piezoelectric actuator is proposed in this article, which combines asymmetric flexure hinge with triangular displacement amplification mechanism. The designed linear piezoelectric stick-slip actuator can achieve high speed at lower frequency. The configuration of the actuator and driving principle are illustrated and designed by theory and simulation. In order to study its performance, a prototype is fabricated, and an experimental system is established. The experimental results confirm that the maximum step efficiency of the prototype is 97.9 %. The maximum speed is 20.17 mm/s under the driving voltage of 100 V P-P , the driving frequency of 610 Hz and the locking force of 2.5 N. The maximum load capacity is 2.4 N under the locking force of 3.5 N. The proposed piezoelectric stick-slip actuator increases the step efficiency and improves the output speed at lower frequency.

Actively controlling the contact force of a stick-slip piezoelectric linear actuator by a composite flexible hinge

Stick-slip piezoelectric actuators have been widely employed in those fields where both large working stroke and high positioning accuracy are required. However, the problems of backward motion and relatively low load capability limit their applications, and these two problems are usually contradictory. Attempted to solve these two problems at the same time, in this study, a composite flexible hinge was designed to actively control the contact force between the driving foot and the slider of a stick-slip piezo-driven linear actuator. To confirm the validity, a prototype actuator was designed and fabricated. The dimensions of the actuator in X, Y and Z directions are about 80 mm, 60 mm and 20 mm, respectively. The output characteristics of the actuator were evaluated by experiments. The results showed that without the active control of the contact force, the maximum speed being free of external load were 1.39 and 2.18 mm/s when the driving frequencies were 100 and 200 Hz, respectively. Correspondingly, the maximum horizontal loads of the actuator were 25 g and 50 g, respectively. However, with the active control of the contact force, the maximum speed were 1.74 and 4.1 mm/s under the driving frequency of 100 and 370 Hz, respectively. Moreover, the maximum horizontal loads under 100 Hz and 200 Hz were improved to be 40 g and 70 g, respectively.

A novel piezoelectric rotary actuator with a constant contact status between the driving mechanism and rotor

Taking advantage of simple structure and control, stick-slip piezoelectric actuators have been widely employed to realize precision positioning in precision machinery and instrument. However, their output characteristics could be significantly affected by the contact status between the driving mechanism and the mover (or rotor). If the contact status changes in the motion process, strong nonlinearity will appear in the displacement–time curve, deteriorating the performances. To achieve a constant contact status, the gravity of the rotor was used in this paper, and accordingly, a novel stick-slip piezoelectric rotary actuator was developed. The structure design, motion principle, as well as output characteristics of the actuator were addressed and discussed in detail. Experimental results indicated that when the driving frequency was below 350 Hz, stable stepping motions with quite small backward motion could be achieved. By changing the driving frequency, voltage and radius, various stepping rotation angles and speeds were easily obtained. The output characteristics changing with the vertical load were further characterized. Furthermore, by simply changing the direction of the driving waveform, forward and reverse rotation motions showing good linearity with time were achieved in a very large motion range, corresponding to a millimeter scale linear displacement. Comparative experiments with a normal stick-slip actuator further confirmed the validity and advancement of the proposed strategy for keeping a constant contact status, which will be beneficial to the subsequent motion control and mass production.

Simple and high-performance stick-slip piezoelectric actuator based on an asymmetrical flexure hinge driving mechanism

This article presented a new type of stick-slip piezoelectric actuator based on an asymmetrical flexure hinge driving mechanism. The key of the driving mechanism was a four-bar mechanism with different minimum thicknesses of right-circle flexure hinges. Combined with a symmetrical indenter, the asymmetrical flexure hinge driving mechanism generated controllable tangential displacement by changing the locking force. Therefore, the simple structured stick-slip piezoelectric actuator achieved considerable improvements especially in output speed and efficiency. In order to obtain improved actuator properties, the minimum thicknesses of asymmetrical flexure hinge driving mechanism, the tangential and normal displacements of the indenter were analyzed and investigated by finite element method. A prototype was fabricated and experiment investigation of the actuator characteristics was presented. Testing results indicated that the actuator achieved the maximum velocity of 15.04 mm/s and its maximum load reached 440 g under a voltage of 100 Vp-p and a frequency of 490 Hz. The maximum efficiency of the actuator was 3.66% with a load of 280 g under a locking force of 5 N and the actuated velocity of 10.17 mm/s.

Design and experimental performances of a piezoelectric stick-slip actuator for rotary motion

In order to reduce the regression phenomenon of the piezoelectric stick-slip actuator, and improve the output performance, a piezoelectric stick-slip actuator with regular octagonal flexible hinge mechanism is proposed in this paper. The pseudo-rigid body method is used to analyze the regular octagonal flexible hinge mechanism and the flexible driving foot respectively.A prototype is fabricated to test the working performance and the results demonstrate that the minimum step is 0.01μm, the maximum speed is 145251μrad/s, and the maximum load carrying capacity is 500g. The experimental results show that the parasitic motion suppresses the regression of the actuator and improves the output stability.

Evolution of one-stepping characteristics of a stick-slip piezoelectric actuator under various initial gaps

To investigate the effects of initial gap on the one-stepping characteristics of stick-slip piezoelectric actuators, a stick-slip piezoelectric rotary actuator with changeable initial gap was designed and fabricated. Its output characteristics were tested under various initial gaps. Experimental results indicated that the initial gap indeed significantly affected the output characteristics in one driving cycle, especially at the final stage when the driving voltage was decreased quickly. Gradually increasing the initial gap, an interesting phenomenon was observed that the one-stepping characteristics in the final stage transformed from the sudden return (the so-called backward motion) to a critical status (nearly smooth motion), and finally to sudden jump. By analyzing the practical driving waveform as well as the additional deformation of the actuator, the evolution of one-stepping characteristics was rationalized. These findings and discussion are expected to enhance our fundamental understanding of the stick-slip principle and actuators. In addition, this study suggests a method to suppress the backward motion by simply changing the initial gap.

Improving load capacity of stick-slip actuators in both driving directions via a shared driving foot

Stick-slip piezoelectric actautors are promising actautors with prinicipally unlimited stroke and positioning resolution. However, it is challenged with a low load capacity, which limits the field of application. Various types of compliant driving foot were proposed in literature to improve the load capacity but the improved load capacity is direction-dependent. To improve the load capacity in both forward and backward directions, this paper proposes an approach via a shared driving foot. The basic idea is to employ two piezoelectric actuators and a shared driving foot to work in a way that either forward or backward driving is a stick-slip process and both involve a clamping action during the ‘stick’ phase and a releasing action during the ‘slip’ phase, so that a large driving force/load capacity can be achieved in both driving directions. Following this approach, a shared driving foot was proposed and designed. Finite element simulations were carried out and have validated that the designed driving foot can realize the proposed approach as desired. A prototype was built and tested and the effectiveness of the proposed approach has been validated by experiments. Under the sawtooth waveform voltage of 100 V at 1 kHz, the prototype achieved a free-load forward and backward driving speed as large as 18.6 mm s−1 and 16 mm s−1 respectively and a load capacity larger than 2 kg for both driving directions. Under a driving load of 2 kg, it can still move stably with forward and backward driving speeds of 1.8 mm s−1 and 0.6 mm s−1 respectively.

Design and performance evaluation of a novel stick–slip piezoelectric linear actuator with a centrosymmetric-type flexure hinge mechanism

A stick–slip actuator with a centrosymmetric type flexure hinge mechanism was presented in this paper. The dimension of the actuator is approximately 83 mm × 82 mm × 19 mm. The positive and the negative motions could be achieved by two piezo stacks and one flexure hinge mechanism. To study the output characteristics, the actuator was fabricated and tested under various experimental conditions. The results showed that the maximum speeds of the positive and negative motions were 2.893 mm/s and 2.747 mm/s respectively, the maximum load was 3.8 N for both the positive and negative motions, the real displacement of a step of the positive and negative motions were 8.367 μm and 8.412 μm. Furthermore, the backward motion of the actuator had been greatly suppressed, which was beneficial to their wide applications in the fields of aerospace, precision-optics, nanomechanics, and so on.

An Umbrella-Shaped Linear Piezoelectric Actuator Based on Stick-Slip Motion Principle

Piezoelectric actuators are widely utilized in many research and industrial fields, since they could achieve high positioning accuracy based on inverse piezoelectric effect. However, the working stroke of piezoelectric actuators is always limited, which restricts the further application of piezoelectric actuators. In order to solve this problem on short working stroke, this study introduces an umbrella-shaped linear piezoelectric actuator to achieve a large working stroke. Unlike traditional stick-slip actuators, the PZT stack inside the umbrella-shaped flexure mechanism is assembled vertically to the slider. The composition and motion principle are discussed, and FEM (Finite Element Method) and experiments are utilized to explore the performance of the proposed actuator. Experimental results show that the minimum stepping displacement is $0.495~\mu \text{m}$ in the case that the input voltage $U=30\text{V}$ and the frequency $f=1$ Hz; the maximum speed is $992.4~\mu \text{m}$ /s under the condition of the input frequency $f=400$ Hz and the input voltage $U=120\text{V}$ ; the maximum load is 220g in the case of the input voltage $U=120\text{V}$ and the frequency $f=1$ Hz. This study indicates that the proposed umbrella-shaped linear piezoelectric actuator is feasible and could achieve a stable large working stroke.

A Voltage/Frequency Modeling for a Multi-DOFs Serial Nanorobotic System Based on Piezoelectric Inertial Actuators

Nanorobotic systems using piezoelectric stick-slip actuators are widely used in nanotechnology. They operate mainly in a coarse-positioning mode and a fine-positioning mode. In the first mode, the actuator performs large displacements with a maximal range of a dozen millimeters but with a low resolution. In the second mode, the displacements are of a few micrometers and below with a nanometer resolution. In order to achieve efficient automated tasks, it is often necessary to define closed-loop tracking strategies. To this end, an accurate multiscale model of the nanorobotic system is required. This paper deals with a new modeling approach to describe the dynamics of this class of systems in the time and the frequency domains for both coarse- and fine-positioning modes. We propose an augmented voltage/frequency modeling of the friction force based on a multistate elastoplastic formulation. Necessary conditions on the presliding modeling are studied to deal with the two operating modes and the motion direction. This model is combined with a nonlinear rate dependent hysteresis model. The main result and contribution of this paper is to demonstrate that a complete nanorobotic task involving closed-loop multiscale displacements can be precisely defined by simulations upstream of a real-time implementation with a mean error of 9.05%. The proposed model opens new perspectives for the definition of control strategies for complex nanorobotic tasks through simulation software tools.

Design, analysis and experimental performance of a novel stick-slip type piezoelectric rotary actuator based on variable force couple driving

A novel stick-slip type piezoelectric rotary actuator is proposed in this paper. The actuator equips with a parallelogram driving mechanism to generate a pair of variable force couple to drive the rotor. Two piezo-stacks are used to deform the parallelogram driving mechanism to realize large range motions with high resolution in both forward and backward directions. By utilizing pseudo-rigid-body method, geometric model of the parallelogram driving mechanism is established to analyze the motion of the actuator. Finite element analysis is conducted to simulate the deformation of the driving mechanism. A prototype is fabricated and a series of experiments are carried out. The experimental results indicate that the actuator prototype can achieve various angular velocities by changing the driving voltage and frequency and it can output large range rotary motions in both forward and backward directions. The driving resolutions are 0.75 μrad in forward direction and 0.82 μrad in backward direction and the maximum loading capacities are 74 N and 78 N, respectively. The angular displacement outputs under various driving voltages and frequencies show good linear relationships with the time in both forward and backward motions.

Investigation on driving characteristics of a piezoelectric stick–slip actuator based on resonant/off-resonant hybrid excitation

A resonant/off-resonant hybrid excitation of a piezoelectric stick–slip actuator is proposed in this paper. It is accomplished by a resonant sinusoidal friction regulation wave (RSFR-wave) and an off-resonant saw-tooth wave (ORST-wave). The RSFR-wave is applied to the rapid deformation stage of the ORST-wave. In this stage, the first-order longitudinal vibration mode of the stator can be obtained. By this longitudinal vibration mode, the kinetic friction between the slider and frictional rod is obviously decreased utilizing ultrasonic friction reduction. The backward displacement is remarkably restrained. The high velocity, large mass of load and smooth displacement are achieved. The operation principle of hybrid excitation was discussed in detail, and a prototype was simulated, designed, and fabricated. A series of experiments were carried out and the results indicate that the step efficiency under the saw-tooth excitation and resonant/off-resonant hybrid excitation can realize 36.9% and 91.2%, respectively. The output velocity is increased by 147.23% relative to saw-tooth excitation. The minimum input power and the minimum driving voltage are decreased by 89.56% and 58.33%, respectively. Besides, the maximum mass of load capacity is 2.88 times that of saw-tooth excitation. The driving capacity of the actuator is increased by 466.13%.

A Symmetrical Hybrid Driving Waveform for a Linear Piezoelectric Stick-Slip Actuator

A symmetrical hybrid driving waveform (SHDW) is proposed in this paper, which includes a symmetrical saw-tooth driving waveform and a sinusoidal friction regulation waveform, and the sinusoidal friction regulation waveform is applied to the shrinkage period of the symmetrical saw-tooth driving waveform. In other words, the proposed SHDW can be achieved when the waveform symmetry of the hybrid driving method is 50%. The SHDW can effectively drive the designed symmetrical linear piezoelectric stick-slip actuator, and the motion direction is also easily regulated. The excitation principle of the actuator excited by the SHDW is explained in detail. A prototype is fabricated and the experimental investigations of the actuator characteristics are carried on. The higher velocity and the larger driving capacity are realized using by the SHDW relative to the asymmetrical hybrid driving waveform. Testing results show that the prototype excited by the SHDW can obtain the peak no-load speeds of 0.41 and 0.39 mm/s in the forward and reverse directions when the saw-tooth driving waveform voltage is 10 $\text{V}_{\text {p-p}}$ for 800 Hz and the sinusoidal friction regulation waveform voltage is 2 $\text{V}_{\text {p-p}}$ for 39 kHz. The step efficiencies can reach 92% and 90%. The driving capacities can reach 10.52 and 9.85 [(mm/s)g/mW] with the load of 70 g under the locking force of 0.1 N. The actuator excited by the SHDW will make it ideal for miniature information technology devices.

Experimental optimization of power-function-shaped drive pulse for stick-slip piezo actuators

Motion of a stick-slip piezo actuator is generally controlled by the parameters related to its mechanical design and characteristics of the driving pulses applied to piezoceramic shear plates. The goal of the proposed optimization method is to find the driving pulse parameters leading to the fastest and the most reliable actuator operation. In the paper the method is tested on a rotary stick-slip piezo actuating system utilized in an atomic force microscope.The optimization is based on the measurement of the actuator response to driving pulses of different shapes and repetition frequencies at various load forces. To provide it, a computer controlled testing system generating the driving pulses, and detecting and recording the corresponding angular motion response of the actuator by a position sensitive photo detector (PSPD) in real time has been developed. To better understand and interpret the experimental results, supportive methods based on a simple analytical model and numerical simulations were used as well.In this way the shapes of the single driving pulses and values of the load force providing the biggest actuator steps were determined. Generally, the maximal steps were achieved for such a combination of the pulse shapes and load forces providing high velocities at the end of the sticking mode of the actuator motion and, at the same time, lower decelerations during the slipping mode.As for the multiple driving pulses, the pulse shapes and values of repetition frequency ensuring the sticking mode of the actuator motion during the pulse rise time together with the maximum average angular rotor velocity were specified. In this way the effective and stable operation conditions of the actuator were provided.In principle, the presented method can be applied for the testing and optimization of any linear or angular stick-slip actuator.

Experimental comparison of five friction models on the same test-bed of the micro stick-slip motion system

Abstract. The micro stick-slip motion systems, such as piezoelectric stick-slip actuators (PE-SSAs), can provide high resolution motions yet with a long motion range. In these systems, friction force plays an active role. Although numerous friction models have been developed for the control of micro motion systems, behaviors of these models in micro stick-slip motion systems are not well understood. This study (1) gives a survey of the basic friction models and (2) tests and compares 5 friction models in the literature, including Coulomb friction model, Stribeck friction model, Dahl model, LuGre model, and the elastoplastic friction model on the same test-bed (i.e. the PE-SSA system). The experiments and simulations were done and the reasons for the difference in the performance of these models were investigated. The study concluded that for the micro stick-slip motion system, (1) Stribeck model, Dahl model and LuGre model all work, but LuGre model has the best accuracy and (2) Coulomb friction model and the elastoplastic model does not work. The study provides contributions to motion control systems with friction, especially for micro stick-slip or step motion systems as well as general micro-motion systems.

An ARX-Based PID-Sliding Mode Control on Velocity Tracking Control of a Stick-Slip Pi-ezoelectric-Driven Actuator

Piezoelectric-driven stick slip actuators have been drawn more and more attention in the nano- positioning application due to the high accuracy and theoretical unlimited displacement. However, the hysteresis of piezoelectric actuator (PEA) and the nonlinear friction force between the end- effector and the stage make control of piezoelectric-driven stick slip actuator challenge. This paper presents the development of an autoregressive exogenous (ARX)-based proportional-integral-derive (PID)-sliding mode control (SMC) for the velocity tracking control of the piezoelectric-driven stick slip actuator. Stability is guaranteed by rigorously choosing the appropriate PID parameters and the zero steady state error is achieved. To verify the effectiveness of the proposed method, experiments were carried out on a commercially-available piezoelectric-driven stick slip actuator. The tracking errors were compared with the traditional PID controller, illustrating that in spite of existing of modeling error, the ARX-based PID-SMC is able to better improve the velocity tracking performance of piezoelectric-driven stick slip actuator, compared with the traditional PID controller.

Development and characterization of a novel piezoelectric-driven stick-slip actuator with anisotropic-friction surfaces

This paper reports a novel piezoelectric-driven stick-slip (PDSS) actuator with working surfaces of anisotropic friction. Compared to existing PDSS actuators, the new PDSS actuator has the higher efficiency and higher loading capability. The working surfaces of the new actuator were fabricated by employing hot filament chemical vapor deposition and ion beam etching. The surfaces were constructed such that they can provide with different levels of friction dependent on the direction of their relative motion, thereby providing a means to enhance the actuator performance. The performance of the novel actuator was characterized and compared to that of a PDSS actuator with the normal working surfaces, demonstrating its performance improvement.

Modeling of Piezoelectric-Driven Stick–Slip Actuators

Piezoelectric-driven stick-slip actuators have been drawing extensive attention in various applications of long-range and ultraprecision positioning. In such an actuator, the dynamics of the end-effector displacement is of importance for its design and control, yet challenging to be modeled due to the complexity involved. By taking into account the linear dynamics and hysteretic behavior of the piezoelectric actuator (PEA), as well as the presliding friction on the end-effector, a model representative of the end-effector displacement is presented in this paper. The effectiveness of the developed model is illustrated by the experiments on the piezoelectric-driven stick-slip actuator prototyped in the authors' laboratory.

Measurements and Potential Applications of Force-Control Method for Stick-Slip-Driven Nanohandling Robots

This paper describes the transition of a recently invented force-generation method to mobile nanohandling robots and outlines future applications. The presented mobile nanohandling robot makes use of miniaturized, piezo-driven Stick-Slip actuators. This allows for very accurate and fast positioning. The drives are fully developed and have proven their performance in fast pickand- place applications. On the other hand, the mentioned force-generation method allows a Stick- Slip axis to exert a dedicated force to any object, which could be useful in many micro- and nanohandling scenarios. However, the method was tested yet only in a testbed similar to the conditions in the robot. Therefore this paper deals with the extrapolation of the results to the real conditions in the robots and discusses benefits and drawbacks. After an introduction of the robot and the force-generation method, measurements are presented and discussed. The paper ends with a sketch of a possible application, which could boost the application potential not only of such mobile robots, but of Stick-Slip-based setups in general.