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  • 45 Reads
Initially Clamped Piezoelectric Inchworm Linear Motor based on Force Amplification Mechanisms Design for Miniaturized and Large Force Actuation Applications

Piezoelectric inchworm linear motor (PZT-ILM) are common in high precision positioning applications, such in optical equipment and precision manufacturing. PZT-ILM can be realized with one or multiple PZT stacks. The positioning of an object is performed either through direct contact of PZT elements that are functioning in shear mode [1-2], or indirect contact, through flexural mechanisms, where the PZT elements are functioning in normal mode [3-4]. The main advantage of using flexural mechanism is to enhance the reliability against damaging. Fortunately, flexural mechanisms can be also designed to amplify the generated displacement or force by PZT stack. However, miniaturization, large-force actuation capability, large internal stresses, fragile flexural design based on lever concept and requirement for high precision manufacturing are main challenges for realizing PZT-ILM based amplified mechanisms.

In this paper, a novel monolithic structural design of PZT-ILM utilizing three Force-Amplification-Mode (FAM) mechanisms is presented as an approach to overcome the fore mentioned design challenges. The new design consists of three main integrated mechanisms, such that each is driven by single PZT element. Two clamping mechanism, initially confined by a mechanical guidance, and become released when the corresponding PZT element is electrically polarized.

The other mechanism is centered between the clamping units, and perform device stretching when the corresponding PZT element is electrically polarized. In this work, a mechanical system model based on Simulink software was developed for a proposed design of a FAM PZT-ILM. The dynamic response of the motor was simulated at the moment of releasing the pre-stressed stretching mechanism, where one clamping mechanism is subjected to friction force, while the other clamping unit is free to move. The results showed backlash response due to the mass acceleration of the mechanisms. The effect of applying mechanisms of different mass amounts on the overall dynamic behavior was also investigated.

Literature
[1] H. Huang, L. Wang, Y. Wu; Design and Experimental Research of a Rotary Micro-Actuator Based on a Shearing Piezoelectric Stack, Micromachines 2019, 10, 96; 2019.
[2] B. Zhao, R. Fang, W. Shi; Modeling of Motion Characteristics and Performance Analysis of an Ultra Precision Piezoelectric Inchworm Motor; Materials 2020; 13, 3976; 2020.
[3] L. Ma, C. Jiang, J. Xiao, K. Wang; Design and analysis of a piezoelectric inchworm actuator; Journal of MicroRobot 2014, 9:11-21; 2014.
[4] X. Chen, M. Li, H. Zhang, Q. Lu, S. Lyu; Improvement on the Structure Design of a Kind of Linear Piezoelectric Motor with Flexible Drive-Foot; International Journal of Precision Engineering and Manufacturing 2020, 21:81-89; 2020.

  • Open access
  • 45 Reads
Force Amplification Mechanism for Increased Stroke and Speed Responses of Piezoelectric Stick-Slip Miniaturized Linear Motor

Piezoelectric stick-slip miniaturized linear-motor (PZT-SS-MLM) based on mechanical advantage mechanism design exhibits amplified displacement response and enhanced motor speed compared to conventional designs [1-4]. Due to the physics of mechanical advantage, the displacement amplification results definitely with specific force attenuation, which limits the load actuation-capacity. Therefore, critical design challenges will be encountered when large force actuation and miniaturized motor scale are required, such in medical implantable motors.

In this work, the Force-Amplification-Mode (FAM) configuration of mechanical advantage was investigated as alternative design approach for the conventional Displacement-Amplification-Mode (DAM) PZT-SS-MLM. In stick-slip motor, the total-displacement actuation consists of two components. One results from expansion deformation of mechanical advantage mechanism, after deformation of the PZT element. Another component is an extended
displacement results due to the gained acceleration of slipping mass, after the mechanical expansion of mechanical advantage mechanism, or in other words, after releasing of elastic energy stored in mechanical advantage mechanism, to a kinetic energy of the moving slipping mass. The larger the stored elastic energy, the larger the transferred kinetic energy. Therefore, the aim of comparison study in this work was to analyse the effect of applying larger actuation force, thus larger acceleration on the displacement, speed and load force limitation of the actuated object.

In this work, a mechanical system model based on Simulink software was developed for a proposed design of stick-slip motor. Only the orientation of a cubic PZT element identifies the mode configuration of the motor. The preliminary results showed that FAM exhibited roughly five times more speed, at hundred times more loading force, compared to DAM. Interestingly, when the output displacement was compared to maximum expansion of mechanical advantage mechanism, then FAM showed larger response compared to DAM. Therefore, FAM might be key design approach for further improved PZT-SS-MLM compared to conventional DAM ones.

Literature
[1] M. Hunstig; Piezoelectric Inertia Motors – Acritical Review of History, Concepts, Design, Applications, and Perspectives, Actuators 2017, 6(1), 7; 2017.
[2] A. Guignabart, A. Pages, O. Freychet, F. Barillot, J. Stentz, C. Belly, T. Maillard, F. Claeyssen; Improvement of MSPA: Module of Stepping Piezo Actuator; Actuator 2018; Bremen, Germany, 25-27 June 2018.
[3] W. Huang, M. Sun; Design, Analysis, and Experiment on a Novel Stick-Slip Piezoelectric Actuator with a Lever Mechanism; Micromachines 2019, 10, 863; 2019.
[4] X. Lu, Q. Gao, Y. Li, Y. Yu, X. Zhang, G. Qiao, T. Cheng; A Linear Piezoelectric Stick-Slip Actuator via Triangular Displacement Amplification Mechanism; IEEEAccess; vol. 8, 2020.

  • Open access
  • 131 Reads
ROBOTIC ORTHOSIS FOR UPPER LIMB REHABILITATION
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Subjects with impaired upper limb have motor limitations that interfere with their ability to independently perform activities of daily living. An alternative rehabilitation consists of Robot Assisted Therapy, a method that increases the intensity, dosage and consequently the effectiveness of the treatment. Therefore, news robotic actuators were developed, external to the device with components manufactured using additive manufacturing, to assist the upper limb rehabilitation. One of them aims to actively perform the finger extension and the flexion passively, using a servo motor coupled to a rope system. At the elbow, one DC-motor combined with a gear-box, was coupled to a system of pulleys and ropes designed to actively perform your flexion and extension movements. Triggering the system was used an Arduino-NANO® and a mobile application for Android. Evaluating the prototype performance, the fingers opening and closing movements were performed, together with the elbow flexion and extension and the gripping of objects in three post-stroke volunteers. It was observed with these actuators the volunteer has the ability to perform the proposed movements, using a torque of 12 Nm for the elbow movement and 0.8 Nm for the fingers opening. The volunteers showed forearm pronation during the tests, causing a torsion in the elbow support structure, making structural reinforcement necessary in the region, which resulted in an increase in the component's weight. After that, the pronation problem was solved and the movements could be performed. Therefore, this work presented new robotic devices composed by more robust motors and actuators, which are located externally to the device structure. Despite not being portable for everyday use, the device was able to perform the movements effectively, being possible to use it exclusively in rehabilitation clinics, so that it helps in the recovery of upper limb.

  • Open access
  • 49 Reads
Efficient SMA Actuation - Design & Control Concepts

The versatility in form factors of thermal shape memory alloys (SMA) in combination with their unique actuation and sensing abilities allow for the design and construction of innovative multifunctional systems. Despite the considerable number of advantages, like their exceptional energy density, only a few SMA-based actuator systems are commercially available. One of the main reasons for this is their inefficient thermal activation and the resulting high energy consumption. The efficiency of SMA-based actuator systems can be improved by innovative design and control approaches.

In the first part, the intelligent combination of SMA actuator wires with bi-stable, nonlinear spring elements is described. This combination eliminates oftentimes-quoted disadvantages of SMAs – slow actuation and energy-inefficiency – for a wide range of applications. In particular, two energy-free actuator configurations are realized, which can be applied to any non-proportional actuation tasks. The second approach for the realization of high-speed actuation and energy-efficiency is the activation of SMA wires with high voltage pulses, which leads to actuation times in the millisecond-range and energy-savings up to 80 % in comparison to the suppliers’ recommendations. It is shown that even high AC voltages like typical mains supplies can be directly used for highly efficient SMA activation.

  • Open access
  • 31 Reads
Evaluation on Topology of Switching Power Amplifier for Active Magnetic Bearings
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Switching power amplifier is a key component of the actuator of active magnetic bearing, and its reliability has an important impact on the performance of magnetic bearing system. This paper analyzes the topologies of switching power amplifier of active magnetic bearing. In the case of different coil pair arrangements and bias current distributions, comprehensive evaluation on different topologies of switching power amplifier is introduced. The valuation has a guiding role in the design of switching power amplifier of active magnetic bearing.

  • Open access
  • 78 Reads
Towards the Development of an Alternating Pressure Overlay for the Treatment of Pressure Ulcers Using Miniaturized Air Cells

This paper presents a study on design and development of an alternating pressure overlay consists of inflatable mini air-bladders, which could be used in relieving and reducing tissue pressure for the treatment of pressure ulcers. Pressure ulcers, which are predominant in the bony prominences of the body, is a skin deformity due to the limitation of blood circulation to the muscle tissues as a result of high pressures applied on the skin for longer durations. This research aims to design miniaturized air bladders which could provide alternating pressure sequences for the treatment of the pressure ulcers. The optimally designed geometries of mini air-bladders provide proper envelopment of the patient’s body and create a high resolution of pressure distribution. The optimum geometry and the 3-D deformation profile of the mini air-bladders are analyzed using the finite element method. Furthermore, the real-time interface pressure profile between the body and the overlay is mapped by using the back pressure of mini air-bladders. The actuator system includes an integrated control unit that regulates the internal pressures via electro-pneumatic valves operated based on the backpressure sensor feedback. This actuator system provides the alternating pressure patterns required for inflation and deflation of the mini air-bladders controlling the airflow of the support surface, providing proper pressure distributions to heal the ulcers.

  • Open access
  • 180 Reads
Finding the Perfect Match—Different Heavy-Duty Mobile Applications Call for Different Actuators

For the longest time, valve-controlled, centralized hydraulic systems have been the state-of-the-art technology to actuate heavy-duty mobile machine (HDMM) implements. Due to the typically low energy efficiency of those systems, several promising, more-efficient actuator concepts have been proposed by academia as well as industry over the last decades as potential replacements for valve control—namely electro-mechanic actuators (EMAs), displacement control and different types of electro-hydraulic actuators (EHAs). This paper takes a closer look on the application side to figure out where which of these novel solutions can be a better alternative to conventional concepts, and where they fail to improve. Application characteristics such as number and sizes of actuators, typical frequency and amount of power demands, or recuperation potential are classified as low or high for different machines fulfilling typical work tasks. To classify, duty-cycle video analyses and/or simulations in Simcenter Amesim were done for wheel loaders, excavators, backhoes and telehandlers. As counterparts, actuators are rated in their compatibility with the application characteristics. The ratings of both, applications and actuators, are numerically expressed and used to calculate mismatch values for different application-actuator pairings. The calculation method is modular and can be easily applied to additional applications or actuator concepts. Finally, the lowest mismatch value indicates the actuator concept which is the "perfect match" for a certain application. Low mismatch values could be found for wheel loaders in combination with zonal EHAs, excavators and telehandlers with displacement control or centralised EHAs, and backhoes with conventional load-sensing actuators.

  • Open access
  • 78 Reads
Multi-objective optimization design of a 30 kW Electro-hydrostatic Actuator

Electro-hydrostatic actuators (EHAs) combine the advantages of electric and hydraulic actuators, and it is resulting in a preferable solution for the heavy load actuation in applications such as aircrafts, ships, construction machines, and machine tools. The required power level of the EHA is increasing because the EHA is being introduced to heavier vehicles such as submarines and heavy launch vehicles. Thus, a 30 kW EHA is under development for launch vehicles, which simultaneously require high dynamic performance, light weight, high efficiency, etc. However, the existing optimization design methods of EHA do not take in account all the requirements, especially the dynamic performance. Therefore, a dedicate multi-objective optimization design method is proposed for the preliminary design for the 30 kW EHA. In this study, firstly, the design requirements were analyzed for the launch vehicle application, and the objectives and the constraints of the optimization design were defined for the 30 kW EHA. Secondly, dedicate models were developed for evaluating each objective or constraint. Among these models, the EHA weight is estimated through the scaling law method and analytical calculation, the bandwidth is estimated based on the cascaded control method, the energy consumption is evaluated by the inverse dynamic simulation utilizing dedicate Matlab codes. Thirdly, the multi-objective EHA optimization design was implemented based on the genetic algorithm. Hereby, the key parameters were decided for the proposed EHA design. At last, the optimization design results were evaluated through simulation analysis, which demonstrated that the 30 kW EHA achieved more than 10 Hz bandwidth with under 70 kg weight while the efficiency was also optimized. In addition, the proposed method is shown to be competent for the preliminary design of high power EHAs which are subject to multiple critical requirements.

  • Open access
  • 40 Reads
Development of pneumatic soft actuator using high strain elastic material with stress anisotropy by short fibers

In recent years, attention has been focused on soft robots, such as robots with a high human affinity and robots that imitate the excellent movements of natural creatures. As actuators used in soft robots, structurally flexible soft actuators are required, not conventional motors or hydraulic/pneumatic cylinders. Various types of soft actuators have been developed depending on the driving principle. Pneumatic rubber artificial muscle is a kind of soft actuator that obtains power by injecting a working fluid such as air into an elastic structure such as rubber. The authors are developing the Straight fiber type artificial muscle as an actuator with excellent contraction characteristics. This artificial muscle has a structure in which a rubber tube contains reinforcing fibers arranged in the axial direction. When air pressure is applied to this, it expands only in the radial direction and contracts in the axial direction due to the restraint of the reinforcing fiber. While this artificial muscle has excellent contraction properties, it has a problem that it is difficult to enclose the reinforced fibers that have been gathered together in a rubber tube, which makes it difficult to manufacture. Therefore, in this study, as a material for pneumatic rubber artificial muscle, we investigated short fiber reinforced rubber in which aramid short fibers were oriented in one direction in the rubber. In the orientation direction of the short fibers, the tensile stress was 1.5 times and the elongation at break was 0.25 times that in the direction perpendicular to the orientation. It was confirmed that the artificial muscle made of short fiber reinforced rubber has a maximum contraction ratio of 17% and can be used as a rubber material for artificial muscle.

  • Open access
  • 78 Reads
Manufacturing of a helical, self-coiling dielectric polymer actuator

For the next generation of Soft Robotics novel materials are needed that overcome the limitations of established active materials like shape memory alloys or dielectric elastomer actuators. These new actuator types should offer fast actuation and good electromechanical coupling. In this publication, the manufacturing process and the resulting prototype of a helical dielectric polymer actuator are presented. The actuator material consists of several layers of thermoplastic elastomer and thermoplastic polymer layers with conductive fillers that are thermally bonded and stretched afterwards, which leads to self-coiling into a helical configuration. In the targeted set-up the thermoplastic dielectric layer, that is compressed by Maxwell pressure, is significantly thinner but much easier to handle than silicone films frequently used in dielectric elastomer actuators. Several manufacturing strategies are discussed and experimentally evaluated. This includes the use of different materials, their preliminary treatment, the implementation of electrically conducting layers functioning as electrodes and the contacting of the conducting layers. By identifying feasible settings and properties for these parameters, potential defects occurring during manufacturing or high-voltage activation can be minimized. By pre-stretching and then releasing a thin strip of the laminate structure, a helix is formed. The resulting prototype actuator set-up is characterized under voltages of 3 kV and shows high-speed actuation at deformation speeds of > 5 %/s. Due to the helical configuration, the observed contraction is orders of magnitude higher than the theoretical value for the corresponding flat configuration, showing the potential of the newly developed actuator material.

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