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  • Open access
  • 28 Reads
Electromechanical actuators for large sized vavles

In modern hydraulics, it is crucial to investigate possible enhancements for components, which lead to increased performance or new improved system designs. Previous research of the switching process of a large valve pointed out that electromechanical valve actuators can replace hydraulic pilot control systems. Especially in systems, which currently, depend on a separate pilot circuit electromechanical actuators can lead to a huge decrease in the system acquistion costs. Actuators for large valves have to fulfill varying requirements. For example they need to apply high forces over large strokes. In order to define these requirements conveniently and to develop new valve actuators a functional structure of the “valve and his actuation system” has been derived in this paper. Using this design tool, the main function of the component is devided into different elementary functions. The graphical presentation of the system helps to define the requierements by outlining the correlations and to develop a new system by adding or deleting elementary functions. Using the functional structure, all acting forces have been identified and a prototype of a new electromechanical actuator for large directional control vales. A Force of up to 500 N and a stroke larger than 10 mm is realizible. Due to the new actuator design, further friction, clamping and resistance forces occur. Therefore, possible improvements on the actuator are suggested. In conclusion the paper summarizes significant points during the design process of electromechanical valve actuators and is intended as a basis for the development of new valve actuators.

  • Open access
  • 24 Reads
A method for smoothly disengaging the load-holding valves of energy-efficient electro-hydraulic systems

A novel self-contained, electro-hydraulic cylinder drive capable of passive load-holding, four-quadrant operations, and energy recovery was presented recently and implemented successfully. This solution improved greatly the energy efficiency and motion control in comparison to state-of-the-art, valve-controlled systems typically used in mobile or offshore applications. The passive load-holding function was realized by two pilot-operated check valves placed on the cylinder ports, where their pilot pressure is selected by a dedicated on/off electro valve. These valves can maintain the actuator position without consuming energy, as demonstrated on a single-boom crane. However, a reduced drop of about 1 mm was observed in the actuator position when the load-holding valves are disengaged to enable the piston motion using closed-loop position control. Such a sudden variation in the piston position that is triggered by switching the load-holding valves can increase up to 4 mm when open-loop position control is chosen. For these reasons, this research paper proposes an improved control strategy for disengaging the passive load-holding functionality smoothly (i.e., by removing this unwanted drop of the piston). A two-step pressure control strategy is used to switch the pilot-operated check valves. The proposed experimental validation of this method eliminates the piston position’s drop highlighted before and improves the motion control, mainly when operating the crane in open-loop. Theses outcomes benefit those systems where the kinematics amplifies the piston motion significantly (e.g., in aerial platforms) increasing, therefore, the operational safety.

  • Open access
  • 17 Reads
Development of Control Circuit for Inductive Levitation Micro-Actuators
Vitor Vlnieska, Achim Voigt, Sagar Wadhwa, Jan Korvink, Manfred Kohl, Kirill Poletkin

The control circuit for inductive levitation micro-actuators is developed in this research. The circuit performance and its electrical parameters are discussed. The developed control circuit was fabricated on a 4-layer PCB board having a size of 60 mm by 60 mm. It consists of a generator based on high-speed Flip-Flop components and a current amplifier build on a bridge configuration. The circuit is able to generate ac current with squared shape in a range of frequency from 8 to 43 MHz and with peak-to-peak amplitude up to 420 mA. To demonstrate the efficiency of the developed circuit and its compatibility with the micro-actuation system, an inductive levitation micro-actuator was fabricated by using 3D micro-coil technology. The device was composed of two solenoidal coil design, which consists of levitation and stabilization coil, having 2 mm and 3.8 mm in diameters, respectively. The levitation coil has 20 turns of a gold wire of a 25 µm diameter, while the stabilization one has 12 turns similar to the micro-structure presented previously by our group. Using the developed control circuit, the micro-actuator was successfully excited and it demonstrated the actuation of aluminum disc-shaped micro-objects having a diameter of 2.7 and 3.2 mm and, for the first time, an aluminum square shaped micro-object having a side-length of 3.4 mm at a frequency of 10 MHz. To characterize the actuation, the levitation height and the rms amplitude of current were measured. In particular, we showed that the square shaped micro-object can lift up on a height of 100 µm with rms current of 160 mA. The characterization is supported by the simulation using a 3D model based on the quasi-FEM approach.

  • Open access
  • 37 Reads
Origami-Inspired Shape Memory Folding Microactuator

This paper presents the design, fabrication and performance of origami-based folding microactuators based on a cold-rolled NiTi foil of 20 µm thickness showing the one-way shape memory effect. Origami refers to a variety of techniques of transforming planar sheets into three-dimensional (3D) structures by folding, which has been introduced in science and engineering for, e.g., assembly and robotics. Here, NiTi microactuators are interconnected to rigid sections (tiles) forming an initial planar system that self-folds into a set of predetermined 3D shapes upon heating. While this concept has been demonstrated at the macro scale, we intend to transfer this concept into microtechnology by combining state-of-the art methods of micromachining. NiTi foils are micromachined by laser cutting or photolithography to achieve double-beam structures allowing for direct Joule heating with an electrical current. A thermo-mechanical treatment is used for shape setting of as-received specimens to reach a maximum folding angle of 180°. The bending moments, bending radii and load-dependent folding angles upon Joule heating are evaluated. The shape setting process is particularly effective for small bending radii, which, however generates residual plastic strain. After shape setting, unloaded beam structures show recoverable bending deflection between 0° and 140° for a maximum heating power of 900 mW. By introducing additional loads to account for the effect of the tiles, the smooth folding characteristic evolves into a sharp transition, whereby full deflection up to 180° is reached. The achieved results are an important step towards the development of cooperative multistable microactuator systems for 3D self-assembly.

  • Open access
  • 21 Reads
Tracking Control for Piezoelectric Actuators with Advanced Feed-forward Compensation Combined with PI Control.

Piezoelectric actuators (PEA) are devices which can support large actuation forces compared to their small size and are widely used in high precision applications where micro- and nanopositioning is required. Nonetheless, these actuators have undeniable non-linearities were the well-known are creep, vibration dynamics and hysteresis. The latter mentioned is originated due to a combination of mechanical strain and electric field action; as a consequence, these can affect the PEA tracking performance and even reach instability. The scope of this paper is to reduce the hysteresis effect using and comparing different control strategies like feedback with feed-forward (FF) structure which is often used to compensate the non-linearities and diminish the errors due to uncertainties. In this research, black-box models were analysed; subsequently, a classic feedback control like proportional-integral (PI) was combined with the FF methods proposed separately and embedded into a dSpace platform to perform real-time experiments. Results were analysed in-depth in terms of the error, the control signal and the integral of the absolute error (IAE). It was found that with the proposed methods, the hysteresis effect could be diminished to acceptable ranges for high-precision tracking with a satisfactory control signal.

  • Open access
  • 22 Reads
Numerical studies on the design of self-resetting active bistable cross-shaped structure for morphing applications
P. M. Anilkumar, A. Haldar, S. Scheffler, B. N. Rao, R. Rolfes

Multistable structures are highly attractive for advanced shape-changing (morphing) applications due to their low weights, excellent mechanical properties, and large deformation capabilities. Aim of the paper is to develop a bistable cross-shaped structure, consisting of symmetric and unsymmetric laminates actuated using Macro Fibre Composite (MFC) actuators. The cross-shaped bistable laminates find potential applications in solar tracking models and energy harvesters. The critical snap-through voltages required to change the shapes are investigated using commercially available finite element package. Use of planar MFC actuators to snap the bistable laminate from one equilibrium shape to another, and back again (self-resetting) is demonstrated. For the design of the active bistable cross-shaped structure, the cross-shape is split into four rectangles on the four legs and a square on the middle portion. All the rectangles are made up of unsymmetric laminates, and the central portion is designed with a symmetric laminate. MFC actuators are bonded on both sides of the four legs to trigger snap-through and snap-back actions. An attempt is made to address the possible design difficulties arising from the additional stiffness contribution by MFC layers on the naturally cured equilibrium shapes of cross-shaped bistable laminates. Suitable potential applications using the designed self-resetting active bistable cross-shaped laminate are proposed.

  • Open access
  • 22 Reads
Linear motors based on piezoelectric MEMS

The miniaturization of actuators for applications that need large displacements, high energy efficiency or output forces is an ongoing challenge [1]. Piezoelectric ultrasonic motors (USM) have proven to be a suitable solution to obtain long motion range, high torque, quick response, high power to weight ratio and high efficiency in comparison to electrostatic, magnetic, and thermal alternatives [2]–[4]. Despite the advantages of USM for linear motion, scaling down to the millimetre range remains a challenge, due to the difficulties in generating standing or travelling waves at high frequencies with enough amplitude [5].

The monolithic fabrication based on silicon micromachining, in combination with the use of integrated piezoelectric films was successfully applied to the effective size reduction of such positional devices. Furthermore, the addition of 3D-printed legs, for a controlled contact, allowed for a further step into the manufacturing of efficient linear motors. Such hybrid devices have recently demonstrated the conveyance of sliders – surpassing several times the motor weight – with speeds of 1.7 mm/s, while operated at 6 V and 19.3kHz and positional resolution of 70 nm [6]. However, by the optimisation of various aspects of the device such as the vibrational modes and excitation signals, or the legs dimension and distribution, speeds above 30 mm/s could be reached with payloads above 25 times the motor weight.

[1] Kenji Uchino, MicroMechatronics, Second Edition.

[2] M. L. Chan et al., ‘Design and characterization of MEMS micromotor supported on low friction liquid bearing’, Sens. Actuators Phys., vol. 177, pp. 1–9, Apr. 2012, doi: 10.1016/j.sna.2011.08.003.

[3] A. Khiat et al., ‘Linear and rotational thermal micro-stepper motors’, Microelectron. Eng., vol. 98, pp. 497–501, Oct. 2012, doi: 10.1016/j.mee.2012.07.086.

[4] E. Sarajlic, C. Yamahata, M. Cordero, and H. Fujita, ‘Three-Phase Electrostatic Rotary Stepper Micromotor With a Flexural Pivot Bearing’, J. Microelectromechanical Syst., vol. 19, no. 2, pp. 338–349, Apr. 2010, doi: 10.1109/JMEMS.2010.2040139.

[5] J. S. Pulskamp et al., ‘Piezoelectric PZT MEMS technologies for small-scale robotics and RF applications’, MRS Bull., vol. 37, no. 11, pp. 1062–1070, Nov. 2012, doi: 10.1557/mrs.2012.269.

[6] V. Ruiz-Díez, J. Hernando-García, J. Toledo, A. Ababneh, H. Seidel, and J. L. Sánchez-Rojas, ‘Bidirectional Linear Motion by Travelling Waves on Legged Piezoelectric Microfabricated Plates’, Micromachines, vol. 11, no. 5, Art. no. 5, May 2020, doi: 10.3390/mi11050517.

  • Open access
  • 23 Reads
Sub-gram in-plane vibration-driven robot with inclined legs

Despite the breakthroughs in the locomotion of robots at the macroscale, there is not a counterpart at the miniature scale. A recent review [1] pointed out the limitations of sub-gram systems. Locomotion based on legs is already well established for robotic platforms. Assuming a back and forth motion of the legs, a net displacement can be attained when the forward slip is not equal to the backward slip. The use of inclined legs is a common approach to achieve such an asymmetric slip. Reference [2] provides an excellent review of this approach.

Here we propose a sub-gram system based on flexible materials. The body of the robot was a 3 cm long thin film of piezoelectric polyvinylidene fluoride (PVDF) polymer. The actuation mechanism was an in-plane extensional vibration mode of the PVDF film. Two U-shaped 3D printed nylon legs were fabricated, each attached to the edges of the PVDF support. The total mass of the PVDF/legs combination was below 20 mg for all the cases under study. Unidirectional locomotion was achieved, with a maximum speed of 47 mm/s, equivalent to 1.5 body lengths/s, at a voltage of 15 V, with 2 mm long legs at an angle of 60º to the PVDF film.

[1] Ryan St. Pierre, Sarah Bergbreiter, “Toward Autonomy in Sub-Gram Terrestrial Robots”. Annual Review of Control, Robotics, and Autonomous Systems 2, 16.1-16.22, 2019.

[2] Walter Driesen, “Concept, Modeling and experimental characterization of the modulated friction inertial drive (MFID) locomotion principle: Application to mobile microrobots”. PhD thesis, École polytecnique fédérale de Lausanne, 2008.

  • Open access
  • 28 Reads
A Low-Cost Miniature Electrohydrostatic Actuator

This paper presents a low-cost, small-scale, electrohydrostatic actuator (EHA). This actuator leverages low-cost mass-produced hydraulic components from the radio-controlled model industry, combined with a novel 3D printed valve. The system is capable of relatively high bandwidth operation, with much higher power- and force-density than comparable electrical actuators. This paper presents a dynamic system model, investigating the range of stability and presents simulated and experimental results for systems stabilized by both physical leakage and pressure feedback terms. We also investigate the feasibility of two 3D printed valve options, concentrating on the limits of leakage for low-cost production: one fully 3D printed and another with a metal sleeve that can be machined using only hand tools.

  • Open access
  • 25 Reads
Modeling and simulation of an array of Dielectric Elestomeric Actuator Membranes
Sipontina Croce, Julian Neu, Jonas Hubertus, Stefan Seelecke, Günter Schultes, Gianluca Rizzello

Recent technological advances in miniaturized actuators and sensors have enabled the development of cooperative systems, in which a complex global task is achieved through the cooperation of several microactuators. Achieving system miniaturization while maintaining the desired actuation/sensor and cooperative functionality, however, is in general a highly challenging task. To reach this goal, one viable approach consists of implementing transducers based on intelligent materials, such as dielectric elastomers (DE). By designing a miniaturized array of DE membrane taxels, their simultaneous actuation and sensing capabilities can be used to develop flexible, large deformation, energy-efficient, and multi-functional cooperative systems. In addition, the high flexibility of DE material makes the developed system highly suitable for new fields of application, such as wearables and soft robotics.

In order to properly understand and optimize DE array systems, accurate models and simulation tools play a fundamental role. Due to the strongly nonlinear behavior of the material, however, DE modeling is generally highly challenging. In addition, the electro-mechanical coupling and the neighboring effects existing between closely packed actuators further complicates the overall modeling task.

In this paper, we present a physics-based model for an array of three DEAs. Such a model represents the first step towards the development of a complex cooperative matrix actuator. Through the proposed model, it is possible to describe the electromechanical coupling existing between the DE elements, and how such a cupling affects the complete system performance. These interactions depend on several design parameters, such as the size of the individual membranes, their relative spacing, and the mechanical pre-tensioning. After presenting the model, the influence of geometrical parameters on the spatial coupling response is studied by means of numerical simulations. The developed model will allow, in a future stage, to effectively design and optimize cooperative DE systems.