Actuators are defined as transducers that convert electrical energy to mechanical movement. Similar to sensors and control systems, actuators are essential devices in various industrial applications, such as robotics, precise positioning systems, and automobiles. The performance required of each actuator depends on its practical application, and the actuators may determine the total performance of the systems. Various types of actuators have been proposed, not only for high efficiency, torque, and power output but also for flexibility, miniaturization, and drivability under extreme conditions. In the case of fluid-based actuators, the control of the working gas or liquid becomes an indispensable technology. The creation of a device with a simple structure yet multiple degrees of freedom would be quite worthy of research. Such an actuator would lead to future applications, which would in turn enable humanlike movements in robots, ultra-precise positioning systems under extreme high (or low) temperature conditions, or MEMS devices that operate in the human body.
This special issue, entitled Innovative Actuators, is a collection of seventeen papers related to these considerations. In addition to electromagnetic motors, various types of actuators, such as piezoelectric, electrostatic, and pneumatic motors. Although the primary focus is on new driving principles, the fabrication process for micro devices and the control system are also involved. These proposals are attractive and sure to stimulate further innovative research. I hope you enjoy this special issue, but beyond that I hope that the papers in it contribute to your future research and innovative breakthroughs. On a final note, I wish to express my appreciation to the authors, reviewers, publisher (Mr. S. Wakai), and two editors (Assoc. Prof. T. Kanda and Assoc. Prof. K. Takemura) for their devoted work on this special issue, Innovative Actuators.
In this paper, we propose a triangular prism and slit electrode pair (TPSE) and its micromechanical systems (MEMS) fabrication process for a novel micropump using electro-conjugate fluid (ECF), which is based on a thick photoresist (KMPR) micromold (≥500 μm) and nickel electroforming. ECF is a kind of functional and dielectric fluid. The strong and active jet flow of an ECF is generated between two electrodes surrounded by the ECF when a high direct-current voltage is applied to the electrode pair. The micropumps generated by the ECF jetting can be used as micro hydraulic pressure sources for soft microrobots. By substituting these ECF micropumps for bulky air compressors or hydraulic pumps utilized in soft robots, we can realize advanced soft microrobots in which the driving sources are embedded. An MEMS-based TPSE for an ECF micropump was successfully fabricated by using the proposed MEMS fabrication process. The maximum output pressure without a flow and the flow rate without a load were 24.6 kPa and 27.5 mm3/s, respectively, at an applied voltage of 2 kV. The experimental results show that the MEMS-fabricated TPSE is a good candidate for electrode-type ECF micropumps utilized in various applications of soft microrobots whose pressure sources are embedded inside.
Since colonoscopic insertion requires a high level of skill on the part of the examining physician, the patient may experience pain if the physician is not so highly skilled. In this study, our objective is to realize an easy-to-execute endoscopic insertion that does not rely on the physician’s skill. We develop a pneumatic actuator that gives the endoscope self-propulsion capability. The actuator is configured with three bellows made of polyethylene film. By applying pneumatic pressure to the bellows in a specific sequence to extend and contract them, the end of the actuator moves elliptically. Thus, the endoscope can be given propulsion performance by attaching several actuators and driving them in different phases. In this paper, the basic characteristics of the actuator are determined geometrically from the characteristics of the bellows, and then those characteristics are compared to the results of experiments. In addition, experiments are conducted in which a rod, used as a dummy endoscope, is transported through a pipe and inserted in an intestinal tract model. The experiments confirm and validate the proposed concept.
This paper presents the modeling of a thin soft McKibben actuator using the system identification (SI) method and its force control. Procedures from the system identification method are used to create a mathematical model (transfer function) from the test data. The autoregressive with exogenous input (ARX) model was chosen as the model structure of the system. Next, a PSO-PID controller was proposed for the force control of the actuator. The simulation data were verified against the test data for the force control using PSO-PID and conventional PID. Results showed that the developed model represents the actual system by giving the same characteristics in the force control analysis in step, multi-step, and sinusoidal input.
This manuscript explains the employment of flexible actuators to act as a soft robot and transporting agent to assist medical X-ray examinations. Although soft robots from silicone material can be transparence and a human compliance used as medical assistive devices, soft robots have some problems: they tend to be sluggish, have long and imprecise gait trajectories, and need their control parameters to be adjusted for motion diversion. A soft robot with omnidirectional locomotion has been created, one that has a combination of pneumatic rubber legs that form a soft robot platform and an associated hardware setup. Tests have confirmed its omnidirectional locomotion ability; it has a maximum speed of 6.90 mm/s in forward locomotion and a maximum payload of 70 g. These features indicate that the robot can be used as a medical assistive device for fluoroscopy examinations.
This paper describes a joint angle control considering the passive joint stiffness of robotic arms driven by rubberless artificial muscle (RLAM), which is a pneumatic actuator. The contraction mechanism of RLAM is the same as that of the McKibben artificial muscle. Unlike the McKibben artificial muscle, RLAM is constructed using an airbag made of a nonelastic material instead of a rubber tube.
The objective of this study is to realize a soft contact movement of robotic arms by applying the passive compliance characteristics of RLAMs. In this study, we derive a mathematical expression for the relationship between the output of an RLAM and the joint stiffness of a robotic arm. In addition, we suggest a control scheme for each RLAM. We confirm the validity of these suggestions experimentally. From the result, we observe a good control performance of the joint angle. A robotic arm moves smoothly according to the force added from outside by setting the passive stiffness of the arm.
Although pneumatic rubber actuators have unique advantages, (e.g., compliance, lightness, and cheapness) they require an air compressor, valves, and air supply hoses, limiting their use in portable devices. In our previous paper, we proposed the basic working principle of a novel pneumatic source for rubber actuators. This was based on the reversible chemical reaction of water electrolysis/synthesis, using a proton-exchange membrane fuel cell (PEMFC). In the current study, we developed a small PEMFC reactor based on this principle and applied it to a flexible micro actuator (FMA), which is a typical pneumatic rubber actuator, thereby realizing a hose-free pneumatic actuator without a compressor. The results of the driving experiments show that the proposed actuator can be successfully controlled by electric current control.
Soft rubber actuators are very useful in applications involving humans, such as in medicine and reflexology. Additionally, they are useful in industrial devices because of their softness. However, many soft rubber actuators are driven by pneumatic power, and the power source is usually bulky. This makes the application of soft rubber actuators difficult. In this study, we propose a novel small power source for soft rubber actuators, which uses the gas/liquid phase change phenomenon of the actuator working fluid. When fluids change their phase between liquid and vapor, a large volume change occurs. We assume that this volume change is sufficient to drive a single soft rubber actuator. We fabricated a prototype of an actuator comprised entirely of silicone rubber via a molding process. Using the first prototype, we confirmed that the actuator can be driven by the gas/liquid phase change of the actuator fluid. Then, we fabricated a second prototype that includes a cartridge heater inside its body. We applied an electronics coolant fluid to this actuator. From the results of several experiments, we confirmed that the actuator produced a maximum output force of 405 mN. When the actuator was driven by the gas/liquid phase change, its trajectory was almost the same as that when driven by air pressure. Hence, the proposed pressure source maintained the characteristics and advantages of the soft rubber actuator. We believe that a pressure source using the gas/liquid phase change phenomenon of a working fluid will mitigate the problems of the driving system of soft rubber actuators.
This paper describes the driving characteristics of a three degree-of-freedom (three-DOF) electrostatic induction actuator, which can demonstrate surface-drive characteristics with translational and rotational motions. It consists of a sheet-type slider without electrodes and a planar stator with an array of three-phase driving electrodes. The electrodes with different orientations are aligned in a regular manner to construct a four-by-four checkerboard pattern. Controlling applied voltage patterns can generate translational or rotational patterns of electrostatic fields, which drive the slider. The performance of the three-DOF actuator with regards to translational and rotational motion was investigated.
Future lunar, planetary, and asteroid exploration will strongly demand in situ analysis of rock samples to obtain data related to various aspects. For precise composition analysis, a sample surface should be smoothed. In this paper, a surface shaver with a piezoelectric actuator is proposed and its machining performance in air is investigated. Shaving teeth are mounted at the ends of a pair of lever mechanisms. The device is pressed through four springs onto the workpiece with a linear actuator. When a sinusoidal voltage of 50 Vp-p and an offset voltage of 25 V were applied, the resonance frequency was 556 Hz and the unloaded amplitude of the shaving teeth was 0.77 mmp-p. Basalt workpieces were machined for 10 min in air. Increasing the thrust force reduced the surface roughness, although the amount removed diminished with a further increase in the thrust force. The surface roughness varied widely not only due to the amount removed but also due to containing the pores.
The authors have previously developed a compact, light-weight air flow control valve, which realizes continuous flow control. The vibration produced by a piezoelectric device (PZT) was used to excite particles confined in a flow channel to control the valve opening for the developed control valve. Therefore, the voltage applied to the PZT can be changed to continuously control the flow rate. A new working principle was developed for the control valve to stabilize flow rate characteristics. Different types of particles were used to change the valve opening condition. A prototype was manufactured to demonstrate the effectiveness of the control valve.
We propose output shafts with a preload generation mechanism to improve the output torque and thrust force of the rotary-linear ultrasonic motor. The stator is comprised of a single metallic cube with a through-hole, and the output shafts are inserted into the hole to generate motion in both its circumferential and axial directions arbitrarily. In this paper, two design concepts for optimizing the preload using the output shafts are examined. The first involves a cylinder shaft with micron-order accuracy diameter realization. The cylinder shaft makes contact with the entire inner surface of the stator and generates a preload between the stator and shaft. The second concept employs a spring shaft having a slightly larger diameter than the stator hole, which expands in the radial direction and generates the preload. Experiments show that these design concepts improve the output torque and thrust force.
A linear ultrasonic motor (LUSM) with two parallel beams and two multilayer piezoelectric actuators (MPAs) has been developed. The MPAs are aligned across the beams, and the force and displacement generated by the MPAs result in the deformation of the beams in the orthogonal direction. The LUSM has two types of operation modes: dynamic and static. In dynamic operation, the MPAs are driven by alternating voltages with a phase difference, and elliptical displacement motions are generated on the surfaces of the beams. Objects touching the surfaces of the beams can be moved in the same direction by friction. In addition, micro positioning is available over a wide range by combining dynamic and static operations. The characteristics of the LUSM include a maximum speed of 41 mm/s and a maximum thrust of 3.4 N at an operating voltage of 20 Vp-p. A movement range of approximately 8 μm has been confirmed during static operation.
Surface acoustic waves (SAWs) excited by bursts of sinusoidal waves have been used in various applications. However, the SAW actuators used for this purpose are expensive because each SAW transducer must be equipped with a radio frequency linear amplifier and a function generator. To simplify the driving circuits of these actuators, SAW excitation using a pulse wave is proposed in this report. Simulated results for an equivalent circuit of a single interdigital transducer and measurements of SAWs excited by pulse waves are presented. The generation of tactile sensations using a SAW excited by a pulse wave is also reported. Furthermore, the power requirements for SAW excitation by a sinusoidal wave and by a pulse wave are compared.
Surface acoustic waves (SAWs) are used in many applications. Here, we consider application of SAWs to actuators, which require relatively large vibration amplitudes. In conventional applications, a SAW propagates on a LiNbO3 substrate that serves as an elastic medium. This implies that the maximal size of a SAW transducer is limited by the LiNbO3 wafer size. Better actuators require larger-size SAW transducers. Here, we propose a transducer in which an excited SAW propagates on an inexpensive elastic medium (indirect excitation method). The method combines a piezoelectric material and a non-piezoelectric material substrate. These two materials are coupled. Electric energy is provided by an interdigital transducer (IDT). We designed and studied three different transducer configurations. To determine the optimal configuration, various materials and their combinations were considered with the proposed method. Electrical and mechanical characteristics were quantified in terms of the frequency response of admittance and vibration response, respectively. A suitable combination of materials was determined after measuring and analyzing the properties of different transducers. For this combination, the vibration velocity of the novel transducer was as large as that obtained using the conventional direct excitation method.
Three huge vertical holes have been found on the Moon and their scientific explorations are planned by the UZUME (Unprecedented Zipangu (Japan) Underworld of the Moon Exploration) Project. For such explorations, a rover with large wheels is preferred for climbing over bumps. However, the exhaust materials from landers or rovers should be avoided to prevent contamination of the terrain. This paper proposes a rover with inflatable tubes that function as outer wheels. A prototype with one degree of freedom was built. The inflatable wheel was 1000 mm in diameter and 400 mm in width, and weighed 2.0 kg. A small cart, which was used as a weight, was moved on the torus to revolute the rover. Each cart weighed 0.5 kg. The performance of the rover was tested and compared with the calculated results. The climbable step height and slope angle were statistically calculated and were independent of gravity. The climbable step height and slope angle were 15 mm and 9°, and they almost agreed with the calculated results.
Conventionally, many single-degree-of-freedom (single-DOF) actuators have been used to realize devices with multiple-degrees-of-freedom (multi-DOF). However, this makes their structures larger, heavier, and more complicated. In order to remove these drawbacks, the development of spherical actuators with multi-DOF is necessary. In this paper, we propose a new 3-DOF outer rotor electromagnetic spherical actuator with high torque density and wide rotation angles. The dynamic characteristics are computed employing 3-D FEM and its effectiveness is verified by carrying out measurements on a prototype. Then, in order to realize further high torque density, the electromagnetic pole arrangement is optimized using Genetic Algorithm (GA) and the effectiveness of the optimized stator poles arrangement is verified.
This paper describes the development of a spherical motor, hereinafter called “14-12 spherical motor.” This spherical motor utilizes two polyhedrons – a truncated regular octahedron and a regular dodecahedron – for the arrangement of permanent magnets on the rotor and electro-magnets on the stator. The 14-12 spherical motor has two types of rotation axes and six rotation axes in all. Five-phase alternating current was applied to the electro-magnets to rotate the rotor. This study also developed a simulation model for the 14-12 spherical motor to numerically simulate the dynamic behavior of the motor. Basic performance was measured and simulated to evaluate (1) the relation between rotation speed and maximum output rotation torque and (2) cogging torque. Waveforms of the five-phase alternating current were improved using the simulation model in order to increase output rotation torque for the rotation axis with the smaller torque.
This paper firstly gives an introduction to the development of machining accuracy, and the contemporarily feasible compensations in the field of machine tools. The metrological means used for primarily static and kinematic compensations are discussed. Furthermore the focus is laid on the kinematic, dynamic and thermal compensation approaches, using various examples for these fields. The different phenomena to be compensated and the associated models are discussed in detail. As conclusions to be drawn, the repeatability of the systems, the ability of the models used in the CNC to represent the systematic behavior and the capabilities of the CNC can be seen as significant prerequisite for a successful application of compensation means.
To improve the machining preciseness of X-ray telescope mirrors for astronomical use, the molds of electroless nickel and electro nickel are diamond-turned, and the tool wear and machining accuracy are then quantitatively evaluated. The machined surface roughness is measured and discussed in terms of the effects of cutting conditions on the resulting quality. Finally, the actual nickel-plated molds of X-ray mirrors are test cut, and their form accuracy and surface roughness are measured and evaluated. These experiments reveal that a surface roughness of 0.5 nm Ra and a form accuracy of 0.1 μm P-V can be obtained under the optimized cutting conditions.
Multinational corporations produce products at relatively few factories and then sell those products in all areas of the world. Longer lead times increase the risk of fluctuations in product demand. To reduce this risk, the entire business chain, from production to sale, must be optimized. In this study, we propose, implement, and verify a total optimization system. This system uses multi-agent simulation on big time series data. It consists of management, integrated database, and operation modules.
Ultrashort-pulsed laser irradiation is a more efficient approach to the fabrication of fine surface structures than traditional processing methods. However, it has some problems: the equipment expenses usually increase as the pulse shortens, and the process principle has not been clarified completely, although the collisional relaxation time (CRT) is assumed to be a major factor. In this study, a 20-ps pulsed laser was employed to fabricate nanometer-sized periodic structures on a stainless steel alloy, SUS304. The pitch length of the fabricated fine periodic structures was similar to the laser wavelength, and the results suggested that periodic structures could be fabricated within a limited range of the laser fluence. In order to expand the effective fluence range (EFR) and to control the pitch length, laser irradiation was carried out with different workpiece temperatures and the laser wavelengths. In this way, CRT was extended and EFR was expanded by cooling the workpiece, and the pitch lengths were approximately equal to the laser wavelengths. As a result, two things were found: it is easier to fabricate the fine periodic structures by cooling the workpiece, and it is possible to control the pitch length of the fine periodic structures by changing the laser wavelength.
As titanium alloys such as Ti-6Al-4V provide several benefits, including high-temperature strength and high corrosion resistance, the demand for such materials has rapidly increased, particularly in the aircraft industries. On the other hand, they are known to be among the most difficult-to-cut materials due to their mechanical and chemical properties, which make tool life extremely short. In order to solve this problem, this paper proposes a new cutting method employing ultra-low-frequency (ULF) vibration. ULF vibration ranges from less than 1 Hz to approximately 10 Hz and is generated by using a numerically-controlled machine tool axis and an NC program. The results of turning experiments showed that the developed method significantly reduces crater wear in the machining of Ti-6Al-4V, even under dry machining conditions. Moreover, the mechanism that ULF vibration affects and the effect of actual cutting time and non-cutting time in each individual vibration period on the amount of crater wear were investigated. As a result, it was found that the developed process is a promising method for achieving high performance dry machining of titanium alloys.
A low level of automation, low accuracy of control, and high dependence on operator proficiency are general deficiencies of traditional overhead cranes. In order to improve the level of automation of overhead cranes, genetic algorithms and the grid method were applied to plan the global path of an overhead crane in a static environment. An automatic travel control system for an overhead crane was designed on the soft PLC platform CoDeSys. A slip control variable frequency regulating system was used to guarantee the accuracy of the travel system. A Simulink model of the slip control variable frequency regulating system was built with parameters optimized, and the control signal generated by the PLC was input into the model to conduct the simulation, which verified the feasibility of automation and the accuracy of the control system.