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  • Open access
  • 128 Reads
A concept design of an adaptive tendon driven mechanism for active soft hand Orthosis.

The Hands exert a vital role since the simplest to complex tasks and lose the ability to make those movements, which is usually caused by spinal cord injury or stroke impacts dramatically the quality of life. In order to counteract this problem, several assisting devices have been proposed, but they still present several usage limitations. The marketable orthoses are generally either the static type or over-expensive active orthosis that cannot perform the same degrees of freedom (DoF) that a hand can do. This paper presents a conceptual design of a tendon driven mechanism for hand’s active orthosis. This study is a part of an effort to develop an effective and low-cost hand’s orthosis for people with hand paralysis. The tendon design proposed was thought to comply with some requisitions, how lightness, and low volume, as well as fit with the biomechanical constraints of human tendons to enable a comfortable use. The mechanism employs small cursors on the phalanges to allow the tendons to run on the dorsal side and by both sides of the fingers, allowing 2 DoF for each finger, one extra tendon enlarges the hands’ adduction nuances. It is simple enough to execute the flexion and extension movements (the movements most used in daily actives) using one single DC actuator for one DoF, reducing costs, or expanding it, with more DC actuators to enable more natural hand coordination. This system of actuation is suitable to create soft exoskeletons for hands easily embedded into 3D printed parts, which could be merged over statics thermoplastic orthosis. The final orthosis design allows dexterous finger movements and force to grasp objects and perform tasks comfortably.

  • Open access
  • 75 Reads
Biomimetic Design of a Planar Torsional Spring to an Active Knee Prosthesis Actuator Using FEM Analysis.

Lower-limb prostheses have an important function to partially recover the leg movement after amputation. In order to improve the mechanical joint behavior towards a healthy human knee, compliant elements have been introduced to the active prostheses, composing the well-known Series Elastic Actuators (SEAs). SEAs are specially used in lower-limb assistive devices due to their ability to tolerate impacts and passive store mechanical energy during ground-walking. Based on the healthy human knee in the stance phase of walking, this paper brings the design, prototyping, and analysis of a customized planar torsional spring. To enhance the compliance of a rigid active knee prosthesis, the proposed spring will substitute a torque flange between the transmission and the output of the actuator, and this carries a series of constraints to the design. The finite element method (FEM) is applied to the development and exploration of the three initially proposed geometries and the material selection along with its heat treatment is based on the maximum stress obtained in the simulations. The proposed geometry, chosen by comparison of the three, is made of AISI 4340 steel and has a torsional stiffness of 105 Nm/rad with maximum angular displacement of 2.5 °, and 0.093 kg. In future work, we intend to compare the results of the rigid actuator against the SEA one during walking on the ground.

  • Open access
  • 55 Reads
“Hi-Fi Stake” Piezoelectric Actuators and New Developments

“Hi-Fi Stake” piezoelectric actuators are constructed by bonding [011]-poled d32-mode lead-based relaxor-PT single crystals with polycarbonate edge guides into a square-pipe structure. They contract under positive-polarity applied voltage due to d32 values being negative for [011]-poled relaxor-PT single crystals. Under quasi-static loading conditions, “Hi-Fi Stake” single crystal actuators exhibit highly linear displacement response with negligible hysteresis. Over the years, we have successfully developed the following three versions of “Hi-Fi Stake (HFS)actuators: cost-effective (CE), large-stroke (LS) and High-load (HL), all of maximum use temperature of up to 60 oC. Of which, the LS version, of 2-level construction, displays strokes of up to 50 mm @ 240 V and the HL version, of 2-layer construction, has maximum loads allowed of 14 kg-f at room temperature and 7 kg-f at 60 oC. Also described in this work are the developments Cryogenic Hi-Fi Stakes (HFS-CG) and High-Temperature Hi-Fi Stake (HFS-HT) piezoelectric actuators. The selection of suitable crystal compositions, recommended working conditions and measured performance of fabricated prototypes of these two new versions of Hi-Fi Stakes are presented and discussed.

  • Open access
  • 40 Reads
New “HAPA”, “FTA” and “HD-FTA” Piezoelectric Actuators

“HAPA” stands for High-Authority Piezoelectric Actuator, which describes high-performance piezoelectric actuators of large stroke and blocking force. “HAPAs” are made possible by high-bending-stiffness connectors which connect multiple units of piezoceramic stacks into a 2-level actuation structure. Present HAPA actuators are fitted with commercial piezoceramic stacks. For instance, a “HAPA-(2+2)” comprises 4 PZT stacks, 2 in the upper level with displacement projecting upward and 2 in the lower level with displacement projecting downward. They not only double the axial displacement of individual stacks with only fractional increase in device length but also of 1.5´ to 3´ larger blocking force depending on the actual design.

“FTA” stands for Flextensional Actuator, in which the horizontal extensional displacement of PZT stacks is amplified to yield much larger contractional vertical displacement via a diamond-shaped elastic frame structure. A range of new FTAs have been developed by us using single or multiple units of PZT stacks, of which their performances are described in this work.

“HD-FTA” stands for HAPA-Driven Flextensional Actuator, in which HAPA piezoelectric actuators are used as the motor section to drive diamond-shaped elastic members of various designs for further displacement amplification. Several HD-FTAs, driven by a HAPA-(2+2) actuator, have been developed. Compared with standard FTAs of comparable stroke, HD-FTAs display higher working loads but of smaller overall length.

“HAPA, “FTA” and HD-FTA” piezoelectric actuators find applications when a smaller actuator length is advantageous in addition to the required large displacement and working load.

  • Open access
  • 37 Reads
Machine Learning Models Applied to Predictive Maintenance in Automotive Engine Components
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Fault detection on automotive engine components is an important feature that motivates research from different engineering areas due to the interest of automakers on its potential to increase safety, reliability and lifespan and to reduce pollutant emissions, fuel consumption and maintenance costs. The fault detection can be applied to several types of maintenance strategies, ranging from finding the faults that generated a component failure to find them before the failure occurs. This work is focused on predictive maintenance, which aims to constantly monitor the target component to detect a fault at the beginning, thus facilitating the prevention of target component failures. Due to production costs, it is not possible to have sensors installed in all engine components, which makes it difficult to apply predictive maintenance for all of them. One way to work around that problem is to use predictors based on machine learning paradigms, which take signals from indirect sensors from other components and predict a fault. To accomplish that, it is necessary to acquire data that contains both normal and faulty behaviors from the target component in order to train a machine learning method to recognize the defective behavior prior to embedding it into the software of the engine electronic control unit. Data acquisition can be an expensive process as well, as it may require several rounds of destructive testing for different driving cycles, which must be performed in real-time on instrumented vehicles in a dynamometer. Since machine learning methods are capable of handling a certain amount of noise, the data to train them can be generated by simulating the model of the respective engine in which the target component is installed. That process does not require real-time executions and vehicle instrumentation in a dynamometer lab, which decreases the cost of the data acquisition as a whole. This work presents the results of different machine learning methods implemented as classification predictors for fault detection tasks including Random Forest (RF), Support Vector Machines (SVM), Artificial Neural Network (ANN), and Gaussian Process (GP). The data used for training was generated by a simulation testbed of an engine system, whereby its operation was modeled using industrial-standard driving cycles, such as the Worldwide Harmonized Light Vehicle Test Procedure (WLTP), New European Driving Cycle (NEDC), Extra-Urban Driving Cycle (EUDC), and U.S. Environmental Protection Agency Federal Test Procedure (FTP-75).

  • Open access
  • 133 Reads
Multifunctional Smart Window based on Dielectric Elastomer Actuator

Soft actuators are the compliant-material based devices capable of producing large deformation upon external stimuli. Dielectric elastomer actuators(DEA) are a type of soft actuators that operate on voltage stimuli. Apart from soft robotics, these actuators can serve many novel applications, for example, tunable optical gratings, lens, diffusers, smart windows and so on. This talk presents our current work on tunable smart windows which can regulate the light transmittance and the sound absorption. This smart window can promote daylighting while maintaining privacy by switching between transparent and opaque. As a tunable optical surface scatters, it turns transparent with smooth surfaces like a flat glass; but it turns ‘opaque’ (translucent) with the micro-rough surface. The surface roughness is varied by means of surface micro-wrinkling or unfolding using dielectric elastomer actuation. In addition, this smart window is equipped with another layer of transparent micro-perforated dielectric elastomer actuator (DEA), which acts like Helmholtz resonators serving as a tunable and broader sound absorber. It can electrically tune its absorption spectrum to match the noise frequency for maximum acoustic absorption. The membrane tension and perforation size are tuned using DEA activation to tune its acoustic resonant frequency. Such novel smart window can be made as cheap as glass due to its simple all-solid-state construction. They are used to green building and could potentially enhance the urban livability.

  • Open access
  • 53 Reads
Automated Insertion of Objects Into an Acoustic Robotic Gripper

Acoustic levitation forces can be used to manipulate small objects and liquid without mechanical contact or contamination. To use acoustic levitation for contactless robotic grippers, automated insertion of objects into the acoustic pressure field is necessary. This work presents analytical models based on which concepts for the controlled insertion of objects are developed. Two prototypes of acoustic grippers are implemented and used to verify the lifting of objects into the acoustic field experimentally. Using standing acoustic waves and dynamically adjusting the acoustic power, the lifting of high density objects (≥ 7 g/cm3) from acoustically transparent surfaces is demonstrated. Moreover, a combination of different acoustic traps is used to lift lower density objects from acoustically reflective surfaces. The provided results open up new possibilities for the use of acoustic levitation in robotic grippers, which have the potential to be applied in a variety of industrial applications.

  • Open access
  • 134 Reads
Design of a Cable-driven Actuator for Pronation and Supination of the Forearm to Integrate an Active Arm Orthosis

The pronation/supination of the forearm is an important set of movements to properly accomplish the activities of daily living. While several exoskeletons have been proposed for the rehabilitation of the arm, few of them have actively implemented the movements of pronation/supination. Often, the addition of this degree of freedom to the mechanism results in a bulky and heavy structure. Consequently, the overall exoskeleton is too big for a wearable solution. This paper proposes a digital prototype and kinematic evaluation of a cable-driven orthosis for pronation/supination movement assistance. The actuator is based on an open ring (semi-circle) to be attached to the forearm, while a stationary guide drives the ring into a rotary movement. By considering anthropomorphic data in the design stage it is possible to develop a rigid, compact, and high power to weight ratio solution for the actuator responsible for pronation and supination. The proposed actuator can achieve the full range of motion for the activities of daily living and 83% of the rotation of the forearm total range of motion with a total mass of only 150 grams.

  • Open access
  • 40 Reads
Open-Loop Control Design of Shape Memory Alloys and Polymers through Tapping Motion

Shape Memory Alloys and Polymers are a class of smart materials that remember a pre-trained shape or form when exposed to an appropriate temperature. In this work, Shape Memory Alloys consisting of wires, 1-way springs, and 2-way springs are described; an open-loop control of Shape Memory Alloys and Polymers is also implemented. Since the amount of electric current that flows through a wire is directly proportional to temperature, control of the electric circuit is used for open-loop temperature control. The designed smart control is applied to rotate a lever mechanism through the conversion of the linear motion of the Shape Memory Alloy into the rotational motion of the lever through the tapping of a piezoelectric transducer to deliver the open-loop control. When the piezo transducer is deformed by mechanical stress via tapping, striking or any other mechanical stimulus, it produces an electrical signal which when sent to the microelectronic circuit activates the SMA. The implemented system can be applied in robotic systems and autonomous applications.

  • Open access
  • 36 Reads
Design of a Quasi Direct drive Actuator for Dynamic Motions
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In recent years several legged/wheeled robots have been developed and proved their effective functionality in locomotion on uneven terrains. Many robotics researchers have been focusing on improving the locomotion speed, as well as the stability and robustness of such robots. High-speed locomotion of robots is however subject to various design challenges, especially in the development of actuators. The robotic applications which require high-speed motion in high torque operations along with the ability to manage dynamic physical interactions are not satisfied by the conventional robotics actuators deploying high reduction gearings. In this work, we present a quasi-direct drive actuator designed for continuous high-speed motions in high torque such as wheeled motions in mobile robot or joint motion in dynamic legged robots. The presented actuator exploits low reduction gearing so that it can render over 25Nm continuous torque while the actuator speed can exceed 20 rad/s. Such characteristics enable exhibiting dynamic motions and dealing with large external impacts. The selection of motor and design of the gearing unit was carried out iteratively so that commercial items with minimum customization are employed and the outer diameter of the motor and the gearbox can be matching. A single-level planetary gearbox is devised for the reduction unit to ensure highly back drivability and transparency of the actuator thereby making the actuator robust against external impacts and allowing for accurate torque control using motor current measurement. The gear set design was carried out based on the AGMA gear torque calculation. Given the radial space required for the gearbox dealing with the torque requirements, the actuator motor was chosen to be small in height (pancake type), which ensures high torque density within smaller dimensions at high-speed operation. The mechanical design of the actuator is presented in this paper and the FEM analysis conducted for the design of critical parts is reported. Finally, actuator specifications in terms of size and performance are compared with similar state-of-the-art actuators.

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