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  • Open access
  • 28 Reads

Maintenance Strategy Selection Based on FMEA/FMECA Approach Using Time Dependent Failure Probability

Industrial maintenance is playing an increasingly important role in production systems. The interconnections between machines and systems are becoming more complex, partly due to increasing digitization and automation. Malfunctions and failures not only need more time to be resolved but also have greater consequences on the production system. To respond to these increasing demands, maintenance must make intelligent use of the available resources. One of the most important factors that determines the use of resources and the resulting availability is the selection of the maintenance strategy for the production machines. In literature, there are many approaches to select a maintenance strategy. For complex machines consisting of different components, each of which can have several failure causes, maintenance strategy selection based on failure mode and effect analysis (FMEA) is particularly suitable. The combination of failure probability and failure effect of each component allows an evaluation of different maintenance actions. The expected risk reduction of an action can be compared to its cost. The aim of this publication is to introduce a new approach allowing failure probabilities of the components to be time dependent. With this approach the expected time and usage dependent wear of the components and the respective failure probabilities of each wear state can be introduced into the risk prognosis, leading to a time dependent risk for each failure possibility. This in turn can lead to different ideal maintenance strategies, based on the expected wear state of a component. This new time dependent approach is validated in a real production environment with maintenance experts.

  • Open access
  • 33 Reads
The Influence of Silicon Carbide Abrasive on Machining of Ti-6Al-4V by AWJ

Machining hard-to-cut materials is challenging and demands specific process conditions in order to be effective. Apart from conventional machining methods, non-conventional methods are also able to provide high quality and efficiency. In particular, one of the most appropriate non-conventional methods used for cutting those materials is Abrasive WaterJet (AWJ) technology, which is related both to high material removal rates and environmentally friendly conditions. As the properties of the abrasive material can influence the erosion process, surface topography, and the geometrical features of the cut, the performance of alternative abrasive materials should be investigated. Thus, in this research, we decided to analyse how silicon carbide (SiC) used as an abrasive will affect the width and depth of the cut shaped by the water jet. The experiment has been designed using the Taguchi method, which allows for the collection of the necessary data to determine which factors most affect the outcome of the process, rather than testing all passible parameters combinations. Experiments were conducted on Ti–6Al–4V titanium alloy sample using several different process parameters, such as jet pressure, stand-off distance, abrasive mass flow rate and traverse feed rate and obtained grooves were measured using a confocal microscope to determine their dimensions in each case.

  • Open access
  • 38 Reads
Design of a novel 8-DOF Hexapod based Motion Platform

In motion simulation, motion platforms enable the simulation of forces and angular velocities acting on a person in a car or an airplane, for example. Other applications for motion platforms are, for instance, perceptual research or testing the dynamic behavior of mechanical structures. In this work, a novel motion platform is presented that consists of a hexapod with two additional degrees of freedom. A hexapod robot can perform highly dynamic movements, which is why high forces and torques act on objects mounted on it. The actuators of the additional axes must be designed in such a way that they provide sufficient drive torque for each movement of the hexapod to prevent slippage. By solving an optimization problem, joint trajectories were determined in which the drive torques become maximum. These torques can be used to select suitable drives. A similar optimization problem was used to determine load cases to perform a stress analysis of the entire structure on the hexapod using finite element simulation. To be able to move the motion platform along a Cartesian trajectory, a path planning algorithm is needed. In this work, a simple algorithm based on inverse kinematics is used, which was due to the hybrid and redundant structure of the system calculated using differential kinematics.

  • Open access
  • 33 Reads
Energy-Saving in an Autonomous Excavator via Parallel Actuators Design and PSO-Based Excavation Path Generation

In this study, in order to increase the energy efficiency in autonomous excavators, which are great solutions for the high labor costs and harsh and hazardous environmental conditions of the construction industry, two approaches have been proposed. First, a new and unique design with two parallel arm and bucket actuators has been proposed for the electric excavator manipulator. In the conventional design for excavators, the three actuators of the boom, the arm, and the bucket are in series. Therefore, they cannot share the external load between them. However, in the proposed new design, the arm and the bucket actuators are in parallel, which helps them to share the load between themselves. This approach helps the excavator to overcome the higher external load with the same actuators. Additionally, in this design, to reduce the energy consumption during the idling time of the excavator, the hydraulic actuators have been replaced with electric linear actuators. Since these actuators have low back drivability, they can handle relatively high external forces without spending energy while they are not in motion. Secondly, a PSO-based path generation algorithm has been developed for autonomous excavation to minimize energy consumption, while it's trying to generate a path as close as possible to the desired path, and avoid collision with undesired obstacles. In the end, two scenarios have been considered to test the performance of the algorithm to save energy. Since in the PSO algorithm, by changing the gains in the cost function, it's possible to change the priorities of the elements to minimize, simulations have been performed to compare results between scenarios with and without considering energy-saving. The simulations show that the proposed algorithm considering the energy-saving decreases the energy consumption in each cycle of digging by 18.51%.

  • Open access
  • 54 Reads
Studying the influence of the impact gap value on the average translational speed of the wheeled vibration-driven robot

The general design of the wheeled vibration-driven robot is developed in the SolidWorks software on the basis of the double-mass semidefinite oscillatory system. The idea of implementing the vibro-impact working regimes of the internal (disturbing) body is considered. The corresponding mathematical model describing the robot motion conditions is derived using the Euler–Lagrange equations. The numerical modeling is carried out by solving the obtained system of differential equations with the help of the Runge-Kutta methods in the Mathematica software. The computer simulation of the robot motion is conducted in the MapleSim and SolidWorks software under different robot’s design parameters and friction conditions. The experimental prototype of the wheeled vibration-driven robot is developed in the Vibroengineering Laboratory of Lviv Polytechnic National University. The corresponding experimental investigations are carried out in order to verify the correctness of the obtained results of the numerical modeling and computer simulation. All the results are presented in the form of time dependencies of the robot’s basic kinematic characteristics: displacements, velocities, accelerations of the wheeled platform and disturbing body. The influence of the impact gap value on the average translational speed of the robot’s wheeled platform is studied, and the corresponding recommendations for designers and researchers of the similar robotic systems are stated. The prospective directions of further investigations on the subject of the present paper and on similar vibration-driven locomotion systems are considered.

  • Open access
  • 39 Reads
Studying the dynamics of vibratory finishing machine providing the double-sided lapping and polishing of flat surfaces of cylindrical and prismatic parts

The improved design of a vibratory lapping machine is developed in the SolidWorks software on the basis of the suspended double-mass oscillatory system. The system is set into motion by three pairs of electromagnets generating periodic excitation forces applied between the upper lap and the lower one. By adopting the same forced frequencies and the certain phase shifts of the excitation forces, it is planned to provide the antiphase translational (circular) oscillations of the laps. In such a case, the largest accuracy and operational efficiency of the lapping (polishing) process can be reached. The present research is aimed at analyzing the dynamic behavior of the lapping machine’s oscillatory system. In particular, the motion trajectories of the laps, as well as their kinematic characteristics (displacements, velocities, and accelerations) are considered. The mathematical model of the oscillatory system is developed using the Euler-Lagrange equations. The numerical modelling of the system motion is performed in the Mathematica software with the help of the Runge-Kutta methods. The computer simulation of the laps oscillations is conducted in the SolidWorks software under different friction conditions. The experimental prototype of the vibratory lapping machine is implemented in the Vibroengineering Laboratory of Lviv Polytechnic National University. The possibilities of providing the controllable translational (circular) oscillations of laps are theoretically studied and experimentally confirmed. Further investigations on the subject of the present paper can be focused on the physical-mechanical and technological parameters (surface flatness, roughness, hardness, wear resistance, etc.) obtained due to performing the lapping and polishing processes using the proposed vibratory finishing machine.

  • Open access
  • 31 Reads
Development of a nonmotorized mechanism for ankle rehabilitation

Robotics has a wide area of application which includes the development of a device for movement rehabilitation for different types of patients, such as stroke victims. Brain injuries can impair the necessary movements of the lower limb, influencing human gait. The use of robotic structures can generate benefits such as reducing costs with active labor for movement-based rehabilitation treatments, as well as expanding the range of exercises performed helping patients to maintain mobility through continuous therapy. The objective of this paper is to present the development of a novel nonmotorized mechanism for ankle rehabilitation. The structure is a mechanical device, to obtain the system with simple operation for both patients and health professionals. The mathematical modeling of the mechanism is based on the four-bar linkage and the static equilibrium of the system. The mechanism transmits angular movement generated by the patient’s arm to an oscillatory movement on the ankle joint. The design of the mechanisms used a differential evolution algorithm and singularity analysis based on the geometrical matrix of the systems. To validate the system, a prototype was constructed to verify the angular outputs, check the existence of singularities, and execute movements with a wooden test dummy.

  • Open access
  • 30 Reads
An Approach for Precise Distance Measuring using Ultrasonic Sensors

Ultrasonic sensors are commonly used as an affordable way to measure distance in industry. However, the accuracy of measurement is often low, especially when inexpensive sensors and reasonably low-priced equipment are used. In this article, a low-cost ultrasonic sensor module which is used for threshold detection techniques is examined. Several numerical techniques such as Least Square Method (LSM), piecewise LSM and Van der Monde Method are applied to the sensor data to increase the accuracy of distance measurement.

In conclusion, the Smart Filter Signal Detection algorithm is applied to the sensor data and results are compared. The Smart Filter Signal Detection algorithm provides 0.4 millimeters accuracy. In order to achieve this accuracy, the environment temperature is taken into account.

  • Open access
  • 42 Reads
Fault Diagnosis and Retrofit of a Heat Pump (HP) Unit

With a constant increase in Heat Pumps (HP) use it has become of great importance the application of Fault Diagnosis (FD) methods to detect faults at an early stage and thus ensure a proper working condition and improve reliability of the equipment. Based on that, the present paper addresses a FD and retrofit of a water-to-water HP unit. The faulty equipment, completely out of operation, was entirely analyzed and a catastrophic failure in the three-phase compressor was identified. After identifying the faulty component, it was concluded that it should be replaced. Thereby, an adequate solution for this HP is retrofitting with a smaller capacity compressor, which is more suitable for the considered environment. The replacement is also motivated by the fact that the equipment cannot even be started without tripping the circuit breaker. To detect and identify the faults, the electrical part was analyzed first, starting with the verification of the components in the electrical circuits. After that, the resistance of each one of the windings was measured and it was concluded that they were out of the manufacturer’s specification. The process of retrofitting with a new unit followed some steps. First, it was considered the thermal loads required for the environment and then, a suitable compressor capable to fulfill such requirements was selected. This selection considered the compatibility with the other system components. Finally, to avoid future faults and failures, after retrofitting with the new compressor, temperature sensors will be installed to be used as a basis for virtual sensors which enable an efficient FD approach.

  • Open access
  • 39 Reads
A real-time estimation method of soil-bucket interaction of an autonomous excavator via marching cube and constructive solid geometry methods

The control of an autonomous excavator during the digging process is a complex task as the interaction of the bucket and the soil creates significant external forces and moments on the excavator’s attachment. Due to the harsh working environment of the excavators, it is not practical to install sensors on the attachment of the excavator to measure parameters. Also, a series of external noises such as vibrations, impacts, dust, etc. are affecting the sensor measurements. In this paper, a real-time simulation method based on the marching cube method is presented which captures the initial condition of the soil and estimates the shape of the soil as well as the amount of the soil banked into the bucket. The marching cube method provides an a simple, yet accurate model for estimating soil shape, which eliminates the need for complex and computationally intensive processes required in previous studies using the voxel simulation method. The depth camera also provides sufficient information to capture the soil shape in the noisy environment of construction sites. Thus, the marching cube method combined with a depth camera can produce an accurate ground shape model for monitoring digging procedures. Initially, the shape of the ground will be captured by a depth camera and translated into the marching cube method to represent the current shape of the ground. These two steps are only executed once before starting the excavation process. Then, the pose of the bucket will be determined by the joint angles to define the bucket traverse. The volume created by the bucket motion and marching cube representation of the ground will be subtracted from each other using the constructive solid geometry approach to update the shape of the ground, as well as the amount of the soil which is currently held in the bucket. The proposed method can estimate the soil-bucket interaction without the need for any extra sensory information. Also, the low computational power required to execute the mentioned process makes it viable to run in real time on decent hardware. The other widely used approaches require installing the external sensors on the attachment of the bucket, which is not applicable or demands high computational powers which can not be calculated in real-time. Thus, the proposed method can address the issues of the previously proposed methods.

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