مجله مهندسی ساخت و تولید ایران
سال پنجم شماره 4 (زمستان 1397)

In this paper, an improved sample of capacitive-type linear encoder with untethered slider is presented that has higher resolution and lower error. This encoder has a simple structure consisting of two main parts, stator and slider. Both parts are made of hard PCB. The stator has a sequence of four-phase receiver electrodes and the slider contains two-phase transmitter electrodes. The electrical energy is supplied to transmitter electrodes by the electrostatic induction. Therefore, there is no need to connect any wire to the slider. These features make the encoder to use in limited spaces. By improving resolusion, smooth and precise movement of motors is facilitated in the closed loop systems. Thus, the improved encoder is equipped with two ground electrodes between the receiver electrodes and induction electrodes on the stator board to reduce electrostatic interface between these electrodes. As, output error goes down. In addition, the step of electrodes are reduced to increase resolution. Making an experimental sample of improved encoder and testing it, showed 15µm error in 1µm resolution. This indicates, the error and resolution are improved than the previous one.

Shield metal arc welding on the high strength low alloy steels in pipelines to transport natural gas from Iran is of great importance. In this paper, mechanical and metallurgical properties of multi-pass weld in weld zone, heat affected zone (HAZ), and base metal (with 36 inch outside diameter) for determination of critical area is investigated. Also Chemical analysis, metallography, tensile, impact and hardness testes in different positions of pipe (hours 12-1:30, 1:30-3, 3-4:30 and 4:30-6) were carried out. Tensile test results showed the lowest ultimate strength (Vertical to weld and in position 3-4:30) equal to 463mpa, and the lowest energy impact (Vertical to weld and in position 1:30-3) equal to 96J that determine 61 percent reduction compared to the base metal. The amount of hardness variation in different areas and positions is negligible (less than 5 percent). Images of metallographic test made by light and electron microscopes demonstrated that the amount of perlite cap pass weld and heat affected zone near the base metal were decreased compared to main metal to respectively 12.5 and 25 percent. The amount of Nb reduction in position (4:30-6) relative to the base metal is 0.025.

The laser-assisted additive manufacturing based on the powder is an efficient layer manufacturing process that uses a high-energy laser for the fabrication of polymeric components. The thermal stresses of the laser arise from the thermal gradients generated by the laser and other parameters of the device. Reducing thermal gradients decreases the deformations in the part and increases the fabrication accuracy. The main aim of this paper is to determine the temperature parameters including the preheating temperature or the powder bed temperature, the ambient temperature, scanning power and spot diameter in such a way that the temperature gradient is minimized. The finite element modeling is performed for the selective laser sintering process for polyamide-12 powder. In this paper, thermal gradient by changing temperature parameters based on the temperature model of the finite element and Taguchi experimental design is optimized. In order to reach this aim, the finite element simulation of the selective laser sintering process is first carried out for polyamide-12 powder. In order to verify the simulations, the experimental test is performed by a selective laser sintering device and the obtained results are compared with the finite element model. Then, using the Taguchi method, experiments are designed at the different levels and optimal temperature parameters are obtained. According to obtained results, optimal parameters were obtained to minimize thermal gradients at 451K preheat temperatures, 359K ambient temperature, 10W laser power, and 0.5mm spot diameter.

Fiber-reinforced thermoplastic composites have drawn much attention due to higher toughness in comparison with thermosets. Polycarbonate is of particular concern because of low weight, high thermal and impact resistance. In this paper, effect of manufacturing parameters such as temperature, pressure and time on mechanical properties of Polycarbonate/Glass laminate is investigated using Taguchi method. In order to evaluate effects of various parameters, an experimental design planned using L9 orthogonal array with three level of time, pressure and temperature with the help of Minitab software. For this, composite beams having arrangement [0]8 were produced in film staking procedure in a hot-pressing apparatus. The 3-points bending tests were carried out to assess manufacturing quality. Comparison of flexural modulus and flexural strength of various specimens were made and the results are commented upon and discussed. Results show that the temperature of 215 Celsius degree results higher mechanical properties than other temperatures because of preventing resin degradation and adequate viscosity. Furthermore, results indicated that the time factor was more significant, than time and pressure, on curing quality. Optimum values of factors such as time, pressure and temperature to achieve higher flexural modulus and flexural strength are determined using analysis of Signal to Noise Ratio (SNR).

In this paper, using shape memory alloy (SMA) wires, a model-based controller for force tracking of fingertips of an artificial hand finger is developed. Different aspects of modeling including static analysis, heat transfer analysis and also investigation of SMA wires, which are used as actuators, are studied. In order to parametrize the SMA wires a modified Brinson’s model is used. Brinson’s original model was not capable of accurately predicting all loading conditions thus some modifications are utilized. In order to control the applied potential difference of memory wires and consequently to control the electrical current to these wires and based on the model of shape memory wires a controller is designed. The main goal of presented controller is force controlling of a two DOF hand finger in order to grasp objects. This model contains SMA model and for compensation of system uncertainties, a proportional integrator derivative (PID) controller has been included in the closed-loop system. The effect of compensator will act only on the derivative type states and this is a new approach compared to similar literature. Simulation results of tracking a reference signal is reported which confirm that the model is in good agreement with experimental tests. The analysis of the relative tracking error for an arbitrary reference signal is 18% for the maximum normalized overshoot in experimental tests and 5% in the simulation.

Due to its complex nature, the chatter phenomenon in turning processes has always been important for the researchers of machine ‎science and many efforts have been made to control it‏.‏‎ Active methods of vibration control have the ‎ability to suppress the vibrations properly in different situations. This paper aims to develop a new, active and economic method for ‎detection and controlling chatter phenomenon before it occurs in the boring process. First, various signal processing methods were briefly ‎reviewed and compared, then two methods which are faster and more accurate in determining the occurrence of chatter were chosen, and ‎the time required for the transition from the stable to unstable mode was determined based on the signals. Then many tests were ‎performed with and without a control system. The accelerometer’s output signal which was measured in 0.1 seconds were used in these ‎tests. Two methods of signal processing (Fourier transform and spectral density) were also applied as indicators of the chatter occurrence ‎at the initial moment. Then, using an active control system, the command was given to slow down the speed of the milling machine to ‎switch the system back to its stable state. Using this control method, many tests were performed with different parameters for boring ‎process. In all tests, when the process was stable, the control system did not enter the circuit, and when the process went into the unstable ‎stage, the chatter phenomenon was detected and controlled in the pre-chatter stage before the surface was damaged.‎