نشریه مهندسی مکانیک مدرس
سال بیست و سوم شماره 5 (اردیبهشت 1402)

The non-reproducibility of the measured results of a work piece by reference laboratories is a problem that often causes differences of opinion in production workshops and doubts about the adjustment of production devices with the results provided by laboratories. In this paper, the effect of geometric parameters created by machining on the ability to measure control tools through statistical techniques of quality engineering is investigated, so that first a piece was subjected to drilling and machining, after measurements The exact diameter of the hole with geometric deviation was determined to be cylindrical error to 0.01 mm. Then it was examined with two common measuring systems of air gauge and coordinate measuring machine (CMM) and the capability of the instruments was calculated as follows through the mini-tab software. Capability of air gauge (Cg) in measuring the diameter of hole was 0.27 and capability of CMM device in controlling the said diameter was 0.28. After removing the scattering caused by geometric parameters to calculate the ability of measuring instruments, The power of the instruments was improved to 1.20 in the wind gauge and 1.05 in the CMM and finally, by removing or reducing the geometrical error of the work piece, It should be noted that in this study, after removing the error of workpiece the lack of repeatability in the air gauge increased from 74% to 16.66% and in the coordinate measuring machine (CMM) from 70.80% to 19.13%.

Metal and especially aluminum mirrors have wide applications in the optical industry due to their desirable properties, hence requiring very high polished surfaces. One of the methods of preparing aluminum mirrors is single-point diamond turning. In this research, the manufacturing process of 6061-grade aluminum mirrors has been studied using diamond turning and consequent polishing process in order to reach surfaces with acceptable optical properties. In the first part, the effective range of turning parameters was determined. The results showed that the feed values less than 5 µm/rev, the cutting edge radius between 0.2 and 0.8 mm, and the rotational speed of 2250 rpm have a greater effect on the surface roughness. In the second part of the research, initially, the turning process was performed with effective parameters and then the polishing process was applied as the final finishing process. Surface finish is evaluated by surface roughness and surface interferometry parameters. The results showed that the smaller surface roughness after the diamond tool turning process led to higher optical properties after the final polishing process. The lowest PV value equal to 0.293 µm was obtained by diamond turning with 1.5 µm/rev and a cutting edge radius of 0.8 mm.

Ultrasonic vibration assisted drilling is a new technique, and one of the modern and promising processes for drilling metals, especially metal alloys with low machinability. In this paper, a set of laboratory tests is used to investigate the effect of using ultrasonic vibrations on the force required for drilling of the thin aluminum specimens. For this purpose, three aluminum workpieces with different thickness are drilled under three different rotation speeds, and four different penetration rates. The results showed that in two aluminum workpieces, 1 and 1.5 mm, the use of ultrasonic vibrations generally reduced the axial force, but in the 2 mm workpiece, it is impossible to understand a meaningful effect of applying ultrasonic vibrations. In other words, it can be said that adding ultrasonic vibrations with constant amplitude and frequency does not have the same effect on drilling in different conditions, and to reach the most efficient drilling; the characteristics of optimal vibration should be studied.

Fused deposition modeling (FDM) is one of the most common 3D printings technologies. Low cost and the ability to produce models using wide range of thermoplastic polymers, makes this process suitable for rapid prototyping and manufacturing some commercial parts. The manufacturing complicated parts and increasing their qualities are possible, using more than three degrees of freedom printers. In this paper, a 5-DOF 3D printer is introduced. The mechanism of this printer is 4-DOF parallel mechanism with one additional degree of freedom resulting from rotation of printer bed about Z-axis. In order to generate tool path for 5-DOF printer, a CAM software was developed with python. For controlling the printer, control software was designed based on open-source Repetier framework. Since original framework only supports 3-axis printers, source code needed to be changed such as extending source code to support 5-axis and adding mechanism inverse kinematics. By using this 5-Dof mechanism, the prints of complicated parts without using the support are possible.

The human hand is one of the most complex organs of the human body, capable of performing skilled tasks. Manipulation, especially grasping is a critical ability for robots. However, grasping objects by a robot hand is a challenging issue. Many researchers have used deep learning and computer vision methods to solve this problem. This paper presents a humanoid 5-degree-of-freedom robot hand for grasping objects. The robotic hand is made using a 3D printer and 5 servo motors are used to move the fingers. In order to simplify the robotic hand, a tendon-based transmission system was chosen that allows the robot's fingers to flexion and extension. The purpose of this article is to use deep learning algorithm to grasping different objects semi-automatically. In this regard, a convolutional neural network structure is trained with more than 600 images. These images were collected by a camera mounted on the robot's hand. Then, the performance of this algorithm is tested on different objects in similar conditions. Finally, the robot hand is able of successfully grasping with 85% accuracy.

Employing machine tools with more than three degrees of freedom, is one of the effective methods for increasing the flexibility and accuracy of the machining parts. The milling machines with parallel mechanisms and higher degrees of freedom, have great stiffness and flexibility and also have great capability in the machining of the complicated parts. The calibration of this type of device, allows for increasing the accuracy and repeatability of the produced parts. In this article, a 4DOF milling machine with a parallel mechanism is introduced and necessary tests are performed to detect the movement errors of its rails. Again, the movement errors of the device have been measured by means of a dial indicator on a fixed part of the device using a magnetic base for positioning and linear movement of the device, and the measurement of errors after calibration has shown that the errors of the device have been significantly reduced. And it has increased the accuracy of the movement axes of the milling machine. Furthermore, the straightness of the axes is measured using a dial indicator and the error compensations are done. It is shown that the straightness of each axis with the adjustment of limit switches are improved very well.