The design of the projects treated with the students can be effectively combined with the subsequent production using 3D printing. By using a digital prototype and realizing it directly from 3D data, we get a wide range of interesting options. Also, at this time, we should not just focus on simple component design solutions. Modern production methods offer a unique opportunity to produce virtually any shape demanding geometry and components. We dedicate our article to several procedures that we used in Žďár nad Sázavou High School and High School during this year’s online teaching to optimize the production of one of the robotic arm projects.
Technical and technological procedures in the online laboratory
The high availability of technical and technological software for our students offers a unique opportunity to combine school work with online self-study at home. We took advantage of several interesting topics that were assigned to our students as longer-term projects with consultations. One of these subjects was the design and technological preparation for the realization of a robotic arm controlled by an Arduino microcomputer. Let’s look at the experience with the design of the robotic arm, with the optimization of its construction and with our own production strategy. We used Autodesk 2021 series products and Prusa Research FDM 3D printing to implement the project. This combination, together with standardized design elements, turned out to be an excellent opportunity not only to prepare the project in the form of a digital prototype, but also to systematically work on its technological preparation and production.
During development, a number of dynamic simulations were used.
Digital prototype influenced by production technology
During the project, our goal was to optimize the production of the robotic arm with regard to its construction and design. The objective was not only to refine the numerical kinematic study, but also to meet the basic requirements concerning the rigidity of the robot and the precision of its movement. We structurally required all actuators to be encapsulated under self-supporting covers, so the robot looked more like consumer electronics than a purely purpose-built machine.
The robot model was continuously optimized using PrusaSlicer technology software.
The robotic arm is driven by model digital servo drives that can be effectively controlled by a very low-cost Arduino microcomputer. However, the disadvantage of this solution is the low axial and radial stiffness of the drive. The basis of a successful construction for us became the optimization of the design of the servo drives for their easy installation in the robotic arm with a minimization of the load on the bearings of the miniature gearbox. Thanks to FEM analyses, modular drive adapters with built-in robust bearings were designed and manufactured in a short time. A pleasant surprise during the production test of the first adapter was the high accuracy of the FDM printing method used. In this area, the Czech manufacturer really scores at full throttle.
Design optimization compared to 3D printing
From the first ideas, we worked with 3D printing as the final production method. Due to the robot’s cost and ease of processing, a cheap but workable PLA material from a two kilo spool was used. This plastic behaves favorably in 3D printing, is recyclable and has good mechanical properties. The disadvantage of PLA is its low resistance to heat, which makes it unsuitable for use outdoors or near heat sources.
Adapter to ensure high rigidity of the actuator
We wanted to solve the fundamental question of how to put the components together with a minimum of sticking. PLA plastic is glued well with instant glue and activator. However, we thought more about the modular construction of a robot with variable arm length. The use of self-tapping screws has proven ineffective in terms of the low temperature resistance of PLA plastic. When the screw is tightened faster, it heats up intensely and the thread melts. An excellent design solution is to use conventional hex or square nuts embedded in the slots. The robot design has been completely adapted to this assembly procedure and has proven to be an effective solution for joints that can be dismantled on several occasions. When working with slots along the printing layers, it is necessary to pay attention to the breakage of the part due to possible overlapping of the nut. It is more advantageous to make the slot with a smaller overlap, or to fix the nut inside the slot with glue.
We have used several types of axial and radial bearings in several structural units of the robot. Their installation turned out to be trouble-free even in serial production. All repetitive prints have always proven accurate, and installing the bearing with a smaller overlap has always been accurate. However, from the perspective of preparing for larger mass production using FDM printing, it is good to measure the part and optimize its geometry after printing the first part. Dimensions vary slightly depending on orientation of print layers and print angles. In absolute units, these are mostly hundredths of a millimeter.
Final controls of the robotic arm, including the axial stabilizer in the foreground
A separate chapter of production was the proper choice of part print orientation. We have tried to minimize the number of supports, which are compensated by structural elements at a maximum angle of 45 degrees.
Cooperation of application solutions
When working with 3D printing, we have tried several interesting Autodesk solutions available within the student community. The basic construction of the robot was created and optimized in Autodesk Inventor 2021. In this application, we used the FEM solver to analyze the deformation of the robot’s self-supporting arms. Some components have been optimized in the Autodesk Fusion cloud application. The main objective was to show other interesting possibilities of applications, including the newly available generative design for the school.
We used FEM technology and cloud services to design the arms.
Model transfers and processing in Prusa Slicer are completely hassle-free from both products. It is always advisable to consider the wall thickness in terms of technology. After analyzes and verification tests, we stayed on a light shell construction. The bonus of this solution is the minimization of the actuator load and the ability to deliver its torque from a greater arm load capacity.
You can find more information about projects solved using PLM / BIM technologies in vocational education at www.spszr.cz, or on our Facebook school.
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