Altra-01 - Building & Constructing a Robotic Arm 2018 - Jayden Downes.
Currently there are a lack in automation in construction, most work is currently done by builders manually which can easily result in injury or buildings taking long periods of time to build. You are to create a robotic arm that is capable of building houses and larger structures. The robotic arm needs to be able to lift heavy loads, be easily transportable and very heavy duty as it will be placed on construction sites. The robot should also be able to reach into places that would normally be difficult for cranes and must be faster then original methods of building structures and moving objects / materials.
- Mounting points on claw for safety to secure load.
- Concrete and other building materials can’t easily stick to the arm's material or easily break the arm if they were to fall on any part of the robot.
- Extra safety features like sensors to stop the arm before it hits something or someone.
- Compact - Must be able to packed up with ease (Modular).
- Must be redundant for safety (If one belt or pulley breaks another one will support the load) – Auto belt tensioning.
- It must be hard for operators get anything stuck in the machine such as hands or objects.
- The robot must be precise.
- Must include mounting holes for the base to be secured to the ground easily.
- Failsafe's built in (ensures G2 timing belts won’t slip and cause the arm to drop).
Current designs for robotic arms include; Polar, cylindrical, Cartesian, Joined-arm and SCARA robotic arms. These designs all come with advantages and disadvantages, for example a precise robotic arm is usually slow in order to ensure accuracy of the motors and to prevent inertia which would make a robot unprecise due to “play” if not built to the proper specification for the speed of the robot. Another issue that is commonly found in robotic arms is the material the arm is made of and what it is actually capable of lifting. Usually robotic arms are made up of high-strength low-alloy (HSLA) steels. HSLA steels contain relatively low levels of carbon, typically about 0.05%. They also contain a small amount of one or more other elements that add strength. These elements include chromium, nickel, molybdenum, vanadium, titanium, and niobium. Besides being strong, HSLA steels are resistant to atmospheric corrosion and are better suited to welding than carbon steels which are used in applications where the steel is not needed to be as strong as that of a crane or robotic arm.
|Materials||Stainless Steel, HSLA Steel, Aluminum||Plastic (Can be made out of any 3D printing material).||HSLA Steel, Aluminium, Steel.|
|Reliablilty||High (Sensors)||High (Stepper Motors - Rare failiture)||High (Sensors, Stepper motors are from reliable source)|
|Motors||Clearpath Servos||Nema 17 & 23||ClearPath Servo|
|Redundancy||Low||Low (Only one belt per axis)||None|
Materials (For Prototype):
|Material / Item||PLA (Polylactic acid) Plastic Filiment - 1.75mm Ø||ABS (Acrylonitrile butadiene styrene) Plastic Filiment - 1.75mm Ø||Stainless Steel Screws|
|Density kg m-3||Varies per manufacture and can be found in the product specifications.||Varies per manufacture and can be found in the product specifications.||7600|
|Elastic (Young’s) modulus kN mm-2||3.5||2.3||200|
|Ultimate tensile strength N mm-2||50||40||860|
|Yield stress N mm-2||6||48.3||502|
|Notes:||Warps at tempratures exceding 40°C meaning it is not suitible for use in outdoor or non-controlled environments.
Diameter 1.75mm / 3.0mm
Diameter Tolerance ±0.05 mm
Ovality Tolerance ±0.01 mm
Extrusion Temperature 170°C to 218°C
|Due to being recycled the Plastic can vary in properties. Thus making it unreliable for a final real world robotic arm unless aquired from a trusted source.
Diameter 1.75mm / 3.0mm
Diameter Tolerance ±0.05 mm
Ovality Tolerance ±0.01 mm
Extrusion Temperature 170°C to 218°C
The G2 Pulley is the main type of pulley used in the robotic arm, it allows the system's G2 belts to spin around an axis with extreeme precision using the engraved teeth. G2 belts and pulleys are commonly used in the producing of machines such as CNCs and 3D printers. They allow the movement of two or more diffrent pulleys in the same direction and are reinforced with stainless steel cables to prevent expanding of the belt under pressure and thus minimising output inconsistancies. The setup used in the 3D model below is not used throughout the design and only the actual pulley is used. At times the pulley is also modified to act as a bearing to position the belts in the correct location within the Robotic Arm Frame as seen in the models below.
|Pitch Length||152 teeth per ft. (500 teeth per meter)|
|Standard Widths||.236, .354 & .472 in. (6, 9 & 12 mm)|
|Material||Nylon Covered Neoprene Belt, Fiberglass Reinforced, Stainless Steel.|
3 Part Pulley:
The Three Part Pulley is the main pulley which is used as a positioning system for the belts in order to keep them in the correct location within the Robotic Arm Frame. The bearing pulleys have a bearing each 180 degrees in order to prevent the belt from drifting off to one side when the robotic arm is not in a upright (stright) position.
As can be seen in the model below the G2 Pulleys are longer then the parrallel bearings, this later caused issues and was replaced with the same type of pulley as seen in the middle position and the pulley on the right was fixed to the cover and frame before 3D printing, this allows for a stronger bond due to the print angle and thicker layers (decreasing possible failiture points).
The frame makes up the most part of the robotic arms area. It is made of structural steal beams that are placed inside of an aluminum shell that is coated in rubber to prevent damages to the frame upon being hit by objects. It also prevents concrete or other building materials from sticking to the frame in a building environment. Due to this project being in a prototyping phase it is made out of PLA (Polylactic acid) Plastic as it is strong and brittle [not flexible], and can withstand outside tempratures after the hardening proccess.
The turn mechanism is responsible for positioning the Pulley System. It's main purpose is to ensure the belts are always in line with the center of each frame so the two systems never come into contact. The turn mechanism works by one clyndrical plate being fasened to the frame section and the other being locked into thr turn mechanism it's self. This allows one of the designated pulleys/belts to drive the section of frame.
Evaluation:This part under went many prototypes due to issues with the; Pulley Lengths (Coliding with the Turn Mechanism), One face of the turn mechanism had locks on it which prevented movement and the cylindrival turn plate tollerances being too tight for a smooth movement in the robotic arm sections.
Time Plan & Journal:
|9th Febuary||Introduction to Task 3||Introduction to Task 3 - Research, gather, sort, analyse information in order to plan, design, make and evaluate a pneumatic Robotic Arm.|
|16th Febuary||Timeplan Layout + Design Brief||Design Timeplan and set out a Design Brief for the Robotic Arm (What is it being made for / Purpose).|
|23rd Febuary||Analysis||Analysis on what current designs include and their advantages, disadvantages & what they include.|
|1st March||Research on 3 Designs||Drawings of Robotic Arms already made and what are their specifications, advantages & disadvantages.|
|9th March||Material Analysis + Specification||Material Analysis / Specification on what materials could be used fro the final production in a production environment and what requirements does the final design need to follow.|
|16th March||Concepts||Concepts on diffrent componenets of the Robotic Arm (Base, Mechanisms, Frame, Claw)|
|23rd March||Final Model Concpet Design||A Concept drawing / model that incorperates ideal parts functioning together from the previous concepts - this includes the materials and measurements which are tied into the cad model.|
|6th & 13th April||Prototyping in CAD||Prototyping for final design in CAD to test if the main components (Pulley Mechanisms and Frame) will work together and function as required.|
|3rd, 4th, 7th, 8th & 10th May||TurboCad Lessions - Lukas De Klerk||Introduction & Explination of Modification Tools, Drawing Tools, Basic Functions + Selecting, Settings (Measurements - Metric/Imperial).|
|11th, 14th & 15th May||CAD - 123D Design / Fusion 360 - Base + Mechanisms.||Transformation from Concept Drawings to CAD (123D Design / Fusion 360) - Includes Evaluation and Prototyping of the Final / Proposed Part.|
|17th, 18th, 21st & 22nd May||CAD - 123D Design / Fusion 360 - Base + Mechanisms.||Transformation from Concept Drawings to CAD (123D Design / Fusion 360) - Includes Evaluation and Prototyping of the Final / Proposed Part.|
|24th, 25th, 28th & 29th May||CAD - 123D Design / Fusion 360 - Master Claw Layout & Design.||Transformation from Concept Drawings to CAD (123D Design / Fusion 360) - Includes Evaluation and Prototyping of the Final / Proposed Part.|
|May 31st, 1st, 5th, 7th & 8th June||CAD - 123D Design / Fusion 360 - Fixing Errors between diffrent parts.||Transformation from Concept Drawings to CAD (123D Design / Fusion 360) - Includes Evaluation and Prototyping of the Final / Proposed System.|
|11th, 12th, 14th & 15th June||CAD - 123D Design / Fusion 360 - 2D/3D Renders of Parts + Drawings of Models.||Transformation of parts from CAD (123D Design / Fusion 360) into JPG/JPEG [More Colours] and PNG [Transparcency] Images for Web - Includes Evaluation of the Final / Proposed Renders.|
|18th, 19th, 21st & 22nd June||Printing and Building Design||Parts were printed in White Polylactic Acid (a biodegradable and bioactive thermoplastic aliphatic polyester derived from renewable resources) on a FDM 3D Printer (Flashforge Creator Pro's) - Some Parts took up to 48 Hours to Print due to limitations on speeds avaliable due to the 3D printer Hoteneds and limited printers being avaliable due to the ending of the semester and abundance of other year's projects that also required printing.|
|25th, 26th, 28th & 29th June||Evaluation of Parts and Functionality + Finalising Theory||Parts that were faulty were reprinted and/or redesigned. Theory work was also checked - This includes going though the Task 3 Merking Criteria to ensure all Items were included as specified.|
|16th July||Reprints & Rebuidling reprinted Parts + Testing Final Design||Reprinting Parts that had errors in them or that didn't print correctly. Parts that were printed were rebuilt into the Robotic Arm and tests and evaluations where conducted.|
Tools and Safety:
"A team of scientists has published a study that details the health hazards of 3D printing in enclosed spaces, which it says causes the release of toxic and carcinogenic particles." For this reason it is recommended to keep 3D printers in a well ventelated environment. The same can be said for laser cutters as dangerous gasses can be expelled from the machine when cutting Synthetic polymers such as; plastics like polyethylene, polycarbonate, polypropylene, as well as synthetic rubber, polyvinyl chloride (PVC), polyethylene, phosgene and many other materials.
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Gideon Hillman Consulting (n.d.). 26 best Robotic Process Automation. [image] Available at: https://i.pinimg.com/736x/77/d7/4f/77d74fb8faf71c6c68663f600463e46b--industrial-robots-robot-kits.jpg [Accessed 1 Mar. 2018].
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