Design of Universal Robotic Manipulator

A robotic manipulator is a type of articulated robot which is suitable for various repeating tasks in industrial manufacturing and automation process. A 5-axis robotic manipulator consists of five joints or actuators and few links which connects joints together. Nowadays, industrial robotic manipula

Project Title

Design of Universal Robotic Manipulator

Project Area of Specialization

Robotics

Project Summary

A robotic manipulator is a type of articulated robot which is suitable for various repeating tasks in industrial manufacturing and automation process. A 5-axis robotic manipulator consists of five joints or actuators and few links which connects joints together. Nowadays, industrial robotic manipulator is commonly deployed for various industrial applications such as welding, drilling, painting, screwing, surface treatment and pick and place of items from one place to another place. The industrial robots can perform the repeated task much faster than humans with greater accuracy and precision. The purpose of this project is to design and develop a 5-axis universal robotic manipulator which could be used for various industrial application where accuracy and precision is required in repeated tasks. The objective is to design and develop a low cost, locally manufactured, industrial grade robotic manipulator with higher accuracy, precision, resolution, and appropriate pay load capability. The robotic manipulator is 3D printed prototype which could be scaled up and can be manufactured in industrial grade metals such as aluminum. The parts of conceptual prototype model are created in SolidWorks and can be 3D printed. The robotic manipulator has five joints/actuator consists of two stage planetary gearbox with high torque capability and back-drivability. The actuators are powered through NEMA 23 bipolar stepper motors which offers precise control of joints with smaller resolution of angular movement. The stepper motors are controlled through TB6600 stepper motor driver using Arduino MEGA 2560 board. The robotic manipulator will be capable of recording and replaying the joint movement. Each stepper motor has incremental optical rotary encoder of 400 pulses per revolution with three output phases such as A, B and Z. For recording joint movements, each stepper motor has separate ATtiny85 microcontroller which records total number of output pulses from phase A and phase B and calculates angular position of a joint in degrees. The instant position of all joints will be stored in Electrically Erasable Programmable Read-only Memory (EEPROM) and all motors will be moved in coordinated fashion to replay the recorded pose of the manipulator.

Project Objectives

Our goal is to design a 5-axis universal robotic manipulator which could be used for various small, repeated tasks in industry. The universal robotic manipulator will not be designed for only specific application however, it could be used for various applications such as pick n place, screwing, drilling, welding, and painting. The manipulator can be used for various application by changing end-effector tools. Furthermore, the design could be scaled up or down for various applications as required by industry. The prototype will be 3D printed robotic manipulator with five robotic actuator and joints to link the actuators. The robotic manipulator will be capable of recoding and replaying joint movements as this will create ease of use in industrial application and can be trained by skilled technicians and labor.

Project Implementation Method

The proposed robotic manipulator consists of five 3D printed actuators/joints powered by NEMA 23 bipolar stepper motors. The stepper motors are controlled using Arduino Mega 2560 board through TB6600 stepper motor drivers in 1/8 microstepping mode and operated at 36 V DC for higher output torque. Each 3D printed actuator has three hall-effect sensors mounted on output ring of planetary gearbox which help in determining and reaching home position. Each stepper motor has incremental optical rotary encoder, and its output phase A is connected external interrupt INT0 of a ATtiny85 microcontroller so that any output pulse should not be missed. Thus, there are five encoders and five ATtiny85 microcontrollers to counter total number of pulses in both clockwise and anti-clockwise direction and compute the angular position of a joint in degrees. All five ATtiny85 microcontrollers are connected to Mega 2560 via Inter-Integrated Circuit (I2C) bus. The Arduino Mega 2560 is configured as master and all ATtiny85 are slave devices.

When the robotic manipulator is powered up, the Mega 2560 drives stepper motors and get feedback from hall-effect sensors to align all joints in homing position. The Mega 2560 will search for any recorded pattern of joint movement in EEPROM, if any pattern is available then all stepper motors will be driven to repeat that recording pattern. Initially, there will be no movement pattern, thus user will be asked via Serial communication to record a pattern. There are three push buttons connected to Mega 2560 via external interrupts: 1) Start Recording, 2) Next Position and 3) Stop Recording. When start recording is pressed, the Interrupt service routine (ISR) will first disable power to stepper motor so that user can manually move the manipulator and can record joint position in degrees. Secondly, the ISR will send a message via I2C to all ATtiny85 to count total number of pulses in clockwise and anti-clockwise direction and computer angular position of joints. When Next Position button is pressed, the ISR will send message to all ATtiny85 to store current position of joints in EEPROM of Mega 2560 and again count output pulses of encoder to compute angular position. In this way, as many times the user will press Next Position the angular position of joints will be stored in EEPROM in sequential order. When Stop Recording is pressed, the Mega 2560 will send message via I2C to all ATtiny85 to disable INT0 for counting pulses. Furthermore, the Mega 2560 will enable power to all stepper motors, bring robot to homing and start moving joints as per angular position stored in EEPROM. Arduino boards are capable of driving ten stepper motors simultaneously using Acceleration.h and Multistepper.h library which supports coordinated movement of joints such as all motors will start and stop at same instant however, their speed will depend upon total number of steps required to reach target position.

Benefits of the Project

Nowadays, many industrial tasks such as welding requires higher level of accuracy and precision on production line. If the robotic manipulator is not precise, then there will be defects in welding. For example, the Tesla motors hire one of the best welders and asked him to train their robots for welding. However, those robots are being trained using machine learning and requires complex programming algorithms. The proposed robotic manipulator would be capable to record its joints movement and replay that continuously without using machine learning or other complex techniques. This technique will be helpful in local industry of Pakistan where technicians would be able to transfer their skill such as welding, painting, drilling to the proposed robotic manipulator. This will eventually help in reducing idle time during operation and reduce quality assurance issues of products. Furthermore, the robotic manipulator could be scale up or down depending upon application requirement and can be manufactured locally. The manipulator could be used for various application by changing end-effector tools such as welding, painting, drilling, screwing, pick n pack via gripper and electromagnetic etc. The robotic manipulator could be made as open-source where students and learns can contribute and re-design as per their requirements.

Technical Details of Final Deliverable

The five-axis 3D printed robotic manipulator will be delivered as final year project. The completed prototype would be able to record the joint movements and replay that recorded pattern precisely. However, there will be any end-effector tool such as welding, spray-painting or drilling as those will be included in future work of this project.

Final Deliverable of the Project

Hardware System

Core Industry

Manufacturing

Other Industries

Core Technology

Robotics

Other Technologies

Sustainable Development Goals

Industry, Innovation and Infrastructure

Required Resources

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