Design of a 4 DOF parallel robot arm and the firmware implementation on embedded system to transplant pot seedlings

Abstract

This paper presents a firmware design and its implementation on a real time embedded system for driving a 4 DOF parallel robot arm. The firmware primarily comprised of two components to produce motion of the robot arm: a) generation of continuous position coordinates and b) generation of actuating signals. These two components were processed in two different microcontrollers with a common communication bus. The position generation algorithm produced and transmitted continuous position data to the motion generation algorithm in the form of G-code strings by reading the input positions which were previously stored by the user in EEPROM memory of the microcontroller. The receipt of a handshake signal synchronized the data transmission between these components through a communication bus. An LCD display and keypad were used as human-machine interface (HMI) to communicate with the user to set the robot target coordinates. The mechanical structure of the robot arm comprised of multiple links which were actuated by stepper motors. The workspace boundary were sensed by limit switches. The kinematic equations represented the gripper position for the corresponding input joint angles. A microcontroller was used to compute kinematic equations of the robot arm with the help of motion generation algorithm to generate actuation signals for the simultaneous movement of robot joints. The kinematic equations were solved with the dual-core capability of the microcontroller using real time operating system (RTOS), which made the computation faster with an average computation time of 198 μs per step. The developed firmware was implemented and tested on a 4 DOF parallel manipulator using embedded microcontrollers for continuous pickup and place of the paper pot seedlings for automating the metering of pot seedlings. The cycle time taken for pickup and dropping of each seedling was 3.5 s with a success rate of 93.3%.