Industrial Robot Electrical Design
Electrical Design Illustrated Overview
Toolchain for Toolpaths
Electrical Schematic Designer (gschem) > export ( __ filetype)> PCB Layout Creator (PCB) > export (gerber filetype)> G-code generator from gerber files (PCB2gcode) > export (gcode filetype) > Machine Controller (EMC2) > export (logic signals) > Machine ( __ ) > export (work)
Micro-controller
The microcontroller is the programmable command unit of the industrial robot. The microcontroller can send signals to the stepper motor drivers and solenoid drivers to move the robot; the microcontroller can receive signals from the shaft encoder to determine how far the robot has moved at each of the 6 joints.
Possibility is an Arduino microcontroller (such as the Arduino Mega 2560) Arduino Website
The microcontroller will need 6 analog outputs with PWM to give signals to the solenoid drivers.
The microcontroller will need X ___ outputs ___ to give signals to the stepper motor drivers.
The microcontroller will need X ___ inputs ___ to receive signals from the shaft encoders.
The microcontroller will need a universal serial bus (USB) port to interface with the computer.
Solenoid Driver
The function of the solenoid driver is to power on and off the solenoid valves. The solenoid driver receives a pulse width modulation signal from the microcontroller and amplifies that signal; the amplified signal is a DC output that energizes the solenoid valve.
Possibility is the PWM Driver 1.1 from RepRap wiki PWM Driver 1.1
Stepper Motor Driver
The function of the stepper motor driver is to power the stepper motors in discrete increments; the stepper motor shaft then rotates based on how much energy was provided by the stepper motor driver.
More information on stepper motor controllers can be found in the following link; the design contained in that link is the one planned to be used for the industrial robot. Stepper Motor Controller
Off-the-Shelf options include EasyDriver on sparkfun and A4983 Stepper Motor Driver on pololu
Shaft Encoder
Mechatronics on Digital Encoders
The function of the shaft encoder is to determine the position of a motor shaft as time passes. This function is necessary for the industrial robot to perform tasks with accuracy, because the robot's movement is determined not only by the power supplied to the motors but also the load being moved. For instance, more power is required to lift a boulder than a baseball. It is easier, more practical, and more accurate to have a position sensor (shaft encoder) than having to calculate different power inputs for each load.
An absolute encoder can identify different positions of the measured shaft, but is more complex than an incremental encoder. However, an incremental encoder only provides relative position information. An incremental encoder can be used as an "absolute" one by saving the relative movement information; for instance, for day 1, joint A moves 5 degrees clockwise from the home position, then day 2, joint A moves 10 more degrees clockwise; by saving the information from day 1, the microcontroller can understand that joint A has moved a total of 15 degrees clockwise from the home position, not just 10 degrees.
Resource for Incremental Encoder Design
Society of Robots on Incremental Encoder Design
The current development plan is to use incremental encoders for their low cost, high resolution, and simplicity of design and fabrication relative to absolute encoders.
Incremental encoders can be split into 2 types: magnetic and optical. The current plan is to use optical encoders.
A phototransistor pair can be found here Digikey PT pair
Combining that with schmidt trigger'd comparators, 2 digital outputs can carry signals to the microcontroller, one output to determine direction of shaft rotation and the other output to determine speed of shaft rotation. (if output B changes when output A is high, the shaft is rotating in one direction; if output B changes when output A is low, the shaft is rotating in the other direction).