1.8 BASIC DEMONSTRATION STEPS
1. Discuss Microbot, and show simple programming. Allow students to move robot to feel backlash, and stepper motor slip.
2. Go to CRS robot, and discuss robot in general terms. Show controller, wires, hoses, robot, gears, chains, and allow students to move robot and feel backlash and DC servo motor for comparison. Servo motors and encoders are discussed.
3. Set up PC as terminal, then, power up robot. Point out that the controller is on, but the robot arm does not have power yet. Give power to arm, (point out the separate power on for safety) then calibrate the robot home position. The robot is positions using the ‘manual’ command with the teach pendant, then the ‘home’ command is used to zero the robot.
4. Basic motion commands for the controller are displayed using the commands ‘joint’, ‘ready’, ‘manual’, ‘motor’, ‘limp’, ‘nolimp’, ‘jog’.
5. The other I/O capabilities of the robot are shown using ‘open’, ‘close’, ‘output 2’, to control the gripper, and the pneumatic vice respectively.
6. Robot position feedback is displayed using the commands ‘w0’, ‘wz’ ‘status’, to show various positions in encoder pulses, degrees, Cartesian coords.
7. The joint control algorithms are discussed, and the effect of gain parameters on the PID controllers is demonstrated by varying the gain with the command ‘gain 0’. (The parameters are changed from 8,.25,100 to 5,.25,100 for one long sweep of the arm, and vibrations will be noticed because of controller overshoot). Discuss effects, and attempt to give practical implications. The tradeoff of speed and accuracy should be obvious here.
8. Programming is discussed using the program lists in the machines. The concept of memory instead of disk is used. Programs are displayed, listed. etc using commands ‘free’, ‘dir’, ‘listp’, ‘edit’, ‘run’. A simple program is run for demonstration, and listed. (Also the RAPL language is compared to Basic)
9. The use of points for enhancing programming is discussed. A list of points are shown using ‘listl’, and then the ‘approach’, ‘depart’, ‘move’, and ‘move ,s’ commands are used to move to points by reference. ‘teach’ and ‘here’ are used to instruct the robot where the points are.
10. Positioning accuracy is measured using a sheet of paper taped to the table. A pen is put into the robot gripper, and then a straight line motion is made. The distance measured will be slightly different due to accuracy, and the line will wiggle because of control problems.
11. Repeatability is measured by putting a displacement gauge dial on the milling machine bed. The robot is moved back, and forth to touch the gauge, and the readings are taken. The values will vary because the robot is not a perfect device, and is prone to variations between motions.
12. The students will then ‘teach’ a set of points for pegs in the workcell (from set ‘p’ to set ‘q’, using tool orientation ‘tool pegtool’). The points will then be used to run the ‘pegs’ program. The students should notice failures to pick up pegs due to friction, positioning problems, etc. A Short discussion follows. Different modes are used for teaching, ‘manual joint’, ‘manual cylindrical’, and ‘limp’.
13. A sheet of paper is taped down, and the robot is outfitted with a pen. Four points are then taught to the gripper (point set ‘r’ and ‘tool weldtool’). The ‘weld’ program is then run, and the robot traces out the path with straight line, and continuous motion. In both cases the paths are not perfect, due to controller action. The program is run again to show the repeatability of the process.