Analyzing path control of servo-controlled robots

1. Analyzing path control of servo-controlled robots (I) Objectives After this lesson, you should be able to: • Explain what is Point-to-Point control. • Explain what is Continuous Path control. • Illustrate, using a real application, a Point-to-point servo-controlled robot. • Illustrate, using a real application, a Continuous-path servo-controlled robot.

2. Analyzing path control of servo-controlled robots (II) Point-to-Point servo-controlled robot • widely used for moving parts from one location to another and also for handling various types of tools. • Can perform all of the tasks of the pick-and-place robot. • More versatile than the pick-and-place robot because of their ability to be multiplyprogrammed and their program storage capability.

3. Analyzing path control of servo-controlled robots (II) Point-to-Point servo-controlled robot (con’t) Click in the picture on the left to play this movie

4. Analyzing path control of servo-controlled robots (II) Point-to-Point servo-controlled robot (con’t) • Example of such application is the loading and unloading of a pallet of parts. As a part on a conveyer moves & interrupts the light beam from a photo emitter, the robot controller commands the robot to acquire the part and placed it in an empty slot in a partitioned carton.

5. Analyzing path control of servo-controlled robots (II) Point-to-Point servo-controlled robot (con’t) In the unloading case, the robot would be taught each of the n locations on the pallet. Then, it would move to the first of these taught points to pick up the part, move to a position above the conveyor, and place the part onto the conveyor.

6. Analyzing path control of servo-controlled robots (II) Point-to-Point servo-controlled robot (con’t) • Such an application, though possible with a non-servo pick and place device, would probably require a servo-driven x-y table that would actually move the pallet relative to the fixed pickup point.

7. Analyzing path control of servo-controlled robots (II) Point-to-Point servo-controlled robot (con’t) • The computer actually calculates the actual path of the manipulator. • If no changes was expected, the initially taught points can be stored in a read-only memory (ROM). • A combination of random-access memory (RAM) and ROM can be used for teaching new points and storing the old ones.

8. Analyzing path control of servo-controlled robots (II) Point-to-Point servo-controlled robot (con’t) • In general, these robots have a working range and load capacity that is quite high. • They most often use hydraulic actuators, although recently, the trend has been toward servo-motor actuated systems.

9. Analyzing path control of servo-controlled robots (III) Continuous-path servo-controlled robot • Used in applications where it has to follow a complex path through space and possibly to have the end of the arm move at high speeds. • The tool carried by the manipulator is fairly light but the required motion to perform the task may be quite complex.

10. Analyzing path control of servo-controlled robots (III) Continuous-path servo-controlled robot (con’t) • Examples of these applications include spray painting, polishing, grinding and arc welding. Click in the picture on the left to play this movie

11. Analyzing path control of servo-controlled robots (III) Continuous-path servo-controlled robot (con’t) • In the teaching mode, an automatic sampling routine is activated. Points are recorded at a rate of 60 to 80 times a second for about 2 minutes. • An operator moves the tool over the desired path with the sampler running, at a desired speed to facilitate the accurate recording of a path of certain complexity.

12. Analyzing path control of servo-controlled robots (III) Continuous-path servo-controlled robot (con’t) • The sampling rate should be high so that when the recorded points are “played back”, smooth motion results. • The playback is independent of the recorded speed, so that a rapid and accurate curve tracing is possible. • This means that a large memory is required to store such many points.

13. Summary of Lesson • Point-to-point (PTP) servo controlled robots are suitable for tasks in which the end effector is actuated only after the arm has come to rest, and not while the arm is in motion. • Some of the applications of the PTP robots are: • loading or unloading of a pallet of parts; • spot welding. • PTP robots sometimes have the ability to perform CP motion, but the method is teaching is not that convenient.

14. Summary of Lesson • In continuous path (CP) servo controlled robot, the end of the arm move at high speed to follow a complex path through space. They are used to perform work while the arm is in motion. • Unlike in PTP control, points are not recorded manually in the CP robot. • In general, CP robots can be used for only a limited number of tasks and are often single-task devices.

15. Summary of Lesson • Some of the applications of CP robots are : • spray painting; and • continuous arc welding.

16. ~~ End of Lesson ~~

17. Analyzing path control of servo-controlled robots Point-to-Point servo-controlled robot • Movie clip on the top left shows an example of such a robot. Click on it to play. • Example of such application is the loading and unloading of a pallet of parts, shown on top right.