Analyzing path control of servocontrolled robots

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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.

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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 multiply
  programmed and their program storage capability.

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Analyzing path control of servo-controlled robots

• (II) Point-to-Point servo-controlled robot
  (cont)
• Click in the picture
• on the left to play
• this movie

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Analyzing path control of servo-controlled robots

• (II) Point-to-Point servo-controlled robot
  (cont)
• 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.

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Analyzing path control of servo-controlled robots

• (II) Point-to-Point servo-controlled robot
  (cont)
• 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.

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Analyzing path control of servo-controlled robots

• (II) Point-to-Point servo-controlled robot
  (cont)
• 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.

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Analyzing path control of servo-controlled robots

• (II) Point-to-Point servo-controlled robot
  (cont)
• 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.

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Analyzing path control of servo-controlled robots

• (II) Point-to-Point servo-controlled robot
  (cont)
• 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.

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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.

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Analyzing path control of servo-controlled
robots

• (III) Continuous-path servo-controlled robot
  (cont)
• Examples of these applications include spray
  painting, polishing, grinding and arc welding.
• Click in the picture
• on the left to play
• this movie

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Analyzing path control of servo-controlled robots

• (III) Continuous-path servo-controlled robot
  (cont)
• 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.

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Analyzing path control of servo-controlled robots

• (III) Continuous-path servo-controlled robot
  (cont)
• 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.

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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.

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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.

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Summary of Lesson

• Some of the applications of CP robots are
• spray painting and
• continuous arc welding.

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End of Lesson
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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.