Elnasr University
College of Engineering
Department of Electrical Engineering
ﺣﻜﻢ5101
Industrial Robotics
Lecture 3
Robot Motion Control
abusabah22@hotmail.com
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Lecture Outline
Introduction
Type of Robot Motions
Motion Control System
Troubles in Motion Control Systems
Robot Motion Planning
Accuracy and Repeatability
Development Trends
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Introduction
Automatic: able to activate, move or regulate itself.
Control: command, direct, rule, check, limit, restrain, regulate
or operate.
System: a group or combination of interrelated, independent, or
interacting elements forming a collective entity.
Control engineering is concerned with modifying the behavior
of dynamical systems to achieve desired goals.
Control System Terminologies
Input - Excitation applied to a control system from an external
source.
Output - The response obtained from a system
Feedback - The output of a system that is returned to modify
the input.
Error - The difference between the input and the output.
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Types of Robot Motion
PTP Joint movement PTP
Joint Motion Point-To-point
Linear CP Movement
Linear Motion
CP
Continuous
Path
Circular CP Movement
Circular Motion
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Types of Robot Motion
The robot controller drives the motors of individual
axes and axial movements coordinated by the TCP
to manage accordingly.
The robot controller controls I / Os (digital and
analog input and output signals) in order to operate
external devices (grippers, tools) synchronized with
the robot motion.
The robot controller communicates with other
controllers, PCs, or with higher-level computers.
The robot controller uses sensors to gather
information from the robot environment and to
modify accordingly the robot task.
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Types of Robot Motion
Motion Drivers
Electric
Uses electric motors to actuate individual joints,
Preferred drive system in today's robots
Hydraulic
Uses hydraulic pistons and rotary vane actuators
Noted for their high power and lift capacity
Pneumatic
Typically limited to smaller robots and simple
material transfer applications
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Motion Control System
The primary purpose of the servo system is to control the
motion of the load
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Motion Control System
The digital ac servo system is typically available with three
modes of operation:
Torque Control Mode
Velocity Control Mode
Position Control Mode
In other words, in order to control the position the torque
and velocity should be controlled.
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Troubles in Control System
Actuator Hysteresis
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Troubles in Control System
Mechanical Hysteresis
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Troubles in Control System
Friction
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Troubles in Control System
Electronic Hysteresis
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Robot Motion Planning
An important, interesting, spatial reasoning problem.
Let A be a robot with p degrees of freedom, living in
a 2-D or 3-D world.
Let B be a set of obstacles in this 2-D or 3-D world.
Call a configuration LEGAL if it neither intersects
any obstacles nor self-intersects.
Given an initial configuration qstart and a goal config
qgoal, generate a continuous path of legal
configurations between them, or report failure if no
such path exists.
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Robot Motion Planning
Playback with point-to-point control –records work
cycle as a sequence of points, then plays back the
sequence during program execution.
Playback with continuous path control –greater
memory capacity and/or interpolation capability to
execute paths (in addition to points).
Intelligent control –exhibits behavior that makes it
seem intelligent, e.g., responds to sensor inputs,
makes decisions, communicates with humans
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Robot Motion Planning
The robot will execute the task, or is unsatisfactory
from all over!
- Positions are not exactly known
- Position change during processing
- Measure objects are not known in advance
Solution: integration of sensors with information
from the environment!
- Visual Information
- Force Information
- Position information
Modification of the robot task
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Robot Motion Planning
Perception Cognition Action
Sensors Actuators
External World
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Robot Motion Planning
Sony AIBO Robot
18 degrees of freedom with a
continuously controllable range of
motion
3 DOF in each leg (12 total)
3 DOF in the head
2 DOF in the tail
1 DOF in the jaw
Each joint is controlled by
specifying to a desired joint angle
to O Virtual Robot Comm.
2 binary motors for the ears
A speaker for general sound
production
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Robot Motion Planning
Each message to O Virtual Robot Comm contains a set of
target angles for the joints
Each target is used for a PID controller (part of the OS)
that controls each motor
Each target angle is used for one 8ms motor frame
Each message contains at least 4 motor frames (32ms)
Walk Parameters Motion Frames
Walk Engine Frame Interpolator
Dynamic Walking Motion Static Frame-Based Motion
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Accuracy and Repeatability
Three terms used to define precision in robotics,
similar to numerical control precision:
1. Control resolution -capability of robot's positioning
system to divide the motion range of each joint into
closely spaced points.
2. Accuracy -capability to position the robot's wrist at a
desired location in the work space, given the limits of
the robot's control resolution.
3.Repeatability -capability to position the wrist at a
previously taught point in the work space.
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Development Trends
Increase accuracy of the robot positioning
- Integration of modules for the accuracy increase
- Robot calibration (Off-line programming)
Increase use of sensors
- For programming (recognition)
- After programming (consequences)
- Integration of multiple sensor data - Sensor fusion
Open architecture of the robot controller
- Integration of PC-based applications
- Openness to the selected applications
- Security - domain of the robot manufacturer
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