Robot Control Systems 317

“Robot Control Systems” is an overview of the control systems that provide continuous process and motion control for industrial robots. Robots use both open and closed control loop systems to maintain a process variable at a desired set point. Most robots use feedback loops that adjust for error in order to obtain a desired output. Robots commonly use PID controllers, which set parameters in order to more accurately control the position, velocity, and force of an industrial robot.

After taking this class, users will be able to describe a robot control system. A foundation in robot control systems is important given the increased integration of industrial robots in manufacturing.

Class Details

Class Name:
Robot Control Systems 317
Difficulty:
Advanced
Number of Lessons:
11

Class Outline

  • Industrial Control Systems
  • Open Loop Systems
  • Closed Loop Systems
  • Robot Control System Components
  • Review: Control Systems
  • Robot Control System Hierarchy
  • Position Control
  • Force Control
  • PID Control
  • Controller Tuning
  • Review: Types of Control

Objectives

  • Describe control systems.
  • Describe open loop systems.
  • Describe closed loop systems.
  • Describe components in a robot control system.
  • Describe the hierarchy of robot control.
  • Describe position control.
  • Describe force control.
  • Describe PID control.
  • Describe robot controller tuning.

Job Roles

Certifications

Glossary

Vocabulary Term Definition
actuator A device that activates linear or rotary movement. Robot actuators are often motors located at the joints between linkages.
actuator control Robot control that operates the individual robot actuators. Actuator control is the most basic level of robot control.
algorithms A logical and mathematical expression that models a process or action. Algorithms are coded into a computer program that forms the rules that determine how a device such as a robot interacts with its environment.
assembly A manufacturing process in which two or more components are joined together to create a finished part. Assembly robots are fast and consistent, and they effectively self-inspect their work.
automation The use of self-regulated equipment, processes, or systems that meet manufacturing requirements with limited human intervention. Automation is an efficient means of assembly.
autotune A feature in some control devices that automatically adjusts the PID control at start-up. Autotune adjusts control parameters more efficiently and accurately.
axes A theoretical straight line that is used to measure the location and orientation of an object in three-dimensional space. Axes in the Cartesian coordinate system include the X, Y, and Z axes.
Cartesian coordinate system A positioning system that uses three perpendicular linear axes to locate positions in three-dimensional space. The Cartesian coordinate system's axes are the X axis, Y axis, and Z axis.
Cartesian robots A type of robot that moves along three orthogonal axes. Cartesian robots have linear joint movement that gives them a highly rigid structure, allowing them to lift heavy objects.
closed loop system A type of control loop where the setpoint (SP) is dependent on the process variable (PV). Closed loop systems, or servo systems, adjust the setpoint using feedback from a sensing system.
constant A variable or number that does not change value. The constant value for correction in proportional control is matching the error value.
control loops A process control system designed to maintain a process variable (PV) at a setpoint (SP). Control loops can be open or closed.
control signal An electrical signal that the controller sends to a robot to power actuators or another robotic device. Control signals are commands for a robotic process.
control systems A network of control loops used to manage dynamic processes by adjusting or maintaining physical variables. Control systems allow for more precise and repeatable processes.
controller The main device that processes information and communicates instructions to a robot. A controller operates the entire robotic system.
controller tuning A method of adjusting the controller's response to error by adjusting PID control values. Controller tuning is typically achieved using algorithms.
cumulative The total sum of a range of values, which increases as each new value is added. The cumulative error value is used to calculate adjustment values in integral control.
Delta robots A stationary, high-speed parallel robot. Delta robots are usually suspended above their work area and have three parallel arms that attach together with an end effector and are driven by motors in the base of the robot.
derivative A correction based on the rate of change of error value. Derivative control allows a controller to anticipate whether the PV will overshoot the SP and reduces the output as needed.
disturbance Any unwanted change or variation in a manufacturing environment. Disturbances can be caused by debris, shifting components, and operator error.
drive Any device that introduces motion into a system. Electric motors are the most common robot drive.
encoders A device that translates rotary or linear motion into a digital signal. Encoders can determine a robot's position.
end effector A device attached to the end of a robot arm that allows it to interact with a part, component, or material. The end effector may be a gripper that allows the robot to pick up objects and place them down.
error value The difference between the setpoint (SP) and process variable (PV). When error values are detected, the controller sends instructions to the control system to adjust the output to compensate.
errors The difference between a measured value and its correct value. Errors must be adjusted for a more precise robotic process.
feedback Information sent from a sensing system to a controller to show disturbances or error value. Feedback allows the system to adjust the robot's position or force.
force A push or pull that changes an object's motion or state of rest. Forces have specific directions and magnitudes.
force control Controlling the amount of force and torque of a robot's actuators. Force control can be applied when contact is made between the robot's end effector and its environment.
force control systems A type of control system that controls the precise force and torque of a robot's actuators. A force control system compensates and regulates a robot's force based on the specific application.
force torque sensors A type of sensor that detects linear and rotational forces applied to a robot's wrist or end effector. Force torque sensors allow robots to make adjustments when handling material.
human-machine interfaces HMI. A handheld device used to program, monitor, or control a robot's movements. A human-machine interface may have a touch screen or control pad.
hybrid control The combination of position control and force control. Hybrid control allows a robot to maintain a certain force while following a specific trajectory.
input device A piece of equipment that allows a human being to communicate with and program a robot. Input devices include personal computers and teach pendants.
input signal A message or command sent electronically to a controller. An input signal is created by a program.
integral A correction based on accumulated error over time. In PID control, the integral control corrects offset error left after proportional control.
inverse kinematics The calculation and translation of Cartesian coordinates into joint angles. Inverse kinematics is used to convert the end effector's position and orientation coordinates into joint angles.
joint space The set of joint positions defined by a robot's joint angles rather than Cartesian coordinates. Joint space comprises the area in which all of the robot's joints and end effector move.
machine tending The process of loading and unloading materials into machinery for processing. Machine tending robots are precise and often use sensors to monitor processes.
main control Robot control that interprets the programmed instructions for a process or task. Main control is the highest level of robot control.
manipulators An arm-shaped robot that is typically mounted on a base or placed on or suspended from a track. Manipulators, or robotic arms, typically have all revolute joints.
material handling The process of loading, unloading, placing, or manipulating material. Material handling operations often require highly repetitive tasks that are ideal for robotic work.
mobile robots A robot that is able to move through space. Mobile robots require sensors to avoid collision.
motion control Controlling the movement of machine elements. Motion control is produced by using a mechanical source of power like an actuator.
non-servo system A type of control loop that uses a setpoint (SP) to control a process variable (PV). A non-servo system, or open loop system, does not detect errors or disturbances.
offset error A sustained error that cannot be eliminated by proportional control alone. Offset error is typically corrected with integral control.
open loop system A type of control loop that uses a setpoint (SP) to control a process variable (PV). An open loop system, or non-servo system, does not detect errors or disturbances.
orientation Rotational position in three-dimensional space. Orientation is determined by rotation around the X, Y, and Z axes.
oscillation The act of correction values overshooting or underhooting the setpoint. Oscillation can be caused by miscalculating error correction.
output A calculated result or action produced by a computing device after processing data inputs. An output is the correct task completed by a robot process.
path The route taken by a robot to travel from one location to another. A robot's path can be adjusted using feedback.
path control Robot control that coordinates the separate movements along the axes and combines them into the desired robot path. Path control is an intermediate level of robot control.
payload The maximum amount of weight that a machine mount is able to carry. Payload limits vary robot to robot.
peripheral devices A physical device connected to a wired or wireless network that performs an auxiliary function. Peripheral devices communicate with a controller.
personal computers PC. A processor-driven device for an individual user and commercial software. A personal computer may be used as an input device for a robot control system.
pick-and-place robot A robot or robotic device that moves parts from one location to another. Pick-and-place robots, sometimes called part-transfer robots, improve the precision, quality, and speed of manufacturing operations.
PID Proportional-integral-derivative control. A type of process control that adjusts system outputs by reacting to three values, one that is proportional to an error, one that represents the error over time, and one that represents the rate of change of the error. PID control is one of the most common types of process control.
position Location in three-dimensional space. A robot's position is determined by control systems.
position control Controlling the location and orientation of a robot or mechanical device. Position control maps a path for the robot to reach the desired position.
position control system A type of control system that controls the precise position and orientation of a robot regardless of outside forces. A position control system uses algorithms to decide where a robot will move.
process control An approach to manufacturing that attempts to closely monitor and control all aspects of a process. Process control methods include collecting and analyzing data to help reduce errors.
process variable PV. The measured value of the process output. A process variable could measure velocity, position, temperature, or any other process-related condition.
program A computer-based series of commands that contains all pertinent instructions and information for the completion of a specific task. Programs are used by CNC machines, PLCs, and robots.
programmable logic controller PLC. A processor-driven device that uses logic-based software to provide electrical control to machines and processes. A programmable logic controller is used in factory automation.
programming device A peripheral device connected to a controller that is used to enter instructions into a controller's memory. Programming devices include personal computers and handheld programmers.
proportional A correction based on equally compensating for the error value. With proportional control, if the error value changes, the output will change in a predictable manner to maintain the same ratio.
proportional-integral-derivative control PID control. A type of process control that adjusts system outputs by reacting to three values, one that is proportional to an error, one that represents the error over time, and one that represents the rate of change of the error. Proportional-integral-derivative control is one of the most common types of process control.
PV Process variable. The measured value of the process output. A PV could measure velocity, position, temperature, or any other process-related condition.
robot control system A network of control loops used to manage dynamic processes in robots by adjusting or maintaining physical variables. Robot control systems create more precise and repeatable processes.
robotic arms An arm-shaped robot that is typically mounted on a base or placed on or suspended from a track. Robotic arms, or manipulators, typically have all revolute joints.
Selective Compliance Assembly Robot Arm robots SCARA robots. A type of cylindrical robot that has four axes of movement: X, Y, Z, and Theta Z. Selective Compliance Assembly Robot Arm robots are often used for material handling applications.
sensing system A collection of hardware and software that detects environmental or robotic information and communicates it to a controller as feedback. Sensing systems provide intelligence to robots.
sensors A device that detects the presence or absence of an object, certain properties of an object, environmental changes, or the internal state of a robot, and provides feedback. Sensors allow robots to have an awareness of their environment.
servo system A type of control loop where the setpoint (SP) is dependent on the process variable (PV). Servo systems, or closed loop systems, adjust the setpoint using feedback from a sensing system.
setpoint SP. The desired or target value of a controlled or monitored condition. A setpoint is the desired value for the process variable.
SP Setpoint. The desired or target value of a controlled or monitored condition. An SP is the desired value for the process variable.
steady-state error The resulting error value for a PID controller. Steady-state error can be decreased by tuning a controller.
teach pendants A handheld device used to program or control a robot's movements. Teach pendants may have control buttons, a joystick, or a touch screen.
three-dimensional 3D. Having height, width, and depth. Robots follow a trajectory in three-dimensional space.
tooling Assorted tools used in various manufacturing processes. Robotic tooling includes material removal tools and welding torches.
torque A force that causes rotation. Torque attempts to twist or rotate an object.
trajectory The timed path a robot moves along beginning at an initial starting point and ending at a desired destination point. Trajectories determine how and where a robot will move.
variables A changing value or an unknown value. Variables can affect the way a robot performs tasks or operates in its environment.
velocity The rate of change in an object's speed in a given direction. A constant surface speed ensures a steady velocity.