As China's manufacturing industry accelerates its transformation, robots are being used more and more frequently. As technical engineers in factories, it is essential to understand the relevant technologies of robots. So, what components make up a general-purpose robot?
As a system, a robot consists of the following components:
Robotic arm or mobile vehicle: This is the main body of the robot, composed of links, movable joints, and other structural components, enabling the robot to reach a specific position in space. Without these other components, the robotic arm alone is not a robot.
An end effector is a component attached to the last joint of a robotic arm. It is typically used to grasp objects, connect with other mechanisms, and perform required tasks. Robot manufacturers generally do not design or sell end effectors; in most cases, they only provide a simple gripper. End effectors are mounted on robots to perform tasks in a given environment; welding, painting, gluing, and parts loading/unloading are among the few tasks that may require a robot to perform. Usually, the movement of the end effector is directly controlled by the robot controller, or signals from the robot controller are transmitted to the end effector's own control unit (such as a PLC ).
Drivers: Drivers are the "muscles" of a robotic arm. Common drivers include servo motors, stepper motors, cylinders, and hydraulic cylinders. There are also some newer drivers used in special applications, which will be discussed in Chapter 6. Drivers are controlled by a controller.
Sensors: Sensors are used to collect information about the robot's internal state or to communicate with the external environment. The robot controller needs to know the position of each link to determine the robot's overall configuration. Humans can identify their arms and legs even in complete darkness because neural sensors in the central nervous system within the tendons send information to the brain. The brain uses this information to determine the degree of muscle contraction and thus the state of the arms and legs. For robots, sensors integrated within the robot send information from each joint and link to the controller, allowing the controller to determine the robot's configuration. Robots are often equipped with many external sensors, such as vision systems, tactile sensors, and speech synthesizers, to enable them to communicate with the outside world.
Controller: The robot controller acquires data from the computer, controls the actions of the actuators, and coordinates the robot's movement together with feedback information from sensors. For example, if the robot wants to retrieve a part from a cabinet, its first joint angle must be 35°. If the first joint has not reached this angle, the controller sends a signal to the actuator (sending current to the motor), causing the actuator to move. Then, feedback sensors on the joint (potentiometers or encoders, etc.) measure the change in joint angle. When the joint reaches the predetermined angle, the controller stops sending control signals. For more complex robots, the robot's speed and force are also controlled by the controller. The robot controller is very similar to the human cerebellum. Although the cerebellum's function is not as powerful as the human brain, it controls human movement.
Processor: The processor is the brain of the robot. It calculates the movement of the robot's joints, determines how much and how far each joint should move to reach a predetermined speed and position, and supervises the coordination of the controller and sensors. A processor is typically a dedicated computer. It also needs an operating system, programs, and external devices such as monitors.
Software: The software used for robots generally consists of three parts. The first is the operating system, which operates the computer. The second is the robot software, which calculates the movements of each joint based on the robot's motion equations and then transmits this information to the controller. This software comes in various levels, ranging from machine language to the high-level languages used by modern robots. The third part is a collection of routines and applications, which are developed for using external devices on the robot (such as general vision programs) or for performing specific tasks.
The maximum distance a robot can reach within its work area. A robot can reach many points within its work area in any pose (these points are called dexterous points). However, for some other points close to the limits of the robot's range of motion, its pose cannot be arbitrarily specified (these points are called non-dexterous points). Note: Range of motion is a function of the robot's joint lengths and its configuration.
Accuracy: Accuracy refers to how precisely a robot reaches a designated point. Note: It is related to the resolution of the actuator and the feedback mechanism. Most industrial robots have an accuracy of 0.001 inches or higher.
Repeatability: Repeatability refers to the precision with which a robot reaches the same position when an action is repeated multiple times. For example, suppose a robot is driven to reach the same point 100 times. Due to many factors affecting the robot's positional accuracy, it's impossible for the robot to reach the exact same point every time, but it should reach within a circle centered on that point. The radius of this circle is formed by the series of repetitive actions; this radius is the repeatability. Note: Repeatability is more important than precision. If a robot's positioning is not precise enough, it will usually exhibit a fixed error. This error is predictable and can therefore be corrected through programming. For example, suppose a robot always deviates 0.01mm to the right . Then, all position points can be specified to be offset 0.01mm to the left , thus eliminating the deviation. Note: If the error is random, it is unpredictable and therefore cannot be eliminated. Repeatability limits the range of this random error and is usually determined by repeatedly running the robot a certain number of times.
