Industrial robots typically consist of four parts: actuator, drive system, control system , and sensing system, as shown in the figure below.
The interaction relationships between the components of an industrial robot are shown in the following figure.
Executive agency
An actuator is the physical component that enables a robot to perform its tasks; it typically consists of a series of links, joints, or other forms of kinematic pairs. Functionally, it can be divided into the hand, wrist, arm, waist, and base.
1.1 Hands
The hand of an industrial robot, also known as an end effector, is a component mounted on the robot's wrist that directly grasps the workpiece or performs tasks. The hand is one of the key components for evaluating the quality and dexterity of a robot's task completion.
1.2 Wrist
Wrist rotation refers to the rotation of the wrist around the axis of the forearm, also known as arm rotation. Some robots limit their wrist rotation angle to less than 360 degrees, while others are only limited by the number of turns of the control cable, allowing the wrist to rotate a certain number of times.
1.3 Arm
The arm is a crucial component of a robot's actuator. Its function is to support the wrist and hand, and to transport the grasped workpiece to a given position. The robot's arm mainly consists of the lever and components related to its movement, including the transmission mechanism, drive unit, guiding and positioning device, support connection, and position detection elements.
The various movements of the robot arm are typically achieved through drive mechanisms and various transmission mechanisms. Therefore, it not only bears the weight of the workpiece being grasped, but also the weight of the end effector, wrist, and the arm itself. The arm's structure, working range, flexibility, grasping weight (arm strength), and positioning accuracy all directly affect the robot's performance. Therefore, the arm's structural form must be determined based on factors such as the robot's motion patterns, grasping weight, degrees of freedom, and motion accuracy.
A typical robotic arm has three degrees of freedom: extension and retraction, left and right rotation, and lifting and lowering. The arm's rotation and lifting movements are achieved through the pillars of its base; the lateral movement of these pillars corresponds to the arm's lateral movement. All arm movements are usually implemented by drive mechanisms and various transmission mechanisms.
1.4 Waist
The waist section connects the arm and the base, and is typically a rotating component. Its rotation, combined with the arm's movement, enables the wrist to perform spatial movements. The waist section is a critical component of the actuator; its manufacturing errors, motion accuracy, and stability have a decisive impact on the robot's positioning accuracy.
1.5 Base
The base is the supporting part of the entire robot, and there are two types: fixed and mobile. Mobile bases are used to expand the robot's range of motion; some are dedicated walking mechanisms, while others are tracks and roller mechanisms. The base must have sufficient rigidity and stability.
drive system
The drive system of an industrial robot is a device that provides power to the various components of the execution system. It consists of two parts: the drive unit and the transmission mechanism, which are usually integrated with the execution mechanism. Drive units typically include electric, hydraulic, and pneumatic devices, as well as integrated systems that combine these technologies. Commonly used transmission mechanisms include harmonic drives, screw drives, chain drives, belt drives, and various gear drives.
control system
The task of the control system is to direct the robot's actuators to perform fixed movements and functions based on the robot's work instructions and signals fed back from sensors . If the industrial robot does not have information feedback characteristics, it is an open-loop control system; if it does have information feedback characteristics, it is a closed-loop control system.
The control system of an industrial robot mainly consists of a main control computer and a joint servo controller , as shown in the figure.
The host computer primarily programs the robot according to the job requirements and issues commands to control the various servo drive devices, ensuring coordinated operation of the linkages. It also handles information transmission and coordination between environmental conditions and peripheral equipment. The joint servo controller is used for servo control of the drive units, trajectory interpolation calculations, and system status monitoring. Different industrial robot control systems vary; the figure shows an actual control system of an ABB industrial robot.
Industrial robots typically employ two control methods: teach-and-playback and position control. Teach-and-playback control involves the operator programming the work sequence into a memory device using a teach pendant. Upon receiving an external start command, the robot reads the information from the memory device and sends it to the control unit, which then issues control signals. The drive mechanism then controls the robot 's movement, enabling it to perform the given actions within a certain precision range, according to the information stored in the memory device.
In fact, the biggest difference between industrial robots and general automated machinery is that they have a "teach-and-playback" function, thus exhibiting the characteristics of being versatile and flexible.
There are two main methods for position control of industrial robots: point-to-point control and continuous path control. Point-to-point control only considers the start and end positions of the robot's end effector, without concern for the trajectory between these points. This method can perform operations such as spot welding, loading/unloading, and material handling under unobstructed conditions. Continuous path control, on the other hand, requires the robot to reach the target point with a certain level of precision, and also demands a certain accuracy in its movement trajectory, as seen in operations like robot painting and arc welding. In fact, this control method is based on point-to-point control, using a position trajectory interpolation algorithm that meets the required precision between every two points to achieve trajectory continuity.
Sensing system
Sensing systems are a crucial component of robots. Based on the location of the information they collect, sensors are generally categorized into internal and external sensors. Internal sensors are essential for robot motion control, such as position and velocity sensors. They collect information from within the robot and are indispensable basic components. External sensors detect the robot's environment, the state of external objects, or the relationship between the robot and external objects. Commonly used external sensors include force sensors, tactile sensors, proximity sensors, and vision sensors. Robots used in some specialized fields may also require sensors with sensing capabilities for temperature, humidity, pressure, slippage, and chemical properties.
Traditional industrial robots rely solely on internal sensors for precise control of their movement, position, and posture. Using external sensors, however, enables the robot to adapt to its external environment to a certain extent, thus exhibiting a degree of intelligence .
