An industrial robot is a multi-jointed manipulator or multi-degree-of-freedom machine device designed for industrial applications. It can automatically perform tasks, relying on its own power and control capabilities to achieve various functions. It can be commanded by humans or operate according to pre-programmed sequences. Modern industrial robots can also act according to principles established using artificial intelligence technology.
An industrial robot consists of three basic parts: the body, the drive system, and the control system. The body, including the base and actuators, comprises the arm, wrist, and hand; some robots also have a locomotion mechanism. Most industrial robots have 3–6 degrees of freedom, with the wrist typically having 1–3 degrees of freedom. The drive system includes the power unit and transmission mechanism, used to enable the actuators to produce corresponding movements. The control system issues command signals to the drive system and actuators according to the input program and performs control.
Industrial robots are classified into four types based on the movement of their arms:
1. Cartesian coordinate arms: move along three Cartesian coordinates;
2. Cylindrical coordinate arms: perform lifting, rotation, and extension/retraction movements;
3. Spherical coordinate arms: rotate, pitch, and extend/retract;
4. Articulated arms: have multiple rotational joints.
Today, let's break down these four types of industrial robots and see which one you are most familiar with.
Multi-axis Robots
Multi-axis robots, also known as single-axis manipulators, industrial robotic arms, electric cylinders, etc., are robot systems built on an XYZ Cartesian coordinate system as their basic mathematical model. They use servo motors or stepper motors as their driven single-axis manipulators as their basic working units, and ball screws, synchronous belts, and rack and pinion gears as common transmission methods. They can reach any point in the XYZ three-dimensional coordinate system and follow a controllable motion trajectory.
Multi-axis robots employ a motion control system for drive and programmable control. Linear and curved motion trajectories are generated using multi-point interpolation, and operation and programming are achieved through guided teaching programming or coordinate positioning.
SCARA Robot
A SCARA robot is a special type of industrial robot with cylindrical coordinates. It has three rotary joints with parallel axes for positioning and orientation in a plane. The remaining joint is a translating joint, used for end effector movement perpendicular to the plane. The wrist reference point is determined by the angular displacements φ1 and φ2 of the two rotary joints and the displacement z of the translating joint, i.e., p = f(φ1, φ2, z), as shown in the figure. These robots are lightweight and have a fast response time; for example, the Adept 1 SCARA robot can reach speeds of up to 10 m/s, several times faster than typical articulated robots. It is best suited for planar positioning and vertical assembly operations.
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XY coordinates (front, back, left, right)
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Z coordinates (up, down)
Coordinate robot
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A coordinate robot is a multi-purpose manipulator capable of automatic control, reprogrammable operation, multiple degrees of freedom, and spatial Cartesian relationships. Its operation primarily involves linear motion along the X, Y, and Z axes. Coordinate robots utilize a motion control system for drive and programming control. Linear and curved trajectories are generated through multi-point interpolation, and operation and programming are achieved through guided teaching programming or coordinate positioning.
As a low-cost, simple-structured automated robot system solution, coordinate robots can be applied to common industrial production fields such as dispensing, drip molding, spraying, palletizing, sorting, packaging, welding, metal processing, handling, loading and unloading, assembly, and printing. They offer significant application value in replacing manual labor, improving production efficiency, and stabilizing product quality.
Serial and Parallel Robots
A serial robot's serial structure is an open kinematic chain; its moving links do not form a closed structural chain. Serial robots offer a large workspace and are easier to move, avoiding coupling effects between drive axes. However, each axis must be controlled independently, requiring encoders and sensors to improve motion accuracy.
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Parallel robots, on the other hand, complement traditional industrial serial robots in application, forming a closed kinematic chain. Parallel robots are less prone to dynamic errors, exhibiting high accuracy with no error accumulation. Furthermore, their compact and stable structure, with most output axes bearing axial force, results in high rigidity and load-bearing capacity. However, for parallel robots, forward solving is more difficult than inverse solving.
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2-DOF Parallel Robot
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3-DOF Parallel Robot
DDoS parallel mechanisms are diverse and complex, generally falling into the following categories:
1. Planar 3-DOF parallel mechanisms, such as the 3-RRR mechanism, which has two translational and one rotational axes;
2. Spherical 3-DOF parallel mechanisms, such as the 3-UPS-1-S spherical mechanism. The kinematics of this type are simple in both forward and inverse kinematics, making it a widely used 3D mobile spatial mechanism;
3. Spatial 3-DOF parallel mechanisms, such as the Delta parallel robot. These mechanisms are underranked, and their most prominent characteristic is that their motion varies at different points within the workspace.
4. Another category includes spatial mechanisms with added auxiliary links and kinematic pairs.
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4-DOF Parallel Robot
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6-DOF Parallel Robot
6-DOF parallel mechanisms are a major category of parallel robot mechanisms and are the most studied parallel mechanisms by scholars both domestically and internationally. They are widely used in flight simulators, 6D force and torque sensors, and parallel machine tools. However, many key technologies for these mechanisms have not been fully resolved, such as their forward kinematics, the establishment of dynamic models, and the accuracy calibration of parallel machine tools.
