Industrial robots are the protagonists of advanced production workshops. From large manufacturing enterprises to small workshops, the bustling robot market always finds suitable workshop partners. The most common industrial robot on the market currently is a multi-joint robot, which is a type of robot with a motion structure composed of several joints and linkages.
This article introduces three common structures of multi-joint industrial robots: vertical series structure, vertical-horizontal structure, and parallel structure.
ONE Vertical Serial Robot
Vertical serial robots are the most common structural form in industrial robots, with joints connected in series along the vertical direction, typically consisting of 5 to 7 joints. This structure mimics the movement of the human waist to wrist, enabling complex movements in three-dimensional space, and is suitable for various scenarios such as processing, transportation, assembly, and packaging.
These rotatable joints (similar to human arms with joints such as shoulders, elbows, wrists, etc.) are divided into two main parts:
(1) Positioning mechanism: This can determine the position of the "hand", which is composed of three joints: the waist joint, lower arm joint, and upper arm joint, to move the "wrist root" of the robot to any position in three-dimensional space.
Lumbar joint: Rotate left and right like a person twisting their waist (1st axis)
Lower arm joint: controls the forward and backward swing of the upper arm (2nd axis)
Upper arm joint: controls the up and down swing of the forearm (3rd axis)
(2) Directional mechanism: It determines the posture of the "hand" and consists of three parts: wrist rotation, wrist bending, and hand rotation. It controls the orientation of the "hand", such as tilting the gripper or aligning the screwdriver at an angle.
Wrist rotation: Rotate the wrist left and right (4th axis)
Wrist Bend: Nodding the wrist up and down (5th axis)
Hand rotation: End tool rotation (6th axis)
Six-axis vertical serial robots are widely used in fields such as automotive manufacturing and electronic assembly due to their high degree of freedom and flexibility. However, vertical serial robots also have some limitations:
Motion interference problem: Just like how it feels awkward for a person to reach behind their back, 6-axis robots also have "blind spots". The first blind spot is the upper/front restriction, which makes it difficult to move in certain directions when the arm is fully extended or folded; The second "blind spot" is the difficulty of reverse operation, such as suddenly switching from front to back operation, which may require overall adjustment of posture.
It is worth mentioning that in some scenarios where horizontal operations are the main focus (such as handling and packaging), the number of robot motion axes can be simplified from the standard 6 axes to 4-5 axes. This is because horizontal homework often does not require complex wrist rotation movements, and after omitting 1-2 rotation axes, the robot structure is simpler and more rigid.
Secondly, for large heavy-duty robots such as palletizing robots, parallelogram linkage drive mechanisms are often used. This design moves the traditional drive motor located on the upper arm down to the robot's waist and transmits it through a linkage mechanism. There are three major benefits to doing this: firstly, it lowers the center of gravity of the entire machine and improves the stability of motion; The second is to use the lever principle to amplify the motor torque and improve the load capacity; The third is to enhance structural rigidity, which is more suitable for high-speed and heavy-duty operations. This parallelogram structure has become a signature design for large handling and palletizing robots.
BORUNTE's four-axis robot is specifically designed for palletizing operations
TWO horizontal serial robots
Horizontal serial robot is a type of planar articulated robot, whose joints are arranged in series along the horizontal direction, usually consisting of 2 to 3 rotating joints. This structure gives it high rigidity and speed in a horizontal plane, making it suitable for fast and precise flat operations such as welding, assembly, and handling tasks. SCARA robots are commonly used in light-load, high-speed flat work scenarios, such as the 3C industry (electronic component installation) and automotive component assembly.
BORUNTE horizontal robot
(1) Plane positioning: The collaborative work of these horizontal rotating joints enables SCARA robots to achieve precise positioning within a plane. This means that robots can perform complex operations on a fixed plane without the need for complex three-dimensional movements.
(2) Vertical lifting motion: The entire arm can be lifted and lowered through a vertical linear movement axis (Z-axis). This enables the robot to move vertically, thereby expanding its working range.
Three parallel robots
A parallel robot consists of multiple parallel arms connected to a base through a parallel mechanism, forming a whole. The characteristics of this structure are high rigidity and strong load-bearing capacity, but the difficulty of position detection and control technology is relatively high. Parallel robots are typically used in scenarios that require high precision and fast response, such as heavy material handling, machine tool loading, and precision assembly. Typical parallel robot structures include Delta robots, which have a simple design and fast movement speed, and are widely used in fields such as food processing and electronic material inspection.
The basic structure of the Delta robot
Hanging arrangement: The Delta robot is placed on the base, with the wrist supported by three parallel connecting rods evenly distributed in space.
Control of linkage swing angle: The robot positions the wrist within a certain spatial cylinder by controlling the swing angle of the linkage.
Advantages of Delta robots
Simple structure: The Delta robot has a relatively simple structure, making it easy to design and manufacture.
Easy motion control: Due to its structural characteristics, the motion control of Delta robots is relatively easy to implement.
Easy installation: The installation process of Delta robots is relatively simple, making it easy to deploy and maintain.
Limitations of Delta robots
Small carrying capacity: The lightweight design of Delta robots is aimed at optimizing the design rather than optimizing the load, so their carrying capacity is usually small (compared to vertical robots), which limits their use in heavy-duty applications and makes them more suitable for sorting and transporting lightweight items. Due to the limitation of carrying capacity, Delta robots are mostly used for sorting and transporting lightweight items in industries such as electronics, food, and pharmaceuticals.
The above is a comparison of three different structures of multi-joint industrial robots. Their respective image characteristics are still very different. These robots have their own advantages and limitations. Therefore, choosing the one that is suitable for their production line is the best. Currently, these robots are all under development and production by BORUNTE Robot. Those interested can take a look at the BORUNTE robot information.