"What type of robot should be chosen for the automation transformation of the production line?" "For precise assembly, is it better to use a series or a parallel robot?" "Which type of robot is more durable in high-timing scenarios?" - These are the most perplexing questions that many manufacturing enterprises encounter when upgrading their production lines. In the field of industrial robots, series robots (multi-joint robots) and parallel robots are the two main choices. The former dominates various scenarios due to its flexibility, while the latter occupies specific fields with its high speed. Choosing the right one can increase production efficiency by over 30%, while choosing the wrong one not only wastes millions of investments but also slows down the production rhythm. Today, we will analyze the differences between the two from three dimensions: structural principle, core performance, and scene adaptation. We will also provide a comprehensive selection guide for all scenarios to help you precisely match and avoid mistakes! 

I. Understand this: Series vs. Parallel. The core difference lies in "structure". 

Many people cannot distinguish between serial and parallel robots. In fact, the core difference between the two lies in their mechanical structure, and the structure directly determines the performance limit. In simple terms: A serial robot is "a series of joints connected together", while a parallel robot is "multiple branches working together simultaneously". 

Comparison dimension

Core structure 

Serial robot (multi-joint robot): Composed of 3 to 6 rotating joints connected in series, similar to the "shoulder-elbow-wrist" structure of a human arm. The end effector (gripper) is driven sequentially through the joints. 

Parallel robot (delta robot): It consists of a fixed platform, a moving platform, and 3 to 6 parallel branches. The branches simultaneously drive the movement of the moving platform, similar to "the multiple legs of a spider" 

Work Space 

Serial robots (multi-joint robots): Have a large space and are flexible, capable of performing multi-directional and multi-angle movements, and can cover a wide range of working areas. 

Parallel robot (delta robot): The working area is relatively small, with a conical shape centered around the moving platform, and is suitable for precise operations in a small range. 

Speed and Precision 

Serial robots (multi-joint robots): Medium speed (end speed 1-3 m/s), high repeatability positioning accuracy (±0.02 - ±0.1mm), the greater the load, the more stable the accuracy. 

Parallel robot (delta robot): Extremely fast (end speed 3-10 m/s), with extremely high positioning accuracy (±0.01 - ±0.05 mm), but the accuracy significantly decreases when the load increases. 

Load capacity

Serial robots (multi-joint robots): Have a wide load range (1kg - 1000kg+), and have significant advantages in heavy-load scenarios. 

Parallel robots (delta robots): Have a relatively small load capacity (typically ranging from 0.1kg to 50kg), and are mostly suitable for light-load operations. 

Cost and Maintenance 

Serial robots (multi-joint robots): High to medium cost (100,000 - 5 million per unit), many joints require regular lubrication, and maintenance cost is moderate. 

Parallel robot (delta robot): Mid-range cost (80,000 - 800,000 per unit), simple branched structure, low failure rate, and lower maintenance cost. 

II. Scene Adaptation: How to choose the appropriate production line? Just use the one that is directly applicable. 

The type of operations, load size and cycle requirements of the production line directly determine the selection of robots. Precise solutions are provided for six core scenarios: 

1. Light load, high cycle rate scenario: Parallel robots are the "limiting factor" 

The core requirement of this type of scenario is "fast and accurate". A single device needs to complete hundreds or even thousands of operations per hour, and there is no comparable speed advantage for parallel robots: 

Food/medicine sorting and packaging: For instance, sorting and packaging of cookies and chocolates, counting and packaging of medicine capsules. These scenarios have a light load (single item ranging from 0.1 to 1 kg), high cycle requirements (3000-6000 times per hour), and parallel robots can achieve "grabbing - placing" responses in milliseconds with precise positioning and no missed grabs or placements. When combined with a vision system, they can also distinguish different specifications of products and meet the requirements of flexible sorting. 

Electronic component assembly: For instance, installation of camera lenses in mobile phones, and positioning and welding of chip pins. The operation accuracy is required to be within ±0.02mm. The highly rigid structure of the parallel robot can ensure stability during high-speed movement, preventing damage to the components and increasing efficiency by 2-3 times compared to the serial robot. 

Safety warning: If the single load exceeds 5kg, do not choose the parallel robot. In high-speed movement, if the load is too heavy, it will cause the moving platform to tremble and the accuracy to drop significantly. 

2. Heavy and medium-load multi-process scenarios: Serial robots are the "main force" 

Such scenarios require the robots to be "capable of carrying, reaching, and performing multiple actions". The multi-joint advantages of the robots are perfectly suited to these requirements: 

Automobile component manufacturing: such as engine cylinder body welding, door assembly, and chassis bolt tightening. The load is usually 50-500 kg. The serial robots (mainly 6-axis type) can easily bear this load, and their arms can flexibly rotate to avoid obstacles, completing multiple processes such as welding, grasping, and assembly. There is no need to frequently replace equipment. For example, in the automobile welding production line, the repetitive positioning accuracy of the 6-axis serial robots is ±0.05mm, which can ensure that the welding points are uniform and firm. 

Appliance shell processing: For example, the transportation of the refrigerator shell after stamping, and the assembly of the air conditioner outdoor unit. The scope of work is extensive (it needs to cover stamping machines, conveyor belts, and assembly platforms), and the large working space of the series of robots enables "cross-regional operations". One robot can replace 2-3 workers, and it can operate continuously for 24 hours without getting tired. 

Selection criteria: For loads ranging from 1 to 50 kg, choose 4-6 axis serial robots, which offer sufficient flexibility; for loads above 50 kg, select heavy-duty serial robots and also need to be equipped with tracks to expand the working range. 

3. Complex Trajectory Operation Scenario: The Serial Robot "Unique Mode" 

When complex motion trajectories such as curves and arcs need to be accomplished by robots, the multi-joint linkage capability of serial robots is something that parallel robots cannot replace: 

Surface coating: For tasks such as furniture surface painting or car body spraying, robots need to move along the curved surface contour at a constant speed to ensure uniform coating. Serial robots can achieve complex trajectory planning through programming, and the end effector can always remain perpendicular to the curved surface, resulting in coating quality far superior to that of manual work. However, parallel robots can only perform simple linear movements and cannot be adapted for curved surface operations. 

Precision grinding and polishing: For operations such as mold cavity grinding and stainless steel kitchenware polishing, the grinding angle and force need to be adjusted according to the shape of the workpiece. The force control system of the connected robot can promptly sense the grinding pressure, preventing over-grinding or missed grinding, and even complex cavities can be easily covered. 

4. Miniaturized flexible production line: The two can "work together" 

Nowadays, many enterprises are adopting "small batch, multiple varieties" production methods. A single robot is insufficient to cover the entire process. The combined solution of series connection and parallel connection can achieve "1 + 1 > 2": 

Example: Mobile phone assembly line - Parallel robots are responsible for quickly grasping light and small components such as screens and chips and precisely placing them on the workbench; 6-axis serial robots are responsible for grasping the components on the workbench for assembly, tightening screws, and then transporting the semi-finished products to the next process; Finally, the parallel robots complete the sorting and packaging of the finished products. The entire process is fast and flexible. When changing production models, only reprogramming is required, and it can be adapted to different types of mobile phone production. 

5. Operating scenarios in harsh environments: Series-connected robots are more "robust" 

In harsh environments such as high temperatures, dust, and oil contamination, the structural stability of robots is of utmost importance: 

High-temperature forging scenario: For instance, in steel mills, when transporting steel billets or when sorting aluminum alloys after forging, the ambient temperature ranges from 100 to 300 degrees Celsius. Serial robots can be customized with high-temperature protective coatings and cooling systems. The sealing structure at the joints can prevent dust from entering. However, for parallel robots, the gap between the branches is relatively small, making it easy for dust to accumulate and cause jamming, resulting in extremely high failure rates. 

Chemical raw material handling: For the transportation of corrosive liquid barrels, the tandem robots' heavy-duty grippers can be equipped with anti-corrosion materials. The multi-joint structure enables the flipping and stacking of the barrel bodies, ensuring safety and efficiency while avoiding the risk of manual contact.