With the proposal of Germany's "Industry 4.0" and China's "Made in China 2025" strategy, robots and intelligent equipment have attracted great attention from the scientific and engineering circles at home and abroad. Undoubtedly, robots will have a far-reaching impact on the development of the future society. According to statistics, about 57,000 industrial robots were sold in The Chinese market in 2014, an increase of 55% over the previous year, accounting for about 1/4 of the total sales volume in the global market, making China the world's largest industrial robot market for two consecutive years. However, China's robot density is still only 10 percent that of Germany and Japan, and by 2020 there should be at least 237,000 industrial robots to replace the space. As an important industrial robot, parallel robot has many advantages, such as large stiffness, strong bearing capacity, small accumulative error and high control accuracy. Compared with joint robots, parallel robots occupy less than 5% of the industrial site, and food, medicine, 3C electronic products and printing industries have urgent needs for it, so it has a broad application prospect.
In the early stage of robot development, most of them exist in series. The serial mechanism mentioned here means that the moving chain is open, which means that all the moving rods do not form a closed structural chain. Relative of parallel connection structure appeared later than in series, the concept derived from the earliest Bricard, including six degree of freedom parallel robot development earlier, Stewart later for flight simulator, training pilots, this type of robot is named by Stewart platform himself, because of the outstanding contribution of the Stewart platform, Stewart platform is called the father of the parallel robot. In the 80 s, the lausanne, Switzerland, tech Clavel DELTA parallel mechanism was proposed, for the first time the agency by the moving platform, the static platform, of three symmetrical branched chain, the static platform through the motor and the branched chain link, each branched chain consists of master and slave arm, follower lever arm of a parallelogram group structure, brother motion pair of rotation, the agency only three degrees of freedom, the moving platform can only achieve translation, this type of robot called rapid development of industrial robots.
Series mechanism and parallel structure have their own characteristics naturally
As shown in FIG. 1, the tandem mechanism is an open moving chain, and all the moving bars do not form a closed structural chain. Because of this, it has the following characteristics:
1. Large working space;
2. Motion analysis is relatively easy;
3. The coupling effect between driving shafts can be avoided;

4. Each axis of the mechanism must be independently controlled, and encoders and sensors should be used to improve the accuracy of movement of the mechanism;

As shown in Figure 2, parallel robot is complementary to traditional industrial series robot in application. It is a closed chain of motion. Compared with series robot, parallel robot has the following characteristics:
1. No kinetic energy error, no cumulative error, high precision;
2. Small motion inertia;
3. Compact and stable structure, most of the output shafts bear axial stress, high rigidity of the mechanism and large bearing capacity;
4. It is designed for thermal symmetry with small thermal deformation;
5. As for the position solution, the series mechanism is easy to solve the positive problem, but difficult to solve the reverse problem, while the parallel mechanism is difficult to solve the positive problem and easy to solve the reverse problem;
6. Small work space;
7. The driving device can be placed on or near the fixed platform, so that the moving part has light weight, high speed and good kinetic energy response;
8. Perfectly symmetric parallel mechanism has good isotropy;
According to these characteristics, parallel robots have been widely used in the fields that need high stiffness, high precision, heavy load and simplified working space.

In China, as early as in the 1980s, Professor Huang Zhen took the lead in the prospective study of parallel mechanism, and in 1991, he developed China's first 6-DOF parallel robot prototype.
At present, parallel robots have been widely used in production and assembly, material handling, precision measurement, precision positioning, torque sensing, medical devices, motion simulation and other fields. For a variety of applications, many products launched its own parallel robot, for example, FANUC company production can be used in the production of assembly F200i parallel robot, ABB company IRB340 robot can be used for material handling, Adept company production can be used in materials handling Adept Quattro parallel robot, Decoration Technology company production of COPRA parallel robot can be used in the mechanical processing, Physik Instrumente company produces can be used for precision measurement of F206 parallel robot and can be used in medical equipment M850 parallel robot, ALIO company produces can be used for precision positioning of operating range and AI AI - HEX -, TRI - HEX series parallel robot MoogFCS company produces can be used for motion simulation platform of E - Cue series parallel robot, Bob Kent (tianjin) technology co., LTD., production can be used for material handling and teaching equipment the BKT series of parallel robot. With the progress of science and technology, the application scope of parallel robot is still expanding, and its influence on human industrial production and daily life will be more and more profound.