Academician discusses six key technologies for innovative robot design

▍ 1. Research background and significance

1.1 Manufacturing and

Intelligent manufacturing is an inevitable trend in the development of high-end equipment manufacturing industry, and it is also the inevitable path to promote my country's transformation from a manufacturing power to a manufacturing power. When talking about intelligent manufacturing, we cannot avoid it. As one of the important contents of the development of intelligent manufacturing in my country, industrial robots are also the key to promoting the development of Chinese manufacturing towards informatization, automation, integration and intelligence.

1.2 Industrial Robots: Rethinking the Manufacturing Industry

According to the 2016 Presidential Economic Report, between 1993 and 2007, robots contributed 0.36% to the growth of labor productivity, accounting for about 16% of the growth of the labor force during this period. This effect is the same order of magnitude as the impact of the steam engine on labor productivity. Robots have become one of the main driving forces of industry, and at the same time have brought a new understanding of the manufacturing industry: the "manufacturing revolution" has brought a huge market for robots; full automation accounts for only a small part of the manufacturing industry; the vast majority is undertaken by people.

Faced with the difficulties of hiring and recruiting workers, the popularity of robots in China is increasing year by year. This is also the reason why countries around the world, including the United States, Germany, the European Union, and Japan, have made robots their main development direction.

1.3 Seven aspects of innovative robot design

In order to make good use of robots and apply them to various industries, the design of robots has become the key. The development of industrial robots is inseparable from design, and even more inseparable from the innovative design of the entire life cycle, which involves seven aspects of robot demand, function, structure, physics, process, industry, and market.

The first aspect is the demand innovation design of robots. In the past, it was considered that robots could not be used in areas where users are now guided and demand is created. Therefore, demand innovation design should include the creation, guidance, and customization of robot product needs. The second aspect is the functional innovation design of robots. In different occasions, robots should have different functions, so the product functions of robots should be expanded, extended, and integrated. The third aspect is the structural innovation design of robots. The simplest structure with the best function and the easiest implementation should be achieved. The fourth aspect is the physical innovation design of robots. Ensure the physical properties of product functions, including strength, rigidity, reliability, etc. The fifth aspect is the process innovation design of robots. Ensure that robots can complete molding, processing, assembly and other tasks more efficiently. The sixth aspect is the industrial innovation design of robots. Make robots more beautiful and more in line with the needs of consumers' ergonomics. The seventh aspect is the innovative design of the robot market. Including the consumer positioning and customer base of robot products.

1.4 Current status of industrial robot design and application

my country's industrial robot industry is in a period of rapid development, but the current domestic industrial robot design and application still faces many problems: there are safety risks in the operation process, smooth and stable movement coordination is difficult, the operation sequence and layout are strong, the degree of collaboration between robots and humans is low, the robot operation autonomy is low, the robot fault intelligent prediction is difficult, the robot maintenance efficiency is low, and there are many differences in operation.

To this end, it is necessary to break through the key technologies of industrial robot design and closely integrate digital twin technology to solve the outstanding problems in the entire process of industrial robot design and application. To design and apply robots well, there are three requirements: first, the robot needs to be stable and efficient in application, and the movement needs to be relatively stable; second, human-machine collaboration; third, the combination of virtual and real.

First, stability and efficiency require us to ensure the accuracy and stability of the operation while realizing the autonomous planning of the robot's operation sequence, path, trajectory, etc., and improving the operation efficiency. This is the basic requirement of robot design. Secondly, human-machine collaboration should include human-machine interaction, human-machine communication, and human-machine integration, so that robots can work directly side by side with humans, eliminate the protective isolation between humans and machines, and realize the anthropomorphism of human-machine interaction. Thirdly, virtual-real integration requires full use of physical models, updating, and running historical data, completing virtual-real mapping and feedback control in virtual space, and improving the intelligence of robots.

Based on these three practical goals, we need to solve the problem of how to improve the efficiency of the robot operation while ensuring the accuracy and stability of the robot operation? How to achieve the collaborative control of multiple robots and the coordinated operation of robots and humans? How to improve the credibility of virtual-real mapping and realize the virtual control of the real by industrial robots? At present, the following six key technologies have been realized through research: robot body and design, industrial robot dynamic stability design, collaborative robot intelligent interaction design, robot visual perception and autonomous learning, robot operation planning and layout design, robot virtual teaching and digital twin.

▍ 2. Key technologies of robot design

2.1 Design of robot body and control system

By breaking through various technical links in the design and development of the robot body, building the robot body, and combining the research on robot motion control technology, robot operation planning and teaching technology, we developed a complete set of software systems for industrial robots. While supporting the teaching of multiple brands of robots, we also reduced the system cost of the whole machine. These include: joint deceleration mechanism design, internal heat dissipation system design, robot body assemblability analysis, robot body 3D printing manufacturing, and robot high-performance general control system design. (1) Joint deceleration mechanism design

Figure 1 shows the design of the robot joint deceleration mechanism, which is mainly used to improve the shortcomings of the robot's long transmission chain, complex transmission structure, and large transmission error. It uses a high-strength built-in steel wire synchronous belt for secondary deceleration to ensure transmission accuracy, and uses the system to compensate for position errors and reverse clearance to ensure position repeatability accuracy.

Figure 1 Design of the robot's fourth axis reduction mechanism

(2) Internal cooling system design

The robot's drive motor brake generates serious heat. At the same time, the installation space is relatively closed, and the temperature of the closed space is high after long-term operation. Based on computational fluid dynamics (CFD) analysis, the internal heat dissipation system and air duct are designed, simulated and optimized (Figure 2) to achieve air circulation and heat dissipation.

Figure 2 Internal cooling system design

(3) Assembling analysis of the robot body

Through physical modeling, the impact of structural factors on the assemblability of parts is analyzed, the human-machine factors of the assembly process are quantified, and the assemblability of the assembly sequence and all sub-assemblies is combined to achieve product-level assemblability evaluation (Figure 3). Compared with the traditional fuzzy evaluation based on expert scoring or assembly experience, the evaluation results are more accurate and reliable, ensuring the assemblability of the robot.

Figure 3 Assembling analysis of the robot body

(4) 3D printing manufacturing of robot body

In order to effectively improve the manufacturing accuracy of robot 3D printed structural parts to ensure the assembly quality, the 3D printing orthogonal test and regression analysis were carried out on the test samples, and the optimal combination of 3D printing process parameters and the correction method of dimensional error were proposed. The robot body structural parts with good adhesion to the positioning surface and high precision were manufactured, which provided technical guarantee for improving the accuracy of the 3D printed robot body.

(5) Design of high-performance general control system for robots

The robot high-performance universal control system has designed and developed HRM-P pulse type and HRM-E bus type high-performance, open, platform-based, and standardized robot motion and motion control software, supporting hardware-free virtual simulation, including multiple types of robot kinematic models, and providing point-to-point, linear arc, and mixed trajectory planning functions.

2.2 Dynamic stability design of industrial robots

Aiming at the dynamic stability design, the author proposed a robot position inverse solution method based on the decoupling of the cut-off point freedom (Figure 6), and proposed the position inverse solution of the cut-off point freedom decoupling.

Figure 6 Robot position inverse solution method based on cut-off point degree of freedom decoupling

This aspect mainly utilizes the geometric structure characteristics of the robot to cut the mechanism motion chain into two parts, so that the coupling degree of the two sub-motion chains on a certain component of the motion freedom at the cutting point is minimized, thereby converting the high-dimensional transcendental equations into a nonlinear equation with only one unknown variable, solving the position inverse problem of a non-traditional 6-DOF industrial robot whose three terminal axes do not intersect at one point, laying a solid foundation for robot motion control.