How many axes should an industrial robot have?

In recent years, multinational giants have launched seven-axis robots to seize new high-end markets. This has prompted us to think deeply about seven-axis robots. What unique technical advantages does it have? What are the research and development difficulties? What industrial seven-axis robots have been released internationally in recent years? What stage has the research and development and industrialization of my country's seven-axis industrial robots entered?

At present, industrial robots have been widely used in all walks of life, but we also found that industrial robots not only have different shapes, but also different numbers of axes. The so-called axes of industrial robots can be explained by the professional term degree of freedom. If a robot has three degrees of freedom, it can move freely along the x, y, and z axes, but it cannot tilt or rotate. When the number of axes of a robot increases, it means higher flexibility for the robot. So how many axes should an industrial robot have to be reasonable?
A three-axis robot is also called a rectangular coordinate or Cartesian robot. Its three axes allow the robot to move along the three axes. This type of robot is generally used for simple handling work.
A four-axis robot can rotate along the x, y, and z axes. Unlike a three-axis robot, it has an independently moving fourth axis. Generally speaking, a SCARA robot can be considered a four-axis robot.

Five axes are the configuration of many industrial robots. These robots can rotate through the three spatial circles of x, y, and z. At the same time, they can rely on the axes on the base to achieve turning movements, as well as axes that can be flexibly rotated by the hands, which increases their flexibility.
The six-axis robot can pass through the x, y, and z axes, and each axis can rotate independently. The biggest difference from the five-axis robot is that it has an additional axis that can rotate freely. The representative of the six-axis robot is the Universal Robots. Through the blue cover on the robot, you can clearly calculate the number of axes of the robot. The seven-axis robot, also known as the redundant robot, allows the robot to avoid certain specific targets compared to the six-axis robot, making it easier for the end effector to reach a specific position, and can adapt to certain special working environments more flexibly. As the number of axes increases, the flexibility of the robot also increases. However, in current industrial applications, the most commonly used are three-axis, four-axis and six-axis industrial robots. This is because, in some applications, high flexibility is not required, and three-axis and four-axis robots are more cost-effective, and three-axis and four-axis robots also have great advantages in speed. In the future, in the 3C industry that requires high flexibility, the seven-axis industrial robot will have its place. As its accuracy continues to increase, in the near future, it will replace manual assembly and other precision. What is the advantage of the seven-axis industrial robot over the six-axis industrial robot? From a technical point of view, what are the problems with six-axis industrial robots and what are the strengths of seven-axis industrial robots?

(1) Improve kinematic characteristics

In the kinematics problem of the robot, three problems greatly restrict the movement of the robot.

The first is the singular configuration. When the robot is in a singular configuration, its end effector cannot move in a certain direction or apply torque, so the singular configuration greatly affects motion planning.

The second is the over-limit of joint displacement. In real working conditions, the angular range of motion of each joint of the robot is limited. The most ideal state is plus or minus 180 degrees, but many joints cannot do this. In addition, the seven-axis robot can avoid excessive angular velocity movement and make the angular velocity distribution more even.
The third is the existence of obstacles in the working environment. In industrial environments, there are various environmental obstacles in many occasions. Traditional six-axis robots cannot only change the posture of the end mechanism without changing the position of the end mechanism.
(2) Improve dynamic characteristics
For seven-axis robots, using their redundant degrees of freedom can not only achieve good kinematic characteristics through motion trajectory planning, but also we can use their structure to achieve the best dynamic performance. The seven-axis robot can realize the redistribution of joint torque, which involves the problem of static balance of the robot. That is to say, the force acting on the end can be used to calculate the force borne by each joint. For traditional six-axis robots, the force of each joint is certain, and its distribution may be unreasonable. However, for seven-axis robots, we can adjust the torque of each joint through control algorithms to make the torque borne by the weak links as small as possible, so that the torque distribution of the entire robot is more even and more reasonable.
(3) Fault tolerance
When a robot fails, if one of its joints fails, a traditional six-axis robot will not be able to continue to work, while a seven-axis robot can continue to work normally by re-adjusting the speed of the faulty joint (kinematic fault tolerance) and redistributing the torque of the faulty joint (dynamic fault tolerance). Whether from a product perspective or an application perspective, seven-axis industrial robots are still in the initial development stage, but major manufacturers have been promoting related products at major exhibitions, and it can be imagined that they are still very optimistic about their future development potential.