With the rapid development of the robotics industry, industrial robots have been widely used in various industries, from material handling to machine maintenance, from welding to cutting, from assembly to painting. We have found that these industrial robots have different shapes and functions. So what determines the flexibility and range of motion of industrial robots? This question is quite complex, but there is a key factor that largely determines the flexibility and range of motion of robots, which is the degree of freedom of industrial robots, usually called the number of axes.
What are the degrees of freedom of an industrial robot?
Typically used as a technical indicator of robots, it reflects the flexibility of robot movements and can be expressed by the number of linear, oscillating, or rotating movements of axes. The number of joints that a robot mechanism can move independently is called the robot mechanism's degrees of freedom, or simply Degree of Freedom (DOF). Currently, the control method used for industrial robots treats each joint on the robotic arm as an individual servo mechanism, that is, each axis corresponds to one servo, each servo is controlled via a bus, and the controller uniformly controls and coordinates the work.
ISO 8373 defines an industrial robot as: "A robot with automatic control, reprogrammability, and multi-purpose capabilities, whose manipulator has three or more programmable axes, and whose base can be fixed or movable in industrial automation applications." Therefore, the number of axes is a crucial technical specification for industrial robots.
Applications of robots with different degrees of freedom in industry
The number of axes a robot has determines its degrees of freedom. Is more degrees of freedom always better? More degrees of freedom mean closer resemblance to human hand movements and better versatility; however, more degrees of freedom also mean greater structural complexity and higher overall requirements for the robot – a contradiction in robot design. As the number of axes increases, the robot's flexibility also increases. However, in current industrial applications, three-axis, four-axis, five-axis dual-arm, and six-axis industrial robots are most commonly used. The choice of axis number usually depends on the specific application. This is because some applications do not require high flexibility, and three-axis and four-axis robots are more cost-effective and offer significant speed advantages. For simple applications, such as picking and placing parts between conveyor belts, a four-axis robot is sufficient. If the robot needs to work in a confined space and the robotic arm needs to twist and turn, a six-axis or seven-axis robot is the best choice.
Currently, six-axis robots are the most widely used in the industrial field. An industrial robot with six joints is very similar to a human arm, having sections corresponding to the shoulder, elbow, and wrist. Its "shoulder" is usually mounted on a fixed base structure. While the human arm moves the hand to different positions, the six-axis robot moves end effectors. Various actuators suitable for specific applications are installed at the end of the robotic arm, such as grippers, blowtorches, drills, and paint sprayers, to complete different work tasks.
Recently, various robot manufacturers have released their latest collaborative robots, almost all of which are seven-axis redundant degrees of freedom industrial robots. Internationally renowned robot manufacturers are making efforts to launch new seven-axis robot products in order to seize the high-end new market. However, compared with traditional four-axis and six-axis industrial robots, the gap in product variety and sales share of truly commercialized seven-axis industrial robots is currently very significant.
Development trend of redundant degree-of-freedom robots
Six degrees of freedom (DOF) is the minimum number of degrees of freedom required for spatial positioning. Robots with more than six axes are collectively referred to as redundant degree-of-freedom (DOF) robots. Robot kinematics research aims to solve the translational or rotational motions of the joints of a robot arm's end effector when it reaches a certain spatial pose; it is the cornerstone and key to the entire field of robotics. With the rapid development of human civilization, robots are needed for work in many industrial, high-altitude, deep-sea, nuclear waste, and hazardous environments, placing higher demands on the reliability, operability, and intelligence of robot motion control. In the future, with increasing precision, redundant degree-of-freedom robots will have more advantages in obstacle avoidance, overcoming singularities, flexibility, and fault tolerance. Facing complex working environments and changing operational needs, redundant degree-of-freedom industrial robots will have more applications. It is believed that in the near future, they will replace humans in performing more precise operations.
