In recent years, multinational robotics giants have launched seven-axis industrial robots to seize new high-end markets. This has prompted us to think deeply about seven-axis industrial robots. What are their unique technological advantages? What are the research and development challenges? What industrial seven-axis robot products have been released internationally in recent years? And what stage has my country's research and development and industrialization of seven-axis industrial robots entered?
How many axes should an industrial robot have?
Currently, industrial robots are widely used in various industries. However, we have also found that industrial robots not only vary in shape but also in the number of axes. The axis of an industrial robot can be explained using the technical 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. Increasing the number of axes means greater flexibility for the robot. So, how many axes should an industrial robot ideally have?
Three-axis robots, also known as Cartesian robots or Cartesian robots, allow the robot to move along three axes. These robots are generally used for simple material handling tasks.
A four-axis robot can rotate along the x, y, and z axes. Unlike a three-axis robot, it has a fourth axis that moves independently. Generally speaking, a SCARA robot can be considered a four-axis robot.
Five-axis is a common configuration for many industrial robots. These robots can rotate in three spatial circumferences (x, y, z), and can also turn around using axes on their base, as well as have axes that allow for flexible hand rotation, increasing their flexibility.
A six-axis robot can move along the x, y, and z axes, and each axis can rotate independently. The biggest difference between a six-axis robot and a five-axis robot is the addition of one more freely rotating axis. A representative example of a six-axis robot is Universal Robots; you can clearly calculate the number of axes using the blue covers on the robot's body.
A seven-axis robot, also known as a redundant robot, has an extra axis compared to a six-axis robot. This allows the robot to avoid certain targets, facilitates the end effector to reach specific positions, and can adapt more flexibly to certain special working environments.
As the number of axes increases, the robot's flexibility also increases. However, in current industrial applications, three-axis, four-axis, and six-axis industrial robots are the most commonly used. This is because some applications do not require high flexibility, and three-axis and four-axis robots are more cost-effective, and they also have a significant advantage in speed.
In the future, seven-axis industrial robots will find their place in the 3C industry, which requires high flexibility. As their precision continues to increase, they will replace manual labor in assembling precision electronic products such as mobile phones in the near future.
What are the advantages of a seven-axis industrial robot over a six-axis industrial robot?
From a technical perspective, what are the problems with six-axis industrial robots, and what are the advantages of seven-axis industrial robots?
(1) Improve kinematic properties
In the kinematics of robots, three problems severely restrict the movement of robots.
The first is the singular configuration. When a robot is in a singular configuration, its end effector cannot move in a certain direction or apply torque, thus the singular configuration greatly affects motion planning.
▲A singularity occurs when the sixth and fourth axes of a six-axis robot are collinear.
Secondly, there's the issue of joint displacement exceeding limits. In real-world working conditions, the range of motion for each joint of a robot is limited; ideally, it's within ±180 degrees, but this is impossible for many joints. Additionally, a seven-axis robot can avoid excessively high angular velocity, allowing for a more even distribution of angular velocity.
Siasun 7-axis robot ▲ Range of motion and maximum angular velocity of each axis
Third, there are obstacles in the working environment. In industrial environments, there are various environmental obstacles in many situations, and traditional six-axis robots cannot change the posture of the end effector without changing its position.
(2) Improve dynamic characteristics
For a seven-axis robot, its redundant degrees of freedom can not only achieve good kinematic characteristics through motion trajectory planning, but we can also use its structure to achieve optimal dynamic performance.
Seven-axis robots can redistribute joint torques, which involves the static balance of the robot. That is, the force acting on the end effector is calculated using a specific algorithm to determine the force borne by each joint. In a traditional six-axis robot, the force on each joint is constant, and its distribution may be unreasonable. However, in a seven-axis robot, we can adjust the torque of each joint through control algorithms, minimizing the torque on weaker joints and resulting in a more even and rational torque distribution throughout the robot.
(3) Fault tolerance
When a robot malfunctions, if one joint fails, a traditional six-axis robot cannot continue to perform its work, while a seven-axis robot can continue to work normally by readjusting the speed (kinematic fault tolerance) and torque (dynamic fault tolerance) of the failed joint.
Seven-axis industrial robot products from international giants
Whether from a product perspective or an application perspective, seven-axis industrial robots are still in the early stages of development. However, major manufacturers are vigorously promoting related products at various exhibitions, which shows that they are very optimistic about their future development potential.
KUKA LBRiiwa
In November 2014, KUKA unveiled its first seven-DOF lightweight and sensitive robot, LBRiiwa, at the China International Industry Fair Robotics Exhibition.
The LBRiiwa seven-axis robot is designed based on the human arm, incorporating an integrated sensor system that gives this lightweight robot programmable sensitivity and very high precision. All axes of the seven-axis LBRiiwa are equipped with high-performance collision detection and integrated joint torque sensors to enable human-robot collaboration.
The seven-axis design gives KUKA's LBRiiwa robot high flexibility, allowing it to easily overcome obstacles. Constructed of aluminum, the robot weighs only 23.9 kg. It comes in two payload options: 7 kg and 14 kg, making it the first lightweight robot with a payload exceeding 10 kg.
ABBYuMi
On April 13, 2015, ABB officially launched YuMi, the world's first truly human-machine collaborative dual-arm industrial robot, at the Hannover Messe in Germany.
Each YuMi arm has seven degrees of freedom and weighs 38 kg. Each arm can carry a load of 0.5 kg and achieves a repeatability of 0.02 mm, making it particularly suitable for small parts assembly, consumer goods, toys, and other fields. From the precision components of mechanical watches to the handling of parts in mobile phones, tablets, and desktop computers, YuMi can handle it all, demonstrating the excellent characteristics of this redundant robot, including an expanded workspace, flexibility, agility, and precision.
Yaskawa Motoman SIA
Yaskawa Electric, one of Japan's four major robot manufacturers, has also released several seven-axis robot products. Among them, the SIA series is a lightweight, agile seven-axis robot that offers human-like dexterity and rapid acceleration. Its lightweight and streamlined design makes it ideal for installation in confined spaces. The SIA series offers a high payload (5 kg to 50 kg) and a large working range (559 mm to 1630 mm), making it well-suited for assembly, injection molding, and inspection operations.
In addition to its lightweight seven-axis robot products, Yaskawa also released a seven-axis robotic welding system. Its high degrees of freedom allow it to maintain the most suitable posture for high-quality welding results, making it particularly suitable for internal surface welding and achieving optimal access positions. Furthermore, the product can be deployed in a high-density layout, easily avoiding interference with axes and workpieces, demonstrating its excellent obstacle avoidance capabilities.
Nachi Futago PrestoMR20
As early as the end of 2007, Nachi-Fujikoshi developed the seven-DOF robot "PrestoMR20". By adopting a seven-axis design, the robot can perform more complex workflows, mimicking the human arm, and move within confined work areas. Furthermore, the torque of the robot's front end (wrist) has increased to approximately twice that of traditional six-axis robots, with a standard torque of 20 kg. Through setting the range of motion, it can handle items up to 30 kg, with a working range of 1260 mm and a repeatability of 0.1 mm. The seven-axis structure allows the MR20 to operate from the side of the machine tool when picking up and placing workpieces. This improves the efficiency of pre-operation preparation and maintenance. The space required between machine tools can be reduced to less than half that of traditional six-axis robots.
In addition, Nachi-Fujikoshi also released two industrial robots, the MR35 (35 kg payload) and the MR50 (50 kg payload), which can be used in confined spaces and obstacle-prone environments.
OTC 7-axis industrial robot
Japan's DAIHEN Group has launched its latest seven-axis robots (FD-B4S, FD-B4LS, FD-V6S, FD-V6LS, and FD-V20S). Thanks to their seventh axis of rotation, these robots can perform twisting movements similar to a human wrist, enabling welding more than a full rotation. Furthermore, the seven-axis robots (FD-B4S and FD-B4LS) conceal the welding cable within the robot body, eliminating concerns about interference between the robot and the welding fixture or workpiece during teaching operations. This results in very smooth movements and improved freedom of welding posture, overcoming the limitations of traditional robots that are unable to enter the welding area due to interference with the workpiece or welding fixture.
Baxter and Sawyer of Rethink Robotics
Rethink Robotics is a pioneer in collaborative robots. Among its early developments, the Baxter dual-arm robot has seven degrees of freedom in each arm, with a maximum working range of 1210 mm per arm. Baxter can handle two different tasks simultaneously to increase its versatility, or process the same task in real time to maximize output.
Last year's Sawyer is a single-arm, seven-axis robot. Its flexible joints use the same series of elastic actuators, but the actuators have been redesigned to make them smaller. Thanks to its seven-axis design and extended working range of 100 mm, it can perform heavier workloads, with a payload of up to 4 kg, significantly larger than the Baxter robot's 2.2 kg payload.
