In recent years, multinational robot giants have launched seven-axis industrial robots one after another to seize high-end new markets. This has triggered our in-depth thinking about seven-axis industrial robots. What unique technical advantages does it have, what are the difficulties in research and development?
How many axes should industrial robots have?
At present, industrial robots have been widely used in various industries, but we also found that industrial robots not only have different shapes, but also have different axes. The axis of the so-called industrial robot can be explained by the professional term degree of freedom. If the 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 the robot increases, it means higher flexibility for the robot. So how many axes should an industrial robot have?
A three-axis robot is also called a Cartesian or Cartesian robot. Its three axes allow the robot to move along three axes. This robot is generally used for simple handling tasks.
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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.
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Five-axis is the configuration of many industrial robots. These robots can rotate through the three space circles of x, y, and z. At the same time, they can rely on the axis on the base to realize the turning action, and the axis that can be flexibly rotated by the hand increases its flexibility.
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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 there is one more 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.
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A seven-axis robot, also known as a redundant robot, has an extra axis compared to a six-axis robot that allows the robot to avoid certain specific targets, making it easier for the end effector to reach a specific position, and can be more flexible to adapt to certain special working environments.
As the number of axes increases, so does the flexibility of the robot. However, in current industrial applications, three-axis, four-axis and six-axis industrial robots are used the most. This is because, in some applications, high flexibility is not required, while three-axis and four-axis robots are more cost-effective, and three-axis and four-axis robots also have a great advantage in speed.
In the future, in the 3C industry that requires high flexibility, seven-axis industrial robots will have a place to play. With its increasing precision, it will replace manual assembly of precision electronic products such as mobile phones in the near future.
Seven-axis industrial robots are better than six-axis industrial robots
Where is the strength?
From a technical point of view, what are the problems with six-axis industrial robots, and what is the strength of seven-axis industrial robots?
(1) Improve kinematic characteristics
In the kinematics problem of the robot, three problems make the movement of the robot very restricted.
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 a moment, so the singular configuration greatly affects the motion planning.
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Singularity occurs when the sixth and fourth axes of a six-axis robot are collinear
The second is that the joint displacement exceeds the limit. In a real working situation, the angular range of motion of each joint of the robot is limited, and the ideal state is plus or minus 180 degrees, but many joints cannot do it. In addition, the seven-axis robot can avoid excessive angular velocity movement, so that the angular velocity is distributed more evenly.
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The movement range and maximum angular velocity of each axis of the SIASUN seven-axis robot
The third is the presence of barriers in the work environment. In the industrial environment, there are various environmental obstacles in many occasions, and the traditional six-axis robot cannot only change the posture of the end mechanism without changing the position of the end mechanism.
(2) Improve dynamic characteristics
For the seven-axis robot, using its redundant degrees of freedom can not only achieve good kinematics characteristics through motion trajectory planning, but also we can use its structure to achieve the best dynamic performance.
The seven-axis robot can realize the redistribution of joint torque, which involves the static balance of the robot, that is to say, the force acting on the end, through a certain algorithm, calculates how much force each joint bears. For the traditional six-axis robot, the force of each joint is certain, and its distribution may be very unreasonable. But for the seven-axis robot, we can adjust the torque of each joint through the control algorithm, so that the weak link bears the torque as small as possible, so that the torque distribution of the whole robot is relatively uniform and more reasonable.
(3) Fault tolerance
When a robot fails, if a joint fails, the traditional six-axis robot cannot continue to complete the work, while the seven-axis robot can continue to work normally by re-adjusting the failure joint speed (kinematics fault tolerance) and the redistribution of the fault joint torque (dynamics fault tolerance).
Seven-axis industrial robot products of international giants
No matter from the perspective of products or applications, seven-axis industrial robots are still in the initial stage of development, but major manufacturers are promoting related products at major exhibitions. It is conceivable that they are still very optimistic about their future development potential.
- Kuka LBR iiwa
In November 2014, KUKA first released KUKA's first seven-degree-of-freedom lightweight sensitive robot LBRiiwa at the China International Industry Fair Robot Exhibition.
The LBRiiwa seven-axis robot is designed on the basis of the human arm, which, combined with an integrated sensor system, gives the lightweight robot programmable sensitivity and makes it very precise. All axes of the seven-axis LBRiiwa are equipped with high-performance collision detection functions and integrated joint torque sensors to achieve human-machine collaboration.
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The seven-axis design makes this KUKA product highly flexible and can easily overcome obstacles. The structure of the LBRiiwa robot is designed with aluminum material, and its own weight is only 23.9 kg. It comes in two payloads, 7kg and 14kg, making it the first lightweight robot with a payload of more than 10kg.
- ABB YuMi
On April 13, 2015, ABB officially launched YuMi, the world's first dual-arm industrial robot that truly realizes human-machine collaboration, to the market at the Hannover Messe in Germany.
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Each single arm of YuMi has seven degrees of freedom, and the body weight is 38 kg. The load of each arm is 0.5 kg, and the repeat positioning accuracy can reach 0.02 mm, so it is especially suitable for small parts assembly, consumer goods, toys and other fields. From the precision parts of mechanical watches, to the processing of mobile phones, tablet computers, and desktop computer parts, YuMi is no problem, and this just reflects the excellent characteristics of this redundant robot, such as expanded work space, flexibility, agility, and precision.
- Yaskawa Motoman SIA
Yaskawa Electric, a well-known robot manufacturer in Japan and one of the "Four Families", has also released a variety of seven-axis robot products. Among them, the SIA series robots are light and agile seven-axis robots, which can provide human-like flexibility and fast acceleration. The lightweight and streamlined design of this series of robots makes them ideal for installation in tight spaces. The SIA series can provide high payload (5kg to 50kg) and large working range (559mm to 1630mm), which is very suitable for assembly, injection molding, inspection and other operations.
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In addition to light seven-axis robot products, Yaskawa has also released a seven-axis robot welding system. Its high degree of freedom can maintain the most suitable posture as much as possible to achieve high-quality welding results. It is especially suitable for internal welding and achieves the best approach position. Moreover, the product can be arranged in a high density, and it is easy to avoid interference with the shaft and the workpiece, showing its excellent obstacle avoidance function.
- Nachi Fujiko PrestoMR20
As early as the end of 2007, Nachi Fujikoshi developed a seven-degree-of-freedom robot "PrestoMR20". By adopting a seven-axis design, the robot can perform more complex workflows and move in narrow working areas like a human arm. In addition, the torque of the front part (wrist) of the robot has increased to about twice that of the original traditional six-axis robot. The torque of the standard configuration is 20 kg. By setting the range of motion, it can carry objects up to 30 kg. The working range reaches 1260 mm, and the repeat positioning accuracy is 0.1 mm. By adopting a seven-axis structure, the MR20 can work from the side of the machine when picking and placing workpieces on the machine. As a result, work efficiency such as advance preparation and maintenance can be improved. The space between machine tools can be reduced to less than half that of conventional six-axis robots.
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In addition, Nachi Fujikoshi also released two industrial robots, MR35 (with a load of 35 kg) and MR50 (with a load of 50 kg), which can be used in small spaces and places with obstacles.
- OTC seven-axis industrial robot
Japan's DAIHEN Group has launched the latest seven-axis robots (FD-B4S, FD-B4LS, FD-V6S, FD-V6LS, FD-V20S). Due to the rotation of the seventh axis, they can realize the twisting action like the human wrist, and can realize welding for more than one week; in addition, the seven-axis robot (FD-B4S, FD-B4LS) has welding cables built into the robot body, so there is no need to care about the interference between the robot, the welding fixture and the workpiece during the teaching operation, the movement is very smooth, and the degree of freedom of welding posture is also improved.
- Baxter and Sawyer, Rethink Robotics
Rethink Robotics is a pioneer of collaborative robots. Among them, the first developed Baxter dual-arm robot has seven degrees of freedom for both arms, and the maximum working range of a single arm is 1210 mm. Baxter can handle two different tasks at the same time to increase applicability, or process the same task in real time to maximize output.
Introduced last year, Sawyer is a single-arm, seven-axis robot that uses the same serial elastic actuators for its flexible joints, but the actuators for its joints have been redesigned to make them smaller. Due to the seven-axis design and the extension of the working range to 100 mm, it can complete tasks with a larger load. The load can reach 4 kg, which is much larger than the 2.2 kg payload of the Baxter robot.
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- Yamaha seven-axis robot YA series
In 2015, Yamaha launched three seven-axis robots, "YA-U5F", "YA-U10F", and "YA-U20F", all of which are driven and controlled by the new controller "YA-C100".
The 7-axis robot has an E-axis equivalent to the human elbow, so it can freely complete actions such as bending, twisting, and extending. Even in narrow spaces where it is difficult for robots with less than 6 axes to perform operations, operations and installations can be completed smoothly. Also allows for low squat positions and movements around the back of the unit. A hollow actuator is adopted, and the device cable and air hose are built into the robot arm, so that it does not interfere with surrounding equipment, and a compact production line can be realized.
In addition, the Taiwan Precision Machinery Research and Development Center has also developed a prototype of a dual-arm seven-axis robot, which is expected to help Taiwanese companies create a powerful tool for 3C electronics manufacturing and narrow the technological gap between domestic and foreign countries.
The domestic seven-axis robot is here
Can you achieve corner overtaking?
The research and development of China's seven-axis industrial robot began in the early 1990s. At that time, the leader of the project was Zhang Qixian, a late famous robotics expert in my country and academician of the Chinese Academy of Engineering. One of the main contributions of Academician Zhang Qixian was to complete the development of a seven-degree-of-freedom redundant robot prototype.
At the end of the 1980s, due to the extremely difficult development, very few countries in the world developed seven-degree-of-freedom redundant robot prototypes. Academician Zhang Qixian led the research team to complete the development of the first seven-degree-of-freedom redundant robot prototype at the end of 1993 after several years of hard work, and passed the "863" project acceptance and ministerial appraisal at one time.
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A typical redundant arm
Although my country has made certain achievements in redundant degree of freedom robots, it mainly stays at the stage of academic papers, scientific research reports and experimental prototypes, and has not achieved real product development. This undoubtedly restricts the pace of my country's robot products moving towards high-end industrialization.
As a leading enterprise of domestic industrial robots, SIASUN took the lead in releasing the first domestic seven-axis industrial robot at the 2015 Industry Fair. Its own weight is 29 kg, the load is 5 kg, the repeat positioning accuracy can reach 0.02 mm, and the working radius can reach 800 mm. It has functions such as quick configuration, traction teaching, visual guidance, and collision detection. It is especially suitable for flexible production lines with compact layout and high precision, and meets the needs of industrial operations such as precision assembly, product packaging, grinding, testing, and machine tool loading and unloading.
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At present, the vast majority of industrial robot companies in my country have not yet released seven-axis industrial robot products. Some of them said that they are developing related products, and related products will come out within this year, while some other companies expressed concern about seven-axis industrial robot products, but have not yet planned to design and develop related products.
my country's robot industry has made great progress in the theoretical research of seven-axis industrial robots, but there is still a big gap with foreign countries in terms of commercial products. The reason is mainly in the following two aspects:
First, the ability of independent innovation is weak. Lacking original achievements and innovative concepts of core and key technologies, the overall technology of my country's industrial robots is more than ten years behind the advanced level of foreign countries.
Second, the profitability of enterprises is low, and R&D funds are in short supply. The lack of core component technology has led to high production costs for enterprises, and foreign manufacturers have cut prices one after another. In 2015, more than 70% of the enterprises' ontology business was in a state of loss.
According to experts, the gap between the overall technology of industrial robots in my country and foreign countries is more than ten years. The emergence of domestic seven-axis industrial robots shows that our research and development in industrial robot technology is accelerating, but we should have a clear understanding that there is a real gap. If we want to overtake in a curve, we need to overcome the core technical difficulties as soon as possible. At the same time, we must also pay attention to the research and development of next-generation technologies such as artificial intelligence, perception, recognition, drive and control.
