Currently, there are two common types of robots in the industrial field: collaborative robots and robotic arms. This article introduces the specific requirements of encoder products for these two robot systems.
In China, based on their application environment, robotics experts classify robots into two main categories: industrial robots and special-purpose robots. Industrial robots are multi-jointed manipulators or multi-degree-of-freedom robots designed for industrial applications. Collaborative robots are not significantly different from traditional robots; they are simply industrial robot products manufactured based on different design philosophies. Currently, the two most common types of robots in the industrial field are collaborative robots (Figure 1) and robotic arms (Figure 2), each with its own specific encoder requirements.
Figure 1: Collaborative robot and its joint structure
Figure 2: Robotic arm and servo motor
The characteristics of encoders used in collaborative robots are: thinness, hollow structure, and large aperture. The outer diameter should ideally be as small as possible to allow for smaller joint dimensions, resulting in a smaller robot. The large aperture allows for cable routing, saving space. It's important to note that high-power cables should not be placed in the same cable tray as the encoder cable to avoid interference and signal abnormalities. Generally, these encoders use single-turn absolute encoders, often paired with an incremental encoder.
Many foreign products use split-type absolute encoders, which require very precise technical parameters for the matching motor; otherwise, the equipment's accuracy will be lost.
To support the development of collaborative robots in China, the encoders for the corresponding joints also need to be customized. Parameters such as encoder thickness, aperture, and outer diameter all require specific technical requirements. Cooperative robot encoders are available in two types: integral mounting and split mounting. Integral encoders have relatively lower requirements for the client's motor technical parameters, and are simpler to install and debug, but are relatively more expensive. If a split encoder is used, both parties need to cooperate to design the corresponding interface, also for the sake of simpler installation and debugging, but it is still more complex to install and debug than an integral product, although the cost is relatively lower.
General-purpose industrial robotic arms typically employ a combination of an integrated servo motor and an encoder. Due to the increasing demand for miniaturization of servo motors, the corresponding requirements for miniaturization and ultra-thinness of encoders are also becoming more stringent. Servo motor manufacturers require encoders with small diameters, thinness, high precision, and low cost. The encoders available for these motors are divided into two types: integrated and separate. Separate encoders have relatively high requirements for axial runout, radial runout, and stop dimensional tolerances, requiring motor manufacturers to confirm the motor's parameters for better compatibility with the encoder. Integral encoders, however, are difficult to make thinner; currently, the thinnest integrated grating encoder in China is approximately 20mm thick. Although the grating encoder is only one component within the robotic arm, it plays a crucial role in its functionality.
In 2017, approximately 136,000 new industrial robots were added to the domestic market, representing a year-on-year increase of about 60%. However, in the market competition, domestically produced industrial robots still lag behind for a long time; many robot companies currently rely on imported brands for key components, making them vulnerable to external control. In fact, some domestic manufacturers have accumulated rich knowledge and experience in developing customized communication protocols and product customization cards, and several robot companies are already using domestically produced products to complete key component support. Furthermore, the emergence and growth of collaborative robots in recent years have brought new opportunities to domestic robot manufacturers.
China's domestically produced industrial encoders have been developing for over 50 years, accumulating a wealth of experience and narrowing the gap with foreign brands. Some products have even surpassed international standards. With the support and collaboration of various industries, the pace of development and improvement will accelerate, bringing more cost-effective products to various sectors.
In short, whether it's encoders, motors, or even upstream products in the industry, the road to domestic production is long and arduous. Weakness in any link will affect the development of the entire industry and make it subject to restrictions from foreign products. The "ZTE incident" in the previous period can well illustrate this point.
