Motion control is turning to Ethernet
so far, engineers engaged in mechanical design still need to deal with a large number of network technologies, including one or two fieldbuses for all i/o (input/output), a motion control network and Ethernet with proprietary intellectual property rights for all other purposes. However, supporting all these networks is not easy. This may require different professionals to implement network planning and bus configuration. The whole system needs to integrate all kinds of hardware from different manufacturers, write integrated software, and may also need to purchase expensive special equipment and special cables. If one kind of network can do all these jobs, isn't it a beautiful thing
this is the design demand of industrial Ethernet. Because it can reduce the cost of factory automation and be compatible with enterprise IT systems, industrial Ethernet will have a huge growth momentum in the next few years. Harry Forbes, senior analyst of arc Consulting Group, showed in a recent study that the market for industrial Ethernet switches and related network infrastructure will rise from US $260 million in 2006 to nearly US $1billion in the next five years
in order to understand how fast industrial Ethernet is, Beckhoff automation company
launched extreme fast control
System Based on EtherCAT network, which can make the response time of the whole system as fast as 100 microseconds
it is not just people in the IT industry who promote this growth. "Engineers believe that if they can transfer to industrial Ethernet, they can connect everything in the factory with CAT5 wires and networking devices purchased from local electronic stores," said Scott Hibbard, vice president of technology at Bosch Rexroth transmission and control. "This is indeed an ideal prospect for automation."
until recently, motion control has not been able to accept this view. "To use ether for motion control, we must let it do things that have never been designed to do," Hibbard said. As originally envisaged, Ethernet cannot provide cycle time, certainty, or the quality of service needed to close high-performance servo loops in real time or quickly update complex tracks. "Ethernet tcp/ip was not used for motion control," said Dr. ed Nicolson, electrical engineer and technical development director of Yaskawa electric
however, in the past seven years, engineers have developed some smart methods to make the Ethernet have real-time performance, which is not only suitable for i/o applications with low requirements, but also suitable for complex motion control operations. Forbes predicts that the future of motion control based on ether is very bright. "If not most, many motion control applications will eventually be transferred to the industrial Ethernet."
but first, engineers must find out which of the many competitive industrial ethers can best meet their motion control needs. Due to the large number of network technologies that claim real-time performance, this is not an easy thing. At present, there are 22 kinds listed on the real-time Ethernet station
only a few of them are technologically advanced and can be used as open standards, which may be based in larger automation systems that require a lot of motion control. These technologies include rofinet, SERCOS III, Ethernet tcp/ip, EtherCAT, Ethernet Powerlink, and MODBUS. Some motion control experts exclude Ethernet tcp/ip and MODBUS from the real-time network because their performance is not as good as the other four
according to Matheus bulko, the motion control product manager of Rockwell Automation, ethernet/ip Ethernet, which has an absolute advantage in North America, is strengthening real-time performance by adding CIP sync (General Industrial Protocol), which is a network time synchronization protocol based on IEEE1588 standard. However, the real product using CIP Sync has not been released yet. After these products come out, many motion control applications will go beyond the scope of Ethernet tcp/ip, said Bill Seitz, President of ixxat, an industrial and automotive application hardware and software developer. "For motion control applications, you need to think of Ethernet tcp/ip and Ethernet tcp/ip with CIP sync as two different networks," Seitz said. Seitz's company is a value-added design partner of Rockwell Automation. He has been very proficient in Ethernet tcp/ip through participating in many activities of the company. Nicolson also believes that for Ethernet tcp/ip, "CIP sync can change the rules of the game". "Without CIP sync, I don't think the certainty of ethernet/ip is enough for any application that is more complex than sending simple terminal commands."
Industrial Ethernet has the flexibility to deal with the layout of different types of machinery, including the layout of large modular machinery,
as shown in the above automation concept SERCOS III network
what makes industrial ether more puzzling is the hype surrounding various network technologies. Supporters of each real-time Ethernet competitor have been committed to a large number of "specification tricks", and they use various means to try to stand out from their peers. Most of the methods are such as "my cycle time is faster than your cycle time", or "my network certainty is higher than your network certainty."
what matters is not only the best cycle time, but also the cycle
time you can get when you apply a certain number of axes. For example, here is the relationship between cycle time and the number of drives that may appear in SERCOS III
obviously, cycle time and certainty are very important in motion control applications, but these specifications alone can't tell you which network is most suitable for your application. The reason is:
when it comes to the cycle time of each network or the time required for network node communication, it is easy to think that the faster the better. But the reality is that among all the real-world motion control requirements, none of the above four networks can claim a real cycle time advantage. "At present, all deterministic Ethernet approaches on the market can provide sufficient performance for a large number of motion control applications," Seitz said
in injection molding, cycle time is very important.
in motion control applications, the cycle time of the communication bus is indeed very important. "When you try to control a mechanical system, there is a point of diminishing efficiency," said Chris Choi, technical director of husky injection molding Systems Co., Ltd. He should be quite clear about these. His company has built some of the world's fastest injection molding machines, whose applications include high-speed production of preformed bottles and thin-walled packagingLike several other motion control experts mentioned in this article, Choi believes that considering the dynamic response of most actuators and mechanical components in industrial machinery, the small cycle time difference of various real-time industrial ethers is not much. "Factors like inertia are usually more restrictive than the cycle time of Fieldbus in mechanical systems," he said
when you try to control a fast process like injection molding, even a small cycle
time advantage can make a big difference. This chart shows the significant improvement in the ability to track the pressure value of the injection molding process when the control cycle
changes from 2 milliseconds to 250 subtleties
but he immediately added that in the application of high-speed injection molding, even the seemingly small cycle time can make a great difference. Husky's goal of mechanical control is not only to control the execution of mechanical components of the machine, but also to control the injection molding process. To achieve this, Husky's control algorithm must infer the state of plastic melt from the performance of the machine, that is, temperature, pressure, shear state, etc. "When you control such a fast process, every microsecond is critical." He said
therefore, when husky company began to establish a new external condition 1 for its high-speed bottle making and packaging machinery, which can reflect the current experimental external condition in the report, Choi chose EtherCAT as the new communication bus. Choi said, "we are now installing EtherCAT. With EtherCAT, husky can see a reaction time as fast as 100 microseconds in the process control system." Husky chose EtherCAT not only to introduce the technology of motorcycle chain tensile testing machine for the speed of network communication, but also because it can quickly process its unique data packets without using switches or other hardware that will increase the overall response time. From the result of using EtherCAT to reduce response time, only saving materials can save us $182000 per machine per year
in terms of the response time required for general mechanical applications, the performance of all fast networks with 1 millisecond and less than 1 millisecond is sufficient to meet the requirements. Zuri Evans, product manager of SIMOTION of Siemens, said that the reaction time of the hydraulic shaft of injection molding machinery is generally between 250 microseconds and 1 millisecond, and that of the printing machinery shaft is usually 3 milliseconds. He said that the reaction time of the converting machine was between 2 and 6 milliseconds, and that of the packaging equipment was between 2 and 4 milliseconds. "PROFINET's performance far exceeds these requirements," he said
the same is true of the other three fastest collaterals. Don't forget that the difference between the cycle times of the fastest network is only a few microseconds. Such a small time difference rarely plays a role in motion control applications in the real world, because the power of mechanical devices and the frequency response of many industrial machines limit the speed much more than the network cycle time. Nicolson said, "before you notice the subtle differences in etheric cycle time, you will have encountered the dynamic problems of mechanical systems long ago. Engineers need to ask themselves, what kind of cycle time do they really need."
Nicolson is not alone in this view. "Remember, real time is only a relative concept," said Wayne Baron, President and former technical director of Galil Motion control. "It all depends on the actual needs of the application."
jitter (the greater the axial tension is, jitter), or the ability of the network to communicate in precise time, is a sign of network certainty; The four main networks with motion control performance can provide suitable performance with jitter value less than 1 microsecond. In this sense, jitter and cycle time are the same. "In most applications, a little jitter won't do you any harm," Baron said. "You can easily handle it through software."
what really distinguishes various real-time networks is the way they provide certainty. Hibbard, who is also a member of the SERCOS III standards committee, pointed out that there is a technical response map for the lack of internal certainty of the standard ether. Through this map, we can usually track the vibration detection mechanism of the original ether and its occasional accidental delay in the sending of data packets. (e TC6 titanium alloy ingot used in the experiment is smelted by vacuum consumable arc furnace for 3 times to obtain nd)