Ethernet motion control speed
Although the PCI data transfer rate may be significantly faster than Ethernet, the important issue is how to take advantage of throughput.
Motion control applications are less likely to take up the entire bandwidth of the PCI bus. Typically, a computer shares a PCI bus with several other devices, such as an Ethernet card, sound card, or video application. In fact, being able to handle Fast Ethernet and other high-bandwidth features is one of the main reasons why PCI has been upgraded from 32-bit to 64-bit. PCI must act as a backbone to carry all the information transmitted by the network and other devices on the PCI bus. Even though the entire PCI bandwidth is available, most PC-based motion controllers are not fast enough to send and receive large amounts of data as fast as the PCI bus allows. In other words, the bottleneck is not a data transfer protocol, but the device itself sends and receives data.
Even though the entire PCI bandwidth is available, most PC-based motion controllers are not fast enough to send and receive large amounts of data as fast as the PCI bus allows.
In other words, the bottleneck is not a data transfer protocol, but the device itself sends and receives data.
Another issue related to speed is whether most motion control applications require throughput associated with the PCI bus. If we look at the type of information that is normally sent and received by the motion controller (ie position, velocity, acceleration or error), the actual amount of data transmitted per cycle is relatively small – probably 512 bytes. With an Ethernet motion controller, these 512 bytes are only equivalent to 4% of the total bandwidth in a 10 Mbps network.
Ethernet motion control flexibility
Nowadays motion control applications perform with a variety of controllers. Depending on the application, a bus-based standalone or network motion controller may be required.
Unfortunately, PCI solutions only allow one form: bus-based. A PCI-based solution is simply not feasible in applications where the motion controller must perform functions independently of the PC, or if there is no PC control on the machine. On the other hand, most Ethernet or Fieldbus controllers can also operate as standalone devices.
As for the network, PCI-based solutions are not a viable option for remote access. Implementing a motion controller on a factory network requires a controller with a network interface; since most factory networks are Ethernet, the choice becomes easier.
Ethernet motion control package size
Often, when choosing between a stand-alone or network-enabled controller and a PC-based controller, engineers mistakenly believe that a PC-based controller can save space because it is located in a PC. Although the controller itself is also true, an external box is required to connect the servo motor, stepper motor, encoder, and I/O. In many cases, this external box is larger or larger than comparable independent controllers.
Ethernet motion control and PLC compatibility
In many applications today, the PLC is used for master control, which tells the motion controller when to move, move distance, and movement speed. The communication between two devices can range from discrete I/O to network connections. Discrete I/O is not a popular solution due to the time and effort required to route and install the system. In this case, an Ethernet or Fieldbus solution is preferred. Most PLCs on the market today offer Ethernet as a standard network option in addition to Fieldbus.
Ethernet motion control installation and maintenance
Not all companies can hire employees with DeviceNet or Profibus who fully understand the network protocol. Even if there is, Fieldbus is unlikely to be their specialty. However, almost every company has a network administrator who is proficient in and focused on Ethernet protocols, making Ethernet more attractive for industrial control.
Unlike connecting a bus-based controller card to a computer, connecting Ethernet to a PC is simple. However, the only connection between the PC and the external Ethernet motion controller is a Category 5 Ethernet cable. To add additional control axes, simply use an off-the-shelf Ethernet hub or switch. Replacing the controller simply means configuring the new motion controller via software and making the same simple Ethernet connection.
On the other hand, bus-based controller card installations require shutting down most computers or taking them offline.
Then you have to remove the PC cover, which is a particularly difficult task if the PC chassis is buried in the machine. Finally, most bus-based motion controllers require two or more PCI slots to be installed. Additional control shafts require additional slots, and bulky cables must pass through another open expansion slot. If the controller fails for any reason, the entire process must be repeated to replace the controller.
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