And servo drives are trending, as well. Historically, the drives were controlled by analog signals through a centralized controller or an attached digital controller. The units still had digital-to-analog conversion. Modern drives are mostly all digital, so the feedback and the control signals are digital, and the drive might feature a digital signal processor. This lets users configure the drives as dumb drives that take commands from a centralized control and provide digital handshaking information such as the drive's position and speed. Current drives are easily configured to perform multiple tasks in one package, whereas older drives required lots of add-on hardware.
Previously, servo drives mostly targeted motion control. But programmable automation controllers (PACs) contain motion control and machine control (PLC) in one PLC-style device. The units have more memory and faster processing. PACs are easy to configure, and they can perform complex functions such as loop control, latching, and data acquisition and delivery.
Changes are also ongoing in open-loop vector control systems. They are much improved over older volts-to-hertz or volts-to-frequency-control drives. Open-loop vector systems offer better accuracy and speed control and better torque characteristics than volts-to-hertz systems -- without requiring a feedback device. Current AC drives can use sensorless vector control on permanent magnet servo motors, as well as the more traditional squirrel-cage-style induction motors. The systems provide more torque and power in a smaller package for applications such as a new pump on a printing press. In addition, this technology is more dynamic, because permanent magnet motors can stop and start quicker than motors that must generate two fields. This arrangement is a cost-effective and high-performance option for lower-power applications.
Yet another trend has certain drives moving toward a common bus technology on multi-axis machines such as printing presses. Older technologies required bus fuses, terminal strips, and additional wiring to connect the DC buses together. Newer drives such as Parker's AC890 have a bookshelf design. The individual axes of motion physically fit together, and the bus bars go along the top.
For a multi-axis machine, instead of giving every axis its own individual AC drive, with its own AC line connection and power supply, the drives let a single power supply convert the AC to a DC bus voltage. The DC bus voltage is then shared across the multiple individual drives and converted to AC to run the motors. This reduces component costs and cabinet space. In addition, when one drive is regenerating because it is slowing down, the excess power goes back into the DC bus and can be consumed by another drive -- an approach similar to that of an AFE system. A good application example here is equipment that might have 10-20 motors, all of which must be coordinated.
Also evolving are the methods for cooling drives. Typically, most drives are air cooled. But recent higher-power applications instead employ refrigerant cooling to take the heat away from the integrated gate bipolar transistors (IGBT). This method lets drives get more power out of a smaller footprint with reduced IGBT thermal cycling as an additional benefit. Parker has developed patented advanced two-phase cooling systems which are integrated into high-power drives which have very high power density.
Pneumatics turn to FieldBus technology
Understanding an important trend in pneumatics takes a basic understanding of FieldBus technology. A FieldBus is used to replace point-to-point links between field devices such as sensors and actuators of a plant and their controllers (for instance, PLCs or CNCs) by a digital single link on which all the information is transmitted. A protocol or set of rules facilitates data transfer between the units along the bus (unlike traditional point-to-point transmission, whereby any two connected devices send data to each other whenever it is available). FieldBus systems are increasingly favored because data transmission is done in a standard form suitable for factory communication. Pneumatic systems come into play because they are evolving from traditional manual to FieldBus installations.
This trend is being driven largely by increased labor costs. To ship a piece of equipment from one place to another often requires a significant amount of labor to dismantle the machine. More traditional manual systems are hardwired. But FieldBus systems use only a few wires and power cords. This makes it much easier to remove the control panel of the whole working device and ship the machine without having to undo fistfuls of wire.