Smart actuators meet increasing demands
03 July 2017
Actuators have always been on the frontline of automation, providing the “push and pull” that extends human capabilities. Now, as the industrial world becomes increasingly digitised and connected, a new generation of actuators have emerged with greater intelligence, simplicity and economy.
The embedding of microcomputer chips into the actuators themselves was a pivotal point in smart actuation history. This innovation enabled incorporation of previously external functions such as switching, position feedback and system diagnostics into the actuator itself.
The benefits of integrated electronics
By integrating electronics within the actuator housing, smart actuators enable switching, synchronisation and networking to be managed automatically based on signals from a common external source, such as a programmable logic controller (PLC) or other control unit. Participation in more complex automation schemes becomes feasible, and a more compact system footprint simplifies operation and lowers cost of ownership.
Key among the embedded functionalities that enable this integration are:
Low-level power switching: Traditional actuators often rely on large, power-inefficient relays or independent controllers to extend, retract or stop the extension tube. By using on-board electronics to manage the power, current at the switches or contacts can be reduced from 20A to less than 22mA, which enables a simpler, less expensive system design. Actuators can be programmed to extend, retract or stop the tube using low-current signals, providing a soft start. This improves safety by reducing the hazard of electrical shock, simplifies design by allowing lower-rated control components, and puts less stress on system batteries and charging systems.
Low-level power switching also improves position control by enabling dynamic braking control. Once the power is cut to an actuator, it could take between 5 and 10mm to coast to a full stop, depending on how the actuator is mounted. Electronic actuators enable dynamic braking functionality, which can reduce that coast to about a half millimeter by electronically forcing a short between motor leads inside the actuator.
End-of-stroke indication: Knowing when the actuator has reached the end of a stroke is important for safety and performance reasons. If an actuator is used to lock a device into place, a simple LED light triggered by the output can confirm it is locked and will protect the operator from an unsafe condition. This functionality can also be configured to notify the end user of an end of a stroke, providing a safety interlock while also extending the working life of the actuator.
Bus operation: Integrated electronics make it possible for actuators to apply networking standards, such as the J1939 standard proliferated by the Society of Automotive Engineers to be the Controller Area Network (CAN) bus for heavy duty vehicles. J1939 is a high-level communications protocol that provides a standard messaging structure for communications among network nodes under control of an electronic control unit (ECU). Every message on an actuator module representing a J1939 bus node has a standard identifier indicating message priority, data and ECU source. This enables plug-and-play interchanges of supporting devices that share the same network and comply with the messaging structure.
Where J1939 is a communications protocol that is popular for off-highway applications, integrated electronics are increasingly applied in plant floor, material handling and other applications. Actuators with integrated electronics can now be programmed to participate in networks and systems involving industrial communication protocols such as HART and network protocols such as Ethernet. Such advanced position control and switching enable programming of the drive to perform with an infinite number of movement profiles and custom motion strategies.
Synchronisation: With integrated electronics and networking, system developers will have much greater capability to synchronise operations among multiple actuators.
Electromechanical actuators already provide advantages over fluid-driven actuators in heavy duty, precision applications by delivering absolute position feedback but have traditionally done so with external potentiometers, encoders, limit switches and controls. Integrating the components into the actuator provides additional benefits, enabling absolute analogue or digital position feedback at every point in the stroke.
To provide analogue position feedback, potentiometers simulated in the internal electronics send voltage signals that alert users of the absolute analogue position, speed and direction of the drive ? from beginning to end of stroke. They also remember that position, so if power is lost, there is no need to return to a home position and reset the device. Because many mobile off-highway (MOH) machines are run by season and can sit idle for eight or nine months, it might sometimes be valuable to disconnect the battery to prevent it from draining. Without absolute position capability set at the factory, the user will have to recalibrate once they reconnect the battery.
Digital position readings can come from an integrated Hall Effect encoder, which provides a single-pulse train digital signal to indicate of incremental position and speed. This improves control by indicating actual position changes and speeds.
Smarter monitoring, diagnostics and maintenance
In addition to returning real-time position data to the user, the network can return results for ongoing monitoring of temperature, current, speed, voltage and other variables. Feedback can arrive as quickly as 10 times per second, as the actuator constantly tests itself. If it detects a problem, the actuator can stop mid-stroke or finish its programmed move, either fully retracted or extended, and send an error flag to the computer.
With integrated electronics, all such functionality is available instantly to the end user and, via the network, it is potentially sharable in support of external troubleshooting. Once problems are identified, the plug-and-play capability gained by integrated standards simplifies repair and replacement. Where replacing a problematic hydraulic actuator might require a service call from the manufacturer for hours or even days of disassembly, reassembly, system bleeding and testing, a smart actuator can be replaced in less than 20 minutes.
Ensuring reliable operation requires designing smart actuators to meet the most stringent industry standards for protection from ingress by solid objects and liquids, extreme temperatures, operational shock, vibration, corrosion, voltage variation and electromagnetic interference.
Not every actuator must be protected from all environmental assaults, and each OEM requires its own profile of standards. Likewise, vendors have developed their own sets of procedures for meeting those standards. A major advantage of actuators that embed previously external devices is that compliance with the appropriate standards is done at the factory and need not be repeated once the systems are installed.
The next generation
Given their computational and communications capabilities, it is not difficult to imagine extending the reach of smart actuators for increased integration with other similarly enhanced sensors, data acquisition devices and production equipment, as well as other actuators. As such, today they are fully ready to participate in the emerging industrial internet of things (IIoT,) where every device not only has intelligence and networking capability but also an internet address and the ability to share and subscribe to information sources.
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