Actuators have always been on the frontline of automation, providing the “push and pull” that extends human capabilities to operate everything from delicate pick-and-place applications to 10-ton agricultural combines. Now, as the industrial world becomes increasingly digitized and connected, a new generation of actuators is fulfilling that role with more intelligence, simplicity, and economy, while overcoming increasingly challenging environmental conditions.
The Benefits of Integrated Electronics
By integrating electronics within the actuator housing, smart actuators enable switching, synchronization, 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 (Figure 1). 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 onboard electronics to manage the power, current at the switches or contacts can be reduced from 20 A to less than 22 mA, 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 10 mm 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. This improves repeatability and positioning capability.
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.
A typical CAN bus network can be illustrated with four actuators using built-in CAN bus-compliant intelligence and connected directly to both a battery and control source (Figure 2). The green box represents gears, sensors, or other components that could also be connected to the network. The orange line represents the two-wire bus that transmits the low voltage of power needed for the system, and the blue line represents the wires that are used for information exchange.
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. Users can, for example, program the actuator to seek forward a few millimeters or make a small set of movements back and forth to reach a desired position. And because the system knows what it is supposed to do and monitors performance in real time, it can flag potential variances and trigger advanced algorithms to manage further alarms, corrections, or shutdown.
Synchronization. With integrated electronics and networking, system developers will have much greater capability to synchronize operations among multiple actuators. Users of smart actuators will be able to configure start-and-stop instruction, and the actuator electronics will handle the synchronization.
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 analog or digital position feedback at every point in the stroke.
To provide analog position feedback, potentiometers simulated in the internal electronics send voltage signals that alert users of the absolute analog 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 measure 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 monitor and report temperature, current, speed, voltage, and other variables, which enable advanced condition monitoring, diagnostics, and error handling. Feedback can arrive up to 10 times per second, as the actuator constantly tests itself. If it detects a problem, such as surpassing a temperature threshold, the actuator can stop mid-stroke or finish its programmed move, either fully retracted or extended, and send an error flag to the computer — all in fractions of a second. Following are some of the variables that can now be efficiently monitored:
- Current. Current monitoring is a critical safety feature that shuts down the actuator on overload and eliminates the need for the traditional noisy mechanical clutch.
- Voltage. Continuous monitoring of voltage protects the actuator by preventing motion if it detects it is operating in an environment outside of the acceptable range.
- Temperature. Internal temperature is monitored and, if outside the acceptable temperature range, the actuator is shut down after extending or retracting stroke. Built-in temperature compensation allows the actuator to push the rated load at lower temperatures without nuisance tripping.
- Load. Trip points can be calibrated at assembly to ensure repeatable overload trip points independent of component and assembly variations. This produces repeatable performance, and relieves the end user of the need to recalibrate in the field.
With integrated electronics, such functionality is available to the end user on demand, 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.
The ability to monitor themselves not only makes smart actuators easier to operate and maintain, their complex electronics also present a level of vulnerability that make this monitoring essential. Ensuring reliable operation requires designing smart actuators to meet 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.
Putting Smart Actuators to Work
Smart actuators are finding their way into numerous industries (Figure 3). Following are a few examples of markets that are already going “smart.”
Factory Automation: A provider of customized industrial automation systems for the textile industry has used the low-level switching capability provided by smart actuators to eliminate costly external relays. This made it easier to provide customers with a more compact automation system. Built-in potentiometers also provide them crucial position information.
Robotics: Designers of an automated valet parking system most likely could not have realized their solution without smart actuators. Patrons signal that they are ready to pick up their cars with their mobile phones, and an actuator-driven, robotic assembly delivers the car to them.
Material Handling: Manufacturers of logistics trains use smart actuators to help increase load capacity, regulate operations, and reduce maintenance. Low-level switching, verified positioning, and end of stroke shut off are among the features frequently applied in material handling.
Construction and Agricultural Equipment: A startup combine manufacturer used J1939 networking capability to enter its market with an attractive product. It could offer integrated control of actuators on five axes, including the rock trap door, gate latch, ladder, grain tank, and auger.
Solar energy: To store maximum energy, numerous solar panels must move in sync to follow the sun. One solar panel manufacturer accomplished this with smart actuators that fully leverage the embedded J1939 CAN bus compatibility.
Waste disposal: A garbage handling system manufacturer relies on low-level switching to eliminate the need for expensive relays, and it uses integrated end-of-stroke signals to remove the cost and complexity of external limit switches. Integrating the electronics and routing the cables to a common plug also eliminated the need for both five meters of external cabling and creating specialized wiring harnesses to accommodate it.
The Next Generation
Given their computational and communications capabilities, smart actuators will likely be increasingly integrated with other similarly enhanced sensors, data acquisition devices, and production equipment, as well as other actuators. 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. And the IIoT is part of an even broader industrial revolution, in which computational, communications, and physical domains increasingly interact without human command. Known as cyber-physical systems or, sometimes, just Industry 4.0, this promises new levels of efficiency, economy, and safety.
This article was written by Anders Karlsson and Travis Gilmer, Product Line Specialists for Industrial Linear Actuators at Thomson Industries, Inc., Radford, VA. For more information, Click Here .