APPLIED TECHNOLOGY MECHANICAL COMPONENTS
NEW ERA OF CLEAN, HIGH-PERFORMANCE OPERATION IN MOBILE OFF-HIGHWAY APPLICATIONS
M
anufacturers of agricultural, construction and other mobile off-highway (MOH)
equipment are increasingly deploying electromechanical actuators over hydraulic actuators, primarily for their simplicity and environmental benefits. But now, as electromechanical actuators become more intelligent through support of the Controller Area Network (CAN) bus networking standard, equipment designers have even more reasons to choose these solutions.
ENVIRONMENTAL PROTECTION PLUS Hydraulic cylinders require fluids that are toxic to people and the environment. Chemicals such as butane, esters and organophosphates can be released from damaged equipment, and during normal operations or routine maintenance. The production, transport and handling of materials also contribute to the risk. These concerns have opened the door for alternative solutions. Electromechanical actuators have emerged as
an environmentally friendly alternative to hydraulic actuation. Their performance in heavy duty applications is comparable to that of hydraulic actuators, and with added support for the CAN bus protocol, this new generation of smart electromechanical actuators offer significantly enhanced position control, monitoring and overall lifecycle cost savings.
SMART ARCHITECTURE The MOH market predominantly uses CAN bus version J1939, which has been advanced to address the specific needs of agriculture, construction and other MOH applications. 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 control source. This enables ‘plug & play’ interchanges of devices that share the same network and comply with the messaging structure. The result is an efficient, compact solution that provides unprecedented monitoring and advanced control capability. With on-board J1939 compatibility, actuators speak the same language as the ECU, allowing communication across a shared bus. It is dramatically different from conventional electronic architectures, since they require a standalone ECU for each operation. Additionally, this enables more complex control strategies, which may include deploying the same actuator in multiple applications.
6 MAY 2017 | DESIGN SOLUTIONS
EMBEDDED POSITION CONTROL Position control with an embedded J1939-compliant actuator is superior to that of a hydraulic actuator because it provides an absolute reading of position. Achieving positional accuracy on a hydraulic system is expensive and hard to maintain. CAN bus systems, on the other hand, use encoders, limit switches and potentiometers to control position, and these are designed into the system electronics to enable absolute position determination. One key benefit of absolute position control
is that it enables consistent, reliable position memory. Because many MOH machines are run by the season and might sit idle for eight or nine months, it is sometimes 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.
LOW-LEVEL POWER SWITCHING Low-level power switching is standard with the J1939 protocol, allowing operators to program the actuator to extend, retract or stop smoothly using low-level electronic signals, rather than a higher-energy electrical current. This improves safety by reducing the hazard of electrical shock and simplifying design by allowing lower-rated control components.
PROGRAMMING CAPABILITY Users can program the actuator to seek
forward a few millimetres, or make a small set of movements back and forth to hunt down a desired position. As 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. With the J1939, system developers will have
much greater flexibility to program the sensors and internal electronics to synchronise operations among multiple actuators. For example, they can program units to vary in speed depending on load or change speed to compensate if units speed up or slow down. Electromechanical actuators without J1939 support can provide absolute position readings, but they typically require significant power, heavier wiring, relays and other space- consuming and vulnerability prone wiring. J1939 enables all of this to be embedded directly into the actuator and managed by embedded, low- level switching connected to the 2-wire CAN bus communications network and two power wires.
Soft start capability also allows use of lower-
rated power supplies and puts less stress on batteries and charging systems in vehicles. It enables controlling standard inrush to be to up to three times the full load amperage, for up to 150ms. This would enable direct programmable logic controller (PLC) connections, eliminating the need for expensive relays and the related installation costs. It can also include a sleep mode when the actuator is idle, which extends battery by reducing energy consumption. Dynamic braking control is yet another benefit
of low-level power switching. Once the power is cut to an actuator, it could take between 5mm 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 0.5mm.
DIAGNOSTICS AND MAINTENANCE In addition to returning real-time position data to the user, J1939-enabled actuators are constantly returning results of on-going monitoring of temperature, current, speed, voltage and other variables, which enables advanced diagnostics and error handling. Feedback can arrive as quickly as ten times per second as the actuator constantly tests itself. If it detects a problem, such as surpassing a temperature threshold, the actuator finishes its programmed move – either fully retracted or extended – stops and sends an error flag to the computer, all in fractions of a second. Variables can be monitored with unprecedented efficiency. All such functionality can now be embedded
within the actuator, available instantly and potentially sharable via the network for assistance with external troubleshooting.
Thomson Industries
www.thomsonlinear.com
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