Electromechanical actuators require smart integrated driver solutions for enhanced edge intelligence
Stephan Kubisch, Director
Stephan Kubisch, Director
To enhance edge intelligence, electromechanical actuators require intelligent and highly integrated driver solutions. These smart edge devices combine actuator and sensor capabilities to enable better real-time decision-making at the machine level and provide in-situ feedback to higher control layers, cloud or AI productivity solutions. This article discusses smart driver solutions and technologies for the intelligent edge, where analog and digital technologies intersect.
In the quest to enhance edge intelligence, physical edge devices such as electromechanical actuators require more intelligence to gain advantages such as better real-time machine decision-making. These actuators provide smart, valuable and rich sensor-based feedback. Such edge devices are key to Industry 4.0 and beyond. They control robots, manipulate and automate factory processes, and transform digital information into physical movement while providing high levels of intelligence and self-awareness1. While actuators manipulate objects, sensors are used to measure and quantify actual parameters and convert physical values back to digital values. Therefore, actuators and sensors are still considered different devices or components most of the time.
Stepper motors and solenoid valves make up a large portion of these electromechanical actuators and can be found on every factory floor, in various automotive applications, laboratory automation, and more. The global stepper motor and solenoid valve market is a multi-billion dollar and growing market, driven by laboratory and medical applications, industrial applications, and automotive applications. These applications place increasing demands on automation and miniaturization of actuator and drive electronics. Traditional drive solutions cannot adapt to these new requirements and lack detection capabilities.
The new silicon cDriver™ solution consists of an intelligent controller and driver that fuses sensor and actuator functionality into a single integrated component for use within embedded motion control solutions, enabling smart actuators at the edge2,3. System parameters and state variables that are only available directly in the electromechanical actuator can be measured and evaluated locally (such as temperature, solenoid valve reaction times and motor load values).
This fusion of sensor functionality and actuators changes the paradigm of electromechanical actuators. They evolve from simple power conversion systems to self-aware sensors that can effectively control actuators and provide in-situ feedback data to higher control layers, cloud or AI productivity solutions. The electromechanical unit becomes the sensor.
Electromechanical Actuators – Overview
Stepper motors and solenoid valves are widely used in automotive, industrial and medical health fields. The two have many similarities: A copper coil of wire is energized to cause mechanical movement.
Two-phase stepper motors are typically controlled by two current sources that induce sinusoidal and cosine-shaped currents in the two phases of the stepper motor that are 90° phase shifted. The current flowing through the stepper motor coil (stator) determines the direction of the magnetic field. The rotor is oriented like a compass in the magnetic field of the stator coils. By controlling the rotation of the magnetic field electrically, the rotor can be rotated by its orientation in the magnetic field. Figure 1 shows the stator/rotor arrangement of a standard hybrid stepper motor and some examples of different types of stepper motors.
Figure 1. Hybrid stepper motor with 50 pole pairs (left) and different types of stepper motors (right).
Solenoid valves are comparable to stepper motors. Energizing the coil causes mechanical movement. Instead of a rotating magnet, the moving part is a metal plunger, which creates linear motion. From a control perspective, there are two types of solenoid valves: on-off valves and proportional valves. Switch solenoid valves are used to realize the on/off function of pneumatic or hydraulic valves. When the coil is energized, a magnetic field is generated and the metal plunger moves in the direction of the magnetic field. To move the plunger, the initial current (rush current) is quite high, but only a smaller current is required to hold the plunger in place (holding current). When the coil is de-energized, the magnetic field disappears and the plunger can retreat freely under the action of external forces (springs, gravity). Figure 2 shows a typical current curve when driving a switching valve. The small decrease in the current rising phase (energization time) is caused by the back electromotive force (BEMF) generated by the plunger movement. When the excitation time is over, the current can be reduced to a holding level to hold the plunger in place as needed. Proportional valves can hold the plunger in any position by controlling energy flow and regulating solenoid valve current. Proportional valves are often used in closed-loop control systems to control specific system variables such as pressure, air or fluid flow.
Figure 2. Current waveform of switching valve.
Why is a new approach to controlling electromechanical actuators needed?
Driver IC solutions on the market today are not tailor-made for solenoid valve driving applications and efficient and cost-effective implementation. They lack embedded timing controllers, application-specific features, diagnostics, and protection features. System complexity arises whenever advanced control features (drive sequencer, dither, fast degaussing, current measurement) or advanced diagnostic functions (plunger motion detection4, on/off status detection, inductance measurement, open load detection) are required will increase significantly due to the need for additional external workarounds and circuitry5,6,7,8. Designers need to design each module (digital controller, current sensing, signal conditioning, power stage, protection) separately and connect them to each other. Designers still have to face issues including board space usage, long design times, application reliability, long bills of materials (BOMs) and lack of flexibility.
Here are some global trends that are leading to additional requirements and demands for embedded control and drive solutions for electromechanical actuators.
The evolution of microactuators
Continued miniaturization makes electromechanical actuators cost- and space-effective components in medical equipment, the chemical industry, laboratory automation, semiconductor manufacturing, the food and beverage industry, and industrial and automotive applications. Examples of miniaturized valves and manifolds as well as hybrid solutions (stepper motors + solenoid valves) are shown in Figure 3. Diameter sizes are as small as a few millimeters. While the advantages of microactuators are expected to drive growth, these markets impose additional requirements such as: longer effective life, durability and reliability, small form factor embedded controller and driver solutions (due to space constraints), and simplification operation and control.
Figure 3. Examples of miniature solenoid valves, manifolds and mixing manifolds (Image source: with permission of Lee Hydraulische Miniaturkomponenten GmbH/The Lee Company).
Electromechanical actuators are susceptible to degradation during long-term operation and may develop other failure conditions, both electrical (coil problems, residual coil power, overheating, insulation failure) and mechanical (valve partially closed or open, manual override, pressure differential , dust accumulation, valve mechanical damage, grease drying). These challenges impact the performance, longevity and operational availability of the actuator and the system in which it resides. Therefore, the need for digitalization is urgent: detailed and high-quality diagnostic feedback on local system parameters to monitor the health of actuators and their control electronics for better decision-making and reaction to changes at the local machine level , and pass preprocessed diagnostic information or raw data from the edge to higher control levels. Need feedback and diagnostics beyond simple drive error flags!
Today, carbon footprint plays an important role. Energy efficiency is driven by global environmental policies, costs and application constraints. Energy is one of the world's most valuable resources, and its cost continues to grow. Therefore, we need to effectively control and reduce the power consumption of the actuator as much as possible. Another positive side effect is that solenoid valves or stepper motors can stay cooler in applications when power consumption is effectively controlled. This will simplify cooling the system and potentially allow it to be used in specific applications with strict temperature requirements, such as sensitive laboratory applications.
time to market
While system complexity increases, development time needs to decrease. Highly integrated, proven, and ready-to-use building blocks and subsystems help reduce or hide overall complexity and reduce design risk, thereby keeping time to market at reasonable levels9. System design is increasingly dominated by communication interfaces and a software-centric perspective. Therefore, the selection of active system components and building blocks will be based on the flexibility and capabilities of their communication and control interfaces.
total cost of ownership
The total cost associated with the entire life cycle of a product is often understood as total cost of ownership (TCO). This covers not only development costs or other non-recurring engineering costs, but also all direct and indirect types of operating expenses: energy costs (energy efficiency), maintenance costs, work availability and supply chain risks. Energy costs can be measured directly, while maintenance costs can be estimated in advance. In market segments where product life is very long, such as in industrial and medical applications, total cost of ownership needs to be considered and will be minimized.
Impact of sensor-actuator fusion in cDriver
Referring to the different global trends discussed, we need to integrate sensor-like capabilities into the cDriver of electromechanical actuators. Multi-chip and single-chip chip-scale solutions are emerging that will not only include the analog driver portion but will be dominated and defined by enhanced digital capabilities, sensing capabilities and decision-making, and communication interfaces. This sensor-actuator fusion meets many needs and brings a wide range of advantages to solenoid and stepper motor-based applications.
The evolution of microactuators: compact embedded hardware solutions
For microvalve, manifold and multi-axis stepper motor applications, it is advantageous to use highly integrated and embedded hardware solutions to drive and control them. If the controller and driver electronics could be equally small and compact, the entire actuator subsystem would bring competitive advantages in reduced size for space-constrained applications.
A typical embedded hardware solution for a single solenoid, manifold or multi-axis stepper system consists of a bus interface for communication, a microcontroller unit (MCU) for application control, and one or more controllers/drivers The unit composition is shown in Figure 4.
Figure 4. Typical solenoid or stepper motor controller and driver solution/simplified diagram.
The communication interface and MCU depend on the application and overall system architecture and are usually only required once per unit. In contrast, manifold/multi-axis systems may require the actuator controller/driver stage multiple times, which provides significant optimization potential. Typical driver solutions for solenoid valves also offer expanded features, but the BOM is larger and requires a lot of space to place all the devices5,6,7,8.
By fully integrating these expanded control and sensing functions into a single device, the required board space can be significantly reduced. For example, solutions with integrated current sensing eliminate the need for large external sense resistors and additional shunt amplifiers. The low RDS(ON) integrated driver stage enables excellent efficiency and reduced thermal losses, which also has a positive impact on the required thermal area or in critical application environments.
Figure 5 shows a typical manifold example. Space savings and BOM reduction enable ultra-compact solutions and cost savings on internal components, PCBs and housing materials for these applications.
Figure 5. Example of a manifold (Image source: with permission of Lee Hydraulische Miniaturkomponenten GmbH/The Lee Company).
Like solenoid valves, stepper motor solutions are also dominated by the driver section. The highly integrated stepper cDriver offers significant space savings while providing excellent control. In addition to diagnostics and feedback functions, they feature integrated motion controllers and power stages10,11, as well as fully integrated current sensing functions12,13.
Reto Himmler, principal electronics engineer at Hombrechtikon Systems Engineering AG in Switzerland, confirms: “We have been using Analog Devices’ Trinamic™ stepper motor drivers for more than ten years and they have industry-leading characteristics. The TMC524013 is exactly the device we have been waiting for! Taller motors Current, small size and integrated current sensing help save valuable board space in laboratory automation equipment. Low losses due to low RDS(ON) provide greater freedom in mechanical design. The 8-point ramp is very Not bad, although the 6-point ramp of the existing product was perfect for our application.”
Augmented Diagnostics: Paving the Way for Predictive Maintenance and Self-Awareness
Smart cDrivers provide sensor-like data locally. But what can be done with this rich set of information?
Parameters provided by the smart cDriver solution include: driver temperature, coil resistance and temperature information, coil inductance estimate, supply voltage, actual coil current and BEMF information. Intelligent integration of algorithms and functions allows derivation of system and application conditions as well as other system parameters such as: reaction and travel times of solenoid valves, local current dips, load open circuit detection, overcurrent and short circuit detection, component closure and plunger movement detection , plunger displacement measurement and real-time current monitoring. For stepper motors, actual load information based on StallGuard™ and CoolStep™ current reduction levels can also be read out14,15. StallGuard load values are valuable information for many applications because long-term drift may indicate degradation of the machinery and gears in the application or defective mechanical end stops. The StallGuard value is directly related to the load conditions on the motor shaft and can change over time in the application, depending on motor acceleration or external forces. The StallGuard value can even be used to detect in advance whether the actual motor is about to stall. This information can then be used for sensorless end stop detection or calibration in the application.
Local detection capabilities and diagnostics, and the acquisition of this in-situ feedback, paves the way for predictive maintenance and self-awareness on three different levels, as shown in Figure 6:
• Local, inside cDriver component
• At the application level, in the local MCU of the embedded subsystem
• At a higher level such as factory floor, factory control or cloud
Figure 6. Availability and flow of sensor and diagnostic data.
Thanks to local monitoring and self-diagnostics, better real-time decisions can be made directly inside the controller and drive electronics. These features include: configurable thermal protection limits, configurable short-circuit detection, drive protection in fault conditions, automatic switching from surge current to holding current, and instant fault reporting, for example when a solenoid valve's plunger becomes stuck.
More granular functionality can be achieved using a local MCU to interpret sensor-like data within the context of the application. Real-time monitoring can be achieved through the serial interface of cDriver. Diagnostic information and parameters are available from the actuator and cDriver as a continuous feedback stream. This enables more detailed condition monitoring, long-term fault identification, and even pattern detection. Reaction and travel time measurements, local dip searches, plunger displacement and load values: Drifts in these parameters over time are signs of actuator aging and indicate the need for preventive maintenance during its service life. Sensor data can be aggregated. In addition to detecting simple faults, application statistics can also be preprocessed and converted into the correct format and then communicated via communication bus interfaces such as IO-Link®CANopen, and even derivative interfaces of Industrial Ethernet) are transmitted to higher control layers.
At higher control levels, data comes from dispersed individual actuators, manifolds or multi-axis systems. Another possibility is to centralize information silos on the factory floor and provide additional options to improve control, monitor system health, simplify maintenance, or put it into context with metadata. For example, knowing the response and travel times of a manifold can help synchronize multiple valves, or improve the orchestration of different solenoid valves and other actuators for better interaction and throughput. Defective actuators are identified and located.
Energy efficiency: outstanding control quality
The ability to measure solenoid response and travel times and detect local dips in current can have a positive impact on power consumption. Control parameters such as target current and slew rate are adjusted to optimize response and travel times. Additionally, the automatic switch from surge to hold current can occur at an optimal point in time, rather than waiting for some static, preconfigured hit time window. Unnecessary energy is saved by not being pumped into the solenoid valve coil, which in turn further increases the efficiency of the solenoid valve unit. This is especially true in the case of bistable pulse solenoid valves (latch valves), since the holding state is guaranteed mechanically (spring) so that the holding current is zero and the source of the total power consumption is only the excitation surge current.
In stepper motor applications, significant energy savings can also be achieved using the ADI Trinamic CoolStep solution based on StallGuard load values14,15. CoolStep thus provides a sensorless dynamic current level control that takes into account the actual load on the motor shaft. When the load on the shaft is low, it is not necessary to drive the motor with the full nominal target current. The target current can be adjusted to the required minimum value. As the load increases, the target current adjusts in the same manner to provide greater motor torque. Even peak loads can be captured and the target current can be temporarily raised above the nominal current without damaging the motor. It will drive the stepper motor with minimum current, reducing the motor's energy consumption by up to 90%.
This increase in energy efficiency also results in less heat dissipation and less thermal stress, thereby extending the life of the solenoid valve 16 or stepper motor and increasing its reliability and functional availability. Keeping actuators cooler opens up the possibility for a wider range of applications and use cases. For example, in laboratories, chemistry or medical fields, temperatures need to be properly controlled to prevent them from reaching critical limits.
Time to market: Simplified control/ease of use
The cDriver component adopts an interface-centric architecture. The bidirectional nature of the interface supports the collection of sensor data and parameters provided within cDriver, and the configuration and adjustment of control parameters according to the application. cDriver components are subsystems themselves, providing ready-to-use high-end building blocks for solenoid and stepper motor control that support a wide range of configurations. Software development (for the solenoid valve or stepper motor parts) is greatly reduced - basically not required at all. Developers do not need to become experts in solenoid valve or stepper motor control, but can focus on their own specialized functionality and communications. This communication-centered, interface-focused way of thinking has given rise to "software-defined hardware", which is not only beneficial to system designers or software engineers, but also shortens time to market and effectively reduces design risks.
total cost of ownership
The intelligent and highly integrated cDriver components discussed in this article help reduce total cost of ownership. Cost savings are expected at three different levels: energy costs, maintenance costs and unplanned expenses incurred for risk mitigation.
Features that improve energy efficiency and reduce power consumption directly impact operating expenses - saving energy means saving money.
Predictive maintenance measures based on large amounts of diagnostic data and sensor-based feedback help reduce the cost of unplanned maintenance and generally simplify maintenance processes because the point of failure can be easily located. A continuous flow of feedback from the actuator subsystem helps monitor system conditions and improve work availability, which in turn prevents additional costs due to production downtime.
Another important impact of the high level of integration of cDriver components is a significant reduction in BOM, which also cannot be underestimated, as shown in the above example. However, this is not just a reduction in BOM costs. Global supply chain challenges, fab capacity, and semiconductor and electronic component shortages caused by trade wars or other global events compromise the ability to manufacture and deliver products in a timely manner, or even create a situation where manufacturing and delivery are impossible at all. This is not just a risk, it is a fact. The reduction in BOM component count helps eliminate dependencies and prevents unplanned redesigns of controller and driver electronics and subsequent requalification efforts.
With the fusion of sensors and actuators, the new cDriver part enables intelligent electromechanical actuators at the edge. The cDriver component does more than just switch solenoid valves or turn a motor. It also provides extensive diagnostic functions and is therefore a sensor in its own right. It leverages pre-processed data to make decisions locally and provides security and monitoring capabilities. This intelligent detection actuator solves mechanical challenges, hides complexity, encapsulates complex functions, provides rich information to higher control layers for further processing, and reduces cost and power consumption to provide future information- Physical systems and factory floors provide additional value. This is a new level of digitalization and a paradigm change in edge electromechanical actuator control. Guido Gandolfo, motion control product line manager at MEV Elektronik Service GmbH in Germany, said: "The new stepper motor driver series enables our customers to develop smaller, smarter and more efficient products in less time. This is The next step in maintaining Analog Devices’ Trinamic driver leadership position.” MEV is a distributor specializing in motion control and design-in support.
1 Jeff DeAngelis. "Intelligence at the Factory Edge: Increase Productivity and Reduce Costs." Electronic Products, May 2021.
2 “Introduction to Embedded Motion Control.” Trinamic, November 2018.
3 “Beyond sensors and cameras: How embedded motion and motor control are driving the Internet of Things.” Trinamic, December 2018.
4 Roberto Casiraghi, Luigi Franchini and Pietro Introini. "Solenoid valve plunger motion detection." Analog Devices, 2020.
5 Manu Balakrishnan and Navaneeth Kumar N. “Plunger motion detection.” Texas Instruments, 2015.
6 “Current Controlled Driver Reference Design for 24V DC Solenoid Valve with Plunger Failure Detection.” Texas Instruments, November 2014.
7 “Robust closed-loop control and monitoring system for solenoid valve actuators.” Analog Devices, 2019.
8 Scott Beversdorf and Chuck Whiting. “Current measurement in solenoid valves for automotive control systems.” Analog Dialogue, Volume 38, Issue 2, April 2004.
9 “How motion control defines system design—an engineering perspective.” Trinamic, August 2017.
10 TMC5072 intelligent integrated dual-axis stepper driver and controller. ADI Corporation.
11 TMC5130 intelligent integrated stepper driver and controller. ADI Corporation.
12 TMC2240 intelligent integrated stepper driver. ADI Corporation.
13 TMC5240 intelligent integrated stepper driver. ADI Corporation.
14 StallGuard and CoolStep. ADI Corporation.
15 How to configure StallGuard2 and CoolStep on TMC5130-EVAL-KIT. ADI Corporation.
16 Jun Peng, Xuanheng Tang, Bin Chen, Fu Jiang, Yingze Yang, Rui Zhang, Dianzhu Gao, Xiaoyong Zhang, and Zhiwu Huang. "Predicting failure types using physical indicators and data characteristics of solenoid valves." Applied Sciences, Volume 10, No. 4, 2020.
About Analog Devices
Analog Devices, Inc. (NASDAQ: ADI) is a leading global semiconductor company dedicated to bridging the physical and digital worlds to enable breakthrough innovations at the intelligent edge. ADI provides solutions that combine analog, digital and software technologies to promote the continued development of digital factories, automobiles and digital health, address the challenges of climate change, and establish reliable interconnections between people and everything in the world. ADI's fiscal year 2023 revenue exceeds US$12 billion and has approximately 26,000 employees worldwide. Working with 125,000 customers around the world, ADI empowers innovators to exceed what is possible. For more information, please visit www.analog.com/cn
About the Author
Stephan Kubisch is Director of Trinamic™, INA, CMR Solutions at ADI. Stephan is responsible for the R&D management of motor and motion control solutions in the Connected Motion and Robotics team of the Industrial Automation Division. At Trinamic Motion Control (formerly Maxim Integrated, now part of Analog Devices), he held a variety of positions, including director of product definition, director of R&D, and senior IC designer. Stephan holds a PhD in Information Technology.
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