For some applications, stock servodrives are the most suitable. Elsewhere, custom solutions justify the extra investment.
For most motion-control applications, standard servodrives are the most suitable solution. Off-the-shelf units balance proven performance, immediate availability, and straightforward integration for a wide array of industrial, commercial, and consumer equipment. In contrast, certain applications involving challenging space constraints, harsh environments, and unique controls need custom drives.
Meeting physical and environmental challenges
Standard servodrives typically come in panel-mounted or PCB-mounted formats, which work well for conventional installations. In contrast, specialized equipment often has limited real estate for electronics, making standard shapes or sizes impractical. For high-volume OEM design engineers who don’t need all the connectors and full functionality of a standard enclosed product, some suppliers sell board-only versions of standard products. These boards pair with custom heat sinks to deliver the same performance as standard off-the-shelf solutions but in a smaller package.
Embedded drives (integrated directly with the motor to make a motor-mounted drive) are another customized option. Or for systems that can’t accommodate a typical rectangular enclosure, there are round drives that directly mount onto motor ends. Yet other drives can be customized into ultra-compact PCB assemblies or with adapted standalone chassis mounts to fit specific enclosure or mounting schemes.
- Drives can also be customized with ruggedization features to withstand:
- Applications with ambient temperatures exceeding 100° C or operating outside standard industrial temperature ranges.
- Military and defense systems needing drives that satisfy MIL-SPEC requirements for shock, vibration, and temperature extremes.
- Deep-sea and marine applications, which need structural modifications to withstand high pressures at depths reaching several thousands of meters.
To protect against contaminants, drives can be customized with covers, conformal circuit-board coatings, or even encasement in potting compound for complete contamination prevention. Such modifications are employed most in food and beverage processing, industrial machinery, and agricultural automation.
Case in point: One supplier developed an IP69K-rated drive-motor package for an agricultural application in which up to fifty drives and motors mount onto a tractor implement. The latter automatically controls dispensing for each row in a field being farmed. Basically, a standard drive board and motor were given a sealed enclosure with waterproof cables and connectors. The assembly’s IP69K rating ensures the drives withstand high-pressure washdown as well as the tractor’s extreme vibration and exposure to outdoor temperatures.
Consider another example: One custom drive integrates into the joystick of a steering system needing haptic force feedback. The drive meets MIL-SPEC requirements for shock, vibration, temperature, and ingress protection with a conformally-coated board in a sealed package.
Matching drive power to motor and duty cycle
A motor’s duty cycle and size may need input power beyond that of a standard servodrive. Because standard servodrives offer fixed ranges of operating voltages and output currents, precisely matching the power source to a specific motor often requires a custom unit. That’s also true of an application needs current or voltage levels beyond standard specifications — for example, an output between the continuous currents of standard models or a very specific voltage for efficient operation.
Engineers with very specific requirements should look for a supplier that can customize drives for any voltage or any wattage within their platform’s capabilities and any reasonable current level. Standard ElectroCraft offerings are scaled at 6-A, 12-A, 24-A, 40-A, and 50-A continuous with the largest drive capable of 100-A peak, but end users needing specific current ratings between these values can request custom configurations.
Recently, a large OEM in laboratory diagnostics needed a drive to control a NEMA 34-frame BLDC motor in a low-current application — only 3 to 4 A. The specification also called for a universal ac line-input capability because the drive needed to accept 85 to 26 Vac anywhere in the world and convert it to dc to run the motor without any jumper settings or physical adjustments.
The customized solution includes an integrated power factor controller that reduced harmonics on the ac line while allowing operation at universal voltages — similar to a laptop power supply. So there’s no need to size electronics to the highest voltage (220 V) when using 120 V and pay for the higher voltage capability. The power-factor controller draws current in phase with the line voltage to producing constant dc power and run the motor at the appropriate stepped-down voltage.
Other important factors are duty cycle and torque requirements. High-acceleration applications — sometimes called pulse-duty operations — demand substantial peak current to generate the peak torque needed for rapid starts and stops. Some drives typically allow peak current values that are double the continuous rating for a couple of seconds, which is useful for quickly accelerating heavy loads. The drives automatically limit current and reduce performance until operation returns to the continuous range, preventing thermal damage. If the needed peak current and continuous current exceed what a standard drive can handle, a custom solution becomes essential to prevent overheating and failure.
Don’t forget regenerative braking
Applications needing regenerative braking represent another scenario where standard drives might not suffice. When motors decelerate under load — common in robotics and electronics manufacturing — they generate energy that flows back into the drive. Many standard drives handle this with an onboard shunt regulator that dissipates the excess energy as heat to keep DC bus voltage safe.
Standard drives have fixed limits for how much regenerative power their internal shunt can handle. Applications with high-inertia loads or vertical axes, such as elevators or gantries where gravity assists downward motion, can generate more power than a standard shunt can dissipate. When the regenerative continuous or peak power exceeds these built-in limits, a custom drive with enhanced capabilities or a standard drive with an external shunt resistor module becomes necessary to safely handle the additional energy and prevent drive damage.
Control algorithms for specialized motion profiles
Standard drives come with preconfigured algorithms that work well for typical applications. For example, some standard drives include advanced field oriented control (FOC) for brushless and closed-loop stepper motors, delivering good dynamic response and acceptable torque ripple for most use cases. Certain universal drives can run brushed dc, BLDC, and stepper motors with the unique ability to control steppers as if they were brushless motors using FOC. This feature provides both cost and mechanical advantages. BLDC motors tend to have longer and skinnier form factors while steppers are shorter and wider, giving designers greater mechanical flexibility when space constraints vary.
Additionally, built-in motor databases and preconfigured settings allow engineers to complete most configurations in seconds, with auto-tuning handling basic optimization. For applications needing standard velocity control, torque control or basic positioning, these algorithms are more than sufficient.
Customization often becomes necessary when the motor-load combination has characteristics that standard tuning can’t accommodate, necessitating custom control algorithms and feedback processing. For example, applications needing smooth motion at low speeds, minimal torque ripple or precise tracking may need highly specialized parameter tuning. In these use cases, suppliers can develop custom-tuned FOC algorithms specifically matched to the motor’s electrical characteristics and the application’s performance requirements.
The choice of commutation method also factors into customization decisions. Some suppliers can implement simple trapezoidal commutation for cost-sensitive or basic applications or deploy more advanced sinusoidal commutation with custom FOC algorithms when applications demand both high efficiency and superior control resolution.
Consider an application benefitted by custom software: In the semiconductor industry, an inspection station needed positioning accuracy within 50 mrad of the commanded position for precise instrument alignment — a resolution that no encoder could directly sense. One motion-technology supplier developed a unique algorithm using software interpolation to control the torque vector in the motor, maintaining accurate positioning.
Because the application used a small motor, engineers rescaled the drive’s voltage and current feedback to maximize resolution. Starting with a standard 48-V drive with 16-bit PWM, engineers dropped the voltage to 12 V — making each PWM step four times smaller. They also reduced the current measurement range from 10 A to 500 mA full-scale, spreading the finite digital resolution of the analog-to-digital converter across a narrower range to increase feedback resolution and fidelity.
The motion-technology supplier later adapted this same fine-resolution technology for another use case — a vinyl turntable manufacturer. The tight control enabled detection of flaws in master discs by virtually eliminating wow and flutter.
Integrating nonstandard feedback devices
Drives can also be customized for feedback. Standard drives work with common encoders and sensors using industry-standard interfaces. These units typically support Hall sensors for commutation and optical encoders for speed and position along with Sin-Cos encoders, magnetic encoders, various serial encoder protocols, and other feedback types through selectable drive parameter settings.
One caveat: When applications use proprietary position sensing technology or nonstandard feedback devices the drive must be customized to correctly accept, process, and communicate those specific signals. Similarly, while standard drives provide basic fault diagnostics, custom versions can be configured to monitor and report specific internal functions such as following error or other application-critical parameters.
Bridging communication gaps with custom protocols
Beyond modifications to the drives themselves, customization also addresses how servodrives communicate and integrate with broader control systems. Servodrives need to integrate into large often complex communication networks and system architectures. Standard units support common industrial protocols such as CANopen or EtherCAT, but applications that need integration with unique, specialized, or proprietary networks outside these standard offerings may demand a custom solution.
Leading suppliers have extensive experience creating custom serial-based control protocols (RS-232 and RS-485) when standard interfaces can’t meet an application’s requirements. This capability is particularly valuable for integrating drives with legacy equipment or when a new accessory must work in harmony with existing systems using proprietary communication schemes.
Further, in distributed control systems that locate the drives closer to motors, custom features let the drives serve as intelligent nodes that can command electronic gearing or motion trajectories for tightly coordinated or synchronized axes. These advanced control features are key in industrial automation, medical and laboratory equipment, and semiconductor processing applications.
Customizing I/O for enhanced functionality
Custom I/O is perhaps one of the most frequently requested customizations. Here, custom drives often include modified firmware to let I/O invert inputs, provide an indicator status, or report feedback based on control variables. For one design, the motion-technology supplier created a drive that is preconfigured to automatically select one of eight configurations based on I/O pin states. Using a custom harness that tied specific pins to ground, the drive detects and loads the appropriate configuration so there’s no need for manual setup steps.
Closing thoughts: When customization makes sense
Standard servodrives work well when an application fits within typical voltage, current, and environmental ratings, requires basic control functionality, and uses common form factors and protocols. Custom drives often become necessary in applications with space constraints, harsh environments, demanding power requirements, ultra-precise motion control, non-standard interfaces or advanced features such as haptics.
In addition, customization is suitable high-volume OEMs. Buying large drive volumes justifies the development effort for optimized solutions at a lowest cost per unit. Engineers also avoid paying for unnecessary features while gaining precisely tailored capabilities.
Because standard products serve as an excellent jumping-off point for custom solutions, it’s recommended to start with standard off-the-shelf options to test and validate performance requirements. When a standard drive performs well but needs additional features or modifications, that’s the suitable time to explore customization. This approach reduces risk by proving the basic concept before investing in custom development.
ElectroCraft | electrocraft.com
Leave a Reply
You must be logged in to post a comment.