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Off-the-shelf Motor Control Platforms: How Intelligent Controllers are Accelerating Development of New Motor Drives
By Martin Schiel
EMEA Vertical Segment Manager (Embedded Systems), Future Electronics
Read this to find out about:
- Why new technologies and new use cases are leading to faster growth in demand for industrial robots
- How more integrated motor-control ICs and the provision of ready-made firmware support faster, more effective system development
- A complete reference design kit from STMicroelectronics for controlling a 100W three-phase BLDC motor
When an electronic function is widely adopted in a more or less generic manner and in high-volume products, the semiconductor industry has a talent for stepping into the system designer’s shoes and creating an off-the-shelf implementation. Reference designs developed by chip manufacturers form the basis of the hardware of many familiar products such as PCs, solid-state disks, smartphones and TVs.
This phenomenon can now be observed in the field of motor control: an explosion in the number of new robot designs is leading semiconductor manufacturers to explore ways to reduce their customers’ development overhead, accelerate time-to-market and enhance functionality by providing sophisticated new reference design platforms for small, power-efficient motors.
As a broadline distributor with a large, global customer base which includes many industrial OEMs, Future Electronics has a bird’s-eye view of the semiconductor product offerings suitable for robot system developers. In the company’s view, robotic equipment designers should look for three essential elements in the semiconductor-based motor-development platforms that they evaluate.
This article describes those elements, and illustrates how they can help accelerate system design by reference to a platform supplied by STMicroelectronics.
Motor control: an increasingly attractive market to semiconductor vendors
The reason that motor-system designers are benefiting from semiconductor vendors’ provision of rapid development platforms is the prospect of dramatic growth in the servo drives and robot market. And the reason for this growth is that the industrial market has hit a sweet spot, at which the increased performance and speed of processors enables increasingly sophisticated operations, leading in turn to a new set of use cases for robots which can support, mimic, enhance or replace human capabilities, especially when enhanced by the use of Artificial Intelligence (AI).
According to the International Federation of Robotics, the top trends in robotics as this decade begins will be:
- Robots become smarter
Digital sensors combined with smart software allow direct teaching methods – so called ‘programming by demonstration’. Machine learning tools will in future enable robots to learn by trial and error or by video demonstration, and then optimize their movements autonomously. - Robots collaborate with workers
Currently, shared workspace applications for cobots are most common: robot and worker operate alongside each other, completing tasks sequentially. Development work is now focused on even more challenging methods to enable robots to respond in real time, including voice, gesture and recognition of intent from human motion. - Robots go digital
Industrial robots are the central components of digital and networked production in Industry 4.0 settings. This makes it all the more important for them to be able to communicate with each other, regardless of their manufacturer. Here, new standards such as the OPC Robotics Companion Specification will help robots to connect to the Industrial Internet of Things (IIoT).
As these trends play out over the coming months and years, we will see more robots, and more different types of robot, performing a wider array of functions in more locations. Every robot contains at least one motor; robots with articulated, jointed, Cartesian or other types of arms often contain many motors. Hence the forecasts for rapid growth in the market for motors and motor-control systems – and the interest of semiconductor companies in helping motor-system designers to accelerate product development through the provision of reference design platforms.
In Future Electronics’ view, there are three important features of a motor-control development platform which are of most value to industrial users: integration, configurability, and ecosystem compatibility. So why are these features particularly important?
1. High level of chip integration
A motor-control system is a complex arrangement of functional blocks. Traditionally, motor control board designs have contained a large number of discrete components, an approach which tends to increase Bill-of-Materials (BoM) cost, make the board layout more difficult, and raise board and assembly costs.
This is driving chip manufacturers to create more integrated solutions for motor circuits, combining drive, control, signal processing and power management functions into a single device. Integration provides benefits which are the mirror image of the drawbacks of a multi-component system: smaller, less complex and cheaper, an integrated solution can accelerate the user’s design implementation while providing higher performance, because functions integrated into a single device are optimized to work in concert with each other.
Fig. 1: the STSPIN32F0A system-in-package, part of the STSPIN family of integrated motor controller/drivers. (Image credit: STMicroelectronics)
An example of this new trend towards integrated solutions for motor control is the STSPIN32 series from STMicroelectronics (see Figure 1). The STSPIN32F0A is a System-in-Package (SiP) which provides an integrated solution for driving three-phase Brushless DC (BLDC) motors. It integrates three motor-drive functions which are traditionally implemented in three separate devices:
- A fully protected triple half-bridge gate driver able to drive power MOSFETs with a current capability of 600mA (sink and source). The bootstrap diodes for high-side driving are embedded inside the driver.
- An internal DC-DC buck converter provides the 3.3V supply for both the embedded microcontroller core and external components. An internal 12V LDO linear regulator provides the supply voltage for the triple gate driver.
- Operational amplifiers are available for signal conditioning, for instance for amplifying the current sensing signal across external shunt resistors, or for conditioning the signals from Hall position sensors.
In addition to the driver functions, the STSPIN32F0A SiP also incorporates an STM32F031 microcontroller, which is based on an Arm® Cortex®-M0 processor core operating at a clock frequency of up to 48MHz. This 32-bit MCU offers sufficient processing throughput to run sophisticated BLDC control algorithms such as Field-Oriented Control (FOC), as well as providing multiple analogue and communications interfaces to support peripheral elements in a motor system such as a position sensor and user controls.
2. Easily configurable, ready-to-run firmware for motor control
Even if a ready-made hardware platform is available, a huge development task still remains: implementing the motor-control firmware to ensure that the motor’s speed and position can be controlled, and that it will run efficiently and safely.
This development task can be greatly reduced through the use of off-the-shelf firmware. And there are indeed many sources of IP for generic motor-control algorithms such as FOC and six-step control. The problem for the designer is that it is often much more difficult to port this firmware to a specific hardware host than IP providers acknowledge.
So this is the second test of any rapid development platform under evaluation: does it provide comprehensive motor-control firmware? ST’s suite of firmware excels in this regard: ST provides a choice of algorithms on the STSPIN32 platform, which means that robot system developers can experiment with different motor-control systems on a single host. This gives the designer the flexibility to build two proofs-of-concept, one of which implements FOC with positioning capabilities, the other implementing six-step control, and test which is more suited to the intended application. The STSPIN32 platform also helps the OEM to build a family of products with different features and value propositions for different applications, all on a single hardware platform.
Fig. 2: the EVALKIT-ROBOT-1 kit features an STSPIN32F0A SiP controlling a Maxon EC-i 40 motor. (Image credit: STMicroelectronics)
3. Integration into a wider platform for application software development
By satisfying tests 1) and 2), the motor-control system developer has already selected a dedicated motor-control hardware platform, with the firmware required to control the chosen motor type.
The last important factor to consider is the method for integrating the motor into the rest of the robot’s systems. This means that the question of the wider development ecosystem needs to be taken into account.
In any robotic system, the motor is only one, all be it important, element of the application. It saps developer time and energy if engineers are required to learn and become productive in multiple development environments. Developer efficiency is therefore enhanced if the development of the motor can take place in the same environment as development of other functions.
In the case of the STSPIN32 family, motor-control firmware can be configured and implemented within STM32Cube, the development environment which is used to configure any MCU in the STM32 family. Users of ST MCUs will already be spending most of their development time in STM32Cube. The ST motor-control firmware development software, the X-CUBE-MCSDK, is just one additional module within STM32Cube. So an STM32 user who adopts the STSPIN32 family for motor control will be working in the same environment, with the same controls and functions, as for every other element of their system development.
Ready-made hardware reference design
Growth in the market for robots is, as we have seen, inducing semiconductor manufacturers to step up their efforts to provide ready-made implementations of motor-control systems for driving and controlling robot arms. ST’s investment in this area is particularly attractive because of the availability of highly integrated motion-control SiPs, various motor-control algorithms, and a highly developed tool suite for developing the entire application. ST continues to extend the family: the 250V-rated STSPIN32F025x and 600V-rated STSPIN32F060x devices are available, and new parts with higher processing capability are planned for release.
For STSPIN32F0A users, development time can be accelerated even more through use of a reference design system created by ST, based on a Maxon EC-i 40 motor. This reference design, called the EVALKIT-ROBOT-1, includes an STSPIN32F0A device, a power stage based on ST power MOSFETs, Hall sensors, a Maxon ENX 16 EASY 1024-pulse incremental encoder and peripheral components on a single board measuring just 40mm x 40mm.
Its analog circuit implements inverter-stage driving, current sensing and over-current protection, and the MCU performs FOC with closed-loop position sensing. This hardware is accompanied by ready-to-use firmware for FOC position control in BLDC motors.
Fig. 3: key technical specifications of the EVALKIT-ROBOT-1 motor development platform. (Image credit: STMicroelectronics)
The system achieves very high torque density and very low cogging torque, and is notable for its reliable, robust and precise position and speed control. It can also be used in other industrial servo motor-control applications.
The EVALKIT-ROBOT-1 kit is available on request from Future Electronics, which can also provide help and guidance in implementing motor-control systems through its Munich, Germany-based engineering Centre of Excellence.
