Motion control design and mixed signal FPGA solution
As the performance and integration of electronic components continue to increase and prices continue to decrease, the development of electronic control units is progressing rapidly. With the emergence of various technologies and applications, from the field of home appliances to industrial automation production lines, the focus of everyone's attention is still on increasing design and improving power efficiency while reducing design, development and overall system costs. Welcome to reprint, this article comes from the electronic enthusiast network (http: //)
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At the same time, motion control applications are becoming more and more complex, and have evolved from simple on / off control to variable speed applications with precise control in a highly integrated environment. Whether it is AC, DC, brushed and brushless motors, the various control circuits are mainly composed of three parts: human-machine interface, microcontroller (MCU) and control logic. For closed-loop motion control, the sensor interface is an additional component (Figure 1). Incorporating motion control logic into the digital domain can achieve distributed environment control. The combination of motion control electronics and distributed network can realize a variety of new functions in the workshop, including remote management; adapt to changing protocols; performance monitoring; and regular maintenance. 
Figure 1: Traditional motion control implementation methods require multiple discrete components. This closed-loop motion control system uses a network interface, microcontroller, analog device, hall sensor interface, and control logic.
For example, in today's automotive industry, manipulators driven by stepper motors are widely used. The manipulator system makes distributed control more complicated, and different manipulators must install different parts on several vehicles at the same time. One of the main challenges for system designers is to synchronize the various robots and other automation equipment through the local area network. To make matters more complicated, remote management functions (such as monitoring, data sharing, and remote configuration) are often critical to complex central control topologies, that is, there must be an effective distributed control mechanism.
With the improvement of semiconductor technology and integration, field programmable gate array (FPGA) has become an important alternative platform for many electronic motion control applications. The rapid development of FPGA has replaced the application specific integrated circuit (ASIC) in many application fields. Non-volatile FPGAs are a cost-effective alternative to ASICs, and there are no issues involving high development costs and long development times when using ASICs. Moreover, by using FPGA to replace fixed logic, designers can efficiently and reliably implement product upgrades and customized functions at the design stage or at the application site.
Flash-based mixed-signal FPGAs (such as Actel Fusion PSC) can achieve unprecedented integration on a single chip. Therefore, this type of device can replace multiple discrete components, which can reduce costs and occupy board space by at least 50%, while maintaining system reliability (Figure 2). Moreover, the integrated Flash memory on the mixed-signal device allows designers to store design documents, unlike FPGAs based on SRAM that require additional PROM configuration. In addition, as with other reprogrammable FPGA solutions, configurable and flexible mixed-signal FPGA devices can be easily changed during development and even after application.
As we all know, FPGA can speed up mathematical operations through parallel processing, making it an ideal choice for implementing motor control logic. FPGAs can implement tighter control loops, thus providing better control and less fluctuations and noise. Designers can also integrate soft processor cores in mixed-signal FPGAs with integrated Flash memory to run directly from on-chip memory, thereby closely matching the needs of control logic and interrupt drivers. Because the number and types of logic gates in the design and the functions of the control logic vary depending on the application, that is, based on performance requirements; therefore, programmable logic is often best suited to implement various user interfaces and digital control logic, including network and Peripheral interface, pulse width modulation (PWM), and quadrature encoder interface and sensor input; this is very important for today's motion control systems.
Network and peripheral interfaces
In the motion control system, the network and peripheral interface allow users to issue instructions to initialize, configure and control the logic circuit, and remotely manage the control system. Depending on the function and topology, each network and peripheral interface of each motion control system may adopt a unique implementation, but one thing in common is that they all use the interface to improve the accessibility of the system.
There are already a variety of industry standard interfaces, such as a universal serial bus (USB) for local access, a serial port based on RS232 and a controller area network (CAN) interface, and 10/100 based on TCP / IP network protocol Ethernet. In harsh environments, such as automobile manufacturing plants, wireless network interfaces may also be required. This interface can realize system synchronization, data sharing, status monitoring and fault alarm in the manufacturing workshop. In addition, TCP / IP-based network interfaces are used to extend the ability to remotely access central manufacturing control facilities from any distance. 
Figure 2: Actel Fusion PSC can achieve unprecedented functional integration for motion control systems on a single chip, integrating configurable analog, large-capacity Flash memory modules, comprehensive clock generation and management circuits, and high-performance programmable logic. In a single chip. This architecture can be used with Actel's ARM or 8051 soft core and other IP cores developed for specific applications (such as pulse width modulators).
In many cases, industrial automation applications require special control algorithms and devices to complete special tasks. In order to realize the functions that these standard interfaces cannot provide, special interfaces need to be considered. In order to fully exploit the potential of a distributed control system, standard interfaces or specialized network protocols must be added to the board level or embedded in programmable logic. FPGA is the best platform to integrate all the interfaces together. In particular, today's mixed-signal FPGA devices have analog front-ends that can support a wide variety of user inputs, as well as the voltage, current, and temperature monitoring functions needed to implement motion control.
Pulse Width Modulation (PWM)
PWM logic is not a suitable solution for all motion control applications. Since the number of winding turns, rated voltage / current, torque curve and other parameters of different motors are very different, each PWM system needs to consider these differences. In a PWM-controlled system, the order of applying voltage determines the direction of motor rotation. At a given winding inductance, the duty cycle (or pulse frequency and pulse train length) determines the peak current and magnetic flux of the motor (that is, its torque). Mechanical momentum and winding inductance (partly determined by the number of winding turns) will smooth the PWM voltage. By controlling the pressure sequence, frequency and duty cycle of the drive circuit, the PWM system can control the direction, speed and average torque. Using FPGA devices, designers can build the PWM solution that best suits the system requirements without having to use traditional MCU / DSP solutions.
Quadrature encoder interface (QEI)
Most high-precision motors (such as servo stepper motors for robots) support quadrature encoder interfaces. The control system must provide quadrature encoder interface logic to accurately motor speed, position and acceleration. Of course, using programmable logic technology can accurately and dynamically adjust the speed in various modes depending on the characteristics of the motor used in the motion control system.
Sensor input
For closed-loop motion control systems, rotor position and / or revolution inputs are required. These inputs can be built-in Hall effect sensors or external optical position encoders, synchronization resolvers, or magnetic induction sensors. Using an integrated analog front end, mixed-signal FPGAs will provide a more integrated solution that can reduce the number of components, reduce system costs, and increase reliability.
Reliability and system uptime
For today's electronic systems, high performance, low integration costs, and rapid diagnostic capabilities are critical. Diagnosis and forecasting, that is, the function of determining the type of failure and making a forecast, are becoming more and more important in system management. The function of reading the operation of various boards with time-stamped system parameters or the function of analyzing failures afterwards is invaluable for system development. Similarly, being able to build a "black box" will save precious time and effort in finding fault types and design defects.
The on-chip Flash memory of the mixed-signal FPGA can save key system parameters and time-stamp them, such as power line current consumption, device temperature, and voltage fluctuations. These data can be used not only for post-mortem failure analysis, but also for innovative designers to analyze system trends in operation. For example, a designer can measure (when a certain voltage is input) the current of the winding and the vibration of the motor to determine when to shut down the device in a planned manner. In industrial applications, considering the cost required to solve the failure problem and the profit loss caused by the equipment shutdown, the cost of shutting down the equipment according to the planned scheme is much less than the unexpected shutdown. Mixed-signal FPGAs allow designers to analyze how a particular parameter changes the life of the board and make predictions before failures occur, thereby maximizing machine utilization, extending system uptime, and reducing potential losses. Risk of system crash.
The application range of the motor is very wide, and many applications are shifting from electromechanical design to electronic design. The cost of computers and power electronics has always been one of the obstacles to the widespread use of electronic motor control. With the advancement of semiconductor technology and functional integration technology, this obstacle is slowly disappearing. Moreover, because the cost of implementing fixed-function implementations is still high today, often requiring different components and making board-level changes in various design iterations, FPGAs have become an alternative solution for many motion control applications.
The ideal motion control design often needs to put together some components that can be operated together, so that they can be harmoniously coordinated during operation. The mixed signal FPGA solution has a very high degree of functional integration, which can meet this demand, and can greatly reduce the number of components, board space and overall system cost, thereby increasing system reliability and uptime.