Chip-Based Motion/Motor Control: The Way to Go for Some Users
Motion system engineers, developers, and original equipment manufacturers (OEMs) have another tool in their hands thanks to advances in microelectronic design and processing. This online extra article provides added information to the main article on chip-based control in Control Engineering, October 2002.
Motion system engineers, developers, and original equipment manufacturers (OEMs) have another tool in their hands thanks to advances in microelectronic design and processing. Chip-based motion processors, digital signal processors (DSPs), and associated software development tools offer a ''build it yourself'' alternative to motor and motion control.
Although this technology started from a small base, its emergence is propelled by savings in cost, space, and time-to-market. Chip-based controls are now bringing advanced features to all product levels, including lower cost models. For further information and discussion, click here to read the primary article.
Buying general-purpose chips directly from manufacturers or off-the-shelf motion chipsets from specialist sources are two alternatives to implement this technology. Not surprisingly, Performance Motion Devices Inc. ( PMD , Lincoln, MA) recommends the latter. Going the off-the-shelf route, where motion chipset can be customized if needed, allows users to concentrate their design effort on the overall card design and motion software development, explains PMD chairman Chuck Lewin.
''Another advantage of using an off-the-shelf motion chip is that card products using these same chips are readily available, thus a particular project can quickly get to market....Then, a custom card for [further] cost reduction can be designed later without having to rewrite the software, since the motion chipset stays the same,'' adds Mr. Lewin.
Single- or multi-processors?
An ongoing issue for chip-based motion control is whether to use single- or multi-processors in the so-called "high-performance space" of applications. According to Finbarr Moynihan, product line manager at Analog Devices Inc. ( ADI , Norwood, MA), many customers are opting for multi-processor solutions.
In this approach, ADI's latest mixed-signal ADSP-2199x chips handle prime motor control and rotor-position-interface functions for which they're optimized. Then, another chip, optimized for human-machine interface (HMI) tasks-which are of growing importance to motion systems-would take care of such items as user interface, communication with CNC machines, and coordination of multiple motion axes. For example, ADI's ADSP-21535 (part of the Blackfin family) brings together 300-MHz DSP and 32-bit RISC-like architectures, and makes available communication interfaces and a variety of third-party RTOS (real-time operating system) support.
Says Dr. Moynihan, ''It's conceivable that motor control and HMI functions will remain separated for the foreseeable future due to (a) very different task requirements and (b) physical separation within the system partition. For example, the motor control function (ADSP-2199x) may be placed inside the isolation barrier of the power converter or even integrated into the motor, as more integrated motor/controller systems become available, while it may be more appropriate to maintain the HMI function closer to the user.''
More on development tools
Software development tools provide programmability to chip-based controls, among other things. Chip manufacturers can develop these tools directly or rely on third-party software specialists to supply the tools.
Visual Solutions Inc. ( VSI , Westford, MA) is one such supplier of development tools, and a member of Texas Instruments' third-party network. The company's VisSim software tool is a visual-block language for defining embedded control algorithms.
Jim Webb, VSI's product manager, explains that parameters in a DSP can be changed on the fly through VisSim, and behavior of the DSP interactively plotted, for quick tuning of control parameters. ''[Such] DSP-in-the-loop testing is done via a JTAG hotlink. VisSim also provides Flash burn support to deploy the finished controller,'' says Mr. Webb.
Besides general software blocks (math, Boolean, dynamic, etc.), VisSim also provides motion-control blocks, such as ac induction 3rd harmonic space vector wave-form generation, brushless dc commutation and PWM generation, PI and PID controllers, and fixed-point filter design/generation. ''Tremendous time savings are seen by designing at a higher, more intuitive level of abstraction. This lowers training costs, decreases time to market, and increases code reusability,'' adds Mr. Webb.
Dramatic energy savings result from changing on-off control of motors (and other rotary machines) to adjustable-speed control. Some control suppliers seem to suggest that digital control is behind the energy savings; however, the ability to regulate speed relative to the
Much of the energy efficiency issue is associated with larger electric motors that run for very long time periods. Also included are motors that power a myriad of appliances (refrigerators, washing machines, air conditioners, pumps, fans, etc.). While the high-performance side of motor/motion control also can benefit from energy efficiency-more aptly in the form lower power consumption of components-the operating environment and power-up periods are different here. The perspective is on performance. As Analog Devices' Dr. Moynihan puts it, ''Performance cannot be sacrificed in a servo motion system.''
Analog Devices produces different chip products to match specific motor control needs. Differentiation is by package types, memory integration, and peripheral sets. An example at the low-cost end is the DashDSP family of mixed-signal DSP products in a 28-pin SOIC package. Says Dr. Moynihan, ''The latest members of this family (ADMCF34x and ADMC34x) integrate an innovative current sensor interface that eliminates the need for many external analog components (amplifiers and comparators) so that true energy-efficient, single-chip motor control is possible.''
Motorola Semiconductor Products Sector Austin, TX) views energy efficiency of chip devices in terms of power consumption. ''Consumers and regulators are requesting increased energy efficiency, thereby pushing OEMs to reduce power consumption of devices,'' remarks Renee Mitchell, marketing development manager at Motorola SPS.
PMD's Mr. Lewin sees an increase of control precision leading to more equipment uptime and lower power consumption. ''So energy efficiency and other considerations, such as reducing torque ripple, controlling over-torque situations, performing variable-speed control, as well as other functions, are very much realistic in chip-based control,'' he says. As a result, ''... there will be a lot of activity in this area in coming years, and lower-end DSP-based products will be released, which will provide cost-effective, yet sophisticated control of motors in torque and velocity control applications.''
Even leading-edge technology, such as chip-based control, must look ahead. One development making its way form the research phase toward products is the so-called ''clockless'' chip. Different design methods are being applied to make microprocessors without the need to synchronize their various integrated circuits and functional blocks to a single clock. Among companies active in this sector are Theseus Logic Inc . (Maitland, FL ) and Fulcrum Microsystems Inc . (Calabasas, CA), along with some major chip manufacturers.
Still higher performance and faster, more efficient design cycles are promises of these clockless, asynchronous processors for system-on-a-chip products. Commercialization may be well into the future, but designers and users in the motor/motion-control community will be eager to get on board.
Chip-level motion/motor control products
High-performance motion-control ICs
Palo Alto, CA -HCTL-1100 Series high-performance, general-purpose motion-control ICs are designed for position and velocity control of dc, brushless dc, and stepper motor systems. These CMOS integrated-circuit devices are TTL-compatible and operate in the 100 kHz to 2 MHz range. Features include programmable digital filter and commutator, eight-bit parallel port, PWM motor-command port, and encoder-input port. All control parameters are programmable to streamline the design of control systems. A Sync pin is provided for coordinating multiple HCTL-1100 ICs. A complete control system consists of HCTL-1100, a host processor to input commands, an amplifier, and a motor with an incremental encoder. No analog compensation or velocity feedback is necessary. Agilent Technologies www.agilent.com
Three-phase motor controller/driver
Worcester, MA -A3936 is a motor controller/driver intended for pulse-width modulated (PWM) current control of three-phase brushless dc motors. The device is rated at peak output current toitry is provided. Internal circuit protection includes thermal shutdown with hysteresis and crossover current protection. No special power-up sequencing is required. A tachometer output is provided for external speed-control loop. Allegro MicroSystems Inc . www.allegromicro.com
`Smart' power module for motor control
San Jose, CA -Smart Power Module (SPM) in a dual in-line (DIP) package format offers full adjustable-speed drive control, along with integrated circuit protection for ac motors used in consumer appliances. DIP-SPM delivers low-voltage control and a high-voltage output stage rated at 10-20 A at 230 V ac. For these ratings, the integrated SPM reportedly needs less than 50% the board space of a discrete IGBT design. The 60 x 31 mm ceramic-based molded package optimizes heat transfer from the power-switching IGBTs, resulting in a 27% greater power rating than a conventional TO-220F package, says the manufacturer. SPM's design is simplified through a built-in high-speed/high-voltage control circuit (HVIC) that eliminates the need for opto-couplers. It also allows driving the IGBTs with one only bias supply, with attendant lower cost. Pricing is in the $14 to $19 range, each (on a 1,000-piece basis), depending on the SPM model. Fairchild Semiconductor www.fairchildsemi.com
Function library for DSP motor control design
Dallas, TX -Digital Motor Control (DMC) function library works with the company's RIDE component-based DSP design software (and related VAB for C2000 product) to create intuitive control algorithms for use with Texas Instruments TMS320C24xx DSP motor controllers. The DSP-based motor control library is said to bring efficiencies to real-time DSP programming. DMC's simple procedure starts with users selecting motor-control blocks from a pull-down menu or toolbar. Then, blocks are graphically connected to form the data flow of the particular design. Run-time parameters are set via pop-up dialog boxes. One button push executes in real-time the complete algorithm generated on the target TMS320C24xx DSP. DMC software library contains such motor control design elements as current and speed measurement, tachogenerator position, space vector PWM, PID controller, V/Hz profile, and power-factor correction. Hyperception www.hyperception.com
Motor control and power conversion chip
Chandler, AZ -A family of motor control and power conversion devices named dsPIC Digital Signal Controllers combines a 16-bit Flash microcontroller, a "fully implemented" DSP, and various peripherals on one chip. Featured in the dsPIC30Fxx family is a 6-/8-channel PWM motor-control module; 10-bit, high-speed analog-to-digital converter (500K samples/s); quadrature encoder interface; input/output compare units; and communication peripherals. Target applications of the chip include various motor topologies-sensorless brushless dc, switched-reluctance, ac induction-as well as power inverters and uninterruptible power supplies. These 30-Mips (non-pipelined performance) DSPs offer up to 144 Kb Flash program memory and up to 8-Kb data space. Microchip Technology Inc . www.microchip.com
Sophisticated motor control, no software expertise needed
Austin, TX -MC3PHAC Motor Control Unit is a pre-programmed, variable-speed three-phase ac device intended for the control of low-power HVAC motors for washing machines, dishwashers, commercial appliances, process controls, pumps, and fans. MC3PHAC contains functions needed to implement open-loop (V/Hz) speed control, along with DSP filtering and dynamic bus ripple cancellation for quieter, more precise motor control. No software is required for operation. Other features include selectable PWM polarity, 50/60-Hz base speed, and up to 32-bit, high-precision internal calculations. An Internet enabled MC3PHAC system allows remote control of the motor via a PC. Pricing that starts at $4.95 each. Motorola Semiconductor Products Sector www.motorola.com/semiconductors
32-bit mixed signal DSPs with 150 MIPS capability
Houston, TX -New TMS320F2810 and TMS320F2812 mixed-signal 32-bit DSPs offer 150 million instructions per second (MIPS) plus features such as single-cycle 32 x 32-bit MAC capability, huge Flash memory, 12-bit analog-to-digital converter (both on-chip). These processors give designers a complete system-on-a-chip. They combine the DSP's efficiency for math-code with the general-purpose processor's ease and system-code efficiency to speed-up the development process. To provide simple reprogramming during development and in-field software updates, F2810 DSP integrates 64 Kw (kilowords) of Flash memory, while F2812 DSP integrates 128 Kw. Optimized event managers include a pulse-width modulation generator. F2810 low-profile quad flat pack (LQFP) is priced at $17.98 and F2812 microstar ball-grid array (and LQFP version) costs $22.99 in 10 ku quantities. Texas Instruments www.ti.com
Chips have 20 Megasamples/sec A/D converter
Norwood, MA -ADSP-2199x family of mixed-signal DSPs integrates a 160 MIPS, C/C++ programmable DSP core with a 14-bit, 20 Msamples per second analog-to-digital converter (ADC), and various motor-control peripherals. Embedded control peripherals include a three-phase PWM generation unit (for control of power switching converters); 32-bit incremental encoder interface (with noise filtering, flexible speed-measurement hardware, flexible reset and latching modes); dual auxiliary PWM outputs (for control of secondary switching circuits, such as power factor corrected front-end converters or dynamic dc link braking circuits); and a watchdog timer. The DSP is implemented in 0.25-micron CMOS technology. Serial communications support consists of SPI, SPORT, and CAN. Analog Devices Inc. www.analog.com
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