Digital Signal Controllers And Their Applications In Mechatronics

Digital Signal Controllers andtheir Applications inMechatronicsDr. Tarek TutunjiSSD08, July 20-23, 2008Amman, Jordan

Abstract Mechatronics engineering has gained muchattention in recent years.As the requirements for real-time, fast, andaccurate controllers increased, the use of DigitalSignal Processors (DSP) as controllers gainedmomentum.This is due to the fact that DSP architecture hasmany advantages over regular microcontrollers.DSP has many applications in mechatronics suchas hard disc drives.

Presentation layoutThis presentation will be divided into:1. Mechatronic Systems Overview2. Digital Signal Controllers (DSC)3. DSC Applications4. Hard Disc Drives (HDD)5. DSC in HDD6. Summary

1. Mechatronic Systems Overview

Definition: What is Mechatronics?Mechatronics Engineering is the Analysis Design Manufacturing Integration and maintenanceof mechanics with electronics throughintelligent computer control.

History Mechanical Engineering experienced an exponential growthin the early 19th century because of the industrialrevolution.The rise of semiconductors in the 1950s and computers inthe 1980s have revolutionized all engineering products andprocesses which in turn affected mechanical engineeringsystems.The term mechatronics was first used in the late 1960s by aJapanese Electric Company to describe the engineeringintegration between mechanical “mecha” and electronics“tronics” systems.Since then it has spread throughout Europe and is growingis the USA.Today, many mechanical systems use some form ofelectronics and computers to control its functionality.Mechatronics system engineering has gained muchrecognition and importance in the industrial world.

Mechatronics Main ComponentsSource: Wikipedia

Block Diagram for GeneralMechatronic SystemActuatorsElectrical Motors,Pneumatic, HydraulicGraphicaldisplayLED, LCD, CRTMechanicalsystemConditioning &InterfaceOutput:D/A, PowerCircuitInput:A/D, Filter,AmplifierControlArchitecturesmcontroller, PLC, PC, DSPControl AlgorithmSensorsInductive, Capacitive,Resistive, Ultrasonic,Photo

Examples of Mechatronic Systems

Examples of Mechatronic Systems

Examples of Mechatronic Systems

Examples of Mechatronic Systems

Examples of Mechatronic Systems

Control in Mechatronic Systems Control is an essential part of a mechatronicsystem.Since mechatronics involves intelligent softwaredesign, programmable digital controllers areoften used.These controllers are usually embedded inmicrocontrollers or Programmable LogicControllers (PLCs).Due to the rapid needs for fast and accurateresponses, Digital Signal Controllers (DSC) arebecoming the controller of choice.

2. Digital Signal Controllers

Digital Signal Processing (DSP) Digital Signal Processing (DSP) is thearithmetic processing of discrete-timesignals.A/D is needed for analog signals.The increasing importance of DSP in the1980’s led major electronicsmanufacturers, such as Texas Instrumentsand Motorola, to develop Digital SignalProcessor chips.

Commonly used DSP Operations ConvolutionCorrelationFourier TransformPower SpectrumDigital Filtering

DSP Operations: Convolution Consider a system h(n) with input x(n) and output y(n)x(n)h(n)y(n)y(n) x(n) * h(n)Then, Y(Z) X(Z)H(z)The convolution of two signals, x(n) and h(n), is given by y(n) x(n)* h(n) x(n)h(n k)k - One signal is flipped and shifted with respect to the other . Each element of one signal is multiplied by the correspondingelement of the other. All the elements are summed. Correlation requires a lot of calculations.

DSP Operations Correlation between two signals is a measure of thedegree to which the two signals are similarThe cross-correlation of two signals, x(n) and y(n), isgiven by r xy (k) x(n)y(n k)k - The Discrete Fourier Transform (DFT) is a discretenumerical equation that transforms signals from the time-domainto the frequency-domain using sums of sinusoids.X(ejω) - jωx(n)e n 0Xk 2πj N 1 x(n)e N n 0 kn By lettingz ejw and w 2pf 2pk/N

DSP Operations Power Spectrum (or Frequency Spectrum) Decomposes a signal into its basic frequency components Shows the distribution of the power in the frequency domain some signals are easier to visualize in the frequency domainwhile others are easier to visualize in the time domain . A digital filter uses a digital processor to perform numerical calculations on sampled values of thesignal in order to pass wanted frequencies and blockunwanted ones. The analog input signal must first be sampled anddigitized using an ADC.

FIR FilterFinite Impulse Response (FIR) filters contain only zeros andtherefore depend only on inputs. FIR is presented as:L -1y(n) ci x(n i)i 0Computing the result requires the following steps:1. Fetch instruction from program memory.2. Fetch two operands, ci and x(n-i) from memory.3. Multiply ci by x(n-i) to obtain the product.4. Add product to the accumulator.5. Repeat steps 2,3, and 4 for i 1 to L-16. Store the result, y(n), in memory.7. Update pointers for ci and x(n-i) to get next sample andrepeat steps 2 6.

FIR Block

Digital Signal Processors (DSP) DSP chips are specialized microprocessors (i.e.programmable devices with its own instruction code) witharchitectures designed to reduce the number of instructionsand operations necessary for efficient signal processing.The programmable flexibility of DSP chips enablesdevelopers to implement complex algorithms in software.DSP chips are used to perform computationally efficient andfast algorithms, such as Digital Filtering, Spectral Analysis,Parameter Estimation, and Data Compression.Implementing DSP, especially in real-time, is generallytreated separately from the theory.

DSP for Control Systems The simultaneous development of “digital controltheories" and Digital Signal Processing offers anopportunity for practical implementation ofadvanced control techniques.As a result, sophisticated control-systemapplications using DSPs have increasedexponentially in recent years.The term “Digital Signal Controllers (DSC)”refers to the use of DSP as control elements

Digital Signal Controllers Additions and multiplications operations requirethe following: fetch two operands perform the addition or multiplication store the result or hold it for a repetition delay operation require the following: hold a value for later use Array operation require the following: fetch values from consecutive memory locations copy data from memory to memory

DSC Features DSC chips have a specialized architecture enablingdevelopers to close the control loop quickly parallel processing parallel multiply and add multiple memory accesses (to fetch two operands and storethe result) lots of registers to hold data temporarily deep pipelines specialized internal compute engines integrated peripherals. efficient address generation for array handling special features such as delays or circular addressing Communication peripherals used to reduce the burden ofinterrupt servicing by the CPU. Ultra-fast A/D with dual sample and hold enable controllers tocapture data efficiently with low peripheral overhead.

Controller Algorithms used in DSC PID if the parameters of the actuator (itsmass, new motor, friction) are changed,new PID parameters can bereprogrammed quickly. Neural Networks.Fuzzy.Adaptive Control.State-Space based-control.

Digital Control Block Diagram

PIDu( n ) K p e( n ) K D e( n ) e( n 1 ) K I e( n i )i T T T T u( n ) u( n 1 ) K 1 D e( n ) 1 2 D e( n 1 ) D e( n 2 ) T T TI T

Neural NetsPlantOutputTDLWeights PlantInputTDLLogFunctionWeights WeightsFirst LayerSecond LayerLogNetFunction Output

FuzzyFuzz RuleBaseFuzzifierDefuzzifierFuzzyInferenceEngine

Architecture Features Modified HarvardInstructions PipelineHardware MultiplierBarrel ShifterRISC

Modified Harvard Architecture A Harvard architecture employs separateprogram and data buses to access separate dataand program memories.A modified Harvard architecture. DSP use multiple data buses (and multiple associatedaddress buses) so that the processing of two signals canbe done in parallel. The address buses are also separate. This multiple busarrangement increases speed since instructions and datacan move in parallel, and execute simultaneously ratherthan sequentially.

Modified Harvard erAccumulatorsDAGENCMemoryCShifterDAGENB

Instruction Pipelining Up to six levels of pipelining are implemented.DSP can execute instructions in parallelOverall execution times are accelerated so that high

Hardware Multiplier A 16- by 16-bit hardware multipliermultiplies and stores results in a 40-bitaccumulator (8 guard bits) in a singleinstruction cycle.Thus, multiply and accumulate operationscan be performed in a single clock cycle ina DSP; conventional processors mayrequire tens of cycles for this operation.

Shifters and RISC Hardware shifters allow scaling, prevent overflows, andmaintain required precision. An on-chip hardware stack reduces interrupt response timeand minimizes stack pointer manipulations. DSC use reduced instruction sets tailored to digital signalprocessing operations. For example, the MACD commandimplements four operations in one instruction: multiplies two valuesmoves dataadds the product to a previous resulttransfers the result to an adjacent register.

Digital Signal ControllersManufacturers Texas Instruments. TMS320C2000 DSP Platform Microchip. dsPIC30F3010 Motorola

TMS320C2801

dsPIC: DSP Engine Block Diagram

Custom made DSP Engines

3. Digital Signal ControllerApplications

DSP Applications FilteringSpeech Processing and RecognitionSignal analysisImage ProcessingData CommunicationWaveform GenerationTarget Track and RADAR processingControl

DSP Tasks in Digital Control Systems Command generation Spline, polynomial, look-up tables Controller Efficient control algorithms, parameter estimation,vector control transformations, sensorless algorithms Signal Conditioning Notch filter, data smoothing and correction Power / Driver PWM generation, commutation control for AC motors,power factor correction

DSP Tasks in Digital Control Systems Modeling System and parameter identification, system simulation Diagnostic and Supervisory Current and voltage monitoring, temperature monitoring Communication Networking Host and peripheral communication and interface Noise Control Accoustic noise reduction, mechanical vibration control,measurement noise reduction

DSC Applications Automotives. Military. Hard Disc Drives. Industrial Applications. Office Equipment. Robotics.

DSC Applications: AutomotivesAutomotives: engine performance, cruise control,power steering, and anti-lock brakes.

DSC Applications: MilitaryMilitary: missile control, targeting, aircraft and jet engine control

DSC Applications: HDDHDD: Head seek and tracking control, spindle motor control,data READ/WRITE filtering, and bus control.

Other DSC Applications Industrial Applications: precision tooling machines, smooth operationsof nonlinear electric machines, and HVAC. Office Equipment: position and speed control using AC motorcontrol of copiers and printers. Robotics: Multi-axis and multi-variable linear andnonlinear controllers for industrial, medical,and military applications.

4. Hard Disc Drives

Hard Disc Drives: HDD Hard disc drives are the mainstorage units in Personal Computers. Network Storage Systems. Enterprise Workstations. DVD Players. Game Boxes.

HDD Components The Hard Disk Design include Electronic Parts Mechanical Parts The Mechanical Parts are used to Magnetically Store the data Rotate the disks and move the arm The Electronic Parts are used to Control the Mechanical movement Transfer Data between the Disks and the Host Hard Disks are a good example of MechatronicSystems

Mechanical Parts The Mechanical parts are all assembled in asealed chamber referred to as Head DiskAssembly (HDA) The HDA includes Platters or DiscsSpindle MotorActuator ArmVoice Coil MotorRead/Write Heads

Mechanical: Actuators