Digital Signal Controllers and
their Applications in
Mechatronics
Dr. Tarek Tutunji
SSD08, July 20-23, 2008
Amman, Jordan
Abstract
Mechatronics engineering has gained much attention in recent years.
As the requirements for real-time, fast, and accurate controllers increased, the use of Digital Signal Processors (DSP) as controllers gained momentum.
This is due to the fact that DSP architecture has many advantages over regular microcontrollers.
DSP has many applications in mechatronics such as hard disc drives.
Presentation layout
This presentation will be divided into:
1. Mechatronic Systems Overview
2. Digital Signal Controllers (DSC)
3. DSC Applications
4. Hard Disc Drives (HDD)
5. DSC in HDD
6. Summary
1. Mechatronic Systems Overview
Definition: What is Mechatronics?
Mechatronics Engineering is the
• Analysis
• Design
• Manufacturing
• Integration
• and maintenance
of mechanics with electronics through intelligent computer control.
History
Mechanical Engineering experienced an exponential growth in the early 19th century because of the industrial revolution.
The rise of semiconductors in the 1950s and computers in the 1980s have revolutionized all engineering products and processes which in turn affected mechanical engineering systems.
The term mechatronics was first used in the late 1960s by a Japanese Electric Company to describe the engineering integration between mechanical “mecha” and electronics “tronics” systems.
Since then it has spread throughout Europe and is growing is the USA.
Today, many mechanical systems use some form of electronics and computers to control its functionality.
Mechatronics system engineering has gained much recognition and importance in the industrial world.
Mechatronics Main Components
Source: Wikipedia
Block Diagram for General
Mechatronic System
ActuatorsElectrical Motors,
Pneumatic, Hydraulic
Mechanical system
SensorsInductive, Capacitive, Resistive, Ultrasonic,
Photo
Conditioning & Interface
Input:A/D, Filter, Amplifier
Output:D/A, Power
Circuit
Control Architectures
mcontroller, PLC, PC, DSP Control Algorithm
Graphical display
LED, LCD, CRT
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 mechatronic system.
Since mechatronics involves intelligent software design, programmable digital controllers are often used.
These controllers are usually embedded in microcontrollers or Programmable Logic Controllers (PLCs).
Due to the rapid needs for fast and accurate responses, Digital Signal Controllers (DSC) are becoming the controller of choice.
2. Digital Signal Controllers
Digital Signal Processing (DSP)
Digital Signal Processing (DSP) is the arithmetic processing of discrete-time signals.
A/D is needed for analog signals.
The increasing importance of DSP in the 1980’s led major electronics manufacturers, such as Texas Instruments and Motorola, to develop Digital Signal Processor chips.
Commonly used DSP Operations
Convolution
Correlation
Fourier Transform
Power Spectrum
Digital Filtering
DSP Operations: Convolution Consider a system h(n) with input x(n) and output y(n)
h(n)x(n) y(n)
X(Z)H(z)Y(Z)
h(n)*x(n)y(n)
Then,
The convolution of two signals, x(n) and h(n), is given by
-k
k)x(n)h(nh(n)*x(n)y(n)
•One signal is flipped and shifted with respect to the other .•Each element of one signal is multiplied by the corresponding element of the other.
•All the elements are summed. •Correlation requires a lot of calculations.
DSP Operations
Correlation between two signals is a measure of the degree to which the two signals are similar
The cross-correlation of two signals, x(n) and y(n), is given by
-k
xy k)x(n)y(n(k)r
The Discrete Fourier Transform (DFT) is a discrete numerical equation that transforms signals from the time-domain to the frequency-domain using sums of sinusoids.
1N
0n
knN
2πj-
k
0n
jω-jω
x(n)eX
x(n)e)X(eBy 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 domain
while others are easier to visualize in the time domain .
A digital filter uses a digital processor to• perform numerical calculations on sampled values of the
signal in order to pass wanted frequencies and block unwanted ones.
• The analog input signal must first be sampled and digitized using an ADC.
FIR Filter
Computing 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 and
repeat steps 2 6.
Finite Impulse Response (FIR) filters contain only zeros and therefore depend only on inputs. FIR is presented as:
1-L
0ii i)x(ncy(n)
FIR Block
Digital Signal Processors (DSP)
DSP chips are specialized microprocessors (i.e. programmable devices with its own instruction code) with architectures designed to reduce the number of instructions and operations necessary for efficient signal processing.
The programmable flexibility of DSP chips enables developers to implement complex algorithms in software.
DSP chips are used to perform computationally efficient and fast algorithms, such as Digital Filtering, Spectral Analysis, Parameter Estimation, and Data Compression.
Implementing DSP, especially in real-time, is generally treated separately from the theory.
DSP for Control Systems
The simultaneous development of “digital control theories" and Digital Signal Processing offers an opportunity for practical implementation of advanced control techniques.
As a result, sophisticated control-system applications using DSPs have increased exponentially 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 require the 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 enabling developers to close the control loop quickly • parallel processing• parallel multiply and add• multiple memory accesses (to fetch two operands and store
the 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 of
interrupt servicing by the CPU.• Ultra-fast A/D with dual sample and hold enable controllers to
capture data efficiently with low peripheral overhead.
Controller Algorithms used in DSC
PID• if the parameters of the actuator (its
mass, new motor, friction) are changed, new PID parameters can be reprogrammed quickly.
Neural Networks.
Fuzzy.
Adaptive Control.
State-Space based-control.
Digital Control Block Diagram
PID
)n(eT
T)n(e
T
T)n(e
T
T
T
TK)n(u)n(u
)in(eK)n(e)n(eK)n(eK)n(u
DDD
I
iIDp
212111
1
Neural Nets
TDL
TDL
Weights
Weights
Log
Function+ Weights +
Log
Function
Plant
Output
Plant
Input
Net
Output
First Layer Second Layer
Fuzzy
Fuzzifier Defuzzifier
Fuzzy
Inference
Engine
Fuzz Rule
Base
Architecture Features
Modified Harvard
Instructions Pipeline
Hardware Multiplier
Barrel Shifter
RISC
Modified Harvard Architecture
A Harvard architecture employs separate program and data buses to access separate data and program memories.
A modified Harvard architecture.
• DSP use multiple data buses (and multiple associated address buses) so that the processing of two signals can be done in parallel.
• The address buses are also separate. This multiple bus arrangement increases speed since instructions and data can move in parallel, and execute simultaneously rather than sequentially.
Modified Harvard Architecture
DAGENA
DAGENBMemory
AMemory
B
ALUMultiplier
Shifter
Accumulators
ShifterMemory
C
DAGENC
Instruction Pipelining
Up to six levels of pipelining are implemented.
DSP can execute instructions in parallel
Overall execution times are accelerated so that high
Hardware Multiplier
A 16- by 16-bit hardware multiplier multiplies and stores results in a 40-bit accumulator (8 guard bits) in a single instruction cycle.
Thus, multiply and accumulate operations can be performed in a single clock cycle in a DSP; conventional processors may require tens of cycles for this operation.
Shifters and RISC
Hardware shifters allow scaling, prevent overflows, and maintain required precision.
An on-chip hardware stack reduces interrupt response time and minimizes stack pointer manipulations.
DSC use reduced instruction sets tailored to digital signal processing operations. For example, the MACD command implements four operations in one instruction: • multiplies two values• moves data• adds the product to a previous result• transfers the result to an adjacent register.
Digital Signal Controllers
Manufacturers
Texas Instruments.
• TMS320C2000™ DSP Platform
Microchip.
• dsPIC30F3010
Motorola
TMS320C2801
dsPIC: DSP Engine Block Diagram
Custom made DSP Engines
3. Digital Signal Controller
Applications
DSP Applications
Filtering
Speech Processing and Recognition
Signal analysis
Image Processing
Data Communication
Waveform Generation
Target Track and RADAR processing
Control
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: Automotives
Automotives: engine performance, cruise control, power steering, and anti-lock brakes.
DSC Applications: Military
Military: missile control, targeting, aircraft and jet engine control
DSC Applications: HDD
HDD: Head seek and tracking control, spindle motor control, data READ/WRITE filtering, and bus control.
Other DSC Applications
Industrial Applications:• precision tooling machines, smooth operations
of nonlinear electric machines, and HVAC.
Office Equipment:• position and speed control using AC motor
control of copiers and printers.
Robotics:• Multi-axis and multi-variable linear and
nonlinear controllers for industrial, medical, and military applications.
4. Hard Disc Drives
Hard Disc Drives: HDD
Hard disc drives are the main storage 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 Mechatronic Systems
Mechanical Parts
The Mechanical parts are all assembled in a sealed chamber referred to as Head Disk
Assembly (HDA)
The HDA includes
• Platters or Discs
• Spindle Motor
• Actuator Arm
• Voice Coil Motor
• Read/Write Heads
Mechanical: Actuators
Mechanical: Platters or Discs
Made of aluminum alloy coated with a magnetic medium
Stores the data in magnetic patterns
Each Platter (Disc) is divided into tracks
• The tracks have circular shapes around the center spindle and are grouped into cylinders
• The cylinders are divided into sectors of 512 bytes each
Servo Information (stored between data sectors) is used for positioning
Mechanical: Spindle and
Voice Coil Motors The discs are stacked on top of each other through a
shaft
The Motor Spindle turns the whole assembly
Magnetic read/write heads are mounted on the end of an Actuator Arm that flies at each side of the platters
The Voice Coil Motor moves the actuator arm
Electronic Parts
The Electronic parts are assembled on a Printed Circuit Board (PCB)
The PCB includes the following Integrated Chips (ICs)
• DSP
Interface Controller
R/W Channel
Motor Controller
• Memory
5. DSC in HDD
DSC in HDD
DSP is becoming the standard in hard disk servo systems.
Ever-increasing bandwidths of HDD control loops requires a digital controller to complete calculations in only a few microseconds.
HDD requirements impose the following on control loops;• Thousands of tracks-per-inch to increase track capacity• Increased speed and accuracy for the spindle motor• Reduced power to maximize operating time from a
battery pack• Make the HDD resistant to disturbances coming from
numerous electrical and mechanical shocks.
Electronics Block Diagram for HDD
Electronics (PCB) Mechanical (HDA)
Motor
Controller
R/W
Channel
DSP
Memory
Interface
Controller
P
C
H
O
S
T Platters
Spindle
Motor
Arm
DSC in HDD are used for
Head seeking and tracking controls.
Spindle motor control.
Arm position control.
Data READ/WRITE filtering.
Shock /vibration control
Bus control.
• Supervises the transfer of data between the host and the disks.
• Organizes the Interaction between all the other ICs
Block Diagram for Track Following
5. Summary
Summary
An essential block in Mechatronic systems is the Controller.
Digital Signal Controllers have unique architecture that makes them ideal for Digital Control Algorithms.
DSC are becoming the controller choice in many mechatronic systems.
One example is the HDD where the DSC controls the VCM and spindle motors (for fast and accurate responses), R/W data, communication protocols, and shock/vibration.