Transcript ppt - San Diego State University

Real-Time Measurement of
Prehensile EMG signals
Master Thesis
Saksit Siriprayoonsak
Supervisor: Marko
Vuskovic
Department of Computer Science
San Diego State University
August 24, 2005
Copyright 2005 by Saksit Siriprayoonsak
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Contents






Introduction
EMG Overview
Apparatus for EMG Measurement
Implementation of EMG Capture Program
Experimental Results
Conclusion
Copyright 2005 by Saksit Siriprayoonsak
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Multifunctional Prosthetic Hand Control
A research in Robotics Laboratory, SDSU
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Object of Thesis
Main purpose:
 Design and develop hardware and software for
measuring surface EMG signals from real
human muscles in real-time.
Immediate application:
 To control the existing SDSU multifingered robot
hand.
Copyright 2005 by Saksit Siriprayoonsak
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EMG Overview
• EMG – Electromyography
• Electromyography measures the electrical impulses of muscles at
rest and during contraction.
• Amplitudes of EMG signal range between 0 to 10 mV (peak-to-peak)
or 0 to 1.5 mV (rms).
• Frequency of EMG signal is between 0 to 500 Hz.
• The usable energy of EMG signal is dominant between 50-150 Hz.
Source:
http://www.delsys.com/library/papers/SEMGintro.pdf
Copyright 2005 by Saksit Siriprayoonsak
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Amplification of EMG Signals
Factors to be considered:
• Boost signal to TTL standard level (± 5 V.)
– Enough gain
• Noise/Artifact problem
– Filter, stability of electrodes attached to skin, proper
grounding
• DC offset or bias problem
– Bias adjustment
• Power consumption
– Consume less current
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EMG Measurement Stages
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EMG Amplifier: Electrode and Extension
• Stereo phone wire with 3 conductors
– Positive input to preamplifier
– Negative input to preamplifier
– Shield as the input of body reference circuit
• Velcro strap for securing the electrode to the skin
Copyright 2005 by Saksit Siriprayoonsak
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EMG Amplifier: Electrode and Extension
(cont.)
•
•
•
•
Plastic piece and snap on for holding electrode elements
Dimension of 1 inch between electrode contacts
4 electrode extensions and 1 body reference extension
Total of 9 electrode contacts
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EMG Amplifier: Power Supply
• Dual Supply
– Positive Power Supply
– Negative Power
Supply
• Two 9-volt batteries
connected in series
• Capacitors provide
stability of electrical
current.
Power Supply Unit Circuit
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EMG Amplifier: Preamplifier
• Industry standard instrumentation amplifier
op-amp (INA2128)
– Accuracy: providing high bandwidth at high
gain and output offset current
• Differential amplifier circuit with 2 inputs
• High gain to boost the EMG signals
• Body Reference Circuit or Feed Back
(OPA2604)
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EMG Amplifier: Preamplifier (cont.)
BURR-BROWN INA2128 Application Information
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EMG Amplifier: Preamplifier (cont.)
Preamplifier with Body Reference Circuit (1 channel)
Gain Equation:
Find RG at Gain = 1,000:
50k
RG
RG 1
50k 
 
2
2 (Gain  1)
1
50k 
 
2 (1000  1)
 25.025 
Gain  1 
where
RG
 R1  R 2
2
Find Gain at RG = 22 ohm:
Copyright 2005 by Saksit Siriprayoonsak
Gain  1 
50k
 1137.364
2  22
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EMG Amplifier: Averaging Body Reference Circuit
• Common body reference circuit for 4 channels
• Using summing amplifier circuit and sign changing circuit
Inverting Summing Amplifier Circuit
For independent R1, R2, R3, and R4:
Sign Changing Circuit
(Inverting Amplifier Circuit)
For independent R1, and R2:
V V
V
V 
Vout   RF  1  2  3  4 
 R1 R2 R3 R4 
For R1= R2= R3= R4:
Vout  
Vout  
R2
Vin
R1
For R1= R2:
RF
V1  V2  V3  V4 
R1
Vout  Vin
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EMG Amplifier: Average Body Reference Circuit
(Cont.)
Average Body Reference Circuit
Common Body Reference Output:
VoutA  
1k
 Bodyref1  Bodyref 2  Bodyref3  Bodyref 4 
4.7k
1k
VoutA 
1k
 1k  1k 
    
  Bodyref1  Bodyref 2  Bodyref3  Bodyref 4 
 1k  4.7k 
1
  Bodyref1  Bodyref 2  Bodyref3  Bodyref 4 
4
VoutB  
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EMG Amplifier: Filter
• Suppress noise that has been amplified by
the preamplifier
• Help to sink any DC current that cause
bias to the output
• Select particular signal frequency range
• Use RC High Pass Filter of 12 Hz
Copyright 2005 by Saksit Siriprayoonsak
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EMG Amplifier: Filter (cont.)
RC High Pass Filter
Cutoff Frequency:
 1 
f cutoff  

 2 RC 
RC High Pass Filter
Cutoff Frequency of 12Hz
Cutoff Frequency of 12 Hz:
1


f cutoff  

 2  91k  150nF 
 11.66
 12Hz
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EMG Amplifier: Amplifier and Bias Adjustment
• Provide abilities to amplify and adjust
reference level of output signals
• Individual amplifier and bias adjustment
unit for each channel
• Use Non-Inverting circuit for amplifier unit
• Use Voltage Follower Offset Adjustment
circuit for bias adjustment unit
• Provide Gain of 21 times
• Provide Offset of ± 9 volts
Copyright 2005 by Saksit Siriprayoonsak
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EMG Amplifier: Amplifier and Bias Adjustment
(cont.)
Non-Inverting Amplifier Circuit
Non-Inverting Output:
 R 
Vout  Vin 1  3 
 R1 
 R 
Gain   1  3 
R1 

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EMG Amplifier: Amplifier and Bias
Adjustment (cont.)
Amplifier Circuit with Gain Adjustment
Amplifier Circuit with Gain Adjustment
Amplifier Gain:
At
R40  0:
 R 
Gain  1  40 
 R35 
0 

 1 

 10k 
1
At R
40
 200k :
 R 
Gain  1  40 
 R35 
 200k 
 1 

10k 

 21
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EMG Amplifier: Amplifier and Bias Adjustment
(cont.)
Case 1: at 0% of R2 : ( R2  0 ohms; Vadj  Vcc volts )
Gain  1 
R3
R1
 R 
Vout  Vin 1  3   Vcc
 R1 
Case 2: at 50% of R2 : ( R2 
R3
Gain  1 
Offset Adjustment for Voltage Follower
Output of the circuit:
Vout  (Vin  Gain)  Vadj
where : V1  Vadj  V2
R2
ohms; Vadj  0 volts )
2
R1 
R2
2


R3
Vout  Vin 1 
R
 R1  2
2






Case 3: at 100% of R2 : ( R2  R2 ohms; Vadj  Vcc volts )
R3
Gain  1 
R1  R2

R3 
Vout  Vin 1 
  Vcc
 R1  R2 
Copyright 2005 by Saksit Siriprayoonsak
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EMG Amplifier: Amplifier and Bias Adjustment
(cont.)
Case 1: at 0% of R2 : ( R2  0 ohms; Vadj  Vcc volts )
Gain  1 
R38
R37
 1
1k
10k
 1.1
Bias Adjustment Circuit
Output of the circuit:
Vout _ final  Vout ( Amp)  9V
where :
 9  Vout _ final  9V volts.
R
Case 2: at 50% of R2 : ( R2  2 ohms; Vadj  0 volts )
2
R38
Gain  1 
R
R37  41
2
1k
 1
50k
10k 
2
 1.029
Case 3: at 100% of R2 : ( R2  R2 ohms; Vadj  Vcc volts )
Gain  1 
R38
R37  R41
1k
10k  50k
 1.017
 1
Copyright 2005 by Saksit Siriprayoonsak
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A/D Interface Card
•
•
•
•
NI 6220 M-Series Multifunction DAQ
Clock Speed: 8 Hz, up to 1 MHz
Analog Input Resolution: 16 bits
Number of Analog Input Channels: 8
Copyright 2005 by Saksit Siriprayoonsak
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Final Product Assembly
• Circuit designed and tested on breadboard
• Schematic created by Multisim8
• PCB layout created by Ultiborad7
Copyright 2005 by Saksit Siriprayoonsak
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Final Product Assembly (cont.)
• A schematic diagram is drawn using
Multisim8.
• Netlist contains all circuit connections.
• Netlist is transferred to Ultiboard7 for PCB
layout.
• PCB is a double layer (top copper layer
and bottom copper layer)
• Through holes connect between 2 layers.
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Final Product Assembly (cont.)
PCB shipped by the manufacturer
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Final Product Assembly (cont.)
PCB after soldering
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Calibration Procedure
• Each channel is individually calibrated.
• Input is equal to output (100 mV.)
• If an arbitrary gain is needed, the output is desired gain
value multiplied by input.
Copyright 2005 by Saksit Siriprayoonsak
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EMG Capture
• Provides 3 play modes: Real-Time,
Record, and Playback mode.
• Able to save and open EMG data to/from
file.
• Display features:
– Voltage scales
– Time scales
– Readout of exact values
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EMG Capture: User Interface
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EMG Capture: Main Parameter Subpanel
• Working with Real-Time mode and Record
mode.
• Maximum Buffer Size (Samples per Channel)
• Sampling Rate (Hz)
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EMG Capture: Play Mode
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EMG Capture: Real-Time Mode
START
-
Start real time mode
STOP
-
Stop real time mode
Pause
-
Freeze output display for
examine interesting segments
or save the data
Resume
-
Resume real time mode
Save
-
Save data in buffer to file
Copyright 2005 by Saksit Siriprayoonsak
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EMG Capture: Record Mode
START
Save
- Start to Record the
signals in specific
time range in
seconds.
- Save the data to file
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EMG Capture: Playback Mode
Open
- Open EMG data file (.emg)
Standard window open dialog
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EMG Capture: Voltage Scale
• Voltage scale is
independent for each
channel.
• Alternative voltage
scales:
–
–
–
–
–
200 mV/Div.
500 mV/Div.
1 V/Div.
2.5 V/Div.
5 V/Div.
Copyright 2005 by Saksit Siriprayoonsak
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EMG Capture: Time Scale
• All channels use the
same time scale
• Alternative time
scales:
–
–
–
–
–
–
–
1 mSec/Div.
5 mSec/Div.
10 mSec/Div.
50 mSec/Div.
100 mSec/Div.
200 mSec/Div.
400 mSec/Div.
Copyright 2005 by Saksit Siriprayoonsak
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EMG Capture: Time Slider
• Scroll time slider to view data from beginning to the end.
• The numbers on the left and right corner correspond to
the time stamp of the first and the last sample shown on
the output display screen.
• ‘5.416’ is 5 seconds and 416 milliseconds.
Copyright 2005 by Saksit Siriprayoonsak
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EMG Capture: Readout
• Read extract value at pink vertical line
• Need not to compute the value of scale
• Unit: Time (sec) , Voltage (V)
Copyright 2005 by Saksit Siriprayoonsak
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EMG Capture: Output Display
• Displays 4 channels
• Voltage: 4 divisions
– 2 positive divisions
– 2 negative divisions
• Time: 15 divisions
• Maximum Display:
– ±10 volts with 5 volts/Div.
– 6 seconds with 400
mSec/Div
Copyright 2005 by Saksit Siriprayoonsak
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EMG Capture: Status Bar
• Guide user through the usage
• Display important message
eg. Number of samples that went into the buffer.
Copyright 2005 by Saksit Siriprayoonsak
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EMGC Implementation
• Developed by using Microsoft Visual C++ tool
• GUI developed with MFC (Microsoft Foundation Class)
library
• Runs on Windows 2000 machine which has A/D
interface card installed
• A/D Interface Card: Multifunction Data Acquisition
(DAQ), M-6220 series from National Instrument
Company
Copyright 2005 by Saksit Siriprayoonsak
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EMGC Implementation: Output Buffer Structure
struct SOutputData
{
int output_ii;
double time;
double volt1;
double volt2;
double volt1;
double volt1;
};
//Iteration start from 0
//Time stamp in Second
//Voltage value for CH1, CH2, CH3, and CH4
CArray <SOutputData, SOutputData> dumpDataArray;
• CArray class from MFC Library used to store
input signal data.
• CArray can dynamically shrink and grow if
necessary.
Copyright 2005 by Saksit Siriprayoonsak
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EMGC Implementation: Creating Voltages and Time Scales
//For Calculation
double voltScaleSet[5]= {5.0, 2.5, 1.0, 0.5, 0.2};
//For Screen Display
CString voltScaleStrMap[5]
//unit in volt/div
= {“5 Volt/Div”, “2.5 Volt/Div”,
“1 Volt/Div”, “500 mVolt/Div”, “200 mVolt/Div”};
• Use spin control to select the scales.
• Spin control increase/decrease spin value by a
specific number of steps.
• Use spin value as the index of scale array.
Copyright 2005 by Saksit Siriprayoonsak
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EMGC Implementation: Draw Grid for Graph Output
• Use CDC class (Class Device-Context object) to draw
output on the screen.
• The CDC class is a class from the MFC library.
• CDC provides various kinds of drawing functions
(working with drawing tool, converting the coordinates,
drawing rectangles, drawing circles, drawing text,
changing the color)
Copyright 2005 by Saksit Siriprayoonsak
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EMGC Implementation: Draw Grid for Graph Output (cont.)
private:
//Variables for drawing output
int _maxTimeDiv; //Max number of divisions to display on Output-Panel
int _maxVoltDiv; //time axis = 15 divisions
//volt axis = 4 divisions (2 positive Divs)
//
(2 negative Divs)
int _ptsPerDiv;
//How many points are there in 1 division.
//1 point = 0.1 milimeter
//Default 100 points = 1 division is 1 cm wide
// ** Base on: Display Resolution= 1024 x 768
int _maxDrawPtsX;
int _maxDrawPtsY;
// _maxTimeDiv*_ptsPerDiv, Max Drawing Point for
// time
// _maxTimeDiv*_ptsPerDiv, Max Drawing Point for volt
//Default x=1500, y=400
Copyright 2005 by Saksit Siriprayoonsak
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EMGC Implementation: Draw Grid for Graph Output (cont.)
Copyright 2005 by Saksit Siriprayoonsak
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EMGC Implementation: Drawing Graph Output
The output can be drawn by using (x,y) coordinate to
specify position to draw.
Function CEMGCDlg::voltToDC()
 _ ptsPerDiv
  _ maxDrawPtsY 
drawValueY  
 volt   

vScale
2

 

Function CEMGCDlg::voltToDC()
 _ ptsPerDiv 
drawValueX  
   time  startTime 
 curTimeScale 
Copyright 2005 by Saksit Siriprayoonsak
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EMGC Implementation: Saving Data Buffer To File
• File Extension (‘.emg’)
• Header line contains
– Sampling rate (HZ)
– Record time period (sec)
• Data speparate by a
‘space’.
• Each record separated by
a ‘carriage return’ (put in
front).
Copyright 2005 by Saksit Siriprayoonsak
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EMGC Implementation: Read File To Data Buffer
• Read header file
– Sampling rate -> computes sampling period
– Record time period -> verifies the data file (completed or in
completed)
• Store data in buffer (dumpDataArray)
struct SOutputData
{
int output_ii;
double time;
double volt1;
double volt2;
double volt1;
double volt1;
};
//Iteration start from 0
//Time stamp in Second
//Voltage value for CH1, CH2, CH3, and CH4
CArray <SOutputData, SOutputData> dumpDataArray;
Copyright 2005 by Saksit Siriprayoonsak
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Results
Our EMG Amplifier
ME3000 Muscle Tester
A comparison of cylindrical grasp recorded from our EMG amplifier and ME3000.
Copyright 2005 by Saksit Siriprayoonsak
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Results (cont.)
Our EMG Amplifier
ME3000 Muscle Tester
A comparison of preshaping of cylindrical grasp recorded from our EMG amplifier and ME3000.
Copyright 2005 by Saksit Siriprayoonsak
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Conclusion
 This thesis presents an implementation of EMG amplifier
device and EMG Capture program.
 Major problems were:
• To reduce noise, moving artifacts, system grounding and DC
bias.
 Problems solved through:
• Proper choice of discrete components (resistors, capacitors, and
ICs)
• Proper design of circuitry
• Final implementation of the device using PCB technology
• Systematic experimentation with the prototype (implemented on
a breadboard)
• Extensive testing of the device after implementation and
executing final corrections.
Copyright 2005 by Saksit Siriprayoonsak
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Future Work
 EMG amplifier
• Smaller size of the housing unit.
• Eliminate electrode extensions
 EMG Capture program
• Add print feature
• Add properties feature for changing system
parameters
• Improve drawing ability
Copyright 2005 by Saksit Siriprayoonsak
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