copyright 2005 by saksit siriprayoonsak1 real-time measurement of prehensile emg signals master...

Copyright 2005 by Saksit Siriprayoonsak 1

Real-Time Measurement of Prehensile EMG signals

Master Thesis

Saksit Siriprayoonsak

Supervisor: Marko Vuskovic

Department of Computer ScienceSan Diego State University

August 24, 2005


Contents

Introduction EMG Overview Apparatus for EMG Measurement Implementation of EMG Capture Program Experimental Results Conclusion


Multifunctional Prosthetic Hand Control

A research in Robotics Laboratory, SDSU


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.


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


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


EMG Measurement Stages


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


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


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


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)


EMG Amplifier: Preamplifier (cont.)

BURR-BROWN INA2128 Application Information


EMG Amplifier: Preamplifier (cont.)

Gain Equation:

501

1 22

G

G

kGain

R

Rwhere R R

Find RG at Gain = 1,000:

1 50

2 2 ( 1)

1 50

2 (1000 1)

25.025

GR k

Gain

k

Find Gain at RG = 22 ohm:

501 1137.364

2 22

kGain

Preamplifier with Body Reference Circuit (1 channel)


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

Sign Changing Circuit (Inverting Amplifier Circuit)

For independent R1, R2, R3, and R4:

4

4

3

3

2

2

1

1

R

V

R

V

R

V

R

VRVout F

For R1= R2= R3= R4:

1 2 3 41

FRVout V V V VR

2

1

RVout Vin

R

For independent R1, and R2:

For R1= R2:VinVout


EMG Amplifier: Average Body Reference Circuit (Cont.)

Common Body Reference Output:

Average Body Reference Circuit

1 2 3 4

1 2 3 4

1

11 1

1 4.7

1

4

kVoutB VoutA

kk k

Bodyref Bodyref Bodyref Bodyrefk k

Bodyref Bodyref Bodyref Bodyref

1 2 3 4

1

4.7

kVoutA Bodyref Bodyref Bodyref Bodyref

k


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


EMG Amplifier: Filter (cont.)

Cutoff Frequency: Cutoff Frequency of 12 Hz:

RC High Pass Filter RC High Pass Filter

Cutoff Frequency of 12Hz

1

2cutofffRC

Hz

nFkf cutoff

12

66.11

150912

1


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


EMG Amplifier: Amplifier and Bias Adjustment (cont.)

Non-Inverting Amplifier Circuit

Non-Inverting Output:

3

1

1R

Vout VinR

3

1

1R

GainR



Amplifier Gain:

40

35

1

01

10

1

RGain

R

k

At :

040 R

Amplifier Circuit with Gain Adjustment

Amplifier Circuit with Gain Adjustment

At :

kR 20040 40

35

1

2001

10

21

RGain

R

k

k



Offset Adjustment for Voltage Follower

2R 2 0R Vadj VccCase 1: at 0% of : ( ohms; volts )

3

1

1R

GainR

3

1

1R

Vout Vin VccR

2RCase 2: at 50% of : ( ohms; volts )22 2

RR 0Vadj

3

21

1

2

RGain

RR

3

21

1

2

RVout Vin

RR

2RCase 3: at 100% of : ( ohms; volts )Vadj Vcc2 2R R

3

1 2

1R

GainR R

3

1 2

1R

Vout Vin VccR R

Output of the circuit:

( )Vout Vin Gain Vadj

1 2: where V Vadj V



Bias Adjustment Circuit

2R 2 0R Vadj VccCase 1: at 0% of : ( ohms; volts )

38

37

1

11

101.1

RGain

R

k

k

2RCase 2: at 50% of : ( ohms; volts )22 2

RR 0Vadj

38

4137

1

21

150

102

1.029

RGain

RR

kk

k

2RCase 3: at 100% of : ( ohms; volts )Vadj Vcc2 2R R

38

37 41

1

11

10 501.017

RGain

R R

k

k k

_ ( ) 9Vout final Vout Amp V

Output of the circuit:

: 9 _ 9 volts.where Vout final V


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


Final Product Assembly

• Circuit designed and tested on breadboard• Schematic created by Multisim8• PCB layout created by Ultiborad7


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.



PCB shipped by the manufacturer



PCB after soldering


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.


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


EMG Capture: User Interface


EMG Capture: Main Parameter Subpanel

• Working with Real-Time mode and Record mode.

• Maximum Buffer Size (Samples per Channel)• Sampling Rate (Hz)


EMG Capture: Play Mode


EMG Capture: Real-Time Mode

- Start real time mode

- Stop real time mode

- Freeze output display for examine interesting segments or save the data

- Resume real time mode

- Save data in buffer to file

START

STOP

Pause

Resume

Save


EMG Capture: Record Mode

- Start to Record the signals in specific time range in seconds.

- Save the data to file

START

Save


EMG Capture: Playback Mode

- Open EMG data file (.emg)Open

Standard window open dialog


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.


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.


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.


EMG Capture: Readout

• Read extract value at pink vertical line• Need not to compute the value of scale• Unit: Time (sec) , Voltage (V)


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


EMG Capture: Status Bar

• Guide user through the usage• Display important message

eg. Number of samples that went into the buffer.


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


EMGC Implementation: Output Buffer Structure

• CArray class from MFC Library used to store input signal data.

• CArray can dynamically shrink and grow if necessary.

struct SOutputData

{

int output_ii; //Iteration start from 0

double time; //Time stamp in Second

double volt1; //Voltage value for CH1, CH2, CH3, and CH4

double volt2;

double volt1;

double volt1;

};

CArray <SOutputData, SOutputData> dumpDataArray;


EMGC Implementation: Creating Voltages and Time Scales

• 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.

//For Calculation

double voltScaleSet[5] = {5.0, 2.5, 1.0, 0.5, 0.2}; //unit in volt/div

//For Screen Display

CString voltScaleStrMap[5] = {“5 Volt/Div”, “2.5 Volt/Div”,

“1 Volt/Div”, “500 mVolt/Div”, “200 mVolt/Div”};


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)


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; // _maxTimeDiv*_ptsPerDiv, Max Drawing Point for // time

int _maxDrawPtsY; // _maxTimeDiv*_ptsPerDiv, Max Drawing Point for volt

//Default x=1500, y=400


EMGC Implementation: Draw Grid for Graph Output (cont.)


EMGC Implementation: Drawing Graph Output

_ ptsPerDivdrawValueX time startTime

curTimeScale

Function CEMGCDlg::voltToDC()

_ _

2

ptsPerDiv maxDrawPtsYdrawValueY volt

vScale

Function CEMGCDlg::voltToDC()

The output can be drawn by using (x,y) coordinate to specify position to draw.


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).


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; //Iteration start from 0

double time; //Time stamp in Second

double volt1; //Voltage value for CH1, CH2, CH3, and CH4

double volt2;

double volt1;

double volt1;

};

CArray <SOutputData, SOutputData> dumpDataArray;


ResultsOur EMG Amplifier ME3000 Muscle Tester

A comparison of cylindrical grasp recorded from our EMG amplifier and ME3000.


Results (cont.)Our EMG Amplifier ME3000 Muscle Tester

A comparison of preshaping of cylindrical grasp recorded from our EMG amplifier and ME3000.


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.


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 siriprayoonsak1 real-time measurement of prehensile emg signals master...

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