Helping Hand – 7 DOF

Haptic Robotic Arm Project

Group 10 – Spring 2013

Taylor Jones, Kurt Graf, Matt Carlson,

Eric Donley

University of Central Florida,

DEPARTMENT OF ELECTRICAL

ENGINEERING AND COMPUTER

SCIENCE, Orlando, Florida, P.O.Box

160000 Orlando, FL 32816, USA

Abstract -- The purpose of the senior design project,

from the course description of objectives is "To provide students a complete design experience, including the necessity to set design goals and objectives, integrate

knowledge, exercise engineering judgment, plan to meet a budget and schedule, to work as a team member, and to communicate in writing." To accomplish these

objectives our group, Helping Hand, designed a tele-operated master-slave 7 DOF robot arm which motion tracks a human operator's arm motion including open-

close hand tracking by the end-effector. The project is exclusively focused on the electronics and software to control an electrically operated robotic arm. Stock

mechanical robot arms were utilized as needed to accomplish the project. Index Terms — Haptic interfaces, Human robot interaction, Humanoid robots,

Intelligent robots, Intelligent systems, Robotics and automation, Robotic assembly, Robot control, Robot motion, Robot programming, Robot sensing systems, Tele-operators, Tele-robotics.

I. INTRODUCTION

The Helping Hand haptic robotic arm is

investigating robotics as smart (or skilled) as the

human operator, a new phase in human-robotic

interact-ability. Potential applications range from the

pure athletic application of Real Steel (Hollywood

robotic boxing movie) [1] or the Sci-Fi television

channels’ Robot Combat League [2] to augmenting

traditional robotic surgery (Da Vinci systems) [3], or

a simpler programming interface for increasingly

ubiquitous, light-assembly and manufacturing

robotics like RethinkRobotics’ Baxter[4].

Wiki describes haptics as: “Haptic technology, or

haptics, is a tactile feedback technology which takes

advantage of the sense of touch by applying forces,

vibrations, or motions to the user. This mechanical

stimulation can be used to assist in the creation of

virtual objects in a computer simulation, to control

such virtual objects, and to enhance the remote

control of machines and devices (tele-robotics).

Haptic devices may incorporate tactile sensors

that measure forces exerted by the user on the

interface.” [5] “It has been described as "doing for

the sense of touch what computer graphics does for

vision". [6] The new cheap and readily usable MEMS

gyros make motion analysis of a human operator

directly programmable into an embedded robotic

control system very facile and readily

accomplishable.

Essentially, the Helping Hand is an exteroceptive

control system “activated by, relating to, or being

stimuli received by an organism from outside

<exteroceptive feedback>.” [7] More simply, the

human operator provides spontaneous control

feedback of the human-robot interactive system. The

current system is direct mechanical control of the

robot arm by the human operator’s arm motion.

Potential future applications include a sensor glove

for human hand motion duplication - for skilled work

robotic duplication - or direct human - motion

programming e.g. programmer’s sensor jacket,

directly programming a humanoid worker robot in a

one-to-one learning/programming dynamic.

II. PROJECT DESCRIPTION

Our project is a Haptic Robotic Arm controlled by

Velcro strap mounted motion and force sensors on a

human operator's arm – which controls the motion-

tracking robotic arm's proportional motion. "These

robots have a wide range of industrial and medical

applications such as pick and place robots, surgical

robots etc. They can be employed in places where

precision and accuracy are required. Robots can also

be employed where human hand cannot

penetrate."[8]

III. PROJECT CONCEPT

Why study the human-operated robot arm? The

future of robotics in manufacturing and assembly is

increasing flexibility both in mechanical performance

and ubiquitous integration with human workers. The

future of robotics is greater dexterity, easier and

quicker programmability, and safe operation with

human co-workers. Building a tele-operated master-

slave robot arm driven by sensors worn on a human

arm is investigating future possibilities and general

performance considerations of advanced robotics. An

observation: in current formal academia, most studies

of robotics are only available at the graduate level.

Some graphic explanations of the idea:

Fig. 1 Basic concept of Haptic Robot Arm

Fig. 2 Motion capturing sensors mounted on human-operator’s arm

Fig. 3 Exteroceptive feedback control schematic

Fig. 4. System schematic of Helping Hand

IV. PROJECT DESIGN

Fig. 5 Plastic arm prototype OWI-535

Robotic Arm Edge

Beginning with a plastic robot arm prototype, a 3-

axis gyro sensor board was used to horizontally and

vertically rotate the arm base and shoulder-elbow

link. Next, a metal robot arm was acquired with 4 + 1

Fig. 6 Lynxmotion AL5D metal robot arm 5+1

degrees of freedom. Two additional degrees of

freedom were added at the wrist (rotatable) and

Fig. 7 Lynxmotion AL5D 6 + 1 DOF metal robot arm with 7 servos mounted

elbow (additional rotation) to the arm to better

approximate a human arm motion. The plastic arm

used five 3V dc motors to drive the linkages. The

metal arm uses seven 4.8-6.0 volt analog and digital

servo motors to power the final design motion.

V. COMPONENTS

A. MEMS Gyros and Accelerometers

MEMS (micro-electrical mechanical systems)

gyroscopes measure the rate of change around an

axis, which means to determine the amount of

angular change - needed for the robot arm control –

the output of the gyro has to be integrated to find the

amount of angular change.[9] The gyroscopes are

available in basic IC chip format. The physics of

operation of the gyro is a measured Coriolis force

that occurs when a massive object has both

translational and rotational motion simultaneously. If

a rotational motion is applied perpendicularly to the

direction of velocity of an object a Coriolis force is

developed by the right-hand-rule perpendicular to

both the velocity vector and the angular momentum

vector. A capacitive sensing mechanism measures the

force and the measurement is used to determine the

rate of change of angle of motion.

Fig. 8 MEMS 'two masses design' [9]

The MEMS device used is the MPU-6050

Fig. 9 MEMS implementation of above 'two masses design' [10]

Fig. 10 MEMS MPU-6050 4 x 4 x 1 mm (actual size) [11]

The gyro gives data in degrees/second. To

determine actual angle of rotation requires integration

with respect to time:

B. GYRO SENSOR PCB

Three MPU-6050 six-axis gyroscope-accelerometer

combination sensors were implemented on test

boards to measure the human-operator’s arm motion.

Fig. 11 MEMS 6-axis gyro-accelerometer test board

(1)

Fig. 12 MEMS test board pcb diagram

Fig. 13 close-up of MEMS test board for human operator’s arm

Fig. 14 Velcro mounted test board MEMS sensors for human operator’s arm motion detection

Fig. 15 MEMS test boards attached to human operator’s arm

C. FSR (Force Sensitive Resistor) SENSOR

A Force Sensitive Resistor exhibits the functionality

of increasing the force or pressure on the FSR causes

a reduction in the electrical resistance through the

FSR as illustrated in the graph below:

Fig. 16 FSR Resistance versus Force log-log curve [12]

The FSR circuit is implemented with a “simple

force-to-voltage conversion, the FSR device is tied to

a measuring resistor in a voltage divider

configuration” shown next:

Fig. 17 FSR signal acquisition [12]

“The output is described by the equation:

VOUT = (V+) / [1 + RFSR/RM]. (2)

In the shown configuration, the output voltage

increases with increasing force:”

“If RFSR and RM are swapped, the output swing

will decrease with increasing force. These two output

forms are mirror images about the line VOUT = (V+)

/ 2.

Fig. 18 FSR Resistance versus Force log-log curve [12]

The measuring resistor, RM, is chosen to maximize

the desired force sensitivity range and to limit

current. The current through the FSR should be

limited to less than 1 mA/square cm of applied force.

Suggested op-amps for single sided supply designs

are LM358 and LM324. FET input devices such as

LF355 and TL082 are also good. The low bias

currents of these op-amps reduce the error due to the

source impedance of the voltage divider.

A family of FORCE vs. VOUT curves is shown on

the graph above for a standard FSR in a voltage

divider configuration with various RM resistors. A

(V+) of +5V was used for these examples.”[12]

Fig. 19 1.5 inch square FSR for human operator end-effector (gripper) open-close [14]

D. CONTROL PCB

Initial developmental work was done on an Arduino

2560 mcu board. Final system performance is on an

Atmel ATxmega128A1 test board:

Fig. 20 MCU Schematic for robot arm controller

Fig. 21 MCU pcb diagram for robot arm controller

Of special importance to the mcu implementation is

the use of the TWI (two wire interface – serial data

and serial clock) to connect the gyro sensor boards

into the microcontroller.

E. MOTOR ACTUATORS OF ROBOT ARM

Although dc motors driven by motor driver boards

connected to an Arduino microcontroller unit were

used to operate the plastic prototype arm, the metal

arm linkages are all driven by digital (or analog

replacement) servo motors.

Of the three types of motors available to actuate a

robot arm (neglecting hydraulic) – dc, stepper, and

Fig. 22 Three types of motors to actuate robot arm [13]

servo – servos were chosen for their superior control

qualities and the fact that the current payload

(maximum of 13 grams) does not require much

power. Standard robot shop analog and digital servos

were obtained as needed to complete the project.

F. POWER SUPPLY

There are two basic operating voltages on the

system. The sensor and microcontroller boards

operate on 3.3 Volts DC and the servos operate on

4.8V to 6.0V DC and draw about 0.2 to 1.5 amperes

of current each. A very inexpensive and effective

shared dc power bus power supply was implemented

using a discarded and still functioning personal

computer power supply unit:

Fig. 23 Shared dc power bus power supply

An STM TO-220 LD1117AV33 low drop voltage

regulator was used to step down the standby 5 volt

supply from pin #9 of the PC power supply connector

to 3.3 volts. The 5 volt supply powers the servo

motors and the 3.3 volt supply powers the sensors

and mcu.

VI. SOFTWARE

Initial software development for both the plastic arm

prototype and the metal arm was done on an Arduino

2560 micro-controller.

Final software development is done on an Atmel

ATxmega128A4U in Atmel Studio software

available free of charge for 8/16 bit AVR micro-

controller at

http://www.Atmel.com/tools/Atmelstudio.aspx

The system control flowchart is:

Fig. 24 Operating flow chart

There is a significant amount of number-crunching

involved in converting the raw data of the very

sensitive gyro sensors:

X: -4 Y: 109 Z: -9 // these are values when the gyro isn't moving

X: -5 Y: 72 Z: -17 // they average near zero

X: 22 Y: 81 Z: 5

X: 13 Y: 75 Z: 30

X: 11 Y: 75 Z: 67

X: 9 Y: 89 Z: 4

X: 27406 Y: -2091 Z: -29629 // these are values after a quick

// move of the gyro

X: 35 Y: 67 Z: 12 // next values after motion stopped

X: 26 Y: 74 Z: 50 // back near zero

Fig. 25 Sample Gyro Data (degrees/second)

II. CONCLUSION

Although the project has not progressed to final

performance fine-tuning, a sequence of photos of a

team member demonstrating the arm:

Fig. 26 Hardware system without sensor sleeve

Fig. 27 3- Photo sequence of arm in use

The motion shown above was achieved using only

the accelerometer data. Utilizing the gyroscope

angle-rotation data should yield much smoother and

more accurate motion-mirroring.

As a point of observation about senior design

projects, it is crucial to maintain your original build

schedule! Helping Hand made an unwise design

change from developing from 4+1 to 6+1 to direct

development of 6+1 which created a delay of waiting

for the additional rotational (elbow) unit that was

followed by a vendor delay in component (servos)

delivery that cut available development time by at

least 50%.

“Wearing the arm sleeve was very comfortable. The

fact that the sensors were sewn onto the Velcro straps

made it very easy for adjustment. Using the arm

sleeve to control the arm was also a breeze. The wire

lengths to where the sensors were placed were taken

into account and allowed for no issues when the

operator moved their arm.” – Matt Carlson

REFERENCES

[1] Website: http://www.steelgetsreal.com/ [2] Website: http://www.syfy.com/robotcombatleague [3] Website: http://www.intuitivesurgical.com/products/davinci_surgical_system/ [4] Website: http://www.rethinkrobotics.com/ [5] Website: http://en.wikipedia.org/wiki/Haptic_technology [6] Website: http://www.isfh.org/GR-Virtual_Reality_TouchHaptics2009.pdf [7] def. exteroceptive Website: http://www.merriam-webster.com/medical/exteroceptive [8] Website: http://www.ijera.com/papers/Vol2_issue3/SQ2330983103.pdf [9] Accessed Nov. 18, 2012, Website: http://clifton.mech.northwestern.edu/~me381/project/done/Gyroscope.pdf [10] Accessed Nov. 21, 2012, Website: http://www.sensorsmag.com/files/sensor/nodes/2003/970/fig6.jpg [11] Website: http://invensense.com/mems/gyro/sixaxis.html [12] Accessed Nov 26, 2012, Website: http://www.pololu.com/file/0J383/fsr_datasheet.pdf from www.interlinklelectronics.com [13] Accessed Nov. 25, 2012, Website: http://openmoco.org/node/179 [14] Accessed Nov 26, 2012, Website: http://www.pololu.com/catalog/product/1645 [15] Accessed Mar 23, 2013, Website: http://www.lynxmotion.com/p-627-force-sensing-resistor.aspx

graduation he will be looking for employment in the

electrical engineering profession.

Email: mcarlson.ucf@gmail.com

URL:

www.eecs.ucf.edu/seniordesign/fa2012sp2013/g10

Currently two-thirds completed mba at UCF,

looking for employment after graduation while

finishing mba in evening courses.

Email: kgraf@knights.ucf.edu

Website:

www.eecs.ucf.edu/seniordesign/fa2012sp2013/g10

Email: tjones629@gmail.com

Website:

www.eecs.ucf.edu/seniordesign/fa2012sp2013/g10

Email: edonleyucf@knights.ucf.edu

Website:

www.eecs.ucf.edu/seniordesign/fa2012sp2013/g10

Candidate for

Bachelor of

Science in Electrical

Engineering UCF

spring 2013.

Previously graduated

from UCF in BS

electrical engineering

technology.

Matthew Carlson is

currently a senior at

the University of

Central Florida and

will receive his

Bachelors of

Science in Electrical

Engineering in May

of 2013. Upon

Taylor Jones is currently a senior at the University of Central Florida and will receive his Bachelors of Science in Computer Engineering in May of 2013. He has an interest in Artificial Intelligence, game design, and robotics.

Eric Donely is currently a senior at the University of Central Florida and will receive his Bachelors of Science in Computer Engineering in May of 2013. He has an interest in computers, electronics, and robotics.