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DEVELOPMENT OF HARDWARES AND COMPUTER 

INTERFACE FOR A TWO-DEGREE-OF-FREEDOM ROBOT 

by 

CHARLES C. NGUYEN, Principal Investigator 

FARHAD J. POORAN,Graduate Research Assistant 

Department a+ Electrical Engineering 

The CatbaLic University of. America 

Mash i ng.i-ic?r? DiZ 200c14 

NASA 

GODDARD SPCICE FLIGHT CENTER 

June 1987 
SUMMARY 

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This report presents the research work performed at 

The Catholic University of America on the research grant 

entitled “Active Control of Robot Manipulator Compliance, I’ 

(Grant No. NAG 5-780). supported by NASA/Goddard Space 

Flight Center. The research was performed from November 

16th, 1986 to May 15th, 1987. 

In this report we first review the research results 

that have been obtained through the project. Then the robot 

actuator, the selection of the data acquisition system and 

the design of the power amplifier will be discussed. The 

machine design of the robot manipulator will then be 

presented, After that, we will discuss the integration of 

the developed hardwares into the open-loop system. The 

report is concluded by addressing the current and future 

research work. 
CONTENTS 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

a. 

9. 

Introduction and Previous Results 

The Robot Actuator 

The Data Acquisition System 

The Power Amplifier 

The Robot Manipulator 

The Open-Loop System 

Current and Future Work 

Conclusion 

References 

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Robotics has promising applications in the space 

a 

station program as pointed out in [ll, Assembly of large 

space structures can be performed by autonomous robots, 

Product assembly in space such as mating and fastening of 

parts requires a very high precision, Because of the 

enormous difference in tolerance between position and robot 

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manipulators, compliance should be provided to the 

manipulator so that it can comply with the task-imposed 

constraint 171. This can be done by employing the hybrid 

control scheme that controls position along specified 

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degrees of freedom and independently controls force along 

the remaining degrees of freedom [41. We started our 

analysis of the hybrid control scheme with the 

two-degree-of-freedom robot. In [71 the dynamics of a 

robot with two degrees of freedom was modeled, Then by 

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using the system simulation language (SYSL), the complete 

system including the actuators, the robot dynamics, force 

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and positon feedback was simulated on an IBM PC [Fig.ll. As 

pointed out in [8], proper adjustments of the controller 

gains enabled the robot to perform successful operations. 

Even though good results have been obtained, no clear 

relationship between the controller gains and the system 

responses have been identified. 

In order to test the performance of the hybrid control 

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scheme on a physical system, it was proposed to actually 

build the two-degree-of-freedom robot and interface it 

with an IBM personal computer through a data acquisition 

system. In the following, we will present the development 

of the hardwares for the robot implementation and design 

of the necessary electrical devices and computer 

interfaces, 

2. THE ROBOT ACTUATOR 

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Two ball screw actuators, manufactured by Motion 

Systems Corporation were used to implement the robot arms 

[Fig. 21. This is an in-line actuator that has a stroke of 

16 inches and is driven by a permanent magnet DC motor 

(24 VDC, 3000 RPM, 3" diameter, 2.5 Amps no-load current) 

[Fig. 31. The ball screw actuator 85262 if equipped with 

heavy duty brake, support bushing, cover tube, rod end and 

trunnion pins is numbered by 85261. 

3, THE DATA ACQUISITION SYSTEM 

The interfacing between the outside world consisting 

of the robot manipulator, drivers, sensors and the IBM 

computer is done through a data acquisition system, The 

data acquisition system consists of an IBM data 
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acquisition and control adapter , a dist.ribution panel 

and a selected software package running the system. We 

selected the Labtech Notebook software package because 

open and closed-loop control algorithms are readily 

implemented and PID (Proportional-Integral-Derivative) 

controllers can be set up for closed-loop control. The 

data acquisition and control adapter has 4 analog input 

channels (12-bit resolution) and 2 analog output channels 

(12-bit resolution). The voltage of the input and output 

channels can be selected to be either unipolar (0 to 10 

volts) or bipolar (2 5 volts or 2 10 volts). The input 

current assumes 5 4 milliamps at maximum input voltage. 

The maximum output load current is - +5 milliamps. 

4. THE POWER AMPLIFIER 

Since the maximum power that the data acquisition 

board can deliver is not sufficient (+lo V, +5 milliamps) 

to drive the DC motor whose no-load consumption is 

characterized by +24 volts and 2.5 amps, a power amplifier 

was designed to amplify the output signal of the data 

acquisition board. The design employed high-power 

operational amplifiers OPA501 manufactured by Burr-Brown 

corporation and compatible heat sinks 0805HS (3' c/watt), 

The maximum current (7 Amps) delivered by the power 

amplifiers can be set by selecting a proper resistor R . 

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In order to make the gain of the power amplifier 

adjustable, the feedback resistor R, was set to 

(fixed) and the value of the input resistance could be 

varied between 0 and 1OkD potentiometer [Fig. 51.The power 

amplifier was housed in an Archer instrument case whose 

front panel provided all necessary connections to power 

supplies, input from data acquisition board and output to 

DC motors. 

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Fig, 2 illustrates the two-degree-of-freedom robot 

manipulator that mainly consists of 2 ball screw in-line 

actuators, a fixed upper platform, motor cover tubes and 

connecting joints and bearings. The upper platform was 

made out of a 36x9~1 (inch) solid board that was secured 

to the concrete wall by 3 steel brackets. To hang the 

actuators under the upper platform, we made two aluminium 

tubes and slided them over the two motors. The actuators 

were then secured to the cover tubes by 2 bolts. 

Intermediate caps and bearings were used to attach the 

cover tubes to the upper platform. Each upper joint that 

allows rotation about the z-axis, consists of a linear 

pillow block, a shaft hanger and a steel shaft that were 

all manufactured by Winfred M. Berg Inc and were modified 

to fit the design of the robot, The essential part of 
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the design was the development of a joint to couple the 

two end points of the two actuators, Several types of 

joint were designed, tested and modified to optimize the 

gripper motion in terms of conversion of rotation to 

linear motion, vibration and workspace. The finalized 

joint consists of a shaft hanger, bearing mounting plate 

and a low friction ball bearing, Some mechanical parts 

were manufactured by Winfred M. Berg Inc and some were 

made by In-house machine shop. 

The overall dimensions of the robot is described 

below: 

-Width (distance between the 

attachment points of the 

arms to the upper platform): 

-Length of each arm 

(fully extended) : 

-Height (distance between 

the upper platform and the 

gripper) : 

29" 

51" 

51" 
6. - THE OPEN-LOOP SYSTEM ___L_----_____ 

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Fig, 6 illustrates the overall configuration of the 

hardwares and computer interface that have been developed 

up to now, This is mainly an open-loop system in which no 

sensors for position and force have been integrated. The 

completion of a closed-loop feedback system will be 

discussed in the next section, 

7. CURRENT AND FUTURE WORK 

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Currently and in the future we will make all efforts 

to accomplish the following: 

-Troubleshooting the open-loop system and making proper 

adjustments in the data acquisition board and in the power 

amplifiers, 

-Modifying the robot manipulator hardwares if needed, 

-Selecting a proper position sensor (LVDT) and a force 

sensor and integrating them into the open-loop system, 

-Using the Labtech Notebook software package to implement 

the hybrid control scheme, 

-Running the complete closed-loop system and making 

evaluations, 
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8. CONCLUSION 

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This report updated the development of the hardwares 

and computer interface for a two-degree-of-freedom robot. 

The robot manipulator was implemented by 2 ball screw 

actuators and necessary machine designs. A data acquisition 

system consisting of a data acquisition and control adapter 

and the Labtech Notebook software package was selected to 

interface the robot manipulator to the IBM computer. We 

then discussed the design of a power amplifier that drives 

the DC motor of the robot actuator. The integration of the 

developed hardwares into an open-loop system was then 

presented. The report was finally concluded by discussing 

all current and future work of the research project. 

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REFERENCES 

1. 

2. 

3. 

4. 

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5. 

6. 

7. 

8. 

9. 

NASA, "Advancing Automation and Robotics Technology 

for the Space Station and for the U.S. Economy, I' 

~01.11, NASA TM 87566, Advanced Technology Advisory 

Committtee, March 1985. 

Paul, Richards P. and Shimano, Bruce, I' Compliance 

and Control, I' Robot Motion, Plannins and Contxol. 

Brady, M. et al., eds, MIT Press, Cambridge, Mass.; 

1983. 

Whitney, Daniel E,, "Force Feedback Control of 

Manipulator Fine Motions, I' ASME, Journal of Dynamic 

Systems, Measurement and Control, June 1977. 

Raibert, M. H. and Craig, J. J., I' Hybrid Position/ 

Force Control of Manipulators,, I' ASME, Journal of 

Dynamic Systems, Measurement and Control, 102, pp. 

126-133, June 1981. 

Premack, Timothy et al., "Design and Implementation of 

a Compliant Robot with Force Feedback and Strategy 

Planning Software, I' NASA TM 86111, GSFC, May 1984. 

Nyuyen, Charles C. and Premack, Timothy, I' Active 

Compliant Control of Robot Manipulators, "NASA Report, 

NASA/GSFC, July 1985. 

Nguyen, Charles C. and Pooran, Farhad J., "Active 

Control of Robot Manipulator Compliance, I' SemiAnnual Progress Report, NASA/GSFC, November 1986. 

Nyuyen, Charles C. , Pooran, Farhad J.,and Premack, T. 

,"Control of Robot Manipulator Compliance, I' in Recent 

Trends in Robotics: Modeling, Control and Education, 

Chapter 2, edited by M. Jamshidi, Newyork, pp. 237-242 

, 1986. 

Dieudonne, J. E. et al, I' An Actuator Extension 

Transformation for a Motion Simulator and an Inverse 

Transformation Applying Newton- Raphson's Method, 

"NASA Technical Notes, NASA TN D-7067, November 1972. 
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ROBOT GRIPPER 

Fig. 2: The Robot Manipulator 
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ORIGINAL PAGE IS 

OF POOR QUALITY 

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10 14'1 6-32 1hre.d 

0805HS 3'C/WATT 

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Fig. 4: Elements of the Power Amplifier: a) Operational 

Amplifier, b) Heat Sink. 

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10 kohms Inputs 

from data acquisition 

and control adapter * - -*.$ -____- . - 

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POWER SUPPLY i 

Motor 

Fig. 5: The Power Amplifier 
2-DEGREE-OF-FREEDOM 

ROBOT MANIPULATOR 

TATA 

ACQUISI 

*TION & 

CONTROL 

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DISTRI POWER 

PANEL - 

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Fig. 6: The Organization of the Open-Loop System 

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Fig. 7: Bearings and Joints for the Robot