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Sensor-Based Motion Planning of Robotic Arm Manipulators

Motion control of robotic arms with sensor skin information

Work at Yale

In 1985, after graduating from WPI, I transferred to Yale University.  Once there, one of the first classes I took was with Prof. Vladimir Lumelsky in the robotics/electrical engineering department.  That fall, he had just started his professorship after working at General Electric's robotics department.  Prof. Lumelsky's research direction was motion planning of wheeled vehicles or arm manipulators, and he was looking for a student with hardware experience.  I was soon building sensor circuits and running the GE P5 robot arm he brought from his previous post.

Prof. Lumelsky described to me that he wanted someone to help him build a sensor 'skin' for a robotic arm, which would allow it to maneuver and move around in a cluttered and unknown environment.  This had not been done before in the field of robotics, and would be a great way to work on my dissertation.


The first proximity sensor array prototype.  


A closeup of the acrylic strip that holds the optical components.  The
emitter is in the exposed black hole, and the receiver is covered by
red tape to cut down on ambient light.

I started by building a sensor array arranged in a single line.  The components were mounted on standard printed circuit board material, and a black acrylic strip functioned as the means to mount the emitter-receiver pair, preventing direct coupling of light.  This was then placed on the surface of a PUMA 560 robot arm, and the motion of the arm limited to a plane.  In this two dimensional arrangement, the sensor system could detect obstacles that obstructed the motion of the arm.  


The linear array sensor mounted on a PUMA robot arm.


Almost the entire perimeter of the arm is covered including the tip of the arm.

Our first paper describing this work was an internal technical report of the Electrical Engineering department.


Later that year, we edited this paper and published it at the 1988 IEEE International Conference of Robotics and Automation (ICRA-88), which took place in Philadelphia, PA.


We then took this paper through the peer review process and it was published with several edits in the IEEE robotics journal.


I spent the summer of 1988 at the Philips Labs in Briarcliff Manor, NY, under the direction of Dr. Leo Dorst.  Prof. Lumelsky had a research agreement with this facility, and I used the PUMA robot arm that was there for the installation of the linear sensor array.  I then wrote the software to move the arm under closed-loop sensor control around an unknown environment.

Having completed the work in 2D, where we use only two joints of the arm to restrict its motion to a plane, I now had to find a way to wrap the entire surface of a robot arm in proximity sensors, and perform the same work in full three-dimensional space.


The two dimensional sensor array was built using flex
circuit board material.

The approach I thought of was to build the sensor skin out of flexible circuit board material, and fasten this to the arm.  This substrate would allow both electrical connection of the circuitry as well as mechanical support.  I drew the artwork for the circuit board on my Macintosh computer, ordered the board, and built the sensor.  


Close-up view of the sensor skin.  One can see the electro-optical components.
The flex circuit board was built by Bar-Pat, Inc in Bridgeport, CT.


One complicated part of the skin was the main elbow joint of the P5 robot.  
Near the bottom of this image, one can also see the cable connecting the sensor array.  
By using a serial protocol, the cable is very slender and easy to manage.

The hardware details of this skin was published in an internal technical report.


This paper became my submission to ICRA-89, held in Scottsdale Arizona.


It was at this conference that I met Dr. Daniel Wegerif, who worked at the McDonnell Douglas Space Systems at the Kennedy Space Center.  He thought my research would be very useful to NASA, and was very interested in it.  We would continue our contacts in the coming years (update below).


In addition to the P5 arm, one can see here an input device next to
my elbow that was built to do this research.  Its kinematic structure
matches the robot arm's so that a user can move the big arm in an
intuitive manner by handling the small one.

Of course, the sensitive skin is not useful without an algorithm to use this data for motion planning of the entire arm, and I developed that next and it was described in our next technical report.


We then took this paper to ICRA-90, held in Cincinnati Ohio.


I spent the summer of 1989 at Philips Labs one more time, and this time worked on making an integrated circuit chip that would miniaturize the proximity sensor circuit into a single microchip.  They fabricated this onto a semiconductor wafer, but the project was terminated due to lack of funding.  I still have one of these manufactured wafers today.


Plot of the microchip we made at the Philips Lab along
with one of the manufactured silicon wafers.

Over the course of the the next year, we made improvements and augmentations to the motion control algorithm that uses the entire skin of sensors.  The improvements included an algorithm that followed the commands from a Mini-Master handcontroller unless an obstacle was encountered.  This controller matches the kinematic structure of the P5 arm, and creates a situation where the user can very intuitively command the big arm.  If an obstacle was encountered, the arm then stopped and performed a sliding motion along the obstacle (in a non-contact sense) to best comply with the commands.  In this simple control algorithm, it was not always possible to autonomously find a path around the obstruction, but the arm would always move in a 'safe' manner.  The operator would then use his/her view of the workspace to work out an overall path.


I called the input device the "Mini-Master".  An algorithm was developed to have the
big arm follow the little one unless an obstacle was encountered.

Another mode that is contained in the previous algorithm is one I called "repeller mode".  If the environment moved in the direction of the arm, it could 'push' (in a non-contact sense) the arm around.  This became one of my favorite ways of putting the arm into a desired configuration during setting up of robot experiments: I would simply push the arm into place.

However, these two functions were ancillary to the main operating mode I developed as part of my dissertation.  In this mode, the algorithm (using the skin sensor) autonomously searches the work space for a path from a starting point to a desired end point.  Although this seems easy at first glance, it had been Prof. Lumelsky's findings in his prior research that there is not always an intuitive solution.

One way Prof. Lumelsky illustrated this to others was to have one of his students develop a type of video game where a visitor is asked to move a robot arm through a cluttered environment using only skin sensor information.  Inevitably, the visitor would find it difficult to find a path in a time shorter than the automatic algorithm.


Prof. Lumelsky is here inside the robot workspace, and I (in the background)
am handling the Mini-Master to move the arm around him and obstacles.

We published a description of these algorithms in an internal technical report.


We reedited this paper, and submitted it to ICRA-91, held in Sacramento, CA.


Finally, to sum it all up, I published my doctoral dissertation in 1991.  It was the culmination of the work over the past several years.


Additional information on my doctoral dissertation also available on-line
at the ACM Digital Library here.

I wrote much of this thesis while working at the Kennedy Space Center in the summer of 1990.  Dan Wegerif had obtained a summer position for me at McDonnell Douglas, and we worked on a study to understand the amount of time the International Space Station would need to be serviced by astronaut crew once it was completed.  It made a strong case for robotic servicing in space.


Video of the sensitive skin project.

My thesis was subsequently reedited and tailored for publication in the following forms:
Most of the above publications have not been converted to pdfs at this point.

The years I spent at Yale were a great learning experience, and I am grateful to my mentor Professor Vladimir Lumelsky.  Shortly after I left Yale in 1991, he took another post at the University of Wisconsin, and continued his research there.  Then in 2004, he moved (coincidentally) to the Goddard Space Flight Center and retired in 2012 from there.

This work appeared in numerous newspaper articles.
See the bottom of the Press page.

I also worked on an SBIR with Merritt Systems Inc using a planar
3 DOF arm (early 1990s).

Moving to NASA

Thanks to Dan Wegerif, my work at KSC led me in 1991 to a post at the Goddard Space Flight Center (GSFC), where I started working at the robotics lab in the high bay of Building 11.  At the time, NASA was building the Flight Telerobotic Servicer (FTS), which was to be a compliment to the SPDM robot built by the Canadian Space Agency.

At GSFC, I switched from optical proximity sensors to a capacitance-based sensor developed by John Vranish and Lou Palumbo, called "Capaciflectors".  I made several improvements on this sensor, and used them in an array fashion as I did with the optical ones.


Among the manipulators in the lab were two 1607 arms from the
Robotics Research Corporation (RRC).


Close-up of the WAM/WAF end-effector of the RRC arm.  It is one that can
quick connect to a complimentary half, and has connectors
that mate electrical circuits.

We used the Capaciflector for obstacle detection and avoidance, and also in applications requiring careful alignment between the robot and its environment.  One example is the Worksite Attachment Mechanism/Worksite Attachment Fixture (WAM/WAF) end-effector that was developed by John Vranish.  In this application, we applied copper strips to the WAM/WAF, and wrote algorithms for it to be able to locate, center and mate to its other half.  In this manner, it could pick up tools, and perform robotic tasks.


A video showing the GSFC robot at work with its Capaciflectors.  

Another example is shown in the above video where we put Capaciflectors on the tool of the robot.  The tool in this case is a 7/16" nutdriver, which is standard on the Hubble Space Telescope (HST).  The system uses the Capaciflectors to locate and open the latches on a container meant for astronaut use.  This container, known as the Small ORU Protective Enclosure (SOPE), is how HST components are flown into space.  The robot in this case assists the astronaut crew by opening up containers and prepares the worksite for use.


Mosaicked image of the SOPE task experiment.

During these years, we published several papers, including:
  • E. Cheung, M Manzo, and R. McConnell, Using Capaciflectors for ORU Docking, Third Annual Conference on Intelligent Robotic Systems for Space Exploration, Nov 1991.
  • E.Cheung, Docking Orbital Replacement Units with Capaciflectors, Proc. 1992 International Symposium on Robotics and Manufacturing, Santa Fe, NM, November 1992.
  • S. Leake and E.Cheung, Recent Developments at the Goddard Engineering Test Bed, Proc. SPIE OE/Technology 92, Boston, MA, November 1992
  • E. Cheung, S. Leake, End-to-End Robotic Module Changeout Procedure on the Explorer Platform Spacecraft, Proc. 1993 SPIE Conference on Telerobotics, Boston, MA, 1993.
  • E. Cheung, Automated Work Site Preparation for the On-Orbit Servicing of Hubble Space Telescope, International Symposium on Robotics and Manufacturing, Maui, Hawaii, August 1994.
  • E. Cheung, J. Vranish, Use of Proximity Sensors for a Robotic Servicing Mission, Proceedings of the Tech Trends 2004 Conference, Pittsburgh PA., July 2004.
Most of the above publications have not been converted to pdfs at this point.

2007 Update

In 1995, FTS was canceled, and I transferred to the Hubble Servicing Project.  
Eventually, I would return to robotics during the Hubble Robotic Mission (2007)
where I (surprisingly) did more work with the Capaciflector,
and then the Robotic Refueling Mission (2011).


2019 Update
30 years after my presentation at the 1989 Conference on Robotics & Automation in Scottsdale Arizona, my work on JPSS-2 took me back to that city.  It occurred to me that it would be interesting to revisit the site of the conference, where I first met Dr Dan Wegerif, and where it all started.  After some Internet searching, I found the following information.

Site of the RAC 89
An Internet search showed me the location of the conference:
The Registry Resort

It became clear that the resort where the conference took place was no longer operating, but I did find a post card from the resort with its address on the back: 7171 N. Scottsdale Rd, Scottsdale, AZ.  It was only 20 minutes away from the site where we built the spacecraft so we visited one afternoon.  

At the resort
I reflected on the past 30 years with this post on Facebook.

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