LabVIEW Robotics

RAPHaEL: Another incredible robot design from RoMeLa September 29, 2009

A lot of you may have already heard about the second- generation air-powered robotic hand on Engadget from Dr. Hong and his engineering students at RoMeLa. But seeing as how NI and RoMeLa have been long time friends and have worked on many robotics projects together, we’ve got an inside story on how the new and improved RAPHaEL came to be. The following is a recap from Kyle Cothern, one of the undergrads that worked on RAPHaEL 2. He explains how closed-loop control for the mechanical hand was implemented in less than 6 hours, proof that seamless integration between hardware and software can make a big difference in robotic designs.

RAPHaEL (Robotic Air Powered HAnd with Elastic Ligaments) is a robotic hand that uses a novel corrugated tubing actuation method to achieve human like grasping with compliance. It was designed by a team of four undergraduate students working under advisor Dr. Dennis Hong in the Robotics Mechanisms Lab (RoMeLa) at Virginia Tech.  The hand was originally designed to be operated with simple on off switches for each solenoid, providing limited control by a user. The first version was modified to use a simple micro controller to accept switch input and run short routines for demos.

The second version of the hand was designed to include a micro controller to allow for more complicated grasping methods that require closed loop control. These grasping methods included closed loop position and closed loop force control to allow for form grasping and force grasping, the two most commonly used human grasping methods. Each method would require analog input from one or more sensors, analog output to one or more pressure regulators, and digital output to control the solenoids, along with a program to calculate the proper control signal to send to the pressure regulators based on the sensor data.  Using the micro controller from the first version of the hand was considered, however it would have taken about a month for the team to redesign the controller to accept sensor input and analog output for the pressure regulator. It would have then taken weeks to program the controller and calibrate it properly, and a complete redesign would be necessary to add more sensors or actuators.

At this point 3 of the 4 students working on the hand graduated and left the lab. With only one student left it would take a considerably long amount of time to implement a micro controller, and due to the complexity of a custom designed micro controller if that student were to leave the lab, it would take a very long time for a new person to be trained to operate and continue research with the hand. The remaining team member decided to search for an easy to implement, expandable solution to the problem, to allow future research to continue without an extensive learning curve. The stringent requirements for this new controller lead the final team member to consult with a colleague. The colleague recommended an NI CompactDAQ (cDAQ) system for its ease of implementation and expandibility, along with it’s ability to acquire the sensor data, control the solenoids and control the pressure regulator.

Upon receiving the cDAQ, the solenoids were attached, and the control software was written in LabVIEW in about 1 hour. Then the electronic pressure regulator was attached in line with the hand, allowing for proportional control of the pressure to the hand within 1 more hour. At this point a force sensor was attached to the fingertip to make a closed loop system.  The interpretation code for the sensor was written in about 40 minutes, and PID control of the grasping force was functional in a grand total of about 6 hours.

The RoMeLa team plans to upgrade their robotic hand even further by upgrading to a CompactRIO controller. The  CompactRIO would allow control calculations and response to happen at a much faster rate since there is a dedicated FPGA combined with a real-time, embedded PC processor. With a new, beefed up controller, they plan to test other control schemes such as position or vision based control.  They also plan to incorporate additional degrees of freedom (as if there weren’t already enough?!) by adding control of a wrist or arm mechanism.

Dr. Hong also gave a heads up that Discovery Channel will be featuring some the robotic innovations from RoMeLa, so keep an eye out for an update to this blog post with a link to that footage.