OPENING a door is trickier for robots than you might expect, but a gripper designed to help wheelchair users seems to have cracked the problem.
A door-opening robot must be able to grasp a variety of designs of door knobs and handles. It also needs to calculate 鈥渉ow much force is needed to open the door, the twisting angles to unlatch the door, and how much force is needed to unlatch it鈥�, says Erin Rapacki, now at Anybots in Mountain View, California.
鈥淭he robot needs to know how much force is needed to open the door and the twist angle to unlatch it鈥�
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Rapacki knew that wheelchair users are often unable to reach and turn handles, and sophisticated general-purpose robotic arms that may have helped come with a big price ticket. So as a student project at the University of Massachusetts, Lowell, she and her colleagues designed a low-cost special-purpose gripper, which she presented at an IEEE robotics conference in Woburn, Massachusetts, last week.
The door-opening robotic arm (Dora) cost just $2000 to build and was able to open doors with 14 different handles in 85 per cent of tests involving pushing the door and 65 per cent of pulling tests.
To keep her device simple, Rapacki used a single motor and avoided the expense of cameras and elaborate sensors. Instead, a motor-driven set of gears extends the gripper towards the handle with its three fingers spread apart (see diagram).
Rapacki first tried flexible neoprene fingers, thinking that they could bend to grasp the knob, but these proved too thick and soft. Stiff plastic fingers with plates to constrain their sideways motion proved much more effective.
She also added a slip clutch to the drive system, to allow the device to hold and turn the knob at the same time as pushing or pulling.
The results are 鈥渧ery impressive,鈥� says Ted Kochanski, an engineering consultant based in Lexington, Massachusetts, who was also at the conference. He suggests that adding more electronic sensors and actuators would improve performance and cut costs.
