A method, using a particle filter, has been created for identifying the location, orientation, and shape of an object that a robot hand touches. An appropriate motion model has been defined that characterizes the motion of the robot hand as it moves relative to an object. The measurement model also estimates the likelihood of an observation of contact position, velocity, and tactile sensor information given handobject states, and is approximated analytically based on a geometric model, or on a corpus of training data. In either case, the measurement model distribution is encoded as a Gaussian, or using radial basis functions.

Motivated by the fact that humans rely heavily on a sense of touch during manipulation, this design includes a method for using force, or haptic sensors mounted in a robot hand, to estimate the hand-object state. The invention proposes using a combination of contact positions, contact velocities, and force sensor measurements to identify contact state between the robotic hand and an object. The model is simplified by conditioning on a measurement of manipulator velocity. While this approximation does not take into account the inertial dynamics of the manipulator, it is sufficiently accurate for the purposes of the invention. The motion model is calculated by marginalizing over the space of the manipulator velocities that can be produced by the command signal.

The measurement model describes the probability of sensor measurements z as a function of system state y. This invention uses measurements of contact position, velocity, and force. These measurements are implicitly conditioned on a mechanism for finding and maintaining object contact with the hand. It is assumed that the hand makes partial object contact in the course of a given manipulation of an assembly task. At this point, compliance in the hand and arm can be used to improve and expand the number of contacts. Compliance can be achieved using mechanical compliance built into the hand, or an active torque control system. In addition, the mechanism must exist for estimation of where on the hand contact actually occurs. This can be achieved by designing the mechanical structure such that contact always occurs in the same place. Alternatively, it can be achieved by contact force sensors that directly measure loads applied to the fingers.

This work was done by Robert Platt and Craig M. Corcoran of Johnson Space Center, Frank Noble Permenter of Oceaneering, and Charles W. Wampler of General Motors Corporation. For further information, contact the JSC Technology Transfer Office at (281) 483-3809. MSC-24688-1

NASA Tech Briefs Magazine

This article first appeared in the January, 2016 issue of NASA Tech Briefs Magazine.

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