2,127 research outputs found
Method and apparatus for positioning a robotic end effector
A robotic end effector and operation protocol for a reliable grasp of a target object irrespective of the target's contours is disclosed. A robotic hand includes a plurality of jointed fingers, one of which, like a thumb, is in opposed relation to the other. Each finger is comprised of at least two jointed sections, and provided with reflective proximity sensors, one on the inner surface of each finger section. Each proximity sensor comprises a transmitter of a beam of radiant energy and means for receiving reflections of the transmitted energy when reflected by a target object and for generating electrical signals responsive thereto. On the fingers opposed to the thumb, the proximity sensors on the outermost finger sections are aligned in an outer sensor array and the sensors on the intermediate finger sections and sensors on the innermost finger sections are similarly arranged to form an intermediate sensor array and an inner sensor array, respectively. The invention includes a computer system with software and/or circuitry for a protocol comprising the steps in sequence of: (1) approach axis alignment to maximize the number of outer layer sensors which detect the target; (2) non-contact contour following the target by the robot fingers to minimize target escape potential; and (3) closing to rigidize the target including dynamically re-adjusting the end effector finger alignment to compensate for target motion. A signal conditioning circuit and gain adjustment means are included to maintain the dynamic range of low power reflection signals
Smart hands for the EVA retriever
Dexterous, robotic hands are required for the extravehicular activity retriever (EVAR) system being developed by the NASA Johnson Space Center (JSC). These hands, as part of the EVAR system, must be able to grasp objects autonomously and securely which inadvertently separate from the Space Station. Development of the required hands was initiated in 1987. Outlined here are the hand development activities, including design considerations, progress to date, and future plans. Several types of dexterous hands that were evaluated, along with a proximity-sensing capability that was developed to initiate a reflexive, adaptive grasp, are described. The evaluations resulted in the design and fabrication of a 6-degree-of-freedom (DOF) hand that has two fingers and a thumb arranged in an anthropomorphic configuration. Finger joint force and position sensors are included in the design, as well as infrared proximity sensors which allow initiation of the grasp sequence when an object is detected within the grasp envelope
An integrated dexterous robotic testbed for space applications
An integrated dexterous robotic system was developed as a testbed to evaluate various robotics technologies for advanced space applications. The system configuration consisted of a Utah/MIT Dexterous Hand, a PUMA 562 arm, a stereo vision system, and a multiprocessing computer control system. In addition to these major subsystems, a proximity sensing system was integrated with the Utah/MIT Hand to provide capability for non-contact sensing of a nearby object. A high-speed fiber-optic link was used to transmit digitized proximity sensor signals back to the multiprocessing control system. The hardware system was designed to satisfy the requirements for both teleoperated and autonomous operations. The software system was designed to exploit parallel processing capability, pursue functional modularity, incorporate artificial intelligence for robot control, allow high-level symbolic robot commands, maximize reusable code, minimize compilation requirements, and provide an interactive application development and debugging environment for the end users. An overview is presented of the system hardware and software configurations, and implementation is discussed of subsystem functions
Recommended from our members
Forcing of globally unstable jets and flames
In the analysis of thermoacoustic systems, a flame is usually characterised
by the way its heat release responds to acoustic forcing. This
response depends on the hydrodynamic stability of the flame. Some
flames, such as a premixed bunsen flame, are hydrodynamically globally
stable. They respond only at the forcing frequency. Other flames,
such as a jet diffusion flame, are hydrodynamically globally unstable.
They oscillate at their own natural frequencies and are often assumed
to be insensitive to low-amplitude forcing at other frequencies.
If a hydrodynamically globally unstable flame really is insensitive to
forcing at other frequencies, then it should be possible to weaken
thermoacoustic oscillations by detuning the frequency of the natural
hydrodynamic mode from that of the natural acoustic modes. This
would be very beneficial for industrial combustors.
In this thesis, that assumption of insensitivity to forcing is tested
experimentally. This is done by acoustically forcing two different selfexcited
flows: a non-reacting jet and a reacting jet. Both jets have
regions of absolute instability at their base and this causes them to
exhibit varicose oscillations at discrete natural frequencies. The forcing
is applied around these frequencies, at varying amplitudes, and
the response examined over a range of frequencies (not just at the
forcing frequency). The overall system is then modelled as a forced
van der Pol oscillator.
The results show that, contrary to some expectations, a hydrodynamically
self-excited jet oscillating at one frequency is sensitive to
forcing at other frequencies. When forced at low amplitudes, the jet
responds at both frequencies as well as at several nearby frequencies,
and there is beating, indicating quasiperiodicity. When forced at
high amplitudes, however, it locks into the forcing. The critical forcing
amplitude required for lock-in increases with the deviation of the
forcing frequency from the natural frequency. This increase is linear,
indicating a Hopf bifurcation to a global mode.
The lock-in curve has a characteristic ∨ shape, but with two subtle
asymmetries about the natural frequency. The first asymmetry concerns
the forcing amplitude required for lock-in. In the non-reacting
jet, higher amplitudes are required when the forcing frequency is above
the natural frequency. In the reacting jet, lower amplitudes are required
when the forcing frequency is above the natural frequency. The
second asymmetry concerns the broadband response at lock-in. In the
non-reacting jet, this response is always weaker than the unforced response,
regardless of whether the forcing frequency is above or below
the natural frequency. In the reacting jet, that response is weaker
than the unforced response when the forcing frequency is above the
natural frequency, but is stronger than it when the forcing frequency
is below the natural frequency.
In the reacting jet, weakening the global instability – by adding coflow
or by diluting the fuel mixture – causes the flame to lock in at lower
forcing amplitudes. This finding, however, cannot be detected in the
flame describing function. That is because the flame describing function
captures the response at only the forcing frequency and ignores all
other frequencies, most notably those arising from the natural mode
and from its interactions with the forcing. Nevertheless, the flame describing
function does show a rise in gain below the natural frequency
and a drop above it, consistent with the broadband response.
Many of these features can be predicted by the forced van der Pol
oscillator. They include (i) the coexistence of the natural and forcing
frequencies before lock-in; (ii) the presence of multiple spectral peaks
around these competing frequencies, indicating quasiperiodicity; (iii)
the occurrence of lock-in above a critical forcing amplitude; (iv) the
∨-shaped lock-in curve; and (v) the reduced broadband response at
lock-in. There are, however, some features that cannot be predicted.
They include (i) the asymmetry of the forcing amplitude required
for lock-in, found in both jets; (ii) the asymmetry of the response at
lock-in, found in the reacting jet; and (iii) the interactions between
the fundamental and harmonics of both the natural and forcing frequencies,
found in both jets.Gates Cambridge Trust, Emmanuel College, Trinity Colleg
- …