29 research outputs found
Safe Supervisory Control of Soft Robot Actuators
Although soft robots show safer interactions with their environment than
traditional robots, soft mechanisms and actuators still have significant
potential for damage or degradation particularly during unmodeled contact. This
article introduces a feedback strategy for safe soft actuator operation during
control of a soft robot. To do so, a supervisory controller monitors actuator
state and dynamically saturates control inputs to avoid conditions that could
lead to physical damage. We prove that, under certain conditions, the
supervisory controller is stable and verifiably safe. We then demonstrate
completely onboard operation of the supervisory controller using a soft
thermally-actuated robot limb with embedded shape memory alloy (SMA) actuators
and sensing. Tests performed with the supervisor verify its theoretical
properties and show stabilization of the robot limb's pose in free space.
Finally, experiments show that our approach prevents overheating during contact
(including environmental constraints and human contact) or when infeasible
motions are commanded. This supervisory controller, and its ability to be
executed with completely onboard sensing, has the potential to make soft robot
actuators reliable enough for practical use
The Zwicky Transient Facility Alert Distribution System
The Zwicky Transient Facility (ZTF) survey generates real-time alerts for
optical transients, variables, and moving objects discovered in its wide-field
survey. We describe the ZTF alert stream distribution and processing
(filtering) system. The system uses existing open-source technologies developed
in industry: Kafka, a real-time streaming platform, and Avro, a binary
serialization format. The technologies used in this system provide a number of
advantages for the ZTF use case, including (1) built-in replication,
scalability, and stream rewind for the distribution mechanism; (2) structured
messages with strictly enforced schemas and dynamic typing for fast parsing;
and (3) a Python-based stream processing interface that is similar to batch for
a familiar and user-friendly plug-in filter system, all in a modular, primarily
containerized system. The production deployment has successfully supported
streaming up to 1.2 million alerts or roughly 70 GB of data per night, with
each alert available to a consumer within about 10 s of alert candidate
production. Data transfer rates of about 80,000 alerts/minute have been
observed. In this paper, we discuss this alert distribution and processing
system, the design motivations for the technology choices for the framework,
performance in production, and how this system may be generally suitable for
other alert stream use cases, including the upcoming Large Synoptic Survey
Telescope.Comment: Published in PASP Focus Issue on the Zwicky Transient Facility (doi:
10.1088/1538-3873/aae904). 9 Pages, 2 Figure
The ``Outside-In'' Outburst of HT Cassiopeiae
We present results from photometric observations of the dwarf nova system HT
Cas during the eruption of November 1995. The data include the first
two--colour observations of an eclipse on the rise to outburst. They show that
during the rise to outburst the disc deviates significantly from steady state
models, but the inclusion of an inner-disc truncation radius of about 4
and a ``flared'' disc of semi-opening angle of produces
acceptable fits. The disc is found to have expanded at the start of the
outburst to about , as compared to quiescent measurements. The
accretion disc then gradually decreases in radius reaching during
the last stages of the eruption. Quiescent eclipses were also observed prior to
and after the eruption and a revised ephemeris is calculated.Comment: 9 pages, 11 figures, to appear in MNRA
Cataclysmic Variables in the First Year of the Zwicky Transient Facility
Using selection criteria based on amplitude, time, and color, we have identified 329 objects as known or candidate cataclysmic variables (CVs) during the first year of testing and operation of the Zwicky Transient Facility. Of these, 90 are previously confirmed CVs, 218 are strong candidates based on the shape and color of their light curves obtained during 3–562 days of observation, and the remaining 21 are possible CVs but with too few data points to be listed as good candidates. Almost half of the strong candidates are within 10 deg of the galactic plane, in contrast to most other large surveys that have avoided crowded fields. The available Gaia parallaxes are consistent with sampling the low mass transfer CVs, as predicted by population models. Our follow-up spectra have confirmed Balmer/helium emission lines in 27 objects, with four showing high-excitation He ii emission, including candidates for an AM CVn, a polar, and an intermediate polar. Our results demonstrate that a complete survey of the Galactic plane is needed to accomplish an accurate determination of the number of CVs existing in the Milky Way
The Zwicky Transient Facility Alert Distribution System
The Zwicky Transient Facility (ZTF) survey generates real-time alerts for optical transients, variables, and moving objects discovered in its wide-field survey. We describe the ZTF alert stream distribution and processing (filtering) system. The system uses existing open-source technologies developed in industry: Kafka, a real-time streaming platform, and Avro, a binary serialization format. The technologies used in this system provide a number of advantages for the ZTF use case, including (1) built-in replication, scalability, and stream rewind for the distribution mechanism; (2) structured messages with strictly enforced schemas and dynamic typing for fast parsing; and (3) a Python-based stream processing interface that is similar to batch for a familiar and user-friendly plug-in filter system, all in a modular, primarily containerized system. The production deployment has successfully supported streaming up to 1.2 million alerts or roughly 70 GB of data per night, with each alert available to a consumer within about 10 s of alert candidate production. Data transfer rates of about 80,000 alerts/minute have been observed. In this paper, we discuss this alert distribution and processing system, the design motivations for the technology choices for the framework, performance in production, and how this system may be generally suitable for other alert stream use cases, including the upcoming Large Synoptic Survey Telescope
Cataclysmic Variables in the First Year of the Zwicky Transient Facility
Using selection criteria based on amplitude, time, and color, we have identified 329 objects as known or candidate cataclysmic variables (CVs) during the first year of testing and operation of the Zwicky Transient Facility. Of these, 90 are previously confirmed CVs, 218 are strong candidates based on the shape and color of their light curves obtained during 3–562 days of observation, and the remaining 21 are possible CVs but with too few data points to be listed as good candidates. Almost half of the strong candidates are within 10 deg of the galactic plane, in contrast to most other large surveys that have avoided crowded fields. The available Gaia parallaxes are consistent with sampling the low mass transfer CVs, as predicted by population models. Our follow-up spectra have confirmed Balmer/helium emission lines in 27 objects, with four showing high-excitation He ii emission, including candidates for an AM CVn, a polar, and an intermediate polar. Our results demonstrate that a complete survey of the Galactic plane is needed to accomplish an accurate determination of the number of CVs existing in the Milky Way
The Zwicky Transient Facility: Data Processing, Products, and Archive
The Zwicky Transient Facility (ZTF) is a new robotic time-domain survey
currently in progress using the Palomar 48-inch Schmidt Telescope. ZTF uses a
47 square degree field with a 600 megapixel camera to scan the entire northern
visible sky at rates of ~3760 square degrees/hour to median depths of g ~ 20.8
and r ~ 20.6 mag (AB, 5sigma in 30 sec). We describe the Science Data System
that is housed at IPAC, Caltech. This comprises the data-processing pipelines,
alert production system, data archive, and user interfaces for accessing and
analyzing the products. The realtime pipeline employs a novel
image-differencing algorithm, optimized for the detection of point source
transient events. These events are vetted for reliability using a
machine-learned classifier and combined with contextual information to generate
data-rich alert packets. The packets become available for distribution
typically within 13 minutes (95th percentile) of observation. Detected events
are also linked to generate candidate moving-object tracks using a novel
algorithm. Objects that move fast enough to streak in the individual exposures
are also extracted and vetted. The reconstructed astrometric accuracy per
science image with respect to Gaia is typically 45 to 85 milliarcsec. This is
the RMS per axis on the sky for sources extracted with photometric S/N >= 10.
The derived photometric precision (repeatability) at bright unsaturated fluxes
varies between 8 and 25 millimag. Photometric calibration accuracy with respect
to Pan-STARRS1 is generally better than 2%. The products support a broad range
of scientific applications: fast and young supernovae, rare flux transients,
variable stars, eclipsing binaries, variability from active galactic nuclei,
counterparts to gravitational wave sources, a more complete census of Type Ia
supernovae, and Solar System objects.Comment: 30 pages, 16 figures, Published in PASP Focus Issue on the Zwicky
Transient Facility (doi: 10.1088/1538-3873/aae8ac