Whole-Body Compliant Motion by Sensor Integration of an EHA-Driven Humanoid Hydra

2021 ◽  
pp. 2150002
Author(s):  
Tianyi Ko ◽  
Kazuya Murotani ◽  
Ko Yamamoto ◽  
Yoshihiko Nakamura
Keyword(s):  
High Speed ◽  
Null Space ◽  
Pressure Sensors ◽  
Biped Robot ◽  
Joint Space ◽  
Whole Body ◽  
Mass Motion ◽  
Feedback Gain ◽  
Response Property ◽  
Operational Space

Joints’ backdrivability is desired for robots that perform tasks contacting the environment, in addition to the high torque and fast response property. The electro-hydrostatic actuator (EHA) is an approach to realize force-sensitive robots. To experimentally confirm the performance of a biped robot driven by EHAs, we developed the fully electro-hydrostatically driven humanoid robot Hydra. In this paper, we evaluate the whole-body control performance realized by integrating encoders, pressure sensors, and IMU through a high-speed communication bus to the distributed whole-body control system. We report the first example of bipedal locomotion by an EHA-driven robot in both position-controlled and torque-controlled approaches. The robot could keep the balance even when the ground condition was changing impulsively and utilize its high joint backdrivability to absorb a disturbance by the null space compliance. We also report practical challenges in implementing compliant control in real hardware with limitations in parameter accuracy, torque, and response. We experimentally confirmed that the resolved viscoelasticity control (RVC), which has indirect feedback of operational space tasks by projecting the operational space feedback gain to the joint space one, was effective to tune a proper gain to stabilize the center-of-mass motion while avoiding joint-level oscillation invoked by the control bandwidth limitation. The attached multimedia file includes the video of all experiments presented in the paper.

scholarly journals Whole-Body Operational Space Control for Locomotion and Manipulation

2015 ◽  
Vol 137 (06) ◽  
pp. S2-S6
Author(s):  
Luis Sentis
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Humanoid Robots ◽  
Rigid Body Dynamics ◽  
Joint Torque ◽  
Whole Body ◽  
Operational Space ◽  
Body Dynamics ◽  
Service Oriented ◽  
High Level

This article discusses the various researches being undertaken to study and develop Whole-Body Operational Space Control (WBOSC). The WBOSC emerges as a capable framework for real-time unified control of motion and force of humanoid robots. It could theoretically outperform high-speed industrial manipulators while providing the grounds for new types of service-oriented applications that require contact, by exploiting the rigid body dynamics of systems. By relying on joint torque sensors, WBOSC opens up the potential to interact with the physical environment using any part of the robot’s body while regulating the effective mechanical impedances to safe values. With ControlIt!, the developers provide a strict and easy way to use the WBOSC API consisting of compound tasks which define the operational space, and constraint sets that define the contacts with the environment as well as dependent degrees of freedom. ControlIt! is easy to connect to high level planners.

Effects of Dynamic Model Errors in Task-Priority Operational Space Control

Robotica ◽  
2021 ◽  
pp. 1-12
Author(s):  
Paolo Di Lillo ◽  
Gianluca Antonelli ◽  
Ciro Natale
Keyword(s):  
Inverse Kinematics ◽  
Degrees Of Freedom ◽  
Inverse Dynamics ◽  
Null Space ◽  
Control Algorithms ◽  
Model Errors ◽  
Operational Space ◽  
Dynamic Level ◽  
Concurrent Tasks ◽  
Modeling Errors

SUMMARY Control algorithms of many Degrees-of-Freedom (DOFs) systems based on Inverse Kinematics (IK) or Inverse Dynamics (ID) approaches are two well-known topics of research in robotics. The large number of DOFs allows the design of many concurrent tasks arranged in priorities, that can be solved either at kinematic or dynamic level. This paper investigates the effects of modeling errors in operational space control algorithms with respect to uncertainties affecting knowledge of the dynamic parameters. The effects on the null-space projections and the sources of steady-state errors are investigated. Numerical simulations with on-purpose injected errors are used to validate the thoughts.

scholarly journals Stochastic Uncertainty in a Dam-Break Experiment with Varying Gate Speeds

2021 ◽  
Vol 9 (1) ◽  
pp. 67
Author(s):  
Hiroshi Takagi ◽  
Fumitaka Furukawa
Keyword(s):  
High Speed ◽  
Pressure Sensors ◽  
Dam Break ◽  
Maximum Pressure ◽  
Vertical Acceleration ◽  
Ship Wakes ◽  
Dam Break Flow ◽  
Statistical Relationships ◽  
Flow Propagation ◽  
Impulsive Pressure

Uncertainties inherent in gate-opening speeds are rarely studied in dam-break flow experiments due to the laborious experimental procedures required. For the stochastic analysis of these mechanisms, this study involved 290 flow tests performed in a dam-break flume via varying gate speeds between 0.20 and 2.50 m/s; four pressure sensors embedded in the flume bed recorded high-frequency bottom pressures. The obtained data were processed to determine the statistical relationships between gate speed and maximum pressure. The correlations between them were found to be particularly significant at the sensors nearest to the gate (Ch1) and farthest from the gate (Ch4), with a Pearson’s coefficient r of 0.671 and −0.524, respectively. The interquartile range (IQR) suggests that the statistical variability of maximum pressure is the largest at Ch1 and smallest at Ch4. When the gate is opened faster, a higher pressure with greater uncertainty occurs near the gate. However, both the pressure magnitude and the uncertainty decrease as the dam-break flow propagates downstream. The maximum pressure appears within long-period surge-pressure phases; however, instances considered as statistical outliers appear within short and impulsive pressure phases. A few unique phenomena, which could cause significant bottom pressure variability, were also identified through visual analyses using high-speed camera images. For example, an explosive water jet increases the vertical acceleration immediately after the gate is lifted, thereby retarding dam-break flow propagation. Owing to the existence of sidewalls, two edge waves were generated, which behaved similarly to ship wakes, causing a strong horizontal mixture of the water flow.

scholarly journals Evidence for a vertebrate catapult: elastic energy storage in the plantaris tendon during frog jumping

2011 ◽  
Vol 8 (3) ◽  
pp. 386-389 ◽  
Author(s):  
Henry C. Astley ◽  
Thomas J. Roberts
Keyword(s):  
Energy Storage ◽  
Elastic Energy ◽  
High Speed ◽  
Angular Acceleration ◽  
Whole Body ◽  
Joint Motion ◽  
Joint Movement ◽  
Fascicle Length ◽  
Muscle Fascicle ◽  
Muscle Shortening

Anuran jumping is one of the most powerful accelerations in vertebrate locomotion. Several species are hypothesized to use a catapult-like mechanism to store and rapidly release elastic energy, producing power outputs far beyond the capability of muscle. Most evidence for this mechanism comes from measurements of whole-body power output; the decoupling of joint motion and muscle shortening expected in a catapult-like mechanism has not been demonstrated. We used high-speed marker-based biplanar X-ray cinefluoroscopy to quantify plantaris muscle fascicle strain and ankle joint motion in frogs in order to test for two hallmarks of a catapult mechanism: (i) shortening of fascicles prior to joint movement (during tendon stretch), and (ii) rapid joint movement during the jump without rapid muscle-shortening (during tendon recoil). During all jumps, muscle fascicles shortened by an average of 7.8 per cent (54% of total strain) prior to joint movement, stretching the tendon. The subsequent period of initial joint movement and high joint angular acceleration occurred with minimal muscle fascicle length change, consistent with the recoil of the elastic tendon. These data support the plantaris longus tendon as a site of elastic energy storage during frog jumping, and demonstrate that catapult mechanisms may be employed even in sub-maximal jumps.

scholarly journals High systemic bone mineral density increases the risk of incident knee OA and joint space narrowing, but not radiographic progression of existing knee OA: the MOST study

2009 ◽  
Vol 69 (01) ◽  
pp. 163-168 ◽  
Author(s):  
M C Nevitt ◽  
Y Zhang ◽  
M K Javaid ◽  
T Neogi ◽  
J R Curtis ◽  
...  
Keyword(s):  
Bone Mineral Density ◽  
Bone Mineral ◽  
Joint Space Narrowing ◽  
Weight Bearing ◽  
Joint Space ◽  
Whole Body ◽  
Mineral Density ◽  
Knee Oa ◽  
Increased Risk

Objectives:Previous studies suggest that high systemic bone mineral density (BMD) is associated with incident knee osteoarthritis (OA) defined by osteophytes but not with joint space narrowing (JSN), and are inconsistent regarding BMD and progression of existing OA. The association of BMD with incident and progressive tibiofemoral OA was tested in a large prospective study of men and women aged 50–79 years with or at risk for knee OA.Methods:Baseline and 30-month weight-bearing posteroanterior and lateral knee radiographs were scored for Kellgren-Lawrence (K-L) grade, JSN and osteophytes. Incident OA was defined as the development of K-L grade ⩾2 at follow-up. All knees were classified for increases in grade of JSN and osteophytes from baseline. The association of gender-specific quartiles of baseline BMD with risk of incident and progressive OA was analysed using logistic regression, adjusting for covariates.Results:The mean (SD) age of 1754 subjects was 63.2 (7.8) years and body mass index was 29.9 (5.4) kg/m2. In knees without baseline OA, higher femoral neck and whole body BMD were associated with an increased risk of incident OA and increases in grade of JSN and osteophytes (p<0.01 for trends); adjusted odds were 2.3–2.9-fold greater in the highest compared with the lowest BMD quartiles. In knees with existing OA, progression was not significantly related to BMD.Conclusions:In knees without OA, higher systemic BMD was associated with a greater risk of the onset of JSN and K-L grade ⩾2. The role of systemic BMD in early knee OA pathogenesis warrants further investigation.

High Speed Imaging and Two-Phase Flow Patterns During Flow Boiling in a Single Microchannel

2008 ◽  
Author(s):  
Jacqueline Barber ◽  
Khellil Sefiane ◽  
David Brutin ◽  
Lounes Tadrist
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Pressure Sensors ◽  
Flow Patterns ◽  
Bubble Nucleation ◽  
Phase Flow ◽  
Vapour Bubble ◽  
Two Phase ◽  
Over Time

Boiling in microchannels remains elusive due to the lack of full understanding of the mechanisms involved. A powerful tool in achieving better comprehension of the mechanisms is detailed imaging and analysis of the two phase flow at a fundamental level. We induced boiling in a single microchannel geometry (hydraulic diameter 727 μm), using a refrigerant FC-72, to investigate several flow patterns. A transparent, metallic, conductive deposit has been developed on the exterior of rectangular microchannels, allowing simultaneous uniform heating and visualisation to be conducted. The data presented in this paper is for a particular case with a uniform heat flux of 4.26 kW/m2 applied to the microchannel and inlet liquid mass flowrate, held constant at 1.33×10−5 kg/s. In conjunction with obtaining high-speed images and videos, sensitive pressure sensors are used to record the pressure drop profiles across the microchannel over time. Bubble nucleation, growth and coalescence, as well as periodic slug flow, are observed in the test section. Phenomena are noted, such as the aspect ratio and Reynolds number of a vapour bubble, which are in turn correlated to the associated pressure drops over time. From analysis of our results, images and video sequences with the corresponding physical data obtained, it is possible to follow visually the nucleation and subsequent both ‘free’ and ‘confined’ growth of a vapour bubble over time.

Experimental Inverstigations On the Pressure Fluctuations in the Sealing Gap of Dry Gas Seals with Embedded Pressure Sensors

2021 ◽  
Author(s):  
Jingjing Luo ◽  
Dieter Brillert
Keyword(s):  
High Speed ◽  
Gas Flow ◽  
Static Pressure ◽  
Pressure Sensors ◽  
Operating Conditions ◽  
Test Facility ◽  
Experimental Investigations ◽  
Mechanical Seals ◽  
Process Gas ◽  
Sealing Gap

Abstract Dry gas lubricated non-contacting mechanical seals (DGS), most commonly found in centrifugal compressors, prevent the process gas flow into the atmosphere. Especially when high speed is combined with high pressure, DGS is the preferred choice over other sealing alternatives. In order to investigate the flow field in the sealing gap and to facilitate the numerical prediction of the seal performance, a dedicated test facility is developed to carry out the measurement of key parameters in the gas film. Gas in the sealing film varies according to the seal inlet pressure, and the thickness of gas film depends on this fluctuated pressure. In this paper, the test facility, measurement methods and the first results of static pressure measurements in the sealing gap of the DGS obtained in the described test facility are presented. An industry DGS with three-dimensional grooves on the surface of the rotating ring, where experimental investigations take place, is used. The static pressure in the gas film is measured, up to 20 bar and 8,100 rpm, by several high frequency ultraminiature pressure transducers embedded into the stationary ring. The experimental results are discussed and compared with the numerical model programmed in MATLAB, the characteristic and magnitude of which have a good agreement with the numerical simulations. It suggests the feasibility of measuring pressure profiles of the standard industry DGS under pressurized dynamic operating conditions without altering the key components of the seal and thereby affecting the seal performance.

Characteristics of Stable Rotating Stall Cells in an Axial Compressor

2017 ◽  
Author(s):  
Adam R. Hickman ◽  
Scott C. Morris
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Pressure Ratio ◽  
Pressure Sensors ◽  
Axial Compressor ◽  
Field Measurements ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Stable Operation ◽  
Double Phase

Flow field measurements of a high-speed axial compressor are presented during pre-stall and post-stall conditions. The paper provides an analysis of measurements from a circumferential array of unsteady shroud static pressure sensors during stall cell development. At low-speed, the stall cell approached a stable size in approximately two rotor revolutions. At higher speeds, the stall cell developed within a short amount of time after stall inception, but then fluctuated in circumferential extent as the compressor transiently approached a stable post-stall operating point. The size of the stall cell was found to be related to the annulus average flow coefficient. A discussion of Phase-Locked Average (PLA) statistics on flow field measurements during stable operation is also included. In conditions where rotating stall is present, flow field measurements can be Double Phase-Locked Averaged (DPLA) using a once-per-revolution (1/Rev) pulse and the period of the stall cell. The DPLA method provides greater detail and understanding into the structure of the stall cell. DPLA data indicated that a stalled compressor annulus can be considered to contained three main regions: over-pressurized passages, stalled passages, and recovering passages. Within the over-pressured region, rotor passages exhibited increased blade loading and pressure ratio compared to pre-stall values.

scholarly journals Whole Body Vibration Analysis of Baby Hammock

2018 ◽  
Vol 217 ◽  
pp. 01005
Author(s):  
Ying Hao Ko ◽  
Chia Sin Geh
Keyword(s):  
High Speed ◽  
Whole Body Vibration ◽  
Whole Body ◽  
Asian Countries ◽  
Body Vibration ◽  
Limit Value ◽  
Exposure Limit ◽  
Rocking Motion ◽  
Action Value ◽  
Iso 2631

Studies have been carried on the effect of rocking on a baby and concluded that baby sleeps easier while being rocked. In Malaysia, as in many Southeast Asian Countries, it is common to put babies to sleep in a baby hammock. the vertical rocking motion generated by baby hammock has exposed babies to whole-body vibration (WBV). It has been shown by ISO2631 (1997) that WBV may lead the discomfort and adverse effect on health. Standards have been set by ISO 2631 (1997) concerning the WBV for people in a recumbent position and consider weighted vibrations of more than 2 m/s2 to be extremely uncomfortable. However, standards concerning the allowable amount vibrations a baby in a baby hammock can safety endure are currently lacking. WBV analysis of the baby hammock with the weight ranged from 3kg to 14kg is conducted. For each measurement, four conditions are considered: manual rocking, auto rocking with low, medium and high speed. In this study, average root-mean-square values for the acceleration were found to be at a maximum of 2.46 m/s2, and to be above the extremely uncomfortable level. This study develops a baseline exposure time for the baby hammock before it reaches the safety values of exposure action value (EAV) and exposure limit value (ELV) set by ISO 2631(1997).

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